Thermal properties and phase stability of Yttria-Stabilized Zirconia (YSZ) coating deposited by Air Plasma Spray onto a Ni-base Superalloy Ceram. Int. (IF 2.986) Pub Date : 2017-11-20 D.F. Zambrano, A. Barrios, L. Tobón, C. Serna, P. Gómez, J.D. Osorio, A. Toro
Thermal properties and microstructure characterization of Yttria Stabilized Zirconia (YSZ) Thermal Barrier Coatings (TBCs) deposited by Air Plasma Spray (APS) onto a Ni-base superalloy (Inconel 625) were studied. Two separate sets of tests were performed. The first one consisted in Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) performed over free-standing TC samples detached from TBCs. The second one included the analysis of the cross section of samples heat treated at 1100 °C with holding times of 600, 1000, and 1700 h. The TC porosity was analyzed for different heat treatment conditions so that inter-lamellar, intra-lamellar and globular pores, as well as cracks, were identified and quantified independently. An initial porosity reduction related to inter-lamellar and intra-lamellar pores, as well as cracks, was observed during the first 600 hours of heat treatment, due to sintering. However, porosity continually increased during heat treatment from 600 to 1700 h driven by volumetric changes associated to phase transformations. During this period, yttrium diffused from the metastable tetragonal phase favoring the transformation to cubic phase while monoclinic phase transformed after cooling from the yttrium-depleted tetragonal phase. Energy absorption curves and the variation of heat capacity with temperature were also determined and correlated to microstructural changes.
The sintering behavior of plasma-sprayed YSZ coating over the delamination crack in low temperature environment Ceram. Int. (IF 2.986) Pub Date : 2017-11-20 Hui Dong, Jian-Tao Yao, Xiao Li, Yong Zhou, Yuan-Bo Li
The sintering behavior of plasma-sprayed yittra-stablized zirconia (YSZ) coating over the delamination crack and its influence on YSZ cracking were investigated via gradient thermal cycling test and finite element model (FEM). The gradient thermal cycling test was performed at a peak surface temperature of 1150 °C with a duration of 240 s for each cycle. A three-dimensional model including delamination cracks with different lengths was employed to elaborate the temperature evolution characteristics in YSZ coating over the delamination cracks. The temperature over the delamination crack increases linearly with the crack propagation, which continuously promotes the sintering of YSZ coating in the region. As a result, the YSZ coating over the delamination crack sinters dramatically despite of the low temperature exposure. Meanwhile, the temperature distribution difference in YSZ coating induces an nonuniform sintering along both free surface and thickness of YSZ coating. Correspondingly, the maximum vertical crack driving force locates at the YSZ free surface over the delamination crack center, which makes the vertical cracks generate in this region and propagate to the interface of YSZ /bond coat with YSZ further sintering. The vertical crack promotes the delamination crack propagation via accelerating the oxidation velocity of the bond coat. The influence of temperature rise on delamination crack propagation can be divided into two stages: the little contribution stage and the promotion stage. For the actual engine exposure to low temperature, the study of phase transformation of YSZ over the delamination crack is indeed needed because of an extended remarkable temperature rise period.
Hydrothermal synthesis of TiO2 nanotubes from one-dimensional TiO2 nanowires on flexible non-metallic substrate Ceram. Int. (IF 2.986) Pub Date : 2017-11-20 Yin-Yu Sun, Zhi-Min Zong, Zhan-Ku Li, Xian-Yong Wei
TiO2 nanotubes (NTs) immobilized on carbon fibers (CFs) were successfully prepared by a hydrothermal synthesis method based on alkali treatment of TiO2 nanowires (NWs). The as-prepared CFs with TiO2-NTs (CFs/TiO2-NTs) were characterized with a field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectrometer (XPS), and X-ray diffractometer (XRD). The images on FESEM and TEM show that the entire surfaces of CFs are covered by TiO2-NTs with the thickness of ca. 7.4 μm. The inner and outer diameters of TiO2-NTs are ca. 4.6 and 8.7 nm, respectively. The analyses with EDS and XPS indicate that the main elements on the surface of CFs/TiO2-NTs are C, O, and Ti. According to the analysis with XRD, the transformation from titanate NTs to anatase TiO2-NTs was realized after annealing treatment. This work may provide a novel method for immobilizing TiO2-NTs on flexible non-metallic substrates.
Discrete element simulation of SiC ceramic containing a single pre-existing flaw under uniaxial compression Ceram. Int. (IF 2.986) Pub Date : 2017-11-17 Shengqiang Jiang, Xu Li, Li Zhang, Yuanqiang Tan, Ruitao Peng, Rui Chen
A model of a SiC ceramic containing a single pre-existing flaw was established based on the discrete element method. The effects of the flaw inclination angles, which ranged from 0° to 75°, on the mechanical properties of the specimen under uniaxial compression were studied. The evolution of the force-chain field, displacement field and stress field around the pre-existing flaw in the process from the load to failure was also analysed. The results showed that the flaw inclination angle affected the mechanical properties of the specimen as well as the initiation and propagation of the first crack. Based on the investigation of the force chain field, it was found that the distribution curve of the normal force carried by the parallel bond in the specimen with the corresponding angles under compression is similar to the “peanut” rose diagram, while the shear force distribution curve is similar to the "butterfly wings" rose diagram. In addition, in the analysis of the displacement field and the stress field, the displacement field around the flaw can be divided into four types in the process from specimen loading to its failure. Meanwhile, it was found that initiation of the first crack was affected by tensile stress. With the propagation of the first crack, the tensile stress concentration region at the flaw tip moved and dissipated correspondingly.
Effect of biaxial cold pressure densification (BCPD) on Ba0.6K0.4Fe2As2 round wire using optimized precursor Ceram. Int. (IF 2.986) Pub Date : 2017-11-17 X. Li, E.W. Collings, F. Wan, M.D. Sumption, S.C. Xue, D.L. Zhang, M.A. Rindfleisch, M.J. Tomsic, Z.X. Shi
(Ba,Sr)1-xKxFe2As2 superconductor is of great interest as a wire for practical applications. In this paper, Ba0.6K0.4Fe2As2 precursor powder was prepared by high-energy ball-milling aided sintering (12 h/750 °C). The prepared precursor was drawn to powder-in-tube round wire. Partial as-drawn wires were subjected to biaxial cold pressure densification (BCPD) at 0.5 and 1.0 GPa, followed by an annealing for 1 min/770 °C. According to our results, the BCPD improved the grain connectivity of the BCPDed wires without degrading the superconductivity. A (Ba,Sr)1-xKxFe2As2 round-wire record transport critical current density, 1.14×105 A/cm2 (4.2 K, 2 T), was observed in our BCPDed samples.
Cu doped LiNi0.5Mn1.5-xCuxO4 (x=0, 0.03, 0.05, 0.10, 0.15) with significant improved electrochemical performance prepared by a modified low temperature solution combustion synthesis method Ceram. Int. (IF 2.986) Pub Date : 2017-11-17 H.Y. Sun, X. Kong, B.S. Wang, T.B. Luo, G.Y. Liu
A series of Cu-doped LiNi0.5Mn1.5-xCuxO4 (x=0, 0.03, 0.05, 0.10, 0.15) spinel samples have been successfully prepared using a modified low temperature solution combustion synthesis method. X-ray diffraction(XRD) and infrared spectroscopy(FT-IR) analysis are used to characterize the phase structure. Scanning electron microscopy(SEM) is used to observe the microstructure of the products. The electrochemical performance are studied by galvanostatic charge-discharge testing, cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS). No obvious sencondary phases were observed in XRD patterns of as-synthesized LiNi0.5Mn1.5-xCuxO4 powders. The samples have a combination structure of ordered and disordered space group and the order degree increases with the increase of Cu doping content obtained from FT-IR spectra. The electrochemical performances show that although the specific capacity decreases with the Cu-doping content, the cycle-life both at room temperature and 55°C and the C-rate performance are remarkably improved. The factors of stable structure, grain refinement, better crystallinity and lower charge transfer resistance lead to the excellent performance of Cu-doped samples.
Microstructure, phase compositions and in vitro evaluation of freeze casting hydroxyapatite-silica scaffolds Ceram. Int. (IF 2.986) Pub Date : 2017-11-17 Zheng-Quan Jia, Zuo-Xing Guo, Fei Chen, Jing-Juan Li, Lei Zhao, Li Zhang
Hydroxyapatite-silica (HA-SiO2) scaffolds with different SiO2 content (0, 2, 5 and 10 wt.% SiO2) were fabricated by freeze casting. After sintering, the scaffolds maintained the interconnected unidirectional pore channels by removing the frozen ice crystals via sublimation. X-ray diffraction (XRD) analysis indicated that SiO2 promoted the decomposition of HA to tricalcium phosphate (TCP), comprised of α-TCP and β-TCP, which became more apparent with the increase of SiO2 content. The microstructure observation of scanning electron microscope (SEM) showed that the scaffolds surface feature had great changes in terms of grain size and grain boundary with the addition of SiO2. Moreover, the addition of SiO2 could increase the porosity and pore size of the scaffolds, even allowing it to reach a maximum as the SiO2 content increased to 5 wt.%. Compression tests investigated the variation in the compressive strength of the scaffolds with the increase in the SiO2 content, which showed first decreasing and then increasing behavior. In vitro evaluation results in simulated body fluid (1.5×SBF) revealed that the introduction of SiO2 enhanced the growth rate of bone-like layer, especially the scaffold with 5 wt.% SiO2, which exhibited faster growth rate of bone-like layer than the other scaffolds. The XRD and fourier transformed infrared spectroscopy (FT-IR) characterization confirmed that the bone-like layer formed on the scaffold surface was a carbonate-containing hydroxyapatite bone-like layer.
Preparation, Characterization of 1D ZnO nanorods and their gas sensing Properties Ceram. Int. (IF 2.986) Pub Date : 2017-11-17 Supriya B. Jagadale, Vithoba L. Patil, Sharadrao A. Vanalakar, Pramod S. Patil, Harish P. Deshmukh
The 1D ZnO nanorods (NR's) were grown with Zinc (Zn) ion precursor concentration variation on seed layer glass substrate by the low temperature hydrothermal method and utilized for nitrogen dioxide (NO2) gas sensing application. Zn ion precursor concentration varied as 0.02, 0.03, 0.04, 0.05 and 0.06 M and thin films were characterized for structural, morphological, optical, electrical, surface defect study and gas sensing properties. All the film showed dominant orientation along the (002) direction, the intensity of the peak vary with the length of the nanorods. SEM cross images confirmed that nanorods had vertical alignment perpendicular to the plane of the substrate surface. The PL intensity of oxygen vacancy related defects for prepared samples was found to be linearly proportional to gas sensing phenomena. This result in good agreement with the theoretical postulation that, oxygen vacancies plays the important role for adsorption sites to NO2 molecule. The gas sensing performance was studied as a function of operating temperature, Zn ion precursor concentration variation, and gas concentration. The maximum gas response is 113.32 to 100ppm NO2 gas at 150 °C for 0.05 M sample out of all prepared samples. Additionally, ZnO thin film sensor has potential to detect NO2 as low as 5 ppm.
Room temperature ferromagnetic behavior, linear and nonlinear optical properties of KNbO3 microrods Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 S. Raja, R. Ramesh Babu, K. Ramamurthi, S. Moorthy Babu
Microrods of potassium niobate (KNbO3) were synthesized at 700, 800 and 900 °C by solid state reaction method and their structural, morphological, linear optical, nonlinear optical and magnetic properties were studied. X-ray diffraction and Rietveld refinement reveal that all the prepared KNbO3 samples belong to single phase orthorhombic structure with space group of Cm2m. Fourier transform infrared and Raman spectral analyses confirmed the Nb-O symmetric stretching vibrational modes of NbO6 octahedron. The grain growth direction (001) and inter planar spacing (0.38 nm) of KNbO3 were determined by high resolution transmission electron microscopy. Field emission scanning electron microscopy images revealed that KNbO3 are formed with nearly rod shape morphology with average diameter varying from 471 to 678 nm and length lies between 1.2 and 2.3 µm. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy studies confirmed the presence of K, Nb and O elements in the KNbO3 matrix. UV- visible diffuse reflectance spectra showed that the band gap of KNbO3 microrods varies between 3.18 and 3.22 eV. The existence of blue (492 nm) and green (521 nm) emissions evidently showed the presence of oxygen vacancy in the samples. All the synthesized KNbO3 microrods exhibited relatively high SHG efficiency as compared with that of the standard KDP. Vibrating sample magnetometer analysis showed the existence of ferromagnetic behavior at room temperature. The saturation magnetization (Ms) of KNbO3 microrods lies between 0.015 and 0.012 emu g−1 and coercive field (Hc) varies in the range from 489 to 420 Oe.
p-type conductive NiOx:Cu thin films with high carrier mobility deposited by ion beam assisted deposition Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 Hui Sun, Sheng-Chi Chen, Pei-Jie Chen, Sin-Liang Ou, Cheng-Yi Liu, Yan-Qing Xin
Transparent conductive NiO thin films with 18 at.% Cu dopant were fabricated by ion beam assisted deposition (IBAD). Their structural and optoelectronic properties were compared with undoped NiO films and NiO films doped with 12 at.% Cu, and also compared with NiO:Cu (18 at.%) films deposited by RF sputtering as reported in our previous work. The results show that the crystallinity of NiO thin films deposited through IBAD technology is much better than that of the films deposited by RF sputtering. Thanks to this reason, the highest carrier mobility above 45 cm2V−1s−1 for NiO:Cu (18 at.%) film can be realized here. Meanwhile, the films’ resistivity remains an acceptable value, varying from 2.05 to 0.064 Ω·cm with oxygen ion beam current changing from 0.2 to 0.8 A. This feature is imperative for p-type transparent conductive oxides (TCOs) applied in various domains. In addition, with oxygen ion beam current increase, the increase of the Ni3+/Ni2+ ratio leads to more Ni2+ vacancies be introduced into NiO films, which is beneficial to generate holes and improve carrier concentration. In this work, the optimal carrier mobility of NiO film doped with 18 at.% Cu is obtained when the oxygen ion beam current is 0.2 A. Its carrier concentration and electrical resistivity are 7.26 × × 1016 cm−3 and 2.05 Ω·cm, respectively.
Restacking-Inhibited Nitrogen-Incorporated Mesoporous Reduced Graphene Oxides for High Energy Supercapacitors Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 Manikantan Kota, Ho Seok Park
Graphene is considered a promising active electrode material due to a large surface area, high electronic conductivity, and chemical and mechanical stabilities for supercapacitor (SC) applications. However, the current bottleneck is the fabrication of restacking-inhibited graphene on an electrode level which otherwise loses the capability to achieve the aforementioned properties. Herein, we demonstrate the synthesis of restacking-inhibited nitrogen (N)-incorporated mesoporous graphene for high energy SCs. The melamine-formaldehyde acts as a restacking inhibitor by forming a bonding with reduced graphene oxide (RGO) through a condensation reaction and as an N precursor to be decomposed to create open pores and N sources upon heat treatment. The d-spacing increases up to 0.352 nm and the surface area is as high as 698 m2 g-1 with high mesoporosity, confirming restacking inhibition by N incorporation decomposed by melamine-formaldehyde. The restacking-inhibited RGO-based SC cells in organic electrolyte show the specific capacitance of 25.8 F g-1, the energy density of 21.8 kW kg-1 and 85% of capacitance retention for 5000 cycles, which are better than those of pristine RGO-based cells. These improved SC performances are attributed to the fast ion transport through a mesoporous channel in crumpled structure and the doping effect of N incorporation. This work provides a simple yet effective chemical approach to fabricate restacking-inhibited RGO electrodes for improved SC performances.
Effect of Copper- and Silver-Based Films on Alumina Substrate Electrical Properties Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 Jan Reboun, Jiri Hlina, Pavel Totzauer, Ales Hamacek
This paper focuses on evaluating the influence of thick films on the electrical properties of ceramic substrates, especially their dielectric strength. Dielectric strength is one of the most important parameters of the substrates used in power electronics. Increasing the thickness of the conductive films on these substrates is necessary to achieve sufficient current capability. The glass phase of thick film metal pastes, particularly if they are printed and fired several times on the same area of the substrate, can significantly affect the dielectric strength value and other electrical parameters (resistivity, dielectric constant) of the substrates. The change of the substrate parameters using different thicknesses of copper (thick printed copper) and silver films is described in this paper.
Low-temperature sintering of Ti1-xCux/3Nb2x/3O2 (x=0.23) microwave dielectric ceramics with CuO and B2O3 addition Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 Hui Shao, Zhifu Liu, Gang Jian, Yongxiang Li
The influence of CuO and B2O3 addition on the sintering behavior, microstructure and microwave dielectric properties of Ti1-xCux/3Nb2x/3O2 (TCN, x=0.23) ceramic have been investigated. It was found that the addition of CuO and B2O3 successfully reduced the sintering temperature of TCN ceramics from 950 to 875 °C. X-ray diffraction studies showed that addition of CuO-B2O3 has no effect on the phase composition. The TCN ceramics with 0.5 wt% CuO-B2O3 addition showed a high dielectric constant of 95.63, τf value of +329 ppm/°C and a good Q×f value of 8700 GHz after sintered at 875 °C for 5 h, cofirable with silver electrode.
Improved oxidation resistance of expanded graphite through nano SiC coating Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 Ning Liao, Yawei Li, Jiangbo Shan, Tianbin Zhu, Shaobai Sang, Dechang Jia
Expanded graphite with nano SiC and amorphous SiCxOy coating was successfully prepared through pyrolysing silane coupling agent (SCA), where the grafting of SCA dominated the final products. The results show that mainly amorphous SiCxOy coating covers expanded graphite at 1000 ℃, regardless of the SCA concentration. In comparison, nano SiC coating can be synthesized at 1200 ℃ depending on the good dispersion of SCA (with a SCA concentration of 50 vol%). The formed SiC coating contributes to much higher peak oxidation temperature (812.1 ℃) than 678.0 ℃ of the pure expanded graphite. Meanwhile, the oxidation activation energies of expanded graphite are remarkably improved from 149.15 kJ/mol to 176.16 kJ/mol (based on Kissinger method), attributing to the derived nano SiC and SiCxOy coating.
Spin-orbit coupling in manganese doped calcium molybdato-tungstates Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 T. Groń, M. Pawlikowska, E. Tomaszewicz, M. Oboz, B. Sawicki, H. Duda
The manganese doped calcium molybdato-tungstates with the formula of Ca1-xMnx(MoO4)0.50(WO4)0.50 (x = 0.01, 0.03, 0.05, 0.10, 0.125, and 0.15) were successfully obtained by two-step synthesis using in both steps a solid state reaction route. All ceramics show scheelite-type tetragonal structure with space group I41/a. The electrical and magnetic studies within the temperature range of 2–300 K showed a weak p-type electrical conductivity and the paramagnetic state of Mn-doped ceramic materials. With increasing Mn content in samples under study, a change in the short-range interactions from ferromagnetic to antiferromagnetic as well as an increase in the orbital contribution to the magnetic moment, resulting in a strong spin-orbit coupling, were observed. The Brillouin procedure was used to estimate the Landé factor.
Carbon content-dependent microstructures, surface characteristics and thermal stability of mechanical alloying derived SiBCN powders Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 Daxin Li, Zhihua Yang, Dechang Jia, Xiaoming Duan, Yu Zhou, Dongli Yu, Yongjun Tian, Zihuan Wang, Yinglong Liu
Three types of SiBCN: carbon-lean, -moderate and -rich powders with the same Si/B/N mole ratio were subjected to high-energy ball milling to yield an amorphous structure. The effects of carbon content on microstructures, solid-state amorphization, surface characteristics and thermal stability of the as-milled powders were studied in detail. Results showed that the increases in carbon content can drive solid-state amorphization accompanied by strain-induced, crystallite refinement-induced and/or chemical composition-induced nucleation of nano-SiC from an amorphous body. The specific surface area increases as carbon content increases. The amorphous networks of Si-C, C-B/C-C, C-N, B-N and C-B-N bonds that compose the amorphous nature, but the species and contents of the chemical bonds are carbon content-dependent. Carbon-moderate powders possess satisfying thermal stability while carbon-rich ones perform the worst. Mechanical alloying derived SiBCN powders have outstanding oxidation resistance below 800 °C; however only carbon-moderate powders show desirable anti-oxidation ability at higher temperatures. Thus, mechanical alloying of SiBCN appears a suitable technique for developing amorphous matrix materials for practical applications.
Infiltration Behavior of Cu and Ti fillers intoTi2AlC/Ti3AlC2 Composites During Tungsten Inert Gas (TIG)Brazing Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 N. Chiker, A. Haddad, Y. Hadji, M.E.A. Benammar, M. Azzaz, M. Yahi, T. Sahraoui, M. Hadji, M.W. Barsoum
Herein we study the infiltration behavior of Ti and Cu fillers into a Ti2AlC/Ti3AlC2MAX phase composites using a TIG-brazing process. The microstructures of the interfaces were investigated by scanning electron microscopy and energy dispersive spectrometry. When Ti2AlC/Ti3AlC2 comes into contact with molten Ti, it starts decomposing into TiCx, a Ti-richandTi3AlC; when in contact with molten Cu, the resulting phases are Ti2Al(Cu)C, Cu(Al), AlCu2Ti and TiC. In the presence of Cu at approximately 1630°C, a defective Ti2Al(Cu)C phase was formed having a P63/mmc structure. Ti3AlC2 MAX phase was completely decomposed in presence of Cu or Ti filler-materials. The decomposition of Ti2AlC to Ti3AlC2was observed in the heat-affected zone of the composite. Notably, no cracks were observed during TIG-brazing of Ti2AlC/Ti3AlC2 composite with Ti or Cu filler materials.
Microstructures, dielectric response and microwave absorption properties of polycarbosilane derived SiC powders Ceram. Int. (IF 2.986) Pub Date : 2017-11-16 Yichen Wang, Peng Xiao, Wei Zhou, Heng Luo, Zhuan Li, Wenbo Chen, Yang Li
Carbon-rich SiC powders with high dielectric loss were prepared via pyrolysis of polycarbosilane (PCS). The effects of pyrolysis temperature on microstructures, dielectric response and microwave absorption properties in X-band (8.2–12.4 GHz) of PCS-derived SiC powders were investigated. The PCS-derived SiC powders are mainly composed of SiC nanocrystal, turbostratic carbon and amorphous phase (SiC and/or C). The size of SiC nanocrystals and the graphitization degree of carbon both increase with the elevation of pyrolysis temperature. Furthermore, the residual carbon is transformed from amorphous into turbostratic structure with a phenomenon of regional enrichment. Moreover, the relative complex permittivity increases notably with the higher pyrolysis temperature. Meanwhile, the dielectric loss tangent increases from 0.19 to 0.57, while the microwave impedance decreases from 73.20 to 53.58. The optimal reflection loss of −35 dB for PCS-derived SiC powders is obtained when the pyrolysis temperature is 1500 °C, which exhibits a great application prospect in microwave absorbing materials.
Scratch behavior of boron nitride nanotube/boron nitride nanoplatelet hybrid reinforced ZrB2-SiC composites Ceram. Int. (IF 2.986) Pub Date : 2017-11-15 Y. Chen, D. Zhao, F. Qi, W.W. Liu
Spherical instrumented scratch behavior of ZrB2-SiC composites with and without hybrid boron nitride nanotubes (BNNTs) and boron nitride nanoplatelets (BNNPs) was investigated in this research. Typical brittle fracture such as microcracks both in and beyond the residual groove and grain dislodgement was observed in ZrB2-SiC composite, while hybrid BN nanofiller reinforced ZrB2-SiC composite exhibited predominantly ductile deformation. The peculiar three-dimensional hybrid structure in which BNNPs retain their high specific surface area and de-bundled BNNTs extend as tentacles contributes to the improved tolerance to brittle damage. Additionally, easier grain sliding due to BN hybrid nanofillers located at grain boundaries and these BN hybrid nanofillers attached on the scratch surface would provide significant self-lubricating effect to reduce lateral force during scratch and to alleviate contact damage.
3D Interconnected Mesoporous Si/SiO2 Coated with CVD Derived Carbon as an Advanced Anode Material of Li-ion Batteries Ceram. Int. (IF 2.986) Pub Date : 2017-11-15 Kuikui Xiao, Qunli Tang, Zheng Liu, Aiping Hu, Shiying Zhang, Weina Deng, Xiaohua Chen
3D interconnected mesoporous C/Si/SiO2 composite was synthesized via two facile processes (including magnesiothermic reduction and CVD method) with the SBA-15 as Si source and CH4 as carbon precursor. The micro/mesopores inside the Si/SiO2 particles greatly increase the specific surface area, thus shortening the diffusion distance of lithium ions, electron and guaranteeing fast penetration of electrolyte. Raman spectra shows that the CVD derived carbon is partly graphitized, thus largely enhancing its conductivity. Si/SiO2 coated with two-track carbon (both longitudinal and transverse) and Si/SiO2 coated with single-track carbon are formed by only changing the experiment order. Such two-track C/Si/SiO2 electrode for lithium-ion battery exhibits 63% higher capacity than the single-track C/Si/SiO2 electrode at high-rate performance, attributed to the fast electrochemical reaction kinetics and electron transport rendered by the conductive 3D interconnected structure. This functional structure can effectively accommodate the volume expansion of Si/SiO2 and maintain the electrical connection between electrode and active materials, improving the cycling stability of active materials.
Design of dual-carbon modified MnO electrode improves adsorption and conversion reaction in Li-ion batteries Ceram. Int. (IF 2.986) Pub Date : 2017-11-15 Ruiyi Wang, Liyun Cao, Jiayin Li, Zhanwei Xu, Jianfeng Huang, Yali Cui, Caiwei Wang
MnO is considered one of the most promising anode materials, but how to design and improve its structure is still of importance. In this paper, novel composites structure of carbon coated MnO anchored on reduced graphene oxides sheets (C@MRGO) are fabricated by a two-step hydrothermal and following heat treatment process. The prepared C@MRGO exhibits a superior performance of 1178, and 665 mAh g−1 at 100 and 1000 mA g−1, respectively. Comparison study finds that this novel structure greatly improved the conversion reaction and adsorption capacity of MnO particles. Further study shows that two different carbons both promote the lithium storage process from a different perspective. Typically, graphene greatly improves conductivity and controls the crystallization and growth of MnO particles, while carbon coating could provide a good elastic restricted body to effectively keep the integrity of the SEI film, inhibited volume expansion and make the conversion reaction reversible. In addition, carbon coating adsorbs much Li+ to achieve higher capacity, due to the nature adsorption properties of carbon materials. The design of using different carbon to enhance MnO electrode is believed to bring inspiration to the structural construction in other transitional metal oxide systems for superior performance of energy storage.
Growth of SiOC/SiC nanostructures from cured polysiloxane-silica composite Ceram. Int. (IF 2.986) Pub Date : 2017-11-15 K. Indulekha, Deepthi Thomas, R.S. Rajeev, K.N. Ninan, C. Gouri
SiOC/SiC nanostructures were produced by the pyrolysis of silica reinforced silicone polymer cured through platinum catalyzed hydrosilylation route. The base polymers used were vinyl terminated poly(dimethyl-co-diphenyl) siloxane (V-PMPS) and trimethylsilyl terminated poly(dimethyl-co-diphenyl-co-methyl hydrogen) siloxane (TMS-PMPHS). While TMS-PMPHS was synthesized from non-halogenated precursors by acid catalyzed ring opening/co-condensation approach, V-PMPS was used as received. The cured polymers were characterized for their spectral and thermal properties. Incorporation of silica filler to V-PDMS resulted in composite with higher onset of decomposition temperature compared to the unfilled counterpart. Pyrolysis of the filled polymer was carried out at different temperatures and the products were analyzed by FTIR, Raman spectroscopy, XRD, FESEM and EDAX. It was found that one dimensional ceramic nanostructures are produced from the silica filled composite at lower temperature of 900 °C compared to the unfilled system. The size of the nanostructures increased with increase in the pyrolysis temperature.
Formation of closed-pore foam ceramic from granite scraps Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Congcong Jiang, Shifeng Huang, Guozhong Li, Xiuzhi Zhang, Xin Cheng
Utilization of granite scraps and minor clay tailings to prepare closed-pore foam ceramic was investigated using SiC as foaming agent. The foam ceramic presented promising results with a bulk density of 237.4 kg/m3, compressive strength of 0.85 MPa, flexural strength of 0.42 MPa, porosity of 83.31%, water absorption of 2.21% and thermal conductivity of 0.051 W/(m k), which had good potential application in the field of building insulation.
Synthesis and Characterization of Nanocrystalline NiO-GDC via Sodium Alginate- Mediated Ionic Sol-Gel Method Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Shaghayegh Pezeshkpour, Babak Salamatinia, Bahman Horri Amini
In this study, nanocrystalline nickel oxide gadolinium-doped ceria (NiO-GDC) powder was synthesized in-situ using Na-Alginate as the template via ionic sol-gel technique. The effects of calcination time and temperature on the particle size and the physiochemical properties of nanocrystalline NiO-GDC are presented in this paper. Using this method, gel beads were formed by contacting sodium alginate solution as the gelling template and metal (gadolinium/cerium/Ni) nitrates as the precursor. The obtained nanocrystallites were characterized using Field Emission Scanning Electron Microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, thermo gravimetric analysis, nitrogen adsorption/desorption analysis, and Fourier transform infrared spectroscopy. It was observed that the increasing calcination temperature had affected both the particle size and the surface area of the NiO-GDC, whereas the increasing calcination time had only impacted the size of the particles. The smallest mesoporous nanocrystalline NiO-GDC powder (12.1225 ± 0.005 m2/g surface area), composed of cubic GDC (5.18 nm crystallite size) and cubic NiO (7.99 nm crystallite size) were synthesized at a calcination temperature of 500 °C for 2 hours. This study hopes to inspire more researches on the ionic-gelation method for synthesizing other metal nanostructures as well as other reaction parameters.
Effects of the Binder Compositions on the Homogeneity of Ceramic Injection Molded Compacts Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Jiaxin Wen, Wei Liu, Zhipeng Xie, Chaogang Lou, Xianfeng Yang
In this study, the effects of different binder compositions on the homogeneity of injection molded ceramic compacts are discussed from the standpoint of the rheological properties of the feedstocks, density, density deviation, and flexural strength of the as-prepared compacts, and the microstructures of the as-prepared compacts, compacts after solvent debinding, and compacts after thermal debinding. Also the pore size distribution of the compact after thermal debinding was characterized to examine the distribution of the binders in the as-prepare compacts. The feedstock with 30% macromolecular binders attains the minimum power-law index n value at 160 °C, hence it is the most appropriate feedstock for injection molding. The optimal composition is feedstock B30, which is the most homogeneous at an injection temperature of 160 °C. The macromolecular binder-to-PW weight ratio of 3:7 allows best mixing of feedstock and more homogeneous binder distribution. B30 has the highest density, the lowest density deviation and the lowest deviations in flexural strength of the as-prepared compact. Compacts prepared with B30 have the most homogenous pore size distribution after thermal debinding, as determined from the sharp, narrow peaks on the pore size distribution curves.
On the mechanical and biological properties of Bredigite-Magnetite (Ca7MgSi4O16-Fe3O4) nanocomposite scaffolds Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Amirsalar Khandan, Neriman Ozada, Saeed Saber-Samandari, Mazyar Ghadiri Nejad
The aim of the present study was to study the mechanical and biologocal properties of the bredigite-magnetite (Ca7MgSi4O16-Fe3O4) nanocomposite with various amounts of magnetite (0, 10, 20 and 30 wt. %). According to the obtained results, the properties of the constructed scaffolds have an extreme dependence on the magnetite content. In this research, the bredigite-30wt. % magnetite as the optimum sample showed a fracture toughness of 2.69 MPa m1/2 and a Young's modulus of 29 GPa. Increasing bredigite content led to the increase of pH values in the SBF solution. This was originated from the interchange/interaction of Ca2+ ion on the scaffold surface. The sample containing 10 wt. % magnetite presented a rocky and irregular surface while that of 30 wt.% illustrated a smooth and flat outer layer with coarse projections. The results confirmed that the biodegradation rate of the pure bredigite is more than that of 20 wt.% sample. The event is originated from the dissolution of the Si ions of the bridigite particles in the absence of magnetite.
Preparation of High-quality Transparent Al-rich Spinel Ceramics by Reactive Sintering Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Dan Han, Jian Zhang, Peng Liu, Gui Li, Liqiong An, Shiwei Wang
Transparent Al-rich spinel ceramics (MgO·nAl2O3, n = 1.05−2.5) were prepared by reactive sintering in air followed by the hot isostatic press (HIP). Commercial MgO and γ-Al2O3 powders were used as the raw materials, and the effects of composition and HIP temperature on the transmittance and microstructure of resulting samples were investigated. To obtain the high optical quality, extra alumina (n ≥ 1.1) was used to help eliminate residual pores and suppress abnormal grain growth during the sintering process. The appropriate HIP temperature was also critical to realize the single-phase formation and prevent the generation of second-phase precipitates. The resulting samples with n = 1.1 and 1.3 exhibited excellent optical quality and fine grains below 5 μm after HIPed at 1550 °C.
Thermoluminescence studies of CaSO4:Dy,P,Si phosphor under X-ray irradiation Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Resmi G. Nair, K. Madhukumar, C.M.K. Nair, S. Jayasudha, V.M. Anandakumar, T.S. Elias, Manoj Komath
Results of thermoluminescence studies on CaSO4:Dy,P phosphor with Si co-doping under X-ray irradiation are presented here. The peak emission temperature of the phosphor is found to be at 360 °C without any compromise in the intensity of emission when compared to commercially available standard phosphor CaSO4:Dy. The fading rate of the phosphor is around 2% over a period of 100 days.
Electrolytic synthesis of TiC/SiC nanocomposites from high titanium slag in molten salt Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Zhongren Zhou, Yingjie Zhang, Peng Dong, Yixin Hua, Qibo Zhang, Ding Wang, Jianguo Duan, Zhen Zhang
The molten salt electrolytic method for the preparation of titanium carbide and silicon carbide composites has been subjected to a systematic investigation by experimental analyses and thermodynamic calculations. It has been confirmed that the electrolysis of high titanium slag in the presence of mixed graphite powders generates intermediates CaTiO3, Ti2O3, TiO, Fe3Si and objective carbonous products TiC/SiC. It has been furthermore found that the deoxidization process depends critically on a number of process parameters, namely, electrolyte composition, graphitic regime, reaction temperature, cell voltage and reaction time. After careful optimization of these parameters, TiC/SiC nanocomposites with particle sizes of 10 nm~174 nm has been produced by electrolysis of high titanium slag and graphite mixtures in molar ratio of 1:2 referred to Ti:C under 3.2 V at 900°C for 6 h in 1 mol%CaO-CaCl2-NaCl molten salt and with particle sizes of 12 nm~207 nm in 1 mol%CaO-CaCl2 electrolyte.
Copper-Alumina Nanocomposite Coating on Copper Substrate through Solution Combustion Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 E. Mohammadi, H. Nasiri, J. Vahdati Khaki, S.M. Zebarjad
The main objective of the present research is to investigate the production of Cu-Al2O3 nanocomposite coating on a copper substrate using solution combustion synthesis. Solution combustion synthesis is mainly used to produce nanocomposite powders; however, in this study it is applied to produce nanocomposite coat. For this purpose, both copper and aluminum nitrates (Cu (NO3)2.3H2O and Al (NO3)3.9H2O) are used as oxidizers. Also, urea and graphite are respectively used as fuel to synthesize the Cu-Al2O3 nanocomposite and as inhibitor to prevent the oxidation of the synthesized copper. The microstructure and morphology of the nanocomposite coating, which includes 25 wt.% alumina as the reinforcing phase, was studied using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy at different fuel/oxidizer ratios ranging from 0.9 to 2. The temperature variation during the process was measured as a function of time using a precise thermocouple. Finally, micro-hardness and wear tests were conducted on the nanocomposite coating. The results verified the formation of Cu-Al2O3 nanocomposite coating. Time-temperature curve illustrated that the highest temperature was achieved at the fuel/oxidizer ratio of 1.25. The results of the microhardness and wear resistance test showed that these properties depend heavily on the fuel/oxidizer ratio, with the best condition attained at the ratio of 1.25.
Preparation and Characterization of Multilayer Anti-Reflective Coatings via Sol-Gel Process Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Ömer Kesmez, Esin Akarsu, H. Erdem Çamurlu, Emre Yavuz, Murat Akarsu, Ertuğrul Arpaç
Single layer and multilayer films consisting of SnO2, Ta2O5, SiO2, TiO2, indium tin oxide (ITO) and antimony tin oxide (ATO) have been prepared by sol-gel dip coating technique. All of the multilayer films contained a SiO2 top layer, which was composed of SiO2 nanoparticles. The other films had polymeric character. Obtained films were characterized by ellipsometry, XRD, AFM and SEM. Light transmittance values of the films were compared. Films other than SiO2 and Ta2O5 were found to have crystalline structure. Thickness values of the films were in the range of 30–115 nm and roughness values were in 1.2–23 nm range. Single layer porous silica provided 95% light transmittance, whereas ITO-TiO2-SiO2 multilayer film provided a light transmittance of 97.2%.
Failure analysis of thermally cycled columnar thermal barrier coatings produced by high-velocity-air fuel and axial-suspension-plasma spraying: A design perspective Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Ashish Ganvir, Venkatesh Narayanan, Nicolaie Markocsan, Mohit Gupta, Zdenek Pala, Frantisek Lukac
Axial-suspension-plasma spraying (ASPS) is a fairly recent thermal spray technology which enables production of ceramic top coats in TBCs, incorporating simultaneously the properties of both the conventional-plasma sprayed (highly insulating porous structures) and electron-beam-physical-vapor-deposited (strain-tolerant columnar structures) top coats. TBCs are required to insulate the hot components in a gas turbine engine against high temperature and harsh operating conditions. Periodic heating and cooling of turbine engines during operation can create sever thermal cyclic fatigue conditions which can degrade the performance of these coatings eventually leading to the failure. An in-depth experimental investigation was performed to understand the failure behavior of columnar TBCs subjected to thermal cyclic fatigue (TCF) test at 1100ᵒC. The study revealed that the TCF performance was influenced to an extent, by the top coat microstructure, but was primarily affected by the severity of thermally grown oxide (TGO) growth at the bond coat-top coat interface. Mixed failure modes comprising crack propagation through the bond coat-TGO interface, through TGO and within the top coat were identified. Based on the analysis of the experimental results and thorough discussion a novel design of microstructure for the high TCF performance columnar TBC is proposed.
Effect of spraying parameter and injector angle on the properties of in-flight particles and alumina coatings on Al alloy with PA-HT Ceram. Int. (IF 2.986) Pub Date : 2017-11-14 Guoliang Hou, Xiaoqin Zhao, Yulong An, Huidi Zhou, Jianmin Chen
Bonding strength is one of the most important properties of plasma sprayed coatings, especially ceramic coatings on complexly shaped light alloys, which is mainly determined by the properties of in-flight particles and their flattening behaviors on substrate surface. Consequently, the influence of current, voltage, primary gas flow rate and injector angle on temperature and velocity of in-flight alumina particles and morphology of splats on Al alloy with plasma arc-heat treatment (PA-HT) were investigated in detail by DPV Evolution, optical microscope and 3D non-contact surface mapping profile. The bonding strength, hardness and wear behavior of corresponding alumina coatings were measured by universal testing machine, nano-indentation test and wear test. Results showed that particle temperature and velocity increased with increase of input current and voltage, while their trends were reverse with increasing primary gas flow rate. The droplets could melt Al alloy surface and penetrate into its interior that greatly affected the morphology and corresponding shape factor (SF) of splats. Moreover, reducing injector angle caused droplets to glide on substrate surface and then to form “sole-like” splats. The morphology change of these splats obviously influenced the interfacial bonding strength, compactness, hardness and wear resistance of alumina coatings.
Separation and characterisation of fused alumina obtained from aluminium-chromium slag Ceram. Int. (IF 2.986) Pub Date : 2017-11-13 Pengda Zhao, Han Zhang, Hongjun Gao, Yuqian Zhu, Jun Yu, Qi Chen, Huizhong Zhao
Aluminium-chromium slag is a by-product of the thermal reduction of aluminium during chromium smelting, which is generally considered solid waste with a low utilisation rate. In this work, a fused carbonisation reduction method has been proposed to separate the Al2O3 and Cr2O3 from the slag and produce fused alumina and chromium carbide materials for refractory applications. The thermodynamic parameters of this process were determined using a standard thermal analysis method. In the molten slag, Cr2O3 reacts with C to produce high-density chromium carbide, which effectively precipitates at the bottom of the reaction vessel, while Al2O3 is converted into the corundum phase during cooling. The results of chemical analysis showed that the Al2O3 content in fused alumina was greater than 95 wt.%, while its main crystalline phase was the corundum with a bulk density of 3.57 g·cm−3, thermal conductivity of 6.4–7.4 W·m−1·K−1 (at temperatures above 600 °C), and average thermal expansion coefficient of about 7.5–8.2×10−6/°C (in the temperature range of 800–1300 °C).
Effect of Ni diffusion into BaZr0.1Ce0.7Y0.1Yb0.1O3−δ electrolyte during high temperature co-sintering in anode-supported solid oxide fuel cells Ceram. Int. (IF 2.986) Pub Date : 2017-11-13 Hiroyuki Shimada, Toshiaki Yamaguchi, Hirofumi Sumi, Yuki Yamaguchi, Katsuhiro Nomura, Yoshinobu Fujishiro
Diffusion behavior of Ni during high temperature co-sintering was quantitatively investigated for anode-supported solid oxide fuel cells (SOFCs) that had BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) proton-conducting electrolyte and NiO-BZCYYb anode. Although diffused Ni in such SOFCs effectively acts as a sintering aid to densify the BZCYYb electrolyte layer, it often negatively affects the electrolyte conductivity. In the present study, field emission electron probe microanalysis (with wavelength dispersive X-ray spectroscopy) clearly revealed that Ni diffused into the BZCYYb electrolyte layer, and that the amount of diffused Ni increased with increasing co-sintering temperature. In particular, relatively high Ni concentration within the electrolyte layer was observed near the electrolyte/anode interface, e.g., approximately 1.5 and 2.8 wt% at co-sintering temperature of 1300 and 1400 °C, respectively. Electrochemical measurements showed that, compared with the lower co-sintering temperatures (1300–1350 °C), the highest co-sintering temperature (1400 °C) led to the highest ohmic resistance because of lower electrolyte conductivity. These results suggest that high co-sintering temperature causes excessive Ni diffusion into the BZCYYb electrolyte layer, thus degrading the intrinsic electrolyte conductivity and consequently degrading the SOFC performance.
Honeycomb-like NiCo2O4@Ni(OH)2 Supported on 3D N−Doped Graphene/Carbon Nanotubes Sponge as an High Performance Electrode for Supercapacitor Ceram. Int. (IF 2.986) Pub Date : 2017-11-13 Hao Tong, Shihong Yue, Fengqiao Jin, Liang Lu, Qing Meng, Xiaogang Zhang
In order to increase the energy density of supercapacitor, a new kind electrode material with excellent structure and outstanding electrochemical performance is highly desired. In this article, a new type of three-dimensional (3D) nitrogen-doped single-wall carbon nanotubes (SWNTs)/graphene elastic sponge (TRGN−CNTs−S) with low density of 0.8 mg cm−3 has been successfully prepared by pyrolyzing SWNTs and GO coated commercial polyurethane (PU) sponge. In addition, high performance electrode of the honeycomb-like NiCo2O4@Ni(OH)2/TRGN-CNTs-S with core-shell structure has been successfully fabricated through hydrothermal method and then by annealing treatment and electrochemical deposition method, respectively. Benefited from 3D structural feature, the compressed NiCo2O4@Ni(OH)2/TRGN-CNTs-S electrode exhibits high gravimetric and volumetric capacitance of 1810 F g−1, 847.7 F cm−3 at 1 A g−1. The high rate performance and long-term stability was also obtained. Furthermore, an asymmetric supercapacitor using NiCo2O4@Ni(OH)2/TRGN-CNTs-S cathode and NGN/CNTs anode delivered high gravimetric and volumetric energy density of 54 Wh kg−1 at 799.9 W kg−1 and 37 Wh L−1 at 561.5 W L−1. In summary, an excellent electrochemical electrode with new elastic 3D SWNTs/graphene supports and binder free pseudocapacitive materials was introduced.
Ultrasonic vibration mill-grinding of single-crystal silicon carbide for pressure sensor diaphragms Ceram. Int. (IF 2.986) Pub Date : 2017-11-12 Jian Li, Daxi Geng, Deyuan Zhang, Wei Qin, Yonggang Jiang
Single-crystal silicon carbide (SiC) has gained tremendous attention for harsh-environment sensor applications due to its high-temperature tolerance and chemical resistance. However, there are many technological challenges in the fabrication of single-crystal SiC sensing microstructures such as thin SiC diaphragms for pressure sensors. This paper presents an ultrasonic vibration mill-grinding (UVMG) technique for the fabrication of 6H-SiC sensor diaphragms. The fundamental machining characteristics of UVMG are investigated experimentally compared with conventional mill-grinding (CMG). The experimental results show that the axial grinding force in UVMG is reduced by 60–70% compared to that in CMG. In addition, the wheel loading is severe in CMG, while the issue of wheel loading is significantly alleviated in UVMG due to the discontinuous cutting characteristic achieved in this method. As a result, sharp increase of the axial grinding force, which is accompanied by the crack of SiC workpiece, happens frequently in CMG after a total grinding depth of 200 μm. By contrast, the axial grinding force is stable in UVMG during the total grinding depth of at least 900 µm. The ultrasonic vibration in UVMG results in rough surface finish due to the material-removal mechanism of brittle fracture. However, by taking the advantages of better machining stability in UVMG and better surface roughness in CMG, extremely thin SiC sensor diaphragms with satisfactory surface quality can be achieved. Finally, we demonstrate the successful fabrication of a thin SiC diaphragm with a thickness of 20.3 μm.
Surface morphology evolution and optoelectronic properties of heteroepitaxial Si-doped β-Ga2O3 thin films grown by metal-organic chemical vapor deposition Ceram. Int. (IF 2.986) Pub Date : 2017-11-12 Daqiang Hu, Ying Wang, Shiwei Zhuang, Xin Dong, Yuantao Zhang, Jingzhi Yin, Baolin Zhang, Yuanjie Lv, Zhihong Feng, Guotong Du
Heteroepitaxial growth of conductive Si-doped β-Ga2O3 films on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD) was successfully performed. The effect of Si content on the structural, morphological, electrical and optical properties of Si-doped β-Ga2O3 films was investigated in detail. Distinctive surface morphology evolution of films depending on Si content was observed and presented. The Si-doped β-Ga2O3 films exhibited high transmittance in the ultraviolet-visible regions. The temperature-dependent PL was carried out especially to discuss the photoluminescence properties of Si-doped β-Ga2O3 films. More importantly, the results suggested that the conductivity of heteroepitaxial Si-doped β-Ga2O3 films by MOCVD could be realized and controlled by adjusting the Si content. The minimum resistivity of 1.79×10−1 Ω·cm was obtained for the films grown under the SiH4 flow rate of 0.08 sccm.
Aqueous tape casting of Al2O3 for multilayer co-fired ceramic based microfluidic chips with translucent windows Ceram. Int. (IF 2.986) Pub Date : 2017-11-12 Jin Luo, Richard Eitel
Multilayer co-fired ceramic (MLCC) material systems and fabrication methods allow the easy fabrication of three dimensional features and integration of microfluidic channels and cavities into monolithic ceramic modules. In this work, an alumina based multilayer co-fired ceramic formulation and sintering methods suitable for producing transparent ceramic microfluidic modules is developed. Alumina slurries with high solid loading were prepared using an aqueous DuramaxTM B-1000 binder systems. The rheological properties and casting behavior were studied for slurries with varying the binder additions. Sintering behavior of the green tapes were studied as well. Fundamental results indicated that the transparency of the ceramic with density over 3.98 g/cm3 can be greatly improved after long time sintering at 1612oC in the H2. Finally, a microfluidic MLCC module with transparent window was demonstrated by patterning, laminating, and sintering the developed Al2O3 green tapes.
Ceramic nanoparticles addition in pure copper plate: FSP approach, microstructure evolution and texture study using EBSD Ceram. Int. (IF 2.986) Pub Date : 2017-11-12 Akbar Heidarzadeh, Hesam Pouraliakbar, Soheil Mahdavi, Mohammad Reza Jandaghi
In this study, the effect of ceramic nanoparticles addition on the microstructure and texture of friction stir processed (FSP) copper has been investigated. For this purpose, two pure copper plates with and without Al2O3 nanoparticles were FSPed at rotational speed of 800 rpm and traverse speed of 100 mm.min−1. Electron back scattered diffraction (EBSD) technique was employed in order to study the microstructure and texture of the fabricated samples. Based on the obtained results, considerable grain refinement by dynamic recrystallization (DRX) mechanism was observed in both specimens. However, Al2O3 inset led to evolution of ultrafine grained (UFG) structure with an average grain size of 0.7 µm. In addition, Al2O3 addition caused formation of lower twin boundaries and stronger texture components compared with the sample without ceramic reinforcements. The presence of nanoparticles increased the proportion of the continuous DRX mechanism (CDRX) compared to the discontinuous mechanism (DDRX) during grain structure formation.
Microstructure and mechanical properties of Ti(C,N)-based cermets fabricated by in situ carbothermal reduction of TiO2 and subsequent liquid phase sintering Ceram. Int. (IF 2.986) Pub Date : 2017-11-12 Guotao Zhang, Yong Zheng, Wei Zhou, Yijie Zhao, Jiajie Zhang, Zheng Ke, Lixin Yu
Ti(C,N)-based cermets were prepared by in situ carbothermal reduction of TiO2 and subsequent liquid phase sintering in one single process in vacuum. The densification behavior, phase transformation, and microstructure evolution of the cermets were investigated by DSC, XRD, SEM, and EDX. The results showed that the carbothermal reduction of TiO2 was completed below 1250 °C, and Ti(C,N)-based cermets with refined grains were obtained after sintered at 1400 °C for 1 h by this method. The hard phase of the cermets mainly exhibited white core/gray rim structure, in great contrast to the typical black core/gray rim structure of hard phase in traditional cermets. Ti(C,N)-based cermets prepared by this novel method showed excellent mechanical properties with a transverse rupture strength of 2516±55 MPa, a Rockwell hardness of 88.6±0.1 HRA, and a fracture toughness of 18.4±0.7 MPa•m1/2, respectively.
Enhanced charge separation of CuS and CdS quantum-dot-cosensitized porous TiO2-based photoanodes for photoelectrochemical water splitting Ceram. Int. (IF 2.986) Pub Date : 2017-11-12 Jimin Du, Mengke Yang, Fangfang Zhang, Xuechun Cheng, Haoran Wu, Huichuang Qin, Qingsong Jian, Xialing Lin, Kaidi Li, Dae Joon Kang
Photoelectrochemical (PEC) water splitting using high-performance catalysts shows considerable promise in generating environment-friendly hydrogen energy. Its practical applications, however, suffer from several shortcomings, such as low photocurrent density, large onset-voltage value, and poor durability. In this study, CuS and CdS quantum-dot-cosensitized porous TiO2-based PEC catalysts (CuS-CT) have been successfully synthesized via in situ sulfuration of CuO and CdO coexisting inside a porous TiO2 monolith by a hydrothermal method. Compared to porous TiO2, CuS-sensitized porous TiO2 (CuS-TiO2), and CdS-sensitized porous TiO2 (CdS-TiO2) in terms of PEC performance, the CuS-CT photoanode exhibited a significantly high anodic photocurrent for water splitting under simulated sunlight radiation. The photocurrent produced by the optimized sample of 7% CuS-5% CdS-TiO2 (7% CuS-CT) was nearly 2.7 times higher than that of pure porous TiO2 at 1.0 V versus a reversible hydrogen electrode (RHE). Porous TiO2 possesses large surface areas that can drive fast electrolyte transport and afford more surface reaction active sites. On the other hand, CuS and CdS quantum dots not only broaden the visible light absorption range, but also improve photoinduced electron-hole separation efficiency. The co-sensitized multi-nanostructures photoanodes lead to a remarkable and promising application in PEC water splitting reactions.
Solid-state synthesis of mullite from spent catalysts for manufacturing refractory brick coatings Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Fabio Vargas, Edward Restrepo, Jhon E. Rodríguez, Freddy Vargas, Lizeth Arbeláez, Pablo Caballero, Jhoman Arias, Esperanza López, Guillermo Latorre, Gloria Duarte
This paper shows the results of the solid-state synthesis of mullite from spent catalysts discarded from fluid catalytic cracking (FCC); the catalysts are mainly composed of silica and alumina but are polluted with SOX, forming a non-crystalline network. The synthesized mullite was used as a feedstock to thermally spray a coating onto a silica-alumina refractory brick, and its chemical resistance at high temperature was subsequently evaluated by contact with K2CO3 at 950 °C. Initially, the spent catalyst was thermally treated for 2 h at 600, 900, and 1200 °C to eliminate the SOX pollutant. The heat treatment at 1200 °C completely removed the SOX in the sample. Additionally, four thermal processes were performed by heating the spent FCC catalyst in an electrical furnace to 1500 and 1600 °C and by using an oxyacetylene flame to synthesize mullite. Thermal treatments at 1500 °C were performed with and without alumina added to the spent FCC catalyst, whereas those conducted at 1600 °C and using a flame were performed using only added alumina. In the powders thermally treated at 1500 °C, silica-rich mullite (3Al2O3.2SiO2) accompanied by an excess of alumina or silica was obtained with or without alumina added, respectively. In contrast, the materials treated at 1600 °C formed alumina-rich mullite (2Al2O3.SiO2), which was accompanied by an excess of alumina. Mullite was not synthesized in the flame-heated powder. The silica-rich mullite accompanied by an excess of alumina was used as feedstock powder to modify the surface of a refractory brick, improving its resistance to chemical attack by K2CO3 at high temperature.
Catalytic graphene formation in coal tar pitch- derived carbon structure in the presence of SiO2 nanoparticles Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Maciej Gubernat, Aneta Fraczek- Szczypta, Janusz Tomala, Stanislaw Blazewicz
A simple and effective way to manufacture graphene from a coal tar pitch (CTP) is demonstrated. Silica (SiO2) nanoparticles were used to modify the CTP as carbon precursor. A silica nanofiller introduced into the CTP matrix underwent carboreduction during heat treatment to 2000 °C, resulting in the formation of silicon carbide. Surfaces of SiC grains were sites for graphene formation. The influence of SiO2 on the structure and microstructure of CTP- based carbon matrix, after annealing up to 2800 °C, was studied. Carbon samples were analyzed using X- ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Raman Spectroscopy. Crystallite sizes (La, Lc) and interplanar distance (d002) were determined. The presence of SiO2 in CTP carbon precursor favored the crystallites’ growth in the ‘a’ crystallographic graphite direction, and inhibited their growth on the ‘c’ axis. The crystallites composing of graphene layers, were characterized by an elongated dimension in the ‘a’ axis direction. Above 2000 °C silicon carbide decomposed, followed by the sublimation of silicon from the carbon matrix.
Anisotropic growth of α α -Fe2O3 nanostructures Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 J.R. Jesus, J.G.S. Duque, C.T. Meneses, R.J.S. Lima, K.O. Moura
In this work, we report on the anisotropic growth of α α -Fe2O3 nanoslabs which are produced by co-precipitation method with the addition of sucrose. In our previous work, we have argued that such behavior can be related with the chelating agent. Experiments of X-ray diffraction (XRD), high-resolution transmission electronic microscopy (HRTEM) and magnetic measurements as a function of temperature and applied magnetic field are used to characterize the samples. The HRTEM image of the sample prepared with 10 mmol/l of sucrose consists of faceted-like nanoslabs while that prepared without sucrose exhibits particles with a non-uniform shape. Besides, both the HRTEM image and the analysis of the XRD pattern show clearly a preferential growth of the  crystallographic direction. To strengthen our supposition, besides T - and field-dependence of magnetization are consistent with a superparamagnetic behavior the fits of the ZFC-FC curves for sample grown with 10 mmol/l of sucrose present a strong increase of the effective anisotropy constant, Keff K eff , which can be related with the increasing of the shape magnetic anisotropy.
Ultra-high temperature ceramic coating for carbon/carbon composites against ablation above 2000 K Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Yulei Zhang, Haohao Wang, Tao Li, Yanqin Fu, Jincui Ren
To improve the ablation resistance of carbon/carbon composites at the temperature above 2000 K, a ZrB2-SiC-ZrC ultra-high temperature ceramic coating was prepared by combination of supersonic atmosphere plasma spray (SAPS) and reaction melt infiltration. The micro-holes in ZrB2-Si-ZrC coating prepared by SAPS were effectively filled and the compactness and interface compatibility between the coating and C/C composites was improved through the reaction melt infiltration process. The ultra-high temperature ceramic coating exhibited good ablation resistance under oxyacetylene torch ablation above 2000 K. After ablation for 120 s, the mass and linear ablation rates of the ZrB2-SiC-ZrC coated C/C samples were only −0.016×10−3 g/s and 1.30 μm/s, respectively. Good ablation resistance of the ultra-high temperature ceramic coating is mainly attributed to the dense coating structure and the improvement of interface compatibility between the coating and C/C composites.
Microtopography and mechanical properties of vacuum hot pressing Al/B4C composites Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Liu Zhang, Zhi Wang, Qinggang Li, Junyan Wu, Guopu Shi, Fangfang Qi, Xin Zhou
Al/B4C composites with various volume contents of B4C (5, 10, 15, 20, and 25%) reinforcing the Al matrix, have been fabricated by vacuum hot press sintering at 680 °C, with a soaking time of 90 min and external pressure of 30 MPa. Mechanical properties, phase composition, and microstructure of the Al/B4C composites are discussed to reveal the physical properties of the composites. Field emission transmission electron microscopy and selected area electron diffraction have been employed to verify the interior structure and crystal growth direction, respectively. The Vickers hardness, fracture strength, tensile strength, and maximum force attained the optimal values of 108.45 ± 4.02 HV, 585.70 ± 23.26 MPa, 196.18 ± 2.48 MPa, and 4.44 ± 0.17kN, respectively, for 25 vol. % B4C/Al composites. The static compression strength increased before the 15 vol. % B4C addition and then decreased, acquiring the highest value of 292.15 ± 2.09 MPa for 15 vol. % B4C/Al composites. In general, the relative density and ductility of these composites consistently increased, with an increase in the volume content of Al, achieving a maximum of 99.22% and 54.63 ± 7.34%, respectively, for 5 vol. % B4C/Al composites.
Porous carbon -bonded carbon fiber composites impregnated with SiO2-Al2O3 aerogel with enhanced thermal insulation and mechanical properties Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Huimin Li, Yanfei Chen, Panding Wang, Baosheng Xu, Yongbin Ma, Weibin Wen, Yazheng Yang, Daining Fang
To improve the thermal insulation and mechanical properties of lightweight carbon- bonded carbon fiber composites (CBCF), a porous CBCF decorated with nano SiO2 -Al2O3 aerogel was prepared by sol-gel impregnation. Results showed that the nano aerogel were uniformly assembled within the pores in the CBCF framework. The aerogel played a significant role on reducing the thermal conductivity of CBCF, which could be mainly ascribed to reduced radiation and gas thermal conductivity of CBCF. Moreover, the aerogel in the CBCF pores hindered the bending fracture or elastic bending/rotation of the fibers and enhanced the mechanical properties of the composites.
Effect of microsilica addition on the properties of colloidal silica bonded bauxite-andalusite based castables Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Jia Quanli, Zhang Ju, Zhou Ying, Jia Gaoyang, Liu Xinhong
Colloidal silica bonded bauxite-andalusite based castables were prepared using homogenized bauxite and andalusite as aggregates, andalusite fines, corundum fines, ultrafine Al2O3 as matrixes and colloidal silica as binders. Effects of microsilica addition on the green strength, physical properties, hot strength and thermal shock resistance of castables were investigated. Moreover, phase composition and morphological evolution of specimens were characterized by XRD and SEM analysis. Green strength after demoulding, cold strength and hot strength as well as thermal shock resistance of the castables are enhanced with microsilica addition, which attribute to generating more chemical bond (–Si–O–Si–) after demoulding and heating at intermediate temperature (up to 1100 °C), and creating a stronger mullite bonding at higher temperature (1400 °C) compare to the specimens without microsilica.
Photoluminescence properties of Pr3+ ion-doped YInGe2O7 phosphor under an ultraviolet irradiation Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Lay-Gaik Teoh, Mu-Tsun Tsai, You-Chia Chang, Yee-Shin Chang
Pr3+ ion-doped YinGe2O7 phosphors are synthesized by a vibrating milled solid state reaction. There is a red shift for the excitation peak for the charge transfer transition between In3+ and O2- ion because the numbers of oxygen vacancies change the structure, which leads to a change in the crystal field. The results indicate that the emission spectra for the YinGe2O7:Pr samples under an excitation of 263 nm exhibit two dominant peaks at 486 and 604 nm, which are respectively assigned to the 3P0→3H4 and 1D2→3H4 transitions. The chromaticity coordinate for (Y1-xPrx)InGe2O7 phosphors varies with the Pr3+ doping concentration, from white, to greenish, to blueish. This has a potential application as a white light emitting phosphor for ultraviolet light-emitting diodes.
Crystal Structure and electric properties of (Li, Ce, Nd)-multidoped CaBi2Nb2O9 high temperature ceramics Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Xiangxiong Zeng, Feng Cao, Zhihang Peng, Xinghe Xing
(Li, Ce, and Nd)-mutlidoped CaBi2Nb2O9 (CBN) Aurivillius phase ceramics were prepared via conventional solid-state sintering route. The crystal structure including bond lengths and bond angles, microstructure, dielectric constant, DC resistivity, and piezoelectric properties were systematically investigated. Rietveld-refinements of X-ray results indicated that small quantity of (Li, Ce, Nd) doping (<2.5 mol%) increases orthorhombic distortion, because of the smaller ionic radii of doping ions. However, orthorhombic distortion obviously decreased with increasing (Li, Ce, Nd) doping concentration from 5 to 25 mol%. The replacement of asymmetric A-site Bi3+ with 6 s2 lone pair electrons by symmetric Li+, Ce3+, and Nd3+ decreased orthorhombic distortion. The morphologies and electrical properties of sintered ceramics were tailored by the introducing (Li, Ce, Nd) multi-dopants. The improvement of piezoelectric properties of modified-CBN ceramics were attributed to decreasing grain sizes and morphotropic phase boundary (MPB). Ca0.85(Li0.5Ce0.25Nd0.25)0.15Bi2Nb2O9 (CBNLCN-15) ceramics had optimum properties, and d33 and Tc values were found to be ~13.1 pC/N and ~900 °C, respectively.
Graphenothermal Reduction Synthesis of MnO/RGO Composite with Excellent Anodic Behavior in Lithium Ion Batteries Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 P. Rosaiah, Jinghui Zhu, O.M. Hussain, Yejun Qiu
Mn(II) oxide/graphene oxide (MnO/RGO) composites were synthesized by an easy and cost-effective graphenothermal reduction method. The surface morphology, structure, chemical composition and electrochemical behavior of the resulting composites were investigated in detail. The MnO/RGO composite exhibited a high surface area (115.7 m2/g), which led to the high discharge capacity, enhanced cycling stability, and outstanding rate capability as anode in Li-ion batteries (LIBs). The MnO/RGO composite exhibited an higher initial discharge capacity of 1607 mAh/g at a current density of 100 mA/g and maintained 94% of its reversible capacity over 100 consecutive cycles. Furthermore, MnO/RGO composite could preserve a significantly higher capacity of 847 mAh/g for 150 cycles even at a high current density of 250 mA/g. The excellent electrochemical properties result from the existence of highly conductive RGO and a short transportation span for both Li-ions and electrons. The developed MnO/RGO composite materials hold highly promising prospects in LIBs.
Facile synthesis and electrochemical performance of nitrogen-doped porous hollow coaxial carbon fiber/Co3O4 composite Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Zifeng Wang, Xing Zhang, Yan Sun, Hui Zhang, Congliang Wang, Anjian Xie
Economy and efficiency are two important indexes of lithium-ion batteries (LIBs) materials. In this work, nitrogen doped hollow porous coaxial carbon fiber/Co3O4 composite (N-PHCCF/Co3O4) is fabricated using the fibers of waste bamboo leaves as the template and carbon resource by soaking and thermal treatment, respectively. The N-PHCCF/Co3O4 exhibits an outstanding electrochemical performance as anode material for lithium ion batteries, due to the nitrogen doping, coaxial configuration and porous structure. Specifically, it delivers a high discharge reversible specific capacity of 887 mA h g−1 after 100 cycles at the current density of 100 mA g−1. Furthermore a high capability of 415 mA h g−1 even at 1 A g−1 is exhibited. Most impressively, the whole process is facile and scalable，exhibiting recycling of resource and turning waste into treasure in an eco-friendly way.
Hierarchical Li4Ti5O12 nanosheet arrays anchoring on carbon fiber cloth as ultra-stable free-standing anode of Li-ion battery Ceram. Int. (IF 2.986) Pub Date : 2017-11-11 Chunhai Jiang, Weiqiang Ding, Huiqing Wu, Zhiyang Yu, Lili Ma, Zhimin Zou
A flexible, free-standing composite anode with Li4Ti5O12 nanosheet arrays anchoring on plain-weaved carbon fiber cloth (LTO@CC) is prepared by a hydrothermal and post-annealing process assisted by a TiO2 seed layer. The LTO@CC anode free from polymeric binder and conducting agent exhibited much higher lithium storage capacity and cycling stability than the conventional slurry-processed electrode using the dandelion-like Li4Ti5O12 microspheres prepared by the same hydrothermal process. A high specific capacity of 128.8 mAh g−1 was obtained at a current rate of 30 C (1 C=175 mA g−1), and almost negligible capacity loses was observed when the cell was cycled at 10, 20 and 30 C each for 100 cycles. The carbon fiber matrix contributed to Li storage at low current rate, but the LTO nanosheet arrays have played the dominant role on the excellent rate capability. The improved electrochemical performance can be attributed to the synergetic effect between the hierarchical Li4Ti5O12 nanosheet arrays and the carbon fiber matrix, which integrated short Li+ diffusion length, three-dimensional conductive architecture and well preserved structural integrity during the high rate and repeated charge-discharge measurements.
Densification mechanisms and microstructural evolution during spark plasma sintering of boron carbide powders Ceram. Int. (IF 2.986) Pub Date : 2017-11-10 Mei Zhang, Tiechui Yuan, Ruidi Li, Siyao Xie, Minbo Wang, Qigang Weng
Micron-sized boron carbide (B4C) powders were subjected to spark plasma sintering (SPS) under temperature ranging from 1700°C to 2100 °C for a soaking time of 5, 10 and 20 min and their densification kinetics was determined using a creep deformation model. The densification mechanism was interpreted on the basis of the stress exponent n and the apparent activation energy Qd from Harrenius plots. Results showed that within the temperature range 1700–2000 °C, creep deformation which was controlled by grain-boundary sliding or by interface reaction contributed to the densification mechanism at low effective stress regime (n=2,Qd=459.36 kJ/mol). While at temperature higher than 2000°C or at high stress regime, the dominant mechanism appears to be the dislocation climb (n=6.11).
Interfacial origin of enhanced energy density in SrTiO3-based nanocomposite films Ceram. Int. (IF 2.986) Pub Date : 2017-11-10 Yong Peng, Manwen Yao, Xi Yao
SrTiO3-based films doped with different Al-precursors were prepared by sol-gel methods and the dielectric strengths and leakage currents of the materials were investigated. The best performance was found in SrTiO3 films doped with Al2O3 nanoparticles (nano-Al2O3). When 5 mol% of nano-Al2O3 was added to SrTiO3 films with Al electrodes, the dielectric strength was enhanced to 506.9 MV/m compared with a value of 233.5 MV/m for SrTiO3 films. The energy density of the 5 mol% nano-Al2O3 doped SrTiO3 films was 19.3 J/cm3, which was also far higher than that of the SrTiO3 films (3.2 J/cm3). These results were attributed to interfacial anodic oxidation reactions, which were experimentally confirmed by cross-sectional transmission electron microscope studies and theoretically modelled based on Faraday's laws. The films with added nano-Al2O3 featured many conducting paths at the interfaces between the host phase and the guest nano-Al2O3, which promoted ion transport and contributed to the strong anodic oxidation reaction capability of the 5 mol% nano-Al2O3 doped SrTiO3 films.
Effect of Al2O3-SiO2 substrate on gas-sensing properties of TiO2 based lambda sensor at high temperature Ceram. Int. (IF 2.986) Pub Date : 2017-11-10 Maolin Zhang, Tao Ning, Peng Sun, Yangxi Yan, Dongyan Zhang, Zhimin Li
Alumina is widely used as substrate material for oxygen lambda sensors. It has been reported that response properties of sensors are highly dependent on surface state of substrates. In this work, Al2O3-x%SiO2 (x=2~30) substrates were specially prepared for TiO2 based lambda sensors for high temperature operation. Structure and surface state of prepared substrates were characterized by XRD, SEM and XPS. TiO2 sensing film was prepared by screen printing method. Results indicated that sensors fabricated on Al2O3−10%SiO2 substrate exhibited the best sensing properties. Moreover, final steady-state voltages of all sensors were limited to less than 100 mV at 600~800 ℃.
Sintering characteristics of plasma-sprayed TBCs: Experimental analysis and an overall modelling Ceram. Int. (IF 2.986) Pub Date : 2017-11-10 Guang-Rong Li, Guan-Jun Yang, Cheng-Xin Li, Chang-Jiu Li
In this study, sintering behaviour of plasma-sprayed thermal barrier coatings (PS-TBCs) was investigated experimentally and theoretically. Results show that the sintering kinetics of PS-TBCs is highly stage-sensitive. The sintering proceeds significantly faster at initial short thermal exposure (<20 h), while it slows down dramatically at following long thermal exposure. A detailed examination on microstructural evolution of the PS-TBCs was carried out to understand their sintering behaviour. Results show that, different from the conventional sintering theory, the healing of 2D pores was dominantly responsible for the stage-sensitive sintering kinetics during thermal exposure. In brief, the sintering characteristics of the PS-TBCs are highly structure specific. In addition, a structural model was developed based on the structural characteristics of the PS-TBCs; and the model predicts a well consistent sintering behaviour with experiments. Finally, an outlook towards TBCs with higher performance was put forward.
Structural investigations of perlite and expanded perlite using 1H, 27Al and 29Si solid-state NMR Ceram. Int. (IF 2.986) Pub Date : 2017-11-10 Zoran Zujovic, Walt V.K. Wheelwright, Paul A. Kilmartin, John V. Hanna, Ralph P. Cooney
Industrial grade perlite and expanded perlite systems were investigated by multifield and multinuclear Solid State Nuclear Magnetic Resonance (SSNMR), Fourier Transform Infra-Red (FTIR) spectroscopies and Scanning Electron Microscopy (SEM). The SSNMR studies focussed on the 1H, 29Si and 27Al nuclei using single pulse excitation (SPE) and 1H, 29Si cross-polarization Magic-Angle-Spinning (CP-MAS) conditions, with 27Al Triple Quantum Magic-Angle-Spinning (3QMAS) measurements also being implemented. The resonances at ~52 ppm detected in the 27Al MAS NMR spectra of the industrial grade and expanded systems are tentatively assigned to tetrahedrally coordinated aluminium, while the resonance at ~5 ppm, which was only observed in the industrial grade perlite spectrum, is attributed to octahedrally coordinated aluminium. In neither case could the pentahedrally coordinated positions be identified using 27Al MAS and 3QMAS techniques. 27Al data suggests that tetrahedrally coordinated aluminium atoms do not have a significant role in the grain expansion process. The broad resonance envelopes found in the 29Si MAS NMR and FTIR data of both perlites were analyzed by the second-order derivative. The analyses confirmed complex Qn configurations for the perlitic structure suggesting the prevalence of Q3 and Q4 species. 1H-29Si CP-MAS spectra support the presence of Q2 units suggested by FTIR and SPE data. SEM micrographs revealed the honeycomb morphology of expanded domains in perlite after heat treatment.
HIPed TiO2 DENSE PELLETS WITH IMPROVED PHOTOCATALYTIC PERFORMANCE Ceram. Int. (IF 2.986) Pub Date : 2017-11-10 M. Erol, O. Ertugrul
The effects of heating method and temperature on physical, structural and photocatalytic behaviors of TiO2 pellets prepared by conventional heating and hot isostatic pressing have been evaluated. The pellets of submicron TiO2 powders were heated to 600, 650, 700, 750 and 1000⁰C using both processing methods in order to compare anatase to rutile phase transformation and densification behaviors. Bulk densities and porosities were calculated using the Archimedes method. XRD analysis were performed to calculate anatase/rutile ratios. Microstructures were characterized using SEM. Photocatalytic experiments have been performed under full spectrum irradiation. Degraded methylene blue samples were periodically monitored through UV-Vis spectrophotometer to determine degradation kinetics. Anatase to rutile transformation is slightly faster and densification is better for lower temperatures for conventional heating, however HIPing gives better densification above 750 °C as it also retards rutile transformation. Mixed phase structures and HIPed samples showed the best photocatalytic performance which makes this method advantageous.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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