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Reflectance Spectroscopy of Ammonium Salts: Implications for Planetary Surface Composition
Minerals ( IF 2.5 ) Pub Date : 2020-10-11 , DOI: 10.3390/min10100902
Maximiliano Fastelli , Paola Comodi , Alessandro Maturilli , Azzurra Zucchini

Recent discoveries have demonstrated that the surfaces of Mars, Ceres and other celestial bodies, as well as asteroids and comets, are characterized by the presence of ammonium-bearing minerals. A careful study of remote data compared with the analyses of more accurate laboratory data might allow a better remote characterization of planetary bodies. In this paper, the reflectance spectra of some ammoniated hydrous and anhydrous salts, namely sal-ammoniac NH4Cl, larderellite (NH4)B5O7(OH)2·H2O, mascagnite (NH4)SO4, struvite (NH4)MgPO4·6H2O and tschermigite (NH4)Al(SO4)2·12H2O, were collected at 293 and at 193 K. The aim is to detect how the NH4 vibrational features are affected by the chemical and structural environment. All samples were recovered after cooling cycles and were characterized by X-ray powder diffraction. Reflectance spectra of the studied minerals show absorption features around 1.3, 1.6, 2.06, 2.14, 3.23, 5.8 and 7.27 μm, related to the ammonium group. Between them, the 2ν3 at ~1.56 μm and the ν3 + ν4 at ~2.13 μm are the most affected modes by crystal structure type, with their position being strictly related to both anionic group and the strength of the hydrogen bonds. The reflectance spectra of water-rich samples [struvite (NH4)MgPO4·6(H2O) and tschermigite (NH4)Al(SO4)2·12(H2O)] show only H2O fundamental absorption features in the area from 2 to 2.8 μm and a band from hygroscopic water at 3 μm. Thermal analyses (TA), thermal gravimetry (TG) and differential scanning calorimetry (DSC) allowed to evaluate the dehydration temperatures and the occurring phase transitions and decompositions in the analyzed samples. In almost all samples, endothermic peaks at distinct temperatures were registered associated to loss of water molecules, differently linked to the structures. Moreover, an endothermic peak at 465 K in sal-ammoniac was associated to the phase transition from CsCl to NaCl structure type.

中文翻译:

铵盐的反射光谱:对行星表面成分的影响

最近的发现表明,火星,谷神星和其他天体的表面以及小行星和彗星的特征是存在含铵的矿物。与对更精确的实验室数据进行分析相比,对远程数据进行仔细研究可能会更好地对行星体进行远程表征。本文研究了一些氨水和无水盐的反射光谱,即盐铵NH 4 Cl,长石(NH 4)B 5 O 7(OH)2 ·H 2 O,辉石(NH 4)SO 4,鸟粪石(NH 4)MgPO 4 ·6H 2O和tschermigite(NH 4)的Al(SO 42 ·12H 2 O,在293收集并在193 K的目的是检测NH如何4振动特征由化学和结构环境的影响。冷却循环后回收所有样品,并通过X射线粉末衍射进行表征。所研究矿物的反射光谱显示出与铵基团有关的吸收特征,分别为1.3、1.6、2.06、2.14、3.23、5.8和7.27μm。在它们之间,2ν 3在〜1.56微米,ν 34在〜2.13μm处,受晶体结构类型影响最大的模式,其位置与阴离子基团和氢键的强度都严格相关。富含水的样品[鸟粪石(NH 4)MgPO 4 ·6(H 2 O)和硅藻土(NH 4)Al(SO 42 ·12(H 2 O)]的反射光谱仅显示H 2O基本吸收特征在2至2.8μm的区域内,吸湿性水的吸收带在3μm处。热分析(TA),热重量分析(TG)和差示扫描量热法(DSC)可以评估脱水温度以及分析样品中发生的相变和分解。在几乎所有样品中,都记录了在不同温度下的吸热峰,这与水分子的损失有关,而水分子的损失与结构不同。此外,盐氨中465 K处的吸热峰与从CsCl到NaCl结构类型的相变有关。
更新日期:2020-10-11
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