Abstract

The morphology, microstructure, and chemical composition of the surface and near-surface layers of polycrystalline wire of an industrial platinoid gauze composed of Pt (81 wt %), Pd (15 wt %), Rh (3.5 wt %), and Ru (0.5 wt %) are investigated by scanning electron microscopy and energy dispersive X-ray spectroscopy. After oxidizing NH₃ with air at T = 1133 K under a pressure of 3.6 bar for 50 h, a continuous rough layer of the cauliflower-type agglomerates formed during catalytic etching is detected on the frontal surface of the gauze. On the surface of wire fragments from 100 to 150 μm in size with a smooth micrograined structure, nanometer-size etch pits are detected at a concentration of 1.0 × 10⁸–6.0 × 10⁸ cm^–2, which may be etching sites of the hotspot type. The growth of etch pits and the formation of crystalline terraces on the grain surface are caused by the surface diffusion of metal atoms. The continuous etching layer contains porous crystalline agglomerates (cauliflowers) with a linear size of 3 to 18 μm (mean size about 10 μm) at a concentration of 4.9 × 10⁵ cm^–2. Pores with a diameter of 0.1 to 1.7 μm are detected on the surface of agglomerates at a concentration of 1.3 × 10⁷ cm^–2. The specific surface area of the platinoid gauze, which is calculated from microscopic images taking into account the surface area of agglomerates and pores, is about 260 cm²/g. In the process of highly exothermic oxidation of NH₃ with oxygen, on the surface of agglomerates with a low concentration of defects and in pore voids 5–15 μm in width and up to 10 μm in depth with an increased specific surface area and a high concentration of defects, vapor of volatile oxides and metals that are formed at hot regions of the bottom of pore voids can be condensed on the overlaying cold regions of the surface of agglomerates and single crystals. These processes give rise to the formation of a continuous etching layer of porous crystalline agglomerates, massive single crystals, and deep pore voids. The formed etching layer substantially increases the specific surface area of the catalyst, which leads to an increase in the volumetric rate of NH₃ oxidation that accelerates the etching process.

中文翻译：

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氨在空气中氧化过程中的类脂网的催化腐蚀：1133 K NH3氧化过程中类脂网的前表面的腐蚀

摘要

由Pt（81 wt％），Pd（15 wt％），Rh（3.5 wt％）和Ru（组成）的工业类铂金丝网的多晶线的表面和近表面层的形貌，微观结构和化学成分通过扫描电子显微镜和能量色散X射线光谱法研究了0.5wt％）。在T = 1133 K的空气中于3.6 bar的压力下将NH ₃氧化50小时后，在纱布的前表面上检测到连续的粗糙层的花椰菜型团聚物，该团簇在催化蚀刻过程中形成。在具有平滑微晶结构的尺寸为100至150μm的导线碎片的表面上，可以检测到浓度为1.0×10 ⁸ –6.0×10 ⁸ cm ^–2的纳米级蚀刻坑。，可能是热点类型的蚀刻部位。腐蚀坑的生长和晶粒表面上晶体台面的形成是由金属原子的表面扩散引起的。连续蚀刻层包含浓度为4.9×10 ⁵ cm ^–2的多孔晶体附聚物（花椰菜），其线性尺寸为3至18μm（平均尺寸约为10μm）。在附聚物表面上以1.3×10 ⁷ cm ^–2的浓度检测到直径为0.1至1.7μm的孔。铂金薄纱的比表面积约为260 cm ²，这是从显微镜图像计算得出的，其中考虑了团聚体和孔的表面积/G。在用氧气高度放热地氧化NH ₃的过程中，团聚体表面上的缺陷浓度低，孔洞宽度为5–15μm，深度最大为10μm，比表面积增加，并且比表面积大。缺陷的集中，在孔隙底部的较热区域形成的挥发性氧化物和金属的蒸气可凝结在附聚物和单晶表面的较冷区域上。这些过程导致形成多孔晶体附聚物，块状单晶和深孔空隙的连续蚀刻层。形成的蚀刻层实质上增加了催化剂的比表面积，这导致了NH ₃的体积率的增加。 氧化加速蚀刻过程。