No abstract

Durch Mikroröntgenspektralanalyse wird der Homogenitätsbereich von.

The thermal decomposition of nanosized aluminum hydroxides, which are precipitated from solution in direct and inverse mixing of the chemical agents, is studied. The thermal treatment of hydroxides between 370 and 870 K results in their two-stage thermal decomposition. Intermediate decomposition products are amorphous aluminum oxyhydroxide AlO(OH) 1+x and boehmite. Nanosized γ-Al 2 O 3 begins forming even at 570 K. The thermal decomposition of amorphous oxyhydroxide AlO(OH) 1+x ceases when amorphous alumina forms at 770-870 K. This results in powders representing a mixture of amorphous and γ-alumina.

Articles made of carbon materials which exhibit unique physicochemical and mechanical properties are used in various branches of science and technology, i.e., from structural elements for space equipment to everyday articles. With the aim of expanding the range of application for carbon materials, particularly in the field of high-temperature technology, it is necessary to improve their heat resistance. As a rule this problem is resolved either by creating heat-resistant composites (for this purpose corrosion-resistant additions are made to the composition of the carbon matrix) or by applying protective coatings. The second path is assumed to be more promising.Information about multilayer coatings on carbon materials is presented in [1]. A substrate of titanium carbide with a thickness of the order of ten microns was precipitated from a mixture of titanium chloride and methane gases, and a protective coating of molybdenum disilicide with a thickness of 100 #m was applied by plasma deposition followed by annealing. The heat resistance of these coatings in air at 1600°C was of the order of tens of hours. The most promising are multilayer coatings of silicon carbides and nitndes, molybdenum and tungsten silicides, and also zirconium and hafnium oxides [2]. Thesecoatings arecapable ofprotecting carbon-carbonmaterials in oxygen-containing atmospheres at temperaturesup to 1800°C.The aim of the present study is to develop high-temperature and anti-corrosion coatings for carbon materials based on transition metal borocarbides and silicides.Considering the comparatively low linear expansion coefficients for carbon materials, the nonuniformity of their structure, high porosity, and high vapor pressures of carbon oxides with their greater chemical activity, in order to obtain high-temperature and heat-resistant coatings the methods of diffusion impregnation, deposition from the gas phase, and impregnation through the liquid phase and fusion were used. Experience in applying high-temperature (up to 2000°C) protective coatings on refractory metals and their alloys [3-5] was used.The original specimens made of carbon material, in particular graphite grade ARV and graphite bonded with pyrocarbon (GBP), were cylindrical in shape 8 mm in diameter 8 mm and 70 mm high. The carbon-borosilicides of refractory metals were selected as protective coatings. Titanium, niobium, and zirconium for subsequent preparation of a carbide substrate were applied by thermal decomposition from chlorides and iodides in the gas phase. A high-frequency generator or a furnace with an electric heater was used in order to heat the specimens. The temperature was measured by an optical pyrometer of the 'Promin' type or a tungsten-rhenium thermocouple. Titanium (zirconium) iodide was prepared directly in the device for applying coatings by passing iodine vapor through titanium (zirconium) turnings. The layout of the device and the procedure for applying coatings from the gas phase are described in [6]. In order to provide good coating adhesion with the base c...

Low-temperature sintering of a tetragonal zirconia solid solution proceeds through the fracture of all agglomerates during pressing of samples from hydroxide powder coprecipitated from an aqueous solution and through the increased reactivity of amorphous zirconium hydroxide and oxide. Thermal treatment at 1100ºC for 1 h produces ceramics with relative density 0.928, grain size 120-135 nm, and pore size 50-75 nm. Sintering is most intensive in the temperature range 950-1150ºC and is less active in the range 800-950ºC.