Surrounding Gas Atmosphere Research Articles

Thermal decomposition of titanyl oxalates—V. Magnesium titanyl oxalate

Thermal decomposition of barium titanyl oxalate tetrahydrate (BTO) has been investigated employing TGA, DTG and DTA techniques and gas and chemical analysis. The decomposition proceeds through five steps and is not affected much by the surrounding gas atmosphere. The first step which is the dehydration of the tetrahydrate is followed by a low-temperature decomposition of the oxalate groups. In the temperature range 190–250°C half a mole of carbon monoxide is evolved with the formation of a transient intermediate containing both oxalate and carbonate groups. The oxalate groups are completely destroyed in the range 250–450°C, resulting in the formation of a carbonate which retains free carbon dioxide in the matrix. The trapped carbon dioxide is released in the temperature range of 460–600°C. The final decomposition of the carbonate takes place between 600–750°C and yields barium titanate. The i.r. spectra, surface area measurements and X-ray, powder diffraction data support entrapment of carbon dioxide in the matrix.

Thermal decomposition of titanyl oxalates—I: Barium titanyl oxalate

Thermal decomposition of barium titanyl oxalate tetrahydrate (BTO) has been investigated employing TGA, DTG and DTA techniques and gas and chemical analysis. The decomposition proceeds through five steps and is not affected much by the surrounding gas atmosphere. The first step which is the dehydration of the tetrahydrate is followed by a low-temperature decomposition of the oxalate groups. In the temperature range 190–250°C half a mole of carbon monoxide is evolved with the formation of a transient intermediate containing both oxalate and carbonate groups. The oxalate groups are completely destroyed in the range 250–450°C, resulting in the formation of a carbonate which retains free carbon dioxide in the matrix. The trapped carbon dioxide is released in the temperature range of 460–600°C. The final decomposition of the carbonate takes place between 600–750°C and yields barium titanate. The i.r. spectra, surface area measurements and X-ray, powder diffraction data support entrapment of carbon dioxide in the matrix.

Annealing and refinement of platinum in gas atmospheres

The influence of surrounding gas atmosphere on the purity of thin platinum wires annealed at medium and high temperatures is experimentally studied. The residual resistance ratio serves as a measure of the “purity” of the specimens, and is supplemented by the determination of the changes of geometrical factor of the specimen during annealing. Empirical rules are deduced and partly explained.

Burning-out of a carbonaceous residue from a porous body

A study of the burning-out of a carbonaceous residue from a porous cylindrical body is presented. The amount of residue in the pores is very small. Only one end surface of the body is in direct contact with the surrounding gas atmosphere during the burning-out process. Experiments are performed in a stream of air at 480, 510, 540 and 660°C. The course of the process is determined by analysing the off-gases from the reactor in which the body is placed. Two successive periods are defined in the process. The end of the first period is reached when the outside of the body which is in contact with the gas is just free of carbon. The second period is completed when all residue is burnt out. Equations based on some simplifying assumptions are derived for the length of the first period and of the total process. The experimental results are explained with the model proposed.

Photoelectric determination of the work function of gold-platinum alloys

Films of platinum, gold, and their alloys were prepared by vapor deposition of the metals—either simultaneously or successively—and subsequent sintering under ultrahigh vacuum. The photoelectric emission of these films was investigated and it was found that equilibrated alloys of compositions within the miscibility gap of the PtAu phase diagram possessed identical work functions. This agrees with the expectation, based on thermodynamic and diffusion data, that the gold-rich alloy should envelop crystallites of the coexisting Pt-rich alloy. The work function of the gold-rich alloy is lower than that of gold or that of platinum. These results are completely analogous to those found previously for the CuNi system. The previously predicted dependence of surface composition on the surrounding gas atmosphere has been experimentally verified. Carbon monoxide causes an enrichment of the platinum in the surface. This process takes several days at room temperature and may be reversed by pumping off the carbon monoxide at elevated temperature.