Powder decomposition

TDS-SPECTRA OF HYDRIDE POWDER DECOMPOSITION MODELLING WITH SIZE REDUCTION EFFECT... 

The semiconducting forms of the transition metal oxides are almost never fully oxidized but often have nearly Daltonide stoichiometry. Oxidation of the metal powder, decomposition of the carbonates, and oxidation of a volatile precursor are all employed. Metal carbonyls, such as Ni(CO)4 and Fe(CO)s, are very useful, since distillation is a facile method of purification for these volatile liquids. Caution Ni(CO)4 is very toxic, and generates CO upon decomposition. 

Interpretation of Unusual Effects Modelling of the temperature distribution has allowed, for the first time, some unusual effects observed for powder decomposition to be explained quantitatively. One of these is associated with an independence of the overall decomposition rate on the powder mass, which seems to be inexplicable at first thought. However, when the self-cooling of the sample is taken into account, this effect seems obvious. Irrespective of the total number of layers, i.e., of the powder mass, the effective number of layers Ue, involved in the decomposition process should remain practically constant (the height of powder filling is assumed to be much less than its diameter). 

A theoretical simulation of the powder decomposition rate was attempted by L vov et al. [2, 3] in 1998 (Chapter 6). Later L vov and Ugolkov [4] continued these theoretical and experimental studies with dolomite crystals and powders of various particle sizes. Calculations performed for powders with varied numbers of layers n = 10 and 100), emittance coefficients (from 0.01 to 1), and residual air pressures in the reactor (10 and 10 bar) showed that the differences in the particle size and powder mass do not noticeably affect the temperature distribution and the effective number of powder layers Ue (see Sect. 6.3) decomposing at the same rate as does the surface layer. Furthermore, it was found that the decomposition rates of crystals and powders with the same external surface area and coefficients ranging from 0.01 to 0.3 should differ by a factor of no more than 2. 

Ewing J, Bemto D, Searcy AW (1979) Nature of CaO produced by caldte powder decomposition in vacuum and in CO2. J Am Ceram Soc 62 580-584... 

In addition to characterizing binder decomposition, thermal analysis is also useful to characterize precursor powder decomposition and dehydration prior to sintering. 

Appearance Fine yellow powder Decomposition Temperature Range 195-201C Gas Volume (ral/g) 0 STP 230-250 Average Particle Size (Fisher Subsiever) ... 

Appearance Fine white powder Decomposition Temperature Range 148-154C Gas Volume (ml/g) B STP 113-118... 

Appearance Fine yellow powder Decomposition Temperature Range KL-9 ... 

Appearance Fine yellow powder Decomposition Range ACMP-F 196-201C... 

Appearance White fine powder Decomposition Teaiperature Range 229-235C Gas Volume (ml/g) 8 STP 140-150... 

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