Zinc oxide decomposition

It catalyses the decomposition of potassium chlorate(V). Mixed with zinc oxide, it is used as a catalyst in the manufacture of methanol. It is used as a pigment, being very resistant to weathering. 

Azocarbonamide (I) Carbonamide N2, CO, CO2 190-230 220 Most widely used blowing agent in PVC and polyolefins. High decomposition temperature reduced by a variety of metal salts and oxides such as lead carbonate, lead phosphite and zinc oxide. High gas yield. Reaction products show little odour or discoloration. ... 

The zinc oxide used in ZOE cements differs entirely from that used in zinc phosphate cements. Whereas the latter has to be ignited to a very high temperature to deactivate it, the opposite is true of the zinc oxides used in the ZOE cement, which are of an activated variety. They are normally prepared by the thermal decomposition of zinc salts at 350 °C to 450 °C such oxides are yellow. Zinc oxides prepared by oxidizing zinc in oxygen may also be used these are white. 

Zinc oxide is made either by the oxidation of the metal in oxygen (the indirect, IP, or French process), by the direct decomposition of zinc ores in air (the direct or American process) or by the thermal decomposition of zinc salts (TD zinc oxide). IP zinc oxides differ from TD zinc oxides in that their surfaces do not contain absorbed water. Also, whereas TD zinc oxide reacts with plain eugenol, IP zinc oxide hardly reacts unless activated by an acetic add or zinc acetate accelerator (Table 9.2). 

Absolutely different situation occurs in case of polycrystalline semiconductors obtained under vacuum conditions. Thus, in paper [30] three types of ZnO samples were studied ZnO 1 obtained during heating of carbonates containing zinc in air at 600 C ZnO 2 obtained through vacuum decomposition of carbonate followed by heating at 500°C ZnO 3 powder of spectrally pure zinc oxide. 

In a review of the course and mechanism of the catalytic decomposition of ammonium perchlorate, the considerable effects of metal oxides in reducing the explosion temperature of the salt are described [1], Solymosi s previous work had shown reductions from 440° to about 270° by dichromium trioxide, to 260° by 10 mol% of cadmium oxide and to 200°C by 0.2% of zinc oxide. The effect of various concentrations of copper chromite , copper oxide, iron oxide and potassium permanganate on the catalysed combustion of the propellant salt was studied [2], Similar studies on the effects of compounds of 11 metals and potassium dichromate in particular, have been reported [3], Presence of calcium carbonate or calcium oxide has a stabilising effect on the salt, either alone or in admixture with polystyrene [4],... 

ADCA is activated by zinc oxide, zinc stearate (strongly) and urea (slowly). Barium stearate, calcium stearate and triethanolamine, when added at 10 phr, moderately activate gas evolution from ADCA. They do not have very much effect on decomposition rate when the cure temperature is at 170 °C, but a marked effect above 180 °C. The rate of decomposition of ADCA is significantly influenced by the particle size of the additive. Effective dispersion and heat transfer through the particle can be a means of controlling the cell quality and the manufacturing method for the product. The correct particle size is selected to achieve the optimum balance between cure and cell development. 

This reaction was therefore negligible when C6D12/Zn(CH3)2 = 13. The rates of reactions (1) and (14) are strongly dependent on the nature of the surface. In an ampoule coated with tar from decomposition of a large quantity of dimethyl zinc, the rate of both reactions is only J-i the rate observed in unconditioned vessels (tested at 348 °C with fraction Zn(CH3)2 reacted in conditioned vessel = 0.035). It has also been shown that in 90 min at 290 °C, the overall decomposition of dimethyl zinc in the absence of cyclohexane is 94 % complete if a zinc oxide surface is used, but only 4.5 % complete in a conditioned vessel. Decompositions carried out in conditioned vessels were assumed to be homogeneous. 

Towards metallic oxides the behaviour of thionyl chloride is similar to that of sulphur monochloride, which is perhaps hardly surprising in view of the course of its thermal decomposition. The reaction is fairly general, the oxide being converted into the corresponding anhydrous chloride. From the action of the chloride on zinc oxide (at 150° C.), cadmium oxide (at 200° C.), arsenious oxide (up to 200° C.), antimony trioxide (at room temperature), bismuth trioxide (at 150° to 200° C.), ferric oxide (at 150° C.), magnesium oxide (at 150° to 200° C.), cupric oxide (at 200° C.) and cuprous oxide (at 200° C.), it may be concluded that the main reaction, assuming a bivalent metal, M, is as follows ... 

That reversion to the white form requires oxygen, was substantiated by several workers (91,93-96), indicating that a reoxidation step generates zinc oxide. However, if this mechanism is correct, this system should not be classed as photochromic, since the system itself undergoes permanent decomposition with each reversal by liberation ofS02. 

As in the case of normal supported catalysts, we tried with this inverse supported catalyst system to switch over from the thin-layer catalyst structure to the more conventional powder mixture with a grain size smaller than the boundary layer thickness. The reactant in these studies (27) was methanol and the reaction its decomposition or oxidation the catalyst was zinc oxide and the support silver. The particle size of the catalyst was 3 x 10-3 cm hence, not the entire particle in contact with silver can be considered as part of the boundary layer. However, a part of the catalyst particle surface will be close to the zone of contact with the metal. Table VI gives the activation energies and the start temperatures for both methanol reactions, irrespective of the exact composition of the products. 

Inversely, the addition of an inhibitor to stabilize a compound may be an adequate measure to reduce the thermal risks due to decomposition. As an example, in Figure 11.18, the effect of adding zinc oxide to DMSO is shown [42], This kind of study determines the required inhibitor concentration after, for example, a distillation for solvent recovery. 

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