Zinc oxide ignition

Two methods are available for the preparation of the powder (Smith, 1969). In one, zinc oxide is ignited at 900 to 1000 °C for 12 to 24 hours until activity is reduced to the desired level. This oxide powder is yellow, presumably because zinc is in excess of that required for stoichiometry. Alternatively, a blend of zinc oxide and magnesium oxide in the ratio of 9 1 is heated for 8 to 12 hours to form a sintered mass. This mass is ground and reheated for another 8 to 12 hours. The powder is white. Altogether the powder is similar to that used in zinc phosphate cements. 

Magnesium oxide is always blended with the zinc oxide prior to ignition. Magnesium oxide promotes densification of the zinc oxide, preserves its whiteness and renders the sintered powder easier to pulverize (Crowell, 1929). The sintered mixed oxide has been shown to contain zinc oxide and a solid solution of zinc oxide in magnesium oxide (Zhuravlev, Volfson Sheveleva, 1950). Specific surface area is reduced compared with that of pure zinc oxide and cements prepared from the mixed oxides are stronger (Crowell, 1929 Zhuravlev, Volfson Sheveleva, 1950). 

Crisp and coworkers found that the development of surface crystallinity was related to the speed of set. The faster the reaction, the shorter was the inhibition period before surface crystallization took place. When the setting time of a cement was between two and three minutes, surface crystallinity developed in a few minutes. When it was seven minutes, surface crystallinity was delayed by three hours. The reaction rate was affected by the chemical composition and physical state of the cement components. Well-ignited zinc oxide, the presence of magnesium in the... 

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 prepared by ignition of zinc carbonate. A powder liquid 2 0 g cnr was used for cement preparation. 

Pytlewski, L. L Rep. AD-A028841, 13, Richmond (Va.), USNTIS, 1976 Contact of gaseous ammonia with the /V-chlorourea. either alone, or mixed with zinc oxide, leads to ignition. The same could happen in contact with cone, aqueous ammonia, solid ammonium carbonate or organic amines. 

The pelleted explosive ( ammonpulver , containing 10% charcoal) normally ignites at 160-165°C, but presence of rust, or copper oxide or zinc oxide lowers the temperature to 80-120°C. 

Procedure 1.5 g of freshly ignited and cooled zinc oxide is accurately weighed and dissolved with 2.5 g of ammonium chloride in 50 ml of 1 N sulphuric acid with the help of gentle heating. After complete dissolution, add methyl orange and titrate the excess of sulphuric acid with 1 N sodium hydoxide. Each millilitre of 1 N sulphuric acid is equivalent to 40.6 mg of ZnO. 

The zinc sulphate produced in this process can be turned more easily to commercial account than iron sulphate. If to the solution of the zinc sulphate resulting from the process sodium carbonate or sodium hydrogen carbonate is added, a precipitate of hydrated zinc basic carbonate or zinc carbonate is obtained, which on ignition in a furnace yidds zinc oxide (commercially known as zinc white ), water, and carbon dioxide. Zinc white has a commercial value as a basis or body In paints it has one great advantage over white lead, which is used for the same purpose, in that it is far less poisonous. This method of treatment of the residual... 

The original HC smoke mixtures (Type A) contained zinc metal and hexachloroethane, but this composition is extremely moisture- sensitive and can ignite spontaneously if moistened. An alternative approach involves adding a small amount of aluminum metal to the composition, and zinc oxide (ZnO) is used in place of the moisture-sensitive metal. Upon ignition, a sequence of reactions ensues of the type [6]... 

Ignition of the latter leads to zinc oxide and cobalt(II) oxide in the correct proportion for the formation of cobalt zincate, whilst carbon from the filter paper (see below) prevents the formation of cobalt(III) oxide. All other metals must be removed. 

Violent reactions with ammonium salts, chlorate salts, beryllium fluoride, boron diiodophosphide, carbon tetrachloride + methanol, 1,1,1-trichloroethane, 1,2-dibromoethane, halogens or interhalogens (e.g., fluorine, chlorine, bromine, iodine vapor, chlorine trifluoride, iodine heptafluoride), hydrogen iodide, metal oxides + heat (e.g., beryllium oxide, cadmium oxide, copper oxide, mercury oxide, molybdenum oxide, tin oxide, zinc oxide), nitrogen (when ignited), silicon dioxide powder + heat, polytetrafluoroethylene powder + heat. 

These serve, on the one hand, to increase the flection, and on the other to retard the explosion on igniting the match-head, so that the flame has time to act on the other materials, sulphur, paraffin, etc., which propagate the combustion. Brown umber is a variety of clay colour by the oxides of iron and manganese. Venetian red is ferric oxide, FctOa, and is obtained by the calcination of green vitriol. The use of chalk u 1 Riling material is now rare. Zinc oxide is employed chiefly In the compositions of matches containing phosphorus sesquisulphide, red phosphorus and the like. 

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