Silica crucible

The equilibrium levels of the reaction products are very small, but both can dissolve in liquid sodium, and sodium oxide can form compounds with silica. As a consequence, the reaction moves to the right, leading to further reduction of silica. Nevertheless, vitreous silica crucibles have been used sucessfully for containing molten antimony (850°C), copper (1 210°C), gallium (1 100°C), germanium (1 100°C), lead (500°C) and tin (900 C). 

Silica crucibles of similar pattern are also available, and, although expensive, have certain advantages in thermal stability. 

Attention is directed to the fact that if ignition is carried out in a platinum crucible at a temperature above 1100°C some reduction to the oxide Fe304 may occur, and at temperatures above 1200 °C some of the oxide may be reduced to the metal and alloy with the platinum. This accounts in part for the contamination of the platinum crucible by iron which sometimes occurs in analytical work. This oxide is not produced if silica crucibles are employed for the ignitions. 

In this method lg dried soil in a silica crucible is mixed with 5ml 0.2N sodium hydroxide and 10ml absolute ethanol and left to evaporate on a hot plate for 12h. The residue is digested with 0.6N sulphuric acid. After treatment with ethylene oxide and acetonitrile the acetonitrile layer is recovered. 

Procedure Moisten 1 g of carbenicillin sodium in a silica crucible with 2 ml of sulphuric acid. Heat, gently at first, then more strongly until all carbon is removed and a white ash is obtained. Allow to cool and add 5 ml of a mixture of nitric acid and hydrochloric acid and evaporate to dryness on a water-bath. Add 3 ml of hydrochloric acid, warm to dissolve and add sufficient water to produce 25 ml. 

Transfer a 5.0g sample to a tared porcelain or silica crucible (previously heated and cooled in a desiccator) and add sufficient ale to cover the sample. Place the crucible on a hot plate at low heat and ignite the ale. When the ale bums out and the sample is completely carbonized, heat the crucible over a Bunsen burner und1 all the carbonaceous matter of sample disappears. Then cool In a desiccator and weigh. Calc the gain in wt as % ash. In case of an abnormally high result, run a blank on the ale used... 

Usually, green-emitting ZnS Cu phosphors are used for industrial applications. The preparation consists of firing a mixture of ZnS, Cu(N03)2 6H20 (corresponding to 50-1000 ppm Cu in the phosphor), and 5wt% NaCl at 900-1000 °C in covered fused silica crucibles [5.327]. 

The alkali-metal halide phosphors are produced by firing the corresponding alkali-metal halide and the activator in platinum or fused-silica crucibles under an inert atmosphere. 

Residue on Ignition Ignite 1 g of sample as directed under Residue on Ignition, Appendix IIC, using a silica crucible and moistening the residue with 2 mL of nitric acid and 1 mL of sulfuric acid. 

In summary, the apparatus comprised a conventional (domestic) microwave oven with a maximum power output of 1.2 kW (1). The reactor (2) was a fused silica crucible placed in a moulded microwave-transparent insulating brick (3) that was suspended from the... 

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