Abstract
A methanolic bromine method for determination of chromium oxide inclusion in Cu-Cr alloy has been presented. In order to decide the optimum condition for extracting the inclusion, the effects of decomposition temperature, decomposition time, etc. on the solubility (recovery) of chromium oxide have been studied by the use of synthesized pure chromium oxides and internally oxidized Cu-Cr alloys. The chromium oxide inclusion has been isolated completely as residue from matrix by the methanolic bromine method.
An acid decomposition method has also been studied, but it is not suitable for the determination of the oxide inclusion. On the other hand, it has been found that precipitated metallic chromium and the chromium present as α-solid solution in Cu-Cr alloy can be fractionally determined by the acid decomposition method.
The recommended procedures are as follows.
(1) Methanolic bromine method (determination of chromium oxide inclusion) : 15g of Cu-Cr alloy is decomposed with methanolic bromine (methanol 200ml+bromine 20ml) in a decomposition flask at 6065°C for 3hr. The solution is filtered through a filter paper. The residue is washed with methanol, ignited in a porcelain crucible and fused with 3g of potassium pyrosulfate. The melt is leached with 6ml of 18N sulfuric acid and water, then made up to 50ml with water. The amount of chromium in this solution (chromium present as oxide inclusion) is determined spectrophotometrically with diphenylcarbazide.
(2) Acid decomposition method (determination of precipitated metallic chromium and the chromium present as α-solid solution): 1g of Cu-Cr alloy is decomposed with 16ml of nitric acid (1+2) in a 200ml beaker on a water bath. The solution is filtered through a filter paper and the residue is washed with nitric acid (1+100). The washing solution is combined with the filtrate and the amount of chromium in the combined solution (the chromium present as α-solid solution) is determined spectrophotometrically with diphenylcarbazide. On the other hand, the residue is treated in accordance with the above mentioned procedure (1), and the chromium isolated as residue (precipitated metallic chromium+chromium oxide inclusion) are determined spectrophotometrically. Then, a correction is made by deducting the chromium present as oxide inclusion determined by methanolic bromine method from the chromium isolated as residue in this procedure, and finally the precipitated metallic chromium in Cu-Cr alloy is determined.
