The determination of carbon in titanium, zirconium and zircaloy

As the carbon concentrations of titanium, zirconium and zircaloy range from 10 to 100 tiq/q their determination seems easier than for aluminium. 

It is however complicated by the fact that these materials can mostly not be burnt in compact form and that finely divided samples may react in an explosive way. 

The first carbon determinations in titanium were based on a known method of steel analysis (11), namely the photometric measurement of the yellow colour resulting from the decomposition of carbides with nitric acid. The procedure is as follows a 1 g sample is dissolved in 20 ml sulphuric (1+3) and 10 ml fluoroboric acid (prepared by addition of 130 g boric acid to 280 ml hydrofluoric acid (48 %) under ice cooling) under gentle heating. After dissolution, 5 ml nitric acid (1+1) is added and the solution is filtered into a 50 ml calibrated flask and analyzed by photometry at 450 nm. The colour is stable for 3 hrs. Impurities present in technical titanium do not interfer. 

Although this method seems easy to apply, it found no use in practice, but is interesting from a theoretical point of view. 

A combustion method with 3r vimetric determinati of carbon dioxide after absorption on ascarite is described by Nunemaker and Shrader (12). 0.5 g finely divided sample is mixed with 0.5 g iron chips and 0.3 to 0.5 g brass, and is burnt at 1200°C in an oxygen stream in a sintercorundum boat fitting in a quartz tube. Before absorption, the combustion gases are purified in a tube filled with copper oxide, platinum asbestos and silver wool at 600°C. The method allows the determination of 50 to 10000 Mg/g carbon with an accuracy of 50 Mg/g. 

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