Hafnium test solutions

An often-used test schedule in testing zirconium or hafnium is the 2-4-2 day cycle. This schedule gives some indication about the time effect on the corrosivity of the test solution and the corrodibihty of the test specimen. 

Procedure. One drop of the test solution in perchloric acid or cone, hydrochloric acid is treated with a drop of 0.1 % aqueous solution of the dye. A red-violet color indicates hafnium. A blank test with high-purity zirconium is recommended to detect hafnium in the presence of zirconium. 

Procedure. A drop of the test solution is mixed with 5-6 drops of cone, perchloric acid in a micro test tube and one drop of a M solution of quercetin in 96% ethanol is added. A green fluorescence under ultraviolet light indicates the presence of hafnium. 

Most hafnium compounds requite no special safety precautions because hafnium is nontoxic under normal exposure. Acidic compounds such as hafnium tetrachloride hydroly2e easily to form strongly acidic solutions and to release hydrogen chloride fumes, and these compounds must be handled properly. Whereas laboratory tests in which soluble hafnium compounds were injected into animals did show toxicity, feeding test results indicated essentially no toxicity when hafnium compounds were taken orally (33,34). 

In field testing, zirconium or hafnium specimens should be placed nearest the inlet of the process solution when other metals are also being tested. It is desirable to have the specimen or test rack securely fixed in place. Eliminate the possibility of galvanic effects resulting from metal-to-metal contact by using an insulating material. 

The precipitability by polyhydroxyanthraquinones from weakly acid solution is specific for zirconium (and hafnium). The precipitate is an adsorption compound (lake) of zirconium hydroxide and alizarin (compare Al-alizarin lake, page 97). The production of the lake involves the binding, through chemical adsorption, of alizarin on the surface of the Zr(OH)4 sol particles, which are present in solutions of zirconium salts as a result of the hydrolysis Zr+ -f- 4 HgO- Zr(OH)4 -f 4 H+. The hydrolysis equilibrium is constantly disturbed by the removal of Zr(OH)4, so that, in a not too acid solution, there is extensive precipitation of zirconium in the form of the alizarin lake. This lake is also produced by precipitating solutions of zirconium salts with ammoniacal solutions of alizarin. The lake is stable against dilute hydrochloric acid. In strong hydrochloric acid solutions of zirconium salts, alizarin produces a fairly stable hydrosol of the lake (compare the test for fluoride, page 221). 

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