Hafnium oxide sulfate

Figure 4.3. Chemical sequence representing deposition of hafnium oxide sulfates and generalized formulation for HafSOx. ...

In the initial thiocyanate-complex Hquid—Hquid extraction process (42,43), the thiocyanate complexes of hafnium and zirconium were extracted with ether from a dilute sulfuric acid solution of zirconium and hafnium to obtain hafnium. This process was modified in 1949—1950 by an Oak Ridge team and is stiH used in the United States. A solution of thiocyanic acid in methyl isobutyl ketone (MIBK) is used to extract hafnium preferentially from a concentrated zirconium—hafnium oxide chloride solution which also contains thiocyanic acid. The separated metals are recovered by precipitation as basic zirconium sulfate and hydrous hafnium oxide, respectively, and calcined to the oxide (44,45). This process is used by Teledyne Wah Chang Albany Corporation and Western Zirconium Division of Westinghouse, and was used by Carbomndum Metals Company, Reactive Metals Inc., AMAX Specialty Metals, Toyo Zirconium in Japan, and Pechiney Ugine Kuhlmann in France. 

After extraction, the loaded solvent contains 6 g T1 zirconium as zirconium oxide with 0.2% hafnium oxide. The raffinate is left with 0.2 to 0.3 g l l of the oxides of zirconium and hafnium of this, 70-90% is hafnium oxide. This raffinate can act as a feed solution for the recovery of pure hafnium oxide. The loaded extractant, on the other hand, is subjected to a scrubbing operation with pure zirconium sulfate solution to eliminate any co-extracted hafnium. This scrubbing operation is essentially a displacement reaction ... 

Hafnium Acetate. Hafnium acetate [15978-87-7], Hf(OH)2(CH2COO)2, solutions are prepared by reacting the basic carbonate or freshly precipitated hydroxide with acetic acid. The acetate solution has been of interest in preparing oxide films free of chloride or sulfate anions. 

The crude tetrachloride mixture of zirconium and hafnium is dissolved in ammonium thiocyanate solution. The solution is extracted with methyl isobutyl ketone (MIBK). MIBK is passed countercurrent to aqueous mixture of tetrachloride in the extraction column. Halhium is preferentially extracted into MIBK leaving zirconium in the aqueous phase. Simultaneously, zirconium tetrachloride oxidizes to zirconyl chloride, ZrOCb. When sulfuric acid is added to aqueous solution of zirconyl chloride, the chloride precipitates as a basic zirconium sulfate. On treatment with ammonia solution the basic sulfate is converted into zirconium hydroxide, Zr(OH)4. Zirconium hydroxide is washed, dried, and calcined to form zirconium oxide, Zr02. 

Explosive reaction with acetylene, antimony powder, hafnium powder + heat, tetraamine copper(II) sulfate + ethanol, trioxygen difluoride (possibly ignition), polyacetylene (at 113°C). Forms sensitive, explosive mixtures with potassium (impact-and heat-sensitive), sodium (shock-sensitive), oxygen difluoride (heat-sensitive). Reacts to form explosive products with ammonia, ammonia + Uthium 1-heptynide, ammonia + potassium, butadiene + ethanol + mercuric oxide, silver azide. 

Hafnium (IV) oxide is prepared by calcination of the hydroxide, oxalate, oxychloride or sulfate at 600-1000°C. The crystallization of the oxide starts at 400°C. 

Hafnium Content. The hafnium concentration is best determined by the method of Claasen as modified by Schumb and Pittman, Willard and Freund, and the checkers of this synthesis. An aliquot of. the zirconium hafnium solution that will provide about 1 g. of the oxide is diluted with water in a 250-ml. beaker. An excess of ammonium hydroxide is added to precipitate the hydroxide. The precipitate is filtered, washed free of sulfate, and then dissolved in 10 ml. of hot concentrated hydrochloric acid. The solution is placed in a 50-ml. beaker and is evaporated almost to dryness to dehydrate the silicic acid. The residue is treated with 15 ml. of hot 8 N hydrochloric acid and the insoluble material removed by filtration on a coarse paper. 

Total Oxide, RO2. An aliquot of the zirconium hafnium solution that will provide approximately 0.5 g. of the ignited oxide is diluted with water to 100 ml. and treated with ammonium hydroxide to precipitate the mixed hydroxides. The precipitate is filtered on quantitative paper, washed free of sulfate, placed in a weighed crucible, and ignited (900°) to constant weight in a muffle furnace or over a Fisher burner. 

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