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RATES OF DISSOLUTION OF HAFNIUM METAL IN HYDROFLUORIC ACID

Technical Report ·
OSTI ID:4062222
; ;
The rates of dissolution of crystal bar hafnium in hydrofluoric acid (0.050 to 1.00N) were determined from volume measurements of evolved hydrogen according to the established stoichiometry of the equation: Hf + 4HF yields HfF/ sub 4/ + 2H/sub 2/. The reaction followed a first-order rate law for the entire concentration range. The rate of hafnium dissolution was dependent only upon the molecular HF concentration and independent of small additions of Na/sup +/, K/sup +/, F/sup -/, H/sup +/, NO/sub 3//sup / ->s, Bi/sup -/, C/sub 6/H/sub 5/O/sub 7// sup 3-/ to the acid. Large additions of alkali fiu orides resulted in passivation of the metal surface by fluohafnates. The extent of passivation was determined by the relative solubilities of the salt layers in aqueous HF. Small additions of Cr/sub 2/O/sub 7//sup 2-/, MnO/sub 4//sup -/, and BiO/sub 3//sup -/ caused a decrease i n the rate of hydrogen evolution. Addition of equivalent amounts of noble metal salts resulted in passivation of the metal surface. Platinum was most effective, followed by silver and gold. The slow step of dissolution was apparently controlled by the diffusion of un-ionized HF through a protective layer to attack the metal surface. Support for this concept was evidenced by the first-order rate dependence of un-ionized HF and the relatively small activation energy of 5.3 plus or minus 0.5 kcal obtained in both hydrofiuoric and hydrofiuoric-hydrochloric acid mixtures. (auth)
Research Organization:
Missouri. Univ., Rolla. School of Mines and Metallurgy
NSA Number:
NSA-15-014172
OSTI ID:
4062222
Report Number(s):
TID-11932
Country of Publication:
United States
Language:
English

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Related Subjects

BISMUTH
CHEMISTRY
CHROMATES
DIFFUSION
FLUORIDES
HAFNIUM
HAFNIUM FLUORIDES
HYDROCHLORIC ACID
HYDROGEN
IONS
MANGANESE COMPOUNDS
MEASURED VALUES
METALS
MIXING
NITRATES
PLATINUM
POTASSIUM
QUANTITATIVE ANALYSIS
SILVER
SODIUM
SOLUTIONS
SURFACES
VOLUME