Pyrophoric metal powders

Reduction. Hafnium oxide can be reduced using calcium metal to yield a fine, pyrophoric metal powder (see Calciumand calciumalloys). This powder contains considerable oxygen contamination because of oxygen s high solubility in hot hafnium, and caimot be consoHdated into ductile metal. To obtain low oxygen ductile hafnium, the feed must be an oxygen-free halide compound such as hafnium tetrachloride or potassium hexafluorohafnate [16871-86-6]. 

Thermites, pyrophoric metal powders, high explosive incendiaries (HEI)... 

Metal Oxides. Finely dispersed sodium reduces metal oxides on heating at temperatures between 100°C and 300°C, producing pyrophoric metal powders.19... 

Pyrophoricity and detonation behaviour of titanium hydride powders of various particle sizes were studied in comparison with those of titanium metal powders [1]. Maximum dust explosion pressures of 8.2 bar, with a maximum rate of rise of 816 bar/s have been recorded [2]. 

Caution. The metal powder obtained when filtering the reaction solutions may be pyrophoric when dry. 

Although very unreactive in massive forms, the finely divided metal may be pyrophoric, a Japanese study of this hazard has been reported [1]. Consequent upon an explosion in a tantalum dust collector, further study of powder explosion was made. Minimum ignition energies were found to be much lower than previously supposed. An oxide coating makes it susceptible to electrostatic charge generaton and discharge [2]. See entry PYROPHORIC METALS (references 3,9)... 

In finely divided forms (sponge or powder) it readily burns in air to the heptaoxide. See other METALS, PYROPHORIC METALS... 

The important solid hydride UH3 is often more suitable for the synthesis of compounds than is the bulk metal which reacts reacts rapidly and exothermically with hydrogen at 250 to 300PC to give a pyrophoric black powder. The reaction is reversible ... 

Although we have described powder metallurgy as being an ideal process, without limitations or hazards, it does pose some serious safety risks and limitations. The majority of metallic powders and other finely divided solids are pyrophoric, meaning... 

SYNS C.I. 77805 COLLOIDAL SELENIUM ELEMENTAL SELENIUM SELEN (POLISH) SELENIUM ALLOY SELENIUM BASE SELENIUM DUST SELENIUM ELExMEKTAL SELENIUM HOMOPOLYMER SELENIUM METAL POWDER, NON-PYROPHORIC (DOT) VANDEX... 

SELENIUM DISULPHIDE (DOT) see SBROOO SELENIUM DUST see SB0500 SELENIUM ELEMENTAL see SB0500 SELENIUM FLUORIDE see SBSOOO SELENIUM HEXAFLUORIDE see SBSOOO SELENIUM HOMOPOLYMER see SB0500 SELENIUM HYDRIDE see HICOOO SELENIUM METAL POWDER, NON-PYROPHORIC (DOT) see SB0500... 

Oxidation of Tungsten Metal Powder. Tungsten powder, of average grain size > 1 pm, reacts like bulk tungsten. Finer powder qualities, depending on grain size and preparation method, can be pyrophoric. 

Chromium Doping. Additions of chromium compounds can be used to produce very fine metal powder grades (<0.5 pm). Chromium oxide is formed during reduction and acts as a grain refiner. Such powders are subsequently carburized to ultrafine WC. Special precautions have to be taken because of the high pyrophoricity of the metal powder. 

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