Metal powders, flammability

Ammonium nitrate Acids, metal powders, flammable liquids, chlorates, nitrites, sulfur, flnely divided organic or combustible materials, perchlorates, urea... 

Mercury, chlorine, calcium hypochlorite, iodine, bromine, and hydrogen fluoride Acids, metals powder, flammable liquids, chlorates, nitrites, sulphur, finely divided organics or combustibles Nitric acid, hydrogen peroxide... 

Ammonium Nitrate with acids, metal powders flammable fluids chlorates, nitrates, sulphur and finely divided organics or other combustitnes. 

Einely divided zirconium is classified as a flammable soHd and shipping regulations are prescribed accordingly (103). Metal powder finer than 74 ]lni (270 mesh) is limited to 2.26 kg per individual container. 

FIG. 20-7 Effect of fineness on the flammability of metal powders. Hmi-mann, Nagy, and Brown, U.S. Bur. Mines Rep. Invest. 3722, 1943.)... 

Finely powdered calcium metal is flammable in air because it liberates hydrogen from the moisture. It can be extremely reactive in water but can be dissolved in acids. Calcium is harder than sodium metal, but softer than aluminum. In its elemental form it can be machined (cut on a lathe), extruded (pushed through a die), and drawn (stretched into rods or wires). 

The dust and fumes from the powder form of most manganese compounds, especially the oxides, are very toxic to plants, animals, and humans. Even inhaling small amounts is toxic. The powder form of manganese metal is flammable, and manganese fires cannot be extinguished with water. They must be smothered by sand or dry chemicals. 

The powder and dust of rhodium metal are flammable in air. Some of the compounds may cause skin irritations. It is best to use approved laboratory procedures when handling any of the six elements in the platinum family of metals. 

The limits of flammability of dusts have been investigated (30G, 34G, 35G). Using various metal powders, Boyle and Llewellyn (15G) have found the minimum ignition energy to be proportional to particle size. Browning, Tyler, and Krall (10) report a variation of the lean limit as a function of particle size particles of about 60-micron diameter give the leanest combustible mixtures. 

Metal powders or fibres ignite in an oxygen-fed resonance tube [1], There have been fires in aluminium pressure regulators for oxygen. Aluminium and its alloys can become flammable at as low a pressure as 2 bar. Aluminium regulators are being replaced by brass, use of aluminium cylinders is still regarded as safe [2]. 

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