Document wNZa8Kya0xeL9x3BYkgeoXXd

minute. In very recent experiments on the effect of the thickness of dust lay| was found that, in the equipment used, the lowest ignition temperatures reached with layers Vs inch thick. In nearly all cases, 90 per cent or more off powder was finer than 74 p. Selected results are given for metal powders6 ini. 2, for dusts in the plastics industry6 in Table 3, and for agricultural andS dusts11'16 in Table 4. Data for coal dust clouds in air and in .oxygen and of coal dusts of various volatile contents8 are shown in Figure 1. Powder Aluminum, atomized Aluminum, stamped Antimony Cadmium Chromium Copper Dowmetal Iron, hydrogon reduced Iron, carbon reduced Iron carbonyl Lead, atomized Lead, stamped Magnesium, atomized Magnesiumrmilled Magnesium, stamped TABLE 2 Ignition Temperatures of Metal Powders ,,SU ' '*{ Ignition Ignlfijoj temperature tempera! r C.) Dust Dust ( DuBt cloud 640 layer 750 Powder Manganese cloud 1 & 550 470 Silicon 415 330 570 250 900 -- 700 -- Tin Thorium Thorium hydride (ThHi)" Titanium 030 270!*$ 260 ft .130 430 480 Titanium hydride (Tills) 440" . 315 290 Uranium* 20; 425 390 Uranium hydride (UH.)"* 20 320 230 Vanadium 500; 710 270 5SO 300 Zinc Zirconium* 600' 20 600 490 Zirconium hydride (ZrHO 350. 540- . 475-.... ......Ferrosilicon-(88%-Si).....-- _____-Ml 520 480 Ferrotitanium, low-carbon 370 Magnesium-aluminum (50-50 ) 535 "On exposure in air for several minutes at normal laboratory temperature, layers and UHi ignited spontaneously. ^ "During dispersion through furnace at room temperature, dust clouds of U, UHi; ignited. TABLE.3 Ignition Temperatures of Dusts in Plastics Industry ""Powder Ignition tempera ture of dust cloud rc.j Powder Resins Shellac, rosin, gum ...Vinylbutyral.. Cellulose acetate Pine-rosin base Polyethylene 390 ,390 370 440 410 Molding compositions Ethyl cellulose .. ;Rubb.er,.synthetic,... CelEQoso acetate Kutyrate"^?' Cellulose acetate Methyl methacrylate..... H I. Hartmann, in L. S. Marks, Mechanical Engineers' Handbook, 5th ed 1951, pp. 795-800. 111. Hartmann, Ind. Eng. Chem., 40, 752 (1948). 560 -vMMr-prp,1 TABLE 3 (conltnued) Ignition tempera ture of dust cloud CC.) Powder 450 Uroa 460 Phenolic 460 Polystyrene 470 Vinyl chloride-vinyl ace 490 tate 500 520 520 840 Fillers for molding composi 350 tions Ground alpha pulp 410 Ground cotton flock 450 Ground wood flour Ignition tempera ture of dust cloud (C.) 450 490 560 690 480 470 430 Ignition temperature of dust cloud ( C.)