Dusts and powders

A. D. TSvcaoa, Adhesion of Dust and Powder, Consultants Bureau, New York, 1982. 

ILZRO Zinc dust and powder, ILZRO, Res Triangle Park, NC, 118, (1982)... 

Zimon, A. D. Adhesion of Dust and Powders Consultants Bureau New York, 2nd Edition, 1982. 

Dry dusts and powders Fine rubber dust, bakelite moulding powder dust, cotton dust, light shavings, soap dust, leather shavings 3000-4000 15-20... 

The next task in considering the electrostatic hazards associated with a fluidized bed is to consider the specific conditions required for the ignition of suspended dust and powders. It is crucial to cover this subject because... 

Preliminaries. The combustion of suspended dusts and powders is quite complex and only imperfectly understood. The complexity stems from both fundamental and practical considerations. On the fundamental side, the ignition of suspensions of finely divided solids is influenced by hard-to-quantify factors such as the time-varying concentration of solids, the chemical activity and morphology of the particulate, and the degree of confinement provided by the vessel. On the practical side, industrial conditions are seldom sufficiently well-controlled or characterized to justify application of existing theoretical models. For all the above reasons, this chapter can provide only a very abbreviated coverage of ignition basics. The reader is referred to other sources for in-depth treatment of dust and powder explosions (Bodurtha, 1980 Bartknecht, 1981 Bartknecht, 1987). 

The relative rarity of dust and powder ignitions makes them a unique sort of industrial safety threat. Because their occurrence is not routine, operating personnel eventually relax their guard, and too often this sort of behavior leads to dangerous incidents. The evidence that dust explosions are almost unknown within fluidized beds is an especially challenging problem for the safety officer, who must encourage vigilance even when no one remembers the last electrostatic incident. 

Zinc is a bluish-white metal which dissolves readily in strong acids. In nature it occurs as a sulfide, oxide, or carbonate. In solution, it is divalent and can form hydrated Zn2+ cations in acids, and zincated anions — probably Zn(OH)42 — in strong bases (USEPA 1980, 1987). Zinc dust and powder are sold commercially under a variety of trade names Asarco, Blue powder, Cl 77949, Cl pigment metal 6, Emanay zinc dust, granular zinc, JASAD Merrillite, LI 5, and PASCO (USPHS 1989). Selected physical and chemical properties of zinc, zinc chloride, and zinc sulfate are listed in Table 9.2. 

Iron dust from most iron compounds is harmful if inhaled and toxic if ingested. Iron dust and powder (even filings) are flammable and can explode if exposed to an open flame. As mentioned, excessive iron in the diet may cause liver damage. 

The dust and powder of cobalt metal, ores, and some compounds, such as cobaltous nitrate [ColNOfljT bH O], are flammable and toxic if inhaled. Cobaltous acetate [ColCjHjOjlj dHjO], which is soluble in water, is not allowed to be used in food products because of its toxicity. 

Nickel dust and powder are flammable. Most nickel compounds, particularly the salts, are toxic. NiSO is a known carcinogen. 

Copper dust and powder, as well as a few of its compounds, are flammable, or even explosive when ignited in contained areas. Many of copper s compounds are extremely toxic and poisonous either with skin contact or when inhaled or ingested and should be handled by pro-... 

As mentioned, zinc dust and powder are very explosive. When zinc shavings are placed in acid or strong alkaline solutions, hydrogen gas is produced, which may explode. Many of zinc s compounds are toxic if inhaled or ingested. 

Rhenium is flammable in powder form. Rhenium dust and powder and many of its compounds are toxic when inhaled or ingested. 

The elemental metal form of iridium is almost completely inert and does not oxidize at room temperatures. But, as with several of the other metals in the platinum group, several of iridiums compounds are toxic. The dust and powder should not be inhaled or ingested. 

All forms of tellurium are toxic in gas form. The vapors of all the compounds of the dust and powder forms of the element should not be inhaled or ingested. When a person is poisoned with tellurium, even in small amounts, the breath will smell like garlic. 

The dust and powder of thulium are explosive and toxic if inhaled or ingested. As with all radioactive elements, thuhum can cause radiation poisoning. 

Ytterbium dust and powder can explode and may be toxic if inhaled. The compound, ytterbium arsenate is a poison. 

After a pesticide is manufactured in its relatively pure form (the technical grade material) the next step is formulation - processing a pesticide compound into liquids, granules, dusts, and powders to improve its properties of storage, handling, application, effectiveness, or safety [9]. The technical grade material may be formulated by its manufacturer or sold to a formulator/ packager. 

Dry products can include dusts, powders, and granules. Dusts and powders are manufactured by mixing technical grade material with the appropriate inert carrier and grinding the mixture to obtain the correct particle size. Several rotary or ribbon blender-type mixers mix the product. Figure 6 shows a typical dry formulation unit for pesticides [8]. 

Jewelers and diamond cutters, however, were skeptical. To remove certain flaws, they had often heated diamonds, carefully packed in chalk dust and powdered charcoal, and had never experienced any loss. After several inconclusive experiments had been made by others, Maillard, a famous gem cutter, placed three diamonds, closely packed in charcoal dust, in the bowl of a tobacco pipe, and enclosed it in sheet iron inside a crucible filled with a lining of chalk dust and a fusible sand used for castings. After moistening the mixture with salt water and letting it dry, Maillard heated the crucible in Macquer s furnace. The contents soon became so fluid that it was necessary to allow the furnace to cool. 

The polished powder, bathed and dried, should undergo final screening to separate dust and powder grains. 

A. Zimon, Adhesion of dust and powder, Plenum Publishing Corporation, 1982. 

Capillary condensation is also important in the binding of dust and powder particles by water. Particles separated by a thin layer of water are held together very strongly by capillary forces. The inhibition of evaporation due to the concave shape of the air-water interface enhances the duration of this particle binding. 

The dust and powder preparations of copper compounds are irritating to the skin, respiratory tract, and particularly to the eyes. The soluble copper salts (such as the sulfate and acetate) are corrosive to mucous membranes and the cornea. Limited solubility and absorption probably account for generally low systemic toxicities of most compounds. The more absorbable organic copper compounds exhibit the greatest systemic toxicity in laboratory animals. 

Disperse systems with gaseous dispersion medium, regardless of the aggregate state of dispersed phase, are referred to as aerosols. The systems in which the dispersed phase is liquid are referred to as fogs those in which it is solid are called smokes in the case of finely dispersed matter or dusts and powders in the case of coarsely dispersed matter. Aerosols in which the liquid phase is present due to vapor condensation at the surface of solid particles along with the solid phase, are commonly referred as smogs . Aerosols of this type are usually present in the atmosphere of large industrialized cities. 

Combustible solid.Dust may form explosive mixture with air (flash point 334°F/168°C Fire Rating 1). Violent reaction with nitric acid forms explosive nitro materials in the presence of sulfuric acid. Dust and powder forms explosive mixture with air. Incompatible with strong acids, alkalis, aliphatic amines, alkanolamines, alkylene oxides, ammonia, epichlorohydrin, isocyanates, nitrates, nitromethane, sodium nitrite, strong oxidizers. On small fires, use dry chemical powder (such as Purple-K-Powder), Halon , alcohol-resistant foam, water spray, or CO2 extinguishers. Combustion produces phthalic anhydride and carbon oxides. 

BENZENEDIOL (120-80-9) C HsOj Combustible solid (flashpoint 260°F/127°C cc autoignition tenq) 915°F/510°C Fire Rating 1). Dust and powder can form explosive mixture with air. A reducing agent. Violent reaction with strong oxidizers concentrated nitric acid acid chlorides acid anhydrides. Flow or agitation of substance... 

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