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clinging between grains does not have a dominant effect on the bulk behavior of the material. Only when the grains are very small and lightweight does the Van der Waals force become predominant, causing the material to clump like a powder. The cross-oversize between flow conditions and stick conditions can be determined by simple experimentation.
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that causes individual grains to cling to one another. This force is present not just in powders, but in sand and gravel, too. However, in such coarse granular materials the weight and the inertia of the individual grains are much larger than the very weak Van der Waals forces, and therefore the tiny
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instead of traveling in straight lines. For this reason, powders may be an inhalation hazard. Larger particles cannot weave through the body's defenses in the nose and sinus, but will strike and stick to the mucous membranes. The body then moves the mucus out of the body to expel the particles. The
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forces between the particles tend to resist their becoming airborne, and the motion of wind across the surface is less likely to disturb a low-lying dust particle than a larger sand grain that protrudes higher into the wind. Mechanical agitation such as vehicle traffic, digging or passing herds of
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that cross continents and oceans before settling back to the surface. This explains why there is relatively little hazardous dust in the natural environment. Once aloft, the dust is very likely to stay aloft until it meets water in the form of rain or a body of water. Then it sticks and is washed
263:
than can a coarser granular material. When deposited by sprinkling, a powder may be very light and fluffy. When vibrated or compressed it may become very dense and even lose its ability to flow. The bulk density of coarse sand, on the other hand, does not vary over an appreciable range.
372:". It is an important powder property which is relevant to powder aerosolization. It also has implications for human exposure to aerosolized particles and the associated health risks (via skin contact or inhalation) in workplaces.
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Powders are transported in the atmosphere differently from a coarse granular material. For one thing, tiny particles have little inertia compared to the drag force of the gas that surrounds them, and so they tend to
390:. Since powders have a very high surface area, they can combust with explosive force once ignited. Facilities such as flour mills can be vulnerable to such explosions without proper dust mitigation efforts.
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provide upward forces that may counteract the downward force of gravity. Coarse granulars, on the other hand, are so heavy that they fall immediately back to the ground. Once disturbed, dust may form huge
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flows differently than a powder, because a liquid cannot resist any shear stress and therefore it cannot reside at a tilted angle without flowing (that is, it has zero
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conveying is the transport of powders or grains through a pipe by blowing gas. A gas fluidized bed is a container filled with a powder or granular substance that is
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Duran, J., Reisinger A., Sands, Powders, and Grains: An
Introduction to the Physics of Granular Materials. November 1999, Springer-Verlag New York, Inc., New York,
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might become a powder after it has been thoroughly dried, but is not considered a powder when it is wet because it does not flow freely. Substances like dried
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deposits in a quiet lake or sea. When geological changes later re-expose these deposits to the atmosphere, they may have already cemented together to become
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smaller particles on the other hand can travel all the way to the lungs from which they cannot be expelled. Serious and sometimes fatal diseases such as
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Some powders may be dustier than others. The tendency of a powder to generate particles in the air under a given energy input is called "
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Many other powder behaviors are common to all granular materials. These include segregation, stratification, jamming and unjamming,
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Because of their importance to industry, medicine and earth science, powders have been studied in great detail by
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Fayed, M.E., Otten L. (editor), Handbook of powder science & technology, second edition, Chapman & Hall,
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Many common powders made in industry are combustible; particularly metals or organic materials such as
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The aerodynamic properties of powders are often used to transport them in industrial applications.
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Smalley, I.J. 1964. Flow-stick transition on powders. Nature 201, 173–174. doi:10.1038/201173a0
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refer to the coarser granular materials that do not tend to form clumps except when wet.
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are a result from working with certain powders without adequate respiratory protection.
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Rodhes, M (editor),Principles of powder technology, John Wiley & Sons, 1997
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in the atmosphere for a very long time. Random motion of the air molecules and
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Typically, a powder can be compacted or loosened into a vastly larger range of
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are sometimes used to distinguish separate classes of material. In particular,
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between the grains, and therefore they do not flow freely like a powder. A
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Some metals become especially dangerous in powdered form, notably
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Also, if powder particles are sufficiently small, they may become
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The clumping behavior of a powder arises because of the molecular
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Microstructure of a steel powder particle (image 0.15 mm wide)
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when shaken or tilted. Powders are a special sub-class of
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This article is about the substance. For other uses, see
37:"powders" redirects here. For the Eartheater album, see
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Dry, bulk solid composed of fine, free-flowing particles
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refer to those granular materials that have the finer
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by blowing gas upwardly through it. This is used for
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Many manufactured goods come in powder form, such as
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152:, and that therefore have a greater tendency to
549:Fundamentals of Particle Technology – free book
365:, chemically reacting the gas with the powder.
436:and therefore may display an angle of repose.
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94:Learn how and when to remove this message
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243:, and researchers in other disciplines.
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57:This article includes a list of general
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535:Physics of Blown Sand and Desert Dunes
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401:Comparison with other substances
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342:contains dust but no mudstone.
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330:downstream to settle as
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1116:Extra-amniotic infusion
721:Molecular encapsulation
653:Osmotic delivery system
648:Time release technology
78:more precise citations.
32:Powder (disambiguation)
1419:Central nervous system
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122:composed of many very
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247:Mechanical properties
134:, although the terms
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948:Metered-dose inhaler
933:Anesthetic vaporizer
229:mechanical engineers
1373:Transdermal implant
1333:(into tissue/blood)
1110:Intrauterine device
991:Anaesthetic machine
986:Oxygen concentrator
293:Reynolds' dilatancy
269:Van der Waals force
220:are also examples.
1485:Nanocell injection
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893:Dry-powder inhaler
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225:chemical engineers
196:powders, and some
132:granular materials
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1465:Intracardiac
1404:Intravitreal
1366:Injector pen
1361:Subcutaneous
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1302:Jet injector
1287:Dermal patch
1100:Vaginal ring
1068:Insufflation
820:Effervescent
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1432:Intrathecal
1356:Intradermal
1348:transdermal
1315:Parenterals
1221:Topical gel
1177:Murphy drip
1155:Suppository
1043:Nasal spray
977:Oxygen mask
826:Chewing gum
765:Oral mucosa
327:dust storms
154:form clumps
150:grain sizes
128:flow freely
110:Iron powder
76:introducing
1515:Categories
1320:Injections
1083:Urogenital
1019:Ophthalmic
875:inhalation
849:Toothpaste
777:sublingual
741:Suspension
711:Herbal tea
479:References
462:Grain size
359:fluffed up
322:turbulence
289:compaction
287:shearing,
285:frictional
279:, loss of
241:geologists
237:physicists
84:April 2010
59:references
1325:infusions
1257:Liposomes
1053:Eye drops
1048:Ear drops
959:Vaporizer
954:Nebulizer
844:Mouthwash
773:sublabial
696:Electuary
686:Decoction
370:dustiness
355:Pneumatic
318:suspended
311:silicosis
299:Transport
277:fragility
190:gunpowder
176:, ground
158:Granulars
126:that may
1496:PIC line
1437:Epidural
1277:Lip balm
1252:Hydrogel
1243:solution
1226:Liniment
1211:Ointment
1170:Hydrogel
1165:Solution
1150:Ointment
1090:Ointment
1063:Hydrogel
1058:Ointment
854:Ointment
815:Lozenges
805:Lollipop
751:Tincture
736:Solution
716:Hydrogel
701:Emulsion
643:Pastille
440:See also
419:cohesion
395:titanium
347:cohesive
340:regolith
336:mudstone
233:chemists
218:regolith
194:cosmetic
141:granular
1531:Powders
1196:topical
1134:enteral
1095:Pessary
925:Liquids
898:Smoking
836:Liquids
731:Softgel
678:Liquids
638:Capsule
615:enteral
204:, fine
146:powders
72:improve
18:Powders
1391:Organs
1272:Lotion
1192:Dermal
1130:Rectal
1105:Douche
885:Solids
822:tablet
787:Solids
769:buccal
726:Powder
691:Elixir
633:Tablet
625:Solids
541:
524:
514:
503:
423:liquid
178:coffee
136:powder
116:powder
61:, but
1267:Cream
1231:Paste
1160:Enema
1112:(IUD)
1028:nasal
950:(MDI)
858:Spray
746:Syrup
407:paste
388:flour
186:toner
174:sugar
170:flour
164:Types
120:solid
1492:pump
1344:Skin
1241:DMSO
1236:Film
1024:otic
979:and
800:Film
602:Oral
539:ISBN
522:ISBN
512:ISBN
501:ISBN
415:clay
345:The
291:and
210:snow
208:and
206:sand
202:dust
138:and
969:Gas
411:gel
409:or
332:mud
1517::
1026:,
775:,
771:,
592:,
533:,
405:A
397:.
295:.
283:,
239:,
235:,
231:,
227:,
212:,
192:,
188:,
180:,
172:,
114:A
1449:,
1350:)
1346:(
1198:)
1194:(
1136:)
1132:(
1021:,
917:0
913:0
877:)
873:(
779:)
767:(
617:)
613:(
582:e
575:t
568:v
545:.
507:.
430:.
97:)
91:(
86:)
82:(
68:.
41:.
34:.
20:)
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