Abstract: Master alloys and methods of producing same are disclosed, wherein an intermetallic compound is first prepared via thermite processing, then size reduced, then mixed with other components in amounts yielding a mixture in the desired proportion for the master alloy. The mixture is compacted, then heated to produce the master alloy, which is used for making Nickel-based alloys used, (for example), in hydrogen battery electrodes.

Abstract: A new silicon carbide material is made following a procedure including hot pressing to provide a finished product having a microstructure with an optimal grain size of less than 7 micrometers. The material exhibits a dominant failure mode of intergranular fracture requiring significant energy for crack propagation. The method of manufacturing is cost-effective by allowing the use of "dirty" raw materials since the process causes impurities to segregate at multi-grain boundary junctions to form isolated pockets of impurities which do not affect the structural integrity of the material. End uses include use as optical and electronic substrate materials.

Abstract: A method for insulating metal powder particles comprises steps of placing the metal powder particles in a mixing container and adding a monomer in solution to the metal powder particles to form a mixture. The mixture is then stirred to provide an even consistency and is baked to remove solvents. The mixture is then stirred and the monomer is polymerized by exposing the monomer coated carbonyl iron particles to moist gas. The mixture is then ground to form a powder. The powder is suitable for incorporation into plastic resins for subsequent casting to form radio frequency shields having high DC resistance.

Abstract: A slurry compound prepared by a sintering powdery material and a binder is press-molded to obtain a contour for the final product applicable to a bone-implant such as hip prosthesis. The molded body is given a programmed movement of rotation and/or swinging to impart a centrifugal force to the sintering particles which direct toward the inner wall of the mold cavity. The final product obtained after sintering has a hollow interior having no communication to the outside. Imparting conditions of rotating/swinging movement may be changed or programmed in order to achieve a desired structure or constitution of the final product. By way of example, larger particles concentrate near the inner wall of the mold to provide a rough, porous surface of the body, whereas it has a dense core consisting mainly of sintered fine particles. A hip prosthesis having a ceramic-rich femoral head and a metal-rich stem may also be produced by so programming the movement imparting conditions.

Abstract: The invention provides a method of mechanical alloying a titanium-base metal powder. Titanium-base metal powder is provided in a mechanical alloying apparatus. The mechanical alloying apparatus has a controlled atmosphere to prevent excessive oxidation of the titanium-base metal powder. An effective amount of tin process control agent is added to the mechanical alloying apparatus. The mechanical alloying apparatus is operated to weld and fracture the titanium-base metal powder in a manner controlled by the tin process control agent. The controlled welding and fracturing ultimately forms a titanium-base mechanically alloyed powder.

Abstract: A process for producing a thermoelectric material comprises molding a material powder comprising two or more elements selected from the group consisting of bismuth, tellurium, antimony and selenium and having average diameter in the range from 0.05 to 100 .mu.m and sintering the molded material powder with or without hot isostatic pressing. The material powder may be calcinated before the molding. A process for producing a thermoelectric element comprises cutting out pieces of a pillar-like shape from each of a p-type thermoelectric material and a n-type thermoelectric material, connecting the pieces cut out from the p-type thermoelectric material and the pieces cut out from the n-type thermoelectric material alternately with electrodes at the upper faces or the lower faces of the pieces and attaching insulating base plates to the surfaces of the electrodes. The p-type thermoelectric material and the n-type thermoelectric material are respectively produced by the process described above.

Abstract: Tungsten and molybdenum powders are advantageously conditioned for metal injection molding by fluid energy milling the powder prior to batching. A preferred method of conditioning, jet milling, has been found to beneficially effect the particle characteristics to render the metal powder more suitable for injection molding.

Abstract: A titanium-tungsten target material capable of limiting the amount of particles generated during sputtering and a method of manufacturing this titanium-tungsten material. The titanium-tungsten target material has a titanium-tungsten alloy phase which occupies 98% or more of the whole area of the material as observed in a micro-structure thereof. In one example of the manufacturing method, an ingot obtained by melting tungsten and titanium is processde by a solution treatment to form a titanium-tungsten target, or a power obtained by melting the ingot is sintered to form a target. Preferably, the melting may be performed under reduced pressure in an electron beam melting manner. In another example of the manufacturing method, a powder is formed from a molten metal by an atomization method and the obtained powder is sintered to form a titanium-tungsten target. For sintering of the powder, it is preferable to apply hot isostatic pressing or hot pressing.

Abstract: The present invention presents a method of processing ferrous powder materials to produce small component parts exhibiting excellent soft magnetic properties, in particular, residual magnetic flux density. The processing steps involve, in part, mixing with a binder, dewaxing or presintering at a temperature higher than in the conventional dewaxing process, followed by final sintering and a further conversion sintering, at a temperature lower than in the conventional sintering process, to produce parts having density values of over 96% theoretical density and excellent soft magnetic properties. The invented method is suitable for producing small component parts having sufficient strength and excellent soft magnetic properties to make them suitable for miniaturized electrical and electronic equipment.

Abstract: The invention relates to a composite hard metal body of hard material, a binder and embedded reinforcing material, as well as to a process for the production of the composite hard metal body by methods of powder metallurgy.In order to create a composite hard metal body with improved toughness under load, improved hardness and a lower fracture susceptibility, the invention proposes to build in monocrystalline, preferably needle-shaped and/or platelet-shaped reinforcing materials, coated with an inert layer with respect to the binder metal phase and consisting of borides and/or carbides, and/or nitrides and/or carbonitrides of the elements of Groups IVa or Va or mixtures thereof and/or coated monocrystalline reinforcing material of SiC, Si.sub.3 N.sub.4, Si.sub.2 N.sub.2 O, Al.sub.2 O.sub.3, ZrO.sub.2, AlN and/or BN.

Abstract: An (Fe, Co)-B-R tetragonal type magnet having a high corrosion resistance, which has a boundary phase stabilized by Co and Al against corrosion, and which consists essentially of:0.2-3.0 at % Dy and 12-17 at % of the sum of Nd and Dy;5-10 at % B;0.5-13 at % Co;0.5-4 at % Al; andthe balance being at least 65 at % Fe.0.1-1.0 at % of Ti and/or Nb may be present. Alloy powders therefor can be also stabilized.

Abstract: A rivet is formed from a friction-actuated extrustion. The extrusion is produced by a process that utilizes a comminuted rapidly solidified aluminum alloy ribbon as the in-feed for a continuous friction-actuated extruder. Gumming and flow problems are eliminated. The extruded product is devoid of surface blistering. The extrusion is converted into a rivet that has improved ambient and elevated temperature mechanical properties.

Abstract: Ti-W target material for sputtering includes a structure composed of a W phase, a Ti phase, and a Ti-W alloy phase of which 20% or more consist of the area ratio of a micro structure covering the cross section of the Ti-W target material. The Wi-W target material further includes dispersed tungsten particles, the Ti-W alloy phases substantially surrounding the W grains, and the Ti phases dispersed adjacent to the Ti-W alloy phase or the W grains. The formation of the Ti-W alloy phases is capable of reducing a substantial amount of the Ti phase in the target material. It is thus possible to prevent the generation of particles attributable to a difference between sputtering speeds of Ti and Ti-W.

Abstract: A magnesium based metal matrix composite is made from rapidly solidified magnesium alloy powder and SiC particulate using liquid suspension coprocessing or mechanical alloying. The composite is suitable for consolidation into bulk shapes having, in combination, high strength, high stiffness, low density, low coefficient of thermal expansion, and high hardness. The composite is suited for uses in such applications as space and missile guidance and navigation and control system precision components where low density, very high specific stiffness and long term dimensional and environmental stability are principal performance criteria.

Abstract: A process for the production of a powder having a nanocrystalline structure from powders of at least two materials of the groups including metals, metallic compounds, and ceramic materials, in a composition which tends to develop an amorphous phase. The starting powders are subjected to high stresses of at least 12 G in a neutral or reducing atmosphere at about 20.degree. C. until there are no crystallites larger than about 10 nm.

Abstract: In a process for producing a high strength structural member by sintering a starting powder material, a powder mixture of a basic powder and an additional powder is used as the starting powder material. The basic powder is comprised of at least one of an amorphous single-phase alloy powder and at least one kind of a mixed-phase alloy powder which contains a crystalline phase and an amorphous phase and has a crystalline phase volume fraction C (Vf) less than 30%, and the additional powder is comprised of a mixed-phase alloy powder containing a crystalline phase and an amorphous phase and having a crystalline phase volume fraction C (Vf) of at least 30% to less than 80%. The relationship between the minimum volume fraction Pm (Vf) of the additional powder in the starting powder material and the crystalline phase volume fraction C (Vf) in the additional powder is established such that Pm (Vf)=-0.7 C (Vf)+61. This ensures that a structural member having a high strength and a high toughness can be produced.

Abstract: A method for the high volume manufacture of Fe-B-R-T alloy powders without sacrificing the resultant magnetic properties (such as intrinsic magnetic coercivity) of the alloy involves hydrogen decrepitation of vacuum cast or die-upset billets of the alloy. Hydriding is carried out at a partial pressure of hydrogen of between 250 and 760 mm Hg at 100.degree. to 500.degree. C. for 30 minutes to 6 hours or longer, depending upon load size. Dehydriding occurs in a vacuum below 10.sup.-2 mm Hg or in an inert atmosphere possessing a partial pressure of hydrogen below 10.sup.-2 mm Hg. The alloy powder is preferably incorporated in matrix or composite magnets by the addition of a binder prior to pressing and orienting. The binder may set during pressing in a hot die, or by heating after pressing in a cold die.

Abstract: According to the present invention there is now provided a method of making a sintered titanium-based carbonitride alloy. According to the method, melt-metallurgical raw materials containing the metallic alloying elements for hard constituent-forming as well as binder phase-forming elements are melted and cast, using no intentional additions of the elements C, N, B and O, to form a pre-alloy which in solidified condition of brittle intermetallic phases with hard constituent-forming and binder phase-forming elements mixed in atomic scale. The pre-alloy is crushed and/or milled to powder with grain size <50 .mu.m. The powder is carbonitrided for simultaneous formation in situ of extremely fine-grained <0.1 .mu.m, hard constituent particles enclosed in their binder phase.

Abstract: A method is disclosed for preparing an intimate mixture of powders of nickel-chromium-boron-silicon alloy, molybdenum metal powder, and Cr.sub.3 C.sub.2 /NiCr alloy suitable for thermal spray coatings which comprises milling a starting mixture of the above two alloys with molybdenum powder to produce a milled mixture wherein the average particle size is less than about 10 micrometers in diameter, forming an aqueous slurry of the resulting milled mixture and a binder which can be an ammoniacal molybdate compound or polyvinyl alcohol, and agglomerating the milled mixture and binder. The intimate mixture and binder may be sintered in a reducing atmosphere at a temperature of about 800.degree. C. to 950.degree. C. for a sufficient time to form a sintered partially alloyed mixture wherein the bulk density is greater than about 1.2 g/cc.

Abstract: A beryllium metal matrix phase includes up to 70% by volume of beryllium oxide single crystals dispersed therein. The composites are useful for electronics applications because of their light weight, high strength and effective thermal properties.

Abstract: There are described metallic powders comprising agglomerated nanocrystals of an electroactive alloy. The main component of the alloy can be of nickel, cobalt, iron or mixtures thereof while the alloying element is one or more transition metals such as Mo, W, V. Preferably the nanocrystals will be made of an alloy of nickel and molybdenum. An electrode which is used by compacting the powders is also disclosed. Also disclosed, is a process for producing the metallic powders by providing particles of nickel, cobalt and iron with particles of at least one transition metal, (Mo, W, V) and subjecting the particles to high energy mechanical alloying such as ball milling under conditions and for a sufficient period of time to produce a nanocrystalline alloy. Electrodes produced from these powders have an electrocatalytic activity for the hydrogen evolution which is comparable or higher than the electrodes which are presently used in the electrochemical industry.

Abstract: A method of manufacturing a porous electrode for a molten carbonate fuel cell comprises the steps of: pulverizing an Al-base intermetallic compound: mixing Ni powders with the pulverized intermetallic compound to form a slurry which contains Ni powders and the pulverized intermetallic compound, the pulverized intermetallic compound serving as a reinforcement; shaping the slurry like a sheet or a tape; and sintering the sheet or tape-like slurry to form the porous electrode.

Abstract: A metal oxide-type superconductive material is produced by a process which comprises a first step of subjecting a powder raw material containing given proportions of metal elements to be contained in said metal oxide-type superconductive material, to mechanical grinding and alloying simultaneously to obtain an alloy powder and a second step of heat-treating the alloy powder in an oxygen-containing gas atmosphere to obtain a metal oxide.The superconductive material obtained has a high density, a low porosity, a high strength and a high critical current density.

Abstract: A rare earth metal-iron group metal target for a magneto-optical disk is produced by mixing power (a) produced by the rapid quenching treatment of an alloy composed of at least one rare earth metal and at least one iron group metal in a composition range which permits the formation of an eutectic structure, with powder (b) from at least one iron group metal in an amount necessary for meeting the composition requirements of the target; and subjecting the resulting mixture to pressure sintering in vacuum or in an inert gas atmosphere at a temperature lower than a liquid phase-appearing temperature of the mixture to produce a rare earth metal-iron group metal intermetallic bonding layer betwen the particles.

Abstract: A method for making rare earth element, iron and boron sintered permanent magnets, and a particle mixture for use therein. A hydrided 100% dross or particle mixture of virgin alloy particles and scrap alloy particles and/or dross alloy particles are dehydrided and sintered to produce a substantially fully dense article for use as a permanent magnet.

Abstract: Vias each having no pore are formed in a multilayer ceramic substrate by filling through holes of green sheets with conducting material obtained by: kneading mixed powder particles, the powder particles produced by adding copper oxide powder particles in the amount of 50% (in weight) or less to copper powder particles, with a solution including methyl ethyl ketone and 0.5% (in weight) of isosulfonyltridecylbenzene titanate; drying and cracking the kneaded mixed powder particles, producing cracked mixed powder particles; classifying the cracked mixed powder particles with a 100 mesh filter, producing classified mixed powder particles; spheroidizing the classified mixed powder particles with a collision method performed in gases flowing at high speed; and firing the green sheets at a temperature of about 800.degree. C.

Abstract: A complex part composed of rapidly solidified magnesium base metal alloy is produced by superplastic forming at a temperature ranging from 160.degree. C. to 275.degree. C. and at a rate ranging from 0.00021 m/sec to 0.00001 mm/sec, to improve the formability thereof and allow forming to be conducted at lower temperature. The rapidly solidified magnesium based alloy has a composition consisting essentially of the formula Mg.sub.bal Al.sub.a Zn.sub.b X.sub.c, wherein X is at least one element selected from the group consisting of manganese, cerium, neodymium, praseodymium and yttrium, "a" ranges from 0 to about 15 atom percent, "b" ranges from 0 to about 4 atom percent and "c" ranges from about 0.2 to 3 atom percent, the balance being magnesium and incidental impurities, with the proviso that the sum of aluminum and zinc present ranges from about 2 to 15 atom percent. Such an alloy contains fine grain size and finely dispersed magnesium-, aluminum- rare earth intermetallic phases.

Abstract: A method of manufacturing dispersion-strengthened material wherein a first material having a metal matrix M and at least one metal X capable of reacting with boron is supplied in a molten state to a mixing region at a first velocity. A second material having a metal matrix M and boron is supplied to the mixing region at a second velocity. The materials impinge on one another to produce a reaction between the metal X and the boron to form a boride in the metal matrix M. The mixture is solidified and pulverized to a powder which is then cleaned and consolidated.

Abstract: Thermoelectric elements with excellent thermoelectric characteristics such as Seebeck coefficient thermoelectromotive force and thermal conductivity can be produced by molding a powder of metal or metal alloy as the raw material and then sintering; by using as such raw material, ultra fine powders containing Fe and Si as main components and having a mean particle diameter of 50 to 5,000.ANG..

Abstract: To permit an economical manufacture of high-strength sintered members for use in valve timing mechanisms of internal combustion engine by powder metallurgy with liquid-phase sintering, an iron-base powder mixture is provided, which contains 13 to 18% by weight chromium or 3 to 6% by weight molybdenum as a carbide-forming alloying element in the iron alloy powder and also contains 1.5 to 2.6% carbon and 0.4 to 1.0% by weight phosphorus. A corresponding molten iron alloy is atomized into an entraining gas or water jet and is subsequently mixed with the remaining components of the powder.

Abstract: A method is disclosed for preparing an intimate mixture of powders of nickel-boron-silicon alloy and molybdenum metal powder suitable for thermal spray coatings which comprises milling a starting mixture of the alloy and molybdenum powder to produce a milled mixture wherein the average particle size is less than about 10 micrometers in diameter, forming an aqueous slurry of the resulting milled mixture and a binder which can be an ammoniacal molybdate compound or polyvinyl alcohol, and agglomerating the milled mixture and binder. The intimate mixture and binder are preferably sintered in a reducing atmosphere at a temperature of about 800.degree. C. to about 950.degree. C. for a sufficient time to form a sintered partially alloyed mixture wherein the bulk density is greater than about 1.2 g/cc.

Abstract: An aluminum based metal matrix composite is produced from a charge containing a rapidly solidified aluminum alloy, a carbidiferous agent and particles of a reinforcing material present in an amount ranging from about 0.1 to 50% by volume of the charge. The charge is ball milled energetically to uniformly mix the carbidiferous agent within the aluminum matrix, and to enfold metal matrix material around each of the particles while maintaining the charge in a pulverulent state. Upon completion of the ball milling step, the charge is hot consolidated at suitable temperatures to decompose the carbidiferous agent and result in the formation of carbide and oxide particles, and to provide a powder compact having a formable, substantially void-free mass. The compact is especially suited for use in aerospace, automotive, electronic, wear resistance critical components, and the like, which often encounter service temperatures approaching 500.degree. C.

Abstract: A method for producing metal carbide grade powders which comprises forming a wax mixture consisting essentially of in percent by weight about 5 to about 15 paraffin oil, with the balance being an esterified wax and paraffin, heating the wax mixture to a temperature above the melting point to melt the wax mixture and maintain it in the molten state, forming a powder-wax mixture consisting essentially of metal carbide powder, a binder metal, and the wax mixture while heating to a temperature above the melting point of the wax mixture to maintain the wax mixture in the molten state to result in a uniform distribution of the wax mixture on the carbide and binder metal particles, forming a slurry of the powder-wax mixture and water, attritor milling the slurry at a temperature below the melting point of the wax mixture, and removing water and agglomerating to produce metal carbide grade powder wherein a densified article made therefrom exhibits less linear shrinkage than articles made from carbide grade powder abs

Abstract: A method for the production of a metallic powder molding material is disclosed which comprises a step of imparting mechanical energy due to at least one of such physical actions as vibration, pulverization, attrition, rolling, shocks, agitation, and mixing a metallic particles in a vessel whose interior is held under vacuumized atmosphere or an atmosphere of inert gas thereby enabling the metallic particles to contact each other and acquire improvement in surface quality and a step of hot molding the metallic particles thereby producing a molding material.

Abstract: The invention provides a process for production of silver-containing precursor alloys to oxide superconductors, said alloys having reduced amounts of intermetallics. Powders containing metallic elemental components of an oxide superconductor are high energy milled for a predetermined amount of time to increase homogeneity of the mixed metallic elemental components of the oxide superconductor. Silver is then high energy milled into the metallic components. The mixed silver and metallic elemental components of the oxide superconductor are compacted for the silver-containing superconductor precursor. The compacted powder is preferably hot worked at a temperature of at least 50% of the precursor alloy's melting temperature in degrees Kelvin.

Abstract: Process for the powder-metallurgical production of work pieces, particularly tools, containing high-melting point carbides and/or carbonitrides homogeneously distributed in a matrix, in which an amount of elements of the IVa and Va groups, or secondary groups, of the periodic table is adjusted to at least 3 weight percent of the alloy, a low carbon and/or nitrogen concentration is established, and primary precipitates are prevented; and a desired carbon and/or nitrogen content is created by atomization of the melt into powder vaporizing medium.

Abstract: A rapidly solidified aluminum base alloy is formed into a powder and plasma sprayed onto a substrate to provide a uniform and contiguous coating. Deposition and retention of the alloy onto the substrate are effected in a single process step. The coating exhibits improved mechanical and physical properties including excellent corrosion and oxidation resistance and improved elevated temperature strength and thermal stability.

Abstract: A heat-resistant aluminum alloy sinter comprises 5 to 12% by weight of Cr, less than 10% by weight of at least one selected from the group consisting of Co, Ni, Mn, Zr, V, Ce, Fe, Ti, Mo, La, Nb, Y and Hf, and the balance of Al containing unavoidable impurities. A silicon carbide fiber is included for reinforcing the sinter in a fiber volume fraction range of 2 to 30%.

Abstract: A metal extrusion process and apparatus in which a semisolid material is fed into a passageway formed between first and second members, with one of the members being moved toward a die such that the semisolid material is drawn through the passageway and solidifies before passing through the die means.

Abstract: An improved ceramic-metal composite comprising a mixture of a ceramic material with a ductile intermetallic alloy, preferably Ni.sub.3 Al.

Abstract: A metal extrusion process and apparatus in wich a semisolid material is fed into a passageway formed between first and second members, with one of the members being moved toward a die such that the moveable member draws the semisolid material through the passageway and through the die means.

Abstract: A process for dewaxing injection molded metal pieces consisting of a metal/binder mixture, wherein a metal oxide is added to the metal/binder mixture.

Abstract: Rare-earth alloy anisotropic powders consist of, in atomic percent, over 12 percent and not more than 20 percent of R (R is at least one on neodymium and praseodymium or at least one of them and or more rare-earth elements), not less than 4 percent and not more than 10 percent of boron, not less than 0.05 percent and not more than 5 percent of copper and the rest that consists of iron and unavoidable impurities. Up to 20 percent of the iron contained is replaceable with cobalt. The alloy powders are made up of flat crystal grains having mean thickness h (the shortest measure), d not smaller than 0.01 .mu.m and not larger than 0.5 .mu.m and ratio d/h not smaller than 2, where d is the means measure of the grains taken at right angles to the widthwide direction thereof, and the alloy powders are magnetically anisotropic.

Abstract: A method for producing metal carbide grade powders suitable for isostatic compaction which comprises combining a binder metal powder with an esterified wax and heating the wax to a temperature above the melting point of the wax to melt the wax and maintain it in the molten state to form a first mixture, with the amount of wax being sufficient to result in a level of wax in the subsequently produced second mixture of no greater than about 1/2% by weight, combining a metal carbide powder component with the first mixture while maintaining the wax in the molten state, forming a slurry of the second mixture and water, attritor milling the slurry at a temperature below the melting point of the wax, and removing water from the resulting attritor milled mixture to form the metal carbide grade powder.

Abstract: At least two kinds of element metal or half-metal powders are mechanically alloyed in a non-oxidizing atmosphere in a blending machine. Then, the resultant mechanically alloyed powdered blend is heated and pressurized in the non-oxidizing atmosphere at a temperature higher than a minimum temperature required for generating the intermetallic compound from the element powders.

Abstract: This invention relates generally to materials and processes for making materials and, more particularly, to high performance boride dispersion strengthened materials, including alloy-modified, boride dispersion strengthened materials and techniques for making such materials.

Abstract: Magnesium alloy having a breaking load of at least 290 MPa, more particularly at least 330 MPa, having the following composition by weight: Al 2-11%, Zn 0-12%, Mn 0-0.6%, Ca 0-7%, but with the presence of at least Zn and/or Ca, having a mean particle size less than 3 .mu.m, a homogeneous matrix reinforced with intermetallic compounds having a size less than 1 .mu.m precipitated at the grain boundaries, this structure remaining unchanged after storage at 200.degree. C. for 24 hours; and a process for producing it by rapid solidification and consolidation by extrusion at a temperature between 200.degree. and 350.degree. C.

Abstract: The invention describes a method of manufacturing a magnet on the basis of Re.sub.2 Fe.sub.14 B. To this end, a shaped body of the said composition is sintered by means of induction heating to a density exceeding 95% of the theoretical maximum density. The method according to the invention enables the manufacture of magnets having excellent properties in a very short time, these properties being: a high energy product, a large remanence, a high density, a large intrinsic coercive force and a small particle size.

Abstract: An improved method is proposed for the preparation of a sintered permanent magnet of a rare earth-iron-boron alloy having remarkably improved magnetic properties and stability by the powder metallurgical process. The scope of the inventive method consists in the particle size classification of the alloy powder for compression molding into a powder compact to be sintered, by which particles having a finer particle diameter and, preferably, a coarser particle diameter than the respective critical values are removed so as to effectively prevent oxidation of the too fine particles and improving the magnetic orientation of the particles as well as the sintering behavior of the particles.

Abstract: A tungsten carbide powder and cemented tungsten carbide article made from the powder are disclosed. The powder has a particle size of greater than 20 micrometers in diameter and no particles less than one-half the average particle size or greater than two and one-half times the average particle size.