Submicron powder

Li et al. [80] reported SrTi03 submicrmi crystallites and nanocrystals from a starting raw material of Ti02 powder (submicron or nanosized) at 700 C by an eutectic NCl-KCl molten-salt method, and found that Ti02 played an important role in the morphology and size of the obtained SrTiOa. 

Production of submicron powder for hot pressing or hot isostatic pressing of high-precision tooling (see Ch. 19). 

Submicron pSiC powder by reacting silane and acetylene in a 10-50 W continuous-wave CO2 laser beam.P" l... 

Aluminum nitride submicron powder from aluminum alkylP5] and from the reaction of aluminum powder, lithium salt, and nitrogen at 1000°C.P 1... 

Bauer,R., Smulders,R, Geus,E., vanderPut, J., and Schoomman, J., Laser Vapor Phase Synthesis of Submicron Silicon and Silicon Nitride Powders from Halogenated Silanes, Ceram. Eng. Sci. Proc., 9(7-8) 949-956(1988)... 

Activation methods can be divided into two groups. Activation by addition of selected metals (a few wt%), mainly transition metals, e.g., fine powders of Fe, Ni, Co, Cr, Pt, Pd, etc. ", or chlorides of these metals when these are reducible to the metal by hydrogen during presintering. The mechanism of activation is not understood (surface tension, surface diffusion, etc.) but is related to the electronic structure of the metal additive. Activation by carbon is also effective. Alternatively, activation utilizes powders in a specially activated state, e.g., very fine (submicronic) powders. ... 

For the production of preceramic slurries, fillers in the submicron range have to be used to achieve homogeneous infiltration of a fiber bundle with several thousands of filaments. This requires detailed knowledge of the rheological behavior of the powder-filled dissolved polymers. Additives are necessary to achieve high filler contents and good rheological behavior. 

The reductions generate a finely divided black powder. Particle size analyses indicate a range of sizes from one to two microns to submicron depending on the metal and, more importantly, on the method of preparation. 

A variety of techniques are available for sizing particles of pharmaceutical interest. The goal of this chapter is to provide an overview of common techniques currently in use for sizing of powders, and to illustrate their applications. The discussion will focus on techniques used to characterize powders above one micron (jxm) however, it should be emphasized that in some cases the same methods may also be applicable to submicron particles. 

It has been suggested that the explanation of pulmonary disease among powder workers in other countries may lie in the duration of exposure, the size of the particles, the density of the dust, and especially the fact that all reported cases have been associated with exposure to a submicron-sized aluminum pyrotechnic flake (powder), which has been lubricated with a nonpolar aliphatic oil rather than the usually employed stearic acid 7... 

This is consistent with the result that Horowitz et al. have found on submicron particles obtained by a hyponitrite method they are too small to give any diamagnetic behavior. However, the heat capacity measurement shows a break at 90 K that corresponds to about 90% of superconducting phase in the powder (16). 

However, copper alkoxides with longer chains appear to be more soluble in their parent alcohol. S. Shibata et al. (20) have used the n-butoxides of Y, Ba and Cu dissolved in n-butanol and hydrolyzed with water. They obtain a precipitate of oxides that is composed of a very fine submicron powder that readily sinters starting above 250°C. However, the different reaction rates for the hydrolysis and the precipitation of the three different cations lead to cationic segregation. 

To obtain effective materials for catalytic combustion, Arai and co-workers developed a preparation method based on the hydrolysis of the alkoxides of the components.12 This sol-gel method was originally developed to prepare high-purity submicron powders of alkaline or alkaline-earths titanates or zircon-ates.13,14 The method is particularly suitable for low-temperature production of mixed oxides due to the effective mixing of the components at the atomic level that can be obtained in the gel precursor. 

Considerable recent activity in the area of ceramic processing is aimed toward the formulation of materials with high strengths, comparable to the room temperature strength of metal alloys, at high temperatures (of the order of 2000 K). The impetus comes from the significant gains made in the last 20 years with materials formed from submicron powders of silicon nitride and silicon carbide and the promise of similar improvements in the near future. 

Powders from organometallics. Fine pigment powders are also possible. Metal alkoxides such as titanium isopropoxide, which is soluble in supercritical ethanol, can undergo rapid expansion spraying to form submicronic titanium dioxide powders. 

To a mixture of KF/A1203 (0.950 g, 40% by weight) and palladium black (0.050 g, 0.470 mmol, 99.9+% as a submicron powder) contained in a clean, dry, round-bottomed flask was added p-methylphenylboronic acid 2 (0.150 g, 1.10 mmol). The solid mixture was stirred at room temperature in the open air... 

It has to be kept in mind that particulate materials are dispersions. In fact, the classical powder is a concentrated dispersion of solid particles in air. At a very low concentration, very Lne particles (micron, submicron size) can form an aerosol. In such a case-ewing to the large interparticulate distance-fhe particle-particle interactions can be neglected. In general, a particle can exhibit a substructure, that is, a particle may have external and internal pores. An external pore can be related to the roughness of the surface of a particle. 

S. Mende, J. Schwedes, F. Stenger, W. Peukert, Mechanical production and stabilization of submicron particles in stirred ball mills, Powder Technol. 132 (2003) 64—73. 

The collection efficiency of a fiber is defined as the ratio of the number of particles striking the fiber to the number which would strike it if the streamlines were not diverted [Dorman, 1966]. For particles with dp > 1 pm, the particles are collected primarily by inertial impaction and interception. Collection by diffusion is only important for submicron particles. In the following, we only discuss the methodology of collection efficiency by interception. Details about the filtration of fine and ultrafine powders or granular filtration in general can be found in Davies (1973), Fuchs (1964), Dickey (1961), Matteson and Orr (1987), and Tien (1989). 

A direct application to chemical process technology of the principle of electric wind is in electrostatic precipitators (Leonard et al.,1983) and electrocyclones for size separation of particles in powder technology (Nenu et al., 2009). Electrostatic precipitators applied to exhaust gas cleaning have recently been reviewed 0aworek et al., 2007). A particularly interesting development is that of a small electrocyclone with a diameter of 75 mm (Shrimpton and Crane, 2001). With this device it was shown that the separation quality of the smallest size particles with a diameter below 38 pm doubled upon application of the electric wind. Later experiments performed with submicron silica particles demonstrated that classification of such particles is possible by use of an electrical hydrocyclone (Nenu et al., 2009). 

Nd2Ni04+5 powder was prepared by nitrate-citrate route as described by Courty, et a1. (1973). Stoichiometric amounts of neodymium and nickel oxides were dissolved in diluted nitric acid. After addition of a large excess of citric acid, the solution was dehydrated and heated until self-combustion of the precipitate to obtain submicronic precursor particles (Boehm, 2005). The final annealing was performed at 1000°C for 12 hours to obtain a single crystalline phase. The particles were then ball milled to obtain an average grain size (d0 5) of about 0.8 pm. A terpineol-based slurry was prepared from this powder and this was deposited on the electrolyte by screen printing and then sintered at 1100°C for three hours in air (Lalanne, 2008). 

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