Metallic and ceramic particles

Particulate Composites. These composites encompass a wide range of materials. As the word particulate suggests, the reinforcing phase is often spherical or at least has dimensions of similar order ia all directions. Examples are concrete, filled polymers (18), soHd rocket propellants, and metal and ceramic particles ia metal matrices (1). 

Ceramic Metallic and ceramic particles and fibers Elevated temperature strength Chemical resistance Thermal resistance... 

Apart from latexes, S-FFF has been used to fractionate and determine the size distribution of numerous industrial colloids including water-based titanium dioxide dispersions [6,171], carbon black dispersions [6],phthalocyanineblue [6], various silica sols [141,171,176], gold and silver sols [385], pigments, metal and ceramic particles, clay and a host of latexes [294]. Gold, palladium, silver and copper particles in the size range 0.3-15 pm were separated by steric-S-FFF and their size distributions determined in less than 12 min [69]. 

The small particles are reported to be very harmful for human health [98]. To remove particulate emissions from diesel engines, diesel particulate filters (DPF) are used. Filter systems can be metallic and ceramic with a large number of parallel channels. In applications to passenger cars, only ceramic filters are used. The channels in the filter are alternatively open and closed. Consequently, the exhaust gas is forced to flow through the porous walls of the honeycomb structure. The solid particles are deposited in the pores. Depending on the porosity of the filter material, these filters can attain filtration efficiencies up to 97%. The soot deposits in the particulate filter induce a steady rise in flow resistance. For this reason, the particulate filter must be regenerated at certain intervals, which can be achieved in the passive or active process [46]. 

This chapter aims to present some recent results on the characterization and properties of small metallic and intermetallic particles (a few nanometres (nm) in diameter) supported on ceramic oxide substrates or on carbon. Due to the rapidly expanding development in materials sciences and technology and,... 

Available results on the preparation, characterization, and utilization of metallic and catalytic particles (Sect. 3), semiconductor particles and particulate films (Sect. 4), conductors and superconductors (Sect. 5), magnetism and magnetic particles and particulate films (Sect. 6), and advanced ceramic materials (Sect. 7) will constitute the main body of the monograph. An attempt will be made to cover these materials exhaustively. 

Metals and ceramics (claylike materials) are also used as matrices in advanced composites. In most cases, metal matrix composites consist of aluminum, magnesium, copper, or titanium alloys of these metals or intermetallic compounds, such as TiAl and NiAl. The reinforcement is usually a ceramic material such as boron carbide (B4C), silicon carbide (SiC), aluminum oxide (A1203), aluminum nitride (AlN), or boron nitride (BN). Metals have also been used as reinforcements in metal matrices. For example, the physical characteristics of some types of steel have been improved by the addition of aluminum fibers. The reinforcement is usually added in the form of particles, whiskers, plates, or fibers. 

The ratio of surface area to bulk volume of the reinforcing particles can have important implications on optical properties, where the contribution of surface states can result in unique properties.56,57 These surface states cause shifts in the plasmon absorption frequencies and can be manipulated by use of different combinations of metals and ceramics.56 Another possibility due to the high surface area of the metal particles is catalysis applications, provided the ceramic matrix contains open pores.19... 

Many polymers are biocompatible and may be used as coatings for metallic or ceramic particles, or can serve as hosts by either capturing... 

The electrochemical reactions occurring within a SOFC are shown in Equations 25 and 26. The anode consists of a porous mixture of a Ni or Co catalyst on yttria-stabilized zirconia. Such a mixture of metal and ceramic is referred to as a cermet. The zirconia acts to inhibit grain growth of the catalyst particles of nickel or cobalt and protects against thermal expansion. The cathode is generally a Sr-doped... 

In general, polymers have low stiffness and strength in comparison with other materials, e.g., metals and ceramics, and consequently these materials present serious difficulties in structural applications. To improve their mechanical properties, polymers are reinforced by the addition of rigid particles or fibers to form composite materials (1). Thus, polymer matrix composite materials are made up of a low modulus phase, the polymer matrix, and a high modulus phase, the reinforcement, which is usually carbon or glass. The modulus of the composite is higher than that of the polymer matrix, and the increment is proportional to the volume fraction of the reinforcement. In general, the properties of the composite depend not... 

Ceramic coatings on fibers and powders have a variety of uses. For example, porous ceramic coatings on nanoscale metallic or ceramic particles can improve the catalytic properties of a powder. Also, the carbon fibers used as reinforcement in metallic matrices can be coated with a thin ceramic film (such as SiC or TiN) to reduce the rate of interdiffusion that may occur between the matrix materials and the fibers, and enhance the wetting of the fiber surface by metals. ... 

Microfiltration membranes are similar to UF membranes but have larger pores. Microfiltration membranes are used to separate particles in the range of 0.02-10 pm from liquid or gas streams. Commercial MF membranes are made from a wide variety of materials including polymers, metals, and ceramics. A wide variety of membrane module designs are available including tubular, spiral wound, pleated sheet, hollow fiber, and flat sheet designs. Some modules are best suited for crossflow filtration, and others are designed for dead-end filtration. In dead-end filtration, the feed liquid flows normal to the surface of the membrane, and retained particles build up with time as a cake layer on the membrane surface or within the pores of the membrane. 

Although the emphasis here will, by necessity, be placed on more recent data, several key reviews of transport in nanocrystalline ionic materials have been presented, the details of which will be outlined first. An international workshop on interfacially controlled functional materials was conducted in 2000, the proceedings of which were published in the journal Solid State Ionics (Volume 131), focusing on the topic of atomic transport. In this issue, Maier [29] considered point defect thermodynamics and particle size, and Tuller [239] critically reviewed the available transport data for three oxides, namely cubic zirconia, ceria, and titania. Subsequently, in 2003, Heitjans and Indris [210] reviewed the diffusion and ionic conductivity data in nanoionics, and included some useful tabulations of data. A review of nanocrystalline ceria and zirconia electrolytes was recently published [240], as have extensive reviews of the mechanical behavior (hardness and plasticity) of both metals and ceramics [13, 234]. 

In abrasion or erosion, particles with lower hardness cause less wear than harder particles. When particles are much harder than a surface, the exact value of their hardness matters much less. The relative wear rates by two-body abrasion are associated with a wide range of metals and ceramics, abraded by various types of grit particle. The wear rate becomes much more sensitive to the ratio of abrasive hardness //., to the surface hardness Hs when H.J1 Is is less than 1. Table 5.2 lists the bulk material hardness values for common abrasive particles.12... 

Another type of lamination is that caused by inner gliding surfaces due to the relative movement of the ceramic body and auger respectively extruder barrel. Segregation occurs in the boundary layer between metal and ceramic body. The coarser material particles in particular are pressed inside the body whilst the liquid phase and the very fine particles concentrate in the boundary layer (Fig. 5). 

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