Porous Fillers

Tripoli. TripoH [1317-95-9] is a fine grained, porous, decomposed siHceous rock produced mainly in Arkansas, Illinois, and Oklahoma. It is widely used for polishing and buffing metals, lacquer finishing, and plated products. Since tripoH particles are rounded, not sharp, it has a mild abrasive action particularly suited for polishing. TripoH is also used in toothpastes, in jewelry polishing, and as filler in paints, plastics, and mbber. Rottenstone and amorphous siHca are similar to tripoH and find the same uses. In 1987 the abrasive use of tripoH in the United States totaled 26.6 million tons and was valued at about 3.1 million however, the portion used as a filler totaled 71.1 million tons and had a value of almost 10 million (4). 

True Density or Specific Gravity. The average mass per unit volume of the individual particles is called the tme density or specific gravity. This property is most important when volume or mass of the filled composition is a key performance variable. The tme density of fillers composed of relatively large, nonporous, spherical particles is usually determined by a simple Hquid displacement method. Finely divided, porous, or irregular fillers should be measured using a gas pycnometer to assure that all pores, cracks, and crevices are penetrated. 

Fillers are added to emulsion adhesives to build the total soflds content, to reduce penetration into a porous substrate, and to lower costs. 

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

Some rubber base adhesives need vulcanization to produce adequate ultimate strength. The adhesion is mainly due to chemical interactions at the interface. Other rubber base adhesives (contact adhesives) do not necessarily need vulcanization but rather adequate formulation to produce adhesive joints, mainly with porous substrates. In this case, the mechanism of diffusion dominates their adhesion properties. Consequently, the properties of the elastomeric adhesives depend on both the variety of intrinsic properties in natural and synthetic elastomers, and the modifying additives which may be incorporated into the adhesive formulation (tackifiers, reinforcing resins, fillers, plasticizers, curing agents, etc.). 

The solvent-borne NR adhesives show an important mechanical component in the bonding process, and therefore bulk mechanical and rheological properties (addition of fillers is quite effective) are important. In fact, these adhesives are mainly suitable when at least one of the surfaces to be joined is water-porous (paper, concrete, leather, textiles). 

Porous refractory (tungsten) infiltrated with a low melting point metal (silver) Hot-pressed refractory metal containing an oxide filler... 

Syntactic foam contains an orderly arrangement of hollow sphere fillers. They are usually glass microspheres approximately 100 microns (4 mils) in diameter, provide strong, impervious supports for otherwise weak, irregular voids. As a result, syntactic foam has attracted considerable attention both as a convenient and relatively lightweight buoyancy material and as a porous solid with excellent shock attenuating characteristics. The latter characteristic is achieved... 

A porous siliceous rock resulting from the decomposition of chert or siliceous limestone. Used as a base in soap and scouring powders, in metal polishing, as a filtering agent, and in wood and paint fillers. A cryptocrystalline form of free silica. 

Nonmetal electrodes are most often fabricated by pressing or rolling of the solid in the form of fine powder. For mechanical integrity of the electrodes, binders are added to the active mass. For higher electronic conductivity of the electrode and a better current distribution, conducting fillers are added (carbon black, graphite, metal powders). Electrodes of this type are porous and have a relatively high specific surface area. The porosity facilitates access of dissolved reactants (H+ or OH ions and others) to the inner electrode layers. 

Most adhesive preparations consist of at least two main components an adhesive and a solvent. The adhesive is the binding substance that, when dry, attaches and joins together adjacent surfaces, or sizes (covers and seals) porous surfaces. Water was, for many millennia, practically the only solvent used in adhesive preparations. Adhesives soluble in water form solutions and, if insoluble, become suspended in the water, usually in such concentration as to render the preparation viscous and tacky. As well as the adhesive and the solvent, a variety of additives have often been added to adhesive preparations so as to improve their spreading properties or modify other qualities. Additives, which increase the viscosity of the preparations, are known as fillers, while those that increase their volume are referred to as diluents (Eagland 1988 Masschelein-Kleiner 1985). 

Some fillers such as zeolites are sufficiently porous to accommodate monomers, which can then be polymerized. This threads the chains through the cavities, with unusually intimate interactions between the reinforcing phase and the host elastomeric matrix [238,240], as is illustrated in Figure 11. Unusually good reinforcement is generally obtained. 

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