Filler Silica flour

Finally, metal- and resin-bonded composites are also classified as particulate composites. Metal-bonded composites included structural parts, electrical contact materials, metal-cutting tools, and magnet materials and are formed by incorporating metallic or ceramic particulates such as WC, TiC, W, or Mo in metal matrixes through traditional powder metallurgical or casting techniques. Resin-bonded composites are composed of particulate fillers such as silica flour, wood flour, mica, or glass spheres in phenol-formaldehyde (Bakelite), epoxy, polyester, or thermoplastic matrixes. 

Particulate fillers, on the other hand, are believed to extend the pathway along which the water must diffuse, resulting in a reduction in the rate of water absorption. Silica flour (1 to 75 pm) has been reported as improving the boiling water resistance of epoxy films. Figure 9.8 shows the water absorption rate at 40°C of water in DGEBA epoxy filled with various types of materials. 

The common availability of silica is not the sole reason for its extensive use. Probably, it is the chemical inertness and durability of silica which determined its popularity. The fillers discussed here include not only natural minerals but also a variety of synthetic products. Natural products can be divided into crystalline and amorphous. Crystalline silica fillers include sands, ground silica (or silica flour), and a form of quartz - tripoli, whereas the amorphous types include diatomaceous earth. 

Typical fillers calcium carbonate, talc, glass fiber, glass beads, glass flakes, silica flour, wollastonite, mica, sepiolite, magnesium hydroxide, carbon black, clay, metal powders (aluminum, iron, nickel), steel fiber, si-licium carbide, phenolic microspheres, wood fiber and flour, antimony trioxide, hydrotalcite, zinc borate, bismuth carbonate, red phosphorus, potassium-magnesium aluminosilicate, fly ash, hydromagnesite-huntite... 

De Miranda et al. (1997) showed the effects of silica flour on the cure of DGEBA/DDM epoxy-resin systems. They noted that there were appreciable decreases in reaction rates for systems with higher filler concentrations than 10 wt.% at high temperatures and conversions above 50%. 

When sand is used as a filler, the composite is referred to as a polymer mortar. Other fillers include crushed stone, gravel, limestone, chalk, condensed silica fume (silica flour, silica dust), granite, quartz, clay, expanded glass, and metallic fillers. Generally, any dry, nonabsorbent, solid material can be used as filler [4],... 

Silica, fumed Strontium sulfate Talc Vermiculite Whiting Wollastonite Wood flour filler, rubber articles food-contact for repeated use... 

Mineral fillers used are calcium carbonate (CaCOj), China Clay (Al/0H [Si.,0 J), miea especially muscovite (KAyOHjFlJAlSijOj J), silica flour (SiO ), talc (Mg, (OH)j[Si Oj J), and wollastonite (CaSiOj). Parameters that need to be considered during inorganic filler selection are basicity, filler impurities that may influence the resin euring proeess, and filler hardness that eauses abrasion of the mold [1]. Mica filled phenolics are used in electrical parts because mica adds outstanding dielectric properties, high thermal and chemical resistance and low water absorption [1]. 

Thermosetting plactics are often reinforced by as much as 100 phr of various fillers, for example, wood flour, cotton flock asbestos and synthetic fibre used with phenolic thermosets, and silica flour, mica or talc with epoxies. Glass fibre reinforcement of polyester resins for structural, automotive, aerospace and marine applications is too well known to require comment. 

Fillers are relatively nonadhesive substances added to the adhesive formulation to improve its working properties, strength, permanence, or other qualities. The improvements resulting from the use of fillers are listed in Table 1.8. Fillers are also used to reduce material cost. By selective use of fillers, the properties of an adhesive can be changed significantly. Thermal expansion, electrical and thermal conduction, shrinkage, viscosity, and thermal resistance are only a few properties that can be modified by the use of fillers. Common fillers are wood flour, silica, alumina, titanium oxide, metal powders, china clay and earth, slate dust, and glass fibers. Some fillers may act as extenders. 

Commonly used fillers for epoxy systems are calcium carbonate, micas, silica, clays, powered metals, talc, wood flour, aluminium silicate etc. The properties imparted by fillers to an epoxy system are given in Table 2.4 (Dow Chemical Company, undated d). 

Fillers. Fillers mentioned for epoxy systems (subsection 2.2.6.4) are used in polyurethanes too. Ground calcium carbonate (coated as well as uncoated) is commonly used. Barium sulphate, silica fumes, wood flour and milled glass fibres are also used. 

Typical fillers barium sulfate, calcium carbonate, carbon black, calcium sulfate whiskers, diatomaceous earth, glass fiber, glass spheres, hollow silicates, kaolin, mica, talc, wollastonite, silica, magnesium hydroxide, hydrotalcite, red mud, ground tire rubber, ferromagnetic powder, nickel fibers, wood flour, zirconium silicate, starch, soot, marble, aluminum, lignin, sand... 

The use of inert materials in vinyls is widely practiced. The filler can be used to lower cost and increase hardness. The most common types of fillers in use today include the calcium carbonates and silicate types. Also available are various silica gels, barytes, gypsum, alums, wood flour, and antimony oxide. Depending upon the oil absorption value of the inert material, a filler will (1) lower tensile properties, (2) increase hardness, (3) lower flexibility, and (A) increase processing temperatures. 

U.S. Pat. No. 3,546,158 [20] describes a flooring composition involving a terpolymer, a nonflbrous filler (calcium carbonate, silica, clay, kaolin, and carbon black) and a fibrous filler, such as wood flour, cellulose fibers, and asbestos. Compositions may include 25-53% by weight of nonfibrous filler and 17-40% by weight of fibrous filler, with the fillers accounting for 50-80% of the total composite weight. 

Fillers in Thermosets and Rubber. Thermosets such as phenolformalde-hyde, melamineformaldehyde, and ureaformaldehyde resins are filled with wood flour, a-cellulose, or paper to add bulk, prevent cracking, and reduce cost. Asbestos imparts heat resistance, mica gives excellent electrical properties, aluminum powder improves heat transfer, and powdered silica or china clay reduces water absorption. 

Examples of inert or extender fillers include china clay (kaolin), talc, and calcium carbonate. Calcinm carbonate is an important filler, with a particle size of about 1 pm. It is a natural product from sedimentary rocks and is separated into chalk, limestone, and marble. In some cases, the calcium carbonate may be treated to improve interaction with the thermoplastic. Glass spheres are also used as thermoplastic fillers. They may be either solid or hollow, depending on the particular application. Talc is a filler with a lamellar particle shape. It is a namral, hydrated magnesium silicate with good slip properties. Kaolin and mica are also natural materials with lamellar structures. Other fillers include woUastonite, silica, barium sulfate, and metal powders. Carbon black is used as a filler primarily in the rnbber industry, but it also finds application in thermoplastics for conductivity, for UV protection, and as a pigment. Fillers in fiber form are often used in thermoplastics. Types of fibers inclnde cotton, wood flour, fiberglass, and carbon. Table 1.3 shows the fillers and their forms. An overview of some typical fillers and their effect on properties is shown in Table 1.4. Considerable research interest exists for the incorporation of nanoscale fillers into polymers. This aspect will be discussed in later chapters. 

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