Mineral fibers Properties

In this book we define inorganic fibers in a general sense as small elongate solid objects composed of any compound or element usually nonbio-logic in origin and often exhibiting distinctive physical, especially mechanical, properties. Inorganic fibers can occur naturally, that is, as mineral fibers or can be produced synthetically. 

Not really. Charlemagne was aware of the miraculous properties of a mineral fiber composed of various versions of magnesium silicate. In fact, the ancient Romans had discovered that this naturally occurring material was the ideal wick for the oil lamps of the vestal virgins, the watchers of the perpetual flame on the goddess Vesta s altar, because it did not burn away. We know this fiber as asbestos. 

Asbestos constitutes several types of hydrated silicate mineral fibers. The types of asbestos, their chemical compositions, and CAS Numbers are presented in Table 3.8.1. These substances occur in nature in rocks, silicate minerals, fibrous stones, and underground mines. This class of substances exhibits unique properties of noncombustibility, high resistance to acids, and high tensile strength for which they were widely used in many products, including floor and roofing tiles, cement, textiles, ropes, wallboards, and papers. Because of the health hazards associated with excessive exposure to asbestos, the use of these substances is currently banned. 

Fibers axe particles with great length in one dimension compared to much smaller lengths in the other two dimensions. Examples are prisms, needles, and threads or mineral fibers such as asbestos. Recent concern over the health hazard posed by inhalation of asbestos fibers has prompted study of fiber properties in air. There is still not as much known about fibers as isometric particles. 

Bonneau L, Malard C, Pezerat H. 1986. Studies on surface properties of asbestos II. Role of dimensional characteristics and surface properties of mineral fibers in the induction of pleural tumors. Environ Res 41 268-275. 

Important properties of mineral fiber insulating materials ... 

The mineral fiber insulating materials dealt with in this chapter, are generally amorphous and consist mainly of Si02 and AI2O3 with different contents of metal oxides. The most important properties of mineral fiber insulating materials are their thermal conductivity (in the range of 0.03 to 0.04 W/mK), their low bulk densities (between 10 and 200 kg/m ), their porosity, their elasticity, their temperature stability and their flammability. 

Thermal insulators comprise an equally broad range of materials. Such inorganics as mineral fibers, magnesia, aluminum silicate, cellulose, and glass fibers are widely used for steam and hot-water pipes, furnaces, and blown-in home insulation. Organic products that are effective include plastic foams (polyurethane, polyvinyl chloride, polystyrene) and cellular rubber. There are a number of materials that may be called double insulators, since they have both electrical and thermal insulating properties,... 

Theimotropic liquid crystalline polymers can be formulated with high concentration of glass fiber to withstand working temperatures in excess of 300°C. In processing LCP, one problem arises. LCP orients itself in the direction of shear or flow - the process which benefits many materials but makes products from pure LCP excessively anisotropic. To balance mechanical properties it has been suggested that some quantities of short glass or mineral fibers be added to LCP. 

Another benefit of copolyermization of ethylene is incorporation of appropriate polar groups such as carboxylic acid groups or salt groups in the ionomers. Du Pont is still the only producer of the Surlyn-type of polyethylene ionomers. However, several companies produce copolymers of ethylene with acrylic acid (EAA). Such copolymers offer improved thermal properties with retention of clarity, improved heat-seal strength, and impact strength, as well as improved adhesion to a variety of substances, such as aluminum foil, glass fibers, and mineral fibers. 

In the field of high temperature thermal insulation advantage is taken of the special powder properties and the amorphous character of fumed silicas. In principle, mixtures of fumed silicas, an opacifier to reflect the heat radiation and a small quantity of mineral fibers for reinforcing are used for temperatures up to 1000°C. It is necessary to density the mixture to approximately 200 g/1 to obtain the minimum of the superposition of gas and the solid state thermal conduction. Important is also the absence of mineralizing ions, like sodium or potassium, to prevent sintering effects. Commercial thermal insulation systems based on this principle have thermal conductivities of approximately 25 mW/mK at a mean temperature of 200°C and of approximately 30 mW/mK at a mean temperature of 4(X)°C. Therefore, they are... 

CaCOs compounds. Wollastonite s fiber-like shape provides similar properties as those of the glass fibers discussed below, and also like glass, its abrasiveness can damage processing equipment. However, unlike other mineral fiber, asbestos, its particles are nonhazardous [1-1, 3-4, 7-6, 7-13, 7-15]. 

Other fibers may be used in POs, though some of these may be chosen more for their special properties. Basalt mineral fibers or Kevlar can provide extreme reinforcement for ballistics applications other fibers include metal fibers for electromagnetic shielding purposes (discussed in Chapter 6). However, as in the case of stainless steel fibers, just because an additive is in fiber form does not necessarily mean it provides meaningful mechanical property reinforcement, but it may provide the opposite of what is wanted [6-4, 7-57]. 

Table 29 Properties of silicate and other mineral fibers at room temperature [18]...

The density of sisal fiber varies from 1.35 to 1.45 g/cm. Literature shows that sisal fiber exhibits tensile strength in the range of 400-700 MPa, which is nearly similar to many commercially used natural fiber such as jute, flax, banana, and sun hemp. Therefore, we can use sisal for commercial application as we can use jute, flax, banana, pineapple leaf fiber, etc. The mechanical properties of some of the natural fibers and other mineral fibers are shown in Table 22.4. 

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