Platy minerals talcs

Nonfibrous Reinforcements. Because of the higher costs associated with nonasbestos fibers and the performance requirements needed in replacing asbestos, platy minerals such as mica and talc, and metal powders such as iron and copper, are being used as a portion of the total reinforcement package in NAOs. 

Fibers are rolled around their long axis by gently tapping the cover slip with a dissection needle. Keep the fiber in view at all times as this is done. If a mineral plate is seen on edge it may resemble a fiber. Rolling the plate over reveals the true nature of the plate. This is a useful test when platy minerals such as talc or mica are being examined for the possible presence of asbestos. 

Platy minerals such as clays and talcs, are useful for providing stiffness to hot, semi-processed rubber products. This is particularly useful for thin-walled extrusions, which emerge from the die at high temperatures. The stiffening effect is usually sufficient to prevent collapse under the product s own weight immediately prior to and during cure. 

Talc is a hydrated magnesium silicate, which has a platy shape, similar to clays. Unlike clays, the mineral does not possess a significant level of surface hydroxyl groups, which is the primary reason for the application differences between the two minerals. Talcs have a surface that interacts poorly with rubber (it has a characteristic slippery feel), is basic in character, and is relatively hydrophobic. Good sources of talc are relatively scarce. This has ensured that the cost of talc is relatively high. 

Luzenac America offers a broad selection of talc products designed specifically for plastic applications. Talc is a white, crystalline, platy mineral. It Is the softest of all minerals, and in many applications, its shape imparts cost-effective and beneficial structural properties to the final product. Luzenac talcs are available in various particle size distributions and from a wide variety of Luzenac-owned ore sources. 

Talc is a white, crystalline, platy mineral. It is the softest of all minerals. It must be mixed in the polymer melt to insure good dispersion. 

Commercial talc is composed primarily of the mineral talc, a sheet sihcate, but may contain related sheet silicates such as chlorite and serpentine, plus prismatic tremolite, anthophyllite, and carbonates such as magnesite, dolomite, and calcite. Talc particles are characteristically platy in morphology and are oleophihc/hydrophobic they are wetted by oil instead of water. Talc s reinforcing and pigmenting properties, together with good color, make it desirable as a functional filler in both aqueous and nonaqueous appHcations. For nonaqueous uses its naturally good matrix compatibility can be further enhanced by surface treatment. 

Talc A mineral with the approximate chemical formula Mg3Si40io(OH)2 (see chapter 2). The term has been used as a commercial name for fibrous or platy deposits formed by hydrothermal alteration of rocks rich in silica, magnesium, and iron. 

The term clay refers to fine-grained aluminosilicates that have a platy habit and become plastic when mixed with water [11], Dozens of minerals fall under the classification of clays and a single clay deposit can contain a variety of individual clay minerals along with impurities. Clay minerals are classified as phyllosilicates because of their layered structure [12], The most common clay mineral is kaolinite, although others such as talc, montmorillonite, and vermiculite are also abundant. Each of the... 

Talc is hydrated magnesium silicate, a nonmetallic mineral, white-colored, chemically inert. Unlike many other minerals, its particles have a distinct platy shape. It has a natural affinity to oil and, therefore, serves as a good filler for hydrophobic plastics, such as polyethylenes and polypropylene. Platy particles of talc are structurally not uniform they have a layered composition, in which a brucite (magnesium-based, tetrahedron-cell atomic structure) sheet is sandwiched between two silica (octahedron-cell atomic structure) sheets. The elementary sheet is of ik (0.7 nm) thick. 

Talc loses its water of hydration at 1000°C. At this temperature, the talc crystal restructures itself to form the mineral enstatite (MgSiOs), which is significantly harder than talc, with a Mohs hardness of 5-6, and less platy. Talc is inert to most chemicals. It normally will absorb an equilibrium 0.2-0.3% by weight of moisture under normal atmospheric conditions. 

Fig. 5.62 Optical micrographs show the size and shape of several minerals used as fillers for composites (A) mica flakes appear platy in shape with irregular boundaries, (B) talc particles have a much finer, platy texture and the particles exhibit a range of shapes from nearly fibrous to platy and (C) clay particles are very fine grained with no characteristic shape.

TALC. 3Mg0-4Si02-H20. Talc is a hydrous magnesium silicate, with the composition 63.4% SiOj, 31.9% MgO and 4.7% HjO when found in pure form. It is an extremely soft mineral with a Mohs hardness of 1, has a platy structure and it is naturally hydro-phobic. Talc occurs as a relatively pure massive mineral in Montana, Australia and China. Elsewhere it occurs in conjunction with magnesite (Vermont, Quebec, Ontario and Finland), with tremoUte and serpentine in New York and with chlorite in France and Austria. In many ceramic applications, the presence of non-talc minerals such as chlorite and tremolite are beneficial. 

Fibrous reinforcements, such as glass and asbestos, and acicular reinforcements, such as wollastonite, also tend to orient parallel to the flow direction. Since they all have lower thermal expansions than plastics, use of these minerals tend to promote warping, especially in crystalline polymers. Fillers such as mica, talc and kaolin, also orient in the flow direction, but their platy, more two-dimensional shape does not contribute to warping. High aspect ratio mica, because of its extreme platiness, is used to counteract the natural warping tendency of highly crystalline thermoplastic polyesters. 

Mineral fillers are naturally occurring or synthetic nonblack, nonmetallic solid-surface particles. Such fillers have assorted shapes, from nodular to platy to aci-cular. When describing filler shape, the term aspect ratio is employed to describe the relationship of one dimension to another. Mineral fillers for PVC have historically included calcium carbonate (ground and precipitated), alumina trihydrate (ATH), barytes, talc, mica, kaolin, feldspar and nepheline syenite, and wollastonite. 

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