Talc and Mica

and clays are silicate minerals with structures of this type. Talc has the chemical structure Mg3H2Si40i2 = MgO Si40jo H2O = MgO Si40g (OH)2, while mica has roughly the structure IG l2H2Si30j2 = KAl2Si30jo(OH)2- There are many different variations of minerals called mica as we shall presently describe. 

In talc, the silicate is layered with MgO. These layers are electrically neutral and loosely superposed on one another to form a crystalline material. The layers slide readily over one another, resulting in easy cleavage and a soapy feeling. In the old literature, talc is called soapstone. It is soft (having a Moh s hardness of 1.0). 

In mica, the layers are negatively electrically charged and positive ions, generally potassium, K, but also Al, Mg, Ca and li, must be between the layers to produce electrical 

Talc and mica particles are shown in Figs. 1.13a and 1.13b. They have flake-like shapes as should be seen. 

both Phlogopite and Muscovite types, are high-aspect-ratio particles that are generally coarser than talcs and range from 40 to 600 pm in average particle size. Mica flakes are large platelets and can reinforce in two directions. 

---

Miscellaneous uses include textile bobbins, guns for hot melt adhesives and bilge pump housings. These materials are normally found in reinforced form. In addition to glass fibres, other fillers such as glass beads, talc and mica are used in conjunction with coupling agents. 

It has been suggested that the three-dimensional network structures discussed above, which are believed to occur from particle interactions at high filler loadings, may, in the case of plate-like particles, lead to anisotropic shear yield values [35]. Although this effect has not been substantiated experimentally, further theoretical interpretation of shear yield phenomena in talc- and mica-filled thermoplastics has been attempted [31,35]. 

Fillers. Fillers are used to improve strength and stiffness, to lower cost, and to control gloss. The most common filler is calcium carbonate, which ranges in size from 0.07 to well over 50 m. Some forms are treated with a stearic acid coating. Clay fillers, such as calcined clay, improve electrical properties. Glass fibers, talc, and mica improve tensile strength and stiffness, but at a loss in ductility. 

Access to information was not enough by itself, however. The gathered facts also had to be put together in the right way to form an answer. In 1928, Pauling applied himself to solving the complicated structures of an important family of minerals called the silicates, which include topaz, talc, and mica. He knew it was likely that these minerals... 

Aluminosilicates form an extensive family of compounds that include layered compounds (such as clays, talc, and micas), 3-D compounds, (e.g. feldspars, such as granite), and microporous solids known as molecular sieves. The structural diversity of these materials is contributed to by aluminum s ability to occupy both tetrahedral and octahedral holes as it also does in y-Al203. Thus, aluminum substitution for silicon in silicate minerals may lead to replacement of silicon in tetrahedral sites or the aluminum can occupy an octahedral environment external to the silicate lattice. Replacement of Si with Al requires the presence of an additional cation such as H+, Na+, or 0.5 Ca + to balance the charge. These additional cations have a profound effect on the properties of the aluminosilicates. This accounts for the many types of layered and 3-D structures (see Silicon Inorganic Chemistry). 

Compare the properties of talc and mica, and explain their differences in terms of their structure. 

The derivation of clays from talcs and micas provides a direct way to understand the structures of the clays. The infinite-sheet mica pyrophyllite, Al2(Si40io)(OH)2, serves as an example. If one of six AI ions in the pyrophyllite structure is replaced by one Mg ion and one Na ion (which together carry the same charge), a type of clay called montmorillonite, MgNaAl5(Si40io)3(OH)g, results. This clay readily absorbs water, which infiltrates between the infinite sheets and hydrates the Mg and Na ions there, causing the montmorillonite to swell (Fig. 22.5). 

February 29th) into the calendar to make it match the. solar year. Most work on intercalation compounds has been on synthetic systems in which atoms, ions, or molecules have been inserted between layers of the host material. However, some aluminosilicates that we have encountered above provide useful examples. Thus talc and micas form layered structures with ions between the silicate sheets (Fig. 16.3). Some minerals, including all clays, have water molecules intercalcatcd between the framework sheets. In some, such as vermiculile, the water may rapidly and dramatically be evacuated by heating. The water molecules leave faster than they can ditfuse along the layers—exfoliation occurs. The result is the familiar expanded vermiculile used as a packing material and as a potting soil conditioner. 

U.S. Pat. No. 6,632,863 [115] (by Crane Plastics Company, Timber-Tech) discloses a wood-plastic composition manufactured as feedstock pellets comprising 55-90% cellulosic material such as wood flour and wood fiber, 10-40% of polyolefin such as HDPE, LDPE, and polypropylene, and 0-35% total of additive(s), such as lubricants and inorganic fillers, such as talc and mica. 

Another example that now shows the effects of mineral fillers on oxidation of WPCs (in terms of the OIT, that is, the oxidative induction time) is the durability of GeoDeck experimental deck boards made with talc and mica, in addition to the conventional composition. GeoDeck board without added antioxidants had the OIT of... 

The CdCl2 lattice is related to the Cdl2 layer-structure but with the Cl ions in a cubic close-packed arrangement. Examples of compounds adopting this structure are FeCl2 and C0CI2. Other layer structures include talc and mica (see Section 13.9). 

Waterborne bitumens may be anionic, cationic, or rarely nonionic emulsions, and are produced with the aid of emulsifiers and, if necessary, stabilizers conventionally used in the paint industry. The properties of bitumen paint (solutions and emulsions) (e.g., stability mechanical, weather, water, and chemical resistance corrosion protection properties) can be substantially improved by incorporating extenders. Suitable extenders include ground slate, ground limestone, chalk, talc, and mica (25 45 wt%, depending on extender type and required properties). The use of extenders... 

Solvents are used to carry dissolved or suspended resin and evaporate from the coating after application. Additives in small amounts are used as mildew inhibitors (cuprous compounds), surface-drying additives (manganese and cobalt naphthanates), and barrier-forming additives to protect the resin from heat and UV degradation. Fillers (talc and mica) decrease the permeability of oxygen and water in the coating. 

The effects of composite formation are not only restricted to the improvement of mechanical properties, such as toughness, tensile strength, and many other, but also include, improvement of thermal and electric conductivities (carbon black, pol yrrole), reduction of water migration (platelet fillers such as talc and mica), improvement fire resistance (alumina trihydrate), improvement of quality (wood-like feel with wood filler), and decorative value. 

TSs, like TPs, offer a wide range of matrix materials for reinforcement by fibers, flakes, beads, or particulate materials such as talc and mica. They are compounded with reinforcing materials. Among the fibers, glass is the main reinforcement. Examples of these TPs follow ... 

Layered nanoparticles, like the aggregates of silicates talc and mica, form close proximity sheets of polymer—clay hybrids due to the immiscibility of clay in polymer. The degree of dispersion in these composites is normally referred to as the following ... 

The platelet reinforcements in common use are all minerals. Two in particular are notably successful talc and mica. Talc in a magnesium silicate, while mica is an aluminium silicate. 

As a result, when they are used to reinforce plastics, significant increases in modulus (with talc and mica) and strength (with mica onfy) can be obtained at Uttle or no increase in cost There is also a further advantage over fibres when platelets are aligned parallel to each other (as they are in the surface layers of an injection moulding) they provide reinforcement in all directions in their plane, not merely in one direction as with uniaxially aligned fibres. 

High aspect ratio fillers, such as woUastonite and glass fibers can have an even stronger effect than talc and mica on increasing the modulus of elasticity, tensile strength, and heat-distortion temperature of poly(lactic acid) (PLA)-based systems. 

Polypropylene/Acid Grafts. Grafts have been made with maleic anhydride or acrylic acid. These are useful for example in coupling talc and mica into polypropylene. 

In some platelet-type fillers such as talc and mica, the platelets can align with the streamlines at higher shear rates, and the viscosity increase is less than that predicted by the above equation (see Chapter 2). 

High aspect ratio fillers include wollastonite and talc, and mica, a lamellar or plate-like filler, also has a modest reinforcing effect. 

Talc and mica are suggested for the use as nucleating agents in poly(ether sulfone). Also, boron nitride was used in PES as the nucleating agent. ... 

---