Pure talc

Pure talc is thermally stable up to 930°C, and loses its crystalline bound water (4.8%) between 930 and 970°C, leaving an enstatite (dehydrated magnesium siUcate) residue. Most commercial talc products have thermal loss below 930°C on account of the presence of carbonates, which lose carbon dioxide at 600°C, and chlorite, which loses water at 800°C. Talc is an insulator for both heat and electricity. 

The Arnold Pit is on the steeply dipping, overturned limb of the Sylvia Lake Syncline, the structural hanging wall is the stratigraphic footwall. Commercial talc occurs in Unit 13 near the contact with Unit 14 of the Upper Marble from the metamorphism or impure evaporative dolomite. The upper section of Unit 13 grades from tremolite-rich talc ore into a pure talc schist up section. Unit 12 is a white massive doiomitic marble with convolute bands of grey and orange to... 

Toxieology. The nonasbestos form of talc, also termed nonfibrous or pure talc, has not been proven to cause the effects produced by exposure to fibrous talc, namely, fibrotic pneumoconiosis and an increased incidence of cancer of the lungs and pleura. 

Although there are a number of contradictory reports regarding the effects of talc, the contradiction has been ascribed to the differences in mineral composition of the various talcs, which include pure talc, talc associated with silica and other nonasbestiform minerals, and talc containing asbestiform fibers such as tremolite and anthophyllite. ... 

Natural hydrated magnesium silicate Talc 14807-96-6 Mg3Si40io(OH)2 (Pure talc)... 

Talcosis, caused by inhalation of pure talc, may include acute or chronic bronchitis as well as interstitial inflammation radiographically, it appears as interstitial reticulations or small, irregular nodules, typical of small airway obstruction. 

Another example of inorganic materials and their quality evaluation involves the mineral impurities of industrial talc [42]. Talc is commonly used for plastic reinforcement. Pure talc (determined by XRD analysis) only shows a mass loss in TG at about 900 C. When samples of talc are analyzed using TG, other mass losses can be seen in the temperature ranges of 500-600 °C and 600-700 C, as shown in Figure 28. By comparing the XRD results of the impurities with the... 

TLV as resi raUe dust and it applies to talc without asbestos fibers. Industrial talcs, esp. containing fibers, can sometimes include asbestos fibers these coukJ cause lung disorders if Inhaled. In this case the rules for- asbesfosapply. No special precautions required for pure talc. 

Pure talcs of fine particle size and high lamellar structure, in combination with a new generation bromine compound, make it possible to obtain optimum mechanical properties and fire resistance as well as a limitation on the emission of corrosive by-products. Good results have been recorded with polyolefins in synergy with bromine compounds, for applications such as connectors and appliances. 

The theoretical chemical composition of pure talc by weight is 19.2% magnesium, 29.6% sUicon, 50.7% oxygen, and 0.5% hydrogen. In terms of metal oxides, it is 31.7% MgO and 63.5% Si02 with the remaining 4.8% being H2O. Other elements found in impure talcs in variable amounts are Ca, Al, and Fe. Trace elements include Pb, As, Zn, Ba, and Sb [1, 2]. 

Figure 8.2 Molecular structure of pure talc mineral. (OH)sMg,281,6040 or (OH)2...

Talc is inert to almost all chemical reagents and does not decompose when in contact with various acids. Pure talc is a very soft material and has a slippery texture. Natural talc may be white, gray, yellow, pale blue, or pale green with a characteristically silver or pearllike luster. Most commercial talcs used as fillers are finely ground. The finest grinds usually have an average size of 1 p,m coarser sizes are in the region of 10-75 pm. 

Adapting the formulation may allow the application of a more reliable sterilisation method. An example is talc powder used in pleurodesis. The easiest and cheapest sterilisation method for talc powder is prolonged dry heat exposure. But this sterilisation method is more difficult to validate than autoclaving. Instead of pure talc powder, a talc suspension in 0.9 % NaCl solution was prepared and autoclaved [45]. 

Figure 9.7 shows results of the TGA experiments for the mixture talc A - Irganox 1010, the curve denoted 1 is for pure talc and curve 2 for the mixture talc - Irganox 1010. 

Figure 9.7 Curves of TGA experiments for talc A 1 - pure talc A 2 - mixture of talc...

For the pure talc the weight loss was very low, 0.45-1.8% for pure talcs heated to 500-700 °C due to loss of water only. For mixtures of talc and Irganox 1010 three stages of degradation were identified (Table 9.2). 

Microfibrous silica is probably produced when chrysotile asbestos reacts with stomach acids. Asbestos in food was implicated in stomach cancer. A statistical study by Merliss (229) indicates that rice that has been treated with talc that contains some asbestos is the cause of a high incidence of stomach cancer in Japan where such rice is commonly consumed. The talc is held to the surface of the rice grains by glucose to help preserve the flavor. This is a practice limited to the Japanese. Pure talc appears harmless. 

Pure talc is the softest known mineral with a hardness of 1 on the Mohs hardness scale, specific gravity is 2.8, and it has three indices of refraction, 1.539, 1.589 and 1.589, according to crystal direction. Typical particles are shown in Figure 2.7. 

Colour is also changed by the mineral filler pure talc gives translucent, almost colourless compounds while high quality calcium carbonate gives a white colour with some opacity. Increasing levels of impurities in both minerals causes colour degradation. Colour will also be caused by any instability introduced into the polypropylene by the mineral. 

Cordierite bodies can be formed from pure talc (44%), plastic kaolin (41%) and alumina (15%) or from 50/50 mixtures of kaolin and chlorite. Cordierite has very low coefficients of thermal expansion (CTE), which accounts for its use in kiln furniture and automotive catalysts supports. Firing temperatures have to be much higher for the pure talc containing bodies. The talc based body is preferred for automotive catalyst supports although it is more expensive, it is possible to get better control of minor elements such as iron and calcium which have a major impact on CTE. For kiln furniture, chlorite-hased bodies are preferred because of their lower cost and better high temperature creep resistance. In kiln furniture modified with rnnUite to improve shock resistance, French sourced chloritic talc is utilized. 

For steatite bodies used in electrical insulating apphcations, pure talc along with about 10% plastic kaolin and 10% barium carbonate is fired at cone 12-13 to form low loss bodies. Low calcium and alkah metal levels are critical, so only high purity Montana talc is used. Consistency is also critical, since... 

Pure talc, when it causes pneumoconiosis, leads to a mixture of rounded (q or r) and irregular (t or u)... 

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