Hard, manufacture

Minimize the compression force required to achieve target tablet hardness Manufacturability Compaction simulator or tablet press Compression force... 

CH2=CHC = CCH = CH2. a colourless liquid which turns yellow on exposure to the air it has a distinct garlic-like odour b.p. 83-5°C. Manufactured by the controlled, low-temperature polymerization of acetylene in the presence of an aqueous solution of copper(I) and ammonium chlorides. It is very dangerous to handle, as it absorbs oxygen from the air to give an explosive peroxide. When heated in an inert atmosphere, it polymerizes to form first a drying oil and finally a hard, brittle insoluble resin. Reacts with chlorine to give a mixture of chlorinated products used as drying oils and plastics. 

The formation of silicon carbide, SiC (carborundum), is prevented by the addition of a little iron as much of the silicon is added to steel to increase its resistance to attack by acids, the presence of a trace of iron does not matter. (Addition of silicon to bronze is found to increase both the strength and the hardness of the bronze.) Silicon is also manufactured by the reaction between silicon tetrachloride and zinc at 1300 K and by the reduction of trichlorosilane with hydrogen. 

Chromium is used to harden steel, to manufacture stainless steel, and to form many useful alloys. Much is used in plating to produce a hard, beautiful surface and to prevent corrosion. Chromium gives glass an emerald green color and is widely used as a catalyst. 

Big name science houses and chemical manufacturers These include such names as Fisher, Baxter, VWR, Cole-Parmer, Alltech, Aldrich and Sigma. It is very hard to get a fledgling account with these giants, but if one can then the sky s the limit. Most chemists should be happy getting these companies products through the distributors. 

Prepared feeds are marketed in various forms from very fine particles through cmmbles, flakes, and pellets. Pelleted rations may be hard, semimoist, or moist. Hard pellets typically contain less than 10% water and can be stored under cool, dry conditions for at least 90 days without deterioration of quahty. Semimoist pellets are chemically stabilized to protect them from degradation and mold if they are properly stored, while moist pellets must be frozen if they are not used immediately after manufacture. Moist feeds are produced in machines similar to sausage grinders. 

Semolina is the coarsely ground endosperm of dumm wheat. High in protein, it is used by U.S. and ItaHan manufacturers for high quaHty pasta products such as macaroni and spaghetti. In Africa and Latin America it is also used for a dish called couscous. Dumm flour, a by-product in the production of semolina, is used to make commercial American noodles. Farina is the coarsely ground endosperm of hard wheats. It is the prime ingredient in many American breakfast cereals. It is also used by manufacturers for inexpensive pasta. 

Diamond. Diamond [7782 0-3] is the hardest substance known (see Carbon, diamond, natural). It has a Knoop hardness of 78—80 kN/m (8000—8200 kgf/m ). The next hardest substance is cubic boron nitride with a Knoop value of 46 kN/m, and its inventor, Wentorf, beheves that no manufactured material will ever exceed diamond s hardness (17). In 1987 the world production of natural industrial diamonds (4) was about 110 t (1 g = 5 carats). It should be noted that whereas the United States was the leading consumer of industrial diamonds in 1987 (140 t) only 260 kg of natural industrial diamonds were consumed this is the lowest figure in 48 years (4), illustrating the impact that synthetic diamonds have made on the natural diamond abrasive market. 

The combination of durability and clarity and the ability to tailor molecules relatively easily to specific applications have made acryflc esters prime candidates for numerous and diverse applications. At normal temperatures the polyacrylates are soft polymers and therefore tend to find use in applications that require flexibility or extensibility. However, the ease of copolymerizing the softer acrylates with the harder methacrylates, styrene, acrylonitrile, and vinyl acetate, allows the manufacture of products that range from soft mbbers to hard nonfilm-forming polymers. 

Spandex Fibers. Spandex fibers are suppHed for processing into fabrics in four basic forms as outlined in Table 3. Bare yams are suppHed by the manufacturer on tubes or beams and can be processed on conventional textile equipment with the aid of special feed and tension devices. In covered yams, the spandex fibers are covered with one or two layers of an inelastic filament or staple yam the hard yam provides strength and rigidity at full extension, which faciUtates knitting and weaving. 

Filament. Eully drawn flat yams and partially oriented (POY) continuous filament yams are available in yam sizes ranging from about 3.3—33.0 tex (30—300 den) with individual filament linear densities of about 0.055 to 0.55 tex per filament (0.5—5 dpf). The fully drawn hard yams are used directly in fabric manufacturing operations, whereas POY yams are primarily used as feedstock for draw texturing. In the draw texturing process, fibers are drawn and bulked by heat-setting twisted yam or by entangling filaments with an air jet. Both textured and hard yams are used in apparel, sleepwear, outerwear, sportswear, draperies and curtains, and automotive upholstery. 

Chemical Applications. The chemical processing industry uses large amounts of granular and fine powder PTFE. Soft packing appHcations are manufactured from dispersions, and hard packings are molded or machined from stocks and shapes made from granular resin. 

Raw Materials. PVC is inherently a hard and brittle material and very sensitive to heat it thus must be modified with a variety of plasticizers, stabilizers, and other processing aids to form heat-stable flexible or semiflexible products or with lesser amounts of these processing aids for the manufacture of rigid products (see Vinyl polymers, vinyl chloride polymers). Plasticizer levels used to produce the desired softness and flexibihty in a finished product vary between 25 parts per hundred (pph) parts of PVC for flooring products to about 80—100 pph for apparel products (245). Numerous plasticizers (qv) are commercially available for PVC, although dioctyl phthalate (DOP) is by far the most widely used in industrial appHcations due to its excellent properties and low cost. For example, phosphates provide improved flame resistance, adipate esters enhance low temperature flexibihty, polymeric plasticizers such as glycol adipates and azelates improve the migration resistance, and phthalate esters provide compatibiUty and flexibihty (245). 

ASTM committees must be balanced in that the number of voting producers must not be greater than the number of voting nonproducers. Eor petroleum products, nonproducers are regulators, consumers, and equipment manufacturers. Committee chairs must be nonproducers. Although standards must be approved by a majority, aH negative votes must be carefully considered and a response made. In practice, because aH issues are fully discussed and the discussions are based on hard data, very few negative votes are cast when standards are submitted for final approval. 

Anisotropy in metals and composite materials is common as a result of manufacturing history. Anisotropic materials often display significantly different results when tested along different planes. This appHes to indentation hardness tests as well as any other test. 

Other Food. Tartaric acid is also used ia the manufacture of gelatin (qv) desserts and ia fmit jellies, especially ia pectin jellies for candies where a low pH is necessary for proper setting. It is used as a starch modifier ia starch jelly candies so that the product flows freely while being cast. It is used ia hard candy because its melting poiat permits it to fuse iato the "glass" and does not contribute to moisture. 

Most manufacturing methods now available are similar to this but with the following modifications in the first step, the polymers for fibers are mainly made of polyester, nylon, or thein blends. AcryUcs and polypropylene are also sometimes employed. A regular fiber as thick as 0.01—0.4 tex (0.1—4 den) may sometimes be used instead of the special fiber to imitate the hard leather. 

Silica and Alumina. The manufacture of Pordand cement is predicated on the reaction of lime with siUca and alumina to form tricalcium sihcate [12168-85-3] and aluminate. However, under certain ambient conditions of compaction with sustained optimum moisture content, lime reacts very slowly to form complex mono- and dicalcium siUcates, ie, cementitious compounds (9,10). If such a moist, compact mixture of lime and siUca is subjected to steam and pressure in an autoclave, the lime—silica reaction is greatiy accelerated, and when sand and aggregate is added, materials of concrete-like hardness are produced. Limestone does not react with siUca and alumina under any circumstances, unless it is first calcined to lime, as in the case of hydrauhc lime or cement manufacture. 

Hard-burned magnesias may be used in a variety of appHcations such as ceramics (qv), animal feed supplements, acid neutralization, wastewater treatment, leather (qv) tanning, magnesium phosphate cements, magnesium compound manufacturing, fertilizer, or as a raw material for fused magnesia. A patented process has introduced this material as a cation adsorbent for metals removal in wastewater treatment (132). 

Medicine. The polymethacrylates have been used for many years in the manufacture of dentures, teeth, denture bases, and filling materials (116,117) (see Dental materials). In the orthodontics market, methacrylates have found acceptance as sealants, or pit and fissure resin sealants which are painted over teeth and act as a barrier to tooth decay. The dimensional behavior of curing bone-cement masses has been reported (118), as has the characterization of the microstmcture of a cold-cured acryUc resin (119). Polymethacrylates are used to prepare both soft and hard contact lenses (120,121). Hydrogels based on 2-hydroxyethyl methacrylate are used in soft contact lenses and other biomedical appHcations (122,123) (see Contactlenses). 

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