High-purity plastics

Comminution of the sample presents significant opportunity for contamination. Contamination of the sample from abrasion of the comminution equipment is fundamentally unavoidable, so efforts must be made to select the best possible equipment for each particular analytical task. Equipment is preferred in which the sample comes into contact only with surfaces fabricated from such high-purity plastics as polytetrafluoroethyl-ene (PTFE), since this permits the sample to be used without restriction for the determination of a large number of elements. Friability can be increased by deep-freezing or drying the sample prior to comminution. 

Lead sesquioxide is used as an oxidation catalyst for carbon monoxide ia exhaust gases (44,45) (see Exhaust control), as a catalyst for the preparation of lactams (46) (see Antibiotics, P-lactams), ia the manufacture of high purity diamonds (47) (see Carbon, diamond-natural), ia fireproofing compositions for poly(ethylene terephthalate) plastics (48), ia radiation detectors for x-rays and nuclear particles (49), and ia vulcanization accelerators for neoprene mbber (50). 

Developments in the 1980s and 1990s include phosphoric acid-based formulations for the cleaning of exterior automotive plastic parts and the demand for high purity electronics-grade phosphoric acid. 

In electrical porcelains (often called steatite bodies), high purity talc products with low levels of alkali metals ate preferred. A typical steatite is made from 85% talc, 10% plastic kaolin, and 5% BaCO. Steatites ate used as insulators on high voltage equipment such as automotive starters, microwave oven generators, and laser generators. 

Calcium carbonate is one of the most versatile mineral fillers (qv) and is consumed in a wide range of products including paper (qv), paint (qv), plastics, mbber, textiles (qv), caulks, sealants (qv), and printing inks (qv). High purity grades of both natural and precipitated calcium carbonate meet the requirements of the Food Chemicals Codex and the United States Pharmacopeia and are used in dentifrices (qv), cosmetics (qv), foods, and pharmaceuticals (qv). 

The main contaminant and its concentration ia commercial caprolactam usually is water at <0.1 wt%. Anhydrous caprolactam is produced ia small quantity for use ia anionic polymerisa tion processes. Commercial product of very high purity is required by the users, ie, the fibers and plastics producers, most of whom utilise technologically advanced processes that are sensitive to monomer quality. 

High purity orthoxylene is used almost solely in the manufacture of phthalic anhydride. The anhydride is an intermediate for the manufacture of plasticizers, alkyd resins, polyester resins and other derivatives, such as phenolphthalein. 

Vacuum deposition of high-purity aluminium has been used as a bright finish of a decorative nature on domestic items and some car accessories, as well as special items for space missions where opacity to solar radiation was required. Continuous deposition on plastic strip at speeds up to 450m/min has been achieved. 

Titanium dioxide (E171, Cl white 6) is a white, opaque mineral occurring naturally in three main forms rutile, anatase, and brookite. More than 4 million tons of titanium dioxide are produced per year and it is widely used for industrial applications (paints, inks, plastics, textiles) and in small amounts as a food colorant. ° "° Production and properties — Titanium oxide is mainly produced from ilmenite, a titaniferous ore (FeTiOj). Rutile and anatase are relatively pure titanium dioxide (Ti02) forms. Titanium oxide pigment is produced via chloride or sulfate processes via the treatment of the titanium oxide ore with chlorine gas or sulfuric acid, followed by a series of purification steps. High-purity anatase is preferred for utilization in the food industry. It may be coated with small amounts of alumina or silica to improve technological properties. 

Applications NAA is a powerful technique for ultratrace analysis of metallic impurities in plastics. PE is one of the most important canning materials for NAA, mainly on account of its high purity and low price. The cross-section of PE for thermal neutrons amounts to... 

The product obtained by this procedure is pure enough for most purposes. Its melt, however, is faintly cloudy. A product of high purity, giving a clear melt, can be obtained by recrystallization from about 15 ml. of dry carbon tetrachloride per gram of sulfenyl chloride. When stored in a sealed brown bottle with a plastic cap (no metal ), the sulfenyl chloride is stable for years. 

Fig. 2.45 (a) Desorption curves at various temperatures under an initial hydrogen pressure of 0.1 MPa for MgH ABCR commercial powder which was stored under high-purity argon for almost a year but whose container was frequently opened in a plastic glove bag filled with argon, (b) The Arrhenius plot of the desorption rate for the estimate of the apparent activation energy, using kinetics data for three temperatures 350, 375, and 400°C -217 kJ/molH ). Coefficient of fit... 

Lead trioxide is a catalyst for oxidation of carbon monoxide in exhaust gases. Other uses are vulcanizing neoprene rubber fireproofing plastics detecting radiation and manufacturing high-purity diamonds. 

---