Specialized wares

Tunnel kilns are usually heated with gas or liquid fuels, and in some instances by means of electrically heated metal or SiC or M0S12 elements. The firing schedule can be controlled directly by burners and draught, and by adjusting the car speed. More uniform temperature distribution over the cross-section-is attained in small tunnel kilns which find application in the firing of special ware however, kilns with large cross-section arc used in normal ceramic operation. The functioning of a tunnel kiln is shown in Fig. I86. 

Phosphorus compounds are very important as fertilizers (world use 1976/77 27-3 megatonnes as P2O5) but are widely used in matches, pesticides, special glasses and china ware, alloys (sleels. phosphor bronze), and metal treating (10%), detergents (40%), electrical components (e.g. GaP), foods and drinks (15%). Phosphates are an essential constituent of living organisms. U.S. production of phosphorus 1982 372 000 tonnes. 

Lithium carbonate is used in enamels, specialty glasses and special ceramic wares. It is used to produce glazes on ceramics and porcelains. It also is used as an additive to molten aluminum fluoride electrolyte in Hall-Heroult process. It is the starting material to prepare many other hthium salts. The compound also is used in medicine as an antidepressant. 

Experiments are performed in special laboratory ware made from thin or thick laboratory glass. Thin glassware must be chemically and thermally stable. Ware in which reactions are performed with heating is made from heat-resistant Pyrex glass and quartz. 

Ware Washing. Thoroughly wash laboratory ware before using it in an experiment. First rinse it with tap water. If the dirt is not removed, use a special test-tube brush. Never wash ware with water and sand because scratches may appear on the glass that detract from its strength. 

Always place all apparatuses and ware containing mercury on a special enamelled tray made from iron and having high sides. 

Perforin all the experiments in the presence of your instructor. Arsenic compounds are very poisonous even in minimal doses Perform all work with arsenic compounds in a fume cupboard Pour residues of solutions into special jars and hand them in to the laboratory assistant. After completing work, thoroughly wash the ware in which the experiments were run. Wash your hands with soap. 

This examination includes numerous technical tests and investigations made with the object of determining the physico mechanical properties of the wares. The results obtained, together with those of the microscopic and chemical examinations, indicate if the material possesses the necessary characters for the required purpose and also allow of its value being established. This examination is carried out on a sample so chosen that it represents as far as possible the whole parcel. The tests made are numerous and only a few of the more important are given shortly here further details may be found in special books on the subject.1... 

The reduction and oxidation of radicals are discussed in Chapter. 6.3-6.5. That in the case of radicals derived from charged polymers the special effect of repulsion can play a dramatic role was mentioned above, when the reduction of poly(U)-derived base radicals by thiols was discussed. Beyond the common oxidation and reduction of radicals by transition metal ions, an unexpected effect of very low concentrations of iron ions was observed in the case of poly(acrylic acid) (Ulanski et al. 1996c). Radical-induced chain scission yields were poorly reproducible, but when the glass ware had been washed with EDTA to eliminate traces of transition metal ions, notably iron, from its surface, results became reproducible. In fact, the addition of 1 x 10 6 mol dm3 Fe2+ reduces in a pulse radiolysis experiment the amplitude of conductivity increase (a measure of the yield of chain scission Chap. 13.3) more than tenfold and also causes a significant increase in the rate of the chain-breaking process. In further experiments, this dramatic effect of low iron concentrations was confirmed by measuring the chain scission yields by a different method. At present, the underlying reactions are not yet understood. These data are, however, of some potential relevance to DNA free-radical chemistry, since the presence of adventitious transition metal ions is difficult to avoid. 

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