Glass processing

Liquid or solid films which reduce or prevent adhesion between surfaces solid-solid, solid-paste, solid-liquid. Waxes, metallic soaps, glycerides (particularly stearates), polyvinyl alcohol, polyethene, silicones, and fluorocarbons are all used as abherents in metal, rubber, food, polymer, paper and glass processing. 

Traditionally, production of metallic glasses requites rapid heat removal from the material (Fig. 2) which normally involves a combination of a cooling process that has a high heat-transfer coefficient at the interface of the Hquid and quenching medium, and a thin cross section in at least one-dimension. Besides rapid cooling, a variety of techniques are available to produce metallic glasses. Processes not dependent on rapid solidification include plastic deformation (38), mechanical alloying (7,8), and diffusional transformations (10). 

Fig. 1. Gel—sihca glass process sequence showing the process steps A, mixing B, casting C, gelation D, aging E, drying F, dehydration or stabilization ...

In the float-glass process, adopted by all leading plate-glass manufacturers, the molten glass is allowed to float and soHdify on the surface of a pool of molten tin which provides an ideally flat surface. The endless glass ribbon has a surface so smooth that cosdy grinding and polishing are unnecessary. 

About two-thirds of the N2 produced industrially is supplied as a gas, mainly in pipes but also in cylinders under pressure. The remaining one-third is supplied as liquid N2 since this is also a very convenient source of the dry gas. The main use is as an inert atmosphere in the iron and steel industry and in many other metallurgical and chemical processes where the presence of air would involve fire or explosion hazards or unacceptable oxidation of products. Thus, it is extensively used as a purge in petrochemical reactors and other chemical equipment, as an inert diluent for chemicals, and in the float glass process to prevent oxidation of the molten tin (p. 370). It is also used as a blanketing gas in the electronics industry, in the packaging of processed foods and pharmaceuticals, and to pressurize electric cables, telephone wires, and inflatable rubber tyres, etc. 

These films are deposited at atmospheric pressure on the hot glass in a continuous operation (float-glass process). The CVD reactions are described in Ch. 11. 

Tin has many uses, including coating (tins/cans for food), alloys such as bronze, organ pipes, solder, and the float glass process. It is also important in laboratory syntheses, in spite of the well-known toxicity problems. 

Figure 3. Temperature dependence of a width parameter used for sub-glass processes (equation (6)).

Gel-silica glass process sequence, 23 58 Gel spun fibers, 13 382-383 Gel surface, schematic representation of, 23 70... 

Vitrification Various molten-glass processes are commercially available for the destruction and/or immobilization of hazardous wastes (Freeman, 1998). The vitrification method destroys the combustible and some toxic portions of the waste while at the same time incorporating residuals into a glass form. 

For minerals featuring modifying transformations with temperature increase, the decline in hardness is not continuous in character—a temporary increase in hardness takes place in the vicinity of the transformation temperature. This phenomenon is presented in Fig. 6.4.8 (curve 4) for a quartz sample. It is also true for silica glass processed by quartz melting. The curves for silica glass (Fig. 6.4.8, curves 1, 2, 3) show two breakdowns... 

Fig. 6.4.8. Hardness-temperature relationship for glass (1-3) and quartz (4). Glass processed from crystalline quartz (/), from fused silica (2) and Brasilian quartz (J). (After Westbrook, 1960)...

Cellular Glass. Composed of glass processed to form a rigid foam usually having a predominantly closed-cell structure... 

One of the most innovative approaches to ceramic and glass processing is the sol-gel technique. A brief description of the process is given below. The sol-gel route of making any glass or ceramic involves the formation of the... 

The inoculated straw was added to clean, initially sterile columns fabricated from glass process pipe as previously described (4). The columns were prepared in triplicate with approx 50 g dry wt of inoculated stems in each column. The loaded columns were supplied with humidified oil-free instrument air at 193 kPa and a flow rate sufficient to turn over the air in the system once per day (about 10 mL/min). Approximately 2.5 g (dry wt) of straw was sampled from the top and bottom of each column initially and approx every 3 to 4 wk thereafter for 12 wk. The samples were combined, dried to constant weight overnight at 105°C, and ground to 60 mesh in a Wiley mill for compositional analyses. 

For example one area well known in the chemical industry is process de-bottlenecking. Another example is the need for more environmentally friendly processes. Drucker s example is plate glass making by the float glass process (Pilkingtons). 

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