All-electric melt

Fig. 3.13. An all-electric melt furnace with side electrodes in two levels [551]...

Boron is a covalently bonded, refractory, non-metallic insulator of great hardness and is thus not directly comparable in its physical properties with Al, Ga, In and Tl, which are all low-melting, rather soft metals having a very low electrical... 

The thermal efficiency of glass melting furnaces is relatively low, in particular that of pot furnaces. Values of 20—35% are reported for tank furnaces with classical heating (see below). Efforts to raise thermal efficiency led to experiments with shaft and rotary furnaces, with fluidized bed melting furnaces, etc. Only electric boosting and all electric glass furnaces have so far found wider practical application. 

For continuous melting of domestic and technical glass, small electric furnaces have been developed a longitudinal cross section of one such type is shown in Fig. 102. At the working end, the temperature is controlled by resistance heating elements. The direction of melt flow is shown by the arrow. All-electric furnaces have to be heated up by auxiliary gas burners since the cold batch does not conduct electrically. 

Crystal glasses were traditionally melted in pot furnaces, but nowadays small continuous tank furnaces are used. Lead glasses are conveniently melted in Unit-Melter furnaces, lead-free glasses in all-electric furnaces with a daily output of several tons (cf. Fig. 102). Machine forming is being gradually introduced even for these types of glass. 

All-electric shaft furnaces of unconventional design, e.g. in the shape of hexagonal prism, are being developed for higher melting outputs (up to 1001 day" ). The melting batch advances vertically downwards. Such a furnace allows for uniform distribution of electric input using symmetrically positioned electrodes at several levels this also facilitates adjustment of the required temperature profile. 

Extensive regions of homogeneous solid solutions close to indium arsenide were established by physicochemical methods of analysis in the following quaternary systems InAs-CdS, InAs-CdSe, InAs-CdTe, InAs-ZnS, InAs-ZnSe, InAs-ZnTe. All the melts crystallize in the sphalerite structure and exhibit a linear relationship between the lattice constant and composition. The results ate presented of studies of the electrical conductivity, the Hall effect, and the thermoelectric power, and of electron-microscope studies of the cleaved surfaces of the alloys. 

Hard borosilicates—tending to all electric or heavily boosted regenerative melt temperatures above 1600°C... 

A major insurance company conducted a series of electrical inspections and found that 75 percent of all electrical failures are caused by a lack of preventive maintenance. Connections could be dirty or loose, moisture could be a problem, defective or inadequate insulation or short circuiting could be an issue. These conditions could easily cause a buildup of heat, which could melt equipment and potentially cause arcing that could ultimately result in a breakdown or fire. 

Tetrafluoroethylene. Emulsion polymerisation of tetrafluoroethylene, catalysed by oxygen, yields polytetrafluoroethylene (Tejlon) as a very tough horn-hke material of high melting point. It possesses excellent electrical insulation properties and a remarkable inertness towards all chemical reagents, including aqua regia. 

---