Lead glass composition

As compared with potentiometry, voltammetry presents special experimental problems, because of the necessity for insulation of a microelectrode of a reproducible surface area. The most common metal seals are glasses, which become increasingly conductive at higher temperatures. Lead glass compositions have especially good properties for sealing to metals, but must be avoided due to the cathodic deposition of lead (22). Voltammetry also places stringent demands on solvent purity. 

The process of pulverized cuUet reduction yields a product having near-batch equivalent sizing (—12 mesh (<1.7 mm mm)) and in a furnace-ready condition. Foil-backed paper, lead and other metals, and some tableware ceramics can be removed in an oversized scalping operation after the first pass through the system. Other contaminants are reduced to a fine particle size that can be assimilated into the glass composition during melting. 

Glasses for electrical and electronic components are represented by the lead tubing and cathode-ray-tube screen and cone glasses. These glasses do not operate under severe corrosion conditions, but surfaces must not leach excessive alkali under damp conditions or electrical breakdown can occur. The glass compositions are formulated to give the maximum electrical resistivity and moisture resistance compatible with other necessary properties. 

For the soda-Hme-silica glasses this is about 2-5 gm/cm for the borosilicate glasses it is very nearly 2-25 gm/cm and hardly changes with slight variations in composition. Wembley L.l. lead glass has a density of 3-08. A very dense lead glass has a density of 5-2. 

Thermoplastics can also lead to composites and hybrids including other conventional materials - such as paper, cardboard, metals and glass - to integrate several functionalities thanks to the exceptional combination of properties for example, multilayers of polyethylene (a water barrier) and PVA (an oil barrier), shatterproofing of glass containers. .. 

Enamels used on cast iron and aluminum have traditionally been composed of SiO., B Oi. PjOs, and PbO. The lead oxide produces good surface quality, fusibility, and acid resistance when properly formulated with other oxides. More recently some non lead-bearing compositions have been developed for both cast-iron and aluminum metals. Glasses containing lead oxide are not recommended for food contact surfaces. 

Hundreds of thousands of different glass compositions have been devised, and they have been used in different ways. Much has been learned about which combination of chemicals will make the best glass for a particular purpose. For example, in 1664 an Englishman named Ravenscroff found that adding lead oxide (PbO) to a glass melt produced a brilliant glass... 

The thermal expansion of Dumet, as this composite wire is called, is about 7.0 x 10 per °C in the longitudinal direction of the wire, and in the radial direction it is about 9-1 x 10 per °C which is nearly the same as that of lead glass. Seals made between Dumet and lead glass are only partly annealed and the glass is left in compression in the longitudinal direction. 

Figure 7.1. A ° Pb/ ° Pb versus Pb/ Pb diagram of starting anorthite and samarskite Lead isotopic compositions of silica glass (Qtz), stainless steel, blank sample 0577-1 annealed at 1050°C, and blank run 570 shocked at 34 GPa are also shown in the inset diagram.

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