It is well known that hydrofluoric acid (HF) will completely destroy glasslined Vessel. Even at concentration as low as 20 ppm, fluorides in acid environment have a devastating effect on glass surface, specially in continuous reactions where the fluoride as HF are repeatedly replenished. Hydrofluoric acid reacts with silicon dioxide, the main ingredient in glass, destroying the SiO2 structure and producing a rough surface.
Preventing fluorides attack on glasslined surface requires constant vigilance by the users. Reactants which can contain fluoride impurities must be carefully analysed to determine the fluoride level before they are used. In particular technical grade phosphoric acid and its salts are often fluoride contaminated as are other mineral acids.

Corrosion Inhibition

Chemical reactions are sometimes so severe that they cause a rapid wear of glass lining. The use of additives to the reacting substances can inhibit this corrosion permitting the use of glass-lined equipment. When using acids, several hundred ppm of silica protect the glass lining and considerably reduce the rate of corrosion in liquid phase. Refer figure 3. The same result can be obtained in vapor stage by adding silicon oils. Generally, the higher the temperature, the greater the quantity of silica required and the more concentrated the acids are, the less silica needs to be used. In presence of fluorine, silica also has a favorable influence. Refer figure 4. With alkalies, a few hundred ppm of calcium, aluminum or zinc may reduce corrosion, especially in dilute solutions.

* Speed of attack depends on part per million (ppm) of micronised silica added to the batch solution.

Mechanical Properties

Glass has the disadvantages of brittleness and low tensile strength. One remedy is to place the glass lining under compression. This is achieved during cooling of the glassed item after firing. This is caused by the difference between the coefficients of thermal expansion of the glass and the base metal and the excellent bond between them.
If the glass steel composite is subjected to a mechanical strain due to handing, mechanical or thermal shock, the compressive stress must not be overcome before putting the glass into tension, causing it to fail. Therefore, the residual compressive stress in the glass acts as an effective shock absorber.

Abrasion

Abrasion of the glass lining is simply a wearing away of the glass by abrasive solids in the reactor. It is characterized by a loss of fire polish and in severe cases, a rough sandpaper-like finish.

Experience has shown that failure due to abrasion alone is very uncommon. In combination with acid corrosion, however, failure can be quite severe: abrasion weakens the silica net-work mechanically, allowing acid corrosion to accelerate.

Gel 2200 has good resistance to abrasion as well as better physical characteristics such as mechanical shock, impact resistance, thermal shock resistance etc.