Silicate melting points

The word glass commonly means the transparent substance obtained when white sand is fused with metal oxides or carbonates to give a mixture of silicates. Ordinary or soda-glass has the approximate composition NajO. CaO. 6Si02. (This is the composition obtained by analysis it does not represent the compounds present.) If sodium is replaced by potassium the melting point is... 

Molten salts promote rapid corrosion of many constmctional materials at relatively low temperatures. Low-melting-point salts include sodium salts from saline atmospheres, fireside ash, silicate insulation, contaminants in the feed, etc. Corrosion rates of several mm/year can be observed at temperatures as low as 520°C. High chromium- and nickel-containing alloys up to 50% Cr/50% Ni are employed. 

The crude product is dissolved in benzene-hexane (1 1) and applied to a column containing 125 g. of silicic acid (Note 10). Elution with the same solvent gives traces (less than 5 mg. each) of the two fast-moving components in fractions 2 and 4 (125-ml. fractions) and chromatographically pure cholane-24-aI in fractions 5-8 (Note 11). Evaporation of the pooled fractions yields 870 mg. (84%) of the pure crystalline aldehyde, m.p. 102-104°. Recrystallization from 5 ml. of acetone raises the melting point to 103-104° (Note 12). 

Compound SP-A was prepared according to the method of Zajtseva, et al., (11). The final product obtained from the synthesis was purified on a silicic acid column and recrystallized from 1 10 hexane. Positive identification was made through IR and NMR analysis. The colorless crystalline material had a melting point which was heating rate dependent and had a maximum value of 105°C. 

If one moves pn a step farther, binoxide of iln presente ltselfj a substance already more pronounced in its chemical character than charcoal. Still It is inclined to combine equally as well with bases as with acids, showing a transition character. Now, if pumice be soaked In a solution of bichloride of tin, and then dipped into a solution of carbonate of soda, the pumice acquires all the properties of animal charcoal. Very porous pumice, finely-divided silica, cotton fibre—all these show Bigne of chemical power depending on their extant of surface and it may well be supposed that this chemical power would he more prominent, could they be obtained in the fluid state. Silicic add, which is as inert as charcoal at the ordinary temperature, drives out the powerfal sulphuric acid from its combinations at a temperature nearer Its own melting point. 

The time required to cool to 1450°C.—the approximate melting point of silicate rock—is estimated as t =. 49W 5 sec., where W is in kilotons (9). Thus, condensation times of 50 sec. are predicted for 10... 

For certain metal alloys, a calcium silicon alloy is required. This alloy also is used as a steel deoxidizer and is favored because it forms a low-melting-point calcium silicate product A representative composition of the alloy is 30-33% Ca, 60-64% Si, 3-5% Fe, 1-2% Al, 0.3-0.6% C, and less than 0.15% S and P. 

Glass is made from silicates. Silicates have high melting points. Sodium carbonate and calcium carbonate are added to bring down the melting point. The mixture is heated in a furnace to 1400°C. The transparent and jelly-like substance is cooled slowly and then blown into desired shapes. 

Montes (176) analysed the essential oil constituents using the principle of chromatographic adsorption with the aid of columns of silicic acid and bentonite. The compounds were then crystalized and their melting points were deter-det ermined. 

Alumina is a widespread component of siliceous minerals. It occurs as single crystals in the form of sapphire, and with chromium impurity as ruby, and in large deposits as the hydrated oxide bauxite (A1203-2H20). The dehydration of this and other hydrated oxides at temperatures below 1000°C leads to the formation of y-Al203 which is converted to a-Al203 above 1000 °C. The transformation is irreversible and the a-polymorph is stable from absolute zero to its melting point at 2050 °C. 

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