The Effect of Impurities upon the Physical Properties of Silica Gel by the Heat-Treatment

Abstract

The effects of various kinds of inorganic salts upon the physical properties of silica gel heated in the range up to 1200°C were studied. We measured the polymorphic behavior by means of X-ray diffraction, the simultaneous measurement of the differential thermal analysis, and the thermogravimetric analysis, and the specific surface area by means of the BET N2 method and by means of studying the water-adsorption capacity. The cationic impurities which were found to have strong effects upon the physical properties mentioned above are Na+, K+, Ca2+, Pb2+, Cd2+, Zn2+, and Sb3+. Cations such as Al3+, Cr3+, Mn3+, and Co2+ were shown to have weak but positive effects upon the physical properties of silica gel.

Hi‐NicalonTM‐SSiC Fiber Oxidation and Scale Crystallization Kinetics

“…Crystallization rates for 100 h at 1000°C and 10 h at 1100°C are comparable to some rates found in the literature, albeit with more tridymite formation than cristobalite . Presence of impurities, particularly sodium, is often suggested to promote tridymite crystallization over that of cristobalite, but the literature is inconsistent on this; some studies are ambiguous or suggest that sodium promotes cristobalite crystallization . Both higher and much lower crystallization temperatures were reported for oxide scales formed on a single crystal and CVD (β) SiC.…”

“…3,72 Presence of impurities, particularly sodium, is often suggested to promote tridymite crystallization over that of cristobalite, 3,5,11,73 but the literature is inconsistent on this; some studies are ambiguous or suggest that sodium promotes cristobalite crystallization. [74][75][76] Both higher 21 and much lower 20 crystallization temperatures were reported for oxide scales formed on a single crystal and CVD (b) SiC. Neither study reported the type of furnace tube that was used, or other details helpful in assessment of the possible role of impurities.…”

The influence of cationic impurities in silica on its crystallization and point of zero charge

“…The available literature data show that the change in silica structure from the amorphous to the crystal state occurs at a temperature of 1000 • C [9][10][11]. Kondo et al [9,10] studied the influence of impurities and pH of the solution on the structure change of thermally treated silica gel.…”

“…Kondo et al [9,10] studied the influence of impurities and pH of the solution on the structure change of thermally treated silica gel. They concluded that the amorphous to crystal structure change depends on the type and concentration of cations and is independent of the type of anions present as impurities.…”

Improved photoluminescence properties of sol-gel derived Er3+ doped silica films

“…The cross-section TEM micrograph of S-500O1000N sample ͓Fig. 30,31 No crystalline features have been observed by the selected area electron diffraction analysis in agreement with the GIXRD pattern ͓Fig.…”