Siliceous materials, factors affecting

Kuhn, A. T., Lesan, W. Setchell, D. (1983). Some further factors affecting the solubility of silicate cements. Journal of Materials Science letters, 2, 191-4. 

The rates of hydrolysis of siliceous materials will be affected by several factors. For instance, the rate will be directly related to surface area, explaining the low rates observed for silica deposition from the Vycor apparatus. Also, the composition of the siliceous material will Influence the rate of hydrolysis, explaining the differing amounts of silica transferred from pure silica, silica alumina, zeolite, and the high alumina cracking catalyst. 

It is most often prepared by acid hydrolysis of sodium silicate followed by emulsification in an alcohol water mixture and subsequent condensation to give solid silica gel. This is then washed and dried for use as HPLC column packing. The exact conditions under which these procedures are carried out (e.g. pH, catalysts, temperature) will affect the properties of the resulting material. The most important qualities with regard to the chromatographic performance of the gel are the average particle size, the particle shape, the specific surface area and the pore size. Other factors which are also important are the pH of the gel surface, the number of active silanol groups and the presence of metal ions. 

Most syntheses of zeolites were conducted in strongly basic media. The silicate solution containing alkali metal cations such as Na+ or K+ is one of the main silicon sources in the synthesis of zeolites. The concentration of the basic species in the starting material for the synthesis of zeolites is usually about 0.5 5.5 mol/L. Within this concentration range, aluminate and silicate ions with various polymerization degrees existed in the system. The state and distribution of these ions could be affected by many factors. When the temperature and the concentration of SiC>2 were kept constant, the acid-base... 

Recently, Lopez-Sanz et al. have described an interesting study regarding the catalytic behavior of acidic carbon materials in the Friedlander condensation [154]. The authors reported different series of acidic AC materials, which can be considered as cheaper alternatives to the traditional acidic mesoporous silicates, or even zeolites, for the synthesis of quinolines 51 /quinolones 52. Textural parameters of the acidic AC materials together with their acidic properties are important factors that affect the reaction selectivity. In addition, computational calculations have provid mechanistic insights into the catalytic behavior of different types of catalytic active sites. 

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