Parameters Of Silica Research Articles

Effect of ammonium salts on dispersive and adsorptive parameters of silicas precipitated from sodium metasilicate solution

Abstract Studies were conducted on precipitation of highly dispersed silicas from sodium metasilicate solution using five types of ammonium salts. Effects of the applied ammonium salts were examined on principal physicochemical parameters of the obtained silica (particle size, bulk density, tendency to form agglomerate structures) and on adsorptive parameters (specific surface area, volume and size of pores). In the course of precipitation the reactive system was supplemented with the hydrophobicity-inducing agent, Rokafenol N-9 (nonylphenyl polyoxyethylene glycol ether) and the system was mixed using a top stirrer or a homogeniser. The most active silicas were precipitated using ammonium hydrogen salts (NH 4 HCO 3 and NH 4 H 2 PO 4 ) without supplementation of non-ionic surfactant. Addition to the silica precipitation reactive system of a hydrophobicity-inducing agent and a rapidly revolving mixer clearly improved principal physicochemical, adsorptive and dispersive properties of the silica independently of the employed precipitating agent.

On the determination of polarity parameters of silica by means of solvatochromic probe dyes

Empirical “solvent” parameters of silica surfaces are determined by means of solvatochromic dyes, e.g., Cu(tmen) (acac)+ ClO 4 − /B(C6H5) 4 − , Fe(phen)2(CN)2, and Michlers Ketone dissolved in 1,2-dichloroethane or cyclohexane. The values obtained by UV/VIS-measurements are compared with both the polarity scales of Kamlet and Taft and with Gutmann's donor and acceptor numbers. Kamlet and Taft's α-parameter (the hydrogen-bond donation capacity of a solvent) is determined independently by means of salicylideneaniline. The π* of silica is determined using 5-N,N-dimethylamino-5′-nitro-2,2′-bithiophene and the complex of tetracyanoethylene with Michlers Ketone, respectively. Further on the reliabilities of the obtained Kamlet-Taft parameters α, β, and π* are checked by comparism with experimental and calculated values of theET(30)-parameter of silica by means of multi-parameter regression analysis. The surface properties of silica are influenced mainly by HBD-properties α (75%) and dipolarity/polarizability π* (20%), but hardly by the HBA-properties β (<5%). UV/VIS-measurements were carried out in a special equipment with glass fiber optics, A drawing of the apparatus is given.