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Univerzitet u Zenici
  Doctoral theses defended at the University in Zenica

Date and place of thesis defense:
09.05.2011. Faculty of Metallurgy and Materials Science
mr. sc. MujkanoviŠ Adnan
prof. dr. Petar Petrovski

Thesis title:

Defining conditions for synthesis of amorphous SiO2, filler for rubber, by precipitation from Na-metasilicate solution

Reinforcing fillers are used to enhance the mechanical properties of polymers in general and elastomers in particular. Silica has been used in recent years as an alternative to carbon black for the reinforcement of rubbers, specifically for tire applications. The silane coupling of silica offers alternative choices in rubber compounding that have proven to be advantageous in a number of applications. Precipitated silica has the ability to improve the rolling resistance with little or no sacrifice in traction or wear, which results in improved fuel efficiency. In this work, the process of producing precipitated silica from aqueous solution of sodium silicate was studied. The production of precipitated silica started with the carbonation of sodium silicate solution with a gas mixture of CO2 and air. In the next phase, dilute hydrochloric acid was added to the solution until pH dropped to the target value. The influence of process parameters (concentration of SiO2 in sodium silicate solution, final pH value and silicate module of solution, precipitation temperature and drying regime) on the properties of precipitation products was studied. Silica samples were characterized by scanning electron microscopy, measuring the oil absorption and specific surface area, particle size distribution and the effect of sonication on silica agglomerates by a laser particle size analyzer. After examination of all process parameters, the most influential parameters were selected for the next stage. Statistical analysis showed that key parameters of process were SiO2 concentration and precipitation temperature, and in the second stage of investigation more detailed analysis of the two parameters were conducted. It was found that, from the standpoint of usage as active filler in rubber, silicas achieve the best properties at the precipitation temperature 40-60 ░C and SiO2 concentration 7-9% in the solution of sodium silicate. To assess the quality of synthetic SiO2 fillers, besides the determination of their physical and mechanical properties, tests related to its behavior in the tire were also carried out. It has been shown that synthesized SiO2 filler can be successfully used in the manufacture of tires, where high values of oil absorption and specific surface area and good ability of dispersion in a rubber matrix are required.

Key words:
silica, precipitation, sodium silicate, reinforcement filler, oil adsorption, specific surface, dispersion ability, structure

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