Micropozzolan spheres, condensed from the vapors of a metallic silicon/ferrosilicon liquid, possess multifunctional applications in oilwell cements. Commonly available and cost-effective, this amorphous substance imparts significant improvements in the physical and mechanical properties of Portland cements. The practical utility of silica fume as an admixture is primarily attributable to its particle size, chemical composition, and reactivity. Composed largely of silicon dioxide (SiO2), silica fume has an average particle diameter of 0.1 μm (100 times finer than cement or fly ash) and yields a surface area on the order of 20 m2/g.

When silica fume was added to cements or cement/fly ash mixtures, several beneficial effects were noted: (1) the water consumptive nature of silica fume allows it to function as an extender and a pozzolan substitute for lightweight cements; (2) high water adsorption combined with an increased pozzolanic reactivity promotes enhanced compressive strengths; (3) the purity and solubility of the material makes it suitable for combating strength retrogression in cements at temperatures above 230°F (110°C); (4) permeability and alkali content of the set product are reduced, both desirous properties in a carbon dioxide (CO2) environment.

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