The physical properties of silicon powder

The main quality indicators of silicon powder are its SiO2 content and fineness. The higher the SiO2 content and the finer the fineness, the better its modification effect on concrete. Due to different testing methods in different countries, their regulations on the main quality indicators of silicon powder are also different (1) Silicon powder is a very fine powder, mainly composed of amorphous silica with extremely fine particles (0.1-0.2um). Its average particle size is 100 times smaller than cement, and its specific surface area is about 15-20m2/g (2) Because silicon is obtained by condensation from steam, its powder has a spherical shape (3) This powder contains over 85% -95% active silica in the glass state (4) The density of silicon powder is 2.2-2.59/cm3, and the bulk density is 200-300kg/m3 The effect of silicon powder added to concrete on newly mixed hardened concrete is related to the above characteristics. The physical properties of silica fume determine that the small particles of silica fume have a high degree of dispersion, which can be fully filled between cement particles to improve the compactness of the hardened slurry

2. Chemical Properties

Silicon powder generally contains over 90% SiO2, and most of it is amorphous silicon dioxide. Its composition varies depending on the alloy variety.

. The chemical composition of silicon powder produced in some regions of China is shown in Table 4.5-3 According to Table 4.5-3-1, the main chemical composition of silica fume is amorphous amorphous amorphous silica (SiO:), which generally accounts for over 90%. High fineness amorphous SiO: It has high Volcanic ash activity, that is, under the alkaline excitation of the cement hydration product Calcium hydroxide (Ca (OH) z), SiOz can quickly react with Ca (OH): to generate calcium silicate hydrate gel (C-S-H), improve the strength of concrete and improve the performance of concrete Silicon powder is a type of fly ash collected from smoke and dust during the smelting of ferrosilicon alloy or metallic silicon in ferroalloy factories. The particles of silicon powder are mainly spherical, with a particle size of 1um smaller and an average particle size of about 0.1um. The specific surface area measured by nitrogen adsorption method reaches 180000cm2/g, which is two orders of magnitude finer than cement particles The main component of silicon powder is amorphous SiO2. Similar to pulverized coal, silica fume can react with Ca (oH) 2 produced by cement hydration to form C.S.H gel. Due to the extremely high SiO2 content of silica fume (usually used in high-strength concrete, the SiO content of silica fume is more than 85%), it has extremely high Volcanic ash activity, which is particularly beneficial to the strength development of concrete in the early and middle stages In addition, when it is uniformly distributed in the hydration products, its extremely fine particles also have a good micro filling effect, making the pore structure of the concrete fully dense The above two characteristics significantly improve the strength and durability of high-performance concrete