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Properties
Silica fume (also called silicon ash or condensed silica fume) is formed by condensation and sediment of strongly-volatile SiO2 and Si from ore-smelting electric furnaces which are exhausted and oxidized with air during smelting of ferrosilicon and industrial silicon (metallic silicon) with ferroalloy. It is one byproduct of large-scale industrial smelting, and the whole process requires dedusting device to recycle it. As its mass is low, sometimes it needs an encryption device due to different purposes.
Applications
It is widely applied in refractory industry, and plays an important role in improvement of amorphous refractory.
(1) There are many pores in conventional refractory, and to fill silica fume in the pores is good for improvement of volume density, reduction of porosity and sharp enhancement of strength.
(2) Silica fume has stronger activity, can form colloid particles in water. After adding some dispersing agent, it can enhance flowability and improve casting property.
(3) Silica fume is easy to form Si-OH base in water, and has stronger hydrophilicity and activity, so it is able to enhance refractory condensation, improve high-temperature property and prolong service life of refractory products.
Silica fume is extensively used in the refractory industry, specifically showing as following in practice.
(1) Replace pure aluminum oxide mud to make refractory;
(2) Function as additive to make formed and amorphous refractory products, good for great improvement in strength and high-temperature property of products.
(3) Function as coagulant for whole pouring of teeming ladle.
(4) Function as adhesive, agglutinant, coagulant, and additive in other refractory products.
| Index of Silica Fume (Take SiO2 92% for example) | ||
| Item | Index(%) | Typical Value |
| Loss on ignition | ≤6 | 1-2 |
| Cr | ≤0.02 | 0.02 |
| SiO2 | ≥92 | 92-94 |
| Moisture | ≤3.0 | 0.5-1 |
| Water demand ratio | ≤125 | 120 |
| Specific surface area | ≥15000 | 18000-20000 |
what is silica fume