The Role Of Silica Fume/ Microsilica In Refractories

Microsilica fume has been used to improve refractory materials for more than 40 years. Microsilica fume used for refractory materials will have the following characteristics:

1. Improve the fluidity of castable refractories, reduce water consumption, make it easy to form, and greatly improve production efficiency;

2. Due to the interstitial effect of its ultra-microstructure, the compactness and strength of refractories have been greatly improved;

3. Micro-silica fume has high activity. Under the premise of Al 2 O 3 component, it is easier to form mullite phase, which obviously improves the high temperature strength and thermal shock of refractories.

According to the different properties of refractory materials, orthogonal design is carried out, and the best formula is selected through comparative tests. The company's technical experts can assist the refractory plant to carry out its work. Refractory materials usually use non-encrypted micro-silica powder. At present, in addition to being widely used in castable refractories, it is also being widely used in fused and sintered refractories. For example, it is used as a low-cement castable. Low-cement castable is a new high-performance refractory castable developed in the 1970s. It was first developed by France. It is widely used in various industrial high temperature kilns and has good technical and economic effects. In 1983, Pittsburgh General Refractories Company used low-cement castables for the lining of the main tapping trench cover of dry blast furnaces. The service life was three times that of the original ordinary castables, which was increased from 75-100 furnaces to 300-400 furnaces. The General Building Research Institute of the Ministry of Metallurgy has been conducting research on low cement castables since 1985 and passed the ministerial appraisal in 1988. It has been used in Baosteel and Shougang thermal equipment, and some have replaced Japanese imported materials with domestic materials. Both low cement castables and ordinary castables use calcium aluminate cement. , But after mixing silica fume and superplasticizer in the former, the amount of cement is 4-8%, and the amount of water added is only 5-8%, which is larger than the latter’s 15-20% of cement and 10-15% of water. The range is reduced. Low cement castables can not only save 50-70% of expensive aluminate cement, but also improve performance. The test results of low-cement castables by the General Institute of Building Research of the Ministry of Metallurgy are as follows:

Porosity and Pore Structure Reduction The comparison of the apparent porosity of cement castables and ordinary castables after heating at 1400°C is 20.4% for the former and 26.4% for the latter, an increase of nearly 30%. The total porosity of low-cement castables is lower than that of ordinary castables by the pressure pump method. The ordinary castable after heating at 800℃ increased by nearly 40% compared with that when dried at 110℃. From the aspect of pore size distribution, the pore size larger than 100A in ordinary castables is 2-3 times that of low cement castables, and the pore size smaller than 1000A is only 30-50% of low cement castables. Strength change characteristics The strength of low cement castables can continue to increase regardless of the low temperature, medium temperature and high temperature stages, while the medium temperature strength of ordinary castables has significantly decreased. The thermal flexural strengths of the two castables are as follows: 1100℃*1h 1400℃*1h low cement castable 9.4Mpa 2.0Mpa, ordinary castable 4.8Mpa 0,7Mpa 　　 line changes during heating, low cement castable shrinkage value Lower than ordinary castables, when the temperature reaches 1500℃, low cement castables show a slight expansion of 0.1-0.8%, so the material will not crack. The refractoriness of low-cement castables is determined to be 1790-1830°C, which is higher than that of ordinary castables (1690-1710°C).

The test results of the softening point under load are as follows: ordinary castable low cement castable

Load softening point KD 4% KD 4%, Temperature, ℃ 1170 1325 1240 1395 　　

Thermal expansion is basically the same before 1400℃. After 1400°C, the low cement castable shrinks slightly and then starts to expand. The expansion rate is .5% at 1500°C, while the ordinary castable shrinks sharply after 1400°C. The expansion rate at 1500°C is already negative (-1.8%).　　 Corrosion resistance The converter slag is heated to 1450℃ for 3 hours at a constant temperature. The erosion amount of low cement castable is about 4CM2, which is better than 7CM2 of ordinary castable. So far, China Metallurgical Construction Institute has successfully developed DJ series of various grades of cement castables and used them in many projects. DJ-C165Z and DJ-C17Z two kinds of low cement castables are used in the iron trench cover of Baosteel's blast furnace. The original Japanese imported castables have a usual life of 20 days. Now they have all been replaced by domestic low-cement castables, and the average lifespan is about 20 days. Up to 26 days, saving a lot of foreign exchange. DJ-C70 and DJ-60 low cement castables are used on the burner bricks of Shougang's 250 walking reheating furnace and 430 reheating furnace. The service life of the 250 non-entry heating furnace is 9 months (the original use was only half a month), which is nearly 20 times longer. DJ-C60 low cement castable is used in the depressed parts of Shougang 500 billet heating furnace that are severely worn out by high temperature steam flow, and it is still intact after one year of use. DJ-C60 low cement castable is used in the lining of the CO generator of the Nanjing Chemical Industry Company Research Institute. The service life reaches 68 days, which is 10-20 times longer than that of the original corundum tube.

According to existing reports, low-cement castables are widely used abroad, and have been used in coke ovens, sintering, ironmaking, steelmaking, steel rolling, non-ferrous metallurgy, petroleum and chemical, cement, glass ceramics and power generation industries.