What Are All The Ways in Which Trilithon (bluestone, Rhodochrosite, Silica Nepheline) Can Be Used in Unshaped Refractories?

     In the field of non-metallic and refractory materials, especially in the refractory materials, for the sake of convenience, the three minerals of bluestone, sillimanite and rhodochrosite, referred to as the "three stones", belong to the same high-alumina mineral raw materials.

The main applications of trilithon in amorphous refractories are:

    (1) As refractory aggregate, e.g. using coarse-grained rhodochrosite as refractory aggregate.

    (2) As refractory powder, such as the use of rhodochrosite and silica concentrates as powder.

    (3) As an admixture, mainly as an expansion agent.

    Among the trilithic minerals, blueschist is the most used. Because of the largest expansion value accompanied by blue crystal mullite reaction, so blue crystal is a good expansion agent for amorphous refractories to offset the contraction of refractories at high temperatures and improve their high-temperature performance.

 In recent years there are four main areas of research on the application of trilithon in refractory castables:

1,Application of bluestone in refractory castables

    Adding bluestone in the castable, mainly choose the hidden mountain, Shuyang Hanshan two places of bluestone as the expansion agent of refractory castable, in terms of expansion, to Tongbai's bluestone has a larger expansion value, more suitable for the expansion agent of non-conformal refractory materials. In the iron package castables, adding Nanyang Hidden Mountain bluecrystal as an expansion agent improves the rate of change of the line of castables, thus eliminating the material in the high temperature and the cooling process of shrinkage cracks, and improves the service life of the material. In the use of iron water package, the bottom of the package and other necessary repairs, a package throughout the use of package age 1200 ~ 1300 times. High-alumina castables formulated with bluestone as an expansion agent improved the post-burning line change of the castables. When the castables are not added blueschist, the post-firing line changes are negative, and with the increase in temperature, the shrinkage becomes larger. 1300 ℃ for -0.09%, 1500 ℃ for -1.05%. However, after adding bluestone, the shrinkage of the castables is reduced or positive expansion, such as the addition of 8%, 10% of different grain size (0.175mm or 0.09mm) bluestone, at a temperature of 1300 ~ 1500 ℃, the castables are positive, i.e., offsetting the shrinkage of the material at elevated temperatures, but also show expansion.

    In production, the comprehensive material index requirements, a reasonable choice of bluestone concentrate particle size, not only to ensure that the material does not shrink at high temperatures (or little shrinkage), but also to ensure that there is a high strength. General selection of 0.174 ~ 0.074mm specifications for the size of the moderate.

2,Effect of adding rhodochrosite on the performance of castables

    (1) Application of Rhodochrosite in Iron Gully Material

    With the large-scale blast furnace, the scouring force of iron and slag, wear and tear increase, especially the main ditch of the increasingly harsh working conditions, life expectancy is reduced, in order to change this phenomenon, LiYePu et al. in the production of the iron ditch main ditch material in the use of rhodochrosite, using rhodochrosite's characteristics to improve the performance of the iron ditch main ditch castable material. In the production of different use requirements, adding different particle size (0 ~ 1mm, 0.074mm) of rhodochrosite iron gully castable material, is conducive to reducing the apparent porosity of the castable material, improve the room temperature compressive strength, improve the thermal shock stability of the castable material. The better the quality of rhodochrosite, the more superior its effect and high temperature performance.

    With the use of iron ditch castable with added erythrite, the one-time iron throughput of 250m3 blast furnace single outlet reaches 80,000 tons to 120,000 tons, and the service life can reach more than 1.5 million tons after spraying and pouring repair in the middle of the process, which reduces the cost of production. The use of the mechanism is mainly used in the high temperature decomposition of rhodochrosite, can produce a certain amount of mullite and liquid phase, the generation of mullite to help the castables thermal shock stability and load softening temperature, and the liquid phase can not only promote the sintering so that the matrix and the aggregate close collection, but also close the pores, reduce the products of the apparent porosity, improve the compressive strength of the castables and other characteristics.

    (2) Desulphurization gun with castables

    Iron pretreatment desulfurization gun is always in the violent hot and cold temperature changes, at this time the general damage to the gun is not erosion, but thermal stress cracks, penetration of iron and destruction. By improving the thermal shock resistance of the castables, to prevent the gun body cracks and spalling phenomenon. By adding rhodochrosite, the shrinkage is compensated and the volume stability of the gun body is ensured to improve its usability. Li Yupu et al. reached more than 200 times at one time during the trial in a steel plant in Ningbo, with a small amount of repair in the middle.

3,Effect of adding silica and bluestone on the performance of castables

    In the casting material, the addition of silica nepheline, or silica nepheline and blueschist concentrate composite improved the line change of the products after firing. In addition, it also makes the load softening temperature and compressive strength of the products have more obvious effects. Silica concentrate grade is high, its effect is more obvious. Such as the use of Al2O3 content of 59% of the silica, aggregate for the first grade of alumina SC-3 sample, its load softening temperature (4%) is greater than 1600 ℃; when the use of silica Al2O3 content of 48%, the aggregate is still the first grade of alumina, its load softening temperature (4%) is significantly lower, such as the SC-12 sample, for 1565 ℃.

4,Effect of adding natural silica and rhodochrosite composite mineral powder on the performance of castables

    The thermal shock resistance of the specimens was improved and the rate of post-firing line change was reduced by adding composite mineral powder to the castables. The main technical indexes of the low-cemented, high-alumina castables with moderate addition of natural silica-rhodolite composite minerals were improved. The main reason is the large amount of mullite generated in the matrix. Composite mineral powder at lower temperatures (1000 ~ 1300 ℃) to form a liquid phase, and the liquid phase is favorable to the generation of in situ mullite, secondary mullite, which has a beneficial effect on the performance of the castables. The suitable amount of compound mineral powder is 5%.

    The main role of bluestone used in refractory castables in the past is as an expansion agent to offset the shrinkage of the material at high temperatures, with the improvement of understanding, the application of rhodochrosite, silica wire stone, or a composite of the three stones can effectively improve and enhance the quality of the Al2O3-SiO2 system of materials, in the stereotyped refractory materials is so, and the same is true of the non-conformable refractory materials, all show the unique nature of the three stones.

 In the refractory plastic, add blue crystalline stone and not add blue crystalline stone to do comparisons, in 1400 ℃ after burning line change, the former line change is larger, the latter is smaller, the general expansion increase and add blue crystalline stone, 1400 ℃ after burning the specimens, the line change is an expansion state. This is favorable to the use of plastics, enhance the stability of the structure of the building block, reduce cracks, slow peeling. The line change at 1600°C was again slightly expanded compared to 1400°C.

 After adding trilithon minerals, the post-firing line change of high alumina refractory pounding material changed from line contraction to line expansion. Among them, bluestone has the best effect, with the post-firing line change increasing from -0.40% to +1.60% at 1400℃. This shows the expansionist effect of trilithonite minerals.

 The addition of trilithon minerals has no significant effect on the compressive strength of high alumina refractory pressed materials at 1400 ~ 1500°C, because at this temperature stage, the rapid decomposition of blueschist and rhodochrosite is not completely mullitized.

 The following precautions should be taken to prevent clogging of the lattice bricks in the heat storage chamber of coke ovens heated with blast furnace gas.

    ①Purge the gas heat storage room with compressed air regularly.

    ② The dust content of blast furnace gas should be controlled below 15mg/m3.

    ③ physical and chemical indexes of clay lattice bricks for coke oven should be set up as standard, and the content of Al2O3 and low melting point

substances should be appropriately reduced with reference to foreign standards.

    ④ The top 3~5 layers of the heat storage room of the new coke oven should use half-silica lattice bricks.

    ⑤ For the lattice bricks which have been found to be clogged, replace them immediately and replace them with half-silica lattice bricks.

 With the development of non-shaped refractory materials, refractory slurry in the development, production, inspection and other aspects have been widely developed. With the expansion of the scope of application of refractory slurry, ordinary refractory slurry in the use of performance and other aspects can not fully meet the requirements of the construction of the furnace. New refractory slurry, the addition of blue crystal plays a big role. In the refractory slurry, the addition of sapphire concentrate, due to the mullite expansion reaction of sapphire, to compensate for the contraction of the slurry at high temperatures.

 Blast furnace iron out of the ditch with high strength slag wall prefabricated with expansion agent, so that the material at all temperatures under the uniform expansion (especially in the temperature range of 1000 ~ 1500 ℃), offsetting or attenuating the material at each temperature stage of the contraction. The material with expansion agent can fill the micro-cracks caused by the shrinkage of the material matrix and its own internal stress, and improve the volume stability of the material.

 Examples of the application of trilobite concentrate as an expander in amorphous refractories are shown in Table 1.

Table 1

 To summarize, the various varieties of indefinite refractory materials, such as castables, plastics, pounding materials and refractory slurry, are used to varying degrees to the bluestone, rhodochrosite and silica, especially the bluestone is more widely used. The main mechanism is the use of three stone mineral decomposition at high temperatures, mullite reaction accompanied by volume expansion, to compensate for the contraction of non-conformable refractories at high temperatures, so that the linear expansion tends to be positive, to reduce the structure of the flaking, and to enhance the volumetric stability of the material.

 In addition, the decomposition of trilithonite minerals to form mullite minerals has a favorable effect on the load softening temperature and strength of the material.

  Expansion agents for amorphous refractories also use quartz (SiO2). The expansion generated by the homogeneous multi-phase transformation of quartz is utilized to compensate for the shrinkage of unshaped refractories at high temperatures. Among them, the main application of α-quartz (high temperature quartz) into α-squartz expansion, because it is the largest volume change.

 However, comparing quartz with blueschist, blueschist is better to use. One is the expansion value is relatively large, and the other is due to the decomposition of blueschist, obtain mullite crystal phase, the material high temperature performance is favorable. Therefore, at present, in the unshaped refractory materials commonly used blue crystal as an expansion agent, or with rhodochrosite or silica composite as an additive use.

 The decomposition of mullite reaction using sapphire, rhodochrosite and silica threads has a good effect on the properties of the material, and it is necessary to choose a good grade, dosage and particle size according to the operating temperature, otherwise it will deteriorate the material internally, resulting in expansion cracks and a decrease in the density and strength of the material.

 The above methods use the decomposition of trilithonite minerals, the expansion reaction accompanying mullite mineralization and the expansion reaction produced by quartz crystalline transformation to compensate for the shrinkage of amorphous refractory materials at high temperatures and to enhance volumetric stability. However, the expansion reaction has more than just a favorable effect on the material. For example, low creep bricks for hot blast stove, modified high alumina brick series, etc., is to use the expansion reaction within the material to improve the load softening temperature and creep resistance, thermal shock resistance and other properties. So we have to make good use of trilithion to improve the performance of refractory materials.

  It is noted here in passing that the problem of expansion reactions is present in refractories in large numbers. For example, the development of low creep bricks for hot blast furnaces discussed above had a swelling effect in the matrix. In conclusion, in addition to paying attention to the expansion reaction that exists in large quantities in materials, it is more important to try to utilize and control it to improve the properties of the materials.

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