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By adding these few things, the performance of ultra-low cement refractories tends to increase

Words:[Big][Medium][Small] Mobile Page Two-Dimensional Code 2018-10-15     


Superfine powder

Ultrafine powder of ultra-low cement castable mainly includes active silica fume, a-al2o3 powder and Cr2O3 powder, etc. Their composition content (%) is 93.2, more than 90 and more than 99 respectively.

The mix ratio of refractory castable is the same, CaO content is about 0.6%.Three groups of samples were mixed with active SiO2, a-al2o3 (a aluminum oxide powder) and ultrafine powder composed of them, with the same dosage.With the increase of heating temperature, the strength of castable mixed with different ultrafine powder increases.

At the same time, the contributions of different ultrafine powders to castable strength are also different.The superfine powder mixed with active SiO2 and a-al2o3 has the highest strength, followed by the castable mixed with active SiO2 superfine powder, and the castable mixed with alumina superfine powder has the lowest strength.When the heating temperature reaches 1500℃, three kinds of ultra-fine powder castable are added, and their strength is basically similar.That is to say, the preparation of ultra-low cement refractory castable, it is best to use composite ultrafine powder, used alone, should give priority to the selection of active SiO2 ultrafine powder.

However, the increasing amount of SiO2 ultrafine powder will reduce the content of Al2O3 in castable and increase the free quartz, which will inevitably lead to the decrease of slag resistance of castable.For example, the mix ratio of iron channel castable: 70% alumina aggregate, sic14.2%, c5.8%, 0.2% dispersant, 6.5% water, 10% alumina powder and SiO2 ultrafine powder.Slag resistance test was carried out in reducing atmosphere by crucible method.Test conditions: standard slag alkalinity is 1.105, heating temperature and holding time 1500℃, 4h.With the increase of SiO2 ultrafine powder dosage, slag resistance has an optimal value, that is, when the dosage of ultrafine powder is about 5%, slag resistance is the best.

The mix ratio of castable remains unchanged, and the combined amount of refractory fine powder and ultra-fine powder remains unchanged.With the increase of ultrafine powder dosage, the compressive strength also increases after burning at 1600℃, but there is an optimal value.SiO2 ultrafine powder dosage is about 5%, Al2O3 and Cr2O3 ultrafine powder dosage is about 7%, at this time, the strength is good, and other performance is excellent.From the variety of ultrafine powder, the best enhancement effect is SiO2 ultrafine powder, followed by Al2O3 ultrafine powder and Cr2O3 ultrafine powder.Meanwhile, the enhancement of SiO2 ultrafine powder was 2.5~4.4 times higher than that of the latter two ultrafine powders.

The second


There are many kinds of additives, taking dispersants and water-reducing agents as examples to illustrate the effect on the properties of ultra-low cement castable.

When the mixing ratio of castable is fixed, adding different amount of dispersant can reduce the amount of construction water.When the amount of construction water is constant, with the increase of the amount of dispersant, the drying compressive strength has an optimal value.That is, when the dosage of dispersant is 0.15%~0.2%, the strength is the best.When the amount is more than 0.5%, the strength will become worse or the sample will crack. This is because of the poor fluidity of castable and the formation body is not dense.

There are many kinds of water-reducing agent, which should be reasonably selected through test.After determining the mix ratio of ultra-low cement corundum castable, sodium polyphosphate, melamine condensates and naphthalene sulfonate condensates were used as water-reducing agents respectively to screen the appropriate dosage and prepare refractory castable.

To see from the table, add and subtract water castable, due to the spontaneous reunion superfine powder, unable to effectively fill the pore, and its uneven distribution, large amounts of water was wrapped in flocculation or filling in the pores in the body, thus lead to water consumption increased, after the heat treatment of low volume density, high porosity, low intensity, but also conducive to sintering;Polyphosphate has a certain dispersion water reduction effect, to a certain extent can prevent the spontaneous agglomeration of ultrafine powder, make it more fully in the pores, improve the utilization rate of water, that is, reduce the amount of water, water reduction rate of about 17%.

Therefore, the volume density of castable increased and the porosity decreased. Compared with those without water reducer, the compressive strength increased by 0.6~1.9 times after burning, and the high temperature flexural strength increased by 1.25 times.B and C are organic superplasticizers, and their dispersion water reduction effect is particularly significant. The water reduction rate is 25% and 28% respectively. Compared with castable without superplasticizer, its volume density is about 3.5% higher, porosity is 15% lower, compressive strength after burning is increased by 1-4 times, and high temperature flexural strength is increased by 3.5 times.Meanwhile, it can be seen that the effect of C water reducer is better than that of B.In short, when preparing ultra-low cement refractory castable, water reducing agent must be added, and organic and efficient water reducing agent should be preferred.


Aluminum powder

In iron ditch refractory castable, generally add metal aluminum powder, play a role in drying and strengthening.Its particle size and dosage have great influence on the properties of castable, so it should be reasonably selected.

In al2o3-sic -C ultra-low quality cement castable, the smaller the particle size of metal aluminum powder and the higher the construction environment temperature are, the more intense the chemical reaction will be, and the more gases generated, the higher the material temperature will be.This is beneficial to the dehydration of castable, can be quickly baked, but the reaction is too fast, easy to form false coagulation, adverse to strength.The proportion of castable is the same.It is assumed that the aluminum powder has a large particle size, which is unfavorable to the strength, and its particle size is too small, which has certain benefits to the drying compressive strength, but the other strengths have decreased.When the particle size of aluminum powder is 88~44mm, the strength is good.The amount of aluminum powder should be determined according to the performance of refractory castable and construction conditions, and should be used as little as possible under the premise of ensuring favorable exhaust and quick drying.


Plus content

SiC and carbon materials should be added in al2o3-sic -C super low quality cement castable to improve slag resistance and thermal stability.It is proved by test and application that the grade and quantity of SiC and carbon materials have great influence on the performance of castable, so it should be reasonably selected.At the same time, the blast furnace size and the use of different parts, the grade and dosage are different.In general, large and medium blast furnace main iron ditch or slag ditch, with high quality SiC and carbon materials, medium and small blast furnace with low grade SiC and carbon materials;SiC dosage is generally 5%~35%.Carbon materials mainly include asphalt, flake graphite, electrode powder and earthy graphite, etc., the amount of which is 2%~6%.

In tiegou refractory castable, SiC and carbon materials are generally mixed in the state of fine powder, SiC best used ultrafine powder.Because the material contains SiC and carbon materials, the oxidation resistance is reduced.That is, carbon oxidation, leaving more microholes, molten iron or slag is constantly infiltrated into the interior, at the same time, the formation of decarburization layer, leading to the lining damage.Adding aluminum powder can improve the oxidation resistance of castable.The results show that the compound use of metal silicon powder, namely Al powder and Si powder, has better oxidation resistance and can improve the strength of castable.This is because silicon and aluminum react with carbon at high temperature to form SiC and Al4C3, making their microstructure and surface denser.

In al2o3-sio ultra-low quality cement refractory castable, adding 2%~8% of blue SPAR powder, in the high temperature of 1200~1400℃ to overcome the formation of mullite, so as to improve its strength.That is to say, the bluestone is not only an expansive agent, but also a mineralizing agent.


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