- Effect of spinel on normal temperature compressive strength of sintered sliding plate of magnesia bricks:
When the mass fraction of spinel powder is less than a certain range, the normal temperature compressive strength of refractory decreases gradually with the addition of spinel powder. When the amount of spinel fine powder is zero, the periclase particles in the matrix are easy to recrystallize during the firing process of the product, the structural strength of the refractory is large, and the compressive strength at room temperature is high. With the addition of fine spinel powder, the recrystallization of periclase in the structure is limited, and the different expansion coefficient between spinel and periclase will produce microcracks and reduce the normal temperature compressive strength of products.
When the mass fraction of spinel exceeds a certain range, the normal temperature compressive strength increases gradually with the increase of the amount of spinel fine powder. Mainly because the increase of the amount of spinel in the matrix promotes the direct combination of periclase and spinel, the normal temperature compressive strength of refractory also increases with the increase of the content of spinel.
And when in refractory α- When the mass fraction of Al2O3 increases to 5%, the normal temperature compressive strength of refractories also shows a similar phenomenon. With the increase of spinel content, the normal temperature compressive strength of refractories first decreases and then increases, and with the further addition of spinel powder, the change of normal temperature compressive strength of refractories tends to be gentle, α- The increase of Al2O3 content is conducive to the formation of spinel and the stability of normal temperature compressive strength.
- Effect of spinel on apparent porosity and bulk density of sintered sliding plate of magnesia multiphase refractory:
The apparent porosity and bulk density of refractories are important standards to judge the performance of products, which affect the normal temperature performance and high temperature performance of refractories. With the increase of the amount of spinel fine powder, the bulk density of the brick decreased first and then increased, and the apparent porosity increased first and then decreased.
The main reason may be that when a small amount of spinel powder is added, substances with different thermal expansion coefficients appear in the refractory matrix, resulting in cracks in the structure. With the increase of the addition amount, the number of cracks increases, the apparent porosity increases and the bulk density decreases;
When the amount of spinel reaches a certain amount, with the increase of the amount of spinel in the matrix, the chance of spinel recrystallization in the matrix increases, and the distribution tends to be uniform in the matrix, reducing pores and cracks in the matrix. Therefore, with the increase of the amount of spinel fine powder, the bulk density increases and the apparent porosity decreases.
- Effect of spinel on thermal shock stability of sintered sliding plate of magnesia multiphase refractory:
With the increase of magnesia alumina spinel content, the thermal shock stability of brick shows an upward trend. Due to the large thermal expansion coefficient of periclase, the cracks formed by the thermal expansion of refractory are easy to expand during rapid cooling and heating, so the thermal shock stability is poor.
Because the thermal expansion coefficient of magnesia alumina spinel is small, such as that of magnesia, and the volume expansion rate is different during firing, a small number of microcracks are formed in the brick. With the increase of the content of magnesia alumina spinel, the microcracks increase, and the resulting microcracks can buffer the impact of thermal stress on the brick, so the thermal shock stability of the sliding plate is gradually improved. However, the amount of spinel added also has a certain range. It can be observed that when the mass fraction of spinel reaches a certain amount, the thermal shock stability of refractory tends to be gentle.
When α- When the addition amount (mass fraction) of Al2O3 is 5%, the thermal shock stability of brick also shows an upward trend with the increase of magnesia alumina spinel content, which also shows that the mismatch of cracks formed by the thermal expansion of refractory is conducive to the improvement of thermal shock stability during rapid cooling and heating. With the increase of the content of magnesia alumina spinel, the microcracks gradually increase, which gradually improves the thermal shock stability of the sliding plate.
However, it is also found that when spinel is added too much, the thermal shock stability will decline. This problem is mainly due to the large difference between the thermal expansion of spinel in the matrix and periclase in the aggregate when the content of spinel in the matrix increases to a certain extent. When the refractory is subjected to strong temperature changes, coarse cracks will appear in the structure, which is not conducive to the improvement of thermal shock stability.
- Effect of spinel on Microstructure of sintering sliding plate of magnesia multiphase refractory:
When the addition amount of spinel fine powder is small, because the spinel content in the matrix is particularly small and in an aggregated state, there is almost no recycled spinel, and there is a large gap between the aggregate and the matrix. This structure is not conducive to the improvement of the performance of refractories.
With the increase of the content of spinel fine powder, the content of spinel in the matrix increases, and the distribution is gradually uniform, which is conducive to the direct combination of periclase and spinel, and the stress generated by volume expansion in the firing process is evenly dispersed, which plays a role in improving the thermal shock stability of the sliding plate.
When α- The microstructure of magnesia composite refractory with Al2O3 content (mass fraction) of 5% and spinel powder content of D1%, D3%, D5% and D8%.
When α- Mass fraction ratio of spinel in microstructure when Al2O3 mass fraction is 5% α- When the mass fraction of Al2O3 is 2.5%, because α- The amount ratio of regenerated spinel formed when the mass fraction of Al2O3 is 5% α- The amount of spinel formed when the mass fraction of Al2O3 is 2.5% is more, which improves the direct combination between aggregates, makes the structure more compact and has good performance after burning. Moreover, the microcracks formed by the volume expansion of regenerated spinel in the structure improve the thermal shock stability of magnesium composite refractories.
When α- When the mass fraction of Al2O3 is 5%, the distribution ratio of spinel is α- As for the thermal stress of Al2O3, the thermal stress of Al2O3 is relatively uniformly distributed, which can improve the thermal stability of the refractory material.
The mismatch of thermal expansion characteristics between spinel and periclase is the main reason for increasing the resistance to thermal cycle failure. The thermal expansion coefficient of spinel is small, so that each spinel particle can be wrapped by the pores of the grooved ring during the use of the refractory, so that they can be effectively separated from the periclase matrix. In the case of high stress, this kind of pore can act as a "crack suppressor" and eliminate the damage energy of the through structure, rather than producing a single coarse crack.