JPH0515665B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a zirconia refractory made by sintering partially stabilized zirconia. [Prior Art] Zirconia has a high degree of fire resistance and is therefore widely used as a refractory material. However, since monoclinic zirconia undergoes a large volume change during phase transition at around 1000°C, it is generally put to practical use as stabilized zirconia containing calcium oxide or magnesium oxide as a solid solution. [Problems to be Solved by the Invention] However, even conventional zirconia refractories partially stabilized with calcium oxide, for example, still have insufficient spalling resistance, and there is a strong demand for improvement. is the reality. Generally, it is known that pores inside a refractory have a large effect on the spalling resistance of the refractory. This is considered to be because when an appropriate amount of pores with an appropriate diameter are present inside the refractory, the stress inside the refractory caused by thermal expansion and contraction is alleviated. However, simply increasing the porosity of a refractory, for example when used on the wall of a melting furnace, makes it easier for the molten material to penetrate into the refractory, which in turn reduces the corrosion resistance of the refractory. This causes problems. An object of the present invention is to provide a zirconia refractory that can improve spalling resistance without reducing corrosion resistance. [Means for Solving the Problems and Their Effects] As a result of various experiments and research, the present inventors have found that by partially stabilizing zirconia by dissolving yttrium oxide as a solid solution, the volume change due to phase transition can be suppressed. The present invention was completed by discovering that not only can the refractory be made smaller, but also the wettability of the molten material to the refractory can be lowered. That is, the zirconia refractory according to the present invention contains 90 to 97% by weight of zirconia and
Contains 10-3% by weight of yttrium oxide, with a stabilization degree of 50-70% and a porosity of 10-30%.
It is characterized by the fact that 80% of the total pores are made up of pores with a diameter of 1 μm or less. When zirconia is partially stabilized by dissolving yttrium oxide as a solid solution, the volume change due to phase transition is reduced and the spalling resistance is improved. In this case, it is necessary to set the degree of stabilization to 50 to 70% by containing 90 to 97% by weight of zirconia and 10 to 3% by weight of yttrium oxide. If the degree of stabilization is less than 50%, it will not be effective in improving spalling resistance because the volume change during the heating process is large, and if it exceeds 70%, it will become close to complete stabilization and the spalling resistance will actually decrease. It is. The reason why the porosity of the refractory is set to 10 to 30% is that the spalling resistance is further improved within this range. If the porosity is less than 10%, even if the strength of the refractory itself increases, the propagation speed of cracks will become too fast and spalling will easily occur;
If it exceeds 30%, spalling tends to occur due to insufficient strength. From the standpoint of improving spalling resistance, it is most desirable that 80% or more of the pores of the refractory be 1 micron or smaller. This is because if less than 80% of the pores have a diameter of 1 μm or less, the tissue becomes locally dense and cracks are likely to occur. Moreover, for this purpose, the average grain size of each crystal grain is not set to approximately 1 μ (about 0.5 to 5 μ, most preferably within the range of 0.7 to 1.3 μ).
If the average particle size is less than 0.5μ, sintering will progress too much.
The average particle size is not more than 80% with pores of 1μ or less.
This is because when the diameter is 5μ or more, most of the pores are 1μ or more. In the present invention, the porosity is set to 10 to 30%, so when refractories are used, for example, on the walls of a melting furnace, there is a possibility that the molten material will easily penetrate into the refractories, resulting in a decrease in corrosion resistance. is possible. However, in the present invention, this possibility can be eliminated by using yttrium oxide to stabilize zirconia. In other words, conventional partially stabilized dicornia stabilized with calcium oxide or magnesium oxide has too good wettability with melts, so unnecessary reactions with melts cannot be suppressed.
While there was a problem of poor corrosion resistance, dicornia stabilized with yttrium oxide has poor wettability with molten materials, which suppresses unnecessary reactions with molten materials and improves the corrosion resistance of refractories. This is something that can be improved. In addition, when manufacturing the refractory according to the present invention,
It is desirable to granulate 90% or more of the entire material so that the particle size is 100 to 4000μ. Further, the firing temperature is preferably 1500 to 1700°C. [Examples] The present invention will be illustrated below using some examples. Examples 1 to 6 and Comparative Examples 1 to 8 In zirconia with an average particle size of approximately 1μ, an average particle size of approximately
A predetermined amount of 1 μm yttrium oxide was added, mixed, and a PVA aqueous solution was added, followed by granulation into relatively soft particles with a low bulk specific gravity using a spray dryer. After drying the granulated material to a moisture content of 0.1% or less, it is molded using a hydraulic press to form a molded product (180 x 90 x 50 mm).
It was fired at 1650℃. The amount of yttrium oxide added can be set to various values to obtain a stabilization degree within the range of 45 to 73%, and the porosity can be set to various values within the range of 6 to 35% by appropriately setting the pressure of the hydraulic press, etc. I made it possible to do so. A spalling test was conducted on the zirconia sintered body thus obtained. In the spalling test, a heat cycle was repeated in which a sample was heated from room temperature to 1500°C and then cooled to room temperature again, and the number of heat cycles until a crack occurred was measured. The results of the spalling test are shown in the table below.

【table】

【table】

[Table] From the above table, it is clear that the spalling resistance was significantly improved in each of the Examples. Further, although the test results are omitted, the refractories of each example were sufficiently superior in corrosion resistance to conventional ones. [Effects of the Invention] As described above, the present invention contains 90 to 97% by weight of zirconia and 10 to 3% by weight of yttrium oxide to achieve a stabilization degree of 50 to 70% and a porosity of 10%. ~30%, and pores smaller than 1μ accounted for more than 80% of the total pores,
This has the excellent effect of significantly improving the spalling resistance of the refractory and also improving the corrosion resistance of the molten material.

Claims (1)

[Claims] 1 90-97% by weight zirconia and 10-3% by weight
Contains yttrium oxide with a stabilization degree of 50-70
%, and the porosity is 10 to 30%, and the pores less than 1 μ account for 80% of the total pores.
A zirconia refractory characterized by occupying the above.