JPH0643269B2 - Magnesia-zirconia refractory brick with excellent thermal shock resistance - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a magnesia-zirconia refractory brick having excellent thermal shock resistance.

Background of the Invention: Magnesia refractory bricks have a significantly higher melting point than other siliceous bricks and chamotte bricks, and particularly have excellent resistance to erosion against basic slag during metal refining, and liners for metal refining furnaces. Used in large amounts as a refractory material. However, it has a drawback that it is inferior in thermal shock resistance, so when operating a metal refining furnace using this, a crack is generated behind the operating surface due to thermal shock due to repeated heating and cooling at the start and end of the process, Peeling and damage were severe, and the life of the furnace was short-lived.

Prior art: As a measure to impart thermal shock resistance to magnesia bricks,
A so-called magnesia-chromic direct bond brick, which is provided with thermal shock resistance due to microcracks formed around the chromium ore particles after being mixed with the chromium ore particles and fired, is disclosed in JP-A-55-116.
Proposed in Japanese Patent No. 661. However, even in magnesia-chromic direct bond bricks, the microcracks deteriorate the roof tile structure due to repeated thermal shocks, which leads to the drawback of lowering corrosion resistance, and the magnesia roof tile is resistant to basic slag. It was not possible to fully demonstrate the characteristics of corrosion resistance.

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above problems, and magnesia imparting excellent thermal shock resistance by dispersing local fine pores to eliminate the entire thermal stress. -The purpose is to provide zirconia fireproof roof tiles.

Structure and function of the invention: The present invention will be described below.
5 to 20wt of 2mm diameter unstable zirconia raw material
% To make a 100 wt% blend, which is mixed and molded and then fired at 1650 ° C. or higher to convert the above zirconia raw material into stable zirconia grains in which fine pores are uniformly incorporated. This part is a magnesia-zirconia refractory brick in which the entire thermal stress is absorbed to improve the overall thermal shock resistance.

In the thus obtained refractory brick of the present invention, the medium-sized unstable zirconia mixed in the magnesia raw material reacts with magnesia to become stable zirconia. As shown in FIG. 1, the zirconia grains at this time are changed to grains having fine pores of 5 to 30 μm uniformly incorporated therein. And, such a zirconia grain serves as a magnesia-zirconia refractory brick having a structure in which it is uniformly dispersed in another refractory material.

Next, the mechanism of development of thermal shock resistance of the magnesia-zirconia refractory brick having such a structure will be described. The brick structure after repeated thermal shock tests is shown in FIG. As is clear from FIG. 2, cracks are generated through the fine pores in the zirconia grains containing the fine pores of 5 to 30 μm. No cracks were found in the other refractory areas. In other words, the thermal stress caused by thermal shock is absorbed by only the cracks generated in the fine pore area and alleviated. In other words, intermediate particles of zirconia having innumerable fine pores of 5 to 30 μm are formed. The texture uniformly distributed in the magnesia brick can absorb and relieve thermal stress. This locally generated crack is caused by the first and second embodiments described below.
As is clear from FIGS. 2A to 2C, the physical properties of the whole brick are hardly affected, and even if repeated thermal shock is applied, strength reduction or structure deterioration does not occur.

The zirconia raw material to be blended in the present invention needs to be unstable zirconia. When stable zirconia is used from the beginning, fine pores of 5 to 30 μm are not formed in the grains. The particle size of the unstable zirconia raw material to be blended is 0.3 to 2.0.
mm is preferable. Mixing with fine particles of less than 0.3 mm causes excessive mixing of zirconia particles to disperse the cavities in the brick and the thermal shock absorption is small, and crack propagation during thermal shock is too easy to promote spall resistance. Spoil. Mixing with a particle size of more than 2 mm tends to result in uneven dispersion in the brick,
It becomes difficult to develop thermal shock resistance.

The effect of thermal shock resistance is recognized within the range of 5 to 20% by weight of the total amount of refractory material in the amount of the unstable zirconia raw material to be blended. If it is less than 5 wt%, the thermal stress cannot be completely absorbed only by the crack generation in the zirconia particle portion, resulting in damage to the entire brick. On the other hand, if it exceeds 20 wt%, cracks mainly occur in the zirconia particles, which may damage the entire brick.

Unstable zirconia raw material reacts with magnesia, 5-30μ
The firing temperature must be at least 1650 ° C. or higher in order to change into stable zirconia grains in which m fine pores are uniformly incorporated. If it is less than 1650 ° C, the reaction between the unstable zirconia and magnesia is insufficient, and the change to stable zirconia having fine pores of 5 to 30 µm does not proceed sufficiently. If the fine pores contained after the change to stable zirconia grains are less than 5 μm, the zirconia is less likely to collapse and the strength is increased, but cracks are easily transmitted during thermal shock and propagate to the surrounding magnesia. If the pore size exceeds 30 μm, the zirconia grains will be deeply collapsed and the strength will be reduced.

Example: A refractory material and a binder were blended at the blending ratios shown in Table 1, both were kneaded with a fret mill, molded into a parallel shape with a press, and dried at 80 to 150 ° C. for 48 hours, and then a tunnel kiln was formed. It was used and baked at 1750 ° C. for 7 hours. No. 1 of the examples
Nos. 4 to 4 are examples of the present invention, Nos. 5 to 6 are comparative examples in which the compounding ratio of unstable zirconia is out of the range of the present invention, and Nos. 7 to 9 are conventional examples. Sintered magnesia and fused magnesia are both
A MgO component of 98 wt% or more was used.

Each of the obtained example bricks was tested, and the results are also shown in FIG. The methods and evaluation criteria of various tests are as follows.

[Apparent specific gravity], [Bulk specific gravity], [Apparent porosity] A normal refractory test was conducted.

[Compressive strength]

A 55 × 55 × 55 mm cube was cut out from a normal-shaped brick and measured with a hydraulic compression tester.

[Bending strength]

A test piece having a width of 30 mm, a thickness of 15 mm and a length of 120 mm was cut out from the normal-shaped brick, heated in an electric furnace kept at 1500 ° C. for 1 hour, and then subjected to a three-point bending test.

[Spolling resistance]

A 55 × 55 × 230m prismatic test piece is cut out from a brick in parallel shape, and one side is kept in an electric furnace kept at 1400 ° C for 15 minutes, then taken out of the furnace and forced-air cooled for 15 minutes. I went to. The evaluation was made based on the state of crack occurrence and the number of work cycles until peeling. The spall resistance is better when the number of repetitions of the work cycle until peeling is large.

EFFECTS OF THE INVENTION As is clear from the results shown in Table 1, the examples of the present invention are:
All show good spall resistance. In particular, NO.2 and NO.4 containing 10 wt% of the unstable zirconia raw material did not cause visible cracks. On the other hand, the conventional examples NO.7 and NO.8 are those in which the unstabilized zirconoa raw material is not added, and the spall resistance is inferior, that is, the number of repetitions until stripping is 15 and 2. Further, the conventional example NO.9 is a mixture of chrome ore instead of zirconia, fine pore structure seen in the case of adding unstable zirconia raw material is not formed, it does not peel off at 25 times of repetition but cracks. Occurrence was confirmed remarkably.

As described above, the magnesia-zirconia-based refractory brick of the present invention has significantly improved spall resistance without causing structural deterioration and exhibits excellent thermal shock resistance.

[Brief description of drawings]

FIG. 1 is a reflection microscopic photograph of the grain structure in one example of the present invention, which is 5 to 30 μm in a zirconia grain having a diameter of about 1 mm.
It shows that the micropores of are incorporated. FIG. 2 is a reflection micrograph showing the change in the grain structure of the product of the present invention after the spall resistance test. Cracks are observed only in the magnesia-zirconia grains (between A and A '), but other magnesia regions. It shows that no cracks are found in all of them.

Claims (1)

[Claims] 1. A magnesia raw material is added with 5 to 20 wt% of an unstable zirconia raw material of 0.3 to 2 mm as an intermediate grain to obtain 100 wt%.
Thermal shock resistance, characterized in that after mixing and molding the mixture, the mixture was fired at 1650 ° C. or higher, and the above zirconia raw material was changed to stable zirconia grains uniformly incorporating fine pores of 5 to 30 μm. Excellent magnesia-zirconia refractory brick.