JPH04132656A - Alumina-chromia sintered compact and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title dense sintered compact excellent in resistance to heat shock, wear and corrosion by sintering at a specified temperature a mixture of ceramic matrix powder and agglomerated granules composed of alumina-chromia and unstable zirconia. CONSTITUTION:A mixture of (A) a ceramic matrix material comprising (1) >=40wt.% of aluminum oxide, (2) <=60wt.% of chromium oxide and (3) <=1.5wt.% of titanium dioxide and/or talc (3MgO.4SiO2.H2O) and (B) 3-70vol.% of agglomerated granules 10-20mum in size consisting of a homogeneous mixture of (4) a raw material of the same composition as that of said ceramic matrix material and (5) unstable zirconia is molded and then sintered at >=1500 deg.C, thus obtaining the objective sintered compact.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dense and high-strength alumina-chromia sintered body having excellent thermal shock resistance, corrosion resistance, and wear resistance, and a method for producing the same.

[Conventional technology]

In recent years, in various industries that use refractories and ceramics, including the steel industry, improvements in various properties such as high corrosion resistance, high thermal shock resistance, high strength, and high wear resistance have been made due to the harsher usage conditions of various furnaces. There is a growing demand for high-quality refractories and ceramics.

In general, refractories are required to have thermal shock resistance to withstand rapid temperature fluctuations, and denseness from the viewpoints of strength, wear resistance, and corrosion resistance.

Ordinary refractories have an apparent porosity of 10 to 30%.
Although it has excellent thermal shock resistance, it has the disadvantage of poor corrosion resistance because the reaction between the molten material and the refractory proceeds rapidly due to the penetration of molten material such as slag into the pores.

On the other hand, electroformed large-sized refractories are well known as dense refractories, and have the characteristics of low porosity and high strength.
Although it has a high degree of corrosion resistance, it has the disadvantage of poor thermal shock resistance against repeated heating and cooling, so it cannot be used in areas subject to severe thermal changes and is used only in extremely limited areas.

Generally, refractories with many fine cracks are
It is known that refractories have excellent thermal shock resistance, and a method has been adopted in which fine cracks are controlled and formed within the refractory during the manufacturing stage.

The method of forming these fine cracks has mainly been to adjust the chemical composition, grain size, molding, sintering conditions, and other manufacturing conditions of the aggregate or matrix.

However, with this conventional method, although the thermal shock resistance is improved due to the formation of cracks, the apparent porosity is 10%.
Therefore, its corrosion resistance is significantly inferior to that of dense brick.

On the other hand, fine ceramics or electroformed bricks are dense and exhibit excellent corrosion resistance when used in areas where there is no thermal fluctuation. However, when the usage environment is a location with thermal fluctuations, the thermal shock resistance is poor, and it has been extremely difficult to use the material as a corrosion-resistant member as it may break due to thermal shock.

In addition, an attempt was made to improve the thermal shock resistance of fine ceramics by forming microcracks.
It is disclosed in Publication No. 48.

That is, in firing a ceramic in which unstable zirconia grains with a grain size of 2 to 15 μm are dispersed, microcracks are generated in the ceramic sintered body due to expansion during the transformation from a tetragonal product to an orthorhombic crystal when the firing temperature is lowered. It is stated that improvement in fracture toughness value is observed.

However, the formation of microcracks by this method uniformly disperses individual unstable zirconia particles and causes microcracks in the ceramic matrix due to crystal transformation of the zirconia particles. However, in this method, the amount of transformation expansion is unique to the substance called unstable zirconia, and the amount of transformation expansion cannot be arbitrarily controlled.

Therefore, as a method for controlling stress generated by transformation expansion,
It is controlled by the amount of unstabilized zirconia added, the selection of the zirconia particle size, and the firing conditions. In this case, when the amount of zirconia added is small, the microcracks that occur are very small and their distribution is limited to the vicinity of the zirconia grains. Furthermore, if the amount added is large, a large number of cracks will occur, and the cracks will become more likely to connect, causing cracks in the sintered body and making it unusable. Therefore, the drawback of the conventional method is that the control range during production is small, and it is difficult to obtain a large-sized sintered body that is satisfactory.

Generally, the thermal shock resistance of an alumina sintered body in which unstabilized zirconia is dispersed is improved by using a bent sample conforming to JI SR1601, and by a thermal shock test method using an underwater drop method.
It is said that the temperature is about 50 to 150°C, and it cannot be said that this is a significant improvement in thermal shock resistance.

In addition, as the unstabilized zirconia particle size increases, the strength decreases significantly.
SEN', JORG 5TIEEB and REI
NERP, PABST.

11Effect of Induced Micro
cracking on the fracture
Toughness of Ceramics, C
ermic Elulletin.

Vol, 56. No. 6559-562 (1977
) will be reported.

Therefore, when manufacturing such a sintered body, the optimum firing temperature range and the optimum addition amount to obtain a sintered body with appropriate microcracks are extremely limited. If there is too much, large cracks will appear in the sintered body itself.

On the other hand, if the firing temperature is too low, a sufficiently dense sintered body cannot be obtained, its corrosion resistance is low, and the strength of the sintered body varies widely.

As described above, the thermal shock resistance of dense sintered bodies is currently still inferior to that of conventional general refractories.

An object of the present invention is to provide a dense sintered body having high thermal shock resistance.

[Means to solve the problem]

The alumina-chromia sintered body of the present invention consists of a dense alumina-chromia ceramic matrix and a second phase dispersed therein. The above object was achieved by forming an aggregate whose phase was a homogeneous mixture of the same ceramic matrix and unstabilized zirconia.

Specifically, a ceramic matrix consisting of 100 to 40% by weight of aluminum oxide, 0 to 60% by weight of chromium oxide, and containing 1.5% by weight or less of titanium oxide and/or talc (3MgO・4S10□・H2O) and dispersed therein. Second to do
In the ceramic sintered body with high thermal shock resistance, the ceramic matrix contains controlled fine cracks, and the dispersed second phase is a precipitated material consisting of a homogeneous mixture of the same ceramic matrix material and unstable zirconia. It is characterized by being a collection.

Further, the size of the dispersed second phase is 10 to 200 μm, the proportion of the second phase in the ceramic matrix is 3 to 70% by volume, and the particle size of the unstable zirconia in the second phase is 0.3 to 200 μm. At 20 μm, the proportion of unstabilized zirconia in the second phase is between 5 and 100% by volume.

This sintered body is prepared by mixing aggregates with a second phase size of 10 to 200 μm with ceramic matrix powder so that the aggregate particles account for 3 to 70% by volume relative to the ceramic matrix. , by molding this mixture into a desired shape and then sintering it at a temperature of 1500° C. or higher.

[Effect]

Dense alumina with excellent heat resistance and corrosion resistance according to the present invention
The high thermal shock resistance of chromia sintered bodies is due to, firstly, the crack blanching effect caused by controlled microcracks of appropriate size, secondly, the particle crosslinking effect due to the coarsening of matrix particles, and thirdly, the This is achieved by stress-induced transformation by zirconia transformation in the stable zirconia-rich second phase and further by crack deflection at the 4'&4' agglomerate grain boundaries.

The details of the mechanism that produces the above thermal shock resistance will be explained.

The first controlled micro-cracks with an appropriate size are those with a crack width of about 3 to 20 μm, and when these cracks are appropriately distributed, crack blanching occurs when the crack propagates. Absorbs and disperses fracture energy, preventing crack growth.

The particle cross-linking effect due to the coarsening of the second matrix particles is due to the coarsening of the matrix crystals, so that the cracks caused by thermal shock fracture progress in a zigzag pattern along the grain boundaries, and the path is determined by the matrix crystal diameter. Since the crack propagates over a longer distance than when the particle size is small, the fracture energy of the crack is consumed more easily than when the particle size is small, and the crack propagation resistance is high. In addition, large particles in the fractured matrix portion at the rear of the crack develop mechanically bite each other due to friction, and the so-called particle crosslinking effect prevents the progress of fracture.

In the stress-induced transformation due to zirconia transformation in the third unstable zirconia-rich second phase, if a crack enters the second phase containing unstable zirconia, the zirconia transforms and expands within the second phase. Due to the absorption of fracture energy and the compressive stress generated inside the second phase, a compressive force acts on the tip of the crack, inhibiting the development of the crack.

In crack deflection at the fourth agglomerate grain boundary, tensile stress acts on the boundary between the second phase and the ceramic matrix, and when the crack reaches this boundary, the crack is deflected in the tangential direction of the boundary, resulting in The progress of Kushitsuku is hindered.

Furthermore, the excellent corrosion resistance of the sintered body according to the present invention is due to the following factors: firstly, controlled crack size; secondly, the use of an alumina-chromia solid solution as a matrix, which has excellent corrosion resistance;
This is due to the presence of a second phase containing zirconia which has excellent corrosion resistance, and fourthly, the matrix particles are sufficiently large and have excellent corrosion resistance.

In other words, it is the first factor to obtain excellent corrosion resistance.
Although controlling the crack size will result in some pores in the sintered body, it is possible to control the crack width to prevent molten steel from infiltrating when used as a steelmaking furnace, and the distribution of cracks can also be controlled. Therefore, infiltration of slag or molten steel can be prevented. Therefore, when the ceramic of the present invention is applied to steel manufacturing equipment, there is no damage caused by internal infiltration of slag, etc., and the corrosion resistance is extremely excellent because the main cause is only melting loss from the surface.

In the ceramics of the present invention, the matrix, which is the second factor that exhibits excellent corrosion resistance, forms a solid solution consisting of alumina and chromia, and the corrosion resistance of this solid solution is extremely superior to that of alumina alone. Therefore, especially when alumina chromium is 1=1, it exhibits excellent corrosion resistance.

Further, the second phase rich in zirconia added to the matrix, which is the third factor, is itself rich in zirconia, which is poor in corrosion resistance, and this contributes to improvement in corrosion resistance.

The fourth factor, M)IJx grains, is usually made into l'l1 grains by sintering. Generally, if the particles are fine,
Since erosion from grain boundaries tends to progress, it is desirable to make the grains as coarse as possible. In the present invention, the matrix particles corresponding to the matrix in the refractory are dense and coarse-grained, and therefore exhibit extremely excellent corrosion resistance.

As described above, a dense sintered body having excellent heat shock resistance and a porosity of 4 to 5% or less can be produced by a method that allows for more precise control of crack size. That is, the feature is that unstable zirconia, which undergoes transformation and expansion during firing, is added in the form of aggregates rather than being uniformly dispersed. The aggregate particles are composed of the same material as the ceramic matrix and unstable zirconia, and the amount of unstable zirconia is 5 to 100% by volume, and is uniformly dispersed. The amount of transformation expansion of the agglomerated grains is approximately proportional to the amount of unstable zirconia added within the agglomerated grains, so that the amount of expansion of the agglomerated grains can be controlled. Furthermore, by controlling the diameter of the aggregate particles and the amount of aggregate particles added into the ceramic matrix, it is possible to arbitrarily control the size and distribution of the particles generated inside the ceramic matrix. Furthermore, by controlling the particle size of the unstable zirconia particles themselves inside the agglomerated grains, it is possible to control the cracks that occur in the ceramic matrix. It is dispersed in

The matrix and zirconia-rich second phase agglomerates are granulated using a conventional spray dryer. The granulation may be carried out by a granulation method similar to a spray dryer, such as Henschel Mixer Spartan Reuser, filter-pressed clay, dried, crushed and sieved into granules. The mixing method includes uniform mixing using a V-type mixer, an omnimixer, or the like. Next, this mixed powder is molded using a conventional molding machine, and the resulting S base is fired at 1500° C. or higher in an electric furnace, gas furnace, or the like.

In addition, when preparing the matrix, it is not necessary to make it into granules, and a mixture of very fine primary particles may be used, but it is necessary that the agglomerated particles of the zirconia-rich second phase are uniformly dispersed in the matrix. It is.

When the size of the second phase agglomerated grains is 10 μm or less, the agglomerated grains are not much different from individual zirconia, and the effect is not much different from that of known zirconia dispersion-strengthened ceramics. Next, when the second phase agglomerated grains exceed 2111f) μm, the amount of transformation expansion of the agglomerated grains increases, the width of cracks generated in the matrix becomes large, and the crack density decreases, so that no effect can be obtained. Therefore, in the present invention, the size of the second phase agglomerated grains is defined to be 10 to 200 μm.

Next, the unstable zirconia particle size within the second phase agglomerated grains is 0.3μ
If it is less than m, the amount existing in the form of a tetragonal product increases even at room temperature, and transformation expansion from monoclinic to tetragonal crystal of unstable zirconia does not occur, and the effects of the present invention cannot be obtained. When the particle size is 20 μm or more, the amount of expansion increases, and the crack width that occurs becomes wider.<1. In addition, the number of cracks decreases, and the effect of the present invention cannot be obtained, and in some cases, cracks occur in the sintered body, making it impossible to obtain a good sintered body. Therefore, in the present invention, the grain size of the unstabilized zirconia is reduced to 0. .3~2
It is defined as 0 μm.

Next, the excellent features of the sintered body according to the present invention will be explained in comparison with known sintered bodies.

The particles of the matrix in which unstabilized zirconia is uniformly dispersed are more uniform and finer than those in the case where unstabilized zirconia is not added. This is due to the fact that dispersed unstable zirconia has the effect of inhibiting matrix crystal growth. If the matrix particles are uniform and fine, only crank blanching and zirconia stress-induced transformation can be expected, whereas the underlying microcracks develop due to fracture.

In the case of the present invention, unstabilized zirconia is concentrated within the agglomerated grains, and since IJ Fuchs has agglomerated grains dispersed with a size of 10 to 200 μm, the crystal particles in the matrix other than the agglomerated grains are reduced to their original particle size. It is possible to grow. In the present invention, by growing the ceramic matrix particles, the coarse particles exhibit a crosslinking effect equivalent to that of coarse particles in refractories. In other words, mechanical friction between coarse particles causes them to get stuck behind the developed crack, and this force has the effect of inhibiting the progress of the crack.

Inside the agglomerated grains, the crystal grains are very fine and compressive stress is acting on them, so when a crack enters the agglomerated grain, due to the internal compressive stress, compressive stress acts on the tip of the crack, inhibiting its growth rate. be done.

This effect can be seen even in the type in which zirconia is uniformly dispersed, but in the method of the present invention, the effect is more pronounced because the amount of unstable zirconia inside the aggregated grains is larger than in the case of uniformly dispersed particles.

Tensile stress acts around the unstabilized zirconia and the matrix, and when the propagating crack reaches this stress field, it deflects. On the other hand, the size of the aggregated particles in the present invention is 10
Since it is large at ~200 μm, the crack deflection is large, and the energy consumption for crack propagation due to deflection is also large, resulting in a large crack propagation effect.

Furthermore, the matrix with coarse particles and the aggregate with uniform fine particles correspond to the coarse particles and matrix in refractories, and because they have a macroscopically non-uniform structure, cracks caused by fracture are simple. Instead of crack propagation, cracks tend to propagate in a zigzag manner due to the non-uniform structure, further increasing the resistance to fracture.

Furthermore, since it is dense, it has excellent wear resistance, making it ideal for hot structural members that are subject to thermal shock and require further wear resistance.

From the above, the present invention is a method for manufacturing a sintered body that arbitrarily controls the generation and distribution of cracks inside ceramics and has high thermal shock resistance, compared to the conventional method of generating microcracks in ceramics. It is an alumina-chromia ceramic sintered body that is dense and has excellent corrosion resistance and wear resistance.

Furthermore, by adding the matrix and second phase agglomerated grains according to the present invention as a matrix part of a refractory compound and sintering, the matrix of a conventional refractory corresponds to the ceramic sintered body of the present invention. A significant improvement in heat resistance and prayer resistance was observed. Therefore, the effect of the present invention is recognized not only in a sintered body made only of fine powder, but also in a refractory material to which coarse particles are added, due to its effect expression mechanism.

〔Example〕

Example 1 As matrix materials, 50% by weight of aluminum oxide with an average particle size of 0.4 μm and 50% by weight of chromium oxide with an average particle size of 0.3 μm
Titanium oxide or talc powder as a sintering aid, an organic binder, and purified water were added to a mixture consisting of The resulting slurry was granulated using a spray dryer to obtain matrix powder. The average particle size was 50 μm.

Next, as the second phase agglomerated grains, a powder made by adding 50% by volume of unstable zirconia with an average particle size of 2 μm to 100% by volume of powder having the same raw materials and the same composition as the ceramic matrix material. Weighed and mixed, added a predetermined amount of organic binder and purified water, pre-mixed in a ball mill for 24 hours, mixed and dispersed in an attriter for 3 hours, and granulated the resulting slurry with a spray dryer. Second
A neck grain powder/agglomerated grains for phase use was obtained. The granules/agglomerates obtained had an average size of 50 μm.

Next, the matrix granules and the second phase granules were mixed at the mixing ratio (volume ratio) shown in Table 1 using a V-type mixer for a certain period of time to obtain a mixed powder. Next, this mixed powder was molded using a uniaxial molding machine at a pressure of 1.4 tons/cut into 65 square
It was molded into a 12mmt shape.

For comparison, a matrix-only base without the addition of a zirconia-rich second phase was also molded.

The obtained base material was heated in an electric furnace at 1650℃ under a cloud atmosphere for 2 hours.
It was held for a while and fired.

The bulk density and apparent porosity of the sintered body were measured by the Archimedes method. In addition, the bending strength at room temperature is J I SR1
Measured in accordance with 601. Thermal shock resistance is JISR1
A bent sample conforming to 601 was held at a specified temperature for 1 hour, rapidly dropped into water, and then dried. The bending strength was measured and compared with the bending strength at room temperature. The difference between the temperature and the water temperature was defined as ΔT ('C), and the higher the ΔT, the better the thermal shock V resistance.

Table 1 shows the firing results of the above-mentioned base material and the characteristic evaluation of the fired body.

In addition, the signs of the firing results used in the table are as follows: ○ indicates that a good sintered body was obtained, Δ indicates that about half of the sintered body was obtained with cracks, and X
The mark indicates that cracks occurred in almost all of the samples, and a good sintered body could not be obtained.

From the results in Table 1, it can be seen that the implementation code ■ according to the present invention (adding 3% by volume of zirconia-rich second phase to the matrix) has a significantly higher ΔT than 00 in the comparative example in which no second phase is added. It can be seen that it has been improved. Also, implementation code ■
However, cracks occurred and a satisfactory sintered body could not be obtained. The reason for this seems to be that in case (2), the amount of zirconia added was large, and the cracks that occurred were connected to each other, resulting in large cracks in the sintered body.

Furthermore, when the second phase is 2% by volume, the thermal shock resistance is improved, but not significantly.

From the above, in the present invention, the amount of the zirconia-rich second phase added is defined as being within the range of 3% by volume to 40% by volume, preferably 40% by volume or less, within the range of the amount of zirconia added in the second phase in Example 1. did.

Example 2 Next, a powder containing alumina-chromia as a matrix was prepared for comparison according to Japanese Patent Publication No. 59-25748. As a matrix, 50% by weight of aluminum oxide with an average particle size of 0.4 μm, chromium oxide 5 with an average particle size of 0.3 μm
0% by weight, and titanium oxide and talc as sintering aids +1
．． The unstable zirconia (average particle size 2 μm) used in Example 1 was weighed into a powder consisting of 0% by weight (external layer) at the ratio (volume%) shown in Table 2, and a predetermined amount of purified water was added as an organic binder. The slurry was prepared in a ball mill for 24 hours, then mixed and fractionated in an attritor for 3 hours, and the resulting slurry was granulated in a spray dryer to obtain IJ Fuchs grain powder.

Further, molding and firing were carried out in the same manner as in Example 1.

Table 2 shows the characteristics of the sintered body obtained by this method compared with those of the method of the present invention shown in Example 1. Further, the cut surface of the obtained sintered body was polished and subjected to carbon vapor deposition treatment, and then observed with a scanning electron microscope to measure the particle size of the matrix.

When the fine grain structure was observed using a scanning electron microscope, it was found that in Example No. 1L12, the matrix was extremely fine, and the unstabilized zirconia was uniformly dispersed. On the other hand, the matrix portions ① and ② of the present invention have almost the same large particle size as the comparative example ②, and there are about 3
A zirconia-rich second phase of about 5 to 40 μm was uniformly dispersed, and the second phase consisted of a fine matrix of about 5 μm and unstable zirconia.

Here, the volume percentages of unstable zirconia in the sintered bodies of Example Nos. 1 and 2 in Example 1 were 5 and 10 volume %, respectively.

Therefore, although the dispersion state of zirconia is completely different between Comparative Example 11 and the present invention (2), and Comparative Example 12 and the present invention (2), the % by volume of unstable zirconia in the sintered body is the same.

From the results in Table 2, it can be seen that in Example 2 based on Japanese Patent Publication No. 59-25748, the heat impact resistance was improved due to uniform dispersion of unstable zirconia, but the effect was not as remarkable as that of the present invention. is clear.

Example 3 Corrosion resistance test was carried out in Example 1 using the present invention ■ and ■ as a comparative example @, 11.12 in Example, and as a comparative example, corrosion resistance was tested using AG brick (alumina graphite brick) and Sialon. compared.

Corrosion resistance test conditions are sample 10 x 10 x 80
mm, connected to an alumina pipe with mortar, and a pre-dried soot sample held in an iron holder without preheating (
The steel was immersed in molten steel for 1 minute or less (holding on the furnace for less than 1 minute). Soaking time is 1
It was time. Note that no rotation was applied to the sample. The depth of the sample immersed in the molten steel was about 40 mm. The steel type is low-order alkylated steel, and the molten steel free oxygen content is 8 to 9 pp.
m, the molten steel temperature was 1550°C. To evaluate the corrosion resistance, the sample after the immersion test was cut at the center with a diamond cutter, the dimensions of the molten steel eroded area were measured with a micrometer, and compared with the dimensions before erosion, the corrosion rate on one side ( μm7min) was calculated. The results are shown in Table 3.

Table 3: Corrosion Resistance Test Results As is clear from Table 3, conventional fine ceramics (Co., Ltd.) and conventional zirconia dispersion-strengthened ceramics (11, 12) used in comparative examples have poor thermal shock resistance, so Tests cannot be conducted and comparisons cannot be made. In addition, in the case of conventional bricks made of AG material, the molten steel portion was completely eroded by immersion for one hour, and the erosion rate was 0.08 mm 2 /volume. Further, while the Sialon was 0.03 n++++/min, the inventive products were all below 0.001 mm 2 /min, and no melting loss was observed within the measurement accuracy. As described above, it is recognized that the product of the present invention has good thermal shock resistance and very good corrosion resistance.

Example 4 In Example 3, the wear resistance of the sintered bodies shown in Table 3 was evaluated. The test conditions were sandblasting, where a steel grid of 1mmφ20kg was sprayed with 7kg/cm' of compressed air, and the size was 50 x 50 x 10+++ mt.
The sample was sprayed at an angle of 45° C. for 60 hours, and the wear volume (cm') was determined from the weight loss of the sample. The results are shown in Table 4.

Table 4 shows that the present invention exhibits superior wear resistance compared to brick, and is a conventional fine ceramic.
It can be seen that the wear is almost the same even when compared to the above, and the sintered body according to the present invention has excellent wear resistance.

Example 5 In Example 1, the amount of zirconia added in the second phase was fixed and the ratio of the amount added to the second phase was studied, but in this example, the amount of zirconia added in the second phase was studied. do. The same unstabilized zirconia used in Example 1 was used, and the addition ratio (volume %) of the matrix and unstabilized zirconia in the second phase agglomerated grains was as shown in Table 5, as shown in Example 1. Second phase agglomerated granules were manufactured using the same method as the granule manufacturing process. M) The composition of the IJ socks was the same as in Example 1. The average particle size of the obtained granules is approximately 50 μm
Met. The resulting various second phase agglomerated grains and matrix granules with different amounts of unstable zirconia added were mixed in the proportions shown in Table 6.7.8, molded, fired, and sintered in the same manner as in Example 1. The heat-shock resistance of the body was evaluated using the same method as in Example 1, and the results are shown in Table 6.7.8.

Table 5 = Mixing ratio in second phase agglomerated grains (volume %) Table 8 = Second phase
Optimum addition amount of phase agglomerates N053 agglomerates*: M) IJx neck granule proportion: 50% by weight of aluminum oxide, 5% by weight of chromium oxide
From the results in Table 6, if the unstable zirconia in the second phase agglomerated grains is 100%, the optimal amount to add is 3% to 20% by volume. I understand.

From the results in Table 7, when the unstabilized zirconia in the second phase agglomerated grains is 5% by volume, the optimum amount of addition is between 30% by volume and 7% by volume.
It can be seen that it is 0% by volume.

From the results in Table 8, when the amount of unstable zirconia in the second phase agglomerated material is 3% by volume, no significant improvement in thermal shock property was observed no matter how the addition ratio of matrix granules and second phase agglomerated particles was changed. I can't.

From the results in Tables 6 to 8, the effect of the present invention is not recognized when the amount of unstable zirconia in the second phase agglomerated grains is less than 5% by volume. Therefore, in the present invention, the proportion of unstable zirconia in the second phase agglomerated grains is defined as 5 to 100% by volume. In addition, the amount of second-phase agglomerated grains to be added changes as the amount of unstable zirconia in the second-phase agglomerated grains changes, and the optimal addition ratio of second-phase agglomerated grains changes. It can be seen that when the amount of unstabilized zirconia added is 5 to 100 volumes, the optimum amount of second phase agglomerated particles added is 3 to 70% by volume.

Example 6 In Example 1, the basic composition of the ceramic matrix part is 50% by weight of aluminum oxide, 50% by weight of chromium oxide, +1.0% by weight of titanium oxide (external layer), and the addition of second phase agglomerated particles rich in zirconia. We considered the proportions. In this example, the basic composition of the ceramic matrix portion is changed to ensure the effects of the present invention.

As the ceramic matrix material, the average particle size is 0.4.
90% by weight of aluminum oxide in μm, average particle size 0.3 μm
m chromium oxide and titanium oxide and/or talc (3MgO・45iO7・H2O) as a sintering aid.
) Weigh the powder consisting of +1.0% by weight (external weight), add 1'if water as an organic binder to a predetermined amount,
After premixing in a ball mill for 24 hours, the mixture was mixed and dispersed in an attritor for 3 hours, and the resulting slurry was granulated in a spray dryer to obtain matrix granule powder. The average particle size was 50 μm.

Next, as the zirconia-rich second phase aggregate particles dispersed in the ceramic matrix material, 100% by volume of particles having the same raw materials and the same composition as the ceramic matrix material.
In contrast, a powder made by adding 50% by volume of unstable zirconia with an average particle size of 2 μm was weighed and mixed, a predetermined amount of organic binder and purified water were added, and after premixing in a ball mill for 24 hours, Mixing and dispersion treatment was carried out using an attritor for 3 hours, and the resulting slurry was granulated using a fountain dryer to obtain granular powder/agglomerated particles for the second phase. The granules/agglomerates obtained had an average size of 50 μm.

Next, (ma) IJ sock granules and second phase granules were each weighed at the blending ratio (volume ratio) shown in Table 9, and mixed for a certain period of time in a VB2 type mixer to obtain the powder of the present invention.

Next, this mixed powder was processed using a uniaxial molding machine at a rate of 1.4 tons/
It was molded into a 65 square x 12 mmt shape under a pressure of c++l.

In addition, for comparison, a base material containing only the matrix without the addition of the zirconia-rich second phase was also molded.

The obtained base material was fired in an electric furnace by holding it at 1650° C. in the air for 2 hours. Table 9 shows the results of evaluating the thermal shock resistance of the obtained sintered body using the method of Example 1.

In addition, in the table, the signs of the firing results used are as follows: ○ indicates that a good sintered body was obtained, Δ indicates that about half of the sintered body was obtained with cracks,
The mark X indicates that almost all of the samples had cracks and a good sintered body could not be obtained.

From the results in Table 9, it can be seen that the implementation code 902 according to the present invention (adding 3% by volume of zirconia-rich second phase to the matrix) has a ΔT of 910 in the comparative example without adding the second phase.
It can be seen that there is a significant improvement compared to . Moreover, cracks occurred in Example No. 909, and a satisfactory sintered body could not be obtained. The reason for this is that 909 has a large amount of zirconia added, and the cracks that occur are connected to each other.
This is thought to be due to large cracks occurring in the sintered body.

Further, when the second phase is 2% by volume, discoloration of the thermal shock resistance is observed, but it is not significant.

From the above, in the present invention, the amount of the zirconia-rich second phase added is defined as being within the range of 3% by volume to 40% by volume, preferably 40% by volume or less, within the range of the amount of zirconia added in the second phase in Example 9. It is something to do.

Example 7 As the basic composition of the ceramic matrix, aluminum oxide 1
The addition ratio of the second phase agglomerated particles rich in zirconia at 0.00% by weight was investigated.

As a ceramic matrix material, the average particle size is 0.4μ
Weighed 100% by weight of aluminum oxide, added a predetermined amount of purified water as an organic binder, pre-prepared it in a ball mill for 24 hours, mixed and dispersed it in an attritor for 3 hours, and sprayed the obtained slurry. The mixture was granulated using a No. 6 dryer to obtain a matrix regular granule powder. The average particle size was 50 μm.

Next, as the zirconia-rich second phase aggregate particles dispersed in the ceramic matrix material, 100% by volume of particles having the same raw materials and the same composition as the ceramic matrix material.
In contrast, a powder made by adding 50% by volume of unstable zirconia with an average particle size of 2 μm was weighed and mixed, a predetermined amount of organic binder and purified water were added, and the mixture was pre-prepared in a ball mill for 24 hours. The slurry was mixed and separated for 3 hours using an attritor, and the resulting slurry was granulated using a spray dryer to obtain granular powder/agglomerated particles for the second phase. The average size of the obtained granules/agglomerates was 50 μm.

Next, M) IJ Fuchs granules and second phase granules were each weighed at the blending ratio (volume ratio) shown in Table 10, and mixed for a certain period of time in a V-type mixer to obtain the powder of the present invention. Next, this mixed powder was molded into a 65 square x 12 mm thick shape using a uniaxial molding machine at a pressure of 1.4 tons/cnt.

In addition, for comparison, a base material containing only the matrix without the addition of the zirconia-rich second phase was also molded. The obtained base material was fired in an electric furnace by holding it at 1600° C. for 2 hours under a cloud atmosphere in the atmosphere. Table 10 shows the results of evaluating the heat shock resistance of the obtained sintered body using the method of Example 1.

In addition, in the table, the signs of the firing results used are as follows: ○ indicates that a good sintered body was obtained, Δ indicates that about half of the sintered body was obtained with cracks,
The x mark indicates that cracks were generated in almost all of the samples, and a good firing/feeding body could not be obtained.

From the results in Table 10, it can be seen that implementation code 1002 according to the present invention (zirconia-rich second phase is 3% by volume relative to the matrix)
1100 in a comparative example without adding a second phase
It can be seen that this is a significant improvement compared to ΔT. Further, in Example No. 1009, cracks occurred and a satisfactory sintered body could not be obtained. The reason for this is thought to be that in 1009, the amount of zirconia added was large, and the cracks that occurred were connected to each other, resulting in large cracks in the sintered body.

Furthermore, when the second phase is 2% by volume, the thermal shock resistance is improved, but not significantly.

From the above, in the present invention, the amount of the zirconia-rich second phase added is within the range of the amount of zirconia added to the second phase in Example 10, from 3% by volume to 40% by volume, preferably 40% by volume or less. It is something.

Example 8 The amounts of titanium oxide and talc added as sintering aids to the alumina-chromia matrix were investigated. First, alumina and chromia powder were mixed in the composition ratio shown in Table 11, and a firing test was conducted at 1700° C. for 4 hours in the air.

The relative density obtained is also shown.

Table 11 = Alumina and Chromia atmospheric firing result No.
In a system containing 3Qv+t% or more of chromia 4 to 6,
Only a porous sintered body with a relative density of 70% or less could be obtained.

Therefore, a study was conducted on sintering aids for the purpose of obtaining a dense sintered body having a composition of chromia of 30 wt % or more. As sintering aids, we investigated titanium oxide and talc, which are used as liquid phase sintering aids for alumina. These are multiplied by Q, 5wt%, and l, Qwt%.

1.5 wt%, 2.09+1% added, 1600 °C,
Firing was performed in an atmosphere surrounded by clouds for 4 hours.

The results are shown in Tables 12-19.

Table 12: Titanium oxide Q, 5ivt% addition system firing results Table 1
4 Titanium dioxide Table 15 = Titanium oxide 5wt% addition system firing results Qv+t% addition system firing results Table 13 Titanium dioxide 1, Qwt% addition system firing results Based on the above results, aluminum oxide 70-5Qwt% chromium oxide 30-5 Qv+ t%, titanium oxide or talc is added as a sintering aid to 1.5 wt% or less of sintering agent, and if fired in the atmosphere, the relative strength of 95% or more, which is considered as a guideline for sintering, can be achieved. Density is obtained,
It can be seen that sintering is almost completed.

On the other hand, the amount of sintering aid was reduced to 2. When added up to Qv+t%,
It was not possible to achieve densification with the sintering aid studied in this study.

From the above, the amount of sintering aid added in the present invention is 1.5wt.
% or less.

〔Effect of the invention〕

The alumina-chromia sintered body of the present invention is dense, has excellent thermal shock resistance, and has excellent wear resistance and corrosion resistance.

Therefore, its uses are wide, and for example, in iron making, it is suitable for use in blast furnace tuyeres, tuyere sleeves, morning glory parts, shafts, sun exposure of desulfurization pig iron mixers, slag lines, etc.

In addition, related to steelmaking, the steel bath, tuyere, tuyere bridge, etc. of special refining furnaces with tuyeres such as AOD, CLV, QBOP, etc., the tap port and main damaged areas of converter furnaces, hot spots of electric furnaces, various Sliding nozzle plate and upper and lower nozzles,
Lining suction pipes for DH and RH furnaces, nozzle receivers for pots, immersion nozzles, sunlight for Tundish furnaces, nozzles, immersion nozzles, lance nozzles and tips for gas injection, porous plugs, gas injection bricks, for uniform furnaces, As heat-resistant and corrosion-resistant structural members for heating furnace skid rails, beam buttons, rolling rolls, glass melting furnaces, coke ovens, protection tubes, various baking shelves and jigs, electronics jigs, + and l phase for electronic furnaces, etc. suitable for the purpose.

Patent applicant: Kurosaki Ceramics Co., Ltd. (and one other person)
Masu Kobori

Claims (3)

[Claims] 1. 40% by weight or more of aluminum oxide, 60% by weight or less of chromium oxide, titanium oxide and/or talc (3MgO.
In a ceramic sintered body formed by dispersing a second phase in a ceramic matrix containing 1.5% by weight or less of 4SiO_2.H_2O), the ceramic matrix contains controlled fine cracks, and the dispersed second phase An alumina-chromia sintered body which is an aggregate consisting of a homogeneous mixture of matrix-forming material and unstable zirconia. 2. 2. In accordance with claim 1, the particle size of the unstabilized zirconia in the second phase dispersed in the ceramic matrix is 0.50.
3 to 20 μm, the content is 5 to 100% by volume, and the dispersed second phase has a size of 10 to 200 μm, and the content is 3 to 70% by volume with respect to the ceramic matrix.
An alumina-chromia sintered body. 3. Agglomerated particles with a diameter of 10 to 200 μm made of a homogeneous mixture of alumina-chromia and unstable zirconia are added to the alumina-chromia mixture at a ratio of 3 to 7.
A method for producing an alumina-chromia sintered body, which comprises mixing alumina-chromia sintered body with a ceramic matrix powder to a concentration of 0% by volume, molding the mixture, and sintering the mixture at 1500°C or higher.