JP4721947B2 - Corrosion-resistant magnesia sintered body, heat treatment member comprising the same, and method for producing the sintered body - Google Patents

Description

  The present invention relates to a magnesia sintered body having excellent corrosion resistance, a heat treatment member comprising the same, and a method for producing the sintered body.

  With the recent rapid development of electronic components, more advanced electronic component materials are being developed and commercialized, and precise composition control is indispensable. Suppression is achieved. For this reason, a dense ceramic sintered body excellent in corrosion resistance is used for the heat-treating member used in the firing process without causing compositional variation of the electronic component material. In particular, a member for heat treatment of a magnesia sintered body having high corrosion resistance to PbO has been used in a heat treatment process of an electronic component material such as a piezoelectric body containing PbO.

  For example, Patent Document 1 discloses a high-purity magnesia sintered body having a magnesia content of 99.9% or more and a porosity of 2% or less and excellent in corrosion resistance and spalling resistance. However, even if the magnesia content is 99.9%, there is a reaction with the material to be fired in the recent firing of a highly functional piezoelectric body or the like, and it is not satisfactory. Moreover, since high-purity magnesia has extremely poor sinterability, it is necessary to make the firing temperature very high in order to obtain a dense sintered body, which is problematic in terms of energy saving and cost.

  On the other hand, Patent Document 2 discloses a magnesia porcelain composition having a specific range of contents of magnesia, alumina, and zirconia, and porcelain at a low temperature. Patent Document 3 uses ultrafine alumina as a sintering aid. A high purity magnesia sintered body is disclosed. However, although these sintering aids can be fired at a low temperature, these sintering aids have a problem of reacting with the body to be fired to significantly reduce the corrosion resistance of the magnesia sintered body, and have a precise composition. There is a problem that it is not satisfactory in terms of corrosion resistance when used for firing high-performance electronic component materials that require control.

Japanese Patent Laid-Open No. 1-18859 JP-A-6-191926 JP-A-62-83358

  An object of the present invention is to provide a magnesia sintered body having excellent corrosion resistance and capable of firing at a lower temperature than a high-purity magnesia sintered body, a heat treatment member comprising the same, and a method for producing the magnesia sintered body There is in point to do.

As a result of intensive studies in view of the present situation as described above, the present invention adds Nb ₂ O ₅ to a specific amount of magnesia to obtain a porosity and an average crystal grain size within a specific range. The present inventors have found a magnesia sintered body that is superior in corrosion resistance to pure magnesia and that can be fired at a low temperature, a heat treatment member comprising the same, and a method for producing the sintered body, thereby completing the present invention. The reason why the corrosion resistance is improved by adding Nb ₂ O ₅ is not clear, but a small amount of Nb ₂ O ₅ is dissolved in magnesia, which promotes sintering and improves the corrosion resistance of grain boundaries. _{It is} considered that a compound of ₂ O ₅ and magnesia is generated at the magnesia grain boundary and prevents penetration of components contained in the fired body.
That is, according to the first aspect of the present invention, (a) the total amount of magnesia and Nb ₂ O ₅ is 98% by weight or more, (b) magnesia / Nb ₂ O ₅ (weight ratio) is 80/20 to 98/2, ( c) It relates to a corrosion-resistant magnesia sintered body having a porosity of 1.0% or less and (d) an average crystal grain size of 3 to 60 μm.
2nd of this invention is related with the member for heat processing which consists of a corrosion-resistant magnesia sintered compact of Claim 1.
The heat-treating member comprising the corrosion-resistant magnesia-based sintered body in the present invention is a member for storing a body to be fired used for heat-treating various materials, or various members used in or around various firing furnaces or melting furnaces. Means. Specifically, for example, calcining containers, setters, metal melting crucibles, glass melting containers, slag melting containers, single crystal growth crucibles, and phosphor materials used for calcining synthesis and molding of ceramic powder Containers, tubular furnace core tubes, radiant tubes, heater support tubes, temperature measuring protection tubes, gas blowing tubes, gas sampling tubes, lining furnace materials, etc.
A third aspect of the present invention is a magnesia raw material powder having a purity of 99% by weight or more and an Nb ₂ O ₅ raw material powder having a purity of 99% by weight or more, and the total amount of magnesia and Nb ₂ O ₅ is 98% by weight or more. Mixing so that the weight ratio of ₂ O ₅ is 80/20 to 98/2, molding using powder pulverized and mixed to an average particle size of 0.4 to 3 μm, and firing at 1300 to 1700 ° C. The method for producing a corrosion-resistant magnesia sintered body according to claim 1.

(A) The total amount of magnesia and Nb ₂ O ₅ is 98% by weight or more In the present invention, the total amount of magnesia and Nb ₂ O ₅ needs to be 98% by weight or more, preferably 99% by weight. That's it. When the total amount of magnesia and niobium is less than 98% by weight, the amount of impurities such as alkali metals increases, and a large amount of the second phase or glass phase is generated at the crystal grain boundary, which is not preferable. The upper limit is about 99.8% by weight.

(B) Magnesia / Nb ₂ O ₅ (weight ratio) is 80/20 to 98/2 In the present invention, the weight ratio of magnesia / Nb ₂ O ₅ needs to be 80/20 to 98/2. The weight ratio is preferably 85/15 to 95/5. When the weight ratio of magnesia / Nb ₂ O ₅ is less than 80/20, the Nb ₂ O ₅ content, which is an expensive raw material cost, increases, resulting in an increase in the cost of the magnesia sintered body. In addition, it is not preferable because it lowers the inherent corrosion resistance of magnesia. When the weight ratio of magnesia / Nb ₂ O ₅ exceeds 98/2, the Nb ₂ O ₅ content decreases and the effect of adding Nb ₂ O ₅ cannot be obtained, so that excellent corrosion resistance cannot be obtained. This is not preferable because the firing temperature required for sintering is also increased.

(C) Point whose porosity is 1.0% or less In the present invention, the porosity needs to be 1.0% or less, preferably 0.5% or less. When the porosity exceeds 1.0%, the pores of the sintered body increase, and the pores serve as a starting point for corrosion (corrosion here means that the corrosion-resistant magnesia sintered body reacts with the fired body. Chemical degradation damage phenomenon that is gradually destroyed) and reaction (here, reaction means that when a fired body is heat-treated, another substance is formed on the surface of the corrosion-resistant magnesia sintered body that is in contact with the fired body. This is not preferable because the corrosion resistance is lowered and the mechanical properties are lowered and the durability is lowered. The lower limit of the porosity is about 0.04%. In addition, the porosity in this invention shows an open porosity, and a measurement is performed based on JISR1634.

(D) The point that an average crystal grain diameter is 3-60 micrometers In this invention, an average crystal grain diameter needs to be 3-60 micrometers, Preferably it is 5-50 micrometers, More preferably, it is 10-40 micrometers. When the average crystal grain size is less than 3 μm, the corrosion resistance is lowered, which is not preferable. When the average crystal grain size exceeds 60 μm, not only the mechanical properties are lowered, but also the thermal shock resistance is lowered, the durability is lowered, and the practicality as a heat treatment member is inferior.
The average crystal grain size is obtained from a ten-point average by an intercept method after mirror-finishing the sintered body, applying thermal etching, and observing with a scanning electron microscope. The following calculation formula is used.

The corrosion-resistant magnesia sintered body in the present invention can be produced by various methods, and an example thereof is shown below.
The magnesia raw material powder preferably has a magnesia purity of 99% by weight or more. The average particle size of the magnesia raw material powder is preferably 10 μm or less, more preferably 8 μm or less. When the average particle size exceeds 10 μm, the predetermined pulverization / mixing treatment time becomes long, and as a result, a large amount of impurities are mixed due to wear from the pulverizer and the corrosion resistance is lowered. In addition, the minimum of the average particle diameter of magnesia raw material powder is about 0.5 micrometer.
The Nb ₂ O ₅ starting material powder, it is preferable _Nb 2 _{O 5} purity of 99 wt% or more. Further, the average particle size of the Nb ₂ O ₅ raw material powder is preferably 3 μm or less, and more preferably 2.0 μm or less. When the average particle diameter exceeds 3 μm, the distribution of the Nb ₂ O ₅ component tends to be non-uniform in the sintered body, the effect of adding Nb ₂ O ₅ cannot be obtained, and the corrosion resistance is lowered. The average lower limit of the particle size of the _Nb 2 _{O 5} starting material powder is about 0.3 [mu] m.
In order to make the total amount of magnesia and Nb ₂ O _{5 in} the product 98% by weight or more, impurities are likely to be mixed during the manufacturing process, particularly in the pulverizer, so the purity of the magnesia raw material and the Nb ₂ O ₅ raw material is 99 The weight percent or more is preferred.
In the present invention, both magnesia and Nb ₂ O ₅ raw material powder may be used after being pulverized in advance and adjusted to a predetermined average particle diameter. Moreover, as magnesia raw material powder, you may use what calcined magnesium hydroxide etc. and adjusted to predetermined magnesia purity and average particle diameter.
The total amount of SiO ₂ , CaO, Al ₂ O ₃ , ZrO ₂ , TiO ₂ , Fe ₂ O ₃ , Na ₂ O and K ₂ O contained in the sintered body must be less than 2% by weight, and more Preferably it is less than 1% by weight. When the total amount of these components is 2% by weight or more, a large amount of the second phase or the glass phase is generated at the crystal grain boundary, and the corrosion resistance is lowered. In addition, the current lower limit is about 0.2% by weight.
The above raw materials are blended so as to have a predetermined composition, and are wet-ground and mixed in water or an organic solvent by a pot mill, an attrition mill, a medium stirring mill or the like. The average particle size of the powder obtained by the pulverization / mixing process in the present invention (indicated as “average particle size of the treated slurry” in Table 1) needs to be 0.4 to 3 μm, preferably 0.6 to 2.0 μm. An average particle size of less than 0.4 μm is not preferable because many defects are contained inside the sintered body due to a decrease in moldability, mechanical properties are decreased, and durability is decreased. When the average particle diameter exceeds 3 μm, the sinterability is lowered, the porosity is increased, and the corrosion resistance and durability are lowered.
The average particle size of the powder after pulverization / mixing is controlled by selecting the powder concentration at the time of pulverization / mixing, selecting the ball diameter to be used and adjusting the processing time.
When adopting a method such as press molding or rubber press molding as a molding method, a known molding aid (for example, acrylic resin, PVA, etc.) is added to the pulverized / mixed slurry as necessary, and a known method such as a spray dryer is used. A molding powder is produced by drying, and the molding powder is filled into a mold or a rubber mold and molded. In addition, when adopting a casting method, a known binder (for example, wax emulsion, acrylic resin, etc.) is added to the pulverized / mixed slurry as necessary, and a waste mud casting method using a gypsum mold or a resin mold. Molded by filling casting method, pressure casting method, etc. Further, when an extrusion molding method is adopted, the obtained pulverized / mixed slurry is dried, sized, and a binder for extrusion molding (a known binder such as carboxyl methyl cellulose and wax emulsion can be used) and water or an organic solvent. Is added, mixed and kneaded to form a molding clay. Using this molding clay, it is extruded to a predetermined shape by a known extruder. The molded body obtained as described above is fired at 1300 to 1700 ° C., more preferably 1400 to 1650 ° C., to obtain a corrosion-resistant magnesia sintered body.

  The magnesia sintered body of the present invention is superior in corrosion resistance and durability equal to or higher than that of high-purity magnesia, and can be fired at a lower temperature than the high-purity magnesia sintered body, so it is advantageous in terms of energy saving and low cost. It has become a high quality. Therefore, it is suitable for heat treatment containers and setters for electronic component materials such as piezoelectrics and dielectrics, as well as heat treatment tool materials such as phosphors, β-alumina, and ceramic materials, and furnace tubes for various electric furnaces. It is useful in applications such as protective tubes for various devices. Moreover, it can be effectively used as, for example, a burner nozzle, a radiant tube, a heater support tube, a gas blowing tube, a gas sampling tube, and a lining furnace material by utilizing the point having excellent corrosion resistance.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

Examples 1-7, Comparative Examples 1-8
A magnesia raw material powder having a purity of 99.5% by weight and an average particle size of 1 to 6 μm and an Nb ₂ O ₅ raw material powder having a purity of 99.5% by weight and an average particle size of 1 to 3 μm were used. In Example 6 and Comparative Example 6, magnesia raw material powder having a purity of 99.9% by weight and an average particle diameter of 0.6 μm was used. Comparative Example 3 used a magnesia raw material powder having a purity of 99.5% by weight and an average particle diameter of 12 μm, and Comparative Example 7 used an Nb ₂ O ₅ raw material powder having a purity of 99.5% by weight and an average particle diameter of 4 μm.
Table blended in a weight ratio of magnesia / Nb ₂ O ₅ shown in 1, it was treated by attrition mill using an alcohol as a solvent. The average particle diameter of the obtained slurry is shown in Table 1. 3% by weight of an acrylic resin binder was added to this slurry and spray dryer drying was performed to obtain a molding powder. The obtained molding powder was press-molded with a mold at a pressure of 1 tonf / cm ² and fired at 1250 to 1750 ° C. to produce a plate-like sintered body having a 100 mm square and a thickness of 3 mm. The obtained sintered body characteristics are shown in Table 1.
Evaluation of corrosion resistance was carried out by placing a molded product of commercially available PbO powder having a diameter of 10 mm and a thickness of 1 mm on a plate-like sintered body, holding it at 850 ° C. for 5 hours, and performing 5 cycles, and showing a cross section of the sintered body after the test. EDX (Energy Dispersive X-ray spectrometer: energy dispersive X-ray analyzer, which detects the characteristic X-rays generated from the sample by applying an electron beam to the observed sample, and detects the elements in the observed sample. The erosion depth was measured with a device to be examined). The results are shown in Table 1.
The magnesia sintered body excellent in corrosion resistance of the present invention showed excellent corrosion resistance with an erosion depth of 400 μm or less with respect to PbO, but the sintered body not satisfying at least one requirement of the present invention is When the thickness is 400 μm or more, it is apparent that the corrosion resistance is inferior.

Durability was evaluated for Examples 3 and 4 and Comparative Examples 4 and 7 in Table 1. In the test, the plate-like sintered body was placed on a refractory and inserted into an electric furnace heated and held at 500 ° C., held for 30 minutes and then taken out of the furnace while being placed on the refractory, at room temperature. After cooling, the test was repeated 10 times for the occurrence of cracks by fluorescent flaw detection. The results are shown in Table 2.
The magnesia sintered body of the present invention has excellent durability compared with a sintered body that does not satisfy even one of the requirements of the present invention because no cracks were generated even after 10 repeated tests. Is clear.

Claims (3)

(A) The total amount of magnesia and Nb ₂ O ₅ is 98% by weight or more, (b) magnesia / Nb ₂ O ₅ (weight ratio) is 80/20 to 98/2, and (c) the porosity is 1.0%. Hereinafter, (d) a corrosion-resistant magnesia sintered body having an average crystal grain size of 3 to 60 μm.   A heat-treating member comprising the corrosion-resistant magnesia sintered body according to claim 1. A magnesia raw material powder having a purity of 99% by weight or more and an Nb ₂ O ₅ raw material powder having a purity of 99% by weight or more, the total amount of magnesia and Nb ₂ O ₅ being 98% by weight or more, and the weight ratio of magnesia / Nb ₂ O ₅ is 2. A powder prepared by blending to 80/20 to 98/2, pulverized and mixed to an average particle size of 0.4 to 3 μm, and fired at 1300 to 1700 ° C. The manufacturing method of the corrosion-resistant magnesia sintered body of description.