JP2005179101A - Forsterite raw material composition and method of manufacturing forsterite sintered compact using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prepare a powdery granule suitable for molding with a metallic mold. <P>SOLUTION: In this forsterite raw material composition using magnesia as a main raw material, the magnesia contains ≤0.05 wt.% B<SB>2</SB>O<SB>3</SB>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention can be used for slurry preparation and granule production of a forsterite composition using magnesia, baked talc, and clay as main components. Since the obtained granules are continuously molded by a mechanical press molding machine using a mold, the ceramic does not adhere to the mold during molding, has good fluidity, and has few appearance defects such as chipping, cracking, and bending of the molded product. The present invention relates to an excellent granule production method for obtaining a sintered body.

In general, forsterite porcelain is a mixture of magnesia and silica in a ratio of 2MgO · SiO ₂ , pulverized and mixed with a fine pulverizer such as a ball mill using water as a medium, and the slurry is filtered with a filter press / dryer or spray dryer Sintering aids such as CaO, BaO, and SiO ₂ are added to the forsterite calcined material that has been calcined and synthesized at 1000 to 1300 ° C., and the water is again used as a medium in a fine mill such as a ball mill. An organic binder such as polyvinyl alcohol (hereinafter referred to as PVA) is added to and mixed with the pulverized and mixed slurry, and then granulated by spray drying and granulating with a spray dryer.

Conventionally, 0.40 wt% B ₂ O ₃ was contained in the magnesia used. According to Patent Document 1, impurities contained in the forsterite porcelain sintered body are regulated, but B ₂ O ₃ contained in magnesia to be used is not regulated. Further, in this document, B ₂ O ₃ is not regulated even in the impurities of the ceramic sintered body (see Patent Document 1).

Conventionally, in forsterite, H ₃ BO ₃ and CaCO ₃ are mixed at a weight ratio of 1: 1 as a sintering aid and then calcined at a temperature of 440 ° C. (hereinafter referred to as colemanite glass) is used. Was. _{Incidentally,} H 3 BO ₃ is a boric acid component, the _{H 2} O disappeared _B 2 _{O 3} by calcination. According to Patent Document 2, a frit containing SiO ₂ , CaO, Al ₂ O ₃ , B ₂ O ₃ , KNaO, ZnO, BaO, SrO ₂ , ZrO, MgO, Li ₂ O and the like as a forsterite sintering aid. Is restricted (see Patent Document 2).

According to Patent Document 1, ZrO ₂ contained in the forsterite porcelain sintered body was controlled to 0.40% by weight or less as an impurity level. In Patent Document 2, ZrO ₂ is controlled to 2% by weight or less as the amount of sintering aid. Further, the same document describes an example in which 5% by weight of ZrO ₂ is added as a color former.

According to Patent Document 3, PVA is a main component as a binder, and an aqueous PVA solution is first added, and then polyethylene glycol (hereinafter referred to as PEG), vinyl acetate, and stearic acid are added. Moreover, the density | concentration of PVA aqueous solution was added at 20 weight% (refer patent document 3).
JP-A-5-262562 JP-A-11-130522 JP 2002-128570 A

  Conventionally, when a forsterite raw material composition is charged into a ball mill and ground using water as a medium, the slurry thickens. Therefore, when discharging the slurry from the mill, there is a problem that the viscosity is high and it is difficult to discharge the slurry.

Moreover, since the calcining temperature of the colemanite glass is low, a part of H ₃ BO ₃ does not vitrify and remains in the form of B ₂ O ₃ , so that when PVA is added, B ₂ O ₃ and PVA are gelled. There was a problem that the slurry viscosity was increased to 2-3 dPa · s or more. Further, B ₂ O ₃ contained in magnesia also has a problem that gelation reaction with PVA similarly occurs depending on the content thereof and the slurry is thickened. The slurry thickened in this way cannot be transferred by a slurry pump, and cannot be spray-dried with a spray dryer as it is. Therefore, it was necessary to add water to adjust the slurry viscosity to 1 to 2 dPa · s or less to lower it. However, when water is added, the concentration of the slurry is lowered, and as a result, the bulk density of the granule is reduced, and the fine powder of the granule is increased, resulting in poor fluidity.

Also, the amount of zircon added as a sintering aid component may be 5% by weight as the amount of ZrO ₂ , but all are added as color formers in the sintered body, and the thermal shock resistance of forsterite porcelain is increased. It did not reach improvement.

Further, in the binder addition procedure, when the PVA aqueous solution is added before PEG, there is a problem that gelation is vigorously progressed and the dispersion cannot be performed. When PVA comes into contact with the slurry from which B ₂ O ₃ is eluted, a gelation reaction occurs and PVA is not uniformly dispersed throughout the slurry. Therefore, the granules obtained by adding water to lower the slurry viscosity and spray-drying have a problem that the mold adheres due to the tackiness of the granules during molding and cannot be continuously molded. That is, there is a problem that it is impossible to produce granules having a high powder bulk density, good fluidity, and good releasability.

  The present invention has been made in view of the above-described problems, and an object thereof is to enable the production of powder granules suitable for molding.

In the forsterite raw material composition using magnesia as a main raw material, the present invention is characterized by using magnesia whose B ₂ O ₃ content is 0.05% by weight or less.

  In the forsterite, 1 to 2% by weight of colemanite glass is used as a sintering aid component.

  In the forsterite, 15 to 25% by weight of zircon is used as a sintering aid component.

  In the forsterite, PEG is first added as a binder to the slurry of the raw material composition, and then PVA, vinyl acetate, and stearic acid are added as an aqueous solution or emulsion.

  The PVA is added after the concentration of the aqueous solution is adjusted to 15% by weight or less.

According to the present invention, in a forsterite raw material composition using magnesia as a main raw material, a prescribed amount of dispersant is only added by using magnesia whose B ₂ O ₃ content is 0.05 wt% or less. Thus, the slurry can be discharged without increasing the viscosity of the slurry.

In addition, by using 1-2% by weight of colemanite glass in which B ₂ O ₃ is completely vitrified by raising the calcining temperature to 550 ° C. or more as a sintering aid component in the forsterite, Even when the PVA aqueous solution is added, thickening of the slurry can be suppressed.

  In addition, if 15 to 25% by weight of zircon is used as a sintering aid component in the forsterite, a forsterite porcelain having excellent thermal shock resistance can be obtained by reducing the thermal expansion coefficient without increasing the optimum firing temperature. be able to.

In the above forsterite, first, PEG is added as a binder to the slurry of the raw material composition, and then PVA, vinyl acetate, and stearic acid are added as an aqueous solution or emulsion to add PVA after PEG is dispersed. As a result, the gelation reaction with B ₂ O ₃ was suppressed, and as a result, uniform dispersion of PVA in the slurry became possible.

  Further, the PVA can be added after adjusting the concentration of the aqueous solution to 15% by weight or less to further reduce the gelation reaction by further reducing the concentration, and furthermore, the PVA can be uniformly dispersed in the slurry. .

  Embodiments of the present invention will be described below.

Forsterite material composition of the present invention is silica source and the amount of B ₂ O ₃ contained is characterized in that it comprises as a main component magnesia is 0.05 wt% or less, the atmosphere talc as silica source What is calcined at a temperature of 1,200 to 1,300 ° C. (hereinafter referred to as baked talc), Kibushi clay, Sasame clay or a mixed Sasame Kibushi clay is used.

  Sintering aids such as lime, barium carbonate, silica stone, colemanite glass, zircon, and raw talc are added to magnesia, calcined talc, and clay as main components, and similarly pulverized with water as a medium in a fine mill such as a ball mill. -An organic binder such as PEG, PVA, vinyl acetate, stearic acid, etc. is added to and mixed with the mixed slurry, and then spray-dried and granulated granules are molded and fired to obtain a forsterite porcelain.

According to the present invention, in a forsterite raw material composition using a silica source and magnesia as the main raw material, a specified amount of dispersant is obtained by using magnesia whose B ₂ O ₃ content is 0.05% by weight or less. Only by adding, the slurry viscosity does not increase and the slurry can be discharged without any problem.

This is because when the amount of B ₂ O ₃ is large, the amount of elution into water also increases, and at the same time, a hydrate is generated by causing a hydration reaction on the surface layer of magnesia pulverized fine particles, and the slurry further thickens. Therefore, it is considered that the slurry viscosity does not decrease even when a specified amount of dispersant is added.

Obtain a 0.02 wt% magnesia clinker 140 mesh pass product with a small amount of B ₂ O ₃ in magnesia and add a 20 wt% PVA aqueous solution to the slurry obtained by pulverizing and mixing the forsterite raw material composition with a ball mill or the like in water. When the mixture was added and stirred, the gelation reaction did not occur, the viscosity of the slurry did not increase, and PVA could be uniformly dispersed. In this regard, when the amount of B ₂ O ₃ contained in magnesia is 0.1% by weight or more, a tendency of thickening of the slurry due to the gelation reaction is observed, and when 0.4% by weight, the gelation reaction is remarkably generated. confirmed.

Moreover, by using 1-2% by weight of colemanite glass in which the calcining temperature is increased to 550 ° C. and H ₃ BO ₃ is completely vitrified as a sintering aid component in the forsterite, a PVA aqueous solution is obtained. Even if it adds, the thickening of a slurry can be suppressed.

This is because H ₃ BO ₃ is completely vitrified, so that the elution of B ₂ O ₃ from the colemanite glass to water is eliminated, and thus the gelation reaction with PVA is suppressed, and the slurry is thickened. By not doing.

As a specific means, H ₃ BO ₃ and CaCO ₃ are mixed at a weight ratio of 1: 1, and then packed in a synthetic cordierite or synthetic mullite mortar and kept in a tunnel electric furnace at 440 ° C. for 3 hours, 500 The calcined composites calcined at atmospheric temperature of ℃ × 3 hours, 550 ° C × 3 hours, and 600 ° C. × 3 hours are finely pulverized, respectively, and B around 2θ = 27.8 degrees by an X-ray diffractometer. The presence or absence of ₂ O ₃ peak was determined. As a result, at 500 ° C. × 3 hours keeping the following there are _B 2 _{O 3} peaks was confirmed that no is the _B 2 _{O 3} peak at 550 ° C. × 3 hours keeping more.

Further, in a compatibility test with a 10% by weight PVA aqueous solution, a viscosity increase of the slurry due to the gelation reaction is observed at 500 ° C. × 3 hours or less. Therefore, firing at 550 ° C. × 3 hours or more based on the above results eliminates the elution of B ₂ O ₃ from the colemanite glass into water and suppresses the gelation reaction with PVA. Was confirmed.

  Further, in the forsterite, the coefficient of thermal expansion can be lowered by adding zircon as a sintering aid component, so that a forsterite porcelain excellent in thermal shock resistance can be obtained. In particular, it was confirmed that the addition of zircon in the range of 15 to 25% by weight was preferable in that the optimum firing temperature was not increased and the thermal shock resistance Δt (° C.) was 250 ° C. or higher.

Here, the linear expansion coefficient of the forsterite porcelain obtained by adding 21.58% by weight of zircon to the forsterite composition was measured in the range of 40 to 400 ° C., and the measured value when no zircon was added was 10 × 10 ⁻⁶ / A value of 8.9 × 10 ⁻⁶ / ° C. was obtained with respect to ℃, and a 4 × 3 × 45 mm sintered body test piece was prepared, heated in a box-type dryer, and then dropped into water. In the evaluation method for examining the presence or absence of cracks, cracks are observed at a temperature difference Δt of about 190 ° C. with water temperature without the addition of zircon, whereas in the products containing zircon 21.58 wt%, cracks are observed until Δt = 270 ° C. Was not seen. This is considered to be a synergistic effect of the addition of zircon which is excellent in the effect of reducing the linear expansion coefficient and the thermal shock resistance.

  However, when the amount of zircon added is 25% by weight or more, the optimum firing temperature rises to 1,300 ° C. or more.

In the above forsterite, PEG is first added as a binder to the slurry of the raw material composition, and then PVA, vinyl acetate, and stearic acid are added as an aqueous solution or emulsion, so that the PEG is dispersed and then PVA. Is added to suppress the gelation reaction with B ₂ O _3, and as a result, PVA can be uniformly dispersed in the slurry.

  This is presumably because by adding PEG first, the PEG dispersed in the slurry exhibits a buffer function, and the thickening of the slurry due to the gelation reaction is suppressed.

  The above binders can be obtained from manufacturers as 40 wt% PEG aqueous solution, 20 wt% PVA aqueous solution, 49 wt% vinyl acetate emulsion, and 18 wt% stearic acid emulsion, respectively. Among them, when added to the forsterite composition slurry, only the 20% by weight PVA aqueous solution can be dispersed without any problem with gelling and thickening.

  However, in the case of an emulsion such as vinyl acetate or stearic acid, emulsion emulsion breakage may occur if stirring is continued with a stirrer or the like for a long time of 24 hours or longer after addition to the slurry.

  Therefore, a 40 wt% aqueous PEG solution that is dispersed in the slurry and has no problem for stirring for 24 hours or more because of the aqueous solution is first added and stirred for 30 minutes or longer. Next, 20% by weight PVA aqueous solution is added with water to a concentration of 13.3% by weight, mixed with stirring, then added to the slurry, and stirred and mixed for 30 minutes or longer. Next, a 49 wt% vinyl acetate emulsion is similarly diluted with water to a 24.5 wt% concentration and added. Finally, the 18% strength stearic acid emulsion is similarly diluted with water to a 13% strength by weight and added.

  Further, the PVA can be added after adjusting the concentration of the aqueous solution to 15% by weight or less, whereby the gelling reaction can be suppressed by lowering the concentration, and PVA can be uniformly dispersed. This is because the forsterite composition slurry and PVA are not directly mixed by reducing the concentration, and water functions as a buffer material. As a result, the dispersibility is improved and the thickening of the slurry due to the gelation reaction is suppressed. It is considered a thing.

Further, when 20 wt% PVA aqueous solution was added to the slurry as it was and stirred and mixed, it was confirmed that in magnesia where the amount of B ₂ O ₃ was 0.05 wt%, the thickening of the slurry was caused by a light gelation reaction. .

Moreover, it discovered that the viscosity increase of the slurry by gelation reaction was suppressed when it became 15 weight% or less density | concentration.
(Example 1)

In Table 1, water is added to 100% by weight of five types of forsterite compositions A to E having different amounts of B ₂ O ₃ contained in magnesia, and then added to a ball mill containing siliceous boulders. After 96 hours of pulverization and mixing, the average particle size becomes 3.5-4.5 μm, and then 0.98% by weight of sodium lignin sulfonate is dissolved in water at the ratio shown in Table 1 and then added to the ball mill. After rotating and mixing for 30 minutes or more, the slurry viscosity was measured.

  Next, as a binder, a PVA aqueous solution with a concentration of 20% by weight of 7.35% by weight is added, and a PVA polymer with a concentration of 20% by weight is added with 3.92% by weight. To do.

Finally, 2.45 wt% of 49 wt% vinyl acetate emulsion was added, 4.31 wt% of 18 wt% stearic acid emulsion was added, stirred and mixed for 30 minutes or more, and the slurry viscosity was measured again. . The results are shown in Table 1. In types D and E, no thickening of the slurry is observed even after addition of the dispersant or after the addition of the binder, but in types A, B and C, the thickening of the slurry is remarkably confirmed. It was done.

(Example 2)

Table 2 shows the presence or absence of a B ₂ O ₃ peak around 2θ = 28 ° by an X-ray diffractometer for each calcining temperature of the colemanite glass used in this forsterite composition, and a 10 wt% PVA aqueous solution. The compatibility was compared. The results are shown in Table 2. It was confirmed that the slurry was thickened by the gelation reaction up to the calcining temperature of 500 ° C., but when the calcining temperature was 550 ° C. or higher, the thickening of the slurry by the gelation reaction was suppressed.

Example 3

Table 3 shows the result of comparison of the effects of the amount of zircon added in the forsterite raw material composition (type E) using magnesia in which the amount of B ₂ O ₃ contained is 0.02% by weight. After adding 103% by weight of water to 100% by weight of the forsterite composition and grinding and mixing in a ball mill containing siliceous cobblestone for 48 to 96 hours, the average particle size becomes 3.5 to 4.5 μm. Then, 0.98% by weight of sodium lignin sulfonate was dissolved in water at the ratio shown in Table 3, and then added to a ball mill, rotated and mixed for 30 minutes or more, and then the slurry was discharged.

  Next, as a binder, a PVA aqueous solution with a concentration of 20% by weight of 7.35% by weight is added, and a PVA polymer with a concentration of 20% by weight is added with 3.92% by weight. To do.

  Finally, 2.45% by weight of a 49% vinyl acetate emulsion was added, and 4.31% by weight of 18% stearic acid emulsion was added and stirred and mixed for 30 minutes or more. The granulated granules are molded and fired to obtain forsterite porcelain.

This granule is filled into a mold, press-molded at a pressure of 1 ton / cm ² , sintered in an oxidizing atmosphere electric furnace at 1,270 ° C. or 1,300 ° C. as the optimum firing temperature, width 4 mm × thickness 3 mm × A test piece having a length of 45 mm was prepared.

  The test piece was heated in a box dryer for 30 minutes or more, then dropped in water, and the thermal shock resistance was confirmed by the presence or absence of cracks generated in the test piece. The temperature setting condition was increased from 220 ° C. in increments of 10 ° C. and continued until a crack occurred in the test piece, and the highest temperature at which no crack occurred was defined as thermal shock resistance Δt (° C.). The results are shown in Table 3.

From this result, it was confirmed that the thermal shock resistance Δt (° C.) was improved by adding zircon. In particular, a zircon addition amount in the range of 15 to 25% by weight is preferable in that the optimum firing temperature does not increase and the thermal shock resistance Δt (° C.) is 250 ° C. or higher.

Example 4

Table 4 shows the results of comparing the binder addition method to the forsterite raw material composition (type D) slurry using magnesia having 0.05% by weight of B ₂ O ₃ contained therein.

  As binder addition method N, a PVA aqueous solution with a concentration of 20% by weight of 7.35% by weight is added, and a PVA polymerization with a concentration of 20% by weight of 3.92% by weight is added, followed by stirring for 30 minutes or more. After mixing, a 40 wt% aqueous PEG solution was added and mixed for 30 minutes or more. Finally, 2.45 wt% of a 49 wt% vinyl acetate emulsion was diluted with water in the ratio shown in Table 4, and 4.31 wt% of 18 wt% stearic acid emulsion was added in the ratio shown in Table 4. The mixture was diluted and added, stirred and mixed for 30 minutes or more, and then the slurry viscosity was measured.

  Similarly, the measurement results of the slurry viscosity of the binder addition method O in the case where the PVA aqueous solution is diluted with water and added, and the method P in which the binder below the PVA aqueous solution is added after first adding and mixing the PEG aqueous solution are shown.

From this result, 20% by weight PVA aqueous solution is the method of adding a solution diluted with water to 15% by weight or less, and the method of adding PVA aqueous solution first after adding PEG aqueous solution as the order of addition is the most gelation reaction It was confirmed that the thickening of the slurry due to the above was suppressed.

It is a flowchart figure which shows the manufacturing method of the forsterite raw material composition of this invention. It is a flowchart figure which shows a prior art example.

Claims (6)

Silica source and, forsterite material composition amount of B ₂ O _3, characterized in that it comprises as a main component magnesia is 0.05 wt% or less contained. 2. The forsterite raw material composition according to claim 1, comprising 1-2% by weight of colemanite glass. The forsterite raw material composition according to claim 2, wherein a colemanite glass having a calcining temperature of 550 ° C or higher is used. The forsterite raw material composition according to any one of claims 1 to 3, comprising 15 to 25% by weight of zircon. First, polyethylene glycol is added as a binder to the forsterite raw material composition according to any one of claims 1 to 4, and then polyvinyl alcohol, vinyl acetate, or stearic acid is added as an aqueous solution or emulsion, and then dried, prepared. A method for producing a forsterite sintered body comprising the steps of granulating, forming and firing. 6. The method for producing a forsterite sintered body according to claim 5, wherein the polyvinyl alcohol is added as an aqueous solution having a concentration of 15% by weight or less.

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