JPH11240748A - Production of oxide ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an oxide ceramic comprising calcium silicate and lithium aluminosilicate, containing the lithium aluminosilicate in an amount of 55-98 wt.% based on the total amount of the calcium silicate and the lithium aluminosilicate, and especially having excellent thermal shock resistance and low thermal expansibility, capable of reducing the irregularity of the color and heat impact resistance of the sintered product and stabilizing the heat impact resistance at a high dimension. SOLUTION: This method for producing the oxide ceramic comprises treating a raw material mixture at a sintering temperature T1 of 1,000-1,360 deg.C for compacting the sintered product and subsequently holding the sintered product at a reheating temperature T3 of 800-1,100 deg.C which is lower by >=50 deg.C than the sintering component T1. The method for producing the oxide ceramic comprises treating the raw material mixture at the sintering temperature T1, transferring the temperature to a cooling temperature T2 which is lower by >=40 deg.C than the reheating temperature T3 and subsequently transferring the temperature to the reheating temperature T3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to various low- and high-temperature parts / jigs / equipments requiring thermal shock resistance, various precision mold materials / precision inspection equipment parts / high-temperature instrument parts requiring low thermal expansion properties, and heat insulating properties. Insulating materials for semiconductors that require, precision processing required for various precision parts, etc., suitable for the production method of oxide ceramics mainly composed of calcium silicate and lithium aluminosilicate, particularly, the coloration of the sintered body and The present invention relates to a method for producing an oxide ceramic which can reduce variation in thermal shock resistance and can stabilize thermal shock resistance to a high level.

[0002]

2. Description of the Related Art In the firing of fine ceramics such as alumina and zirconia, there has been a problem of variations in the coloration of sintered bodies due to differences in firing conditions such as trace components, firing temperature, time, and oxidation-reduction atmosphere. For example, Fe
, Etc., when a very small amount is contained, the valence changes between divalent and trivalent due to subtle differences in firing conditions such as firing temperature and holding time, resulting in a different coloration of the sintered body There is. Also, the crystallinity of the main crystal, the composition of the crystal grain boundaries, and the crystallized state may fluctuate due to subtle differences in firing conditions, and may cause variations in the coloration of the sintered body.

[0003] These situations have been known for various ceramics. As a result, in the conventional ceramics, the variation in the coloration of the sintered body was suppressed by using a raw material having a high purity from which the raw material impurity component was removed as much as possible. It is coming. Further, the inventors of the present application have previously made oxide ceramics excellent in many properties such as thermal shock resistance, workability, low thermal expansion, and heat insulating properties by using calcium silicate and lithium aluminosilicate as the main components of the crystal structure. (JP-A-4-305046, JP-A-6-5)
5394).

[0004] Among the above oxide ceramics in which calcium silicate and lithium aluminosilicate are the main constituents of the crystal structure, particularly, oxides containing 55 to 98% by weight of lithium aluminosilicate with respect to the total amount of calcium silicate and lithium aluminosilicate. Ceramics are particularly excellent in thermal shock resistance and low thermal expansion. However, the color of the sintered body depends on various firing conditions such as variation in holding temperature and holding time in the firing furnace, and difference in cooling rate. In addition, there is a problem that variations from white to pink occur, and there is also a problem that variations occur in thermal shock resistance.

[0005]

SUMMARY OF THE INVENTION In the present invention, calcium oxide and lithium aluminosilicate are mainly composed of oxide ceramics. In particular, lithium aluminosilicate is used with respect to the total amount of calcium silicate and lithium aluminosilicate. 55 to 98% by weight, especially in oxide ceramics having excellent thermal shock resistance and low thermal expansion property, reducing the variation in coloration and thermal shock resistance of the sintered body and stabilizing the thermal shock resistance at a high level The purpose is to make

[0006]

Means for Solving the Problems Under such circumstances, the present inventors have conducted intensive studies and found that calcium silicate and lithium aluminosilicate are mainly composed of a crystal structure, and the total amount of calcium silicate and lithium aluminosilicate is determined. And the lithium aluminosilicate is 55
In the firing of the oxide ceramics containing up to 98% by weight, after passing through a firing temperature T1 of 1000 to 1360 ° C. for densification, the firing temperature T1 is 800 to 1100 ° C.
By maintaining the reheating temperature T3 at a temperature lower by 50 ° C. or more for a predetermined time, it is possible to reduce the variation in the coloration of the sintered body and the variation in the thermal shock resistance, and to stabilize the thermal shock resistance to a high level. I found that I can do it. (Claim 1)

Further, after passing through the firing temperature T1 for densification, and before shifting to the reheating temperature T3, the temperature is shifted to the cooling temperature T2 which is lower than the reheating temperature T3 by 40 ° C. or more. Was found to be able to. (Claim 2)

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
According to the present invention, by performing a reheating treatment at a low reheating temperature T3 after a firing temperature T1 for densification, variation in coloration and thermal shock resistance of a sintered body is reduced, and It has been found that the stability is high. Here, the reason why the coloration of the sintered body and the variation in thermal shock resistance can be suppressed by such a method is not clear, but is presumed as follows.

Oxide ceramics mainly composed of calcium silicate and lithium aluminosilicate,
In particular, lithium aluminosilicate is 5 to the total amount of calcium silicate and lithium aluminosilicate.
In those containing 5 to 98% by weight, a small amount of the amorphous phase is present at the firing temperature T1 for densification, and recrystallizes during the cooling process. It is considered that the degree of this recrystallization causes variations in the coloration of the sintered body due to the difference in the firing conditions, and further causes variations in the coefficient of thermal expansion, and consequently variations in the thermal shock resistance. In contrast, by performing the reheating treatment at a temperature T3 lower than T1 after the firing temperature T1 for densification, recrystallization of the sintered body occurs uniformly and sufficiently, and as a result, the coloration of the sintered body Since there is no variation and the coefficient of thermal expansion also has a lower value, it is considered that a higher thermal shock resistance can be obtained.

As a method of such a reheating treatment, there is a method of performing a reheating treatment while maintaining the temperature T3 when the temperature falls to a reheating temperature T3 in a cooling process from a firing temperature T1 for densification. There is a method of performing a reheating treatment by temporarily cooling from a firing temperature T1 for densification to a temperature T2 lower than the reheating temperature T3 and then raising the temperature to maintain the temperature at the reheating temperature T3. An effective method is to perform a process in which the temperature is once decreased from the firing temperature T1 for densification to the cooling temperature T2, and then the temperature is increased to the reheating temperature T3.

The process from the firing temperature T1 to the reheating temperature T3 may be continuously performed in the same batch and the same furnace, apart from lowering the cooling temperature T2. After passing through the temperature T1), it may be cooled to room temperature once and taken out of the furnace, and thereafter, a reheating step (reheating temperature T3) may be performed again in another furnace.

The firing temperature T1 varies somewhat depending on the composition of the calcium silicate and the lithium aluminosilicate, the particle size of the raw material, the size of the sintered body and other various conditions, but is preferably in the range of 1000 to 1360 ° C. The firing time is preferably in the range of 0.1 to 24 hours, and more preferably in the range of 0.3 to 6 hours. That is, when the firing temperature T1 is low or the holding time is short, the sintered body is not sufficiently densified. Conversely, when the firing temperature T1 is high or the holding time is long, the sintered body melts or In addition to sticking of powder to the sintered body, firing costs increase.

The range of the reheating temperature T3 is 800 ° C.
~ 1100 ° C, more preferably 850 ~ 1050 ° C. When the reheating temperature T3 is 800 ° C. or less, the effect of eliminating the variation in coloration and thermal shock resistance is small, and when the reheating temperature T3 is 1100 ° C. or more, it becomes equivalent to extending the firing time of the sintered body. Meaning. In addition, the reheating temperature T3 needs to be lower than the firing temperature T1 by 50 ° C. or more. That is, when the reheating temperature T3 is close to the firing temperature T1, the effect of the present invention by reheating is reduced, as in the case of extending the firing time. The holding time of the reheating temperature T3 is preferably 0.1 to 12 hours, more preferably 0.3 to 3 hours, in order to sufficiently secure the effect of the reheating treatment and avoid unnecessary cost increase. .

By interposing a cooling step at a cooling temperature T2 between a sintering step at a sintering temperature T1 and a reheating treatment step at a reheating temperature T3, the effect of eliminating variations in coloration and thermal shock resistance is further enhanced. In this case, the cooling temperature T2 needs to be lower than the reheating temperature T3 by 40 ° C. or more. If the cooling temperature T2 exceeds this, the reheating temperature T3 becomes too close to the reheating temperature T3, so that the cooling effect is not sufficient, and the reheating is performed while maintaining the reheating temperature T3 as it is in the cooling process from the firing temperature T1 for densification The effect is the same as when processing is performed.

The oxide ceramics to be used in the present invention are mainly composed of calcium silicate and lithium aluminosilicate as the main components of the crystal structure, and thus have many points such as thermal shock resistance, workability, low thermal expansion, and heat insulation. In particular, lithium aluminosilicate is 55 to 98% by weight based on the total amount of calcium silicate and lithium aluminosilicate.
By including it, among the above characteristics,
In particular, it is intended for a sintered body having excellent thermal shock resistance and low thermal expansion properties.

The calcium silicate constituting the oxide ceramic according to the present invention is CS, C ₂ S, C ₃ S, C ₃ S when CaO is abbreviated as C and SiO ₂ is abbreviated as S.
_{2, and the} like. Of these, CS wollastonite is preferable, and there are two types of wollastonite, α and β, and β wollastonite is the most preferable.
C ₂ S, C ₃ S and the like may be contained, but if the amount is large, the densification becomes difficult to proceed, so that the content is preferably 5% by weight or less based on the total amount of calcium silicate.

[0017] Examples of the lithium aluminosilicate constituting the oxide ceramics of the present invention, the Li ₂ O L, the Al ₂ O ₃ A, when the SiO ₂ is abbreviated in S, eucryptite LAS _2, LAS ₄ Or a solid solution of spodumene. Of these, spodumene is more preferable than eucryptite in terms of cost. There are two types of spodumene, α and β, and β spodumene is most preferred.

In addition to these, Fe ₂ O ₃ , TiO ₂ , MgO, MnO, Na ₂ O,
There is no problem even if K ₂ O, P ₂ O _{5 and the} like are contained up to about 2% by weight with respect to the total amount of calcium silicate and lithium aluminosilicate. As long as it is a nate powder, it can be used without any particular restrictions.

[0019]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. A preliminary test was performed on the crystal phase of the sintered body,
Beta wollastonite and α spodumene at 45: 5
When the crystal phases of the sintered bodies at the ratios of 5, 30:70, 10:90 and 2:98 were confirmed, the crystal phase was β
It was wollastonite and β-spodumene, and no reaction product was observed. Therefore, in consideration of the weight loss (ignition loss) of each starting material at a high temperature, the ratio of the crystalline phase of the sintered body is determined from the blending of the starting materials.

That is, β wollastonite is Ca
It contains 1.6% by weight of impurity components other than O and SiO ₂ , the loss on ignition is 1.1% by weight, and α-spodumene is Li
_It contains 1.2 wt% of impurity components other than ₂ O, Al ₂ O ₃ and SiO ₂ , and has a loss on ignition of 0.2 wt%. Therefore,
When the raw material ratio is 10:90, the pure content of calcium silicate β-wollastonite is 9.73% by weight, the pure content of lithium aluminosilicate β-spodumene is 88.74% by weight, and the others are 1%. .24% by weight
Including.

The total amount of calcium silicate and lithium aluminosilicate excluding impurities is 10% by weight of calcium silicate and 90% by weight of lithium aluminosilicate. The numerical values in Table 1 are values excluding the impurities, and as a result, the values are almost the same as those of the initial raw material blend including the impurities and the loss on ignition. This is the same in other examples and comparative examples.

(Example 1) Natural β wollastonite (CaO: 46.2% by weight, SiO ₂ : 51.1% by weight, other: 1.6% by weight, ignition loss 1.1 as a calcium silicate raw material ) Wt%) of natural α-spodumene (Li ₂ O:
7.6 wt%, Al ₂ O _3: 26.5 wt%, SiO _2:
64.5% by weight, others: 1.2% by weight, loss on ignition 0.
2% by weight).

[0023] 10% by weight of natural β-wollastonite,
90% by weight of natural α-spodumene was mixed and pulverized for 24 hours by a wet ball mill using water as a solvent to obtain a slurry having an average particle size of 2.5 μm. 3% by weight of polyvinyl alcohol was added as a binder to this and granulated by a spray drier. The obtained granules are put into a mold and 1 ton / c
molded in m ^2, and respectively fabricated molded body shape and the following dimensions.

(Baking furnace used) Furnace A: Gas furnace: Furnace size 2000 × 1000 × 1000 (mm) Furnace B: Box type electric furnace (MoSi ₂ heater): Furnace size 600 × 600 × 600 (mm) Furnace C: Box type electric furnace (SiC heater): Furnace size 300 × 300 × 200 (mm) Furnace D: Tubular electric furnace (SiC heater): Furnace size 100φ × 500 L (mm)

(Shape and Size of Molded Body) Molded Body in Furnace A: 50φ-50t (mm) Molded Body in Furnace B: 50φ-20t (mm) Molded Body in Furnace C: 20 × 20 × 15 (mm) Molded product placed in furnace D: 15 × 15 × 15 (mm)

(Arrangement of Molded Products in Furnace) Furnace A: 5 pieces × 2 rows × 5 rows, 50 pieces in total Furnace B: 3 pieces × 2 rows × 5 rows, 30 pieces in total Furnace C: 5 pieces × 3 Row x 2 rows, total 30 furnaces D: 10 x 1 row x 1 row, total 10

Using the above furnaces A to D, the green body was placed as described above, and calcined at a temperature T1: 1200 ° C. for 2 hours, and cooled to 700 ° C. by cooling in the furnace to a temperature T2: 700 ° C. After the temperature was maintained for 1 hour and a reheating treatment was performed at a temperature T3: 1000 ° C. for 1 hour, the resultant was gradually cooled in a furnace.

Each of the obtained sintered bodies was 10 × 10 × 5 (m
m) and the density was measured by the Archimedes method.
The coloration of the sintered body was visually determined. The thermal shock resistance of the sintered body was determined by measuring the cut sintered body in an electric furnace at 550 ° C.
After heating for 5 hours, the mixture was dropped into water, and a color check was performed to confirm whether cracks occurred. As for those having no cracks, 600 ° C. and 650
The same test was performed at temperatures of 700 ° C., 700 ° C., and 750 ° C., and the lowest temperature at which cracks occurred was defined as thermal shock resistance.

Table 1 shows the above-mentioned raw material composition, manufacturing conditions, sintered body density, thermal shock resistance, and sintered body coloration. In addition, all of the obtained sintered bodies were white sintered bodies, and there was no variation in coloration. In addition, the thermal shock resistance of all 120 pieces showed an excellent value of 700 ° C. or more.

[0030]

[Table 1]

(Example 2) In Example 1, except that the treatment at the reheating temperature T3 was continuously performed in the process of cooling in the furnace from the firing temperature T1 without performing the treatment at the cooling temperature T2.
The same test as in Example 1 was performed. Most of the obtained sintered bodies were white sintered bodies, and the variation in coloration was greatly reduced as compared with Comparative Example 1 described below. In addition, the thermal shock resistance was excellent at 700 ° C. or higher, ie, 110 out of 120 pieces.

Comparative Example 1 The procedure of Example 1 was repeated except that the firing at the firing temperature T1 was performed without performing the processing at the cooling temperature T2 and the processing at the reheating temperature T3, and then the inside of the furnace was gradually cooled. The same test as in Example 1 was performed. As for the coloration of the sintered body, more spots and pink sintered bodies were present than in Examples 1 and 2. The thermal shock resistance is 12
Of the 0 pieces, 46 pieces had a temperature of 550 to 650 ° C., and although they were completely the same as Example 2 except that the reheating treatment was not performed, a large difference was recognized in both coloration and thermal shock resistance.

Example 3 As a calcium silicate raw material, the same natural β-wollastonite as in Example 1 was used, and as a lithium aluminosilicate raw material, natural mineral petalite (Li ₂ O: 4.2 wt. %, Al ₂ O
_3: 16.6 wt%, SiO _2: 76.8 wt%, Other: 1.4% by weight, with ignition loss 1% by weight).

The above materials were used as the raw materials, and the mixing amount was 30% by weight of a calcium silicate raw material and 70% by weight of a lithium aluminosilicate raw material.
Performed at 0 ° C. for 2 hours, cooled in the furnace to a temperature T2: cooled to room temperature, randomly rearranged the sintered bodies in the furnace, and further reheated at a temperature T3: 950 ° C. for 1 hour.
The same test as in Example 1 was performed except that the furnace was gradually cooled in the furnace.

Each of the obtained sintered bodies was a white sintered body, and no variation in color was observed. In addition, the thermal shock resistance of 650 ° C. or higher showed an excellent value of 113 out of 120 pieces.

(Comparative Example 2) In Example 3, firing was performed at a temperature T1 of 1100 ° C. for 2 hours without performing a process at a cooling temperature T2 and a process at a reheating temperature T3.
The same test as in Example 3 was performed except that the temperature was gradually cooled in the furnace. As for the coloration of the sintered body, more spots and pink sintered bodies were present than in Example 1. The thermal shock resistance is 1
Of the 20 pieces, 81 pieces had a temperature of 550 to 600 ° C. and were completely the same as Example 3 except that the cooling treatment and the reheating treatment were not performed. Was.

(Comparative Example 3) In Example 1, the firing furnace D
Only at a temperature of T1: 1380 ° C. for 2 hours, and then cooled to a temperature of T2: 700 ° C. by cooling in a furnace to obtain 2
The same test as in Example 1 was performed, except that the temperature was kept for another hour, and a reheating treatment was performed at 900 ° C. for 1 hour.
As a result, the firing temperature was too high and the sintered body was melted.

(Comparative Example 4) In Example 1, the firing furnace D
Only at a temperature of T1: 950 ° C. for 12 hours, and then cooled to a temperature of T2: 700 ° C. by cooling in a furnace to obtain 2
The same test as in Example 1 was performed, except that the temperature was kept for another hour, and a reheating treatment was performed at 900 ° C. for 1 hour.
As a result, the firing temperature was too low and the sintered body was not densified.

(Comparative Example 5) In Example 1, the firing furnace D
The same test as in Example 1 was performed, except that only T3 was used and reheated at 750 ° C. for 1 hour. As a result, the reheating temperature T3 was too low, and the effect of the reheating treatment was not recognized.

(Comparative Example 6) In Example 1, the firing furnace D
The same test as in Example 1 was performed, except that only T3 was used and the temperature T3 was reheated at 1150 ° C. for 1 hour. As a result, the reheating temperature was too high, and the effect of the reheating treatment was not recognized.

[0041]

As described above, according to the present invention, 55 to 98% by weight of lithium aluminosilicate is contained based on the total amount of calcium silicate and lithium aluminosilicate. In an oxide ceramic having excellent heat resistance, it is possible to reduce variation in coloration and thermal shock resistance of a sintered body and to stabilize thermal shock resistance at a high level.

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Norihiko Misaki 6276 Onoda, Onoda-shi, Yamaguchi Prefecture Chichibu Onoda Co., Ltd.

Claims (2)

[Claims] 1. The crystal structure is substantially composed of calcium silicate and lithium aluminosilicate, and lithium aluminosilicate is 55 to 98% by weight based on the total amount of calcium silicate and lithium aluminosilicate.
In the method for producing the oxide ceramics contained, a firing temperature T of 1000 to 1360 ° C. for densification is used.
1. A method for producing an oxide ceramic, comprising maintaining a reheating temperature T3 at 800 to 1100 ° C. and at least 50 ° C. lower than a firing temperature T1 for a predetermined time after passing through Step 1. 2. After a firing temperature T1 for densification, a transition is made to a cooling temperature T2 which is lower than the reheating temperature T3 by 40 ° C. or more before transitioning to the reheating temperature T3. The method for producing an oxide ceramic described in 1.