JP3031865B2 - Manufacturing method of thermal shock resistant ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal shock resistant ceramic having durability against rapid temperature changes such as rapid heating and rapid cooling, and a method for producing the same. Withstand fire heating,
Also, the present invention relates to dense heat-resistant ceramics used as heat-resistant dishes or cookers for frozen storage of foods and the like.

[0002]

BACKGROUND OF THE INVENTION Such rapid heating, as the ceramic used for ovenware or cooker is required durability to rapid temperature change, such as quenching, low thermal expansion coefficient petalite (Li ₂ O · Al ₂ O ₃ · 8SiO ₂₎ crystal or spodumene _{(Li 2 O · Al 2 O} 3 · 4S
There are so-called lithia ceramics containing iO ₂ ) crystals as a main component. This kind of lithia ceramics usually uses a base material in which a petalite raw material and a kaolin raw material are mixed, and the kaolin raw material is in a range of 30 to 60% by weight.
When priority is given to cost and formability, the amount is increased, and when the coefficient of thermal expansion is to be reduced, the amount is adjusted.

[0003] Such a base obtained by mixing a petalite raw material and a kaolin raw material is sufficiently sintered to, for example, have a water absorption of 3.
In order to make dense Lithia ceramics less than 0%,
High temperature firing at 1350 ° C. or higher is required. However, in the case of a baking furnace capable of such high-temperature baking, furnace construction costs and heating fuel costs are relatively high, and kiln tools such as baking shelf furnace materials, pillar furnace materials, and platen setters also use expensive materials. It has to be used and there is a problem that the operating cost increases. Furthermore, the thermal expansion coefficient of the thus obtained lithia ceramics is about 15 to 40 × 10 ⁻⁷ / ° C., which is less than half that of general ceramics, but further improvement and improvement of thermal shock resistance are desired. Was.

With respect to the firing temperature, attempts have been made to use firing furnaces for tiles, sanitary ware, or general porcelain which can be fired at 1300 ° C. or lower, but ceramics having a water absorption of 4% or more are used. Because of its high water absorbency, glaze is applied to the surface to reinforce the water resistance, and the lack of strength is increased by increasing the wall thickness of the vessel, etc. Something like that has been put to practical use. However, during use, it may leak from cracks in the glaze, or the permeated water may expand and break when heated, causing it to break, and it is only used for specific cooking such as hot pot cooking using a large heat capacity. Could not be widely applied.

[0005] Improvements have also been made to reduce the thermal expansion coefficient of dense ceramics obtained using petalite and kaolin as raw materials. For example, it is intended to add kaolin raw material to petalite or spodumene having a low coefficient of thermal expansion by adding lithium carbonate (Li ₂ CO ₃ ) and quartz to the raw material. In this case, plain lithium carbonate is used. The base containing erosion of the gypsum mold for molding shortens the life, or causes inconvenience such as swelling after firing.

As a further improvement, a technique has been developed in which a mixture of lithium carbonate and quartz in a predetermined ratio, such as quartz, is calcined to obtain a solid, which is reground and used as a frit. However, lithium carbonate itself is expensive. In addition to this, the cost of the calcining heat treatment and the pulverization treatment is high, so that there has been a problem that the cost becomes extremely high.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and provides a ceramic which is dense, has a low thermal expansion characteristic, has excellent thermal shock resistance, and has a lower ceramic strength than conventional ceramics. Provided is a method for producing a thermal shock-resistant ceramic which can be densely fired at a firing temperature and can use a low-cost raw material.

[0008]

[0009]

SUMMARY OF THE INVENTION The above-mentioned problems are raised to 30-7.
5% by weight of petalite or spodumene raw material
Lithium silicate raw material is, 20 to 55 wt% of the kaolin material, in terms of MgO 1.5 to 10% by weight of MgO
Compound raw material, and SiO ₂ supplied from each of the raw materials
0 to 15% by weight of SiO ₂ in terms of SiO _2
2 compounds were prepared were green body blended, and molded, the thermal shock resistance ceramic, characterized in that to obtain a dense sintered body by firing <br/> maximum temperature at most 1300 ° C. during sintering Manufacturing method.

[0010] Incidentally, 20 in thermal shock resistance ceramics described above, 1.5 to 2.4 wt% of Li ₂ O oxide composition, the MgO 5.0 to 10 wt%, the Al ₂ O ₃
30 wt%, and component composition including SiO ₂ 58 to 73 wt%, or like-Li ₂ O oxide composition 2.4
~ 3.5 wt%, MgO 2.0 ~ 7.0 wt%, Al
17% to 27% by weight of ₂ O ₃ and 63% to 7% of SiO ₂
8% by weight component composition or oxide composition
i ₂ O and 3.5 to 4.5 wt%, the MgO 1.0 to 4.
0 wt%, the Al ₂ O ₃ 14 to 24 wt%, and Si
The O ₂ can be embodied in the component composition containing from 68 to 83 wt%.

In addition, in the raw material mixing ratio of the above-mentioned method for producing a thermal shock resistant ceramic, the lithium silicate raw material is 30 to 45% by weight, the kaolin raw material is 35 to 55% by weight, and the MgO compound raw material is 5% in terms of MgO. 0.0 to 10
Weight percent or 45% lithium silicate raw material
~ 60 wt%, kaolin raw material is 25 ~ 45 wt%, Mg
O-compound raw material is 4.0 to 7.5% by weight in terms of MgO
Or the lithium silicate raw material is 60-75
It can be more preferably embodied by a composition in which the amount of the kaolin raw material is 20 to 35% by weight, and the amount of the MgO compound raw material is 1.5 to 6.0% by weight in terms of MgO.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the thermal shock resistant ceramic according to the present invention will be described. In the present invention, Li ₂ O, MgO, Al ₂ O ₃ and S
iO ₂ is an essential component. Here, the raw materials from which these oxides are derived are not particularly limited, but as described below,
Lithium silicate raw materials such as petalite, kaolin raw materials such as clay, and natural raw materials such as talc are preferable in terms of cost. Furthermore, in the present invention, these terms of oxide in the chemical composition, the Li ₂ O 1.5 to 6.5 wt%, the MgO 1.0 to 10 wt%, the Al ₂ O _3. 14 to
30% by weight, and 58 to 83% by weight of SiO ₂ , and in crystal microstructure, one or both of petalite crystal and spodumene crystal, which are low-expansion lithium silicate crystals, and low-expansion A ceramic comprising a cordierite crystal as an essential main crystal phase, and a dense sintered body to the extent that there is substantially no risk of water leakage. In this case, the degree of the density is 3.0% at the maximum and preferably 1.0% at the maximum when the water absorption is a scale.

In the thermal shock resistant ceramic of the present invention, L
i ₂ O and MgO components coexist, is characterized where a dense porcelain comprising a petalite crystal or the like and the cordierite crystals, baked conventional petalite raw material and 30-60 wt% of the kaolin material were mixed matrix In the sintered dense Lithia ceramics, a coefficient of thermal expansion of only about 15 to 40 × 10 ⁻⁷ / ° C. was obtained, whereas as described later, 6 × 10 ⁻⁷ was obtained as a sufficiently dense porcelain. / ° C.

Further, in the oxide composition of the thermal shock resistant ceramic, the following is embodied as follows.
In the Li ₂ O 1.5 to 2.4 wt%, the MgO 5.0
A composition containing 10 to 10% by weight, 20 to 30% by weight of Al ₂ O ₃ and 58 to 73% by weight of SiO ₂ has a thermal expansion coefficient of about 10 to 15 × 10 ⁻⁷ / ° C., Li
_{Since the 2} O component can be reduced, there is an advantage in cost.

Second, Li ₂ O is 3.5 to 4.5% by weight, MgO is 1.0 to 4.0% by weight, and Al ₂ O ₃ is 14% by weight.
Those having a component composition containing ２４24% by weight and SiO ₂ 〜68-83% by weight have a disadvantage in terms of cost because the proportion of the relatively expensive Li ₂ O component is high, but the thermal expansion coefficient is 6６. Can be reduced to about 8 × 10 ⁻⁷ / ° C.,
The advantage of excellent thermal shock resistance is obtained.

Third, in the intermediate oxide composition described above, Li ₂ O is 2.4 to 3.5% by weight, and MgO is 2.
0 to 7.0 wt%, Al ₂ O ₃ and 17-27 wt%, and that of the component composition comprising SiO ₂ sixty-three to seventy-eight wt%, practically with a good cost and balance well by low coefficient of thermal expansion A high thermal shock resistant ceramic can be obtained.

The thermal shock resistant ceramic of the present invention described in detail above can be manufactured by the method for manufacturing a thermal shock resistant ceramic which is the main invention of the present invention described below. Here, the embodiment will be described. First, a petalite raw material or a spodumene raw material as a lithium silicate raw material, a kaolin raw material, for example, a clay-rich clay, a clay-rich clay mineral such as kaolin clay, a MgO compound raw material, For example, in addition to talc, magnesite, etc., a raw material such as MgO, magnesium hydroxide, or the like is used as an essential material, and a SiO ₂ compound material, for example, a material such as silica stone, silica sand, or quartz is blended as necessary to form a substrate. Prepare.

In this case, as the lithium silicate raw material, 30
~ 75% by weight, 20-55% by weight as kaolin raw material,
It is important to mix the MgO compound raw material in an amount of 1.5 to 10% by weight in terms of MgO.

And here, as a lithium silicate raw material,
Such as petalite raw or spodumene raw material 30
If the content is less than 20% by weight, it is difficult to obtain a material having a coefficient of thermal expansion of 20 × 10 ⁻⁷ / ° C. or less, and the firing temperature increases, making it impossible to fire at the following firing temperature. If it exceeds 75% by weight,
Also in this case, the firing degree increases and it becomes impossible to fire at the following firing temperature in the firing step.

In addition, as a kaolin raw material, Frogme clay is 2
If the amount is less than 0% by weight, it is insufficient to secure the moldability of the mold and prevent the occurrence of cracks after molding. If it exceeds 55% by weight, the fire resistance and the coefficient of thermal expansion increase. It is difficult to obtain one having a thermal expansion coefficient of 20 × 10 ⁻⁷ / ° C. or less.

Further, when the MgO compound raw material such as talc is out of the range of 1.5% by weight to 10% by weight in terms of MgO, the fire resistance is increased due to an increase in the ratio of the petalite raw material or the kaolin raw material. Is not preferred.

Next, the base material obtained as described above is formed into an appropriate shape, and then fired at a firing temperature of at most 1300 ° C., thereby obtaining a dense structure substantially free from water leakage. For example, it is possible to obtain a dense sintered body having a structure having a water absorption of at most 3.0% at most and a coefficient of thermal expansion of 20 × 10 ⁻⁷ / ° C. or less, preferably 10 × 10 ⁻⁷ / ° C. or less. Can be.

In the production method of the present invention, as described above, a kaolin raw material and a MgO raw material are added to petalite, and a SiO ₂ raw material is added as necessary, whereby a sintered body substantially free from water leakage can be obtained. Ceramics having a reduced firing temperature and a low coefficient of thermal expansion can be obtained. This is because Li ₂ O, MgO, Al ₂ O
₃ , while vitrification of SiO ₂ etc. promotes sintering of petalite, the compounded kaolin raw material and MgO raw material change into cordierite or quartz glass having a small coefficient of thermal expansion, and the main crystal phase becomes petalite crystal ( Or cordierite crystal (2MgO.2Al)
₂ O ₃ · 5SiO ₂ ).

In the above composition, SiO 2 supplied from each of the above-mentioned petalite raw materials, kaolin raw materials, etc.
_It is preferable to add a separate SiO ₂ component in addition to the _two components, but in this case, the amount of the SiO ₂ component may be selected so as to correspond to the production of the cordierite crystal,
A range of 0 to 15% by weight in terms of SiO ₂ is sufficient. In addition, like kaolin raw materials, kaolin component and SiO ₂
Needless to say, a raw material having both components can be appropriately applied.

[0025] In the manufacturing method of the present invention, the mixing ratio of other raw materials can be embodied by limiting as follows according to the blending ratio of Li <br/> lithium silicate material as described above. That is, first, the lithium silicate raw material is 30 to 45% by weight,
When the kaolin raw material is 35 to 55% by weight and the MgO compound raw material is 5.0 to 10% by weight in terms of MgO, the thermal expansion coefficient is slightly higher at about 10 to 20 × 10 ⁻⁷ / ° C. Nevertheless, since the proportion of the relatively expensive lithium silicate raw material is small, there is an advantage in cost.

Second, the lithium silicate raw material is 60-75.
In the case of a composition in which the weight percentage of kaolin raw material is 20 to 35% by weight and the raw material of MgO compound is 1.5 to 6.0% by weight in terms of MgO, it is cost effective contrary to the first case. On the other hand, a sintered body having the lowest coefficient of thermal expansion can be obtained, and a ceramic suitable for applications requiring severe thermal shock resistance can be obtained.

Third, the lithium silicate raw material is 45-60.
% By weight, 25 to 45% by weight of kaolin raw material, and 4.0 to 7.5% by weight of MgO compound raw material in terms of MgO, a quality intermediate between the above first and second cases, For example, ceramics having a coefficient of thermal expansion of about 10 × 10 ⁻⁷ / ° C. can be obtained.

[0028]

Next, the present invention will be described in detail based on the test results shown in Table 1. In Table 1, those with asterisks (*) indicate the specimens, and the others are based on the mixing ratio of the raw materials according to the production method of the present invention. The chemical composition in the center column indicates the chemical component composition calculated from the raw material mixing ratio in the left column in terms of% by weight.

Here, the raw materials used were usually available, blended in accordance with the raw material blending ratios in the table, wet-pulverized and mixed by a ball mill, and then dried and kneaded to prepare a substrate. A pot-like container having a diameter of about 15 cm was formed from this base by pressurized potter's wheel molding, and the moldability was good with the potter's wheel.
Mark) No (display x mark in the table) was determined. Also, 10 × 1
It was press-formed into a long column of 0 × 60 mm to obtain a test body for the next evaluation.

The specimen was heated in an electric heating test furnace at a heating rate of 200 ° C./hr up to 1200 ° C.
At 1200 ° C. or higher, heating was performed at a reduced heating rate of 120 ° C./hr, and when the water absorption of the sintered specimen reached 3.0% or less, a sufficiently dense sintered body was obtained. The temperature at that time was taken as the maximum firing temperature in Table 1. Further, the test piece thus obtained was measured for a coefficient of linear thermal expansion by measuring a coefficient of thermal expansion in a range from room temperature to 500 ° C. using a normal tester for measuring thermal expansion. The moldability, the maximum firing temperature was 1300 ° C. or less, and the coefficient of thermal expansion was 20 × 10 ⁻⁷ / ° C. or less.

The frit powder in the raw material was prepared by the following method. The chemical composition of lithium carbonate, kaolin and quartz powder is 4Li ₂ O.Al ₂ O ₃ .4S
The mixture formulated to be iO ₂ was wet-pulverized and mixed in a ball mill, dried, kneaded, cut into small pieces, dried sufficiently, and then sufficiently heated and sintered at 950 ° C. This was finely pulverized again by a ball mill to obtain a frit powder.

According to Table 1 showing the above test results, first, No. 1 and No. 2 in the table are conventional general ones, which are blends using petalite and kaolin. High temperature is required, and a low coefficient of thermal expansion cannot be obtained. No. 3 to No. 5 in the table are components prepared so that the added kaolin can be changed to a petalite composition using the above frit powder, and a ceramic having a low coefficient of thermal expansion can be obtained, but it can be seen that the firing temperature does not drop much. .

No. 6 to No. 8 in the table are examples in which the mixing ratio of the kaolin raw material is less than 20%, and is considered to be sufficiently applicable to products in which a molding method using a mold such as a press molding method can be adopted. However, in the case of tableware, which is a product in the application field of the present invention, for example, the potter's wheel molding method is generally used.

No. 9 to No. 21 in the table depend on the mixing ratio of the present invention, and the following facts have been found from these. (1) Without using a frit or the like prepared by man-hours from lithium carbonate, SiO ₂ , Al
By adding appropriate amounts of ₂ O ₃ and MgO, the firing temperature for densification can be lowered and the coefficient of thermal expansion can be kept low. The reason for this is that petalite has SiO ₂ , A
When l ₂ O ₃ , MgO, etc. are added, low-melting glass is formed to promote sintering of petalite,
This is probably because the O ₂ , Al ₂ O ₃ , and MgO components mainly form cordierite crystals having a small coefficient of thermal expansion. Therefore, the initial SiO ₂ , Al ₂ O ₃ , MgO
Preferably, the proportions of the components approximate the cordierite composition.

(2) When the proportion of petalite is in the range of 30 to 85% by weight, the coefficient of thermal expansion can be maintained at 20 × 10 ⁻⁷ / ° C. or less, and the firing temperature can be reduced to approximately 1300 ° C. or less;
It becomes possible to fire in a general firing furnace used for firing tiles and the like. In particular, the firing temperature can be minimized at around 50 to 70% by weight, and can be lowered by about 100 ° C. as compared with the case of conventional Lithia ceramics. By firing at a maximum of 1300 ° C., dense ceramics having a water absorption of 1% or less can be obtained.

(3) When the amount of petalite is less than 30% by weight (for example, like No. 22 in the table), the relative SiO
_{2. Since} the ratio of Al ₂ O _{3 and the} like increases, they dominate the sintering action, and it is difficult to achieve both firing for densification at a low temperature and a low coefficient of thermal expansion. If the amount of petalite exceeds 75% by weight, the ratio of the kaolin raw material exhibiting the potter's wheel moldability is relatively reduced, so that the potter's potter's wheel becomes difficult to perform potter's wheel moldability.

[0037]

According to the thermal shock resistant ceramics of the present invention, since the lithiasilicate and cordierite crystals coexist, a ceramic having a high thermal shock resistance, which is dense and has low thermal expansion characteristics is provided. In addition, according to the manufacturing method, the material is sufficiently dense at a low sintering temperature of 1300 ° C. or less without using a raw material such as lithium carbonate which requires a large number of manufacturing steps and using a low-cost natural material. It has an excellent effect of providing a practical method for producing a thermal shock-resistant ceramic which can be fired into a versatile sintered body having a ratio of 3.0% or less and has moldability. Accordingly, the present invention has a thermal shock resistant ceramic which has solved the conventional problems and a method for producing the same, which has an extremely large industrial value.

[0038]

[Table 1]

Claims (4)

(57) [Claims] 1. A petalite raw material or 30 to 75% by weight.
Is a lithium silicate raw material which is a raw material of spodumene , 20
~ 55% by weight of kaolin raw material, 1.5 in terms of MgO
10 wt% of MgO compound materials, and in terms of SiO ₂ wherein in addition to the SiO ₂ component supplied from the raw material 0
A base material containing up to 15% by weight of a SiO ₂ compound is prepared, molded, and fired at a maximum temperature of 1300 ° C. at the highest.
A method for producing a thermal shock-resistant ceramic, characterized in that a dense sintered body is obtained by sintering the ceramic. Wherein said lithium silicate material is 30 to 45 wt%, kaolin material is 35-55 wt%, claim MgO compound raw material is 5.0 to 10 wt% in terms of MgO
2. The method for producing a thermal shock-resistant ceramic according to 1 . Wherein the lithium silicate material is 45 to 60 wt%, kaolin material is 25 to 45 wt%, according to claim 1, wherein MgO compound raw material is 4.0 to 7.5 wt% in terms of MgO Production method of thermal shock resistant ceramics. Wherein said lithium silicate material is 60 to 75 wt%, kaolin material is 20 to 35 wt%, according to claim 1, wherein MgO compound raw material is 1.5 to 6.0 wt% in terms of MgO Production method of thermal shock resistant ceramics.