Composition for forming β-spodumene and heat-resistant clay material

Abstract

To provide a material capable of forming a fired body containing a β-spodumene phase that achieves excellent low expansibility while using raw materials that are stably obtainable.SOLUTION: A heat-resistant clay raw material comprises lithium salt and clay and forms a fired body containing a β-spodumene phase by firing, wherein: the lithium salt does not contain aluminum or has an aluminum content of 0.1 mass% or less; the clay is contained in an amount of 20 mass% or more relative to the total raw material; and the lithium salt is contained in an amount of 0.1 to 25 mass% relative to the total raw material. Furthermore, the raw material contains fused silica in an amount of 0.01 to 45 mass% relative to the total composition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a composition for forming a β-spodumene phase, a heat-resistant clay raw material for forming a fired body containing a β-spodumene phase, and the like. [Background technology]

[0002] Although ceramic sintered bodies generally have high melting points and excellent heat resistance, materials such as alumina and zirconia have relatively large thermal expansion coefficients. For this reason, lithium-based silicate sintered bodies such as β-spodumene (Li2O·Al2O3·4SiO2) and β-eucryptite (Li2O·Al2O3·2SiO2) are used for applications such as heat treatment jigs that require thermal shock resistance. Furthermore, for applications such as heat-resistant tableware and cookware like earthenware pots, roofing tiles, and bricks, a sintered body made by blending clay with petalite (Li2O·Al2O3·8SiO2), a natural lithium ore, and then heat-treating it to produce the β-spodumene phase, resulting in low thermal expansion, is used.

[0003] Here, because petalite has an extremely low lithium content, it is necessary to add a large amount of petalite to improve thermal shock resistance. In response to this, a technique has been proposed in Patent Document 1, for example, as a method for producing a β-spodumene phase without using petalite. Patent Document 1 proposes a technique for producing β-spodumene by firing natural spodumene (Li2O·Al2O3·4SiO2) at approximately 1100 to 1350°C and transforming its crystal structure to α-β. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-65315 Summary of the Invention [Problem to be solved by the invention]

[0005] However, since Japan relies on imports for many of its minerals, availability is subject to changes in resource conditions, etc. In particular, in recent years, there have been increasing restrictions on the export of raw ores that have not undergone certain processing (for example, calcination or refining), and there is a risk that obtaining unprocessed ores such as petalite and α-spodumene will become difficult in the future.

[0006] The present invention has been made in view of the above background, and aims to provide a material that can be used to form a fired body containing a β-spodumene phase that achieves excellent low expansion properties, while using raw materials that are stably available. [Means for solving the problem]

[0007] The β-spodumene-forming composition of the present invention contains a lithium salt and clay, and is a composition that forms a fired body containing a β-spodumene phase upon firing, characterized in that the lithium salt does not contain aluminum or has an aluminum content of 0.1 mass% or less, and the lithium salt is contained in an amount of 0.01 to 30 mass% of the entire composition.

[0008] The β-spodumene forming composition of the present invention is characterized in that it contains fused silica, and the fused silica is contained in an amount of 0.01 to 45% by mass relative to the entire composition.

[0009] The β-spodumene forming composition of the present invention is characterized in that the lithium salt is lithium carbonate.

[0010] The heat-resistant clay raw material of the present invention contains a lithium salt and clay, and is characterized in that the lithium salt does not contain aluminum or has an aluminum content of 0.1% by mass or less, the clay accounts for 20% by mass or more of the total heat-resistant clay raw material, and the lithium salt accounts for 0.1 to 25% by mass of the total heat-resistant clay raw material.

[0011] The heat-resistant clay raw material of the present invention is characterized in that it contains fused silica, and the fused silica is contained in an amount of 0.01 to 45 mass % based on the total mass of the composition.

[0012] The heat-resistant clay raw material of the present invention is characterized in that the lithium salt is lithium carbonate.

[0013] The heat-resistant clay raw material of the present invention is characterized by containing at least one additive selected from iron oxide, pyrophyllite, feldspar, chamotte, dolomite, lime, talc, magnesite, alumina, petalite, cordierite, a barium compound, and a strontium compound.

[0014] The fired body of the heat-resistant clay raw material of the present invention has a thermal expansion coefficient of 5.0 × 10 -6 / K or less.

[0015] The ceramic of the present invention is a heat-resistant ceramic which is a fired body made from a heat-resistant clay raw material, characterized in that the heat-resistant clay raw material is the heat-resistant clay raw material described above. [Effects of the Invention]

[0016] The β-spodumene forming composition of the present invention contains a lithium salt and clay, and is a composition that forms a fired body containing a β-spodumene phase by firing. The lithium salt does not contain aluminum or has an aluminum content of 0.1 mass% or less, and the lithium salt is contained in an amount of 0.01 to 30 mass% of the entire composition, so that a fired body containing a β-spodumene phase can be obtained without using lithium ore. In another embodiment, the composition contains fused silica in an amount of 0.01 to 45 mass % of the total composition, thereby reducing the coefficient of linear expansion. Furthermore, the lithium salt is lithium carbonate, which provides excellent handling, safety, availability, and the like.

[0017] The heat-resistant clay raw material of the present invention contains a lithium salt and clay, and is a heat-resistant clay raw material that forms a fired body containing a β-spodumene phase when fired, and the lithium salt does not contain aluminum or has an aluminum content of 0.1 mass% or less, and the clay is contained in 20 mass% or more of the entire raw material, and the lithium salt is contained in 0.1 to 25 mass% of the entire raw material, so that a fired body containing a β-spodumene phase and having excellent low expansion properties can be obtained without using lithium ore. In another embodiment, the raw material contains fused silica in an amount of 0.01 to 45 mass % of the total raw material, thereby further reducing the linear expansion coefficient. Also, the lithium salt is lithium carbonate, which provides excellent handling, safety, availability, and the like.

[0018] Furthermore, the heat-resistant clay raw material contains at least one additive selected from iron oxide, pyrophyllite, feldspar, chamotte, dolomite, lime, talc, magnesite, alumina, petalite, cordierite, barium compounds, and strontium compounds, which can impart various characteristics to the sintered body.

[0019] The ceramics of the present invention are fired bodies of the heat-resistant clay raw material of the present invention, and therefore do not rely on conventional expensive petalite, but are made from stably available raw materials, and contain the β-spodumene phase, which achieves excellent low expansion. Therefore, they can be suitably used as tableware and cookware for use over an open flame, for example. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 10 is a diagram showing the results of the X-ray diffraction pattern in Example 8. [Figure 2] FIG. 10 is a diagram showing the results of the X-ray diffraction pattern of Example 9. [Figure 3] FIG. 1 is a diagram showing the results of the X-ray diffraction pattern of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0021] The β-spodumene-forming composition and heat-resistant clay raw material of the present invention are compositions and raw materials that contain clay and a specified lithium salt, and form a fired body containing a β-spodumene phase upon firing.

[0022] β-Spodumene is a tetragonal lithium-based aluminosilicate with the composition Li2O·Al2O3·4SiO2, and the β-spodumene phase is its crystalline phase (also called β-spodumene solid solution) that precipitates in the fired body. Since the β-spodumene phase is a crystalline phase with low thermal expansion, the formation (precipitation) of the β-spodumene phase in the fired body can reduce the thermal expansion of the fired body. This low thermal expansion coefficient is thought to be due to the anisotropy of the crystal axis direction and the resulting presence of microcracks. The greater the anisotropy in the crystal axis direction, the more likely microcracks are to occur.

[0023] The precipitation of the β-spodumene phase can be confirmed by X-ray diffraction. For example, CuKα radiation is used in X-ray diffraction, measuring the Bragg angle (2θ) range from 10° to 80° to obtain a diffraction pattern. The appearance of diffraction peaks allows for identification of precipitated crystals. β-Spodumene is a crystal that typically exhibits diffraction peaks at Bragg angles (2θ) of 25.55°±0.05°, 22.71°±0.05°, and 28.20°±0.05° in an X-ray diffraction pattern. The presence or absence of the β-spodumene phase can be confirmed by analyzing the crystal structure using standard identification methods (such as the Hanawald method or the Rietveld method) provided with the instrument, based on the pattern (chart) obtained by X-ray diffraction, such as the Powder Diffraction File (PDF) provided by the International Centre for Diffraction Data (ICDD).

[0024] In clay materials and glazes commonly used for ceramics, naturally occurring lithium ores such as petalite and α-spodumene are mixed with clay and fired to produce β-quartz solid solution crystal phases and the more stable β-spodumene solid solution crystal phases, ensuring low thermal expansion (thermal shock resistance) for the fired and molded products as a whole. This type of ceramic is widely distributed as heat-resistant lithia-based (Li2O-Al2O3-SiO3) ceramics. However, as mentioned above, the availability of raw ores has become increasingly limited in recent years, and there is a risk that unprocessed ores such as petalite and α-spodumene will become increasingly difficult to obtain in the future. Therefore, using relatively readily available raw materials for low-expansion molded products using β-spodumene is crucial from the perspective of ensuring stable raw material availability. In the present invention, by using a specific lithium salt (such as lithium carbonate) as a lithium source, a β-spodumene phase can be formed and low expansion can be achieved, even when minerals such as the above-mentioned petalite are not used.

[0025] The β-spodumene-forming composition and heat-resistant clay raw material of the present invention contain clay and a predetermined lithium salt. The clay used in the present invention is a soil component formed from clay minerals containing silica and alumina, such as clays containing kaolin minerals (such as frogeye clay, kibushi clay, kaolinite, dickite, nacrite, halloysite, New Zealand kaolin, Korean kaolin, and Hadong kaolin), and sericite. These clays may be used alone or in combination of two or more. The silica and alumina components contained in these clays serve as aluminum and silicon sources for the formation of the β-spodumene phase (LiO·AlO·4SiO).

[0026] In the β-spodumene forming composition of the present invention, the content of clay relative to the entire β-spodumene forming composition is not particularly limited as long as it is an amount that allows the formation of β-spodumene. The content of clay relative to the entire β-spodumene forming composition can be adjusted to, for example, 1 to 99 mass%, 5 to 95 mass%, 10 to 90 mass%, 20 to 80 mass%, 30 to 70 mass%, etc.

[0027] In the heat-resistant clay raw material of the present invention, the clay content relative to the entire heat-resistant clay raw material is set to 20% by mass or more, taking into consideration the possibility of forming β-spodumene, as well as sufficient low thermal expansion and moldability. By setting the content in this range, it is possible to mold into the product shape while ensuring low thermal expansion (thermal shock resistance). The clay content relative to the entire heat-resistant clay raw material can be adjusted to, for example, 20 to 98% by mass, 30 to 95% by mass, 30 to 90% by mass, 30 to 80% by mass, 30 to 70% by mass, 30 to 60% by mass, 30 to 55% by mass, 40 to 50% by mass, etc.

[0028] The lithium salt used in the present invention is preferably not a mineral-based lithium salt but a lithium salt obtained by purification or synthesis. Mineral-based lithium salts contain alumina and silica. Therefore, the lithium salt used in the present invention does not contain aluminum (Al) or has an aluminum content of 0.1 mass% or less. When aluminum is in an oxide state (alumina: Al2O3), the aluminum content is expressed as mass% relative to the total mass of the lithium salt in terms of metallic aluminum. When aluminum is contained, its content is more preferably 0.01 mass% or less.

[0029] Examples of lithium salts include lithium carbonate (Li2CO3), lithium chloride (LiCl), lithium nitrate (LiNO3), lithium sulfate (Li2SO4), lithium hydroxide (LiOH), and lithium citrate. Among these, it is preferable to use lithium carbonate because of its ease of handling, safety, and availability. Lithium carbonate may be a secondary material produced by extraction and purification from lithium minerals, or it may be recycled lithium carbonate that has been recovered and purified after industrial use.

[0030] The lithium salt is contained in a powder (particulate) form. The average particle size of the lithium salt is not particularly limited. Examples of the average particle size range of the usable lithium salt include 1 to 500 μm, 1 to 100 μm, 1 to 50 μm, 5 to 100 μm, 5 to 50 μm, 5 to 30 μm, 10 to 100 μm, 10 to 50 μm, and 10 to 30 μm. The particle size of the lithium salt is desirably determined taking into consideration the reactivity contributing to the formation of a β-spodumene phase, the mechanical strength of the fired body, the effect on microcracks (low thermal expansion), and the like. In the present invention, the particle size is preferably 1 to 100 μm, and more preferably 1 to 50 μm.

[0031] The "average particle size" in the present invention means the particle size (D50) at which the cumulative value reaches 50% when the frequency (%) of particle sizes is accumulated from the smaller particle size side when the particle size distribution (particle size distribution) is measured using a known particle size distribution measurement device (for example, a laser diffraction particle size distribution measurement device).

[0032] In the β-spodumene forming composition of the present invention, the content of the lithium salt relative to the entire β-spodumene forming composition is 0.01 to 30% by mass. By setting the content within this range, β-spodumene can be precipitated during firing. The content of the lithium salt relative to the entire β-spodumene forming composition can be adjusted to, for example, 0.01 to 28% by mass, 0.01 to 25% by mass, 0.1 to 30% by mass, 0.1 to 28% by mass, 0.1 to 25% by mass, 0.5 to 30% by mass, 0.5 to 28% by mass, 0.5 to 25% by mass, 1 to 30% by mass, 1 to 28% by mass, 1 to 25% by mass, 3 to 30% by mass, 3 to 28% by mass, 3 to 25% by mass, 5 to 30% by mass, 5 to 28% by mass, or 5 to 25% by mass.

[0033] In the heat-resistant clay raw material of the present invention, the content of the lithium salt relative to the entire heat-resistant clay raw material is 0.1 to 25% by mass. By setting it within this range, it is possible to suppress cracking during firing while ensuring low thermal expansion (thermal shock resistance). The content of the lithium salt relative to the entire heat-resistant clay raw material can be adjusted to, for example, 0.3 to 25% by mass, 0.5 to 25% by mass, 1 to 25% by mass, 2 to 25% by mass, 3 to 25% by mass, 5 to 25% by mass, etc.

[0034] The β-spodumene-forming composition and heat-resistant clay raw material of the present invention can contain fused silica. The inclusion of fused silica can contribute to a reduction in the thermal expansion coefficient of the fired body. This may be due not only to the physical properties of fused silica itself (low expansion), but also to its influence on the formation of the β-spodumene phase. Furthermore, the inclusion of fused silica can relatively reduce the amount of lithium carbonate in the composition and raw material to ensure the desired low thermal expansion.

[0035] The fused silica used in the present invention is quartz (silica) with a low linear expansion coefficient, unlike crystalline quartz or rock crystal. Examples of fused silica (also called quartz glass, fused silica, or silica glass) that can be used in the present invention include powders obtained by pulverizing rock crystal or rock crystal that has been melted at high temperatures using an oxyhydrogen flame, electricity, or plasma arc, and then rapidly solidified, or powders obtained by chemical vapor deposition or the sol-gel method. Because fused silica is artificially produced, it is therefore readily available. This allows for a stable supply of the β-spodumene-forming composition and heat-resistant clay raw material of the present invention.

[0036] Compositions and ingredients containing a large amount of natural ingredients are prone to variations in composition due to the natural ingredients. Therefore, from the perspective of product quality stability, it is desirable to use artificially produced fused silica with minimal variation in composition to achieve durability and appearance equal to or better than conventional products. Fused silica produced by a method using electricity to melt quartz and other materials at high temperatures (hereinafter referred to as the "electrical fusion method") is characterized by the absence of OH (hydroxyl) groups, which reduce heat resistance. This gives fused silica produced by the electric fusion method superior heat resistance compared to fused silica obtained by other methods.

[0037] Crystalline quartz (silica) is found in feldspar materials and is widely used as a raw material for ceramics. The main reasons for adding quartz to clay and glazes are to improve the strength and luster of ceramics after firing. However, most quartz found in nature is crystalline, and adding quartz increases the coefficient of linear expansion. In contrast, fused silica is amorphous and, as mentioned above, is a raw material with a low coefficient of linear expansion. By maintaining at least a portion of the fused silica unmelted during firing, it offers excellent thermal shock resistance. Furthermore, when using fused silica produced by the electric melting method, its excellent heat resistance, as mentioned above, makes it easier for some of the fused silica to remain unmelted.

[0038] The fused silica is contained in particulate form. The average particle size of the fused silica is not particularly limited. Examples of the average particle size range of usable fused silica include 0.01 to 5.00 mm, 0.01 to 1.00 mm, 0.01 to 0.80 mm, and 0.01 to 0.50 mm. Two or more types of fused silica with different average particle sizes may be mixed and used. When the fused silica particle size is within the above range (0.01 to 5.00 mm), a good balance is achieved between melting near the particle surface and non-melting at the particle center during firing of the composition / raw materials, which tends to improve the thermal shock resistance and toughness of the fired body, leading to improved bending strength.

[0039] In the β-spodumene-forming composition and heat-resistant clay raw material of the present invention, the content of fused silica relative to the entire composition and raw materials is 0.01 to 45% by mass. By setting it to 0.01% by mass, low thermal expansion (thermal shock resistance) can be improved. Furthermore, by setting it to 45% by mass or less, cracking during firing after drying can be suppressed. The content of fused silica relative to the entire composition and raw materials can be adjusted to, for example, 0.1 to 45% by mass, 1 to 45% by mass, 3 to 45% by mass, 5 to 45% by mass, 1 to 35% by mass, 5 to 35% by mass, 5 to 15% by mass, etc.

[0040] The heat-resistant clay raw material of the present invention may contain additives known in general heat-resistant ceramic raw materials. Examples of additives include iron oxide, rosestone, feldspar, chamotte, dolomite, lime, talc, magnesite, alumina, petalite, cordierite, barium compounds, and strontium compounds. These may be used alone or in combination of two or more. Among these, iron oxide, rosestone, feldspar, and chamotte are preferred. Iron oxide (ferric oxide) is used for coloring and improving strength, rosestone is used as a lubricant, feldspar is used for glossing, chamotte is used as a cushioning material during firing, and petalite and cordierite are used as low-expansion additives. These additives may also be added to the β-spodumene-forming composition of the present invention.

[0041] Specific examples of iron oxides include ferrous oxide (FeO), ferric oxide (FeO), triiron tetroxide (FeO), etc. Examples of ferric oxides include NAT iron oxide, HRT iron oxide, NSK iron oxide, and red iron oxide.

[0042] Petalite, when included as a low-expansion additive, is added in small amounts and is not included as a lithium source for the formation of the β-spodumene phase. Cordierite (2MgO·2Al2O3·5SiO2) is a magnesium-containing silicate mineral. Other low-expansion additives, such as mullite (3Al2O3·2SiO2), zircon (ZrO2·SiO2), and borosilicate glass (Na2O-B2O3-SiO2), may also be added.

[0043] Other additives that may be added include sodium silicate and bentonite. Bentonite and sodium silicate are used as viscosity improvers and are effective in preventing cracks when the base material is formed and dried. Bentonite, in particular, is effective in improving viscosity even with a small amount added; for example, even a content of 1% by mass relative to the total heat-resistant clay raw material can significantly improve viscosity.

[0044] The content of the additive relative to the total heat-resistant clay raw material can be adjusted to, for example, a total of 0.1 to 30 mass%, 0.1 to 20 mass%, 0.1 to 10 mass%, 0.1 to 8 mass%, 0.1 to 6 mass%, 0.1 to 5 mass%, etc. When feldspar is blended as an additive, as mentioned above, the feldspar raw material contains crystalline quartz, which may increase the linear expansion coefficient. Therefore, the feldspar content is preferably 15 mass% or less (for example, a lower limit of 0.1 mass%), and more preferably 10 mass% or less (for example, a lower limit of 0.1 mass%) relative to the total composition and raw materials.

[0045] The firing temperature range for firing the β-spodumene-forming composition and heat-resistant clay raw material of the present invention can be adjusted to, for example, 1000 to 1400°C, 1000 to 1300°C, 1000 to 1250°C, 1100 to 1400°C, 1100 to 1300°C, or 1100 to 1250°C. By firing at 1000°C or higher, the β-spodumene phase can be sufficiently precipitated. Furthermore, by firing at 1400°C or lower, if fused silica is contained, the fused silica can be sintered without being completely melted. Furthermore, the firing time can be adjusted as appropriate. Furthermore, firing conditions include oxidation firing and reduction firing, and either condition may be used.

[0046] The ceramics of the present invention are fired bodies made from the heat-resistant clay raw material of the present invention. Heat-resistant ceramics are produced by the following steps: (A) molding a clay body made from the heat-resistant clay raw material; (B) applying a glaze to the surface of the molded clay body as needed; and (C) firing the body in a firing furnace and then cooling it.

[0047] In the molding process (A), the minerals that make up the heat-resistant clay raw material are mixed in predetermined amounts. This mixing can be done using either the well-known wet or dry method. When mixing using the wet method, the mixture (sludge) is dehydrated and caked to produce the clay for molding. The material is then molded after being kneaded. Methods that can be used include roller machine molding, press molding, pressure casting (compression) molding, slip casting, water trowel molding, hand mixing, and tatara molding, and the clay is molded into the desired shape, such as a clay pot or dish. The heat-resistant clay raw material can be either red clay or white clay.

[0048] The glazing step (B) is carried out as needed. In this step, a glaze is applied to the surface of the molded body formed in step (A). Any glaze can be used as long as it can form a glassy glaze layer. Glazing methods that can be used include dipping and spraying, and the glaze is applied to the surface of the molded body.

[0049] In the firing step (C), the molded body obtained above is placed in a gas kiln or electric kiln and fired under the firing conditions described above, for example, at a temperature of 1000 to 1400°C. The firing time is approximately 1 to 24 hours. By firing at 1400°C or below, the fused silica can be sintered without being completely melted, as described above. The firing conditions may be either oxidation firing or reduction firing. Note that oxidation firing is a method in which a large amount of air (oxygen) is supplied into the kiln and firing is performed under conditions in which sufficient oxygen is present. Reduction firing is a method in which, for example, wood, coal, gas, etc. are fed into the kiln to the extent that incomplete combustion occurs.

[0050] Furthermore, in the molding step (A), the heat-resistant clay raw material may be pre-fired. For example, a heat-resistant clay raw material with a portion of the clay content removed from the final composition may be used, and pre-fired to form a β-spodumene phase. This may then be pulverized, and the clay may be mixed and kneaded using the above method to form the final composition. In this case, adhesion to the mold during molding can be suppressed. The pre-fired temperature may be lower than the firing temperature, for example, at 500°C or higher. The upper limit of the pre-fired temperature is not particularly limited, but for the same reasons as in the firing step (C), it is preferable to fire at a temperature of 1400°C or lower.

[0051] This pre-firing differs from the pre-firing process (B) commonly used before the glazing process in ceramics, in that it is a process that partially promotes the formation of β-spodumene in the material before molding. As a result, as described above, the effect of preventing the material from sticking to the mold during molding can be obtained. Furthermore, regardless of whether or not this pre-firing is performed, a general pre-firing process may be performed before the glazing process (B). The pre-firing process is performed at a temperature of, for example, 700 to 1100°C.

[0052] The ceramics of the present invention can be produced so that, when exposed to direct fire, they satisfy the standard of a temperature difference of 350°C or more specified in JIS S 2400 based on the Industrial Standardization Act for factories certified by the Ministry of Economy, Trade and Industry. In particular, by blending lithium carbonate with clay to form a β-spodumene phase and blending fused silica, it is possible to produce heat-resistant ceramics that have excellent low thermal expansion (thermal shock resistance) as a whole, are resistant to direct fire, and have sufficient durability for practical use.

[0053] The calcined body made from heat-resistant clay has a linear expansion coefficient of 5.0 x 10 from room temperature to 700°C. -6 / K or less, and more preferably 4.0 × 10 -6 / K or less, more preferably 3.5 × 10 -6 / K or less, more preferably 3.0 × 10 -6 / K or less, more preferably 2.5 × 10 -6 / K or less, and more preferably 2.0 × 10 -6 / K or less. The linear expansion coefficient may be a negative value. Therefore, the linear expansion coefficient is preferably in the above ranges as an absolute value.

[0054] In addition, the difference in the linear expansion coefficient measured under the same temperature conditions in the cases of reduction firing and oxidation firing is -1.0 to 1.0 × 10 -6 / K, more preferably -0.8 to 0.8 × 10 -6 / K, more preferably -0.5 to 0.5 × 10 -6 / K. The difference in linear expansion coefficient is ±1.0×10 -6 By keeping the temperature within the range of 1 / K, a sufficiently low expansion property (thermal shock resistance) can be obtained regardless of the firing conditions. [Example]

[0055] Examples 1 to 26, Comparative Example 1 The compositions shown in Table 1 were prepared, and the specified test specimens were molded using these. These were then fired in an oxidizing atmosphere at 1200°C for 20 hours to produce the test specimens. Korean kaolin was used as the clay. Commercially available lithium carbonate (white powder, purity 99.9%, Al content 0.001% by mass or less, average particle size 1-100 μm) was used as the lithium carbonate. Commercially available fused silica (average particle size 0.01-5.00 mm) was used as the fused silica. Silica stone is crystalline silica. The linear expansion coefficients of these test specimens were measured using a thermomechanical analyzer by heating from room temperature (25°C) to 700°C at a heating rate of 7°C / min. The results are shown in Table 1.

[0056] [Table 1]

[0057] As shown in Table 1, the linear expansion coefficient of all test specimens used in the test was 5.0 × 10 -6 / K or less, and it was confirmed that the coefficient of linear expansion was lower than that in the case of clay alone (Comparative Example 1).

[0058] Next, the crystalline phases of Example 8 (lithium carbonate 5% by mass, clay 95% by mass), Example 9 (lithium carbonate 5% by mass, clay 90% by mass, fused silica 5% by mass), and Comparative Example 1 (clay 100% by mass) were identified using an X-ray diffraction measurement device. The X-ray diffraction patterns are shown in Figure 1 (Example 8), Figure 2 (Example 9), and Figure 3 (Comparative Example 1), respectively. The Rigaku "RINT2500" device and "JADE5" qualitative analysis software were used.

[0059] As shown in Figures 1 and 2, in the composition containing lithium carbonate, a peak of the β-spodumene phase (JCPD-ICDD: 35-0797) was observed, which was not confirmed in Figure 3. Furthermore, as shown in Table 1 above, the actual linear expansion coefficients of Examples 8 and 9 were also significantly reduced compared to Comparative Example 1. [Industrial Applicability]

[0060] The β-spodumene-forming composition and heat-resistant clay raw material of the present invention are materials that can form fired bodies containing a β-spodumene phase that achieve excellent low expansion properties while using stably available raw materials, and therefore can be stably mass-produced and widely used as raw materials for industrial and household materials that require a low linear expansion coefficient, etc. In particular, they can be suitably used for heat-resistant ceramics such as tableware and cooking utensils for use over an open flame.

Claims

1. A composition comprising a lithium salt and a clay, which upon firing forms a fired body containing a β-spodumene phase, the lithium salt is a lithium salt that does not contain aluminum or has an aluminum content of 0.1% by mass or less, A β-spodumene forming composition, characterized in that the lithium salt is contained in an amount of 0.01 to 30 mass % based on the total mass of the composition.

2. The β-spodumene forming composition according to claim 1, characterized in that the composition contains fused silica, and the fused silica is contained in an amount of 0.01 to 45 mass% based on the total mass of the composition.

3. 3. The β-spodumene forming composition according to claim 1, wherein the lithium salt is lithium carbonate.

4. A heat-resistant clay raw material containing a lithium salt and clay, which forms a fired body containing a β-spodumene phase by firing, the lithium salt is a lithium salt that does not contain aluminum or has an aluminum content of 0.1% by mass or less, The clay is contained in an amount of 20% by mass or more based on the total amount of the heat-resistant clay raw material, The heat-resistant clay raw material is characterized in that the lithium salt is contained in an amount of 0.1 to 25 mass % based on the total mass of the heat-resistant clay raw material.

5. The heat-resistant clay raw material according to claim 4, characterized in that the heat-resistant clay raw material contains fused silica, and the fused silica is contained in an amount of 0.01 to 45 mass% of the total composition.

6. 6. The heat-resistant clay raw material according to claim 4, wherein the lithium salt is lithium carbonate.

7. The heat-resistant clay raw material according to claim 4 or claim 5, characterized in that the heat-resistant clay raw material contains at least one additive selected from iron oxide, pyrophyllite, feldspar, chamotte, dolomite, lime, talc, magnesite, alumina, petalite, cordierite, a barium compound, and a strontium compound.

8. The calcined body of the heat-resistant clay raw material has a thermal expansion coefficient of 5.0 × 10 -6 6. The heat-resistant clay raw material according to claim 4, wherein the viscosity is 1 / K or less.

9. It is a ceramic ware made from a fired heat-resistant clay material, 6. A ceramic ware, wherein the heat-resistant clay raw material is the heat-resistant clay raw material according to claim 4 or 5.

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