JP4488444B2 - Method for producing porous ceramics and porous ceramics - Google Patents

Description

  The present invention relates to a porous ceramic, particularly a porous ceramic that can be suitably used as a reaction vessel for the production of a positive electrode material for a lithium ion secondary battery, and a method for producing the same.

In 1000 ° C. before and after the heat treatment in the production of the lithium ion secondary battery positive electrode material (eg _{LiMnO 2, LiCoO 2, LiNiO 2} ), although the ceramic reaction vessel is used, since the thermal shock is severe, steel refractories A mullite-cordierite-based porous reaction vessel having a high thermal shock resistance, which is mainly used as, is widely used.

Such a mullite-cordierite porous reaction vessel is vulnerable to alkali. Specifically, gas bodies (H ₂ O, CO ₂ , halogen, nitrogen, sulfur oxides, etc.) that are decomposed and generated in the formation reaction of a lithium compound and a transition metal (Mn, Co, Ni) compound and a high temperature accompanying heating Since the reaction vessel is exposed to vapor pressure Li ₂ O gas, it reacts with highly alkaline Li ₂ O gas, Li ₄ SiO _{4 and the} like are produced, and the reaction vessel deteriorates with repeated use. .
In particular, the reaction vessel is manufactured by mixing raw materials of various particle sizes such as coarse mullite and cordierite and fine alumina as raw materials with clay (mainly quartz and kaolinite). However, raw materials of various particle sizes and clay decomposition products are packed in a sparse state and are not homogeneous. Residual quartz (SiO ₂ ) reacts with alkali gas to produce Li-containing crystals such as Li ₄ SiO ₄ , and the produced Li ₄ SiO ₄ absorbs 25 wt% of CO ₂ gas in the temperature range of 400 to 700 ° C. , There is a peculiarity of release at 700 ° C., and as a result, an increase in internal stress and strain accompanying partial volume expansion in the reaction vessel occur. Since this distortion leads to cracking of the reaction vessel, it can be used only about 10 times in repeated reaction (firing). This is because the container and container reaction product may collapse into the product (lithium ion secondary battery positive electrode material) due to distortion or cracking of the ceramic reaction container, which may deteriorate the battery performance.
Therefore, the number of times of use of the conventional mullite-cordierite-based ceramic reaction vessel is broken in about 10 cycles, and a large amount is discarded as industrial waste after use.

  Further, since the apparent specific gravity of the reaction vessel is as heavy as around 2.0, there is a disadvantage that a burden is imposed on the operator during handling work, and a large amount of fuel is consumed during firing.

Osaka Ceramics Refractory Brick Co., Ltd. Technical Research Institute Shinichiro Odanaka, Kameyoshi Hara, Hiroshi Hirose, Kazutoshi Tokunaga "Transition and Present Status of Cement Refractories" Proceedings of the 1st Cement Refractory Research Group 105-117 (1960) Osaka Ceramics Refractory Brick Co., Ltd. Technical Research Institute Kameyoshi Hara, Hiroshi Hirose, Isao Mochimochi and Kazushi Tokunaga “Consideration of high performance spinel bricks” The 2nd refractory research meeting for cement 32-32 (1961) Refractory Technology Association Edition Refractory Notebook '99 IV Industrial Furnace and Refractory 3 Furnace and Refractory for Ceramic Industry 3.2 Cement and Lime Kiln 391-397 (1999) Ceramic Engineering Handbook Japan Ceramic Society 832 874 2006 2011 2012 (1989)

  Accordingly, an object of the present invention is to solve the above-mentioned conventional problems, and to provide a porous ceramic that has both alkali resistance and thermal shock resistance and can be suitably used as a reaction vessel, and a method for producing the same.

First, the inventor paid attention to the following industrial facts in order to fundamentally suppress the chemical reaction between the raw material for producing a positive electrode material for a lithium ion secondary battery and the reaction vessel.
(1) Silica-alumina brick is used as the lining fireproof brick in the calcined zone of the rotary kiln for cement production, which is considered to be severely eroded by alkali. Silica-alumina brick is worn away by alkali erosion. has occurred, silica - cristobalite contained in alumina bricks (SiO ₂₎ reacts with an alkali to produce an alkali minerals and glass phases, that these properties and production amount is considered to affect the brick damage .
(2) Even in heat treatment at around 1000 ° C. in the production of a lithium ion secondary battery positive electrode material (for example, LiMnO ₂ , LiCoO ₂ , LiNiO ₂ ), the material of the reaction vessel is alkali gas (Li ₂ O with high vapor pressure accompanying heating). ), Cristobalite, which is a decomposition product of kaolinite contained in Kibushi clay, Sasame clay, unused clay, etc., and quartz (SiO ₂ ) contained in the clay is eroded by Li ₂ O gas with strong alkali Therefore, as described above, it is considered that Li ₄ SiO ₄ that easily absorbs and releases CO ₂ reacts with free SiO ₂ in the ceramic material of the reaction vessel to accelerate the deterioration rate of the reaction vessel.

Therefore, in order to suppress the chemical reaction between the raw material for producing the positive electrode material of the lithium ion secondary battery and the ceramic reaction vessel during production, the alkaline earth oxide strong against Li ₂ O gas and Li melt, at least spinel, is homogenized. Was considered the best material design. This is based on the knowledge that alkaline earth oxides, especially spinel ceramic materials, are excellent in alkali erosion resistance. The lining bricks actually used in rotary kilns for cement production are chemically Spinel brick is used in the firing zone part of the rotary kiln, which is a severe condition part, and shows a good track record.

In addition, in order to improve thermal shock resistance, a fine space that escapes the elongation based on the high expansion coefficient of the spinel is placed around the fine spinel crystal generated when creating the reaction vessel to absorb rapid thermal contraction and thermal expansion. It is necessary to let For this, clay, alumina hydroxide, and rhododendron are used. During firing, the CO ₂ content of rhodolite (MgCO ₃ ), the alumina hydroxide (Al (OH) ₃ ), and the moisture of the clay decompose. It can be carried out by utilizing the fact that it comes off and becomes a pore.

Accordingly, in order to achieve the above object, the invention described in claim 1 is a method for producing porous ceramics, comprising a plastic clay from which quartz is removed or finely ground, an alumina component, and a bitter earth component, respectively. In addition to mixing 20% by weight or more, when mixing the three components, the total of oxides in the raw mineral components containing Na, K, Ca and Fe elements is 5% by weight or less (excluding 0% by weight) It adjusts so that it may become, It shape | molds in a predetermined shape, It bakes at the temperature of 1200 to 1350 degreeC, It is characterized by the above-mentioned.
According to a second aspect of the present invention, in the configuration of the first aspect, in order to suitably suppress shrinkage of the fired body, an aggregate made of ceramic particles is mixed and molded within a range of 10 wt% to 60 wt%. It is characterized by this.
On the other hand, in order to achieve the above object, the invention described in claim 3 is a porous ceramic obtained by the method for producing a porous ceramic according to claim 1, wherein the crystallized spinel and cordier are obtained. Including light, the apparent porosity is 40% or more, and the thermal expansion coefficient is 6.66 × 10 ⁻⁶ / ° C. or less at 1000 ° C.
Invention of Claim 4 is a porous ceramic obtained by the manufacturing method of the porous ceramic of Claim 1, Comprising: Crystallized spinel and cordierite are included, and an apparent porosity is 40% or more The thermal expansion coefficient is 6.66 × 10 ⁻⁶ / ° C. or less at 1000 ° C., and the specific surface area is 0.3 m ² / g or more by the BET method.
The invention described in claim 5 is characterized in that the structure of claim 3 or 4 does not contain a quartz component.
The invention described in claim 6 is characterized in that, in the structure of claim 3 or 5 , the sintered body has an aggregate made of ceramic particles, and the firing shrinkage rate is less than 10%.

According to the present invention, an alkaline earth oxide excellent in alkali resistance and thermal shock resistance, particularly a ceramic containing crystallized spinel and cordierite and in which pores are homogeneously distributed, is made of MgO ₂ -Al ₂ O _3. It can be produced at a temperature lower than 1370 to 1453 ° C. in the equilibrium diagram of —SiO ₂ .
Moreover, since it is excellent in alkali resistance, it can be used as a ceramic reaction vessel at a high temperature of about 1000 ° C. in the production of a lithium ion secondary battery positive electrode material (for example, LiMnO ₂ , LiCoO ₂ , LiNiO ₂ ). At this time, even when exposed to an alkaline attack by Li ₂ O gas, the amount of glass that is a reaction product of the ceramic reaction vessel component and the ceramic reaction vessel component is suppressed, and erosion is small. In particular, since the ceramic reaction vessel does not contain single-component quartz (SiO ₂ ), there is no strong alkaline Li ₂ O gas and reaction products of these single components.
Specifically, by quartz and Li _{2 O} gas reaction, so that there is no cause volumetric expansion caused to generate a lithium-containing crystal such as Li ₄ SiO ₄ to absorption and release of CO ₂ gas, the ceramic reaction vessel It is also possible to prevent expansion and destruction and contamination of foreign substances such as debris into the product lithium ion secondary battery positive electrode material. Further, the life of the ceramic reaction vessel can be extended.
On the other hand, since the thermal shock resistance is also increased and it becomes difficult to break, the amount of industrial waste discarded after use can be greatly reduced. In addition, since the apparent specific gravity is small, it is easy to carry around, and a small amount of fuel is sufficient for firing. Further, in the gas atmosphere firing, the gas can be uniformly supplied into the porous ceramic reaction vessel in the oxidation, reduction and humidification reactions.
And if aggregate is used, shrinkage | contraction of a baking body can be suppressed effectively.

  The plastic clay used in the present invention is selected from at least one of Kibushi clay, Sasame clay, Kaolinite clay, Bauxite clay, Porcelain clay, Mica clay and various artificial clays. The selected clay is removed as much of the quartz as possible using a water tank or an industrial centrifuge. The important thing is that when the firing in the production of ceramics is completed, the quartz disappears and it becomes an alkaline earth compound, so if the quartz disappears after firing, there is no problem even if it is not completely removed. Alternatively, it is possible to promote the firing reaction by finely pulverizing quartz so that it does not remain after firing.

Next, an alumina component is used in the present invention. The alumina component may be one or more selected from porous Al ₂ O ₃ , hydroxides, carbonates / ammonium groups / hydroxyl salts and double salts.
However, it is desirable to use raw materials with few alkali components such as Na ions as a measure for improving the fire resistance. For example, industrial waste Al (OH) ₃ sludge from a sash factory can be used as an alumina component, but since this Al (OH) ₃ contains a large amount of alkali components such as Na ions, the pH is set to 8. Use water that has been thoroughly washed.

  The plastic clay thus obtained, an alumina component, and a bitter earth component (these hydroxides, carbonates, and double salts) may be prepared at least 20% by weight, respectively, and an alkaline earth compound, particularly A crystal containing spinel is made. At this time, it is important to prepare such that quartz is not left alone in the composition.

  At this time, in order to make the produced ceramics homogeneous, raw materials with coarse particles are not used. This is because when a raw material having a coarse particle size is used, a product subjected to a decomposition reaction remains, and it is not uniform below submicron. If a coarse grain is required for the convenience of blending the grain size, it is effective to grind and use the one prepared and fired from the same material as the ceramic.

  The prepared ceramic substrate is molded into various shapes by various methods, dried, and then fired by selecting a firing temperature in the range of 1100 ° C to 1350 ° C. Regarding the firing temperature, the firing shrinkage ratio increases as the firing temperature increases. In addition, since the reaction is promoted as the firing temperature is increased, spinel crystals also grow reliably.

  First, it is impossible to satisfy heat resistance, alkali resistance, and thermal shock resistance with a single material (see Table 1, Refractory Handbook '99, Kyocera Corporation Characteristics Table, Ceramic Engineering Handbook, Ceramic Technology Assembly) Reference was made to alumina-based refractories, and the coefficient of thermal expansion is a value at 1000 ° C.). Regarding alkali resistance, there is almost no data corresponding to Li-resistant gas and its melt in the refractory-related data collection, but it can be considered as shown in Table 1 by analogy with Na gas data.

Zirconia and quartz react with Li ₂ O gas, and Li ₄ ZrO ₄ , Li ₄ SiO _{4 and the} like are produced and undergo volume expansion accompanying the absorption and release of CO ₂ due to repeated use, thereby degrading the reaction vessel. In particular, as described above, Li ₄ SiO ₄ has the specificity of absorbing 25% by weight of CO ₂ gas in the temperature range of 400 to 700 ° C. and releasing it at 700 ° C. As a result, partial volume expansion in the reaction vessel Increase in internal stress and distortion occur.

The inventors considered that the average thermal expansion coefficient should be 5 to 6 × 10 ⁻⁶ / ° C. or less, judging from industrial use conditions. Then, the selected material is necessarily reduced to spinel or spinel-cordierite eutectic. For example, if both are assumed to be 1: 1, the thermal expansion coefficient is 4.3 to 4.5 × 10 ⁻⁶ / ° C., and is 5.0 × 10 ⁻⁶ / ° C. or less. However, the temperature at which both crystals can coexist is 1370-1453 ° C (Mineral Engineering Bunpei Yoshiki 626 (1959)). As a result of searching for a method for crystallizing these even under lower temperature firing, as a result of the mica group mineral group (sericite, sea chlorite, etc.) having Na, K, Ca, Fe as a main component as an alkaline sintering aid. It was found that it would be effective if clay made of weathered material was used.
However, crystallization-type spinel grows at a high temperature firing of 1100 ° C. or higher, and the absolute thermal expansion is large. In order to avoid this, it is necessary to arrange escape pores in the vicinity of the spinel. In order to take advantage of the characteristics of spinel and withstand thermal shock, it was judged that there was only a method for introducing holes.

First, a reaction in which spinel and pores can be formed simultaneously by a uniform reaction was considered. In addition, considering the convenient method for forming ceramics, the raw material analysis values of aluminum sash industrial waste Al (OH) ₃ sludge, Sasame clay, and rhododendron are shown (Table 2-1). The substrate was prepared (Table 2-2).

Table 3 shows a base composition in which the clay component of the following compounding name 006 is replaced with a mica-based clay in which 10% by weight of 30% by weight is used as a baking aid and for improving moldability. Here, the total of Na ₂ O, K ₂ O, CaO, and Fe ₂ O _{3 serving} as firing aids is adjusted to be 5% by weight or less. This adjustment makes it possible to prepare a compound suitable for low-temperature sintering.
Table 4 shows the X-ray diffraction results of the sintered bodies at each temperature, which were fired in an electric furnace for 1 hour every 100 ° C from 600 ° C to 1300 ° C and every 50 ° C from 1300 ° C to 1400 ° C. did. Table 5 shows the firing shrinkage, bending strength, thermal expansion coefficient, and thermal shock resistance at each firing temperature.

From Table 4, if the reaction during the calcination is estimated, the rhodolite (MgCO ₃ ) remaining at 500 ° C. starts to change from amorphous MgO after decarboxylation to crystalline MgO (periclase) at 600 ° C. . Periclase continues to grow, but spinel begins to crystallize around 1100 ° C. and decreases. Cordierite begins to appear at 1200 ° C., and coexists with mullite, corundum, forest light, periclase, etc. at 1200 ° C. to 1300 ° C. There is no periclase around 1300 ° C, and only spinel and cordierite at 1350 ° C and above. FIG. 1 shows a powder X-ray diffraction pattern of the fired body at 1350 ° C. 2 shows changes in specific surface area at 600 ° C. to 1400 ° C., and FIG. 3 shows changes in apparent porosity. The specific surface area is measured by the BET method using N ₂ gas adsorption.
This shows that up to 1350 ° C., the apparent porosity exceeds 40% and the specific surface area exceeds 0.3 m ² / g.
According to the equilibrium diagram of the ternary system MgO—Al ₂ O ₃ —SiO ₂ , spinel and cordierite coexist at 1370 ° C. to 1453 ° C., but according to this example, 1200 ° C., which is a lower temperature than this. Coexisted at ˜1350 ° C. However, since spinel is crystallized from 1100 ° C. as described above, porous ceramics containing crystallized spinel can be obtained by selecting a range of 1100 ° C. to 1350 ° C. as the firing temperature.

From Table 5, the firing shrinkage ratio increased as the firing temperature increased. In particular, significant shrinkage was observed at 1350-1400 ° C. Thermal expansion coefficient is lower than 8.66 × ^{10 -6} / ℃ both at 1100 ° C. or higher.
Moreover, the bending strength increased as the firing temperature increased from 600 ° C to 1200 ° C. However, the bending strength decreased at 1300 ° C. and increased as the firing temperature increased. The thermal shock resistance is more effective than the thermal expansion coefficient value in terms of heat resistance, alkali resistance, and thermal shock resistance. found.

Al ternary for confirming the formulation ranges (OH) _3, gairome clay (which was purified by centrifuge as in Example 1), the diamond bitter debris, 6 patterns 001-006 illustrated in Table 6 The base was prepared at a ratio of 1 to 5 and formed into a rod-like test body similar to that in Example 1 by a mud casting method. This is air-dried and then placed in an electric furnace and X-ray diffraction identification crystals of each fired body fired at a temperature of 1400 ° C., and the thermal expansion coefficient and apparent pores of each fired body fired at a temperature of 1350 ° C. Table 6 shows the measurement results of the rate.

From Table 6, the identification result of X-ray diffraction shows that the compounded name 006 is a material containing crystallization type spinel as a main component and cordierite, and has the lowest thermal expansion coefficient.
Table 7 shows the firing shrinkage and apparent porosity of 500 ° C., 1100 ° C., and 1350 ° C. and the thermal shock test ΔT of the fired product fired at each temperature of 1100 ° C. and 1400 ° C. = 1000 ° C results are shown.

From Table 7, the firing shrinkage ratios of the respective fired bodies of 001 to 006 were all increased as the firing temperature increased to 500 ° C., 1100 ° C., and 1350 ° C. The apparent porosity was higher at 1100 ° C than at 500 ° C, and lower at 1350 ° C than at 1100 ° C. In the thermal shock test ΔT = 1000 ° C., the results of the 1100 ° C. fired product of 003 and the 1400 ° C. fired products of 001, 002, and 006 were good.
From the above results, the results of the formulation names 002 and 006 were good.

[Durability test as a reaction vessel]
Al (OH) ₃ , Sasame clay, and Rhizome stone are mixed at a ratio of 6 patterns 001 to 006 shown in Table 6 and formed into a reaction vessel φ85 × 45H and a wall thickness of 8 mm by the mud casting method. This was air-dried and then placed in an electric furnace and fired at a temperature of 1350 ° C. Then, the reaction of the following formula 1 (oxygen atmosphere 800 ° C. to 1000 ° C.) was performed in the container of each fired body, and the deterioration status due to lithium gas was compared with the number of service life. The reaction firing conditions were a temperature increase of 150 ° C./h and a keep time of 1000 ° C. for 1 h. The service life was determined by visually judging the deterioration state of the reaction vessel, and the time when cracking occurred was defined as the service life. Table 8 shows the difficulty of molding, the situation after firing, the number of times of use, and lithium resistance.
[Formula 1]
(O ₂₎
3 / 2Li ₂ CO ₃ + Co ₃ O ₄ → 3LiCoO ₂ + 3 / 2CO ₂ ↑

  According to the result of this test, the fired body material of the compound names 002, 004, 005, 006 was better than the conventional product. Based on the results of Example 2, if a plastic clay, an alumina component, and a bitter earth component are each blended at least 20% by weight, a porous ceramic having alkali resistance and thermal shock resistance and particularly suitable for a reaction vessel can be obtained. It became clear that it can be made industrially.

  In the preparation base shown in Table 3, in order to obtain a fired body having good moldability and less distortion, alkali-resistant spinel aggregates (average particle diameters of 3 mm, 1 mm, and 18 μm) of 10% by weight to 80% The mixture was mixed at different ratios in the range of% by weight. These substrates were press-molded with a mold (150 × 150 × 50H), dried, and then baked at 1350 ° C. for 2 hours in an electric furnace. Tables 9 to 11 show the firing shrinkage rate for each particle size. In addition, both the numbers of spinel and preparation are weight%. In addition, “molding” indicates moldability (good is ◯, defective is ×), and “fired” indicates the presence or absence of cracks (◯ when there is no crack, × when there is a crack).

  According to this example, in any case of three kinds of particle diameters, if the aggregate is mixed in the range of 10 wt% to 60 wt%, the firing shrinkage ratio of the base material in Table 3 is 11.2%. Thus, the firing shrinkage ratio of the base material with any addition ratio of the aggregate was less than 10%, and a suitable shrinkage suppressing effect was confirmed. Especially when the particle diameter is 1 mm and 18 μm, mixing is possible up to 65% by weight. Further, at the same aggregate ratio, the firing shrinkage tends to decrease as the particle diameter increases. Naturally, the contraction stops when the aggregates come into contact with each other during firing, and a large space corresponding to the aggregate particle diameter is formed, so that the apparent strength of the fired body decreases. In order to avoid a large space (hole), it is preferable to reduce the particle diameter of the aggregate. Preferably, the aggregate particles are not in contact with each other in the fired body.

Depending on the application, the particle size and mixing ratio of the aggregate to be added to the substrate need not be limited to the above examples. Further, the material of the aggregate is not limited to the spinel, but it is preferable to use a powder of a fired product made of the same material as the base material, and an aggregate of an alkali-resistant material can also be used.

It is a powder X-ray diffraction pattern of the sintered body (1350 degreeC) of the mixing | blending 006 base. It is a table | surface and a graph which show the specific surface area change of the sintered body (600-1400 degreeC) of the base material which replaced 10% of the clay content of 30% of the mixing 006 with the mica system clay. It is a table | surface and a graph which show the change of the apparent porosity of the baking body (600-1400 degreeC) of the base | substrate which replaced 10% of the clay content of 30% of the mixing 006 with the mica-type clay.

Claims (6)

The raw material mineral component containing Na, K, Ca, and Fe elements when mixing the plastic component from which quartz has been removed or finely ground, the alumina component, and the clay component, respectively, in an amount of 20% by weight or more. A porous material characterized in that the total amount of oxides therein is adjusted to be 5% by weight or less (excluding 0% by weight) of the whole and formed into a predetermined shape and fired at a temperature of 1200 ° C to 1350 ° C. Of manufacturing ceramics.   The method for producing a porous ceramic according to claim 1, wherein the aggregate made of ceramic particles is mixed and molded within a range of 10 wt% to 60 wt%. A porous ceramic obtained by the method for producing a porous ceramic according to claim 1 or 2, comprising crystallized spinel and cordierite, an apparent porosity of 40% or more, and a thermal expansion coefficient of 1000 ° C. And 6.66 × 10 ⁻⁶ / ° C. or less. A porous ceramic obtained by the method for producing a porous ceramic according to claim 1, comprising crystallized spinel and cordierite, an apparent porosity of 40% or more, and a thermal expansion coefficient of 6 at 1000 ° C. Porous ceramics characterized by having a specific surface area of 0.3 m ² / g or more by the BET method of .66 × 10 ⁻⁶ / ° C. or less .   The porous ceramic according to claim 3 or 4, which does not contain a quartz component. The porous ceramic according to claim 3 or 5 , wherein the fired body has an aggregate made of ceramic particles and has a firing shrinkage rate of less than 10%.

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