KR20140072345A - Cordierite composite having lower thermal expension coefficient and high strength and the manufacturing method of the same - Google Patents

Abstract

The present invention relates to a cordierite composite material having a low thermal expansion coefficient and high strength as a main material, which is devised by using cordierite effectively used as a material for an element for heat exchangers requiring high heat-resisting impact properties or a material for a catalyst carrier for exhaust purification as a mother material and a manufacturing method thereof. More specifically, the cordierite composite material with low thermal expansion coefficient and high strength can be easily prepared by mixing cordierite as a main ingredient, lithium aluminosilicate which is a low expansion material as a sintering aid and aluminum titanate, zircon, etc. as a reinforcing agent in predetermined amount so as to make mixed materials thereby lowering sintering temperature and widening the sintering temperature range.

Description

TECHNICAL FIELD The present invention relates to a cordierite composite material having a low thermal expansion coefficient and high strength and a manufacturing method thereof,

The present invention relates to a cordierite composite material having a low thermal expansion coefficient and high strength devised by using promising cordierite as a base material for a heat exchanger device or a catalyst support for purification of exhaust gas, More particularly, the present invention relates to a method for producing a composite material by using a cordierite as a main raw material, a lithium aluminosilicate as a sintering aid as a low heat expandable material and a certain amount of aluminum titanate and zirconium as a reinforcing agent, By lowering the sintering temperature range and widening the sintering temperature range, a dense cordierite composite material having low thermal expansion and high strength can be easily manufactured.

Considering that the material for a heat exchanger and the catalyst carrier for purification of exhaust gas are used in a harsh environment, it is required to have a thermal shock resistance so as to withstand a rapid temperature change between a high temperature and a room temperature. In addition, a low thermal expansion material having a low thermal expansion coefficient (<3 ppm / ), It must have compactness to prevent gas tightness and corrosion, have excellent mechanical properties in order to have a resistance to impact, and have various physical properties such as no phase change at operating temperature do.

Ceramic materials are mainly used for these devices and catalyst carrier materials, and metallic materials are limited in their use because of their poor corrosion resistance. Among such ceramic materials, non-oxide based materials such as silicon carbide or silicon nitride have advantages of high strength and high stability even at a high temperature of 1200 ° C or higher, but their use is limited due to high raw material cost and manufacturing cost, And when it is 1200 ° C or less, heat-resistant oxide-based materials are mainly used instead of silicon carbide or silicon nitride.

As having a low thermal expansion of these heat-resistant oxide-based material, cordierite _{(MAS: 2MgO · 2Al 2 O} 3 · 5SiO 2, thermal expansion coefficient: 2 ~ 3ppm / ℃), lithium aluminosilicate (LAS: Li ₂ O · Al _{2 O 3 · 2SiO 2, LAS2} : Li 2 O · Al 2 O 3 · 4SiO 2, thermal expansion coefficient: 0.1 ~ 2ppm / ℃), aluminum titanate _{(AT: Al 2 O 3 ·} TiO 2, the thermal expansion coefficient: 1 ~ 2ppm / ° C), and aluminosilicate (AS: Al ₂ O ₃ .SiO ₂ ) obtained by acid treatment of LAS materials and dissolving and removing Li ₂ O and re-firing. Among these, The most desirable material is cordierite.

However, the greatest problem with cordierite is that the densification is performed only within a narrow temperature range (<20 ° C) near the melting point in the production of the sintered body, and the sintering temperature condition is set The sintered body of relatively pure cordierite exhibits a high porosity due to the presence of a large amount of liquid phase due to the partial melting of the cordierite or low densification, and the high porosity of the cordierite sintered body is higher than that of the product And when used as a material of a heat exchanger element, acts as a cause of gas leakage.

That is, when an industrial baking furnace is used, there is a temperature gradient between the adjacent portion and the separated portion of the heating element of the baking furnace, and the temperature gradient is formed such that the adjacent portion of the heating element is high and the spacing is low. This temperature gradient may have a value of 50 DEG C or more depending on the position, which causes difficulty in setting the sintering temperature. The position of the thermocouple for measuring the sintering temperature is generally the center of the sintering furnace, and the sintering temperature is set by considering the temperature of the central portion of the sintering furnace as the reference sintering temperature.

If the sintering temperature is set normally, the cordierite placed at a position spaced apart from the heating element depending on whether the cordierite is adjacent to the heating element can be sintered normally according to the planned sintering temperature. However, The elite immediately reaches the melting temperature immediately after the sintering temperature is exceeded, and at least a part of the cordierite is melted, resulting in a sintered product of the defective product containing the liquid phase. On the other hand, if the sintering temperature is lowered considering the melting of the cordierite, the cordierite adjacent to the heating element can be sintered normally, but the cordierite at the position spaced apart from the heating element does not reach the sintering temperature, It can happen. That is, the narrow sintering temperature range of cordierite has a difficulty in giving much attention to the sintering process of cordierite.

Thus, US Patent No. 4,015,048 discloses a method of adding an alkali metal oxide as a method for widening the sintering temperature range of cordierite and a method of adding a rare earth metal oxide in US Patent No. 4,194,917. However, There is a disadvantage in that the physical properties of cordierite are lowered due to the formation of a large amount of liquid phase by the sintering aid.

Japanese Unexamined Patent Publication No. 55-27871 discloses a composite material production method in which aluminum titanate is added to cordierite to increase the sintering temperature range while preventing deterioration of cordierite properties. However, when sintering temperature is 1350 And the range of the sintering temperature to be applied is still narrow to 50 ° C or less, which makes it difficult to control the temperature of melting and sintering, so that it is still difficult to control the sintering temperature.

In order to solve this problem, Korean Patent Registration No. 79184 discloses a cordierite-cell cyan composite material to which Celsian (BaO.Al ₂ O ₃ .2SiO ₂ ) is added and a cordierite-cell cyan- However, the sintering conditions and the strength are not greatly improved, but the thermal expansion coefficient is greatly increased compared to cordierite.

The invention consists of a such, the present inventors have found that the BaO component in the cell cyan does not significantly effective in improving the sintering conditions and the strength is determined, and Li ₂ O component is used as a sintering aid made in view of solving the problems as described above, By adding at least any one of eucryptite or spodumine crystal structure compounds, which are aluminosilicate compounds, to form a composite phase together with a reinforcing agent such as aluminum titanate, a lower sintering temperature can be realized and a sintering temperature range can be widened Heat-expandable cordierite-based composite material composition having high density and high strength. The present invention has been accomplished on the basis of this finding.

Accordingly, it is an object of the present invention to provide a method for producing a sintered product by adding a proper amount of lithium aluminosilicate to prevent or improve the thermal expansion coefficient and strength property of cordierite, To prevent the melting of the cordierite in the course of the production of the cordierite composite material. Thus, the amount of the liquid phase formed is small and the porosity is low.

Another object of the present invention is to make it easier to control the sintering condition of the cordierite composite material, thereby contributing to the improvement of the yield of the cordierite sintered body.

In order to achieve the above-mentioned object, the present invention is characterized in that it comprises a cordierite, a lithium aluminosilicate, and at least one reinforcing agent selected from aluminum titanate and zircon. Based composite material composition.

The lithium aluminosilicate is preferably in an amount of more than 0 to 10 parts by weight based on the total weight of the composition.

The amount of the reinforcing agent is preferably in the range of more than 0 to 20 parts by weight based on the total weight of the composition.

The lithium aluminosilicate is preferably at least one selected from among compounds having a eucryptite crystal structure or a spodumine crystal structure.

The present invention also relates to a method for producing a composite material, comprising the steps of: mixing a mixture of cordierite, lithium aluminosilicate, at least one of aluminum titanate and zirconium, and pulverizing and drying the mixture; Molding the mixture; And sintering the mixture. The present invention also provides a method for producing a cordierite-based composite material.

The lithium aluminosilicate and the reinforcing agent are each preferably in an amount of more than 0 to 10 parts by weight, and more preferably more than 0 to 20 parts by weight based on the total weight of the composition.

The step of sintering the mixture is preferably carried out at a temperature in the range of 1250 to 1350 ° C.

Further, the present invention provides a cordierite composite material having a low thermal expansion coefficient and high strength, which is produced by the above-described production method.

INDUSTRIAL APPLICABILITY According to the present invention, sintering of a composite material using a cordierite-based composite material composition having low thermal expansion and high strength is expected to produce an action effect capable of producing a dense sintered body even though the sintering temperature is lowered. do.

Further, by lowering the sintering temperature, it is anticipated that the cost of the process can be reduced.

In addition, since the sintering temperature range is wide and the temperature gradient in the sintering furnace is easy to cope with, it is possible to reduce the amount of the liquid phase in the sintered body due to melting of the cordierite, thereby producing a high quality cordierite composite material , And an action and effect that can improve the yield are expected.

Further, it is expected that the coordinating-type composite material composition can be applied to a heat exchanger device or a material for catalyst support for exhaust gas purification, etc.

In addition, although the sintering temperature of the cordierite-based composite material is kept lower than that of the conventional cordierite-based composite material, an operation effect is expected to be able to sufficiently maintain predetermined physical properties required for applications such as high strength and low thermal expansion.

FIG. 1 is a graph showing the density change of a cordierite-lithium aluminosilicate-aluminum titanate composite material according to an embodiment of the present invention.
2 is a graph showing the density change of a cordierite-lithium aluminosilicate-zircon composite material according to an embodiment of the present invention.
3 is a graph showing the density change of a cordierite-lithium aluminosilicate-aluminum titanate-zircon composite according to an embodiment of the present invention.
FIG. 4 shows X-ray analysis results of a cordierite-lithium aluminosilicate-titanate and cordierite-lithium aluminosilicate-zircon composite according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings and preferred embodiments.

The present invention relates to an oxide composite material having low thermal expansion and high strength using a cordierite as a base material which can be applied as a material for a heat exchanger and a catalyst carrier for purification of exhaust gas, which requires high heat shock resistance, Together with lithium aluminosilicate as a sintering aid and a certain amount of aluminum titanate and zircon as a reinforcing agent, the sintering temperature is lowered and the sintering temperature range is wide. The present invention relates to a cordierite composite material composition having excellent low thermal expansion performance and high strength in spite of lowering sintering temperature as well as easily producing a dense sintered body by reducing the amount of liquid phase in the sintered body by preventing melting, will be.

<Composition examples>

The composition ratio of the cordierite-based composite material composition having low thermal expansion and high strength according to the present invention may be specifically expressed by the following formula: (100-xy) cordierite + x lithium aluminosilicate + y represents the respective weight%, x is adjusted to within 10 wt%, and y is adjusted to within 20 wt%.

The lithium aluminosilicate is not suitable because it causes a decrease in strength when it exceeds 10% by weight as a sintering auxiliary agent, and the reinforcing agent is at least one selected from aluminum titanate and zircon compounds. When it exceeds 20% by weight, the lithium aluminosilicate is inhibited from being densified In order to easily produce a dense sintered body by lowering the sintering temperature and ensuring a wide sintering temperature range, the above-mentioned composition range is preferable and its critical significance is present.

However, it is also possible to increase the addition amount of lithium aluminosilicate and reinforcing agent above the above-mentioned value, provided that a commercially available strength can be secured. In other words, there is a primary significance that lithium aluminosilicate is used, and it is of secondary importance that the content of lithium aluminosilicate is controlled for improvement of physical properties.

<Production Example>

The cordierite composite material composition having low thermal expansion and high strength of the present invention can be easily produced by the following general oxide mixing method.

Here, the composite material composition means a composition before sintering, and after sintering, it is called a composite material.

First, a natural raw material or a reagent grade compound containing components such as Al ₂ O ₃ , SiO ₂ , MgO, Li ₂ O, TiO ₂ and ZrO ₂ is used as a raw material composition, and cordierite, Tide or a compound having a spodumine crystal structure, aluminum titanate and / or zircon, to prepare respective raw material mixtures, and then these raw material mixtures are mixed and crushed using an alumina ball mill.

In the present invention, cordierite, which serves as a base material of the composite material, is prepared by adding a small amount of MgO and Al ₂ O ₃ based on kaolin and caustic soda from Indonesia, and other additive compounds are prepared by using reagent grade compounds as basic raw materials Respectively.

Here, the raw materials may be present in the form of a compound or exist in the form of a salt. In the derivation of the composite material composition according to the present invention, the shape, grade and quantitative composition ratio of the starting material can be controlled and selected appropriately, It shall not be specifically listed. However, it is needless to say that the ratio should be adjusted so that the critical meaning according to the composition ratio is characteristic of the present invention.

The cordierite mixture serving as a base material of the composite material in the raw material mixture is calcined at a temperature in the range of 1100 to 1300 ° C after drying, and the eucryptide and / or the spodumene added to the sintering aid in the composite material is calcined at 1000 to 1100 ° C, Aluminum titanate and / or zircon compounds added as a reinforcing agent are synthesized at 1300 to 1500 ° C to prepare respective synthetic powders.

However, the synthesis temperature condition of each raw material is not limited to the above, and it goes without saying that it is variable depending on the synthesis method.

As shown in the following Table 1, the synthesized powders obtained through such a process were each weighed to an amount contained within the composition range of the composite material of the present invention, and then mixed and pulverized using an alumina ball mill. And then sintered in a temperature range of 1250 to 1400 DEG C to obtain an oxide composite material of the present invention.

Characteristics of low expansion, high strength cordierite composite material composition number MAS
(wt%) LAS
(wt%) LAS2
(wt%) AT
(wt%) ZS
(wt%) Sintering temperature (℃) Relative density
(%) Flexural strength
(Mpa) Thermal Expansion Coefficient (ppm /) Example 1 95 5 0 0 0 1350 98.6 122 0.91 Example 2 90 10 0 0 0 1325 98.1 100 0.784 Example 3 95 0 5 0 0 1400 98.8 125 1.25 Example 4 90 0 10 0 0 1375 98.3 113 0.837 Example 5 85 5 0 10 0 1300 99.1 150 2.121 Example 6 75 5 0 20 0 1300 99.9 160 2.842 Example 7 80 10 0 10 0 1250 99.8 153 1.934 Example 8 70 10 0 20 0 1250 100 172 2.423 Example 9 85 5 0 0 10 1350 99.1 137 2.011 Example 10 75 5 0 0 20 1350 99.9 131 1.316 Example 11 80 10 0 0 10 1300 98.1 142 1.845 Example 12 70 10 0 0 20 1300 99.2 122 1.215 Example 13 85 5 0 5 5 1250 99.6 143 2.085 Example 14 75 5 0 10 10 1250 99.8 155 1.875 Example 15 80 10 0 5 5 1250 99.5 148 1.835 Example 16 70 10 0 10 10 1250 99.3 162 1.687 Comparative Example 1 90 10% Celsian 1300 - 97 1.9 Comparative Example 2 70 10% Celsian 20% AT 1350 - 133 3.5

_{MAS: 2MgO · 2Al 2 O 3} · 5SiO 2,

_{LAS: Li 2 O · Al 2} O 3 · 2SiO 2,

LAS2: Li ₂ O.Al ₂ O ₃ .4SiO ₂ ,

AT: Al ₂ O ₃ .TiO ₂ ,

ZS: ZrO ₂ .SiO ₂ ,

_{Celsian: BaO · Al 2 O 3} · 2SiO 2

Comparative Example: Korean Registered Patent No. 79184

&Lt; Evaluation example &

The sintered body thus obtained was evaluated for sinterability, crystal analysis, strength and thermal expansion coefficient, and the desired properties were evaluated. Through such a manufacturing process, the sintering temperature was lowered and the sintering temperature range was broadly secured. The sintered compact of the cordierite composite material can be easily manufactured which is dense, low heat expandable and high strength.

The sinterability of the prepared specimens was evaluated by the linear shrinkage and the density measurement by the Archimedes method. The sinterability was evaluated by the three point method according to ASTM E855-84, and the thermal expansion coefficient was measured at 40 to 800 ° C. according to ASTM D696-79 . X-ray diffraction analysis was also performed to examine the reaction between the constituents during sintering.

<Result>

FIG. 1 and FIG. 2 are schematic cross-sectional views illustrating a method of manufacturing a lithium secondary battery according to a preferred embodiment of the present invention. FIG. 1 is a cross- The densification starting temperature is 1250 ° C., and the densities of the sintered bodies at 1350 ° C. are almost equal to each other. According to FIGS. 2 and 3, The temperature was 1275 占 폚 and the density was almost equal to that of the sintered body at 1350 占 폚 Respectively show a stable sintering range of 100 DEG C or more and 75 DEG C or more. This shows that the sintering range of the composition as a cordierite starter generally becomes broader than that of less than 20 DEG C, and the comparative cordierite- - In comparison with aluminum titanate composite material, it has advantages in sintering temperature and sintering range.

The characteristics of the sintered cordierite composite material according to the present invention shown in Table 1 are as follows: the strength (100 MPa or less) and the thermal expansion coefficient (2 to 3 ppm / ° C.) It was found that the characteristics were improved in all the composition ranges as compared with the cordierite-cel-cyanititanate composite material of the comparative example. In comparison with the cordierite-cel-cyanititanate composite material of the comparative example, It can be seen that the bending strength characteristics of the composite material to which at least one of aluminum and zircon are added is remarkably improved as compared with the examples and comparative examples of other composite materials.

That is, as can be seen from Table 1, within a range having a thermal expansion coefficient that can be used for commercialization It is possible to produce a composite material having a more enhanced strength value.

The sintering temperature range is preferably 1250 to less than 1400 ° C, more preferably 1205 to 1350 ° C. When the sintering temperature is lower than 1250 DEG C, it is difficult to ensure the desired strength. When the sintering temperature is higher than 1400 DEG C, the composite material is likely to be melted, which is not preferable. Therefore, the sintering temperature is critical in the above range, The sintering temperature must be maintained to completely eliminate the risk of melting. Further, the upper limit of the sintering temperature is maintained at a lower temperature under the condition that the thermal expansion coefficient is kept under a condition that maintains a superior strength compared with the sintering temperature of the conventional composite material, and a sintering temperature as low as 1300 캜 in Comparative Example 1 is maintained, In Comparative Example 2, the sintering temperature was raised to 1350 DEG C, and the strength value was increased to 133 MPa. However, since the thermal expansion coefficient is too high to be 3.5 ppm / DEG C, the superiority of the present invention is proved .

As can be seen from the X-ray analysis results of the sintered body shown in FIG. 4, these results show that the added materials together with the cordierite base material form a stable composite material in which a secondary phase or an amorphous phase is not formed besides aluminum titanate and zircon It can be seen that the functional role of the composite material is performing as intended. That is, it is confirmed that the amorphous phase does not exist and is not melted, and it can be deduced that the strength is sufficiently improved because the second phase is not produced.

In addition, the cordierite-based composite material produced according to the present invention exhibits sintering properties and strength characteristics when aluminum aluminate or zircon, which is a strengthening agent, is added to the cordierite as a sintering aid, instead of lithium aluminosilicate alone , The strength is aluminum titanate, and the coefficient of thermal expansion is effective when zircon is added.

As can be seen from the above results, the coefficient of thermal expansion and the strength are the most important factors that determine the thermal shock resistance of the material. Therefore, the cordierite composite material of the present invention is a combination of monodisperse cordierite and cordierite-cell cyan- The sintering temperature is low and the sintering range is wide, so that it is possible to more easily manufacture a dense sintered body stably.

In short, the present invention derives the distinguished effect that the cordierite, the lithium aluminosilicate and the reinforcing agent are organically bonded to each other to lower the sintering temperature, expand the sintering temperature range, and realize high strength and low thermal expansion.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the invention is not limited to the disclosed exemplary embodiments. will be.

Claims (8)

A cordierite composite material composition having a low thermal expansion coefficient and a high strength, the composite material composition comprising cordierite, lithium aluminosilicate, and at least one reinforcing agent selected from aluminum titanate and zircon. The method according to claim 1,
Wherein the lithium aluminosilicate is in a weight ratio of not less than 10 and not more than 10 based on the total weight of the composition, and has a low thermal expansion coefficient and high strength. 3. The method according to claim 1 or 2,
Wherein the reinforcing agent is a weight ratio of not less than 20 and not more than 20 with respect to the total weight of the composition, and has a low thermal expansion coefficient and high strength. 3. The method according to claim 1 or 2,
Wherein the lithium aluminosilicate is at least one selected from among compounds having a eucryptite crystal structure or a compound having a spodumene crystal structure, and has a low thermal expansion coefficient and high strength. Preparing a mixture by mixing, pulverizing and drying cordierite, lithium aluminosilicate, at least one of aluminum titanate and zirconium;
Molding the mixture; And
Sintering the mixture;
Based composite material according to claim 1, 6. The method of claim 5,
Wherein the lithium aluminosilicate and the reinforcing agent are each in an amount of more than 0 to 10 parts by weight and more than 0 to 20 parts by weight based on the total weight of the composition, . The method according to claim 6,
Wherein the step of sintering the mixture is carried out at a temperature in the range of 1250 to 1350 DEG C, and a method of producing the cordierite composite material having a low thermal expansion coefficient and high strength. A cordierite-based composite material having a low thermal expansion coefficient and high strength, which is produced by the manufacturing method of claim 5.

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