KR102644852B1 - Synthesis of low thermal expansion cordierite ceramics using kaolin group minerals and cordierite ceramics with low thermal expansion thereof - Google Patents

Abstract

The present invention provides a method for manufacturing low thermal expansion cordierite ceramics containing kaolin minerals to improve the difficult firing conditions of kaolin minerals in MAS-based cordierite with low thermal expansion and increase mechanical properties, and a low thermal expansion cordierite containing kaolin minerals using the same. It relates to a light-based ceramic composition.
The method for manufacturing low thermal expansion cordierite ceramics containing kaolin mineral according to the present invention includes halloysite kaolin, clay, kaolinite kaolin, talc, and aluminum oxide (Al ₂ O ₃ ) and magnesium oxide (MgO) to prepare a raw material mixture; A second step of milling the raw material mixture using a ball mill and a pot mill; A third step of press molding by applying pressure to the milled raw material mixture; A fourth step of drying the press molded raw material mixture; A fifth step of sintering the dried raw material mixture by firing it in an oxidizing atmosphere.

Description

Method for manufacturing low-thermal expansion cordierite ceramics using kaolin minerals and low-thermal expansion cordierite-based ceramic compositions containing kaolinite minerals using the same

The present invention is to improve difficult firing conditions and increase mechanical properties by using optimal mixing conditions using kaolin minerals (clay, kaolin, talc) to produce MAS-based cordierite ceramics with low thermal expansion coefficient (coefficient). The present invention relates to a low-thermal expansion cordierite ceramic manufacturing method for low-cost synthesis of cordierite synthetic powder with a composition of kaolinite mineral under optimal conditions and a low-thermal expansion cordierite-based ceramic composition containing kaolinite mineral using the same.

Ceramics generally have low thermal conductivity, so when they experience a sudden temperature change, a significant thermal gradient occurs within the material, and stress occurs due to volume change. The surface of the material undergoes compressive stress as the temperature rises, but most materials have high compressive strength, so they are less susceptible to damage due to temperature rise. However, when the temperature drops suddenly, the surface of the material undergoes tensile stress and breaks. Therefore, the main method for developing ceramic materials with high thermal shock resistance is to reduce stress within the material due to thermal shock by inducing a low thermal expansion coefficient. Materials with a representative MAS (MgO-Al ₂ O ₃ -SiO ₂ )-based composition are attracting attention as mechanical structural materials despite their weaknesses in mechanical properties. This is due to the possibility of developing heat-resistant materials by applying their low thermal expansion characteristics. . In the case of MAS-based cordierite (2MgO·2Al ₂ O ₃ ·5SiO ₂ ), it exhibits properties such as low thermal expansion coefficient, thermal shock resistance, low dielectric constant, and high electrical insulation, but pure cordierite has a plasticity range when synthesized. is very narrow, so if the sintering temperature is 5℃ lower, no crystals are formed, and if it is even slightly higher, cordierite decomposes back into postelite, spinel, and mulite, etc., and the thermal expansion coefficient of the material decreases. will increase significantly.

Despite these difficult firing conditions, the thermal expansion rate is very low and the raw materials are easy to procure, so the utilization is very high. Accordingly, research is underway to synthesize high-purity fine cordierite synthetic powder at low cost. Materials that require thermal shock resistance are used for industrial purposes. Recently, lithium-ion anode materials have been used for box refractories for raw material firing and ceramic filters for high-temperature air purification and water purification. They have high specific gravity and high heat capacity, so they are expensive, have low thermal shock resistance, and cannot be rapidly heated or quenched. There is a problem in that it becomes difficult for gases from organic materials to be discharged during firing. Therefore, in order to improve this problem, the present invention conducted research and development tests on the properties of cordierite by synthesizing it using kaolin.

(Non-patent Document 1) D. Kim, H. T. Kim, S. S. Ryu and H. J. Kim, Korean J. Met. Mater. 53, 16 (2015).

The present invention was created to solve the above problems, and the purpose of the present invention is to manufacture a low-thermal expansion cordierite ceramic containing kaolin mineral to solve problems that may occur when the firing range of MAS-based cordierite is exceeded. is to provide.

The technical problems to be solved by the invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below. You will be able to.

The method for manufacturing low thermal expansion cordierite ceramics containing kaolin mineral according to the present invention,

The first step of producing a raw material mixture by mixing halloysite kaolin, clay, kaolinite kaolin, talc, aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO). ;

A second step of milling the raw material mixture using a ball mill and a pot mill;

A third step of press molding by applying pressure to the milled raw material mixture;

A fourth step of drying the press molded raw material mixture;

A fifth step of sintering the dried raw material mixture by firing it in an oxidizing atmosphere.

The magnesium oxide (MgO)/aluminum oxide (Al ₂ O ₃ ) mole ratio of the mixture of halloysite kaolin, clay, and kaolinite kaolin is 0.9 to 1.1. It is characterized by In addition, the silicon dioxide (SiO ₂ )/aluminum oxide (Al ₂ O ₃ ) mole ratio of the mixture of halloysite kaolin, clay, and kaolinite kaolin is 2.4 to 2.4. It is characterized by 2.6.

When maintained at 1,380°C for 1 hour after sintering in the fifth step, the thermal expansion coefficient is 2.20×10 ^-6 /°C at 800°C. In addition, when maintained at 1,380°C for 1 hour after sintering in the fifth step, the thermal expansion coefficient is 2.57×10 ^-6 /°C at 1,000°C.

In the first step, the raw material mixture contains 34.00 (w/w)% of Halloysite Kaolin, 20.00 (w/w)% of Clay, and 12.50 (w/w)% of Kaolinite Kaolin. , 18.90 (w/w)% of talc, 9.30 (w/w)% of aluminum oxide (Al ₂ O ₃ ), and 5.30 (w/w)% of magnesium oxide (MgO) are mixed.

In addition, the low thermal expansion cordierite-based ceramic composition containing kaolin mineral according to the present invention,

It is characterized in that it contains halloysite kaolin, clay, kaolinite kaolin, talc, aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO).

The low thermal expansion cordierite-based ceramic composition containing the kaolin mineral,

The bending strength is 52 to 54 N according to the KS L 1591 standard method, the bulk specific gravity is 2.00 or less, and the moisture absorption rate according to KS L 3412 is 8.0 to 9.0%.

In addition, a filter containing a low thermal expansion cordierite-based ceramic composition containing kaolin mineral according to the present invention,

It is characterized in that it contains halloysite kaolin, clay, kaolinite kaolin, talc, aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO).

As a means of solving the above problem, the present invention solves problems that may occur when the MAS-based cordierite is outside the firing range and provides a low thermal expansion cordier that exhibits the characteristics of low thermal expansion coefficient, thermal shock resistance, low dielectric constant and high electrical insulation. A light ceramic manufacturing method can be provided.

Additionally, the present invention can provide optimal mixing conditions for producing low thermal expansion cordierite ceramic.

In addition, the present invention can provide conditions for developing cordierite ceramic materials considering physical properties and shrinkage rate.

Figure 1 is a flow chart showing the method of manufacturing low thermal expansion cordierite ceramic including kaolin mineral according to the present invention.
Figure 2 is a graph showing the pulverized particle size distribution of raw materials according to an embodiment of the present invention.
Figure 3 is a graph showing the shrinkage results due to the formation of cordierite crystals according to the raw material combination at various temperatures according to an embodiment of the present invention.
Figure 4 is a graph showing the results of bending strength due to the formation of cordierite crystals according to the raw material mix at various temperatures according to an embodiment of the present invention.
Figure 5 is a graph showing the results of moisture absorption rate by cordierite crystal formation according to raw material mixing at various temperatures according to an embodiment of the present invention.
Figure 6 is a graph showing the results of volume specific gravity due to the formation of cordierite crystals according to the mixing of raw materials at various temperatures according to an embodiment of the present invention.
Figure 7 is a graph showing the porosity results due to cordierite crystal formation according to raw material mixing at various temperatures according to an embodiment of the present invention.
Figure 8 is a graph showing the results of measuring the coefficient of thermal expansion due to the formation of cordierite crystals according to the mixing of raw materials according to an embodiment of the present invention.
Figure 9 is an XRD result of cordierite crystals calcined at a temperature of 1,200 to 1,380°C according to an embodiment of the present invention.
Figure 10 is an SEM result of cordierite crystals calcined at a temperature of 1,220°C according to an embodiment of the present invention.
Figure 11 is an SEM result of cordierite crystals calcined at a temperature of 1,260°C according to an embodiment of the present invention.
Figure 12 is an SEM result of cordierite crystals calcined at a temperature of 1,300°C according to an embodiment of the present invention.
Figure 13 is an SEM result of cordierite crystals calcined at a temperature of 1,340°C according to an embodiment of the present invention.
Figure 14 is an SEM result of cordierite crystals calcined at a temperature of 1,380°C according to an embodiment of the present invention.

The terms used in this specification will be briefly explained, and the present invention will be described in detail.

The terms used in the present invention are general terms that are currently widely used as much as possible while considering the function in the present invention, but this may vary depending on the intention or precedent of a person working in the art, the emergence of new technology, etc. Therefore, the terms used in the present invention should be defined based on the meaning of the term and the overall content of the present invention, rather than simply the name of the term.

When a part in the entire specification is said to “include” a certain element, this means that it does not exclude other elements but may further include other elements, unless specifically stated to the contrary.

Below, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein.

Specific details, including the problem to be solved by the present invention, the means for solving the problem, and the effect of the invention, are included in the examples and drawings described below. The advantages and features of the present invention and methods for achieving them will become clear by referring to the embodiments described in detail below along with the accompanying drawings.

In general, it is known that the polymorphism of cordierite crystals exists in three phases: α, β, and μ. Alpha cordierite crystals are stable at high temperatures, while beta cordierite crystals are relatively unstable and the transition from β type to α type occurs around 830°C. Cordierite crystals exhibit unique thermal properties of anisotropic thermal expansion along the crystal axis direction, and are known to have 2.9x10 ^-6 /℃ in the a-axis direction and -1.1x10 ^-6 /℃ in the c-axis direction. This anisotropy is influenced by the orientation of the raw materials used for synthesis, but it causes a difference in thermal expansion behavior when heated and cooled, causing micro cracks in the crystal grains, which reduces mechanical strength. In order to improve mechanical strength, a study was conducted to increase strength by adding mulite (3Al ₂ O _3· 2SiO ₂ ) to cordierite and sintering it at high temperature.

Materials with MAS (MgO-Al ₂ O ₃ -SiO ₂ )-based compositions are attracting attention as mechanical structural materials despite their weaknesses in mechanical properties. This is due to the possibility of developing heat-resistant materials by applying their low thermal expansion characteristics. In the case of MAS-based cordierite (2MgO·2Al ₂ O _3· 5SiO ₂ ) crystal, it exhibits properties such as low thermal expansion coefficient, thermal shock resistance, low dielectric constant, and high electrical insulation, but the firing range during synthesis is very narrow, making it difficult to sinter. If the temperature is low, cordierite crystals are not sufficiently formed, and if the temperature is even slightly high, cordierite decomposes back into postelite, spinel, and mullite, and the coefficient of thermal expansion of the material increases significantly. I do it.

In order to solve this problem, the present invention adjusts the mixing range of clay minerals in the cordierite composition and manufactures optimal cordierite ceramic by checking the thermal expansion coefficient, bending strength, bulk specific gravity, and moisture absorption rate according to firing conditions. did.

Hereinafter, the present invention will be described in more detail with reference to the attached drawings.

The method for manufacturing low thermal expansion cordierite ceramic containing kaolinite mineral according to the present invention is as shown in Figure 1 and is described in more detail below.

First, in the first step (S10), halloysite kaolin, clay, kaolinite kaolin, talc, aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO) are mixed. To prepare the raw material mixture.

More specifically, the raw material mixture contains 34.00 (w/w)% of halloysite kaolin (HK), 20.00 (w/w)% of clay (CL), and 12.50 (w/w)% of kaolinite kaolin (NK) ( w/w)%, talc (TL) 18.90 (w/w)%, aluminum oxide (Al ₂ O _3, AL) 9.30 (w/w)% and magnesium oxide (MgO, MG) 5.30 (w/w) )% mixing is desirable.

The chemical composition of kaolin-talc-alumina raw materials used for cordierite synthesis is shown in Table 1.

Chemical composition
(%) SiO ₂ Al ₂ O ₃ Na ₂ O _K2O CaO MgO _{Fe2O3 _} TiO ₂ SO ₃ particle
Size (㎛) HK 51.42 31.72 0.03 0.80 1.80 0.31 0.12 0.03 13.7 7.0 CL 52.90 31.20 0.34 0.59 0.15 0.10 1.27 0.67 12.78 5.00 NK 48.10 36.80 0.86 1.24 0.04 0.07 0.39 0.01 12.49 5.00 Talc 54.58 0.38 0.00 0.01 2.05 35.78 0.20 0.00 7.00 2.80 Al ₂ O ₃ 0.02 99.97 0.01 - - - - - - 5.00 MgO 0.00 0.00 0.02 - - 99.60 0.38 - - 7.00 HK: Halloysite Kaolin, NW: Kaolinite Kaolin, CL: Clay

The MgO source was talc (Sandong, China), and the Al ₂ O ₃ source was alumina (DCP-05, Daehan ceramics Ltd, Korea) with an average particle size of 0.5 μm considering sinterability. Considering the formation of the cordierite crystal phase, kaolin is composed of kaolin (PA, Pungsan mineals, Korea), which has a tubular haloysite crystal phase with few impurities other than Fe ₂ O ₃ , and plate-shaped kaolinite crystal phase. It is kaolinite kaolin (Auckland, New Zealand), and the clay is based on China Clay (Honyama, China) and clay minerals, and insufficient amounts of Al ₂ O ₃ and MgO were added.

If the raw material mixture contains more than 12.50 (w/w)% of kaolinite kaolin (NK), peeling occurs during molding, so it is preferable to carry out the above conditions.

In addition, it is higher than the theoretical cordierite magnesium oxide (MgO)/aluminum oxide (Al ₂ O ₃ ) mole ratio of 1.0 and the silicon dioxide (SiO ₂ )/aluminum oxide (Al ₂ O ₃ ) mole ratio of 2.5. Aluminum oxide (Al ₂ O ₃ ) and magnesium oxide (MgO) were maintained, and the silicon dioxide (SiO ₂ ) content was reduced from 0.84% to a maximum of 1.9% by weight.

Next, in the second step (S20), the raw material mixture is milled using a ball mill and a pot mill. More specifically, the raw material mixture was milled in a ball mill and a pot mill for 24 hours, respectively, and then a particle size equivalent to the standard sieve of 44 ㎛ was used.

Next, in the third step (S30), press molding is performed by applying pressure to the milled raw material mixture. More specifically, the milled raw material mixture is press molded at a pressure of 200 kg/cm2.

Next, in the fourth step (S40), the raw material mixture subjected to press molding is dried. More specifically, it is dried at 100 to 120° C. for 3 hours.

Next, in the fifth step (S50), the dried raw material mixture is sintered in an oxidizing atmosphere. More specifically, it is fired at 1,220 to 1,380°C and then sintered for 3 hours.

When maintained at 1,380°C for 1 hour after sintering in the fifth step (S50), the thermal expansion coefficient is 2.20×10 ^-6 /°C at 800°C. In addition, when maintained at 1,380°C for 1 hour after sintering in the fifth step (S50), the thermal expansion coefficient is 2.57×10 ^-6 /°C at 1,000°C.

The low-thermal expansion cordierite-based ceramic composition containing kaolinite mineral of the present invention is preferably manufactured by the method for manufacturing low-thermal expansion cordierite-based ceramic containing kaolinite mineral described above, and is the same as the technical composition described above.

The low thermal expansion cordierite ceramic composition containing the kaolin mineral includes halloysite kaolin, clay, kaolinite kaolin, talc, aluminum oxide (Al ₂ O ₃ ), and magnesium oxide. It is characterized in that it contains (MgO). More specifically, the Halloysite Kaolin 34.00 (w/w)%, Clay 20.00 (w/w)%, Kaolinite Kaolin 12.50 (w/w)%, talc It is preferable to mix 18.90 (w/w)%, aluminum oxide (Al ₂ O ₃ ) 9.30 (w/w)%, and magnesium oxide (MgO) 5.30 (w/w)%.

The low thermal expansion cordierite ceramic composition containing the kaolin mineral is magnesium oxide (MgO)/aluminum oxide (Al ₂ O) of a mixture of halloysite kaolin, clay, and kaolinite kaolin. ₃ ) It is characterized by a mole ratio of 0.9 to 1.1. In addition, the silicon dioxide (SiO ₂ )/aluminum oxide (Al ₂ O ₃ ) mole ratio of the mixture of halloysite kaolin, clay, and kaolinite kaolin is 2.4 to 2.4. It is characterized by 2.6.

The low thermal expansion cordierite ceramic composition containing the kaolin mineral is characterized by a thermal expansion coefficient of 2.20 × 10 ^-6 / ℃ at 800 ℃ and a thermal expansion coefficient of 2.57 × 10 ^-6 / ℃ at 1,000 ℃.

The low thermal expansion cordierite-based ceramic composition containing the kaolin mineral is characterized in that the bending strength KS L 1591 is 52 to 54 N, the bulk specific gravity is 2.00 or less, and the moisture absorption rate according to KS L 3412 is 8.0 to 9.0%. .

The filter containing the low-thermal expansion cordierite-based ceramic composition containing the kaolin mineral of the present invention is preferably manufactured by the low-thermal expansion cordierite-based ceramic composition containing the kaolin mineral described above, and includes the kaolin mineral described above. It is the same as the technical composition of the low thermal expansion cordierite ceramic composition.

Below, comparative examples and examples are shown in Table 2 under different mixing conditions of the raw material mixture according to one embodiment of the method of manufacturing low thermal expansion cordierite-based ceramics containing kaolinite mineral according to the present invention.

com-
pounding compounding ratio (wt%) HK CL NK T.L. AL MG SUM Comparative Example 1: C-1 66.50 - - 18.90 9.30 5.30 100 Comparative Example 2: C-2 - 66.50 - 18.90 9.30 5.30 100 Comparative Example 3: C-3 34.00 32.50 - 18.90 9.30 5.30 100 Example 1: C-4 34.00 20.00 12.50 18.90 9.30 5.30 100 HK: Halloysite Kaolin, NW: Kaolinite Kaolin, CL: Clay, TL: Talc, AL: Al ₂ O ₃ , MG: MgO

The raw material combination for the synthesis of cordierite was milled for 24 hours in a ball mill and pot mill, respectively, as shown in Table 2, and a particle size of 4 ㎛ was used. In order to examine the effectiveness of cordierite synthesis using these kaolinite minerals, the combination was conducted based on the theoretical composition of cordierite: MgO 13.8%, Al ₂ O ₃ 34.9%, SiO ₂ 51.3%. Table 3 shows the mixing ratio of the sample based on a mole ratio of MgO/Al ₂ O ₃ of 1.0 and a mole ratio of SiO ₂ /Al ₂ O ₃ of 2.5.

NO. Chemical component mole, ratio 800
×10 ^-6 /℃ 1,000
x10 ^-6 /℃ SiO ₂
(wt%) Al ₂ O ₃
(wt%) MgO
(wt%) MgO/Al ₂ O ₃
(mole rate) SiO ₂ /Al ₂ O ₃
(mole rate) C-1 49.73 34.00 13.71 1.0270 2.4860 2.28 2.66 C-2 50.46 33.36 13.45 1.0275 2.5029 2.51 2.91 C-3 50.08 33.68 13.58 1.0272 2.4601 2.45 2.87 C-4 49.40 34.45 13.57 1.0059 2.4277 2.20 2.57 st 51.30 34.90 13.80 1.0087 2.4782

Mixing and grinding of the materials was carried out using alumina balls of various sizes in an alumina pot mill with a capacity of 300 cc. 90 c of water was added to 100 g of material and milled for 24 hours, and 85-90% of the pulverized mixed powder was adjusted to have a particle size of 10 ㎛ or less. Particle size analysis (Particle Size Analyzer) measured dynamic light scattering particle size distribution using Horiba's LA-950, and the measurement range was 0.1 to 8,00 nm. In addition, three items (nanoparticle measurement, zeta potential measurement, and molecular weight measurement) were additionally analyzed with high sensitivity and high accuracy for the evaluation of single nanoparticles.

The specimens of the comparative examples and examples in Table 2 were manufactured using a hand press process using a mold with a molding pressure of 20 kg/cm2 to produce a circular specimen of Φ30 mm and a rectangle bar of size 20 x 5 x 10 mm. The specimen was manufactured by dry molding and dried at 10 ℃ for 24 hours, then fired in an electric furnace in an oxidizing atmosphere at a temperature increase rate of 2 ℃/min at 1,220 ℃, 1,260 ℃, 1,300 ℃, 1,340 ℃, and 1,380 ℃ for 2 hours at each temperature. maintained.

Below, the present invention addresses the disadvantage of high manufacturing costs when using synthesized cordierite, examines the synthesis conditions and sintering behavior by using talc-alumina-clay multi-component natural raw materials for high thermal shock resistance, and develops new natural raw materials. The effect of changes in addition amount on the sintering behavior of cordierite was examined.

(1) Measurement of moisture shrinkage rate

For the shrinkage rate, specimens were molded at 30 mm intervals using a vernier caliper, and after drying and firing, the change in length of each specimen was measured based on KS L 3412.

(2) Modulus of Rupture (MOR)

The bending strength is defined as the maximum tensile stress on the surface of the specimen that breaks when bent according to the KS L 1591 standard method. In ceramics, the alumina bending strength test is very frequently used. Common specimen shapes include bars or beams with cylindrical or rectangular cross-sections, or round, square, or rectangular plates. Here, b is the width of the specimen, and d is the thickness of the specimen. The three-point bending strength is бf =3pl/2bd ² , where p is the breaking load and l is the distance between the supporting points.

(3) Absorption rate, volume specific gravity, and porosity

1) The water absorption rate is a value expressed as a percentage of the water absorption per unit weight. The water absorption rate test was calculated by calculating the absolute dry mass and standard dry mass of the test specimen according to KS L 3412.

2) Bulk Density (BD)

It refers to the weight specific gravity of the volume of the test specimen.

3) Apparent Porosity (AP)

Apparent porosity (%) represents the volume occupied by open pores in the total volume of the test specimen as a percentage.

(4) Thermal expansion coefficient

The thermal expansion coefficient of the sintered specimen was measured by making the diameter and length of the specimen each 4 did.

Below shows the experimental results of cordierite ceramics manufactured through the mixing conditions of the comparative examples and examples.

(1) Cordierite particle size grinding and characteristics

The optimal dispersion conditions for cordierite have variables depending on ① linear speed, ② grinding time, ③ grinding media size, and ④ type of dispersant. The average particle diameter of the raw materials used in this experiment is shown in Table 1, and the mixed and pulverized As shown in Figure 2, the average particle size was confirmed to be 10 ㎛.

(2) Shrinkage rate

As shown in Table 2, which shows changes in the addition of kaolin and clay minerals in the distribution of shrinkage, the increase in kaolin in clays with fewer particles and higher plasticity due to the nature of clay minerals is shown in Figure 3 for the standard mix. For the C-1 mix, it was 1.26% at 1,220 ℃, for 1,380 ℃, it was 4.40%, and for the C-2 mix, which had the most shrinkage, it was 1.80% to 10.30%. Other C-3 and C-4 combinations were found to be 6.20% and 8.40% at a moderate temperature of 1,380°C. In other words, the order of lowest shrinkage is halloysite kaolin, kaolinite kaolin, and clay, which have low plasticity. Overall, shrinkage increases rapidly at 1,340℃. This phenomenon is an inflection point, and cordierite synthesis is completed, and the liquid phase increases again at 1,380℃. It is predicted as

(3) Bending strength (MOR)

In the case of bending strength in the present invention, as shown in FIG. 4, the C-2 mix was the highest at 5.10 N/mm ² at 1,340°C, but decreased overall at 1,380°C. This phenomenon peaks at 1,340°C, as shown in the shrinkage rate above.

(4) Absorption rate, volume specific gravity and porosity

Cordierite is used as a high-temperature refractory material with excellent high-temperature characteristics due to its high thermal shock resistance and low coefficient of thermal expansion. Therefore, an important factor depending on the material during manufacturing is the change in thermal expansion coefficient depending on porosity and water absorption. In general, clay minerals have a lot of shrinkage, and as the firing temperature increases, water absorption and porosity decrease and bulk specific gravity increases.

In the case of this experiment, the general phenomenon shown in Figure 5 is that as the temperature increases from 1,220°C, sintering and cordierite are synthesized, and the water absorption rate decreases from 2.30% to 2.0%. However, the absorption rate also decreased rapidly when the inflection point was above 1,340 ℃, and was found to be 2.00-2.50% at 1,380 ℃, except for C-1. As the firing temperature of the clay mineral increases, as shown in Figure 6, the bulk specific gravity also increased from about 1.81 at 1,220 ℃ to a maximum of 2.26 at 1,380 ℃. As shown in Figure 7, porosity and water absorption decreased as the firing temperature increased, but all four types of cordierite mixtures showed a rapid decrease above 1,340°C.

(5) Cordierite thermal expansion coefficient measurement test results

As shown in Figure 8, the test results of the C-4 mix, which has the lowest cordierite thermal expansion coefficient, are 2.20x10 ^-6 /℃ at 800 ℃ and 2.57x10 ^-6 /℃ at 1,000 ℃.

The ranking of kaolin minerals is that C-1, a kaolin mixture, is 2.28x10 ^-6 /℃ at 800 ℃ and 2.6x10 -6 /℃ at 1,000 ℃, and C-2 is ^{2.51x10 -6 /} ℃ and 2.91x10 ^-6 /℃. It is relatively high in ℃. In the case of C-3, kaolin and clay were mixed at a ratio of 1:1, and the results were 2.45x10 ^-6 /℃ and 2.87x10 ^-6 /℃.

The thermal expansion coefficient is based on kaolin minerals, C-4, which is a mixture of tubular kaolin and plate-like kaolin clay, followed by C-1, which is a mixture of tubular kaolin, which is of low order, and C-3, which is a mixture of tubular kaolin and clay. It is a mixture of the highest C-2 clay. Since the sources of Al ₂ O ₃ and MgO are under the same conditions, it can be seen that the forms of kaolin minerals appear as tubular kaolin and plate-shaped kaolin for comparison.

(6) Chemical composition and thermal expansion coefficient characteristics

As shown in Table 3, based on the MgO/Al ₂ O ₃ mole ratio of 1.0 and SiO ₂ /Al ₂ O ₃ mole 2.5, the MgO/Al ₂ O ₃ mole ratio is 1.06 and the SiO ₂ /Al ₂ O ₃ mole ratio is 2.427. The thermal expansion coefficient of phosphorus C-4 was 2.20x10 ^-6 /℃ at 800 ℃, and at 1,000 ℃, it showed the lowest thermal expansion coefficient of 2.57x10 ^-6 /℃.

In the case of C-2, when the MgO/Al ₂ O ₃ mole ratio is 1.027 and the SiO ₂ /Al ₂ O ₃ mole ratio is 2.502, the thermal expansion coefficient is 2.51x10 ^-6 /℃ at 800 ℃, and 2.91x10 ^-6 /℃ at 1,000 ℃. It increased to ℃. This is because, based on the mole ratio of SiO ₂ /Al ₂ O ₃ of 2.5, 2.502 satisfies the low thermal expansion coefficient when the SiO ₂ component is lower than 2.5. Therefore, C-4 is a synthesis condition with an excess of Al ₂ O ₃ that is lower than the mole ratio of 2.5 of SiO ₂ /Al ₂ O ₃ , which is the theoretical composition of cordierite, which is the same as the conditions for adding mullite to cordierite. It ranged from 2.427 to 2.486 for C-1, and in the case of MgO/Al ₂ O ₃ with high MgO, the condition of a low thermal expansion coefficient of 1.0 or more was confirmed.

(7) XRD and crystal characterization review

The raw material usage conditions for cordierite synthesis using kaolin-talc-alumina using kaolin mineral raw materials are shown in Table 2, and the crystal phase analysis results at each temperature of cordierite manufactured are shown in Figure 9. The alpha cordierite crystal phase began to develop at 120°C, and the intensity of the peak increased as the temperature increased. In case (b), you can see the phenomenon of mulite phase seeds gradually precipitating, and in case (c) at 1,300 ℃, you can see that mulite crystals are clearly precipitated inside the cordierite, and in the case of the next sintering temperature of 1,340 ℃. In (d), cordierite gradually liquefies and progresses to complete densification. In the case where the sintering temperature increased to (e) 1,380 ℃, cordierite forms a solid solution surrounding the mullite structure.

(8) SEM analysis results

SEM analysis of the cordierite crystal phase was shown in Figures 10 to 14. Looking at the crystal phases at each temperature, first, as shown in Figure 10, in the case of a low sintering temperature of 1,220°C, the cordierite crystals showed densification as in the case of XRD, where the μ phase disappeared and the α phase was clearly visible. can see.

In addition, as shown in Figure 11, in the case of 1,260 ℃, other crystal phases such as mullite (3Al ₂ O _3· 2SiO ₂ ), spinel (MgO·Al ₂ O ₃ ), and hypothetical silca were observed before 1,220 ℃. and hypothetical silca was not observed above 1,220 ℃. The mullite crystal phase gradually disappeared from 1,260°C, and as shown in Figure 12, mullite was not observed at 1,340°C, and only a slight spinel crystal phase was observed. The absorption rate and bulk density at each temperature are shown in Figures 5 and 6. The absorption rate decreased as the temperature increased, rapidly decreasing from 1,380 ℃ to 2.50%. The bulk density increased as the absorption rate decreased and showed a value of 2.20 g/cm ³ at 1,380 ℃.

In conclusion, materials with MAS (MgO-Al ₂ O ₃ -SiO ₂ )-based compositions are attracting attention as mechanical structural materials despite their weaknesses in mechanical properties, which suggests the possibility of developing heat-resistant materials by applying their low thermal expansion characteristics. Because. In the case of MAS-based cordierite (2MgO·2Al ₂ O _3· 5SiO ₂ ), it exhibits properties such as low thermal expansion coefficient, thermal shock resistance, low dielectric constant, and high electrical insulation, but the firing range during synthesis is very narrow, so the firing temperature is low. If it is low, cordierite crystals are not sufficiently formed, and if it is even slightly high, cordierite decomposes back into postelite, spinel, and mullite, and the coefficient of thermal expansion of the material increases significantly. do.

In order to solve this problem, we reviewed the mixing range of clay minerals in the cordierite composition and found that the optimal mixing conditions for the raw material mixture were magnesium oxide (MgO)/aluminum oxide in a mixture of hallosite kaolin, clay, and kaolinite kaolin. The (Al ₂ O ₃ ) mole ratio was 1.06, and the silicon dioxide (SiO ₂ )/aluminum oxide (Al ₂ O ₃ ) mole ratio was 2.427.

In addition, under conditions maintained at 1,380℃ for 1 hour, the coefficient of thermal expansion is 2.20x10 ^-6 /℃ at 800℃, and 2.57x10 ^-6 /℃ at 1,000℃, and considering physical properties and shrinkage rate, cordierite material is optimal. We conducted material development for next-generation firing ceramic tools for industrial use.

In addition, in the synthesis of low thermal expansion cordierite using kaolin minerals through this study, the optimal mixing conditions of the raw material mixture were 34.00 (w/w)% of Halloysite Kaolin (HK) and Clay (CL) by weight. ) 20.00 (w/w)%, kaolinite kaolin (NK) 12.50 (w/w)%, talc (TL) 18.90 (w/w)%, aluminum oxide (Al ₂ O _3, AL) 9.30 (w/w)% and magnesium oxide (MgO, MG) 5.30 (w/w)%.

In addition, under the optimal mixing conditions of the raw material mixture, the bending strength was found to be 53.10 N, the bulk specific gravity was 2.0 or less, and the moisture absorption rate was 8.40%, which satisfied the standards of KS L 3412.

As a means of solving the above problem, the present invention solves problems that may occur when the MAS-based cordierite is outside the firing range and provides a low thermal expansion cordier that exhibits the characteristics of low thermal expansion coefficient, thermal shock resistance, low dielectric constant and high electrical insulation. A light ceramic manufacturing method can be provided.

Additionally, the present invention can provide optimal mixing conditions for producing low thermal expansion cordierite ceramic.

In addition, the present invention can provide conditions for developing cordierite ceramic materials considering physical properties and shrinkage rate.

As such, a person skilled in the art will understand that the technical configuration of the present invention described above can be implemented in other specific forms without changing the technical idea or essential features of the present invention.

Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive, and the scope of the present invention is indicated by the claims described later rather than the detailed description above, and the meaning and scope of the claims and their All changes or modified forms derived from the equivalent concept should be construed as falling within the scope of the present invention.

S10. The first step of producing a raw material mixture by mixing halloysite kaolin, clay, kaolinite kaolin, talc, aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO).
S20. The second step of milling the raw material mixture using a ball mill and pot mill.
S30. The third step of press molding by applying pressure to the milled raw material mixture.
S40. The fourth step of drying the raw material mixture that has been subjected to press molding.
S50. The fifth step of sintering the dried raw material mixture in an oxidizing atmosphere.

Claims (17)

The first step of producing a raw material mixture by mixing halloysite kaolin, clay, kaolinite kaolin, talc, aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO). ;
A second step of milling the raw material mixture into a standard sieve of 44 ㎛ using a ball mill and a pot mill for 24 hours each;
A third step of press molding the milled raw material mixture by applying pressure at 200 kg/cm2;
A fourth step of drying the press molded raw material mixture at 100 to 120° C. for 3 hours;
A fifth step of sintering the dried raw material mixture at 1,220 to 1,380° C. in an oxidizing atmosphere for 3 hours,
The raw material mixture contains 34.00 (w/w)% of halloysite kaolin (HK), 20.00 (w/w)% of clay (CL), and 12.50 (w/w) of kaolinite kaolin (NK). %, talc (TL) 18.90 (w/w)%, aluminum oxide (Al ₂ O ₃ , AL) 9.30 (w/w)%, and magnesium oxide (MgO, MG) 5.30 (w/w)%. , the aluminum oxide (Al ₂ O ₃ , AL) has an average particle size of 0.5 ㎛,
The magnesium oxide (MgO)/aluminum oxide (Al ₂ O ₃ ) mole ratio of the mixture of halloysite kaolin, clay, and kaolinite kaolin is 0.9 to 1.1,
The silicon dioxide (SiO ₂ )/aluminum oxide (Al2O3) mole ratio of the mixture of halloysite kaolin, clay, and kaolinite kaolin is 2.4 to 2.6,
When maintained at 1,380°C for 1 hour after sintering in the fifth step, the thermal expansion coefficient is 2.20×10 ^-6 (/°C) at 800°C, and the thermal expansion coefficient is 2.57×10 ^-6 (/°C) at 1,000°C. A method for manufacturing low thermal expansion cordierite ceramics containing kaolin mineral.
delete delete delete delete delete delete Contains halloysite kaolin, clay, kaolinite kaolin, talc, aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO),
Halloysite Kaolin 34.00 (w/w)%, Clay 20.00 (w/w)%, Kaolinite Kaolin 12.50 (w/w)%, Talc 18.90 (w/) w)%, 9.30 (w/w)% aluminum oxide (Al2O3) and 5.30 (w/w)% magnesium oxide (MgO) were mixed,
The magnesium oxide (MgO)/aluminum oxide (Al ₂ O ₃ ) mole ratio of the mixture of halloysite kaolin, clay, and kaolinite kaolin is 0.9 to 1.1, The molar ratio of silicon dioxide (SiO ₂ )/aluminum oxide (Al2O3) is 2.4 to 2.6,
When held at 1,380 ℃ for 1 hour after sintering, the thermal expansion coefficient is 2.20×10 ^-6 (/℃) at 800 ℃, and 2.57×10 ^-6 (/℃) at 1,000 ℃.
The bending strength is 52 to 54 N,
The bulk specific gravity is 2.00 or less,
A low thermal expansion cordierite-based ceramic composition containing kaolin mineral, characterized in that the moisture absorption rate according to KS L 3412 is 8.0 to 9.0%.
delete delete delete delete delete delete delete delete Contains halloysite kaolin, clay, kaolinite kaolin, talc, aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO),
Halloysite Kaolin 34.00 (w/w)%, Clay 20.00 (w/w)%, Kaolinite Kaolin 12.50 (w/w)%, Talc 18.90 (w/) w)%, 9.30 (w/w)% aluminum oxide (Al2O3) and 5.30 (w/w)% magnesium oxide (MgO) were mixed,
The magnesium oxide (MgO)/aluminum oxide (Al ₂ O ₃ ) mole ratio of the mixture of halloysite kaolin, clay, and kaolinite kaolin is 0.9 to 1.1, The molar ratio of silicon dioxide (SiO ₂ )/aluminum oxide (Al2O3) is 2.4 to 2.6,
When held at 1,380 ℃ for 1 hour after sintering, the thermal expansion coefficient is 2.20×10 ^-6 (/℃) at 800 ℃, and 2.57×10 ^-6 (/℃) at 1,000 ℃.
The bending strength is 52 to 54 N,
The bulk specific gravity is 2.00 or less,
A filter comprising a low thermal expansion cordierite-based ceramic composition containing kaolin mineral, characterized in that the moisture absorption rate according to KS L 3412 is 8.0 to 9.0%.

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