KR20150129415A - Low-Thermal-Expansion Ceramic Ware - Google Patents

Abstract

The present invention relates to a low thermo-expandable and heat-resistant pottery. Heat shock resistance of clay can be maximized by minimizing thermal expansion coefficient of the heat-resistant pottery clay, selectively adding, into the clay, natural petalite or synthetic eucryptite as an Li_2O-Al_2O_3-SiO_2-based (LAS) material and controlling thermal expansion properties by content ratio of a mixture and a heat treatment temperature. The produced clay heat-resistant shock sensitivity without few or no thermal expansion. Beta-eucryptite (β-eucryptite) powder used as a low thermos-expandable ingredient is artificially synthesized by adding lithium carbonate (Li_2CO) and aluminum hydroxide (Al(OH)_3) into silica (SiO_2).

Description

Low-Thermal-Expansion Ceramic Ware}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-expandable heat-resistant magnet, and more particularly, to a heat-resistant magnet having improved thermal shock resistance by applying β-eucryptite or petalite.

In the industry where heat treatment is repeated at high temperature, heat resistant magnetism is widely used. Heat resistant magnets maintain durability not only in terms of fire resistance but also in thermal shock resistance which can withstand repeated thermal changes.

LAS (Li ₂ O-Al ₂ O ₃ -SiO ₂ ) -based materials are generally known to have low thermal expansion properties. The reason the thermal expansion is small, due to the low thermal expansion property which comes from the crystal structure, such as _{Li 2 O · Al 2 O 3} · 4SiO 2 composition of β-spodumene and _{Li 2 O · Al 2 O 3} · 2SiO 2 The composition of the β-eucryptite .

In particular, β-eucryptite has been reported to exhibit a negative (-) thermal expansion characteristic. Gaillery et al. Investigated the thermal expansion anisotropy of β-eucryptite crystals using XRD. Roy et al. First demonstrated that α → β transition of eucryptite irreversibly occurs at 972 ° C by hydrothermal reaction. In addition, according to another LAS-based materials in these studies petalite _{(Li 2 O · Al 2 O} 3 · 8SiO 2) is a study using petalite since the announcement that the transition to the β-spodumene in the range of 700~950 ℃ heat possession The activity has been progressing. Fishwick et al. Investigated the low thermal expansion properties of spodumene, petalite and kaolin mixed compositions. Particularly, in heat resistance magnetic research, researches have been continued to increase the thermal expansion coefficient and the thermal shock resistance by inducing β-spodumene crystal phase by adding petalite.

Despite these studies, there is little research on the eucryptite-clay system. In addition, while general β-spodumene synthesis methods have been studied, such as solid phase synthesis, coprecipitation and sol-gel methods, eucryptite artificial synthesis methods have been rarely studied.

SUMMARY OF THE INVENTION The present invention has been developed under the technical background described above, and an object of the present invention is to provide ceramics having a high thermal shock resistance.

Another object of the present invention is to provide a new heat resistant magnet containing a low heat expandable LAS material.

Another object of the present invention is to provide a method for artificially synthesizing a low heat expandable LAS material and a method for manufacturing a heat resistant magnet including the same.

Other objects and technical features of the present invention will be more specifically described in the following detailed description.

In order to achieve the above object, the present invention is a heat-resistant magnet produced by mixing a clay and a LAS (Li ₂ O-Al ₂ O ₃ -SiO ₂ ) -based material, comprising 30 to 60 wt% of clay, _{β-eucryptite (Li 2 O ·} Al 2 O 3 · 2SiO 2) or _{petalite (Li 2 O · Al 2} O 3 · 8SiO 2) provides a low thermal expansion heat-resistant self containing 40 ~ 70 wt%.

The β-eucryptite is preferably contained in a range of 50 to 70 wt%, and the petalite is preferably contained in a range of 60 to 70 wt%.

The invention also and 30 ~ 60 wt% clay, LAS-based material as a _{β-eucryptite (Li 2 O ·} Al 2 O 3 · 2SiO 2) or _{petalite (Li 2 O · Al 2} O 3 · 8SiO 2) 40 ~ 70 wt% of the clay and the LAS material, mixing the clay and the LAS material to prepare a molded product, and heat-treating the molded article at a temperature of 1200 캜 or higher and sintering the same.

When β-eucryptite is selected as the LAS-based material, it is contained in an amount of 60 wt% or more, and the heat treatment is preferably carried out at a temperature of 1250 ° C. or more from the viewpoint of thermal shock resistance. In addition, when petalite is selected as the LAS-based material, it is contained in an amount of 60 wt% or more, and the heat treatment is preferably carried out at a temperature of 1300 ° C or more from the viewpoint of thermal shock resistance.

The β-eucryptite can be synthesized by mixing silica (SiO ₂ ), lithium carbonate (Li ₂ CO) and aluminum hydroxide (Al (OH) ₃ ). In this case, the raw materials are mixed, It is preferable to sinter.

According to the present invention, ceramics having a high thermal shock resistance can be produced, and by adding a low heat expandable material, it is possible to lower the thermal expansion coefficient of the heat resistant self-supporting material to nearly zero.

In addition, according to the present invention, it is possible to artificially synthesize a low thermal expansion LAS material and develop heat-resistant ceramics for various uses by using it.

1 shows XRD graphs showing crystal phase changes of synthesized β-eucryptite powder according to the synthesis temperature
Fig. 2 is a SEM photograph showing the surface microstructure of the heat-treated specimen of the β-eucryptite powder compact.
3 is a graph showing the results of thermal expansion behavior of? -Eucryptite powder
FIG. 4 is a graph showing the thermal expansion characteristics of petalite-clay and eucryptite-clay type fired at 1200 ° C.
FIG. 5 is a graph showing the thermal expansion characteristics of petalite-clay and eucryptite-clay type fired at 1250 ° C.
FIG. 6 is a graph showing thermal expansion characteristics of petalite-clay and eucryptite-clay specimens fired at 1300 ° C.
7 is a graph showing the thermal expansion characteristics of petalite-clay and eucryptite-clay-based specimens fired at 1350 ° C

The present invention proposes a heat-resistant magnet that maximizes the thermal shock resistance of the substrate by minimizing the thermal expansion coefficient to an extreme limit.

Specifically, natural petalite and synthetic eucryptite were added to clay to investigate the crystallization behavior and thermal properties of the substrate, and the physical change behavior according to the heat treatment temperature was observed to realize a thermally expandable heat resistant magnet. do. The β-eucryptite powder used in the examples of the present invention was artificially synthesized by adding lithium carbonate (Li ₂ CO) and aluminum hydroxide (Al (OH) ₃ ) to silica (SiO ₂ ).

In the present invention, β-eucryptite and petalite among LAS-based low thermal expansion ceramics were used to produce a substrate having excellent thermal shock resistance. The crystal phase change and thermal expansion characteristics of the produced substrate were investigated. First, the β-eucryptite powder synthesized from silica and lithium carbonate formed β-eucryptite phase at 900 ℃ and β-eucryptite single phase was well developed from above 1000 ℃. The thermal expansion coefficient of the synthesized β-eucryptite was -7.15 × 10 ^-6 / ° C., indicating the negative thermal shrinkage behavior of β-eucryptite.

Petalite clay-based carrying case of the form the lithium alumina silicate in the previous step of the β-spodumene crystals in the sintering temperature 1250 ℃ ~ 1350 ℃ region _{(Li 2 O · Al 2 O} 3 · 7.5SiO 2) a main crystal phase, at high temperatures When petalite content was increased, β-spodumene of keatite structure was formed. These crystals exhibit positive (+) thermal expansion behavior, which indicates that there is a limit to lowering the coefficient of thermal expansion of the substrate.

On the other hand, in the case of Eucryptite-clay base, a general β-spodumene having β-quartz structure was observed as a main crystal phase with mullite at 1250 ° C. β-spodumene with β-quartz structure shows negative (-) thermal expansion behavior, and the coefficient of thermal expansion of the substrate increases continuously with increasing eucryptite content and as the firing temperature increases, the thermal expansion coefficient of 0.7 × 10 ^-6 / Lt; RTI ID = 0.0 > a < / RTI >

Hereinafter, the technical structure and effects of the present invention will be described in more detail with reference to preferred embodiments.

1-1. β-eucryptite synthesis

As a raw material for the synthesis of β-eucryptite, Kimcheon silica (SiO ₂ ), which is mainly used as a silica source in the general ceramics industry, was used. Aluminum hydroxide (Al (OH) ₃ , 99.7%, KC Ltd . Lithium carbonate (Li ₂ CO ₃ , 99.8%, Wako Pure Chemical Industries Ltd., Japan) was used as the lithium source. The chemical analysis (wt%) of each raw material is shown in Table 1.

lithium carbonate, aluminum hydroxide and silica having an average particle size of 3 μm were mixed at a batch composition ratio as shown in Table 2 so as to match the stoichiometric composition of β-eucryptite.

Each raw material for β-eucryptite synthesis was mixed and milled. The raw materials and balls were put into a milling vessel and iso-propyl alcohol was used as a milling medium instead of water. This is because lithium carbonate has a solubility of 1.34 g / 100 g.H ₂ O in water, so it is difficult to obtain a uniform sample, and insoluble alcohol is used. The detailed ball milling process conditions for mixing are shown in Table 3.

The β-eucryptite synthesis mixture was milled for 72 hours through a milling process, passed through a 200-mesh standard, dried thoroughly in a 110 ° C dryer for 24 hours, and then crushed and heat-treated. The heat treatments were heat treated at 900 ° C, 1000 ° C, 1100 ° C, 1200 ° C, 1300 ° C and 1350 ° C, respectively, while maintaining the temperature at a maximum temperature of 5 ° C / min for 90 minutes.

The heat-treated powders were pulverized in agate mortar, passed through a 200-mesh standard, and analyzed for crystal phase using an X-ray diffractometer (Rigaku 2200, Tokyo, Japan). The microstructure of the prepared specimens was observed using a scanning electron microscope (SEM, 3500N / Hitachi, Japan). The specimens were heat-treated at 1300 ° C for 2 hours to measure the thermal expansion coefficient.

1-2. Synthesis of β-eucryptite powder

Crystalline phase changes of synthesized β-eucryptite powder by XRD analysis are shown in FIG. Three phases of β-eucryptite, α-quartz and lithium silicate (Li ₂ SiO ₃ , Li ₂ O · SiO ₂ ) were observed at 900 ° C. At this temperature, the crystallinity of β-eucryptite is very low and free silica from the silica is mixed with α-quartz in unreacted state. It is also confirmed that lithium reacts with silica to form Li ₂ SiO ₃ phase, which is the intermediate phase of β-eucryptite. From 1000 ° C or higher, the lithium silicate phase disappeared and the crystallinity of β-eucryptite rapidly increased, indicating that β-eucryptite was present as a single phase.

The surface microstructure of the heat-treated specimen of the β-eucryptite powder compact was observed and shown in FIG. It is composed of irregular shaped grains with a size of several micrometers, and a slight liquid phase surrounds the crystal grains, and there are fine cracks and pores. It was judged that fine cracks exist due to anisotropy of thermal expansion, and relatively good sinterability was exhibited.

The results of the thermal expansion behavior of the sintered specimen are shown in Fig. (-) thermal expansion from room temperature to 800 ° C and showed a thermal expansion coefficient of -7.15 × 10 ^-6 / ° C.

2-1. Heat resistant self-made

Petalite-clay and eucryptite-clay substrates were prepared by mixing petalite and synthetic eucryptite in clay for heat-resistant self-assembly. Natural materials from Zimbabwe were used as petalite, and Kaolinite quality Gairome clay, which is Japanese refined, was used as a raw material to impart plasticity to the substrate. Chemical analysis of each raw material is shown in Table 1 described above.

The composition of the specimens was maintained at over 30 wt% clay, which is the limit of formability, and the contents of petalite and eucryptite were varied. The composition ratios (wt%) of each sample were shown in Table 4.

The slip for slip casting was prepared using the same conditions as in Table 3 for the ball milling for mixing. However, instead of alcohol, water was added at 0.7 times of the raw material, and 1 cc of a sodium silicate solution, which is a cracking agent, was added thereto, followed by mixing for 24 hours.

The prepared slip was injected into a gypsum mold to prepare specimens. The cast specimens were completely dried in a 110 ° C drier and then heat treated. The heat treatment of the substrate was maintained at 1200 ° C, 1250 ° C, 1300 ° C and 1350 ° C at a heating rate of 5 ° C / min and a maximum temperature for 3 hours.

After sintering the petalite-clay and eucryptite-clay substrates, the thermal expansion characteristics and crystalline phases formed in the substrate were observed. The thermal expansion coefficients of the specimens were measured using a dilatometer (DIL 402C, Netzswch, Germany) at a heating rate of 5 ° C / min and a thermal expansion coefficient between 30 ° C and 800 ° C. The crystal morphology of the specimens was observed using an X-ray diffractometer.

2-2. Observation of crystalline phase of heat resistant specimen

The results of the crystal phase observation by XRD measurement of each specimen shown in Table 4 are shown in Table 5 with the heat treatment temperature as a variable.

In the Petalite-clay system, mullite, α-quartz and cristobalite phases were formed at a firing temperature of 1200 ° C. The transition from a relatively low temperature to the cristobalite phase is consistent with the theory that Li ⁺ ion breaks the crystal lattice of α-quartz structure of free silica to facilitate rearrangement and transforms to cristobalite, indicating that cristobalite is formed at low temperature . Lithium alumina silicate (Li ₂ O · Al ₂ O ₃ · 7.5SiO ₂ ), mullite and cristobalite were observed at the sintering temperature of 1250 ℃. Lithium-alumina silicate appears to be a pre-phase of β-spodumene solid solution, and α-quartz is transformed into cristobalite and disappears. When petalite content is 70 wt% at 1300 ℃ and petalite content is 60 wt% and 70 wt% at 1350 ℃

keatite-type β-spodumene was observed. In the LAS system, β-spodumene solid solution has β-quartz structure or keatite structure. β-quartz type spodumene is a general β-spodumene structure and is thermodynamically relatively stable and exhibits a negative thermal expansion behavior. On the other hand, when β-quartz type structure increases in heat treatment temperature and annealing time becomes longer, bond of crystal lattice is broken and transition to keatite solid solution structure by rearrangement of atoms occurs. The Keatite structure is thermodynamically unstable compared to the β-quartz structure and is known to have positive (+) thermal expansion. Alumina silicate (Li ₂ O · Al ₂ O ₃ · 7.5SiO ₂ ) is mostly formed at the composition and temperature of keatite-type β-spodumene in petalite-clay base with high calcination temperature and high petalite content. Was formed as a main crystal phase.

The β-eucryptite-clay system showed mullite and cristobalite phases at 1200 ℃. When the eucryptite content was increased to more than 60 wt%, lithium-alumina silicate phase was formed together with petalite-clay system. Solidification of mullite and β-spodumene was formed at a sintering temperature of 1250 ° C., and these phases were retained when the temperature was increased to 1300 ° C. and 1350 ° C. When the content of eucryptite was more than 60 wt% at 1350 ℃, the peak intensity of β-spodumene gradually increased and the intensity of mullite peak gradually weakened. From the above results, it can be seen that the production of β-spodumene increases with increasing eucryptite content at the higher baking temperature when eucryptite is added to the clay substrate.

2-3. Properties of heat resistant specimen

The absorption rates and densities of the Petalite-clay and eucryptite-clay substrates according to the firing temperature were measured and the results are shown in Table 6.

At 1200 ℃, the water uptake was lower and the bulk density increased as the amount of clay in the substrate composition increased. This is because the sintering behavior of clay during sintering first appears. β-eucryptite-added substrate had a lower water absorption than petalite, which is considered to be the result of promoting liquid-phase sintering because β-eucryptite contains 2.64 times more Li ₂ O than petalite . Eucryptite-clay substrates EB-3 and EB-4 exhibited a low absorption rate of less than 1% at 1300 ° C or higher, indicating that it is possible to produce a dense, heat-expandable heat-resistant self-

2-4. Thermal expansion characteristic

4 to 7 show the thermal expansion characteristics of petalite-clay and eucryptite-clay type specimens, respectively.

At relatively low firing temperature of 1200 ° C (Fig. 4), the coefficient of thermal expansion decreased relatively slowly even when the amount of petalite and eucryptite increased. This is attributed to the fact that the formation of α-quartz and cristobalite is promoted by petalite and Li ⁺ ion in eucryptite at 1200 ° C, resulting in swelling.

At 1250 ° C (Fig. 5), the thermal expansion coefficient decreases rapidly from the eucryptite amount of 50 wt% or more. This is a phenomenon that is marked by a marked increase in the formation of β-spodumene, and the coefficient of thermal expansion is steeply decreasing with increasing eucrtptite content. However, in case of petalite-clay substrate, the modulus of thermal expansion was decreased. It is believed that this is due to solid solution formation and cristobalite formation before spodumene formation such as lithium alumina silicate (Li ₂ O · Al ₂ O ₃ · 7.5SiO ₂ ).

It can be seen that the eucryptite-clay substrate at 1300 ° C (FIG. 6) has a very low thermal expansion coefficient of from 1.3 to 1.0 x 10 ^-6 / ° C at 60 wt% and 70 wt%. This is thought to be due to the development of β-spodumene crystals. However, the thermal expansion coefficient of the petalite-clay substrate is smaller than that of the eucryptite-clay substrate at 60 wt%, and the difference between the eucryptite-clay substrate and the thermal expansion coefficient is increasing.

At 1350 ° C (Fig. 7), a very low thermal expansion coefficient close to zero at 0.7 x 10 ^-6 / ° C was measured at 70 wt% eucrytite content. As shown in the XRD analysis in Table 5, the mullite phase disappears and the β-spodumene crystal phase is further developed and the thermal expansion coefficient is lowered. In the case of petalite, the decrease of the thermal expansion coefficient is progressing gently even if the content is increased to 70 wt%.

These results suggest that it is difficult to lower the thermal expansion coefficient of petalite-clay substrate to 2.0 × 10 ^-6 / ℃ or less. On the other hand, it is considered that it is possible to lower the coefficient of thermal expansion close to zero in the eucryptite-clay substrate.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Modified, modified, or improved.

Claims (9)

As a heat resistant magnet produced by mixing clay and LAS (Li ₂ O-Al ₂ O ₃ -SiO ₂ ) -based materials,
30 to 60 wt% of clay,
And 40 to 70 wt% of β-eucryptite (Li ₂ O · Al ₂ O ₃ · 2SiO ₂ ) or petalite (Li ₂ O · Al ₂ O ₃ · 8SiO ₂ )
Low heat expansion heat resistant self.
The method according to claim 1,
Wherein the β-eucryptite is contained in an amount of 50 to 70 wt%.
The method according to claim 1,
Wherein the petalite is contained in an amount of 60 to 70 wt%.
The method according to claim 1,
Wherein the β-eucryptite is produced by mixing silica (SiO ₂ ), lithium carbonate (Li ₂ CO) and aluminum hydroxide (Al (OH) ₃ ).
30 to 60 wt% of clay and 40 to 70 wt% of β-eucryptite (Li ₂ O · Al ₂ O ₃ · 2SiO ₂ ) or petalite (Li ₂ O · Al ₂ O ₃ · 8SiO ₂ ) and,
The clay and the LAS-based material are mixed to prepare a molded product,
And sintering the shaped article by heat treatment at a temperature of 1200 ° C or higher
(EN) METHOD FOR MANUFACTURING HEAT ENHANCER.
6. The method of claim 5,
Wherein when the β-eucryptite is selected as the LAS-based material, it is contained in an amount of 60 wt% or more, and the heat treatment is performed at a temperature of 1250 ° C. or more.
6. The method of claim 5,
Wherein when the petalite is selected as the LAS-based material, it is contained in an amount of 60 wt% or more, and the heat treatment is performed at a temperature of 1300 캜 or more.
6. The method of claim 5,
Wherein the β-eucryptite is a powder synthesized by mixing silica (SiO ₂ ), lithium carbonate (Li ₂ CO) and aluminum hydroxide (Al (OH) ₃ ).
9. The method of claim 8,
Wherein the β-eucryptite is obtained by mixing raw materials and then sintering at a temperature of 1000 ° C. or higher.

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