KR101575561B1 - Manufacturing Method of Polycrystalline Aluminum Oxynitride with Improved Transparency - Google Patents

Abstract

The present invention provides transparency that, more specifically to sintered oxynitride aluminum mixed powder of Al ₂ O ₃ and AlN in the manufacture normal pressure reaction relates to a process for the preparation of improved polycrystalline oxynitride of aluminum, wherein the content of AlN 17 to 26 mol %, And the raw powder is subjected to first sintering at 1575 ° C to 1675 ° C so as to have a relative density of 95% or more and second sintering at 1900 ° C or more to achieve a higher relative density. According to the present invention, polycrystalline aluminum oxynitride ceramics having a visible light transmittance of 70% or more can be obtained at a relatively low final sintering temperature in a short period of time by removing all of the internal micropores.

Description

[0001] The present invention relates to a polycrystalline aluminum oxynitride with improved transparency,

The present invention relates to a method for producing aluminum oxynitride, and more particularly, to a method for producing polycrystalline aluminum oxynitride with improved transparency.

Polycrystalline ceramics are generally opaque. Light is scattered by pores, grain boundaries or impurities. However, by eliminating this light scattering factor, it can be made transparent as in a single crystal. The best-known translucent alumina is sintered with high-purity powder to almost eliminate pores and enlarge the grain size so that the grain size is reduced to make it transparent. However, since the crystal phase is anisotropic hexagonal crystal, the transmission of light is influenced by the directions of the crystal grains, so that it is not transparent like glass, but is transparent.

Aluminum oxynitride (Al ₂₃ O ₂₇ N ₅ ) is commonly called "AlON". In particular, γ-AlON is known to be a unique material that isotropic, cubic and highly sinterable and relatively easy to remove pores. have. However, in most high-strength wear-resistant transparent window applications that replace transparent tempered glass or sapphire, the higher the light transmittance of sapphire, which is close to 85%, the higher the value of the product. For this purpose, the pores in the aluminum oxynitride ceramic, which is the greatest factor for decreasing the transmittance, should be removed as much as possible, which can also alleviate the reduction of the transmittance with increasing thickness. U.S. Patent No. 4,241,000 discloses for the first time that Al ₂ O ₃ and AlN powder are mixed with these materials and heat-treated at 1200 ° C for 24 hours under a nitrogen gas atmosphere and sintered at 1800 ° C or higher at normal pressure to form a translucent polycrystalline aluminum oxynitride And a method for producing the same.

In addition, U.S. Patent No. 4,520,116 discloses that AlN and Al ₂ O ₃ powders are calcined and synthesized as aluminum oxynitride powder, and then a boron (B) compound, a yttrium (Y) compound or a lanthanum (La) A polycrystalline with a relative density of 99% or more and a visible light transmittance of 1.78 mm in thickness with a visible light transmittance of 43% was prepared by adding a small amount.

In addition, U.S. Patent Nos. 4,481,300 and 4,686,070 disclose that a yttrium (Y) compound or a lanthanum (La) compound is added as a sintering accelerator, in which Al ₂ O ₃ powder and carbon black powder are mixed at an appropriate ratio, after ℃ made of AlN and Al ₂ O ₃ by calcination at a temperature of around, it back boron nitride; and heat-treated at a temperature of 1800 ℃ and out from (boron nitride BN) vessels synthesized as acid aluminum nitride to ball milling for a long time this fine mountain Discloses a method for producing an aluminum oxynitride having an infrared transmittance of 80% at a thickness of 1.45 mm by molding the powder and sintering the aluminum nitride at atmospheric pressure under a nitrogen gas atmosphere at 1900 to 2140 캜 for 24 to 48 hours .

U.S. Patent No. 4,720,362 discloses a manufacturing process in which boron (B) compound or yttrium (Y) compound is added in an amount of 0.5 wt% or less to aluminum oxynitride powder and sintered at 1900 ° C or higher for 20 to 100 hours, The boron compound B ₂ O ₃ and yttrium compound Y ₂ O ₃ added as a sintering additive form a liquid phase during sintering to promote densification in the early and middle stages of sintering. In the last stage, solute drag or precipitated secondary Discloses that pinning the grain boundaries prevents abnormal grain growth and thus prevents pores from entering the mouth and not being removed any more.

In addition, U.S. Patent No. 5,231,062 discloses a method of producing transparent magnesium aluminum oxynitride (AlMgON) by adding 2.0 to 16% by weight of MgO.

In addition, U.S. Patent No. 5,688,730 discloses a method for producing aluminum oxynitride powder by reacting Al ₂ O ₃ having a high specific surface area with AlN powder.

In addition, U.S. Patent No. 6,955,798 discloses a method for producing an aluminum oxynitride powder by heat-treating a mixture of aluminum and aluminum oxide powder in a nitrogen gas atmosphere to form a mixture of aluminum nitride and aluminum oxide, milling the mixture, A method is disclosed.

In addition, U.S. Patent No. 7,045,091 discloses that instead of sintering aluminum oxynitride powder which has conventionally been conventionally used for producing transparent oxynitride, a mixed powder of Al ₂ O ₃ and AlN is mixed with a solid phase and a liquid phase Sintering with the help of a liquid phase at a temperature of 1950 ° C to 2025 ° C and then resintering at a temperature of at least 50 ° C lower than that in which only a solid phase exists to convert the liquid phase to solid phase , And the visible light transmittance of the 1 mm thick aluminum oxynitride thus produced was only above 10%.

In addition, U.S. Patent No. 7,163,656 discloses a method of manufacturing comprising the use of uniaxial hot pressing to produce high density AlON, regardless of transparency. Uniaxial high temperature sintering is a method which is used for obtaining a theoretical high density or sintering a material which is difficult to be densified due to a low sintering property. However, since uniaxial pressing causes unstable sintering, the shape after sintering is largely limited, productivity is low and cost is high. In addition, since the graphite mold is used for pressurization, the color of AlON is often darkened to produce a transparent product.

AlON starts to evaporate at temperatures above 1950 ° C. It is well known that evaporation during high-temperature sintering is preferably reduced as much as possible and evaporation can be easily suppressed even with a low nitrogen gas pressure of 0.1 MPa to 0.3 MPa in the case of AlON. This is a process in which overpressure of only 1 atm to 3 atm is applied in an electric furnace with nitrogen gas in a normal pressure sintering performed in a flowing nitrogen gas atmosphere, and the cost increases little. In addition, a special pressure electric furnace can be used as a process capable of greatly increasing the gas pressure to about 10 MPa, and gas pressure sintering (GPS) is used, but the gas pressure sintering furnace is used, but the cost is increased and the productivity is lowered . It has been developed to increase the sintering density by increasing the sintering power by suppressing the evaporation in the high temperature sintering of the silicon nitride which is evaporated, and it can be used for the production of AlON, but the size of the product is limited and the cost is greatly increased . Furthermore, there is HIP (hot isostatic pressing) which can give a gas pressure of about 200 MPa, but the size of the high-pressure chamber is further reduced and the cost is further increased.

Thus aluminum, most of oxynitride made from a prior art ceramic is, Al ₂ O ₃ to react into the carbon powder in the appropriate ratio to or hayeoseo AlN and Al ₂ O by heating a ₃ powder at a high temperature synthesis the acid aluminum nitride powder separately There is a problem in that the cost is increased since the manufacturing process is used and the cost is increased and the sintering is performed at a high temperature of 2000 ° C or higher or a sintering for a long time at a temperature lower than 2000 ° C to increase transparency. On the other hand, it was difficult to obtain high transparency of the oxynitride aluminum ceramics produced by the reaction-sintering reaction of Al ₂ O ₃ and AlN powder at atmospheric pressure.

Meanwhile, WO 08/047955, filed by the present inventors, relates to a method of producing aluminum oxynitride by reaction sintering of Al ₂ O ₃ and AlN powder, wherein the content of AlN is fixed to 35 mol% In addition to the previously known sintering aids, addition of 0.1% to 0.2% by weight of MgO as a sintering aid and pre-sintering at a temperature of 1650 ° C during sintering and final sintering were carried out to obtain a visible ray Discloses a method for producing transparent oxynitride with a transmittance close to 80%. However, in the above patent application, there is a problem that the final sintering is performed at a relatively high temperature of 2000 占 폚 for 5 hours. Nevertheless, since the visible light transmittance of a 1.9 mm thick specimen does not exceed 80% There is a need for a new manufacturing method capable of producing aluminum oxynitride with a significantly improved transmittance even at a low final sintering temperature.

The chemical formula of aluminum oxynitride is generally denoted Al ₂₃ O ₂₇ N ₅ but may be a nonstoichiometric (nonstoichiometric) material having a relatively broad range of N, which may be an aluminum oxynitride single phase, _{(64 + x) / 3} O _(32-x) N _x .

However, in the above-mentioned prior arts, in the production of transparent oxynitride, the aluminum oxynitride powder is sintered through a separate process of synthesizing aluminum oxynitride powder, or a mixed powder in which Al ₂ O ₃ and AlN powders are mixed The study of the visible light transmittance according to the ratio of Al ₂ O ₃ and AlN powder regardless of reaction sintering is as follows: "x" value in the formula of Al _{(64 + x) / 3} O _(32-x) N _x is the visible light transmittance Has not been studied.

The prior art assumes that the x value of 27 to 40 mol%, i.e. 3.4 to 6.0, will be appropriate, and in all the academic researches, it has been found that the AlN content in Al ₂₃ O ₂₇ N ₅ , Mol%, i.e. x value of 5.0, or any 30 mol% AlN, i.e. x value of 3.9, to produce or study aluminum oxynitride.

According to the paper "Alon: A brief history of its emergence and evolution" published in Jounal of the European Ceramic Society 29 (2009), Transmetal nitride of Surmet Corporation of America, which is the only successful commercialization of transparent oxynitride aluminum in the world The x value of aluminum ceramics is reported to be 4.0, or 31 mol%, AlN. Such aluminum oxynitride is known to synthesize AlON powder and sinter it, according to the above paper, and has been made to have an average grain size of 200 to 250 mu m in order to obtain high transparency. In order to obtain such a very large grain size, High sintering temperature and long time sintering. Generally, in ceramics, a large grain size results in a decrease in strength.

Thus, the inventors of the present invention have found that, in the production of aluminum oxynitride produced by reaction sintering, the molar fraction of Al ₂ O ₃ and AlN, which are raw material powders, is appropriately controlled to improve the light transmittance of aluminum oxynitride . In particular, ceramics in general can be produced in a short time at a lower final sintering temperature to obtain the same density, if the sinterability is enhanced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for manufacturing a more transparent aluminum oxynitride ceramic by further removing pores of an aluminum oxynitride ceramic.

In order to accomplish the above object, the present invention provides a method for producing a transparent polycrystalline aluminum oxynitride in which a mixed powder of Al ₂ O ₃ and AlN is sintered at atmospheric pressure, wherein the content of pure AlN is 17 to 26 mol% Sintering at a temperature of 1575 ° C to 1675 ° C so as to be 95% or more; And second sintering at 1900 ° C to 2050 ° C to achieve a higher relative density than the primary sintering, wherein the 1.5 mm thick specimen produced has a visible light linear transmittance of 70% or more A process for producing aluminum nitride is provided. In this case, the content of the pure AlN corresponds to 1.9 to 3.3 in the formula Al _{(64 + x) / 3} O _(32-x) N _x , and in particular, the content of the pure AlN is 21 to 23 mol% More preferable.

If the content of AlN is out of the above range and less than 17 mol%, a large amount of secondary phase is formed and the permeability can be largely decreased. If it is more than 26 mol%, sinterability starts to decrease and is a function of sintering temperature and time There may be a problem that the transmittance is significantly reduced.

The process comprises the steps of adding 0.02 wt.% To 0.5 wt.% Of Y ₂ O ₃ or La ₂ O ₃ as sintering additives, Yttrium (Y) compound or lanthanum (La) compound. As the yttrium compound, yttrium oxide may be used, and as the lanthanum compound, lanthanum oxide may be used. If the content of the sintering additive is out of the above range, the liquid phase formed by the sintering additive may be excessively formed, and the sintering additive may not evaporate after sintering, thereby remaining in the specimen and decreasing the permeability.

The manufacturing method may further include 0.06 wt% to 0.29 wt% of MgO as a sintering additive, or a magnesium (Mg) compound corresponding to the weight of MgO. As the magnesium compound, magnesium oxide may be used. If the content of the sintering additive is out of the range, the transmittance of the final sintered specimen may be decreased.

Sintering at 1575 ° C to 1675 ° C so as to have a relative density of 95% or more; And secondary sintering at 1925 ° C or higher, preferably 1900 ° C to 2050 ° C to achieve a higher relative density than the primary sintering.

More particularly, the method comprises: a first sintering step at 1650 ° C for 10 hours to have a relative density of 95% or more; And secondary sintering at 1970 DEG C for 5 hours to achieve a higher relative density than the primary sintering.

The relative density disclosed in the present invention means a ratio of the relative density of the relative density to the theoretical density, and the porosity is obtained by subtracting the relative density from 100. [ Relative density can also be measured by immersion method using Archimedes principle.

 The above production method can be overpressure-sintered at 0.1 to 10 MPa under a nitrogen gas pressure, more preferably at 0.1 to 0.3 MPa. Such overpressure sintering can suppress evaporation of aluminum oxynitride during high-temperature sintering.

The aluminum oxynitride produced by the process according to the present invention has a pure AlN content of 17 to 26 mol% and a visible light linear transmittance of 70% or more, preferably 80% or more, and the content of pure AlN 17 to 21 mol%, it was confirmed that there was a small amount of? '-AlON phase in the? -AlON phase and a Vickers hardness of 16.5 GPa or more while having a visible ray linear transmittance of 75% or more.

Further, the present invention provides a method of producing a transparent polycrystalline aluminum oxynitride by synthesizing an aluminum oxynitride powder and sintering the aluminum oxynitride powder, wherein x is 1.9 to 3.3 in the formula (1) 0.02 to 0.5% by weight of Y ₂ O ₃ or La ₂ O ₃ as an additive, (Mg) compound corresponding to one or more of yttrium (Y) compound or lanthanum (La) compound and 0.06 to 0.29% by weight of MgO or a weight thereof, characterized in that it comprises aluminum oxynitride Of the present invention.

[Chemical Formula 1]

Al _{(64 + x) / 3} O _(32-x) N _x

Further, when both high transparency and hardness are desired, x is 1.9 to 2.4, a small amount of? '- AlON phase exists in the? -AlON phase, and the Vickers hardness may be 16.5 GPa or more.

Hereinafter, the present invention will be described in more detail with reference to specific embodiments.

According to one embodiment of the present invention, in order to produce a transparent polycrystalline aluminum oxynitride ceramic, the amount of nitrogen and oxygen in the aluminum oxynitride to be reaction-sintered, that is, Al ₂ O ₃ The molar ratio of the powder to the AlN powder is optimized, and the sintering additive is mixed with the sintering additive, and finally sintered through preliminary sintering.

In this case, the molar ratio of the two main raw material powders is determined in the range of 17 to 26 mol% of AlN and therefore 74 to 83 mol% of Al ₂ O ₃ , and more preferably, in order to maximize the transparency, the molar ratio of AlN is set to 21 to 23 mol% I decide.

Aluminum oxynitride sintered in this manner is first sintered at about 1650 ° C and then secondarily sintered at a temperature of 1900 ° C or higher. In the first sintering, transparency is lowered unless the pores are removed as much as possible. When the temperature of the sintering furnace is increased to a final sintering temperature of 1900 ° C or more without first sintering, Al ₂ O ₃ and AlN react with each other at a temperature of about 1675 ° C. and phase transformation occurs to aluminum oxynitride. The aluminum oxynitride particles formed without the first sintering are already relatively large and the pore size is too large to remove the pores in the subsequent final sintering, making it difficult to obtain a high density. Generally, it is difficult to remove pores or densify the pores as the size of the particles sintered in the powder sintering is larger and the pore size is larger.

Therefore, before the phase transformation with aluminum oxynitride occurs, that is, the mixture of Al ₂ O ₃ and AlN should be densified as much as possible. In general, Al ₂ O ₃ begins to be densified at about 1500 ° C., and aluminum nitride is densified at about 1700 ° C. or higher when a sintering additive of several wt% is present. Therefore, the higher the content of Al ₂ O _3, the lower the sintering temperature, the easier the densification of the two mixed powders. For this reason, in order to produce transparent high-density aluminum oxynitride without pores, first sintering at a relatively low temperature must be performed, and the proportion of Al ₂ O ₃ having a high sinterability in the first sintering should be high, The lower the ratio, the better. However, since the ratio of AlN is too low, the transparency decreases when the secondary phase is precipitated during the secondary sintering.

In addition, aluminum oxynitride has an inverse spinel structure and can be represented by the formula Al _{(64 + x) / 3? (8-x) / 3} O _(32-x) N _x . The square (□) means the vacancy of the Al ion, which varies with the value of the "x", the amount of nitrogen. According to this formula, the lower the amount of nitrogen, that is, the x value, the higher the concentration of vacancies. In general, when the number of vacancies in a crystal is large, the diffusion rate of atoms or ions increases and sintering ability may increase. Therefore, as the ratio of AlN to Al ₂ O ₃ , ie, γ-AlON phase, is lower, the Al concentration increases and the sinterability increases and the removal of pores becomes easier.

In the present invention, as the x value becomes smaller, the sinterability of the AlON phase is further increased to help densify the aluminum oxynitride in the secondary sintering. In addition, the small x value increases the content of Al ₂ O ₃ having a high sinterability, We have found that increasing the densification and reducing the pore quickly increases the relative density, which results in almost all of the pores being removed in the secondary sintering, resulting in very high light transmittance by reducing the x value as much as possible.

As described above, according to the present invention, it is possible to provide cubic polycrystalline aluminum oxynitride ceramics in which almost all of the pores therein are removed to obtain a visible ray linear transmittance of 80% or more. Particularly, since such a transparent polycrystalline aluminum oxynitride ceramic has high strength, hardness and abrasion resistance, products such as a transparent board, a window of an infrared ray sensor, a radar dome, a transparent watch window, and a transparent display window which require high strength, hardness and abrasion resistance are required . Further, according to the manufacturing method of the present invention, even when Al ₂ O ₃ and AlN powder are directly mixed and sintered without the need to synthesize and sinter the aluminum oxynitride powder, a very transparent sintered aluminum nitride The manufacturing process can be simplified and the process cost can be reduced.

FIG. 1 is a photograph taken in order to compare transparency of aluminum nitride ceramic specimens subjected to the second sintering without first sintering and second sintered specimens after the first sintering.
FIG. 2 is a graph comparing the visible light transmittance according to the x value of the aluminum nitride ceramic specimens having only the second sintering without the first sintering and the second sintered specimens after the first sintering,
3 is a photograph of a fracture section of a specimen having a different x value, which was subjected to a first sintering, under a scanning electron microscope (magnification: 10,000 times)
4 shows the relative density according to the x value of the aluminum oxynitride specimen subjected to the first sintering at 1660 ° C for 10 hours,
5 shows a spectrum of a linear light transmittance over a range of 200 to 2500 nm according to the x value of the aluminum oxynitride specimens subjected to the first sintering and the second sintering,
6 is a photograph of a fractured section of aluminum oxynitride specimens subjected to the first sintering and subjected to the second sintering with a scanning electron microscope (magnification: 1,500 times)
FIG. 7 is a photograph of a specimen having an x value fixed to 2.5 and having a temperature of 1625 ° C to 1725 ° C for 10 hours and having a first sintering, and observing a broken section thereof with a scanning electron microscope (magnification: 10,000 times)
8 is a result of the x value is fixed to 2.5, quantitative analysis in the X-ray diffraction pattern of by varying the temperature at 1600 ℃ to 1725 ℃ that only 10 hours a primary sintered sample, AlON, Al ₂ O ₃ and AlN on the Volume fraction,
9 shows the fracture microstructure after the first sintering, which varies with the change of the primary sintering holding time from 1 hour to 10 hours when the x value is 2.5,
FIG. 10 shows the visible light transmittance depending on the x value and the presence or absence of MgO added as the sintering additive,
11 shows the linear light transmittance in the wavelength range of 200 to 2500 nm, which varies depending on the amount of sintering additive MgO,
Fig. 12 shows the linear transmittance change of 632 nm wavelength light according to the amount of sintering additive MgO,
13 shows the results of comparing the visible light transmittances of the different oxynitride aluminum specimens with the second sintering time of 2 hours and 5 hours although the second sintering was performed through the first sintering,
14 shows the grain size and Vickers hardness of the oxynitride aluminum specimens according to the x value,
Fig. 15 shows the linear transmittance of 632 nm wavelength light which varies with the thickness of the specimen.

Hereinafter, the present invention will be described in more detail based on embodiments in which an aluminum oxynitride ceramic is produced by variously changing process conditions according to the present invention. However, the present invention is not limited by these examples.

≪ Example 1 >

Al ₂ O ₃ was produced by changing the molar ratio of AlN from 18.2% (x = 2.0) to 35.7% (x = 5.0) while the Y ₂ O ₃ used as the sintering additive was fixed to 0.08 wt% and MgO was set to 0.15 wt% Respectively. The actual addition amount between the two main ingredients Al ₂ O ₃ and AlN was calculated from the x value considering the amount of oxygen (about 1 wt%) contained in the AlN powder due to oxidation of the surface and the amount of wear of the Al ₂ O ₃ ball in the ball mill process . These raw powders and sintering additive were milled in a polyurethane container using ethyl alcohol as a solvent for 48 hours using a high purity Al ₂ O ₃ ball and dried using a rotary evaporator. The dried powder was formed into a disk having a diameter of 20 mm and a thickness of 3 mm using a dry uniaxial press, and then cold isostatic pressing was performed at 275 MPa. The disk specimens were sintered in a high temperature electric furnace under a nitrogen atmosphere of 1 atm. The first sintering was maintained at 1660 ℃ for 10 hours and the second sintering was maintained at 1970 ℃ for 2 hours. The rate of temperature rise was 20 ° C per minute for temperatures up to 1500 ° C, 10 ° C per minute for temperatures above that, and the cooling rate was 20 ° C per minute. The second sintered specimens were polished on both sides with a 3 μm diamond paste on both sides using an experimental surface grinder after flattening both sides and the thickness of the final specimen was about 1.5 mm. The linear light transmittance of the polished specimens was measured using a Varian Spectrophotometer (Carry 500) for each specimen in the wavelength range from 200 nm to 2500 nm.

FIG. 1 is a photograph of the aluminum oxide ceramic specimens having the second sintering without the first sintering prepared in this manner and arranged in accordance with the x value so that the transparency of the second sintered specimen after the first sintering can be compared , The transparency was clearly lower as the x value was higher, unless the first sintering was carried out.

FIG. 2 shows the comparison of the linear transmittance of 632 nm wavelength light according to x value with the presence or absence of the first sintering. The transmittance of the second sintered specimen without the first sintering is higher than that of the second Which was significantly lower than that of sintered specimens. When the x value was 5.0 (35.7 mol% AIN), the transmittance of both specimens was less than 0.5%. As the value of x decreased, the transmittance of both specimens increased significantly and the value of x was 2.25 (20.0 mol% Of AlN), and decreased again at 2.0. Especially, when the first sintering was carried out, the transmittance of 80% or more, which is the highest value of x value, was obtained at 2.25 and was slightly lower at 2.5, but still close to 80%. In comparison, if an AlN composition of 35.7 mol% (x value of 5.0) or 30 mol% (x value of 3.9), which is generally used in the prior art, is used, the transmittance is only 0.5% or about 45%, respectively.

FIG. 3 is a photograph of the fracture surface of the first sintered specimen observed with a scanning electron microscope. As the x value is lower, that is, as the content of AlN is smaller, the pore size after the first sintering is smaller and the size is smaller. This is because the composite powder of Al ₂ O ₃ and AlN has a reduced sinterability of the composite powder when the content of AlN is increased. The production of aluminum oxynitride starts at the temperature of the first sintering at 1650 ° C., and after 10 hours at 1650 ° C., the volume ratio is about 6 to 10%, which leads to a reduction of Al ₂ O ₃ and AlN. As a result, when the x value is large, that is, when the amount of AlN is large, the Al ₂ O ₃ and the AlN composite powder The sintering property in the first sintering of the sintered body is not deteriorated. In addition, if the temperature of the first sintering is higher than 1675 ° C, a large amount of aluminum oxynitride is generated during the sintering, which makes it difficult to make the sintered compact densely.

FIG. 4 shows relative densities depending on the x values of the first sintered specimens as in the specimens of FIG. 2. When the x value is larger than 2.5, the relative density is remarkably decreased, and the first sintered density Will influence the sintering density or porosity after the second sintering. As shown in FIG. 2, the highest transmittance at an x value of 2.25 to 2.5 is that the first density sintering has a high density, that is, a small porosity and small pore size as described above, and these small pores can be almost removed from the second sintering Because. On the other hand, when x value was 3.0 or more, especially 3.5 or more, large pores with high porosity after the first sintering were not removed during the second sintering.

Fig. 5 shows the linear light transmittance of the oxynitride aluminum specimens having different x values after the first sintering and the second sintering in the wavelength range of 200 nm to 2500 nm. When the x value is 2.25 or 2.5, the visible light wavelength And the transmittance was about 80% in almost the entire region of FIG. Especially, when x value is larger than 2.5, the visible light transmittance decreases and it decreases greatly from 3.5.

FIG. 6 is a photograph of a fractured section of aluminum oxynitride specimens subjected to the first sintering and the second sintering with a scanning electron microscope. At an x value of 2.0, the grain boundary of the left grain was uneven, And the second phase of the? '-AlON phase is generated at 2.25 or less. This second phase was also confirmed by the x-ray diffraction pattern, and when the x value in FIG. 3 was 2.0, the transmittance was somewhat reduced. At the x value of 2.25, a slight secondary phase was found, but the sinterability was higher than 2.5, resulting in the highest light transmittance at 2.25. When the x value was 2.5 or less, it was difficult to find the pores in the specimen. When the x value was higher than 3.0, micropores were observed particularly in the crystal grains. As the x value increases, the porosity is greatly increased and the permeability is greatly reduced. The micropores in the crystal grains have a large amount of AlN which is low in sinterability after the first sintering, so that many large pores are removed during the second sintering But they have not yet entered the crystal grains and have remained.

≪ Example 2 >

The specimens were subjected to the first sintering only in the same manner as in Example 1, except that the temperature was changed from 1600 ° C to 1725 ° C.

FIG. 7 shows fractured cross-sectional images of the specimens having different temperatures from 1625 ° C to 1725 ° C. After 10 hours of the first sintering, the highest density was observed at 1650 ° C, and at 1675 ° C or higher, Respectively. This is because Al ₂ O ₃ reacts with AlN to cause phase transformation to aluminum oxynitride, and aluminum oxynitride sintering is slow at that temperature.

FIG. 8 is a result of quantitative analysis of X-ray diffraction patterns of specimens having different primary sintering temperatures ranging from 1600 ° C. to 1725 ° C. The volume ratios of AlON, Al ₂ O ₃ and AlN phases are shown in FIG. have. After 10 hours at 1650 ° C, phase transformation to aluminum oxynitride phase was much progressed and AlON phase became main phase. At this temperature, densification and phase transformation coincided, but the densification was completed when Al ₂ O ₃ remained relatively large . At 1675 ° C, the phase transformation was completed and only the AlON phase remained. In this case, the phase transformation occurred too early before the densification became densified and the densification did not work well and many pores remained, as shown in Fig. Therefore, it is important to perform primary sintering to increase possible relative density, that is, to remove pores, before phase transformation occurs too much, that is, when a large amount of Al ₂ O ₃ remains. At a temperature of 1600 캜 to 1625 캜, even after 10 hours, Al ₂ O ₃ Phase will remain, but the sintering will be relatively slow due to the low temperature, so at this temperature, the pores should be removed by a first sintering for a relatively longer time.

≪ Example 3 >

Was the primary sintering temperature is 1640 ℃, holding time 1 was varied to 10 hours, as a sintering additive to include all of the MgO and Y ₂ O ₃ or Y ₂ O ₃ only on and is carried out, except that the inclusion Example 1 Aluminum oxide ceramic specimens were prepared.

FIG. 9 shows the fracture microstructure after the first sintering, which varies with the first sintering holding time of the samples including both MgO and Y ₂ O ₃ ranging from 1 hour to 10 hours, When the holding time was short, the porosity was high and the relative density was continuously increased until 10 hours. Therefore, sufficient maintenance of 10 hours is required to obtain a high relative density at this first sintering temperature.

10 shows the linear transmittance of the 632 nm wavelength light depending on the x value and MgO in the first sintering depending on whether or not MgO was included in the sintering additive. In the case of MgO-containing specimens, Y ₂ O ₃ The transmittance was always higher than that of the included specimens. The transmittance of specimens containing only Y ₂ O ₃ increased significantly as the x value decreased from 4.5 to 2.5, as in the specimens containing both specimens. When the retention time of the first sintering was 2 hours, the transmittance was 80.8% at x value 2.5, and gradually increased with increasing retention time. When the retention time was 10 hours, 83.3% A very high transmittance was obtained. This indicates that the higher the relative density after the first sintering, the higher the transmittance, even with the same x value. Therefore, even if the x value is equal to 2.5, the sinterability is increased due to the presence of vacancies in the aluminum oxynitride during the second sintering. However, if the density after the first sintering is not sufficiently high, that is, if the porosity is high, Loses. Therefore, the higher the relative density after the first sintering due to the high sinterability due to the high content of Al ₂ O _{3 in} the first sintering while the x value is as low as 2.5 (21.7 mol% AIN), the higher the light transmittance is obtained.

<Example 4>

Except that Y ₂ O ₃ as a sintering additive was contained in an amount of 0.08% by weight while the amount of MgO was changed from 0 to 0.5% by weight, primary sintering was carried out at 1650 ° C. for 10 hours, and the x value was fixed at 2.5 Aluminum oxynitride ceramic specimens were sintered in the same manner as in Example 1 and subjected to secondary sintering.

Fig. 11 shows the linear light transmittance in the wavelength range of 200 to 2500 nm which varies depending on the amount of MgO added, and Fig. 12 shows the tendency of the transmittance according to the addition amount of MgO. The content of MgO was 78.9%. When MgO was added at 0.05 wt%, it was 79.3%. The addition of 0.15 wt% showed the highest transmittance of 83.0%. On the other hand, the transmittance was remarkably decreased at 0.3 wt%, and at 0.5 wt%, the transmittance was lower than that of the sample not containing MgO at all. According to X-ray diffraction analysis and microstructure observation, a small amount of MgO added of at least 0.3 wt% did not precipitate a secondary phase such as Mg-spinel. The solubility limit of Mg for aluminum oxynitride is known to be 4000 ppm or more at 1870 ℃ (Solubility Limits of La and Y in Aluminum Oxynitride at 1870 ℃, J. Am. Ceram. Soc., 91 [5] , So from 0.5 wt.% It may exceed the solubility limit. This effect of MgO occurs only within the Mg solubility limit of aluminum oxalate because it can reduce sinterability or permeability if the secondary phase precipitates out of the solubility limit. The role of MgO in AlON sintering at these solubility limits may be similar to the MgO effect, which allows the continuous removal of pores by preventing abnormal grain growth at the final stage of Al ₂ O ₃ sintering. Therefore, the addition of MgO seems to be effective for the secondary sintering, that is, to continuously remove the pores at the stage where the grain growth rapidly occurs on the AlON already having a relative density exceeding 95%. Nonetheless, it is a peculiar phenomenon that when the transmittance is increased from 0.15% by weight to 3.0% by weight or more, the transmittance decreases even though it is still within the employment limit. As described above, WO 08/047955 also discloses the MgO effect when the AlN content is fixed at 35 mol%. In the present invention, as in the present invention, the same tendency of transmittance It is also an exciting new phenomenon that promoting effect.

&Lt; Example 5 >

The first sintered aluminum oxalate ceramic specimens were prepared in the same manner as in Example 1, except that the second sintering was performed at 70 ° C for 5 hours.

13 shows the linear transmittance of the 632 nm wavelength light according to the x value of the aluminum oxalate ceramic specimens prepared in this way and the straightness of the specimens after the first sintering and the second sintering in FIG. In comparison with the transmittance. When the second sintering time is prolonged, the pores are not only reduced or removed, but also the grain growth is further increased, so that the light scattering in the grain boundaries is reduced and the transmittance is increased. Therefore, the 5-hour specimens showed higher overall permeability than the 2-hour specimens. Also, the transmittances according to x values showed the same tendency, and the highest transmittance was observed at 2.25 and 2.5, respectively. However, at 5 hours of final sintering, 2.5 samples showed higher permeability than 2.25 samples. This may be due to the more generated φ'-AlON secondary phase in the 2.25 specimen.

The linear transmittance of 632 nm wavelength light was very high at 84.9% when the sintering furnace x value of 2.5 hours at 1970 ℃, which is a relatively low final sintering temperature, was 2.5, considering the surface reflection of aluminum oxynitride with refractive index Reaching 99% or more of the theoretical linear transmittance and approaching the transmittance of sapphire which is a single crystal.

FIG. 14 shows the Vickers hardness and the average grain size measured at a load of 2.94 N for these specimens. The larger the x value, the smaller the grain size under the influence of the relatively large pores during sintering. When x value is 2.5, it is similar to Vickers hardness of AlON which is known as 16.1 GPa, but when x value decreases, it increases greatly from 2.25 to 17.7 GPa and from 2.0 to 17.9 GPa. This is probably due to the φ'-AlON secondary phase with an x value of 2.25. If the x value is larger than 2.5, the hardness is increased somewhat, but it is presumed that the grain size decreases and the transparency may be greatly reduced depending on the final sintering temperature and time. AlON having a very low x value of 2.25 can be a useful transparent ceramic having a high degree of transparency of 81% or more and a high hardness or abrasion resistance because the? '-AlON secondary phase slightly reduces the transparency but greatly increases the hardness. That is to say, regardless of the production method of aluminum oxynitride, that is, when a mixed powder of Al ₂ O ₃ and AlN is reacted or sintered using the synthesized AlON powder, or when the x value is low to 2.25 or less, -AlON secondary phase is generated and the hardness is increased.

&Lt; Example 6 >

The first sintering was carried out at 1650 캜 for 10 hours, the second sintering at 1950 캜 for 7 hours or 20 hours, the x value was fixed at 2.5, and the thickness of the specimen varied from 0.75 mm to 5 mm. 1, the sintered aluminum oxynitride ceramic specimens were prepared by sintering and sintering.

Fig. 15 shows the linear transmittance of 632 nm wavelength light varying from 0.75 mm to 5 mm depending on the thickness of the specimen. The thinner the thickness, the higher the transmittance is. Despite the sintering at 1950 ° C for 7 hours, the transmittance was more than 80% up to about 2 mm. However, as the thickness increases, it is greatly reduced to less than 80%, so for high transmissivity, or for thick applications, increase the final sintering temperature or increase the sintering time. When the thickness is increased, the number of pores in which light is scattered increases, and the increase in the number of polycrystalline grain boundaries scattered by the light becomes a main cause of decrease in transmittance. As the final sintering temperature is increased or the sintering time is increased, the transmittance is increased. This is because the porosity is decreased, but the grain growth is further increased and the grain size is decreased.

However, as shown in Fig. 6, when the x value is 3.5 (28 mol% of AlN) or more, micropores exist in the crystal grains, and during the ceramic sintering, It is well known that removal is difficult. That is, when the value of x is large, there is a limit in increasing the final sintering temperature or increasing the permeability by increasing the time. Therefore, the x value sufficiently low to obtain a high transmittance is crucially important. Of course, as described above, in order to produce transparent oxynitride by reaction sintering of Al ₂ O ₃ and AlN mixed powder, sufficient primary Sintering must be accompanied. In addition, the addition of a relatively narrow range of 0.15 wt.% MgO in the employment limit is also very important for obtaining high transmittance.

The primary sintering is applied to produce transparent oxynitride by reaction sintering of Al ₂ O ₃ and AlN mixed powders, but the significance of the small x value of 2.5 or less is not only the reaction sintering of Al ₂ O ₃ and AlN mixed powder AlON powders can be synthesized and then sintered. When sintering without first sintering, since the temperature is rapidly increased to 600 ° C. per hour, the AlON phase is formed in a state containing many pores which are not densified, and the sintering temperature rises to 1900 ° C. or higher. This is similar to the sintering of AlON specimens without the effect of the primary sintering. FIG. 2 shows the light transmittance of the sintered specimens according to x value without the first sintering. That is, the transmittance obtained by the sintering of the AlON phase showed the same tendency as that of the second sintering of Al ₂ O ₃ and AlN mixed powders having a relative density of around 95% through the first sintering. When the x value decreased to 2.5, the transmittance increased greatly, and decreased to 5.0. From these results, it can be seen that the low x value will have the effect of improving the sinterability or densification as in the reaction sintering of Al ₂ O ₃ and AlN mixed powders even after sintering after synthesizing AlON powder, As a result, it will result in greatly improved transmissivity.

As described above, when aluminum oxynitride is produced by reaction sintering of Al ₂ O ₃ and AlN mixed powder, the x value is improved by increasing the densification of Al ₂ O ₃ and AlN composite in the first sintering, In the second sintering, there are two different effects of increasing sinterability by increasing the vacancies of Al cations in AlON. On the other hand, when AlON powder is synthesized to produce powder, aluminum oxynitride is produced, There is only one effect. However, with the second effect alone, as described above, the tendency of the transmittance obtained by sintering without the first sintering in FIG. 2 has a great influence, so that the low x value means that oxynitride It can be easily expected that the transmittance of aluminum is greatly improved.

Likewise, the effect of MgO as a small amount of sintering additive is also expected to lead to a large increase in transmittance even when aluminum oxynitride is produced through sintering using the synthesized AlON powder as described above. WO 08/047955 discloses that Al ₂ O ₃ and AlN mixed powders in which the AlN composition of the raw material is fixed at 35 mol% are reacted at 2000 ° C. for 5 hours The transmittance of the final sintered specimen in visible light also changed dramatically depending on the amount of MgO added. That is, as the amount of MgO changed from 0 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt% and 0.3 wt%, the transmittance changed greatly to 0.2%, 3.2%, 63.1%, 28.7% and 2.5%. As the amount of MgO increased from 0.05 wt% to 0.1 wt%, the transmittance rose vertically from 3.2% opaque to 63.1% relatively transparent and to 2.5% with 0.3 wt% increase. 10 shows that the MgO effect is effective regardless of the x value, that is, the x value ranges from 2.5 to 4.5. Therefore, it can be easily predicted that the effect of increasing the transmittance of MgO in the second sintering will be exerted in the same manner when aluminum oxynitride is produced through sintering using the synthesized AlON powder.

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. It will be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims (4)

A method for producing a transparent polycrystalline aluminum oxynitride in which a mixed powder of Al ₂ O ₃ and AlN is sintered at atmospheric pressure, characterized in that the content of pure AlN is 17 to 26 mol% and the relative density is 1575 to 1675 ° C. Sintering in a first stage; And second sintering at 1950 ° C to 1990 ° C so as to achieve a higher relative density than the first sintering, characterized in that the prepared 1.5 mm thick specimen has a 632 nm wavelength visible light linear transmittance of 80% or more By weight based on the total weight of the aluminum oxide. The method of claim 1, wherein the method comprises adding 0.02 wt% to 0.5 wt% Y ₂ O ₃ or La ₂ O ₃ as a sintering additive, 0.016 wt% to 0.39 wt% yttrium (Y) And a lanthanum compound containing lanthanum (La) in an amount of from 0.1% by weight to 0.42% by weight. [3] The method according to claim 2, wherein the manufacturing method further comprises a magnesium compound containing 0.06 wt% to 0.29 wt% MgO as a sintering additive, or 0.037 wt% to 0.17 wt% magnesium (Mg) Method of manufacturing aluminum. A method for producing a transparent polycrystalline aluminum oxynitride in which a mixed powder of Al ₂ O ₃ and AlN is reactively sintered, characterized in that the content of pure AlN is 17 to 26 mol% and the relative density is at least 95% Primary sintering at normal pressure; And secondary sintering by pressurizing to a pressure higher than the atmospheric pressure to 10 MPa or lower at a nitrogen gas pressure of 1950 ° C to 1990 ° C to achieve a higher relative density than the primary sintering, Wherein the transparent visible light linear transmittance is 80% or more.

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