A low-porosity corundum and its preparation method

Abstract

The present invention discloses a low-porosity corundum and a preparation method thereof. The low-porosity corundum is composed of the following raw materials by weight percentage of the total weight of the raw materials: 90%-98% of alumina, 1.5%-5% of yttrium oxide, and 0.5%-5% of lanthanum oxide. The preparation method is to weigh each raw material according to the above weight percentages, mix alumina, yttrium oxide, and lanthanum oxide evenly, and then transfer them into an electric melting furnace for electric melting; wait until alumina, yttrium oxide, and lanthanum oxide are completely melted; continue to maintain the melt temperature and carry out refining. After the refining is completed, natural cooling and crystallization are carried out to obtain spherical crystals, that is, the low-porosity corundum. The low-porosity corundum of the present invention contains more than 95% of α-alumina phase, and the porosity of the low-porosity corundum can reach less than 1%; therefore, the low-porosity corundum has the advantages of low porosity, good heat resistance, good toughness, and strong stability.

Description

Technical Field

[0001] The present invention relates to the technical field of refractory materials, and in particular to a low-porosity corundum and a preparation method thereof. Background Art

[0002] Corundum has strong acid and alkali resistance, good dimensional stability, good formability, stable crystal phase, and high hardness, and is widely used in the reinforcement and toughening of various products such as plastics, rubbers, ceramics, and refractory materials; however, at present, the porosity of existing general corundum is as high as 30%-45%, and its crystals are in a needle-like structure or a plate-like structure. The heat resistance, strength, toughness, and structural stability of the products made of such corundum will inevitably be affected. Therefore, reducing the porosity of corundum and changing the crystal structure of corundum are of practical significance for improving the properties of corundum. Summary of the Invention

[0003] Therefore, in view of the above problems, the purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a low-porosity corundum with low porosity, good heat resistance, good toughness, and high stability; in addition, the present invention also provides a preparation method of the low-porosity corundum.

[0004] The technical solution of the present invention to solve the above technical problems is as follows: A low-porosity corundum, calculated by weight percentage of the total raw materials, is composed of the following raw materials: 90%-98% of alumina, 1.5%-5% of yttrium oxide, and 0.5%-5% of lanthanum oxide.

[0005] The beneficial effects of the present invention are: At room temperature, alumina mainly exists in the γ-alumina crystal form and can be completely transformed into α-alumina above 1500°C. Therefore, at the electrofusion temperature above 2300°C, the γ-alumina crystals are completely transformed into α-alumina. In addition, yttrium oxide in the raw materials of the present invention reacts with alumina during the electrofusion process to form yttrium aluminate, which can promote the spherical structuring of alumina crystals during the transformation from the γ-alumina crystal form to the α-alumina crystal form, avoiding the development of α-alumina crystals into needle-like crystal structures or plate-like crystal structures. After the electrofusion and refining are completed, natural cooling and crystallization obtain spherical crystals, and the spherical structure of the crystals effectively reduces the distance between the grains inside the crystals. In addition, lanthanum oxide in the raw materials has a crystallization densification effect and can further improve the structural density of the product. Furthermore, the low-porosity corundum contains more than 95% of the α-alumina phase formed by phase transformation. Thus, the formed corundum has a low porosity, and the porosity can reach less than 1%. The extremely low porosity and high α-alumina phase content can greatly improve the heat resistance, strength, toughness, and structural stability of corundum, making the products manufactured with it have good quality.

[0006] In addition, on the basis of the above technical solutions, the present invention can also be improved as follows and can also have the following additional technical features.

[0007] Furthermore, the low-porosity corundum of this embodiment is composed of the following raw materials by weight percentage of the total raw materials: 95% alumina, 3.5% yttrium oxide, and 1.5% lanthanum oxide. The formed low-porosity corundum has a low porosity, and the porosity can reach below 1%.

[0008] Furthermore, the purity of the alumina is above 95%; the high purity of the alumina and the low content of harmful impurities can reduce the damage to the corundum structure when impurities are transformed into gas and escape during the electrofusion process, avoid the increase of the corundum porosity, and can also reduce the influence of impurities on the properties of the corundum.

[0009] In addition, a preparation method of a low-porosity corundum provided by the present invention includes the following steps:

[0010] (1) Weigh the following raw materials by weight percentage of the total raw materials: 90%-98% alumina, 1.5%-5% yttrium oxide, and 0.5%-5% lanthanum oxide;

[0011] (2) Then mix the alumina, yttrium oxide, and lanthanum oxide evenly, transfer them into an electric furnace for electrofusion, and wait for the alumina, yttrium oxide, and lanthanum oxide to dissolve;

[0012] (3) Electro-fuse until the raw materials are completely dissolved; continue to maintain the melt temperature and carry out refining. After the refining is completed, cool and crystallize to obtain spherical crystals, that is, the low-porosity corundum.

[0013] Through the preparation method of the low-porosity corundum of the present invention, at an electrofusion temperature above 2300 °C, γ-alumina crystals are completely transformed into α-alumina. In addition, yttrium oxide in the raw materials of this embodiment reacts with alumina during the electrofusion process to generate yttrium aluminate, which can promote the spherical structuring of alumina crystals during the transformation from γ-alumina crystal form to α-alumina crystal form, and avoid the development of α-alumina crystals into needle-like crystal structures or plate-like crystal structures. After the electrofusion and refining are completed, natural cooling and crystallization are carried out to obtain spherical crystals, and the spherical structure of the crystals effectively reduces the distance between grains inside the crystals. In addition, lanthanum oxide in the raw materials has a crystallization densification effect, which can further improve the structural density of the product. Moreover, the α-alumina phase formed by phase transformation in the low-porosity corundum reaches more than 95%. Thus, the formed corundum has a low porosity, and the porosity can reach below 1%. The extremely low porosity and high α-alumina phase content can greatly improve the heat resistance, strength, toughness, and structural stability of the corundum, making the products manufactured with it have good quality.

[0014] Furthermore, in step (2) of the preparation method of the low-porosity corundum of the present invention, the electrofusion temperature is 2300 °C - 2700 °C; the high temperature enables the γ-alumina crystal form to be fully transformed into the α-alumina crystal form.

[0015] Furthermore, in step (3) of the preparation method of the low-porosity corundum of the present invention, the cooling method is natural cooling; this is to prevent the generation of large shrinkage stresses due to rapid cooling, which may damage the crystalline crystal structure.

[0016] Furthermore, the porosity of the low-porosity corundum prepared by the preparation method of the low-porosity corundum of the present invention is 1% or less; the low-porosity corundum has a low porosity and excellent properties such as high density, high strength, and high toughness.

[0017] Furthermore, the α-aluminum oxide phase in the low-porosity corundum prepared by the preparation method of the low-porosity corundum of the present invention reaches more than 95%; the high content of the α-aluminum oxide phase in the low-porosity corundum results in good heat resistance and anti-phase change structure stability.

[0018] Furthermore, the alumina, yttrium oxide, and lanthanum oxide are all in powder form; processing alumina, yttrium oxide, and lanthanum oxide into powder form is beneficial for shortening the electrofusion time, reducing the chemical reaction temperature between oxides, increasing the contact area between reactants, accelerating the reaction, and reducing power consumption.

[0019] Furthermore, the particle sizes of the alumina, yttrium oxide, and lanthanum oxide are all 30 - 70 μm; the appropriate particle sizes of alumina, yttrium oxide, and lanthanum oxide result in low processing difficulty and are beneficial for obtaining through processing. Specific embodiments

[0020] The principles and features of the present invention will be described below in conjunction with specific embodiments. The examples given are only for explaining the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0021] Example 1:

[0022] The low-porosity corundum of this example is composed of the following raw materials by weight percentage of the total raw materials: 90% alumina, 5% yttrium oxide, and 5% lanthanum oxide.

[0023] Specifically, the alumina of this embodiment is preferably alumina with high purity to reduce the impact of impurity elements in alumina on the product. For example, the amount of impurity element sodium in alumina is relatively large. At high temperature, that is, in the process of transformation from γ-alumina crystal to α-alumina, sodium reacts with another impurity element boron in alumina to generate gaseous sodium tetraborate. The gaseous substance continuously escapes from the alumina lattice to the melt surface under the impetus of chemical potential, thereby destroying the crystal structure of alumina. In addition, for alumina products with different requirements, the requirements for the purity of alumina are also different; the purity of alumina affects the physical and mechanical properties and service life of the products made from it. Specifically, the "high purity of alumina" in this embodiment refers to the small amount of inevitable or difficult-to-remove impurities contained in alumina. The essence of "corundum" in this embodiment is a product mainly composed of α-alumina-based crystals formed by high-temperature reaction and cooling crystallization of alumina, lanthanum oxide, and yttrium oxide.

[0024] Specifically, the aluminum oxide, yttrium oxide, and lanthanum oxide in the raw materials of this embodiment may be in the form of blocks or particles, or may be processed powder particles.

[0025] Specifically, the raw material of this embodiment contains yttrium oxide. Under electric melting, the temperature is above 2300°C, and the γ-aluminum oxide crystals are completely transformed into α-aluminum oxide. In addition, the yttrium oxide in the raw material of this embodiment reacts with alumina to form yttrium aluminate during the electric melting process. Yttrium aluminate can promote the spherical structure of alumina crystals during the transformation from γ-aluminum oxide crystal form to α-aluminum oxide crystal form, and prevent the α-aluminum oxide crystals from developing into needle-shaped crystal structures or plate-shaped crystal structures. After the electric melting and refining are completed, the natural cooling crystallization obtains spherical crystals. The spherical structure of the crystal effectively reduces the distance between the grains inside the crystal. In addition, the lanthanum oxide in the raw material has a crystal densification effect, which can further improve the structural density of the product. Furthermore, the α-aluminum oxide phase formed by phase transformation in the low-porosity corundum is more than 95%. As a result, the porosity of the formed corundum is low, and the porosity can reach less than 1%. The extremely low porosity and high α-alumina phase content can greatly improve the heat resistance, strength, toughness and structural stability of corundum, making the products manufactured with it have good quality.

[0026] In one embodiment of the present invention, the low porosity corundum of this embodiment is composed of the following raw materials in terms of percentage by total weight of the raw materials: 90% aluminum oxide, 5% yttrium oxide, and 5% lanthanum oxide. The low porosity corundum formed in this embodiment has a low porosity of up to 0.7%.

[0027] In one embodiment of the present invention, the purity of the alumina is above 95%; specifically, the high purity of the alumina and the low content of harmful impurities can reduce the damage to the corundum structure when impurities are transformed into gases and escape during the electrofusion process, avoid the increase in the porosity of the corundum, and also reduce the influence of impurities on the properties of the corundum. The high purity of the alumina means that the inevitable impurities it contains are few, reducing the damage to the corundum structure due to the formation of gas overflow by impurities during the electrofusion process and increasing the porosity of the corundum; and the influence of impurities on the corundum can be reduced. Products made and formed using alumina with a purity above 95% have good heat resistance, good toughness, and high stability; using alumina with a purity above 95%, the heat resistance, toughness, and stability of the products are all better. In addition, the lanthanum oxide and yttrium oxide raw materials in this embodiment are all high-purity raw materials with an impurity mass less than 0.5%.

[0028] In addition, this embodiment provides a method for preparing low-porosity corundum, which includes the following steps:

[0029] (1) Weigh the following raw materials according to the percentage content of the total weight of the raw materials: 90% alumina, 5% yttrium oxide, and 5% lanthanum oxide;

[0030] (2) Then add the alumina, yttrium oxide, and lanthanum oxide into an electric melting furnace, mix and stir evenly, and then perform electrofusion until the alumina, yttrium oxide, and lanthanum oxide are melted;

[0031] (3) Keep electrofusing until the raw materials are completely melted; continue to maintain the melt temperature and perform refining. After the refining is completed, cool and crystallize to form spherical crystals, and the low-porosity corundum can be obtained.

[0032] Specifically, the "refining" in this embodiment refers to removing impurities from the melted melt. The refining technology is commonly used in the art to remove impurities from the melt, and the refining time can be 30 - 60 minutes. Specifically, the electrofusion is carried out in an electric melting furnace, and the required continuous electrofusion time is also related to the amount of raw materials for electrofusion at one time. When specifically performing electrofusion, the electrofusion time can be appropriately set according to the raw materials to be electrofused. In step (3) of this embodiment, the electrofusion temperature is 2500 °C, so that the γ-alumina crystals are fully transformed into α-alumina.

[0033] Specifically, the cooling process in this embodiment is natural cooling; to prevent large shrinkage due to too fast cooling from damaging the crystalline crystal structure.

[0034] Specifically, the porosity of the low-porosity corundum obtained in this embodiment is 0.7%, and the density is 4.05 g / cm 3 ; The low-porosity corundum has good quality and high density.

[0035] Through the preparation method of the low-porosity corundum of this embodiment, under electrofusion, when the temperature is above 2300 °C, γ-aluminum oxide crystals are completely transformed into α-aluminum oxide; yttrium oxide in the raw materials of the present invention reacts with aluminum oxide during electrofusion to generate yttrium aluminate, and yttrium aluminate can promote the spherical structuring of aluminum oxide crystals during the transformation from γ-aluminum oxide crystal form to α-aluminum oxide crystal form, avoiding the development of α-aluminum oxide crystals into needle-shaped crystal structures or plate-shaped crystal structures. After electrofusion and refining are completed, natural cooling and crystallization are carried out to obtain spherical crystals, and the spherical structure of the crystals effectively reduces the spacing between the grains inside the crystals. In addition, lanthanum oxide in the raw materials has a crystallization densification effect, which can further improve the structural density of the product. Moreover, the low-porosity corundum contains more than 95% of the α-aluminum oxide phase formed by phase transformation. Thus, the formed corundum has a low porosity, the porosity can reach 0.7%, and the density is 4.05 g / cm 3 ; The corundum has good heat resistance, toughness and stability, making the products formed by using it have good quality.

[0036] In an embodiment of the present invention, the alumina, yttrium oxide, and lanthanum oxide are all powder particles; the particle sizes of the alumina, yttrium oxide, and lanthanum oxide are all 30-70 μm. Specifically, the smaller the particle size of the alumina, the more beneficial it is for rapid electrofusion; however, the smaller the particle size, the greater the processing difficulty and the higher the processing cost. The particle size of the alumina in this embodiment is 30-70 μm, which is easy to process.

[0037] Example 2:

[0038] This Example 2 is similar to Example 1. The difference between it and Example 1 is that the low-porosity corundum of this embodiment is composed of the following raw materials by weight percentage of the total raw materials: 95% alumina, 3.5% yttrium oxide, and 1.5% lanthanum oxide.

[0039] In this embodiment, the above components are taken according to the ratio, and the preparation method of this embodiment is the same as that of Example 1; the porosity of the prepared low-porosity corundum is 0.6%, and the density of the prepared low-porosity corundum is 4.10 g / cm 3 。

[0040] Example 3:

[0041] This Example 3 is similar to Example 1. The difference between it and Example 1 is that the low-porosity corundum of this embodiment is composed of the following raw materials by weight percentage of the total raw materials: 98% alumina, 1.5% yttrium oxide, and 0.5% lanthanum oxide.

[0042] In this embodiment, the above components are taken according to the ratio, and the preparation method of this embodiment is the same as that of Example 1; the porosity of the prepared low-porosity corundum is 0.9%, and the density of the prepared low-porosity corundum is 4.0 g / cm 3。

[0043] Through multiple experiments, it is found that the properties of the low-porosity corundum obtained in Examples 1-3 of this embodiment are good; the porosity of the formed corundum is below 1%, and the density is 4.0 g / cm 3 or above; thereby improving the heat resistance, toughness and stability of corundum, so that the products formed by using it in production have good quality.

[0044] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. The present invention can be realized within the upper and lower limit values and interval values of the raw materials, and will not be listed one by one here. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of low-porosity corundum, characterized in that, it comprises the following steps: (1) Weigh the following raw materials according to the percentage content of the total weight of the raw materials: 90%-98% of alumina, 1.5%-5% of yttrium oxide, and 0.5%-5% of lanthanum oxide; (2) Then mix alumina, yttrium oxide and lanthanum oxide evenly, transfer them into an electric melting furnace for electric melting, and wait for alumina, yttrium oxide and lanthanum oxide to melt; (3) Electrically melt until the raw materials are completely melted; continue to maintain the melt temperature and carry out refining. After refining is completed, cool and crystallize to obtain spherical crystals, namely the low-porosity corundum; In step (2), the electric melting temperature is 2300°C - 2700°C; The porosity of the obtained low-porosity corundum is below 1%; The density of the obtained low-porosity corundum is 4.0 g / cm 3 or more.

2. The preparation method of low-porosity corundum according to claim 1, characterized in that, in step (3), the cooling process is natural cooling.

3. The preparation method of low-porosity corundum according to claim 1, characterized in that, the alumina, yttrium oxide and lanthanum oxide are all powder particles.

4. The preparation method of low-porosity corundum according to claim 3, characterized in that, the particle sizes of the alumina, yttrium oxide and lanthanum oxide are all 30 - 70 μm.