阅读说明：本技术 一种低钠微晶α氧化铝的制备方法 (Preparation method of low-sodium microcrystalline alpha-alumina ) 是由 赵善雷 齐波 王少武 常帅 于 2021-01-29 设计创作，主要内容包括：本发明特别涉及一种低钠微晶α氧化铝的制备方法,属于无机非金属材料合成技术领域,方法包括：获取原料,原料包括氢氧化铝或氧化铝；将脱钠剂和煅烧助剂混合与原料,获得煅烧混合料,脱钠剂的有效成分包括二氧化硅；将煅烧混合料进行煅烧,冷却后获得低钠微晶α氧化铝；制得的低钠微晶α氧化铝具有独特的优良性能,化学纯度高、原晶粒度小、易粉磨、流动性佳,陶瓷烧结温度更低,易于烧结收缩成致密陶瓷体；整个工艺避免了外来物质的不利影响,如大量矿化剂对产品和环境的污染；且采用的脱钠剂成本低,可以多次重复使用。(The invention particularly relates to a preparation method of low-sodium microcrystalline alpha-alumina, belonging to the technical field of inorganic non-metallic material synthesis, and the method comprises the following steps: obtaining a raw material, wherein the raw material comprises aluminum hydroxide or aluminum oxide; mixing a sodium removing agent and a calcining auxiliary agent with the raw materials to obtain a calcined mixture, wherein the effective component of the sodium removing agent comprises silicon dioxide; calcining the calcined mixture, and cooling to obtain low-sodium microcrystalline alpha-alumina; the prepared low-sodium microcrystalline alpha-alumina has unique excellent performance, high chemical purity, small primary grain size, easy grinding, good fluidity, lower ceramic sintering temperature and easy sintering shrinkage to form a compact ceramic body; the whole process avoids the adverse effects of foreign substances, such as pollution of a large amount of mineralizers to products and the environment; and the adopted sodium removing agent has low cost and can be repeatedly used for many times.)

1. A method for preparing low-sodium microcrystalline alpha alumina, the method comprising:

obtaining a raw material, wherein the raw material comprises aluminum hydroxide or aluminum oxide;

mixing a sodium removing agent and a calcining auxiliary agent with the raw materials to obtain a calcined mixture, wherein the effective component of the sodium removing agent comprises silicon dioxide;

and calcining the calcined mixture, and cooling to obtain the low-sodium microcrystalline alpha-alumina.

2. The method of preparing low-sodium microcrystalline alpha alumina as claimed in claim 1 wherein said silicon dioxide comprises more than 30% by weight of said sodium removal agent.

3. The method of preparing low-sodium microcrystalline alpha alumina as claimed in claim 1, wherein the amount of sodium removal agent added is 0.5-10% by weight of the raw material.

4. The method of preparing low-sodium microcrystalline alpha alumina as claimed in claim 1, wherein the sodium removal agent is added in an amount of 1-5% by weight of the raw material.

5. The method of claim 1, wherein the particle size of the sodium removal agent is 20 mesh to 30 mesh.

6. The method of preparing low-sodium microcrystalline alpha alumina as claimed in claim 1, wherein said calcination aid is a halogenated compound and/or a boron compound; the adding amount of the calcining auxiliary agent accounts for 0.05-1% of the raw materials by weight.

7. The method of preparing low-sodium microcrystalline alpha alumina as claimed in claim 6 wherein said halogenated compound is a fluorine compound and/or a chlorine compound;

the fluorine compound includes at least one of aluminum fluoride, ammonium fluoride, and calcium fluoride;

the chlorine compound comprises at least one of ammonium chloride and magnesium chloride;

the boron compound is boric acid or an organic boride.

8. The method for preparing the microcrystalline alpha-alumina with low sodium content according to claim 1, wherein the calcination temperature of the calcination mixture is controlled to be 1250-1500 ℃, and the calcination time is controlled to be 1-4 h.

9. The method of claim 1 wherein the aluminum hydroxide contains 0.1 to 0.35% by weight Na₂O；

The alumina contains 0.2 to 0.55 percent of Na₂O。

10. The method of making low-sodium microcrystalline alpha alumina of claim 1, further comprising: the low sodium microcrystalline alpha alumina is sieved to isolate the sodium removal agent.

Technical Field

The invention belongs to the technical field of inorganic non-metallic material synthesis, and particularly relates to a preparation method of low-sodium microcrystalline alpha alumina.

Background

The low-sodium microcrystalline alpha alumina is an irreplaceable key basic raw material of special structural ceramics and functional ceramics, is widely applied to industries such as electronic power, metallurgical chemical industry, machinery, energy, environmental protection and the like, and is increasingly applied to high-tech fields such as aerospace, wireless communication, semiconductors, chip packaging, consumer electronics, national defense and military industry and novel industries.

To achieve low sodium microcrystalline alpha alumina, current methods generally include calcination under vacuum, acid washing, or direct mineralizing and sodium removing calcination. The applicant finds in the course of the invention that: the calcination and sodium removal under the vacuum condition have strict requirements on equipment, and the cost is correspondingly increased; the acid elution of sodium is not complete, and the general product Na₂O is more than or equal to 0.10 percent; the direct mineralization and calcination needs the participation of a large amount of mineralizers, the mineralizers react with sodium ions to form gaseous sodium-containing compounds, serious cyclic load is formed in a kiln, the abnormal growth of the primary grain size is caused, and the mineralizers remained in alpha alumina also bring side effects to the production of ceramic products.

Disclosure of Invention

In view of the above problems, the present invention has been made in order to provide a method for preparing low-sodium microcrystalline alpha alumina which overcomes or at least partially solves the above problems.

The embodiment of the invention provides a preparation method of low-sodium microcrystalline alpha-alumina, which comprises the following steps:

obtaining a raw material, wherein the raw material comprises aluminum hydroxide or aluminum oxide;

mixing a sodium removing agent and a calcining auxiliary agent with the raw materials to obtain a calcined mixture, wherein the effective component of the sodium removing agent comprises silicon dioxide;

and calcining the calcined mixture, and cooling to obtain the low-sodium microcrystalline alpha-alumina.

Optionally, the silica accounts for more than 30% by weight of the sodium removal agent.

Optionally, the sodium removing agent is added in an amount of 0.5-10% by weight (based on the weight of the alumina) of the raw material.

Optionally, the particle size of the sodium removing agent is 20-30 meshes.

Optionally, the calcination auxiliary is a halogenated compound and/or a boron compound; the addition amount of the calcination auxiliary agent is 0.05-1% of the raw material (by weight of the alumina).

Optionally, the halogenated compound is a fluorine compound and/or a chlorine compound;

the fluorine compound includes at least one of aluminum fluoride, ammonium fluoride, and calcium fluoride;

the chlorine compound includes at least one of ammonium chloride and magnesium chloride.

Optionally, the boron compound is boric acid or an organic boron compound.

Optionally, during the calcination of the calcined mixture, the calcination temperature is controlled to be 1250-1500 ℃, and the calcination time is controlled to be 1-4 h.

Optionally, the aluminum hydroxide contains 0.1-0.35% by weight of Na₂O；

The alumina contains 0.2 to 0.55 percent of Na₂O。

Optionally, the method further includes: the low sodium microcrystalline alpha alumina is sieved to isolate the sodium removal agent.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

the preparation method of the low-sodium microcrystalline alpha-alumina provided by the embodiment of the invention comprises the following steps: obtaining a raw material, wherein the raw material comprises aluminum hydroxide or aluminum oxide; mixing a sodium removing agent and a calcining auxiliary agent with the raw materials to obtain a calcined mixture, wherein the effective component of the sodium removing agent comprises silicon dioxide; calcining the calcined mixture, and cooling to obtain the low-sodium microcrystalline alpha-alumina; the prepared low-sodium microcrystalline alpha-alumina has unique excellent performance, high chemical purity, small primary grain size, easy grinding and good fluidity, thereby further lowering the sintering temperature of the ceramic and facilitating the sintering and shrinkage of the ceramic into a compact ceramic body; the whole process avoids the adverse effects of foreign substances, such as pollution of a large amount of mineralizers to products and the environment; and the adopted sodium removing agent has low cost and can be repeatedly used, so the method provided by the application is an ideal process for preparing the low-sodium microcrystalline alpha alumina.

The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

FIG. 1 is a flow chart of a method provided by an embodiment of the present invention;

FIG. 2 is a process flow diagram provided by an embodiment of the present invention.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.

Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

To achieve low sodium microcrystalline alpha alumina, current methods generally include calcination under vacuum, acid washing, or direct mineralizing and sodium removing calcination. The applicant finds in the course of the invention that: the calcination and sodium removal under vacuum condition have requirements on equipmentThe method is harsh, and the cost is correspondingly increased; the acid elution of sodium is not complete, and the general product Na₂O is more than or equal to 0.10 percent; the direct mineralization and calcination needs the participation of a large amount of mineralizers, the mineralizers react with sodium ions to form gaseous sodium-containing compounds, serious cyclic load is formed in the kiln, the abnormal growth of the original grain size is caused, and the mineralizers remained in the alpha alumina also bring side effects to the production of ceramic products; therefore, the applicant has conducted a great deal of research on the preparation process of the low-sodium microcrystalline alpha alumina, and the embodiment of the application aims to provide a preparation method for producing high-quality low-sodium microcrystalline alpha alumina, which is economical, feasible, stable, reliable and environment-friendly.

According to an exemplary embodiment of the present invention, there is provided a method for preparing low-sodium microcrystalline alpha alumina, the method including:

s1, obtaining a raw material, wherein the raw material comprises aluminum hydroxide or aluminum oxide;

s2, mixing a sodium removing agent and a calcining auxiliary agent with the raw materials to obtain a calcined mixture, wherein the effective component of the sodium removing agent comprises silicon dioxide;

s3, calcining the calcined mixture, and cooling to obtain the low-sodium microcrystalline alpha-alumina;

s4, sieving the low-sodium microcrystalline alpha-alumina to separate the sodium removal agent.

During high temperature calcination of aluminum hydroxide or aluminum oxide material, the crystal is converted from aluminum tetrahedron structure to octahedron structure with the conversion to alpha crystal phase, during the structure rearrangement, intercrystalline sodium ions are gradually dissociated to the surface of aluminum oxide grains and are gradually gasified and sublimated to gaseous sodium in the thermal field environment higher than 1150 deg.c, and simultaneously, the sodium eliminating agent is converted from stable phase quartz to high activity tridymite, cristobalite, SiO₂The phase change of the sodium silicate-aluminum oxide composite material causes the surface area of crystal grains to be abnormally increased and the activity to be rapidly increased, and gaseous sodium ions can be efficiently adsorbed and react with the gaseous sodium ions to generate sodium silicate or sodium aluminosilicate, so that the sodium ions and the aluminum oxide are removed and separated, and finally, the deep purification is realized; na in low-sodium microcrystalline alpha-alumina prepared by adopting method₂O can be stabilized to be below 0.05 percent, and has unique excellent performance and high chemical purity; and isBecause the addition amount of the mineralizer is greatly reduced, the original grain size can be stabilized to be below 2 mu m, the product has small original grain size, easy grinding and good fluidity, and further, the ceramic sintering temperature is lower, and the ceramic is easy to sinter and shrink into a compact ceramic body; the whole process avoids the adverse effects of foreign substances, such as pollution of a large amount of mineralizers to products and the environment; and the adopted sodium removing agent has low cost and can be repeatedly used for many times.

As an alternative embodiment, the silica represents more than 30% by weight of the sodium remover; the addition amount of the sodium removing agent accounts for 0.5-10% of the raw material (calculated by weight of alumina), and more preferably, the addition amount of the sodium removing agent accounts for 1-5% of the raw material; the particle size of the sodium removing agent is 20-30 meshes.

The selection of the sodium removing agent mainly depends on factors such as the raw material to be treated, the variety of the deep sodium removing agent, the particle size, the calcining temperature and the like. The deep sodium removal agent must be capable of binding sodium ions at high temperatures and must contain a sufficient amount of silicon compound, it being noted that the sodium removal agent preferably does not disintegrate during heating so that the particles remain intact and sufficiently strong to be easily separated from the product after the sodium removal reaction. The reason why the silica accounts for more than 30% of the sodium removing agent is that the silica is an effective component for removing sodium and the content of the silica cannot be too low. The adverse effects of a too small value of the fraction are: so that the sodium removal effect in the calcination process of the alpha alumina is poor; the reason why the addition amount of the sodium removing agent is controlled to be 0.5-10% of the raw material is as follows: the best sodium removal effect can be achieved, and the adverse effects of the ratio being too large are: increasing cost, increasing silicon contamination, with too little adverse effect: can not effectively remove sodium and can not meet the performance requirement of a low-sodium microcrystalline alpha alumina product.

As an alternative embodiment, the calcination aid is a halogenated compound and/or a boron compound; the addition amount of the calcination auxiliary agent accounts for 0.05-1% of the raw materials by weight; the halogenated compound is a fluorine compound and/or a chlorine compound; the fluorine compound includes at least one of aluminum fluoride, ammonium fluoride, and calcium fluoride; the chlorine compound comprises at least one of ammonium chloride and magnesium chloride, specifically can be selected from one or more of aluminum fluoride and ammonium fluoride, calcium fluoride, ammonium chloride and magnesium chloride, and the boron compound is boric acid or an organic boride.

The calcining auxiliary agent aims to reduce the calcining temperature and promote the gasification and sublimation of sodium ions, and the reason why the adding amount of the calcining auxiliary agent is controlled to be 0.05-1 percent of the raw material is as follows: the adverse effect of reducing the phase inversion temperature of alpha alumina while controlling the primary grain size of alpha alumina is that: the effect of mineralizing and calcining cannot be exerted, and the adverse effects of the excessive proportion are that: excessive calcination auxiliary can cause abnormal growth of primary grain size, and the calcination auxiliary remained in the alpha alumina can bring side effects to the production of ceramic products.

As an alternative embodiment, the calcination mixture is calcined, the calcination temperature is controlled to be 1250-1500 ℃, and the calcination time is controlled to be 1-4 h.

As an alternative embodiment, the aluminium hydroxide contains 0.1-0.35% by weight of Na₂O; the alumina contains 0.2 to 0.55 percent of Na₂O; it should be noted that the raw material is metallurgical grade industrial aluminum hydroxide or aluminum oxide, the particle size of the raw material is not critical, and when aluminum hydroxide is used as the raw material, the sodium removal effect may be slightly better, and the primary particle size of the product is smaller.

The deep sodium removal agent is added in a solid form, and is present in a solid form before or during calcination, and the calcination auxiliary agent may be added in a solid or liquid form, and both need to be uniformly mixed with the raw material before calcination, and the amount of the deep sodium removal agent and the calcination auxiliary agent added is controlled to allow the Na content in the alpha alumina to be controlled₂The content of O and the primary grain size are controlled, and Na is generally used₂The content of O is stabilized below 0.05 percent, and the primary grain size is stabilized below 2 mu m.

The method for preparing the low-sodium microcrystalline α alumina of the present application will be described in detail below with reference to examples, comparative examples, and experimental data. It should be noted that the range values in the examples indicate that a plurality of tests are performed by taking the range as an arithmetic mean, in other words, the following examples may not only indicate one test, but may indicate a group of tests.

Example 1

S1, using industrial alumina A (Na)₂The O content is 0.48 percent) as the raw material;

s2, adding 1-5% of deep sodium removal agent and 0.1-0.5% of ammonium chloride (the addition amount accounts for the weight percent of the aluminum oxide), wherein the deep sodium removal agent is added in a particle form, and the ammonium chloride is added in a solid form;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1250-1300 ℃ and preserving heat for 1-4 h;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Example 2

S1, using industrial alumina A (Na)₂The O content is 0.48 percent) as the raw material;

s2, adding 1-5% of deep sodium removal agent and 0.1-0.5% of ammonium chloride (the addition amount accounts for the weight percent of the aluminum oxide), wherein the deep sodium removal agent is added in a particle form, and the ammonium chloride is added in a solid form;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1300-1350 ℃, and preserving heat for 1-4 h;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Example 3

S1, using industrial alumina B (Na)₂O content of 0.30%) as raw material;

s2, adding 1-3% of deep sodium removal agent and 0.05-0.1% of aluminum fluoride (the addition amount accounts for the weight percent of aluminum oxide), wherein the deep sodium removal agent is added in a particle form, and the aluminum fluoride is added in a solid form;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1350-;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Example 4

S1, using industrial aluminum hydroxide C (Na)₂O content of 0.30%) as raw material;

s2, adding 1-5% of deep sodium removal agent and 0.1-0.5% of boric acid (the addition amount accounts for the weight percent of the aluminum oxide), wherein the deep sodium removal agent is added in a particle form, and the boric acid is added in a liquid uniform spraying form;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1300-1400 ℃, and preserving heat for 1-4 h;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Example 5

S1, using industrial aluminum hydroxide D (Na)₂O content of 0.10%) as raw material;

s2, adding 1-3% of deep sodium removal agent and 0.05-0.3% of boric acid (the addition amount accounts for the weight percent of alumina), wherein the deep sodium removal agent is added in a particle form, and the boric acid is added in a solid form;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at 1250-1320 ℃ and preserving heat for 1-4 h;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Example 6

S1, using industrial aluminum hydroxide C (Na)₂O content of 0.30%) as raw material;

s2, adding 0.1-0.5% of boric acid in a solid form (the addition amount accounts for the weight percent of the aluminum oxide); then 5 percent (calculated by weight of alumina) of deep sodium removal agent A (the content of silicon dioxide is 55 percent) is added;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1300-1400 ℃, and preserving heat for 1-4 h;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Example 7

S1. in industryAluminum hydroxide C (Na)₂O content of 0.30%) as raw material;

s2, adding 0.1-0.5% of boric acid in a solid form (the addition amount accounts for the weight percent of the aluminum oxide); then 5 percent (calculated by weight of alumina) of deep sodium removal agent B (the content of silicon dioxide is 98 percent) is added;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1300-1400 ℃, and preserving heat for 1-4 h;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Example 8

S1, using industrial alumina B (Na)₂O content of 0.30%) as raw material;

s2, adding 0.5% of deep sodium removal agent and 0.05% -0.1% of aluminum fluoride (the addition amount accounts for the weight percent of aluminum oxide), wherein the deep sodium removal agent is added in a particle form, and the aluminum fluoride is added in a solid form;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1350-;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Example 9

S1, using industrial alumina B (Na)₂O content of 0.30%) as raw material;

s2, adding 10% of deep sodium removal agent and 0.05% -0.1% of aluminum fluoride (the addition amount accounts for the weight percent of aluminum oxide), wherein the deep sodium removal agent is added in a particle form, and the aluminum fluoride is added in a solid form;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1350-;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Comparative example 1

S1, using industrial alumina B (Na)₂O content of 0.30%) as raw material;

s2, adding 0.1% of deep sodium removal agent and 0.05% -0.1% of aluminum fluoride (the addition amount accounts for the weight percent of aluminum oxide), wherein the deep sodium removal agent is added in a particle form, and the aluminum fluoride is added in a solid form;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1350-;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Comparative example 2

S1, using industrial alumina B (Na)₂O content of 0.30%) as raw material;

s2, adding 11% of deep sodium removal agent and 0.05% -0.1% of aluminum fluoride (the addition amount accounts for the weight percent of aluminum oxide), wherein the deep sodium removal agent is added in a particle form, and the aluminum fluoride is added in a solid form;

s3, uniformly mixing the deep sodium removal agent, the calcination auxiliary agent and the raw materials; calcining in a box-type muffle furnace at the temperature of 1350-;

s4, after calcination, naturally cooling, and sieving and separating the product and the reacted deep sodium removal agent by a 40-mesh sieve.

Examples of the experiments

The alpha alumina prepared in examples 1 to 9 and comparative examples 1 to 2 was examined and the results are shown in the following table.

	Average product Na2Content of O	Primary grain size D of product50
			Example 1	About 0.06%	≤1.5μm
Example 2	≤0.05％	≤1.5μm
			Example 3	≤0.04％	≤2.0μm
Example 4	≤0.04％	≤1.7μm
			Example 5	≤0.04％	≤1.5μm
Example 6	≤0.04％	≤1.8μm
			Example 7	≤0.04％	≤1.8μm
Example 8	≤0.04％	≤2.0μm
			Example 9	≤0.04％	≤1.9μm
Comparative example 1	≤0.2％	≤2.3μm
			Comparative example 2	≤0.04％	≤1.μm

From the data in the table, it can be obtained from the data of the examples, and Na of the alpha alumina prepared by the method provided in the examples of the present application₂The O content is stabilized at about 0.05 percent, the primary grain size is stabilized below 2 mu m, the data of the examples 6 and 7 can be used, and the sodium removing agent with the silicon dioxide content of 55 percent and 98 percent is adopted, so that the final products have nearly the same properties; from the data of examples and comparative examples, the starting material Na₂The higher the O content is, the larger the mixing amount of the sodium removing agent and the auxiliary agent is; the higher the temperature is, the better the sodium removal effect is; the sodium removing agent is added continuously after the adding amount exceeds a certain limit, and the Na of the product cannot be further reduced₂The content of O; the sodium removal effect of alpha alumina in the calcination process can be influenced by insufficient mixing amount of the sodium removal agent.

One or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:

(1) in the embodiment of the invention, the prepared low-sodium microcrystalline alpha-alumina has unique excellent performance, high chemical purity, small primary grain size, easy grinding, good fluidity, lower ceramic sintering temperature and easy sintering shrinkage to form a compact ceramic body. (ii) a

(2) The preparation method of the low-sodium microcrystalline alpha-alumina provided by the embodiment of the invention reduces the adverse effects of foreign substances, such as pollution of a large amount of mineralizers to products and environment. The deep sodium removal agent has low cost and can be repeatedly used;

(3) the alpha alumina prepared by the embodiment of the invention is especially suitable for various advanced ceramic fields such as special structural ceramics, functional ceramics and the like;

(4) the preparation method of the low-sodium microcrystalline alpha-alumina provided by the embodiment of the invention is economical, feasible, stable, reliable and environment-friendly.

Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.