JPH07206514A - Abrasion-resistant alumina ceramic - Google Patents

Abstract

PURPOSE:To obtain an alumina ceramic having excellent abrasion resistance using inexpensive raw materials. CONSTITUTION:This abrasion-resistant alumina ceramic is composed of a sintered alumina containing (a) 95-98wt.% of Al2O3 and (b) 2-5-wt.% of a three- component sintering assistant composed of 40-85-wt.% of SiO2, 10-55wt.% of Mg0 and 5-50wt.% of CaO. It has a crystal particle diameter (D) of >=0.8mum (25vol.%), 1.0mum<=D<=3.0mum (50vol.%) and <=4.5mum (80vol.%), a Vickers hardness of >=1,350 and a bulk density of >=3.70g/cm<3>. The ceramic further contains ZrO2 component in addition to the above components.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to wear resistant alumina ceramics.

[0002]

2. Description of the Related Art Ceramics are excellent in corrosion resistance and wear resistance as compared with metals, and ceramics have come to be used as wear-resistant members which have conventionally been made of metal. . Alumina, zirconia, silicon nitride, silicon carbide, etc. are used as ceramics used as such wear-resistant members. Among them, alumina has high hardness, excellent corrosion resistance, and is cheaper than other ceramics. Therefore, it has been widely used. However, as the conventional wear-resistant alumina ceramics, an alumina content of about 90 to 92% by weight is used, and since it contains a large amount of impurities, it contains a large amount of a glass phase in addition to the alumina crystals. It did not have sufficient characteristics as a member. Therefore, for example, as shown in JP-A-62-187157, the alumina content is set to 99.9.
% Or more, a high-strength, high-hardness alumina ceramics containing almost no second phase amount other than alumina crystals such as a glass phase has been developed, but the cost is high because a high-purity alumina raw material is used. It has the problem of being extremely expensive.

[0003]

In view of the problems of the prior art as described above, the present inventor has earnestly studied to obtain an alumina ceramic having excellent wear resistance by using an inexpensive raw material. It was As a result, in the alumina-based ceramics, while keeping the alumina purity within a certain range, using a certain amount of a sintering aid with a specific composition, and further controlling the crystal grain size, hardness and density of the sintered body within a certain range. It has been found that the alumina ceramics controlled to have a value has extremely excellent wear resistance, and has completed the present invention.

That is, the present invention provides the following wear resistant alumina ceramics.

1. i) a) 95 to 98% by weight of Al ₂ O ₃ , and b) 40 to 85% by weight of SiO _2, 10 to 55% by weight of MgO
And an alumina sintered body containing 2 to 5% by weight of a sintering aid composed of three components of CaO and 5 to 50% by weight, and ii) the crystal grain size (D) is D (25% by volume) ≧ 0.8 μm. ,
1.0 μm ≦ D (50% by volume) ≦ 3.0 μm, D (80
%) ≦ 4.5 μm, iii) Vickers hardness of 1350 or more, iv) Bulk density of 3.70 g / cm ³ or more, wear-resistant alumina ceramics.

2. i) a) Al ₂ O ₃ , b) SiO ₂ 40 to 85% by weight, MgO
Z-O containing each component of the sintering aid consisting of 10-55 wt% and CaO 5-50 wt% and c) ZrO _2.
The amount of Al ₂ O ₃ in the component excluding rO ₂ is 95 to 98% by weight, the total amount of each component of the sintering aid is 2 to 5% by weight, and the sintered body excluding ZrO ₂ is Of an alumina sintered body containing 20 parts by weight or less of ZrO ₂ with respect to 100 parts by weight of ii), ii) the crystal grain size (D) is D (25% by volume) ≧ 0.8 μm,
1.0 μm ≦ D (50% by volume) ≦ 3.0 μm, D (80
%) ≦ 4.5 μm, iii) Vickers hardness of 1350 or more, iv) Bulk density of 3.70 g / cm ³ or more, wear-resistant alumina ceramics.

The requirements to be satisfied by the wear resistant alumina-based ceramics of the present invention will be concretely shown below.

A) The content of Al ₂ O ₃ is 95 to 98% by weight.

It is necessary that the content of alumina in the sintered body be 95 to 98% by weight, and thus a sintered body having high wear resistance can be obtained. Alumina content is 95
If it is less than wt%, the amount of impurities in the sintered body will increase,
A large amount of crystals other than alumina crystals and a glass phase are generated at the alumina crystal grain boundaries, which causes a decrease in hardness and a decrease in wear resistance, which is not preferable. Further, when the alumina content exceeds 98% by weight, the sinterability is deteriorated, and firing at high temperature is required for dense sintering, resulting in a large crystal grain size and reduced wear resistance. Is not preferred. Therefore, the alumina content in the sintered body is 95 to 98% by weight, preferably 95.5 to 97.5% by weight.

B) 40 to 85% by weight of SiO ₂ , MgO 1
Each component of the sintering aid composed of three components of 0 to 55% by weight and CaO of 5 to 50% by weight is contained in a total amount of 2 to 5% by weight.

SiO ₂ 40-85% by weight, MgO 10-
By using the sintering aid composed of the three components of 55% by weight and 5 to 50% by weight of CaO, sinterability is improved and grain growth is suppressed. Further, an appropriate glass phase is formed at the alumina crystal grain boundaries, which is also effective in improving the toughness. The sintering aid used must consist of the three components of SiO ₂ , MgO and CaO of the above composition, and if the composition deviates from this range, the sinterability will decrease, and the sintered body will contain other than alumina. A large amount of crystals and glass phases are formed, which causes deterioration in hardness, strength, toughness, etc., which is not preferable.

In the obtained sintered body, each component of the above-mentioned sintering agent is contained within the same composition ratio range as that of the above-mentioned sintering aid, and the total amount of each component is 2 in the sintered body. ~ 5% by weight
It is necessary to be. If this total amount is less than 2% by weight, the sinterability will be poor and the hardness, strength, etc. will be deteriorated. If it exceeds 5% by weight, many crystals and glass phases other than alumina crystals will be formed. Is not preferred. The total amount of each component is preferably 2.5 to 5 in the sintered body.
It is 4.5% by weight.

The content of the alkali metal oxide is preferably 0.5% by weight or less in the sintered body, and if it exceeds this amount, a large amount of glass phase is formed with SiO _{2 and the} like, which is not preferable.

C) The crystal grain size (D) is D (25% by volume) ≧
0.8 μm, 1.0 μm ≦ D (50% by volume) ≦ 3.0 μ
m, D (80% by volume) ≦ 4.5 μm.

In the wear resistant alumina-based ceramics of the present invention, it is necessary to reduce the crystal grain size and narrow the crystal grain size distribution, which makes the alumina ceramics excellent in wear resistance. That is, in the present invention,
It is important that not only the average crystal grain size in the sintered body but also its distribution width is narrow. In addition, in the above rule, D (2
5% by volume) means that the integrated value of the volume-based particle size distribution is 25% when the particle size distribution is calculated based on the volume of the crystal particles.
It is the crystal grain size at the point. Similarly, D (50% by volume) is the crystal grain size at the point where the integrated value is 50%, and D (80% by volume) is the crystal grain size at the point where the integrated value is 80%.

If the crystal grain size D (50% by volume) is less than 1.0 μm, the toughness is lowered, and as a result, the wear resistance is lowered, which is not preferable. Also, the crystal grain size D
If (50% by volume) exceeds 3.0 μm, hardness is lowered and wear resistance is lowered, which is not preferable. Also, 1.0
Even if μm ≦ D (50% by volume) ≦ 3.0 μm, D
When (80% by volume) ≧ 4.5 μm, a large number of large crystal grains are present, wear is preferentially caused by these grains, wear due to grain detachment wear becomes large, and wear resistance deteriorates. It is not preferable because it causes Further, if D (25% by volume) <0.8 μm, toughness is reduced and wear resistance is reduced, which is not preferable. Preferably, the crystal grain size (D) is D (25% by volume) ≧ 0.9 μ
m, 1.2 μm ≦ D (50% by volume) ≦ 2.5 μm, D
(80% by volume) ≦ 4.0 μm.

In the ceramic of the present invention, as the above-mentioned crystal grain size, a value measured by the following method is used. That is, the sintered body is ground, polished, and finished into a mirror surface, and the obtained mirror surface is subjected to thermal etching or chemical etching, and observed with an electron microscope at a magnification at which 100 or more crystal particles can be observed. Take a picture. The area of one crystal was measured by image analysis from the obtained photograph,
Convert to the equivalent circle diameter to obtain the crystal grain size. In this way, the crystal grain size of any 100 crystals is measured, and the volume of the crystal is calculated based on this value. D (25% by volume), D (50% by volume)
%) And D (80% by volume).

D) The Vickers hardness is 1350 or more.

The alumina-based ceramics of the present invention are JI
Vickers hardness (HV) measured according to S 1610
Is 1350 or more, and if it is less than this value, the grain boundary strength is lowered, so that the grain detachment remarkably occurs, and the wear resistance is likely to decrease. In the present invention, the Vickers hardness is
It is preferably 1400 or more.

F) The bulk density is 3.70 g / cm ³ or more.

If the bulk density is less than 3.70 g / cm ³ , a large amount of pores will be present, and this pore will be the starting point to promote wear and reduce wear resistance, which is not preferable. Therefore, the bulk density is 3.70 g / cm ^3.
Or more, and preferably 3.75 g / cm ³ or more.

The wear-resistant alumina-based ceramics of the present invention satisfy the above-mentioned conditions. However, in addition to the above-mentioned components, the above-mentioned condition is obtained even when a certain amount of ZrO ₂ is present in the sintered body. It has the same excellent characteristics as
Further, the presence of ZrO ₂ improves sinterability and toughness,
The strength can be improved. Specifically, the amount of Al ₂ O ₃ in the components excluding ZrO ₂ in the sintered body is 95.
˜98% by weight, and the total amount of each component of the sintering aid is 2 to 5% by weight, the total amount of the sintered body excluding ZrO ₂ is 100
20 parts by weight or less of ZrO ₂ may be included with respect to parts by weight. When the amount of ZrO ₂ exceeds 20 parts by weight, the toughness and the like improve, but the hardness decreases, which is not preferable. Sinterability improved and toughness due to the presence of ZrO _2, to fully exhibit the effect of improving the strength, the content of ZrO ₂ is preferably the total amount 1 of the sintered body excluding the ₂ minutes ZrO
The amount is 0.05 to 15 parts by weight, more preferably 0.1 to 10 parts by weight, based on 00 parts by weight.

The wear-resistant alumina ceramics of the present invention can be produced, for example, by the following method.

First, a predetermined amount of MgO, C is used as the alumina raw material.
Raw materials of aO, ZrO ₂ and SiO ₂ are added, and the mixture is pulverized, mixed and dispersed by a wet method in water or an organic solvent using a pulverizer such as a pot mill and an attrition mill. As the alumina raw material, alumina purity is 99.7% by weight or more,
It is preferable to use a raw material having a specific surface area of 2 m ² / g or more and an average particle diameter of 3 μm or less. The alumina raw material to be used may be one produced by the alum method, but it is preferable to use the Bayer method alumina raw material and there is an advantage that it can be produced at a low cost. As each raw material of MgO, CaO and ZrO ₂ , MgO and C having an average particle diameter of 0.5 μm or less are used.
Each raw material of aO and ZrO ₂ , or a hydroxide, a carbonate or the like can be used. Further, as the SiO ₂ raw material, silica stone, quartz, silica sol, ethyl silicate, etc. can be used, and further, clay mineral such as kaolin may be added. It is preferable that the powder obtained by pulverization has an average particle size of 1 μm or less and a specific surface area of 5 m ² / g or more.
Then, PVA as a binder in the obtained slurry,
Add acrylic resin, paraffin wax emulsion, etc., dry and granulate with a spray dryer to obtain powder for molding. Then, this powder is molded into a predetermined shape by a die press, CIP, or the like according to a conventional method for producing ceramics. In addition to these molding methods, molding can be performed by molding methods such as cast molding, extrusion molding, and injection molding. The molded product obtained in this manner is used for 1400 to 160
By firing at a temperature of 0 ° C., preferably 1450 to 1550 ° C., the desired wear-resistant alumina ceramics can be obtained.

[0025]

The wear-resistant alumina-based ceramics of the present invention have the following excellent properties.

A) Since it is excellent in hardness, strength and impact resistance, it has good wear resistance under high load.

B) When used as a member for a crusher,
Due to its excellent wear resistance, the abrasion powder is less likely to be mixed into the object to be crushed, and even when the abrasion powder is mixed, the uniformity of the object to be crushed is not adversely affected because the abrasion powder is fine.

C) Inexpensive alumina can be used as a raw material.

The wear-resistant alumina-based ceramics of the present invention is suitable as a wear-resistant member for grinding media, cage mill members, lining materials, grinding containers, nozzles, rollers, gauges, etc. by utilizing these characteristics. is there.

[0030]

The present invention will be described in more detail with reference to the following examples.

Example 1 The respective raw materials were blended so that the sintered body had the composition shown in Table 1 below, and wet milling was performed in a pot mill so that the specific surface area was 6 m ² / g or more, and then PVA was added. After that, it was dried and granulated with a spray dryer to obtain a molding powder. Subsequently, this powder was formed into a spherical shape by CIP at a pressure of ² ton · f / cm ² , and fired at 1350 to 1650 ° C. to make a ball having a diameter of 10 mm, and then the surface of this ball was barrel-polished to be used for a crusher. Got the ball

As the alumina raw material, Sample No. 1-8
For Nos. 10 and 10, the average particle diameter is 2 μm, and the specific surface area is 2.
Using an alumina raw material obtained by the Bayer method with 5 m ² / g and a purity of 99.8%, the sample No. Samples Nos. 9 and 11 were prepared by using an alumina raw material having an average particle diameter of 5 μm, a specific surface area of 0.8 m ² / g, and a purity of 99.8%. 12, the average particle size was 0.8 μm, the specific surface area was 5 m ² / g, and the purity was 9
A reactive alumina raw material of 9.8% was used. MgO
Carbonate is used as the raw material for CaO and ZrO ₂
ZrO ₂ was used as the raw material of, and kaolin was used as the raw material of SiO ₂ . In Table 1, Al ₂
The amount of O _{3 and the} amount of the sintering aid are expressed by the value of wt% based on the amount of the components excluding the ZrO ₂ content in the sintered body.
_{The 2} amount is expressed by the value of parts by weight based on 100 parts by weight of the total amount of the sintered body excluding ZrO ₂ .

[0033]

[Table 1]

The bulk density, Vickers hardness, bending strength, average crystal grain size and maximum grain size of the obtained crusher balls are shown in Table 2 below. Sample No. The sintered bodies of Nos. 1 to 6 satisfy the conditions of the present invention. The sintered bodies Nos. 7 to 12 do not satisfy at least one of the conditions specified in the present invention. These crusher balls are used up to half in a ball mill made of alumina (purity 92%) having a capacity of 2 liters. Then, 0.8 liter of water was further added, and a dry test was performed at a rotation speed of 100 rpm for 48 hours. The difference in ball weight before and after the test was determined as a percentage of the ball weight before the test, and this was taken as the wear rate. The results are shown in Table 2.

[0035]

[Table 2]

As is clear from the above results, the ceramics of the present invention had a wear rate of 0.06% or less and had excellent wear characteristics.

Sample No. Of the same formulation as 3 and 8
Using the raw material, the shape of the sintered body is 20 mm in diameter and 3 mm in thickness
Sample No. Same as 3 and 8
To produce a sintered body. 4g / min for this sintered body
Amount of # 30 fused alumina with compressed air
Impact at an angle of 80 degrees to the sintered body at a speed of 400 m / sec.
I struck it. The weight of the sintered body before and after the collision with the fused alumina
Obtain the difference in volume, convert this from the bulk density of the sintered body to the volume,
The wear volume is the volume loss per unit volume of fused alumina.
I asked. As a result, the sample No. In the case of the sintered body of No. 3, the wear amount
Is 8.5 × 10 ^-Fivecm³/ Cm³While it was
Fee No. The wear amount of the sintered body of No. 8 was 9.5 × 10.^-Fourcm
³/ Cm³The wear amount was 10 times or more.

Claims (2)

[Claims] 1. i) a) 95 to 98% by weight of Al ₂ O ₃ , and b) 40 to 85% by weight of SiO _2, 10 to 55% by weight of MgO.
And an alumina sintered body containing 2 to 5% by weight of each component of a sintering aid composed of 3 components of CaO and 5 to 50% by weight, and ii) the crystal grain size (D) is D (25 volume). %) ≧ 0.8 μm,
1.0 μm ≦ D (50% by volume) ≦ 3.0 μm, D (80
%) ≦ 4.5 μm, iii) Vickers hardness of 1350 or more, iv) Bulk density of 3.70 g / cm ³ or more, wear-resistant alumina ceramics. 2. Each component of a sintering aid comprising i) a) Al ₂ O ₃ , b) SiO ₂ 40 to 85% by weight, MgO 10 to 55% by weight and CaO 5 to 50% by weight, and c. ) ZrO
₂ , the content of Al ₂ O ₃ in the components excluding ZrO ₂ is 95 to 98
Wt%, a total amount of 2-5 wt% of each component of sintering aid, containing 100 parts by weight of the total amount of the sintered body excluding the ₂ minutes ZrO, following the ZrO ₂ 20 parts by weight Ii) The crystal grain size (D) is D (25% by volume) ≧ 0.8 μm,
1.0 μm ≦ D (50% by volume) ≦ 3.0 μm, D (80
%) ≦ 4.5 μm, iii) Vickers hardness of 1350 or more, iv) Bulk density of 3.70 g / cm ³ or more, wear-resistant alumina ceramics.