JPH02180747A - Wear resistant alumina ceramics and production thereof - Google Patents

Abstract

PURPOSE:To obtain a dense alumina sintered body having high hardness and superior wear resistance by adding a specified total amt. of magnesia and silica to alpha-alumina powder, pulverizing and mixing them, molding and sintering the mixture. CONSTITUTION:Magnesia and silica each having <=0.3mum average particle size are added to alpha-alumina powder having 0.05-0.3mum average particle size by 0.025-0.12%, in total, in 2-15 molar ratio of MgO to SiO2, they are pulverized and mixed and the mixture is molded and sintered at 1,300-1,550 deg.C to obtain wear resistant alumina ceramics. In order to regulate the grain size, density, hardness, etc., of the resulting sintered body to a prescribed range, the penetration of TiO2, Na2O, etc., accelerating grain growth is prevented during sintering, the sinterability of the starting materials is improved by pulverizing and the density of the molded body before sintering is regulated to >=1.60g/cm<3>.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to wear-resistant alumina ceramics and a method for producing the same, and more particularly to mechanical parts that require high hardness, wear resistance, erosion resistance, etc. A wear-resistant alumina ceramic suitable as a member for a crusher, etc., and a method for producing the same.

In addition, in this specification, all references to "%" refer to "%".
Means weight %°.

Conventional technology and its problems Traditionally, wear-resistant alumina ceramics were made by adding additives such as clay to materials with an alumina content of about 90%.
For example, “Ceramic Engineering Handbook (New Edition)” Gihodo Co., Ltd., (January 1966)
(Published February 25th), p. 1262). However, this ceramic has low hardness and a non-uniform crystal structure, so it has the drawback of insufficient wear resistance.

Recently, wear-resistant alumina ceramics using high-purity alumina of 99.9% or more have also been proposed.

However, since the grain size increases during the sintering process,
The wear resistance is still not satisfactory. Alumina obtained by adding non-oxides such as TiC to high-purity alumina raw materials and pot pressing them exhibits sufficient wear resistance, but
Since it is necessary to perform firing under pressure in a non-oxidizing atmosphere, there is a problem in that the manufacturing cost is extremely high.

Means for Solving the Problems The present inventor has conducted extensive research in view of the problems of the prior art as described above. In the process, we focused on alumina sintered bodies, which have traditionally been widely used as wear-resistant materials due to their low cost and poor wear resistance, and conducted repeated research to improve their wear resistance. It has been discovered that an alumina sintered body with extremely excellent wear resistance can be obtained by controlling the grain boundary components, crystal grain size, density, hardness, etc. of the alumina sintered body within specific ranges.

That is, the present invention provides the following wear-resistant alumina ceramics and a method for producing the same: ■Magnesia and silica in a total of 0.025 to 0.12%.
A sintered body containing M g O / S i 02 (molar ratio) of 2 to 15, the remainder being alumina, with a density of 3.90 g/cts3 and an average grain size of 1
．． A wear-resistant alumina ceramic characterized by having a diameter of 5 μm or less and a hardness of 1900 kgf/vs2 or more.

■The total content of magnesia and silica in α-alumina powder with an average crystallite diameter of 0.05 to 0.3 μm is 0.025
After adding magnesia and silica with an average particle size of 0.3 μm or less so that the amount is ~0.12% and MgO/5iOz (molar ratio) is 2 to 15, pulverized and mixed, and molded,
A method for producing wear-resistant alumina ceramics, characterized by firing at 1300 to 1550°C.

■The above type (2) in which magnesia and silica components are added in the form of a solution, sol or gel containing Mg and SL.
) A method for producing wear-resistant alumina ceramics.

■The total content of magnesia and silica obtained by adding a solution, sol or gel containing Mg and Si to alumina hydrate or alumina and firing it is 0.02
5 to 0.12% and MgO/SiO2 (molar ratio) is 2 to
A method for producing wear-resistant alumina ceramics, which comprises molding α-alumina powder having an average crystallite diameter of 0.05 to 063 μm in Step 15 and then firing it at 1300 to 1550°C.

■Average crystallite diameter 0.05 to 0.3 μm containing magnesia obtained by adding a solution, sol or gel containing Mg to alumina hydrate or alumina and firing.
α-alumina powder has a total content of magnesia and silica of 0.025 to 0.12%, and MgO/Si
The average particle size is 0.0 so that O2 (molar ratio) is 2 to 15.
A method for producing wear-resistant alumina ceramics, which comprises adding silica of 3 μm or less, mixing and dispersing it, molding it, and then firing it at 1300-1550°C.

Hereinafter, the requirements that the wear-resistant alumina ceramics of the present invention should have and the effects based thereon will be explained in detail. Note that the effects of the present invention are not necessarily achieved by only a single requirement, but may be achieved synergistically by requirements on two sides. Therefore, the following description:
It should be noted that this does not necessarily completely explain the correspondence between the structure and effects of the invention.

(1) The total amount of magnesia and silica in the alumina sintered body is 0.025 to 0.12%, and the MgO/SiO2 (molar ratio) is within the range of 2 to 15.

According to the research of the present inventor, when a specific amount of magnesia and silica are added to the alumina raw material within a range that does not impede the mechanical properties of alumina and sintered, alumina crystal grains appear in the densification process. Spinel crystal in the world (M g A 120
4) A glass phase of magnesium silicate and/or magnesium aluminum silicate is formed, and as a result, grain growth of alumina crystals is suppressed, the crystal structure becomes uniform, and densification is further promoted. found.

If the total amount n of magnesia and silica added to the alumina raw material is less than 0.025% of the alumina sintered body, the effect of suppressing grain growth of alumina crystals will not be sufficiently exhibited. On the other hand, if it exceeds 0.12%, densification is inhibited, so it is necessary to fire at a high temperature in order to suppress the increase of pores or promote densification. the result,
Since the alumina crystal grain size is large and non-uniform, abrasion caused by preferential destruction of the grain boundaries of alumina crystal grains, that is, particle detachment abrasion is likely to occur.

The total amount of magnesia and silica in the alumina sintered body is 0.
More preferably, it is 0.03 to 0.1%.

In addition, when silica is added alone or MgO/5i
C) When z (molar ratio) is less than 2, the amount of spinel crystals produced decreases, whereas when magnesia is added alone or M g O / SiO2 (molar ratio)
If it exceeds 15, the amount of silicate phase produced decreases, and in any case, a highly hard alumina sintered body having a uniform and fine crystal structure cannot be obtained.

MgO/SiO2 (molar ratio) in the alumina sintered body is 3
It is more preferable that it is 15.

(2) The density of the alumina sintered body is 3-90 g/cm3 or more.

The wear resistance of an alumina sintered body is greatly influenced by its density, and the lower the density, the greater the amount of wear. This is thought to be because the lower the density, the more pores exist within the grains, grain boundaries, etc., and these pores serve as starting points for wear, accelerating grain separation wear.

Therefore, in the present invention, the density of the alumina sintered body is set to 3.90.
g/cm3 or more, more preferably 3.92 g/ca
+3 or more.

(3) The average grain size of alumina crystals in the alumina sintered body is 1
．． 5μm or less, Vickers hardness 1900kgf/
Must be arm2 or higher.

When the grain size of the alumina crystals in the sintered body is large, the grain boundaries become wider or the hardness becomes lower in the sintered body having the same composition. As a result, it is assumed that the aforementioned crystal grain detachment wear is likely to occur and the amount of wear increases. According to research conducted by the present inventors, it has been found that wear resistance is significantly improved by setting the average crystal grain size to 1.5 μm or less and the Vickers hardness to 1900 kgf/a+w2 or more.

The average grain size of alumina crystals in the alumina sintered body is 1.2μ
m or less, and Vickers hardness is 1950 kgf/am2
It is more preferable to set it as above.

When producing the alumina sintered body of the present invention, if the sintering temperature is less than 1300°C, sintering will be insufficient and the density will be low, whereas if it exceeds 1550°C, grain growth will occur. becomes significant, and the properties of the sintered body deteriorate.

Therefore, it is essential that the firing be performed in the range of 1300 to 1550°C. It is more preferable that the firing is carried out at a temperature of 1300 to 1500°C.

(4) The average crystallite size of α-alumina powder used as a raw material is 0.05 to 0.3 μm, and the average particle size of magnesia and silica is 0.3 μm or less.

When the α-alumina powder is less than 0.05 μm,
Since agglomeration is likely to occur, formability is reduced and defects such as pores are likely to occur in the sintered body. On the other hand, if the α-alumina powder exceeds 0.3 μm, the crystal grain size of the sintered body becomes large, the hardness becomes low, and the wear resistance decreases. The average crystallite diameter of the α-alumina powder is more preferably 0.05 to 0.2 μm.

If the average particle size of magnesia and silica is larger than that of α-alumina powder, it will be difficult to uniformly disperse the raw material powder, making it impossible to obtain an alumina sintered body with good properties. Therefore, the average particle size of magnesia and silica must be 0.3 μm or less, more preferably 0.2 μm or less. In the case of magnesia and silica, which are used in small amounts, there is no lower limit to the particle size because even if the particle size is too small, the moldability will not be impaired.

The wear-resistant alumina ceramic according to the present invention is produced, for example, as follows. Preferably, magnesia and silica are added to α-alumina powder with a purity of 99.9% or more produced by the alkoxide method, light bread method, etc., and the mixture is homogenized dry or wet using a grinder such as a ball mill according to a conventional method. The raw material powder is obtained by grinding, mixing, and drying. Next, it is molded into a predetermined shape by a conventional method such as cast molding, injection molding, extrusion molding, press molding, etc., and then fired at 1300 to 1550° C. under normal pressure to obtain an alumina sintered body. During molding, if necessary, preparation of a slurry and preliminary granulation using a molding aid are carried out in the same manner as in conventional methods.

In addition, in order to improve the mixing and dispersibility of the magnesia component and the silica component with the alumina component, the magnesia component and the silica component are added to α-alumina powder or alumina hydrate in the form of a solution, sol, or gel containing Mg and Si. The Mg and SL-containing alumina powder (0.05 to 0.3.czm) obtained by firing at a temperature below 1300°C may be molded and then fired at a temperature of 1300 to 1550°C under normal pressure. Alternatively, α- in the state of a solution, sol or gel containing Mg
After adding Mg to alumina powder or hydrated alumina,
Silica powder is pulverized and mixed with Mg-containing alumina powder (0.05 to 0.3 μm) obtained by firing at a temperature below 1300°C, molded, and then fired at a temperature of 1300 to 1550°C under normal pressure. good.

In addition, when manufacturing the above-mentioned sintered compact, the purity and type of forming aids, water, etc., and the selection of crushing equipment, firing jigs, etc. should be appropriately selected to avoid any negative impact on the properties of the sintered compact. It is desirable to prevent the contamination of impurities that may cause

In addition, in order to keep the crystal grain size, density, hardness, etc. of the sintered body within predetermined ranges, it is necessary to (a) prevent the incorporation of Ti02, Na20, etc. that promote grain growth during the sintering process; B)
Finely pulverize the raw material through a process such as pulverization to improve sinterability; (d) the density of the compact before sintering to 1.60 g/c;
It is preferable to set it to 113 or more.

Effects of the Invention According to the present invention, by controlling the grain boundary components, crystal grain size, density, hardness, etc. within specific ranges, a dense alumina sintered body with high hardness and extremely excellent wear resistance can be produced. can get.

In addition, during production, a sintered body with excellent wear resistance can be obtained simply by sintering under normal pressure.

EXAMPLES Examples and comparative examples are shown below to further clarify the features of the present invention.

Example 1 α-alumina powder with a purity of 99.995% and an average particle size of 0.
Magnesia powder and silica powder of 2 μm or less are mixed into the following first
After blending in the proportions shown in the table and pulverizing and mixing in a ball mill for 10 hours, acrylic acid copolymer was added as a molding aid in an amount of 3% of the raw material heavy metal, and a spray dryer was used to reduce the average particle size to 60.
The powder was sized to micrometers to obtain a powder for molding.

Table 1 shows (I) the average crystallite diameter of α-alumina powder (μm
), (II) Ratio (%) of magnesia powder and silica powder in the raw materials, and (m) M g O / Si
02 (molar ratio).

In Table 1, No. 1.2 and 4 are examples, and the others are comparative examples.

Table 1 (I) (II) (II) 0, 040 0, 055 0, 070 0, 090 0.150 0.075 0, 065 (MgO only) 3,5 6,75 1,13 Next, this powder The body is 65mm with a molding pressure of 2ton/cd.
x65mni The product was CIP-molded into a plate shape and fired under normal pressure under the conditions shown in Table 2 below.

Obtained sintered body (IV) density (r/am3), (V)
Average grain size (μ...), (Vl) Micro Vickers hardness (kgf/am2) and (■) Wear resistance (weight loss:
g) are shown in Table 3 below.

Table 3 also shows the results for the sintered bodies obtained in Example 2 and Example 3 below. In Table 3,
Sample Nα1.3.6. 10 and 11 are examples,
The others are comparative examples.

Note that the micro Vickers hardness was measured under a load of 500 g. In addition, wear resistance is improved by using a diamond whetstone.
After grinding the sintered body, the surface roughness RIax =0. 8μ
50+u+ X 50mIIX5m finished below m
Fused alumina grains (35 to 60 meshes) were sprayed onto the sintered body of 100 m for 10 minutes at a pressure of 5 kgf/ej, and the weight loss of the sintered body was measured.

Example 2 The total amount of magnesia and silica in the raw materials was o, oeo%, MgO/
After blending the magnesium nitrate solution and the ethyl silicate solution so that SiO2 (molar ratio) was 5, Example 1
Molded bodies were prepared in the same manner as above and fired under normal pressure under the conditions shown in Table 2.

Example 3 In alumina hydrate, the total amount of magnesia and silica in the raw materials was 0.050%, MgO/5iOz (molar ratio)
A magnesium nitrate solution and an ethyl silicate solution were blended so that
α-alumina powder was obtained. The obtained α-alumina powder was wet-pulverized in a ball mill until the average crystallite diameter became 0.15 μm, and then a molded body was prepared in the same manner as in Example 1, and the powder was crushed under normal pressure under the conditions shown in Table 2. It was fired.

Table 2 Table 3 Powder firing temperature used for samples ("C') Sample No. (IV) (V) (VT) (■) I Nα2 No, 2 Na, 2 Positive, 3 NQ, 4 No, 5 Na6 No. 7 Example 2 Example 3 3.97 3.78 3.97 3.97 3.88 3.97 3.86 3.97 3.97 3.97 0.05 0.32 0.03 0. 58 0.05 0.28 0.51 0.32 0.04 0.04 As is clear from the results shown in Table 3, when the firing temperature of the molded body is less than 1300°C (sample 2
), resulting in insufficient sintering and low density, hardness and wear resistance.

Furthermore, when the firing temperature of the compact exceeds 1550° C. (sample 4), the density is high, but the average crystal grain size is large and the hardness and wear resistance are poor.

Further, when the MgO/SiO2 (molar ratio) is less than 2 (sample No. 5), the density and hardness are low, and the wear resistance is poor.

When the content of magnesia and silica exceeds 0.12% (sample No. 7), grain boundary properties are poor, resulting in poor wear resistance.

When the average crystallite diameter of the α-alumina powder exceeds 0.3 μm (sample NG, 8), the density, hardness, and wear resistance are all poor.

In addition, when blending only magnesia (sample 11h
9) Although the density and average grain size were within a preferable range, the crystal structure was non-uniform and the hardness was low, resulting in poor wear resistance.

In contrast, sample Nα1, which satisfies all the requirements of the present invention,
In the case of 3, 6.10 and 11, excellent wear resistance can be exhibited.

Example 4 Total ff of alumina, magnesia and silica in fired product
The total amount of magnesia and silica in ff1 is LO65%
Alumina hydrate, magnesium nitrate solution, and ethyl silicate solution were weighed so that the MgO/SiO2 (molar ratio) was 10.

Next, a magnesium nitrate solution was mixed with the alumina hydrate, dried, and calcined at 1200 ° C. to obtain a Mg-containing alumina powder, and an ethyl silicate solution was added and mixed.
Wet milling was carried out in a ball mill until the average crystallite diameter was 0.1 μm or less, and molded in the same manner as in Example 1.
It was fired at ℃ under normal pressure.

The physical properties of the obtained sintered body were excellent as shown below.

Density = 3.97 g/cm3, average grain size: 0, 8
μm s Hardness: 2140kgf/mm2 Wear resistance: 0
．． 03g Example 5 The powder of the sample in Table 2 of Example 3 was molded under the same conditions as 3 and 5 to produce a ball with a diameter of 5 mm, and the surface of the ball was barrel-polished.

Put 3.5Q of the balls thus obtained into an attrition mill with a capacity of 5Q, and add 1.6Q of water and 1.6Q of zirconia powder.
After adding kg, turn the attrition mill to 8 at 20 rpm.
The amount of wear on the ball was determined by running the ball for a certain period of time.

The wear amount of the ball per hour according to sample 3 is 20
ppm, whereas the amount of wear of the ball per hour in sample No. 5 was 1900 ppm.

As is clear from these results, the alumina ceramic according to the present invention exhibits excellent wear resistance even when used as a grinding ball.

(that's all)

Claims (5)

[Claims] (1) Total of magnesia and silica 0.025 to 0.1
Contains 2%, MgO/SiO_2 (molar ratio) is 2 to 15
A sintered body with the remainder made of alumina, with a density of 3.90 g/cm^3, an average grain size of 1.5 μm or less, and a hardness of 1900 kgf/mm^2 or more. Alumina ceramics. (2) The total content of magnesia and silica in α-alumina powder with an average crystallite diameter of 0.05 to 0.3 μm is 0.0
Magnesia and silica with an average particle size of 0.3 μm or less are added and mixed so that the concentration is 25 to 0.12% and the MgO/SiO_2 (molar ratio) is 2 to 15. After molding, the temperature is 1300 to 1550 °C. A method for producing wear-resistant alumina ceramics, which is characterized by firing the alumina ceramics. (3) The method for producing wear-resistant alumina ceramics according to (2), wherein the magnesia and silica components are added in the form of a solution, sol, or gel containing Mg and Si. (4) Mg and Si in alumina hydrate or alumina
The total content of magnesia and silica obtained by adding and firing a solution, sol or gel containing magnesia and silica is 0.
025-0.12%, MgO/SiO_2 (molar ratio) is 2-15, and an average crystallite diameter of 0.05-0.3 μm is formed into α-alumina powder, and then fired at 1300-1550°C. A method for producing wear-resistant alumina ceramics. (5) Average crystallite diameter 0.05 to 0.3 containing magnesia obtained by adding a solution, sol or gel containing Mg to alumina hydrate or alumina and firing.
The total content of magnesia and silica in μm α-alumina powder is 0.025 to 0.12%, and MgO/
Wear-resistant alumina ceramics characterized by adding silica with an average particle size of 0.3 μm or less so that SiO_2 (molar ratio) is 2 to 15, mixing and dispersing it, molding, and then firing at 1300 to 1550 ° C. manufacturing method.