JPH08259926A - Alumina-sintered abrasive grain and production thereof - Google Patents

Abstract

PURPOSE: To obtain alumina-sintered abrasive grains excellent in grinding performance and high in hardness and toughness by controlling the crystalline texture thereof in producing the abrasive grains according to a sol-gel method wherein alumina monohydrate is used as the starting material. CONSTITUTION: Lithium-free alumina-sintered abrasive grains have calcium-contg. platy crystal grains of at least 1μm in major axis diameter, and a submicron crystalline texture in the portions thereof other than the platy crystal grains. The abrasive grains are obtd. either by a method wherein fine α-alumina particles are added to an alumina sol contg. calcium ions, followed by gelation and subsequent sintering, or by a method wherein an alumina sol contg. α-alumina particles is turned into gel, dried, calcined, impregnated with calcium ions, and sintered. The amt. of calcium to be added is pref. 0.5 to 3wt.% in terms of CaO based on the alumina-sintered abrasive grains. The BET value of the fine α-alumina particles to be added is pref. at least 40m<2> /g, while the amt. thereof is pref. 0.3 to 3wt.% based on the wt. of alumina in the alumina sol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina-based sintered abrasive grain having excellent grinding performance and high hardness and toughness.

[0002]

2. Description of the Related Art Conventional sintered alumina abrasive grains include abrasive grains having a fine crystal structure produced by a sol-gel method using alumina monohydrate (pseudo-boehmite) as a raw material, and various additives are added thereto. The abrasive is made using the agent. Japanese Patent Application Laid-Open No. 57-207672 discloses a metal-containing sintering aid and a metal-containing sintering aid.
Sodium higher than 05 wt% and lower than 1.8 wt% +
A sol-gel method alumina-based sintered abrasive grain containing calcium and a method for producing the same are described. In addition, Japanese Patent Laid-Open No. 3-
No. 234785 describes a sol-gel method alumina abrasive grain containing lithium oxide and a method for producing the same, in which Mg, Ca, Co, Ni, Cr and F are used as modifying components.
It is described that e, Si, Zn, Mn, Ti and Zr may be added. Regarding the alumina-based sintered body containing calcium, which is obtained by the powder sintering method, the plate-shaped or rod-shaped alumina-based compound structure and the fine granular corundum structure are uniformly dispersed in JP-A-6-157133. An alumina-based composite sintered body and a method for producing the same are described. At this time, in order to grow crystals, CaO, TiO
₂ , B ₂ O ₃ , ZnO, MnO ₂ , LiF, Y ₂ O ₃ ,
It is described that at least one kind of La ₂ O ₃ is added and one kind of ZrO ₂ and MgO is added in order to suppress crystal growth. It is also described that the fine corundum structure at this time has a preferable size of 1 to 10 μm, and the plate-like or rod-shaped alumina compound structure has a preferable size of 10 to 100 μm.

[0003]

In the powder sintering method, it is necessary to raise the sintering temperature in order to obtain a certain degree of hardness of the sintered body, and as a result, the crystal size of the sintered body is considerably large. However, it is difficult to obtain excellent abrasive grains because of problems in strength and toughness. For this reason, a method for producing alumina-based abrasive grains by the sol-gel method has recently been mainly studied for the purpose of obtaining abrasive grains having a submicron structure, but improvement is still desired to increase both hardness and toughness of the abrasive grains. It is rare. Therefore, it is an object of the present invention to provide an abrasive grain that controls the crystal structure, increases the hardness, and has a high toughness value, instead of producing only a uniform microstructure by the sol-gel method.

[0004]

The inventor has made an effort to achieve the above-mentioned object, and as a result of various studies, found the present invention. That is, a sintered alumina abrasive grain characterized by having plate-shaped crystal grains containing calcium and having a major axis of 1 μm or more, and a non-plate-shaped crystal grain having a submicron crystal structure and not containing lithium Α-alumina fine particles are added to an alumina sol containing calcium ions as a production method, and a method for producing an alumina-based sintered abrasive grain characterized by being gelled and then sintered and an alumina sol containing α-alumina fine particles are gelled, The present inventors have found a method for producing an alumina-based sintered abrasive grain characterized by impregnating with calcium ions and sintering after drying and calcination.

First, the manufacturing method of the present invention will be described. (Pseudo) boehmite (eg S from Condea
(Commercially available under the trade name of B Pural Alumina) is mixed with nitric acid and other acids to form a sol. When calcium ions are added to this alumina sol, a water-soluble calcium salt (for example, nitrate, halide, acetate, etc.) is added in a solution state. It is preferable to add this solution as an aqueous solution in terms of cost, but it is also possible to use a solution of a lower alcohol, but the above calcium acetate is insoluble in alcohol. In the present invention, there is a method of adding calcium in a sol state, an impregnation treatment, or both.

[0006] The preferable amount of calcium added is 0.5 to 3 wt% in terms of CaO as alumina-based sintered abrasive grains.
If it is less than 5 wt%, the precipitation of plate-like crystal grains is small and the effect of increasing the toughness is small, and if it exceeds 3 wt%, the plate-like crystal grains are excessively large and the density of the abrasive grains is low, which is not preferable. When the addition of calcium is in the sol state or only in the impregnation treatment, the addition amount is a value such that it becomes a preferable content in the above alumina-based sintered abrasive grains, and when it is added in both stages, the total amount is The addition amount in each stage is adjusted so that the content in the alumina-based sintered abrasive grains is within the above-mentioned preferable range.

In the present invention, α-alumina fine particles are always added to alumina sol. It is also possible to mix α-alumina fine particles with (pseudo) boehmite and form a sol with an acid. The α-alumina fine particles to be added are preferably those having a BET value of 40 m ² / g or more, more preferably 60 m ² / g or more, and the addition amount thereof is 0.3 with respect to the weight of alumina in the alumina sol.
-3 wt% is preferable. If it is less than 0.3 wt%, the alumina crystal size of the abrasive grains will not become fine, and if it exceeds 3 wt%, further refinement of the crystal is hardly recognized, which is not preferable.

Further, a compound such as Mg, Ni, Co or Zr may be added to the alumina sol as a growth inhibitor for the alumina crystal size of the abrasive grains. Gelation occurs when a calcium salt is added to the alumina sol, or when a crystal growth inhibitor such as the above Mg compound is added without adding the calcium salt. Next, the alumina sol is dried, or the gelled product as described above is dried. Both are dried at 80 to 120 ° C. for 10 to 72 hours so as not to be encapsulated in the dry gel.

The dry gel is crushed and sized so that the grain size of the predetermined abrasive grain is obtained. After that, calcination is performed to remove the acid used for sol formation and water of crystallization to form γ-alumina. As calcination conditions, it is preferable to remove 95 wt% or more of the total water content at 550 to 900 ° C., and calcination time is preferably about 2 hours. When the calcination temperature exceeds 900 ° C., pores are not sufficiently formed in the calcination gel, and it becomes difficult to impregnate a predetermined amount of the calcium salt solution into the particles, and particularly it becomes difficult to impregnate the inside of the abrasive grains.
Further, the residual water content in the calcined gel increases, and the same difficulty occurs even when the removal rate is less than 95 wt% of the total water content of the dry gel. If the calcination temperature is less than 550 ° C, the removal rate of water is low, which is also not preferable.

Next, with respect to the calcined gel produced as described above, when the sol state is not added, the above-mentioned whole amount is added, and when the sol state is partially added, the above-mentioned remaining amount is as described above. Impregnate with a solution of calcium salt. As the solvent of the solution,
Although water, ethanol, acetone or the like can be used, ethanol is preferable because the solvent having a small surface tension has a greater effect of impregnating the inside of the abrasive grains, and water is preferable in terms of production cost. Further, it is desirable that the concentration of the solution be as high as possible. Therefore, it is desirable to use the solvent that dissolves the salt in a state where the temperature is raised to increase the solubility. Since the solution in which the salt is dissolved has a high concentration, in order to impregnate the solution into the above-mentioned calcined gel, it is sufficient to mix the solution with the calcined gel. There is a method of picking up the calcinated gel together with the mesh after immersing it in the impregnating solution after placing it on, and the method is not particularly limited.
Although the atmosphere during the impregnation may be pressurized or degassed, a preferable method is to inject a predetermined amount of the impregnating solution so as to cover almost the entire area, and then stir this wet product to homogenize it. preferable. As a more preferable method, it is preferable to spray the solution and bring it into contact with the calcined gel. It may be dried after impregnation, but the operation of impregnation may be repeated to impregnate with the predetermined amount of the calcium salt solution and then dried. After the calcined gel is impregnated with calcium salt, dried, or if the calcined gel is not impregnated, the calcined gel is sintered as follows.

The calcined gel containing calcium is heated and sintered in a furnace such as a rotary kiln. Maximum temperature is 1100
Sinter in the temperature range of ˜1400 ° C. At this time, 900
It is preferable to perform rapid heat treatment within a temperature range of ˜1100 ° C. within 90 seconds. By rapidly heating it
The phase transformation to alumina occurs rapidly, the densification of the structure is promoted, and the hardness is also improved. The higher the temperature, the shorter the holding time at the sintering temperature becomes.
2 to 10 minutes in the range of 00 to 1400 ° C., 11
In the temperature range of 00 to 1200 ° C., 10 minutes to 10 minutes
Hold time is necessary. Also 1100 to 1300
After holding for 2 to 10 minutes in the temperature range of ℃, 1 more
2 such as holding at 000 to 1200 ° C for 1 to 100 hours
Stage sintering treatment may be performed.

Next, the alumina-based sintered abrasive grains of the present invention will be described. The added calcium ions mainly react with alumina, and calcium aluminate CaO ・ 6Al ₂ O ₃
Has become. Whether or not CaO or CaO.6Al ₂ O ₃ exists at the grain boundaries of alumina having a submicron fine crystal structure is unknown by a 1000 times EPMA analysis. CaO.6Al ₂ O ₃ present in the alumina-based sintered abrasive grains of the present invention has a major axis of 1 μm or more, often 10 μm or less, and a major axis / minor axis ratio of 1 to 3 in many cases. In addition, the major axis / thickness ratio is often 2 or more, mainly 3 to 10. CaO ・ 6Al ₂ O ₃
The major axis of the plate-shaped crystal grains is 1 μm or more, but the non-plate-shaped crystal grains in the alumina-based sintered abrasive grains have a fine crystal structure of submicron alumina having an average grain size of 1 μm or less.

The alumina-based sintered abrasive grain of the present invention has extremely high toughness and hardness due to the above-mentioned crystal structure, and exhibits excellent grinding performance. Generally, its toughness value (toughness; measuring method will be described later in Example 1) is C.
The coefficient is 0.7 or less, the hardness (Knoop, 100 g load, holding time 10 seconds) is 15.5 GPa or more, and the density is 9 of the theoretical value.
It is 0% or more.

[0014]

EXAMPLES Hereinafter, examples and comparative examples will be described. Example 1 Pseudo-boehmite manufactured by Condea (SB Pural A
500 g of lumina) was dispersed in 1.9 liters of water. Next, 16.84 g of calcium nitrate tetrahydrate (1.1 wt% in terms of CaO based on alumina) of 200 g of water
, And this aqueous solution was added to the pseudo-boehmite dispersion.
Furthermore, α-alumina fine particles (BET = 64.7 m ² / g)
5.0 g (based on the weight of alumina in the alumina sol,
After adding 30.1 g of a dispersion aqueous solution containing 1.33 wt% (corresponding to 1.33 wt%), a mixed solution of 21.4 ml of a 67.5% HNO ₃ aqueous solution and 21.4 ml of water was added to prepare an alumina sol. This sol was allowed to stand and dry for 24 hours at 100 ° C. in a SUS vat to obtain a dry gel. After crushing and firing, it was granulated into particles of 350 to 500 μm so as to correspond to # 60 of JIS R 6001-1987. The particles were calcined at 650 ° C. for 2 hours. Then, this was rapidly heated from room temperature in a rotary kiln for 60 seconds, retained at 1350 ° C. for 2 minutes and sintered. When the structure of the obtained abrasive grains was observed with a scanning electron microscope, it was found to be composed of plate crystal grains having an average major axis of 3.25 μm and fine crystal grains having an average diameter of 0.23 μm. As shown in Table 1, the density of the obtained abrasive grains was 3.88 g / cm ^{3 as} measured by the water-based Archimedes method, and the Knoop hardness (100 g load, holding time 10 seconds) was 20.1.
It was GPa.

The toughness value of the resulting # 60 abrasive grains is JIS
It was determined by the C coefficient according to R 6128-1987 (a test method for toughness of artificial abrasives). The method of measuring the C coefficient will be described. Approximately 250 g of # 60 abrasive grains to be measured is measured by JIS R 6128-1987. A sample is prepared with a low-tap tester having a standard sieve knitting corresponding to # 60. Next, 100 g of this test sample is used for 114 m inside diameter.
It is put in a ball mill pot of mφ x 120 mm with a capacity of about 1.2 liters, and then a 1/2 inch φ iron ball 180
Put in pieces and grind at a rotation of 95 rpm. Then JI
Operation specified in SR 6128-1987, steps 4 to 7
According to the above, the weight of the sample retained on the sieve of 212 μm is determined, and it is defined as R (X). Next, the same operation as above was performed for # 60 of the black silicon carbide abrasive as a standard sample, and after crushing, the weight of the sample retained on the 212 μm sieve was obtained. Calculate the C coefficient. C coefficient = log (100 / R (X)) ÷ log (100
/ R (S))

The smaller this value is, the higher the toughness is, but the C coefficient of the # 60 abrasive grain obtained in Example 1 is 0.6.
It was 3. In addition, 1000 times E for the obtained abrasive grains
As a result of PMA analysis, it was not clear whether Ca was mainly present in the plate-like crystal grains composed of calcium aluminate and was present in the grain boundaries of alumina composed of a submicron fine crystal structure.

Example 2 Except that 5.7 g of magnesium nitrate hexahydrate (0.25 wt% in terms of MgO content relative to the weight of alumina in the alumina sol) was added when calcium nitrate was added in Example 1. Was subjected to the same conditions and treatments as in Example 1 to obtain abrasive grains. As a result, the obtained abrasive grain characteristics were, as shown in Table 1, the structure grain size was a plate-like crystal grain with an average major axis of 3.02 μm and a fine crystal grain with an average of 0.21 μm. The density was 3.89 g / cm ³ , the Knoop hardness was 20.6 GPa, and the C coefficient was 0.65.

Example 3 Pseudo-boehmite (SB Pural A manufactured by Condea Corporation)
lumina) 400 g in water 1.6 liter,
3. Add α-alumina fine particles (BET = 64.7 m ² / g) to 4.
0 g (1.33 relative to the weight of alumina in the alumina sol)
24.1 g of a dispersion aqueous solution containing (wt% equivalent) was added, and 6
7.5% HNO ₃ aqueous solution 16.8 ml and water 16.8 ml
A mixed solution of and was added to produce an alumina sol. This sol was allowed to stand and dry for 24 hours at 100 ° C. in a SUS vat to obtain a dry gel. JIS R after crushing and firing
In order to obtain a grain size of # 60 of 6001-1987,
The crushed dry gel was granulated into 350 to 500 μm particles. The particles were calcined at 650 ° C for 2 hours to remove NO due to nitric acid.
_{The x} and water of crystallization were removed. Next, 14.27 g of calcium nitrate tetrahydrate (2.2 w in CaO amount relative to alumina)
t%) and magnesium nitrate hexahydrate 4.90 g
70 g of water (0.5 wt% MgO based on alumina)
And was impregnated with 150 g of the calcined gel. After drying, it was calcined again. Then, this was rapidly heated from room temperature to 1350 ° C. in a rotary kiln for 60 seconds and kept at that temperature for 2 minutes. The obtained abrasive grain characteristics are shown in Table 1, and the grain size of the grains was a plate crystal grain having an average major axis of 2.67 μm and a fine crystal grain having an average diameter of 0.19 μm. The density is 3.
60 g / cm ³ , Knoop hardness of 15.8 GPa,
The C coefficient was 0.63.

Example 4 When impregnating a calcined gel, calcium nitrate tetrahydrate 7.
Example 3 except that the amount was 04 g (1.1 wt% in CaO content with respect to alumina) and 2.42 g of magnesium nitrate hexahydrate (0.25 wt% in MgO content with respect to alumina).
The same conditions and the same treatments were performed. As a result, the obtained abrasive grain characteristics are shown in Table 1, and the grain size of the structure is 3.1.
It was a plate crystal grain of 4 μm and a fine crystal grain of 0.19 μm on average. The density was 3.90 g / cm ³ , Knoop hardness was 21.1 GPa, and C coefficient was 0.60. A scanning electron micrograph (magnification: 10,000 times) of the fracture surface of the abrasive grains obtained here is shown in FIG. It can be seen that plate crystal grains and fine crystal grains are mixed.

Comparative Example 1 For comparison with abrasive grains containing calcium but not adding α-alumina fine particles at the sol stage, calcium (2.2% by weight of CaO based on alumina) and magnesium (amount of MgO based on alumina). Alumina-based sintered abrasive grains containing 0.5 wt. That is, the same conditions and the same treatments as in Example 3 were performed except that the α-alumina fine particles were not added. The obtained abrasive grain characteristics are as shown in Table 1.
The texture grain size was only plate-like crystal grains having an average major axis of 2.20 μm. The density is 3.61 g / cm ³ and the Knoop hardness is 1
It was 5.9 GPa and the C coefficient was 0.88.

Comparative Example 2 For comparison with abrasive grains containing no calcium, alumina sintered abrasive grains containing α-alumina fine particles at the sol stage were prepared. That is, a calcined alumina gel containing α-alumina fine particles before impregnation was prepared by the method of Example 3, and was sintered in a rotary kiln at 1280 ° C. for 2 minutes without impregnation. As for the characteristics of the obtained abrasive grains, as shown in Table 1, substantially all the crystal grains of the structure were 1 μm or less, and the grains were fine crystal grains of 0.15 μm on average, and there were no plate-like crystal grains. Further, the density was 3.91 g / cm ³ , the Knoop hardness was 22.4 GPa, and the C coefficient was 0.75.

[0022]

[Table 1]

Examples 5 to 8 10 parts by weight of resorcinol (1,3-dioxybenzene) was dissolved in 10 parts by weight of ethanol, and 100 parts by weight of the abrasive grains obtained in the four kinds of Examples 1 to 4 were dissolved. Parts and each of them were mixed, dried at 100 ° C. for 1 hour, and ethanol was evaporated to obtain four kinds of abrasives whose surfaces were coated with resorcinol. Phenolic resin adhesive BRL-2867 (solid content about 70
%, Manufactured by Showa High Polymer Co., Ltd. at a rate of 100 g / m ² , and the above-mentioned coated abrasive was sprinkled thereon to remove excess abrasive. At this time, the adhesion amount of the abrasive to the base material was 250 g / m for all four types.
^{Was 2} . Each of them was dried at 80 ° C. for 4 hours, and then the adhesive was evenly applied thereon at a rate of 200 g / m ² , dried at 80 ° C. for 4 hours, and then dried at 80 ° C. to 135 minutes in 2 hours. The temperature was raised to ℃ and held at 135 ℃ for 30 minutes to obtain four kinds of polishing cloths. Each polishing cloth was punched out to prepare a disk-shaped polishing cloth of 180 mmφ, and dry grinding was performed under the following conditions.

Thunder: Hitachi PHD-180C Grinding time: 1 minute × 10 times Work material: (a) S-45C 250 mm □ × 10 mmt (b) SUS 304 250 mm □ × 9 mmt Load: 3 lb. The grinding amount values are shown in Tables 2 and 3.

Comparative Examples 3 to 4 Disc-shaped non-woven fabric-based abrasive cloths were made and ground under the same conditions and operations as in Example 5 for the two types of abrasive grains obtained in Comparative Examples 1 and 2, respectively. The test was conducted. The grinding amount values are shown in Tables 2 and 3.

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

INDUSTRIAL APPLICABILITY The present invention has an alumina-based sintered body which does not contain lithium but has calcium-containing plate-like crystal grains with a major axis of 1 μm or more, and the non-plate-like crystal grains have a submicron crystal structure. As the abrasive grains, alumina-based sintered abrasive grains having higher toughness than conventional ones can be obtained and exhibit excellent grinding performance.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph showing a crystal structure or shape of a fracture surface of an abrasive grain obtained in Example 4. (Magnification 10,000 times)

Claims (3)

[Claims] 1. An alumina-based sintered abrasive characterized in that it has plate-like crystal grains containing calcium and having a major axis of 1 μm or more, and the non-plate-like crystal grains have a submicron crystal structure and does not contain lithium. grain. 2. A method for producing alumina-based sintered abrasive grains, which comprises adding α-alumina fine particles to an alumina sol containing calcium ions, gelling the mixture, and then sintering. 3. A process for producing sintered alumina abrasive grains, which comprises gelling an alumina sol containing α-alumina fine particles, drying and calcination, impregnating with calcium ions and sintering.