JPS6330314A - Production of sintered alumina abrasive grain - Google Patents

Abstract

PURPOSE:To economically obtain the titled powder having a high performance from an inexpensive starting material by forming an alumina hydrate contg. a reforming component of the sintered alumina by neutralizing a basic aluminum salt contg. the reforming component, followed by drying a treated material which is obtd. by adding an acid to said hydrate, and then by effecting a hydrothermal treatment of the obtd. hydrate, followed by calcination of the said hydrate. CONSTITUTION:A neutralizing agent, preferably, ammonium salt, is added to the basic aluminum salt contg. the reforming component of the sintered alumina resulted, in the formation of the alumina hydrate. subsequently, the hydrothermal treatment is effected after adding an acid (preferably, a monovalent acid such as hydrochloric acid and acetic acid, etc.) to the hydrate And, the obtd. treated material is dried, followed by calcining it. The reforming component is exemplified by preferably, MgO and ZrO2, and the calcining is effected preferably, at a temp. of 1,200-1,500 deg.C.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides high grinding performance, especially polishing belts, polishing disks,
This invention relates to alumina sintered abrasive grains suitable for offset grindstones, flexible grindstones, etc.

(Conventional technology) Sintered abrasive grains that have been used in large quantities include those made by adding a binder to Bayer alumina powder or bauxite powder, molding it, and then sintering it at a high temperature of 1800°C or higher, but it has poor performance. The range of applications for which it is used is limited. Thereafter, a new type of method for producing sintered abrasive grains was disclosed, in which sintering was performed at a low temperature of 1500° C. or lower using a sol-gel method. The grinding performance of the abrasive grains produced by this method is said to be far superior to commercially available fused alumina abrasive grains, and to be comparable or superior to commercially available fused alumina-zirconia abrasive grains.

All of the methods disclosed in the following patents are products of alumina monohydrate (denoted as A1203 ・H2O, but the actual product corresponding to this is 1.5-1.7 hydrate). NamerDIsPERAL@J or rCATA
The raw material is a colloidal dispersion (so-called alumina sol) of PAL' J.

Published Patent Publication No. 58-32389 discloses a method in which a modifying component, such as magnesia or zirconia, is mixed with the colloidal dispersion and then gelled, and then slowly sintered at a temperature of 1250° C. or higher for several hours. In this case, calcium and alkali metals must not be substantially contained (contained less than about 0.05% by weight).

Published Patent Publication No. 57-207872 uses a similar method, but in this case calcium is contained in 0 to 1.8% by weight and sodium is contained in 0 to 0.4% by weight, which is 120% by weight.
It is said that it is acceptable if the material is rapidly heated to a temperature higher than 0° C. for a period of less than 10 minutes and sintered.

Published Patent Publications 1982-74299 and 1982-80
No. 785 both relate to an electrophoresis method, in which a colloidal dispersion containing the above-mentioned modifying components is prepared, and after drying the material adhered to the cathode and/or membrane by electrophoresis, 1
This method involves rapidly heating the material to 200°C or higher and sintering it.

Published Patent Publication No. 5F3-83932 is a method for producing undoped, high-purity alumina particles with closed pores, in which gels or deposits obtained by a sol-gel method or an electrophoresis method are dried and This method involves rapidly heating the material to 1200°C or higher and sintering it.

(Problems to be Solved by the Invention) However, these disclosed methods have the following problems. That is, first, in order for the alumina monohydrate used as a raw material to be dispersed in a colloidal state, the -order particle size must be 0, IJLII
It must be an ultrafine powder, usually r D l5P
Like ERAL@J, it is expensive because it is obtained by high-temperature hydrolysis of organoaluminum compounds such as alkyl aluminum and aluminum alkoxide.
This makes the abrasive grains very expensive.

Next, even if we try to make nearly 100% pure alumina sintered abrasive grains from only a colloidal dispersion of alumina monohydrate,
It has been confirmed that the performance as an abrasive grain is significantly inferior.
To this end, it suppresses abnormal grain growth of crystals, refines the structure, and
Modifiers such as magnesia (in the form of a magnesium salt as a precursor) for purposes such as densification and zirconia (in the form of a zirconium salt) for purposes such as increasing toughness have been added. However, since these salts have the effect of promoting gelation, when added to a colloidal dispersion, gelation immediately begins and a significant increase in viscosity occurs, making it difficult to homogeneously mix the modifying components. It is difficult and requires a great deal of ingenuity in equipment and operation, and sometimes even fine tissues cannot be uniformly dispersed, resulting in non-uniform areas and deterioration of performance.

In addition, this increase in viscosity tends to increase as the concentration of alumina monohydrate increases, so there is an upper limit to the concentration of alumina monohydrate for homogeneous mixing of the modifying components, and r DIS
For 1.5-1.7 hydrates such as PERAL' J, the content is usually 25% by weight or less, preferably around 20%. This solid content concentration is related to productivity and gel density, and although a higher concentration is desirable from an economical and performance standpoint, it is subject to limitations for the reasons mentioned above.

An object of the present invention is to obtain a highly concentrated alumina solution using inexpensive raw materials as starting materials, and to economically produce high-performance alumina sintered abrasive grains from the solution.

(Means for Solving the Problems) The present invention uses a basic aluminum salt as a raw material in place of the conventional fine alumina monohydrate.

This basic aluminum salt can be made into an aqueous solution at high concentration. Therefore, it is easy to uniformly add the modifying component.A neutralizing agent is added to the basic aluminum salt containing the modifying component to form an alumina hydrate, which is then hydrothermally treated by adding an acid. The method is characterized in that the glassy material is made to a predetermined viscosity and then fired. This results in a fine structure similar to that of the sol-gel method disclosed above, which has much better grinding performance than commercially available fused alumina abrasive grains or fused alumina-zirconia abrasive grains. There was found.

Next, the present invention will be explained in detail in the order of steps.

a. Synthesis of basic aluminum salts There are various ways to make basic aluminum salts.
A preferred method that can obtain a highly concentrated aqueous solution is
This is a method of adding metallic aluminum to various aluminum salts. The aluminum salts used are usually aluminum chloride (Allll: I 8HO) and aluminum nitrate (AI(NO3)3-11)10).
Aluminum acetate (Al2(OH,C00)4Φ4HO
), aluminum sulfate (A12(S04)3・18H
20) is also possible. Although there are no particular limitations on the starting concentration, 2 to 4 mol% is used in order to provide an appropriate reaction rate.

The modifying components added are water-soluble magnesium compounds,
Commonly known modifying ingredients for alumina sintered bodies, such as zirconium compounds, zinc compounds, nickel compounds, chromium compounds, and cobalt compounds, can be used to suppress abnormal grain growth of alumina and increase toughness. In terms of performance and cost, magnesium compounds are preferred. Various magnesium salts are used as magnesium compounds, but magnesium chloride (MgC12.8H20) is preferred in terms of performance.
and magnesium nitrate (Mg(No3)2 ・8H20)
The amount added (content relative to the total amount) is preferably 1 to 8% by weight in terms of oxide after firing due to the performance of the abrasive grains, and preferably 4 to 4% by weight. However, in the post-process In some cases, there may be a loss, so it is possible to adjust by adding more than the theoretical value in advance, or by adding the insufficient amount during hydrothermal treatment, which will be explained next.

Next, the reaction between the aluminum salt and metal aluminum is carried out by adding granular, flaky, etc. aluminum to the aluminum salt aqueous solution and heating it to about 80 to 100 ° C.
The modification component may be added to the raw materials before the reaction, or to the basic aluminum aqueous solution after the reaction.The resulting reaction product is a modified product. It is a basic aluminum salt represented by the formula Al (OH) n When the ratio of AI and X is 2 or more, it may become a gray carmela-like solid,
It can be used without problems by adding water to a predetermined concentration. Other methods for producing basic aluminum salts include, for example, adding an aqueous solution of ICI, HNO3, etc. to an aqueous solution of AI(0)1) under predetermined conditions and carrying out one reaction. Addition of modifying components can also be carried out in the same manner as above.

b. Neutralized basic aluminum salt aqueous solution (normal concentration is A)
(15 to 25% by weight (calculated as 12O3)) is neutralized by adding an alkali to obtain an alumina hydrate containing a modifying component. Depending on the type of modifying component, the decomposition rate may be slow and the content may not reach the predetermined level. In that case, the content may be adjusted by adding it to the slurry in the subsequent process. As alkalis, carbonates such as ammonium carbonate and sodium carbonate, heavy acid groups such as ammonium hydrogen carbonate and sodium hydrogen carbonate, and hydroxides such as aqueous ammonia and sodium hydroxide are used, but in order to avoid containing metal impurities, ammonium Salt is preferred.

There are no particular restrictions on the neutralization temperature as long as it is below the boiling point, but
In order to suppress crystallization of the product and reduce the hydrothermal treatment temperature and time, a low temperature of 50° C. or lower is preferable.

The obtained alumina hydrate containing the modifying component (the hydrate form is Al2O3, H2O on average) is aged as necessary and then filtered and washed repeatedly to remove by-products. Centrifugal dehydration method, filter press method, etc. are used for filtration.

After thorough cleaning.

In order to increase the solid content concentration in the slurry, -150℃
It is preferable to dry and grind to dry powder at the following temperature:
The particle size of the dry powder is preferably as fine as possible in order to shorten the hydrothermal treatment time, but a particle size of 17G mesh or less is sufficient. If azeotropic drying using an organic substance is used during drying, pulverization becomes unnecessary. If the drying temperature exceeds 150°C, the characteristics will deteriorate, which is not preferable.

C0 hydrothermal treatment Add water to the obtained dry powder to reach the desired concentration.

After stirring to form a slurry, an acid and, if necessary, a modifying component for concentration adjustment are added and hydrothermal treatment is performed.

The solid content concentration is preferably as high as possible in order to reduce the energy for drying and solidification in the next step, but if it exceeds 40% by weight in terms of alumina monohydrate, peptization will be insufficient and it is not desirable in terms of abrasive grain performance. is 15 in terms of alumina hydrate
~40% by weight is used, most preferably 25-35% by weight.

The acids used include inorganic acids such as nitric acid and hydrochloric acid, as well as acetic acid and formic acid. ! A monohydric acid is preferable in melting. Polyhydric acids such as sulfuric acid and phosphoric acid have a peptizing effect on alumina inferior to monohydric acids. The amount of acid added is preferably such that the pH of the solution after hydrothermal treatment is 1 to 3 in order to achieve complete peptization, and usually 0.02 to 0.20 mf per tg of solid content is used.

The hydrothermal treatment is carried out at 120 to 300°C for 1 hour or more, preferably at 150 to 180°C for 2 to 8 hours in terms of equipment and energy.

Hydrothermal treatment is important in the present invention, and even if the alumina hydrate slurry obtained in the previous step is dried as it is without hydrothermal treatment, it will not become a glassy solid mass but will be powdered.
By hydrothermal treatment, amorphous alumina hydrate becomes pseudo-boehmite and hardens into a glass-like form when dried. It is necessary to sinter this.

d. Drying and Grinding Φ Classification The hydrothermally treated liquid is dried to form a glassy solid mass, and then crushed and classified to a predetermined particle size.

For drying, spread the treatment solution on a vat to a thickness of several centimeters,
Leave to dry at 150°C or less. It is preferable to move the bat slowly within the soaking zone for better drying efficiency.
In addition, there is no need for uneven drying.The lower the drying temperature, the higher the density of the abrasive grains, which is preferable in terms of performance, but the drying temperature should be selected in consideration of productivity. A temperature of 150° C. or higher is not preferable because unnecessary particle sizes cannot be redispersed in water and regenerated.

For crushing, roll crusher, hammer crusher,
Ball mills, rod mills, etc. are used, but since acicular particles are likely to occur, it is recommended to repeatedly grind the solidified material before firing. This is due to the fact that it is difficult to use. It is also desirable to grind before firing in order to create sharp edges on the abrasive grains.

For classification, a vibrating sieve or a regular mesh sieve is used, but the sieve opening should be determined taking into account shrinkage during firing.

e. Firing The grains adjusted to a predetermined grain size are fired and sintered. Prior to firing, it is convenient to perform preliminary firing at 800 to 800°C to remove bound water and residual acid, but direct firing may be used if there is no problem with the equipment.

For firing, various types of firing furnaces can be used, including electric furnaces such as Matsufuru furnace and trolley furnace, tunnel kilns, and rotary kilns. A suitable firing temperature is 1200 to 1500°C.

Preferably, 1350 to 1450°C is used. 12
Below 00℃, sintering is insufficient and the strength of the abrasive grains is weak.
If the temperature exceeds 0°C, sintering progresses too much and the cutting edge self-growth effect of the abrasive grains becomes poor. There are no particular restrictions on the temperature increase/decrease rate and holding time, but
Rapid heating and rapid cooling is preferred in terms of abrasive grain performance.

Next, the present invention will be explained in more detail by way of examples.

Example 1 Aluminum chloride (AlCl2-8
H20) 20Og, magnesium nitrate (
Dissolve 80 g of Mg(NO2) 3681 (20), heat to 80-100°C while cooling under reflux, then wash with 10% hydrochloric acid and dry to activate the surface of a metal aluminum lathe. 90g of cutting pieces were added and reacted.After the reaction was completed, the reaction solution was filtered and the concentration was 40% as the furnace solution.
．． A 3% by weight aqueous basic aluminum chloride solution was obtained. Analysis of the solute revealed that it was basic aluminum chloride with the molecular formula of A12(OH)2.2C13,8, and the content of the modifying component was 4.8% by weight in terms of oxide (magnesia in alumina). there were.

Next, 150 g of this aqueous solution was diluted by adding 800 ts of water, and 130 am of a 15% by weight ammonium carbonate aqueous solution was added dropwise at a rate of 10 m/sin to neutralize the alumina hydrate while stirring at room temperature. generated. As the amount of alumina hydrate increased during the process, the viscosity increased.
Water was added successively to make the final liquid volume 20,001 Ib.

After aging for 1 hour, filter.

Repeated washing. Finally, it was washed with acetone and dried at 100° C. to obtain 35 g of aluminum hydrate, which was crushed in a ball mill to give 170 mesh (5 under).

This alumina hydrate had an Al2O3 content of 80% by weight, and the content of modifying components was 1.8% by weight in terms of oxides.

30g of this alumina hydrate powder was dispersed in 55g of water, and the solid content was 35% by weight (21% in terms of Al2O2 concentration).
．． 2% by weight) to form a slurry. To this slurry, 3.8 g of magnesium nitrate and 2.0 Il of nitric acid were added to adjust the concentration of magnesia, and the mixture was heated to 180°C in a glass pressure-resistant container.
, Hydrothermal treatment was performed for 3 hours.

100 kg of high viscosity liquid obtained by such method and conditions
It was prepared in units, transferred to a enamel vat to a thickness of 2 to 30 layers, and dried in a hot air drying oven at 80° C. for 24 hours to form a glassy solid mass. This solid mass was crushed in a roll crusher and sieved to 500-1000 final layers.

The sieved grains were placed in an aluminum crucible and pre-calcined in a Matsufuru furnace at 800°C for 5 hours to remove crystallization water and nitrate radicals, and then heated to 1400°C at a heating rate of 5°C/min. ,
It was held for 5 hours. After cooling to room temperature, take out particle size cloud for rubbing 3
It was sieved into 6 parts. The magnesia content of this sample was approximately 5% by weight.

5
After being held for a minute, it was immediately taken out to room temperature, cooled, and then sieved to a particle size for thick cloth @3B.

Example 3 Aluminum nitrate (AI(NO)) was added to 800 mfl of water.
・9)+20) 320 g and 70 g of magnesium nitrate as a modifying component were dissolved, and 100 g of metal aluminum was reacted in the same manner as in Example 1 to obtain an aqueous solution of basic aluminum nitrate with a density of 37.7%.

As a result of solute analysis, A12(OH)2.2(N03)
It was basic aluminum nitrate represented by the molecular formula 3.8, and the content of the modifying component was 5.8% by weight in terms of oxide.

This basic aluminum nitrate solution was subjected to neutralization, hydrothermal treatment, drying, pulverization, classification, and baking in the same manner as in Example 1, and was divided into particles having a particle size of 3B for wear.

Example 4 Using the grains obtained in Examples 1 to 3 and a particle size key 36 of commercially available brown fused alumina (A) and fused alumina-zirconia abrasive grains for comparison, the outer diameter! Using a vulcanized fiber board with a 78φ■ layer, a hole diameter of 23φl, and a thickness of 0.85mm as a substrate, an abrasive disk was manufactured by a conventional method.

Next, this was installed on the Hitachi PDH-180B electric type Sangoo, and the work material was a 545C flat plate (38W x 500mm x
IOtmm) was ground for 20 minutes with a load of 8 kg.

The cumulative amount of grinding is shown in Table 1.

The polishing disks of the examples all exhibited grinding performance about 2.0 times that of conventional fused alumina and about 1.3 times that of fused alumina-zirconia.

Table 1 Effects of the Invention According to the present invention, compared to the disclosed method, the raw materials are cheaper, and the necessary modifying components can be added in advance as an aqueous solution. It is possible to homogeneously mix down to the fine structure of the quality components, and since the modifying components are homogeneously mixed in advance, there is no need to worry about viscosity increase, so it is possible to increase the solid content concentration. Therefore, it can be manufactured advantageously both in terms of performance and economy.

Claims (3)

[Claims] (1) A neutralizing agent is added to the basic aluminum salt containing the modifying component of the alumina sintered body to generate an alumina hydrate containing the modifying component, and an acid is added to the hydrate for hydrothermal treatment. and
A method for producing alumina sintered abrasive grains, which comprises drying and then firing the obtained treated product. (2) The method for producing alumina sintered abrasive grains according to claim 1, wherein the modifying components are MgO and ZrO_2. (3) The method for producing alumina sintered abrasive grains according to claim 1, wherein the firing is performed at 1200 to 1500°C.