KR101238666B1 - High hardness abrasive grains and manufacturing method of the same - Google Patents
High hardness abrasive grains and manufacturing method of the same Download PDFInfo
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- KR101238666B1 KR101238666B1 KR1020100091458A KR20100091458A KR101238666B1 KR 101238666 B1 KR101238666 B1 KR 101238666B1 KR 1020100091458 A KR1020100091458 A KR 1020100091458A KR 20100091458 A KR20100091458 A KR 20100091458A KR 101238666 B1 KR101238666 B1 KR 101238666B1
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Abstract
The present invention comprises the steps of preparing a dispersion by dispersing an abrasive source material in a solvent, (b) adding a source material containing a peptizing agent and a doping element to the dispersion to form a sol, and (c) the sol Heat treatment to reduce the water content contained in the sol; (d) hot pressing the gel formed by the heat treatment to reduce the moisture and pores contained in the gel; and (e) hot pressing the gel. It relates to a method for producing a hard abrasive abrasive grain comprising the step of pulverizing and firing and a high hardness abrasive grain produced thereby. According to the present invention, the pores of alumina can be minimized by reducing the moisture by heat-treating the sol containing the abrasive source material and hot pressurizing the gel, so that it is possible to manufacture very dense alumina having no pores remaining therein, and the firing temperature. Since it can be lower than the existing process can reduce the production cost, it is possible to manufacture high abrasive abrasive grains showing a high hardness.
Description
The present invention relates to abrasive grains and a method of manufacturing the same, and more particularly, to reduce moisture by heat-treating a sol containing an abrasive source material and to minimize the pores of alumina by hot pressurizing the gel so that pores do not remain inside. It is possible to manufacture a very dense alumina, and the firing temperature can be lower than the existing process to lower the production cost, and to a method for producing a high hardness abrasive grain exhibiting a high hardness and to a high hardness abrasive grain produced thereby.
As the semiconductor, ship, and parts industries develop, the market for abrasives is on the rise. Along with the expansion of the precision processing market by forming a light and thin product range, the precision and reliability of abrasives are required.
In the case of the abrasive using the conventional molten and sintered alumina abrasive grains, due to the shape and size of the abrasive grains, many difficulties appear in improving durability and cutting rate. When the abrasive grains are broken during grinding or grinding, and the abrasive grains fall out, the grinding surface and the abrasive grains cannot contact each other.
On the other hand, the development of high-functional abrasive grains for polishing workpieces made of stainless steel, titanium, nickel alloys, aluminum, and the like is required. The development of new abrasive grains is considered essential to prolong the life of the abrasive, to improve the durability, and to improve the degree of processing for the development of highly functional abrasive grains.
In general grinding wheel structures, the binder holds the particles and there is an empty space between them. When the wheel is impacted while the wheel is rotated, the particles are degraded. In general, the alumina abrasive grains are degraded in the mass and have a short lifespan. However, when the abrasive is manufactured in the dendrimer shape by elemental doping, the impact of the grinding wheel is received by the dendrimer shapes of the particles, and the branches are fallen one by one, thereby increasing the life and cutting efficiency.
In particular, alumina abrasives have intermediate properties between artificial diamond or CBN and molten alumina, creating a new market to replace some of the demand for artificial diamond or CBN and molten alumina.
Accordingly, there is a demand for the development of new abrasives having high density and high hardness.
The problem to be solved by the present invention is to heat the sol containing the abrasive source material to reduce the moisture and to hot press the gel to minimize the pores of the alumina can be produced very dense alumina without pores remaining inside, It is possible to lower the firing temperature than the existing process to reduce the production cost, and to provide a method for producing a high hardness abrasive grain exhibiting a high hardness and a high hardness abrasive grain produced thereby.
The present invention comprises the steps of (a) dispersing an abrasive source material in a solvent to prepare a dispersion, (b) adding a source material comprising a peptizing agent and a doping element to the dispersion to form a sol, (c) ) Heat treating the sol to reduce the water content contained in the sol; (d) hot pressing the gel formed by the heat treatment to reduce moisture and pores contained in the gel; and (e) hot pressing. It provides a method for producing a hard abrasive grains comprising the step of grinding and calcining the gel.
The peptizing agent is composed of at least one material selected from nitric acid, hydrochloric acid, acetic acid and hydrobromic acid, and the pH of the peptizing agent is preferably in the range of 1-4.
The doping element is at least one material selected from lanthanum, magnesium, yttrium, and zirconium, and the doping element is preferably contained in an amount of 0.01 to 10% by weight based on the abrasive grains.
The source material including the doping element may be at least one selected from La (NO 3 ) 3 · 6H 2 O, Mg (NO 3 ) 2 · 6H 2 O, Y (NO 3 ) 3 · 6H 2 O, and zirconium acetate. It may be made of.
The heat treatment may be performed for 1 minute to 48 hours at the same or lower temperature than the boiling point of the solvent.
The hot press is preferably performed for 1 second to 24 hours at a pressure of 0.1 to 10 tons at a temperature of 100 to 450 ℃.
The abrasive source material is boehmite, and the high hardness abrasive grain may be alumina abrasive grains forming a corundum crystal phase.
The method may further include adding a modifier to the dispersion in step (b), wherein the modifier may be one or more substances selected from ammonium acetate, ethyltrimethyl acetate and methyltrimethyl acetate.
The step (e) may further include the step of removing the gas by heat treatment before firing after the pulverization, the step of removing the gas is preferably carried out for 1 minute to 12 hours at a temperature of 800 ~ 1000 ℃. .
The firing is preferably carried out for 1 minute to 6 hours at a temperature of 1250 ~ 1450 ℃.
In addition, the present invention is alumina abrasive grains produced by the manufacturing method of the above-mentioned hard abrasive abrasive grains, and form a corundum crystal phase, the dendrimer type secondary phase by at least one material selected from lanthanum, magnesium, yttrium and zirconium It provides a high hardness abrasive grain formed.
According to the present invention, high hardness alumina using the sol-gel method can be produced. In the present invention, the heat treatment process of boehmite sol and the hot pressurization process of boehmite gel were used to remove the pores remaining in the alumina to increase densification. The pores remaining in the alumina were to be reduced because it causes the hardness of the alumina, and the pores of the alumina were reduced by heat treatment on the boehmite sol to gradually decrease the moisture. Pore was minimized. When hot pressing the boehmite gel, it was possible to prepare very dense alumina without remaining pores in the interior, which showed high hardness and developed high hardness alumina.
In addition, according to the present invention, it is possible to lower the cost by a simpler process and a lower firing temperature than the conventional production of abrasive grains by grinding and sintering abrasives. By removing the pores to improve the durability and machinability of the grinding, abrasive, thereby improving the precision of the processing industry, there is an effect of replacing the abrasive grains of the existing molten and sintered abrasive.
In addition, the development of grinding and abrasive abrasives has the effect of import substitution, and the parts industry is expected to be activated due to the improvement of precision and reliability in the precision processing field, and the durability of grinding materials due to the dropping of abrasive grains in the grinding (e) process. Improvements are expected to reduce costs.
1 is a graph analyzing the crystal phase of boehmite (RMP-10).
Figure 2 is a photograph showing the microstructure of boehmite (RMP-10).
3 is a graph showing the specific surface area of alumina after calcination according to the peptizing agent.
4 is a graph showing the specific surface area of alumina after calcination according to the peptizing agent.
5 is a graph showing the specific surface area of alumina after firing according to the peptizing agent.
6 is a graph showing the crystal phase of alumina after calcination according to the peptizing agent.
7 is a graph showing the crystal phase of alumina after firing according to the peptizing agent.
8A and 8B are photographs showing the shape of alumina after firing using nitric acid as a peptizing agent.
9A and 9B are photographs showing the shape of alumina after firing using hydrochloric acid as a peptizing agent.
10A and 10B are photographs showing the shape of alumina after firing using acetic acid as a peptizing agent.
11A and 11B are photographs showing the shape of alumina after firing using hydrobromic acid as a peptizing agent.
Figure 12a is a graph showing the differential thermal analysis of the gel dried powder according to the peptizing agent, Figure 12b is a graph showing the thermogravimetric analysis of the gel dry powder according to the peptizing agent.
13 is a hardness graph of alumina according to the peptizing agent.
14 is a graph showing the specific surface area of dry powders according to the content of modifiers.
15 is a graph showing the specific surface area of dry powder with 2% modifier added.
16 is a graph showing the hardness of alumina according to the modifier.
FIG. 17 is a graph showing H 2 O reduction of boehmite sol over evaporation time.
18 is a graph showing the hardness of alumina according to the H 2 O reduction (15% by weight) process of the boehmite sol.
19 is a graph showing the hardness of alumina according to the H 2 O reduction (25% by weight) process of the boehmite sol.
20 is a graph showing the specific surface area of dry powder after calcination with a stirrer.
Figure 21a is a graph showing the crystal phase of the initial boehmite, Figure 21b is a graph showing the crystal phase of the powder after calcination, Figure 21c is a graph showing the crystal phase of the powder after firing.
22 is a graph showing the specific surface area of the powder after calcination according to the stirring rate of the boehmite sol.
23a and 23b are photographs showing the shape of alumina according to the stirring speed.
24 is a view showing a schematic view and a cross-sectional view of the alumina prepared after firing.
25A to 25D are scanning electron microscope (SEM) images showing the shape of alumina according to the stirring speed.
26 is a graph showing the hardness of alumina according to the stirring rate of the boehmite sol.
FIG. 27 is an X-ray diffraction (XRD) pattern showing an alumina crystal phase when the element is not doped.
FIG. 28 is an X-ray diffraction (XRD) pattern showing the crystal phase of alumina doped with magnesium (Mg). FIG.
FIG. 29 is an X-ray diffraction (XRD) pattern showing the crystal phase of lanthanum (La) doped alumina.
30 is an X-ray diffraction (XRD) pattern showing the crystal phase of yttrium-doped alumina.
FIG. 31 is an X-ray diffraction (XRD) pattern showing the crystal phase of zirconium doped alumina.
32A and 32B are photographs showing the shape of alumina doped with 2% by weight of lanthanum.
33A and 33B are photographs showing the shape of alumina doped with lanthanum by 3% by weight.
34A and 34B are photographs showing the shape of alumina doped with 5 wt% lanthanum.
35A and 35B are photographs showing the shape of alumina doped with magnesium by 1% by weight.
36A and 36B are photographs showing the shape of alumina doped with 1.5 wt% magnesium.
37A and 37B are photographs showing the shape of alumina doped with magnesium by 2% by weight.
38A and 38B are photographs showing the shape of alumina doped with yttrium at 2% by weight.
39A and 39B are photographs showing the shape of alumina doped with
40A and 40B are photographs showing the shape of alumina doped with yttrium at 4% by weight.
41A and 41B are photographs showing the shape of alumina doped with zirconium at 0.4% by weight.
42A and 42B are photographs showing the shape of alumina doped with zirconium 0.7 wt%.
43A and 43B are photographs showing the shape of alumina doped with zirconium by 1% by weight.
44 is a graph showing the density change of lanthanum-doped alumina.
45 is a graph showing the density change of magnesium doped alumina.
46 is a graph showing the density change of yttrium doped alumina.
47 is a graph showing the density change of zirconium doped alumina.
48 is a graph showing the change in hardness of lanthanum-doped alumina.
49 is a graph showing the change in hardness of magnesium doped alumina.
50 is a graph showing the hardness change of yttrium-doped alumina.
FIG. 51 is a graph showing a change in hardness of zirconium-doped alumina.
52 is a graph showing the crystal phase of alumina doped with lanthanum and magnesium, yttrium and zirconium.
53 is a photograph showing the shape of alumina doped with lanthanum and magnesium.
54 is a photograph showing the shape of alumina doped with yttrium and zirconium.
FIG. 55 is an X-ray diffraction (XRD) pattern showing the crystalline phase of alumina doped with lanthanum, magnesium, yttrium and zirconium.
56 is a photograph showing the shape of alumina doped with lanthanum, magnesium, yttrium and zirconium.
57 is a photo showing the grain and toughness change of the alumina with the addition of the doping element
58 is a view showing a change in thickness with pressure.
Fig. 59 shows the results of differential thermal analysis of boehmite gels.
60 is a view showing the results of the crystal phase analysis of alumina with pressing.
61A and 61B are views showing the shape of alumina under pressure.
62 is a view showing a specific surface area of alumina according to pressing.
63 is a view showing the hardness of alumina according to pressing.
64 is a view showing the shape of alumina under pressure.
65 is a diagram showing the result of differential thermal analysis (DTA) of alumina.
66 is a view showing a gas removal experiment process.
67 is a photograph showing alumina particles not subjected to the degassing process.
68 is a photograph showing alumina particles undergoing a gas removal process.
69 is a view illustrating a change in hardness according to the gas removing process.
70 is a view showing the hardness according to the firing process.
71 is a view showing the shape of alumina according to the firing holding time.
72 is a view showing the hardness of alumina according to the firing holding time.
73 is a view showing a density change of alumina according to firing temperature.
FIG. 74 is a view showing a change in hardness of alumina according to firing temperature. FIG.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments are provided to those skilled in the art to fully understand the present invention, and may be modified in various forms, and the scope of the present invention is limited to the embodiments described below. It doesn't happen.
In the present invention, it is intended to develop domain abrasive particles. To this end, the present invention comprises the steps of (a) dispersing an abrasive source material in a solvent to prepare a dispersion, (b) adding a source material containing a peptizing agent and a doping element to the dispersion to form a sol, (c) heat treating the sol to reduce the water content contained in the sol; (d) hot pressing the gel formed by the heat treatment to reduce the moisture and pores contained in the gel; and (e) It provides a method for producing a hard abrasive abrasive grain comprising the step of pulverizing and calcining the hot press gel.
The peptizing agent is composed of at least one material selected from nitric acid, hydrochloric acid, acetic acid and hydrobromic acid, and the pH of the peptizing agent is preferably in the range of 1-4.
The doping element is at least one material selected from lanthanum, magnesium, yttrium, and zirconium, and the doping element is preferably contained in an amount of 0.01 to 10% by weight based on the abrasive grains.
The source material including the doping element may be at least one selected from La (NO 3 ) 3 · 6H 2 O, Mg (NO 3 ) 2 · 6H 2 O, Y (NO 3 ) 3 · 6H 2 O, and zirconium acetate. It may be made of.
The heat treatment may be performed for 1 minute to 48 hours at the same or lower temperature than the boiling point of the solvent.
The hot press is preferably performed for 1 second to 24 hours at a pressure of 0.1 to 10 tons at a temperature of 100 to 450 ℃.
The abrasive source material is boehmite, and the high hardness abrasive grain may be alumina abrasive grains forming a corundum crystal phase.
The method may further include adding a modifier to the dispersion in step (b), wherein the modifier may be one or more substances selected from ammonium acetate, ethyltrimethyl acetate and methyltrimethyl acetate.
The step (e) may further include the step of removing the gas by heat treatment before firing after the pulverization, the step of removing the gas is preferably carried out for 1 minute to 12 hours at a temperature of 800 ~ 1000 ℃. .
The firing is preferably carried out for 1 minute to 6 hours at a temperature of 1250 ~ 1450 ℃.
Hereinafter, as an example of the present invention, alumina-based abrasives using the Sol-Gel method will be described.
Boehmite (Aluminium Oxide Hydroxide) is used to prepare a boehmite sol by mixing alumina with a solvent during synthesis by a sol-gel method. For the densification and hardness improvement of alumina, it is most important to prepare a stable boehmite sol. The characteristics of the boehmite used to prepare a stable and uniform boehmite sol was investigated.
1 is a graph analyzing the crystal phase of boehmite (RMP-10), Figure 2 is a view showing the microstructure of the boehmite (RMP-10). Boehmite (RMP-10) is aluminum oxide hydroxide (AlO (OH)), which shows the crystal phase of a typical boehmite, and circular particles were distributed in uneven size. It is judged that the small particles of boehmite are observed in non-uniform size by the shape of agglomeration. Therefore, in order to prepare a uniform boehmite sol in the production of alumina, a process of dispersing boehmite is important. The density of boehmite (RMP-10) was relatively lower than that of other boehmites, with a loose density of 0.6-0.8 kg /
Influence of stable boehmite sol (Sol) according to peptizing agent and stable boehmite sol (Sol) according to modifier to develop high hardness alumina grains using sol-gel (Sol-Gel method), Pore control according to H 2 O reduction of boehmite sol, stabilization of boehmite sol according to stirring speed, characteristics of alumina according to doping element, hardness change according to porosity of alumina by pressurization, hardness according to firing temperature and holding time Look for change.
1. Formation of stable boehmite sol according to peptizing agent
end. Boehmite Sol with Solvent Ethanol
In order to prepare a stable boehmite sol, boehmite sol was prepared using ethanol as a solvent, and the change according to the peptizing agent was examined. The ratio of ethanol and boehmite was 8: 2, and the change over time was observed. In the case of using nitric acid and hydrochloric acid as the peptizing agent after the initial synthesis, stable boehmite sol state was maintained, and hydrobromic acid was rapidly gelling to a half-gel state. On the other hand, the boehmite sol in which sulfur phase, phosphoric acid, and acetic acid were used as peptizing agents could not be prepared as a stable sol due to layer separation. After 1 hour, nitric acid gelled slightly and remained in a gelled state, and hydrobromic acid gelled completely. Hydrochloric acid, sulfuric acid, phosphoric acid and acetic acid were separated. The change of state from 2 hours to 5 hours was the same. Nitric acid remained half-gel, hydrobromic acid was completely gelled, and hydrochloric acid, sulfuric acid, phosphoric acid and acetic acid were separated.
The specific surface area of alumina calcined with boehmite gel using nitric acid and hydrobromic acid as peptide was investigated. 3 is a graph showing the specific surface area of alumina after calcination according to the peptizing agent. The peptizing agent was mixed in a dispersion mixture of ethanol and boehmite in a ratio of 8: 2 (weight ratio), dried at 100 ° C. for 12 hours, pulverized and calcined at 650 ° C. for 4 hours, and then measured for specific surface areas. .
As a result, alumina using nitric acid as a peptizing agent showed a specific surface area of 177.74 m 2 g -1 , and alumina using hydrobromic acid as a peptizing agent showed a specific surface area of 162.43 m 2 g -1 . When ethanol was used as the solvent, it was found that hydrobromic acid was used as a peptizing agent to produce the lowest specific surface area when alumina was prepared.
I. Boehmite Sol with Solvent as Water (H 2 O)
Previously, the peptizing agent was used to stabilize the boehmite sol by using ethanol as a solvent of the boehmite sol. Below, we investigated the effect of peptizing agent on boehmite sol using water (H 2 O) as a solvent.
In order to disperse the boehmite sol, the peptizing reaction on the boehmite sol was observed using nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, and hydrobromic acid. The ratio of boehmite and H 2 O was prepared in a ratio of 2: 8 where boehmite did not precipitate, and the pH was adjusted to 2.5. After adjustment, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, and hydrobromic acid all maintained stable boehmite sol states. After 1 hour, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and hydrobromic acid maintained stable boehmite sol state, acetic acid gelled, and sulfuric acid separated the layer above boehmite sol. After 2 hours, nitric acid, hydrochloric acid, acetic acid, and hydrobromic acid gelled, and sulfuric acid and phosphoric acid separated. After 3 hours, nitric acid, hydrochloric acid, and hydrobromic acid were gelled, sulfuric acid and phosphoric acid separated, and acetic acid was completely gelled. After 4 hours, nitric acid, hydrochloric acid, sulfuric acid, and hydrobromic acid completely gelled, and sulfuric acid and phosphoric acid separated. After 5 hours, nitric acid, hydrochloric acid, sulfuric acid, and hydrobromic acid were completely gelled, and sulfuric acid and phosphoric acid were separated. Accordingly, sulfuric acid and phosphoric acid, which had completely separated the layers, were found to be unsuitable for use as a peptizing agent for causing peptite reaction of boehmite sol.
Except for these two types, alumina abrasive grains for abrasives were prepared using nitric acid, hydrochloric acid, sulfuric acid, and hydrobromic acid, which were gelled without delamination, and the specific surface area according to calcination and calcination. The viscosity, crystal phase, shape, differential thermal analysis, and hardness were analyzed and compared.
(1) Specific surface area of alumina according to peptizer
The specific surface area of alumina after calcination was investigated. 4 is a graph showing the specific surface area of alumina after calcination according to the peptizing agent. The peptizing agent was mixed with a dispersion mixture of water and boehmite at a ratio of 8: 2 (weight ratio), dried at 100 ° C. for 12 hours, pulverized and calcined at 650 ° C. for 4 hours, and then the specific surface area was measured. .
As a result, the specific surface area of alumina using nitric acid as a peptising agent was the lowest as 168.85 m 2 g - 1, and the specific surface area of alumina using nitric acid as a peptising agent was 190.10 m 2 g - 1 . It was. Therefore, when nitric acid was used as peptizer, it was found that the dispersibility of boehmite sol was improved to maintain the most compact state after calcination.
The specific surface area of alumina after calcination according to the peptizing agent was examined, and the specific surface area of alumina after calcining was investigated. 5 is a graph showing the specific surface area of alumina after firing according to the peptizing agent. The peptizing agent was mixed in a dispersion mixture of water and boehmite in a ratio of 8: 2 (weight ratio), dried at 100 ° C. for 12 hours, then pulverized and calcined at 650 ° C. for 4 hours, and 10 minutes at 1350 ° C. After firing for a specific surface area was measured.
As with calcination, the specific surface area of alumina using nitric acid as peptizing agent was 2.10 m 2 g -1, which was the lowest. Alumina using hydrochloric acid as the peptizing agent had the highest specific surface area of 2.56 m 2 g -1 . Thus, when nitric acid was used as a peptizing agent, the dispersibility of the boehmite sol was improved, and after calcining, it was found that the most compact state was maintained even after calcining with water.
(2) Crystal phase of alumina according to peptizer
The change of crystal phase of alumina according to peptizing system was investigated. Figure 6 is a graph showing the crystal phase of alumina after calcination according to the peptizing agent, the graph shown in Figure 6 is for the case of using nitric acid, hydrochloric acid, acetic acid, hydrobromic acid from the bottom, respectively. 7 is a graph showing the crystal phase of alumina after firing according to the peptizing agent, and the graph shown in FIG. 7 is for the case where nitric acid, hydrochloric acid, acetic acid and hydrobromic acid are used from the bottom.
After calcination, the crystal phase of alumina according to the peptizing agent is Al 2 O 3 for nitric acid, hydrochloric acid, acetic acid, and hydrobromic acid. A phase was formed, and after calcination, the alumina crystal phase showed a corundum phase as a main peak, and a secondary phase of LaMaAl 11 O 19 was formed. Nitric acid, hydrochloric acid, acetic acid, and hydrobromic acid all showed the same crystal phase, but differences in intensity were observed. In the case of alumina crystal phase after calcination, the intensity (intensity) when nitric acid, acetic acid, and hydrobromic acid were used was similar, and the intensity (Intensity) when hydrochloric acid was used was small. After firing, the intensity (intensity) when nitric acid, hydrochloric acid, and hydrobromic acid were used was similar, and the intensity (Intensity) when nitric acid was used was found to be somewhat small.
(3) Shape of Alumina According to Peptizer
The shape of the alumina according to the peptizing agent is shown by comparison at the same magnification of 500 times and 2000 times. 8A and 8B are photographs showing the shape of alumina after firing using nitric acid as a peptizing agent, and FIGS. 9A and 9B are photographs showing the shape of alumina after firing utilizing hydrochloric acid as a peptizing agent, and FIGS. 10A and
In the alumina using nitric acid as a peptizing agent, pores were not observed at 2000 times magnification, and small pores were observed at 500 times magnification, but a relatively compact shape was observed. Alumina using hydrochloric acid as a peptizing agent has a large number of non-uniform pores. Porosity was also observed in alumina using acetic acid as a peptizer, but it was smaller and less powdery than that of alumina using hydrochloric acid as peptizer. Finally, alumina using hydrobromic acid as peptizing agent had large pores and was evenly distributed. The distribution according to the amount of pores was found in the order of hydrochloric acid> hydrobromic acid> acetic acid> nitric acid. In this case, when nitric acid is used as a peptizing agent, it can be seen that it is possible to manufacture dense alumina granules having almost no pores.
(4) Differential Thermal Analysis of Gel Dried Powder According to Peptizers
Differential thermal analysis and thermogravimetric change of alumina according to peptizing agent were investigated. Figure 12a is a graph showing the differential thermal analysis of the gel dried powder according to the peptizing agent, Figure 12b is a graph showing the thermogravimetric analysis of the gel dry powder according to the peptizing agent.
Nitric acid, hydrochloric acid, acetic acid, and alumina utilizing hydrobromic acid all decreased with increasing temperature. In particular, steep curves were shown between 200 ° C and 500 ° C, resulting in a sharp weight loss. As a result of comparing the weight loss by each peptizer, the alumina using nitric acid as peptizer was the biggest decrease to 26.06%. Alumina using hydrochloric acid as a peptising agent decreased 22.19%, and alumina using acetic acid as a peptising agent decreased 23.79%. In addition, alumina using hydrobromic acid as a peptizing agent decreased by 23.12%. This weight reduction is the release of organic gases such as OH remaining inside due to the doping element and the peptizer added during the manufacture of alumina, and when the nitric acid is used as the peptizer, the most gas is discharged. It is thought to help minimize the amount of pores inside the alumina.
(5) hardness of alumina according to peptizing agent
The hardness of alumina according to peptizing agent was investigated. 13 is a hardness graph of alumina according to the peptizing agent. The load was 200g / f and the average value was used after measuring 5 times for 10 seconds. The hardness of alumina using nitric acid as peptizing agent was 18.26 ,, and the hardness of alumina using hydrochloric acid as peptizer was 12.34 ㎬. The hardness of alumina using acetic acid as a peptizing agent was measured to be 16.71㎬, and the alumina using hydrobromic acid as a peptizing agent showed a hardness of 14.59㎬. Among the four peptising agents, the hardness of alumina using nitric acid as the peptising agent was the highest, and the hardness of the alumina using hydrochloric acid as the peptising agent was the smallest. Therefore, the use of nitric acid as a peptizing agent to improve the hardness of alumina seems to have the greatest effect.
Peptides affecting the dispersibility of boehmite sol were investigated. The four peptizing agents of nitric acid, hydrochloric acid, acetic acid and hydrobromic acid showed different characteristics. The crystal phase showed the same crystal phase, but the intensity changed according to the peptizing agent used. The shape of each peptising agent was found to be sintered densely with the smallest pore amount when nitric acid was used as the peptizing agent. This can be seen in the specific surface area measurement results. It was confirmed that both the calcination and the firing showed the lowest specific surface area and the degree of densification was high. In addition, the weight reduction according to the differential thermal analysis decreased 26.06% in the case of alumina in which nitric acid was used as a peptizing agent. As a result, the hardness of alumina is 18.26 를, which indicates the highest hardness among the four peptizing agents and affects the formation of high hardness alumina.
2. Formation of Stable Boehmite Sols by Modifier
Alumina was mixed with a solution of nitric acid (HNO 3 ) (pH 2.5) and a modifier in a dispersion mixture of water and boehmite in a ratio of 8: 2 (by weight), and then dried at 100 ° C. for 12 hours. It was prepared by grinding and calcining at 650 ° C. for 4 hours and calcining at 1350 ° C. for 10 minutes.
The following shows the specific surface area of alumina after calcination according to the change of the content of ammonium acetate (CH 3 CO 2 NH 4 ) in the modifier.
The specific surface area of alumina was measured after calcination according to the change of the ammonium acetate content in the modifier. 14 is a graph showing the specific surface area of dry powders according to the content of modifiers. To the dispersion mixture of water and boehmite in a ratio of 8: 2 (weight ratio), nitric acid (HNO 3 ), a peptizer, and a modifier were mixed, dried at 100 ° C. for 12 hours, then pulverized and 4 at 650 ° C. The specific surface area was measured after calcination for hours.
The specific surface area of 173.15 m 2 g -1 was measured when no ammonium acetate was added, and 169.76 m 2 g -1 and 2% was 169.76 m 2 g -1 when the ammonium acetate content increased from 1% to 5%. m 2 g -1 , 3% is 171.22 m 2 g -1 , 4% has a specific surface area of 171.73 m 2 g -1 , 5% and 171.73 m 2 g -1 . When 2% of ammonium acetate was added, it showed the lowest specific surface area and low porosity.
Next, the specific surface area was compared by adding 2% of ammonium acetate, ethyl trimethyl acetate, and methyl trimethyl acetate in modifiers. The specific surface area of alumina using ammonium acetate, ethyltrimethyl acetate and methyltrimethyl acetate as modifiers was investigated. FIG. 15 is a graph showing a specific surface area of a dry powder to which a modifier is added 2%. In FIG. 15, a first graph is used when ammonium acetate is used as a modifier, and a second graph is used when ethyltrimethyl acetate is used as a modifier. The graph shows the case where methyltrimethyl acetate is used as the modifier.
If the specific surface area of the alumina was added to ethyl acetate in trimethyl modifier showed the lowest to 164.52 m 2 g -1, a case of using ammonium acetate showed a 168.96 m 2 g -1, with methyl trimethyl acetate is 169.72 m The highest specific surface area was shown as 2 g -1 . The porosity of alumina added with ethyltrimethyl acetate is expected to be the lowest.
The hardness results of the alumina according to the modifier are shown. 16 is a graph showing the hardness of alumina according to the modifier. The hardness according to the presence of modifier (Modifier) was found to have a slight difference in hardness when the modifier (Modifier) is not included (graph shown at the bottom in FIG. 16). In addition, it was found that the hardness of the alumina utilizing ethyltrimethyl acetate was the highest among the ammonium acetate and the ethyltrimethyl acetate.
3. Hardness change with decreasing H 2 O of boehmite sol
About 80% of the boehmite sol is H 2 O. Most of these H 2 O evaporate at the drying stage, but there is a possibility of remaining in the form of pores inside the particles. In order to reduce the residual amount of H 2 O prior to the densification of the alumina, a process of applying heat while stirring was used. H 2 O evaporates violently at a temperature of 100 ° C. or higher, and the boehmite gel is immediately dried. On the other hand, at 50 ° C., the boehmite sol maintains a stable sol state and only H 2 O evaporates slowly. Therefore, this process was used to reduce the porosity of alumina.
We investigated the hardness change of alumina abrasive grains with decreasing H 2 O of boehmite sol. In this process, the property of H 2 O that evaporates rapidly above 100 ° C. and slowly evaporates at a slightly later temperature is used.
17 is a graph showing the H 2 O reduction of the boehmite sol with evaporation time, Figure 18 is a graph showing the hardness of the alumina according to the H 2 O reduction (15% by weight) process of the boehmite sol. Referring to FIGS. 17 and 18, the amount of H 2 O decrease was reduced by 5 wt% every hour with a temperature of 50 ° C. After 1 hour, the weight was reduced to 5% by weight, after 2 hours to 10% by weight, after 3 hours to 15% by weight, and after 4 hours, the gel was not maintained in a stable sol state. This was followed by heating and stirring for 3 hours to reduce the H 2 O of the boehmite sol. As a result, the pores inside the alumina particles were removed, showing a high value of 18.91
As a result, it was found that the decrease in moisture significantly affected the hardness of the alumina. The temperature was adjusted to increase the amount of moisture reduction. When the temperature was reduced to 45 ° C. after 3 hours of holding at a temperature of 50 ° C., the amount of water reduction was increased to 25% by weight. 19 is a graph showing the hardness of alumina according to the H 2 O reduction (25% by weight) process of the boehmite sol. Referring to FIG. 19, as a result, as the pores of the alumina particles decreased, the densification of the alumina was increased to improve the hardness to 19.63 kPa.
4. Stabilization of boehmite sol according to the stirring speed
In order to investigate the influence of the stirring speed on the stabilization of the boehmite sol during the experiment, the agitator was rotated at 1000 rpm and the high speed stirrer was rotated at 2000 rpm or more, and then the specific surface area of the alumina was investigated.
The specific surface area of alumina after calcination with stirrer and high speed stirrer was investigated. 20 is a graph showing the specific surface area of dry powder after calcination with a stirrer. The dry powder was mixed with a dispersion solution of nitric acid (HNO 3 ) (pH 2.5) and a modifier in a dispersion mixture of water and boehmite at a ratio of 8: 2 (weight ratio), stirred with a stirrer, and then stirred at 12 ° C. at 12 ° C. After drying for an hour, it was ground and prepared by calcination at 650 ℃ for 4 hours. As a result, the alumina using the stirrer showed a specific surface area of 233.01, and the alumina using the high speed stirrer. As the stirring speed was increased, the densification of the alumina was improved and the specific surface area decreased.
Alumina abrasive grains were prepared by adjusting the stirring speed to 0 rpm, 100 rpm, 500 rpm, and 1000 rpm in order to investigate the change of alumina according to the speed of the stirrer when preparing the boehmite sol. The alumina shape, specific surface area and hardness according to the stirring speed were analyzed and discussed.
end. Crystal phase of dry powder with stirring speed
The dry powder was mixed with a dispersion solution of nitric acid (HNO 3 ) (pH 2.5) and a modifier in a dispersion mixture of water and boehmite at a ratio of 8: 2 (weight ratio), stirred with a stirrer, and then stirred at 12 ° C. at 12 ° C. After drying for an hour, it was ground and calcined at 650 ° C. for 4 hours, and calcined at 1350 ° C. for 10 minutes.
Figure 21a is a graph showing the crystal phase of the initial boehmite, Figure 21b is a graph showing the crystal phase of the powder after calcination, Figure 21c is a graph showing the crystal phase of the powder after firing.
Referring to FIGS. 21A to 21C, the crystal phase of alumina was changed into alumina (Al 2 O 3 ) after calcination at initial boehmite (AlOOH) and alumina (Corundum) after calcination regardless of the stirring speed.
I. Specific Surface Area of Alumina According to Stirring Speed
22 shows the specific surface area of the powder after calcination according to the stirring rate of the boehmite sol. Referring to FIG. 22, the alumina gelled as it was without stirring showed a high specific surface area of 242.94 m 2 g −1 , and the specific surface area decreased as the rotation speed increased. This resulted in a low specific surface area of 233.01 m 2 g -1 at 1000 rpm, and it can be seen that the pore amount in the alumina particles decreased as the stirring speed was increased.
All. Shape of Alumina According to Stirring Speed
23A and 23B are photographs showing the shape of alumina according to the stirring speed, and the shape of the alumina is observed using an optical microscope. Figure 24 shows the shape and cross-sectional schematic diagram of the alumina prepared after firing. Thus, the alumina particles are somewhat difficult to determine the difference in appearance. In order to observe the porosity and secondary phase in the alumina grains, the cross section of the alumina according to the stirring speed is to be observed.
The pore change of the boehmite sol was investigated according to the stirring speed. 25A to 25D are scanning electron microscope (SEM) photographs showing the shape of alumina according to the stirring speed. FIG. 25A is a case where the stirring speed is 0 rpm and FIG. 25B is a case where the stirring speed is 100 rpm. 25C illustrates a case where the stirring speed is 500 rpm and FIG. 25D illustrates a case where the stirring speed is 1000 rpm. In the case of alumina having a stirring speed of 0 rpm, large diagonal pores were irregularly distributed throughout the particles. The shape of the alumina having a stirring speed of 100 rpm was somewhat distributed in irregular pores. As the stirring speed increased from 500rpm to 1000rpm, the pore size significantly decreased. This is believed to minimize the amount of pores generated in the alumina by increasing the stirring speed during the preparation of boehmite sol.
la. Hardness of Alumina According to Stirring Speed
The hardness of alumina according to the stirring speed of the boehmite sol was measured and shown in FIG. 26. The natural gelled alumina without stirring showed a relatively low hardness of 16.45 kPa. The alumina stirred at 100 rpm showed a hardness of 17.71 kPa. The alumina stirred at 500 rpm showed a hardness of 18.26 kPa, and the alumina stirred at 1000 rpm showed a high hardness of 18.46 kPa. As a result, as the stirring speed was increased, the pores of the particles were reduced, indicating that the hardness value was increased.
5. Comparison of Properties of Alumina According to Doping Elements
The element is doped to improve the physical properties of the alumina. Lanthanum, magnesium, yttrium, and zirconium are used as typical doping elements, and elements are doped in the boehmite sol state to affect alumina production. In the present invention, the effect of the doping element on the densification of alumina as much as to improve the hardness by forming a dendrimer (Dendrimer) secondary phase. In this regard, the effects of each doping element and all doped alumina are compared to find out the effect of the doping element. Crystal phase, shape, density, hardness and toughness were measured to compare the properties of alumina according to the elements.
In this experiment, alumina was added to nitric acid (HNO 3 ) (pH 2.5), which is a peptizing agent, to a dispersion mixture of water and boehmite at a ratio (weight ratio) of 8: 2, and then a modifier was added. The mixture was stirred with a stirrer, dried at 100 ° C. for 12 hours, pulverized, calcined at 650 ° C. for 4 hours, and calcined at 1350 ° C. for 10 minutes.
The compounding ratios of the elements added in this experiment are shown in Table 1 below.
The change of crystal phase according to each doping element was examined. Doping elements were compared with lanthanum, magnesium, yttrium, and zirconium, respectively, and the change of crystal phase with increasing doping content was also investigated. 27 is an X-ray diffraction (XRD) pattern showing an alumina crystal phase when the element is not doped, and FIG. 28 is an X-ray diffraction (XRD) showing a crystal phase of alumina doped with magnesium (Mg). ), FIG. 29 is an X-ray diffraction (XRD) pattern showing a crystal phase of lanthanum (La) doped alumina, and FIG. 30 is an X-ray diffraction (XRD) showing a crystal phase of alumina doped with yttrium (Y) FIG. 31 is an X-ray diffraction (XRD) pattern showing the crystal phase of zirconium-doped alumina.
Boehmite (AlOOH) is transferred to the alumina of the α phase through the γ, δ, θ phase, and appears as a corundum phase at 1300 ° C or higher. Corundum alumina crystal phase was present as the main peak in all the crystal phases according to each doping element, and secondary phases were generated according to the elements. Lanthanum-doped alumina produced La 33 Al 7 O 60 , and magnesium-doped alumina and yttrium-doped alumina produced Mg (Al 2 O 4 ) and Y (AlO 3 ) as secondary phases. Zirconium-doped alumina was produced with ZrO 2 . In addition, as the doping content increased, the corundum and the intensity of each secondary phase increased. The alumina doped with lanthanum, magnesium, and yttrium was formed to combine with alumina to form a secondary phase, and the zirconium-doped alumina was produced as a phase that is not dissolved in alumina.
I. Shape of Alumina with Doping Elements and Contents
Each doping element and the shape according to the increase in content were observed by the same 10,000 times and 2,000 times. 32a and 32b are photographs showing the shape of alumina doped with 2% by weight of lanthanum, and FIGS. 33a and 33b are photographs showing the shape of alumina doped with 3% by weight of lanthanum, and FIGS. The photograph shows the shape of 5 wt% doped alumina. Figures 35a and 35b is a photograph showing the shape of alumina doped with magnesium by
All. Density of Alumina with Doping Elements and Contents
44 to 47 show the density of alumina with increasing doping element and content. FIG. 44 is a graph showing a density change of lanthanum-doped alumina, FIG. 45 is a graph showing a density change of magnesium-doped alumina, FIG. 46 is a graph showing a density change of yttrium-doped alumina, and FIG. 47. Is a graph showing the density change of zirconium doped alumina. The density value shows the average value after 5 measurements.
The density of alumina, undoped and identically produced (1350 ° C.), is 3.51 g /
la. Hardness of Alumina with Doping Elements and Contents
48 to 51 show the hardness of alumina with increasing doping element and content. FIG. 48 is a graph showing a change in hardness of lanthanum-doped alumina, FIG. 49 is a graph showing a change in hardness of magnesium-doped alumina, FIG. 50 is a graph showing a change in hardness of yttrium-doped alumina, and FIG. 51 Is a graph showing the hardness change of zirconium doped alumina.
The hardness was used as the average value of 5 points after 10 seconds with a load of 200 g / f. The same undoped (1350 ° C.) alumina hardness is 7.23 kPa. The lanthanum-doped alumina exhibited a high hardness of 15.03 kPa when manufactured at a content of 5% by weight with increasing hardness as the doping content was increased. Magnesium-doped alumina showed the highest hardness from 1.5% by weight to 11.66
The increase in hardness of the doped alumina is believed to be due to the sol-gel process and the secondary phase of the doping element. While the firing temperature of general alumina is 1500 ℃ ~ 1700 ℃ (2h), the alumina manufactured by sol-gel process can be sintered at low temperature due to the added element, so that densification occurs. Sintering does not appear to be complete. As shown in the density results, the element showed a lower value than the doped alumina and the densification was low. In addition, the hardness of each element is in the order of zirconium> yttrium> magnesium> lanthanum, but when doped with alumina, the lanthanum exhibits the highest hardness, indicating that the generated secondary phase is not a doping element. The factors affecting the hardness of the alumina are implied by the densification and the secondary phase according to the element, but the influence of the density is about 10% and the hardness changes by the secondary phase of the element. In particular, the high hardness of the dendrimer-type secondary phase of lanthanum-doped alumina is considered to be due to the high density and the property of dropping off the secondary resin due to external impact. The hardness of the alumina is largely dependent on the secondary phase, and the dendrimer-type secondary phase produced from the lanthanum-doped alumina has a great influence on the hardness of the alumina.
hemp. Alumina doped with lanthanum, magnesium, yttrium and zirconium
Earlier, the effects of the doping elements of lanthanum, magnesium, yttrium, and zirconium on alumina were discussed. The following is to investigate the effect of secondary phase of alumina combined with lanthanum, magnesium, yttrium and zirconium on alumina. Lanthanum, magnesium, yttrium and zirconium were all combined using the EDS and XRD results of doped alumina.
52 shows a crystalline phase of alumina with doping of lanthanum, magnesium, yttrium and zirconium. In both cases, corundum alumina crystal phase was formed as a main peak, and a secondary phase was generated according to the doping element. Lanthanum and magnesium doped alumina produced a secondary phase of LaMgAl 11 O 19 , and yttrium and zirconium doped alumina produced Zr 3 Y 4 O 12 . Zirconium was present as ZrO 2 when each element was doped, but was combined with yttrium to form Zr 3 Y 4 O 12 . The effects of two secondary phases, lanthanum, magnesium, yttrium and zirconium, on alumina can be compared.
Secondary phase shapes of alumina with doping of lanthanum, magnesium, yttrium and zirconium were observed in the same 10,000-fold (COMPO image) and are shown in FIGS. 53 and 54. FIG. 53 is a photograph showing the shape of alumina doped with lanthanum and magnesium, and FIG. 54 is a photograph showing the shape of alumina doped with yttrium and zirconium.
In the case of alumina (LaMgAl 11 O 19 ) combined with lanthanum and magnesium, a uniform dendrimer type secondary phase of 1 μm was observed, and in the case of alumina (Zr 3 Y 4 O 12 ) in which yttrium and zirconium were combined There was a secondary phase of type (Spot). Lanthanum- and magnesium-doped alumina was produced with a more uniform distribution than lanthanum-doped alumina as the two elements were combined. In addition, the alumina doped with yttrium and zirconium exhibits a spot shape similar to that of yttrium-doped alumina (Y (AlO 3 )), but it is combined with zirconium to increase its distribution.
The density and hardness of alumina according to doping of lanthanum, magnesium, yttrium and zirconium are shown in Table 2 below. In Table 2 (a) is a case of alumina doped with lanthanum and magnesium, (b) is a case of alumina doped with yttrium and zirconium.
The density of alumina doped with lanthanum and magnesium and alumina doped with yttrium and zirconium showed the same value of 3.82 g /
bar. Alumina doped with lanthanum, magnesium, yttrium and zirconium
As a result, the effect of the secondary phase of each doping element on the alumina was investigated. Thus, alumina doped with lanthanum, magnesium, yttrium, and zirconium was prepared to compare the crystal phases. FIG. 55 is an X-ray diffraction (XRD) pattern showing the crystalline phase of alumina doped with lanthanum, magnesium, yttrium and zirconium.
Alumina doped with lanthanum, magnesium, yttrium, and zirconium also had a corundum crystal phase as its main peak, and lanthanum and magnesium were bonded to LaMgAl 11 O 19 and yttrium and zirconium to bind Zr 3 Y 4 A secondary phase of O 12 was formed. It can be seen that lanthanum and magnesium, yttrium and zirconium are the same crystal phase as doped alumina.
The shape of alumina doped with lanthanum, magnesium, yttrium and zirconium is shown in FIG. 56. LaMgAl 11 O 19 combined with lanthanum and magnesium produced a dendrimer type secondary phase, and a yttrium and zirconium bonded Zr 3 Y 4 O 12 spot type secondary phase was observed. The dendrimer-type secondary phase was formed to have a uniform 1 μm shape similar to that of alumina doped with lanthanum and magnesium than La 85 Al 11 .55 O 18 .60 (0.4˜1.0 μm) doped with lanthanum only. Spot type secondary phase shows the same shape as yttrium-doped Y (AlO 3 ), but increases its distribution in combination with zirconium.
The density and hardness of lanthanum, magnesium, yttrium, and zirconium-doped alumina are shown in Table 3 below.
The density of alumina doped with lanthanum, magnesium, yttrium, and zirconium was 3.98 g /
four. Grain and Toughness Change by Doping Element Addition
The change in grain size of alumina with the addition of doping element was observed, and the change in toughness was measured accordingly. FIG. 57 is a photograph showing a change in grains and toughness of alumina according to doping element addition. In FIG. 57, (a) shows grains of alumina without doping element added, and (b) shows grains of doped alumina. (C) shows the toughness of the alumina without addition of the doping element, and (d) shows the toughness of the doped alumina.
The undoped alumina had a grain size of 10 μm, and the alumina added with the doping element reduced the grain size and observed a grain size of 8 μm. As the doping element is added, it was found that the grain size of the alumina was reduced. As a result of examining the toughness change of the alumina according to the grain size change, the undoped alumina showed the toughness of 2.6 MPam 0.5 . The toughness of the alumina added with the doping element was 3.8 MPam 0.5 and the toughness value of the alumina was increased by the addition of the doping element. Therefore, when the doping element is added to the alumina, the grain size of the alumina is reduced and the toughness of the alumina is improved by the doped element.
As described above, in order to develop high hardness alumina for abrasives, the influence of the secondary phase of the doping element on the hardness of the alumina was examined. The crystalline phase has a corundum as its main peak, and according to each doping element (lanthanum, magnesium, yttrium, zirconium), dendrimer type La 85 Al 11 .55 O 18 .60 Segregated Mg (Al 2 O 4 ), Spot-like Y (AlO 3 ), and segregated ZrO 2 were produced as secondary phases. As the doping element was added, the density increased by 8.6 ~ 11.7% and the hardness improved by 68.0 ~ 108.0%. Among the dendrimer-type secondary phases having a high density (3.91 g / cm 3), the highest hardness was 15.03 ㎬. Alumina doped with lanthanum, magnesium, yttrium and zirconium was formed in the secondary phase of dendrimer type LaMgAl 11 O 19 and spot type Zr 3 Y 4 O 12 in addition to corundum. Density increased by 8.8% and hardness increased by 81.9 ~ 84.0%. Alumina doped with four elements produced corundum and LaMgAl 11 O 19 in the dendrimer type and Zr 3 Y 4 O 12 in the spot form, with a density of 3.98 g /
6. Changes in hardness due to porosity of alumina by pressurization
In this experiment, alumina was added to nitric acid (HNO 3 ) (pH 2.5), which is a peptizing agent, to a dispersion mixture of water and boehmite at a ratio (weight ratio) of 8: 2, and then a modifier was added. The mixture was stirred with a stirrer and dried to form a gel, then pressed and pulverized, and then calcined at 1350 ° C. for 10 minutes to prepare a gel.
In order to determine the volume change when the heat and pressure were applied to the dried boehmite gel, the pressure was compared under the condition of 3t / 60s. 58 is a view showing a change in thickness with pressure. As a result, it was confirmed that the thickness decreases from 4.19mm to 4.31mm at the thickness of 5.09mm before heating. Therefore, when heat and temperature were simultaneously applied, it was found that more dense particles were obtained than alumina without heat.
end. Differential Thermal Analysis of Boehmite Gels
Differential thermal analysis of the dried boehmite gel to determine the set temperature of the pressurization was investigated for the weight change with temperature. Fig. 59 shows the results of differential thermal analysis of boehmite gels. The thermal analysis was performed by using an air gas to form an oxidizing atmosphere, and evaluated by raising the temperature to 5 ° C. per minute from 0 ° C. to 1000 ° C. As a result, the thermogravimetric curve steeply decreased from 100 ° C. to 500 ° C., indicating a weight loss. This is due to the doping elements added to improve the hardness of the alumina, and this is because -OH, gas and the like remaining in the alumina is discharged. These gases are volatilized as the temperature increases, and most of them are volatilized and removed, but some remaining gases form pores in the alumina particles. The pores thus produced adversely affect the densification of alumina and cause a decrease in hardness. As a result of the increase in temperature, the weight of the alumina was reduced by 25.4%, and it was confirmed that 1/4 of the remaining gases were removed from the weight of the alumina. Among them, particularly, a very steep curve was shown between 300 ° C and 500 ° C, and it was confirmed that a large amount of gas was volatilized. This was to pressurize at 400 ℃ the highest gas volatilization to discharge the maximum amount of gas.
I. Crystal Phase of Alumina Under Pressurization
60 shows the crystal phase change of the alumina utilizing the pressurization process. Initial boehmite exhibited a crystal phase of AlO (OH) and remained the same as before pressing. After pressurization at 400 ° C., alumina was observed in Al 2 O 3 phase in amorphous form. After firing, a corundum alumina crystal phase was formed as a main peak, and a new secondary phase was generated by the doping element. In the secondary phase, lanthanum and magnesium were combined with alumina to form LaMgAl 11 O 19 , and yttrium and zirconium were bonded to form Zr 3 Y 4 O 12 . The phase change according to the transition temperature of the alumina using the pressurization process was confirmed.
All. Shape of Alumina Under Pressurization
The shape change of the alumina utilizing the pressurization process is shown in FIGS. 61A and 61B. The pressure was compared with four conditions of 0t, 2t, 4t, and 6t. In FIGS. 61A and 61B, (a) is a case where the pressure is 0t and (b) is a case where the pressure is 2t. c) shows the case of pressurization under the condition of 4t, and (d) shows the case of pressurization under the condition of 6t. In FIG. 61A and FIG. 61B, the large image is observed inside the cross section of the alumina at a magnification of 1,000 times, and the small image at the upper right shows the cross section of the whole alumina particle. In the case of 0t without applying pressure, large pores of about 10 μm were distributed inside the particles. This is believed to be due to the formation of pores due to the remaining gas generated by the nitric acid and the doping element added to cause the peptizing reaction. Alumina under pressure of 2t had a small amount of pores remaining in a lower distribution than pores of alumina without pressure. In the case of alumina to which pressure of 4t was applied, small pores of 5 μm or less remained. Finally, it was confirmed that in the case of alumina applied with a pressure of 4t, the sintering was carried out with little residual pores. Even when the whole particle was observed, fine pores were not observed and the pores were successfully removed. As the pressure increases, the pore size and distribution decrease, and when the pressure of 6t is applied, the pores are completely removed.
la. Specific Surface Area of Alumina by Pressurization
The specific surface area according to the pressure of the alumina fired using the pressurization process is shown in FIG. 62. In the case of alumina without pressure (0t), a specific surface area of 2.10 m 2 g −1 was shown, and alumina with a pressure of 2t showed a significant decrease in the specific surface area of 0.10 m 2 g −1 . In the case of alumina pressurized at 3t, 0.07 m 2 g -1 and alumina pressurized at 6t exhibited a very low specific surface area of 0.03 m 2 g - 1 . As the pressure increases, the specific surface area decreases. Among them, the specific surface area of the alumina to which 2t pressure was applied was significantly decreased from the alumina to which no pressure was applied. After that, the specific surface area difference was insignificant.
hemp. Hardness of Alumina Under Pressurization
63 and 64 show the hardness and shape according to the pressure of the alumina calcined by using the pressing process. FIG. 63 shows the hardness of alumina according to pressurization, and FIG. 64 shows the shape of alumina according to pressurization (pressurization at a pressure of 6t). Alumina without pressure (0t) exhibited a hardness of 17.04 kPa and alumina with a pressure of 2t exhibited a hardness of 18.01 kPa and increased slightly. Alumina pressurized at 3t exhibited a hardness of 19.59 kPa, and alumina pressurized at 6t showed a very high hardness of 22.02 kPa. This confirmed that the hardness increases as the pressure increases. This is believed to be caused by the increase in the density of alumina by the pressurization and the removal of pores therein. Among them, the hardness of alumina under pressure of 6t (22.02 kPa) was 33.1% higher than that of ordinary alumina (15 kPa) and 18.2% higher than that of alumina without pressure. As a result of observing the shape, the secondary phases of dendrimer type were evenly distributed, and the pores were removed by the pressing process, thus showing a compact shape. As a result, as the pores of the alumina are removed by using the pressurization process, the hardness is improved, and the compact sintering is achieved.
As described above, the hardness improvement by removing the pores of the alumina by using the pressing process was examined. The pressurization temperature was tried to minimize the pore amount by pressurizing at 400 ℃, the highest gas discharge result from differential thermal analysis. As a result, the observation of shape and measurement of specific surface area showed that the amount of pore decreased with increasing pressure. Especially, when the pressure was increased to 6t, the specific surface area decreased significantly to 0.03 m 2 g -1 . Accordingly, it was found that the hardness increased by 18% and the compact sintering occurred from 17.04 kPa to 6t before pressurization to 22.02 kPa after pressurization. This was successful in removing the pores of the alumina for abrasive using the pressing process, it was confirmed that the hardness of the alumina is improved.
7. Hardness change according to firing temperature and holding time
In order to investigate the effect of temperature on the hardness of alumina in the firing process, the changes according to the degassing temperature, the calcining-firing process and the firing process, the hardness according to the holding time, and the hardness change according to the firing temperature were investigated.
In this experiment, alumina was added to nitric acid (HNO 3 ) (pH 2.5), a peptizing agent, to a dispersion mixture of water and boehmite at a ratio of 8: 2 (weight ratio), and then a modifier was added. The mixture was stirred with a stirrer and dried to form a gel, and then pressed and pulverized, and then fired.
end. Pore Change with Degassing Temperature
In preparing the alumina using the sol-gel method, 80% by weight of water and less than 10% by weight of acid, acetate and rare earth elements are used. Water is mostly vaporized during drying and the remainder is volatilized during calcination and firing. However, they are not all volatilized, and a small amount of gases are not volatilized and remain as pores in alumina. The pores thus generated adversely affects the densification of the alumina, causing a decrease in the hardness of the alumina. FIG. 65 is a diagram illustrating differential thermal analysis (DTA) result of alumina, and FIG. 66 is a diagram illustrating a gas removal experiment process. The remaining gas forms pores outside and inside the alumina. The temperature of the firing process was adjusted to remove pores of alumina. The degassing temperature was compared with three temperatures of 800 ℃ ~ 1000 ℃ as a result of differential thermal analysis, and the holding time was compared with 3 hours in which gas was sufficiently volatilized.
FIG. 67 is a photograph showing alumina particles not subjected to a gas removal process, and FIG. 68 is a photograph showing alumina particles subjected to a gas removal process. In FIG. 68, (a) shows a case where a gas removal process is performed at a temperature of 800 ° C. (b) is a case where the gas removal process is performed at the temperature of 800 degreeC, and (c) is a case where the gas removal process is performed at the temperature of 1000 degreeC. 69 is a view illustrating a change in hardness according to the gas removing process. The alumina pore removed at 800 ° C. had pores remaining in the particles, and the alumina pore removed at 900 ° C. showed no pores but a smooth surface. The pores removed at 1000 ° C. by increasing the temperature had some pores remaining. Accordingly, it was found that holding the gas at 900 ° C. to remove the pores using the firing temperature may volatilize the largest amount of gas. As a result of comparing the hardness before and after degassing, the hardness increased from 7.7 경도 to 13.26㎬.
I. Calcination-firing process and firing process
In general, doping of alumina is carried out in the form of a solution after the calcination process, followed by drying and baking. In this experiment, however, the calcination process is unnecessary because it is doped to the sol state. The hardness change of alumina with or without calcination process was compared with A and B as shown in Table 4.
The hardness change of alumina was investigated by the calcining-calcination process and the calcination process. 70 is a view showing the hardness according to the firing process. As a result of the observation of the hardness particles, the particles of alumina that had not undergone the calcination process had a smaller diamond shape than those of the alumina containing the calcination process. Accordingly, the hardness increased from 8.43 8.4 to 18.91. As the calcination process was removed. Accordingly, it can be seen that the simplification and hardness of the process are improved by removing unnecessary calcination processes due to the change of the doping process.
All. Hardness according to holding time
In order to determine the hardness of the alumina according to the change in the holding time of the calcination temperature, the change in hardness was observed at a difference of the holding time of (a) 10 minutes and (b) 60 minutes at 1350 ° C.
The shape and hardness of alumina according to the firing holding time were investigated. FIG. 71 is a view showing the shape of alumina according to firing holding time, and FIG. 72 is a view showing the hardness of alumina according to firing holding time. As a result of the observation of the shape, when the holding time of firing was 10 minutes, a small amount of grains were observed, but the shape was not observed. On the other hand, when the holding time of firing was 60 minutes, crystal grains were formed as a whole and 10 µm of grains were observed. This confirmed that when the firing holding time increases, crystal grains were formed. As a result, the difference in hardness was also large. A short firing time of 10 minutes showed a high hardness of 18.91 kPa, while a 60 minute long firing time had a slightly reduced hardness of 11.78 kPa. In this case, when the firing holding time increases, it was confirmed that the crystal grains formed and the hardness decreased.
la. Hardness according to firing temperature
73 and 74 show changes in density and hardness according to firing temperature. Firing temperature was compared to 1250 ℃ ~ 1450 ℃ in five stages, holding time was fired in 10 minutes. The alumina calcined at 1250 ° C. had a low density of 3.49 g /
As described above, in order to develop alumina-based abrasives using high-purity boehmite gel using the sol-gel method, the type of peptizer, the type and content of modifier, and the moisture of the boehmite gel Reduction, stirring speed of boehmite gel, doping element, pressurization process, firing temperature and holding time were investigated.
It was found that nitric acid, hydrochloric acid, acetic acid, and hydrobromic acid did not separate from water, but changed to boehmite gel and were suitable as a peptizing agent over time among nitric acid, hydrochloric acid, phosphoric acid, sulfuric acid, and hydrobromic acid. Among them, the specific surface area of alumina using nitric acid as a peptizing agent appeared to be the smallest at 2.10 m 2 g -1, which was found to help densification of alumina. In addition, the alumina using nitric acid as a peptizing agent showed the smallest porosity in the shape observation, and the decrease in thermogravimetry with the increase of temperature was 26.06%. As a result, it showed a high hardness of 18.26 ㎬ and helped improve the alumina hardness. The modifier content is the smallest in 168.96 m 2 g -1 after calcination of alumina added with 2% by weight of ammonium acetate (CH 3 CO 2 NH 4 ) and affects densification of alumina I knew it was crazy. According to the type of modifier, it was confirmed that ethyl trimethyl acetate showed the highest specific surface area of 164.52 m 2 g -1 after calcination and helped densification of alumina. The change of boehmite gel according to the moisture reduction amount was reduced by 15% by heating for 3 hours at 50 ° C., and the hardness was greatly changed from 7.07㎬ to 18.91㎬. The change of the boehmite gel with the stirring speed was examined. As a result of manufacturing the alumina abrasive grains by adjusting at 0rpm, 100rpm, 500rpm, 1000rpm, the specific surface area decreased as the stirring speed was increased. Accordingly, the hardness was improved from 16.45 ㎬ to 18.46 ㎬. In addition, to improve the hardness of the alumina doped by adjusting the content of lanthanum, magnesium, yttrium, zirconium. Corundum alumina crystal phase was present as the main peak according to each doping element, and a secondary phase was generated according to the element. Lanthanum-doped alumina produced La 33 Al 7 O 60 , and magnesium-doped alumina and yttrium-doped alumina produced Mg (Al 2 O 4 ) and Y (AlO 3 ) as secondary phases. Zirconium doped alumina coexisted in the phase of ZrO 2 . In addition, as the doping content was increased, the corundum and the intensity of each secondary phase increased. According to the doping element, the lanthanum-doped alumina showed dendrimer-type tissues having a length of 1.0 μm. As the doping content was increased, the length was not changed but the distribution was increased. Magnesium-doped alumina was partially dissolved to form spinel, but was partially segregated above the solid solution limit. Yttrium-doped alumina was found to have spot-shaped secondary phases. Also, as the doping content was increased, the change in size was not observed but the distribution was increased. The alumina doped with zirconium was found to be segregated into the grain shell because it was not dissolved in the alumina as shown in the crystal phase analysis result. The density according to the doping element was examined. The density of undoped alumina is 3.51 g /
As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation by a person of ordinary skill in the art within the scope of the technical idea of this invention is carried out. This is possible.
Claims (11)
(b) adding a source material containing a peptizing agent and a doping element to the dispersion to form a sol;
(c) heat treating the sol to reduce the moisture content contained in the sol;
(d) hot pressing the gel formed by the heat treatment to reduce moisture and pores contained in the gel; And
(e) grinding and calcining the hot pressed gel,
The source material containing the doping element is a high abrasive abrasive grain, characterized in that made of at least one material selected from La (NO 3 ) 3 · 6H 2 O, Y (NO 3 ) 3 · 6H 2 O and zirconium acetate. Manufacturing method.
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| JPH04159386A (en) * | 1990-10-24 | 1992-06-02 | Japan Carlit Co Ltd:The | Production of abrasive grain for polishing |
| KR950011676B1 (en) * | 1986-11-20 | 1995-10-07 | 미네소타 마이닝 앤드 매뉴팩츄어링 컴패니 | Grinding particles and manufacturing method of ceramic |
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| JPH04159386A (en) * | 1990-10-24 | 1992-06-02 | Japan Carlit Co Ltd:The | Production of abrasive grain for polishing |
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