Sintered microcrystalline ceramic material.

(42) Date of commencement of the patent: 15.12.1991 (45) Date of issue: 25. 6.1992

<td>(56) Documents:</td><td>(73) Patent owner:</td>

<td>EP-Al-395091 EP-A2-248788</td><td>TREIBACHER CHEMICAL WORKS AG A-9330 TREIBACH, CARINTHIA (AT).</td>

<td></td><td>(72) Inventor:</td>

<td></td><td>WINTER HERWIG DR. KLAGENFURT, CARINTHIA (AT). JANZ PETER DR. KLAGENFURT, CARINTHIA (AT). GOTTSCHAMEL GEORG DR. TREIBACH, CARINTHIA (AT).</td>

(54) SINTERED MICROCRYSTALLINE CERAMIC MATERIAL (57) An abrasive material having a particularly high grinding performance is achieved by treating the ceramic material consisting of alpha alumina, 0.1 to 30 vol. X whisker-like needles and 0.01 to 0.5 wt .-% of a cerium compound, nor an addition of 0.01 to 15 wt .-%, preferably 0.1 to 3 wt .-% of a chromium compound.

CQ

AT 394 850

KR 0070313

AT394 850 B

The present invention relates to a sintered, microcrystalline, ceramic material based on a-Al₂O₃ with an addition of 0.01 to 2% by weight, preferably 0.01 to 0.5% by weight of a cerium compound and 0.01 to 15% by weight, preferably 0.1 to 5% by weight of a chromium compound.

The basic publications for the production of ceramic material from a-Al₂O₃ The SolGel process has already been mentioned in EP-Al-368 837.

U.S. Patent 4,744,802 suggests the possibility of having a-Fe seed particles₂O₃ additionally mixed sol with a chromium-containing compound. It is known from the literature that chromium (IH) oxide at high temperatures mixed crystals with a-Al₂O₃ forms

EP-A2-395 091 describes the addition of chromium oxide as a nucleating agent as an alternative to a-Al₂O₃ or a-Fe₂OSS. That in the literature different opinions on the effect of chromium compounds on the conversion of transitional aluminas to a-Al₂O₃ are believed to be due to the redox behavior of chromium oxide. GC Bye describes Influence of Cr and Fe on Formation of a-Al₂O₃from gamma-Al₂O₃ (J.Amer.Cer.Soc 57 (1974) pp. 367-371) in addition to the accelerating effect of Fe₂O₃the retarding effect of Cr (VI) on the formation of a-Al₂O₃, At the same time, however, he points out the possibility that the hexagonal Cr (III) oxide crystals found by him between 800 and 900 ° C may have a germinative effect on the formation of the grain mixed crystal.

EP-A-368 837 describes a ceramic material which, in addition to a-Al₂O₃ Whisker-like Needle Crystals The needles contain cerium.

The object of the invention is to provide a ceramic material which is suitable, inter alia, as an abrasive and due to its special chemical composition and structure has a particularly high toughness at the same time existing higher hardness.

This object is achieved in that the ceramic material consists of a crystalline matrix with 0.1 to 30 vol%, preferably 1 to 25 vol% whisker-like particles The particles have diameters between 0.2 and 1 pm, their length is 1-20 pm. The matrix consists of a solid solution of 0.01 to 15 wt% Cr₂O₃ in α-Α1₂Ο₃· The hardness of this mixed crystal is higher than that of pure a-Al₂O₃, The matrix has a preferably crystallite size of less than 0.5 pm and a very uniform structure.

Transmission electron microscopic investigations showed that the embedded particles are in the form of acicular whiskers partly or wholly as platelets may be formed. The respective quantities certainly depend on the conditions of origin. For the sake of simplicity, the particles are referred to as whiskers and should also include monocrystalline platelets therein. The thickness of the platelets corresponds to the whisker diameter, the dimensions perpendicular to the Whiskerlänge.

The whiskers, according to TEM investigations, consist of a Ce-Al oxide compound of the type β-corundum. Part of the Al ions is replaced by Cr, further Ca and other alkaline earth or Alkaline ions incorporated in different amounts in the crystal lattice. Upon formation, the matrix Ca or removes other alkaline earth and alkali ions, thereby increasing the strength, as the amount of grain boundary contaminants decreasing in strength as both a crystalline and a glass phase decreases. The Ca- Alkaline earth and alkali content can be up to 1% without loss of strength. Possibly, a low Ca content is even necessary for whisker formation. The Ca content in the particles is greatly increased compared to the matrix, so that a considerable cleaning effect with respect to the matrix occurs

The incorporation of Cr into the lattice of the whiskers causes an increase in the hardness of the Ce aluminate; ß-KorundStrukturen have a much lower hardness than a-Al₂O₃,

The strength of the inventive ceramic shaped body or abrasive body, the z. As can be tested as usual in diamond grinding Komkom as compressive strength is thereby increased (see also examples). The higher hardness and strength of the whiskers through the incorporation of Cr enhances the pull-out effect and the crack deflecting mechanisms.

In addition, the grinding performance is probably increased by a self-sharpening effect. The crack deflection on the needles can contribute to the formation of new, sharp break edges. The size of the broken fragments is probably determined mainly by the distance of the needles from each other. For certain applications, the wear behavior could thus be adapted and optimized by varying the needle concentration (number / volume unit).

Preferably nucleating agents are added to the α-alumina hydrate suspension in addition to the cerium and chromium addition.

Nucleating agents are finest particles that are made from a-Al₂O₃, Diaspor, A1F₃, a-Fe₂O₃, V₂O₃, Co₂O₃, Nb₂O₃, C ^ Oß, gamma-Al₂O₃, Ga₂O₃, GaOOH, FeOOH, Ti₂O₃, Cr₂O₃ consist. It is also possible to add soluble or insoluble precursors, which are compounds which form on heating the dried material in the

-2AT394 850B convert the above oxides before normal nucleation of the aA ^ Oß begins (ie at lower temperatures). It is also possible to use mixtures or combinations of the abovementioned oxides or precursors, as well as preformed mixed crystals.

The nucleating agent is added in an amount of up to 5% by weight, referred to as oxide on the final product. It has been found that a material thus produced has improved properties. The reason for this is presumably due to the increased ratio of length to diameter of the whisker-like needles, the diameter of the needles is smaller with the same length, at the same time the number of needles per volume unit increases.

Increasing the addition of nucleating agent above 5% by weight did not improve the properties. The nucleating agent can be added to the boehmite suspension in the form of a suspension of very fine particles. Such a nucleant suspension is prepared from commercial powder by milling and sedimentation or any other method which yields a submicron powder. Of course, the nucleating agent may also be added in solid form before or after deagglomeration.

For the formation of the microcrystalline structure, it is advantageous to add magnesium nitrate or another Mg-containing compound to the α-alumina hydrate suspension

Furthermore, the invention relates to a method for producing a ceramic material by stirring a fumed aA ^ Oß hydrate into a dilute acid solution, adding a cerium compound in the amount of 0.01 to 2 wt%, preferably 0.01 to 0.5 wt%, calculated as oxide, based on the AI2O3, adding one

Chromium compound in the amount of 0.01 to 15% by weight, preferably 0.1 to 5% by weight, based on oxide on alumina and optionally addition of Ca and / or magnesium compounds to 1% by weight as oxide, based on Al2O3, drying, comminution and sintering. This process is characterized in that the suspension is deaerated and deagglomerated before drying and that the sintering process is carried out in several stages and preferably under gas pressure. In this case, the sintering process is performed so that form next to a microcrystalline matrix needle-shaped crystals.

The addition of chromium and cerium can take place in the form of inorganic or organic salts, but also in any other compound which can be dispersed or dissolved, such as oxides or hydroxides. The addition of ready C ^ OyA ^ Oß mixed crystal is advantageous. At the same time it results in a higher fineness and homogeneity of the chemical composition of the matrix and the whiskers at higher density (lower porosity) of the material.

The deagglomeration can be carried out in a dispersing device according to the rotor-stator principle. However, it is also possible to use other dispersing devices, such as stirred ball mills, although a greater grinding media abrasion or metal abrasion is detrimental to the quality of the product.

As finely divided α-alumina hydrates, the commercially available pseudoboehmites (Pural, Disperal, Versal) having a purity of over 99% and a specific surface area between 150 and 290 m2g can be used. The solids content of the suspension was between 5 and 40% by weight, preferably between 15 and 25% by weight. As Peptisatorsäure nitric acid, hydrochloric acid, formic acid or acetic acid can be used.

The drying is carried out in a thin-film evaporator with attached belt dryer. However, it can be used any other drying apparatus that allows mixing of the material in the drying phase, so that no segregation is possible. This is necessary to achieve the desired homogeneous distribution of the needles in the final product. The resulting pore structure of the dried material appears to be conducive to the formation of the needles, since substantially fewer needles are created when drying dormantly.

Preferably, the drying is carried out in a microwave-heated belt dryer. The resulting heating of the material from the inside causes a very good homogeneity of the dried products, which pore structure and chemical composition. Whisker formation and sintering activity are promoted thereby improving the properties of the finished product.

The dried material is crushed and sieved The obtained grain can either be sintered directly to Schleifkom or pressed wild in correspondingly fine form as a powder with organic binders to form parts. These are all known pressing methods such. B. die pressing, extrusion or roller presses.

The sintering times depend on the temperature and lie between a few minutes and several hours per stage. The multi-stage sintering process can be carried out in principle in a suitable furnace, but it has proved to be advantageous when the first stage, in particular because of the attack of acidic exhaust gases in a specially lined furnace is performed.

As a further variant of the process, the sintering can be carried out under non-oxidizing or reducing conditions, whereby the intermediate formation of C1O3 at about 300 to 500 ° C is prevented. However, the conditions must not lead to a reduction of the Cr below the 3-valued form.

As a further variant of the process, the precalcined material can be impregnated with solutions or suspensions, this process is known from the patent application 394 213. All abovementioned additives and

-3AT394 850 B

Precursors of the nucleating agents can be added in this way.

The material according to the invention is outstandingly suitable for loop awakening, but can also be used for all known purposes of alumina ceramics. For use in grinding wheels, comminution of the material before sintering proved to be advantageous, for use in belts and flexible disks comminution after sintering is cheaper.

The invention will now be explained in more detail by way of examples.

Example 1: (suspension production)

In a solution of 39.5 kg of water and 440 g conc. Nitric acid was continuously stirred into 10 kg of Disperal (R) alumina hydrate. The suspension was then deaerated in a laboratory vacuum deaerator at 100 mbar and then pumped through a disperser with two feed ports. The flow rate was 3 1 / h, the rotor speed was 15,000 rpm. A solution of 4.5 g / 1 cerium (III) nitrate hexahydrate and 14 g / l chromium (III) nitrate nonahydrate was pumped in at 300 ml per hour to the second inflow opening of the disperser. The deagglomerated suspension was then further processed in Examples 2-6 sintered final product contained 0.1% by weight of CeO₂ and 0.3% by weight of C 2 O 3.

Example 2:

The suspension from Example 1 was evaporated with stirring and dried after coagulation in polypropylene cups in a hot air dryer at 80 ° C for 36 hours to brittle plates. The dried slabs were crushed into granules in a hammer mill and classified in a sieving machine (fineness rate &lt;0.1 mm - see Example 5). Subsequently, the grains were calcined for one hour in a muffle furnace at 600 ° C. Subsequently, the material was heated to 900 ° C. in a gas pressure sintering furnace. The gas atmosphere used was nitrogen. 100 bar, the temperature was increased within one hour to 1100 ° C then the pressure was lowered to 1 bar and the temperature further increased to 1300 ° C. After a further 1.5 h at 1300 ° C was sintered for 15 min at 100 bar. The material had 3 vol% porosity and contained approx. 15 Vol% Whisker with diameters of 0.2 - 0.5 ym and a length between 3 and 5 μτη.

The chemical composition of the matrix and the needles was determined by transmission electron microscopy - energy dispersive analysis (TEM - EDX). The matrix in the vicinity of the whiskers contained, apart from A 2 O 3 and about 0.3% Cr₂No impurities. The whiskers themselves contained about 1% by weight CaO, 5% by weight CeO₂ and about 0.5% Cr₂OSS.

Example 3:

The suspension of Example 1 was dried in a microwave dryer. The dried plates were further processed as in Example 2. The material had 2% by volume porosity and contained 18% by volume whisker.

Example 4:

The dried material of Example 3 was only roughly comminuted and sintered as in Example 2. After sintering, final comminution and sieving were carried out.

Example 5:

Dried fine grain (&lt;0.1 mm, from Example 2 was about 25 wt% H₂O mixed and pressed into cylinders (30 mm 0.5 mm in length) Pressing was uniaxial in a die at 400 MPa. The cylinders were sintered as in Example 2. The sintered material had 2% by volume porosity and exhibited virtually the same microstructure with needles as the material of Example 2. The sintered cylinders were chopped into grain and sieved

Example fc

The cylinders pressed as in Example 3 were crushed and sieved before sintering. The screened grain was sintered as in Example 2

Example 7:

The α-alumina hydrate suspension was prepared as in Example 1. The dosed solution contained 17.9 g / l citrate hexahydrate, 5.6 g / l magnesium nitrate hexahydrate and 14 g / l chromium nitrate nonahydrate so that 0.4% by weight of CeO in the end product₂, 0.3% Cr₂Oss and 0.05% MgO were included. The deagglomerated suspension was further processed as in Example 3. The sintered product contained 2% by volume of pores and 20% by volume of whiskers.

Example &amp;

In a solution of 39.5 kg of water, 440 g conc. Nitric acid, 78 g of citrate hexahydrate, 205 g of chromium nitrate nonahydrate and 25 g of magnesium nitrate hexahydrate were stirred into 10 kg of Disperal (R) and deaerated (as described in US Pat

-4AT394 850 B

Example 1). The suspension was deagglomerated in an agitating ball mill, with the Mahlköiperabrieb (85% alumina balls) less than 02% by weight, based on the final product was. The suspension was processed further as in Example 3. The sintered product contained 0.4% CeO₂, 1% Cr₂Oxygen and 0.05% MgO. Analysis of the matrix in the vicinity of the whiskers - with TEM-EDX - showed next to Al₂Oss only about 0.9% Cr₂Oss, no Ca, Ce, K, Na and Mg. The whiskers contained besides Al₂About 3 wt% CaO, 11 wt% CeO₂ and about 1% C ^ O ^.

Example.?;

In a solution of 39.5 kg of water, 440 g conc. Nitric acid, 78 g of citrate hexahydrate, 61 g of chromium nitrate nonahydrate and 25 g of magnesium nitrate hexahydrate were stirred into 10 kg of Disperal (R). The suspension was deaerated as in Example 1 and deagglomerated in the stirred ball mill. After drying in the microwave dryer, the material was comminuted and sieved. The sieved grain was precalcined in a muffle furnace at 800 ° C. for four hours, then heated in a continuous rotary kiln to 1650 ° C. (residence time in the hot zone approx. 10 min.), cooled rapidly and sintered in a muffle furnace at 1300 ° C for four hours. The sintered material contained 0.4% CeO₂, 0.3% Cr₂Oxygen and 0.05% MgO. The whisker content was about 20% by volume.

Production of the germ image:

A suspension of 6.5 kg of water and 3.5 kg of Bayer alumina with 105 g conc. Nitric acid was milled in a stirred ball mill until the median grain size distribution was 0.6 pm (determined by Sedigraph). The suspension was diluted (35 wt% A1₂0j to 20% by weight) and freed by sedimentation of all particles&gt; 0.2 pm. The resulting fine suspension contained 2% by weight of α-Al₂Oss and was used as a nucleating additive

Alternatively, 4 kg of a pure Cr₂Oxygen pigment in 6 kg of water and 50 g conc. Nitric acid stirred and ground in a stirred ball mill. As with the clay, the sedimentation freed the suspension of the coarse fraction above 0.2 .mu.m. The resulting suspension contained about 1.5% by weight of Cr₂Oβ and was used in Example 12 as a nucleating additive.

A suspension of 10 kg of Disperal (R) was conc. With a solution of 500 g. Nitric acid and 10 kg of chromium nitrate nonahydrate in 39.5 kg of water kneaded in a laboratory kneader to a homogeneous mass (gel). Subsequently, the gel in the muffle furnace at approx. 1200 Annealed The annealed material was crushed and processed as the clay into a fine suspension which was used as the nucleating additive in Example 13. The suspension contained approx. 0.5% solids. This had the crystal structure of the a-Al₂0SS-Cr₂0ß mixed crystal and had a CrOß content of about 25% by weight.

As another example of a nucleating agent, commercially available diaspore such as alumina was made into a fine suspension. The suspension had about 5% by weight Al₂O ^ content and was used as a nucleating additive in Examples 18-21

Beispkl IQ;

In 10 kg of alumina nucleants suspension 29.5 kg of water, 500 g conc. Nitric acid and 10 kg Disperal (R) stirred. The suspension was deaerated and deagglomerated as in Example 1. The pumped solution contained 17.9 g / l citrate hexahydrate and 14 g / l chromium nitrate nonahydrate. The deagglomerated suspension was further processed as in Example 3. The sintered material contained 0.4% by weight of CeO₂ and 0.3% by weight Cr₂OSS. The whisker content was about 30% by volume, the whiskers had diameters of about 0.2-0.5 μm and lengths of 4-10 μm. The porosity was 1% by volume.

Example 11:

The sintered, screened material of Example 10 was precalcined at 900 ° C and sintered in the muffle furnace at 1300 ° C for four hours. The sintered material contained about 25 vol% whisker (diameter 0.2-0.5 pm, length 3-8 pm).

Example 12:

In 13 kg of Cr₂Oss-containing suspension was 26.5 kg of water, 500 g conc. Nitric acid and 10 kg Disperal (R) stirred. The suspension was deaerated and deagglomerated as in Example 1. The pumped solution contained 4.5 g / l citrate hexahydrate, 14 g / l chromium nitrate nonahydrate, and 5.6 g / l magnesium nitrate hexahydrate. The suspension was processed further as in Example 3. The sintered product contained 0.1% by weight of CeO₂, about 3% by weight Cr₂O 3 and 0.05% by weight of MgO. The whiskers contained next to Al₂About 3% by weight of CaO, 5% by weight of CeO₂and 2% by weight Cr₂OSS.

-5AT394 850 B

Example 13:

In 40 kg of the fine mixed crystal suspension 500 g conc. Nitric acid and 10 kg Disperal stirred. The suspension was deaerated and deagglomerated as in Example 1. The added solution contained 4.5 g / l citrate hexahydrate. The suspension was dried in the microwave dryer, crushed and sieved. The sieved grain was precalcined at 900 ° C and sintered in the muffle furnace at 1300 ° C for four hours. The sintered product contained 0.1% by weight of CeO₂ and 0.65 wt% Cr₂O₃,

Example 14:

In a solution of 39.5 kg of water, 440 g conc. Nitric acid, 196 g of cerium nitrate hexahydrate and 20.3 g of chromium nitrate nonahydrate were stirred into 10 kg of Disperal (R). The suspension was deagglomerated in a stirred ball mill. The deagglomerated suspension was further processed as in Example 13. The sintered material contained about 1% CeO₂ and 0.1% by weight Cr₂O₃, In addition to 20 vol% Whiskem it still contained CeC ^ excretions.

Example 15: (without Cr)

The suspension was prepared analogously to Example 10. However, the dosed solution contained no chromium. The further processing likewise corresponded to Example 10. The sintered product contained about 0.4% by weight of CeO₂,

Example 16: (without Cr)

The material was prepared analogously to Example 15, but the comminution and sieving was carried out after sintering.

Example 17:

In 5 kg of alumina nucleant suspension 34.5 kg of water, 500 g conc. Nitric acid and 10 kg Disperal stirred. The suspension was deaerated and deagglomerated as in Example 1. The pumped solution contained 17.9 g / l citrate hexahydrate, 245 g / l chromium nitrate nonahydrate and 5.6 g / l magnesium nitrate hexahydrate. The deagglomerated suspension was further processed as in Example 13. The sintered product contained 0.4% by weight of CeO₂ and 5% by weight Cr₂OSS.

Example 18:

In 4 kg derdiasporhältigen nucleating suspension 35.4 kg of water, 500 g conc. Nitric acid and 10 kg Disperal (R) stirred. The suspension was deaerated and deagglomerated as in Example 1. The pumped solution contained 17.9 g / l citrate hexahydrate, 14 g / l chromium nitrate nonahydrate and 5.6 g / l magnesium nitrate hexahydrate. The deagglomerated suspension was further processed analogously to Example 17.

Example 19:

The suspension was prepared as in Example 18, deaerated and deagglomerated. The pumped solution contained 0.9 g / l citrate hexahydrate and 52 g / l calcium nitrate. Further processing was as in Example 3. The sintered material contained 0.02% CeO₂ and 1% CaO. The whiskers contained about 2% CeO₂ and 10% CaO.

Example 20:

The preparation was carried out analogously to Example 19, except that the pumped solution contained 17.9 g / l citrate hexahydrate, 47 g / l chromium nitrate nonahydrate and 52 g calcium nitrate. The sintered material contained 0.4% CeO₂, 1% Cr₂O₃ and 1% CaO. The whiskers contained about 7% CeO₂, 10% CaO and 2% Cr₂O₃,

Example 21:

The preparation was analogous to Example 19, but the comminution and sieving was carried out after sintering.

Example 22:

The dried material prepared according to Example 15 was crushed, sieved and annealed at 1200 ° C in a muffle furnace for four hours. The eb-cooled grain was evacuated and covered with a solution of 100 g / 1 chromium nitrate nonahydrate. After aerating, the grain was filtered from the residual solution and The sintering took place according to example 20. The sintered material contained 0.4% CeO₂ and 0.4% Cr₂O₃,

-6AT394 850B

Example 23:

The dried material prepared according to Example 15 was crushed, sieved and annealed at 1000 ° C in a muffle furnace for eight hours. The cooled material was evacuated and overcoated with the deagglomerated suspension from Example 17. After aeration, the grain was separated from the suspension and dried. The grain was then sintered in a muffle furnace at 1300 ° C for four hours. The sintered material contained about 1% Cr₂O₃ and 0.4% CeO₂,

Example 24;

Analogously to Example 10, but was comminuted after sintering

Example 25:

The dried, screened material of Example 7 became 1600 ⁰ C annealed in a rotary kiln (residence time approx. 15 min.). It was then rapidly cooled and finish sintered at 1250 ° C for four hours in a muffle furnace

Example 26:

The dried, screened material of Example 7 was precalcined at 800 ° C for four hours and then sintered in the muffle furnace at 1300 ° C for four hours. During sintering, a mixture of 90% nitrogen by volume with 10% hydrogen by volume flowed through the furnace.

The materials described in the examples were tested for porosity, whisker content and compressive strength. Porosity was measured with the mercury pycnometer. The compressive strength of the abrasive grains was tested as follows: The grains were sieved to the fraction 0.5-0.6 mm, the sieved fraction was freed of all elongated grains on a vibrating table and the remainder (cubic shape) in a special diamond pressing tool crushed, each grain is crushed by itself and the necessary force is measured. The table shows the median values ​​of the measured force-number distribution

Metallographic sections were used to produce images in a scanning electron microscope. At these the whisker content and its dimensions was measured. In this case, an average value over 20 grains was formed. Due to the segregation during drying, the whisker content is subject to fluctuations, but the vast majority of the grains contain the amount of whisker indicated in the tables.

The materials produced by the methods described in the examples were processed into grinding wheels, fiber discs and abrasive belts. The grinding tests described below are only examples to show the superior grinding performance. Of course, the material according to the invention can also be used successfully in many other applications.

Ceramic-bonded grinding wheels with the material according to the invention were used in dry grinding for tool grinding. The workpiece consisted of steel with a Rockwell hardness of HRC 65.

The delivery was kept constant and the sweeper of the power consumption was used as a measure of goodness. This value, based on the comparison material without Cr additive (Example 15), is given as a percentage.

Further, the materials of Example 4, 5, 16 and 21 were made into fiber discs (diameter 178 mm) and used for flat grinding of normal steel. The total amount of removal in g after 90 cycles was used as a measure of goodness. The workpiece had a diameter of 25 mm. The comparative material used was a commercially available sol-gel corundum and a semi-precious corundum. The values ​​obtained are listed in the tables and clearly show the excellent grinding performance of the materials produced according to the invention.

table

Properties and grinding tests in grinding wheels

<td>example No.</td><td>Gehaltan CeO₂(Wt%)</td><td>Cr₂°₃</td><td>porosity (Vol%)</td><td>whisker (Vol%)</td><td>compressive ness (N)</td><td>grinding power (%)</td>

<td>2</td><td>0.1</td><td>0.3</td><td>3</td><td>15</td><td>69</td><td>120</td>

<td>3</td><td>0.1</td><td>0.3</td><td>2</td><td>18</td><td>72</td><td>130</td>

<td>6</td><td>0.1</td><td>0.3</td><td>2</td><td>17</td><td>74</td><td>135</td>

-7AT 394 850 B

Table (continued!

Properties and grinding tests in grinding wheels

<td>example No.</td><td>Gehaltan CeO₂(Wt%)</td><td>ϋ^Γ2θ3</td><td>porosity (Vol%)</td><td>whisker (Vol%)</td><td>compressive ness (N)</td><td>grinding power (%)</td>

<td>7</td><td>0.4</td><td>0.3</td><td>2</td><td>20</td><td>70</td><td>130</td>

<td>8th</td><td>0.4</td><td>1.0</td><td>1</td><td>22</td><td>78</td><td>135</td>

<td>9</td><td>0.4</td><td>0.3</td><td>2</td><td>20</td><td>77</td><td>135</td>

<td>10</td><td>0.4</td><td>0.3</td><td>1</td><td>30</td><td>80</td><td>140</td>

<td>11</td><td>0.4</td><td>0.3</td><td>2</td><td>25</td><td>69</td><td>130</td>

<td>12</td><td>0.1</td><td>3</td><td>1</td><td>20</td><td>75</td><td>135</td>

<td>13</td><td>0.1</td><td>0.65</td><td>2</td><td>18</td><td>65</td><td>115</td>

<td>14</td><td>1</td><td>0.1</td><td>2</td><td>20</td><td>60</td><td>105</td>

<td>15</td><td>0.4</td><td>-</td><td>1</td><td>30</td><td>60</td><td>100</td>

<td>17</td><td>0.4</td><td>5</td><td>1</td><td>28</td><td>80</td><td>135</td>

<td>18</td><td>0.4</td><td>0.3</td><td>2</td><td>25</td><td>78</td><td>140</td>

<td>19</td><td>0.02</td><td>-</td><td>1</td><td>5</td><td>55</td><td>95</td>

<td>20</td><td>0.4</td><td>1.0</td><td>1</td><td>30</td><td>81</td><td>140</td>

<td>22</td><td>0.4</td><td>0.4</td><td>2</td><td>30</td><td>81.</td><td>138</td>

<td>23</td><td>0.4</td><td>1.0</td><td>2</td><td>30</td><td>79</td><td>142</td>

<td>25</td><td>0.4</td><td>0.3</td><td>1</td><td>25</td><td>78</td><td>140</td>

<td>26</td><td>0.4</td><td>0.3</td><td>1</td><td>23</td><td>79</td><td>140</td>

table

Properties and grinding tests in fiber discs

<td>4</td><td>0.1</td><td>0.3</td><td>2</td><td>18</td><td>79</td><td>250</td><td>(G)</td>

<td>5</td><td>0.1</td><td>0.3</td><td>2</td><td>17</td><td>81</td><td>260</td><td>tt</td>

<td>16</td><td>0.4</td><td>-</td><td>1</td><td>30</td><td>60</td><td>200</td><td>11</td>

<td>21</td><td>0.4</td><td>1.0</td><td>2</td><td>30</td><td>79</td><td>280</td><td>tt</td>

<td>24</td><td>0.4</td><td>0.3</td><td>1</td><td>30</td><td>79</td><td>270</td><td>tt</td>

<td></td><td colspan="2">Commercially available sol-gel corundum</td><td></td><td></td><td>50</td><td>160</td><td>tt</td>

<td></td><td>semi-friable</td><td></td><td></td><td></td><td>40</td><td>130</td><td>tt</td>