ALUMINA-BASE ABRASION RESISTANT MATERIAL

Abstract: Disclosed herein is an alumina-base abrasion resistant material obtained by adding, as sintering agents, 0.5 - 4.0 parts by weight of each of TiO₂ and CuO and 0.5 - 4.0 parts by weight of each of 3 or 4 oxides selected from the group consisting of Fe₂O₃, MnO₂, ZrO₂ and SiO₂ to l00 parts of Al₂O₃ powder and then sintering the resultant raw batch.

Description: This invention relates to an alumina-base abrasion resistant material which may be sinterable at low temperatures and have high abrasion resistance. Abrasion resistant materials composed of Al₂O₃ or Al₂O₃ and an additive such as ZrO₂ have already been developed and used at places subject to severe mechanical abrasion and wearing, for example, at bent portions of chutes and ducts in powder or solid transport lines, impact-bearing parts onto which powder or solids fall down, etc. As production processes of alumina-base materials having still higher strength and abrasion resistance, it has also been known to add either one or 2 - 3 of MgO, CaO, Y₂O₃, La₂O₃, SiO₂, Ta₂O₅ and the like as grain growth inhibitor(s) or sintering agent(s) to Al₂O₃ and then sintering the resulting raw batches. These processes however require sintering temperatures as high as l,470 - l,700°C and in some instances, need expensive additives such as Y₂O₃. They are hence not preferred from the economical stand point. On the other hand, as an exemplary tech­ nique for lowering the sintering temperature, it has been reported that the sintering temperature for a dried 96% Al₂O₃ body was lowered to l,300 - l,400°C by adding a compound additive of MnO₂ and TiO₂ or CuO and TiO₂ to Al₂O₃. This process however failed to achieve sufficient abrasion resistance. As described above, conventionally-known alumina-base abrasion resistant materials required higher sintering temperatures upon their production. In some instances, they also required certain expensive additives. These requirements increased both energy and material costs, resulting in products of higher prices. On the other hand, it was unable to obtain products of any sufficient abrasion resistance in processes which employed additives to lower the sintering temperatures. It is desirable to be able to achieve one or more of the following objects. The first object of this invention is to provide an alumina-base abrasion resistant material having high abrasion resistance in spite of its low sintering temperature. The second object of this invention is to achieve the above object, namely, to provide an alumina-base abrasion resistant material, which is sinterable at low temperatures and has high abrasion resistance, by using relatively inexpensive sintering additives in combination. The present inventors have carried out an extensive investigation with a view toward attaining the above objects. As a result, the present invention has now been completed. In one aspect of this invention, there is thus provided an alumina-base abrasion resistant material obtained by adding, as sintering agents, 0.5 - 4.0 parts by weight of each of TiO₂ and CuO and 0.5 - 4.0 parts by weight of each of 3 or 4 oxides selected from the group consisting of Fe₂O₃ MnO₂, ZrO₂ and SiO₂ to l00 parts of Al₂O₃ powder and then sintering the resultant raw batch. Owing to the above-specified types and amounts of sintering agents, the abrasion resistant material of this invention may be sinterable at low temperatures, i.e., l,200 - l,350°C and have high abrasion resistance in spite of such low sintering temperatures. The present invention features the addition of an additive, which is composed of 5 or 6 types of metal oxides, as a sintering agent as described above. Although these components of the additive have been known, either singly or in partial combinations, as sintering agents for Al₂O₃, no combinations of sintering agents which combinations are suitable for use with abrasion resistant materials have heretofore been known. The present inventors have conducted screening with respect to numerous combinations of various sintering agents. As a result, it has been found that a combination of TiO₂ and CuO as essential components and at least 3 additional oxides selected from the group consisting of Fe₂O₃, MnO₂, ZrO₂ and SiO₂ can provide an excellent abrasion resistant material sinterable at low temperatures. If any one of the components (will hereinafter be called "sintering agents") is added in an amount less than 0.5 part by weight, it is impossible to impart sufficient sinterability or abrasion resistance. However, any amounts greater than 4 parts by weight result in excessive configurational changes upon sintering and hence lead to reduced dimensional accuracy. It is also undesirable from the economical standpoint to incorporate one or more of the sintering agents in such unduly large amounts if they are more expensive than Al₂O₃. In order to improve not only the formability and sinterability of the resulting raw batch and but also the abrasion resistance of the resulting product, it is preferable to pulverize the principal raw material, Al₂O₃ and the individual sintering agents sufficiently. Their preferable particle sizes may preferably be 2 µm or smaller, more preferably in the range of 0.8 - l.2 µm, both, in terms of median diameter. It is however economically undesirable to reduce their sizes beyond 0.8 µm because substantial energy is required for their pulverization, although no deleterious effects are given to the physical proper­ ties of the resulting product. Although Al₂O₃ and the individual sintering agents may be separately pulverized and then combined together into an intimate mixture, it is more economi­ cal, from the viewpoints of reduced labor for their pulverization and attainment of their intimate mixing, to add the individual sintering agents to Al₂O₃ before their pulverization and then to pulverize and mix them at the same time. The abrasion resistant material of this inven­ tion may be produced, for example, in the following manner. The raw material, Al₂O₃ is pulverized to 2 µm or smaller in terms of median diameter by the dry or wet method. As mentioned above, it is preferable to add the individual sintering agents to Al₂O₃ before their pulverization and then to pulverize and mix them at the same time. After the thus-ground and pulverized raw batch is granulated or subjected to one or more desired treatments such as an addition of a binder, it is formed into a shape conforming with its end use. Any suitable conventional forming methods such as pressing, extrusion forming and slip casting may be employed depending on each shape to be formed. In the case of pressing which is the most popular forming method for abrasion resistant materials of relatively simple configurations, the ground and mixed raw batch is once formed into a slurry. It is then granulated by a method known per se in the art, for example, by the shifting method in which the slurry is dried and ground and rains smaller than a suitable grain size are thereafter collected, or by the spray drying method. The resultant grains are then formed into a desired shape under elevated pressure. Alternatively, the raw batch may be added with a binder and/or dispersing agent as needed, followed by forma­ tion of a slurry. The slurry is then formed into a green body by extrusion forming, slip casting or the like. The green body is fired after drying it suitably. If the green body is dried rapidly, there is a danger that the green body may develop crazing and/or cracks due to its surface shrinkage. It is hence essential to conduct its drying under conditions as mild as possible. Although the drying conditions vary depending on the shape and water content of each green body, it is preferable to dry same under such conditions that minimize the difference between the interior water content of the green body and its surface water content. The dried body, which has been thoroughly dried for the removal of volatile compo­ nents, is then heated in a firing furnace, in which it is maintained at a maximum temperature of l,200 - ­ l,350°C, preferably, l,230 - l,280°C for l - 5 hours so as to complete its sintering. If the temperature is lower than l,200°C, it cannot be sintered sufficient­ ly. If it is heated to a temperature above l,350°C on the other hand, the sintering agents are caused to evaporate so that its sinterability is reduced again and the abrasion resistance of the resulting product is adversely affected. It is therefore undesirable to sinter the dried body at any temperatures outside the above-specified range. Among the sintering agents employed in the alumina-base abrasion resistant material of this invention, TiO₂ and CuO are effective primarily in improving the sinterability of Al₂O₃ and lowering its sintering temperature. On the other hand, MnO₂, ZrO₂, SiO₂ and the like serve primarily to inhibit grain growth and hence to improve the abrasion resistance of the resulting sintered body. Namely, they have mutually contradictory properties. No sintering agents capable of imparting high abrasion resistance at low sintering temperatures have been known to date. The additive useful in the practice of this invention is a compound additive which has been found as a result of an investigation on various combinations of 5 - 6 sintering agents. Use of this additive has made it possible for the first time to obtain an alumina-base abrasion resistant material having extremely high abrasion resistant in spite of its sintering at temperatures as low as l,200 - l,350°C. The present invention will hereinafter be described specifically by the following Examples, in which each abrasion resistance tests was conducted in the following manner. A siliceous sand blasting nozzle (inner diameter: 4 mm) was set upright with the nozzle pointing downwards. On the other hand, a test piece (a plate-like specimen of 80 mm × 50 mm wide and l0 mm thick) of an abrasion resistant material was positioned at a point 20 mm apart from the nozzle and at an angle of 45° relative to the direction of the nozzle. Siliceous sand was blasted against the test piece with compression air of 6.4 - 8.5 kg/cm²(G) through the nozzle. By the difference between the weight of the test piece before the sand blasting and that after the sand blasting, its abrasion resistance was evaluated. Incidentally, the grain size distribution of the siliceous sand employed was as follow in terms of cumulative % coarser. Examples l - l2 & Comparative Examples l - 4: Additives shown in Table l were added in their corresponding amounts prescribed in the same table to a raw material, Al₂O₃. The resulting mixtures were respectively pulverized by the dry method in an "Attritor" (trade mark; manufactured by Mitsui Miike Engineering Corporation) to particle sizes of l.0 µm and smaller in terms of median diameter. After granulating them by the shifting method, they were formed under 300 kg/cm² into plate-like green bodies. Those green bodies were dried and then fired in accordance with the following firing pattern in a shuttle kiln. In Table l, there are shown various conditions employed for the production of the abrasion resistant materials in the Examples as well as results of a test in which test pieces were prepared respectively from the abrasion resistant materials and their abrasion resistance were investigated by the above-described testing method. The densities of the abrasion resistant materials, namely, the sintered bodies are also given in Table l. It is understood that the six types of sintering agents were all added and extremely good abrasion resistance were attained in Examples l - 4. In Examples 5 - l2, the additives had such compositions that the four sintering agents other than TiO₂ and CuO were excluded one in each Example. All of the sintered bodies exhibited superb abrasion resistance in these Examples. On the other hand, it is also envisaged that the abrasion resistance was reduced significantly in Comparative Examples l - 4 in which either TiO₂ or CuO was excluded among the sintering agents. It is also understood from the densities of the sintered bodies that the products of the Examples, which relate to the present invention, were fully sintered although they were sintered at the low temperatures. Example l3: Sintering agents were mixed in the same proportions as those employed in Example 9 with a raw material, alumina (purity: 99.4%). The resulting mixture was pulverized by the wet method in the "Attritor" to a particle size of 0.85 µm in terms of median diameter. The raw batch was thereafter processed in the same manner as in Examples l - l2 to obtain an abrasion resistant material. Its abrasion was 5 mg whereas its density was 3.85 g/cm³. It had extremely good abrasion resistance. Comparative Examples 5 - 25: Following the procedures of Examples l - l2, abrasion resistant materials were separately produced by using various sintering agents either singly or in combinations of two. The proportions of the sintering agents and the sintering temperatures are shown along with their corresponding test results under Comparative Examples 5 - 25 in Table 2. When sintered at l,230°C, the advantageous effects brought about by the addition of TiO₂ and CuO addition are observed compared with the degree of abrasion of Al₂O₃ sintered without using any sintering agents. It was however impossible to achieve sufficient abrasion resistance. The abrasion resistance was either equal to or on the contrary, lowered by the other sintering agents compared with the abrasion resistant material obtained without any sintering agents. No additional effects were observed even when their proportions were increased. Although the abrasion resistance was improved when the sintering temperature was raised to l,300°C, the value was still hardly acceptable. Comparative Examples 26 - 30: Following the procedures of Examples l - l2, abrasion resistant materials were produced by using the sintering agents in larger amounts. The proportions of the sintering agents and the sintering temperatures are given along with their corresponding test results in Table 2. As shown in Table 2, the degrees of abrasion of the abrasion resistant materials are not substantial­ ly different from those of the abrasion resistant materials obtained by using the sintering agents within the range specified in the present invention. Hence, it is also unnecessary from the economical viewpoint to increase the proportions of the sintering agents beyond the upper limit specified in the present invention.

Claims: 1. An alumina-base abrasion resistant material as obtained by adding, as sintering agents, 0.5 - 4.0 parts by weight of each of TiO₂ and CuO and 0.5 - 4.0 parts by weight of each of 3 or 4 oxides selected from the group consisting of Fe₂O₃, MnO₂, ZrO₂ and SiO₂ to l00 parts of Al₂O₃ powder and then sintering the resultant raw batch. 2. The alumina-base abrasion resistant material as claimed in Claim l, wherein the sintering is effected at l,200 - l,350°C. 3. A method of producing an abrasion resistant material comprising adding, as sintering agents, 0.5 - 4.0 parts by weight of each of TiO₂ and CuO and 0.5 - 4.0 parts by weight of each of 3 or 4 oxides selected from the group consisting of Fe₂O₃, MnO₂, ZrO₂ and SiO₂ to l00 parts of Al₂O₃ powder and then sintering the resultant raw batch. 4. A method according to claim 3 wherein the sintering is effected at l,200 - l,350°C. 5. A method according to claim 3 or claim 4 wherein prior to sintering the materials are of particle size 2µm or less.

Inventors: KOBA, KEIICHIRO, MATSUMOTO, AKIRA, MIYAMOTO, TOMOMI, MORITA, YOSHITO
Applicants: MITSUI MINING COMPANY, LIMITED
Application year: 1986
Main classification: C04B35
IPC codes: C04B35