Title of Invention	IMPROVED ADDITIVE COMPOSITION USEFUL FOR THE PREPARATION OF ALUMINA BASED ABRASION RESISTANT MATERIAL HAVING IMPROVED WEAR PROPERTIES, AND METHODS FOR THEIR PREPARATION
Abstract	A process for the production of alumina based abrasion resistant liner materials , having improved mechanical properties . A special inexpensive additive composition is used to reduce the sintering circle time to minimize the powder consumption. The average part to be base of the initial principal raw material. Al2O3 is in the range of 4-5µm. The liner materials sintering temperature can be reduced to relatively low temperature ( 1480 to 1500oC. The process involves wet milling of 90-92% by weight of alpha alumina with an admixture of sintering agent substantially containing SiO2, MgO, BaO, CaO, B2O3. The milked powder was subjected to drying followed by gr pressing the granules in the form of tiles and then substantially liquid phase sintering of the pressed tiles. The sintered tiles showed very good mechanical and wear properties.

Title of Invention

IMPROVED ADDITIVE COMPOSITION USEFUL FOR THE PREPARATION OF ALUMINA BASED ABRASION RESISTANT MATERIAL HAVING IMPROVED WEAR PROPERTIES, AND METHODS FOR THEIR PREPARATION

Abstract

A process for the production of alumina based abrasion resistant liner materials , having improved mechanical properties . A special inexpensive additive composition is used to reduce the sintering circle time to minimize the powder consumption. The average part to be base of the initial principal raw material. Al2O3 is in the range of 4-5µm. The liner materials sintering temperature can be reduced to relatively low temperature ( 1480 to 1500oC. The process involves wet milling of 90-92% by weight of alpha alumina with an admixture of sintering agent substantially containing SiO2, MgO, BaO, CaO, B2O3. The milked powder was subjected to drying followed by gr pressing the granules in the form of tiles and then substantially liquid phase sintering of the pressed tiles. The sintered tiles showed very good mechanical and wear properties.

Full Text	Field of the Invention This invention relates to alumina based abrasion resistant linear materials having improved mechanical properties .The abrasive material of the present invention can be sintered at a temperature of 1500 degree Centigrade and has improved wear resistant properties. The material is useful in industries such as mineral processing, oil and gas and petrochemicals, pipe systems and cyclones in the plant installations, which handle millions of tons of abrasive materials. This invention also provides a process for the preparation of such material. This invention also provides an improved additive composition useful for the preparation of the said abrasion resistant material. The present invention also provides a process for the preparation of the improved additive composition. By far the greatest list for alumina lined pipes has been in coal fired power generating plants and the coal mining industry. Tremendous volumes of coal is consumed daily around the globe to generate power. To feed the burners the coal is pulverised and transferred pneumatically to the burner nozzle at velocities reaching 25 to 30 metres / second. Most coal contains a percentage of quartz, which tend to be highly erosive and is transported along with the coal through the feed pipe causing severe wear problems. Over the years the traditional cast iron pipes has been replaced in the high wear areas by special steels and glass ceramics. In power plants the life expectancy for elbows and bends lined with these materials has been only three years. More recently due to inconsistency in performance of the glass ceramics and steels, alumina has been used as a replacement to further extend the life of the elbows. The handling of fly ash and bottom ash, produced as a by-product of the combustion of coal in coal fired power plants, is one of the most difficult applications for pipe system. The ash content of the coal, which includes the unburned quartz and metallic oxide, can be as high as 20% (see the publication titled Ceramic applications for wear protection of pipe lines and cyclones ' by J Foster, key engineering materials Vol. 122-124 (1996), pp 277-278.) Therefore, each power plant can produce several thousand tons of ash per day, which must be removed from boiler area. The sintered ash is crushed and mixed with water for transfer to settling ponds or de-watering systems. As stated earlier the ash slurries can be both abrasive and corrosive. Alumina lined pipes have proven to be effective in ash slurry lines providing seven times longer service than chrome alloy steel. In one case 1/3 inch thick alumina lining had an expected service life of eight years, equivalent to handling 1,500,000 tons of ash (See the publication of CBP Engineering Corp., Installation Report, Dec. 12, 1982, ppl-12) Background of the invention Alumina based liners have been used for protective applications for several years due to their good erosion and corrosion resistance properties. They have particularly attracted attention in industries such as mineral processing, oil and gas and petrochemicals, pipe systems and cyclones in the plant installations. These industries are required to handle. millions of tons of aggressive materials without the need for replacement of liners In a short span of time.( see the publication titled ' Ceramic applications for wear protection of pipe lines and cyclones ' by J Foster , key engineering materials Vol. 122-124 (1996), pp 277-278. ) Abrasion resistant materials composed of pure Al2O3 or Al2O3 with additives such as ZrO2 have already been developed and used at places subject to severe mechanical abrasion and wear, 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 . In this connection reference may be made to European patent no: 0236507 dated 12.03.87 titled "High-density alumina-zirconia sinter and process for its production. It is well known that additives of MgO, CaO, Y2O3, La2O3, SiO2, Ta2O5 etc. as grain growth inhibitor(s) or sintering agent (s) to Al2O3 results in alumina-base materials having high strength and abrasion resistance. However, it requires sintering temperatures as high as 1470 - 1700oC and in some instances, need expensive additives such as Y2O3. Reference is made in this context to the European patent no: O256182 dated 24.O2.88 titled "Alumina-base abrasion resistant material These materials are hence not preferred from the economical standpoint. On the other hand, it has been reported that the sintering temperature for a dried 96% Al2O3 body was lowered to 1300-140oC by adding a compound additive of MnO2 and TiO2 or CuO and TiO2 to Al2O3. This material, however, failed to achieve sufficient abrasion resistance. Reference may be made to Indian patent application no. : 704 / Del / 91 dated Of filing: 2.8.91 titled "An improved process for the production of alumina based wear resistant Ceramics" and to the United States patent no: 4719188, dated January 12, 1988 tilted Alumina- base abrasion resistant material Normally alumina-base abrasion resistant material is prepared by sintering of green compact containing sintering agents like 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 at low temperatures, i.e. 1200-1350oC. However, to obtain high abrasion resistance product at such a low sintering temperature, the particle size of the principal raw material, alumina and the individual sintering agents should be within the range of 2-3µm or smaller, more preferably in the range of 0.8-1.2 µm, both in terms of median diameter. Reference may be made to the publication titled " Processing high-purity and liquid-phase-sintered alumina ceramics using locally synthesised alumina powders" by B.A. Latella, et al., Journal of Materials Science 33 (1998) 877-886. As described above, conventionally known alumina-base abrasion resistant materials require high sintering temperatures for their production. In some instances, they also require certain expensive additives. These requirements increased both energy- and material costs, resulting in making the resultant products expensive. On the other hand, in general, it is difficult to achieve appreciable abrasion resistance in the product, wherein additives are employed to lower the sintering temperatures. In general most of the conventional processes for producing wear resistant alumina tiles involve either incorporation of sufficient quantity of liquid forming agents or sintering at elevated temperature (> 1600oC) to achieve required density leading to appreciable wear properties. Both the processes also requires very fine raw materials especially alumina which in turn demands for extensive grinding and thereby increasing the processing cost. However, the materials produced through low temperature liquid phase sintering fails to achieve appreciable wear resistant properties due to the presence of various impurity phases. Although, the high temperature sintering process yields good wear resistant properties, the high amount of fuel consumption and use of superior grade refractory increases the cost of production. The main objective of the present invention is, therefore, to develop an alumina-base abrasion resistant material having high abrasion resistance in spite of its low sintering temperature ( Another objective of the present invention is to produce abrasion resistant material using the average particle size of the initial principal raw material, Al2O3 in the range of 4-5 µm so as to reduce the energy required for milling thereby reducing the cost of production. Still another objective of the present 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. Still another objective of the present invention is to provide a process for the preparation of alumina-base abrasion resistant material having high abrasion resistance in spite of its low sintering temperature. Yet another objective of the present invention is to provide a process for the preparation of alumina-base abrasion resistant material having high abrasion resistance in spite of its low sintering temperature. With reduce total sintering cycle to minimise the power consumption. We have carried out extensive research 8B development work with a view towards attaining the above objectives through liquid phase sintering of alumina with the addition of low melting additives. During the said work we observed that the use of liquid phase favours easy and economical processing by allowing sintering at lower temperatures and also use of less pure alumina and sintering aids. We have also observed that although Al2O3 and the individual sintering agents may be separately pulverised and then combined together into an intimate mixture, 11 is more economical to pulverise and mix both Al2O3 and additives together Near full densification in liquid phase sintered alumina was achieved at low temperature such as 1500oC due to the influence of grain- boundary liquid . ■ > - phase. Accordingly the present invention provides an improved alumina based abrasive material having improved wear resistant properties. Accordingly the invention provides an alumina-base abrasion resistant liner material obtained by the incorporation of sintering additives comprising 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5% CaO containing material and 0.5-3.0% B2O3 containing material. According to another feature of the invention there is provided a process for the preparation of improved alumina based' abrasive material having improved wear resistant properties which comprises: (i)Wet mixing of 90-92 percent by weight of alpha-alumina of maximum average particle size of 4.0 micron with an admixture of sintering agents consisting essentially of 2-6% Silica containing material, 0-4.0% MgO containing material, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing material in a conventional manner for a period in the range of 4-6 hrs. (ii) Drying the resultant slurry by any known process (iii) Mixing the dried powder with a liquid binder followed by granulation (iv) Pressing the granules into required shapes by known methods^) (v) Drying the shaped products by any known process and (vi) Liquid phase sintering of the said dried products s emplyoing conventional methods at a temperature in the range of 1480 to 1500°C with soaking period in the range of 3-5 hours and maintaining the total sintering cycle within 20 - 22 hours. /'& According to another feature of the invention there is provided an additive composition useful for the preparation of alumina based abrasive materials having improved wear resistant properties comprising 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing material. According to yet another feature of the invention there is provided a process for the preparation of an additive composition useful for the preparation of alumina based abrasive materials having improved wear resistant properties which comprises nixing 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5 3.0% B2O3 containing material. Among the sintering agents which can be employed in the preparation of alumina-base abrasive material having improved wear resistant properties of this invention, CaO containing material and B2Q3 containing material are effective primarily in improving the sinterability of Al2O3 and lowering its sintering temperature. On the other hand, MgO containing material, SiO2 containing material 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 temperature 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 conducting extensive research on various combinations of sintering agents. Further, the additives in the present invention are used in the form of their precursor to improve their reactivity. The major cation silicon, calcium and magnesium are the chief constituents for developing a glassy phase which helps in densification at lower temperature. Small blocky, equiaxed grains are obtained due to limited solubility of Al2O3 in the glassy phase and the pores remained attached to the grain boundary due to the stabilising influence of MgO. The degree of densification and micro-structural evolution depends critically on the sintering temperature and time regime employed. Use of this additive has made it possible to obtain an alumina-base abrasion resistant material having extremely high abrasion resistant inspite of low sintering temperatures. Present invention features the addition of additives such magnesia containing materials which includes MgO, MgCO3, MgCk, Mg(OH)2 , baria containing materials which includes BaCOs , Ba(0H)2 ,2-6% silica containing materials includes kaolin, quartz, amorphous silica, alumino silicate minerals, B2O3 containing material includes B2O3, H3BO3, Na2B4O7. H2O, 0.5-3.5 % calcia containing materials includes CaCOa, Ca(0H)2, Ca{N03)2.etc. for liquid phase sintering of Al2O3. In a preferred embodiment of the invention all the raw materials in appropriate proportions are mixed in a steel ball mill for 3 - 5 hrs in water media. The mixed slurry is then dried in an oven or in a spray drier to remove the water. However, care is taken to avoid segregation of constituents during oven drying. The oven-dried powder is then granulated in presence of a polymeric binder to required size prior to pressing in a definite shape. The pressed sample is then dried in an oven at 120°C to remove the moisture. The dried sample is then sintered at 1500°C for a soaking period of 3-6 hrs. Heating schedule maintained for sintering are as follows: 120°C /h from room temperature to 480°C dwell Ihr 200°C /h from 480°C to 1180°C dwell 10 mins 1800/h from 11800C to 15000C dwell 6 hrs • 300°C /h from 15000C to room temperature In a preferred embodiment of the present invention the amount of Silica containing material may preferably range from 2 to 6%, the amount of MgO containing material may range from Oto 4 % the amount of BaO containing material may range from 0.1 to2 % and CaO containing material may range from 0.5 to 3.5 % and B2O3 containing material may range from 0.5 to 3% The period of sintering may preferably for a period in the range of 4-6 hrs. The drying of the resultant slurry after mixing is effected either by conventional drying method where the slurry is loaded in a tray drier and dried at around 150°C for 6 to 8 hrs. or the slurry may be spray dried in a spray drier where the slurry is fed as a fine spray in a dynamic hot air chamber resulting in the formation of dry granules. However spray-drying process is preferred over conventional tray drying as the homogeneity of the powder mix is maintained and at the same time it avoids the process of making granules for further processing. The mixing of the dried powder with a liquid binder may be carried out by addition of 2% binder in the mixed slurry prior to spray drying or granulation. In case of spray drying binder solution is first thoroughly mixed with the slurry containing raw materials however in conventional milling and mixing method the mixed slurry is first dried then the binder solution is added and thoroughly mixed to the dried powder. The mix slurry is then semidried to moisture content of around 15 - 20% and made in the form of briquette and then fed in to the granulator. Granules of-30 to +100 mesh are then collected, dried and shaped into a tool steel mould to prepare tiles of required dimension by applying a pressure in the range of 8-10 tons per square inch. These shaped tiles were then dried at 150°C for 6 hrs in a tray drier. The sintering of the said dried tiles was performed in an electrical /gas/oil operated furnaces in the temperature range of 1480 to 1500°C with a soaking period in the range of 4-8 hours keeping total heating and cooling schedule within 20-22 hrs. The present invention will hereinafter be described in detail in the Examples given below which are provided to illustrate the invention only and therefore should not be construed to limit the scope of the invention. In the Examples each abrasion resistance tests were carried out using an ASTMG-65 test. The characteristics of Alumina powders used in the Examples provided 'J below invention are given in the Table I below: Table I Properties Alumina A Alumina B Alumina content (%) 99.5 min 99.4 min Na2O (%) 0.3-0.4 0.35-0.45 SiO2 (%) 0.O2 0.05 Fe2O3(%) 0.O2 0.04 LOI (upto 1050°C) 0.3 0.3 Av. Particle Size (µm) 3.0-4.0 6.0-7.0 Example I 910 gms of Alumina A given in table I is mixed with 15 gms of silica, 34 gms of clay, 50 gms of magnesium carbonate, 7.5 gms of barium carbonate, 10 gms of calcium carbonate and 16 gms of H3BO3 in the form of slurry with addition of 300 ml of distilled water. This slurry is milled for 4 hrs in a steel ball mill followed by drying in an oven at 150°C for removal of water. Dried cake is then crushed and milled in a ceramic pot mill for 15 minutes prior to mixing with 2% PVA solution to form a dough which is then granulated to the size range of -30 to +100 mesh by sifting method. Powder granules are then pressed in a tool steel mould at 8 tsi in the form of tiles having dimensions 70mm X 45mm x 8 mm. The pressed sample is then dried in an oven at 120oC to remove the moisture. The dried sample is then sintered in an electrically heated furnace at a temperature of 1500°C for 6 hrs. Sintered samples are then characterised for various properties. The results are listed in Table II. Example II 910 gms of Alumina B, shown in table I, is mixed with 15 gms of silica, 34 gms of clay, 50 gms of magnesium carbonate, 7,5 gms of barium carbonate, 10 gms of calcium carbonate and 16 gms of H3BO3 in the form of slurry with addition of 300 ml of distilled water. This slurry is milled for 4 hrs in a steel ball mill followed by drying in an oven at 150oC for removal of water. Dried cake is then crushed and milled in a ceramic pot mill for 15 minutes prior to mixing with 2% PVA solution to form a dough which is then granulated to the size range of -30 to +100 mesh by sifting method. Powder granules are then pressed in a tool steel mould at 8 tsi in the form of tiles having dimensions 70mm X 45mm x 8 mm. The pressed sample is then dried in an oven at 120°C to remove the moisture. The dried sample is then sintered in an electrically heated furnace at a temperature of 1500°C for 6 hrs. Example III 910 gms of Alumina B, shown in table I, is mixed with 15 gms of silica, 34 gms of clay, 50 gms of magnesium carbonate, 7.5 gms of barium carbonate, 10 gms of calcium carbonate and 16 gms of H3BO3 in the form of slurry with addition of 300 ml of distilled water. This slurry is milled for 4 hrs in a steel ball mill with 2 % PVA solution followed by spray drying using a spray drier (capacity: 25 kg water evaporation per hour) keeping out let temperature at around 150°C for removal of water and granule formation. The granules collected were in the range of -80 to +100 mesh. Powder granules are then pressed in a tool steel mould at 8 tsi in the form of tiles having dimensions 70 mm X 45 mm x 8 mm. The pressed sample is then dried in an oven at 120°C to remove the moisture. The dried sample is then sintered in an electrically heated furnace at a temperature of 1500°C for 6 hrs. Properties of sintered tiles are listed m Table III. Properties of sintered tiles are listed in Table II. The above table shows the comparison of sintered properties for three examples. The Table indicates that the alumina based abrasion resistant material of the present invention is superior to the samples patented vide Indian patent application no. : 704 / Del / 91 dated Of filing: 2.8.91 titled "An improved process for the production of alumina based wear resistant Ceramics". The present process ases coarser alumina powders as compared to the earlier processes which saves the energy of extensive milling and in turn reduces the cost of production to a larger extent. This invention further reduces the total sintering temperature and the total schedule, which also contributes towards the reduction in cost of production. . The slight difference in properties between them is due to difference in characteristics of starting alumina powders especially with respect to particle size and impurities content. This also indicates that alumina tiles with excellent wear properties can be achieved by proper selection of additives and initial particle size of alumina as well as its impurities content. Advantages of the present invention 1. By maintaining the average particle size of the principal raw material, Al2O3 and the mix in the range of 4-5 ^m, not only reduces the energy consumption for milling but also reduces the cost of production. II. The wear resistance properties of the materials produced is increased many fold than the prior art, by sintering in the range of 1480-1500oC. III. Facilitates employment of cheap raw materials available locally and easy and example processing methods. 1. An improved alumina based abrasion resistant material having improved wear resistant properties having a sintering temperature of 1500°C . 2 An improved alumina-based abrasion resistant material obtained by the incorporation of sintering additives comprising 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing material. 3. A process for the preparation of improved alumina based abrasive material having improved wear resistant properties, which comprises: (i)Wet mixing of 90-92 percent by weight of alpha-alumina of maximum average particle size of 4.0 micron with an admixture of sintering agents consisting essentially of 2-6% Silica containing material, 0-4.0% MgO containing material, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5- . 3.0% B2O3 containing material in a conventional manner for a period in the range of 4-6 hrs. (ii) Drying the resultant slurry by any known process (iii) Molding the dried powder with a liquid binder followed by granulation (iv) Pressing the granules into required shapes by known methods (v) Drying the shaped products by any known process and (vi) Liquid phase sintering of the said dried products s employing conventional methods at a temperature in the range of 1480 to 1500°C with soaking period in the range of 4-6 hours and maintaining the total sintering cycle within 20 - 22 hours. 4. An improved process as claimed in claim 3, wherein SiO2 containing material includes kaolin, quartz, amorphous silica, and alumino silicate minerals. 5. An improved process as claimed in claims 3 to 4, wherein CaO containing material includes CaCO3, Ca (OH )2. 6. An improved process as claimed in claims 3 to 5 wherein CaO containing material includes CaCO3, Ca (OH 2. 7.An improved process as claimed in claims 3 to 6, wherein BaO containing material includes BaCO3- 8 An improved process as claimed in claims 3 to 8, wherein MgO containing material includes MgCO3. 9. An improved process as claimed in claims 3 to 8, wherein B203Containing material includes B2O3. H3BO3, Na2B4O7 .H2O. 10. An improved process as claimed in claims 3 to 9, wherein average particle size of the alumina powder must be less than 4µm. 11. An improved process as claimed in claims 3 to 10, wherein average particle size of the wet mix is in the range of 5-6 µm. 12. An improved process as claimed in claims 3 to 11 wherein the Green density of the compact should be more than 2.1 g/cc. 13. An improved process as claimed in claims 3 to 12, wherein the polymeric binder Used is selected from PVA, Methylcellulose,'gum arabic, and animal glue. 14. An improved process as claimed in claims 3 to 13, wherein a wear resistant polyctystalline alumina material havmg specific gravity greater than 3.60 g/cc is produced 15. An improved process as claimed in claims 3 to 14, wherein a wear resistant polycrystalline alumina material having wear loss (volume) of less than 0.08-1.2x10-8 cc/gm of erodant (av. 200 micron quartz powder) is produced 16.An additive composition useful for the preparation of alumina based abrasive materials having improved wear resistant properties as claimed in claims 1 & 2 which comprises 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BciO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing material. 17. A process for the preparation of an additive composition as claimed in claim 16 useful for the preparation of alumina based abrasive materials having improved wear resistant properties which comprises mixing 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing material.

Full Text

Field of the Invention
This invention relates to alumina based abrasion resistant linear materials having improved mechanical properties .The abrasive material of the present invention can be sintered at a temperature of 1500 degree Centigrade and has improved wear resistant properties. The material is useful in industries such as mineral processing, oil and gas and petrochemicals, pipe systems and cyclones in the plant installations, which handle millions of tons of abrasive materials. This invention also provides a process for the preparation of such material. This invention also provides an improved additive composition useful for the preparation of the said abrasion resistant material. The present invention also provides a process for the preparation of the improved additive composition. By far the greatest list for alumina lined pipes has been in coal fired power generating plants and the coal mining industry. Tremendous volumes of coal is consumed daily around the globe to generate power. To feed the burners the coal is pulverised and transferred pneumatically to the burner nozzle at velocities reaching 25 to 30 metres / second. Most coal contains a percentage of quartz, which tend to be highly erosive and is transported along with the coal through the feed pipe causing severe wear problems. Over the years the traditional cast iron pipes has been replaced in the high wear areas by special steels and glass ceramics. In power plants the life expectancy for elbows and bends lined with these materials has been only three years. More recently due to inconsistency in performance of the glass ceramics and steels, alumina has been used as a replacement to further extend the life of the elbows.
The handling of fly ash and bottom ash, produced as a by-product of the combustion of coal in coal fired power plants, is one of the most difficult applications for pipe system. The ash content of the coal, which includes the unburned quartz and metallic oxide, can be as high as 20% (see the publication titled Ceramic applications for wear protection of pipe lines and cyclones ' by J Foster, key engineering materials Vol. 122-124 (1996), pp 277-278.) Therefore, each power plant can produce several thousand tons of ash

per day, which must be removed from boiler area. The sintered ash is crushed and mixed with water for transfer to settling ponds or de-watering systems. As stated earlier the ash slurries can be both abrasive and corrosive. Alumina lined pipes have proven to be effective in ash slurry lines providing seven times longer service than chrome alloy steel. In one case 1/3 inch thick alumina lining had an expected service life of eight years, equivalent to handling 1,500,000 tons of ash (See the publication of CBP Engineering Corp., Installation Report, Dec. 12, 1982, ppl-12)
Background of the invention
Alumina based liners have been used for protective applications for several years due to their good erosion and corrosion resistance properties. They have particularly attracted attention in industries such as mineral processing, oil and gas and petrochemicals, pipe systems and cyclones in the plant installations. These industries are required to handle. millions of tons of aggressive materials without the need for replacement of liners In a short span of time.( see the publication titled ' Ceramic applications for wear protection of pipe lines and cyclones ' by J Foster , key engineering materials Vol. 122-124 (1996), pp 277-278. )
Abrasion resistant materials composed of pure Al2O3 or Al2O3 with additives such as ZrO2 have already been developed and used at places subject to severe mechanical abrasion and wear, 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 . In this connection reference may be made to European patent no: 0236507 dated 12.03.87 titled "High-density alumina-zirconia sinter and process for its production.
It is well known that additives of MgO, CaO, Y2O3, La2O3, SiO2, Ta2O5 etc. as grain growth inhibitor(s) or sintering agent (s) to Al2O3 results in alumina-base materials having high strength and abrasion resistance. However, it requires sintering temperatures as high as 1470 - 1700oC and in some

instances, need expensive additives such as Y2O3. Reference is made in this context to the European patent no: O256182 dated 24.O2.88 titled "Alumina-base abrasion resistant material
These materials are hence not preferred from the economical standpoint. On the other hand, it has been reported that the sintering temperature for a dried 96% Al2O3 body was lowered to 1300-140oC by adding a compound additive of MnO2 and TiO2 or CuO and TiO2 to Al2O3. This material, however, failed to achieve sufficient abrasion resistance. Reference may be made to
Indian patent application no. : 704 / Del / 91 dated Of filing: 2.8.91 titled "An improved process for the production of alumina based wear resistant Ceramics" and to the United States patent no: 4719188, dated January 12, 1988 tilted Alumina- base abrasion resistant material
Normally alumina-base abrasion resistant material is prepared by
sintering of green compact containing sintering agents like 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 at low
temperatures, i.e. 1200-1350oC. However, to obtain high abrasion resistance
product at such a low sintering temperature, the particle size of the principal
raw material, alumina and the individual sintering agents should be within the
range of 2-3µm or smaller, more preferably in the range of 0.8-1.2 µm, both in
terms of median diameter. Reference may be made to the publication titled "
Processing high-purity and liquid-phase-sintered alumina ceramics using
locally synthesised alumina powders" by B.A. Latella, et al., Journal of
Materials Science 33 (1998) 877-886.
As described above, conventionally known alumina-base abrasion resistant materials require high sintering temperatures for their production. In some instances, they also require certain expensive additives. These requirements increased both energy- and material costs, resulting in making the resultant products expensive. On the other hand, in general, it is difficult to achieve appreciable abrasion resistance in the product, wherein additives are employed to lower the sintering temperatures.

In general most of the conventional processes for producing wear resistant alumina tiles involve either incorporation of sufficient quantity of liquid forming agents or sintering at elevated temperature (> 1600oC) to achieve required density leading to appreciable wear properties. Both the processes also requires very fine raw materials especially alumina which in turn demands for extensive grinding and thereby increasing the processing cost. However, the materials produced through low temperature liquid phase sintering fails to achieve appreciable wear resistant properties due to the presence of various impurity phases. Although, the high temperature sintering process yields good wear resistant properties, the high amount of fuel consumption and use of superior grade refractory increases the cost of production.
The main objective of the present invention is, therefore, to develop an
alumina-base abrasion resistant material having high abrasion resistance in
spite of its low sintering temperature ( Another objective of the present invention is to produce abrasion resistant material using the average particle size of the initial principal raw material, Al2O3 in the range of 4-5 µm so as to reduce the energy required for milling thereby reducing the cost of production.
Still another objective of the present 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.
Still another objective of the present invention is to provide a process for the preparation of alumina-base abrasion resistant material having high abrasion resistance in spite of its low sintering temperature.
Yet another objective of the present invention is to provide a process for the preparation of alumina-base abrasion resistant material having high

abrasion resistance in spite of its low sintering temperature. With reduce total sintering cycle to minimise the power consumption.
We have carried out extensive research 8B development work with a view towards attaining the above objectives through liquid phase sintering of alumina with the addition of low melting additives. During the said work we observed that the use of liquid phase favours easy and economical processing by allowing sintering at lower temperatures and also use of less pure alumina and sintering aids. We have also observed that although Al2O3 and the individual sintering agents may be separately pulverised and then combined together into an intimate mixture, 11 is more economical to pulverise and mix both Al2O3 and additives together
Near full densification in liquid phase sintered alumina was achieved at
low temperature such as 1500oC due to the influence of grain- boundary liquid
. ■ > -
phase.
Accordingly the present invention provides an improved alumina based abrasive material having improved wear resistant properties.
Accordingly the invention provides an alumina-base abrasion resistant liner material obtained by the incorporation of sintering additives comprising 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5% CaO containing material and 0.5-3.0% B2O3 containing material.
According to another feature of the invention there is provided a process for the preparation of improved alumina based' abrasive material having improved wear resistant properties which comprises:
(i)Wet mixing of 90-92 percent by weight of alpha-alumina of maximum average particle size of 4.0 micron with an admixture of sintering agents consisting essentially of 2-6% Silica containing material, 0-4.0% MgO containing material,

0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing material in a conventional manner for a period in the range of 4-6 hrs.
(ii) Drying the resultant slurry by any known process
(iii) Mixing the dried powder with a liquid binder followed by granulation
(iv) Pressing the granules into required shapes by known methods^)
(v) Drying the shaped products by any known process and
(vi) Liquid phase sintering of the said dried products s emplyoing conventional
methods at a temperature in the range of 1480 to 1500°C with soaking period
in the range of 3-5 hours and maintaining the total sintering cycle within 20 -
22 hours.
/'&
According to another feature of the invention there is provided an additive composition useful for the preparation of alumina based abrasive materials having improved wear resistant properties comprising 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing material.
According to yet another feature of the invention there is provided a process for the preparation of an additive composition useful for the preparation of alumina based abrasive materials having improved wear resistant properties which comprises nixing 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5 3.0% B2O3 containing material.
Among the sintering agents which can be employed in the preparation of alumina-base abrasive material having improved wear resistant properties of this invention, CaO containing material and B2Q3 containing material are effective primarily in improving the sinterability of Al2O3 and lowering its sintering temperature. On the other hand, MgO containing material, SiO2 containing material 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 temperature 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 conducting extensive research on various combinations of sintering agents. Further, the additives in the present invention are used in the form of their precursor to improve their reactivity. The major cation silicon, calcium and magnesium are the chief constituents for developing a glassy phase which helps in densification at lower temperature. Small blocky, equiaxed grains are obtained due to limited solubility of Al2O3 in the glassy phase and the pores remained attached to the grain boundary due to the stabilising influence of MgO. The degree of densification and micro-structural evolution depends critically on the sintering temperature and time regime employed. Use of this additive has made it possible to obtain an alumina-base abrasion resistant material having extremely high abrasion resistant inspite of low sintering temperatures.
Present invention features the addition of additives such magnesia containing materials which includes MgO, MgCO3, MgCk, Mg(OH)2 , baria containing materials which includes BaCOs , Ba(0H)2 ,2-6% silica containing materials includes kaolin, quartz, amorphous silica, alumino silicate minerals, B2O3 containing material includes B2O3, H3BO3, Na2B4O7. H2O, 0.5-3.5 % calcia containing materials includes CaCOa, Ca(0H)2, Ca{N03)2.etc. for liquid phase sintering of Al2O3.
In a preferred embodiment of the invention all the raw materials in appropriate proportions are mixed in a steel ball mill for 3 - 5 hrs in water media. The mixed slurry is then dried in an oven or in a spray drier to remove the water. However, care is taken to avoid segregation of constituents during oven drying. The oven-dried powder is then granulated in presence of a polymeric binder to required size prior to pressing in a definite shape. The

pressed sample is then dried in an oven at 120°C to remove the moisture. The dried sample is then sintered at 1500°C for a soaking period of 3-6 hrs. Heating schedule maintained for sintering are as follows:
120°C /h from room temperature to 480°C dwell Ihr 200°C /h from 480°C to 1180°C dwell 10 mins 1800/h from 11800C to 15000C dwell 6 hrs • 300°C /h from 15000C to room temperature
In a preferred embodiment of the present invention the amount of Silica containing material may preferably range from 2 to 6%, the amount of MgO containing material may range from Oto 4 % the amount of BaO containing material may range from 0.1 to2 % and CaO containing material may range from 0.5 to 3.5 % and B2O3 containing material may range from 0.5 to 3% The period of sintering may preferably for a period in the range of 4-6 hrs.
The drying of the resultant slurry after mixing is effected either by conventional drying method where the slurry is loaded in a tray drier and dried at around 150°C for 6 to 8 hrs. or the slurry may be spray dried in a spray drier where the slurry is fed as a fine spray in a dynamic hot air chamber resulting in the formation of dry granules. However spray-drying process is preferred over conventional tray drying as the homogeneity of the powder mix is maintained and at the same time it avoids the process of making granules for further processing.
The mixing of the dried powder with a liquid binder may be carried out by addition of 2% binder in the mixed slurry prior to spray drying or granulation. In case of spray drying binder solution is first thoroughly mixed with the slurry containing raw materials however in conventional milling and mixing method the mixed slurry is first dried then the binder solution is added and thoroughly mixed to the dried powder. The mix slurry is then semidried to moisture content of around 15 - 20% and made in the form of briquette and then fed in to the granulator. Granules of-30 to +100 mesh are then collected, dried and shaped into a tool steel mould to prepare tiles of required dimension

by applying a pressure in the range of 8-10 tons per square inch. These shaped tiles were then dried at 150°C for 6 hrs in a tray drier. The sintering of the said dried tiles was performed in an electrical /gas/oil operated furnaces in the temperature range of 1480 to 1500°C with a soaking period in the range of 4-8 hours keeping total heating and cooling schedule within 20-22 hrs.
The present invention will hereinafter be described in detail in the Examples given below which are provided to illustrate the invention only and therefore should not be construed to limit the scope of the invention. In the Examples each abrasion resistance tests were carried out using an ASTMG-65 test.
The characteristics of Alumina powders used in the Examples provided
'J
below invention are given in the Table I below:
Table I
Properties Alumina A Alumina B
Alumina content (%) 99.5 min 99.4 min
Na2O (%) 0.3-0.4 0.35-0.45
SiO2 (%) 0.O2 0.05
Fe2O3(%) 0.O2 0.04
LOI (upto 1050°C) 0.3 0.3
Av. Particle Size (µm) 3.0-4.0 6.0-7.0
Example I
910 gms of Alumina A given in table I is mixed with 15 gms of silica, 34 gms of clay, 50 gms of magnesium carbonate, 7.5 gms of barium carbonate, 10 gms of calcium carbonate and 16 gms of H3BO3 in the form of slurry with addition of 300 ml of distilled water. This slurry is milled for 4 hrs in a steel ball mill followed by drying in an oven at 150°C for removal of water. Dried cake is then crushed and milled in a ceramic pot mill for 15 minutes prior to mixing with 2% PVA solution to form a dough which is then granulated to the size range of -30 to +100 mesh by sifting method. Powder granules are then

pressed in a tool steel mould at 8 tsi in the form of tiles having dimensions 70mm X 45mm x 8 mm. The pressed sample is then dried in an oven at 120oC to remove the moisture. The dried sample is then sintered in an electrically heated furnace at a temperature of 1500°C for 6 hrs.
Sintered samples are then characterised for various properties. The results are listed in Table II.
Example II
910 gms of Alumina B, shown in table I, is mixed with 15 gms of silica, 34 gms of clay, 50 gms of magnesium carbonate, 7,5 gms of barium carbonate, 10 gms of calcium carbonate and 16 gms of H3BO3 in the form of slurry with addition of 300 ml of distilled water. This slurry is milled for 4 hrs in a steel ball mill followed by drying in an oven at 150oC for removal of water. Dried cake is then crushed and milled in a ceramic pot mill for 15 minutes prior to mixing with 2% PVA solution to form a dough which is then granulated to the size range of -30 to +100 mesh by sifting method. Powder granules are then pressed in a tool steel mould at 8 tsi in the form of tiles having dimensions 70mm X 45mm x 8 mm. The pressed sample is then dried in an oven at 120°C to remove the moisture. The dried sample is then sintered in an electrically heated furnace at a temperature of 1500°C for 6 hrs.
Example III
910 gms of Alumina B, shown in table I, is mixed with 15 gms of silica, 34 gms of clay, 50 gms of magnesium carbonate, 7.5 gms of barium carbonate, 10 gms of calcium carbonate and 16 gms of H3BO3 in the form of slurry with addition of 300 ml of distilled water. This slurry is milled for 4 hrs in a steel ball mill with 2 % PVA solution followed by spray drying using a spray drier (capacity: 25 kg water evaporation per hour) keeping out let temperature at around 150°C for removal of water and granule formation. The granules collected were in the range of -80 to +100 mesh. Powder granules are then pressed in a tool steel mould at 8 tsi in the form of tiles having dimensions 70 mm X 45 mm x 8 mm. The pressed sample is then dried in an oven at 120°C to

remove the moisture. The dried sample is then sintered in an electrically heated furnace at a temperature of 1500°C for 6 hrs. Properties of sintered tiles are listed m Table III.
Properties of sintered tiles are listed in Table II.

The above table shows the comparison of sintered properties for three examples. The Table indicates that the alumina based abrasion resistant material of the present invention is superior to the samples patented vide Indian patent application no. : 704 / Del / 91 dated Of filing: 2.8.91 titled "An improved process for the production of alumina based wear resistant Ceramics". The present process ases coarser alumina powders as compared to the earlier processes which saves the energy of extensive milling and in turn reduces the cost of production to a larger extent. This invention further reduces the total sintering temperature and the total schedule, which also contributes towards the reduction in cost of production. . The slight difference in properties between them is due to difference in characteristics of starting alumina powders especially with respect to particle size and impurities content. This also indicates that alumina tiles with excellent wear properties can be

achieved by proper selection of additives and initial particle size of alumina as well as its impurities content. Advantages of the present invention
1. By maintaining the average particle size of the principal raw material, Al2O3 and the mix in the range of 4-5 ^m, not only reduces the energy consumption for milling but also reduces the cost of production.
II. The wear resistance properties of the materials produced is increased
many fold than the prior art, by sintering in the range of 1480-1500oC.
III. Facilitates employment of cheap raw materials available locally and easy
and example processing methods.

1. An improved alumina based abrasion resistant material having improved wear resistant properties having a sintering temperature of 1500°C . 2 An improved alumina-based abrasion resistant material obtained by the incorporation of sintering additives comprising 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing
material.
3. A process for the preparation of improved alumina based abrasive material having improved wear resistant properties, which comprises: (i)Wet mixing of 90-92 percent by weight of alpha-alumina of maximum average particle size of 4.0 micron with an admixture of sintering agents consisting essentially of 2-6% Silica containing material, 0-4.0% MgO containing material, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5-
.
3.0% B2O3 containing material in a conventional manner for a period in the
range of 4-6 hrs.
(ii) Drying the resultant slurry by any known process
(iii) Molding the dried powder with a liquid binder followed by granulation
(iv) Pressing the granules into required shapes by known methods
(v) Drying the shaped products by any known process and
(vi) Liquid phase sintering of the said dried products s employing conventional
methods at a temperature in the range of 1480 to 1500°C with soaking period
in the range of 4-6 hours and maintaining the total sintering cycle within 20 -
22 hours.
4. An improved process as claimed in claim 3, wherein SiO2 containing
material includes kaolin, quartz, amorphous silica, and alumino silicate
minerals.

5. An improved process as claimed in claims 3 to 4, wherein CaO containing material includes CaCO3, Ca (OH )2.
6. An improved process as claimed in claims 3 to 5 wherein CaO containing
material includes CaCO3, Ca (OH 2.

7.An improved process as claimed in claims 3 to 6, wherein BaO containing material includes BaCO3-
8 An improved process as claimed in claims 3 to 8, wherein MgO containing material includes MgCO3.
9. An improved process as claimed in claims 3 to 8, wherein B203Containing
material includes B2O3. H3BO3, Na2B4O7 .H2O.
10. An improved process as claimed in claims 3 to 9, wherein average particle size of the alumina powder must be less than 4µm.
11. An improved process as claimed in claims 3 to 10, wherein average particle size of the wet mix is in the range of 5-6 µm.
12. An improved process as claimed in claims 3 to 11 wherein the Green density of the compact should be more than 2.1 g/cc.
13. An improved process as claimed in claims 3 to 12, wherein the polymeric
binder Used is selected from PVA, Methylcellulose,'gum arabic, and animal
glue.
14. An improved process as claimed in claims 3 to 13, wherein a wear resistant polyctystalline alumina material havmg specific gravity greater than 3.60 g/cc is produced
15. An improved process as claimed in claims 3 to 14, wherein a wear resistant polycrystalline alumina material having wear loss (volume) of less than 0.08-1.2x10-8 cc/gm of erodant (av. 200 micron quartz powder) is produced
16.An additive composition useful for the preparation of alumina based abrasive materials having improved wear resistant properties as claimed in claims 1 & 2 which comprises 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BciO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing material. 17. A process for the preparation of an additive composition as claimed in claim 16 useful for the preparation of alumina based abrasive materials having improved wear resistant properties which comprises mixing 2-6% Silica containing materials, 0-4.0% MgO containing materials, 0.1-2.0% BaO containing material, 0.5-3.5%CaO containing material and 0.5-3.0% B2O3 containing material.

Documents:

122-mas-2000-abstract.pdf

122-mas-2000-claims filed.pdf

122-mas-2000-claims grand.pdf

122-mas-2000-correspondence others.pdf

122-mas-2000-correspondence po.pdf

122-mas-2000-description complete filed.pdf

122-mas-2000-description complete grand.pdf

122-mas-2000-form 1.pdf

122-mas-2000-form 19.pdf

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Patent Number

198068

Indian Patent Application Number

122/MAS/2000

PG Journal Number

27/2006

Publication Date

07-Jul-2006

Grant Date

16-Dec-2006

Date of Filing

18-Feb-2000

Name of Patentee

INTERNATIONAL ADVANCED RESEARCH CENTRE FOR POWDER METALLURGY AND NEW MATERIALS (ARCI) GOVT. OF INDIA

Applicant Address

OPP: BALAPUR VILLAGE; RANGA REDDY DISTRICT, HYDERABAD-500 005

Inventors:

#	Inventor's Name	Inventor's Address
1	BHASKAR PRASAD SAHA	INTERNATIONAL ADVANCED RESEARCH CENTRE FOR POWDER METALLURGY AND NEW METALLURGY (ARCI) A GOVT. OF INDIA., AT OPP: BALAPUR VILLAGE; RANGA REDDY DISTRICT, HYDERABAD-500 005
2	DR. ROY JOHNSON	INTERNATIONAL ADVANCED RESEARCH CENTRE FOR POWDER METALLURGY AND NEW METALLURGY (ARCI) A GOVT. OF INDIA., AT OPP: BALAPUR VILLAGE; RANGA REDDY DISTRICT, HYDERABAD-500 005
3	DR. IBRAM GANESH	INTERNATIONAL ADVANCED RESEARCH CENTRE FOR POWDER METALLURGY AND NEW METALLURGY (ARCI) A GOVT. OF INDIA., AT OPP: BALAPUR VILLAGE; RANGA REDDY DISTRICT, HYDERABAD-500 005
4	DR. SUBIR BHATTACHARJEE	INTERNATIONAL ADVANCED RESEARCH CENTRE FOR POWDER METALLURGY AND NEW METALLURGY (ARCI) A GOVT. OF INDIA., AT OPP: BALAPUR VILLAGE; RANGA REDDY DISTRICT, HYDERABAD-500 005
5	DR. YASHWANT RAMCHANDRA MAHAJAN	INTERNATIONAL ADVANCED RESEARCH CENTRE FOR POWDER METALLURGY AND NEW METALLURGY (ARCI) A GOVT. OF INDIA., AT OPP: BALAPUR VILLAGE; RANGA REDDY DISTRICT, HYDERABAD-500 005

PCT International Classification Number

C04B035/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA