Title of Invention	"METHOD FOR THE MANUFACTURE OF FULLY STABILIZED CUBIC ZIRCONIA"
Abstract	A method for the manufacture of a fully stabilzed cubic zirconia is disclosed.The method comprises preparing a work piece consisting of a ceramic precursor comprismg mixture of monoclinic zirconia and calcium carbonate in the form of a pellet, layering or covering said pellet with a polymeric susceptor of the kind such as herein described, subjecting said work piece to microwave energy at a temperature in the range of 1000°C to 1400°C to obtam said fully stabilized cubic Zirconia.

Title of Invention

"METHOD FOR THE MANUFACTURE OF FULLY STABILIZED CUBIC ZIRCONIA"

Abstract

A method for the manufacture of a fully stabilzed cubic zirconia is disclosed.The method comprises preparing a work piece consisting of a ceramic precursor comprismg mixture of monoclinic zirconia and calcium carbonate in the form of a pellet, layering or covering said pellet with a polymeric susceptor of the kind such as herein described, subjecting said work piece to microwave energy at a temperature in the range of 1000°C to 1400°C to obtam said fully stabilized cubic Zirconia.

Full Text	Field of the invention The present invention relates to a method for the synthesis and sintering of partially stabilized zirconia ceramics. In particular, the present invention relates to a method for the manufacture of fully stabilized cubic zirconia. More particularly, the present invention relates to a method for the manufacture of fully stabilized cubic zirconia at a much lower temperature as compared to conventional methods. Background of the invention The application of pure zirconia ceramics is restricted due to extensive microcracking caused by the anisotropic volume expansion accompanying tetragonal to monoclinic transition. The solution of this problem is to form a solid solution or "alloys" of cubic zirconia. Thus, partially stabilized zirconia ceramics (PSZ) have found their place and have been extensively investigated. The low temperature monoclinic phase transforms into the tetragonal phase at 1170°C and into cubic phase at 2370°C. Cubic zirconia stabilized with calcium oxide is an important material to both industrial and scientific communities. It is a nonstoichiometnc substance with a defective fluorite structure, the defects being anion vacancies. The general formula is CaxZr1.xO1-x- The properties of this material are functions of the compositional parameters. According to binary oxide phase diagrams the cubic phase exists over wide range of composition and temperature [(P. Duwez, et al; J. Amer. Ceram. Oc. 35 (1952) 107); P. Duran, et al; J. Mater. Sc, 22 (1987) 4348) ]. The conventional methods for the preparation of fully stabilized cubic zirconia require processing at extremely high temperatures, in huge and cumbersome furnaces. These processing time required could be from several hours to days. Therefore, there has been a long felt need in the art for novel methods for the manufacture of fully stabilized cubic zirconia at a much lower temperatures and resident time. Objects of the invention Accordingly, it is an important object of the present invention to provide a novel method for the manufacture of fully stabilized cubic zirconia, which overcomes the disadvantages of the prior art methods. It is another object of the present invention to provide a method for the manufacture of fully stabilized cubic zirconia at a much lower temperature than the prior art methods. It is yet another object of the present invention to provide a method for the manufacture of fully stabilized cubic zirconia at a much shorter resident time than the prior art methods. Summary of the invention The above and other objects of the present invention are achieved based on te unexpected finding that a fully stabilized cubic zirconia can be prepared at 1100°C by microwave processing in 5 minutes. This is truly unexpected smce in the conventional heating, Mly stabilized cubic zirconia cannot be prepared at a temperature as high as 1400°C even in four hours. According to the method of the present invention, a fully cubic calcium stablized zirconia Zro.9Cao.101.9 was prepared at a temperature as low as 1100°C having the dopant (Ca2+)concentration of only 10 mol%. The method of the present invention essentially involves a work piece consisting of a ceramic precursor comprising mixture of monoclinic zirconia and calcium carbonate in the cylindrical pellet form and a polymeric susceptor which acts as a coupling agent and thereafter exposing the work piece to microwave energy. The microwave energy initially couples with the polymeric susceptor and brings the temperature of the zirconia (work piece) to a level at which zirconia body itself absorbs microwave energy to achieve high temperature. The phase transformation occurs at a temperature as low as 1100°C. The susceptor is preferably chosen such that it evaporates at the temperature at which zirconia body itself absorbs microwave energy so that when which zirconia body starts absorbing microwave energy, there is no trace of the susceptor left. An advantage of the present invention is the significant time and energy savings compared to conventional infrared (radiant) heating methods for preparing fully calcium stablized zirconia. Conventional manufacture of ceramics has been done by the use of resistant heating furnaces, which consume relatively large quantities of energy, time, and manpower while subjecting the ceramics to rather hostile environments. The invention concerns a technology for lowering of phase transformation temperature and lowering of dopant concentration to prepare fully calcium stabilized cubic zirconia. Detailed description The present invention is based on the use of Microwave radiation for the phase transformation in Calcium-Stabilized Zirconia (CSZ). A sequential phase transformation for different compositions in CaxZr1-x02-x system according to the present invention reveals that fully stabilized cubic zirconia can be prepared at 1100°C for composition Cao.1Zro.901.9 by microwave processing within five minutes. It has been found that CaZrOs does not form as an intermediate phase. In the conventional heating fully stabilized cubic zirconia cannot be prepared at a temperature as high as 1400°C even in four hours. An additional significant fmding is the elevated bulk conductance at room temperature for composition Cao.1Zro.901.9 by microwave processing at 1000°C within five minutes. For carrying out the process of the present invention, a special microwave apparatus was developed. Accordingly, the present invention provides a method for the manufacture of a fully stabilzed cubic zirconia of the formula (Formula Removed) wherein x, y and z have a value in the range of 0.02, to 0.1, which comprises preparing a work piece consisting of a ceramic precursor comprising mixture of monoclinic zirconia and calcium carbonate in the form of a pellet, layering or covering said pellet with a polymeric susceptor of the kind such as herein described, subjecting said work piece to microwave energy at a temperature in the range of 1000°C to 1400°C to obtain said fully stabilized cubic Zirconia. In a preferred feature, said fully stabilzed cubic zirconia is of the formula Zro.9Cao.iOi.9. In another preferred feature, said fully stabilzed cubic zirconia has a (Ca2+) concentration of not more than 10 mol %. In another preferred feature, wherein said work piece is subjected to microwave energy at a temperature of about 1100°C. In another preferred feature, wherein said work piece is in the form of a cylindrical pellet. In another preferred feature, wherein said work piece is subjected to microwave energy for up to four hours. In another preferred feature, said work piece is subjected to microwave energy for about 5 minutes. In another preferred feature, said susceptor evaporates at a temperature of about 400°C. In another preferred feature, said susceptor is polyvinyl alcohol. The present invention will now be described with reference to the following Examples and accompanying drawings wherein: Fig 1: Schematic display of the microwave processing apparatus according to the present invention. minutes (a) 2 mol% Ca; (b). 4 mol% Ca; (c). 6 mol% Ca; d. 8 mol% Ca; e. 10 mol% Ca. Fig. 2: XRD pattern of Microwave Fired 10 mol% Ca-ZrOa system at 1400°C at different exposure time from 5 to 30 minutes; (a). 5 mm; (b). 10 min.; (c). 15 min; (d). 20 min; (e). 25 min; (f). 30 min. Fig. 3: XRD pattern of Microwave Fired 10 mol% Ca-Zr02 system at different exposure temperatures for 5 min; (a). 1000°C; (b). 1100°C;(c). 1200°C; (d). 1300°C; (e). 1400°C Fig. 4: XRD pattern of Conventional Fired Ca-Zr02 system at 1400°C for 4 Hrs; a. 2 mol% Ca; b. 4 mol% Ca; c. 6 mol% Ca; d. 8 mol% Ca; e. 10 mol% Ca. Fig. 5: FTIR pattern of Microwave Fired Ca-Zr02 system at 1400°C for 20 minutes a. 2 mol% Ca; b. 4 mol% Ca; c. 6 mol% Ca; d. 8 mol% Ca; e. 10 mol% Ca. Fig. 6: FTIR pattern of Conventional Sintered Ca- Zr02 system at 1400°C for 04 Hours; a. 6 mol% Ca; b. 8 mol% Ca; c. 10 mol% Ca. Fig. 7: Relationship between the monochnic phase %age and composition of CaO in Microwave and Conventional sintering of Calcia-Zirconia system. Fig. 8: Relationship between tetragonality (c/a) ratio and CaO concentration in microwave and conventionally sintered samples. Fig. 9: Relationship between tetragonality (c/a) ratio and exposure time in microwave Fired samples for 10 mol% Ca at 1400°C Fig. 10: SEM Micrographs of 10 mol% Ca Microwave Fired at 1400°C for a. 10 min, b. 20 min at X 1500 at 10 µm. he microwave apparatus of the present invention Referring to Fig. 1, a kitchen microwave oven was used to fabricate the microwave furnace in accordance with the present invention. . The specification of the microwave oven is a multimode, 900W (RF magnetron output power), 2.45 GHz, (LG MS-285SD) and the dimensions of the inner cavity are 34.4cm x 34.4cm x 22.5cm in volume. To make this kitchen microwave oven suitable for high temperature sintering experiments, following modifications were made: 1. An insulating packet transparent to microwaves was made to fire the work piece . 2. An aluminum plate was placed below the sintering packet to prevent the cavity from being overheated. 3. To control the heating rate and to achieve the required temperature for desired exposure time, a power control system consisting to two variacs was connected to the power supply of the magnetron. 4. To efficiently cool the magnetron and to maintain the cavity at low temperature so as to avoid excess heat transferred from the cavity to the magnetron, a hosepipe of copper was soldered onto the outside surface (under the outer shell) of the top of the cavity for continuous water circulation. 5. A small hole was drilled in the centre of the roof just above the axis of the fabricated furnace for insertion of the thermocouple. 6. A temperature indicator was connected to the S type thermocouple to measure the cavity temperature with an accuracy of ± 1°C. The packet is made as shown in Fig. 1. It comprises of in essence, an alumina crucible, zirconia cylinder 2 (Zircar Products, Inc. Florida, NY), rods 6, and thermal insulating AL-25/1700 (Zircar Products, Inc. Florida, NY) 5. Zircar alumina insulation type AL-25/1700 insulation 5 is a combination of high purity alumina fibers, refractory fillers and inorganic ceramic binders. The typical chemical composition of the board is 80% AI2O3, 20% Si02, density 0.44 g/cc, modulus of rupture 1.38 Mpa, compressive strength 0.24 Mpa, thermal conductivity 0.27W/m°K at 1650°C. As claimed by the manufacturer, AL-25/1700 offers low thermal conductivity, high temperature stability, good hot strength, dimensional stability and excellent resistance to thermal shock and chemical attack and is not affected by oil or water. It can withstand temperature up to 1700°C (31000F) for continuous use. The zirconia cylinder 2 vertically surrounding the samples 3 functions both as a microwave susceptor as it absorbs and converts microwave to heat, thus preheats the sample if the sample does not absorbs microwaves significantly at low temperatures. As an insulator, it prevents heat of the samples 3 from dissipation. Preheating up to 400°C is necessary in case of zirconia sample because it shows lossy character only after this temperature. Temperature measurement m microwave sintering heating is one area, which is very critical, and matter of concern for its accuracy and reliability. This is very critical, and matter of concern for its ceramics sintering is usually reported as the lowering of processing temperatures, of at the same temperature but improved properties, while only precise measurement can make the comparison between microwave and conventional processing methods more reliable. In a microwave field, the interference of microwaves with the electromotive force of the thermocouple makes the temperature readings random or erroneous before the temperature rises to such a level that microwaves are efficiently absorbed by the sample. When properly shielded and grounded and microwave is allowed to interact immediately with a material (PVA), microwave interference can be totally prevented and theremocouples 4 (shown in Fig 1) can provide rehable temperature readings. In an embodiment of the present invention, a platinum shielded S type Pt-10%Rh/Pt thermocouple was used to measure temperature. The thermocouple 4 is fitted in the microwave so that the tip of the thermocouple 4 was 1mm away from the work piece in the sintering packet. The temperature of the samples 3 was measured with S type thermocouple 4 with an accuracy of ± 1°C. A vertical ball mill was fabricated in the laboratory for milling and mixing the powders at different stages. YSZ balls were used in acetone as grinding medium and milling was done in polythene bottles. A lubricant, preferably, a lubricant based on stearic acid was developed in the laboratory to reduce the friction between walls of die and powder to have the uniform distribution of pressure during consohdation of powders. A uniaxial hydraulic press was used to consolidate the powder in the form of cylindrical pellets. The pressure maintained was 312 Mpa. Conventional furnace A programmable furnace having silicon carbide rods as heating sihcon carbide rods as heating elements was used for the present invention for comparative purposes. The furnace is capable of operating at high temperature up to 1400°C, high heating rate and low thermal inertia. The furnace has the capacity of providing heating rates up to 600°C per hour. The temperature in the conventional sintering was measured with S type Pt-10%Rh/Pt thermocouple. The samples were placed in the alumina crucible, which was in contact with the tip of the thermocouple. The heating and cooling rates can be controlled by programs with desired soaking time. Example: Starting materials The materials used in the present invention comprised of zirconia (Zr02; AR, Indian Rare Earths, Orissa, Assay 99.7%), calcium carbonate (CaCOs; AR, CDH, asay 99.5%), magnesium oxide (MgO; AR, CDH, assay 98.0%), yttrium oxide (Y2O3; AR, CDH, assay 99.9%), polyvinyl alcohol (CDH cold) and stearic acid (C17H35COOH, AR, CDH) were acquired from commercial vendors. The partially stabilized zirconia ceramics 0.04, 0.06, 0.08, 0.10) synthesized during the study and thek proper chemical stochiometries are described hereinafter. Sintering Process Multi pellet runs were conducted in both microwave and conventional sintering experiments. In microwave sintering, the pellets, usually five to six (12.80 mm in diameter and 2.50 mm in thickness stacked one above other were placed in the alumina crucible of the sintering packet. To this layer of pellets poly vinyl alcohol (6.6%) solution is added. Poly vinyl alcohol being lossy having high tangent loss at room temperature interacts with microwave first and gets heated up to its decomposition temperature (400°C). In the course of decomposition it heats the work piece to a temperature where it starts absorbing microwaves and volumetric heating of work piece begins. In conventional sintering the pellets usually six to eight in number were placed in the alumina crucible without any susceptor. Heating rate in microwave was lOO^C per minute and in conventional was 10°C per minute. Since the sintering temperature in both the processing techniques were identical the difference in the sintered samples can be attributed to the microwave effect. The details of the sintering conditions for each material will be given in the respective sections.The precursor of partially stabilized zirconia (PSZ) (Formula Removed) where n = 2-x for M = Ca2+ Mg2+ and n = 2-x/2 for M = Y3+ and x= 0.02, 0.04, 0.06, 0.08, 0.10 were prepared by mixed oxide method. Calcium carbonate (CaOs; AR, CDH, assay 99.9%) and zirconia (Zr02) were used for compositions x= 0.02, 0.04, 0.06, 0.08, 0.10. The powders were ball milled in a polythene bottle using zirconia balls and acetone as a grinding medium for 6 hours. The powders of different compositions were mixed with 4% PVA binder and uniaxially pressed at 312 Mpa in a 12.80 mm die of high carbon content steel. The weight of each pellet was kept 1.00 g to have comparison. The pellets were weighed before and after firing to check the weight loss. Initially, the pellets were fired at 1400°C for 20 minutes. The temperature 1400°C was opted because many publications related to partially stabilized zirconia refers temperature 1400 C as a firing temperature in conventional heating. This provided a reference to evaluate/assess the potentiality of microwave firing. The pellets of PSZ of composition Mo.1Zro.9On where n = 1.90 for M = Ca2+, Mg2+ and n = 1.95 for M = Y3+ were fired at 1400 C for 5, 10, 15, 20, 25, 30 minutes. The pellets were fired in microwave radiation at 1000°C, ll000C, 1200°C, 1300°C and 1400°C for 5 minutes to investigate the minimum temperature of phase transformation. The pellets of composition x= 0.02, 0.04, 0.06, 0.08, 0.10 were fired conventionally at 1400°C was achieved in 3 hours. The phase transformation of each composition fired at various temperatures and times were analyzed by XRD (Philips, PW1710). The quantitative phase transformations were evaluated from XRD [1]. The Scanning Electron Micrograph (JEOL) of pohshed and etched surface of (Formula Removed) was taken. The presence of phases were identified by FTIR (Perkins Elmer RDXl) spectroscopy also. Densities of each pellet were measured by Archimedes Principle using distilled water. Hardness was measured on conventional microhardness machine with Vickers diamond indenters. The square pyramidal indenter created smaller, deeper impressions on pohshed selected sintered samples. The polished pellets were electroded with silver paste on both sides and conductivity measurements were taken at room temperature with LCR Bridge Hewlett Packard (HP) 4284 A (20Hz- IMHz) Results and discussion Crystalline phases of different polymorphs of CSZ in specimens were determined from X-ray diffraction (XRD) patterns. The peaks for monochnic, tetragonal and cubic phases have been identified. Tetragonal and cubic phases were identified from the separation of (400) and (004) diffraction peaks. Lattice parameters were calculated from (400) and (004) peaks of the XRD. The pellet of calcium zirconate (CSZ) (Formula Removed) (Table Removed) were fired under microwave radiation at temperature 1400°C for 20 minutes. Phase transformation in each composition was analyzed by XRD, given in Fig. lA(a-e) and evaluated by disappearance of monoclinic phase and appearance of tetragonal and cubic phase, given in Table I below and Fig. 7: Table 1 The phases formed of the precursor of CaxZr1.x02-x; CSZ; x = 0.02, 0.04, 0.06 and 0.08 were a mixture of monochnic tetragonal cubic as evident in Fig 1 A(e). The phase transformations were studied for each composition and it was found in CSZ that the percentage of monoclinic phase is reducing with increase in the concentration of the dopant. The trend of disappearance of monochnic phase is same in conventional firing given in Fig.4(a-e) as well as in microwave firing. However, the transformation to cubic + tetragonal phase is higher for the sample processed in the microwave field than that of sample fired conventionally. Further by comparing c/a ratio for tetragonahty, it was observed that the fiiUy stabilized cubic zirconia had formed for x = 0.08 and 0.1 m microwave processing while cubic phase formation had not occurred in conventional firing of material as given in Table II below and Fig. 8: Table II Relationship between tetragonality (c/a) ratio and CaO concentration in microwave and conventionally sintered samples (Table Removed) The phase transformations in CSZ of composition corresponding to x = 0.1 was further investigated kinetically. The pellets of this composition were identified by XRD, given in Fig. 2(a-f). The d- values of (111) peak of XRD of each run were constant, given in Table III below and Fig 9: Table-in Relationship between tetragonality (c/a) ratio and exposure time in microwave sintered samples for 10 mol% Ca at 1400"C (Table Removed) The XRD of each run showed the complete transformation was considered to be fully cubic where quantitative contribution of monoclinic phase was less than 5%. The precursor of composition x = 0.1 was fired at 1000°C, 1100°C, 1200°C, 1300°C and 1400°C for 5 minutes and phase transformation of each run was analyzed by XRD, given in Fig. 3(a-e). An XRD of CSZ processed at 1000°C given in Fig.3 (a) showed the mixture of cubic and tetragonal phase, as the contribution due to tetragonal phase was visible at higher angle (20= 74-76°) corresponding to (400)t and (004)t peaks. Other XRD patterns, given in Fig.3 (b-e), showed complete transformation of monoclinic phase to cubic phase in CSZ. . The d-value of (111) peak of cubic phase remained constant in XRD, given in Table IV below, of CSZ fired at temperatures 1100°C, 1200°C, 13000C and 1400°C for 5 minutes: Table-IV Relationship between tetragonality (c/a) ratio and temperature of samples fixed in microwave for 5 minutes of composition corresponding to 10 mol% Ca concentration. (Table Removed) The precursor of CSZ of composition x = 0.02, 0.04, 0.06, 0.08, 0.10 fired at 1400°C for 20 minutes in microwave were analyzed by IR also, given in Fig.5 (a-e). Six bands in the region 514-748 cm-1 originated from internal vibrations of ZrO2 molecule in the unit cell with a specific absorption band at 740 cm"' for monoclinic phase. Peaks due to translations and vibrations appear below 500 cm-1 which could not be characterized due to limitations of the instrument. The IR peak at 740cm' is visible in Fig.5 (a-c) compositions corresponding to x = 0.02, 0.04 and 0.06 indicating the presence of monolinic phase. However, in the compositions corresponding to x = 0.08 and 0.10, the peak at 740cm-1 disappears. The absorption peaks between 1600-1300cm"\ for the composition x = 0.08, may be due to the presence of mixture of tetragonal and cubic phase. A broad peak for composition x = 0.10 is due to the formation of fluorite type ZrO.9CaO.103 which confirmed the symmetrical Zr-0 bonds of cubic structure. An absorption peak at 3200cm"' appeared in the composition x = 0.08 and 0.10 which could not be mterpreted. The IR absorption peaks of the conventionally fired CSZ for composition x = 0.06, 0.08, 0.10 were also analyzed for comparison, given in Fig.6 (a-c). The characteristic IR absorption peak at 740 cm' for monoclinic phase persisted for all the compositions and a peak at 3200cm"' is also present in each sample. The densities have been expressed in Table V, VI and VII below: Table-V Density of CS2 for different dopant concentrations Table-VI Densities of CS2 for different sintering time (Table Removed) Table-VII Densities of CS2 for different sintering temperatures (Table Removed) It was found that the densities of the pellets of composition x=0.10 increased with increase in soaking time and were maximum (5.79 gcm-3) for the soaking time of 20 minutes in microwave firing at 1400°C. The densities decreased for soaking times 25 and 30 minutes. It may be, due to the increase in soak time, grain size of CSZ would have increased beyond a limit and the cubic phase might have started to transform into the monochnic phase as reported in Y203-Zr02 system [22-24]. Scanning Electron Micrographs of CSZ x = 0.10 processed in microwave radiation at 1400°C for 10 minutes and 20 minutes have been taken. The pohshed surface of the pellet was etched with a mixture of HNO3, HCI and HF. The surface was gold plated and then SEM was taken. The SEM depicted the formation of single phase for both the time given in Fig. 10 (a) and Fig. 10 (b), however the grain size was larger in the sample processed for 20 minutes compared to that of 10 minutes at 1500 magnification at the scale of 10µm. From the applicants' lab report it was observed that formation of cubic phase in the microwave processing is dependent upon the size of the dopant, as for 10% Y3+ substitution in zirconia, the stabilized zirconia was a mixture of cubic and tetragonal phase whereas 10 mol% Mg2+ doped zirconia system was a mixture of cubic, tetragonal and monoclinic phases with a contribution of monoclinic phase as high as 30%. It has also been reported that slow sintering rate in conventional firing is due to the low mobility of cations but the phase transformation in microwave firing at a temperature as low as 1 lOO0C may be due to the increase in the cation mobility under the influence of the electric field. It was reported [1], during the stabilization of cubic phase, the reaction of Zr02 and CaO occurs to form the compound CaZrOs first and then the CaZrO3 reacts with excess Zr02 to form cubic Zr02. However, the formation of CaZrO3 has not taken place at temperature as low as l00000C. We claim: 1. A method for the manufacture of a fully stabilzed cubic zirconia of the formula ZrxCayOz Zro.9Cao.101.9 wherein x, y and z have a value in the range of 0.02, to 0.1, which comprises preparing a work piece consisting of a ceramic precursor comprising mixture of monoclinic zirconia and calcium carbonate in the form of a pellet, layering or covering said pellet with a polymeric susceptor of the kind such as herein described, subjecting said work piece to microwave energy at a temperature in the range of 1000°C to 1400°C to obtain said fully stabilized cubic Zirconia. 2. A method as claimed in claim 1 wherein said fully stabilzed cubic zirconia is of the formula Zro.9Cao.1Oi.9. 3. A method as claimed in claim 1 or 2 wherein said fully stabilzed cubic zirconia has a (Ca2+) concentration of not more than 10 mol %. 4. A method as claimed in any preceding claim wherein said work piece is subjected to microwave energy at a temperature of about 1100°C. 5. A method as claimed in any preceding claim wherein said work piece is in the form of cylindrical pellet. 6. A method as claimed in any preceding claim wherein said work piece is subjected to microwave energy for up to four hours. 7. A method as claimed in claim 6 wherein said work piece is subjected to microwave energy for about 5 minutes. 8. A method as claimed in any preceding claim wherein said susceptor evaporates at a temperature of about 400°C. 9. A method as claimed in claim 8 wherein said susceptor is polyvinyl alcohol. 10. A method for the manufacture of a fully stabilzed cubic zirconia substantially as herein described with reference to the accompanying drawings and as illustrated in the foregoing examples.

Full Text

Field of the invention
The present invention relates to a method for the synthesis and sintering of partially stabilized zirconia ceramics. In particular, the present invention relates to a method for the manufacture of fully stabilized cubic zirconia. More particularly, the present invention relates to a method for the manufacture of fully stabilized cubic zirconia at a much lower temperature as compared to conventional methods. Background of the invention
The application of pure zirconia ceramics is restricted due to extensive microcracking caused by the anisotropic volume expansion accompanying tetragonal to monoclinic transition. The solution of this problem is to form a solid solution or "alloys" of cubic zirconia. Thus, partially stabilized zirconia ceramics (PSZ) have found their place and have been extensively investigated. The low temperature monoclinic phase transforms into the tetragonal phase at 1170°C and into cubic phase at 2370°C. Cubic zirconia stabilized with calcium oxide is an important material to both industrial and scientific communities. It is a nonstoichiometnc substance with a defective fluorite structure, the defects being anion vacancies. The general formula is CaxZr1.xO1-x- The properties of this material are functions of the compositional parameters. According to binary oxide phase diagrams the cubic phase exists over wide range of composition and temperature [(P. Duwez, et al; J. Amer. Ceram. Oc. 35 (1952) 107); P. Duran, et al; J. Mater. Sc, 22 (1987) 4348) ].
The conventional methods for the preparation of fully stabilized cubic zirconia require processing at extremely high temperatures, in huge and cumbersome furnaces. These processing time required could be from several hours to days. Therefore, there has been a long felt need in the art for novel methods for the manufacture of fully stabilized cubic zirconia at a much lower temperatures and resident time.
Objects of the invention
Accordingly, it is an important object of the present invention to provide a novel method for the manufacture of fully stabilized cubic zirconia, which overcomes the disadvantages of the prior art methods.
It is another object of the present invention to provide a method for the manufacture of fully stabilized cubic zirconia at a much lower temperature than the prior art methods.

It is yet another object of the present invention to provide a method for the manufacture of fully stabilized cubic zirconia at a much shorter resident time than the prior art methods. Summary of the invention
The above and other objects of the present invention are achieved based on te unexpected finding that a fully stabilized cubic zirconia can be prepared at 1100°C by microwave processing in 5 minutes. This is truly unexpected smce in the conventional heating, Mly stabilized cubic zirconia cannot be prepared at a temperature as high as 1400°C even in four hours.
According to the method of the present invention, a fully cubic calcium stablized zirconia Zro.9Cao.101.9 was prepared at a temperature as low as 1100°C having the dopant (Ca2+)concentration of only 10 mol%. The method of the present invention essentially involves a work piece consisting of a ceramic precursor comprising mixture of monoclinic zirconia and calcium carbonate in the cylindrical pellet form and a polymeric susceptor which acts as a coupling agent and thereafter exposing the work piece to microwave energy. The microwave energy initially couples with the polymeric susceptor and brings the temperature of the zirconia (work piece) to a level at which zirconia body itself absorbs microwave energy to achieve high temperature. The phase transformation occurs at a temperature as low as 1100°C. The susceptor is preferably chosen such that it evaporates at the temperature at which zirconia body itself absorbs microwave energy so that when which zirconia body starts absorbing microwave energy, there is no trace of the susceptor left.
An advantage of the present invention is the significant time and energy savings compared to conventional infrared (radiant) heating methods for preparing fully calcium stablized zirconia. Conventional manufacture of ceramics has been done by the use of resistant heating furnaces, which consume relatively large quantities of energy, time, and manpower while subjecting the ceramics to rather hostile environments. The invention concerns a technology for lowering of phase transformation temperature and lowering of dopant concentration to prepare fully calcium stabilized cubic zirconia. Detailed description
The present invention is based on the use of Microwave radiation for the phase transformation in Calcium-Stabilized Zirconia (CSZ). A sequential phase transformation for different compositions in CaxZr1-x02-x system according to the present invention reveals that fully stabilized cubic zirconia can be prepared at 1100°C
for composition Cao.1Zro.901.9 by microwave processing within five minutes. It has been found that CaZrOs does not form as an intermediate phase. In the conventional heating fully stabilized cubic zirconia cannot be prepared at a temperature as high as 1400°C even in four hours. An additional significant fmding is the elevated bulk conductance at room temperature for composition Cao.1Zro.901.9 by microwave processing at 1000°C within five minutes. For carrying out the process of the present invention, a special microwave apparatus was developed.
Accordingly, the present invention provides a method for the manufacture of a fully stabilzed cubic zirconia of the formula
(Formula Removed)
wherein x, y and z have a value in the range of 0.02, to 0.1, which comprises preparing a work piece consisting of a ceramic precursor comprising mixture of monoclinic zirconia and calcium carbonate in the form of a pellet, layering or covering said pellet with a polymeric susceptor of the kind such as herein described, subjecting said work piece to microwave energy at a temperature in the range of 1000°C to 1400°C to obtain said fully stabilized cubic Zirconia.
In a preferred feature, said fully stabilzed cubic zirconia is of the formula Zro.9Cao.iOi.9.
In another preferred feature, said fully stabilzed cubic zirconia has a (Ca2+) concentration of not more than 10 mol %.
In another preferred feature, wherein said work piece is subjected to microwave energy at a temperature of about 1100°C.
In another preferred feature, wherein said work piece is in the form of a cylindrical pellet.
In another preferred feature, wherein said work piece is subjected to microwave energy for up to four hours.
In another preferred feature, said work piece is subjected to microwave energy for about 5 minutes.
In another preferred feature, said susceptor evaporates at a temperature of about 400°C.
In another preferred feature, said susceptor is polyvinyl alcohol.
The present invention will now be described with reference to the following Examples and accompanying drawings wherein:
Fig 1: Schematic display of the microwave processing apparatus according to the present invention.
minutes (a) 2 mol% Ca; (b). 4 mol% Ca; (c). 6 mol% Ca; d. 8 mol% Ca; e. 10 mol% Ca.
Fig. 2: XRD pattern of Microwave Fired 10 mol% Ca-ZrOa system at 1400°C at different exposure time from 5 to 30 minutes; (a). 5 mm; (b). 10 min.; (c). 15 min; (d). 20 min; (e). 25 min; (f). 30 min.
Fig. 3: XRD pattern of Microwave Fired 10 mol% Ca-Zr02 system at different exposure temperatures for 5 min; (a). 1000°C; (b). 1100°C;(c). 1200°C; (d). 1300°C; (e). 1400°C
Fig. 4: XRD pattern of Conventional Fired Ca-Zr02 system at 1400°C for 4 Hrs; a. 2 mol% Ca; b. 4 mol% Ca; c. 6 mol% Ca; d. 8 mol% Ca; e. 10 mol% Ca.
Fig. 5: FTIR pattern of Microwave Fired Ca-Zr02 system at 1400°C for 20 minutes a. 2 mol% Ca; b. 4 mol% Ca; c. 6 mol% Ca; d. 8 mol% Ca; e. 10 mol% Ca.
Fig. 6: FTIR pattern of Conventional Sintered Ca- Zr02 system at 1400°C for 04 Hours; a. 6 mol% Ca; b. 8 mol% Ca; c. 10 mol% Ca.
Fig. 7: Relationship between the monochnic phase %age and composition of CaO in Microwave and Conventional sintering of Calcia-Zirconia system.
Fig. 8: Relationship between tetragonality (c/a) ratio and CaO concentration in microwave and conventionally sintered samples.
Fig. 9: Relationship between tetragonality (c/a) ratio and exposure time in microwave Fired samples for 10 mol% Ca at 1400°C
Fig. 10: SEM Micrographs of 10 mol% Ca Microwave Fired at 1400°C for a. 10 min, b. 20 min at X 1500 at 10 µm.
he microwave apparatus of the present invention
Referring to Fig. 1, a kitchen microwave oven was used to fabricate the microwave furnace in accordance with the present invention. . The specification of the microwave oven is a multimode, 900W (RF magnetron output power), 2.45 GHz, (LG MS-285SD) and the dimensions of the inner cavity are 34.4cm x 34.4cm x 22.5cm in volume. To make this kitchen microwave oven suitable for high temperature sintering experiments, following modifications were made:
1. An insulating packet transparent to microwaves was made to fire the work piece .
2. An aluminum plate was placed below the sintering packet to prevent the cavity from being overheated.

3. To control the heating rate and to achieve the required temperature for desired exposure time, a power control system consisting to two variacs was connected to the power supply of the magnetron.
4. To efficiently cool the magnetron and to maintain the cavity at low temperature so as to avoid excess heat transferred from the cavity to the magnetron, a hosepipe of copper was soldered onto the outside surface (under the outer shell) of the top of the cavity for continuous water circulation.
5. A small hole was drilled in the centre of the roof just above the axis of the fabricated furnace for insertion of the thermocouple.
6. A temperature indicator was connected to the S type thermocouple to measure the cavity temperature with an accuracy of ± 1°C.
The packet is made as shown in Fig. 1. It comprises of in essence, an alumina crucible, zirconia cylinder 2 (Zircar Products, Inc. Florida, NY), rods 6, and thermal insulating AL-25/1700 (Zircar Products, Inc. Florida, NY) 5. Zircar alumina insulation type AL-25/1700 insulation 5 is a combination of high purity alumina fibers, refractory fillers and inorganic ceramic binders. The typical chemical composition of the board is 80% AI2O3, 20% Si02, density 0.44 g/cc, modulus of rupture 1.38 Mpa, compressive strength 0.24 Mpa, thermal conductivity 0.27W/m°K at 1650°C. As claimed by the manufacturer, AL-25/1700 offers low thermal conductivity, high temperature stability, good hot strength, dimensional stability and excellent resistance to thermal shock and chemical attack and is not affected by oil or water. It can withstand temperature up to 1700°C (31000F) for continuous use. The zirconia cylinder 2 vertically surrounding the samples 3 functions both as a microwave susceptor as it absorbs and converts microwave to heat, thus preheats the sample if the sample does not absorbs microwaves significantly at low temperatures. As an insulator, it prevents heat of the samples 3 from dissipation. Preheating up to 400°C is necessary in case of zirconia sample because it shows lossy character only after this temperature.
Temperature measurement m microwave sintering heating is one area, which is very critical, and matter of concern for its accuracy and reliability. This is very critical, and matter of concern for its ceramics sintering is usually reported as the lowering of processing temperatures, of at the same temperature but improved properties, while only precise measurement can make the comparison between microwave and conventional processing methods more reliable. In a microwave field, the interference of microwaves with the electromotive force of the thermocouple makes the temperature
readings random or erroneous before the temperature rises to such a level that microwaves are efficiently absorbed by the sample. When properly shielded and grounded and microwave is allowed to interact immediately with a material (PVA), microwave interference can be totally prevented and theremocouples 4 (shown in Fig 1) can provide rehable temperature readings. In an embodiment of the present invention, a platinum shielded S type Pt-10%Rh/Pt thermocouple was used to measure temperature. The thermocouple 4 is fitted in the microwave so that the tip of the thermocouple 4 was 1mm away from the work piece in the sintering packet. The temperature of the samples 3 was measured with S type thermocouple 4 with an accuracy of ± 1°C.
A vertical ball mill was fabricated in the laboratory for milling and mixing the powders at different stages. YSZ balls were used in acetone as grinding medium and milling was done in polythene bottles.
A lubricant, preferably, a lubricant based on stearic acid was developed in the laboratory to reduce the friction between walls of die and powder to have the uniform distribution of pressure during consohdation of powders.
A uniaxial hydraulic press was used to consolidate the powder in the form of cylindrical pellets. The pressure maintained was 312 Mpa. Conventional furnace
A programmable furnace having silicon carbide rods as heating sihcon carbide rods as heating elements was used for the present invention for comparative purposes. The furnace is capable of operating at high temperature up to 1400°C, high heating rate and low thermal inertia. The furnace has the capacity of providing heating rates up to 600°C per hour. The temperature in the conventional sintering was measured with S type Pt-10%Rh/Pt thermocouple. The samples were placed in the alumina crucible, which was in contact with the tip of the thermocouple. The heating and cooling rates can be controlled by programs with desired soaking time. Example: Starting materials
The materials used in the present invention comprised of zirconia (Zr02; AR, Indian Rare Earths, Orissa, Assay 99.7%), calcium carbonate (CaCOs; AR, CDH, asay 99.5%), magnesium oxide (MgO; AR, CDH, assay 98.0%), yttrium oxide (Y2O3; AR, CDH, assay 99.9%), polyvinyl alcohol (CDH cold) and stearic acid (C17H35COOH, AR, CDH) were acquired from commercial vendors. The partially stabilized zirconia
ceramics
0.04, 0.06, 0.08, 0.10) synthesized during the study and thek proper chemical stochiometries are described hereinafter. Sintering Process
Multi pellet runs were conducted in both microwave and conventional sintering experiments. In microwave sintering, the pellets, usually five to six (12.80 mm in diameter and 2.50 mm in thickness stacked one above other were placed in the alumina crucible of the sintering packet. To this layer of pellets poly vinyl alcohol (6.6%) solution is added. Poly vinyl alcohol being lossy having high tangent loss at room temperature interacts with microwave first and gets heated up to its decomposition temperature (400°C). In the course of decomposition it heats the work piece to a temperature where it starts absorbing microwaves and volumetric heating of work piece begins. In conventional sintering the pellets usually six to eight in number were placed in the alumina crucible without any susceptor. Heating rate in microwave was lOO^C per minute and in conventional was 10°C per minute. Since the sintering temperature in both the processing techniques were identical the difference in the sintered samples can be attributed to the microwave effect. The details of the sintering conditions for each material will be given in the respective sections.The precursor of partially stabilized zirconia (PSZ)
(Formula Removed)
where n = 2-x for M = Ca2+ Mg2+ and n = 2-x/2 for M = Y3+ and x= 0.02, 0.04, 0.06, 0.08, 0.10 were prepared by mixed oxide method. Calcium carbonate (CaOs; AR, CDH, assay 99.9%) and zirconia (Zr02) were used for compositions x= 0.02, 0.04, 0.06, 0.08, 0.10. The powders were ball milled in a polythene bottle using zirconia balls and acetone as a grinding medium for 6 hours. The powders of different compositions were mixed with 4% PVA binder and uniaxially pressed at 312 Mpa in a 12.80 mm die of high carbon content steel. The weight of each pellet was kept 1.00 g to have comparison. The pellets were weighed before and after firing to check the weight loss. Initially, the pellets were fired at 1400°C for 20 minutes. The temperature 1400°C was opted because many publications related to partially stabilized zirconia refers temperature 1400 C as a firing temperature in conventional heating. This provided a reference to evaluate/assess the potentiality of microwave firing. The pellets of PSZ of composition Mo.1Zro.9On where n = 1.90 for M = Ca2+, Mg2+ and n = 1.95 for M = Y3+ were fired at 1400 C for 5, 10, 15, 20, 25, 30 minutes. The pellets were fired in microwave radiation at 1000°C, ll000C, 1200°C, 1300°C and 1400°C for 5 minutes to investigate the
minimum temperature of phase transformation. The pellets of composition x= 0.02, 0.04, 0.06, 0.08, 0.10 were fired conventionally at 1400°C was achieved in 3 hours. The phase transformation of each composition fired at various temperatures and times were analyzed by XRD (Philips, PW1710). The quantitative phase transformations were evaluated from XRD [1]. The Scanning Electron Micrograph (JEOL) of pohshed and etched surface of
(Formula Removed)
was taken. The presence of phases were identified by FTIR (Perkins Elmer RDXl) spectroscopy also. Densities of each pellet were measured by Archimedes Principle using distilled water. Hardness was measured on conventional microhardness machine with Vickers diamond indenters. The square pyramidal indenter created smaller, deeper impressions on pohshed selected sintered samples. The polished pellets were electroded with silver paste on both sides and conductivity measurements were taken at room temperature with LCR Bridge Hewlett Packard (HP) 4284 A (20Hz- IMHz) Results and discussion
Crystalline phases of different polymorphs of CSZ in specimens were determined from X-ray diffraction (XRD) patterns. The peaks for monochnic, tetragonal and cubic phases have been identified. Tetragonal and cubic phases were identified from the separation of (400) and (004) diffraction peaks. Lattice parameters were calculated from (400) and (004) peaks of the XRD. The pellet of calcium zirconate (CSZ)
(Formula Removed)

(Table Removed)
were fired under microwave radiation at temperature 1400°C for 20 minutes. Phase transformation in each composition was analyzed by XRD, given in Fig. lA(a-e) and evaluated by disappearance of monoclinic phase and appearance of tetragonal and cubic phase, given in Table I below and Fig. 7: Table 1
The phases formed of the precursor of CaxZr1.x02-x; CSZ; x = 0.02, 0.04, 0.06
and 0.08 were a mixture of monochnic tetragonal cubic as evident in Fig 1 A(e). The
phase transformations were studied for each composition and it was found in CSZ that
the percentage of monoclinic phase is reducing with increase in the concentration of the
dopant. The trend of disappearance of monochnic phase is same in conventional firing
given in Fig.4(a-e) as well as in microwave firing. However, the transformation to
cubic + tetragonal phase is higher for the sample processed in the microwave field than
that of sample fired conventionally. Further by comparing c/a ratio for tetragonahty, it
was observed that the fiiUy stabilized cubic zirconia had formed for x = 0.08 and 0.1 m
microwave processing while cubic phase formation had not occurred in conventional
firing of material as given in Table II below and Fig. 8:
Table II
Relationship between tetragonality (c/a) ratio and CaO concentration in
microwave and conventionally sintered samples

(Table Removed)
The phase transformations in CSZ of composition corresponding to x = 0.1 was
further investigated kinetically. The pellets of this composition were identified by
XRD, given in Fig. 2(a-f). The d- values of (111) peak of XRD of each run were
constant, given in Table III below and Fig 9:
Table-in
Relationship between tetragonality (c/a) ratio and exposure time in microwave sintered samples for 10 mol% Ca at 1400"C

(Table Removed)
The XRD of each run showed the complete transformation was considered to be fully cubic where quantitative contribution of monoclinic phase was less than 5%.
The precursor of composition x = 0.1 was fired at 1000°C, 1100°C, 1200°C,
1300°C and 1400°C for 5 minutes and phase transformation of each run was analyzed
by XRD, given in Fig. 3(a-e). An XRD of CSZ processed at 1000°C given in Fig.3 (a)
showed the mixture of cubic and tetragonal phase, as the contribution due to tetragonal
phase was visible at higher angle (20= 74-76°) corresponding to (400)t and (004)t
peaks. Other XRD patterns, given in Fig.3 (b-e), showed complete transformation of
monoclinic phase to cubic phase in CSZ. . The d-value of (111) peak of cubic phase
remained constant in XRD, given in Table IV below, of CSZ fired at temperatures
1100°C, 1200°C, 13000C and 1400°C for 5 minutes:
Table-IV
Relationship between tetragonality (c/a) ratio and temperature of samples fixed in microwave for 5 minutes of composition corresponding to 10 mol% Ca concentration.

(Table Removed)
The precursor of CSZ of composition x = 0.02, 0.04, 0.06, 0.08, 0.10 fired at 1400°C for 20 minutes in microwave were analyzed by IR also, given in Fig.5 (a-e). Six bands in the region 514-748 cm-1 originated from internal vibrations of ZrO2 molecule in the unit cell with a specific absorption band at 740 cm"' for monoclinic phase. Peaks due to translations and vibrations appear below 500 cm-1 which could not be characterized due to limitations of the instrument. The IR peak at 740cm' is visible in Fig.5 (a-c) compositions corresponding to x = 0.02, 0.04 and 0.06 indicating the presence of monolinic phase. However, in the compositions corresponding to x = 0.08
and 0.10, the peak at 740cm-1 disappears. The absorption peaks between 1600-1300cm"\ for the composition x = 0.08, may be due to the presence of mixture of tetragonal and cubic phase. A broad peak for composition x = 0.10 is due to the formation of fluorite type ZrO.9CaO.103 which confirmed the symmetrical Zr-0 bonds of cubic structure. An absorption peak at 3200cm"' appeared in the composition x = 0.08 and 0.10 which could not be mterpreted. The IR absorption peaks of the conventionally fired CSZ for composition x = 0.06, 0.08, 0.10 were also analyzed for comparison, given in Fig.6 (a-c). The characteristic IR absorption peak at 740 cm' for monoclinic phase persisted for all the compositions and a peak at 3200cm"' is also present in each sample.
The densities have been expressed in Table V, VI and VII below:
Table-V Density of CS2 for different dopant concentrations

Table-VI Densities of CS2 for different sintering time

(Table Removed)
Table-VII Densities of CS2 for different sintering temperatures

(Table Removed)
It was found that the densities of the pellets of composition x=0.10 increased with increase in soaking time and were maximum (5.79 gcm-3) for the soaking time of 20 minutes in microwave firing at 1400°C. The densities decreased for soaking times 25 and 30 minutes. It may be, due to the increase in soak time, grain size of CSZ would have increased beyond a limit and the cubic phase might have started to transform into the monochnic phase as reported in Y203-Zr02 system [22-24].
Scanning Electron Micrographs of CSZ x = 0.10 processed in microwave radiation at 1400°C for 10 minutes and 20 minutes have been taken. The pohshed surface of the pellet was etched with a mixture of HNO3, HCI and HF. The surface was gold plated and then SEM was taken. The SEM depicted the formation of single phase for both the time given in Fig. 10 (a) and Fig. 10 (b), however the grain size was larger in the sample processed for 20 minutes compared to that of 10 minutes at 1500 magnification at the scale of 10µm.
From the applicants' lab report it was observed that formation of cubic phase in the microwave processing is dependent upon the size of the dopant, as for 10% Y3+ substitution in zirconia, the stabilized zirconia was a mixture of cubic and tetragonal phase whereas 10 mol% Mg2+ doped zirconia system was a mixture of cubic, tetragonal and monoclinic phases with a contribution of monoclinic phase as high as 30%. It has also been reported that slow sintering rate in conventional firing is due to the low mobility of cations but the phase transformation in microwave firing at a temperature as low as 1 lOO0C may be due to the increase in the cation mobility under the influence of the electric field. It was reported [1], during the stabilization of cubic phase, the reaction of Zr02 and CaO occurs to form the compound CaZrOs first and then the
CaZrO3 reacts with excess Zr02 to form cubic Zr02. However, the formation of CaZrO3 has not taken place at temperature as low as l00000C.

We claim:
1. A method for the manufacture of a fully stabilzed cubic zirconia of the formula ZrxCayOz Zro.9Cao.101.9 wherein x, y and z have a value in the range of 0.02, to 0.1, which comprises preparing a work piece consisting of a ceramic precursor comprising mixture of monoclinic zirconia and calcium carbonate in the form of a pellet, layering or covering said pellet with a polymeric susceptor of the kind such as herein described, subjecting said work piece to microwave energy at a temperature in the range of 1000°C to 1400°C to obtain said fully stabilized cubic Zirconia.
2. A method as claimed in claim 1 wherein said fully stabilzed cubic zirconia is of the formula Zro.9Cao.1Oi.9.
3. A method as claimed in claim 1 or 2 wherein said fully stabilzed cubic zirconia has a (Ca2+) concentration of not more than 10 mol %.
4. A method as claimed in any preceding claim wherein said work piece is
subjected to microwave energy at a temperature of about 1100°C.
5. A method as claimed in any preceding claim wherein said work piece is in the form of cylindrical pellet.
6. A method as claimed in any preceding claim wherein said work piece is subjected to microwave energy for up to four hours.
7. A method as claimed in claim 6 wherein said work piece is subjected to microwave energy for about 5 minutes.
8. A method as claimed in any preceding claim wherein said susceptor evaporates at a temperature of about 400°C.
9. A method as claimed in claim 8 wherein said susceptor is polyvinyl alcohol.
10. A method for the manufacture of a fully stabilzed cubic zirconia substantially as herein described with reference to the accompanying drawings and as illustrated in the foregoing examples.

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Patent Number

268892

Indian Patent Application Number

1861/DEL/2004

PG Journal Number

39/2015

Publication Date

25-Sep-2015

Grant Date

22-Sep-2015

Date of Filing

28-Oct-2004

Name of Patentee

SHAHEED BHAGAT SINGH COLLEGE

Applicant Address

ENGINEERING AND TECHNOLOGY, FEROZEPUR-152 001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	KANCHAN LATA SINGH	SHAHEED BHAGAT SINGH COLLEGE OF ENGINEERING AND TECHNOLOGY, FEROZEPUR-152 001, INDIA
2	ANIRUDH PRATAP SINGH	SHAHEED BHAGAT SINGH COLLEGE OF ENGINEERING AND TECHNOLOGY, FEROZEPUR-152 001, INDIA
3	NAVDEEP KAUR	SHAHEED BHAGAT SINGH COLLEGE OF ENGINEERING AND TECHNOLOGY, FEROZEPUR-152 001, INDIA

PCT International Classification Number

C01G 25/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA