SINGLE-CRYSTAL PARTIALLY STABILIZED ZIRCONIA AND HAFNIA CERAMIC MATERIALS

Abstract: A method of making a single crystal of partially stabilized zirconium dioxide or hafnium dioxide by: mixing powdered zirconium dioxide or hafnium dioxide with 2 to 7 mole percent of a stabilizing agent, such as an oxide of either a transition metal or a rare earth element; heating the above mixture until it melts; and cooling the mixture by withdrawing it from the heating zone at a rate of 2-30mm. per hour. The resulting crystals comprise a matrix of cubic crystalline materials and numerous minute tetragonal and possibly monoclinic crystalline materials. Such crystals can be created having a flexure strength of approximately 200,000 psi and a fracture toughness of approximately 7,85 Ksc.

Description: SINGLE-CRYSTAL PARTIALLY STABILIZED ZIRCONIA AND HAFNIA CERAMIC MATERIALS Description Technical Field 5 This invention is in the field of ceramics, crystallography and chemistry. Background Zirconium (Zr) is an element with an atomic number of 40, an atomic weight of 91.22, and a valence 10 of 4. Hafnium (Hf) has an atomic number of 72, an atomic weight of 178.49, and a valence of 4. The pre¬ dominant oxidized forms are commonly ' referred to as zirconia (ZrO~) and hafnia (HfO_) . Zirconia and hafnia ea h have three principle 15 crystal structures: cubic, tetragonal, and monoclinic. As zirconia is cooled after being heated to its molten state in the absence of stabilizing agents, it progresses through all three crystal structures. In the absence of stabilizing agents, the cubic 20 structure is the most stable, and the monoclinic structure is the least stable. At low temperatures, these relative stabilities are reversed. Therefore, during cooling, zirconia normally progresses from the cubic structure, to the tetragonal structure, 25 to the monoclinic structure. Cubic zirconia can be stabilized by the addi¬ tion of sufficient quantities of one or more sta¬ bilizing agents. For example, U. S. patent 4,153,469 (Alexandrov et al., 1979) discloses that 10 to 30. 30 mole percent of yttrium oxide (Y„0-,, commonly called yttria) stabilizes zirconia in the cubic crystal configuration. Such crystals are transparent and have a high optical quality, and are used as O PΓ artificial precious stones in jewelry, and as laser elements. Oxides of other elements may be added to obtain colored zirconia crystals. ^ Partially stabilized zirconia (PSZ) does not have the desirable transparent optical properties that fully stabilized cubic zirconia possesses. However, PSZ possesses certain other properties that are of interest in the ceramic field. "Partially stabilized" is a functional term. if less than an ascertainable amount of stabilizing agent is added to molten zirconia, then not all of the zirconia will retain the cubic crystal configu¬ ration when it is cooled to room temperature. If this is the case, several things can happen. It is possible for localized areas of cubic, tetragonal and monoclinic crystals to be interspersed in a PSZ crystal. One possible way this can occur is for tetragonal particles to exist in a matrix of cubic zirconia. See D. L. Porter et al., "Mechan- isms of Toughening Partially Stabilized Zirconia (PSZ) ", J. Am . Cera . Soc, 60, No.3-4, pp 183-184 (1977) . as are nonmetallic, inorganic, mat rials that are most commonly used for structural purposes. The structural properties of ceramics, especially at high temperatures, are of great im¬ portance. Two common indices of these properties are: 1. Tensile strength, which measures how much force must be applied to pull apart a ceramic piece with a known cross-sectional area. This parameter can be expressed in OMP terms of pounds per square inch (psi) or pascals (Pa) . A pascal is equal to 1 newton of force applied to 1 square meter; a megapascal (MPa) is equal to 1 million pascals. One MPa is equal to approximately 145 psi. Tensile strength is often approxi¬ mated by measuring flexure strength. In¬ stead of pulling a specimen apart along one axis (which would determine tensile strength) , a specimen is bent until it breaks, and the maximum tensile force (which occurs along one edge of the specimen) is calculated. Flexure strength is measured in psi or MPa. It tends to be somewhat higher than tensile strength, since a flaw in the interior of a speci¬ men that might cause a tensile break might not cause a flexure break. 2. Fracture toughness, usually ex¬ pressed as K-_, Fracture toughness is usually measured by creating a flaw of a known size in the specimen being studied, then breaking the specimen under controlled loading conditions using, for example, a double cantilever beam (DCB) technique. The force required to break the specimen is then divided by the cross-sectional area of the break times the square root of the length of the flaw. K 1C is therefore expressed in 3/2 terms of newtons per meter or m pascalιs ,t-i•mes me * t.er1 2- Porter et al., cited above, recognized that heat-treated PSZ had a higher degree of fracture toughness than fully stabilized cubic zirconia. The maximum toughness they observed in PSZ was ιr of approximately 6 MN/m 3'/2, compared to the tough- 3/2 ness of cubic zirconia of 2.8 MN/m . Those researchers were studying the toughness of poly- crystalline PSZ that was formed by conventional pressing and sintering techniques. In this form, tetragonal crystallite inclusions formed by precipita¬ tion (herein referred to as crystallites; sometimes referred to as precipitates) are believed to exist along two or more major axes within a crystal grain of cubic zirconia. The alignment of the tetragonal crystallites and the cubic matrix in adjacent but distinct grains often is skewed, creating a boundary or a face between the grains. These faces between the grains tend to have substantially less tensile strength than the cross section of a grain. Therefore, when subjected to stress, grain boundaries in poly- crystalline PSZ can be sources oi fra cures, thereby limiting the strength and toughne--"; of PSZ. In addition, grain boundaries in polycrystalline PSZ impede (1) the ionic conductivity cf zirconia, thereby limiting a number of valuable uses of zirconia, such as detectors for analyzing the contents of gases, and (2) the electromagnetic transmissibility of zir¬ conia, thereby limiting the use of zirconia in optical and radio applications that require high strength and toughness. Disclosure of the Invention The Applicants have discovered that single crystals of partially stabilized zirconia (PSZ) possess surprisingly superior ceramic properties. 5 These large single crystals are believed to comprise a dispersion of numerous tetragonal or monoclinic crystallites within a matrix of cubic crystalline material. These single crystals possess tensile strength and fracture toughness charactertistics 10 that greatly exceed the tensile strength and frac¬ ture toughness of any practical ceramic material ever discovered prior to this invention. The experimental results obtained thus far by the Applicants indicate that large single crystals 15 can also be formed of partially stabilized hafnium dioxide, and that such crystals exhibit superior ceramic properties when compared to polycrystalline partially stabilized hafnium dioxide, or to fully stabilized cubic hafnium dioxide. 20 The results obtained to date by the Applicants also indicate that large single crystals of PSZ or PSH can be partially stabilized by the oxides of numerous transition and rare earth elements, in¬ cluding yttrium, calcium, magnesium, scandium, samarium, 25 gadolinium, dysprosium, ytterbium, lutecium, cerium, praseodymium, neodymium, europium, holmium, erbium, thulium, or turbium. The Applicants have invented a method of cre¬ ating such single crystals that are large enough 30 for ceramic uses. Zirconia and hafnia are partially stabilized by adding a predetermined quantity of stabilizing agent to a predetermined quantity of zir¬ conia or hafnia. This normally is accomplished by mixing the stabilizing agent with the zirconia or haf ¬ nia while both substances comprise fine powders at room temperature. The mixture is then heated to a melting temperature (normally in excess of 2500°C) . This can be accomplished by inductive high-frequency radio waves. The powder is placed in a water-cooled vessel prior to heating. The cooling surfaces of the vessel prevent the powder that touches the cooling surfaces from becoming molten. This forms a shell (often called a skull) of sintered material between the cooling surfaces and the molten zirconia or hafnia; this avoids problems that can arise when extremely hot molten substances " come in contact with solid surfaces. After heating the zirconia or hafnia mixture at the proper temperature for an appropriate period of time, the molten mixture is allowed to cool slowly, to promote the formation of a regular crystalline. structure. This can be accomplished by slowly lower¬ ing the vessel out of the heating field, and reduc¬ ing or eliminating the radio frequency power at an appropriate time. The resulting material comprises a large (from approximately 3 inches to over 1 foot in diameter) block of crystalline material surrounded by a sintered shell. The shell is removed by mechani¬ cal means. The resultant crystalline body typically comprises several relatively small (largest dimension approximately 1/4 inch to 1 inch) crystals near the bottom of the block of material, interspersed with larger crystals that may exceed 1 inch in diameter and several inches in length. Although these crystals do not adhere tightly to each other, each crystal has a single consistent composition of tetragonal and possibly monoclinic crystallites within a matrix of cubic crystalline structure. Each such crystal 5 can be referred to as a single grain. These crystals may be machine d into desirable configurations using diamond-edged cutting instru¬ ments and other conventional techniques. In addi¬ tion, numerous crystals may be plastic-deformed into 10 desirable configurations by press-forging at elevated temperatures, although problems involving oxygen loss may require special techniques. Single-crystal PSZ has -ionic conductivity and electromagnetic transmissibility properties that are 15 superior to polycrystalline PSZ. These properties al¬ low for improvements in the use of PSZ for purposes that involve ionic conductivity or electromagnetic transmissibility. Description of Figures Figure 1 is a cross section of an apparatus used to heat zirconia or hafnia mixed with a stabilizing agent to the molten state. Figure 2 is a cross section of zirconia or hafnia mixture being withdrawn from the heating zone. Figure 3 is a cross section of zirconia or hafnia mixture after it has cooled into a crystalline structure. Figure 4 is a graph that indicates the flexure strength and fracture toughness of several partially stabilized zirconia crystals. Figure 5 is a graph that indicates the flexure strength of various ceramic materials as a function of temperature. Best Mode of Carrying Out the Invention In one preferred embodiment of this invention, 450 grams of Y 2 °3 (yttria) powder were dry-mixed with 8,550 grams of ZrO (zirconia) powder, to give 5 , a mixture containing 5 % yttria by weight. The powders were mixed by placing both in a polyethylene jar, and roll-milling for several hours. Alterna¬ tively, V-blending or other conventional mixing means may be used. The mixture was then loaded into a 10 6 inch diameter skull-melting furnace, which has a standard melt capacity of 9 kilograms of zirconia. The powder rests upon a water-cooled plate, and is surrounded by vertical copper tubes which contain circulating cooled water. There is no lid on this 15 furnace, so the top of the powder is exposed to the air. The loaded furnace was then placed in the middle of. a radio frequency generating coil, operating at up to 50 kilowatts of output at 2.5 to 3.5 megahertz. The skull container is first charged with 3,000 20 grams of mixed powder, and a 30 gram cluster of zir¬ conium metal. Since the mixed powder at room tempera¬ ture does not absorb the energy of the high-frequency radio waves, the zirconium metal is added to begin the heating process. The metal chips heat rapidly 25 and cause the surrounding powder to be heated to a temperature at which they begin to absorb the high- frequency waves directly. After approximately 10 minutes, the interior of the 3030 gram initial charge is molten. It is contained within a sintered shell 30 of unmelted powder, which is being cooled by the ■ water in the copper tubes. This sintered shell (often called a skull) prevents the molten zirconia from coming into direct contact with the copper tubes. The remaining 6 kilograms of powder mixture are 35 added to the skull container over a period of ap¬ proximately one hour. As additional feed material is added, the radio frequency input power is slowly increased to approximately 35 kilowatts. The molten charge is allowed to remain stationary for a period, while convection currents mix the zirconia and yttria thoroughly. The skull container is then mechanically lowered at a fixed rate of about 1.1 centimeter per hour. This allows for the bottom portion of the skull container to leave the heating zone and begin the cooling process, allowing crystals to begin forming near the bottom of the skull. Simultaneously with the lowering motion, the skull is rotated with a bi- direction oscillatory motion through an angle of about 45 degrees at a frequency of about 10 times per minute. After the skull container has been lowered approximately 7.7 centimeters (which takes about seven hours) , the radio frequency power is shut off, and the crystals are allowed to cool to room tempera¬ ture before removal. The cooled crystals are sub¬ sequently removed from the skull container. The sintered shell surrounding the crystals is removed, and the crystal grains are separated carefully. Several grains were subsequently analyzed to deter¬ mine their flexure strength, fracture toughness, and other properties, as described in Example 5-7. This process is further described by reference to Figures 1 through 3. As shown in Figure 1, powder mixture 2 is placed in skull container 4. The loaded skull container is then placed within circular high frequency induction heating coil 6. Cooling water enters water inlet 8 r and circulates within vertical tubes 10 and container base 12, before exiting through water outlet 14. When heated to the melting point, the interior 16 of the powder mixture becomes molten. This molten region is surrounded by sintered shell 18, which is prevented from melting because it is in contact with water-cooled tubes 10 and base 12. An un- 5 melted porous crust 20 typically forms above the surface of the melt. Figure 1 indicates the positioning of the skull container 4 and the mixed powder charge 2 within the region that is heated by induction coils 6. In 10 this position, all of the powder will become molten except for sintered shell 18 and crust 20. Figure 2 indicates that the skull container 4 is being slowly lowered by mechanical means. The bottom of molten region 16 leaves the heated region and begins to 15 form crystals 24 upon the base of the centered skull 18. These crystals initially comprise the cubic crystalline structure, which is the most stable crys¬ talline form at temperatures near the melting point. However, as these crystals cool further, a dispersion 20 of numerous minute crystallites, in the form of tetragonal and possibly monoclinic crystallites, forms within the matrix of the partially stabilized cubic zirconia. Figure 3 indicates that skull container 4 has 25 been mechanically lowered by mechanical means 26 until crystals 24 have left the region heated by induction coils 6. The crystal region 24 is comprised of numerous individual grains, including grains 28, 30, 32, 34, and 36. Within each of these grains, 30 the tetragonal crystallites are arranged on a regular OMP basis. Each of these grains exhibits extremely high flexure strength and fracture toughness. However, the boundary or interface between any two grains is relatively weak, and each grain may be separated easily from the other grains. Table 1 and Figures 4 and 5 contain data com¬ paring the flexure strength and fracture toughness of the single-crystal PSZ with several other ceramic materials. PSZ 1027 is a commercially available form of zirconia, partially stabilized with about 3.5 weight percent MgO, with a relatively large grain structure. Zyttrite is a form of zirconia, fully stabilized with from 12 to 20 weight percent of yttria, with an intermediate grain size, that is used as a reference standard. Both are polycrystal- line substances, formed by conventional pressing and sintering techniques. TABLE 1 Comparison of Single-Crystal PSZ with Other Ceramic Materials (Average values and ranges) Material Flexural Flexural Fracture strength strength toughness (MPa) (Kpsi) (κ lc ) Room temperatures Single-crystal PSZ 1050-2100 150-300 4-8 Fully stabilized Cubic Zirconia Single crystal 300-350 40-50 2-2.8 Polycrystalline 200 30 •— 2 Polycrystalline PSZ PSZ 1027 (large grain) 350-630 50-90 4-8 Zyttrite (inter¬ mediate grain) 700-1050 100-150 5-8 Single crystal AI2O3 (sapphire) 350-550 50-80 2 Polycrystalline AI2O3 350-700 50-100 4 Polycrystalline hot-pressed Si3N4 840 120 4-7 Elevated Temperatures Single-crystal PSZ at 1500°C 630-770 90-110 4-8 Cubic zirconiuir 1 at 1500°C 210-350 30-50 . 2 Si 3 N 4 at 1100°C 490-630 70-90 4-7 at 1500°C 70-140 10-20 EXAMPLES Example 1: Preparation of Powder Mixture • • • ■ Zirconia (ZrO„) powder was obtained from Magnesium Elektron, with a purity of 99%. It has an average particle size of approximately 10-16 microns, and contained approximately 2% Hf0 2 . Yttria (^ 2 °3^ powder was obtained from Megon (purity 99.99%). It had an average particle size of approximately 10- 16 microns. Carefully weighed quantities of each powder were mixed by placing both in a polyethylene jar, and rolling the jar on mixing rollers for approximately 12 hours. Approximately 3,000 grams of the mixed powder was placed in a skull container. The skull container comprised a 6 inch diameter water-cooled copper base plate, surrounded by vertical copper tubes at the perimeter of the base plate. Each copper tube contained an inner tube. Cooling water was circulated up through the annulus of each tube, and down through the interior tube. The loaded skull container was then placed within a C-rcular induction heating coil. The heating coil was powered by a 50 kilowatt radio frequency gener¬ ator, v/hich operated at 2.5 to 3.5 megahertz. Example 2: ' Heating the Zirconia Mixture A skull container, loaded with a charge of zirconia powder mixed with yttria powder, was placed within a heating-coil, as described in Example 1. When the generator power is turned on, the radio waves which are concentrated within the coil excite the zirconia and yttria molecules causing them to become heated. However, since the resistance of zirconia powder at room temperature is too high to allow coupling at the frequency used, about 30 grams of zirconium metal (Ventron sponge, purity 99.5%) was placed in a cluster on the surface of the powder. The metal chips heat rapidly and cause the surrounding powder to be preheated to a temperature high enough for direct induction heating. An expanding zone of powder becomes molten, until the entire powder charge becomes molten except for a sintered skull surrounding the molten region. This skull is pre¬ 10 vented from becoming molten by being in contact with the cooled base and vertical tubes. In addition, a porous crust may form on the top surface of the mol¬ ten material, cooled by exposure to the air. A pocket of air may be formed beneath this porous 15 crust. The remainder of the mixed powder is then added to the skull container in small increments over a period of approximately one hour. As the amount of material in the skull container increases, the 20 heating input power is also increased. When the 9 kilogram charge is contained in the skull, the applied heating power is approximately 35 kilowatts. After all of the powder is added to the melt, the heating continues for a period of approximately 25 ιo to 20 minutes to allow the molten substance to become thoroughly mixed by convection currents. Example 3: Controlled Cooling and Crystal Formation After the molten mixture described in Example 2 is allowed to stand for an appropriate time, the 30 skull container is mechanically lowered at a fixed rate of 1.1 centimeter per hour. Since the induction heating occurs only within a certain region, this removes the bottom of the skull out of the heated area, allowing the molten mixture on the bottom to ' O PI begin cooling and crystallizing. Simultaneously with the withdrawal motion, the skull is also rotated about its axis with a bi-directional oscil¬ latory motion through an angle of 45° at a fre- quency of 10 times per minute. During the initial stage of crystal formation, it is believed that the partially stabilized zir¬ conia adopts a cubic crystalline configuration, which is the most stable crystalline configuration at temperatures near the melting point. However, as the crystals are allowed to cool further, it is believed that numerous crystallites, comprising ■ tetragonal and possibly monoclinic crystallites, form within the matrix of cubic zirconia. During the lowering and cooling, operation, the heating power input level, frequency and coupling efficiency are constantly monitored. When the skull container is lowered until the molten/crystalline region is no longer in the region of heating, the heating input power is shut off and the charge is allowed to cool to room temperature before removal. Example 4: Removal " and Grain Separation The crystals that were formed as άescribed in Example 3 were allowed to cool to re temperature. The entire charge was then removed from the skull container by raising the base plate in relation to the vertical cooling tubes. The sintered shell was removed from the crystals. The remaining crystal¬ line material was in a configuration indicated- y grains 28 through 36 in Figure 3. Each grain com¬ prised a matrix of cubic zirconia interspersed with minute tetragonal and possibly monoclinic crystallites that were in a consistent pattern throughout that grain. Example 5: Crystallographic Analysis Crystals with 12 to 20 per cent by weight of yttria were clear or transparent. This indicated that such crystals were fully stabilized in the cύbic crystalline configuration. Crystals with 8% by weight of yttria were cloudy, and crystals with 4% by weight yttria were opaque white. This indicated that the number of minute tetragonal and possibly monoclinic crystallites increases with decreasing yttria content. Examination under light microscope, and x-ray diffrac¬ tion analysis confirmed this correlation. Laue back reflection analysis typically showed a [110] orienta¬ tion along the length of the columnar crystals for all crystal compositions. Crystals with less than 8% by weight yttria contains an additional and distinct stereographic projection with a [100] orientation, indicating a greater percentage of tetragonal crystal¬ lites with a regular orientation within the cubic matrix. Example 6: Determination of Fracture Toughness Fracture toughness, commonly expressed as K-. , was determined by two techniques: indentation using a pyramidal diamond (described by A. G. Evans et al, "Fracture Toughness Determinations by Indenta¬ tion," J. Amer. Ceramics Soc. 59, Nos.7-8, pp 371-372 (1976) ) ; and double cantilevered beam analysis (S. W. Freiman et al, "Crack Propagation Studies in Brittle Materials," J. Mat. Sci. _8_, No. 11, pp. 1527-1533 (1973) . Typical specimen dimensions for the DCB analysis were 1x5x12 mm with a center groove 0.3 OMP mm wide and 0.6 u deep, down the center of one side of the specimen. Both of these tests indicated that K. increased from about 1.7 MN/m 3/2 for cubic zir- 3/2 conia with 20% by weight yttria, to 7.85 MN/m at 4% by weight yttria. Additional data are contained in Table 1 and Figures 4 and 5. Example 7: Determination of Tensile Strength 3-point flexure tests (0.9 centimeter span; 1 mm/min crosshead speed) were conducted on bars that were 0.22 by 0.23 cm in crossection, cut parallel with the crystal length and ground lengthwise. The -tensile strength of the cubic zirconia was approx¬ imately 210 MPa for the 20 and 12 per cent by weight yttria crystals. The tensile strength of 8% by weight crystals increased to approximately 520 MPa, and the tensile strength of 6 and 4 percent by weight yttria crystals increased to approximately 1,000 MPa. The coefficients of variation for all measurements were about 10%. Additional data are contained in . Table 1 and Figures 4 and 5. OMP Industrial Applicability The invention described herein has industrial applicability in the manufacture and use of ceramic materials with superior tensile strength and fracture 5 toughness. Equivalents Those skilled in the art will recognize or be able to determine using no more than routine experi¬ mentation, many equivalents to the specific pro- 10 cedures described herein. Such equivalents are considered to be within the scope of this invention and are intended to be covered by the following claims.

Claims: Claims A ceramic material comprising zirconium dioxide oir hafnium dioxide, partially stabilized by a sufficient quantity of stabilizing agent to cause said ceramic material to crystallize in single crystals comprising a dispersion of numerous tetragonal or monoclinic crystallites within a matrix of cubic crystalline material, whereby said crystallites significantly enhance the flexure strength and fracture toughness of said ceramic material. A ceramic material comprising zirconium dioxide or hafnium dioxide, partially stabilized by a sufficient quantity of stabilizing agent to en¬ hance the flexure strength and fracture toughness of said ceramic material. A ceramic material comprising zirconium dioxide or hafr-ium dioxide, partially stabilized by a stabilizing agent, said ceramic material com¬ e fracture A ceramic material comprising zirconium dioxide or hafnium dioxide, partially stabilized by a stabilizing agent, said ceramic material com¬ prising single crystals that have flexure strength in excess of 1000 MPa. 5. A ceramic material comprising a single crystal made of zirconium dioxide or hafnium dioxide, partially stabilized by a stabilizing agent. P 6. A single-crystal ceramic material comprising from about 93 to about 98 mole percent of zirconium dioxide or hafnium dioxide, partially stabilized by about 2 to about 7 mole percent of 5 a stabilizing agent. 7. A single-crystal ceramic material comprising from about 93 to about 98 mole percent of zirconium dioxide or hafnium dioxide, partially stabilized by about 2 to about 7 mole percent 10 of a stabilizing agent, whereby said stabilizing agent significantly enhances the flexure strength and fracture toughness of said ceramic material. 8. A composition of Claims 1, 2, 3, 4 , 5, 6 or 7 wherein said stabilizing agent is an oxide of 15 an element selected from the following group: yttrium, calcium, scandium, samarium, gadolinium, dysprosium, ytterbium, lutecium, cerium, praseodymium, neodymium, europium, holmium, erbium, thulium, turbium , magnesium, or titanium. 20 9. A composition of Claims 1, 2, 3, 4, 5, 6 or 7 wherein said stabilizing agent comprises an oxide of a transition metal or an oxide of a rare earth element. 10. A composition of Claims 1, 2, 3, 4, or 5 25 wherein said ceramic material is comprised of about 93 to about 98 mole percent of zirconium dioxide or hafnium dioxide and about 2 to about 7 mole percent of a stabilizing agent. 11. A method of creating a ceramic material com¬ prising a single-crystal of partially stabilized zirconium dioxide or hafnium dioxide with en¬ hanced tensile and flexure strength and fracture 5 toughness, comprising the following steps: (a) Thoroughly mixing powdered zir¬ conium dioxide or hafnium dioxide with a sufficient quantity of pow¬ dered stabilizing agent to comprise 10 about 2 to about 7 mole percent of stabilizing agent; (b) heating said mixture to a tempera¬ ture sufficient to melt said mixture; (c) cooling said molten mixture by with- - j e drawing said mixture from the heating zone at a rate of from 2 to 30 mm per hour. 12. A method of Claim 11 wherein said stabilizing agent is an oxide of an element selected from the fol- 20 lowing group: yttrium, calcium, scandium- samarium, gadolinium, dysprosium, ytterb * *"_., lutecium, cerium, praseodymium, neodymiuir, euvopium, holmium, « erbium, thulium, turbium, agnes" ur , or titanium. 13. An improvement of Claim 11 wherein said stabilizing 25 agent comprises an oxide of a transition metal or an oxide of a rare earth element. 14. A ceramic material created by the method of Claim 11. OMPI 15. An improvement of Claim 11 wherein said ceramic material is machined to convert it into a de ¬ sired shape. 16. An improvement of Claim 11 wherein one or more 5 crystals of said ceramic material are press- forged at elevated temperatures to convert said crystals into a desired shape. 17. A composition of matter comprising zirconium dioxide or hafnium dioxide, partially stabilized 10 by a sufficient quantity of stabilizing agent to cause said zirconium dioxide or hafnium diox¬ ide ' to crystallize in single crystal, whereby the absence of numerous crystal boundaries in said crystal substantially enhances the ionic 15 conductivity of said crystal in comparison with polycrystalline partially stabilized zirconium dioxide or hafnium dioxide. 18. In the use of zirconium dioxide or hafnium dioxide for uses involving the property of ionic "20 conductivity, the improvement of using single crystals of partially stabilized zirconium dioxide or hafnium dioxide. 19. A composition of matter comprising zirconium dioxide or hafnium dioxide, partially stabilized 25 by a sufficient quantity of stabilizing agent to cause said zirconium dioxide or hafnium diox¬ ide to crystallize in single crystal, whereby the ahsence of numerous crystal boundaries in said crystal substantially enhances the electro¬ magnetic transmissibility of said crystal in comparison with polycrystalline partially stabilized zirconium dioxide or hafnium dioxide. 20. In the use of zirconium dioxide or hafnium dioxide for uses involving the property of electromagnetic transmissibility, the improve- ment of using- single crystals of partially stabilized zirconium dioxide or hafnium dioxide.

Inventors: MENASHI WILSON P, RICE ROY W, WENCKUS JOSEPH F
Applicants: MENASHI WILSON P, RICE ROY W, WENCKUS JOSEPH F
Application year: 1982
Main classification: C30B11
IPC codes: C30B11