WO1997023429A1 - Modified sintered material - Google Patents

Modified sintered material Download PDF

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Publication number
WO1997023429A1
WO1997023429A1 PCT/GB1996/003150 GB9603150W WO9723429A1 WO 1997023429 A1 WO1997023429 A1 WO 1997023429A1 GB 9603150 W GB9603150 W GB 9603150W WO 9723429 A1 WO9723429 A1 WO 9723429A1
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Prior art keywords
sintered
composition
alumina
dielectric material
temperature
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Application number
PCT/GB1996/003150
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French (fr)
Inventor
Neil Mcneil Alford
Stuart James Penn
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South Bank University Enterprises Limited
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Priority to GB9815549A priority Critical patent/GB2324082B/en
Application filed by South Bank University Enterprises Limited filed Critical South Bank University Enterprises Limited
Priority to AU11639/97A priority patent/AU1163997A/en
Publication of WO1997023429A1 publication Critical patent/WO1997023429A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G4/00—Fixed capacitors; Processes of their manufacture
    • H01G4/002—Details
    • H01G4/018—Dielectrics
    • H01G4/06—Solid dielectrics
    • H01G4/08—Inorganic dielectrics
    • H01G4/12—Ceramic dielectrics
    • H01G4/1209—Ceramic dielectrics characterised by the ceramic dielectric material
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
    • C04B35/111—Fine ceramics
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
    • H01B3/12—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances ceramics

Definitions

  • This invention relates to the production of low dielectric loss ceramic materials, particularly ceramic materials useful in dielectric resonators.
  • technology dielectric resonators DRs
  • DRs technology dielectric resonators
  • Q resonator quality factors
  • the term 'ceramic' means any solid inorganic particulate material, the particles of which can be caused to sinter together by the application of heat.
  • ceramic has been used also to describe single crystals of inorganic materials such as alumina, titania, etc.
  • Low dielectric loss materials are highly desirable in the area of communications over a wide frequency range.
  • resonators using dielectric sintered ceramics may be used in base stations required for mobile communications
  • the materials used are often complex mixtures of elements
  • One ofthe earliest resonator materials was Barium Titanate (BaTiO ⁇ or BaTi ⁇ Og see, for example, T Negas et al American Ceramic Society Bulletin, vol 72, pp 80-89 1993)
  • the dielectric loss of a material is referred to as the tan delta and the inverse of this quantity is called the Q (Quality Factor)
  • the Q factor of a resonator is determined by choosing a resonance and then dividing the resonant frequency by the band width 3dB below the peak
  • the losses in ceramic materials may be associated with molecules or defects which can be spatially oriented (Debye loss), due to the inertia of free charges, e g electrons in a metal or resonant absorption at certain frequencies It is considered that extrinsic factors such as impurities and e g oxygen vacancy concentration as well as microstructure are of overriding importance
  • Single crystals or 'perfect' crystals have a lower loss than corresponding poly-crystalline materials
  • the difference between a 'perfect' single crystal and a polycrystalline ceramic are thought to be due to the huge differences in microstructure and perfection between the two and are clear indicators why it is considered impossible to achieve a dielectric loss approaching that of single crystal counterparts in sintered materials
  • a single crystal is made from a melt
  • the melting temperatures of these crystals is extremely high
  • the melting point of alumina is 2072C, of magnesia 2852C, of zirconia 2700C, of yttria 24 IOC and titania 1850C
  • the particulate ceramic material can be shaped in a variety of ways, for example, by uniaxial powder pressing, by isostatic pressing, by slip-casting or by polymer processing and extrusion
  • the resultant shape is then sintered at high temperature and this is associated with a shrinkage and a decrease in the volume ofthe body
  • the sintering step can take place in air or in special atmospheres be they oxidising, reducing or inert
  • dielectric ceramics have dielectric loss much higher than single crystals
  • Single crystal materials can exhibit very low loss and this is usually attributed to the absence of grain boundaries and the greater perfection in their structure
  • the problem with single crystals is that they are time consuming to manufacture and they are extremely expensive
  • a single crystal of alumina in cylindrical form is around 10,000 times more expensive than an identically shaped sintered alumina
  • a sintered material comprising a major part of alumina and a minor part of metal or semi-metal oxide
  • the metal or semi-metal oxide, which forms the minor part of the materials of the invention, are preferably oxides of elements of Group III and IV of the periodic table such as Ti, Nb, Y and Zr
  • the minor part is preferably present in an amount of less than 5% by weight of the total weight of the composition and, more preferably, less than 2% by weight
  • magnesia may be added to a very pure alumina and this will assist the sintering but will not adversely affect the Q if added in small quantities
  • impurities such as alkali salts (sodium and potassium) and metallic elemental impurities such as iron
  • the invention also comprises a sintered ceramic material comprising an alumina and minor amount of a metal or semi-metal oxide which has a Q value greater than 25,000, more preferably greater than 30,000 and even more preferably greater than 45,000 at 10GHz and at 25°C
  • the aluminas used were commercially available aluminas and the analyses of the powders used in the examples are given in Table 1 with the impurities given in parts per million based on the total weight ofthe sample able 1 Chemical analyses of powders used
  • Examples 1 to 3 are comparative examples
  • Powders A-C inclusive were pressed in a 13 5 mm diameter stainless steel die press at a pressure of 100 MPa.
  • the pressed samples were sintered in air at a temperature of 1550°C for 300 mins
  • the sample density was then measured and the dielectric constant and dielectric loss experiments were carried out using a parallel plate resonator and employing a modified Haaki-Coleman technique described in B W Haki and P.D Coleman 'A dielectric resonator method of measuring inductive capacities in the millimeter range', IFEE Trans Microwave Theory Tech Vol 8, p 402-410 (1960)
  • the dielectric puck is placed not directly onto the lower copper plate but onto a low loss material with a much lower dielectric constant
  • the sample dimensions were approximately 10mm diameter, 4mm thick discs
  • the measurements were made using a Hewlett Packard HP8719C vector network analyser with 1Hz resolution and the TE01 1 mode was examined.
  • Sample A showed a Q of 3,500 while B had a Q factor less than 1000
  • the chemically purer powder C was made into dense discs. Sample C2, was subjected to a sintering temperature of 1600°C for 300 mins.
  • the same alumina powder as used in C was sintered at 1500°C for 300 minutes.
  • Examples 4 to 7 and 10 to 12 are examples of the invention and Examples 8 and 9 are comparative examples.
  • Alumina C was doped with TK ⁇ .
  • Ti ⁇ 2 influences the sintering temperature at which the material achieves high density and for this reason the aluminas doped with Ti ⁇ 2 were sintered at 1500°C.
  • alumina C was also sintered at 1500°C.
  • Ti ⁇ 2 sintered in air to full density displays a very poor Q which was measured at 1,500. This is due to the fact Ti ⁇ 2 is easily reduced. Small deviations from stoichiometric Ti ⁇ 2 causes a random distribution of point defects. As the defect concentration increases, their interaction increases and ordering can occur.
  • alumina C A pure alumina (alumina C) was doped by 0.5% weight of Titanium dioxide powder (Sample name CTO.5) The mixture was sintered at 1500°C as in Example 3 and the Q measured as in Example 1 , and was found to be 47,000
  • a pure alumina (alumina C) was doped with 1% by weight of Ti ⁇ 2 (sample name CTI 0) and sintered at 1500°C, i.e at the same temperature as that used for samples C in Example 3
  • the Q was found to be 35,000.
  • a pure alumina (alumina C) was doped with 5% by weight of Ti0 2 (sample name CT5 0) and sintered at 1500°C, i.e at the same temperature as that used for samples C in Example 3
  • the Q was found to be 12,650
  • a pure alumina (alumina C) was doped with 10% by weight of TiO ⁇ (sample name CT10 0) and sintered at 1500°C, i e at the same temperature as that used for samples C in Example 3 The Q was found to be 7,300
  • a pure Ti02 was sintered to full density in air at 1400°C
  • the purpose of this example is to demonstrate that the Q of Ti0 2 is much lower than the Q of A 1203 and hence demonstrate that it might be expected that any addition of Ti ⁇ 2 to AI2O3 would have the effect of decreasing the Q rather than enhancing the Q
  • a mixtures rule common in the description of dielectrics, it might be expected that at 0 5% Ti ⁇ 2 in AI2O3 the Q should be 33,500 when in fact the measured Q is 47,500
  • Example 10 Example 1 1
  • Example 12 Dopant b 7 0, Y O, ZiO,

Abstract

Low dielectric loss ceramic materials useful in dielectric resonators comprise alumina doped with a minor amount, preferably below 2 % by weight of a metal or semi metal oxide, preferably an oxide of titanium, niobium, yttrium or zirconium. The compositions can be made by sintering the powders together below their melting point and materials with a Q value of greater than 45,000 at 9-10 GHz and at 25 °C, can be obtained.

Description

Modified Sintered Materials
This invention relates to the production of low dielectric loss ceramic materials, particularly ceramic materials useful in dielectric resonators. In current microwave communication, technology dielectric resonators (DRs) are key elements for filters, low phase noise oscillators and frequency standards DRs possess resonator quality factors (Q) comparable to cavity resonators, strong linearity at high power levels, weak temperature coefficients, high mechanical stability and small size.
Ceramic dielectric materials are used to form thermally stable DRs as key components in a number of microwave subsystems which are used in a range of consumer and commercial market products. These products range from Satellite TV receiver modules (frequency converter for Low Noise Broadcast (LNB)), Cellular Telephones, PCN's. (Personal Communication Networks Systems) and VSAT (Very Small Aperture Satellite) systems for commercial application to emerging uses in transportation and automobile projects, such as sensors in traffic management schemes and vehicle anti-collision devices. Dielectric Resonators may be used to determine and stabilise the frequency of a microwave oscillator or as a resonant element in a microwave filter. New systems of satellite TV transmission, based on digital encoding and compression of the video signals, determine the need for improved DR components The availability of advanced materials will also enable necessary advances in the performance of DRs used for other purposes as referred to above.
In this specification, the term 'ceramic' means any solid inorganic particulate material, the particles of which can be caused to sinter together by the application of heat. The term ceramic has been used also to describe single crystals of inorganic materials such as alumina, titania, etc.
Low dielectric loss materials are highly desirable in the area of communications over a wide frequency range. As an example, resonators using dielectric sintered ceramics may be used in base stations required for mobile communications The materials used are often complex mixtures of elements One ofthe earliest resonator materials was Barium Titanate (BaTiO^ or BaTi^Og see, for example, T Negas et al American Ceramic Society Bulletin, vol 72, pp 80-89 1993) The dielectric loss of a material is referred to as the tan delta and the inverse of this quantity is called the Q (Quality Factor) The Q factor of a resonator is determined by choosing a resonance and then dividing the resonant frequency by the band width 3dB below the peak
The losses in ceramic materials may be associated with molecules or defects which can be spatially oriented (Debye loss), due to the inertia of free charges, e g electrons in a metal or resonant absorption at certain frequencies It is considered that extrinsic factors such as impurities and e g oxygen vacancy concentration as well as microstructure are of overriding importance Single crystals or 'perfect' crystals have a lower loss than corresponding poly-crystalline materials The difference between a 'perfect' single crystal and a polycrystalline ceramic are thought to be due to the huge differences in microstructure and perfection between the two and are clear indicators why it is considered impossible to achieve a dielectric loss approaching that of single crystal counterparts in sintered materials
A single crystal is made from a melt The melting temperatures of these crystals is extremely high For example, the melting point of alumina is 2072C, of magnesia 2852C, of zirconia 2700C, of yttria 24 IOC and titania 1850C
The particulate ceramic material can be shaped in a variety of ways, for example, by uniaxial powder pressing, by isostatic pressing, by slip-casting or by polymer processing and extrusion The resultant shape is then sintered at high temperature and this is associated with a shrinkage and a decrease in the volume ofthe body The sintering step can take place in air or in special atmospheres be they oxidising, reducing or inert
Sintering a ceramic involves taking a fine powder of the material, pressing it into the desired shape and then heating it to temperatures less than their melting point (usually about 75% of the melting point) The powders sinter together in an effort to reduce surface energy and this is accomplished by the reduction in surface area until the porosity is reduced substantially or entirely The sintering process involves less expensive capital equipment and is less energy intensive
The major problem with dielectric ceramics is that their dielectric loss is much higher than single crystals Single crystal materials can exhibit very low loss and this is usually attributed to the absence of grain boundaries and the greater perfection in their structure The problem with single crystals is that they are time consuming to manufacture and they are extremely expensive For example, a single crystal of alumina in cylindrical form is around 10,000 times more expensive than an identically shaped sintered alumina
We have now discovered sintered ceramic materials with a low dielectric loss and a method for making them
According to the invention there is provided a sintered material comprising a major part of alumina and a minor part of metal or semi-metal oxide
The metal or semi-metal oxide, which forms the minor part of the materials of the invention, are preferably oxides of elements of Group III and IV of the periodic table such as Ti, Nb, Y and Zr The minor part is preferably present in an amount of less than 5% by weight of the total weight of the composition and, more preferably, less than 2% by weight
The materials ofthe present invention can be made in any conventional way, e g by mixing the powders of alumina and the minor component, for example, of particle size of 0 01 to 2 microns and pressing the mixture into a shape and then heating to a temperature below its melting point, typically 75% of the melting point The powders sinter together until the porosity is substantially or entirely reduced. Preferably the temperature of sintering for powders such as alumina is less than 1600°C and more preferably between 1500°C and 1600°C
It is very surprising that the addition of oxides with a low Q factor to alumina can increase the Q factor of the resulting material very considerably and can approach the value of single crystals It was considered that any material with grain boundaries must inevitably show high dielectric loss The dielectric loss of polycrystalline sintered alumina has been measured by several workers and the results vary widely For example, Ceramic Source, vol 6 1990, American Ceramic Society (publ) reports the loss of alumina as Q - 1000 at 10GHz and 25°C
The highest Q previously measured in alumina at room temperature (i e approximately 25°C) is by Woode et al (RA Woode, EN Ivanov, ME Tobar and DG Blair 'Measurement of dielectric loss tangent of alumina at microwave frequencies and room temperature' Electronics Letters, vol 30 no 25, 8 Dec 1994) who measured a Q of 23,256 This Article noted that purity alone was a poor indicator of the dielectric loss tangent We have found that although an impure alumina will give a poor Q, a very pure alumina is not a guarantee of a high Q Pure alumina can have compounds added to it in order to assist the sintering process. These additions should not adversely influence the Q So, for example, magnesia may be added to a very pure alumina and this will assist the sintering but will not adversely affect the Q if added in small quantities However, adverse effects are observed with impurities such as alkali salts (sodium and potassium) and metallic elemental impurities such as iron
The invention also comprises a sintered ceramic material comprising an alumina and minor amount of a metal or semi-metal oxide which has a Q value greater than 25,000, more preferably greater than 30,000 and even more preferably greater than 45,000 at 10GHz and at 25°C
The invention is described in the following Examples
The aluminas used were commercially available aluminas and the analyses of the powders used in the examples are given in Table 1 with the impurities given in parts per million based on the total weight ofthe sample able 1 Chemical analyses of powders used
Figure imgf000007_0001
Examples
Examples 1 to 3 are comparative examples
Powders A-C inclusive were pressed in a 13 5 mm diameter stainless steel die press at a pressure of 100 MPa. The pressed samples were sintered in air at a temperature of 1550°C for 300 mins The sample density was then measured and the dielectric constant and dielectric loss experiments were carried out using a parallel plate resonator and employing a modified Haaki-Coleman technique described in B W Haki and P.D Coleman 'A dielectric resonator method of measuring inductive capacities in the millimeter range', IFEE Trans Microwave Theory Tech Vol 8, p 402-410 (1960) Here the dielectric puck is placed not directly onto the lower copper plate but onto a low loss material with a much lower dielectric constant We have used a quartz crystal 4mm thick and 10mm in diameter The sample dimensions were approximately 10mm diameter, 4mm thick discs The measurements were made using a Hewlett Packard HP8719C vector network analyser with 1Hz resolution and the TE01 1 mode was examined. All dielectric measurements were carried out at room temperature in air at a relative humidity of approximately 30% No special precautions were taken to prevent the adsorption of water to the sample surface The loss measurements are presented in terms of the Q factor, i e tan delta 1, the measuring frequency was 9-10 GHz at a temperature of 25°C Example 1
Sample A showed a Q of 3,500 while B had a Q factor less than 1000
B
3,500 <1000
Example 2
The chemically purer powder C was made into dense discs. Sample C2, was subjected to a sintering temperature of 1600°C for 300 mins.
Figure imgf000008_0001
Example 3
The same alumina powder as used in C, was sintered at 1500°C for 300 minutes.
Figure imgf000008_0002
Examples 4 to 7 and 10 to 12 are examples of the invention and Examples 8 and 9 are comparative examples.
Examples 4 to 6
In the second series of experiments, Alumina C was doped with TK^. The addition of Tiθ2 influences the sintering temperature at which the material achieves high density and for this reason the aluminas doped with Tiθ2 were sintered at 1500°C. To check the effect of a reduction in the sintering temperature on the pure alumina, alumina C was also sintered at 1500°C. Tiθ2 sintered in air to full density displays a very poor Q which was measured at 1,500. This is due to the fact Tiθ2 is easily reduced. Small deviations from stoichiometric Tiθ2 causes a random distribution of point defects. As the defect concentration increases, their interaction increases and ordering can occur.
Long range ordering produces shear structures At compositions around TiO] 9, Magnelli phases exist but this degree of reduction is severe and is associated with a darkening of the material to blue-black A slight reduction to TiO j ^g causes defects to order on the (132) planes in a series of shear structures. In the 100% Tiθ2 samples studied here, sintering in air has caused a slight reduction resulting in a dense ceramic with a brown-tan colour The dielectric loss has suffered in comparison with the single crystal Q value which was measured at 7,000
Example 4
A pure alumina (alumina C) was doped by 0.5% weight of Titanium dioxide powder (Sample name CTO.5) The mixture was sintered at 1500°C as in Example 3 and the Q measured as in Example 1 , and was found to be 47,000
cm 5
47.000
Example 5
A pure alumina (alumina C) was doped with 1% by weight of Tiθ2 (sample name CTI 0) and sintered at 1500°C, i.e at the same temperature as that used for samples C in Example 3 The Q was found to be 35,000.
CT1.0
Q 35,000 Example 6
A pure alumina (alumina C) was doped with 5% by weight of Ti02 (sample name CT5 0) and sintered at 1500°C, i.e at the same temperature as that used for samples C in Example 3 The Q was found to be 12,650
CT5 0
12.650
Example 7
A pure alumina (alumina C) was doped with 10% by weight of TiO^ (sample name CT10 0) and sintered at 1500°C, i e at the same temperature as that used for samples C in Example 3 The Q was found to be 7,300
CT100
7.300
Example 8
A pure Ti02 was sintered to full density in air at 1400°C The purpose of this example is to demonstrate that the Q of Ti02 is much lower than the Q of A 1203 and hence demonstrate that it might be expected that any addition of Tiθ2 to AI2O3 would have the effect of decreasing the Q rather than enhancing the Q Using a mixtures rule, common in the description of dielectrics, it might be expected that at 0 5% Tiθ2 in AI2O3 the Q should be 33,500 when in fact the measured Q is 47,500
Figure imgf000010_0001
Example 9
By was of comparison, three single crystals (SCl-3) of sapphire (A1203) were tested under identical conditions As expected, the Q of the single crystals was higher than the Q of the sintered aluminas but, surprisingly, the Q factors for the sintered aluminas were only a factor of approximately two lower
SCl SC2 SC3
100.000 100.000 100,000
Examples 10, 11 and 12
Dopants other than Tiθ2 close to Ti in the periodic table, i e Nb, Zr and Y, were also added to alumina C The dopants were added at the 0 25, 0 5, 1 and 5wt% level a total of 12 different compositions All samples were sintered at 1500°C for 300 mins in air In none of the measurements did the Q factor exceed the highest value for the Tiθ2 addition However, there are indications of increases in the Q which is surprising as all three dopants have a higher dielectric loss in comparison with A1203
Examples
Example 10 Example 1 1 Example 12 Dopant b70, Y O, ZiO,
Q (0.25% dopant) 26.000
Q (0 5% dopant) 30.000 25.400 28.400
Q (1 0% dopant) 14.000 36.000 16.600
Q (5 0% dopant) 30.000 30.000 17.000

Claims

Claims
1 A low dielectric loss sintered material composition which comprises a major part of alumina and a minor part of metal or semi-metal oxide
2 A composition as claimed in claim 1 in which the metal or semi-metal oxide is an oxide of an element of Group III and IV ofthe Periodic Table
3 A composition as claimed in claim 2 in which the metal oxide is an oxide of titanium, niobium, yttrium or zirconium
4 A composition as claimed in any one of the preceding claims in which the metal or semi-metal oxide is present in an amount of less than 5% by weight of the total weight of the composition
5 A sintered dielectric material comprising a major portion of alumina and less than 5 weight per cent Tiθ2
6 A sintered dielectric material as claimed in claim 5 wherein the dielectric material is no more than 1 weight per cent Tiθ2
7 A sintered dielectric material as claimed in claim 5 wherein the dielectric material is no more than 0 5 weight per cent Tiθ2
8 A composition as claimed in claim 4 in which the metal or semi-metal oxide is present in an amount of less than 2% by weight of the total weight of the composition
9 A composition as claimed in any one of the preceding claims which has a Q value greater than 25,000 at 9-10 GHz at a temperature of 25°C
10. A composition as claimed in claim 9 which has a Q value greater than 45,000 at 9-10 GHz at a temperature of 25°C
11 A sintered dielectric material as claimed in any one of the preceding claims wherein the alumina has no more than about 300ppm of impurities
12 A sintered material as claimed in any one of claims 1 to 1 1 which has a Q value greater than 250,000 at 9-10 GHz at a temperature of 77K
13 A sintered material as claimed in any one of claims 1 to 12 which has a Q value greater than 320,000 at 9-10 GHz at a temperature of 60K
14 A sintered material as claimed in any one of claims 1 to 13 which has a Q value greater than 600,000 at 9-10 GHz at a temperature of 20K
15 A dielectric material as claimed in any one of the preceding claims in which alumina and TiO^ are sintered at about 1500°C
16 The dielectric material as claimed in any one of the preceding claims in combination with a resonator housing, and means for coupling electromagnetic energy into the housing, wherein the dielectric material is a resonant element located in the resonator housing
17 A method of making a composition as claimed in any one of the preceding claims 1 to 15 which comprises mixing powders of alumina and the minor component together and then heating the mixture to a temperature below its melting point until the porosity is substantially or entirely reduced
18 A method as claimed in claim 17 in which the temperature of sintering is between 1500°C and 1600°C
19 A method as claimed in claim 17 or 18 in which the particle size ofthe powders is from 0 01 to 2 microns
20 A method as claimed in claim 17 or 18 in which the grain size of the sintered particles is less than three micrometers
21. A method as claimed in claim 17 or 18 in which the grain size ofthe sintered particles is less than two micrometers
PCT/GB1996/003150 1995-12-22 1996-12-19 Modified sintered material WO1997023429A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5987341A (en) * 1996-05-29 1999-11-16 Illinois Superconductor Corporation High-purity polycrystalline alumina cryogenic dielectric
EP1065190A2 (en) 1999-06-29 2001-01-03 Hitachi Metals, Ltd. Alumina ceramic composition

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB9928865D0 (en) * 1999-12-07 2000-02-02 Univ South Bank Improved ceramic material
US7056853B2 (en) * 2003-02-05 2006-06-06 Matsushita Electric Industrial Co., Ltd. Oxide ceramic material, ceramic substrate employing the same, ceramic laminate device, and power amplifier module
JP2009302518A (en) * 2008-05-13 2009-12-24 Toto Ltd Electrostatic chuck
US9034787B2 (en) * 2009-05-29 2015-05-19 Corning Incorporated Ceramic articles and methods of producing ceramic articles
US9496731B2 (en) * 2012-01-20 2016-11-15 Samsung Electronics Co., Ltd Apparatus and method for transmitting wireless power by using resonant coupling and system for the same
EP3218324A4 (en) * 2014-11-10 2018-04-11 Saint-Gobain Ceramics&Plastics, Inc. Sintered ceramic component and a process of forming the same

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4668646A (en) * 1985-08-28 1987-05-26 Ngk Spark Plug Co., Ltd. Alumina ceramic composition
US4720471A (en) * 1985-01-31 1988-01-19 Ngk Spark Plug Co., Ltd. Alumina porcelain compositions
US4735926A (en) * 1985-03-15 1988-04-05 Ngk Spark Plug Co., Ltd. Alumina ceramic body

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4762655A (en) * 1985-11-27 1988-08-09 Gte Laboratories Incorporated Method of sintering translucent alumina
KR910009894B1 (en) * 1987-03-26 1991-12-03 도도 기끼 가부시끼가이샤 Ceramic products and process for producing the same
JP3036367B2 (en) * 1994-08-19 2000-04-24 住友金属工業株式会社 Alumina porcelain composition

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4720471A (en) * 1985-01-31 1988-01-19 Ngk Spark Plug Co., Ltd. Alumina porcelain compositions
US4735926A (en) * 1985-03-15 1988-04-05 Ngk Spark Plug Co., Ltd. Alumina ceramic body
US4668646A (en) * 1985-08-28 1987-05-26 Ngk Spark Plug Co., Ltd. Alumina ceramic composition

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5987341A (en) * 1996-05-29 1999-11-16 Illinois Superconductor Corporation High-purity polycrystalline alumina cryogenic dielectric
EP1065190A2 (en) 1999-06-29 2001-01-03 Hitachi Metals, Ltd. Alumina ceramic composition
EP1065190A3 (en) * 1999-06-29 2001-05-16 Hitachi Metals, Ltd. Alumina ceramic composition
US6362120B1 (en) 1999-06-29 2002-03-26 Hitachi Metals, Ltd. Alumina ceramic composition

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GB2324082B (en) 1999-12-29
GB2324082A (en) 1998-10-14
GB9526339D0 (en) 1996-02-21
AU1163997A (en) 1997-07-17
US6610623B1 (en) 2003-08-26
GB9815549D0 (en) 1998-09-16

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