Source: https://patents.google.com/patent/US6482761?oq=flatulence
Timestamp: 2018-02-25 02:18:08
Document Index: 709205182

Matched Legal Cases: ['Application No. 04', 'Application No. 04', 'Application No. 06', 'Application No. 06', 'Application No. 08', 'Application No. 08', 'Application No. 2000']

US6482761B1 - Translucent alumina sintered body and a process for producing the same - Google Patents
US6482761B1
US6482761B1 US09648812 US64881200A US6482761B1 US 6482761 B1 US6482761 B1 US 6482761B1 US 09648812 US09648812 US 09648812 US 64881200 A US64881200 A US 64881200A US 6482761 B1 US6482761 B1 US 6482761B1
US09648812
sintering the green body at a temperature of from 1700 to 1900° C. under reducing atmosphere of from atmospheric pressure to vacuum.
The alumina particle, main raw material of the present invention, has a BET specific surface area preferably from 1 to 10 m2/g. When the BET specific surface area is less than 1 m2/g, a pore having a diameter of over 0.15 μm may be present in a green body, and a sintering temperature of 1900° C. or more is necessary for densification. While when the BET specific surface area is over 10 m2/g, the sintering speed may be non-uniform due to agglomeration of particles, and consequently, the addition amount of sintering agent has to be increased. Further, when the purity is less than 99.99%, the translucency may lower since an impurity absorbs lights, or an abnormal grain growth happens because of the presence of an impurity to remain pores.
The α alumina powder having a BET specific surface area of 1 to 10 m2/g described above has a purity of 99.99% or more. Water, organic substance and halogen contained in raw materials in an amount of less than 1 part by weight which can be removed from the raw materials by sintering at 1000° C. or lower do not deteriorate the features of the alumina sintered body of the present invention, and the presence thereof is permissible.
In the present invention, magnesium oxide, and further, sintering agent such as yttrium oxide and the like are added to the above-mentioned α alumina powder having a BET specific surface area preferably from 1 to 10 m2/g, more preferably from 2 to 7 m2/g, further preferably from 3 to 5 m2/g, and a solvent, organic binder, plasticizer and dispersing agent are mixed into the resulted mixed powder, to prepare a slurry. Next, Forming is effected using this slurry, and the green body is prefired at a temperature of from 500 to 1500° C. in atmosphere if necessary, then, the prefired body is sintered at a temperature of from 1700 to 1900° C. under reducing atmosphere from atmospheric pressure to vacuum, to produce the intended alumina sintered body.
As the sintering agent, a magnesium compound is added, or a magnesium compound and one or more compounds selected from the group consisting of compounds of group IIIA elements or group IVA elements of the periodic table in an amount of 1 to 100 wt % based on magnesium are added. Particularly, a magnesium compound is preferable, or further, a magnesium compound and a yttrium compound are preferable. Examples of these compounds include, but not limited to, oxides, nitrates, acetates, hydroxides, chlorides and the like, providing they are compounds converting into oxides at 1200° C. or less in prefiring in atmosphere. As the most suitable examples, magnesium nitrate is listed, or further, magnesium nitrate and yttrium nitrate are listed. Usually, magnesium is added to the above-mentioned alumina powder in an amount of 10 ppm or more to 100 ppm or less, preferably, 10 ppm or more to 50 ppm or less in terms of the oxide. Alternatively, yttrium is added to the above-mentioned alumina powder in an amount of 1 ppm or more to 100 ppm or less in terms of the oxide, preferably in an amount of 20 wt % of the amount of magnesium, in terms of the oxide, in addition to magnesium. For example, when magnesium oxide is added in an amount of 50 ppm, it is most preferable to add yttrium oxide in an amount of 10 ppm.
A green body obtained by the above-mentioned method is prefired preferably for 1 hour or more at a temperature from 500 to 1500° C., more preferably for 3 hours or more at a temperature from 900 to 1200° C., for binder removal. Next, the green body is sintered at a temperature preferably from 1700 to 1900° C., more preferably from 1750 to 1850° C., further preferably from 1780 to 1820° C. under reducing atmosphere from atmospheric pressure to vacuum, preferably under hydrogen atmosphere of atmospheric pressure, to produce the intended translucent alumina. When the sintering temperature is less than 1700° C., translucency may be lower since the grain does not grow sufficiently. While, when sintering is conducted at a temperature higher than 1900° C., the grain size of the sintered body may increase, pores may remain, translucency may decrease and the mechanical strength of the sintered body may decrease.
This slurry was spray-dried by a spray drier to produce a granule. This granule was humidified to a water content of 0.5 wt %, then, filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.5 t/cm2. Then, this green body was prefired for 3 hours at 900° C. in atmosphere to remove an organic binder, then, sintered for 4 hours at 1800° C. in hydrogen (due point: 0° C.). The in line transmittance of the resulted sintered body was 40%. The average grain size of the sintered body was 36 μl m, and the maximum grain size was 50 μm.
100 g of the AAO4 powder described in Example 1, 300 g of ethanol and 0.016 g of magnesium nitrate hexahydrate were mixed by stirring for 30 minutes while dispersing with an ultrasonic disperser. Then, ethanol was removed by a rotary evaporator to obtain a cake. This cake was dried with hot air at 150° C., then, ground in a mortar. The resulted powder was filled in a die, and formed into a cylindrical molded product having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.0 t/cm2. This green body was prefired at 900° C. in atmosphere, then, sintered for 4 hours at 1800° C. in hydrogen. The in line transmittance of the resulted sintered body was 50%. The average grain size of the sintered body was 40 μm, and the maximum grain size was 55 μm.
This slurry was spray-dried by a spray drier to produce a granule. This granule was humidified to a water content of 0.5 wt %, then, filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.5 t/cm2. Then, this green body was prefired at 900° C. for 3 hours in atmosphere to remove the organic binder, then, sintered for 4 hours at 1820° C. in hydrogen (due point: 0° C.). The in line transmittance of the resulted sintered body was 40%. The average grain size of the sintered body was 36 μm, and the maximum grain size was 50 μm.
This slurry was spray-dried by a spray drier to produce a granule. This granule was humidified to a water content of 0.5 wt %, then, filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.5 t/cm2. Then, this green body was prefired at 900° C. for 3 hours in atmosphere to remove the organic binder, then, sintered for 4 hours at 1800° C. in hydrogen (due point: 0° C.). The in line (linear) transmittance of the resulted sintered body was 49%. The average grain size of the sintered body was 36 μm, and the maximum grain size was 50 μm.
100 g of the AA04 powder described in Example 1, 300 g of ethanol and 0.032 g of magnesium nitrate hexahydrate were mixed by stirring for 30 minutes while irradiating with an ultrasonic wave. Then, ethanol was removed by a rotary evaporator to obtain a cake. This cake was dried with hot air at 150° C., then, ground in a mortar. The resulted powder was filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.0 t/cm2. This green body prefired at 900° C. in atmosphere, then, sintered for 4 hours at1800° C. in hydrogen. The in line transmittance of the resulted sintered body was 64%. The average grain size of the sintered body was 36 μm, and the maximum grain size was 50 μm.
100 g of the AAO4 powder described in Example 1, 300 g of ethanol, 0.032 g of magnesium nitrate hexahydrate and 0.0034 g of yttrium nitrate hexahydrate (10 ppm as yttrium oxide based on alumina powder) were mixed by stirring for 30 minutes while dispersing with an ultrasonic disperser. Then, ethanol was removed by a rotary evaporator to obtain a cake. This cake was dried with hot air at 150° C., then, ground in a mortar. The resulted powder was filled in a die(mold), and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.0 t/cm2. This green body was prefired at 900° C. in atmosphere, then, sintered for 4 hours at 1800° C. in hydrogen. The in line transmittance of the resulted sintered body was 60%. The average grain size of the sintered body was 36 μm, and the maximum grain size was 50 μm.
This slurry was spray-dried by a spray drier to produce a granule. This granule was humidified to a water content of 0.5 wt %, then, filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.5 t/cm2. Then, this molded product was calcined for 3 hours at 900° C. in atmosphere to remove an organic binder, then, sintered for 4 hours at 1800° C. in hydrogen (due point: 0° C.). The in line transmittance of the resulted sintered body was 45%. The average grain size of the sintered body was 36 μm, and the maximum grain size was 50 μm.
This slurry was spray-dried by a spray drier to produce a granule. This granule was humidified to a water content of 0.5 wt %, then, filled in a die , and formed into a cylindrical green body having a diameter of 20 mm and a height of 10 mm by an oil hydraulic uniaxial press machine under a load of 0.7 t/cm2 and a cold isostatic press under a load of 1.5 t/cm2. Then, this green body was prefired for 3 hours at 900° C., then, sintered for 4 hours at 1820° C. in hydrogen (due point: 0° C.). The resulted sintered body was opaque, and the in line transmittance thereof was 0%.
100 g of the AKP-20 powder described in Comparative Example 1,300 g of ethanol and 0.032 g of magnesium nitrate hexahydrate were mixed by stirring for 30 minutes while dispersing with an ultrasonic disperser. Then, ethanol was removed by a rotary evaporator to obtain a cake. This cake was dried with hot air at 150° C., then, ground in a mortar. The resulted powder was filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.0 t/cm2. This green body was prefired at 900° C. in atmosphere, then, sintered for 4 hours at 1800° C. in hydrogen. The resulted sintered body was opaque, and the in line transmittance thereof was 0%.
100 g of the AKP-20 powder described in Comparative Example 1, 300 g of ethanol, 0.032 g of magnesium nitrate hexahydrate and 0.0034 g of yttrium nitrate hexahydrate (10 ppm as yttrium oxide based on alumina powder) were mixed by stirring for 30 minutes while dispersing with an ultrasonic disperser. Then, ethanol was removed by a rotary evaporator to obtain a cake. This cake was dried with hot air at 150° C., then, ground in a mortar. The resulted powder was filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold hydrostatic press under a load of 1.0 t/cm2. This green body was prefired at 900° C. in atmosphere, then, sintered for 4 hours at 1800° C. in hydrogen. The resulted sintered body was opaque, and the in line transmittance thereof was 0%.
This slurry was spray-dried by a spray drier to produce a granule. This granule was humidified to a water content of 0.5 wt %, then, filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 10 mm by an oil hydraulic uniaxial press machine under a load of 0.7 t/cm2 and a cold isostatic press under a load of 1.5 t/cm2. Then, this green body was prefired for 3 hours at 1200° C., then, sintered for 4 hours at 1820° C. in hydrogen (due point: 0° C.). The resulted sintered body was opaque, and the in line transmittance thereof was 0%. In the resulted sintered body, Mg=31 ppm, Li<2 ppm, Na=17 ppm, K=2 ppm, and other alkali metal elements <1 ppm, other alkaline earth metal elements <1 ppm, and the total amount of alkali metal elements and alkaline earth metal elements was over 50 ppm.
100 g of the UA-5105 powder described in Comparative Example 4,300 g of ethanol and 0.032 g of magnesium nitrate hexahydrate (50 ppm as magnesium oxide based on the total alumina powder) were mixed by stirring for 30 minutes while irradiating with an ultrasonic wave. Then, ethanol was removed by a rotary evaporator to obtain a cake. This cake was dried with hot air at 150° C., then, ground in a mortar. The resulted powder was filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.0 t/cm2. This green body was prefired at 900° C. in atmosphere, then, sintered for 4 hours at 1800° C. in hydrogen.
100 g of the USA5105 powder described in Comparative Example 4, 300 g of ethanol, 0.032 g of magnesium nitrate hexahydrate and 0.0034 g of yttrium nitrate (5 ppm as yttrium oxide based on alumina) were mixed by stirring for 30 minutes while dispersing with an ultasonic disperser. Then, ethanol was removed by a rotary evaporator to obtain a cake. This cake was dried with hot air at 150° C., then, ground in a mortar. The resulted powder was filled in a die, and formed into a cylindrical green body having a diameter of 20 mm and a height of 5 mm by an oil hydraulic uniaxial press)machine under a load of 0.3 t/cm2 and a cold isostatic press under a load of 1.0 t/cm2. This green body was prefired at 900° C. in atmosphere, then, sintered for 4 hours at 1800° C. in hydrogen. The resulted sintered body was opague, and the in line transmittance thereof was 0%.
Alumina BET Sintering
specific surface area agent Grain size (μm) In line
Raw Raw (addition Average Maximum Transmit- Amount of element remaining in
material material amount/ppm) Grain grain tance sintered body (ppm)
power m2/g form MgO Y2O3 size size % Li Na K Mg Ca Sr Ba
Example 1 AA04 3.5 Granule 25 36 50 40 <2 <5 <2 16 <1 <1 <1
Example 2 AA04 3.5 Mixed 25 40 55 50 <2 <5 <2 16 <1 <1 <1
Example 3 AA04 3.5 Granule 25 5 36 50 40 <2 <5 <2 16 <1 <1 <1
Example 4 AA04 3.5 Granule 50 36 50 49 <2 <5 <2 32 <1 <1 <1
Example 5 AA04 3.5 Mixed 50 36 50 64 <2 <5 <2 32 <1 <1 <1
Example 6 AA04 3.5 Mixed 50 10 36 50 60 <2 <5 <2 32 <1 <1 <1
Example 7 AA03 5.2 Granule 50 36 50 45 <2 <5 <2 32 <1 <1 <1
Comparative AKP-20 4.2 Granule 50 — — Opaque — — — — — — —
Comparative AKP-20 4.2 Mixed 50 — — Opaque — — — — — — —
Comparative AKP-20 4.2 Mixed 50 10 — — Opaque <2 17 <2 31 <1 <1 <1
Comparative UA5105 9.4 Granule 50 — — Opaque — — — —
example 4 — — —
Comparative UA5105 9.4 Mixed 50 — — 5 <2 45 <2 38 13 <1 <1
example 5 powder
Comparative UA5105 9.4 Mixed 50 10 — — Opaque — — — — — — —
example 6 powder
1. A translucent alumina sintered body wherein the total content of an alkali metal element and an alkaline earth metal element is 50 ppm or less, and the in line transmittance of a light having a wavelength of 600 nm is 40% or more at a thickness of the sintered body of 0.85 mm.
forming a mixed powder prepared by adding a sintering agent to an α alumina powder which comprises a polyhedral primary particle having substantially no fractured surface, has a BET specific surface area of 1 to 10 m2/g and has a purity of 99.99% or more, and
sintering the green body at a temperature of from 1700 to 1900° C. under reducing atmosphere from atmospheric pressure to vacuum.
4. The method for producing a translucent alumina sintered body according to claim 3, wherein the sintering agent is a magnesium compound and the addition amount thereof is 10-100 ppm in terms of the oxide based on the total amount of alumina.
forming a mixed powder prepared by adding a magnesium compound in an amount of 10 to 100 ppm in terms of the oxide based on the total amount of alumina, or a magnesium compound in an amount of 10 to 100 ppm in terms of the oxide based on the total amount of alumina and one or more compounds selected from the group consisting of compounds of group IIIA elements and group IVA elements of the periodic table in an amount of 1 to 100 wt % in terms of the oxide based on the total amount of the magnesium compound, to an α alumina powder which comprises a polyhedral primary particle having substantially no fractured surface, has a BET specific surface area of 1 to 10 m2/g and has a purity of 99.99% or more, and
6. The method for producing a translucent alumina sintered body according to claim 3 comprising the steps of (1) mixing a mixed powder according to claim 3 with organic binder, plasticizer, dispersing agent, lubricant, and water or an organic solvent to prepare a slurry, (2) forming said slurry, and (3) prefiring said green body in atmosphere at a temperature of from 500 to 1500° C., and then sintering the prefired green body under reducing atmosphere of from atmospheric pressure to vacuum at a temperature of from 1700 to 1900° C.
US09648812 1999-08-30 2000-08-28 Translucent alumina sintered body and a process for producing the same Expired - Fee Related US6482761B1 (en)
JP11-243125 1999-08-30
JP24312599A JP2001064075A (en) 1999-08-30 1999-08-30 Translucent alumina sintered body and its production
US6482761B1 true US6482761B1 (en) 2002-11-19
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US09648812 Expired - Fee Related US6482761B1 (en) 1999-08-30 2000-08-28 Translucent alumina sintered body and a process for producing the same
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EP (1) EP1081117B1 (en)
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