CA2001062A1 - Method of heat-treating unstable ceramics by microwave heating and susceptors used therefor - Google Patents
Method of heat-treating unstable ceramics by microwave heating and susceptors used thereforInfo
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- CA2001062A1 CA2001062A1 CA 2001062 CA2001062A CA2001062A1 CA 2001062 A1 CA2001062 A1 CA 2001062A1 CA 2001062 CA2001062 CA 2001062 CA 2001062 A CA2001062 A CA 2001062A CA 2001062 A1 CA2001062 A1 CA 2001062A1
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- bed
- protective
- ceramic
- susceptor
- microwave
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
- B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
- B01J19/122—Incoherent waves
- B01J19/126—Microwaves
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B30—PRESSES
- B30B—PRESSES IN GENERAL
- B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
- B30B11/001—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a flexible element, e.g. diaphragm, urged by fluid pressure; Isostatic presses
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- 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
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/64—Burning or sintering processes
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- 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
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/64—Burning or sintering processes
- C04B35/645—Pressure sintering
- C04B35/6455—Hot isostatic pressing
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
- B01J2219/12—Processes employing electromagnetic waves
- B01J2219/1203—Incoherent waves
- B01J2219/1206—Microwaves
- B01J2219/1209—Features relating to the reactor or vessel
- B01J2219/1212—Arrangements of the reactor or the reactors
- B01J2219/1215—Single reactor
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- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
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- Organic Chemistry (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
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- Mechanical Engineering (AREA)
- Fluid Mechanics (AREA)
- Electromagnetism (AREA)
- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Toxicology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Ceramic Products (AREA)
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Abstract
Abstract:
A method of sintering thermally unstable (usually non-oxide) ceramics by microwave heating. In the method, a body of the ceramic is at least partially surrounded with a protective bed of particulate material and then the body and the bed are subjected to microwave irradiation to cause heating and sintering of the body. In order to allow the method to be carried out in an oxygen-containing gas such as air and at low pressure, the bed contains effective amounts of: (a) a microwave susceptor, if the unstable ceramic is not already a susceptor, (b) a protective material capable of generating a localized atmosphere which reduces decomposition and/or oxidation of the unstable ceramic, (c) an oxygen getter and (d) a material of sufficiently good thermal conductivity to prevent excessive localized heating in the bed. The invention also relates to the bed of particulate material used in the method and to a process for joining bodies of unstable ceramics by microwave irradiation using the protective bed.
A method of sintering thermally unstable (usually non-oxide) ceramics by microwave heating. In the method, a body of the ceramic is at least partially surrounded with a protective bed of particulate material and then the body and the bed are subjected to microwave irradiation to cause heating and sintering of the body. In order to allow the method to be carried out in an oxygen-containing gas such as air and at low pressure, the bed contains effective amounts of: (a) a microwave susceptor, if the unstable ceramic is not already a susceptor, (b) a protective material capable of generating a localized atmosphere which reduces decomposition and/or oxidation of the unstable ceramic, (c) an oxygen getter and (d) a material of sufficiently good thermal conductivity to prevent excessive localized heating in the bed. The invention also relates to the bed of particulate material used in the method and to a process for joining bodies of unstable ceramics by microwave irradiation using the protective bed.
Description
~001(~62 Method of heat-treatin~nstable ceramics by microwave heatinq and susceptors used there~r This invention relates to heat-treating ceramic powders.
More particularly, the invention relates to a method of heat-treating thermally unstable ceramic powders utilizingmicrowaves to generate the required heat and to a susceptor composition used in the method.
~ lthough it is already known to use microwaves to heat and, if necessary, to sinter ceramic powders (i.e. powders comprising compounds of metals and non-metals), such procedures are best suited to heating and sintering stable metal oxide ceramics because other ceramics often do not absorb microwave energy to the n~cessary extent (at least at ambient temperatures) or they decompose or oxidize before heat-treatment temperatures are reached. .
The problem posed by poor microwave absorption can be solved by surrounding a "green" body of a non-susceptor ceramic with a powder made of a material that does absorb microwaves adequately, i.e. a microwave susceptor. The body is then heated by conduction, convection and/or radiation from the susceptor powder either until the desired treatment temperature is reached or until the ceramic reaches a temperature at which it does absorb microwave energy sufficiently for further direct heating to the desired temperature.
The problem posed by the thermal instability or reactivity o~ certain ceramics can also be overcome by providing a suitable protective atmosphere for the green body during the heating procedure. For example, the decomposition and oxidation of silicon nitride can be substantially prevented by heating the material in an atmosphere containing a suitable partial pressure of nitrogen. The partial pressure required in any particular case depends on the temperature and time of the procedure and on the desired treatment temperature. However, at high temperatures (which are , : . :
,. .- . :
-: :
~0~)10~2 required to achieve sintered products of hiyh density), decomposition occurs even under pure nitrogen at one atmosphere. The procedure must co~sequently be carried out at high pressures and this is disadvantageous because it requires the use of atmosphere-controlled, high temperature and high pressure furnaces which are expensive and inconvenient to use.
There is accordingly a need for a method of heat-treating unstable ceramics that makes use o:E microwaves for heating the material but which avoids the need for controlled atmospheres and high pressures. An object of the present invention is to satisfy this need.
According to one aspect of the present invention, there is provided a method of heat-treating a body of thermally unstable ceramic material, which comprises at least partially surrounding said body with a bed of particulate material and irradiating said bed with microwave energy in an oxygen-containing gas, said bed comprising effective amounts of: (a) a microwave susceptor if said unstable ceramic is not itself a microwave susceptor; (b) a protective material capable of generating a localized protective atmosphere which reduces decomposition and/or oxidation of the ceramic material; (c) an oxygen getter: and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said bed.
According to another aspect of the present invention, there is provided a particulate material capable of being used as a protective bed for heat-treating a body of an unstable ceramic material with microwaves in an oxygen-containing gas, said material comprising effective amounts of: (a) a microwave susceptor, if said ceramic material is a non-susceptor; (b) a protective material capable of generating a localized atmosphere which discourages decomposition of the unstable ceramic; (c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said particulate material during microwave irradiation thereof.
According to yet another aspect of the invention, there ~: , ; ,.
:, ... . ..
:. ' ' . ~ , :
,, ~ ' , ~ , is provided a process for joining bodies made of thermally unstable ceramics, which comprises: bringing said bodies into contact; surrounding said bodies in the area of contact with a protective bed of particulate material; irradiating said protective bed in an oxygen-containing gas with microwave radiation sufficiently to heat said bed and bodies to cause i joining of the latter; and allowing said bodies to cool;
wherein said bed of particulate material comprises effective amounts of (a) a microwave susceptor, iE said ceramic material is a non-susceptor;
(b) a protective material capable of generating a localized atmosphere which discourages decomposition of the unstable ceramic;
(c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said particulate material during micxowave irradiation thereof.
By using a susceptor bed of particulate material (powder base) of the above kind for the heat-treating procedure, the method can be carried out in a low pressure oxygen-containing ~ -atmosphere, i.e. in a conventional microwave furnace open to atmospheric air.
The present invention and preferred embodiments thereof are described in further detail with reference to the accompanying drawings, in which Figure 1 is a cross-section of apparatus used to carry out a preferred embodiment of one form of the present invention.
The powder bed used in the present invention may be a mixture of different ingredients each one of which provides one only of the properties (a) to (d) mentioned above.
However, a single ingredient may provide two or more, or possibly even all, of the stated functions so the number of ingredients of the powder bed should be reduced. The number of ingredients should preferably be chosen on the basis that the desired properties should be optimised, even if this means ~:,~ , . . . .
.~,. ; ! ' ' ~
' '' ' ' " . . ' ' ,' . `, '' ; :, ~ ~ ' "' `
''`,' ~ ' , ' ' ' .
. ' ,' ,' ' ' , . .
`. . ' ' . , , ' ~o~o~;z providing a separate ingredient for each property. The various properties required in the powder bed are explained in more detail below.
Unless the unstable ceramic is itself an adequate microwave susceptor, the powder bed should contain at least ; one microwave susceptor.
A microwave susceptor is a material that absorbs energy from microwaves at a rate faster than the rate at which it losPs energy. The microwave susceptor used in the powder bed o~ the present invention can be any material that is capable of absorbing (coupling with) microwave radiation to the extent necessary to raise the temperature of the ceramic body at least partially buried in the bed to the desired temperature (at which the body itself absorbs sufficient energy directly from the microwaves). Silicon carbide, for example, acts as a microwave susceptor and has the advantage of also being an oxygen getter (see below). Other carbides and carbon may replace silicon carbide in this function and other suitable microwave susceptors include porcelain, soda-lime glass and barium titanate The nature of the protective material used in the susceptor bed depends on the nature of the unstable ceramic used for the body to be heat~treated. However, the protective material generally functions by generating an atmosphere around the body to be heated that protects the body against decomposition and/or oxidation. For example, when the ceramic body is made of (or contains) silicon nitride, the protective material may itself be silicon nitride. This decomposes (Si3N4 ~ 3Si + 2N2) and forms an atmosphere having a high nitrogen partial pressure localized around the body which protects the body against further decomposition. The decomposition of the silicon nitride begins in the bed (rather than the body) since the bed heats up ~irst and is always hotter than the body.
When the body itself begins to heat, the protective nitrogen atmosphere has already been established.
In contrast, when carbon is used to protect carbides, it protects the carbides primarily from oxidation, e.g.
. ~ . . .
; ., .. : . .
. . . .
;` ' ', -~ .
10~2 SiC + 2 + C -- SiC ~ C02.
Whenever possible, it is desirable to use a protective material which is the same as the unstable ceramic in the body to be heated because there is then less contamination of the body as a result of the heating method.
Further examples of protective materials for particular non oxide ceramics are:
(a) MoS2 which decomposes when heated to Mo and S2(g), useful for protecting bodies comprising MoS2 and/or MoS3;
lo (b) silicon nitride for protecting oxynitrides;
(c) silicon carbide for protecting borides, e.g. TiB2;
and (d) lead based ceramics, (e.g. lead zirconate titanate and lead lanthanate zirconate titanate) used to protect bodies 15 comprising the same materials. These materials produce lead-based protective atmospheres, have adequate conductivity and are microwave susceptors.
An oxygen getter is a material which at least partially eliminates oxygen from the localized atmosphere around the body to be heated, at least at the temperatures at which the unstable ceramics are vulnerable to oxidation. Getters function by reacting chemically with oxygen to lower the partial pressure of the oxygen to such an extent that oxygen is minimized. Metal carbides generally, and silicon carbide in particular, are effective oxygen getters, as are metals such as Zr, Ca, Al, Ti, W, Mo, Ta and Cu.
The material having good thermal conductivity can be any material that allows uniform heating in the bed and transference of the heat to the body. This prevents the development o~ hot spots tlarge temperature gradients) in the bed leading possibly to thermal runaways as well as instabilities in electrical and thermal distribution. Such a material is often required in the bed because the other ingredients are often ceramics of low thermal conductivity.
Boron nitride is a particularly suitable material for this, but aluminum nitride for example, could alternatively be used.
Moreover, a high metal content in the bed (for example, when .. . . .
,,.,.: - , . :. '' , , . . :
. :; , . - , ~ , : . ., :: . .:: - :
: ~', : ' ~ ' ' . .
:,.,:: ..
~0~ ;2 metals are used as oxygen getters) also provides high thermal conductivity. It is difficult to give preferred conductivity ranges because optimum values vary according to bed size and composition.
The ingredients of the powder bed should sach be present in an "effective" amount, i.e. the amount necessary to exert their desired effect (heating, protection, oxygen removal and conductivity). The minimum amount of each material depends on the nature of the material employed. For e~ample, when the powder bed is a mixture of SiC, Si3N4 and BN, the minimum amounts are respectively 25 wt%, 20 wt% and 10 wt%. 'rhe - preferred relative proportions are about 40:30:30 in wt%
respectively.
The method of the invention can be used to protect a variety of unstable ceramics especially non-oxide ceramics, in addition to those mentioned above, e.g. superconductors I, II
and III using a super-conductor powder bed.
The method of the invention can be used for virtually any type of heat-treating of ceramic bodies including sintering, annealing, recrystallization of glassy phases, other thermal treatments and joining together of ceramic bodies. The joining technique will be described more fully below.
In some cases, when sintering is being carried out, sinteriny aids may have to be incorporated into the bodies to be heated in order to facilitate sintering. Sintering aids are sometimes microwave susceptors, in which case they contribute to the heating of the body, but usually not greatly.
The powder bed can be prepared simply by mixing the powdered ingredients in the normal way (e.g. stirring, shaking, tumbling etc.) and the particle sizes of the different ingredients may be the same or difEerent. The average particle size is not particularly critical, although smaller average particle sizes are preferred in order to confine the protective atmosphere with the bed and to limit the penetration of air from outside. A particularly preferred type of bed can be prepared by the following procedure using , .. . . . . .
~ .. - : ,, . :
~ . .. .
::~ , ` ;' ' : :
..
~OOlC~2 ; particles of different sizes.
Firs~ of all the body to be treated can be buried in a bed of the ingredient having the largest particles. The inyredient having the second largest particles can then be poured on top of the bed and the bed gently shaken ar vibrated until the smaller particles flow down into the interstices between the larger particles. This is continued until the ingredient having the smallest particles is then poured on top of the bed and the bed gently shaken or vibrated until the - 10 small particles flow down and fill the voids remaining in the ~` bed. Naturally, the relative particle sizes must be such that such void filling can take place.
This preferred procedure produces a dense bed, usually having a void component of less than 30% by volume, which is easy to construct. The small remaining void size reduces oxygen permeability and the fact that the particles have considerably different sizes means that the components are easy to separate from each other after use. Desirably, the protective material is used to form the smallest particles because the resulting large s~rface to volume ratio ensures thorough evolution of the protective gases and the size of the particles ensures a dense and uniform layer adjacent to the surface of the green body. i.
Rather than making the susceptor bed uniform throughout, in some cases it may be desirable to vary the composition of the susceptor bed from place to place to take into account different shapes, thicknesses and/or compositions of different parts of the green body and different microwave powers at different positions within the resonant microwave cavity of the furnace. For example, the bed can be arranged in layers of higher or lower thermal conductivity, or areas of higher or lower microwave absorption (i.e. heating). Similar compensatory effects can be made by specifically designing the size and/or shape of the bed itself.
The body to be heat-treated by the method of the present invention is often a compact of a single powdered material but may also be a mixture of different powders or a mixture of a . :
.:: : . : ; . : , : , .
... ~:.. : . .. ..
~: .:. ~ . . . .
,: :- ' . ~: . .. :. .
z~
powder with other solid bodi~s, e.g. fibres. Furthermore, the body may consist solely of one or more unstable ceramics or may be a mixture of one or more unstable ceramics with one or more stable (e.g. oxide) ceramics. The latter may be, for 5 example, sintering aids and are usually present in the minority.
The method of the present invention is particularly - suitable for sintering nitrides, e.g. silicon nitride, aluminum nitride, etc. and also composites su~h as Al203/SiC
~particulates and whiskers) and Al2O3/TiC to high densities without degradation of the non-oxide phase.
As mentioned above, the present invention may also be used for joining bodies of unstable ceramics. This can be achieved by placing (and preferably pressing) toyether the bodies to be joined, if desired, with an intermediary interposed between the bodies. The bodies are then surrounded with a bed according to the invention and the joint area is - irradiated with microwaves to raise the temperature of the materials in the vicinity of the joint so that partial melting or sintering takes place and, upon cooling, a satisfactory joint is fo~med.
A suitable procedure is explained with reference to Fig.
l which shows equipment 10 for joining two ceramic bodies 11 and 12 via an intermediary body 13. The intermediary body 13 ~ 25 is preferably a compressed sinterable green body made of the ; same material as the bodies 11 and 12 to be joined. The resulting joint area is surrounded by a protective powder bed 14. The bodies 11, 12 and 13 are pressed together by means of a load 15. The powder bed is contained within a housing 16 which has microwave-transparent windows 17, 18 on opposite sides of the joint. Waveguides 19 and 20 are aligned with the windows 17, 18. ~ magnetron (not shown) is connected to waveguide 19 and a grounded movable short 21 is positioned in waveguide 20. The apparatus is cooled by water pipes 22 and a linear vertical differential transducer 23 is used to measure movements of the load 15.
The bodies are joined by operating the magnetron and ....
. . - . . . .
, .: ' ' ~0~06Z
adjusting the position of the short 21 to create standing waves 24 and 25 in the wavaguides so that the apparatus forms a resonant cavity with the joint area positioned ~or maximum microwave absorption.
The protective bed 14 increases in temperature and raises the temperature o~ the bodies 11, 12 and 13. The transducer 23 first registers an upward movement o~ the load 15 as the bodies expand and then a downward movsment as the body 13 compacts, densifies and sinters. When there is no further movement of the load 15, the procedure is complete and the bodies can be allowed to cool.
The use of a protective bed in accordance with the invention ensures that there is little or no decomposition of the bodies 11, 12 and 13 in the joint area in the ~inal product.
The present invention is illustrated further by the following Examples, but should nct be construed as limited thereto.
A silicon carbide whisker reinforced alumina body (20% by ~ volume) was sintered to approximately 85% of the theoretical ; density (10% of whiskers by volume sintered to 97%) by burying the body in a packed powder bed consisting of 30% by wt silicon carbide ~susceptor and oxygen getter), 30% by wt boron nitride (good thermal conductor) and 40% by wt silicon nitride (protective material) and heating the body and bed with microwaves in air. The heating time was 40 minutes and the microwave energy was 500 watts.
The sintered sample was analyzed for oxidation products to investigate whether reaction with the external atmosphere had taken place. No such products were observed.
: - , .
'. ~ . .
A composite body consisting of titanium carbide and alumina (27% by weight - 11% TiC by volume sintered to 95%) was sintered to a density of greater than 95% theoretical using a packed powder bed similar to that of Example 1 and a similar heating time, power and conditions.
No oxidation products were observed in the product.
Silicon nitride was sintered to a density o~ 97%
theoretical using a powder bed and procedure the same as that of Example 1.
No oxidation products were observed in the product.
Aluminium nitride was sintered to a density of 97%
theoretical using a powder bed of AlN 30% (good thermal conductor) Si3N4 30% (protective ma'cerial) SiC 40% (susceptor and oxygen getter) and the same procedure as in Example 1.
~''.:'-' : : :
. .
~ :. . . ,.: ~
:: : : ' : . ' ' . ,
More particularly, the invention relates to a method of heat-treating thermally unstable ceramic powders utilizingmicrowaves to generate the required heat and to a susceptor composition used in the method.
~ lthough it is already known to use microwaves to heat and, if necessary, to sinter ceramic powders (i.e. powders comprising compounds of metals and non-metals), such procedures are best suited to heating and sintering stable metal oxide ceramics because other ceramics often do not absorb microwave energy to the n~cessary extent (at least at ambient temperatures) or they decompose or oxidize before heat-treatment temperatures are reached. .
The problem posed by poor microwave absorption can be solved by surrounding a "green" body of a non-susceptor ceramic with a powder made of a material that does absorb microwaves adequately, i.e. a microwave susceptor. The body is then heated by conduction, convection and/or radiation from the susceptor powder either until the desired treatment temperature is reached or until the ceramic reaches a temperature at which it does absorb microwave energy sufficiently for further direct heating to the desired temperature.
The problem posed by the thermal instability or reactivity o~ certain ceramics can also be overcome by providing a suitable protective atmosphere for the green body during the heating procedure. For example, the decomposition and oxidation of silicon nitride can be substantially prevented by heating the material in an atmosphere containing a suitable partial pressure of nitrogen. The partial pressure required in any particular case depends on the temperature and time of the procedure and on the desired treatment temperature. However, at high temperatures (which are , : . :
,. .- . :
-: :
~0~)10~2 required to achieve sintered products of hiyh density), decomposition occurs even under pure nitrogen at one atmosphere. The procedure must co~sequently be carried out at high pressures and this is disadvantageous because it requires the use of atmosphere-controlled, high temperature and high pressure furnaces which are expensive and inconvenient to use.
There is accordingly a need for a method of heat-treating unstable ceramics that makes use o:E microwaves for heating the material but which avoids the need for controlled atmospheres and high pressures. An object of the present invention is to satisfy this need.
According to one aspect of the present invention, there is provided a method of heat-treating a body of thermally unstable ceramic material, which comprises at least partially surrounding said body with a bed of particulate material and irradiating said bed with microwave energy in an oxygen-containing gas, said bed comprising effective amounts of: (a) a microwave susceptor if said unstable ceramic is not itself a microwave susceptor; (b) a protective material capable of generating a localized protective atmosphere which reduces decomposition and/or oxidation of the ceramic material; (c) an oxygen getter: and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said bed.
According to another aspect of the present invention, there is provided a particulate material capable of being used as a protective bed for heat-treating a body of an unstable ceramic material with microwaves in an oxygen-containing gas, said material comprising effective amounts of: (a) a microwave susceptor, if said ceramic material is a non-susceptor; (b) a protective material capable of generating a localized atmosphere which discourages decomposition of the unstable ceramic; (c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said particulate material during microwave irradiation thereof.
According to yet another aspect of the invention, there ~: , ; ,.
:, ... . ..
:. ' ' . ~ , :
,, ~ ' , ~ , is provided a process for joining bodies made of thermally unstable ceramics, which comprises: bringing said bodies into contact; surrounding said bodies in the area of contact with a protective bed of particulate material; irradiating said protective bed in an oxygen-containing gas with microwave radiation sufficiently to heat said bed and bodies to cause i joining of the latter; and allowing said bodies to cool;
wherein said bed of particulate material comprises effective amounts of (a) a microwave susceptor, iE said ceramic material is a non-susceptor;
(b) a protective material capable of generating a localized atmosphere which discourages decomposition of the unstable ceramic;
(c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said particulate material during micxowave irradiation thereof.
By using a susceptor bed of particulate material (powder base) of the above kind for the heat-treating procedure, the method can be carried out in a low pressure oxygen-containing ~ -atmosphere, i.e. in a conventional microwave furnace open to atmospheric air.
The present invention and preferred embodiments thereof are described in further detail with reference to the accompanying drawings, in which Figure 1 is a cross-section of apparatus used to carry out a preferred embodiment of one form of the present invention.
The powder bed used in the present invention may be a mixture of different ingredients each one of which provides one only of the properties (a) to (d) mentioned above.
However, a single ingredient may provide two or more, or possibly even all, of the stated functions so the number of ingredients of the powder bed should be reduced. The number of ingredients should preferably be chosen on the basis that the desired properties should be optimised, even if this means ~:,~ , . . . .
.~,. ; ! ' ' ~
' '' ' ' " . . ' ' ,' . `, '' ; :, ~ ~ ' "' `
''`,' ~ ' , ' ' ' .
. ' ,' ,' ' ' , . .
`. . ' ' . , , ' ~o~o~;z providing a separate ingredient for each property. The various properties required in the powder bed are explained in more detail below.
Unless the unstable ceramic is itself an adequate microwave susceptor, the powder bed should contain at least ; one microwave susceptor.
A microwave susceptor is a material that absorbs energy from microwaves at a rate faster than the rate at which it losPs energy. The microwave susceptor used in the powder bed o~ the present invention can be any material that is capable of absorbing (coupling with) microwave radiation to the extent necessary to raise the temperature of the ceramic body at least partially buried in the bed to the desired temperature (at which the body itself absorbs sufficient energy directly from the microwaves). Silicon carbide, for example, acts as a microwave susceptor and has the advantage of also being an oxygen getter (see below). Other carbides and carbon may replace silicon carbide in this function and other suitable microwave susceptors include porcelain, soda-lime glass and barium titanate The nature of the protective material used in the susceptor bed depends on the nature of the unstable ceramic used for the body to be heat~treated. However, the protective material generally functions by generating an atmosphere around the body to be heated that protects the body against decomposition and/or oxidation. For example, when the ceramic body is made of (or contains) silicon nitride, the protective material may itself be silicon nitride. This decomposes (Si3N4 ~ 3Si + 2N2) and forms an atmosphere having a high nitrogen partial pressure localized around the body which protects the body against further decomposition. The decomposition of the silicon nitride begins in the bed (rather than the body) since the bed heats up ~irst and is always hotter than the body.
When the body itself begins to heat, the protective nitrogen atmosphere has already been established.
In contrast, when carbon is used to protect carbides, it protects the carbides primarily from oxidation, e.g.
. ~ . . .
; ., .. : . .
. . . .
;` ' ', -~ .
10~2 SiC + 2 + C -- SiC ~ C02.
Whenever possible, it is desirable to use a protective material which is the same as the unstable ceramic in the body to be heated because there is then less contamination of the body as a result of the heating method.
Further examples of protective materials for particular non oxide ceramics are:
(a) MoS2 which decomposes when heated to Mo and S2(g), useful for protecting bodies comprising MoS2 and/or MoS3;
lo (b) silicon nitride for protecting oxynitrides;
(c) silicon carbide for protecting borides, e.g. TiB2;
and (d) lead based ceramics, (e.g. lead zirconate titanate and lead lanthanate zirconate titanate) used to protect bodies 15 comprising the same materials. These materials produce lead-based protective atmospheres, have adequate conductivity and are microwave susceptors.
An oxygen getter is a material which at least partially eliminates oxygen from the localized atmosphere around the body to be heated, at least at the temperatures at which the unstable ceramics are vulnerable to oxidation. Getters function by reacting chemically with oxygen to lower the partial pressure of the oxygen to such an extent that oxygen is minimized. Metal carbides generally, and silicon carbide in particular, are effective oxygen getters, as are metals such as Zr, Ca, Al, Ti, W, Mo, Ta and Cu.
The material having good thermal conductivity can be any material that allows uniform heating in the bed and transference of the heat to the body. This prevents the development o~ hot spots tlarge temperature gradients) in the bed leading possibly to thermal runaways as well as instabilities in electrical and thermal distribution. Such a material is often required in the bed because the other ingredients are often ceramics of low thermal conductivity.
Boron nitride is a particularly suitable material for this, but aluminum nitride for example, could alternatively be used.
Moreover, a high metal content in the bed (for example, when .. . . .
,,.,.: - , . :. '' , , . . :
. :; , . - , ~ , : . ., :: . .:: - :
: ~', : ' ~ ' ' . .
:,.,:: ..
~0~ ;2 metals are used as oxygen getters) also provides high thermal conductivity. It is difficult to give preferred conductivity ranges because optimum values vary according to bed size and composition.
The ingredients of the powder bed should sach be present in an "effective" amount, i.e. the amount necessary to exert their desired effect (heating, protection, oxygen removal and conductivity). The minimum amount of each material depends on the nature of the material employed. For e~ample, when the powder bed is a mixture of SiC, Si3N4 and BN, the minimum amounts are respectively 25 wt%, 20 wt% and 10 wt%. 'rhe - preferred relative proportions are about 40:30:30 in wt%
respectively.
The method of the invention can be used to protect a variety of unstable ceramics especially non-oxide ceramics, in addition to those mentioned above, e.g. superconductors I, II
and III using a super-conductor powder bed.
The method of the invention can be used for virtually any type of heat-treating of ceramic bodies including sintering, annealing, recrystallization of glassy phases, other thermal treatments and joining together of ceramic bodies. The joining technique will be described more fully below.
In some cases, when sintering is being carried out, sinteriny aids may have to be incorporated into the bodies to be heated in order to facilitate sintering. Sintering aids are sometimes microwave susceptors, in which case they contribute to the heating of the body, but usually not greatly.
The powder bed can be prepared simply by mixing the powdered ingredients in the normal way (e.g. stirring, shaking, tumbling etc.) and the particle sizes of the different ingredients may be the same or difEerent. The average particle size is not particularly critical, although smaller average particle sizes are preferred in order to confine the protective atmosphere with the bed and to limit the penetration of air from outside. A particularly preferred type of bed can be prepared by the following procedure using , .. . . . . .
~ .. - : ,, . :
~ . .. .
::~ , ` ;' ' : :
..
~OOlC~2 ; particles of different sizes.
Firs~ of all the body to be treated can be buried in a bed of the ingredient having the largest particles. The inyredient having the second largest particles can then be poured on top of the bed and the bed gently shaken ar vibrated until the smaller particles flow down into the interstices between the larger particles. This is continued until the ingredient having the smallest particles is then poured on top of the bed and the bed gently shaken or vibrated until the - 10 small particles flow down and fill the voids remaining in the ~` bed. Naturally, the relative particle sizes must be such that such void filling can take place.
This preferred procedure produces a dense bed, usually having a void component of less than 30% by volume, which is easy to construct. The small remaining void size reduces oxygen permeability and the fact that the particles have considerably different sizes means that the components are easy to separate from each other after use. Desirably, the protective material is used to form the smallest particles because the resulting large s~rface to volume ratio ensures thorough evolution of the protective gases and the size of the particles ensures a dense and uniform layer adjacent to the surface of the green body. i.
Rather than making the susceptor bed uniform throughout, in some cases it may be desirable to vary the composition of the susceptor bed from place to place to take into account different shapes, thicknesses and/or compositions of different parts of the green body and different microwave powers at different positions within the resonant microwave cavity of the furnace. For example, the bed can be arranged in layers of higher or lower thermal conductivity, or areas of higher or lower microwave absorption (i.e. heating). Similar compensatory effects can be made by specifically designing the size and/or shape of the bed itself.
The body to be heat-treated by the method of the present invention is often a compact of a single powdered material but may also be a mixture of different powders or a mixture of a . :
.:: : . : ; . : , : , .
... ~:.. : . .. ..
~: .:. ~ . . . .
,: :- ' . ~: . .. :. .
z~
powder with other solid bodi~s, e.g. fibres. Furthermore, the body may consist solely of one or more unstable ceramics or may be a mixture of one or more unstable ceramics with one or more stable (e.g. oxide) ceramics. The latter may be, for 5 example, sintering aids and are usually present in the minority.
The method of the present invention is particularly - suitable for sintering nitrides, e.g. silicon nitride, aluminum nitride, etc. and also composites su~h as Al203/SiC
~particulates and whiskers) and Al2O3/TiC to high densities without degradation of the non-oxide phase.
As mentioned above, the present invention may also be used for joining bodies of unstable ceramics. This can be achieved by placing (and preferably pressing) toyether the bodies to be joined, if desired, with an intermediary interposed between the bodies. The bodies are then surrounded with a bed according to the invention and the joint area is - irradiated with microwaves to raise the temperature of the materials in the vicinity of the joint so that partial melting or sintering takes place and, upon cooling, a satisfactory joint is fo~med.
A suitable procedure is explained with reference to Fig.
l which shows equipment 10 for joining two ceramic bodies 11 and 12 via an intermediary body 13. The intermediary body 13 ~ 25 is preferably a compressed sinterable green body made of the ; same material as the bodies 11 and 12 to be joined. The resulting joint area is surrounded by a protective powder bed 14. The bodies 11, 12 and 13 are pressed together by means of a load 15. The powder bed is contained within a housing 16 which has microwave-transparent windows 17, 18 on opposite sides of the joint. Waveguides 19 and 20 are aligned with the windows 17, 18. ~ magnetron (not shown) is connected to waveguide 19 and a grounded movable short 21 is positioned in waveguide 20. The apparatus is cooled by water pipes 22 and a linear vertical differential transducer 23 is used to measure movements of the load 15.
The bodies are joined by operating the magnetron and ....
. . - . . . .
, .: ' ' ~0~06Z
adjusting the position of the short 21 to create standing waves 24 and 25 in the wavaguides so that the apparatus forms a resonant cavity with the joint area positioned ~or maximum microwave absorption.
The protective bed 14 increases in temperature and raises the temperature o~ the bodies 11, 12 and 13. The transducer 23 first registers an upward movement o~ the load 15 as the bodies expand and then a downward movsment as the body 13 compacts, densifies and sinters. When there is no further movement of the load 15, the procedure is complete and the bodies can be allowed to cool.
The use of a protective bed in accordance with the invention ensures that there is little or no decomposition of the bodies 11, 12 and 13 in the joint area in the ~inal product.
The present invention is illustrated further by the following Examples, but should nct be construed as limited thereto.
A silicon carbide whisker reinforced alumina body (20% by ~ volume) was sintered to approximately 85% of the theoretical ; density (10% of whiskers by volume sintered to 97%) by burying the body in a packed powder bed consisting of 30% by wt silicon carbide ~susceptor and oxygen getter), 30% by wt boron nitride (good thermal conductor) and 40% by wt silicon nitride (protective material) and heating the body and bed with microwaves in air. The heating time was 40 minutes and the microwave energy was 500 watts.
The sintered sample was analyzed for oxidation products to investigate whether reaction with the external atmosphere had taken place. No such products were observed.
: - , .
'. ~ . .
A composite body consisting of titanium carbide and alumina (27% by weight - 11% TiC by volume sintered to 95%) was sintered to a density of greater than 95% theoretical using a packed powder bed similar to that of Example 1 and a similar heating time, power and conditions.
No oxidation products were observed in the product.
Silicon nitride was sintered to a density o~ 97%
theoretical using a powder bed and procedure the same as that of Example 1.
No oxidation products were observed in the product.
Aluminium nitride was sintered to a density of 97%
theoretical using a powder bed of AlN 30% (good thermal conductor) Si3N4 30% (protective ma'cerial) SiC 40% (susceptor and oxygen getter) and the same procedure as in Example 1.
~''.:'-' : : :
. .
~ :. . . ,.: ~
:: : : ' : . ' ' . ,
Claims (31)
1. A method of heat-treating a body of thermally unstable ceramic material, which comprises at least partially surrounding said body with a bed of particulate material and irradiating said bed with microwave energy in an oxygen-containing gas, said bed comprising effective amounts of:
(a) a microwave susceptor if said unstable ceramic is not itself a microwave susceptor;
(b) a protective material capable of generating a localized protective atmosphere which reduces decomposition and/or oxidation of the ceramic material;
(c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said bed.
(a) a microwave susceptor if said unstable ceramic is not itself a microwave susceptor;
(b) a protective material capable of generating a localized protective atmosphere which reduces decomposition and/or oxidation of the ceramic material;
(c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said bed.
2. A method according to Claim 1 wherein said ceramic material is a non-oxide ceramic.
3. A method according to Claim 1 wherein said ceramic material is a non-susceptor.
4. A method according to Claim 1, Claim 2 or Claim 3 wherein said bed contains at least one component having at least two of the properties (a) to (d).
5. A method according to Claim 1, Claim 2 or Claim 3 wherein said body comprises a material selected from a nitride and an oxynitride and wherein said protective material comprises silicon nitride.
6. A method according to Claim 1, Claim 2 or Claim 3 wherein said body comprises a material selected from a carbide or a boride and said protective material comprises a material selected from the group consisting of metal carbides and carbon.
7. A method according to Claim 1, Claim 2 of Claim 3 wherein said body comprises a material selected from a carbide or a boride and said protective material comprises silicon carbide.
8. A method according to Claim 1, Claim 2 or Claim 3 wherein said body comprises a material selected from MoS2 and MoS3 and said protective material is MoS2.
9. A method according to Claim 1, Claim 2 or Claim 3 wherein said body comprises a lead based ceramic and said protective material is a lead based ceramic.
10. A method according to Claim 9 wherein said lead based ceramic of said body and/or said protective material is selected from the group consisting of lead zirconate titanate and lead lanthanate zirconate titanate.
11. A method according to Claim 1, Claim 2 or Claim 3 wherein said body comprises a superconductor selected from the group consisting of superconductors I, II and III, and said protective material is also a superconductor selected from the group consisting of superconductor I, II and III.
12. A method according to Claim 1, Claim 2 or Claim 3 wherein said oxygen getter is selected from the group consisting of metal carbides, carbon and oxidization metals.
13. A method according to Claim 1, Claim 2 or Claim 3 wherein said oxygen getter is silicon carbide.
14. A method according to Claim 1, Claim 2 or Claim 3 wherein said material having good thermal conductivity is selected from the group consisting of boron nitride, aluminum nitride and metals.
15. A method according to Claim 1, Claim 2 or Claim 3 wherein said material having good thermal conductivity is boron nitride.
16. A method according to Claim 1, Claim 2 or Claim 3 wherein said microwave susceptor is selected from the group consisting of metal carbides, carbon, porcelain, soda-lime glass and barium titanate.
17. A method according to Claim 1, Claim 2 or Claim 3 wherein said susceptor is silicon carbide.
18. A method according to Claim 1, Claim 2 or Claim 3 wherein the protective material is the same as the material used for said body.
19. A method according to Claim 1, Claim 2 or Claim 3 wherein said bed is prepared from components of different particle sizes by at least partially burying said body in a component of said bed having the largest particles, placing said component of said bed having the next largest particles on said bed of largest particles and shaking or vibrating the resulting bed structure until the smaller particles flow down into the interstices formed between the larger particles and, if there are additional components of said bed, continuing said procedure of placing components of the next smaller particles followed by shaking or vibrating the resulting structure until the bed is complete.
20. A method according to Claim 1, Claim 2 or Claim 3 wherein said oxygen containing gas is air.
21. A method according to Claim 1, Claim 2 or Claim 3 wherein said oxygen containing gas is at about atmospheric pressure.
22. A particulate material capable of being used as a protective bed for heat-treating a body of an unstable ceramic material with microwaves in an oxygen-containing gas, said material comprising effective amounts of:
(a) a microwave susceptor, if said ceramic material is a non-susceptor;
(b) a protective material capable of generating a localized atmosphere which discourages decomposition of the unstable ceramic;
(c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said particulate material during microwave irradiation thereof.
(a) a microwave susceptor, if said ceramic material is a non-susceptor;
(b) a protective material capable of generating a localized atmosphere which discourages decomposition of the unstable ceramic;
(c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said particulate material during microwave irradiation thereof.
23. A particulate material according to Claim 22 wherein said bed contains at least one component having at least two of the properties (a) to (d).
24. A particulate material according to Claim 22 wherein said susceptor is selected from the group consisting of metal carbides, carbon, porcelain, soda-lime glass and barium titanate.
25. A particulate material according to Claim 22 wherein said protective material is selected from the group consisting of silicon nitride, metal carbides, carbon, MoS2, lead based ceramics and superconductors I, II and III.
26. A particulate material according to Claim 22 wherein said oxygen getter is selected from the group consisting of metal carbides, carbon and oxidizable metals.
27. A particulate material according to Claim 22 wherein said material having good thermal conductivity is selected from the group consisting of boron nitride, aluminum nitride and metals.
28. A particulate material according to Claim 22 comprising silicon carbide, silicon nitride and boron nitride.
29. A particulate material according to Claim 28 comprising at least 25 wt % of said silicon carbide, at least 20 wt % of said silicon nitride and at least 10 wt % of said boron nitride.
30. A particular material according to Claim 22 comprising a mixture of particles of different sizes, said bed having been prepared by at least partially burying said body in a component of said bed having the largest particles, placing said component of said bed having the next largest particles on said bed of largest particles and shaking or vibrating the resulting bed structure until the smaller particles flow down into the interstices formed between the larger particles and, if there are additional components of said bed, continuing said procedure of placing components of the next smaller particles followed by shaking or vibrating the resulting structure until the bed is complete.
31. A process for joining bodies made of thermally unstable ceramics, which comprises:
bringing said bodies into contact;
surrounding said bodies in the area of contact with a protective bed of particulate material;
irradiating said protective bed in an oxygen-containing gas with microwave radiation sufficiently to heat said bed and bodies to cause joining of the latter; and allowing said bodies to cool;
wherein said bed of particulate material comprises effective amounts of (a) a microwave susceptor, if said ceramic material is a non-susceptor;
(b) a protective material capable of generating a localized atmosphere which discourages decomposition of the unstable ceramic;
(c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said particulate material during microwave irradiation thereof.
bringing said bodies into contact;
surrounding said bodies in the area of contact with a protective bed of particulate material;
irradiating said protective bed in an oxygen-containing gas with microwave radiation sufficiently to heat said bed and bodies to cause joining of the latter; and allowing said bodies to cool;
wherein said bed of particulate material comprises effective amounts of (a) a microwave susceptor, if said ceramic material is a non-susceptor;
(b) a protective material capable of generating a localized atmosphere which discourages decomposition of the unstable ceramic;
(c) an oxygen getter; and (d) a material having sufficiently good thermal conductivity to prevent excessive localized heating in said particulate material during microwave irradiation thereof.
Priority Applications (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2001062 CA2001062A1 (en) | 1989-10-19 | 1989-10-19 | Method of heat-treating unstable ceramics by microwave heating and susceptors used therefor |
| AU65400/90A AU6540090A (en) | 1989-10-19 | 1990-10-19 | Method of heat-treating unstable ceramics by microwave heating and susceptors used therefor |
| JP2514200A JP2628104B2 (en) | 1989-10-19 | 1990-10-19 | Method for heat-treating ceramics decomposed and / or oxidized by heat treatment in oxygen-containing gas by microwave heating and susceptor used therefor |
| EP19900915276 EP0495850A1 (en) | 1989-10-19 | 1990-10-19 | Method of heat-treating unstable ceramics by microwave heating and susceptors used therefor |
| PCT/CA1990/000358 WO1991005747A1 (en) | 1989-10-19 | 1990-10-19 | Method of heat-treating unstable ceramics by microwave heating and susceptors used therefor |
| CN 90109203 CN1054579A (en) | 1989-10-19 | 1990-10-19 | With the method for microwave heating heat-treating unstable ceramics and used receptor |
| CN 91107119 CN1054759A (en) | 1989-10-19 | 1991-01-14 | With green bean rock system potash fertilizer and comprehensive utilization process thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2001062 CA2001062A1 (en) | 1989-10-19 | 1989-10-19 | Method of heat-treating unstable ceramics by microwave heating and susceptors used therefor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2001062A1 true CA2001062A1 (en) | 1991-04-19 |
Family
ID=4143361
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2001062 Abandoned CA2001062A1 (en) | 1989-10-19 | 1989-10-19 | Method of heat-treating unstable ceramics by microwave heating and susceptors used therefor |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0495850A1 (en) |
| JP (1) | JP2628104B2 (en) |
| CN (1) | CN1054579A (en) |
| AU (1) | AU6540090A (en) |
| CA (1) | CA2001062A1 (en) |
| WO (1) | WO1991005747A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5736092A (en) * | 1994-03-31 | 1998-04-07 | Microwear Corporation | Microwave sintering process |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4938673A (en) * | 1989-01-17 | 1990-07-03 | Adrian Donald J | Isostatic pressing with microwave heating and method for same |
| US5194408A (en) * | 1989-02-22 | 1993-03-16 | General Mills, Inc. | Sintered ceramic microwave heating susceptor |
| JP3617076B2 (en) * | 1993-06-30 | 2005-02-02 | 住友電気工業株式会社 | Silicon nitride sintered body and method for producing the same |
| US5698156A (en) * | 1993-06-30 | 1997-12-16 | Sumitomo Electric Industries, Ltd. | Method of producing a silicon nitride based sintered body |
| US5622905A (en) * | 1993-06-30 | 1997-04-22 | Sumitomo Electric Industries, Ltd. | Silicon nitride based sintered body |
| DE4340652C2 (en) * | 1993-11-30 | 2003-10-16 | Widia Gmbh | Composite and process for its manufacture |
| CN1111147C (en) * | 1999-07-22 | 2003-06-11 | 青岛大学 | Microwave sintering method of composite ceramics |
| US7148456B2 (en) * | 2004-09-15 | 2006-12-12 | The Penn State Research Foundation | Method and apparatus for microwave phosphor synthesis |
| JP2007261916A (en) * | 2006-03-29 | 2007-10-11 | Tokuyama Corp | Method for joining ceramics and ceramic joined body |
| BRPI0605383A (en) * | 2006-12-27 | 2008-08-19 | Fundacao Universidade Fed De S | compositions for external susceptors and external susceptors for microwave ceramic sintering |
| JP2013248597A (en) * | 2012-06-04 | 2013-12-12 | Denso Corp | Low-oxygen atmosphere apparatus |
| FR3058138B1 (en) * | 2016-10-28 | 2019-02-01 | Centre National De La Recherche Scientifique | METHOD FOR THERMALLY PROCESSING A PIECE OF MICROWAVE CERAMIC MATERIAL |
| CN113324877A (en) * | 2021-06-01 | 2021-08-31 | 上海应用技术大学 | Ultra-low oxygen partial pressure sealing chamber seat dropping method for observing wetting angle of aluminum and magnesium melt |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS621802A (en) * | 1985-06-27 | 1987-01-07 | Komatsu Ltd | Forging and sintering method under false hydrostatic pressure |
| US4757172A (en) * | 1986-09-24 | 1988-07-12 | Questech Inc. | Method and apparatus for the microwave joining of nonoxide ceramic items |
| EP0329338A3 (en) * | 1988-02-16 | 1990-08-01 | Alcan International Limited | Process and apparatus for heating bodies at high temperature and pressure utilizing microwave energy |
-
1989
- 1989-10-19 CA CA 2001062 patent/CA2001062A1/en not_active Abandoned
-
1990
- 1990-10-19 WO PCT/CA1990/000358 patent/WO1991005747A1/en not_active Application Discontinuation
- 1990-10-19 EP EP19900915276 patent/EP0495850A1/en not_active Withdrawn
- 1990-10-19 AU AU65400/90A patent/AU6540090A/en not_active Abandoned
- 1990-10-19 JP JP2514200A patent/JP2628104B2/en not_active Expired - Lifetime
- 1990-10-19 CN CN 90109203 patent/CN1054579A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5736092A (en) * | 1994-03-31 | 1998-04-07 | Microwear Corporation | Microwave sintering process |
| US5808282A (en) * | 1994-03-31 | 1998-09-15 | Microwear Corporation | Microwave sintering process |
| US5874377A (en) * | 1994-03-31 | 1999-02-23 | Microwear Corporation | Sintered silicon nitride product |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH05500940A (en) | 1993-02-25 |
| JP2628104B2 (en) | 1997-07-09 |
| WO1991005747A1 (en) | 1991-05-02 |
| AU6540090A (en) | 1991-05-16 |
| CN1054579A (en) | 1991-09-18 |
| EP0495850A1 (en) | 1992-07-29 |
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