|Title of Invention
A METHOD OF MANUFACTURE OF CERAMIC BODIES BY MICRO WAVE JOINING
|Disclosed is a method of microwave joining of ceramic bodies comprising of the steps of coating the surfaces of the bodies to be joined with a paste made of a microwave couplant and atleast one surface selected from glass powder, cu powder, Cu/Mo/glass powder and firmly maintaining the said surfaces in contact with each other and heating the bodies in a microwave oven until joining of the bodies is complete.
This invention relates to a method of microwave joining of ceramic bodies and ceramic bodies so joined.
Microwaves are electromagnetic waves and the energy therefrom can be uti1ised for heating materials.
Ceramics are finding wider high technology applicat ions in automotive, electronic and aerospace industries, owing to their excellent properties such as corrosion resistance, high temperature strength, chemical inertness, high hardness and relatively lesser density. A major constraint in the use of these new materials is the problem of fabricating them into useful engineering components. The poor workabi1ity of ceramics, due to their poor fracture toughness, restricts their foramtion into intricate shapes. To get such complex shapes, joining of ceramics is essential.
Conventionally, ceramic bodies have been joined by brazing, diffusion bonding, friction welding and also by the use of microwaves.
However, although microwave joining of ceramic bodies is known to the art, the known methods of microwave joining of such members do not have the advantages of this invention-
In the case of this invention, there is no need to have controlled environment; the source is cheaper; there are/cost savings^ there is higher producti_v^tyjL-.«nd there is superior quality of the j joints-
In the case of the present invention, a low power microwave oven may be used (700 watts 2.45 Ghz). The quality of the joints is largely dependent on parameters such as temperature, time and the viscosity of the slurry applied to the surfaces of the ceramic bodies to be joined.
The method of microwave joining of ceramic bodies, according to this invention, comprises the steps of coating the surfaces of the bodies to be joined with a paste made of a microwave coup1 ant and a at least one substance selected from glass powder. Cu powder, Cu/Mo/glass powder; firmly
maintaining the said surface® in contact with each ) other? and and heating the bodies in a microwave ' / oven until joining of the bodies is complete*
This invention will now be described with
reference to the accompanying drawings which
illustrate by way of example two of several modes
of carrying out the method herein,
Fig.l illustrating two ceramic bodies being joined
in accordance with Example X
Fig. 2 illustrating two ceramic bodies being
joined in accordance with Example II.
EXAMPLE I Two ceramic bodies CI and C2 are firmly maintained with their surfaces 31 82 to be joined in contact with each other by using a clamp or like device (see arrows K).
Before bringing the said faces in contact, a paste made of glycerol and glass powder is applied on the surfaces to be joined. The said bodies are then kept in a microwave oven and heated until the said surfaces are securely joined together*
The microwave oven in the above Example is a
low power model (700 watts 2*49 6hz). To suit the requirements for carrying out the method proposed herein, the rotating glass table in the oven is removed. To withstand higher temperatures generated, the platform for food processing operations inside the oven is replaced by one made of mullite.
Glycerol has been used to form the bonding layer between the contact surfaces, since glycerol readily absorbs microwaves.
The viscous nature of the slurry used is important. If it is too thin, interfacial layer will be deficient of glass and no bonding will occur. On the other hand if the slurry is too thick, the residual glassy face reduces the strength of the joint. Hence the slurry should be of paste like consistency in order to get a good joint.
Example I is repeated except for this difference, namely, that after the paste is applied to the contact surfaces, and the surfaces kept in
contact by a clamp or like device (t»t arrow* K), thE said bodias are haatad by placing tham in a crucible B disposed on tha said platform in tha
oven, tha crucibla containing activatad charcoal
B powder; (a good microwave absorber) with tha bodias
embedded in the said charcoal powder. This is
Example II is rapeatad with this differencef namely, that instead of charcoal powderi SiC powder;(a good microwave absorber) is used for hybrid heating.
Instead of a pasta of glass powder and glycerol, other pastes of glycerol and Cu powder or of glycerol and Cu/Mo/glass powder may be used.
The terms and expressions in this specification are of description and not of limitation, there being no intention in the use of such terms and expressions of excluding any equivalents of tha \ features illustrated and described, but it is understood that various other modes of carrying
out the method proposed herein are possible without departing from the scop* and ambit of this invention.
, ■ ■■ ,=* i ■
We CI aim i ' n t*f J '
1 .A method, " of microwave joining of ceramic bodies comprising the steps of coating tfie surfaces of the bodies to be joined with a paste made of a microwave coup1ant and a at least one
substance selected from glass powder, Cu powder, Cti/Mo/glasB powderi firmly maintaining ! the said surfaces in contact with each otheri and heating the bodies in a microwave oven until joining of the bodies is complete.
2.4 method as claimed in Claim 1 wherein the microwave couplant is glycerol.
3.A method as claimed in any one of the preceding Claims wherein the said bodies are heated in the microwave oven by placing the same on the heating platform of the said oven.
#C"tt method as claimed in any one of the preceding Claims wherein the said bodies are heated in the
microwave ovtn by embedding the bodies in charcoal powder contained in a crucible and placing the crucible on the heating platform of the »aid oven.
/5.A /method as claimed in Claim 5 wherein the charcoal is activated charcoal.
/a.A/method as claimed in any one of the preceding Claims 1 to 3 wherein the said bodies are heated in the microwave oven by embedding the bodies in SiC powder contained in a crucible and placing the crucible on the heating platform of the said oven.
7.A method of microwave joining of ceramic bodies substantially as herein described with reference to, and as illustrated in, the Examples and the drawings.
8.Ceramic bodies whenever joined by a method as claimed in any one of he preceding Claims.
Dated this the &th day of Hay 1998
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|INDIAN INSTITUTE OF TECHNOLOGY
|IIT P.O., MADRAS-600 036.
|PCT International Classification Number
|PCT International Application Number
|PCT International Filing date