Compositions: ceramic – Ceramic compositions – Carbide or oxycarbide containing
Reexamination Certificate
2002-10-29
2004-08-17
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Carbide or oxycarbide containing
C501S089000, C501S092000, C501S097100, C501S080000, C501S081000, C501S085000, C501S096200, C428S698000, C264S625000, C264S627000
Reexamination Certificate
active
06777361
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ceramic Composite material, for example, a ceramic molded body or a layer, as well as a use of the ceramic molded body or a layer.
BACKGROUND INFORMATION
European Published Patent Application No. 0 412 428 refers to a ceramic composite body and a method of producing same, in which an organosilicon polymer, as a precursor material, together with incorporated particles of hard material and/or other reinforcing components, as well as one or more metallic fillers, is subjected to pyrolysis. In pyrolysis, the decomposition products formed from the polymer compounds react with the metallic filler, which may result in a ceramic composite body having a matrix with particles of hard material and/or reenforce embedded components.
For example, carbides or nitrides of titanium, zirconium or other transition metals may be used as the hard material particles or reinforcing components as referred to, for example, in European Published Patent Application No. 0 412 428, in which the particle sizes of the powder particles are in the range of approximately 1 &mgr;m to approximately 300 &mgr;m.
The matrix formed from the organosilicon polymer after pyrolysis is a monophase or polyphase, amorphous, partially crystalline or crystalline matrix of silicon carbide, silicon nitride, silicon dioxide or mixtures thereof.
In addition to microscale powder materials, nanoscale powder materials may be single-phase or polyphase powders having particle sizes in the nanometer range. Due to their small particle dimensions, they are characterized by a very high proportion of particle boundaries or phase boundaries per volume. In addition, the physical, chemical and mechanical properties of such nanoscale powders may differ from those of conventional coarse-grained materials having the same chemical composition. For example, such nanoscale powders may have greater hardness, increased diffusivity and increased specific heat.
Nanoscale powdered materials may be produced by flame pyrolysis, gas condensation, spray conversion or crystallization of amorphous substances. Industrial production has advanced in the case of zirconium dioxide, silicon dioxide, titanium dioxide and aluminum oxide.
It is believed that the properties of ceramic composite materials having microscale fillers are determined largely by the properties of the fillers. Thus, local stress peaks or cracks may occur in the composite material when the properties of the matrix and fillers differ, e.g., different coefficients of thermal expansion. This may result in an increased failure rate of such components.
When using reactive microscale fillers as referred to, for example, in European Published Patent Application No. 0 412 428, the effect of which is based on reaction of the fillers with the ambient matrix, only an incomplete reactive conversion of filler may be achieved in the edge area of the filler grains.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a ceramic composite material, which may be suitable, for example, for producing ceramic molded bodies or layers and with which the profile of electrical and physical properties may be easily and reliably adjusted.
Another object of the present invention is to provide a ceramic composite material, the electric properties of which, porosity, high-temperature stability, mechanical strength, i.e., fracture toughness and homogeneity are improved in comparison with the related art.
It is believed that an exemplary ceramic composite material according to the present invention has the advantage in that the profile of electrical and physical properties of the ceramic composite material obtained after pyrolysis may be adapted to a profile of properties predetermined for the respective application, i.e., the composition of the composite material may be tailored to this profile of properties. For example, the large selection of fillers may permit the properties of the resulting ceramic composite materials to be varied or adjusted over a wide spectrum.
In addition, it is believed that an exemplary ceramic composite material according to the present invention has the advantage in that, due to the small particle size of the reactive filler, the process temperatures may be lowered and the process times required for a complete reaction may be shortened in comparison with the related art, so that with the process temperatures required in the past, liquid or volatile fillers may still be solid and thus may be used at the pyrolysis and sintering temperatures. Furthermore, unwanted phase reactions, which may occur at higher temperatures, i.e., reactions between the matrix and filler, may be avoided by using reduced process temperatures.
It is believed that one advantage of the composite material according to the present invention is that the porosity of the composite material may be adjusted in a defined manner using the fillers, the combination of a suitable nanoscale filler with defined pyrolysis conditions thus allowing the production of both highly porous composite materials and dense composite materials by varying the pyrolysis conditions, while otherwise using the same polymer precursor material, i.e., the same starting mixture.
Exemplary porous ceramic composite materials according to the present invention may also have a very good spalling resistance and may be applied to various applications, for example, as lightweight structural materials, as porous protective shells for sensors, as filters, as catalyst support materials or as a matrix for infiltrated reactive composite materials, while exemplary high-density ceramic composite materials according to the present invention have an increased mechanical strength, improved fracture toughness and improved corrosion resistance.
In production of a n exemplary ceramic composite material according to the present invention, shaping and production methods may be used, so that even ceramic fibers, layers and molded bodies of different sizes or having a complex geometry are readily obtainable, which may permit an exemplary composite material to be applied to a broad spectrum of applications. For example, shaping methods, such as compression molding, injection molding, joining and fiber extrusion may be used. With regard to the production method used, pyrolysis, under a protective gas and laser pyrolysis may be employed.
In this regard, a simple and reliable control or adjustability of the flow properties and pourability of the starting mixture may be achieved through the type and quantity of the nanoscale filler. This may also be true of the process parameters in powder transport, in cold molding, in injection molding, in spin coating or in dip coating.
Moreover, due to the small size of the filler, detailed replicas of embossed, cast or injection molded shapes may also be produced by pouring the starting mixture into a mold and then performing pyrolysis. In addition to the fidelity in detail, these replicas may have a high surface quality, allowing details having dimensions of less than 1 &mgr;m to be molded.
It is also believed that an exemplary ceramic composite material according to the present invention has the advantage in that, due to the use of highly dispersed insulating fillers, the electric resistance of the composite material is increased significantly and the long-term stability of this electric resistance may be improved. In addition, due to the improved homogeneity and stability of the thermal and electrical properties of the resulting composite material, reliability may also increase.
It is also believed that another advantage of an exemplary ceramic composite material according to the present invention is that it may permit high degrees of filling and short pyrolysis times, and the flow properties of the polymer precursor materials used may be regulated through the addition of suitably selected fillers. Thus, for example, suspensions of starting mixtures that remain stable and processable over long periods of time may-be produced.
The polymer precursor material may be an ox
Aichele Wilfried
Boeder Horst
Dressler Wolfgang
Kloncynski Alexander
Knoblauch Volker
Group Karl
Kenyon & Kenyon
Robert & Bosch GmbH
LandOfFree
Ceramic composite does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ceramic composite, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ceramic composite will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3297782