Dental material is content from four main categories:
1- Polymer metal ceramic composite ***
2- Polymer metal ceramic stone.
3- Polymer metal ceramic cement.
4- polymer metal ceramic alginate.
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In the developments and applications of composite ceramics, mainly carbon (C) and silicon carbide (SiC) fibers are used, and sometimes aluminum oxide or alumina (Al2O3) fibers, or mixed crystals of alumina and silicon oxide or silica (SiO2) called mullite (3Al2O3, 2SiO2). The materials used for the matrix in the technical applications are currently mainly alumina, mullite, carbon and silicon carbide.
The development of these ceramics has arisen from the problems encountered in the use of conventional technical ceramics, such as alumina, silicon carbide often used in sintered form under the abbreviation SSiC (English Sintered Silicon Carbide), nitride aluminum (AlN), silicon nitride (Si3N4), zirconium oxide (IV) or zirconia (ZrO2): all these materials break easily under mechanical or thermal stress, because even small imperfections or scratches on the surface can become the starting point of a crack. The material opposes the propagation of crack only a weak resistance, like glass, unlike more ductile metals. This gives a characteristic brittle behavior, which complicates or even prevents many uses. Work aimed at limiting this behavior by the inclusion of heterogeneous particles, small monocrystalline fibers or barbs, or small plates (platelets), only modestly improved their resistance to fracture, and did not practical applications than in some ceramic cutting tools.
It is only with the use of long fibers for the reinforcement of the ceramic that drastically improved the breaking strength, as well as other properties such as the possibility of elongation, the resistance to rupture and thermal shock, which has opened and opens up new fields of application.
CMCs are usually described in the form of "fiber type / matrix type". Thus "C / C" describes carbon fiber-reinforced carbon, "C / SiC" carbon fiber-reinforced silicon carbide. If one wants to include in the abbreviation the method of manufacture, one uses the diagram "process-fiber / matrix". The carbon fiber-reinforced silicon carbide will be referred to as the "LPI-C / SiC" liquid polymer infiltration process (LPI). This type of abbreviation will be used below.
The main CMCs currently available industrially are C / C, C / SiC, SiC / SiC, AdR / IEn and Al2O3 / Al2O3. They differ from conventional technical ceramics mainly by the following properties which will be detailed below.
- Elongation before break enlarged up to 1%.
- significantly better resistance to breakage.
- extreme resistance to thermal shock.
- better resistance to dynamic loads.
anisotropic properties defined by the orientation of the fibers.
Remarks on ceramic fibers:
A fiber, also called monofilament, has a diameter of between 6 and 20 microns. Under the name of ceramic fiber, in the context of composites, one understands not only, as for the technical ceramics, structures of polycrystalline materials, but also materials with an arrangement of the amorphous atoms. Due to the high temperature of the composites, the use of not only organic fibers, but even of metal or glass, is excluded. Only high temperature resistant ceramic fibers: crystalline alumina, mullite, crystalline silicon carbide, zirconia, carbon with the graphitic planes oriented along the fiber, as well as amorphous silicon carbide are used in practice. All these "ceramic" fibers are characterized by an elongation at break up to 2%, much higher than that of normal ceramics (from 0.05 to 0.1%). The reason for this is that ceramic fibers contain various additives defined by the manufacturer (eg, oxygen, titanium, aluminum), without which the SiC fibers would not be able to achieve an elongation at break of 2% and a tensile strength of more than 3,000 MPa.
With these properties, the fibers can also be woven into two- or three-dimensional structures (see figure). In the work, for example weaving, the fibers must have high tensile strengths and withstand small radii of curvature.
Fibers and reinforcement:
Yarns are in fact the basic products found on the market. They are the ones used to produce composite materials. They contain from 500 monofilaments (for the finest threads) to 320000 monofilaments (for the biggest cables). In a yarn, given the large number of monofilaments, the intrinsic dispersion of the properties at break of the fibers is averaged. This value is displayed by the producers.
Due to their small diameter and high elongation at break, the fibers, despite their very high modulus, can be easily bent. As a result, it is possible to use standard textile machines to produce fibrous reinforcements adapted to the geometry and the stresses of the parts to be produced.
All textile reinforcement manufacturing processes used in organic matrix composites (carbon-epoxy for example) are also used for CMC: weaving, braiding, glazing, winding. Parts that are made with CMCs are parts that work in temperature (from 400 to over 3000 ° C) and have heterogeneous temperature fields varying over time. As a result, the parts are subjected to stress fields of thermal origin (heterogeneous thermal expansion field) creating tensile and shear stresses in all directions. A material consisting solely of a stack of 2D tissue layers would quickly perish by delamination (matrix cracking between tissue layers). This is why most CMC parts use fibrous reinforcements of type 2.5 or nD (with n ≥ 3). The most widely used multidirectional reinforcing techniques are needling, multilayer weaving, multilayer braiding and 4D. A 4D structure is made by arranging rods (obtained by pultrusion of son) according to the directions of the 4 diagonals of a cube. Multidirectional fibrous reinforcements are characterized by:
An overall fiber content of between 20 and 40%.
- A pore size distribution with two domains: an intra-wire porosity of the order of one micron and an inter-wire porosity ranging from 50 to 500 μm.
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In the developments and applications of composite ceramics, mainly carbon (C) and silicon carbide (SiC) fibers are used, and sometimes aluminum oxide or alumina (Al2O3) fibers, or mixed crystals of alumina and silicon oxide or silica (SiO2) called mullite (3Al2O3, 2SiO2). The materials used for the matrix in the technical applications are currently mainly alumina, mullite, carbon and silicon carbide.
The development of these ceramics has arisen from the problems encountered in the use of conventional technical ceramics, such as alumina, silicon carbide often used in sintered form under the abbreviation SSiC (English Sintered Silicon Carbide), nitride aluminum (AlN), silicon nitride (Si3N4), zirconium oxide (IV) or zirconia (ZrO2): all these materials break easily under mechanical or thermal stress, because even small imperfections or scratches on the surface can become the starting point of a crack. The material opposes the propagation of crack only a weak resistance, like glass, unlike more ductile metals. This gives a characteristic brittle behavior, which complicates or even prevents many uses. Work aimed at limiting this behavior by the inclusion of heterogeneous particles, small monocrystalline fibers or barbs, or small plates (platelets), only modestly improved their resistance to fracture, and did not practical applications than in some ceramic cutting tools.
It is only with the use of long fibers for the reinforcement of the ceramic that drastically improved the breaking strength, as well as other properties such as the possibility of elongation, the resistance to rupture and thermal shock, which has opened and opens up new fields of application.
CMCs are usually described in the form of "fiber type / matrix type". Thus "C / C" describes carbon fiber-reinforced carbon, "C / SiC" carbon fiber-reinforced silicon carbide. If one wants to include in the abbreviation the method of manufacture, one uses the diagram "process-fiber / matrix". The carbon fiber-reinforced silicon carbide will be referred to as the "LPI-C / SiC" liquid polymer infiltration process (LPI). This type of abbreviation will be used below.
The main CMCs currently available industrially are C / C, C / SiC, SiC / SiC, AdR / IEn and Al2O3 / Al2O3. They differ from conventional technical ceramics mainly by the following properties which will be detailed below.
- Elongation before break enlarged up to 1%.
- significantly better resistance to breakage.
- extreme resistance to thermal shock.
- better resistance to dynamic loads.
anisotropic properties defined by the orientation of the fibers.
Remarks on ceramic fibers:
A fiber, also called monofilament, has a diameter of between 6 and 20 microns. Under the name of ceramic fiber, in the context of composites, one understands not only, as for the technical ceramics, structures of polycrystalline materials, but also materials with an arrangement of the amorphous atoms. Due to the high temperature of the composites, the use of not only organic fibers, but even of metal or glass, is excluded. Only high temperature resistant ceramic fibers: crystalline alumina, mullite, crystalline silicon carbide, zirconia, carbon with the graphitic planes oriented along the fiber, as well as amorphous silicon carbide are used in practice. All these "ceramic" fibers are characterized by an elongation at break up to 2%, much higher than that of normal ceramics (from 0.05 to 0.1%). The reason for this is that ceramic fibers contain various additives defined by the manufacturer (eg, oxygen, titanium, aluminum), without which the SiC fibers would not be able to achieve an elongation at break of 2% and a tensile strength of more than 3,000 MPa.
With these properties, the fibers can also be woven into two- or three-dimensional structures (see figure). In the work, for example weaving, the fibers must have high tensile strengths and withstand small radii of curvature.
Fibers and reinforcement:
Yarns are in fact the basic products found on the market. They are the ones used to produce composite materials. They contain from 500 monofilaments (for the finest threads) to 320000 monofilaments (for the biggest cables). In a yarn, given the large number of monofilaments, the intrinsic dispersion of the properties at break of the fibers is averaged. This value is displayed by the producers.
Due to their small diameter and high elongation at break, the fibers, despite their very high modulus, can be easily bent. As a result, it is possible to use standard textile machines to produce fibrous reinforcements adapted to the geometry and the stresses of the parts to be produced.
All textile reinforcement manufacturing processes used in organic matrix composites (carbon-epoxy for example) are also used for CMC: weaving, braiding, glazing, winding. Parts that are made with CMCs are parts that work in temperature (from 400 to over 3000 ° C) and have heterogeneous temperature fields varying over time. As a result, the parts are subjected to stress fields of thermal origin (heterogeneous thermal expansion field) creating tensile and shear stresses in all directions. A material consisting solely of a stack of 2D tissue layers would quickly perish by delamination (matrix cracking between tissue layers). This is why most CMC parts use fibrous reinforcements of type 2.5 or nD (with n ≥ 3). The most widely used multidirectional reinforcing techniques are needling, multilayer weaving, multilayer braiding and 4D. A 4D structure is made by arranging rods (obtained by pultrusion of son) according to the directions of the 4 diagonals of a cube. Multidirectional fibrous reinforcements are characterized by:
An overall fiber content of between 20 and 40%.
- A pore size distribution with two domains: an intra-wire porosity of the order of one micron and an inter-wire porosity ranging from 50 to 500 μm.
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