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Ceramic Materials (ceramic + material)
Selected AbstractsCLINICAL PERFORMANCE OF LOW FUSING FRAMEWORK VENEERING CERAMIC MATERIALSJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 6 2008David Avery CDT Guest Expert [source] Effects of Six Surface Treatment Methods on the Surface Roughness of a Low-Fusing and an Ultra Low-Fusing Feldspathic Ceramic MaterialJOURNAL OF PROSTHODONTICS, Issue 3 2009Mehmet Dalkiz DDS Abstract Purpose: The purpose of this in vitro study was to determine the effects of six surface treatment methods on the surface roughness of two feldspathic ceramic materials. Materials and Methods: One hundred twenty metal discs were cast (Remanium CS). A low-fusing feldspathic ceramic (Vita Omega 900) was fired onto 60 metal discs, and an ultra low-fusing feldspathic ceramic (Finesse) was fired onto the other 60 metal discs. Six surface treatment methods were selected: (1) autoglazing (AUG), (2) overglazing (OVG), (3) polishing (POL), (4) fine diamond disc grinding + polishing + autoglazing (FDPA), (5) coarse diamond disc grinding + polishing + autoglazing (CDPA), (6) polishing + autoglazing (PA). Omega specimens were assigned to six experimental groups representing six surface treatment methods (Om-AUG, Om-OVG, Om-POL, Om-FDPA, Om-CDPA, Om-PA) (n = 10). Finesse specimens were also assigned to six experimental groups (Fn-AUG, Fn-OVG, Fn-POL, Fn-FDPA, Fn-CDPA, Fn-PA) (n = 10). Treated ceramic surfaces were examined by means of profilometry and transmission electron microscopy. Results: In Omega groups mean roughness values ranged as follows: group Om-AUG = Om-POL > Om-OVG > Om-CDPA = Om-FDPA > Om-PA (p < 0.001). No significant difference was found between groups Om-AUG/Om-POL and Om-CDPA/Om-FDPA (p > 0.05). In Finesse groups mean roughness values ranged as follows: Fn-CDPA > Fn-FDPA = Fn-AUG = Fn-POL = Fn-OVG > Fn-PA (p < 0.001). No significant difference was found between Fn-FDPA, Fn-AUG, Fn- POL and Fn-OVG (p > 0.05). Conclusions: For both ceramic types, the smoothest surfaces were obtained with polishing prior to autoglazing. Diamond disc grinding prior to polishing and autoglazing (Fn-FDPA, Fn-CDPA) displayed the roughest surfaces in ultra low-fusing ceramic (Finesse). Autoglazing alone and polishing displayed the roughest surfaces in low-fusing ceramic material (Om-AUG, Om-POL). [source] Preparing Low-Loss Low-Temperature Cofired Ceramic Material without Glass AdditionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000Heli Jantunen A low-temperature cofired ceramic (LTCC) composition for radio-frequency purposes was accomplished without prior glass preparation. In this process, the formulation was made by mixing the glass-forming oxides (ZnO, SiO2, and B2O3) with the commercial microwave ceramic MgTiO3,CaTiO3. The sintering, microstructure, and microwave properties were compared to a formulation with exactly the same composition, but a conventional production route, including glass preparation. The novel preparation route resulted in improved firing properties of the mixture. Also, the densities, porosities, and phases of the samples were almost the same as those of the conventional samples, but the phase fractions were different. Finally, this preparation route produced better dielectric values. [source] Confocal Examination of Subsurface Cracking in Ceramic MaterialsJOURNAL OF PROSTHODONTICS, Issue 7 2009MMedSc, Maged K. Etman DDS Abstract Purpose: The original ceramic surface finish and its microstructure may have an effect on crack propagation. The purpose of this study was to investigate the relation between crack propagation and ceramic microstructure following cyclic fatigue loading, and to qualitatively evaluate and quantitatively measure the surface and subsurface crack depths of three types of ceramic restorations with different microstructures using a Confocal Laser Scanning Microscope (CLSM) and Scanning Electron Microscope (SEM). Materials and Methods: Twenty (8 × 4 × 2 mm3) blocks of AllCeram (AC), experimental ceramic (EC, IPS e.max Press), and Sensation SL (SSL) were prepared, ten glazed and ten polished of each material. Sixty antagonist enamel specimens were made from the labial surfaces of permanent incisors. The ceramic abraders were attached to a wear machine, so that each enamel specimen presented at 45 degrees to the vertical movement of the abraders, and immersed in artificial saliva. Wear was induced for 80K cycles at 60 cycles/min with a load of 40 N and 2-mm horizontal deflection. The specimens were examined for cracks at baseline, 5K, 10K, 20K, 40K, and 80K cycles. Results: Twenty- to 30-,m deep subsurface cracking appeared in SSL, with 8 to 10 ,m in AC, and 7 ,m close to the margin of the wear facets in glazed EC after 5K cycles. The EC showed no cracks with increasing wear cycles. Seventy-,m deep subsurface cracks were detected in SSL and 45 ,m in AC after 80K cycles. Statistically, there was significant difference among the three materials (p < 0.05). Bonferroni multiple comparison of means test confirmed the ANOVA test and showed that there was no statistical difference (p > 0.05) in crack depth within the same ceramic material with different surface finishes. Conclusions: The ceramic materials with different microstructures showed different patterns of subsurface cracking. [source] Conductivity and Permittivity of Nickel-Nanoparticle-Containing Ceramic Materials in the Vicinity of Percolation ThresholdJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Umar Abdurakhmanov Conductivity and static permittivity of ceramic materials containing nanoparticles of Ni were measured in the vicinity of percolation threshold. It is found that, below this threshold, the experimentally obtained dependences of conductivity and static permittivity on the fractional Ni content in these materials are different from those calculated in the frame of the percolation theory. The origin of this discrepancy is discussed in terms of the network hierarchy model proposed recently by Balberg et al. for composite materials. [source] Design of Ceramic Materials for Chemical Sensors: Effect of SmFeO3 Processing on Surface and Electrical PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2001Hiromichi Aono Perovskite-type SmFeO3 powders were prepared by the thermal decomposition of a heteronuclear complex, Sm(Fe(CN)6)·4H2O and by solid-state reaction between the corresponding single oxides, Sm2O3 and Fe2O3. The thermal decomposition behavior of the complex was studied by thermogravimetric analysis. X-ray diffractometry was used to investigate the structure of the products from the complex thermal decomposition and the formation of SmFeO3 from the oxide mixture. Powders prepared by both methods were used to deposit thick films onto alumina substrates with comb-type gold electrodes. The microstructure and chemical homogeneity of the film surfaces were investigated by scanning electron microscopy and Auger electron spectroscopy. Thick SmFeO3 single-phase films having a homogeneous elemental distribution on the surface were obtained when powder prepared by thermal decomposition of the complex was used for deposition, even when the powder was fired at low temperature (800°C). Surface chemical analysis was performed by X-ray photoelectron spectroscopy (XPS). The O 1s XPS line was deconvoluted into two peaks, attributed to adsorbed oxygen (Oad) and oxygen in the lattice (Olattice). Quantitative analysis showed that the surface coverage of iron, expressed as Fe/(Fe + Sm), was larger for the films prepared using the solid-state reacted powder. Although the Olattice/(Fe + Sm) atomic ratio was not influenced by the processing procedures (and, thus, by iron surface coverage), the amount of Oad decreased with increasing iron surface coverage. A model of the SmFeO3 surface was used to determine that the outermost layer of the perovskite-type SmFeO3 prepared from the complex consisted mainly of samarium ions that could each bond four adsorbed oxygen ions. A single oxygen ion could adsorb onto an iron ion, and therefore, the content of adsorbed oxygen was lower for the film prepared from the solid-state reacted powders, which showed larger iron surface coverage. Electrical conductance measurements, performed with increasing temperature in different gaseous environments, confirmed these findings. Higher conductances and lower activation energies were observed for the films with larger samarium surface coverage. [source] Precursor-derived Si,(B,)C,N ceramics: thermolysis, amorphous state and crystallization,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2001Joachim Bill Abstract The preparation of silicon nitride- and carbide-based ceramics by solid-state thermolysis of polysilazanes and polysilylcarbodiimides is described. Results on the ceramization of the preceramic compounds and the architecture of the corresponding amorphous states obtained by spectroscopic means and by X-ray and neutron scattering are reviewed. Fundamental correlations between the composition and structure of the preceramic compounds and the architecture of the amorphous state are revealed. Furthermore, the crystallization behavior of the amorphous precursor-derived Si,C,N ceramics is treated. Moreover, the influence of boron on the thermal stability of the amorphous state is described. The high-temperature behavior of these Si,B,C,N solids can be correlated with their phase composition. Ceramic materials with compositions located close to the three-phase equilibrium SiC,+,BN,+,C exhibit a high temperature stability up to 2000,°C. This effect is accompanied by the formation of a metastable solid consisting of Si3N4 and SiC nanocrystals that are embedded in a turbostratic B,C,N matrix phase. Based on thermodynamic considerations, a model for the high-temperature stability effect is proposed. Copyright © 2001 John Wiley & Sons, Ltd. [source] A porous-matrix sensor to measure the matric potential of soil water in the fieldEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2007W. R. Whalley Summary The matric potential of soil water is probably the most useful assessment of soil water status. However, the water-filled tensiometer (the benchmark instrument for measuring matric potential) typically only operates in the range 0 to ,85 kPa. In this paper, we report the development of a porous-matrix sensor to measure matric potential in the approximate range ,50 to ,300 kPa. The sensor uses a dielectric probe to measure the water content of a ceramic material with known water retention characteristics. The calculation of matric potential takes into account hysteresis through the application of an appropriate model to measured wetting and drying loops. It is important that this model uses closed, rather than open, scanning loops. The calibrated sensors were tested in the field and the output compared with data from water-filled tensiometers and dielectric measurements of soil water content. These comparisons indicated that conventional tensiometers gave stable but false readings of matric potential when soil dried to matric potentials more negative than ,80 kPa. The porous-matrix sensors appeared to give reliable readings of matric potential in soil down to ,300 kPa and also responded appropriately to repeated wetting and drying. This porous-matrix sensor has considerable potential to help understand plant responses to drying soil. [source] Nanometer-Scale Mapping of Elastic Modules in Biogenic Composites: The Nacre of Mollusk ShellsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Haika Moshe-Drezner Abstract In this study, a newly developed nanoscale modulus mapping is applied in order to visualize the 2D-distribution of mechanical characteristics in the aragonitic nacre layer of Perna canaliculus (green mussel) shells. Modulus maps provide lateral resolution of about 10 nm. They allow the aragonitic mineral (CaCO3) tablets and the interfaces between them to be clearly resolved, which are filled by an organic substance (mainly beta-chitin). The experimental data are compared with finite element simulations that also take into account the tip radius of curvature and the thickness of organic layers, as measured by means of scanning electron microscopy with back-scattered electrons. Based on this comparison, the Young modulus of beta-chitin is extracted. The obtained number, E, = 40 GPa, is higher than previously evaluated. The collected maps reveal that the elastic modules in the nacre layer change gradually across the ceramic/organic interfaces within a spatial range four times wider than the thickness of the organic layers. This is possibly due to inhomogeneous distribution of organic macromolecules within ceramic tablets. According to the data, the concentration of macromolecules gradually increases when approaching the organic/ceramic interfaces. A behavior of this type is unique to biogenic materials and distinguishes them from synthetic composite materials. Finally, three possible mechanisms that attempt to explain why gradual changes of elastic modules significantly enhance the overall resistance to fracture of the nacre layer are briefly discussed. The experimental findings support the idea that individual ceramic tablets, comprising the nacre, are built of the compositionally and functionally graded ceramic material. This sheds additional light on the origin of the superior mechanical properties of biogenic composites. [source] Short Communication: application of a surrogate material in assessing the impact of porosity on re-ignition of wood-based materialsFIRE AND MATERIALS, Issue 2 2002Behdad Moghtaderi Re-ignition behaviour of charred solid fuels after extinction by water is studied. In this communication the effect of material porosity on re-ignition is investigated. A surrogate ceramic material is used so as to separate the pyrolysis and combustion processes from those associated with heat transfer. Experimental data are reported for different sample thickness and porosity, and varying heat flux and water application time. Copyright © 2002 John Wiley & Sons, Ltd. [source] New Design of a Ceramic Filter for Diesel Emission Control ApplicationsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2005Aleksander J. Pyzik Diesel particulate filters (DPF) made from an advanced ceramic material (ACM) based on mullite have demonstrated high filtration efficiency, low-pressure drop, high-temperature handling capability, and excellent mechanical integrity at a porosity of 60% or higher. Due to the ability to control microstructure, total porosity, and particle size distribution, Dow's acicular mullite can be tailored to meet requirements for deep bed filtration and fine particles emission control. In addition, the ACM DPF is suitable for catalyzed applications and it can retain its performance with a broad range of catalysts and over a wide range of catalyst loadings. This study describes a material selected for a DPF design that meets current diesel particulate emission control requirements as well as a four-way NOx control system. [source] Confocal Examination of Subsurface Cracking in Ceramic MaterialsJOURNAL OF PROSTHODONTICS, Issue 7 2009MMedSc, Maged K. Etman DDS Abstract Purpose: The original ceramic surface finish and its microstructure may have an effect on crack propagation. The purpose of this study was to investigate the relation between crack propagation and ceramic microstructure following cyclic fatigue loading, and to qualitatively evaluate and quantitatively measure the surface and subsurface crack depths of three types of ceramic restorations with different microstructures using a Confocal Laser Scanning Microscope (CLSM) and Scanning Electron Microscope (SEM). Materials and Methods: Twenty (8 × 4 × 2 mm3) blocks of AllCeram (AC), experimental ceramic (EC, IPS e.max Press), and Sensation SL (SSL) were prepared, ten glazed and ten polished of each material. Sixty antagonist enamel specimens were made from the labial surfaces of permanent incisors. The ceramic abraders were attached to a wear machine, so that each enamel specimen presented at 45 degrees to the vertical movement of the abraders, and immersed in artificial saliva. Wear was induced for 80K cycles at 60 cycles/min with a load of 40 N and 2-mm horizontal deflection. The specimens were examined for cracks at baseline, 5K, 10K, 20K, 40K, and 80K cycles. Results: Twenty- to 30-,m deep subsurface cracking appeared in SSL, with 8 to 10 ,m in AC, and 7 ,m close to the margin of the wear facets in glazed EC after 5K cycles. The EC showed no cracks with increasing wear cycles. Seventy-,m deep subsurface cracks were detected in SSL and 45 ,m in AC after 80K cycles. Statistically, there was significant difference among the three materials (p < 0.05). Bonferroni multiple comparison of means test confirmed the ANOVA test and showed that there was no statistical difference (p > 0.05) in crack depth within the same ceramic material with different surface finishes. Conclusions: The ceramic materials with different microstructures showed different patterns of subsurface cracking. [source] Effects of Six Surface Treatment Methods on the Surface Roughness of a Low-Fusing and an Ultra Low-Fusing Feldspathic Ceramic MaterialJOURNAL OF PROSTHODONTICS, Issue 3 2009Mehmet Dalkiz DDS Abstract Purpose: The purpose of this in vitro study was to determine the effects of six surface treatment methods on the surface roughness of two feldspathic ceramic materials. Materials and Methods: One hundred twenty metal discs were cast (Remanium CS). A low-fusing feldspathic ceramic (Vita Omega 900) was fired onto 60 metal discs, and an ultra low-fusing feldspathic ceramic (Finesse) was fired onto the other 60 metal discs. Six surface treatment methods were selected: (1) autoglazing (AUG), (2) overglazing (OVG), (3) polishing (POL), (4) fine diamond disc grinding + polishing + autoglazing (FDPA), (5) coarse diamond disc grinding + polishing + autoglazing (CDPA), (6) polishing + autoglazing (PA). Omega specimens were assigned to six experimental groups representing six surface treatment methods (Om-AUG, Om-OVG, Om-POL, Om-FDPA, Om-CDPA, Om-PA) (n = 10). Finesse specimens were also assigned to six experimental groups (Fn-AUG, Fn-OVG, Fn-POL, Fn-FDPA, Fn-CDPA, Fn-PA) (n = 10). Treated ceramic surfaces were examined by means of profilometry and transmission electron microscopy. Results: In Omega groups mean roughness values ranged as follows: group Om-AUG = Om-POL > Om-OVG > Om-CDPA = Om-FDPA > Om-PA (p < 0.001). No significant difference was found between groups Om-AUG/Om-POL and Om-CDPA/Om-FDPA (p > 0.05). In Finesse groups mean roughness values ranged as follows: Fn-CDPA > Fn-FDPA = Fn-AUG = Fn-POL = Fn-OVG > Fn-PA (p < 0.001). No significant difference was found between Fn-FDPA, Fn-AUG, Fn- POL and Fn-OVG (p > 0.05). Conclusions: For both ceramic types, the smoothest surfaces were obtained with polishing prior to autoglazing. Diamond disc grinding prior to polishing and autoglazing (Fn-FDPA, Fn-CDPA) displayed the roughest surfaces in ultra low-fusing ceramic (Finesse). Autoglazing alone and polishing displayed the roughest surfaces in low-fusing ceramic material (Om-AUG, Om-POL). [source] A Silicon Carbonitride Ceramic with Anomalously High PiezoresistivityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008Ligong Zhang The piezoresistive behavior of a silicon carbonitride ceramic derived from a polymer precursor is investigated under a uniaxial compressive loading condition. The electric conductivity has been measured as a function of the applied stress along both longitudinal and transverse directions. The gauge factor of the materials was then calculated from the data at different stress levels. The results show that the material exhibits an extremely high piezoresistive coefficient along both directions, ranging from 1000 to 4000, which are much higher than any existing ceramic material. The results also reveal that the gauge factor decreases significantly with increasing applied stress. A theoretical model based on the tunneling,percolation mechanism has been developed to explain the stress dependence of the gauge factor. The unique piezoresistive behavior is attributed to the unique self-assembled nanodomain structure of the material. [source] Effect of Oxygen Partial Pressure During Liquid-Phase Sintering on the Dielectric Properties of 0.9MgTiO3,0.1CaTiO3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2008Hee-Kyun Shin Microstructural evolution and microwave dielectric properties of liquid-phase-sintered 0.9MgTiO3,0.1CaTiO3 dielectric ceramic material have been investigated as a function of oxygen partial pressure () during sintering. Sintering in a weakly reducing atmosphere (=10,14 atm) generally increased the density, permittivity, quality factor (Q×f), and the temperature coefficient of resonance frequency (,f), but further reducing atmosphere down toof 10,14 atm generally decreased Q×f and ,f. When the 5 wt% lithium borosilicate glass-added specimen was sintered at 950°C and=10,14 atm, it demonstrated a permittivity of 18.8, Q×f of 19 000 GHz, and ,f of 10 × 10,6 K,1. [source] Spark Plasma Sintering as a Useful Technique to the Nanostructuration of Piezo-Ferroelectric Materials,ADVANCED ENGINEERING MATERIALS, Issue 8 2009Teresa Hungría Abstract This review gathers detail on the processing of piezo-ferroelectric ceramic materials by spark plasma sintering for the first time. The results reported here clearly indicate that it is a powerful technique and opens the possibility of processing ceramics with controlled sub-micron or even nanoscale grain sizes. [source] Fracture Toughness Enhancement for Alumina Systems: A ReviewINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2008Osayande L. Ighodaro Investigations have been carried out to determine ways of tailoring ceramic materials in order that one or more toughening mechanisms are activated in service. Microstructural manipulations, as well as composite formulations involving metallic, intermetallics, and ceramic phases have been used with ceramic matrices. Macrostructurally, laminated structures and functional gradient materials (FGMs) have also been formulated to enhance mechanical properties. Although significant improvements in material properties have been reported, ceramics are still below their projected positions on the materials map. This article presents a review of research activities pursuant to improving fracture toughness of alumina matrix systems and the enhancements achieved. [source] Texture Analysis and Finite Element Modeling of Operational Stresses in Ceramic Injection Molding Components for High-Pressure PumpsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2005Martin Wenzelburger Texturization of microstructures in ceramic components during injection of thermoplastic feedstocks into the mold is a well-known problem in ceramic injection molding (CIM) technology. The influences of textures on the mechanical properties of components with anisotropic properties, which depend on crystallite structure and orientation, usually involve weakening of the structure by the formation of separation planes and accumulation of stresses, which can lead to crack initiation and subcritical failure. A light optical texture analysis technique was developed for the analysis of thin section preparations from optically anisotropic ceramic materials. An internal Al2O3 gear rim for high-pressure gear pumps that is manufactured by CIM was chosen for the evaluation of this technique. Components were produced from thermoplastic ceramic feedstocks with different rheological behavior. Thin sections were prepared from the sintered parts. The texture was analyzed by polarized transmission light microscopy of the thin sections and colorimetric analysis of the crystal orientation. For the evaluation of the component properties, function, and lifetime, operating tests on a test bench were carried out as well as finite element (FE) simulation of the stress distribution in the components under operational load with regard to the texturization. The results were used for the localization of stress gradients and their comparison and correlation to the texturization. The functionality of this texture analysis method was proved by the tests, and it is expected to be a convenient novel method for the analysis and optimization of the parameters in CIM processes and the design of injection gate and mold. [source] Fabrication and Structural Evaluation of Beaded Inorganic Nanostructures Using Soft-Electron-Beam Lithography,ADVANCED MATERIALS, Issue 1 2007S. Donthu Soft electron-beam lithography, a simple high-resolution patterning technique, is used to fabricate single-grain-wide nanostructures, as seen in the figure, of functional ceramic materials, such as zinc oxide and bismuth ferrite. Structural characterization of these nanostructures reveal that average grain size decreases with line width (see the plot in the figure). [source] A comparative study of single-line and Rietveld strain,size evaluation procedures using MgO ceramicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2002Suminar Pratapa Strain,size evaluations from diffraction line broadening for MgO ceramic materials have been compared using single-line integral-breadth and Rietveld procedures with the Voigt function. Diffraction data were measured by Bragg,Brentano X-ray diffractometry (XRD), without incident beam monochromatization, and neutron diffractometry (ND) to encompass near-surface and bulk effects, respectively. The specimens consisted of sets of MgO ceramics and MgO,Y2O3 ceramic composites sintered over a range of temperatures. An MgO ceramic sintered at 1723,K for 2,h exhibited slightly less XRD broadening than the standard LaB6 NIST 660 SRM, and was therefore selected to make instrument profile corrections for both XRD and ND data. It was found for both data types that: (a) sintering initially relieves residual strain present in the MgO powder used to sinter the ceramics and also promotes grain growth; (b) residual strain of the MgO ceramic minimizes as the sintering temperature increases, and then increases with further rise in the sintering temperature, presumably as a result of intragranular interactions associated with grain growth; and (c) introduction of the second phase (Y2O3) increases strain and inhibits crystal growth. The single-line and Rietveld methods gave similar strain values from both the XRD and ND data within the limits of experimental error, but there were substantial differences between the single-line and Rietveld size estimates determined with the XRD and ND data. [source] Development of the powder reaction moulding processJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2009Lei Zhao Abstract BACKGROUND: The powder reaction moulding process uses a reactive monomer as carrier and binder for the moulding of metal or ceramic powders. De-binding is achieved using thermal depolymerisation which is followed by sintering to give the finished component. Binder can be recovered for re-use. RESULTS: Moulding compounds, with various powder volume fractions, have been prepared using stainless steel, silicon nitride and alumina with n-butyl cyanoacrylate as binder, and the stability of the compounds established. Rheological properties of the compounds have been measured using both pressure flow and drag flow methods. Compounds are strongly pseudoplastic. Comparison of experimental results with theoretical models, describing suspension flow behaviour shows that experimental maximum volume fractions are close to the theoretical volume fraction of 0.42 for silicon nitride, 0.68 for alumina and 0.7 for stainless steel. Differential scanning calorimetry and thermogravimetry have been used to simulate de-binding and show a rapid loss of binder through depolymerisation. Post-sintering porosity of the ceramic materials is high but this is thought to arise from the low pressure moulding techniques used. Porosity of the stainless steel mouldings is much lower. CONCLUSIONS: The results validate the powder reaction moulding idea and demonstrate applicability to three widely different powder materials. Copyright © 2008 Society of Chemical Industry [source] Clinical Success of Zirconia in Dental ApplicationsJOURNAL OF PROSTHODONTICS, Issue 1 2010Zeynep Özkurt DDS Abstract The application of ceramic materials for the fabrication of dental restorations is a focus of interest in esthetic dentistry. The ceramic materials of choice are glass ceramics, spinel, alumina, and zirconia. Zirconia was introduced into dentistry in the 1990s because of its good mechanical and chemical properties and is currently being used as a material for frameworks, dowels, implants, abutments, and orthodontic brackets. Many in vitro studies about zirconia use have been published, but clinical long-term studies are very important. This article presents data regarding the incidence of clinical success and complications of zirconia in these dental applications. Clinical studies published to date seem to indicate that zirconia is well tolerated and sufficiently resistant. [source] Effects of Six Surface Treatment Methods on the Surface Roughness of a Low-Fusing and an Ultra Low-Fusing Feldspathic Ceramic MaterialJOURNAL OF PROSTHODONTICS, Issue 3 2009Mehmet Dalkiz DDS Abstract Purpose: The purpose of this in vitro study was to determine the effects of six surface treatment methods on the surface roughness of two feldspathic ceramic materials. Materials and Methods: One hundred twenty metal discs were cast (Remanium CS). A low-fusing feldspathic ceramic (Vita Omega 900) was fired onto 60 metal discs, and an ultra low-fusing feldspathic ceramic (Finesse) was fired onto the other 60 metal discs. Six surface treatment methods were selected: (1) autoglazing (AUG), (2) overglazing (OVG), (3) polishing (POL), (4) fine diamond disc grinding + polishing + autoglazing (FDPA), (5) coarse diamond disc grinding + polishing + autoglazing (CDPA), (6) polishing + autoglazing (PA). Omega specimens were assigned to six experimental groups representing six surface treatment methods (Om-AUG, Om-OVG, Om-POL, Om-FDPA, Om-CDPA, Om-PA) (n = 10). Finesse specimens were also assigned to six experimental groups (Fn-AUG, Fn-OVG, Fn-POL, Fn-FDPA, Fn-CDPA, Fn-PA) (n = 10). Treated ceramic surfaces were examined by means of profilometry and transmission electron microscopy. Results: In Omega groups mean roughness values ranged as follows: group Om-AUG = Om-POL > Om-OVG > Om-CDPA = Om-FDPA > Om-PA (p < 0.001). No significant difference was found between groups Om-AUG/Om-POL and Om-CDPA/Om-FDPA (p > 0.05). In Finesse groups mean roughness values ranged as follows: Fn-CDPA > Fn-FDPA = Fn-AUG = Fn-POL = Fn-OVG > Fn-PA (p < 0.001). No significant difference was found between Fn-FDPA, Fn-AUG, Fn- POL and Fn-OVG (p > 0.05). Conclusions: For both ceramic types, the smoothest surfaces were obtained with polishing prior to autoglazing. Diamond disc grinding prior to polishing and autoglazing (Fn-FDPA, Fn-CDPA) displayed the roughest surfaces in ultra low-fusing ceramic (Finesse). Autoglazing alone and polishing displayed the roughest surfaces in low-fusing ceramic material (Om-AUG, Om-POL). [source] Effect of light source and time on the polymerization of resin cement through ceramic veneersJOURNAL OF PROSTHODONTICS, Issue 3 2001Flavio H. Rasetto Odont Purpose The purpose of this study was to evaluate the efficiency of 3 different light sources to polymerize a light curing resin cement beneath 3 types of porcelain veneer materials. Materials and Methods A conventional halogen light, a plasma arc light, and a high intensity halogen light were used to polymerize resin cement (Variolink II; Ivoclar North America Inc, Amherst, NY) through disks of veneer materials. Equal diameter and thickness disks of feldspathic porcelain (Ceramco II; Ceramco Inc, Burlington, NJ), pressable ceramic (IPS Empress; Ivoclar North America Inc), and aluminous porcelain (Vitadur Alpha; Vident Inc, Brea, CA) were used as an interface between the curing light tips and the light polymerized resin cement. The resin cement/veneer combinations were exposed to 4 different photopolymerization time protocols of 5 seconds, 10 seconds, 15 seconds, and 20 seconds for high intensity light units (Apollo 95E [Dental Medical Diagnostic Systems Inc, Westlake Village, CA] and Kreativ 2000 [Kreativ Inc, San Diego, CA]), and 20 seconds, 40 seconds, 60 seconds, and 80 seconds for conventional halogen light (Optilux; Demetron Research Inc, Danbury, CT). A surface hardness test (Knoop indenter) was used to determine the level of photopolymerization of the resin through the ceramic materials with each of the light sources. The data were analyzed by one-way analysis of variance and a post-hoc Scheffe test (p < .05). Results The data indicates that the Variolink II Knoop Hardness Number values vary with the light source, the veneer material, and the polymerization time. For a given light and veneer material, Knoop Hardness Number increases with longer polymerization times. The Kreativ light showed statistically significant differences (p < .05) between all test polymerization times. Use of this light required a polymerization time of greater than 20 seconds to reach maximum resin cement hardness. For samples polymerized with the Apollo light, there were statistically significant (p < .05) differences in surface hardness between samples polymerized at all times, except for the 15-second and 20-second times. Samples polymerized with the halogen light showed no statistically significant (p < .05) differences in hardness between polymerization times of 60 seconds and 80 seconds. Conclusions High intensity curing lights achieve adequate polymerization of resin cements through veneers in a markedly shorter time period than the conventional halogen light. However, the data in this report indicate that a minimum exposure time of 15 seconds with the Kreativ light and 10 seconds with the Apollo 95E light should be used to polymerize the Variolink II resin, regardless of the composition of the veneer. Conventional halogen lights required a correspondingly greater polymerization time of 60 seconds. [source] Micromechanical analysis of silicon nitride: a comparative study by fracture mechanics and Raman microprobe spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2002Shigemi Tochino Raman microprobe spectroscopy was used to characterize in situ microstress fields which develop during fracture of a toughened silicon nitride (Si3N4) polycrystal. Maps of microscopic stress were collected in the neighborhood of a propagating crack both at zero and at critical loading conditions. Micromechanics results by Raman spectroscopy were analyzed and compared with conventional fracture mechanics assessments, such as the evaluation of rising R -curve behavior and crack opening displacement. Outcomes of these assessments illustrate that, despite the approximations involved in the piezo-spectroscopic equations used for calculating the microstress field from a local Raman shift, Raman microprobe spectroscopy is a viable method for semi-quantitative investigations of microfracture mechanisms in advanced ceramic materials. Copyright © 2002 John Wiley & Sons, Ltd. [source] High-energy diffuse scattering on the 1-ID beamline at the Advanced Photon SourceJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2003T. R. Welberry This paper reports on experiments in which high-energy (65.35,keV) X-rays were used to record the detailed diffuse diffraction patterns of a number of ceramic materials. The methodology has enabled a greater q -range to be explored (up to sin,/,,,,0.97) than is possible with laboratory-based experiments, with better q -space resolution and increased sensitivity, thus allowing previously unseen detail in diffraction patterns to be recorded. In all, 11 sections of data have been collected for Ca-CSZ, eight for Y-CSZ and six for wüstite. [source] Crack Patterns in Ceramic Plates after QuenchingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Yingfeng Shao The crack patterns generated in a real ceramic plate and in a plate stacked by ceramic slabs under quenching are experimentally studied. The results here reveal that there are some distinct differences between the two crack patterns. The reasons that caused the differences are the size and boundary effects of the slabs. These crack patterns are very useful to understand the failure mechanisms of ceramic materials in thermal shock. [source] Natural Abundance 43Ca NMR Spectroscopy of Tobermorite and Jennite: Model Compounds for C,S,HJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009Geoffrey M. Bowers There are few effective methods for characterizing the molecular scale structural environments of Ca2+ in hydrated cements, which has limited our ability to understand the structure of, for example, Ca,silicate hydrate (C,S,H). 43Ca nuclear magnetic resonance (NMR) spectroscopy has long been considered too insensitive to provide useful data in this regard, but 43Ca magic angle spinning (MAS) NMR spectra reported here for synthetic tobermorite and jennite with naturally abundant levels of 43Ca demonstrate that this is a viable approach. We show that spectra with useful signal/noise ratios can be obtained in a reasonable acquisition period (,2 days) using an H0 field strength of 21.1 T, 5 mm rotors spinning at a frequency of 5 kHz, and a double frequency sweep preparatory pulse sequence. Tobermorite and jennite produce relatively broad resonances due to their complex structures and structural disorder, however, the chemical shift differences between six-coordinate 43Ca in jennite and seven-coordinate 43Ca in 11 Å tobermorite are large enough that the signals are entirely resolved at this field. These data suggest that signal from ideal tobermorite-like and jennite-like sites in cement C,S,H can most likely be distinguished by 43Ca NMR and that this method will be a powerful approach for studying cement-based ceramic materials in the coming decade. [source] Anelastic Behavior of Plasma-Sprayed Zirconia CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2008Yajie Liu Low-temperature thermal cycling of plasma-sprayed zirconia coatings reveals unique mechanical responses in their curvature measurements, namely nonlinear and cyclic hysteresis, collectively termed as anelastic. These features arise from the inherent layered, porous, and cracked morphology of thermal-sprayed ceramic materials. In this paper, the mechanisms of anelasticity are characterized by crack closure and frictional sliding models, and stress,strain relations of various thermal-sprayed zirconia coatings were determined via an inverse analysis procedure. These results demonstrate process conditions such as powder morphology and spray parameters significantly influence the mechanical behaviors of coatings. The unique anelastic responses can be used as valuable parameters in identifying coating quality as well as process reliability in manufacturing. [source] Conductive Polymer Coating on Nonconductive Ceramic Substrates for Use in the Electrophoretic Deposition ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2008Tetsuo Uchikoshi Uniform coating and line patterning of a conductive polypyrrole (Ppy) film on nonconductive ceramic materials were performed for use as substrates in the electrophoretic deposition (EPD) process. The Ppy was synthesized by chemical oxidation in the pyrrole solution. Direct shaping or line patterning of alumina or zirconia particles by EPD was carried out using the Ppy films as cathodes. [source] | |||||||||||||||||||||||||||||||