Surface Properties Of Ceramics Research Articles

High Dk and ultra-high thermal conductivity ST/μBN/polyolefin composites for microwave applications

In this work, we examined the structure, microwave dielectric, thermal and mechanical characteristics of composites containing SrTiO3/xμBN/polyolefin (with x at 0, 6, 8, 10 and 12 weight percent). SrTiO3 (ST) and micro boron nitride (μBN) powders were fabricated with 1,2-PB/EPDM/SBS (1,2-PB, EPDM and SBS are abbreviations of 1,2-polybutadienes, ethylene-propylene-dicyclopentadiene and styrene-butadiene-styrene triblock copolymer, respectively) by hot-press process after modified by Vinyltrimethoxysilane (VTMS) and 3-aminopropyltriethoxysilane (KH550), respectively. The ball mill and surface modification procedure enhanced the dispersion of the boron nitride in the solution and promoted compatibility between ceramic particles and polyolefin matrix. The incorporation of BN created more effective boron transfer pathways with ST particles, significantly improving the thermal conductivity of the composite. However, as μBN content increased, more ceramic agglomerates and pores were introduced, deteriorating dielectric, thermal and mechanical properties of the samples. The particle size test and XPS were conducted to determine the effect of surface modification on the dispersion and surface properties of ceramics. Cross-plane thermal conductivity, TGA and stress-strain curves were used to evaluate the thermal and mechanical properties of the composites. In all, a composite with high-Dk and high thermal conductivity was obtained when x = 10 wt.%: Dk = 17.4, Df = 0.0071 and λ = 1.784 W/(m*k), which is promising for microwave applications.

55 - Dental Ceramic Surface Properties after Resin-Cement Removal by Burning Technique

There are situations in which resin-cement needs to be removed from the crown's intaglio surface before it can be recemented. Some authors have proposed to burn off this cement; however, questions remain related to the effect of this technique on the surface properties of the ceramics. The goal was to test the effect of burning cements off on the surface properties of zirconia and lithium disilicate dental ceramics. The mechanical properties (hardness and elastic modulus) and removal effectiveness were tested in this study. Two kinds of ceramics: zirconia (Cercon, Dentsply Sirona) and lithium disilicate glass-ceramics (Emax, Ivoclar Vivadent) and two universal resin-cements; Calibra Universal (Dentsply) and Multilink Automix (Ivoclar Vivadent), were used in this research. Samples (n=8) were 1.3 mm thick and were sintered according to manufacturer recommendations. Zirconia samples were sandblasted with 150 aluminum oxide, and lithium-disilicate were etched with 9.6% hydrofluoric acid and then thoroughly rinsed. The application of each resin-cement followed the manufacturer's recommendations, and the samples were light-cured for 20 s. After 15 days of storage (100% humidity and 36 C), the samples were placed into a furnace at a temperature of ~150 C then heated a rate of ~30 C/min until reaching a temperature of 400 C where the temperature was held for 1 minute. The samples were removed from the furnace and allowed to cool before the cement was removed. Fourier Transformed Infra-Red (FTIR) was used, before and after cementation, to check the surface chemical composition and the effectiveness of the resin-cement removal. A nanoindenter (Hysitron TI 750 Ubi Triboindenter) using a Berkovich tip (100 mN) was used to assess the surface properties. Statistical analyses of the results were performed using two-way ANOVA and a post hoc Tukey test (α = 0.05). FTIR showed that the burning technique was effective to remove the residual resin-cement from the ceramic samples. Also, there was no significant statistical difference between the hardness and the elastic modulus of the dental ceramic surfaces from before and after the burning technique. This study showed that the removal of the resin-cements from crowns intaglio by the burning technique could be a viable clinical solution before recementing dental ceramics.

Effect of dielectric barrier discharge on ceramic surface properties

Ceramics, as a commonly used insulating and thermally conductive material, has a wide range of applications in the field of micro-nano manufacturing. In recent years, research on ceramic bonding has also increased. However, ceramic bonding has some problems such as bonding failure and low bonding quality. Learning from other commonly used bonding materials, the important factor for the success of bonding is the surface properties of the material. Therefore, in this study, the surface of ceramic was treated by dielectric barrier discharge (DBD) to improve surface properties. The effects of dielectric barrier discharge on the surface properties of ceramic is investigated from the three aspects: hydrophilic angle, surface energy and surface morphology. In the dielectric barrier discharge experiment, blind via glass is used as the blocking medium for the upper electrode. The lower electrode is covered by ceramic, and the ceramic is also the material to be treated. The influence of processing time, discharge voltage and discharge frequency on the treatment effect is investigated in the experiment. The hydrophilic angle and surface energy of the treated ceramics are measured and calculated by contact angle measuring instrument, and the surface morphology was observed by scanning electron microscopy. The results show that the longer the discharge treatment time is, the larger the discharge output voltage is, the smaller the discharge gap is, the faster the hydrophilicity of the surface of the ceramic sheet is, and the higher the activation energy is. The damage of the ceramic surface after treatment is small, and the impurities on the surface are destroyed. In general, the surface properties of ceramics after dielectric barrier discharge treatment are better than before.

Interaction of human osteoblasts with bioinert and bioactive ceramic substrates

The objective of this study was to compare adhesion, replication, and differentiation of human osteoblasts (OPC1 cell line) on two different ceramic substrates: a bioinert alumina (A1(2)O(3)), and a bioactive hydroxyapatite (HAp). Scanning electron microscopy (SEM) and confocal scanning microscopy were used to assess production and distribution of specific osteoblast proteins. Cells grew readily on HAp and alumina. On alumina and HAp, OPC1 cells produced distinctive cell-to-cell and cell-to-scaffold filopodia and microextensions. OPC1 cells proliferated faster on HAp than on alumina substrates. Adhesion was further assessed by observing production of the protein vinculin. On alumina, vinculin was detected throughout the cytoplasm, with some peripheral punctate regions. On HAp, OPC1 cells developed few punctate peripheral regions of vinculin; rather, the protein was strongly localized within the cytoplasm. Finally, we measured accumulation of the marker osteopontin (OPN). OPN was first detectable on day 5 and increased through day 11 of culture on alumina. OPC1 cells on HAp produced substantial amounts of OPN beginning at day 5, with apparent secretion from the cells by culture day 11. These results suggest that the function of osteoblasts is strongly affected by the properties of ceramic surfaces, and rapid attachment of osteoblasts may result in earlier differentiation on HAp than on alumina.

Direct observation of microstructural changes in ion-beam modified ceramics

A technique for the direct observation of microstructural changes in ceramics following ion- implantation is presented. Ion-implantation produces modifications to the mechanical properties of ceramic surfaces. These modifications have been investigated as a means of improving the hardness and wear of such materials. Examples of these changes will be presented for single-crystal specimens of MgO which have been implanted with Xe+ ions. The resultant microstructural changes are a function of ion fluence and are related to structural modifications at or near the surface.Transmission electron microscopy (TEM) is a powerful technique for examination of microstructure on a nanometer scale. A problem often encountered when conventional methods of specimen preparation, for TEM analysis, are used is the possibility of ion-beam induced damage. Ion-beam damage can be a serious problem especially in the preparation of MgO specimens. In the present study damage resulting from ion-milling can be entirely avoided by ion-implantation directly into an electron-transparent thin-foil specimen.

Ion implanted precipitate microstructure and mechanical properties of ceramic surfaces

Microstructure of precipitates produced by annealing ion implanted surfaces have been investigated in the Al2O3-ZrO2 system and both microhardness and indentation fracture toughness have been measured for correlation with microstructure. Air annealing of 190 keV high dose implants of Al+ in yttriastabilized zirconia and Zr+ in AI2O3 have resulted in A12O3 and ZrO2 precipitates, respectively, as would be expected from phase equilibria. However, annealing schedules drastically alter precipitate microstructure (i.e., crystallite size, morphology, orientation), and changes in microstructure have produced significant variation of surface mechanical properties. Crystallization of the ZrO2 films on AI2O3 was observable by conventional XRD. The precipitated ZrO2 was in the monoclinic structure if the grain size was large or in the tetragonal state if grain size was small. Being able to produce tetragonal ZrO2 particles in A12O3 surfaces suggests the possibility of transformation toughening and strengthening.

Electronic Structure and Properties of Oxide Surfaces and Interfaces

AbstractMany technologically-important areas rely on properties of ceramic surfaces or interfaces. Some of these properties are simply stability, e.g. resistance to dimension change, to grain-size change, or to change in coverage by a metal layer. Other properties rely on well-defined electronic features, e.g. a suitable density of surface states, of surface defects, or of response to adsorbed species. Still further surface characteristics - the precise geometric structures, the near-surface electric fields, and especially impurity segregation - can strongly influence observed behaviour.This survey emphasises the insights gained from atomistic modelling of ceramic surfaces and interfaces. The theoretical methods allow one to identify the features determining surface geometry, the degree of surface segregation by impurities, the role of the image charge and the influence of space-charge layers on intrinsic defect levels. The surface distortion affects defects like the surface Fs+ centre (electron trapped at an oxygen vacancy on an oxide) and similar colour centres. Whilst most of the results will be for oxides, parallels with semiconductor systems and the special features of metal-oxide interfaces are mentioned.