Advanced Materials Research Vols. 750-752

Abstract: Dental ceramic materials have approximate color and translucency with natural tooth, which is unmatched by other restorative materials. Because of its beautiful appearance, good physical and chemical properties, all-ceramic crown restorations are more widely used., However, due to the brittleness of ceramics and the stress mismatch between different materials, dropping or fracture phenomenon of porcelain veneer is often occurred in clinical application during the service period of all-ceramic crowns. The porcelain veneer failure mechanism is still not very clear, in this paper, the force performance of all-ceramic crowns is analyzed using the RFPA (realistic failure process analysis) system. The crack initiation, propagation and failure process of all-ceramic crown can be clearly observed and the research results provide guidance for clinical application

Abstract: This paper studied the change of glass phase splitting structure in Na2O-CaO- Al2O3-B2O3 -SiO2-TiO2 system. It discussed the change of two-phase composition and central ion coordination number of the phase splitting glass in the phase splitting process by using the means of EDS, SEM. The result indicates that the glass structure of two-phase changes significantly in the phase splitting process of this system. When the temperature is low, the glass net work is composed of [BO4], small quantity of [BO3] and large quantity of [AlO4] in the structure of alkali boron-rich phase, and the net adjustment ion is Ca2+ mainly; and then the glass net work is composed of [SiO4] and small quantity of [AlO4] in silicon-rich phase, and there are large quantity of net adjustment ion Na+ in the structure also. With the phase splitting temperature rising, the distribution of the net work central ion in two-phase retains unchanged, small quantity of the coodination number of Al3+ rising, [BO3] transfers to [BO4] gradually, at the same time, the net adjustment ion Na+ enters in alkali boron-rich phase, that is Na+ transfers to alkali boron-rich phase from silicon-rich phase. Along with the proceeding of phase splitting process, TiO2 concentrate and pricipitate at two-phase interface.

Abstract: This article describes the alumina ceramic mixed with two kinds of additives in order to improve the performance of ceramic, such as mixed with submicron ZrO₂ and MnO₂ Monoclinic zirconia (m-ZrO₂) and tetragonal zirconia (t-ZrO₂) of reversible phase transition of volume change is used to improve the toughness and wear resistance of composite alumina ceramic. Through doing various tests about fired products, including hardness testing, SEM test and bulk density measurement, we can understand the microstructure and mechanical properties of samples.

Abstract: Reliability of indentation method in carbon nanotube reinforced ceramics had been proposed in some works, especially of indentation toughness. In this work the traditional indentation hardness of the Multi-wall carbon Nanotube reinforced alumina composites was studied. It is found that the Vickers hardness and nanoindentation hardness of MWNT reinforced alumina fabricated by SPS decreased from about 20GPa to 16GPa at a critical load force about 1kg. While pure alumina showed a Vickers hardness of 20.6GPa in the whole load force range. When the load force or displacement into surface increasing, continuous recorded hardness, contact stiffness and modulus of the MWNT reinforced alumina showed quite different behavior compared with the pure alumina, especially at middle period of indentation. It was believed that different properties in vertical and horizontal directions of the MWNT were the key. MWNT was compressed and deformed as a soften component in the whole indentation processing. And tensile stress caused by MWNT in composite became significant until an enough strain attained and decreased when a critical stress was over. The results mean the definition of hardness or similar ones seemed need deep description in this type of material.

Abstract: Al₂O₃-MgO unfired brick were prepared by using brown corundum, white corundum, fused magnesia and α-A1₂O₃ as main starting materials, Al₂O₃-SiO₂ gel powder as a binder. The effects of Al₂O₃-SiO₂ gel powder on the strength of Al₂O₃-MgO unfired bricks were investigated. The phase composition was characterized by X-ray diffraction (XRD). The results showed that with an increase of Al₂O₃-SiO₂ gel powder content, room temperature strength first increased and then decreased, and reached an optimum value at 5.5% addition. The hot modulus of rupture continuously increased. This mainly was related to the reactivity of Al₂O₃-SiO₂ gel powder and the formation of mullite at high temperature.

Abstract: Unfired Al₂O₃-C slides were prepared by using tabular corundum, reactive Al₂O₃ and fused alumina zirconia (FAZ) as main starting materials, Al powder and Si powder as anti-oxidation agents, phenolic resin as a binder. The effects of addition of fused alumina zirconia on the room temperature physical properties and hot modulus of rupture (HMOR) of unfired Al₂O₃-C slide were investigated. The phase composition and microstructure were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The results showed that with the increase of fused alumina zirconia content, bulk density of the specimens after dried increased, apparent porosity decreased and high temperature strength increased. Phase transformation in ZrO₂ could take place at different temperature, accompanying a volumetric expansion and microcrack formation. This would lead to a first increase and then decrease in HMOR. A maximum value was reached at 11 wt. % ZrO₂. The thickness of decarbonization increased with increasing ZrO₂ content.

Abstract: Al₂O₃-MgO unfired bricks were prepared by using brown corundum, white corundum, fused magnesia and α-A1₂O₃ micropowder as main starting materials, Al₂O₃-SiO₂ gel powder as a binder. The effects of magnesia fines addition on physical performance of Al₂O₃-MgO unfired bricks were investigated. The phase composition and microstructure were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The results showed that with the increase of magnesia fines addition, bulk density of Al₂O₃-MgO unfired bricks after dried decreased and strength increased. After heat treatment at 1100 °C, apparent porosity (AP) slightly reduced, bulk density (BD) slightly increased. Strength had little change. After heat treatment at 1500 °C, AP first decreased and then increased, and strength change correspondingly. The hot modulus of rupture (HMOR) first increased and then decreased with increasing magnesia content. The optimum magnesia addition is at 6.0 wt. %.

Abstract: CaO-SiO₂-B₂O₃-Al₂O₃-La₂O₃ system sealants with different B/Si ratios of 0.38~0.82 were prepared by high-temperature melting method for intermediate temperature solid oxide fuel cell (ITSOFC). The glass transition temperature (Tg) and softening temperature (Ts) of the sealant were analyzed by TG-DSC. The complex phases of the sealants detected by XRD were consistent with the calculation results generally. The resistivity of the sealants tested by electrochemical workstation was above 65 kΩ·cm², and the wetting angle was also calculated. The prepared sealants basically meet the sealing requirement for ITSOFC.

Abstract: The CaO-SiO₂-B₂O₃-Al₂O₃-La₂O₃ sealants with different alumina contents were fabricated by high-temperature melting method for intermediate temperature solid oxide fuel cell (ITSOFC). The glass transition temperature (Tg) and crystal temperature (Ts) of the sealant with different alumina content was characterized by TG-DSC. And the composition phase of the sealant was detected by XRD. The resistivity of sealant tested by electrochemical workstation was higher than 22 kΩ·cm², which met the requirement for ITSOFC. Through the detecting of the wetting angle, the adhesion of sealant and anode materials was very good, and the single cell sealed with alumina tube successfully.

Abstract: Porous fiber metals are a kind of metallic materials which have a through-pore structure by forming and sintering.They have the advantages of light weight,high surface area and high specific strength.They are widely used in engineering field.This paper described the progress and application of porous fiber metals.And analysed the progresses of titanium fiber porous materials,nickel fiber porous materials,FeCrAl fibrous porous materials,copper fiber porous materials and stainless steel fiber porous materials,and prospected their further development.