Papers by Keyword: Sintering Additive

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Authors: Kenji Kaneko, T. Saitoh, Sadahiro Tsurekawa
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Authors: Claudinei dos Santos, Kurt Strecker, M.J.R. Barboza, Sandro Aparecido Baldacim, Francisco Piorino Neto, Olivério Moreira Macedo Silva, Cosme Roberto Moreira Silva
Abstract: The creep behavior of hot-pressed Si3N4 ceramics was investigated. The proposal of this work is to investigate the use of yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, as sintering additive, since the cost of production of this material is 80% inferior to Y2O3. These ceramics were obtained by uniaxial hotpressing using different additive contents and mixtures (CRE2O3-Al2O3 or CRE2O3- AlN). Compressive creep tests were carried out at 13000C and 300 MPa, in air. The Si3N4-CRE2O3-Al2O3 ceramics demonstrated that the creep resistance is inversely proportional to the additive content. Mixtures with high intergranular phase content presented low creep resistance due to high oxidation and more pronounced softening of the intergranular phase. Si3N4-CRE2O3-AlN ceramics demonstrated better creep resistance with a steady-state creep rate of 7 x 10-8 s-1. This behavior is related to the a-SiAlON content, a solid solution of Si3N4 that incorporates a great fraction of intergranular phase, decreasing the amount of intergranular phase.
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Authors: Claudinei dos Santos, Kurt Strecker, M.J.R. Barboza, Sandro Aparecido Baldacim, Francisco Piorino Neto, Olivério Moreira Macedo Silva, Cosme Roberto Moreira Silva
Abstract: a−SiAlON (a’) is a solid solution of a−Si3N4, where Si and N are substituted by Al and O, respectively. The principal stabilizers of the a’-phase are Mg, Ca, Y and rare earth cations. In this way, the possible use of the yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, in obtaining these SiAlONs was investigated. Samples were sintered by hotpressing at 17500C, for 30 minutes, using a sintering pressure of 20 MPa. Creep behavior of the hot-pressed CRE-a-SiAlON/b-Si3N4 ceramic was investigated, using compressive creep tests, in air, at 1280 to 1340 0C, under stresses of 200 to 350 MPa, for 70 hours. This type of ceramic exhibited high creep and oxidation resistance. Its improved high-temperature properties are mainly due to the absence or reduced amount of intergranular phases, because of the incorporation of the metallic cations from the liquid phase formed during sintering into the Si3N4 structure, forming a a’/b composite.
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Authors: Claudinei dos Santos, Kurt Strecker, M.J.R. Barboza, Francisco Piorino Neto, Olivério Moreira Macedo Silva, Cosme Roberto Moreira Silva
Abstract: Commercial α−Si3N4, Al2O3 and a mixed yttrium and rare earth oxides, RE2O3, were used as starting-powders. Powder batches were milled using different Al2O3/RE2O3 contents, as additive. Hot-pressing was done at 1750oC-30 min-20MPa in N2 atmosphere. Specimens neat to 6x3x3mm3 were polished and characterized by XRD and SEM. Specimens were submitted to creep tests, under compressive stresses between 100 and 350 MPa at temperatures ranging from 1250 to 1300oC in air. Higher additive amounts resulted in larger grains of higher aspect ratios and in a decreased anisotropy in the hot-pressed ceramics. The compressive creep behavior depends on the intergranular phase content. While higher amounts of additives resulted in higher creep rates, • ε , and higher stress exponents, n, the activation energy Qss, has been inferior for samples with lower additive contents. Grain sliding has been identified to be the predominant mechanism responsible for creep deformation of these ceramics.
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Authors: H.G. Yu, C.X. Song, Z.H. Shen, Zhao Xian Xiong
Abstract: (Zr0.8Sn0.2)TiO4 ceramics with additives of ZnO, CuO, Bi2O3 and MnCO3 were prepared by the conventional mixed oxide route. They were characterized by TG/DTA, SEM, EDS and a network analyzer. Microwave properties of (Zr0.8Sn0.2)TiO4 ceramics were investigated as a function of the amount of additives. The optimal values of dielectric constant er, quality factors Q*f and temperature coefficient of resonant frequency tf reached 35, 51000 GHz and 26 ppm/°C respectively with 2.0 wt% MnCO3. Specimens with additives of ZnO, CuO and Bi2O3 had microwave properties of er = 35 ~ 39, Q*f = 9000 ~ 35000 GHz and tf = 15~40 ppm/°C.
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Authors: Yu Xin Chai, Xin Gui Zhou, Hua Yu Zhang
Abstract: In this study, the environment-friendly egg white protein was used as foaming agents and binders to fabricate Al2O3 ceramic foams, owing to its excellent foaming and binding properties. The CaO-SiO2-MgO-ZnO-TiO2-B2O3 composite sintering additive was added into Al2O3 ceramic foam to develop the mechanical performance of Al2O3 ceramic foam and facilitate sintering. The modified Al2O3 ceramic foam was investigated on porosity, density, compressive strength, pore morphology and grain size. The investigation revealed that: compared with ordinary Al2O3 ceramic foam, although the samples adding sintering additive had lower porosity, larger density and bigger grain, its compressive strength was significantly much stronger than samples without sintering additive. The XRD result indicated that samples adding sintering additive had spinel, anorthite and a small amount of mullite phase besides the main corundum phase. Adding sintering additive is a new way to develop the mechanical performance of Al2O3 ceramic foam and facilitate sintering which can help grain growth, thereby improving the mechanical properties of Al2O3 ceramic foam.
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Authors: Susana M.H. Olhero, José Maria F. Ferreira
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Authors: Chul Seung Lee, Kee Sung Lee, Shi Woo Lee, Do Kyung Kim
Abstract: Contact damage resistances of silicon nitride ceramics with various grain boundary phases are investigated in this study. The grain boundary phases are controlled by the addition of different types of sintering additives, or the crystallization of intergranular phase in a silicon nitride. We control the microstructures of materials to have similar grain sizes and the same phases to each other. Contact testing with spherical indenters is used to characterize the damage response. The implication is that the grain boundary phase can be another controllable factor against contact damage and strength degradation even though it is not critical relative to the effect of grain morphology.
421
Authors: Jian She Yue, Hong Jie Wang
Abstract: Sm2O3 and MgO as a sintering additives to fabricated porous silicon nitride by reaction-bonded. The phase of as-produced silicon nitride characterized by XRD-diffraction. The microstructure of product was investigated by SEM. The samples were machined into test bar for flexural strength testing. Using Archimedes theory testing the porosity of porous silicon nitride. MgO have restrain effect on the growth of rod-like silicon nitride, because of produce a restrain layer which is MgO reacted with SiO2 on the surface of silicon., the microstructure of crystal is particle like, the maximum flexural strength is 48MPa with porosity of 35%. Sm2O3 can assistant the growth of high aspect ratio Si3N4 crystal at beginning temperature of 1300°C for it’s low melt point and low viscidity in liquid state, the as-product’s morphology is rod-like and the flexural strength is as high as 300 MPa when the porosity is 30%, high than the sample that of low rod-like crystal content.
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Authors: Yu Xia Cao, Ling Zhong Du, Wei Gang Zhang
Abstract: CaB2O4 was added into hexagonal boron nitride (hBN) to improve the sintering behaviors of hBN. CaB2O4 and hBN were mixed and then pressed into plates. The plates were sintered at 2000°C for 5h under a N2 ambience. The phase compositions with different CaB2O4 contents were examined with X-ray diffraction analysis. The fracture cross-sections of the hBN plates were investigated by SEM. The apparent density and Rockwell hardness were also measured. The results show that the hBN particles had a plate-like shape and the grain sizes of hBN increased with increasing CaB2O4 contents. The apparent density and Rockwell hardness decreased with increasing CaB2O4 contents. When the CaB2O4 content was 15(wt) %, the hBN has the average grain sizes of 3μm in diameter and 200nm in thickness, the apparent density of 1.06 g/cm3 and the Rockwell hardness of 3, respectively.
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