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1.
Mineaki Matsumoto Hiroshi Takayama Daisaku Yokoe Kazuo Mukai Hideaki Matsubara Yukio Kagiya Yuuji Sugita 《Scripta materialia》2006,54(12):2035-2039
The effects of La2O3 addition on thermal conductivity, phase stability and thermal cycle life of Y2O3 stabilized ZrO2 plasma sprayed coatings were investigated. Although low thermal conductivity as well as high resistance to sintering was achieved by La2O3 addition, it tended to also result in lower phase stability and thermal cycle life of the coatings. Optimization of the composition and structure of the coatings improved these properties, and the optimized coatings showed prolonged thermal cycle life. 相似文献
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The crystallisation of the oxygen-stabilised amorphous phase in a Zr50Cu50 alloy has been investigated by means of neutron diffraction and electron microscopy. The crystallisation microstructure consists of ZrO2, Zr2Cu and Zr7Cu10. A two-stage crystallisation mechanism is suggested: (i) primary crystallisation of Zr2Cu and (ii) formation of nanocrystals ZrO2 and Zr7Cu10. In (i), it is proposed, Zr2Cu crystallises from the oxygen-stabilised amorphous phase, leaving an oxygen- and copper-enriched matrix ; Zr2Cu rapidly grows and eventually attains a grain size of about 100 nm. In (ii), it is suggested, the residual amorphous matrix crystallises into nanocrystals ZrO2 and Zr7Cu10 due to the sluggish growth of ZrO2 and to the already formed ZrO2 which acts as a growth barrier to Zr7Cu10. In this case there is no particular orientation relationship between Zr2Cu and Zr7Cu10. 相似文献
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在Ni基体电沉积不同厚度的Ni-CeO2复合镀层并对其进行620 °C低温渗铝,制备了剩余复合镀层厚度分别约为10和45 μm厚的δ-Ni2Al3-CeO2/Ni-CeO2涂层体系。1000 °C真空退火5 h后,以上两种涂层体系均可在铝化物/镀层界面形成CeO2富集层。但剩余复合镀层厚度为10 μm的涂层体系由于氧化物富集程度不足,涂层退化程度较剩余复合镀层厚度为45 μm的涂层体系严重。可见,在镀层氧化物颗粒含量一定的情况下,渗铝后剩余镀层厚度是影响扩散障有效性的重要因素。 相似文献
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The n-type Co-doped β-FeSi2 (Fe0.98Co0.02Si2) with dispersion of several oxides, such as ZrO2 or several rare-earth oxides (Y2O3, Nd2O3, Sm2O3 and Gd2O3), was synthesized by mechanical alloying and subsequent hot pressing. The effects of these oxide dispersions on the thermoelectric properties of Fe0.98Co0.02Si2 were investigated. ZrO2 was decomposed in the β phase, and the ZrSi and -FeSi phases, which are metallic phases, were formed in the samples with ZrO2 addition. The Seebeck coefficient and the electrical resistivity were significantly decreased with increasing amount of ZrO2, indicating that a part of the Zr atoms was substituted for Fe atoms in the β phase. In the case of the samples with rare-earth oxide addition, a decomposition of a large amount of these added oxides did not occur. However, the rare-earth oxide addition caused a slight increase in the amount of the phase. The Seebeck coefficient was significantly enhanced by the rare-earth oxide addition especially in the low temperature range. These facts indicated that a small amount of rare-earth oxides was decomposed in the β phase, and rare-earth elements were substituted for Fe atoms as a p-type dopant, resulting in the decrease in the carrier concentration. The rare-earth oxide addition was also effective in reducing the thermal conductivity. 相似文献
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Noriya Izu Takahisa Omata Shinya Otsuka-Yao-Matsuo 《Journal of Alloys and Compounds》1998,270(1-2):107-114
To clarify the existence of metastable phases in the ZrO2–CeO2–CeO1.5 system, evolved-oxygen gas analyses, (EGA), by heating a single phase of t′ and t″ (Ce(1−x)ZrxO2) with various compositions, x, in a reducing gas and successive oxidation were carried out repeatedly. The oxygen release behaviour of the t′ and t″ phases was very complicated. The single κ phases, (Ce(1−x)ZrxO2) with the composition, x=0.5 and 0.6, which were obtained by oxidizing the resulting pyrochlore as a precursor in O2 gas at 873 K, exhibited a sharp oxygen release at the lowest temperature; the composition range of κ phase may be x=0.450.65. A new tetragonal phase t*, (Ce(1−x)ZrxO2), which was attained by cyclic redox process together with annealing in O2 gas at 1323 or 1423 K, exhibited a sharp oxygen release at the highest temperature; the composition range of t* phase may be as wide as x=0.200.65. A metastable solid solution expressed by a chemical formula of Ce(8−4y)Zr4yO(14−δ) (y=01) possessing a CaF2-related structure appeared on deoxidation of the t* phase. A ternary phase diagram containing the t* and Ce(8−4y)Zr4yO(14−δ) solid solution was proposed. 相似文献
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以胶体SiO2溶液作硅源,采用均相沉淀工艺制备壳-核结构完整的CeO2/SiO2纳米复合磨粒。采用X射线衍射仪和透射电子显微镜对复合磨粒样品进行物相组成分析和微观形貌观察;通过粒径分布、Zeta电位分析,研究水相分散系中pH值对CeO2/SiO2复合磨粒分散性的影响。结果表明:所制备的CeO2/SiO2复合磨粒为壳-核包覆结构完整的纳米微球,粒径约110 nm,内核为无定形SiO2,壳层为立方萤石型CeO2;CeO2/SiO2复合磨粒的等电位点pH值约为5,其值由SiO2等电位点向CeO2等电位点明显偏移。CeO2/SiO2复合磨粒在酸性水相介质中分散性差,容易出现严重的团聚现象;而在碱性环境下,CeO2/SiO2复合磨粒分散性良好。 相似文献
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对某厂产品中发现的含ZrO2类Ds夹杂物Ds类夹杂物来源进行了系统性的分析和研究,研究结果表明含ZrO2类Ds夹杂物产生的直接原因在于含Zr浸入式水口发生脱碳,脱碳通道内CaO-Al2O3-SiO2(-MgO)相中的SiO2将被钢液中的Al还原,最终成为CaO-Al2O3(-MgO)相,ZrO2仅起到了类似示踪剂的作用。 相似文献
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The addition of 5 wt.% SiO2, a viscous second phase, to 8 mol% Y2O3 cubic stabilized ZrO2 (8Y-CSZ) made superplastic 8Y-CSZ. This material had a fine grain size of 0.4 μm and exhibited deformations in tension as large as 520% at 1430 °C with a strain rate of 1.0 × 10−4 s−1. 相似文献
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The phase diagrams of the CuGaSe2–SiSe2 and CuInSe2–SiSe2 systems were constructed using the results of differential thermal and X-ray phase analysis. Both systems are of the eutectic type with the eutectic point coordinates 75 mol% SiSe2, 1042 K (CuGaSe2–SiSe2); 67 mol% SiSe2, 1083 K (CuInSe2–SiSe2). Solid solutions based on CuGaSe2 and CuInSe2 were discovered in these systems; their extent at 670 K being 24 and 25 mol% SiSe2, respectively. The crystal structure of the limiting compositions of these solid solutions was refined. 相似文献
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Plasma spraying of Al2O3/ZrSiO4 was performed using spray dried and plasma spheroidised powder feedstock. The mixtures were sprayed using different spray stand-off distances and plasma power levels. X-Ray diffraction (XRD) was used to characterise the phase composition and scanning electron microscopy (SEM) examined the morphology of the sprayed surface and polished cross-sections. The results showed that the plasma spray process parameters played an important role in the final outcome of microstructures of the coatings. The coatings produced with spheroidised powders displayed a much denser structure than those produced with the spray-dried powders. The phase composition analysis showed the presence of amorphous phases in addition to crystalline alumina, zircon and tetragonal (t) zirconia (ZrO2). Transmission electron microscopy (TEM) showed that amorphous phases and t-ZrO2 crystals with particle size 100–200 nm could coexist within a single splat due to the relatively low local cooling rate. 相似文献
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A.K. Khanra L.C. Pathak M.M. Godkhindi 《Journal of Materials Processing Technology》2008,202(1-3):386-390
Production of ZrB2 powder through self-propagating high-temperature synthesis (SHS) from ZrO2, Mg and H3BO3 mixture often leads to incomplete conversion. A new technique, called DSHS (double SHS) has been developed, wherein the reaction product of the first SHS is mixed with calculated amounts of Mg and H3BO3 powder and subjected to a second SHS. The ZrB2 powder produced by DSHS technique yields increased conversion. The NaCl is used as a diluent during SHS to control the particle size of the product. The average particle size of SHS ZrB2 powder found to be 75–125 nm in range, which decrease to 25–40 nm after DSHS. 相似文献
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WO3-doped zinc titanate ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. The effects of WO3 additions on the phase structure and phase transitions of zinc titanate ceramics were investigated by high-temperature X-ray diffractometry (HTXRD) and transmission electron microscopy (TEM). The results showed that the major phase of zinc titanate ceramics transformed from zinc orthotitanate phase to zinc metatitanate phase with the amounts of WO3 additions increasing. Small WO3 (<1.00 mass%) addition accelerated the transition of ZnTiO3 to Zn2TiO4, while excessive WO3 addition restrained the transition. HTXRD showed that WO3 enhanced the stability of Zn2Ti3O8 and weakened the stability of ZnTiO3. A precipitate within the Zn2TiO4 matrix was observed. Viewed along the orientation of Zn2TiO4, the precipitate was found to have a rectangular shape and to be nanometer level in size; its composition was concluded to be Zn2Ti3O8. The dielectric properties of WO3-doped zinc titanate ceramics were measured at different frequencies. The results showed the decreasing tendency with the increasing measuring frequencies for both the dielectric constants and the loss tangents, and there existed maximum values when the amount of WO3 was 0.50 mass%. 相似文献
14.
Faruk Sen Onur Sayman Mustafa Toparli Erdal Celik 《Journal of Materials Processing Technology》2006,180(1-3):239-245
The aim of this study is to investigate residual stresses occurred during cooling procedure of ZrO2 insulation coating on Ag substrate for magnet technologies. ZrO2 coatings were produced on Ag tape substrate by using a reel-to-reel sol–gel technique. SEM inspection showed that ZrO2 coatings had mosaic structures. ANSYS finite element software was used to calculate the temperature and stress distribution of the ZrO2/Ag structure. The effect of coating thickness on residual stresses was also examined. The results obtained showed that thermal stresses in ZrO2 coating and Ag substrate were considerably affected by the cooling time and coating thickness. It is concluded the thermal stresses increase with increase of film thickness. 相似文献
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Transition temperatures between tetragonal and monoclinic polymorphs of ZrO2 nanoparticles, thin films and nanostructured materials are calculated by considering energetic contributions of surface (interface) energy and surface stress on total Gibbs free energy. The transition temperatures drop as the size of the nanocrystals decreases, which is consistent with available results. 相似文献
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A mixture of magnesium, boric oxide and zirconium dioxide were mechanically milled under argon for up to 15 h in a laboratory scale ball mill. X-ray diffraction showed that there was an increasing conversion of ZrO2 to ZrB2 with milling time with >98% reaction after 15 h. Differential thermal analysis revealed there were multiple, overlapping reactions all of which seemed to be formation of ZrB2. The energy evolved decreased with milling time and the sample after 15 h milling showed no thermal reaction. After milling, separation of the ZrB2 from the coproduct MgO was easily achieved by a mild acid leaching leaving essentially pure ZrB2 with a crystallite size of 75 nm. 相似文献
17.
Jian-Feng Huang Xie-Rong Zeng He-Jun Li Xin-Bo Xiong Guo-ling Sun 《Surface & coatings technology》2005,190(2-3):255-259
In order to eliminate the mismatch of thermal expansion coefficient between the ZrO2 outer layer and the internal bonding SiC layer, ZrO2–SiO2 composition-gradient transition layers were prepared by a sol–gel technique using tetraethoxysilane (TEOS) and zirconyl chloride as source materials. Energy dispersive spectroscopy (EDS) analysis displays that the gradient composition ZrO2–SiO2 outer coating could be obtained by immersing the SiC precoated carbon/carbon (C/C) composites into the gradient composition zirconia-silica sols (ZS sol) in turn. Oxidation test shows that, after 10 h oxidation in air at 1773 K, the weight loss of the gradient ZrO2–SiO2 coating coated SiC-C/C is only 1.97%. 相似文献
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Different metal/ceramic composites (Al7Si0.3Mg, Al3Ni, Al6Ni, Al9Ni) reinforced with Al2O3 or ZrO2 were prepared by vortex method. Metallographic investigations reveal that in all the composites -Al did not nucleate on the reinforcement particulates. The particulates were generally observed to be located in the last freezing regions regardless of matrix alloy, particulate type or size. The reason for that was the mismatch in the thermal diffusivity between the ceramic particulates and matrix alloys. SEM micrographs show that the presence of the particulates in the AlSi alloy tends to modify the silicon eutectic. In contrast, the addition of the particulates into AlNi alloys did not result in a significant modification of the NiAl3 phase, but it displaced the eutectic point to lower Ni content. 相似文献
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Without Sr addition, the sintered La2O3 and CuO powder mixture in a mole ratio of 1:2 formed K2NiF4-structured La2CuO4 with excess CuO. When 15% of strontium was added, La2CuO4 transformed into the single perovskite La1−xSrxCuO2.5−δ phase with orthorhombic structure. As the strontium addition increased to 20%, the perovskite lattice changed from orthorhombic to tetragonal. These phase transitions may be attributed to the enhanced oxidation of the divalent cupper ions (Cu2+) to trivalent ones (Cu3+) by the strontium addition. Based on the electroneutrality in an ABO3 perovskite lattice, a divalent cation is unstable in the B-site cation sub-lattice when the A-site is occupied by a trivalent cation such as La3+. As strontium was added into the A-site cation sub-lattice, the oxidation of Cu2+ ion into trivalent Cu3+ ion was enhanced. The increase of Cu3+ concentration strengthened the electrostatic bonding (ESB) of copper ions with their neighboring anions. Consequently, the symmetrical tetragonal Sr-doped lanthanum copper oxide was obtained. 相似文献
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A NiCrAl/ZrO2 composite coating was deposited on the surface of metal carrier FeCrAl alloy by a plasma-spray technique. After static-state oxidation at 800°C, the transitions in structure and composition of the coating was analyzed by XRD, SEM and EDX. The results showed that the surface phases of the as-sprayed coating were mainly composed of Ni and ZrO2. When the oxidation time was extended from 8 to 50 h, NiO crystallites were formed and these grew coarse on the coating surface, and alloy elements were diffused between the NiCrAl/ZrO2 coating and the FeCrAl substrate. With the pretreatment, an intermediate coating was prepared with a coarse and porous structure, high cohesive strength and high heat resistance. These developed properties could provide high geometric surface area for a catalytic γ-Al2O3 washcoat, and enhance the adhesive strength between ceramic washcoat and metal substrate so as to extend the lifetime of the washcoat. 相似文献