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1.
《Journal of the European Ceramic Society》2023,43(15):7228-7233
Present work successfully synthesized two new α-312 MAX phase compounds of Zr3InC2 and Hf3InC2 using spark plasma sintering. The crystal structure and microstructure of two new compounds were characterized by combining X-ray diffraction (XRD) and scanning electron microscopy (SEM). With typical crystal structure of MAX phase, the obvious layered features on the fracture surface of Zr3InC2 and Hf3InC2 grains were observed. The lattice parameters of these two new MAX phase compounds were confirmed as a = 3.3515(3) Å, c = 20.2515(9) Å for Zr3InC2, and a = 3.3370(3) Å, c = 19.9560(1) Å for Hf3InC2, respectively. Also, the atomic positions of Zr3InC2 and Hf3InC2 were determined as M1 at (0, 0, 0), M2 at (1/3, 2/3, 0.12774[Zr]/0.12455[Hf]), In at (0, 0, 1/4), and C at (1/3, 2/3, 0.57087[Zr]/0.54894[Hf]). Two new sets of XRD patterns of Zr3InC2 and Hf3InC2 were collected. 相似文献
2.
The effects of adding 1–8 wt% Y2O3 on phase formation and fracture toughness of Al2O3–xZrO2–Y2O3(AZY) ceramics were studied. Phase formations of the samples were characterized by the X-ray diffraction (XRD) technique. It was found that the major phase was rhombohedral-Al2O3, while the minor phase consisted of the monoclinic-ZrO2, tetragonal-ZrO2 and monoclinic-Y2O3. It was found that Y2O3 contents did not clearly influence grain shape of AZY ceramics. The results obtained from the microhardness test could be used to evaluate the fracture toughness. It was found that the smaller grains had high fracture toughness. The maximum fracture toughness of 4.827 MPa m1/2 was obtained from 4 wt% Y2O3. Refinement of lattice parameters using Rietveld analysis revealed the quantitative phases of AZY ceramics. This shows that under adding Y2O3 conditions the proportion of tetragonal-ZrO2 phase plays an important role for the mechanical properties of AZY ceramics. 相似文献
3.
Influence of annealing treatment on magnetic properties of Fe2O3/SiO2 and formation of ε-Fe2O3 phase
《Ceramics International》2017,43(3):3147-3155
Magnetic properties of Fe2O3/SiO2 samples were studied after being produced by sol-gel synthesis and formation of ε-Fe2O3 polymorph. Samples were thermally treated, using different annealing temperatures and annealing times. The size and morphological characteristics of the iron oxide nanoparticles were examined using a TEM microscope. We used the “ellipticity of shapes”, which is a measure of how much the shape of a nanoparticle differs from a perfect ellipse, in order to quantitatively describe morphological properties of nanoparticles. Coercivity measurements were used to identify and monitor the formation of the epsilon-iron oxide phase during the thermal treatments (annealing). Coercivity values were in the range from 1.2 to 15.4 kOe, which is in accordance with previous experience regarding the existence of ε-Fe2O3. We have determined the optimal formation conditions for the ε-Fe2O3 polymorph (t=1050 °C for 7 h, HC=15.4 kOe), as well as the narrow temperature interval (1050–1060 °C) in which the polymorph abruptly vanished (HC=2300 Oe), on the basis of results of the magnetic properties. The threshold temperature for the ε-Fe2O3 phase transformation was measured as 1060 °C. We found that different annealing temperatures and annealing times significantly affected magnetic properties of the examined samples. 相似文献
4.
《应用陶瓷进展》2013,112(6):256-259
AbstractAmorphous fibres of the Al2O3–Y2O3 system were prepared by a melt extraction technique, and subjected to crystallisation. The quality of the melt extracted fibres is controlled by the wheel edge and rotational speed, with both having a significant effect on fibre diameter and avoidance of irregularities and instabilities along the fibre length. Tensile strength in the glassy state varied from 0·6 to 1·0 GPa. Crystallisation activation energies calculated from scan-rate dependence of DTA peaks are 741 and 1374 kJ mol-1 for E1 (Al2O3–yttrium aluminium garnet (YAG) eutectic), 390 kJ mol-1 for YAG, and 438 kJ mol-1 for E2 (YAG–yttrium aluminium perovskite (YAP) eutectic) by the Kissinger method; and 698 and 1346 kJ mol-1 for E1, 352 kJ mol-1 for YAG, and 399 kJ mol-1 for E2 by the Augis–Bennett method. 相似文献
5.
The local surrounding of copper, antimony, and iodine atoms in multicomponent chalcogenide films CuI-PbI2-As2Se3 and CuI-SbI3-PbI2-As2Se3 deposited from solutions of chalcogenide glass in n-butylamine has been studied by the Mössbauer spectroscopy method on 121Sb and 129I isotopes. It was established that antimony atoms are in the Sb (III) state, where each antimony atom is surrounded by three selenium atoms. Copper atoms are in the Cu (I) state and are surrounded by iodine atoms. The local surrounding of copper, antimony, and iodine atoms in chemically deposited chalcogenide films is analogous to the local surrounding of atoms in the initial chalcogenide glass. 相似文献
6.
《Applied catalysis》1983,5(2):199-206
The catalytic properties of an Al2O3-coated catalyst formed by anodic oxidation of aluminium were compared with those of α- and of γ-Al2O3- bulk catalysts in the dehydration of 2-propanol and in the isomerization of n-butenes. In the dehydration reaction both the Al2O3-coated catalyst and the γ-Al2O3 bulk catalyst show approx. the same activities and activation energies. However, the reaction rate based on the unit of the surface area for the Al2O3-coated catalyst is approx. 30 times larger than that for the γ-A12O3 bulk catalyst. In the isomerization of the individual isomeric n-butenes the Al2O3-coated catalyst was more active than the γ-Al2O3, bulk catalyst and under otherwise equal conditions equilibrium was reached at approx. 80 K lower temperature. 相似文献
7.
W. H. Cassinelli L. S. F. Feio J. C. S. Araújo C. E. Hori F. B. Noronha C. M. P. Marques J. M. C. Bueno 《Catalysis Letters》2008,120(1-2):86-94
The effect of the addition of CeO2 or La2O3 on the surface properties and catalytic behaviors of Al2O3-supported Pd catalysts was studied in the steam reforming of methane. The FTIR spectroscopy of adsorbed CO and the Pd dispersion
suggest the partial coverage of Pd0 by ceria or lanthana species. This could lead to the formation of an adduct MPd
x
O (M = Ce or La) at the surface of the metal crystallites. The addition of ceria or lanthana resulted in an increase of the
turnover rate and specific rate for steam reforming of methane. One possible explanation if that the Pd0*Pdδ+O–M interfacial species (M = Ce or La) are oxidized by H2O or CO2, promoting the O* transfer to the metal surface. This could facilitate the removal of C* species from the metal surface,
resulting in the increase of specific reaction rate and increase of the accessibility of CH4 to metal active sites. 相似文献
8.
以粒径为0.3~0.4 μm的α-Al2O3为原料,通过悬浮液真空抽吸法,制备出平均孔径约为70 nm的完整无缺陷的片状α-Al2O3支撑体;以仲丁醇铝为前驱体,采用颗粒溶胶路线制备出稳定的Boehmite溶胶,以此溶胶采用浸浆法,在制备的α-Al2O3支撑体上制备出完整无缺陷的γ-Al2O3中孔膜,并考察了烧成温度对γ-Al2O3中孔膜性能的影响。结果表明,本文制备出的γ-Al2 O3膜的孔径约为3 nm,对PEG的截留分子量为2800~5300,纯水渗透通量为11.5~25.9 L.m-2.h-1[7.6×105 Pa,(14±1)℃]。说明在孔径为70 nm左右的载体上直接制备孔径为3 nm的完整的中孔膜是可行的。 相似文献
9.
《Journal of the European Ceramic Society》2004,24(6):1195-1198
ZnO–Bi2O3-based varistor samples doped with 0.45 mol% of Y2O3 and varying amounts of Sb2O3 in the range from 1.8 to 0.0 mol% were fired at 1230 °C. Only in the samples co-doped with Sb2O3 did doping with Y2O3 resulted in the formation of a fine-grained Bi–Zn–Sb–Y–O phase (the Y2O3-containing phase) at the grain boundaries, which very effectively hinders the grain growth. Despite of a decrease in the amount of added Sb2O3 from 1.8 to 0.45 mol% and a significant decrease in the amount of spinel phase the samples had a similar ZnO grain size and a threshold voltage of 200 V/mm. The results confirmed that doping with Y2O3 is a very promising route for the production of fine-grained high-voltage ZnO–Bi2O3-based varistor ceramics, and determining the proper amounts of added Sb2O3 and Y2O3 is of great importance. 相似文献
10.
LIANG Yonghe YIN Yucheng WU Yunyun WANG Jibao 《中国耐火材料》2006,15(2):3-6
1IntroductionAs an ideal raw material for refractories produc-tion,mullite has been widely used in refractories in-dustry.But little amount of natural mullite has beenfound so that almost all of the mullite used now has tobe synthesized from natural miner… 相似文献
11.
《Journal of the European Ceramic Society》2000,20(3):277-283
Yttria-doped zirconia powder (3Y-ZrO2) was characterized and dispersed in distilled water. The state of dispersion was evaluated in terms of zeta potential, apparent viscosity and the mean particle size of solid phase in the slip. Zeta potential, apparent viscosity and the mean particle size as a function of pH indicated the pH range of electrostatic stabilization. These results showed that electrostatic stabilization of the slip can be accomplished in low acidic and high basic range of pH. Dissolution of yttria from the powder surface in acidic pH was found to be high and fast, risky to the stability of the slip as well as the microstructure of the sintered body. Electrosteric stabilisation by addition of an anionic polyelectrolyte (PMAA-NH3) shifted the isoelectric point (IEP) to lower pH. The state of dispersion was further investigated by particle size measurements of the solid phase in the slip. The optimum amount of dispersant is discussed in terms of zeta potential and viscosity. The adsorption of polyelectrolyte is considered at pH 4, native pH of suspension and at pH 10, below and above the IEP of powder and correlated with the dissociation rate of polymer and the net surface charge of particles at given pH. Higher adsorption of dissociated polymer to the positively charged surfaces justifies the higher optimum amount of polyelectrolyte at pH 4. 相似文献
12.
《Ceramics International》2015,41(4):5790-5797
Mechanism of combustion synthesis (CS) of ZrB2–Al2O3 composite powders was systematically analyzed by a combustion front quenching method (CFQM). The microstructural evolution during the CS process was investigated by field-emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectrometer (EDS). The combustion temperature and wave velocity were measured by the data acquisition system. Moreover, the phase constituents of the final product were examined by X-ray diffraction (XRD). The thermal behaviors of the stoichiometic powders under the thermal exposure were characterized using differential scanning calorimetry (DSC) and thermogravimetric (TG). The results showed that the combustion reaction started from the melting of the B2O3 and Al particles, which was followed by the formation of ZrO2–B2O3–Al solution. The ignition temperature of this system was determined to be around 800 °C. B and Al2O3 were then precipitated from the solution. As the CS reaction proceeded, Zr and Al2O3 were produced by the reaction between ZrO2 particles and Al and precipitated from the solution. ZrB2 could then be formed by the direct reaction between Zr and B. Finally, the ZrB2–Al2O3 composite powders were obtained. Furthermore, a model corresponding to the dissolution–precipitation mechanism was proposed. 相似文献
13.
The activity and selectivity in the catalytic reduction of NO by a mixture of CO and H2 of three PdO-MoO3/-Al2O3 catalysts are compared in the presence of varying amounts of oxygen at reaction temperatures from 100 to 550°C. The catalysts were prepared by different methods and contain about 2% Mo and 2% Pd. Results are compared with those for PdO/-Al2O3, PdO-MoO3/-Al2O3 containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. The PdO-MoO3/-Al2O3 catalysts are more active for the selective reduction of NO to N2 and N2O than PdO/-Al2O3 under slightly oxidizing conditions at temperatures from 300 to 550°C. At these reaction conditions, the fresh PdO-MoO3/-Al2O3 catalysts are comparable with a commercial Pt-Rh catalyst. The improved activity of PdO-MoO3/-Al2O3 relative to PdO/-Al2O3 is believed to be due to the interaction between Pd and Mo. The effect of O2 on the activity and selectivity of these catalysts is different in the reduction of NO by H2, by CO, and by a mixture of H2 and CO. The results using the mixture of reductants cannot be inferred from the results with the single reductants. 相似文献
14.
《Ceramics International》2020,46(7):9002-9010
Structural ceramics such as Al2O3 and Al2O3–ZrO2 composites are widely used in harsh environment applications. The conventional sintering process for fabrication of these ceramics is time-consuming method that requires large amount of energy. Microwave sintering is a novel way to resolve this problem. However, to date, very limited research has been carried out to study the effects of different ZrO2 crystal structures on Al2O3–ZrO2 composites, especially on the sintering kinetics, when fabricated by microwave sintering.The microwave hybrid sintering of Al2O3 and Al2O3–ZrO2 composites was performed in this study. Tetragonal zirconia and cubic zirconia were used as two different reinforcements for an α–alumina matrix, and the mechanical and thermal properties were studied. It was found that Al2O3 experienced a remarkable increase in fracture toughness of up to 42% when t-ZrO2 was added. Al2O3–c-ZrO2 also showed increased fracture toughness. The sintering kinetics were also thoroughly investigated, and the average activation energy values for the intermediate stage of sintering were estimated to be 246 ± 11 kJ/mol for pure Al2O3, 319 ± 71 kJ/mol for Al2O3–c-ZrO2, and 342 ± 77 kJ/mol for Al2O3–t-ZrO2. These values indicated that the activation energy was increased by the addition of either type of ZrO2, with the highest value shown by Al2O3–t-ZrO2. 相似文献
15.
《Ceramics International》2017,43(4):3465-3474
This study investigated the effect of elemental crystal Ge or/and GeO2 doping on the microstructure and varistor properties of TiO2–Ta2O5–CaCO3 varistor ceramics, which were prepared via the traditional ball milling–molding–sintering process. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy demonstrated that co-doping with Ge and GeO2 changed the microstructure of TiO2–Ta2O5–CaCO3 ceramics, thereby increasing the nonlinear coefficient and decreasing the breakdown voltage. The optimum doping concentrations of Ta2O5, CaCO3, Ge, and GeO2 exhibited the highest nonlinear coefficient (α=14.6), a lower breakdown voltage (EB=18.7 V mm−1), the least leakage current (JL=10.5 μA cm−2), and the highest grain boundary barrier (ΦB=1.05 eV). In addition, Ge and GeO2 function as sintering aids, which reduce the sintering temperature because of their low melting points. 相似文献
16.
《Ceramics International》2023,49(20):33188-33196
Nowadays, Y2O3–Al2O3–SiO2 (YAS) glass joining is considered to be a promising scheme for nuclear-grade continuous silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC). CaO has great potential for nuclear applications since it has low reactivity and low decay rate under nuclear irradiation. In this paper, the effect of CaO doping on the structure, thermophysical properties, and crystallization behavior of YAS glass was systematically studied. As the CaO doping content increased, the number of bridge oxygens and the viscosity at high temperatures reduced gradually. After heat treatment at 1400 °C, the main phases in YAS glass were β-Y2Si2O7, mullite, and SiO2 (coexistence of crystalline and glass phases), while that with 3.0% CaO doping turned into a single glassy phase under the same treatment conditions. Moreover, a structural model and the modification mechanism were proposed, which provided a theoretical basis for the subsequent component design and optimization. 相似文献
17.
《Journal of the European Ceramic Society》2014,34(1):45-53
Phase transformations in ZrO2 + xSc2O3 solid solutions (6.5 < x < 11 mol%) at sintering of ceramics obtained from nanopowders produced by laser evaporation of the ceramic targets have been studied. The Sc2O3 concentration increasing from 6.5 to 11 mol% is accompanied by the sintering temperature decreasing and the average grain size growth from 130 nm to 760 nm. At concentration of about 7 mol% Sc2O3 an abrupt increase of the average grain size and electric conductivity is observed. The sinterability of the ZrO2 − хSc2O3 ceramics is affected by the prehistory of nanopowders preparation. The characteristics of ceramics obtained from nanopowders evaporated from the targets based on (ZrO2 + xmol% Sc2O3) mixture and on the (ZrO2 − 11mol% Sc2O3) solid solution significantly differ, namely, in the latter the sintering temperature is markedly lower and the shrinkage rate is higher. Besides, its average grain size is substantially lower and the conductivity is higher. 相似文献
18.
《Ceramics International》2016,42(9):11003-11009
A low temperature sintering method was used to avoid the relatively high sintering temperatures typically required to prepare 0.67CaTiO3–0.33LaAlO3 (CTLA) ceramics. Additionally, CeO2 was introduced into the CTLA ceramics as an oxygen-storage material to improve their microwave dielectric properties. 0.67CaTiO3–0.33LaAlO3 ceramics co-doped with B2O3–Li2O–Al2O3 and CeO2 were prepared by a conventional two-step solid-state reaction process. The sintering behavior, crystal structure, surface morphology, and microwave dielectric proprieties of the prepared ceramic samples were studied, and the reaction mechanism of CeO2 was elucidated. CTLA+0.05 wt% BLA+3 wt% CeO2 ceramics sintered at 1360 °C for 4 h exhibited the optimal microwave dielectric properties: dielectric constant (εr)=45.02, quality factor (Q×f)=43102 GHz, and temperature coefficient of resonant frequency (τf)=2.1 ppm/°C. The successful preparation of high-performance microwave dielectric ceramics provides a direction for the future development and commercialization of CTLA ceramics. 相似文献
19.
《Journal of the European Ceramic Society》1999,19(12):2125-2131
Al2O3–ZrO2(3Y)–SiC composite powder was prepared by the heterogeneous precipitation method. Calcinating temperature of the powder was important to obtain dense sintered body. The nanocomposites were got by hot-pressing, and addition of ZrO2 did not raise the sintering temperature. Some Al2O3 grain shape was elongated, and Al2O3 grain size was about μm. Nano SiC particles were observed uniformly distributing throughout the composites, and most of them were located within the matrix grains. Because SiC particles located within ZrO2 grains influenced the phase transformation of ZrO2, the sintering of nanocomposites, which controlled grain size and transformable ZrO2 amount, become important to get high performance. The strength of 80 wt% Al2O3–15 wt% ZrO2–5 wt% SiC nanocomposites was 555 MPa, and toughness was 3·8 MPa m1/2, which were higher than those of monolithic Al2O3 ceramics. © 相似文献
20.
《Journal of the European Ceramic Society》1999,19(2):255-262
Laminar composites, containing layers of Y–TZP and either Al2O3 or a mixture of Al2O3 and Y–ZrO2 have been fabricated using a sequential centrifuging technique of water solutions containing suspended particles. Controlled crack growth experiments with notched beams of composites were done and showed the significant effect of barrier layer thickness and composition on crack propagation path during fracture. Distinct crack deflection in alumina layers was observed. The increase of crack deflection angle with the alumina layer thickness was also found. In the case of the barrier layer made of a mixture, crack deflection did not occur independently on layer thickness. The observed changes have been correlated with the radial distribution of residual stresses in barrier layers created during cooling of sintered composites from fabrication temperature. The stresses found were the result of the difference in the thermal expansion and sintering shrinkage of alumina and zirconia and the crystallographically anisotropic thermal expansion of the alumina. The residual stress distribution has been measured by piezo-spectroscopy based on the optical fluorescence of Cr+3 dopants in alumina. 相似文献