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1.
Al2O3-SiC composite ceramics were prepared by pressureless sintering with and without the addition of MgO, TiO2 and Y2O3 as sintering aids. The effects of these compositional variables on final density and hardness were investigated. In the present article at first α-Al2O3 and β-SiC nano powders have been synthesized by sol-gel method separately by using AlCl3, TEOS and saccharose as precursors. Pressureless sintering was carried out in nitrogen atmosphere at 1600 °C and 1630 °C. The addition of 5 vol.% SiC to Al2O3 hindered densification. In contrast, the addition of nano MgO and nano TiO2 to Al2O3-5 vol.% SiC composites improved densification but Y2O3 did not have positive effect on sintering. Maximum density (97%) was achieved at 1630 °C. Vickers hardness was 17.7 GPa after sintering at 1630 °C. SEM revealed that the SiC particles were well distributed throughout the composite microstructures. The precursors and the resultant powders were characterized by XRD, STA and SEM. 相似文献
2.
Youfeng Zhang Dechang Jia Yu Zhou Qingchang Meng Yangai Liu Hua Ke 《Ceramics International》2009,35(8):3475-3478
Highly densified Al2O3/LiTaO3 (ALT) ceramic composites were fabricated by hot-pressing in a nitrogen atmosphere. The addition of Al2O3 particles could significantly improve the densification of LiTaO3. Sintering mechanism of the LiTaO3 ceramic incorporated with Al2O3 particles is proposed. Dielectric constant of 5 vol.% Al2O3/LiTaO3 (5ALT) composite ceramic was slightly increased in the range from 30 kHz to 106 Hz, but the dielectric loss was lowered in the whole range from 103 Hz to 106 Hz. Piezoelectric constant (d33) of the 5ALT ceramic composite is about 50% of that of LiTaO3 single crystal. 相似文献
3.
The influence of sintering temperature and soaking time on fracture toughness of Al2O3 ceramics has been investigated. The samples were prepared by solid state sintering at 1500, 1600 and 1700 °C for different soaking time periods. The fracture toughness of the sintered samples was determined by inducing cracks using Vickers indentation technique. Microstructural investigations on fracture surfaces obtained by three point bend test mode were made and correlated with fracture toughness. Crack deflection in the samples sintered at 1500 and 1600 °C for which ranges of fracture toughness are 5.2–5.4 and 5.0–5.6 MPa m1/2 respectively, are found. The samples sintered at 1700 °C have lower fracture toughness ranging between 4.6 and 5.0 MPa m1/2. These samples have larger grains and transgranular fracture mode is predominant. The crack deflection has further been revealed by SEM and AFM observations on fracture surface and fracture surface roughness respectively. 相似文献
4.
Three bio-phosphate glass-specimens with and without Al2O3 addition were prepared in order to shed light on their bioactivity behavior towards the simulated body fluid biological solution (SBF). The results revealed that Al2O3 has significant effect on the ability of bio-glass to form the hydroxycarbonate apatite layer on its surface. That layer was detected by FTIR spectra, SEM micrographs and EDAX pattern. Also, the effect of Al2O3 on the mechanical properties was studied by measuring the hardness of the glass samples, which increased by Al2O3 addition. The thermal expansion coefficient was decreased by increasing the Al2O3 percent in the bio-glass samples. 相似文献
5.
Zirconia-toughened alumina (ZTA) ceramics were prepared using three different kinds of Al2O3 powders (marked PW-A average particle size: 7.53 μm, marked PW-B average particle size: 1.76 μm, marked PW-C average particle size: 0.61 μm) by gelcasting. Effect of Al2O3 particle size on zeta potential, dispersant dosage and solid volume fractions of ZTA suspensions as well as the mechanical properties of ZTA green bodies and ceramics were investigated. The optimum dosages of dispersant for ZTA suspensions prepared by PW-A, PW-B and PW-C are 0.4 wt%, 0.5 wt% and 0.7 wt%, respectively. The highest solid volume fractions of ZTA suspensions can reach 62 vol% (SP-A), 60 vol% (SP-B) and 52 vol% (SP-C), respectively. The green bodies show a bending strength as high as 20 MPa, which can meet the requirement of machining. The Al2O3 powder with fine particle size is beneficial to the improvement of mechanical properties. The ZTA ceramics prepared by PW-B Al2O3 powder show the highest bending strength (680 MPa) and toughness (7.49 MPa m1/2). 相似文献
6.
The sintering stress of an Al2O3 powder, σs, is evaluated from an equation σs = Fs/ρSa, where Fs is the uniaxial tensile force necessary to just stop the sintering contraction, ρ is the relative density, and Sa is the cross-sectional area. During densification, σs increases to the maximum at a relative density of 85%, and then abruptly decreases. The variation of σs in the intermediate sintering stage suggests a simple cubic packing of particles. Densification in the final sintering stage is explained by shrinkage of the pores at the corners where four tetrakaidecahedra meet. The present surface tensions of the Al2O3 powder evaluated from the σs roughly equal a reported value. 相似文献
7.
Swapan Kumar SarkarByong Taek Lee 《Ceramics International》2012,38(2):1043-1050
A novel layered microstructure in the Al2O3/ZrO2 composites system was fabricated by the multipass extrusion method. The microstructure consisted with very fine alternate lamina of Al2O3-(m-ZrO2) and t-ZrO2. The composites were designed in such a way that a small group of 7 cylindrical alternate layers of Al2O3-(m-ZrO2) and t-ZrO2 made a concentric microgroup around 40 μm in diameter, with a common boundary layer between the adjacent groups. The thickness of both layers was around 2-3 μm. The microstructure was unidirectionally aligned throughout the composites. The composite microstructure was fibrous due to the unidirectional orientation of these microgroups. Detailed microstructure of the fabricated composites was characterized by SEM. The effect of the concentric layered microstructure on mechanical behavior was discussed. Material properties such as density, bending strength, Vickers hardness and fracture toughness were measured and evaluated depending on different sintering temperatures. 相似文献
8.
Akira Morikawa Koichi Kikuta Akihiko Suda Hirofumi Shinjo 《Applied catalysis. B, Environmental》2009,88(3-4):542-549
Oxygen storage capacity (OSC) of CeO2–ZrO2 solid solution, CexZr(1−x)O4, is one of the most contributing factors to control the performance of an automotive catalyst. To improve the OSC, heat treatments were employed on a nanoscaled composite of Al2O3 and CeZrO4 (ACZ). Reductive treatments from 700 to 1000 °C significantly improved the complete oxygen storage capacity (OSC-c) of ACZ. In particular, the OSC-c measured at 300 °C reached the theoretical maximum with a sufficient specific surface area (SSA) (35 m2/g) after reductive treatment at 1000 °C. The introduced Al2O3 facilitated the regular rearrangement of Ce and Zr ions in CeZrO4 as well as helped in maintaining the sufficient SSA. Reductive treatments also enhanced the oxygen release rate (OSC-r); however, the OSC-r variation against the evaluation temperature and the reduction temperature differed from that of OSC-c. OSC-r measured below 200 °C reached its maximum against the reduction temperature at 800 °C, while those evaluated at 300 °C increased with the reduction temperature in the same manner as OSC-c. 相似文献
9.
Amir Javad Nikkhah Omid Torabi Reza Ebrahimi-Kahrizsangi Sanaz Naghibi Amin Jamshidi 《Ceramics International》2014
Alpha-alumina–boron nitride (α-Al2O3–BN) nanocomposite was synthesized using mixtures of aluminum nitride, boron oxide and pure aluminum as raw materials via mechanochemical process under a low pressure of nitrogen gas (0.5 MPa). The phase transformation and structural evaluation during mechanochemical process were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential thermal analysis (DTA) techniques. The results indicated that high exothermic reaction of Al–B2O3 systems under the nitrogen pressure produced alumina, aluminum nitride (AlN), and aluminum oxynitride (Al5O6N) depending on the Al value and milling time, but no trace of boron nitride (BN) phases could be identified. On the other hand, AlN addition as a solid nitrogen source was effective in fabricating in-situ BN phase after 4 h milling process. In Al–B2O3–AlN system, the aluminothermic reaction provided sufficient heat for activating reaction between B2O3 and AlN to form BN compound. DTA analysis results showed that by increasing the activation time to 3 h, the temperature of both thermite and synthesis reactions significantly decreased and occurred as a one-step reaction. SEM and TEM observations confirmed that the range of particle size was within 100 nm. 相似文献
10.
Hao-Tung LinPramoda K. Nayak Bo-Zon LiuWei-Hsio Chen Jow-Lay Huang 《Journal of the European Ceramic Society》2012,32(1):77-83
The fine grains of Al2O3-Cr2O3/Cr-carbide nanocomposites were prepared by employing recently developed spark plasma sintering (SPS) technique. The initial materials were fabricated by a metal organic chemical vapor deposition (MOCVD) process, in which Cr(CO)6 was used as a precursor and Al2O3 powders as matrix in a spouted chamber. The basic mechanical properties like hardness, fracture strength and toughness, and the nanoindentation characterization of nanocomposites such as Elastics modulus (E), elastic work (We) and plastic work (Wp) were analyzed. The microstructure of dislocation, transgranular and step-wise fracture surface were observed in the nanocomposites. The nanocomposites show fracture toughness of (4.8 MPa m1/2) and facture strength (780 MPa), which is higher than monolithic alumina. The strengthening mechanism from the secondary phase and solid solution are also discussed in the present work. Nanoindentation characterization further illustrates the strengthening of nanocomposites. 相似文献
11.
Al2O3/SiC ceramic composites with Y2O3 as an additive, was synthesized using the Taguchi method of design of experiments, so as to develop statistically sound input output relationships. The proportion of SiC was varied from 12 to 21 vol.% whereas that of Y2O3 was varied from 2.5 to 4 vol.%. The composites were sintered at 1500 °C for a soaking time period of 12 h in an air atmosphere. Cracks were induced on the composite surface using a Vickers indenter with a load varying between 20 and 40 kg. Fractographical analyses have been carried out using optical and/or scanning electron microscopy to investigate the surface crack propagation behavior. Thermal aging at 1300 °C in the time range of 0.5-12.5 h was applied to find optimal conditions for healing of the pre-cracked samples. The output parameters such as crack length, healed crack length, hardness and fracture toughness of the samples were correlated with appropriate inputs such as contents of SiC and Y2O3, crack-healing temperature, healing time, compaction pressure, indentation load using statistical analysis. Further, the extent of influence, exerted by pertinent input parameters on output parameters, was also identified. 相似文献
12.
Huanping WangJinmin Chen Wenyi YangSiqiao Feng Hongping MaGuohua Jia Shiqing Xu 《Journal of the European Ceramic Society》2012,32(3):541-545
The effects of Al2O3 addition on the densification, structure and microwave dielectric properties of CaSiO3 ceramics have been investigated. The Al2O3 addition results in the presence of two distinct phases, e.g. Ca2Al2SiO7 and CaAl2Si2O8, which can restrict the growth of CaSiO3 grains by surrounding their boundaries and also improve the bulk density of CaSiO3-Al2O3 ceramics. However, excessive addition (≥2 wt%) of Al2O3 undermines the microwave dielectric properties of the title ceramics since the derived phases of Ca2Al2SiO7 and CaAl2Si2O8 have poor quality factor. The optimum amount of Al2O3 addition is found to be 1 wt%, and the derived CaSiO3-Al2O3 ceramic sintered at 1250 °C presents improved microwave dielectric properties of ?r = 6.66 and Q × f = 24,626 GHz, which is much better than those of pure CaSiO3 ceramic sintered at 1340 °C (Q × f = 13,109 GHz). 相似文献
13.
65.9Cu-24.4Ti-9.7TiB2 (wt.%) composite filler was used to join Al2O3 and Ti-6Al-4V alloy. 30 vol.% TiB whiskers were in situ synthesized as reinforcements in joints. Brazing temperature was 890 °C, 910 °C, 930 °C, 950 °C and 970 °C, and the holding time was 0, 5, 10, 20, and 30 min. The microstructure and mechanical properties of brazed joints were analyzed by scanning electron microscope equipped with energy dispersive spectrometer, shear test and nano-indentation test. Results show that reaction layer Ti4(Cu,Al)2O forms at Al2O3/brazing alloy interface. The reaction between TiB2 powders and Ti atoms in brazing alloy brings on in situ synthesizing TiB whiskers in (Ti,Al)2Cu and AlCu2Ti intermetallics. Formation of TiB whiskers minimizes the mismatch of thermal expansion coefficient between Al2O3 and brazing alloy, and makes the ductile-rigid-ductile multiple layer present in joints, which reduces residual stress of joints. The maximum shear strength of joints can reach 143.3 MPa when the brazing temperature is 930 °C, and holding time is 10 min. 相似文献
14.
In-Jin Shon In-Yong Ko Hyun-Su Kang Kyung-Tae Hong Jung-Mann Doh Jin-Kook Yoon 《Ceramics International》2011,37(7):2159-2164
The rapid sintering of nanostructured Al2O3 and Al2O3 to Al2SiO5 composites was investigated by a high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nanostructured Al2O3 and Al2O3 to Al2SiO5 composites were produced with simultaneous application of a 80 MPa pressure and induced output current of a total power capacity (15 kW) within 3 min. The sintering behavior, grain size and mechanical properties of Al2O3 and Al2O3 to Al2SiO5 composites were investigated. 相似文献
15.
Toshihiro Isobe Keiji Daimon Toshihiko Sato Takashi Matsubara Yasuo Hikichi Toshitaka Ota 《Ceramics International》2008
Al2O3/Ni nanocomposites were prepared by spark plasma sintering (SPS) using reaction sintering method and the mechanical properties of the obtained nanocomposites are reported. The starting materials of Al2O3–NiO solid solution were synthesized from aluminum sulfate and nickel sulfate. These Al2O3–NiO powders were changed into Al2O3 and Ni phases during sintering process. The obtained nanocomposites showed high relative densities (>98%). SEM micrographs showed homogeneously dispersed Ni grains in the matrix. The 3-point strength and the fracture toughness of the composites significantly improved from 450 MPa in the monolithic α-Al2O3 to 766 MPa in the 10 mol% (2.8 vol.%) Ni nanocomposite and from 3.7 to 5.6 MPa m1/2 in 13 mol% (3.7 vol.%) Ni nanocomposite. On the other hand, Young's modulus and Vickers hardness of the nanocomposites were mostly same as those of the monolithic α-Al2O3. 相似文献
16.
A series of short-carbon-fiber/Al2O3 composites with MgO as sintering additive were fabricated by pressureless sintering process. The effects of short carbon fiber (Csf) content on the mechanical, dielectric and microwave absorbing properties of the composite were investigated. The results show that the addition of MgO enhances the density, hardness and the flexural strength of the alumina ceramic. However, these mechanical properties of the Csf/Al2O3–MgO composite decrease with increasing Csf content. Both the real and imaginary parts of the complex permittivity increase with increasing Csf content in the frequency range of 8.2–12.4 GHz, which is attributed to the increasing electron polarization and associated polarization relaxation, respectively. When the Csf content is 0.3 wt%, the reflection loss less than −10 dB and the minimum value of −27 dB are obtained with the coating thickness being 1.4 mm. The results indicate that the Csf/Al2O3 with MgO is an excellent candidate for microwave absorbing material with favorable mechanical property. 相似文献
17.
B. Fernández J.M. AlmanzaJ.L. Rodríguez D.A. CortesJ.C. Escobedo E.J. Gutiérrez 《Ceramics International》2011,37(8):2973-2979
The effects of V2O5, NiO, Fe2O3 and vanadium slag on the corrosion of Al2O3 and MgAl2O4 have been investigated. The specimens of Al2O3 and MgAl2O4 with the respective oxides above mentioned were heated at 10 °C/min from room temperature up to three different temperatures: 1400, 1450 and 1500 °C. The corrosion mechanisms of each system were followed by XRD and SEM analyses. The results obtained showed that Al2O3 was less affected by the studied oxides than MgAl2O4. Alumina was only attacked by NiO forming NiAl2O4 spinel, while the MgAl2O4 spinel was attacked by V2O5 forming MgV2O6. It was also observed that Fe2O3 and Mg, Ni, V and Fe present in the vanadium slag diffused into Al2O3. On the other hand, the Fe2O3 and Ca, S, Si, Na, Mg, V and Fe diffused into the MgAl2O4 structure. Finally, the results obtained were compared with those predicted by the FactSage software. 相似文献
18.
S.M. Lakiza Ja.S. TyschenkoL.M. Lopato 《Journal of the European Ceramic Society》2011,31(7):1285-1291
The phase diagram of the Al2O3-HfO2-Y2O3 system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al2O3 + HfO2 + Y3Al5O12. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al2O3-HfO2-Y2O3 system. 相似文献
19.
WC-40 vol.%Al2O3 composites were prepared by high energy ball milling followed by hot pressing. The tungsten carbide (WC) and commercial alumina (Al2O3) powders composed of amorphous Al2O3, boehmite (AlOOH) and χ-Al2O3 were used as the starting materials. The phase transformation during sintering, the influence of sintering temperature and holding time on the densification, microstructure, Vickers hardness and fracture toughness and the toughening effects of WC-40 vol.%Al2O3 composites were investigated. The results showed that the amorphous Al2O3, AlOOH and χ-Al2O3 were transformed to α-Al2O3 completely during the sintering process. With the increasing sintering temperature and holding time, the relative density increased and both the Vickers hardness and fracture toughness increased initially to the maximum values and then decreased. When the as milled powders were hot pressed at 1540 °C for 90 min, a relative density of 97.98% and a maximum hardness of 18.65 GPa with an excellent fracture toughness of 10.43 MPa m1/2 of WC-40 vol.%Al2O3 composites were obtained. 相似文献
20.
Jin-min ChenHuan-ping Wang Si-qiao FengHong-ping Ma De-gang DengShi-qing Xu 《Ceramics International》2011,37(3):989-993
The effects of CaSiO3 addition on the sintering behavior and microwave dielectric properties of Al2O3 ceramics have been investigated. The addition of CaSiO3 into Al2O3 ceramics resulted in the emergence of Ca2Al2SiO7 and CaAl2Si2O8, which acting as liquid sintering aids can effectively lower the sintering temperature of Al2O3 ceramic. The Q × f value of Al2O3-CaSiO3 ceramics decreased with the CaSiO3 addition increasing because of the lower Q × f value of Ca2Al2SiO7 and CaAl2Si2O8. Compared with the pure CaSiO3 ceramic, the Al2O3-CaSiO3 ceramic with 20 wt% CaSiO3 addition possessed good dielectric properties of ?r = 9.36 and Q × f = 13,678 GHz at the similar sintering temperature. 相似文献