共查询到20条相似文献,搜索用时 31 毫秒
1.
Timothy D. Davis Julia DiCorleto David Sheldon Jodi Vecchiarelli Can Erkey 《The Journal of Supercritical Fluids》2004,30(3):349-358
A novel route for the production of highly porous vitrified grinding wheels was developed via selective extraction of pore inducers with dense CO2. The extraction was performed with liquid and supercritical CO2 (scCO2) at temperatures ranging from 295 to 338 K, pressures from 8.8 to 27.6 MPa and flow rates of 3.4×10−5 and 7.5×10−5 kg s−1 CO2. The extraction rate was a strong function of temperature, flow rate, and flow direction, while unaffected by particle size of the pore inducer and pressure. The extraction had no detrimental effect on the green wheel’s microstructure. Grinding tests were performed on the CO2 extracted pore induced wheels and results were compared to those from a conventionally manufactured pore induced grinding wheel. The extracted grinding wheels performed similarly to the conventional wheels. At high metal removal rates, the extracted wheels with large pore sizes outperformed the wheels with smaller particle sizes as well as the conventional wheel. This may be due to the larger pore sizes increasing lubrication at the surface and increasing the wheel strength. 相似文献
2.
Aspects in Grinding of Ceramics 总被引:1,自引:0,他引:1
Seong-Jai Cho Yong-Hak Huh Kyung-jin Yoon Tomeyoshi Ogawa 《Journal of the American Ceramic Society》1994,77(9):2443-2444
Aspects In the grinding of ceramics have been investigated. Si3 N4 , ZrO2 , SiC, and Al2 O3 were ground with resin-bonded diamond wheels of grit numbers ranging from 80 to 800. Microstructural observations of ground surfaces show that grinding occurs predominantly by flow mode in Si3 N4 and ZrO2 , and by fracture and grain pullout in SiC and Al2 O3 . The measurement of grinding force shows that grinding resistances in Si3 N4 and ZrO2 are significantly larger than those in SiC and AI2 O3 . As the grit number of the grinding wheel increases, maximum surface roughness significantly decreases in Si3 N4 , ZrO2 , and SiC, but it apparently does not change in AI2 O3 . This unexpected result in AI2 O3 is discussed in terms of the observed grinding mode and microstructure. 相似文献
3.
Mehdi Allahverdi Robin A. L. Drew John O. Strom–Olsen 《Journal of the American Ceramic Society》1997,80(11):2910-2916
A melt extraction technique has been used to produce fine fibers from three eutectic compositions in the systems of ZrO2 -Al2 O3 (ZA), ZrO2 -Al2 O3 -SiO2 (ZAS), and ZrO2 -Al2 O3 -TiO2 (ZAT). The liquid surface tension of these ceramics was measured by a new method and estimated to be in the range of 400-567 mJ/m2 at similar ∼2400°C. The wetting between Mo (the extraction wheel material) and liquid ceramics was found to be poor during transient wetting; however, fiber extraction was achieved due to the shear action induced by the wheel rotation. The difficulties in the extraction of ZA fibers at speeds of <1.5 m/s, and also the formation of air pockets on these fibers, are attributed to the poor wetting of the Mo wheel by the liquid ZA. In a wide range of wheel velocities, extracted fibers exhibited alternating sections of uniform diameter and Rayleigh waves, both being the largest for ZAS fibers at any speed. The Rayleigh wave dimensions varied considerably with speed whereas the dimensions of the uniform region of the fibers remained unchanged over the wide range of extraction speeds examined. The fiber dimensions are controlled by both surface tension and viscosity of the molten ceramics at the extraction temperature. 相似文献
4.
Sreekumar Chockalingam David A. Earl Vasantha R. W. Amarakoon 《International Journal of Applied Ceramic Technology》2009,6(1):102-110
A 2.45 GHz microwave-sintered Si3 N4 –Y2 O3 –MgO system containing various amounts of ZrO2 secondary additives have been studied with respect to phase transformation and densification behavior. The temperature dependent dielectric properties were measured from 25°C to 1400°C using a conventional cavity perturbation technique. Phase transformation behavior was studied using X-ray diffractometry. Microwave sintered results were compared with those of conventional sintered results. It has been found that α to β phase transformation was completed at a lower temperature in microwave-sintered samples than those of the conventionally sintered samples. Density of the microwave-sintered samples increased up to 2.5 wt% of ZrO2 addition and thereafter it showed a tendency to decrease or remain constant. The decrease in density is attributed to the pore generation caused by decomposition due to the localized over heating. 相似文献
5.
Porous Ceramic Filters Produced by Hot Isostatic Pressing 总被引:1,自引:0,他引:1
Makoto Nanko Kozo Ishizaki Takao Fujikawa 《Journal of the American Ceramic Society》1994,77(9):2437-2442
Porous TiO2 ceramics were produced by capsule-free hot isostatic pressing (HIPing) and were evaluated by measuring gas permeability and pore size distribution. In comparison to conventionally sintered TiO2 , the HIPed TiO2 has a higher permeability and narrower pore size distribution. The differences are caused by the effects of high-pressure gas during sintering. 相似文献
6.
Vidya S. Tiwari Neelam Singh Dhananjai Pandey 《Journal of the American Ceramic Society》1994,77(7):1813-1818
Ba1–x Cax TiO3 powders have been prepared using a novel route involving solid-state reaction in a mixture of Ba1–x Cax CO3 and TiO2 . The Ba1–x Cax CO3 precursors used in this method were prepared by a chemical coprecipitation route to ensure a uniform supply of Ba and Ca ions during thermochemical reaction with TiO2 . The compositional homogeneity of Ba1–x Cax TiO3 powder prepared by such a semiwet route is compared with those prepared by the conventional dry route, involving thermochemical reaction in a mixture of BaCO3 , CaCO3 , and TiO2 , using principles of X-ray line broadening. It is shown that the powders obtained by the semiwet route possess better compositional homogeneity, over a length scale of 1800 Å corresponding to the coherently scattering domain size, than those prepared by the conventional dry route. Microstructural studies have revealed grain sizes of the order of 1 μm and several micrometers, respectively, for ceramics prepared by the semiwet and conventional dry routes. The solid solubility limit of Ca in Ba1–x Cax TiO3 ceramics fired at 1300°C is 16 mol% for samples prepared by the semiwet route while conventionally processed ceramics had a Ca solid Solubility limit of 12 mol% at the same temperature. 相似文献
7.
Mei-Hwa Lee Hung-Yin Lin James L. Thomas 《Journal of the American Ceramic Society》2006,89(12):3624-3630
A novel synthesis of amorphous hydrous zirconia nanoparticles was performed in a supercritical carbon dioxide (scCO2 ) reverse microemulsion, converting a high concentration of a very inexpensive starting material (zirconyl nitrate hydrate) into a product that was then calcined to yield monoclinic zirconia nanoparticles. The amorphous hydrous zirconia precursor particles were obtained by simply adding a precipitating agent to [Zr4+ (aq) ]/perfluoropolyether/scCO2 . Calcination converts the amorphous hydrous zirconia precursor into the oxide, and the corresponding phase changes that occur were confirmed by differential thermal analysis. Some control of particle size and shape (ellipticity) could be achieved by selecting the reaction pressure from within the range over which stable microemulsions are obtained (13.9–17.3 MPa): a higher reaction pressure yields smaller and more spherical particles. This novel route for the synthesis of zirconia nanoparticles is both "green" (environmentally friendly) and economical. 相似文献
8.
THOMAS L. BARRY V. S. STUBICAN RUSTUM ROY † 《Journal of the American Ceramic Society》1966,49(12):667-670
Phase equilibrium relations in the system CaO-Yb2 O3 were studied. Results of this work demonstrated the existence of four crystalline phases: Yb2 O3 .3CaO, Yb2 O3 .2CaO, Yb2 O3 °CaO, and 2Yb2 O3 °CaO. The 2Yb2 O3 °CaO phase is metastable at all temperatures and was obtained only by rapid quenching from the melt. The crystalline solubility limit of Yba O3 in CaO at 1850°C is slightly greater than 8 mole %, whereas no solubility of CaO in Yb2 O3 was detected. All four compounds have subsolidus minimums of stability and dissociate into the component oxides below 1800°C. Data are also presented for the systems CaO-Gd2 O3 and CaO-La2 O3 . 相似文献
9.
Crystalline solubility relations in the system MgO-Mg2 SiO4 MgAl2 O4 (periclase-forsterite-spinel) were studied using coprecipitated gels as starting materials. The substitution 2Al = Mg + Si was investigated along the join Mg2 SiO4 -Mg-Al2 O4 ,. At 1720°C the maximum crystalline solution in forsterite is about 0.5 mole % MgAI2 O4 , and in spinel it is slightly more than 5.0 mole % Mg2 SiO4 . The solubility of MgO in forsterite was 0.5 mole % at 1860°C, whereas more than 11 mole % Mg2 SiO4 can be dissolved in the periclase structure at this temperature. Ternary crystalline solution exists in the periclase structure to a composition of Mg0.853 Al0.063 Si0.026 O at 1710°C. 相似文献
10.
Ken Ando Masataka Momoda Takeshi Azumi Sadakichi Kitajima 《Journal of the American Ceramic Society》1987,70(11):309-C
Solubility of NiO in Al2 O3 was determined by electron probe microanalysisy A diffusion couple method was used by coupling an NiO-doped Al2 O3 polycrystal to a pure single crystal of Al2 O3 . The solubility of NiO in Al2 O3 in air was 230 wt ppm (157 at. ppm of cations) and 170 wt ppm (116 at. ppm) at 2073 and 1973 K, respectively. The solubility of NiO in Al2 O3 obtained in this work was compared with our previous work of the solubility of MgO in Al2 o3 . 相似文献
11.
This paper focuses on the preparation and characterization of pure TiO2 and ZrO2 xerogels. The preparation method is based on a sol–gel technique using metal tert -amyloxides as precursors to produce nano-sized metal oxide particles which are subsequently packed in a gelation process, eventually resulting in microporous xerogele. The unsupported TiO2 and ZrO2 xerogele produced in this manner have a mean pore diameter less than 2 nm and more than 50% microporosity. However, these gels, in their pure form, are thermally stable only to 350°C. Improved thermal stabilities of mixed metal oxide xerogels will be reported elsewhere. 相似文献
12.
Masahiro Yoshimura Manikpurage Jayaratna Shigeyuki Smiya 《Journal of the American Ceramic Society》1982,65(10):c166-c168
The pseudoternary system ZrO2 -Y2 O3 -Cr2 O3 was studied at 1600°C in air by the quenching method. Only one intermediate compound, YCrO3 , was observed on the Y2 O3 −Cr2 O3 join. ZrO2 and Y2 O3 formed solid solutions with solubility limits of 47 and 38 mol%, respectively. The apex of the compatibility triangle for the cubic ZrO2 , Cr2 O3 , and YCrO3 three-phase region was located at =17 mol% Y2 O3 (83 mol% ZrO2 ). Below 17 mol% Y2 O3 , ZrO2 solid solution coexisted with Cr2 O3 . Cr2 O3 appears to be slightly soluble in ZrO2 (ss). 相似文献
13.
Robert C. Newton Craig E. Manning John M. Hanchar Robert J. Finch 《Journal of the American Ceramic Society》2005,88(7):1854-1858
We exploited the large difference in the solubility of SiO2 and ZrO2 in H2 O to constrain precisely the Gibbs energy of formation of zircon (ZrSiO4 ). Solubility in H2 O was determined at 800°C, 1.2 GPa, by weight loss of synthetic zircon crystals. The experiments yielded fine-grained monoclinic ZrO2 as an incongruent solution product uniformly coating zircon crystals. Experiments on the ZrO2 -coated zircon crystals were also carried out with an initially slightly SiO2 -oversaturated fluid, causing weight gain by zircon regrowth. The mean SiO2 concentration for forward and reverse experiments was 0.069±0.010 mol/kg H2 O (2σ). When combined with precise activity–composition measurements for aqueous SiO2 , the data constrain the Gibbs free energy of zircon from its oxides at 298 K, 105 Pa, to be −19.30±1.16 kJ/mol (2σ). This determination is comparable in precision to the best measurements obtainable by more conventional methods, which suggests that determination of the thermochemical properties of other important ceramic materials may also be amenable to this method. 相似文献
14.
Marina Villegas Amador C. Caballero Carlos Moure Pedro Durán José F. Fernández 《Journal of the American Ceramic Society》1999,82(9):2411-2416
High-temperature piezoelectric ceramics based on W6+ -doped Bi4 Ti3 O12 (W-BIT) were prepared by both the conventional mixing oxides and the chemical coprecipitation methods. Sintering was carried out between 800° and 1150°C in air. A rapid densification, >99% of the theoretical density (rhoth ) at 900°C/2 h, took place in the chemically prepared W6+ -doped Bi4 Ti3 O12 ceramics, whereas conventionally prepared BIT-based materials achieved a lower maximum density, ∼94% of rhoth , at higher temperature (1050°C). The microstructure study revealed a platelike morphology in both materials. Platelike grains were larger in the conventionally prepared W-BIT-based materials. The sintering behavior could be related both to the agglomeration state of the calcined powders and to the enlargement of the platelets at high temperature. The W6+ -doped BIT materials showed an electrical conductivity value 2-3 orders of magnitude lower than undoped samples. The electrical conductivity increased exponentially with the aspect ratio of the platelike grains. The addition of excess TiO2 produced a further decrease of the electrical conductivity. 相似文献
15.
《Ceramics International》2021,47(24):34050-34058
Porous vitrified bond grinding wheels with complex structure, high porosity, controllable pore size have fundamental application in high efficiency and precision grinding of hard and brittle materials. In this paper, direct ink writing (DIW) is proposed to fabricate three kinds of grinding wheels, including solid structure, triangle structure, and lattice structure. Moreover, the rheological property of ceramic ink with different doses of xanthan gum (XG) solution was investigated to ensure printability, demonstrating 3% XG solution can meet requirements. Additionally, the effect of sintering temperature and pore former (PMMA) contents on size shrinkage rate, morphology, mechanical strength, and porosity et al. were studied. The results indicate that the diamond grinding wheel with 30 vol% PMMA and sintered at 670 °C possess the best comprehensive performance. Besides, grinding performance was evaluated by surface morphology, surface roughness, and material removal rate. Among the DIW-fabricated wheels, triangle structure grinding wheel and lattice structure grinding wheel possess a higher material removal rate than solid structure grinding wheel. Therefore, the porous structure grinding wheels fabricated by DIW present the advantage of controllable porosity, excellent self-sharpening ability, and higher bond strength, which may pave the way for designing a new generation vitrified bond diamond grinding wheel. 相似文献
16.
W. A. SCHULZE T. G. MILLER J. V. BIGGERS 《Journal of the American Ceramic Society》1975,58(1-2):21-23
The disappearing-phase method was used to determine the extent of the solid-solution region of the PLZT system for conventionally sintered ceramics prepared at 1100° and 1300°C in a PbO atmosphere provided by pbZrO3 . A decrease in the firing temperature from 1300° to 1100°C lowers the solubility limit by 5 to 8 at.% La. Beyond the limits of solubility, additional La forms La2 Zr2 O7 and/or La2 Ti2 O7 . The limit determined by the disappearing-phase method (1300°C firing) is compared to values determined by the parametric method. The Curie temperature is stabilized at 5 at.% La for modified PbZrO3 (1300°C firing). 相似文献
17.
Huarui Xu Lian Gao Hongchen Gu Jingkun Guo Dongsheng Yan 《Journal of the American Ceramic Society》2002,85(1):139-144
To avoid the formation of hollow particles during spray pyrolysis, a spray hydrolysis reaction method (SHRM) was studied. Unlike the conventional spray pyrolysis that uses metal salt as a precursor and dry air as a carrier gas, the SHRM introduces a mixture of metal salt and dimethyl oxalate (DMO) as precursors and a gas mixture of water vapor and air as the carrier gas. Spherical, solid CeO2 particles characterized by SEM, BET, and density analysis were produced by the SHRM using Ce(NO3 )3 and DMO as the precursors. DMO, as an internal precipitant, hydrolyzed and produced oxalic acid, which precipitated with cerium ions to form volume precipitation in the whole droplet at enough temperature and relative humidity. The volume precipitation induced by the in situ formation of oxalic acid in the whole droplet prevented Ce(NO3 )3 nucleation at the droplet surfaces, thus avoiding the formation of hollow particles which usually occur in the conventional spray pyrolysis process. XRD and IR analysis showed that cerium oxalate was an intermediate product in the SHRM process. 相似文献
18.
Miloslav A. Res Jaroslav Bednarik Jacobus T. Fourie Jonathan L. Albain 《Journal of the American Ceramic Society》1984,67(12):264-C
Clear glasses were produced when SiO2 in sodium borosilicate glasses was replaced by Ga2 O3 . Phase separation and/or crystallization occurred after heat treatment. The porous skeleton of leached material consisted of monoclinic β-Ga2 O3 . The specific surface areas and pore radii are comparable to those of porous SiO2 . Alumina contamination influenced the structure of the porous product. 相似文献
19.
The pseudobinary system CoNb2 O5 –CoTa2 O6 was investigated. CoNb2 O6 crystallizes in either the columbite or rutile structure, whereas CoTa2 O6 assumes only the trirutile structure. In an argon atmosphere at about 1400°C, CoNb2 O6 undergoes a phase transition from columbite or rutile. Between 1000° and 1400°C the solubility of CoTa2 O6 in CoNb2 O6 is about 10 mole %; in the same temperature region the solubility of CoNb2 O6 in CoTa2 O6 varies from about 40 to 70 mole %. The extensive solubility of CoNb2 O6 in CoTa2 O6 is explained by the ability of niobium to induce some disorder in the trirutile phase. The columbite to rutile transformation is also discussed on this basis. 相似文献
20.
This report details development of a route to solution-derived (1− x )Bi1/2 Na1/2 TiO3 · x BaTiO3 powders. The method developed was the citrate-gel method—an evaporative, aqueous technique. When applied to 0.95Bi1/2 Na1/2 TiO3 ·0.05BaTiO3 (BNBT-5), the method produced perovskite phase powders that readily densified in the temperature range of 1000°C. The grain size of the sintered materials was on the order of 1 μm, and the weak-field dielectric properties at 1 MHz were similar to those reported for conventionally prepared materials sintered at higher temperatures (e.g., 1200°C). 相似文献