共查询到20条相似文献,搜索用时 31 毫秒
1.
Effect of Weight Loss on Liquid-Phase-Sintered Silicon Carbide 总被引:3,自引:0,他引:3
Tor Grande Hkon Sommerset Eirik Hagen Kjell Wiik Mari-Ann Einarsrud 《Journal of the American Ceramic Society》1997,80(4):1047-1052
The evaporation of silicon carbide (SiC) ceramics during sintering has been studied by thermogravimetry in a graphite furnace filled with argon. The SiC powder compacts contained 7.5 wt% eutectic composition of Y2 O3 –Al2 O3 to promote liquid-phase sintering. A weight loss of 1–11 wt% was observed during sintering, depending on the sintering temperature and sintering time. The weight loss severely influenced the final density and the microstructure of the SiC ceramics. Particularly, the oxide sintering aids, which were homogeneously distributed in the green ceramics, were observed to segregate and form particular patterns that were dependent on the temperature, sintering time, and the total weight loss. Possible heterogeneous reactions evolving volatile species have been discussed in relation to the experimental observations. 相似文献
2.
The faceting of alumina interfaces in the presence of a glass affects both grain growth and grain-boundary mobility during liquid-phase sintering. The geometry and movement of facets that form during this sintering process are expected to play an essential role in the development of the final microstructure, in particular, by their influence on the topology of the grain boundaries which ultimately control the properties of Al2 O3 compacts. A new method for studying the interaction between Al2 O3 and a glass has been developed. A thin sample of Al2 O3 suitable for examination in a transmission electron microscope is prepared and examined and then reacted with SiO2 and CaO via the vapor phase. This experimental approach allows the faceting behavior of glass/Al2 O3 interfaces to be studied systematically without introducing unnecessary complications during subsequent sample preparation. Faceting occurs almost exclusively on the (0001) and {1 1 02} planes. The interaction between glass and certain structured grain boundaries in alumina has been studied using polycrystalline thin films. 相似文献
3.
Nowadays, the electronic industry demands small and complex parts as a consequence of the miniaturization of electronic devices. Powder injection moulding (PIM) is an emerging technique for the manufacturing of magnetic ceramics. In this paper, we analyze the sintering process, between 900 °C and 1300 °C, of Ni-Zn ferrites prepared by PIM. In particular, the densification behaviour, microstructure and mechanical properties of samples with toroidal and bar geometry were analyzed at different temperatures. Additionally, the magnetic behaviour (complex permeability and magnetic losses factor) of these compacts was compared with that of samples prepared by conventional powder compaction. Finally, the mechanical behaviour (elastic modulus, flexure strength and fracture toughness) was analyzed as a function of the powder loading of feedstock. The final microstructure of prepared samples was correlated with the macroscopic behaviour. A good agreement was established between the densities and population of defects found in the materials depending on the sintering conditions. In general, the final mechanical and magnetic properties of PIM samples were enhanced relative those obtained by uniaxial compaction. 相似文献
4.
Suk-Joong L. Kang Min-Gon Lee Se-Min An 《Journal of the American Ceramic Society》2009,92(7):1464-1471
This paper reports recent theoretical perspectives and experimental results on microstructural evolution during sintering in terms of the interface structure, which is either rough (atomically disordered) or faceted (atomically ordered). The paper presents theoretical predictions and calculations of grain growth during liquid-phase sintering based on crystal growth theories. It is shown that various types of grain growth behavior, which may be normal, abnormal, or stagnant, can appear as a result of the coupling effects of the maximum driving force for growth and the critical driving force for appreciable growth. The predictions are also shown to be valid in the case of solid-state sintering. A number of experimental observations showing the effect of some critical processing parameters have been found to be in excellent agreement with the predictions. Principles of microstructure development (grain growth control) during sintering are suggested. In addition, the effect of the interface structure on densification is briefly described and discussed. 相似文献
5.
Miha Drofenik rej Znidarsic Darko Makovec 《Journal of the American Ceramic Society》1998,81(11):2841-2848
Additions of Bi2 O3 were used to promote grain growth and to increase magnetic permeability during sintering of MnZn ferrites. The results showed that small additions of Bi2 O3 of <0.05 wt% remarkably increase the permeability of MnZn ferrites. On the other hand, addition of 0.05 wt% Bi2 O3 induced the formation of a microstructure composed of giant grains with trapped pores embedded in a normal microstructure. The permeability of these samples showed a pronounced secondary maximum in permeability. At still higher Bi2 O3 concentrations, above 0.2 wt%, the grain growth was retarded and a normal microstructure appeared; however, the magnetic permeability was strongly reduced. 相似文献
6.
Densification and Shrinkage During Liquid-Phase Sintering 总被引:2,自引:0,他引:2
Suk-Joong L. Kang Kwan-Hyeong Kim Duk N. Yoon 《Journal of the American Ceramic Society》1991,74(2):425-427
The process of densification and shrinkage during the final stage of liquid-phase sintering is described. The densification occurs by the liquid filling of pores during grain growth. The pore filling results in an instantaneous drop of liquid pressure in the compact and causes gradual accommodation of grain shape. The grain shape accommodation by the growth causes the specimen shrinkage. At the same time, the grains tend to restore their spherical shape, resulting in microstructure homogenization around filled pores. The process of densification and shrinkage appears to be determined by the growth of grains during sintering. 相似文献
7.
Compositional Effects on the Liquid-Phase Sintering of Praseodymium Oxide-Based Zinc Oxide Varistors
Aldo B. Alles Robert Puskas Gregory Callahan Vernon L. Burdick 《Journal of the American Ceramic Society》1993,76(8):2098-2102
The influence of the formation of eutectic liquid phases during sintering of the ternary varistor system ZnO-Pr6 O11 -Co3 O4 was studied. The temperature at which the samples were observed to be liquid-phase sintered was found to depend on the nominal batch composition. The appearance of the liquid phase had a significant effect on the final microstructure as well as on the electrical properties of the varistors. Small additions of ZrO2 , purposely added or resulting from ball-mill contamination, were found to affect moderately the properties of the liquid phases observed in this system. 相似文献
8.
Lead zirconate titanate (Pb(Zr,Ti)O3, PZT) films were grown on silicon 1 0 0 substrate by aerosol deposition, using solid-state reacted powder containing donor oxide Nb2O5, while the substrate was maintained at room temperature. The PZT films were simultaneously sintered upon deposition on a highly densified ceramic layer. Crystalline phases of the deposited films have been determined by X-ray diffractometry (XRD), and microstructures analysed by transmission electron microscopy (TEM). The cross-section microstructure consisted of several thin layers, including the PZT film and the platinum electrode and titanium-buffered layers on the substrate. High-resolution images revealed that the PZT layer contained a mixture of randomly oriented grains of nanometre size, which were embedded in an amorphous matrix. In contrast to the conventional liquid-phase sintering mechanism, sintering of the PZT films involved amorphised phases generated by pressure-induced amorphisation (PIA) from plastic deformation when the initial powder particles collided amongst one another upon reaching the silicon substrate during aerosol deposition. An analogy may be drawn to the impact of extraterrestrial meteorites in which diaplectic glass, i.e., amorphised phase, was formed and retained metastably at room temperature. The individual PZT grains were joined with the amorphised phase(s) and sintered to become a dense, thin film on the silicon substrate. 相似文献
9.
Development of Functional Microstructure during Sintering of a ZnO Varistor Material 总被引:4,自引:0,他引:4
The effects of sintering time and rate of cooling on the microstructure and current/voltage characteristics of a ZnO varistor material have been investigated. The results provide information about the development of microstructure during sintering and have been interpreted in terms of the role which microstructure plays in the determination of electrical properties. A continuous network of intergranular Bi2 O3 , which lies mainly along the triple junctions between ZnO grains, can give a substantial contribution to the leakage current. The conductivity of this skeleton depends upon its internal microstructure. 相似文献
10.
Brian T. Naughton Pawel Majewski David R. Clarke 《Journal of the American Ceramic Society》2007,90(11):3547-3553
Toroids comprised of silica-coated 10 nm diameter nickel–zinc (Ni–Fe) ferrite nanoparticles (Ni0.5 Zn0.5 Fe2 O4 ) have been fabricated by careful control of both the coating process and subsequent densification by viscous sintering. A narrow processing window is identified between a maximum temperature at which the nanoparticles coarsen, losing their super-paramagnetic properties, and a lower temperature required for viscous flow densification. Key to the successful fabrication was drying and cold isostatic pressing of the silica-coated nanoparticles; other routes invariably led to cracking during either drying or sintering. The super-paramagnetic blocking temperature, the coercive field, and remanent magnetization could all be controlled over a wide range by varying the thickness of the silica coating from 1 to 15 nm. The dipole–dipole coupling distance is estimated to be 4 nm. The high-frequency (1–500 MHz) properties were sensitive to the sintering temperature as well as the thickness of the silica coating. Toroids sintered at 1000°C or less exhibited no high-frequency magnetic losses and their permeability decreased with increasing temperature, suggesting that the permeability was controlled by thermally activated magnetization relaxation. 相似文献
11.
Keith G. Brooks Vasantha R. W. Amarakoon 《Journal of the American Ceramic Society》1991,74(10):2513-2517
Lithium zinc ferrites (Li0.3 Zn0.4 Mn0.05 Fe2.25 O4 ) of > 97% theoretical density were prepared with alkoxide-derived borosilicate sintering additive. A sol-gel technique was used to incorporate the borosilicate phase prior to sintering. The effects of borosilicate composition and additive quantity on microstructural development and densification are reported. Direct current resistivity, dynamic hysteresis, and microwave property data are discussed in terms of processing parameters and resultant microstructures. The microstructure of the sintered ferrites was analyzed using SEM and TEM. Heterogeneities including regions of liquid-phase coalescence and intragranularly included glass phase were observed in some cases. These microstructural features were shown to have deleterious effects on microwave magnetic properties when compared to those of commercial ferrites of the same nominal composition sintered with Bi2 O3 additive. 相似文献
12.
《Ceramics International》2023,49(15):25371-25380
In this work, ultrathin planar alumina-based ceramic membranes with asymmetric structure and thickness less than 0.85 mm were successfully prepared by one-step molding phase transformation/sintering method using low-cost black talc (BT) nanosheets for the first time. The microstructure, pore structure, mechanical strength and permeability of novel ceramic membranes were systematically investigated with different BT amount and sintering temperatures. The doping of BT nanosheets effectively modulated the interfacial bonding area and strength between the grains, achieving significant increase in flexural strength through the evolution of the dense layer structure. The asymmetric structural features formed by the phase transformation/sintering process in combination with polymer substrate significantly reduced the thickness of effective separation layer, thus weakening the loss of flux caused by the densification of the film layer due to the interfacial modification process. Moreover, the organic carbon layers between BT layers were oxidized during the sintering process, forming fine pores and increasing the porosity, which showed to be unique characteristic different from other clay mineral materials. The prepared composite membrane had the pure water flux up to 16335 L m−2 h−1/bar at 1350 °C sintering, which achieved stable permeation of ∼5200 L m−2 h−1/bar and high retention over 90% for O/W emulsions. 相似文献
13.
《Journal of the European Ceramic Society》2007,27(7):2623-2627
Alumina films prepared by tape casting were sintered freely and under geometrical constraint at 1350 °C. The effect of film thickness on sintering kinetics and microstructure development was investigated. A decrease in film thickness in the constrained case leads to enhanced retardation of densification and increased orientation of anisometric pores. 相似文献
14.
Microstructural Investigations of Barium Titanate-Based Material for Base Metal Electrode Ceramic Multilayer Capacitor 总被引:1,自引:0,他引:1
The microstructures of BME-X7R ceramics have been investigated by imaging and analytical TEM. By varying the sintering conditions (pressing, sintering temperature and atmosphere), the microstructure changes drastically, and dislocation loops can be observed. These defects most probably are caused by an ordering of oxygen vacancies in the lattice, and the density appears to be correlated to the oxygen partial pressure applied during the reoxidation step. For pressed and unpressed ceramic foils, a model for different sintering behaviors according to liquid-phase assistance is given that is based on a kinetically determined microstructure rather than thermodynamic equilibrium. 相似文献
15.
Jing-Feng Li Yuhua Zhen Bo-Ping Zhang Li-Min Zhang Ke Wang 《Ceramics International》2008,34(4):783-786
Lead-free piezoelectric ceramics have received more attention due to the environmental protection of the earth. (K, Na)NbO3-based ceramics are one of the most promising candidates. Normal sintering of un-doped and Li/Ta co-doped (K, Na)NbO3 ceramics was investigated to clarify the optimal sintering condition for densification, microstructure and electrical properties. It was found that density increased greatly within a narrow temperature range but turned to decrease when the sintering temperature slightly exceeded the optimal one. Piezoelectric properties also showed similar relationship between the density and sintering temperature, but the highest piezoelectric strain coefficients were obtained at the temperatures lower than that for the highest density. The grain growth and property change as a function of sintering temperature were discussed on basis of the formation of liquid-phase and the composition deviation caused by the volatilization of alkali components during sintering. 相似文献
16.
Dihedral Angle Effects on the Stability of Pore Channels 总被引:1,自引:0,他引:1
W. Craig Carter Andreas M. Glaeser W.D. Kingery 《Journal of the American Ceramic Society》1984,67(6):124-C
The modifying effect of dihedral angle on the morphological stability of continuous pore channels along three-grain junctions was evaluated and quantified. Breakdown of a continuous pore channel is possible when perturbation wavelengths exceed a critical wavelength, λmin , which is found to depend on dihedral angle. The implications of the analysis to microstructure development during sintering are briefly discussed. 相似文献
17.
Yet-Ming Chiang Lee A. Silverman Roger H. French Rowland M. Cannon 《Journal of the American Ceramic Society》1994,77(5):1143-1152
Thick-film resistors arc electrical composites containing ultrafine particles of ruthenate conductor (Pb2 Ru2 O7 in the present materials) distributed in a highly modified silicate glass. We show that conductor particles remain flocced in the absence of any applied or capillary pressures, but are separated at equilibrium by a nanometer-thick film of glass. Microstructures show evidence for liquid-phase sintering, i.e., contact flattening of particles, under van der Waals attraction alone. Titania addition, which in dilute concentrations markedly increases the resistivity, decreases the temperature coefficient of resistance, and improves voltage stability and noise, is found to increase the equilibrium film thickness between particles by a few angstroms. STEM analyses show that the added titania preferentially concentrates in the silicate-rich grain boundary film, as well as at particle–glass interfaces. The roles of interparticle forces and adsorption on the glass film thickness with and without titania are discussed. The large increase in resistivity caused by titania additions is attributed to the increase in Film thickness as well as to local chemical changes of two possible types. Titania enrichment within the glass film itself is expected to decrease the local ruthenium ion solubility, and this along with the possible formation of a more insulating titania-substituted surface layer on ruthenate grains will decrease the tunneling conductivity between conductor grains. 相似文献
18.
Chen-Hui Li Liang Hu Yang Zou Jiang-An Liu Jian-Hua Xiao Jia-Min Wu Yu-Sheng Shi 《International Journal of Applied Ceramic Technology》2020,17(1):255-263
In this study, different posttreatment methods, including silica-sol infiltration (SI), vacuum silica-sol infiltration (vSI), debinding (DB), and pressure-less sintering (PS), were combined with selective laser sintering (SLS) to fabricate Al2O3-SiO2 ceramics. The macro-morphology and microstructure of sample fabricated under different laser processing parameters and posttreatment process were investigated. Results show that the geometric dimension accuracy and surface quality of the final samples can be effectively improved with appropriate SLS parameters and posttreatment. The optimal SLS processing parameters are determined to be 0.15 mm, 10 W, 0.1 mm, and 1500 mm/s for the hatch spacing, laser power, layer thickness, and scanning speed, respectively. The SLS/DB/vIN/FS samples have the smallest linear shrinkage ratio (<1%), the least warpage degree (<3%), and the best surface quality (surface altitude difference <170 μm). Mullite, quartz, corundum, and cristobalite composed the phases of the sample, of which cristobalite came largely from the infiltrated silica-sol. Since a higher amount of silica-sol infiltrated into the sample under SLS/DB/vIN/FS process, more cristobalite phase formed in the pore of the sample during sintering, which avoided excessive microstructure shrinkage during sintering and ensured the high geometric accuracy and surface quality of the final sample. 相似文献
19.
The mechanical properties of Si3 N4 materials depend mainly on the microstructure, which originates during the densification process. The microscopic evidence indicates that β-Si3 N4 seeds incorporated in the starting powders play an important role in microstructural development, especially in the heterogeneous grain growth of β-Si3 N4 grains during sintering. The growth of β-grains is initiated from the β-seeds, resulting in a core/shell microstructure. The presence of Moiré fringes and dislocations is attributed to misfit strain and compositional differences between the core and the shell. Coalescence can occur at the final stage of sintering. 相似文献
20.
Possible Electrical Double-Layer Contribution to the Equilibrium Thickness of Intergranular Glass Films in Polycrystalline Ceramics 总被引:1,自引:0,他引:1
David R. Clarke Thomas M. Shaw Albert P. Philipse Roger G. Horn 《Journal of the American Ceramic Society》1993,76(5):1201-1204
The plausibility of the entropic repulsion of electrical double layers acting to stabilize an equilibrium thickness of intergranular glass films in polycrystalline ceramics is explored. Estimates of the screening length, surface potential, and surface charge required to provide a repulsive force sufficiently large to balance the attractive van der Waals and capillary forces for observable thicknesses of intergranular film are calculated and do not appear to be beyond possibility. However, it has yet to be established whether crystalline particles in a liquid-phase sintering medium possess an electrical double layer at high temperatures. If they do, such a surface charge layer may well have important consequences not only for liquid-phase sintering but also for high-frequency electrical properties and microwave sintering of ceramics containing a liquid phase. 相似文献