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以3种具有不同团聚特征的氧化铝粉料为对象,用粉料剪切仪测定了粉料的流动性。以单向加压成型测定了成型过程中压力与成型体密度变化。用压汞测孔仪及扫描电镜研究了团聚体的外形和气孔结构。通过以上各种观察,讨论了3种粉料的团聚体恃征及团聚特征对粉料流动性和成型性能的关系。 相似文献
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共沉淀喷雾干燥法制备YSZ粉料及其对烧结密度的影响 总被引:11,自引:5,他引:11
用共沉淀结合喷雾干燥法制得了可直接用于煅烧、成型的Y_2O_3稳定的ZrO_2粉料。用扫描电镜观察了喷雾干燥得到的粉料团聚体的尺寸、形貌,以及与喷雾干燥条件的关系。发现了共沉淀悬浮液的球磨对喷雾干燥后粉料的热行为的影响。喷雾干燥制得的粉料在1350、1500℃烧结后,相对密度分别达96.5%、97.8%;而烘箱干燥的粉料在相应温度下烧结,相对密度只达88%、93%。 相似文献
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研究了陶瓷胶态成型过程悬浮体中产生团聚体的微观机理,根据液体介质中陶瓷粉体颗粒之间的作用势,建立了团聚体产生的微观结构模型.利用环境扫描电子显微镜对悬浮体中粉体团聚的显微结构进行"准"直接观察,发现悬浮体中存在2种团聚体形态:Ⅰ型团聚体(硬团聚)和Ⅱ型团聚体(软团聚),揭示了团聚体的产生是由于浆料的固相含量偏离了稳定固相含量.研究发现:悬浮体中的团聚体会遗传到陶瓷体中,并对陶瓷构件的力学性能有显著影响.探讨了团聚体对烧结体的结构及力学性能影响的原因.当悬浮体中固相含量低于稳定固相体积分数ψ0时,悬浮体中会形成松散团聚即软团聚;当固相含量超过ψ0时,悬浮体中会形成紧密团聚即硬团聚:当固相含量等于ψ0时,悬浮体具有均匀分散的稳定结构.由于悬浮体固相含量偏离稳定周相含量ψ0而在悬浮体中产生的团聚体,会由于原位周化而遗传到坯体之中,影响烧结体结构的均匀性. 相似文献
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ZrO2粉料喷雾造粒颗粒的形貌,显微结构及其成型性能 总被引:13,自引:1,他引:12
采用SEM和TEM分析了ZrO2喷雾干燥粉料颗粒形貌和显微结构。发现喷雾干燥粉料颗粒是由固有团聚体组成的人造团聚体;其各团聚态强度随强度随料浆中结合剂合量增加而增大,固有团聚体强度随料浆粘度增大而增大;喷雾干燥粉料成型性与其团聚态结构和强度有着密切关系。 相似文献
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氧化锆粉料中团聚体的结构与强度 总被引:4,自引:1,他引:4
用共沉淀法经不同温度煅烧,制得不同团聚程度的4种含2.5mol%Y2O3的氧化锆粉料。在不同力下等静压成型。用压汞测孔法测定了成型体内孔隙分布。根据孔隙分布由二级分布转变为单级分布来估计粉体中团聚体的强度。实验数据表明:粉料中团聚体强度同煅烧温度有关,并存在团聚强度最低的煅烧温度。 相似文献
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水分和粘结剂含量对坯体冷等静压成型和性能的影响 总被引:3,自引:0,他引:3
以Si粉(粒度≤0.044mm)和聚乙烯醇水溶液(PVA,其中聚乙烯醇质量份数为5%)按一定比例混匀,过筛造粒,振动装料后进行冷等静压成型,研究了水分和PVA含量对硅粉坯体成型和性能的影响。研究表明:当水分含量大于1wt%时,粉料填充密度低,填充不均匀,导致压制时压缩比大,压缩不均匀,坯体外形不规整;当水分在0.5~1wt%时,硅粉填充密度较大,粉料的成型性较好,粉料中水分含量确定为0.5~1wt%。当加入的PVA的量从5wt%增加到15wt%时,坯体强度随PVA含量增加而增加;当加入的PVA的量从15%wt增加到25wt%时,坯体强度有降低的趋势,而且坯体中存在残余颗粒团聚体;当加入的聚乙烯醇溶液质量份数为15wt%时,坯体强度最大(约1.62MPa),并且不存在残余颗粒团聚体,确定粘结剂含量为15wt%。 相似文献
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NH4Cl电解质对Y—TZP陶瓷粉体团聚状态的影响 总被引:4,自引:0,他引:4
研究了用共沉淀法在沉淀反应溶液中NH4Cl电解质含量对Y-TZP陶瓷体团聚状态的影响和粉体的烧结性能,实验结果表明,较低的NH4Cl含量会造成粉体物团聚,但高某某浓度值后,NH4Cl将显著改善粉体的团聚状态,使粉体团聚强度降低,团聚体尺寸减小和烧结性能提高,在沉淀后反应溶液中加入适量NH4Cl电解质,将起到分散剂的作用,有利于提高粉体的分散性。 相似文献
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本文采用低毒的MAM-MBAM凝胶体系代替AM-MBAM有毒体系制备95氧化铝陶瓷,为改善成型后坯体的性能,在凝胶注模成型过程中给予浆料压力.研究发现在压力为0.3 MPa时获得的坯体表面光洁,线收缩率大,体密度高,结构均匀,成品率高,质量好.本文还并研究了压力对95氧化铝陶瓷烧结体线收缩率和体密度以及洛氏硬度的影响.实验结果表明:压力辅助凝胶注模成型所得坯体烧结后性能优于无压直接注模成型坯体,压力为0.3MPa时线收缩率最小,体密度最高可达3.81 g/cm3,洛氏硬度最高.坯体显微结构显示,陶瓷粉料被有机高分子网络很好地粘结在一起,并且压力注模的坯体中陶瓷粉料堆积紧密,结构均匀致密.烧结后,压力注模成型坯体晶粒发育良好,气孔较无压直接注模烧结体少,烧结致密性能优异. 相似文献
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Jian-Lin Shi Jian-Hua Gao Zu-Xiang Lin Tung-Sheng Yen 《Journal of the American Ceramic Society》1991,74(5):994-997
Fully agglomerated superfine zirconia powders were prepared with the coprecipitation and spray-drying method. The compaction of such powders shows no fragmentation of the agglomerates. The sintering behavior of the compacts was studied and two sintering stages were identified: densification within agglomerates at temperatures not higher than 1250°C and the removal of interagglomerate pores at temperatures above 1600°C. The interagglomerate pores are difficult to remove, and sintering between agglomerates even at 1600°C is still insignificant. Heating of the compacts at temperatures above 1600°C leads only to grain growth and the entrapping of pores in large grains. 相似文献
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Chia-Hung Kuo Chih-Jen Wang Hsuan-Min Lee Chi-Yuen Huang Chii-Shyang Hwang 《International Journal of Applied Ceramic Technology》2010,7(6):856-867
This work investigates sintering behaviors of α-alumina powder that were treated by attrition milling with zirconia media. While zirconia wear debris delays initial sintering shrinkage and increases the temperature to reach the maximum shrinkage rate, the agglomerates also influence the final sintering. The final density of the sintered bulk is limited because of the existence of pores among agglomerates. Zirconia wear debris effectively inhibits the grain growth of alumina during the sintering. Varying the degree of deagglomeration and the amounts of zirconia wear debris together can control the microstructure during the final stage of the sintering. 相似文献
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The sintering behavior of mullite powder compacts which contained soft and hard agglomerates was studied, The maximum density achieved depended on the size and packing of the agglomerates. Although the initial % total pore volume was kept constant, the presence of larger pores in the green compact, due to larger agglomerates, resulted in lower final densities after sintering. Densification rates were enhanced by the breakdown of agglomerates by grinding. The particle and agglomerate packing arrangements caused densification substages to occur. A schematic model is presented which agrees well with the observed experimental behavior. 相似文献
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Jun-ll Song Geon-Yong Lee Eui-Jin Hong Carolline S. Lee Jai-Sung Lee 《Journal of the American Ceramic Society》2019,102(6):3791-3801
The most important issue in the processing of nanoscale metal powders is whether the metal nanopowder can be fully consolidated into ultra-fine- or nano-grained powder metallurgy parts by pressureless sintering. This paper focuses on the sintering behavior of bimodal iron (Fe) nanopowder agglomerates by considering their microstructure and densification kinetics. During the sintering, bimodal Fe nanopowder compacts underwent discontinuous shrinkage behavior until they neared full density. Three contributions to the sintering mechanisms, asymmetric sintering, densification enhancement, and grain growth inhibition, are presented in relation to the effect of bimodal nanopowder structure. Smaller nanoparticles in the bimodal nanopowders, which are predominantly present at the boundaries and interstitial spaces of larger nanoparticles, are responsible for the three mechanisms stated above. This result is strongly supported by the apparent activation energy values ranging from 48.2 to 90.6 kJ/mol, which correspond to the energy for grain-boundary diffusion in Fe. The experimental results of this study show that bimodal nanopowder agglomerates can be used to produce full density nano-grained powder metallurgical parts by pressureless sintering. 相似文献
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CaB6陶瓷研究的进展 总被引:8,自引:0,他引:8
综合介绍了CaB6陶瓷粉末、多晶体和单晶体的制备方法。评述了各种方法的基本原理和特点。合成CaB6粉末最常用的方法为碳化硼法,此方法能够以低成本制备较纯的CaB6粉末。但是得到的粉末具有硬团聚现象,使CaB6粉末的烧结有一定的难度。由于CaB6在高温下具有高的化学活性和低的塑性,CaB6多晶多采用热压烧结的方法在高温高压下制备。单晶的制备主要采用区熔法和熔剂法。区熔法适合于生产大尺寸的CaB6单晶,而铝熔剂法制备的CaB6单晶尺寸最大为5mm,对测定其某些物理性能有一定的局限。对CaB6陶瓷的应用及国内外研究现状作了简要的概括,并对其今后的发展趋势作了展望。 相似文献
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Michael J. Readey Ran-Rong Lee † John W. Halloran ‡ Arthur H. Heuer 《Journal of the American Ceramic Society》1990,73(6):1499-1503
Chemical coprecipitation was used to produce ultrafine and easily sinterable MgO-stabilized and (MgO, Y2 O3 ) stabilized ZrO2 powders. The sintering behavior is very sensitive to post-precipitation washing because "hard" agglomerates form when the precipitated gels are washed with water, whereas "soft" agglomerates form when they are washed with ethanol. The soft agglomerates pack uniformly, resulting in homogeneous shrinkage of powder compacts to near-theoretical density. The hard agglomerates result in compacts which have regions of localized densification and a signifiint fraction of residual porosity. 相似文献
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The extent of the thermally induced shrinkage during sintering of nominally homogeneous ceramic compacts depends upon the green density; compacts with a low green density shrink more than those with a higher density. Therefore, shape distortions of compacts with variable density during their sintering is inevitable. The overall shapes of various sintered alumina compacts, prepared using different types of alumina agglomerates, is described. The agglomerates were prepared using organic polymer [poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG)] binders and the influence of the particle agglomerates size and the water content in the agglomerates is considered. The extent of the shape distortions in the cylindrical sintered compacts were reduced with the application of lubricants to the die walls. The agglomerate properties are shown to affect the overall shape of the sintered compacts significantly. The compacts, produced using the wet (plastisized) agglomerates, have the smallest shape distortions. A prediction of the sintered shape evolution is obtained using a first order model. The model predicts that the shape distortions in the sintered compacts increase with the increasing of the sintered density and a good agreement between the predicted and measured data is demonstrated. 相似文献
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Chun-Hway Hsueh Anthony G. Evans Robert M. Mcmeeking 《Journal of the American Ceramic Society》1986,69(4):64-C-
The sintering rate of a powder compact containing heterogeneities was calculated. The calculations reveal a strong retardation of sintering in the presence of nonsinterable agglomerates because of the development of a hydrostatic tensile stress. The variation in sintering rate with volume fraction is shown to be highly nonlinear, such that appreciable effects obtain even for 1% agglomerated powder. Specific results are calculated using constitutive laws pertinent to Al2 O3 . 相似文献
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Seong C. Kim Jing Wang Mark S. Emery Weon Gyu Shin George W. Mulholland David Y. H. Pui 《Aerosol science and technology》2013,47(4):344-355
Most filtration studies have been conducted with spherical particles; however, many aerosol particles are agglomerates of small primary spheres. Filtration efficiency tests were conducted with silver NP agglomerates, with the agglomerate structure controlled by altering the temperature of a sintering furnace. The mobility diameter and mass of the silver NP agglomerates were measured using a differential mobility analyzer together with an aerosol particle mass analyzer. From these measurements, it was found that the fractal-like dimension, D fm, varied from 2.07 to 2.95 as the sintering temperatures was increased from ambient to 600°C. The agglomerates were essentially fully coalesced at 600°C allowing direct comparison of the filtration behavior of the agglomerate to that of a sphere with the same mobility diameter. Other agglomerate properties measured include the primary diameter, the agglomerate length and aspect ratio, and the dynamic shape factor. Agglomerate filtration modeling with no adjustable parameters has been investigated in terms of diffusion, impaction, and interception. The model results agree qualitatively with the experimental results in the particle size range of 50 to 300 nm. The results indicated that the larger interception length of agglomerates is responsible for the smaller penetration through a fibrous filter in comparison to spherical particles with the same mobility diameters. 相似文献
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A coagulation coefficient of agglomerates with different fractal dimensions has not been considered in the past, even though there is a possibility of variations in the fractal dimension of agglomerates at any instant. In this study, a Brownian dynamics simulation was performed with simultaneous collision and sintering, and variations in the fractal dimension of agglomerates were observed. A coagulation coefficient expression for agglomerates with two different fractal dimensions was proposed. The coagulation coefficient based on the different fractal dimensions was at most 140% higher than that based on the average fractal dimension. To determine an accurate coagulation coefficient of agglomerates, the fractal dimension of each agglomerate has to be considered. 相似文献