凝胶注模成型研究进展

凝胶注模成型是20世纪90年代初美国橡树岭国家实验室首创的胶态成型工艺.该工艺利用有机单体聚合反应形成的三维网络凝胶特性,使陶瓷悬浮体注入模具后原位固化成陶瓷坯体.它具有坯体均匀、坯体密度高、坯体强度高、近净尺寸成型等显著优点.本文全面阐述了凝胶注膜成型的近十年来的研究进展,并对其研究前景进行了展望.     

PVA-AM体系凝胶流延成型研究

研究了一种新的凝胶体系聚乙烯醇和丙烯酰胺（PVA-AM）的凝胶流延成型。由于空气中的氧阻止了单体的聚合，不能形成胶体，传统丙烯酰胺体系的凝胶注模成型制备的陶瓷坯体的表层出现裂纹甚至脱落。为了避免这个问题，通常都是选择氮气保护下浇注成型，这个过程繁琐且成本较高。通过使用本研究的凝胶体系，在原有体系的基础上添加适量的新组分聚乙烯醇，在自然环境下就可以获得表面完好的陶瓷坯体。研究了氧化铝粉在含有PVA水溶液中的分散情况，PVA-AM体系浆料的流变行为以及固化情况；同时对坯体的性能和显微结构进行了观察。这种新的体系尤其适用于制备陶瓷薄片或陶瓷薄膜，在利用凝胶流延工艺制备固体氧化物燃料电池电解质中有较好的应用。     

直接发泡法制备泡沫陶瓷过滤器

介绍了一种新型泡沫陶瓷过滤器的制备方法并对其性能进行了测试研究。首先制备凝胶注模成型所需氧化铝陶瓷浆料，再添加吐温（Tween）和曲通（Triton）系列表面活性剂，通过机械搅拌使其直接发泡，再通过有机单体丙烯酰胺聚合，固化泡沫浆料，成型得到坯体，经干燥、烧结之后，制备成氧化铝泡沫陶瓷。研究了该工艺所成型泡沫陶瓷气孔率和通孔率（开孔气孔率）的关系，结果表明，直接发泡法可以制备高通孔率的泡沫陶瓷，能够满足过滤器使用时高开孔率和高强度的要求。     

水溶性环氧树脂的锆钛酸铅压电陶瓷凝胶注模成型

分别以聚丙烯酸铵(NH4PAA)和海因环氧树脂为分散剂和凝胶剂,制备锆钛酸铅陶瓷浆料,研究分散剂及固相含量对浆料流变性能、生坯和烧结样品物理性能的影响。结果表明:当分散剂含量(质量分数)为0.6%时,浆料黏度最低;当固相含量(体积分数)高达57.5%时,浆料仍保持良好的流动性;当固相含量为55%时,陶瓷生坯和烧结坯的强度均达到最大值,分别为34.1和77.8 MPa;与传统模压成型工艺对比表明,采用凝胶注模成型工艺制备的样品具有更优异的物理和压电性能。     

高性能氧化物陶瓷材料的注射成型

系统研究了高纯超细3Y-ZrO2和Al2O3陶瓷粉末的注射成型技术.主要研究了高纯超细3Y-ZrO2和Al2O3粉末,与有机载体混炼后的流变性,获得适于注射成型的悬浮体;注射成型的陶瓷的素坯特性.分析测试了脱脂烧结后3Y-ZrO2和Al2O3陶瓷体的体积密度,显微结构特征,抗弯强度等性能.并采用注射成型技术成功的制备出表面光洁、尺寸精确的光纤连接器陶瓷套筒、生物陶瓷牙桩、陶瓷刀片等高性能精密陶瓷部件.     

氧化铝陶瓷型芯凝胶成型因素研究

溶胶-凝胶成型是制备成分均匀、结构复杂陶瓷型芯最理想的成型工艺。以降低浆料粘度和提高固相含量为研究方向,从不同固相含量、颗粒度、添加剂对型芯性能的影响进行分析,以及研究pH值对浆料流动性的影响,并制备出固相含量为58%、动力粘度为0.46MPa.s的氧化铝陶瓷浆料,其成型后坯体湿强度可达约34MPa,完全满足后续加工要求。     

凝胶注模工艺参数对多孔铝铜合金品质的影响（英文）

通过凝胶注模工艺制备多孔铝铜合金。研究凝胶注模工艺参数如单体含量、交联剂与单体的比例、分散剂和引发体系4个因素对坯体高度、固化时间和坯体品质3个指标的影响。其中分散剂对坯体高度,单体对坯体质量的影响最大。通过分析得出最佳工艺为:单体体积分数10%、交联剂体积分数2%、引发剂体积分数0.2%、分散剂质量1.2 g,在此条件下坯体呈现最好的品质。同时探讨工艺参数消除裂纹和形成孔结构的机理。利用压汞法得出孔直径在10~10000 nm范围内,开孔气孔率达到38.78%。     

ZnO温度响应凝胶注模成型的流变性能和干燥机制（英文）

为解决坯体干燥问题,将含大单体支链的温度响应凝胶体系应用于ZnO的凝胶注模成型,研究大单体支链PIPAAm的加入量与支链长度、总有机物含量和固相体积分数对悬浮液流变性能的影响,并分析坯体的干燥机理。研究表明:添加该凝胶体系的ZnO悬浮液仍表现为剪切变稀流变行为,但其黏度随着PIPAAm支链的加入量与相对分子质量以及总有机物含量的增加而升高。大单体支链的引入抑制甚至消除ZnO温度响应凝胶注模坯体表面"密实层"的形成,加快坯体干燥,促进坯体收缩。     

氧化锆陶瓷磨球的滚制成型法制备技术与性能研究

研究了滚制成型法制备氧化锆陶瓷球坯工艺及烧结温度对陶瓷磨球体积密度、压碎强度和自磨损性能的影响.结果表明,凝胶固相合成法生产的亚微米级3mol% Y_2O_3-ZrO_2陶瓷粉体适用于滚制成型法制备体积密度高、圆度好、大小均匀的球坯.在1500 ℃保温2 h的烧结条件下得到的微晶氧化锆陶瓷磨球在快速研磨机中的自磨损率最低,其微观结构均匀,晶粒尺寸约0.5 μm,体积密度为5.97 g/cm~3,φ2.75 mm和φ6.36 mm陶瓷磨球的平均压碎强度分别达到326和1377 kg.     

ZnO温度响应凝胶注模成型的流变性能和干燥机制

为解决坯体干燥问题，将含大单体支链的温度响应凝胶体系应用于ZnO的凝胶注模成型，研究大单体支链PIPAAm的加入量与支链长度、总有机物含量和固相体积分数对悬浮液流变性能的影响，并分析坯体的干燥机理。研究表明：添加该凝胶体系的 ZnO 悬浮液仍表现为剪切变稀流变行为，但其黏度随着 PIPAAm 支链的加入量与相对分子质量以及总有机物含量的增加而升高。大单体支链的引入抑制甚至消除ZnO温度响应凝胶注模坯体表面“密实层”的形成，加快坯体干燥，促进坯体收缩。     

Three-dimensional printing of hard materials

Tungsten cemented carbide parts have been produced by the “Solvent on Granule” 3D-Printing technique. It consists in growing layer-by-layer a green part by spreading a powder-polymer granule bed, followed by selective solvent jetting, and layer consolidation after solvent evaporation. The granules are prepared by wet blending, drying, milling and sieving to appropriate size range. The printed green parts are consolidated by thermal debinding and liquid phase sintering.Fully dense WC-Co test parts and a drill bit have been produced from presintered powder and elementary Co powder. The microstructures are equivalent to those of press and sintered parts. Good shape retention and tolerances are achieved.     

93W-Ni-Fe粉末挤压成形坯溶剂脱脂工艺

以93W-Ni-Fe粉末挤压成形坯为研究对象,在研究溶剂脱脂动力学的基础上,考察溶剂种类、溶剂加入方式以及脱脂温度对溶剂脱脂过程的影响,并对脱脂前后的坯体断口进行SEM观察。结果表明:以正庚烷作为脱脂溶剂,具有较高的脱脂率,脱脂坯无鼓泡、开裂等缺陷;通过分段优化的脱脂工艺,在45℃的正庚烷中脱脂8 h,脱脂过程中周期性更换溶剂,最终可脱除65%以上的石蜡,且整个脱脂过程均为扩散控制,相应的动力学参数为1.6751×10-5 cm2/s。     

Debinding injection molded materials by melt wicking

For metal and ceramic injection molding procedures which use wax binders in the production of powder-based parts, melt wicking is commonly employed to debind the components prior to sintering. Because debinding is often a time-consuming procedure, the influence of such process variables as powder size, part height, green density and temperature have been investigated to reduce the amount of time required for debinding by melt wicking.     

Solvent de-binding of water-soluble binder in powder injection moulding

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大厚度钨基合金正挤压棒坯的溶剂脱脂特性

为了实现厚度达15 mm钨基合金正挤压棒坯的无缺陷脱脂,对大厚度正挤压棒坯的溶剂脱脂行为和机理以及大厚度棒坯溶剂脱脂过程的优化方法和效果进行研究。结果表明:大厚度棒坯的溶剂脱脂对温度非常敏感,极易产生脱脂缺陷;棒坯厚度增大,粘结剂脱除速率降低,产生缺陷的几率增大,d 12 mm和d 15 mm棒坯的适宜溶剂脱脂工艺为(30℃,12 h);d 15 mm棒坯在30℃下脱脂6 h,脱脂量不足30%,且随着脱脂时间的进一步延长,脱脂速率显著下降;大厚度棒坯的溶剂脱脂受扩散控制,棒坯越厚,扩散路径越长,棒坯脱脂速率越小;采用短周期多次浸溶剂方法来优化脱脂过程,实现了正挤压棒坯的无缺陷脱脂,且d 12 mm和d 15 mm棒坯的脱脂量分别可高达55%和45%以上。     

Atmosphere control during debinding of powder injection molded parts

Atmosphere control during debinding of powder injection molded (PIM) parts is an important parameter to consider. Experimental results have shown that a stagnant atmosphere containing volatiles evolved during debinding can cause slumping of the green samples. Removal of volatiles from the sample zone aids debinding and can reduce cycle times and improve sample quality. Residual carbon and oxygen can be controlled during debinding by adjusting the atmosphere composition. This paper presents the results of PIM 70 vol% spherical copper powder and 30 vol% binder. Debinding atmospheres were altered to determine the effect of debinding on the green body and the sintered sample. This paper was originally presented at the symposium “Paniculate Materials in Rheological Applications,” TMS 1993 Fall meeting, Materials Week Program.     

Fabrication of 93W–Ni–Fe alloy large-diameter rods by powder extrusion molding

A powder extrusion molding (PEM) process has been used for the manufacturing of tungsten heavy alloy rods with large length to diameter ratio. An improved wax-based multi-component binder was developed for PEM of 93W–Ni–Fe alloy. The miscibility of its components and the characteristics of the binder were evaluated and good thermal–physical properties were obtained. Also, the feedstock rheological properties, extrusion molding and debinding process were studied. The feedstock exhibited a pseudo-plastic flow behavior. The large length to diameter ratio rods, with diameters up to 36 mm were extruded at 65 °C by optimizing the extrusion process. A two-step debinding process was employed to remove the binder in the extruded rods. Solvent debinding was carried out in n-heptane at 45 °C to extract the soluble components. A process of repeated short time immersion and drying of the extruded rods (called short-period solvent debinding) was developed and using this novel technique the binder removed was raised from 45% to 60%. SEM analyses indicated that a large volume of pores was formed in debound rods, but had not created interpenetrating pore channels yet. The rest of the binder could be thermally extracted at a high heating rate without defects.     

工程陶瓷注射成型的研究与发展

综述了陶瓷注射成型目前的发展状况以及该成型方法的优点。详细论述了陶瓷粉体性质、有机载体组成特别是表面活性剂对于陶瓷喂料和注射成型所成坯体性质的影响。分析了混炼顺序、注射工艺参数、脱脂对陶瓷喂料的流变性以及所成型坯体性质的影响。     

带内冷却液螺旋孔硬质合金钻头毛坯的挤压成型及相关技术探讨

从成型力学模型、成型工艺、成型设备及相关关键技术等方面初探了带内冷却液螺旋孔硬质合金钻头毛坯的挤压成型的可能性．具有技术上的新颖性和可实施性。     

Fabrication of W–20 wt.%Cu alloys by powder injection molding

W–20 wt.% Cu balls were fabricated by powder injection molding using a binder system consisted of paraffin wax, high density polyethylene, ethylene vinyl acetate and stearic acid. By optimizing the injection molding parameters, defect-free green parts were obtained. A two-step debinding process was employed to extract the binders in the molded samples. All soluble ingredients of the binders in the green parts were extracted during solvent debinding, and the residual binders can be removed in thermal debinding. The debound W–Cu samples were sintered in H₂ atmosphere at temperatures ranging 1050–1150 °C for 2 h. It was shown that relative density of the sintered W–Cu samples increases from 87.37% of the theoretical to 95.58% as sintering temperature rises from 1050 °C to 1150 °C. Microstructures of the molded, the debound and the sintered W–Cu samples were observed by scanning electron microscope, and the sintered W–Cu balls have fine and homogeneous microstructures. Maximum compressive strength of W–Cu balls with 8.5 mm diameter reaches 58 kN.