Effect of microcrystalline wax on the solvent debinding of the Sr-ferrite ceramics prepared by powder injection molding

Powder injection molding (PIM) opens new possibilities to process complex Sr-ferrite components for magnetic applications. In the present study, new binder system with the addition of microcrystalline wax (MW) was used for the Sr-ferrite powder injection molding. The optimum binder composition was determined based on rheological measurement, mircrostructure observation by SEM, thermal change by DSC and debinding process. The results indicated that MW with 10 vol.% addition in the binder system containing high density polyethylene (HDPE), paraffin wax (PW) and stearic acid (SA) decreases the defects of the green parts after solvent debinding because the distribution of the binder system between the Sr-ferrite particles becomes more homogeneous. Using the proper binder system containing MW, the defect-free and dense Sr-ferrite ceramics can be prepared after solvent and thermal debinding and sintering. Based on the experimental results, the effects of MW microcrystalline wax on the solvent debinding of the Sr-ferrite ceramics were detailed discussed.     

氧化锆陶瓷注射成形工艺研究

研究了氧化锆陶瓷粉末注射成形工艺过程，包括粘结剂的选择、喂料粉末装载量的确定、混炼工艺及混炼扭矩的研究，注射压力、注射温度、保压压力、模具温度、注射速度等注射成形工艺对成形坯质量的影响，以及溶剂脱脂温度、样品厚度、粉末粒度及形藐等对溶剂脱脂速率的影响及后续热脱脂工艺，扶得了一条优化的注射成形工艺路线。     

Kinetics and equilibrium of Eco-debinding of PZT ceramics shaped by thermoplastic extrusion

Thermoplastic extrusion can present an alternative shaping process to a well-established powder pressing or tape casting method for lead zirconate titanate (PZT) ceramic sensor structures, if a complex debinding step can be achieved in an economic way.In this study PZT ceramic parts were made by thermoplastic extrusion using ethylene vinyl acetate and paraffin as a binder. Samples were thermally debinded according to different programs with and without a powder bed. A modified second order decomposition kinetics model is proposed which is especially suitable for describing partial debinding. Also a novel simplified model for wick-debinding is proposed to evaluate the contribution of a capillary extraction mechanism.Results show that isothermal debinding leads to partial debinded parts with a well-defined equilibrium residual binder, which is a function of a time-temperature program. We demonstrate that 90% of the binder can be removed at only 200 °C, even for a multicomponent binder system.     

Novel fabrication of more homogeneous water-soluble binder system feedstock by surface modification of oleic acid

Compared to conventional debinding process of wax-based binders used in ceramic injection molding, polyethylene glycol-based binders (water-soluble binders) with its high efficiency and environmental acceptability have appeared as a good alternative. However, water-soluble binder feedstock still presents some problems such as powder–binder separation or particle segregation which limits injected parts’ final properties. In the present work, we have successfully prepared the more homogeneous water-soluble feedstock with lower shear viscosity by a prior ball milling treatment to induce a small quantity of oleic acid to the surface of zirconia powders before the mixing process. Also, the surface modification mechanism of oleic acid to zirconia powders has been systematically discussed. With the modified powder, as-leached part with less agglomeration and phase separation has been fabricated, which suggests a novel modification method for fabricating injection molded ceramic parts by using water-soluble binders.     

注射成型氧化铝陶瓷工艺研究

研究了氧化铝陶瓷注射成型工艺过程,包括粘结剂的选择、粉末装载量的确定及热脱脂工艺的研究。探讨了注射压力、注射温度和模具温度等注射成型工艺参数对试样性能的影响,得到了一条优化的氧化铝注射成型工艺路线。     

Optimization of binder removal for ceramic microfabrication via polymer co-extrusion

The objective of this study is to assess the feasibility of solvent extraction (SE) for partial binder removal in the context of polymer co-extrusion with a thermoplastic binder component. Polymer co-extrusion is able to produce multilayered, functionally graded and/or textured structures in an efficient manufacturing process, but requires a polymer binder system with suitable flow characteristics. Traditionally, the binder is removed by thermal debinding (TD), which, however, is prone to form cracks or blisters, both of which are attributed to a lack of initial pore space that allows pyrolysis products to escape. The primary focus of this work is to demonstrate that a binder system with a high soluble binder content is suitable for conventional polymer co-extrusion and to document that a two-step binder removal process involving both SE and TD eliminates debinding defects. The overall fabrication process is documented for the extrusion of solid ceramic rods and co-extrusion of tubes, where alumina powder was batched with polyethylene butyl acrylate (PEBA) as backbone polymer and polyethylene glycol (PEG) as water soluble binder. SE for specimen with varying PEBA:PEG ratios was tested in water at three different temperatures for various times. The 1:1 mixture showed a PEG removal up to 80 wt.% of the original PEG content after 6 h extraction; after subsequent thermal debinding, rods and tubes sintered successfully without defects, demonstrating the viability of the process.     

Effect of technological parameters on densification of reaction bonded Si/SiC ceramics

Si/SiC composite ceramics was produced by reaction sintering method in process of molten silicon infiltration into porous C/SiC preform fabricated by powder injection molding followed by impregnation with phenolic resin and carbonization. To optimize the ceramics densification process, effect of slurry composition, debinding conditions and the key parameters of all technological stages on the Si/SiC composite characteristics was studied. At the stage of molding the value of solid loading 87.5% was achieved using bimodal SiC powder and paraffin-based binder. It was found that the optimal conditions of fast thermal debinding correspond to the heating rate of 10?°C/min in air. The porous C/SiC ceramic preform carbonized at 1200?°C contained 4% of pyrolytic carbon and ～25% of open pores. The bulk density of Si/SiC ceramics reached 3.04?g/cm³, silicon carbide content was 83–85?wt.% and residual porosity did not exceed 2%.     

氧化锆陶瓷注射成型溶剂脱脂行为的研究

以氧化锆陶瓷粉体为研究对象,采用低毒性、低成本的煤油作为有机脱脂溶剂,研究了注射成型生坯的溶剂脱脂行为,探索了时间、温度、固相体积分数和粘结剂体系对脱脂速率的影响,分别讨论了各因素影响脱脂速率的机理.结果表明:脱脂速率随温度升高而升高,随时间的延长而降低;脱脂初期扩散是控制性环节,温度是影响反应速率的主要因素,脱脂后期溶解成为控制性环节,浓度差成为影响反应速率的主要因素;注射坯体固相体积分数越高,脱脂速率越慢,粘结剂最终脱除率越低;用部分植物油取代石蜡的蜡-油基复合型粘结剂注射坯体的脱脂速率快于传统蜡基型的注射坯体,最终脱脂率也高于传统型的蜡基注射坯体.     

Influence of injection temperature and pressure on the properties of alumina parts fabricated by low pressure injection molding (LPIM)

The quality of ceramics parts made by powder injection molding (PIM) method is influenced by a range of factors such as powder and binder characteristics, rheological behavior of feedstock, molding parameters and debinding and sintering conditions. In this study, to optimize the molding parameters, the effect of injection temperature and pressure on the properties of alumina ceramics in the LPIM process were thoroughly studied. Experimental tests were conducted on alumina feedstock with 60 vol% powder. Injection molding was carried out at temperatures and pressures of 70–100 °C and 0.1–0.6 MPa respectively. Results showed that increase in injection temperature and pressure and the resulting increase in flow rate leads to the formation of void which impairs the properties of molded parts. The SEM studies showed that injection at temperature of 100 °C results in evaporation of binder components. From the processing point of view, the temperature of 80 °C and pressure of 0.6 MPa seems to be the most suitable condition for injection molding. In addition, the effects of sintering conditions (temperature and time) on the microstructure and mechanical properties are discussed. The best final properties were found using injection molding under the above stated conditions, thermal debinding and sintering at 1700 °C during 3 h.     

Fabrication of coloured zirconia ceramics by infiltrating water debound injection moulded green body

Abstract

Abstract

The authors developed a new technique combining ceramic injection moulding and liquid precursor infiltration, presenting a new strategy for fabrication of coloured zirconia ceramics. The authors’ strategy includes ceramic injection moulding 3Y‐TZP powder using a water debinding binder system, debinding moulded parts in water and drying, immersing debound parts in solutions containing different colouring ions and then sintering and creating coloured zirconia ceramics. The fabricated coloured ceramic bars exhibit a core shell structure, and the thickness of the coloured shell can be tailored by adjusting immersion time and temperature. Using solutions containing different colouring ions, ceramic bars with various colours can be prepared.     

Powder injection molding of complex-shaped aluminium nitride ceramic with high thermal conductivity

Aluminum nitride (AlN) is a promising material for heat sinks and microelectronic applications because of the advantages of high theoretical thermal conductivity, high mechanical strength, good electrical insulation, low dielectric constant and low thermal expansion coefficient. However, the difficulties in shaping complex-shaped parts with a high thermal conductivity have retarded the wide applications of AlN ceramic. Herein, we design a new binder system containing resin components and adopt the powder injection molding technology to fabricate complex-shaped AlN parts. After the debinding process, the special binder system would produce residual carbon, which could react with Al₂O₃ and result in decreasing oxygen impurity and forming the yttrium-rich aluminates. The yttrium-rich aluminates can accelerate the densification of AlN ceramic and fasten the oxygen on the triangular grain boundary, leaving the clean grain boundary beneficial for high thermal conductivity. The as-prepared AlN parts with complex shape possess a high thermal conductivity of 248 W m⁻¹ K⁻¹.     

Effects of the binder compositions on the homogeneity of ceramic injection molded compacts

In this study, the effects of different binder compositions on the homogeneity of injection molded ceramic compacts are discussed from the standpoint of the rheological properties of the feedstocks, density, density deviation, and flexural strength of the as-prepared compacts, and the microstructures of the as-prepared compacts, compacts after solvent debinding, and compacts after thermal debinding. Also the pore size distribution of the compact after thermal debinding was characterized to examine the distribution of the binders in the as-prepare compacts. The feedstock with 30% macromolecular binders attains the minimum power-law index n value at 160 °C, hence it is the most appropriate feedstock for injection molding. The optimal composition is feedstock B30, which is the most homogeneous at an injection temperature of 160 °C. The macromolecular binder-to-PW weight ratio of 3:7 allows best mixing of feedstock and more homogeneous binder distribution. B30 has the highest density, the lowest density deviation and the lowest deviations in flexural strength of the as-prepared compact. Compacts prepared with B30 have the most homogenous pore size distribution after thermal debinding, as determined from the sharp, narrow peaks on the pore size distribution curves.     

聚甲醛在新型陶瓷注射成型催化脱脂工艺中的应用

利用聚甲醛对酸性气氛敏感易分解的特性，将其作为主要粘结剂应用于陶瓷注射成型技术中，并采用了新型的催化脱脂技术，使得脱脂速度有了很大提高，实验样品主要粘结剂的脱除量在10h内即达到90％以上，记录了该过程中样品失重的情况，分析了脱脂阶段不同特征及其原因，指出催化脱脂过程速度的控制因素是气态催化剂和气体产物扩散过程，实验观察了脱脂过程不同时刻样品外围与中心区域的微观形貌，证明了脱脂过程由外围逐渐向内部扩散，对物料流变性能的考察表明物料为假塑性，有良好的流动充模性。     

陶瓷的注射成型技术

陶瓷注射成型技术可解复杂形状的高性能陶瓷元件的大批量生产难题,并且产品尺寸精度高,表面条件好,论述了瓷注射成型工艺中粘结剂选取,注射成型,脱脂等步骤,并提出了将来的研究方向。     

陶瓷注射成型中水萃取脱脂粘结剂体系的相容性研究

提出了陶瓷注射成型水萃取脱脂粘结剂组分相容性的三大判断方法:溶解度参数法、热力学计算法、扫描电子显微镜法,以评判水基注射料的相容性,为陶瓷注射成型水萃取脱脂粘结剂的相容性提供了理论依据以及评判标准。并以聚乙二醇(PEG)/聚乙烯醇缩丁醛(PVB)以及聚乙二醇(PEG)/聚甲基丙烯酸甲酯(PMMA)两个水基粘结剂体系为例进行说明,讨论了陶瓷注射成型粘结剂的相容性对注射料流动性及水萃取脱脂速率的影响。     

Effects of Organotitanate Additions on the Dispersion of Aluminum Nitride in Nonpolar Solvents

Organotitanate additives are known to reduce the viscosity of many filled polymer systems, including formulations of interest for ceramic powder injection molding. Mineral oil was used as a model solvent for these systems to examine the effects of Organotitanate additions on the stability and rheology of A1N dispersions. Addition of the titanate coupling agents neoalkoxy tri(neodecanoyl) titanate and neoalkoxy tri(dioctylphosphato) titanate resulted in better dispersion as measured by sedimentation tests and rheological characterizations. Excellent correlation of the sediment heights and measured viscosities with adsorption isotherms for the organotitanates was shown, with both lower sediment height and lower viscosity obtained when a monolayer of the titanate molecules was present on the powder surface. Comparison of the behavior of the mineral oil based systems with the viscosity of corresponding polypropylene based binder systems indicates that the titanate additions are effective in reducing particle-particle interaction effects in both systems.     

金属注射成型用水溶性粘结剂的研究

介绍了一种金属注射成型用水溶性粘结剂的制备方法，该粘结剂使用方便且安全无毒，用于金属注射成型时可用水作溶剂脱除，从而使成本大大降低。     

Novel fabrication of injection-moulded ceramic parts with large section via partially water-debinding method

In this work, we adopt a combination of low molecular weight PEG (L-PEG) and high molecular weight PEG (H-PEG) as water-soluble binder to fabricate injection-moulded ceramic parts with large section. The mechanism of the combination of PEGs removal was proposed for the first time. Defect-free near gear parts with large-sized-section (thickness – 16 mm) were successfully fabricated through water extraction (15 h) followed by rapid thermal pyrolysis (4.5 h). It solves the difficulty of fabricating injection-moulded ceramic parts with large section and our approach is energy saving and high-efficiency as compared with conventional thermal debinding. The results demonstrate that our approach of partially water-debinding followed by rapid thermal pyrolysis could solve the problems of conventional thermal debinding, providing an effective route for the production of injection moulded ceramic parts with large section.     

水溶性胶粘剂在粉末冶金和铸造中的应用

阐述了水溶性胶粘剂的优缺点,介绍了水溶性胶粘剂在铸造成形、粉末注射成形工艺中的应用。     

Numerical and experimental investigations on thermal debinding of polymeric binder of powder injection molding compact

A mathematical model is established to describe the thermal debinding process of polymeric binder from a powder injection molding compact. The model takes into account of the thermal degradation of liquid polymer into liquid volatile fragment, the evaporation of liquid volatile fragment, the capillary driven liquid phase transport, the binary diffusion in solution, the convection and diffusion of gas phases, and the heat transfer in a porous medium. The proposed model is solved numerically based on a finite volume method and validated with experimental data. Based on the numerical results, the binder removal, the pressure buildup, the binder distribution, the mass transfers, and the removal mechanisms during thermal debinding are studied.