Competitive Adsorption Phenomena in Nonaqueous Tape Casting Suspensions

Competitive adsorption phenomena in alumina (α-Al₂O₃)–polyvinyl butyral (PVB)–Menhaden fish oil (MFO) suspensions are studied using diffuse reflectance Fourier transform infrared spectroscopy and thermogravimetric analysis. PVB and MFO commonly serve as binder and dispersant species, respectively, in nonaqueous tape casting systems. Adsorption isotherm measurements reveal that both PVB and MFO have an affinity for α-Al₂O₃ surfaces, with corresponding plateau coverages of 3.4 and 2.3 mg/m², respectively. Sequential competitive adsorption of these species occurred during two-stage milling. MFO was fully adsorbed onto α-Al₂O₃ powder in the absence of PVB during first-stage milling. PVB was then introduced to the system during second-stage milling and found to displace preadsorbed MFO species from such surfaces. At the culmination of milling, PVB composed 25–35 wt% of the adsorbed organic layer. Complete displacement of MFO was not observed, which limited PVB adsorption on α-Al₂O₃.     

Formation of Barrier Ribs for Plasma Display Panel via Roll Forming of Green Tapes

In an attempt to explore the possibility of forming barrier ribs for a plasma display panel by plastically deforming a green tape with a grooved roll, the effects of green tape composition and rolling parameters on the height of the barrier ribs formed were studied. For the analysis of the results, viscosity of the green tape was evaluated using a modified slit rheometer. The results indicated that the effects of organic constituents in the green tape and processing parameters on the dimension of the barrier ribs formed are closely related with the pseudoplastic characteristics of the green tape.     

低温共烧CBS基片的流延成型及其性能的研究

选用4种分散剂(三乙醇胺,磷酸三丁酯,蓖麻油和三油酸甘油酯),通过对分散剂的用量、固含量对浆料流变性能、流延生坯及烧结体性能的研究。分析了分散剂及固含量对流延浆料及陶瓷性能的影响。实验结果表明:以磷酸三丁酯为分散剂,当浆料的固含量为55%时,制备的料浆不仅分散性好而且稳定。流延所得烧结体介电常数为6.47、介质损耗为1.1×10-3。烧结后的样品中主要包含CaSiO3、CaB2O4和SiO2晶相。达到了LTCC材料的要求。     

氮化硅流延膜的制备

流延成型是一种制备高质量陶瓷基片的成型方法.氮化硅是一种高热导率的材料,有望在电子基片领域获得应用.本文利用流延成型制备了具有较好柔韧性和一定强度的氮化硅流延素坯膜.研究了无水乙醇、无水乙醇/丁酮作为溶剂时对浆料粘度的影响.通过优化流延浆料添加剂的各种配比,得出了适合氮化硅粉体(SN-E10)流延的最佳配方.     

水基流延工艺制备陶瓷材料的研究

流延法作为制备片层材料的重要工艺已经被陶瓷研究者广泛应用.但是,有机流延体系带来的环境污染、毒性及易燃性等问题已被社会所关注.因此,研究无毒、无污染的水基流延工艺已得到材料界的广泛重视.本文主要概述了国内外水基流延工艺的研究现状,重点介绍了PVA体系、丙烯酰胺凝胶流延体系、纤维素类粘结剂体系及乳胶体系的不同特点;从粘结剂、分散剂、增塑剂等多个角度分析了影响水基流延工艺的技术因素,并提出了很好的解决方法,最后介绍了乳胶体系水基流延工艺在制备片状或层状陶瓷材料方面的应用.     

Local Flow Behavior of Ceramic Slurries in Tape Casting, as Investigated by Laser–Doppler Velocimetry

The local flow behavior in a tape-casting unit for processing ceramic slurries was investigated by laser–Doppler velocimetry (LDV). The most remarkable feature of the LDV system used was its high spatial resolution (24 μm) and temporal resolution (5 μs). A translucent Newtonian model fluid which, in the relevant processing window, at higher shear rates, exhibits a rheological behavior similar to that of a typical ceramic slurry, was chosen to determine the velocity distribution in the flow channel (i.e., in the tape-casting unit). The flow behavior was measured directly in several particular regions of the flow channel, which substantially consisted of a double doctor-blade assembly. The velocity distribution obtained below the forming doctor blade showed the strong influence of the casting speed on the flow behavior of the model fluid. Furthermore, the measured flow behavior was analyzed, based on the assumptions of fluid dynamics. Below the doctor blade, the flow behavior was considered to be a combination of pressure flow and drag (Couette) flow. The flow rates from the applied hydrostatic pressure and external drag forces were shown to be additive. A comparison between the measured velocity profiles and the model calculations showed excellent agreement. A flow reversal (secondary flow), never before measured quantitatively, was detected between the two inserted rectangular blades. Apparently, secondary flows influenced the surface properties of the cast green tapes.     

Mullite–Aluminum Phosphate Laminated Composite Fabricated by Tape Casting

Mullite–aluminum phosphate (3Al₂O₃·2SiO₂/AlPO₄) laminated composites were fabricated by tape casting. AlPO₄ had a density of 1.56 g/cm³, which corresponds to 61% of theoretical density, and a bending strength of 1.5 MPa after sintering at 1600°C for 10 h. The aluminum phosphate functioned as a porous, weak, and chemically stable interphase which was able to deflect cracks in a laminated composite. To increase the strength of the weak interphase material, 10 and 30 vol% of mullite were added.     

Modified Tape Casting Method for Ceramic Joining: Application to Joining of Silicon Carbide

A simple modified tape casting procedure has been developed for application to ceramic joining when the joining materials are in powder form. The method involves preparation of a slurry from the powder, solvent, and thermoplastic binder, and then casting directly onto the joining surface using a moving doctor blade. Handling of the tape prior to joining is not necessary: therefore, binder content is minimized, plasticizers are not required, and viscosity is controlled by solvent content. The utility of this technique for producing joints with thin, uniform interlayers is demonstrated for silicon carbide materials joined with TiC + Ni and SiC + Si.     

Source of Water and Its Effect on Tape Casting Barium Titanate

The source of water and its effect on rheological and green tape properties of tape cast barium titanate were studied. The total water content, as well as the source, affect the slip rheology, green density, tensile strength, and strain to failure in the unsintered body. Sources of the water were broken down into contributions from the barium titanate powder surface versus from the solvent or ceramic additives. Water adsorbed on the powder surface was generally beneficial compared to water entering through the solvent. For carefully dried systems, below 0.15 wt% total water, properties change dramatically with small changes in water content. Thus, less stringent processing requirements can be used to achieve reproducibility at water contents above 0.15 wt%.     

Tape Casting and Properties of Mullite and Zirconia–Mullite Ceramics

Mullite and ZrO₂-mullite ceramics have been prepared by tape casting mixtures of Al₂O₃, quartz, and ZrO₂ powders and subsequent reaction sintering. Tape casting leads to homogeneous, high-density green materials with good sinterability. The design of a thermal cycle which favors densification with respect to mullitization allows the preparation of nearly dense, nearly fully reacted materials at sintering temperatures below 1600°C. ZrO₂ additions limit grain growth, but the ZrO₂ content must not be too high when a high tetragonal:monoclinic ratio is required.     

水基流延片式ZnO压敏电阻器低温共烧工艺及其性能

用环境扫描电子显微镜（ESEM）、X射线衍射（XRD）和X射线能谱（EDXS）等研究了水基流延片式ZnO压敏电阻器的低温共烧工艺及其对微观结构和电学性能的影响规律。ESEM分析结果表明：当等静压压力为60 MPa时,Ag电极与流延膜生坯界面结合紧密,Ag电极分布连续,900℃共烧时,未出现开裂、分层,两者收缩率接近。EDXS和XRD分析结果表明：900℃共烧时,Ag在片式压敏电阻器中以单质形式存在,流延膜与Ag电极化学兼容性良好,且在共烧界面处未发现有明显的Ag离子扩散。该流延膜可以与Ag电极在900℃时实现低温共烧,用此制备的片式ZnO压敏电阻器具有良好的压敏性能：压敏电压V1mA=6.1 V,非线性系数α=28.1,漏电流IL=0.15μA。     

Alumina and Alumina/Zirconia Multilayer Composites Obtained by Slip Casting

The slip casting technique has been revealed as a powerful method to obtain multilayer composites close to theoretical density. From zeta potential and viscosity measurements of Al₂O₃ and Al₂O₃/ZrO₂ (4 vol% ZrO₂) suspensions, the corditions for the preparation of multilayer composites by slip casting have been determined. A microstructural analysis of the different layers by scanning electron microscopy is also reported.     

Effects of Excess Barium Ions on Aqueous Barium Titanate Tape Properties

The effects of excess free barium ions in aqueous barium titanate slip on the resulting BaTiO₃ tape properties were investigated in terms of the slip behavior, green/sintered tape density and morphology, and dielectric properties. The excess free barium ions expressed by means of the Ba/Ti ratio adversely affected most tape properties. Increase in the slip viscosity, green porosity, and agglomeration along with a decrease in mechanical properties and green/sintered density were found with the increase in the Ba/Ti ratio. However, dielectric permittivity was increased with increase in the Ba/Ti ratio. An effort was made to correlate these phenomena with Ba²⁺ leaching in water for realistic multilayer ceramic capacitor applications.     

Particle Orientation During Tape Casting in the Fabrication of Grain-Oriented Bismuth Titanate

Slurries containing platelike Bi₄Ti₃O₁₂ particles have been tape cast to prepare green sheets with aligned particles. The slurries contain well-dispersed particles and show nearly Newtonian flow behavior. The effect of slurry composition and casting conditions on the particle orientation has been examined. The particle orientation in the green sheet is determined mainly by powder content; other parameters, such as binder content, casting speed, and blade opening, have little effect. The interaction between particles is a main cause for particle alingnment. The slurry with a large powder content is favorable for preparing dense grain-oriented ceramics.     

Mechanical Properties of Coagulated Wet Particle Networks with Alkali-Swellable Thickeners

Alkali-swellable thickeners (ASTs) such as Acusol 820 and Acusol 830, as well as poly(acrylic acid) homopolymers of various molar mass, have been used as additives in aqueous electrostatically stabilized alumina suspensions. These suspensions have been destabilized by internal enzyme-catalyzed reactions (a direct coagulation casting process) to form viscoelastic solids. The ASTs increase the strength and modulus of the wet green bodies on coagulation. The effect of their molecular architecture on the mechanical properties of wet particulate networks has been studied. At low pH (pH 4.5), ASTs are small insoluble polymer particles that have only minor influence on the low viscosity of the high-solids-loading suspensions. After shifting the pH toward the isoelectric point of α-Al₂O₃, the suspension coagulates and the AST polymer particles swell, thereby increasing the compressive strength and modulus of the alumina-particulate wet green bodies. The presence of small amounts of ASTs (0.4 wt%, based on the solids loading) results in a 10-fold increase in the strength of the wet green bodies. The compressive strength of the wet green bodies that contain ASTs correlates with the size of the expanded AST molecules at pH 9. A possible explanation is that swelling of the AST particles locally decreases the interparticle distance, which leads to increased van der Waals forces between the ceramic particles.     

氧化锆PVA-水基流延成型工艺研究

以去离子水为溶剂,加入适量的分散剂三乙醇胺、粘结剂PVA、增塑剂聚乙二醇-400和邻苯二甲酸丁苄酯、消泡剂DF001,采用水基流延工艺成功制备了表面光滑、具有较好强度和韧性的氧化锆(TZ-5Y)薄膜.研究结果表明:聚乙二醇400和邻苯二甲酸丁苄酯配合使用可以获得较好的增塑效果;通过在15 kPa真空度下除泡20 min,同时以5 r/min搅拌,再静置2h的方法可以获得有效的除泡效果.     

Effect of Dispersants on the Rheological Properties and Slip Casting of Concentrated Alumina Slurry

Slip casting is one of the most common forming techniques used in the fabrication of ceramics. To obtain successful casting results, one need first to fully deagglomerate the ceramic powders and get concentrated slurries with good rheological properties. In this work, the rheological properties of concentrated alumina slurries were studied as functions of solid contents and quantities of two different dispersants, i.e., sodium pyrophosphate and diammonium hydrogen citrate. It was found that these properties could be satisfactorily related to the maximum packing fractions which were determined from sedimentation experiments. Our results also indicated that an optimum deflocculation process can always lead to optimal casting and sintering results.     

Effect of Polymer Crystallinity on Morphology in Ceramic Injection Molding

Many ceramic injection molding vehicles include semicrystalline polymers which characteristically adopt a spherulitic growth morphology. Usually the spherulites are rendered invisible by the opacity of the ceramic powder but in this study they are clearly visible. Polyoxymethylene (POM), has been used as the vehicle. The growth of the spherulites is shown to be dependent on cooling rate and hence on position in the molding. Furthermore, migration of low molecular weight additives by syneresis is shown to occur and to influence the crack path in the as-molded state. An unusual composite fractograph is shown in which fracture faces made after molding, after binder removal, and after sintering are contiguous. Only after molding does the crack path follow the spherulite boundaries; behavior that is also widely reported for unfilled POM.     

Tape Casting, Pressureless Sintering, and Grain Growth in Ti3SiC2 Compacts

In this work we demonstrate that fine Ti₃SiC₂ powders can be tape-cast and/or cold-pressed and pressureless-sintered in Ar- or Si-rich atmospheres to produce fully dense, oriented microstructures in which the basal planes are parallel to the surfaces. Carbon- and/or Si-rich environments suppress grain growth. In the case of the tape casting, the C-residue from binder burnout results in small core grains relative to the surface grains that can grow significantly. When sintering in high Si activities, titanium silicide phases form at the grain boundaries that slow grain growth. Annealing the latter in Ar at 1600°C, for extended periods (30 h), rids the samples of these grain-boundary phases, which in turn results in grain growth. The advantage of the latter process is that the final grain size distribution is more uniform from surface to bulk.     

流延法制备对称型ZrO2/不锈钢功能梯度材料

采用流延法制备了成分梯度为10%(体积含量,下同)的对称型ZrO2/不锈钢功能梯度材料,利用成分分布函数和经典层合板理论对成分和残余热应力的分布进行了设计分析,观察了其微观形貌,并对截面的显微硬度进行了表征.结果表明:采用流延法制备的对称型ZrO2/不锈钢功能梯度材料成分过渡良好,梯度层界面结合紧密,与对称型层状ZrO2/不锈钢复合材料相比,最大残余热应力减小,热应力缓和效果明显.