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.     

水基纳米SiC复合料浆的流变性能和稳定性

引言 纳米复相碳化硅陶瓷是在多相复合碳化硅陶瓷基础上发展起来的-种新型碳化硅陶瓷材料,通过引人第二或第三纳米增强相来同时实现细晶结构、梯度残余应力场、裂纹桥联、自增韧等增强增韧机理,从而获得多强韧化机理协同强化碳化硅陶瓷,已成为碳化硅陶瓷的研究方向之一[1-4].其中,纳米增强相在碳化硅基体(包括料浆、复合粉体、陶瓷)中的分布是制备纳米复相碳化硅陶瓷的关键和前提之一[5].     

Preparation of Na-beta″-alumina film by tape casting process

This study focused on the preparation of Na-beta″-alumina film by a tape casting process. The effects of solvent, dispersant, binder, plasticizer contents, as well as milling time on the rheological properties of the slurry were investigated. The dispersion of the ceramic powder in the slurry was optimized by ball milling an azeotropic mixture of methyethylketone (MEK) and ethanol (EtOH) as the solvent, 2 wt% triethanolamine as the dispersant, 7 wt% PVB as the binder for 4 h. Green Na-beta″-alumina thick films with thickness of 100–300 μm and homogeneous microstructure were obtained and further sintered at 1600 °C to obtain a relatively dense membrane with a thickness of ca. 100 μm. The conductivity of the sintered ceramic was comparable to that obtained by the conventional isostatic pressing and sintering method.     

Dispersion of SiC in Aqueous Media with Al2O3 and Y2O3 as Sintering Additives

It has been well accepted that polyethylene imine (PEI) is an effective dispersant for silicon carbide (SiC) in aqueous media. However, after the addition of sintering additives (Al₂O₃ and Y₂O₃), this dispersing effect is reduced significantly. In this work, a second dispersant, citric acid, was used to resolve this problem. It was found that citric acid could decrease the slurry viscosity (without sintering additives) and enhance the PEI adsorption on SiC particle surface. The optimal amount of citric acid required to achieve a minimum viscosity for 55 vol% SiC suspensions was equal to ∼0.87 wt% (at pH ∼6.8). With the aid of citric acid, well-stabilized SiC suspensions (containing sintering additives) were realized, which exhibited slight shear thinning rheologies. After tape casting and SPS sintering, dense SiC samples were obtained with a homogeneous fine-crystalline microstructure. Results showed that citric acid was an effective dispersant for improving the dispersion of SiC particles containing sintering additives.     

通过凝胶注模成型和无压烧结制备碳化硅陶瓷

以四甲基氢氧化铵为分散剂,糊精为碳源,通过静电稳定作用,制备了高固相含量、分散良好的碳化硅陶瓷浆料。以水溶性N,N–二甲基丙烯酰胺为单体,N,N’–亚甲基双丙烯酰胺为交联剂,采用实验室开发的偶氮[2–(2–咪唑啉–2–基)]丙烷HCl引发体系,在45～50℃引发单体聚合,制备出水基凝胶注模碳化硅素坯,素坯的相对密度达58%,抗弯强度大于40MPa。进一步通过无压烧结制备相对密度高于98%,硬度达28GPa,强度达530 MPa的SiC陶瓷。对素坯和SiC陶瓷的微结构和力学性能进行了测试和表征。结果表明:采用糊精作为碳源可以提高凝胶注模浆料的分散性,避免凝胶过程中的碳阻聚问题,有利于制备出高性能的碳化硅陶瓷材料。     

Rheological behaviour of BaZrO3 suspensions in non-aqueous media

The colloidal behaviour of concentrated non-aqueous suspensions of barium zirconate is investigated. Optimum dispersing conditions are investigated for organic suspensions prepared with different solvent systems: methylethylketone (MEK)/ethanol, trichloroethylene (TCE)/ethanol, a methylisobutylketone (MIBK)/methylethylketone/cyclohexanone (CHN) and pure ethanol. Stabilisation of the suspensions is achieved by using two different dispersants: ester phosphate (EPH) and Hypermer KD-6. Rheological studies have been made in order to determine the optimum of each dispersant concentration as a function of the solvent systems. The best stabilisation of 30 vol.% suspensions is obtained by using EtOH with 3 wt.% KD-6 and TCE/EtOH with 1 wt.% EPH. Zeta potential studies show that the use of dispersants increases the positive surface potential on the particles. The zeta potential values increasing from +10 mV in the absence of EPH to +42 mV with 1.0 wt.% EPH and to +33 mV with KD-6. These results suggest that electrostatic repulsion plays an important role on the stability of these organic suspensions. Stabilised suspensions were slip cast in plaster molds and green densities higher than 55% of the theoretical density was obtained.     

Improvement of the Dispersion of Al2O3 Slurries Using EDTA-4Na

Polyacrylic acid (PAA) is known to be an effective dispersant for Al₂O₃ powder in aqueous media. However, at high solid loading (>55 vol%), the dispersion of the Al₂O₃ suspensions became difficult with only PAA as a dispersant. In this paper, ethylenediaminetetraacetic acid, tetrasodium salt, dihydrate (EDTA-4Na) was introduced to improve the dispersion of the Al₂O₃ suspensions. With the aid of EDTA-4Na, the adsorption amount of sodium polyacrylic acid (PAA-Na) increased, while the apparent viscosity of 60 vol% Al₂O₃ slurries decreased significantly. Particle size measurements showed that EDTA-4Na could help to reduce larger agglomerates, possibly by modifying the adsorbed layer thickness. The interactions between EDTA-4Na and PAA-Na were studied using Fourier-transform infrared spectroscopy analysis. Results showed that it was possible to introduce EDTA-4Na as the second dispersant to improve the dispersion of high solid content Al₂O₃ slurries.     

Effect of dispersant on the rheological properties and slip casting of concentrated sialon precursor suspensions

The ability of Hypermer KD1 to disperse high solids loading reaction sialon suspensions for slip casting has been characterised. It has been found to be a very effective dispersant in organic media of 60-vol.% MEK and 40-vol.% Ethanol, yielding fluid and highly homogeneous suspensions. The effects of added amounts of KD1 have been observed through adsorption data, sedimentation tests and rheology measurements. KD1 imparts low viscosity and stability to the suspension. It has been found that 3-wt.% addition of KD1, based on the weight of reaction sialon powders, results in a very stable and high flowable suspension with near Newtonian flow behavior. Less amounts of dispersant lead to unstable suspensions with obvious shear thinning flow behaviors, while adding excessive dispersant leads to high viscosities, especially at high solids loading. Measuring the pore size distribution of green bodies from different suspensions has proved the effects of dispersant amounts on dispersing the slurries and on slip casting performance.     

Temperature-Induced Gelation of Concentrated Sialon Suspensions

A temperature-induced gelation method has been developed for the preparation of sialon green bodies composed of Si₃N₄, AlN, Y₂O₃, and Al₂O₃. Using a polyester/polyamine condensation polymer as dispersant, stable suspension containing sialon, precursor powders could be prepared in methyl ethyl keton (MEK)/ethanol (E) solvent mixture with solids loading as high as 60 vol%. The solvency of the dispersant in MEK/E decreased dramatically on cooling. The sedimentation tests showed that the settling behavior changed from slow accumulation at ∼20°C to fast deposition of clusters at −15°C, because of the collapse of dispersant chains adsorbed at the surface of the particles. Steady shear viscosity and oscillatory measurements performed for 60 vol% suspensions as functions of temperature and added amounts of dispersant proved that suspensions were of low viscosity and high stability at room temperature, becoming predominantly very highly viscous and elastic as temperature decreased. The gelation mechanism was mainly based on the coiling up of dissolved dispersant molecules, inducing in situ gelation and the formation of a rigid network bridging the suspended particles. The green bodies showed negligible shrinkage during gelation, a small shrinkage during drying, homogeneous microstructures, narrow pore size distributions, and high relative density. It was possible to achieve dense α-sialon ceramics through pressureless sintering at 1750°C for 2 h.     

Effect of Concentration of Ammonium Poly(acrylate) Dispersant and MgO on Coagulation Characteristics of Aqueous Alumina Direct Coagulation Casting Slurries

Coagulation of aqueous alumina slurries prepared using various concentrations (0.43–1.04 wt% based on alumina) of ammonium poly(acrylate) dispersant by MgO has been studied for direct coagulation casting (DCC) of alumina. The slurries prepared at dispersant concentration below 0.84 wt% are not suitable for DCC at room temperature (∼30 ° C) as they undergo premature coagulation. Mixing the slurry with MgO at a low temperature of nearly 5 ° C slows down the reactions leading to coagulation and keeps the slurry viscosity low for a sufficient period of time. Coagulation of slurries prepared at a dispersant concentration of 0.92 wt% and above at room temperature requires MgO concentrations much higher than the equivalent amount required for reaction with the dispersant. This anomalous behavior at higher dispersant concentration is explained such that the Mg-poly(acrylate) formed by the reaction between ammonium poly(acrylate) and MgO formed a sheath over the remaining MgO particles and prevented them from further dissolution at room temperature. Faster coagulation could be achieved by heating the slurries after casting in closed molds. The Mg-poly(acrylate) acts as a binder and stabilizes the coagulated bodies as their strength and stability against oscillatory stresses increase with an increase in dispersant concentration.     

Role of organic additives on non-aqueous tape casting of SiAlON ceramics

Suspensions consisting of precursor α/β SiAlON forming powders, azeotropic solvent mixture of 60 MEK/40E, dispersant, binder, and plasticizer were optimized for tape casting by rheological measurements and tape properties. Sodium tripolyphosphate (STPP) was introduced as a dispersant for low temperature applications of α/β-SiAlONs. Optimum STPP amount was determined as 0.012 g/m² (of the particle surface) for stable α/β-SiAlON suspensions. Different amounts of binder/plasticizer mixtures were added to the slurries and the effects on rheological and green tape properties were investigated. Green tapes with dibutyl phthalate (DBP), and plasticizer mixture, poly(ethylene glycol) (PEG) and DBP, exhibited centered cracks with high plasticity, on the other hand, polyvinyl butral (PVB) and PEG showed no crack but low plasticity. Therefore, many different parameters were found to be effective on final tape properties. In addition, tapes were prepared with 6 vol% PVB + PEG, sintered at 1800 °C for 2 h and exhibited almost 97%TD in room temperature applications of α/β SiAlONs.     

The preparation of SiCP/Ag–Cu–Ti hybrid tapes and application in the joining of silicon carbide ceramics

Abstract

A novel method of tape casting to fabricate ceramic-particulate-reinforced composite filler alloy tapes with low organics (no more than 6?wt.%) was developed, with which SiC_P/Ag–Cu–Ti hybrid tapes were successfully prepared and used in joining of sintered silicon carbide ceramics. The stress rheometer, scanning electron microscopy and energy dispersive spectrometer were used to characterize the rheological properties of slurry and microstructure of green tapes and joints. The slurry for tape casting consists of dispersant, binder, solvent, a mixture of ceramics particulates and metal powders, and no plasticizer was added. Castor oil phosphate was proven the suitable dispersant for the slurry, and the content of dispersant, binder, solid loading was optimized as 3?wt.%, 2.6?wt.% and 26?vol.%, respectively. The fabricated hybrid tapes possess good ductility and uniform thickness. The SiC particulates were homogeneously distributed in the metal powders matrix in both sides of the green tapes, and the distribution was retained in the SiC/SiC joints.     

Effect of Solids Loading on Slip-Casting Performance of Silicon Carbide Slurries

The influence of solids loading and particle shape on the green microstructure of slip-cast bodies was investigated. Three commercial silicon carbide (SiC) powders (two coarse varieties with the same particle-size distribution (PSD) but different particle shapes and a finer powder) were used to prepare bimodal PSDs designed to maximize the packing density. Various surface-active agents (anionic, cationic, and non-ionic) were tested. Anionic dispersants were the most effective in dispersing aqueous SiC slurries. The effectiveness of dispersants was evaluated by sedimentation tests using very dilute slurries, by rheology, and by the packing density of slip-cast bodies prepared from suspensions loaded with 62.5 wt% solids, stabilized with a fixed amount of dispersant (0.25 wt%, relative to the solids). Then, the best dispersant was selected to study the effects of dispersant and solids concentrations on the degree of packing of bimodal suspensions that contained the sharper-edged coarse particles. It could be observed that the green density was dependent on both parameters, initially showing an increase to a maximum, followed by a decreasing trend. A high value of 74.5% of the theoretical density (TD) was obtained from suspensions that contained 70 wt% solids and 0.1 wt% dispersant. The substitution of the angular coarse particles by similarly sized but more spherical particles resulted in an additional increase in green density to >76 wt% TD. The results can be interpreted in terms of freedom of particles upon deposition on the cast layer, which enables particle rearrangement, and segregation phenomena.     

硅藻土光固化成型浆料和多孔陶瓷的制备

本文成功开发了用于光固化成型的树脂基硅藻土浆料,系统探讨了分散剂种类、含量及固含量对硅藻土浆料流变特性的影响,并对其作用机理进行了分析,获得了用于光固化成型的高固含量、低黏度的硅藻土浆料,并采用3D陶瓷光固化设备制备了结构复杂的硅藻土多孔陶瓷。结果表明,BYK2009为硅藻土浆料的最佳分散剂,且当分散剂相对粉体质量为3%时,浆料黏度最低。成功制备出粉体体积分数为40%的硅藻土浆料,在剪切速率为30 s^-1时,硅藻土浆料黏度为17.30 Pa·s。在900 ℃烧结时得到显气孔率为51.30%、抗弯强度为(46.28±2.63) MPa的硅藻土多孔陶瓷。本研究为光固化成型具有复杂多级孔结构的硅藻土载体提供了参考。     

Optimization of non-aqueous tape casting of high solid loading slurry for aluminum nitride ceramic substrates

Aluminum nitride (AlN) ceramic substrates have been fabricated using non-aqueous tape casting and pressureless densification under flowing N₂ atmosphere. Considering the economic and environmental impact, a new strategy of solvent and dispersant system was adopted to prepare AlN slurries with high solid loading. According to the viscosity characteristics of AlN slurries, dispersant content was adjusted to be 0.5 wt% of AlN powder in order to optimize the rheological behavior of AlN slurries. The addition contents of binder and plasticizer were both optimized as 5 wt% of AlN powders by combining the viscosity of slurries and tensile strength of green tapes. Green AlN tapes were fabricated with an optimized tape casting process such as dry temperature. The exclusion process of organic additives was investigated by employing thermogravimetric analysis. Flat and dense AlN ceramic substrates with a relative bulk density over 99.75 % were achieved after being sintered under 1800°C for 6 hours, which had a maximum size of 110 × 110 mm. The thermal conductivity of the AlN substrate could reach 145 Wm⁻¹K⁻¹.     

Tape casting of zirconia for ion conducting membranes: A study of dispersants

Powders of fully yttria stabilized zirconium oxide have been studied in order to identify efficient dispersants for zirconia in tape casting slurries, and to verify that they do not impair the oxygen ion conductivity of the final membrane. Of eleven screened dispersants, only three were shown to be efficient. Sintered plates prepared with these dispersants had high and about equal oxygen ion conductivity (0.16–0.19 S cm⁻¹ at 1000°C). The use of a phosphate ester as dispersant, possibly leaving traces of phosphorus in the sintered plate, did not impair the oxygen ion conductivity. Fish oils, common dispersants for tape casting slurries, were not efficient for zirconia in the solvent system that was studied. The addition of binder and plasticizers to the dispersions to form tape casting slurries did not cause reagglomeration.     

聚乙烯吡咯烷酮及钛酸酯对ITO浆料的分散稳定性考察

考察了在乙酸丁酯相中制备稳定均匀分散的纳米ITO浆料。选用两种分散剂聚乙烯吡咯烷酮(PVP)和钛酸酯(titanate),通过球磨分散法制备稳定ITO(indium tin oxide)浆料,并分析比较不同pH、分散剂用量、磨介氧化锆球粒径及用量和球磨时间对ITO浆料分散稳定性的影响,研究分散机理。结果表明,在pH=7.8,分散剂用量为ITO粉体质量的5.5%,磨介氧化锆用量为ITO粉体质量的2.6倍,磨介氧化锆粒径小于0.5 mm,球磨分散时间24 h时,制得的纳米ITO浆料分散稳定性最佳;且比较由两种分散剂制得的ITO浆料在储存时间为0 d与30 d的浆料粒径变化,后者稳定性优于前者。     

溶剂热法合成硫化镉材料实验研究

以硫脲、九水硝酸镉为原料,乙二醇为溶剂,聚乙烯吡咯烷酮（PVP）为分散剂,聚丙烯酰胺（PAM）或N,N-二甲基甲酰胺（DMF）为生长调节剂,采用溶剂热法成功制备了硫化镉纳米材料。探究了分散剂与生长调节剂对溶剂热法合成硫化镉纳米材料的影响。研究表明,仅以PVP为分散剂制得的硫化镉颗粒呈现规则的球形且粒度均匀,小球粒径约为500 nm;以PVP为分散剂,DMF为生长调节剂,两者协同作用抑制了硫化镉的生长,得到的硫化镉颗粒粒度均匀,小球粒径约为250 nm;以PVP为分散剂,PAM为生长调节剂,两者协同作用得到的硫化镉颗粒呈现规则的球形且粒度均匀,小球粒径约为125 nm。X射线衍射（XRD）表征结果表明,合成的硫化镉是纯相硫化镉,生长调节剂具有粒径“倍增效应”。     

Preparation of PZT suspensions for direct ink jet printing

The present paper contains an experimental study of two different kinds of PZT suspensions for direct ink jet printing at 25 and 120 °C, respectively. The effect of processing parameters such as mixing time, the amount of dispersant, solid loading and milling method was investigated for the optimisation of viscosity for feasible jetting. The viscosity of PZT suspensions was within 5–15 mPa·s range for room temperature suspensions with MEK/EtOH medium and 10–20 mPa·s for high temperature suspensions with wax medium. FTIR analysis is also presented to explain the rheological behaviour of PZT suspensions. Finally, a demonstration of room temperature jetting of PZT suspension is shown.     

Sulfanilic Acid: A Novel Consolidation Agent for Al2O3 in Aqueous Media

A new solidifying agent, 4-aminobenzene sulfonic acid (sulfanilic acid), is reported in this paper. The consolidation process and mechanism were followed using on viscoelastic, FTIR, SEM, and Hg porosimetry measurements. It was shown that the Al₂O₃ slurries with PAA-Na as dispersant exhibited a high degree of particle stabilization. After the addition of sulfanilic acid, we observed an exponential increase in the storage modulus ( G ') as a function of consolidation time. Correspondingly, Al₂O₃ slurries exhibited a transition from a viscous to an elastic state (in 62 min). FTIR analysis indicated that the consolidation process might follow two steps: first, the adsorption of sulfanilic acid on the Al₂O₃ particle surface; second, the acid–base interaction between the adsorbed PAA-Na molecules and the sulfanilic acid molecules. This interaction could possibly induce the formation of three-dimensional networks through a bridging or charge neutralization mechanism. The as-consolidated Al₂O₃ green samples were homogeneous, with the relative green density being 54.69%. Results showed that it was feasible to introduce sulfanilic acid for the consolidation of Al₂O₃ slurries in aqueous media.