影响氧化铝水基料浆流变学特性的关键因素

用流变学的方法在RV-20型流变仪上研究不同条件,如:固含量、分散剂加入量、烧结助剂、增塑剂等对碱性氧化铝悬浮体的流变性的影响.结果表明:氧化铝陶瓷碱性料浆(pH＞7)在低的剪切速率(＜100 s-1)时,表现为剪切变稀.在水基料浆中添加MgO时,会发生强烈的水合反应,导致料浆失去流动性.增塑剂甘油的加入导致料浆粘度升高的幅度是有限的,不会对料浆固含量和浇铸工艺造成显著不利的影响.加入水溶性丙烯酸乳液后,在低的剪切速率下,料浆仍然呈现剪切变稀行为,随着乳液含量的增加,料浆的静态粘度逐渐增大.分散剂聚丙烯酸氨的加入量对料浆的稳定性具有显著的影响.在分散剂的加入量为固相质量的0.8%左右时,分散剂在陶瓷颗粒表面形成饱和吸附,此时料浆的稳定性达到了最佳状态.     

YAG ceramic processed by slip casting via aqueous slurries

Stable YAG (Y₃Al₅O₁₂) aqueous slurry with ammonium polyacrylate (NH₄PAA) polyelectrolytes as dispersant was prepared by ball mill method. The effects of polyelectrolyte concentration and pH value on the stability of the suspension is described here, and the stability maps are constructed at different pH value and polymer concentration. The rheological behavior of YAG slips of different solid loading (60–70%) has been studied by measuring their viscosity and shear stress as a function of shear rate and pH of the slurry. An optimal amount of dispersant and pH value for the suspension was found. YAG suspension displays a maximum in zeta potential values and a minimum viscosity in pH range of 9–11. Slips behaved as near Newtonian at the pH value up to a solid loading of 60 wt% and as non-Newtonian with thixotropic behaviors above this solid loading value. The density and the green as well as sintered microstructure of the cast products bear a direct relationship to the state of this slips induced by the alternation in the pH and the concentration of the dispersant as well as solid loading.     

ZTA复相陶瓷凝胶注模成形工艺的研究

本文研究了ＺｒＯ２（３Ｙ）－Ａｌ２Ｏ３复相陶瓷的凝胶注模成形工艺,着重研究了低粘度高固相体积分数浓悬浮体的制备。     

高固含量氧化铝浆料流变性的关键因素研究

制备高固含量、低粘度的浆料是原位固化成型的关键。本工作研究了搅拌磨转速与时间等工艺参数对氧化铝浆料粘度的影响。结果表明,在75 rpm 和 150 rpm 低转速下,浆料的粘度随球磨时间的延长而逐渐减小;而在300 rpm高转速下,浆料粘度出现先减小后增加的现象。通过研究分散剂类型、分散剂加入量、浆料固含量、粉体种类等因素对粘度的影响规律,发现粉体中镁离子是导致浆料高速搅拌球磨后粘度增大的主要原因。该结果对制备高固含量低粘度的陶瓷浆料,尤其是对浆料制备涉及粉体含杂质和添加烧结助剂具有指导意义。     

Temperature induced gelation of non–aqueous alumina suspension using oleic acid as dispersant

A novel temperature induced gelation method for alumina suspension using oleic acid as dispersant is reported. Non–aqueous suspension with high solid loading and low viscosity is prepared using normal octane as solvent. Influence of oleic acid on the dispersion of suspension was investigated. There was a well disperse alumina suspension with 1.3 wt% oleic acid. Influence of gelation temperature on the coagulation process and properties of green body was investigated. The sufficiently high viscosity to coagulate the suspension was achieved at −20 °C. The gelation temperature was controlled between the melting point of dispersant and solvent. The gelation mechanism is proposed that alumina suspension is destabilized by dispersant separating out from the solvent and removing from the alumina particles surface. The alumina green body with wet compressive strength of 1.07 MPa can be demolded without deformation by treating 53 vol% alumina suspension at −20 °C for 12 h. After being sintered at 1550 °C for 3 h, dense alumina ceramics with relative density of 98.62% and flexural strength of 371±25 MPa have been obtained by this method.     

A new approach to prepare highly loaded aqueous alumina suspensions with temperature sensitive rheological properties

Poly(acrylic acid) (PAA)-free alumina suspensions with temperature sensitive rheological properties have been successfully produced using the combination of tri-ammonium citrate and magnesium citrate powders with slurry loading up to 60 vol.%. A new approach using the DLVO concept is proposed to design the suspension composition. Both the shear viscosity and the shear modulus of the suspensions start to increase when the suspension temperature is above a critical value. The flocculation of the suspensions is controlled by the dissolution of the magnesium citrate that increases the ionic strength in the suspensions. The dissolution is controlled by the pH of the suspensions, which decreases with increasing temperature. Compared with the same solid loading suspensions containing PAA, the suspension shear viscosity of 25 °C can be reduced, which is useful in developing new near net shape forming technologies.     

HfB_2-Si_3N_4复合材料浆料流变性的研究

采用注凝成型技术研究了HfB2-Si3N4复合材料浆料的流变性能.主要讨论了pH值、分散剂、固相含量、球磨时间等对HfB2-Si3N4复合材料浆料粘度的影响.结果表明:当分散剂用量为8%(体积分数),pH值为10.9,球磨时间控制在15～20 h时,可制得固相体积含量为38%,粘度为600 mPa·s的HfB2-Si3N4复合浆料.     

Additive Manufacturing of Dense Ceramic Parts via Direct Ink Writing of Aqueous Alumina Suspensions

Additive manufacturing of near‐net‐shaped dense ceramic components has been established via room‐temperature direct writing of highly loaded aqueous alumina suspensions in a layer‐by‐layer fashion. The effect of alumina solid loading on rheology, specimen uniformity, density, microstructure, and mechanical properties was studied. All suspensions contained a polymer binder (~5 vol.%), dispersant, and 51–58 vol.% alumina powder. Rheological measurements indicated all suspensions to be yield‐pseuodoplastic, and both yield stress and viscosity were found to increase with increasing alumina solid loading. Shear rates ranging from 19.5 to 24.2/s, corresponding to viscosities of 9.8 to 17.2 Pa·s, for the 53–56 vol.% alumina suspensions were found to produce the best results for the 1.25‐mm tip employed during writing. All parts were sintered to >98% of true density, with grain sizes ranging from 3.2 to 3.7 μm. The average flexure strength, which ranged from 134 to 157 MPa, was not influenced by the alumina solid loading.     

Novel Coagulation Method for Direct Coagulation Casting of Aqueous Alumina Slurries Prepared Using a Poly(Acrylate) Dispersant

Coagulation of concentrated aqueous alumina slurries prepared using an ammonium poly(acrylate) dispersant by MgO has been studied for direct coagulation casting (DCC). A small amount of MgO (0.2 wt% of alumina) increased the viscosity of the concentrated alumina slurry with time and finally transformed it into a stiff gel. The mechanism of coagulation is proposed such that the time-delayed in situ generation of Mg²⁺ ions from the sparingly soluble MgO forms Mg–poly(acrylate) with the unadsorbed ammonium poly(acrylate) molecules in solution that shift the poly(acrylate) adsorption equilibrium toward the left by depleting the poly(acrylate) molecules adsorbed on the alumina particle surface. This leads to insufficient dispersant coverage on the particle surface and coagulation of the slurry. DCC using MgO is possible only if the slurry is prepared at a dispersant concentration higher than that required for optimum dispersion as the slurries prepared at the optimum dispersant concentration underwent premature coagulation. The gelation time could be tailored within 20 min to a few hours by maintaining the temperature in the range of 70°–30°C. The wet coagulated bodies prepared from 50 vol% alumina slurry showed a compressive strength of nearly 0.05 MPa.     

Rheological properties of nanosized barium titanate prepared by HGRP for aqueous tape casting

The conditions for the preparation of stable nanosized barium titanate suspensions with high solids content for the production of aqueous tape casting are identified. The rheological behavior of colloidal barium titanate suspension with Ammonium polyacrylate (NH₄-PAA) as a dispersant to aid the powder dispersion has been investigated. Nanosized barium titanate powder was synthesized by a continuous high-gravity reactive preparation (HGRP) technique, and then annealed at 900 °C for 2 h. Measuring the zeta potential, the particle size distributions and ball-milling time, assessed the optimum conditions of the suspension with low viscosity and stability. An isoelectric point (IEP) at pH = 2.8 was found. Particle size distribution tests identified an optimum pH value about 10 and an optimum dispersant addition about 1.2 wt.% (based on the dry powder weight). As the ball-milling time was longer than 8 h, the amount NH₄-PAA adsorbed on the barium titanate reached to saturation. The maximum solid content attained during this work was 45 vol.% at pH of 10, with dispersant addition 1.2 wt.%. High green density value (up to ∼55.4% of the theoretical density) in BaTiO₃ sheet was achieved with a solid content 40 vol.%. After sintering at 1200 °C for 2 h a final density of 95% is reached.     

8%Y2O3-ZrO2水基料浆的流变性质研究

详细研究了固含量、球磨时间、分散剂用量和pH值对8％摩尔分数Y2O3稳定ZrO2水基料浆流变性质的影响。结果表明：料浆均表现出剪切变稀行为，且为假塑性流体。确定了最佳实验参数，当pH=10，分散剂用量为2％体积分数，球磨24h的ZrO2水基料浆，稳定性好，适合于成型薄片ZrO2固体电解质材料，并最终制备出体积分数为56％，适合浇注的ZrO2陶瓷料浆。     

流延法制备8YSZ薄膜

采用非水基流延法制备了8mol%氧化钇稳定氧化锆薄膜,研究了球磨时间、固含量、有机添加剂含量及除泡工艺对8YSZ浆料流变性能的影响,通过SEM表征烧结体表面形貌,用电化学阻抗仪对烧结体进行电导率测试。结果表明:分散剂用量1.25wt%,球磨时间15h,浆料的粘度最小,分散效果最好;增塑剂与粘结剂比例为0.7,粘结剂加入量6.5～8.5wt%,二次球磨后,真空除泡可获得适合流延的浆料;生坯1450℃烧结4h,烧结体晶界清晰、致密度较好;烧结体在300～800℃随温度的升高电导率逐渐增大,在800℃时离子电导率达0.046S/cm。     

Tape casting of nanocrystalline ceria gadolinia powder

A ceramic ceria gadolinia solid solution membrane for solid oxide fuel cells was fabricated by tape casting using a nanopowder of 37 nm average particle size. A novel combination of solvent and dispersant was used to disperse the nanoparticles. The polymer was added in a dilute stage to guarantee a homogeneous distribution. After casting a remarkable densification of the cast tape suspension from a solid loading of 20 up to 42 vol.% was observed during drying. The green tape was sintered to >92% theoretical density and was dense towards perfusion. The resulting grain size in the sintered specimen still was <200 nm.     

Injection of Aqueous Slurry for Making Zirconia Fiber

Zirconia aqueous slurry was prepared with fine zirconia powder.Injection process for making zirconia fiber was demonstrated,including preparation of aqueous slurry,injection of slurry,fiber setting in acetone,and fiber firing.The principle of the process was discussed.The effects of solid loading in the zirconia slurry,addition of dispersant in the slurry,and ball milling time on the rheological properties of the slurry,especially yield stress,were illustrated.The role of acetone as curing agent was discussed.Zirconia poly-crystalline fber with at 1 530 ℃ for 5 h.Microstructure of the sintered zirconia fiber was investigated.     

Aqueous tape casting of B4C ceramics

B₄C green tapes are prepared by aqueous tape casting and a spark plasma sintering (SPS) process using polyethylenimine (PEI) as dispersant, hydroxypropyl methyl cellulose (HPMC) as binder and polyethylene glycol (PEG) as plasticiser. The influences of solid content, dispersant content, mass ratio of plasticiser to binder (R value) and milling time on the slurry viscosity are studied. The samples are characterised by means of hardness tester, universal testing machine and scanning electron microscopy. The results indicate that the solid content of B₄C slurry achieves 47.5?wt-% with milling time of 12?h when the content of PEI, HPMC and PEG is 1.5, 5 and 5?wt-%, respectively. The relative density of B₄C ceramics subject to SPS at 1600°C and 50?MPa for 8?min is up to 97.2%. The Vickers hardness, flexural strength and fracture toughness of B₄C ceramics reach 36.5?±?0.7?GPa, 510.3?±?19.4?MPa and 5.04?±?0.29?MPa?m^?1/2, respectively.     

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.     

蛭石基流延浆料的流变性能研究

以改性膨胀蛭石和滑石填料为原料,蓖麻油为分散剂,聚乙烯醇缩丁醛(PVB)为粘结剂,邻苯二甲酸二丁酯(DBP)为增塑剂,采用球磨法制备蛭石基流延浆料。考察浆料固含量和各组分添加量对浆料流变性能的影响,得出了合适的浆料配方为:固含量质量分数为50%、蓖麻油用量为粉体质量的2%、PVB用量为粉体质量的6%、DBP用量为R=0.8时,流延浆料具有典型剪切变稀行为的塑性流体特性,该配方制备的蛭石基流延坯料表面均匀,无裂纹。     

Gel-tape casting as a novel method for the production of flexible fine-grained alumina sheets

The paper reports on the development of a new aqueous gel-tape casting method for processing nanosized powders into thin fine-grained sheets with a high relative density after sintering. The method was based on casting a low-viscosity slurry into a tape, using the doctor-blade method and gelling the slurry after the casting. The gelled tape was removed from the tape carrier without any solvent evaporation and the drying of the gelled tape was performed later in a climate box under controlled temperature and humidity. The epoxy-based ceramic slurry could be prepared with a solid loading of 42 vol.%. Ceramic sheets with flat and smooth surfaces were prepared in a thickness range from 0.08 to 0.4 mm after sintering. The sintered sheets reached a relative density of 99.4%, with an average grain size of about 1.1 μm. The strength and flexibility of alumina sheets were investigated and discussed.     

Si3N4—MgAl2O4—ZrO2系陶瓷凝胶注模成型的研究

本文对Si_3N_4-MgAl_2O_4-ZrO_2系陶瓷料浆注凝成型工艺进行了较系统的研究,着重分析了复合分散剂、PH值及固相含量对粘度的影响,最终获得了固相含量为47vol％,粘度为455mPa·s,注模性能良好的注凝料浆,使用该料浆已制备了多种复杂形状的氮化硅基陶瓷制品。     

Aqueous gelcasting of yttrium iron garnet

N,N-Dimethylacrylamide (DMAA)/N,N′-methylenebis (acrylamide) (MBAM) system was used in the aqueous YIG (yttrium iron garnet) slurry. YIG powders were prepared by using Y₂O₃ and Fe₂O₃ as raw materials through the traditional oxide method. In order to reduce the viscosity and improve the stability of slurries, SD-03 (ammonium polyacrylate) was selected as the dispersant. Zeta potential, pH, dispersant dosage, solid loading and milling time have been optimized. The best conditions were pH 9.86, dispersant dosage 0.2 wt.% and milling time 9 h, which helped to prepare the concentrated slurry with low viscosity and good liquidity. The maximum bending strength of the green body could be up to 13 MPa. The shrinkage and deformation of shaped sintered bodies prepared through gelcasting were small after sintering. The sintering shrinkage, apparent porosity and bulk density were 17%, 0.17% and 5.07 g/cm³, respectively. The dielectric constant and dielectric loss were 14.0 and 2.06 × 10^?4, respectively.