稳定的SrTiO3陶瓷浆料的制备

本采用胶体“电空间稳定机制”，以PMAA-NH4为分散剂，以沉降高度作为衡量浆料稳定性的参数，研究了SrTiO3粉末的悬浮流变特性及分散剂PMAA-NH4加入量对SrTiO3浆料稳定性的影响。在最佳pH值和分散剂加入量条件下，制备了高固相含量（50vol%)，稳定性和分散性好的SrTiO2浆料。     

分散剂用量对碳化硅浆料流变性能的影响

使用四甲基氢氧化铵(TMAH)作为分散剂,研究了分散剂用量对SiC浆料流变性能的影响,并分析了其原因。结果表明：TMAH能够显著提高SiC粉体的zeta电位,降低浆料粘度,从而显著优化浆料的流变性能。在pH为10左右,加入质量分数为0．3％和o．6％NTMAH后zeta电位分别提高了11.7mV和21mV。实验中,在不同体积分数SiC浆料中,加入0．6%TMAH时能够达到最优性能,浆料粘度都达到最低。过量的分散剂则会增加浆料中的离子浓度而导致双电层厚度减小,从而恶化浆料的流变性。     

B_2O_3-CuO复相掺杂对Ba_(0.6)Sr_(0.4)TiO_3陶瓷低温烧结及性能的影响

采用溶胶凝胶法制备了B2O3-CuO复相掺杂Ba0.6Sr0.4TiO3(BST)的陶瓷样品。通过差热分析(DTA)研究了纯Ba0.6Sr0.4TiO3干凝胶煅烧过程中的反应过程;利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)表征了B2O3-CuO复相掺杂Ba0.6Sr0.4TiO3陶瓷的物相组成和微观结构;探讨了掺杂2%6B2O3-4CuO对Ba0.6Sr0.4TiO3陶瓷致密度和烧结温度的影响。最后利用TH2818型自动元件分析仪系统地分析了掺杂不同配比、不同含量B2O3-CuO对Ba0.6Sr0.4TiO3陶瓷材料介电性能的影响,得到了B2O3-CuO复相掺杂影响其性能的规律,即随着B2O3-CuO加入量的增加材料的介电常数和介电损耗开始增大随后减少。     

PbO-SiO2玻璃对Ba0.4Sr0.6TiO3陶瓷致密度和介电性能的影响

为了制备耐高压、高储能密度陶瓷电容器,研究了不同PbO-SiO2(PS)玻璃添加量对Ba0.4Sr0.6TiO3陶瓷致密度和介电性能的影响。结果表明:PS玻璃能有效降低Ba0.4Sr0.6TiO3陶瓷的烧结温度,细化晶粒,提高样品的致密度。添加适量PS玻璃改善了Ba0.4Sr0.6TiO3陶瓷的介电性能。添加质量分数为1%PS玻璃的Ba0.4Sr0.6TiO3陶瓷在1100℃烧结致密,相对密度达到98.3%,平均击穿场强达到15.4kV/mm,相对于纯Ba0.4Sr0.6TiO3陶瓷的提高了1.5倍,1kHz的室温相对介电常数达到1179,介电损耗为6×10-4。     

纳米氧化锆在水中分散性研究

鉴于粉体分散对无机膜制备具有重要意义,研究了添加不同分散剂及其加入量对纳米氧化锆粉在水中的分散性,以及分散性与溶液pH值的关系。结果表明:悬浮液的分散性能受到分散剂及其加入量和pH值的影响,不同的分散剂在各自的加入范围内有其最佳加入量。通过对粒径和zeta电位分析,考察含分散剂时pH值对纳米氧化锆粉的分散性能,从中优选最佳pH值的范围。     

氧化锆水悬浮液的分散

通过考察多元共聚物分散剂对氧化锆zeta电位和浆料流变性的影响,研究了氧化锆浓悬浮液的分散性.结果表明: 多元共聚物分散剂的加入增加了氧化锆zeta电位的绝对值,等电点移至2.4以下.随分数剂加入量的增加,悬浮液的流变性出现复杂的情况:低剪切速率下(100s-1以下),悬浮液粘度略微增加;高剪切速率下(100s-1以上),悬浮液的粘度明显降低;4种分散剂中,二元共聚物分散的氧化锆浆料流动性最好,加入质量分数为0.14%,pH值为9.6左右.并制备了体积分数54%的氧化锆浆料,粘度为0.91Pa·s(100s-1).     

混合碱法制备钛酸锶钡纳米陶瓷粉体的研究

本文以熔融的无水混合碱作为溶剂,以成本低廉的金属无机盐和氧化物作为反应物,成功制备了钛酸锶钡纳米陶瓷粉体.用XRD、SEM对粉体进行了表征.研究结果表明,在温度200℃,加热24h时生成钛酸锶钡(Ba0.77 Sr0.23 TiO3)粉体,在温度245℃,加热24h生成钛酸锶钡(Ba0.6 Sr0.4 TiO3),合成产物为四方形,粉体的粒径为60～120nm,粒度分布均匀.     

石墨凝胶注模工艺研究

采用凝胶注模成型工艺制备了石墨浆料,研究了石墨粉体类型、pH值、分散剂加入量和固相含量对浆料粘度的影响,浆料温度对凝胶固化时间的影响,以及乙酰丙酮对素坯强度的影响.实验结果表明:当采用等静压石墨粉,pH值为7,分散剂加入量为4wt%,固相含量为50vol%时,可制备流动性良好的石墨浆料;浆料温度为3 ℃时,凝胶固化时间为5.6 min;当乙酰丙酮加入量为0.6wt%时,素坯强度达到15.8 MPa.     

TiC—Ni粉体水系共悬浮

通过测定粉体Zeta电位、酸碱性和对分散剂PAA的吸附,探讨了TiC-Ni水系浆料的共悬浮。TiC粉体是酸性,等电点在PH值2.5处,并在PH值为9.5处出现Zeta电位最大值。TiC的Zeta电位随PAA浓度的增加而增加,并且对应于TiC对PAA的饱和吸附,Zeta电位增加到最大值,达到饱和吸附后,继续增加PAA的浓度反而导致Zeta电位的减小。Ni粉体呈碱性,通过理论分析,其等电点应在碱性区。当PAA的加入量为0.3wt％、pH值为6.5时单组分TiC浆料稳定,TiC-Ni浆料相对失稳;当PAA的加入量为0.2wt％、pH值为8.5时,TiC-Ni浆料稳定,并且沉降后的组分均一。     

改进草酸盐共沉淀法制备钛酸锶钡粉体

以硝酸钡、硝酸锶、草酸和钛酸丁酯为原料,通过向锶钡盐溶液中预先添加适量氨水,采用草酸盐共沉淀法制备了草酸氧钛锶钡[Ba0.6Sr0.4TiO(C<2O4)2·4H2O,BSTO]前躯体粉体,将该前躯体800℃煅烧4h得到钛酸锶钡(Ba<0.6Sr0.4TiO3,BST)粉体.改进的工艺省去了在共沉淀同时添加NH3·H2O调节反应体系pH值的过程,使整个工艺方法较之传统工艺更具可操作性.用X射线衍射仪和扫描电镜研究了BST粉体的相组成和微观形貌,并对该工艺所得BST粉体形貌形成机理进行了探讨.结果表明:所制备的BST粉体为高纯立方晶相,粉体呈准球状,粒径为1～2 μm,其比表面积达到18.52 m2/g;BST粉体的"菜花"状软团聚形貌是由于单颗粒BSTO粉体高温煅烧发生分解放出气体而形成.     

Ba0.6Sr0.4TiO3-Mg2TiO4复合陶瓷材料的介电可调性及微波特性

采用常规的陶瓷工艺方法制备了Ba0.6Sr0.4TiO3-Mg2TiO4(BST-MT)复合陶瓷材料,并对其相结构、介电以及可调性和微波特性进行了研究.X射线衍射和介电温度特性测试结果表明,BST-MT复合陶瓷具有BST和MT两相结构,非铁电相MT的增加降低了其铁电性,使其介电常数和介电损耗减小.介电偏压和微波性能测试结果表明,BST-MT复合材料仍能保持较高的可调性,且微波性能得到了明显改善.样品30%BST-70%MT(质量分数)在10 kHz下的介电常数为78,介电损耗为0.000 6,在外加3 kV/mm偏置电场作用下,可调性达到25%,在3.714 GHz频率下的介电损耗为0.0145.     

Synthesis of barium strontium titanate nanopowders by microwave hydrothermal method

Barium strontium titanate (BST) powders of high purity, good crystallinity and well dispersed with a diameter of 50–90?nm are prepared by microwave hydrothermal method using tetrabutyl titanate, barium nitrate and strontium nitrate as the main raw materials. The phase composition, element composition and microstructure of the powders are characterised by X-ray diffraction, Fourier transform infrared spectroscopy, energy dispersive spectroscopy and transmission electron microscopy. The results show that Ba_0.6Sr_0.4TiO₃ powders could be synthesised under the conditions that the reaction temperature is 70°C, the reaction time is 10?min, and the value of pH is 14, which indicates that the reaction temperature, time and the value of pH have a great effect on the crystallinity of nanopowders, and the dispersant (OP-10) plays a role in the dispersion of the nanopowders.     

Aqueous tape casting and crystallization behavior of gadolinium-doped ceria

An aqueous tape casting of gadolinia-doped ceria (GDC) ceramics was developed using Poly(acrylic acid) PAA as dispersant, Poly(vinyl alcohol) PVA as binder, Poly(ethylene glycol) PEG as plasticizer, and deionized water as solvent. Surface properties of GDC powder with and without PAA dispersant were characterized by electrokinetic measurements. The zeta potential measurement revealed that the isoelectric point for GDC powders in the absence of dispersant corresponds to a pH value of 4.06. The experimental results showed that pH value greatly affects the rheology of the slurry. Homogeneous, smooth, and defect-free green tapes were successfully obtained by using an appropriate slurry formula. Moreover, the crystallization kinetics of GDC powders prepared by coprecipitation process also has been investigated in this study. The activation energy of crystallization was calculated by differential scanning calorimetry (DSC) at different heating rates. Analysis of non-isothermal DSC data presented values of 105.3 kJ/mol and 1.171 for the activation energy of crystallization presented and the Avrami exponent, respectively.     

Aqueous processing of Ce0.8Sm0.2O1.9 green tapes

An aqueous tape casting of Ce_0.8Sm_0.2O_1.9 (SDC) ceramics was developed using poly(acrylic acid) (PAA) as dispersant, poly(vinyl alcohol) (PVA) as binder, poly(ethylene glycol) (PEG) as plasticizer, and deionized water as solvent. Surface properties of SDC powder with and without PAA dispersant were characterized by electrokinetic measurements. The rheology of the SDC slurries was evaluated with a rotary viscometer. The zeta potential measurement showed that the isoelectric point (IEP) for SDC powders in the absence of dispersant corresponds to a pH value of 3.66. The experimental results showed that the pH value greatly affects the rheology of the slurry. The optimum content to get a stable dispersed slurry is 2 wt% PAA in pH value range of 9–10. In presence of 2 wt% PAA dispersant, 55 wt% SDC powders exhibited shear thinning behavior, indicating that SDC slurry was homogenous and well stabilized. Homogeneous, smooth, and defect-free green tapes were successfully obtained by an appropriate slurry formula.     

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.     

Dispersion and rheological properties of concentrated silicon aqueous suspension

This work focuses on the optimization of the rheological properties of silicon suspensions by changing the concentration of a dispersant and the pH value of the dispersing medium. The zeta potential and rheological properties of silicon suspensions as a function of tetramethyl ammonium hydroxide (TMAH) concentration were carried out. The results show that the isoelectric point of the silicon particles was at pH 1.6. A silicon suspension with 46 vol.% particles displayed a minimum viscosity at pH 9.6. The results also show that TMAH is an efficient dispersant by enhancing the absolute value of the zeta potential of silicon particles. The optimum dosage of the dispersant was 0.4 wt.% of silicon particles.     

Aqueous tape casting and crystallization kinetics of Ce0.8La0.2O1.9 powder

An aqueous tape casting of Ce_0.8La_0.2O_1.9 (LDC) ceramics was developed using PAA as dispersant, PVA as binder, PEG as plasticizer, and deionized water as solvent. Surface properties of LDC powder with and without PAA dispersant were characterized by electrokinetic measurements. The rheology of the LDC slurries was evaluated with a rotary viscometer. The zeta potential measurement showed that the isoelectric point for LDC powders in the absence of dispersant corresponds to a pH value of 4.02. The experimental results showed the pH value greatly affects the rheology of the slurry. The optimum content to get a stable dispersed slurry is 1.5 wt% PAA at pH value of 9–10. In presence of 1.5 wt% PAA dispersant, 5 wt% PVA binder, 5 wt% PEG plasticizer, and 55 wt% LDC powders exhibited shear thinning behavior, indicating that LDC slurry was homogenous and well stabilized. With an appropriate formulation homogeneous, smooth, and defect-free green tapes were successfully obtained. Moreover, the crystallization kinetics of LDC powders prepared by coprecipitation process also has been investigated in this study. The activation energy of crystallization was calculated on the basis of differential scanning calorimetry (DSC) at different heating rates. From non-isothermal DSC data presented values in the range of 343.3–379.1 kJ/mol and 2.282–2.030 for the activation energy of crystallization and the Avrami exponent, respectively, at specific temperatures ranging from 280 to 285 °C.