BaTi4O9介电陶瓷的低温烧结

研究液相多元添加对BaTi4O9介质陶瓷的烧结和介电性能的影响.通过添加(CuO和V2O5)烧结助剂来达到降低烧结温度的效果,并且使其保持较好的高频性能.实验结果表明在添加合适的烧结助剂下,烧结温度为1180℃时,BaTi4O9介电陶瓷在1MHz下的介电性能:ε=41.2,tan δ=5,τ=82 ppm/℃.基本保持了良好的介电性能.     

单相BaTi4O9柠檬酸凝胶法制备及烧结特性

本文采用柠檬酸凝胶法制备了单相的BaTi_4O_9。干凝胶在750℃煅烧得到了物相为BaTi_5O_(11)和Ba_4Ti_(13)O_(30)、尺寸约为30～50nm前驱体粉体,纳米前驱体粉体在1200℃煅烧2h获得了单相的BaTi_4O_9。单相BaTi_4O_9粉体具有优良的烧结性能,在1250℃烧结保温4h,致密度达到了理论密度的97%。     

Phase evolution and microwave dielectric properties of BaTi4O9 ceramics prepared by reaction sintering method

BaTi₄O₉ microwave dielectric ceramics were prepared by reaction sintering method using BaCO₃ and TiO₂ as raw materials. The phase evolution and the chemical reactions were proposed based on the X-ray diffraction results with sintering temperature. The microstructure characteristics were observed using scanning electron microscopy and energy dispersive spectrometer. The compact ceramics with a single phase of BaTi₄O₉ could be prepared successfully by reaction sintering method, exhibiting optimum microwave dielectric properties: a dielectric constant of 36.9, a high quality factor of 52 735 (at 7.5GHz), and a near zero temperature coefficient of resonant frequency of 5.8 ppm/°C, after sintering at 1200°C for 6 hours.     

Pt负载BaTi4O9的紫外光催化降解甲基橙的研究

采用传统固相合成法制备了BaTi403光催化剂,并利用XRD和UV-Vis光谱分析对催化剂进行了表征。选用甲基橙作为光催化活性的染料模型,研究了Pt的负载量对BaTi409光催化活性的影响,并对其影响机制进行了初步的探讨。实验表明,n的负载对光催化活性影响很大,当Pt的负载量为BaTi403。质量的0．5％时光催化效果达到最好。     

Effect of pH on the properties of barium titanate slurries with an aniomic dispersant

The colloidal stability of barium titanate (BT) aqueous suspensions with poly(acrylamide/4‐carboxylamino‐4‐oxo‐2‐butenate) (PAAM/COB) at pH 7, 9, and 12 has been investigated by means of ζ potential, adsorption, sedimentation, and particle size measurements. The isoelectric point of BT powder is at pH 4.6 and the value of ζ potential decreases as the pH of suspensions increases. The adsorption of PAAM/COB onto BT particles follows the Langmuir adsorption isotherm. The saturated amount of adsorbed polymer decreases with increasing pH. In general, BT particles in basic solutions with PAAM/COB are more stabilized, and less agglomerated than those without any dispersant present. As pH is increased, the resulting ζ potential becomes more negative, although lower polymer concentration is required for monolayer coverage of particle surface. Consequently, the resulting suspensions become more stabilized, and contain powder with smaller particle size. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1082–1088, 2006     

烧结制度对二钛酸钡陶瓷性能的影响研究

二钛酸钡具有优异的介电性能和铁电性能,作为无铅无铋新型的绿色环保材料在动态随机存储器、非挥发铁电存储器等方向将具有广阔的发展空间。本文讨论了烧结致密化对其物相组成及微观形貌的影响。结果表明:在1200℃以内,随烧结温度的升高,晶粒趋于均匀,气孔率下降,致密化程度提高。随烧结压力的升高,试样的相对密度逐渐提高,说明提高烧结压力可有效改善BaTi₂O₅陶瓷的烧结程度。50MPa时,试样的致密度达到最大值86.70%,可基本满足制备薄膜靶材的使用要求。     

BaTi_4O_9(f)/0.64BaTi_4O_9-0.36BaPr_2Ti_4O_(12)复合陶瓷的介电性研究

借助X射线衍射技术 (XRD) ,低频阻抗法 ,X射线光电子能谱 (XPS)等手段对BaTi4O9(f) /0 .6 4BaTi4O9-0 .36BaPr2 Ti4O1 2 复合陶瓷新材料的相组成、介电性能和样品中Ti元素的价态变化进行了研究 .研究结果表明 :该复合陶瓷新材料只由BaTi4O9和BaPr2 Ti4O1 2 两相组成 .加入BaTi4O9纤维后 ,复合陶瓷材料中Ti3 + 离子和Ti2 + 离子的含量降低 ,氧元素的含量提高 ,并对该材料体系的介电性有明显的改善作用 ,其中含 10 %BaTi4O9纤维的BPT10试样的性能最佳 ,其εr=6 4,tgδ =1× 10 - 4 (1MHz) .     

不同粉体制备工艺对Ca3Co4O9陶瓷性能的影响

采用溶胶凝胶法和化学共沉淀法制备了Ca3Co4O9粉体,并烧结为纯相Ca3Co4O9陶瓷。利用XRD、SEM等方法对陶瓷样品的物相以及断面形貌进行了表征,利用四探针法测量了Ca3Co4O9陶瓷的电导率。试验结果表明化学共沉淀法与溶胶凝胶法粉体相比,制得的Ca3Co4O9陶瓷不仅具有更低的气孔率、线收缩率,而且具有更高的电导率,也是一种制备高性能热电材料粉体的有效方法。     

Effects of molecular weight and molecular weight distribution on creep properties of polypropylene homopolymer

The molecular weights of the industrial-grade isotactic polypropylene (i-PP) homopolymers samples were determined by the melt-state rheological method and effects of molecular weight and molecular weight distribution on solid and melt state creep properties were investigated in detail. The melt-state creep test results showed that the creep resistance of the samples increased by M_w due to the increased chain entanglements, while variations in the polydispersity index (PDI) values did not cause a considerable change in the creep strain values. Moreover, the solid-state creep test results showed that creep strain values increased by M_w and PDI due to the decreasing amount of crystalline structure in the polymer. The results also showed that the amount of crystalline segment was more effective than chain entanglements that were caused by long polymer chains on the creep resistance of the polymers. Modeling the solid-state viscoelastic structure of the samples by the Burger model revealed that the weight of the viscous strain in the total creep strain increased with M_w and PDI, which meant that the differences in the creep strain values of the samples would be more pronounced at extended periods of time.     

Adsorption of anionic polyelectrolyte on an SiC surface and effects on dispersion stability

Aluminum nitrate (Al(NO₃)₃) and sodium polystyrene sulfonate (PSS) were used to improve the dispersion of fine silicon carbide (SiC) powders. Effects of modification parameters on the viscosity of modified SiC slurry were studied by orthogonal experiments. Modified SiC slurry with the solid loading of 50 vol% reached the lowest viscosity of 34 MPa s. The adsorption processes of PSS on the as-received and Al(NO₃)₃ premodified SiC surface were investigated. The results indicated that the adsorption between PSS and premodified SiC surfaces was a high affinity type and was mainly controlled by active sites on an SiC surface. The Langmuir model and the pseudo-second-order model could better fit the adsorption isotherm and kinetics data, respectively. The contact angle decreased from 32.8 to 15.2° and the wettability was improved by modification. The isoelectric point of modified SiC powder shifted to the acidic region and the maximum zeta potential was obtained at pH 11. Sedimentation results also showed that a stable dispersed suspension of modified SiC was achieved at pH 11. Density–pressure curves demonstrated that the flowability and formability of SiC powder were improved by modification. The dispersion effect of PSS on SiC and Al₂O₃ composite powder was verified by viscosity and sedimentation results.     

An amphoteric water‐soluble copolymer. II. Effect of its molecular weight on the dispersion of barium titanate in water

An amphoteric water‐soluble copolymer, that is, polyacrylamide/(α‐N,N‐dimethyl‐N‐acryloyloxyethyl)ammonium ethanate (PAAM/DAAE) was synthesized and it showed the ability to disperse BaTiO₃ (BT) particles in aqueous solutions. In this work, the effect of molecular weight of this polymer on the dispersing properties was further examined. The results indicate that the effectiveness of three polymer samples with different molecular weights in the dispersion of BT particles is P2 (M_w = 1.1 × 10⁵) > P1 (M_w = 1.2 × 10⁴) > P3 (M_w = 3.0 × 10⁵). Apparently, P2 is most effective in dispersing the particles, reducing the viscosity of the suspensions, and obtaining highest green and sintered densities. This is attributed to the highest adsorption of this polymer onto BT powder, and causes strongest electrostatic and steric repulsions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 886–891, 2006     

CH4／O2在炭分子筛上的吸附动力学

为消除低浓度煤层气对煤层开采存在的安全隐患,提出了利用甲烷和氧气在炭分子筛上的动力学差异进行脱氧的工艺。采用容积法测定了纯CH4和O2在炭分子筛颗粒上的吸附动力学数据,并利用单床变压吸附装置测定了混合气体在298．15K,各压力下的穿透曲线。研究结果显示：吸附初期,O2在CMS上的扩散速率明显大于CH4;在混合体系穿透曲线上,O2的穿透时间远大于CH4,炭分子筛固定床表现出对O。的优先吸附选择性,可以实现出口直接富集甲烷的目的。0．4MPa时,当产品气中CH4含量为92．44％时,CH4回收率为73．27％。     

Effect of temperature and ph on the adsorption of an anionic detergent on activated carbon

Adsorption of an anionic detergent (sodium dodecyl benzene sulfonate) from aqueous solutions onto activated carbon is investigated as an alternative for eliminating detergents from wastewaters. The adsorption isotherm was measured experimentally at 25°C, 30°C and 35°C and the experimental data were correlated reasonably well by the adsorption isotherm of Prausnitz-Radke. The adsorption capacity is considerably affected by pH and there exists an optimal pH, near pH = 7, where the maximum adsorption takes place. The adsorption capacity increases with rising temperature, the adsorption is irreversible and the heat of adsorption is lessened with the amount of detergent adsorbed and its order of magnitude corresponds to a chemical reaction. It is concluded that the detergent is chemically adsorbed onto the activated carbon.     

氧化淀粉分子量分布对其性能的影响

淀粉氧化得到的产物是一种含有羧基的多糖,对金属离子有较强的络合能力。利用红外、扫描电镜和凝胶色谱对其结构、表面形貌和分子量分布进行了表征。研究了氧化时间对产物分子量分布及性能的影响。在配比为淀粉∶水=100∶500(g),温度85~90℃,时间160~180 m in,加碱量17 g,通氧量6~10 mL/m in时,相对去污力达到1.28。     

Emulsion polymerization of tetrafluoroethylene: effects of reaction conditions on the polymerization rate and polymer molecular weight

The emulsion polymerization of tetrafluoroethylene (TFE) was carried out in a semibatch reactor using a chemical initiator (ammonium persulfate) and a fluorinated surfactant (FC-143). The effects of the reaction condition were investigated though the polymerization rate, molecular weight of polytetrafluoroethylene (PTFE), and stability of the dispersion. The emulsion polymerization of TFE was different from conventional emulsion polymerization. The polymerization rate was suppressed when the polymer particles were significantly coagulated. The polymerization rate increased with operating temperature, surfactant concentration, and agitation speed, due to the enhanced stability of the polymer particles. However, once the parameter value was reached, the rate decreased due to the coagulation of the particles. Stable PTFE dispersion particles were obtained when the surfactant concentration was in the range between 3.48 × 10⁻³ and 32.48 × 10⁻³ mol/liter, which is below critical micelle concentration (CMC). The molecular weight of the PTFE obtained was a function of the surfactant and initiator concentrations, and the polymerization temperature. The molecular weight increased as each parameter decreased. This is against the phenomena observed in a conventional emulsion polymerization. A stable PTFE dispersion polymer having a high molecular weight was obtained by optimizing the reaction conditions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 777–793, 1999     

Effect of molecular weight on shape memory behavior in polyurethane films

Understanding the relationship between the number‐average molecular weight (M_n) and the shape memory behavior of polymers is crucial for a complete picture of their thermomechanical properties, and hence for the development of smart materials, and, in particular, in textile technology. We report here on the study of shape memory properties as a function of M_n of polymers. Shape memory polyurethanes (SMPUs) of different M_n were synthesized, with various catalyst contents or molar ratio(r = NCO/OH) in the composition. In particular, two types of SMPU, namely T_m and T_g types according to their switch temperature type, were synthesized to compare the influence of M_n on their shape memory behavior. X‐ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and shape memory behavior results for the SMPUs are presented. The results indicate that the melting temperature (T_m), the glass transition temperature (T_g), the crystallinity, and the crystallizability of the soft segment in SMPUs are influenced significantly by M_n, before reaching a critical limit around 200 000 g mol^?1. Characterization of the shape memory effect in PU films suggests that the T_m‐type films generally show higher shape fixities than the T_g‐type films. In addition, this shape fixity decreases with increasing M_n in the T_g‐type SMPU, but the shape recovery increases with M_n in both types of SMPU. The shape recovery temperature, in contrast, decreases with M_n as suggested by the result of their thermal strain recovery. It is concluded that a higher molecular weight (M_n > 200 000 g mol^?1) is a prerequisite for SMPUs to exhibit higher shape recovery at a particular temperature. Copyright © 2007 Society of Chemical Industry     

聚丙烯熔体流动指数与分子量及其分布的关系

研究了聚丙烯(PP)的熔体流动指数(MI)与聚合物不同分子量之间的关联性,对于分子量分布较窄的PP,数均分子量(Mn)、重均分子量(Mw)和粘均分子量(Mv)均能较好的关联;反之,MI与Mn关联性下降,而MI与Mn和Mv的关联性仍很好,尤其是MI与Mv的关联性受分子量分布的影响很小;MI与Z均分子量的关联性很差。同时．确定了MI与各种分子量之间的关联式,该式用于本体PP工艺反应器内氢气浓度的计算和MI的预测,与实验测量结果吻合良好。     

烧结工艺对Ca3Co4O9基热电氧化物电性能的影响

采用溶胶-凝胶化学法合成了Ca3Co4O9热电氧化物粉末,分别采用陶瓷烧结工艺方法和放电等离子烧结(Spark Plasma Sintering,SPS)的方法制备了Ca3Co4O9热电氧化物块体材料.利用X射线衍射XRD、扫描电子显微镜SEM和电输运参数测试仪分析了所得样品的物相、微观组织结构、晶粒取向度和电输运性能.结果表明,不同制备方法均可得到纯相的Ca3Co4O9热电氧化物块体材料;通过陶瓷烧结工艺方法制备的Ca3Co4O9热电氧化物块体晶粒取向度较低,但随着成型压力的增加而提高;SPS烧结的方法制备的Ca3Co4O9热电氧化物块体晶粒取向度最高;试样电性能随着晶粒取向度的提高逐渐提高,其中SPS烧结方法制备的块体材料电性能最高,在测试温度最高点700℃时功率因子达3.85 μWmK-2,远高于普通烧结试样.     

Effect of molecular weight on the mechanical properties of polytetrafluoroethylene (PTFE)

Molecular weight has a considerable influence on the mechanical properties and density of polytetrafluoroethylene. Empirical equations have been found relating tensile properties and density to the number-average molecular weight.     

不同分子量木质素磺酸钠染料分散剂的结构及性能

采用超滤方法对木质素磺酸钠进行分离得到3种不同分子量级份。采用凝胶渗透色谱、紫外光谱、电位滴定等方法研究各级份的结构特征及其对分散染料性能的影响。结果表明,随着分子量的增加,木质素磺酸钠颜色加深、纯度提高,分子结构中愈创木基含量增多,酚羟基、磺酸基和羧基的含量降低;高分子量木质素磺酸钠对分散染料具有更优的分散性和高温稳定性,染料上染率也随其分子量的增大而增加,且当木质素磺酸钠浓度较高时,分子量增大,对纤维沾污减弱。木质素磺酸钠对染料的还原破坏作用与分子量和酚羟基含量有关,采用截留分子量大于2.5×10³的膜提纯的木质素磺酸钠级份对染料还原性最低,还原水解率由未提纯时的26.0%降为6.9%,且该级份木质素磺酸钠具有最优的匀染性能。