模板晶粒生长技术制备SrBi2Nb2O9织构陶瓷

以熔盐法制备的片状SrBi2Nb2O9晶体为模板剂,采用模板晶粒生长技术和流延法制备了Sr-Bi2Nb2O9织构陶瓷,研究了模板含量对SrBi2Nb2O9织构陶瓷烧结行为、织构度、显微结构的影响。结果表明:模板含量为10wt%时,1200℃保温2h烧结可获得体积密度最大的SrBi2Nb2O9织构陶瓷,模板含量继续增加,体积密度降低;织构陶瓷的晶粒尺寸随模板含量的增加而逐渐增大,且晶粒取向性生长趋于明显,当模板含量为10wt%时,织构化SrBi2Nb2O9陶瓷的晶粒取向率f达到最大值,为0.81;织构化陶瓷的压电常数d33达到13pC/N,高于固相法制备的陶瓷的压电常数。     

原始粉料对Sr0.4Ba0.6Nb2O6烧结性能与显微结构的影响

对比了以单相Sro.4Bao 6Nb2O6为原料的常规烧结试样(SBN40)以及以SrNb2O6与BaNb2O6混合物为原料的反应烧结试样(RSBN40)的烧结性能与显微结构.结果发现,RSBN40试样的致密化速率较SBN40试样较慢,试样SBN40与RSBN40密度分别在1250与1300℃达到最大,其值分别为5.21与5.27g@cm-3.此外,当烧结温度高于1250℃时,试样SBN40比RSBN40易于出现异常晶粒长大现象.     

丝网印刷技术制备高性能织构化K0.45Na0.55NbO3陶瓷（英文）

以片状NaNbO3晶粒为模板,以K4CuNb8O23(KCN)为助烧剂,通过丝网印刷技术制备出晶粒定向的K0.45Na0.55NbO3(KNN)无铅压电陶瓷.片状的NaNbO3模板是以铋层状Bi2.5Na3.5Nb5O18为前驱物,通过熔盐拓扑微观反应制得.织构化(K0.45Na0.55)NbO3陶瓷的晶粒定向程度达到95%,其定向晶粒沿丝网印刷方向平行排列,块体的相对密度达到92%.在平行和垂直于丝网印刷方向的两个面上,织构化(K0.45Na0.55)NbO3陶瓷表现出不同的定向程度,且其介电、铁电和压电性能均明显优于无织构化陶瓷.介电常数εr、压电系数d33、机电耦合系数kp在平行于丝网印刷方向的表面上,分别提高了75%、44%、42%;在垂直于丝网印刷方向的表面上分别提高了35%、30%、35%.相对于目前其它的晶粒定向技术,丝网印刷方法既简单又高效.     

烧结温度对冲击磨用Al2O3陶瓷靶材性能的影响

利用无压烧结工艺制备了陶瓷靶材,并借助扫描电子显微镜和液压机等测试设备研究了烧结温度对陶瓷靶材显微结构和力学性能的影响.结果表明,随着烧结温度的升高,掺杂Al2O3陶瓷靶材的晶粒尺寸逐渐增大,晶粒形状也由各向异性生长逐步向等轴状发育;靶材的抗弯强度也随着烧结温度的升高先升高后降低,并在1600℃时强度和耐磨性达到最大.     

原始粉料对Sr0.4Ba0.6Nb2O6烧结性能与显微结构的影响

对比了以单相Sr0.4Ba0.6Nb2O6为原料的常规烧结试样(SBN40)以及以SrNb2O6与BaNb2O6混合物为原料的反应烧结试样(RSBN40)的烧结性能与显微结构.结果发现,RSBN40试样的致密化速率较SBN40试样较慢,试样SBN40与RSBN40密度分别在1250与1300℃达到最大,其值分别为5.21与5.27g·cm-3.此外,当烧结温度高于1250℃时,试样SBN40比RSBN40易于出现异常晶粒长大现象.     

钛酸铋钠基陶瓷的烧结机制

应用晶粒生长动力学唯象理论研究籽晶模板对0．94Na0.5Bi0.5TiO3-0．06BaTiO3无铅压电织构陶瓷烧结机制的影响规律,确定了晶粒生长动力学指数和激活能,探讨了籽晶含量对陶瓷晶粒生长的作用机理。实验结果表明：籽晶Bi2.5Na3.5Nb5O18含量小于或等于15wt％时,晶粒生长以界面反应和晶格扩散两种机制控制,籽晶含量大于或等于20wt％时,以界面反应机制为主;取向长条晶需要的激活能小而容易生长,且晶粒尺寸比等轴晶大。     

工艺参数对熔盐法制备Bi4Ti3O12的影响

为了获得片状粉体用于无铅压电陶瓷晶粒的定向生长,采用NaCl-KCl熔盐法制备了各向异性的片状Bi4Ti3O12粉体,研究了预烧温度和熔盐含量对粉体的显微组织结构和形貌各向异性的影响,计算了粉体径向尺寸与厚度尺寸的比值以表征粉体的各向异性.研究表明:随着预烧温度的升高,粉体尺寸不断增加,各向异性逐渐增大,最佳预烧温度为950℃;采用熔盐法可制备出纯Bi4Ti3O12相粉体,随熔盐含量增加,钛酸铋粉体尺寸及各向异性程度明显增大,并在烧结后的Bi4Ti3O12陶瓷中有织构产生.     

工艺参数对熔盐法制备Bi4Ti3012的影响

为了获得片状粉体用于无铅压电陶瓷晶粒的定向生长，采用NaCl-KCl熔盐法制备了各向异性的片状Bi4Ti3O12粉体，研究了预烧温度和熔盐含量对粉体的显微组织结构和形貌各向异性的影响，计算了粉体径向尺寸与厚度尺寸的比值以表征粉体的各向异性．研究表明：随着预烧温度的升高，粉体尺寸不断增加，各向异性逐渐增大，最佳预烧温度为950℃；采用熔盐法可制备出纯Bi4Ti3O12相粉体，随熔盐含量增加，钛酸铋粉体尺寸及各向异性程度明显增大，并在烧结后的Bi4Ti3O12陶瓷中有织构产生．     

Pb1.5Nb2O6.5型微波介质陶瓷粉体的焙烧工艺研究

探讨了合成Pb1.5Nb2O6.5型微波介质陶瓷粉体的焙烧温度、焙烧时间、添加剂等不同工艺因素对Pb1.5-Nb2O6.5粉体物相变化、晶粒生长及形貌的影响,采用X射线衍射(XRD)和扫描电子显微镜(SEM)对制备的粉体进行物相与晶体形貌检测.实验结果表明在其他工艺因素控制得当时,焙烧温度对粉体粒度和物相变化的影响最大,而不同类型的添加剂不仅可以使晶粒生长更为完整,尺寸增大,同时也可以不同程度地改变粉体颗粒的生长趋势与形貌.实验制备出的Pb1.5Nb2O6.5粉体物相单一无杂质、晶粒尺寸较小,适于进一步制备微波介质陶瓷元件.     

烧结方式对共沉淀法制备ZnNb_2O_6陶瓷介电性能的影响

采用化学共沉淀法制备Zn Nb2O6超细粉体,所得的粉体经煅烧压制后通过微波和常规烧结工艺制备Zn Nb2O6陶瓷,并研究两种烧结方法对Zn Nb2O6陶瓷相对密度、物相、表面形貌、介电性能等的影响。结果表明,共沉淀法制得的Zn Nb2O6粉体晶粒细小、均匀,近似棒形,尺寸约为150nm;与常规烧结工艺相比,采用微波烧结工艺可将Zn Nb2O6陶瓷烧结温度降低约150℃,烧结时间缩短1.5 h,进而有效抑制了烧结过程中锌元素的挥发;微波烧结后的Zn Nb2O6陶瓷晶粒粒径约为6μm,排列均匀,且气孔率低;微波烧结可有效改善Zn Nb2O6陶瓷的微波介电性能,与传统烧结方式对比,微波烧结可提高εr和Q×f为4.6%和15.6%左右,τf更趋于正值方向。同时对微波烧结陶瓷介电性能进行了较为系统的理论分析。     

VLE data for CO2-CF2Cl2, N2-CO2, N2-CF2Cl2 and N2-CO2-CF2Cl

Knowledge about vapour-liquid (VLE) is required as a basis of reliable calculations for separation processes. Correlations available for the prediction of T, p, x, y data are less accurate for mixtures at high pressures and mixtures containing supercritical components. The results of VLE experiments are reported and compared with data calculated with equations of state.     

Preparation of ZrO2-CeO2 and HfO2-CeO2 nanopowders

We prepared weakly agglomerated powders of ZrO₂-CeO₂ and HfO₂-CeO₂ solid solutions 5–8 nm in particle size, consisting of monoclinic and tetragonal phases. After heat treatment at 1200°C, the crystallite size was 30 and 14 nm, respectively. We also examined the effect of precipitate freeze drying on the crystallization of hafnia-based solid solutions containing up to 20 mol % CeO₂.     

Thermal diffusion in binary mixtures H2-CCl2F2 and H2-CHClF2

Thermal diffusion coefficients were measured in two gaseous mixtures, in which one component was close to the critical temperature, in the pressure range (19.6–127.4)·10⁴ N/m² and at a freon concentration of 0.25–0.8.     

Comparison of the Electronic Structures of La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2

First-principles cluster calculations are reported of the local electronic structure of the three compounds: La₂CuO₄, Sr₂CuO₂Cl₂, and Sr₂CuO₂F₂. The copper ${\text{3d}}_{x^2 - y^2 } $ and the planar oxygen 2p _σ atomic orbitals exhibit a similar degree of covalency. The out-of-plane orbitals, however, are quite different with the ${\text{3}}d_{3z^2 - r^2 } $ atomic orbital lowered significantly in energy for chlorine and fluorine apical positions.     

Radial GRIN glasses in Li2O-Na2O-Al2O3-TiO2-SiO2 systems

A series of GRIN glass rods have been developed in Li2O-Na2O-Al2O3-TiO2-SiO2 systems. Negative radial refractive index profiles were generated by exchanging Na+ for Li+ ions in these glass rods. It has been observed that TiO2 plays a vital role in increase in the profile depth and maximum change in the refractive index because of its ambivalent nature. Change in the refractive index can be further increased by increasing the concentration of exchanging cation in the base glass.     

Elastic and Electronic Properties of Superconducting CaPd 2 As 2 and SrPd 2 As 2 vs. Non-superconducting BaPd 2 As 2

The first-principles calculations were performed to predict the elastic and electronic properties of the superconducting ThCr₂Si₂-type phases CaPd₂As₂ and SrPd₂As₂ in comparison with the non-superconducting CeMg₂Si₂-type phase BaPd₂As₂. Besides, the same properties were compared for CeMg₂Si₂- and ThCr₂Si₂-type polymorphs of BaPd₂As₂. We found that all these phases are mechanically stable and belong to soft materials with low hardness. The near-Fermi region is formed by the valence states of the blocks [Pd₂As₂] with decisive contributions of Pd 4d states. The values of N(E _F) increase in the sequence: CaPd₂As₂ < SrPd₂As₂ < BaPd₂As₂, i.e. in the reverse sequence relative to the transition temperatures T _C. Thus, the change in T _C cannot be explained by the electronic factor, i.e. by the simple correlation T _C～N(E _F). Most likely the decrease in T _C in the sequence CaPd₂As₂ → SrPd₂As₂ and the absence of a superconducting transition in BaPd₂As₂ are related to the structural factors and the peculiarities of the electron–phonon coupling mechanism.     

Si_2N_2O-Al_2O_3-La_2O_3和Si_2N_2O-Al_2O_3-CaO系统的亚固相关系

本文给出了 Si_2N_2O-Al_2O_3-La_2O_3和 Si_2N_2O-Al_2O_3-CaO 系统的亚固相图。实验结果表明:在 Si_2N_2O-Al_2O_3-CaO 系统中有一个未知结构的新化合物 CaO·Si_2N_2O,在3CaO·Si_2N_2O 和3CaO·Al_2O_3两化合物之间形成连续立方固溶体。而 Si_2N_2O-Al_2O_3-La_2O_3系统中则没有发现新化合物。在两个系统的富 Si_2N_2O区,过量的 Si_2N_2O 与 La_2O_3和 CaO 分别反应形成 Si_3N_4与 La_(10)[SiO_4]_(?)N_2(H-相)(和 CaSiO_3。所研究的这两个三元系统中,分别形成了如下几个四元相容性区。在 Si_2N_2O-Al_2O_3-La_2O_3系统内有:H-Si_3N_4-La_2O_3·Si_2N_2O-La_2O_3·Al_2O_3;H-Si_3N_4-La_2O_3·Al_2O_3-La_2O_3·11 Al_2O_3;H-Si_3N_4-La_2O_3·11 Al_2O_3-Al_2O_3;H-Si_3N_4-Al_2O_3-O′s.s;H-Si_3N_4-O′s.s-Si_2N_2O在 Si_2N_2O-Al_2O_3-CaO 系统内有:Si_3N_4-CaSiO_3-CaO·Si_2N_2O-3CaO·Al_2O_3;Si_3N_3-CaSiO_3-3CaO·Al_2O_3-2CaO·Al_2O_3·SiO_(?);Si_(?)N_(?)-CaSiO_3-2CaO·Al_2O_3·SiO_2-Al_2O_3;Si_3N_4-CaSiO_3-Al_2O_(?)-O′s.s;Si_3N_4-CaSiO_3-O′s.s-Si_(?)N_(?)O