SCS-6 SiC纤维增强钛基复合材料的界面反应

SCS-6 SiC纤维增强Super α2钛基复合材料界面反应较严重,其反应产物分布可达6层之多;SCS-6 SiC/Ti2AlNb及SCS-6 SiC/IMI834复合材料仅形成3-4层界面反应产物SCS-6 SiC/IMI834复合材料在界面处形成的S2硅化物可在一定温度下阻止反应的进一步进行,使复合材料具有很好的热稳定性.对界面反应热力学研究表明,Ti3Al+C→Ti3AlC反应导致了界面反应产物Ti3AlC的形成.     

SCS—6 SiC／Ti2AlNb复合材料的界面反应及机理

运用量子化学计算理论，求出了有关化合物的热化学参数，并根据有关热力学模型，计算了金属间化合物Ti2AlNb中元素的活度，由此计算了SCS－6 SiC长纤维增强Ti2AlNb金属间化合物复合材料界面反应的Gibbs函数变值△rG,用△rG判据推测了界面反应产物并与透射电镜实验结果进行了对比分析。研究表明，由于Ti2AlNb中原子结合力较Ti3Al强，因而SCS－6 SiC/Ti2AlNb复合材料的界面反应较SCS－6 SiC/Ti3Al轻。反应初期形成晶粒非常细上的TiC,Ti5Si3,晶粒较大的TiC和Ti3Si是由于元素扩散和反应所形成。在对复合材料的热暴露中，这些反应产物均进一步长大，并由于反应Ti3Al C→Ti3AlC，在Ti2AlNb基体中形成一些三元反应产物Ti3AlC晶粒。     

SiC纤维增强Ti55复合材料的界面研究

利用纤维涂层法(FMC)、结合热压工艺制备了SiC纤维增强Ti55基复合材料(SiCf/Ti55).主要研究复合材料在经不同条件真空热暴露处理后,其反应产物相形成的反应序列以及界面反应动力学.结果表明,仅C、Si和Ti等元素参与了界面反应.在1000 ℃热暴露时,SiCf/Ti55复合材料界面反应产物序列为SiC | Ti3SiC2 | Ti5Si3+TiC | TiC | Ti55.但是,在低温热暴露的复合材料中不存在Ti3SiC2相.SiCf/Ti55复合材料界面反应产物的生长受扩散控制且遵循抛物线生长规律,其生长激活能Qk及指数系数k0分别为198.16 kJ·mol-1,1.79(10-3 m·s-1/2.相比SiCf/Ti复合材料和SiCf/Ti2AlNb复合材料,SiCf/Ti55复合材料拥有一个高稳定性的界面.然而,相比SiCf/Ti600复合材料和SCS-6 SiCf/ super а2复合材料,SiCf/Ti55复合材料中的纤维与基体更容易发生反应,且界面层更容易生长.     

SiC_f/Ti/Ti_2AlNb叠层复合材料制备及组织性能

针对目前航空航天材料结构轻量化的要求,以连续SiC纤维、Ti箔和Ti_2AlNb箔为原材料,基于真空热压技术,采用Foil-Fiber-Foil法,通过优化制备工艺,获得SiC_f/Ti/Ti_2AlNb叠层复合材料。利用扫描电镜和能谱分析仪对制备的复合材料界面微观组织进行分析,通过密度测试和拉伸试验计算材料的比强度和比刚度。结果表明,在920℃、40 MPa下保温保压1 h,可获得理想的SiC_f/Ti/Ti_2AlNb叠层复合材料,SiC纤维排布均匀,Ti/Ti_2AlNb界面平直。其中,SiC/Ti界面为0. 8μm的TiC,而Ti/Ti2AlNb界面为α+β双相组织和富B2相,均形成良好的冶金结合,有利于载荷传递,保证材料性能。与Ti/Ti_2AlNb相比,制备的SiC_f/Ti/Ti_2AlNb叠层复合材料的比强度和比刚度分别提高了约16%和28%,实现了材料结构的轻量化。     

SiCf/Ti-6Al-4V复合材料界面反应动力学

SiC纤维增强Ti基复合材料（SiCf／Ti）容易发生界面反应，从而影响其力学性能。开展界面反应和动力学的研究，对于SiCdTi复合材料的制备和服役具有指导意义。采用扫描电镜、透射电镜和X射线衍射分析了SICf／Ti-6Al—4V复合材料的界面反应及其动力学，发现SiC纤维的C涂层与Ti-6Al—4V反应形成粗晶粒的和细晶粒的TiC，长期高温热处理使得界面反应加剧，TiC层加厚，当C涂层完全消耗后，界面反应层中除了TiC外，还出现了Ti3SiC2。研究表明，界面反应层的加厚受元素扩散控制，服从抛物线规律，求出的动力学参数Q为268．8kJ／mol，k为0．0057m/s1/2。     

SiC纤维增强钛基复合材料的界面研究

研究了两种纤维增强钛基复合材料(SCS-6/Ti-6Al-4V和SCS-6/TA6V)的界面.实验结果表明,两种复合材料中SiC纤维与基体合金均结合得较好,界面反应层较薄,其厚度分别为0.8和0.6μm.界面反应层随热处理时间的延长、热处理温度的升高而增厚.EDX分析结果表明,界面相中只含有Al,V,Si和Ti元素.     

SiC长纤维增强钛合金基复合材料的界面研究

研究了SiC/TC4和SiC／Ti40复合材料在不同热处理态下的界面行为。结果袭明，SiC／Ti40复合材料相邻两纤维间存在TiC析出物，在1000℃处理后，TiC析出物消失；2种复合材料界面反应厚度随处理温度升高和时间延长而增大：SCS-6SiC／TC4和SiC／Ti40复合材料界面产物均为Ti5Si3。     

SiCf/Ti-6Al-4V复合材料的界面研究

采用扫描电镜、透射电镜和X射线衍射仪研究了用中国制备SiC纤维增强的Ti-6Al-4V复合材料的界面反应,发现在SiC纤维的C涂层和Ti-6Al-4V基体之间形成的界面反应产物为细晶粒和粗晶粒的TiC,而无C涂层的SiCf/Ti-6Al-4V的界面反应产物,从SiC纤维到Ti-6Al-4V基体,依次为细晶粒的TiC+Ti5Si3、粗晶粒的TiC和Ti3SiC2.还测量了界面反应区厚度并讨论了界面反应机理.     

SiC/Ti6Al4V复合材料界面反应产物的形成序列及扩散路径

通过SiC/Ti6Al4V钛基复合材料的制备及在不同条件下的热处理试验，利用SEM，EDS及XRD分析技术研究复合材料界面反应产物相的形成及反应元素的扩散路径。结果表明：反应元素如C，Ti，Si在界面反应层中出现浓度波动，合金元素Al并没有显著扩散进入界面反应产物层，而是在界面反应前沿堆积，其界面反应产物被确认为Ti3SiC2，TiCx，Ti5Si3C，和Ti3Si；在界面反应初期，存在着TiC＋Ti5Si3Cx双相区，当形成各界面反应产物单相区时，SiC／Ti6Al4V复合材料界面反应扩散的完整路径应为：SiC ｜ Ti3SiC2 ｜ Ti5Si3Cx ｜ TiCx ｜ Ti3Si｜ Ti6Al4V＋TiCx；界面反应产物层的生长受扩散控制，遵循抛物线生长规律，其生长激活能Q^k及k0分别为290.935 kJ·mol^-1,2.49× 10^-2 m·s^-1/2.     

SiCf/Ti-22Al-23Nb-2Ta合金复合材料的界面微结构

利用分析电子显微镜（AEM）研究了磁控溅射法＋真空热压方法制备的SiC纤维增强Ti-22Al—23Nb-2Ta（原子分数,％）合金复合材料的界面微结构．该复合材料的纤维／合金界面由细晶粒的TiC＋TiSi层、等轴晶TiC层和（Al,Ti）Nb2相层组成．界面的形成主要是基体合金中的Ti元素与SiC纤维表面的C涂层直接反应生成TiC;同时导致在次层形成贫Ti层和贫Ti层中Nb元素富集,以致形成（Al,Ti）Nb2相．     

Al2O3包覆改善P2型Na2/3Fe1/2Mn1/2O2正极材料的存储性能

采用超声喷雾热解与高温固相烧结相结合的方法合成P2型Na_2/3Fe_1/2Mn_1/2O₂材料。通过X射线衍射仪、扫描电子显微镜和电化学充放电设备对材料的结构、形貌和电化学性能进行全面的表征。此外,在Na_2/3Fe_1/2Mn_1/2O₂表面包覆Al₂O₃薄层,该包覆层可以抑制Na₂CO₃·H₂O的形成,提高Na_2/3Fe_1/2Mn_1/2O₂材料的存储性能,从而改善其电化学性能。这种简单的表面改性方法为合成高性能钠离子电池正极材料提供了新思路。     

Thermodynamics and phase diagrams in the binary systems Na2O-SiO2, Na2O-GeO2, Na2O-B2O3, Li2O-B2O3, CaO-B2O3, SrO-B2O3, and BaO-B2O3

We applied our model to the enthalpy of mixing data of the binary systems Na₂O-SiO₂, Na₂O-GeO₂, Na₂O-B₂O₃, Li₂O-B₂O₃, CaO-B₂O₃, SrO-B₂O₃, and BaO-B₂O₃. The most stable composition in the liquid, that is where the enthalpy of mixing is most negative, is with a metal-oxygen ratio of 4 to 3, for monovalent metals (Na and Li) and 3 to 4 for divalent metals (Ba and Ca) in liquid silicates or borates. The same applies to the CaO-SiO₂, CaO-Al₂O₃, PbO-B₂O₃, PbO-SiO₂, ZnO-B₂O₃, and ZnO-SiO₂ systems. The oxygen to metal ratio, its constant value in various types of systems, reflects and describes the structure of the liquid. Using the analyzed enthalpies of mixing data and the available phase diagrams, we calculated the enthalpies of formation of the various binary compounds. The results are in excellent agreement with data in the literature that were obtained from direct solid-solid calorimetry.     

Synthesis and properties of CaCd2Sb2 and EuCd2Sb2

High density polycrystalline CaCd₂Sb₂ and EuCd₂Sb₂ intermetallics are synthesized by Spark Plasma Sintering and their thermoelectric properties are investigated. X-ray diffraction measurements reveal both materials have a structure in space group, containing a small amount of CdSb as a second phase. Thermoelectric measurements indicate both are p-type conductive materials. The figure of merit value of CaCd₂Sb₂ is 0.04 at 600 K and that of EuCd₂Sb₂ is 0.60 at 617 K. Theoretical calculations show that CaCd₂Sb₂ is a degenerate semiconductor with a band gap of 0.63 eV, while EuCd₂Sb₂ is metallic with DOS of 13.02 electrons/eV. For deeper understanding of the better thermoelectric properties of EuCd₂Sb₂, its low temperature magnetic, transport and heat capacity properties are investigated. Its Nèel temperature is 7.22 K, convinced by heat capacity anomaly at 7.13 K. Hall effect convinced that it is a p-type conductive material. It has high Hall coefficient, high carrier concentration and high carrier mobility of +1.426 cm³/C, 4.38 × 10¹⁸/cm³ and 182.40 cm²/Vs, respectively. They are all in the magnitude of good thermoelectric materials. The Eu 4f level around Fermi energy and antiferromagnetic order may count for the better thermoelectric properties of EuCd₂Sb₂ than that of CaCd₂Sb₂.     

Bi2Sr2CaCu2Ox bulk superconductor with MgO particles embedded

MgO nano-size particles in various concentrations were added to the Bi-2212 superconductor precursor before partial melting. The resulting ceramic superconductors had a transition sharpness and volume fraction which increased with MgO addition up to 9 wt.%. Compositional variations in the superconducting matrix with varying MgO addition were found, with possible important consequences for the pinning mechanism, since compositional variations are expected to be accompanied by variations in T_c. By TEM it was directly documented that MgO particles could be embedded within the superconducting Bi-2212 grains. Hence wetting occurs. Thus, the requirements for MgO to play an effective role in pinning are satisfied. It is suggested that two distinct pinning mechanisms, both related to MgO addition, are likely to be present. Magneto-optic images clearly confirm the improvement of pinning, and screening, with increasing addition of MgO to Bi-2212.     

Gd Mössbauer effect and magnetic properties of GdNi2Sb2, GdCu2Sb2 and GdAl2Ga2

We have investigated the magnetic properties and the ¹⁵⁵Gd Mössbauer spectra of the ThCr₂Si₂-type compounds GdNi₂Sb₂, GdCu₂Sb₂ and GdAl₂Ga₂. These three compounds were found to order antiferromagnetically, with T_N=6.5 K, 15.8 K, and 42.4 K respectively. The electric field gradient V₂₂ derived from the quadrupole splitting of the Mössbauer spectra gives rise to a sign change at the end of the T3d series in GdT₂Sb₂, as was observed previously also for the corresponding compounds with Si and Ge. This behaviour was explained in terms of decreasing hybridization between the Gd valence electron states and the d electron states of the T atoms.     

Corrosion characteristics of LiBH4 film exposed to a CO2/H2O/O2/N2 mixture

LiBH₄ films were prepared by pulsed laser deposition using a LiB target in a background pressure of hydrogen. The corrosion characteristics of LiBH₄ films were measured by exposing them to a gas mixture of CO₂/H₂O/O₂/N₂ at ambient temperature for 1–24 h. Scanning electron microscopy images show some cracks on the surface of corrosion films, which could act as easy paths for H₂O and CO₂ to further react with Li⁺ and B³⁺. The X-ray photoelectron spectroscopy results and theoretical analysis show that LiBH₄ tends to react with H₂O and CO₂ to form Li₂B₄O₇, Li₂CO₃ and LiOH during the corrosion process.     

Fe2+-Ni2+-NH3-NH4+-C2O42-H2O体系的沉淀配合平衡热力学

针对草酸盐配位共沉淀热分解还原法制备超细铁镍合金粉过程中Fe2+-Ni2+-NH3-NH4+-C2O42--H2O体系的溶液平衡建立热力学分析模型,并根据模型进行相关计算,揭示反应体系中各物质随pH值、氨及草酸浓度的变化关系。结果表明:溶液中的Fe主要以[Fe(C2O4)n]2 2n络合物形式存在,而铁氨络合物含量很低。当氨含量较低时,溶液中的Ni主要以[Ni(C2O4)n]2 2n存在;氨含量较高时,在酸性条件下,溶液中的Ni主要以[Ni(C2O4)n]2 2n存在,在碱性条件下,则主要以[Ni(NH3)n]2+存在。低pH值下,Ni的沉淀率较Fe的高,而高pH值下,Ni的沉淀率则较Fe的低。     

Thermodynamic evaluation of phase equilibria in the CaCl2-MgCl2-CaF2-MgF2 system

The phase diagram of the CaCl₂-CaF₂-MgCl₂-MgF₂ reciprocal ternary system was calculated thermodynamically from available data on the common-ion binary subsystems and from available data on the CaCl₂-MgF₂ join. This join is very nearly quasibinary and divides the system into two quasiternary systems: the CaCl₂-MgF₂-CaF₂ system with a ternary eutectic calculated at 724 +-5 °C and the CaC₂-MgF₂-MgCl₂ system with a ternary eutectic calculated at 561 +-5 °C.     

Al2O3-Sm2O3-CeO2电解质的性能（英文）

采用溶胶-凝胶法和低温燃烧技术制备Ce1-xSmxO2（x=0,0.1,0.2,0.3）和掺杂Sm和（2%-8%）Al2O3的二氧化铈;研究其合成、结构、致密化、导电性和热膨胀等性能,并利用XRD研究其结构和相组成。结果表明,于1300°C烧结球团,获得致密的陶瓷,于1250°C在Ce0.8Sm0.2O0.2中加入2%和4%的Al2O3以促进烧结。利用扫描电子显微镜观察烧结后球团的表面形貌,使用双探针交流阻抗谱研究总离子电导率。     

Impact of oxyfuel atmospheres H2O/CO2/O2 and H2O/CO2 on the oxidation of ferritic–martensitic and austenitic steels

In future power plant technologies, oxyfuel, steels are subjected to steam rich and carbon dioxide rich combustion gases. The effect of simulated combustion gases H₂O/CO₂/O₂ (30/69/1 mol%) and H₂O/CO₂ (30/70 mol%) on the corrosion behavior of low alloyed steels, 9–12% chromium steels and an austenitic steel were studied. It was discovered that the formation of protective chromium rich oxides is hampered due to the carburization of the base material and the formation of chromium rich carbides. The kinetics of corrosion and carburization are quantified. The effect of temperature and the effect of gas pressure are analyzed statistically.