ZrO2-SiO2 复合气凝胶的制备及其热稳定性研究

为了改善纯ZrO_2气凝胶的高温稳定性,本研究以TEOS为硅源,以硝酸氧锆为锆源,通过滴加环氧丙烷,制备了ZrO_2-SiO_2复合气凝胶,探索了锆硅比例和热处理温度对复合气凝胶结构和性能的影响,结果表明,当锆硅比例为1:1时,制备的复合气凝胶比表面积最大,为551.7 m2/g;1000°C热处理后的比表面积为239.3 m2/g,1200°C热处理后的比表面积为89.5m2/g。与纯ZrO_2气凝胶相比,本研究所制得的ZrO_2-SiO_2复合气凝胶具有更好的热稳定性。     

放电等离子烧结在钛铝碳表面反应合成氮化铝涂层

采用高纯Ti_3AlC_2粉体为原料,使用放电等离子烧结技术,制备了Ti_3AlC_2块体材料。通过在Ti_3AlC_2粉体上放置涂覆了BN粉体的石墨片,在Ti_3AlC_2块体表面形成了致密的Al N涂层。采用X射线衍射(XRD)、场发射扫描电镜(FE-SEM)结合能谱仪(EDS)分析试样。研究结果表明,在1300℃保温15 min,压力为30 MPa,可烧结得到组织细小、致密的Ti_3AlC_2块体材料。层片状的Ti_3AlC_2晶粒长约10~20μm。样品表面的Ti_3AlC_2晶粒会发生分解,生成Ti C与Al。然后,Al与BN反应可形成致密的Al N涂层,厚度约为10μm。     

热处理对 Ba0.6Sr0.4TiO3 厚膜介电性能的影响

采用柠檬酸盐法制备了Ba_(0.6)Sr_(0.4)TiO_3粉体,通过丝网印刷法制备了Ba_(0.6)Sr_(0.4)TiO_3厚膜,研究了在空气气氛中进行热处理前后厚膜样品的介电性能。研究结果表明,在空气气氛中进行热处理可以有效地提高厚膜样品的介电性能。经过1000°C热处理,厚膜样品在10 kH z下的介电损耗由1.7%降为1.1%,其优质系数由33提高到55。     

电弧离子镀/磁控溅射复合真空退火制备Ti2AlC涂层

采用自主研发的大弧源技术,复合中频磁控溅射石墨靶,避免H元素的引入,在锆合金表面快速沉积了致密、超厚(约20μm)的Ti–Al–C涂层。经过不同温度(550、650、750和850°C)和时间(1、2和3 h)的真空退火后发现,至少在650°C才能获得Ti_2AlC结构,更高的温度会加速Ti_2AlC的生成。高温沉积对制备Ti_2AlC相涂层而言是必备的。     

无压烧结制备高纯层状Ti_3AlC_2材料的研究

利用钛粉、铝粉和石墨粉混合作为原料并添加少量低熔点元素——锡粉以改变烧结温度和铝含量,采用无压烧结技术在烧结温度为1 400℃,原料Ti/Al/C的摩尔比为3∶1.2∶2下制备出三元Ti_3AlC_2材料。通过X射线衍射仪表征其结构,获得的Ti_3AlC_2的纯度为96.7%,利用场发射扫描电子显微镜研究观察其微观形貌为典型的层状结构。为进一步合成锂离子电池负极材料MXene相Ti_3C_2提供基础。     

机械合金化制备Ti_3AlC_2导电陶瓷

以Ti、Al、C单质粉体为实验原料,掺杂适量的Si元素,采用高能球磨机制备Ti_3AlC_2导电陶瓷粉体,研究球磨转速和原料配比对合成Ti_3AlC_2导电陶瓷的影响。研究表明:在球磨转速为550 r/min,球料比5∶1和球磨时间3 h的球磨工艺下,可成功制备出Ti_3AlC_2含量为92.4 wt%的混合粉体,通过增加适量Al元素可以促进Ti_3AlC_2的合成;原料粉体按3Ti/1Al/0.1Si/1.8C的化学计量比进行机械合金化,所得粉体中Ti_3AlC_2的含量高达95.1 wt%,并且Si原子替代部分Al原子而形成Ti_3Al(Si)C_2固溶体。     

双模板法CeO2/g-C3N4形貌结构特征及湿式催化性能

利用微波辅助双模板法、软模板法制备了一系列的CeO₂/g-C₃N₄复合催化材料,通过XRD、N₂吸附-脱附、XPS、SEM和TEM等方式对材料进行表征,并对其湿式催化性能进行研究。结果表明,双模板法制备的D-CeO₂/g-C₃N₄复合材料表现出立方相CeO₂和层叠g-C₃N₄的特征,比表面积和孔径较大,属于介孔结构,表面存在Ce^₃₊和Ce^₄₊,有利于氧空位的形成。加入1 g嵌段共聚物 F127,使用无水乙醇溶液为溶剂,调节混合液呈碱性,微波辐射反应120 min后得到的D-CeO₂/g-C₃N₄(7.5)样品,结构完整均匀,具有最佳形貌特征。控制反应温度75 ℃,D-CeO₂/g-C₃N₄(7.5)投加0.7 g,H₂O₂投加 0.5 mL,初始pH值为5时,100 mg/L的苯酚溶液COD去除率可达80%以上。 D-CeO₂/g-C₃N₄(7.5) 复合催化材料使用五次以后仍可达60%以上的催化降解效果。     

放电等离子烧结制备TiB_2/Ti_3AlC_2陶瓷复合材料

采用TiB_2和Ti_3AlC_2微粉为原料,利用放电等离子烧结技术制备TiB_2/Ti_3AlC_2陶瓷复合材料,研究了Ti_3AlC_2含量对TiB_2陶瓷的致密度、物相微观结构以及力学性能的影响。结果发现在压力30MPa、1400℃条件下,添加钛铝碳含量为20~30wt%时制得的陶瓷复合材料含有较多的孔洞,且主要分布在TiB_2颗粒间,样品密度偏低,硬度低于570HV。当添加的Ti_3AlC_2量为40wt%时,样品的微观结构中孔洞数量降低且孔径变小,硬度高达1040HV。提高60TiB_2烧结温度至1600℃,物相TiB_2沿晶面(001)发生较明显的取向,样品60TiB_2的微观结构中孔洞消失或存在量极少,致密度高达4.393g/cm~3,硬度高达2400HV。     

TiB2对放电等离子烧结法合成Ti3AlC2/TiB2复合材料性能和结构的影响

放电等离子烧结合成了Ti_3AlC_2/TiB_2复合材料,对其进行了密度、硬度、相含量、断裂韧性和弯曲强度以及微观结构的测试,比较系统地研究了TiB_2对Ti_3AlC_2/TiB_2复合材料性能和结构的影响。实验结果表明:在Ti_3AlC_2中添加适量的TiB_2,可以在断裂韧性略有降低的情况下,得到高硬度和高弯曲强度的致密的Ti_3AlC_2/TiB_2复合材料。     

Na2CO3?10H2O-Na2HPO4.12H2O/SiO2复合定形相变材料的制备及应用研究

以十水合碳酸钠(SCD)、十二水合磷酸氢二钠(DHPD)为相变主体,制备了低过冷度,无相分离的共晶水合盐(EHS),以九水合硅酸钠为成核剂。进一步使用气相SiO₂为支撑材料,采用浸渍法制备了相变前后形状稳定的 EHS/SiO₂定形相变储能材料(SSPCM)。所得SSPCM的相变温度为 24.08 ℃,焓值为 146.6 J/g,过冷度为 0.55 ℃,热导率为 0.5454 W/m?K。同保温泡沫相比,其可将模拟房内部中心温度的升温时间延长 3.26 倍,降温时间延长 1.39 倍,具有优异的“热缓冲”性能,在建筑节能领域具有广阔的应用前景。     

Phase diagram of the Al2O3-HfO2-Y2O3 system

The phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al₂O₃ + HfO₂ + Y₃Al₅O₁₂. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system.     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

Investigation of hydrogen transport through Mm(Ni3.6Co0.7Mn0.4Al0.3)1.12 and Zr0.65Ti0.35Ni1.2V0.4Mn0.4 hydride electrodes by analysis of anodic current transient

Hydrogen transport through such metal-hydride electrodes as Mm(Ni_3.6Co_0.7Mn_0.4Al_0.3)_1.12 and Zr_0.65Ti_0.35Ni_1.2V_0.4Mn_0.4 was investigated in 6 M KOH solution by using potentiostatic current transient technique. From the shape of the anodic current transient and the dependence of the initial current density on the discharging potential, the boundary conditions at the electrode surface were established during hydrogen extraction from the as-annealed and as-surface-treated electrodes. Especially, it was experimentally confirmed that the diffusion-limited boundary condition is no longer valid at the electrode surface during hydrogen transport in case hydrogen diffusion is coupled with either the interfacial charge transfer reaction or the hydrogen transfer reaction between adsorbed state on the electrode surface and absorbed state at the electrode sub-surface. From the transition behaviour of the boundary condition, it was further recognised that the boundary condition at the electrode surface during hydrogen transport is not fixed at the specific electrode/electrolyte system by itself, but it is rather simultaneously determined even at any electrode/electrolyte system by the potential step and the nature of the electrode surface, depending upon e.g. the presence or absence of the surface oxide scales.     

Effect of HfO2 content on the microstructure and piezoelectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–xHfO₂ [BNBT–xHfO₂] lead-free ceramics were prepared using the conventional solid-state reaction method. Effects of HfO₂ content on their microstructures and electrical properties were systematically studied. A pure perovskite phase was observed in all the ceramics with x=0–0.07 wt%. Adding optimum HfO₂ content can induce dense microstructures and improve their piezoelectric properties, and a high depolarization temperature was also obtained. The ceramics with x=0.03 wt% possess optimum electrical properties (i.e., d₃₃~168 pC/N, k_p~32.1%, Q_m~130, ε_r~715, tan δ~0.026, and T_d~106 °C, showing that HfO₂-modified BNBT ceramics are promising materials for piezoelectric applications.     

A bi-layered composite cathode of La0.8Sr0.2MnO3-YSZ and La0.8Sr0.2MnO3-La0.4Ce0.6O1.8 for IT-SOFCs

A bi-layered composite cathode of La_0.8Sr_0.2MnO₃ (LSM)-YSZ and LSM-La_0.4Ce_0.6O_1.8 (LDC) was fabricated for anode-supported solid oxide fuel cells with a thin YSZ electrolyte film. The cell with the bi-layered composite cathode displayed better performance than the cell with the corresponding single-layered composite cathode of LSM-LDC or LSM-YSZ. At 650 °C, the cell with the bi-layered composite cathode gave a higher maximum power density than the cells with the single-layered LSM-LDC and LSM-YSZ composite cathodes, by 52% and 175%, respectively. The impedance spectra results show that the thin LSM-YSZ interlayer not only improves the cathode/electrolyte interface but also reduces the polarization resistance of the cathode. The activation energy for oxygen reduction on the bi-layered composite cathode is much smaller than that on LSM-YSZ composite cathode, and it is suggested that the special redox property of Ce⁴⁺/Ce³⁺ in LDC facilitates the oxygen reduction process on the bi-layered composite cathode. The cell with the bi-layered composite cathode operated quite stably during a 100 h run.     

Synthesis of Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 powders through the molten salt method

The Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5TiO₃ powder synthesis through molten salt method was investigated in the temperature range of 650–700 °C for 2–4 h. The XRD results indicated that the optimal synthesizing temperature for molten salt method was 700 °C, significantly lower than that for conventional processing route of solid state reaction method, where a calcining temperature of 850 °C was needed. The SEM results revealed better crystallization of the powders obtained through molten salt method, compared with those through the conventional processing route of solid state reaction method.     

Mixed oxides Ca2Fe2O5 and Ca2Co2O5 as anode materials for Li-ion batteries

The electrochemical performance of mixed oxides, Ca₂Fe₂O₅ and Ca₂Co₂O₅ for use in Li-ion batteries was studied with Li as the counter electrode. The compounds were prepared and characterized by X-ray diffraction and SEM. Ca₂Fe₂O₅ showed a reversible capacity of 226 mAh/g at the 14th cycle and retained 183 mAh/g at the end of 50 cycles at 60 mA/g in the voltage window 0.005-2.5 V. A reversible capacity in the range, 365-380 mAh/g, which is stable up to 50 charge-discharge cycles is exhibited by Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V and at 60 mA/g. This corresponds to recycleable moles of Li of 3.9±0.1 (theoretical: 4.0). Significant improvement in the cycling performance and attainable reversible capacity were noted for Ca₂Co₂O₅ on cycling to an upper cut-off voltage of 3.0 V as compared to 2.5 V. Coulombic efficiency for both compounds is >98%. Electrochemical impedance spectroscopy (EIS) data clearly indicate the reversible formation/decomposition of polymeric surface film on the electrode surface of Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V. Cyclic voltammetry results compliment the galvanostatic cycling data.     

Chemical zoning of calcium aluminoferrite formed during melt crystallization in CaO-SiO2-Al2O3-Fe2O3 pseudoquaternary system

In the CaO-SiO₂-Al₂O₃-Fe₂O₃ pseudoquaternary system, the solid solutions of Ca₂(Al_xFe_1−x)₂O₅, with x<0.7 (ferrite), Ca₂SiO₄ (belite), Ca₃Al₂O₆ (C₃A) and Ca₁₂Al₁₄O₃₃ (C₁₂A₇), were crystallized out of a complete melt during cooling at 8.3 °C/min. Upon cooling to 1370 °C, both the crystals of ferrite with x=0.41 and belite would start to nucleate from the melt. During further cooling, the x value of the precipitating ferrite would progressively increase and eventually approach 0.7. At ambient temperature, the ferrite crystals had a zonal structure, the x value of which successively increased from the cores toward the rims. The value of 0.45 was confirmed for the cores by EPMA. The chemical formula of the rims was determined to be Ca_2.03[Al_1.27Fe_0.68Si_0.02]_Σ1.97O₅ (x=0.65). As the crystallization of ferrite and belite proceeded, the coexisting melt would become progressively enriched in the aluminate components. After the termination of the ferrite crystallization, the C₃A and belite would immediately crystallize out of the melt, followed by the nucleation of C₁₂A₇. The C₁₂A₇ accommodated about 2.1 mass% Fe₂O₃ in the chemical formula Ca_12.03[Al_13.61Fe_0.37]_Σ13.98O₃₃, being free from the other foreign oxides (SiO₂ and P₂O₅).     

Synthesis of LiNi0.9Co0.1O2 from Li2CO3, NiO or NiCO3, and CoCO3 or Co3O4 and their electrochemical properties

Cathode active materials with a composition of LiNi_0.9Co_0.1O₂ were synthesized by a solid-state reaction method at 850 °C using Li₂CO₃, NiO or NiCO₃, and CoCO₃ or Co₃O₄, as the sources of Li, Ni, and Co, respectively. Electrochemical properties, structure, and microstructure of the synthesized LiNi_0.9Co_0.1O₂ samples were analyzed. The curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂ for the first charge–discharge and the intercalated and deintercalated Li quantity Δx were studied. The destruction of unstable 3b sites and phase transitions were discussed from the first and second charge–discharge curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂. The LiNi_0.9Co_0.1O₂ sample synthesized from Li₂CO₃, NiO, and Co₃O₄ had the largest first discharge capacity (151 mA h/g), with a discharge capacity deterioration rate of −0.8 mA h/g/cycle (that is, a discharge capacity increasing 0.8 mA h/g per cycle).     

Comparison of AlPO4- and Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode materials for Li-ion battery

Electrochemical and thermal properties of Co₃(PO₄)₂- and AlPO₄-coated LiNi_0.8Co_0.2O₂ cathode materials were compared. AlPO₄-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 170.8 mAh g⁻¹ and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 177.6 mAh g⁻¹ and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co₃(PO₄)₂ coating. The Co₃(PO₄)₂ coating material could react with LiOH and Li₂CO₃ impurities during annealing to form an olivine Li_xCoPO₄ phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni⁴⁺ ions compared to the AlPO₄-coated cathode. Differential scanning calorimetry results showed Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO₄-coated sample.