激光熔覆SiO2/La2O3梯度生物陶瓷涂层生物活性研究

目的研究SiO_2含量对钛合金表面激光熔覆梯度生物陶瓷涂层生物活性的影响。方法利用激光熔覆技术,采用梯度成分设计思想,固定涂层中稀土氧化物La_2O_3的添加量,在钛合金TC4表面制备了掺杂不同含量SiO_2的梯度生物陶瓷涂层。采用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、噻唑蓝(MTT)及荧光素双醋酸酯(FDA)染色等测试手段,研究了SiO_2含量对激光熔覆制备梯度涂层的组织结构和生物活性的影响。结果 SiO_2在激光熔覆过程中可以降低梯度生物陶瓷涂层的开裂敏感性,并起到细化晶粒的作用。当SiO_2掺杂量为2.5%时,激光熔覆过程中诱导合成的HA+CaTiO_3数量最大;当SiO_2掺杂量为7.5%时,模拟体液(SBF)实验表明,涂层的矿化沉积能力最强。MTT测试表明,SiO_2掺杂量为7.5%的涂层细胞增殖数量的OD值最大,细胞能够紧贴涂层表面生长。FDA染色分析表明,SiO_2掺杂量为7.5%的涂层上细胞数量最多,且分布均匀。结论 SiO_2掺杂量深刻影响着生物活性陶瓷相HA和Ca_2SiO_4数量,进而影响生物陶瓷涂层的生物活性。SiO_2掺杂量为7.5%的涂层具有最佳的生物相容性及生物活性。     

光斑类型对激光熔覆MoFeCrTiWAlNb高熔点高熵合金涂层组织和性能的影响

目的 获得高性能工具钢涂层。方法 分别采用方形光斑及圆形光斑激光熔覆试验,在M2工具钢（W6Mo5Cr4V2）上制备出MoFeCrTiWAlNb高熵合金（HEA）涂层,对比分析两种工艺下,高熵合金涂层的组织结构及性能差异。采用SEM、XRD、EDS分析两种涂层形貌、成分、相结构。采用显微硬度计、摩擦磨损试验机测试两种涂层的硬度及耐磨性。结果 球磨4 h后,合金粉末没有合金化,但是发生了形变,合金粉末更加细小均匀,平均直径为56.1 μm。圆形光斑制备的HEA涂层的主相结构是BCC和MC碳化物,而矩形光斑激光熔覆制备的HEA涂层的主相结构是BCC、hcp-Fe2Nb和MC碳化物。圆形光斑涂层中出现明显的相分离现象,而采用方形光斑的激光熔覆层熔深浅,稀释率小,显微组织主要由不规则树枝晶及 颗粒状碳化物构成。方形光斑激光熔覆涂层平均硬度为850HV左右,圆形光斑激光熔覆涂层平均硬度为680HV左右。相较于圆形光斑所制备的HEA涂层,方形光斑所制备的HEA涂层摩擦系数低,磨损量小,磨损表面光滑,主要磨损机制为磨粒磨损。结论 矩形光斑更适合于激光熔覆MoFeCrTiWAlNb高熵合金 涂层。     

Polymer-derived SiHfN ceramics: From amorphous bulk ceramics with excellent mechanical properties to high temperature resistant ceramic nanocomposites

Within the present work, additive-free amorphous bulk SiHfN ceramics with excellent mechanical properties were prepared by a resource-efficient low-temperature molding method, namely warm-pressing. As densification mechanism viscous flow has been identified based on cross-linking reaction. The critical problems concerning gas evolution and crystallization inducing bloating and cracking are addressed through controlled thermolysis and pressure. The microstructural evolution of the SiHfN ceramics indicates that the incorporation of Hf in perhydropolysilazane not only increases the ceramic yield (97.4 wt%) and crystallization resistance (1300 °C), but also suppresses the transformation from α-Si₃N₄ to β-Si₃N₄ at high temperatures (1700 °C). Especially, HfN/α-Si₃N₄ nanocomposites converted by the SiHfN ceramics at 1500 °C show a slight weight loss of 3.13 wt%, indicating the high temperature resistance of the ceramic nanocomposites. The method proposed in this work opens a new strategy to fabricate additive-free polycrystalline Si₃N₄- and amorphous Si₃N₄-based (nano)composites.     

Structural and electrical characterization of (K0.48Na0.52)0.96Li0.04Nb0.85Ta0.15O3 synthesized by spray drying

The synthesis of lead-free ferroelectric materials with composition (K_0.48Na_0.52)_0.96Li_0.04Nb_0.85Ta_0.15O₃ has been achieved by spray drying technique. Pure perovskite phase was obtained after calcination of as-prepared powders at 800 °C for 1 h. Crystallized powders have a particle size average of 100 nm. Well sintered samples were obtained at 1120 and 1130 °C for 2 h in air with densities of 4.58 and 4.49 g/cm³, respectively. We attributed this improvement as the result of sintering process and the very small particle size in powders. Sintered samples have promising piezoelectric parameters, k_p 0.40–0.41, d₃₁ 50–55 pC/N and dielectric losses around 1%.     

High-entropy alloy: An alternative approach for high temperature microwave-infrared compatible stealth

To achieve microwave-infrared compatible stealth in high temperature conditions, high-entropy alloys (HEAs) thin films were deposited on Al₂O₃ matrix by magnetron sputtering technology. Films were annealed to investigate thermal stability at 500 °C, 600 °C and 700 °C, respectively. Results from X-ray diffract meter (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), and Fourier transform infrared spectrometer (FTIR) suggested that high-entropy alloy (HEA) film was seriously oxidized when the annealed temperature reached 700 °C for 6 h, causing a significant decrease of infrared reflectivity. Conversely, HEA films showed low infrared emissivity of 0.09 at 600 °C. Additionally, the films possessed excellent thermal stability at 500 °C for 20 h with low infrared emissivity of 0.11. Finally, a simple metamaterial design utilizing HEA films was proposed for infrared-microwave compatible stealth. With the ability of incorporating excellent thermal stability and durable high temperature stealth performance, the study shows great potential of introducing HEAs in the field of high temperature compatible stealth.     

Catalytic combustion of toluene on Pt/Al2O3 and Pd/Al2O3 catalysts with CeO2,CeO2-Y2O3 and La2O3 as coatings

CeO₂,La₂O₃,and CeO₂-Y₂O₃ oxides were coated on the surface of spherical granular AI₂O₃(3-5 mm)through impregnation method,and proved as better supports of Pd and Pt catalysts.The influences of rare earth metal doping on the adsorption rates of Pd and Pt ions,as well as the catalytic performance,were investigated.Results show that the H₂PtCl₆·6H₂O adsorption rates of the Al     

Hierarchical membrane by centrifugal casting and effects of incorporating activated carbon as pore-former

Producing ceramic asymmetric membranes usually requires several steps to prepare macroporous support and then the selective layer deposition. This process is energy and time-consuming, which is expensive. In this sense, the one-step centrifugal casting technique is an interesting alternative. Therefore, this work aimed to prepare ultrafiltration ceramic membranes by the centrifugal casting method, investigating the effect of a pore-forming agent on membrane performance. Different concentrations of activated carbon were used in the alumina suspension, and then the tubes were molded, dried, and sintered. The membranes' shrinkage, morphology, apparent porosity, hydraulic permeance, and BSA protein retention were evaluated to identify the effect of using the pore-forming agent. The membrane prepared without activated carbon rejected 91% of the BSA molecules (66 kDa), indicating its molecular weight cut-off. Using more than 2.5% of activated carbon increased the porosity and hydraulic permeance of the membranes, but at the expense of low BSA retention.