Improved 3D porous structures of Ni electrodes prepared by high-pressure cold spray and post annealing for water splitting

For improving the performance of water splitting, high pressure cold spray was applied to prepare Ni electrodes with controlled 3D porous structures. Al was added as pore former to endow the Ni electrodes with porous structures. Heat treatment was performed to improve the adhesion of the prepared coatings and thus boost the durability of the obtained Ni electrodes. The electrochemical results and characterizations revealed that porous Ni electrodes were successfully obtained. The porosity of obtained electrodes was increased with the addition of Al. Alloy phases such as NiAl and Ni₃Al were detected after heat treatment. An oxide layer was found surrounding Ni layers after chemical leaching. The thickness of oxide layer was found increased with heating temperature and Al addition. NiO, Ni(OH)₂ and NiOOH were found in the leached samples. With porous coatings, the electrodes possessed an improved current density of HER/OER. The Tafel slops of HER/OER were about 120mv/dec which indicated that the rate of water splitting was controlled by Volmer step. Due to the existence of oxide layers and unconnected pores, some samples exhibited Warburg diffusion behavior. Benefitting from the loose and porous microstructure, N30A sintered at 400 °C performed the best catalytic activity for HER/OER, and is considered the best sample for water splitting in alkaline condition.     

悬浮液等离子喷涂高效制备TiO2涂层及其光催化性能

目的 解决TiO2粉末催化剂在污水净化过程中易沉降和难回收问题,同时提高TiO2在可见光条件下降解有机污染物的速率。方法 采用悬浮液等离子喷涂(SPS)技术,以H2为辅助气体制备TiO2涂层,借助H2将高温等离子体焰流中熔融态TiO2中的Ti⁴⁺还原成Ti³⁺。通过场发射扫描电子显微镜、X射线衍射仪、X射线光电子能谱光谱仪、紫外-可见光谱仪等对TiO2粉末以及所制备涂层的结构形貌、物相组成、元素价态、光学特性进行分析。以亚甲基蓝为目标污染物,使用光化学反应仪测试粉末和涂层的光催化性能。结果 TiO2涂层表面呈现由熔融和半熔融颗粒组成的“喀斯特”微观形貌,表面粗糙度为2.94 µm,孔隙率为10.2%。TiO2粉末物相为纯锐钛矿,涂层物相由锐钛矿、金红石相及TiO2－x相组成。TiO2涂层中Ti³⁺的存在使其带间隙减小0.6 eV。在紫外光条件下,TiO2粉末的催化速率为0.003 48,而涂层的催化速率为0.003 45。在可见光条件下,粉末的催化速率与亚甲基蓝的光解速率相近,涂层的催化速率是0.003 07。结论 通过SPS技术成功制备了TiO2光催化涂层,其在可见光条件下的催化性能较粉末有显著提升。     

铁氧体表面Cr/Ni/Ag复合薄膜制备及性能研究

目的利用真空镀膜技术对铁氧体电磁感芯表面进行金属化处理,对金属薄膜的结构及性能进行综合分析,为其实现工程应用提供一定的理论基础。方法采用多腔一体式磁控溅射设备在铁氧体磁体表面依次沉积Cr、Ni、Ag,作为铁氧体表面复合金属薄膜。采用扫描电镜对复合薄膜表面、截面形貌进行表征;利用原子力显微镜对复合薄膜表面粗糙度进行测量;利用划格法对复合薄膜附着力进行测试;利用冲压试验对复合薄膜剥离强度进行测试;利用拉伸试验对复合薄膜结合强度进行测试;利用浸锡试验对复合薄膜耐焊性进行测试。结果试验制备的Cr/Ni/Ag复合薄膜各层厚度分别为420、4200、550 nm,Cr层与Ni层有明显柱状晶结构,层间界面清晰、无明显孔隙,Ag层与Ni层紧密结合。复合薄膜表面粗糙度为13 nm,附着力达0B级,结合力为30 N,抗拉强度达42 MPa。复合薄膜经过450℃浸锡18 s后,表面金属薄膜无脱焊或露底。结论采用磁控溅射技术制备的Cr(420 nm)/Ni(4200 nm)/Ag(550 nm)复合金属薄膜结构致密均匀,综合性能优异,达到铁氧体电感磁芯表面金属薄膜技术要求。     

H2对等离子喷涂–物理气相沉积射流及涂层结构性能影响研究进展

首先介绍了目前现有的等离子射流检测方法,着重综述了PS-PVD等离子射流非接触式检测手段—光谱诊断(OES)技术及其计算方法,以及通过此手段检测H2对射流特性的影响。其次,从H2对涂层物相、组织结构相和热导率的影响出发,介绍了现阶段国内外H2工艺参数对于涂层微观形貌结构影响的研究现状。基于此,通过涂层抗粒子冲蚀能力和抗钙镁铝硅酸盐(CMAS)腐蚀能力对涂层的力学性能和热防护性能差异进行了总结与评价。最后展望了今后PS-PVD制备热障涂层技术兼顾力学性能与热防护性能的发展可能性。     

使役环境涡轮叶片EB-PVD热障涂层失效机制

运用场发射扫描电镜、能量色散光谱仪和金相显微镜等测试表征手段,详细检查退役高温发动机涡轮叶片表面涂层残存状况,发现带气膜孔的高温发动机涡轮叶片经服役2000 h后,表面各部位EB-PVD涂层承受CMAS攻击、硬质物撞击和冷热应力冲击程度各异,导致退役叶片表面共存多种损伤.通过对这些损伤现象的分析,了解使役环境下叶片各部位的失效模式和失效机理.研究结果表明:叶棱为受CMAS攻击最严重处,同时也是受硬质点撞击最密集处,存在大面积涂层脱落;气膜孔周围的TBCs涂层受CMAS攻击发生本质性固化,受交变热应力和机械应力共同作用而呈规律性脱落;叶棱周围气膜孔表面(无论是叶背或是叶盆)均存在硬质物碾压划过叶片表面而压实CMAS,引起表面TBCs脱落的现象,同时在气膜孔内发现飞落的TBCs柱和CMAS块,从侧面反应对叶片表面造成实质性伤害的硬质物可能为脱落的TBCs柱或固化的CMAS块.     

过渡层对钕铁硼表面蒸发镀铝涂层耐腐蚀性能的影响

目的提高钕铁硼磁体表面Al防护涂层的结合强度及耐腐蚀性能。方法通过磁控溅射在钕铁硼磁体表面沉积Al过渡层,用高偏压进行轰击后,使用离子辅助蒸发镀技术沉积Al防护涂层。用扫描电子显微镜观察涂层表面及截面形貌,电化学工作站及盐雾试验检测涂层腐蚀性能,拉伸试验评价涂层与基体结合强度。结果随着磁控溅射靶电流从10 A提高到25 A,所制备的Al层自腐蚀电压从-0.7367 V递减到-0.9075 V,耐中性盐雾腐蚀性能下降。在用相同工艺制备表面离子辅助蒸发镀Al防护涂层的前提下,磁控溅射靶电流为25 A时制备的100 nm和500 nm过渡层的防护涂层耐盐雾腐蚀时间分别为48 h和36 h,耐腐蚀性能不如无过渡层的纯蒸发镀铝涂层(72 h);磁控溅射靶电流为15 A制备的100 nm和500 nm过渡层的防护涂层耐盐雾腐蚀时间分别为96 h和103 h,其耐腐蚀性能优于无过渡层的纯蒸发镀铝涂层。采用过渡层技术的Al防护涂层结合强度均大于40 MPa,与钕铁硼基体结合良好。结论过渡层技术均可使Al涂层与Nd Fe B基体结合良好,合适的过渡层工艺可提高离子辅助蒸发镀铝涂层的耐腐蚀性能。     

大气等离子喷涂MoSi2-30Al2O3电热涂层的组织结构及性能

以MoSi₂-30Al₂O₃混合粉末为原料, 利用大气等离子喷涂技术制备MoSi₂-Al₂O₃体系电热涂层。采用XRD、SEM、通电测试、热重-差热分析等对涂层的相组成、组织形貌和热稳定性进行表征。结果表明：MoSi₂-30Al₂O₃电热涂层体系组织均匀致密, 添加Al₂O₃能改善MoSi₂的电阻率及低温抗氧化性; MoSi₂-30Al₂O₃涂层电热性能优异, 在循环加热测试中, 能稳定地加热到320 ℃并长时间保温, 辊面温度分布均匀, 中部温差控制在25 ℃之内; 循环加热过程中的氧化及热应力的弛豫会导致涂层产生裂纹及孔隙进而导致涂层电阻率升高。     

等离子喷涂-物理气相沉积Si/莫来石/Yb2SiO5环境障涂层

采用等离子喷涂-物理气相沉积技术(PS-PVD)在SiC/SiC复合材料表面依次制备了Si(底层)、3Al₂O₃-2SiO₂ (中间层)、Yb₂SiO₅(面层)环境障涂层(EBC)。利用扫描电子显微镜(SEM)观察分析EBC涂层表面与界面的微观形貌, X射线衍射仪对喷涂过程中易非晶化的莫来石涂层进行物相分析, 研究了喷涂粉末与高温等离子体的相互作用并探讨了EBC涂层的沉积机制。结果表明：通过PS-PVD技术可制备出低孔隙率、高致密界面的EBC涂层。通过观察EBC涂层表面, Si涂层表面无裂纹, 而莫来石和Yb₂SiO₅涂层表面均发现有微裂纹, 其中莫来石涂层表面的裂纹尺度大于Yb₂SiO₅涂层。三层结构的致密EBC涂层以液相沉积为主, 同时伴随有气、固沉积。在Yb₂SiO₅涂层沉积过程中, 液相沉积导致涂层为致密的层状结构, 蒸发后气相在等离子焰流中及基体表面发生均匀形核和非均匀形核导致涂层中出现大量的纳米晶粒, 而微熔粒子和溅射粒子则形成涂层中亚微米、微米晶粒。     

Enhanced photovoltaic properties of PbTiO3-based ferroelectric thin films prepared by a sol-gel process

PbTiO₃ (PTO), Pb(Mn_0.1Ti_0.9)O₃ (PMTO), Pb(Sr_0.1Ti_0.9)O₃ (PSTO), and Pb(Zr_0.1Ti_0.9)O₃ (PZTO) were prepared on an indium tin oxide (ITO)/glass substrate by a sol-gel method. PTO, PMTO, PSTO, and PZTO films exhibited energy band gaps of 3.55 eV, 3.63 eV, 3.59 eV, and 3.66 eV, respectively. All these films generated high photocurrents due to high shift currents, because carrier migration channels were successfully introduced by a lattice mismatch between the films and ITO substrates. The PMTO thin film exhibited the best ferroelectric and photovoltaic properties, with a photovoltage of 0.74 V, a photocurrent density of 70 μA/cm², and a fill factor of 43.34%, which confirms that shift current and ferroelectric polarization are two main factors that affect the ferroelectric photovoltaic properties. The PSTO, PZTO, and PTO thin films displayed space-charge-limited current (SCLC) when the electric field strength was below 10 kV/cm, and these three films broke down when the electric field strength was above 10 kV/cm. Analysis of the shift current mechanism confirmed that the breakdown of the PZTO and PSTO thin films resulted from Pool Frenkel emission current. The PMTO thin film displayed SCLC in the test range, which indicates that doping with Mn could inhibit defect formation in ferroelectric thin films.     

Improvement of energy density in SrTiO3 film capacitor via self-repairing behavior

Self-repairing behavior of SrTiO₃ film capacitor was explored to improve the energy density. With Au and Al being deposited on SrTiO₃ thin films as top electrode, the breakdown processes were investigated by a real-time optical microscope system. A high electric field of the electrode edge attributed to edge effect provided the “trigger factor” for the self-repairing behavior. Absorbed water not only provided “mobile phase” for self-repairing process which significantly enhanced breakdown strength but also, and equally important, it supplied additional polarization charges to raise dielectric constant. As a result of the concurrent increase in E_b and ε_r, a higher energy density of 15.7 J/cm³ is achieved. A leakage current platform was observed in the self-repairing process and the thickness of a new layer Al₂O₃ film generated from self-repairing process was estimated according to Ohm's law and breakdown strength. Using relative humidity dependence of breakdown voltage, the maximum breakdown field was explored to realize the optimum self-repairing capability.