电解均匀沉淀法制备纳米二氧化锆粉体及其机理

利用阴离子交换膜将电解槽分为两室,控制阴极电流密度为100A/m2,在电解过程中不断消耗阴极室溶液中H ,促使ZrO2 与阴极均匀释放的OH-进行水解反应,形成ZrO2·xH2O均匀沉淀.在600℃焙烧温度下保温2b,XRD和TEM分析表明:ZrO2粉体为四方晶型,呈球形,粒径约为30～50nm.讨论了焙烧温度对纳米ZrO2粒度的影响.同时对纳米ZrO2形成机理进行了初步的探讨研究.     

水热法合成羟磷灰石及其包覆二氧化锆粉体的制备

羟磷灰石(HA)单独作为生物陶瓷材料存在着强度和韧性的缺陷,加入二氧化锆可以在不影响其生物活性的前提下达到增强增韧的目的.首先研究了pH及水热时间对HA结晶的影响,得出了制备HA的较佳的水热条件.在此基础上,在二氧化锆水合物ZrO2·xH2O微粒上分步加入钙和磷酸根离子,并同时控制pH,使HA在ZrO2·xH2O表面沉积,从而制备出具有包覆结构的胶粒,然后进行水热处理.试验表明,HA与二氧化锆的水热结晶相互影响很大,被HA包覆的二氧化锆很难晶化,证明了包覆结构紧密.     

DRIFT study of the interaction of NO and O2 with the surface of Ce0.62Zr0.38O2 as deNOx catalyst

Gas–solid interactions and surface intermediates evolution after NO adsorption onto calcined Ce_0.62Zr_0.38O₂ were investigated. The results of adsorption and temperature-programmed desorption of NO were explained using diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) coupled with temperature-programmed experiments in environmental cell. Surface NO-containing species such as nitrites and nitrates were identified during evolution of NO on the surface of Ce_0.62Zr_0.38O₂ solid solution at low and high temperature. The ceria–zirconia solid solution was found to be active in deNO_x reaction in the presence of a “toluene, propene and propane” mixture.     

湿化学法制备氧化锆超滤膜及其表征

以湿化学法制备的纳米氧化锆晶粒悬浮液为原料,在管式陶瓷微滤膜上制备了ZrO2超滤膜,用TEM考察了ZrO2晶粒悬浮液的性质,用N2吸附-脱附法和SEM对膜的结构、形貌与孔径分布进行了表征,考察了氧化锆悬浮液的浓度对膜的完整性的影响,并用不同分子量的葡聚糖对膜的截留性能进行了考察.实验表明:用该方法制备出的ZrO2膜完整无缺陷,孔径在16 nm左右,对葡聚糖的截留分子量为42 000 Da.     

若干成纤工艺条件对氧化锆纤维坯体性能的影响

以氧氯化锆为主要原料,以氧化钇为相稳定剂,以醋酸和柠檬酸为有机助剂,采用溶胶凝胶法制备多晶氧化锆纤维。研究胶体黏度、氧化锆含量和甩丝盘转速对纤维坯体性能的影响。试验发现:当溶胶内氧化锆质量分数为27.62%左右、黏度为27 P左右时,制得的纤维坯体直径细且分布均匀;随着胶体黏度的上升,纤维的平均直径呈上升趋势;甩丝盘转速在4 000~5 500 r/min时,成纤性相对较好,且纤维的平均直径随着转速的增加而略有下降,而直径分布变化不明显。     

Effects of interparticle neck size on initiation of selective laser flash sintering of 8-YSZ

The influence of the interparticle neck radius to particle size ratio (X/R) on the laser energy required to initiate selective laser flash sintering (SLFS) in 8% yttria-stabilized zirconia (8-YSZ) is investigated. The interparticle neck radius ratio (X/R) is varied by pre-sintering powder compacts at temperatures ranging from 850°C to 1250°C to produce compacts with calculated X/R = 0–0.62. Experiments show that the onset laser energy to initiate SLFS initially decreases with X/R until X/R = 0.066, when the onset laser energy reaches a minimum. As X/R increases beyond 0.066, the onset laser energy increases. Finite element modeling is used to calculate the local current density and temperature in the neck region when SLFS initiates. When interparticle necks are small, the current density and Joule heating are substantially elevated near necks, resulting in a relatively low laser onset energy required for incipient current flow. When the interparticle neck size is increased, the laser onset energy for incipient current flow is increased because Joule heating in the neck region is lower, but locally high current density spreads into the interior of the particles more quickly with larger necks. These results provide valuable insights into the mechanisms responsible for the initiation of both SLFS and furnace-based flash sintering.     

Tetragonal reconstruction and monoclinic variants rearrangement during heat treatment in zirconia

An in situ monoclinic variants selection and rearrangement study on Y₂O₃–ZrO₂ coatings was conducted using electron backscattered diffraction. The sequence growth of variants with the correspondence of (100)_m ∼// (010)_t, [010]_m ∼// [001]_t, and [001]_m ∼// [100]_t (CAB-OR2) was found initially and converted to the 90°-rotated sequence growth with (100)_m ∼// (100)_t, [001]_m ∼// [001]_t, and [010]_m ∼// [010]_t (ABC-OR2) after heat treatment. In another coating, most of the variants first exhibited interleaving growth and changed to typically fourfold growth. This in situ evolution of both variants orientation relationship and arrangement revealed the effects of stress and stress relief on the martensitic transformation. Moreover, the variants selection might be diversified during the cyclic transformation, and the classical phenomenological theory could mainly be proved by the transformation triggered by temperature, instead of external stress. Furthermore, the variants orientation relationship was exactly confirmed by the tetragonal grain reconstructions. In particular, the orientation variation of reconstructed tetragonal grains was also found and could mainly be explained by the behavior of stress relief and dynamic recrystallization.     

Additive manufacturing of carbon fiber reinforced ceramic matrix composites based on fused filament fabrication

For the first time, carbon fiber reinforced ceramic matrix composites (CMC) were successfully fabricated by additive manufacturing (AM) using the fused filament fabrication (FFF) technology, filaments (“CF-PEEK”) with thermoplastic polyetheretherketone (PEEK) as the matrix and C-precursor, and carbon short-fibers (< 250 μm) as reinforcements. In order to prevent a re-melting of the as-printed CFRPs (C-fiber reinforced plastics) during pyrolysis at 1000 °C in N₂ensuring the freedom of design and complex parts, a prior crosslinking step at 325 °C with a dwell time of 48 h in air was introduced to stabilize and crosslink the CFRP. Due to the stabilization and the printing of degassing channels for the pyrolysis, near net shape and complex CMC parts with different C-fiber orientations (0°; ±45°; 90°) were obtained by the liquid siliconization infiltration process (LSI). The manufactured C/C-SiC parts were characterized regarding their microstructure and mechanical properties. The reinforcing C-fibers were successfully protected during the LSI-process and flexural strengths of almost 60 MPa were obtained.     

Factors governing segmentation crack characteristics in air plasma sprayed ceramics

Air Plasma Spray (APS) is an industrially popular coating technique implemented in vast domains of applications. Among the inherent defects in an APS coating, segmentation cracks have been recognized to enhance the strain tolerance and durability of thermal barrier coatings. However, segmented coatings also exhibit higher thermal conductivity and are susceptible external debris infiltration. Hence, to optimize the coating properties, it is necessary to have processing control over the incorporation of such segmentation cracks.In this study, segmentation characteristics (thickness to cracking and crack spacing) of multiple Yttria Stabilized Zirconia (YSZ) and Gadolinium Zirconate (GZO) coatings were analyzed. The correlations between the processing parameters and the mechanical properties of the coatings were identified, and the cumulative effect of such variations on the segmentation characteristics were observed. In addition, the experimental observations were reconciled with fracture theories in thin films to provide a comprehensive phenomenological interpretation of segmentation in APS coatings.