Characterization of ZrO2-Y2O3 thermal barrier coatings by Raman spectroscopy

Raman spectroscopy is shown to be a useful tool for the observation of phase transitions in Y₂O₃-stabilized ZrO₂ thermal barrier coatings. Data were collected in situ at temperatures up to 1050°C as a function of the Y₂O₃ content. Large hysteresis effects are observed in the phase transition temperatures.     

Preparation of ZrO2 and ZrO2-Y2O3 coatings on silicon carbide fibers

The formation of ZrO₂ and ZrO₂-Y₂O₃ coatings from hydrous metal oxide sols on Nicalon NLM 202 silicon carbide fibers is investigated in detail. The results indicate that the microstructure of the oxide layer and the surface morphology of the coatings depend on the physicohemical properties of the sol. Kinetic studies of the oxidation of uncoated and coated fibers at different Y₂O₃ contents demonstrate that the oxidation rate of silicon carbide fibers decreases with increasing coating thickness. The effect of oxidation on the phase composition of Nicalon cloth samples coated with ZrO₂ and ZrO₂-Y₂O₃ is examined.     

Laser processing of ZrO2 coatings

Potential materials for protective heat-resistant coatings are the so-called fragmentary porous ceramic layers penetrated by a net of microcracks. The fragments can be shifted easily during thermal cycling procedure, and the micro-cracks prevent the throughout crack propagation, which could destroy the coating. Laser surface processing of coatings is one of the effective ways to form the fragmentary layered structure.

The peculiarities of laser processing of ZrO₂+Y₂O₃ plasma sprayed coatings deposited onto the steel substrate with the Ni-Cr-Al-Y sub-layer alloy were investigated. The coatings were processed by CW CO₂ and Nd:YAG lasers (Fig. 1). The laser processing resulted in melting of the coating surface. The modified coating consisted of a number of macro fragments with sizes 200-500 μm and in turn they consisted of a number of micro-fragments with sizes 20-70 μm. Both types of the fragments are separated by wide (10-15 μm) or narrow (1-5 μm) cracks accordingly. The structure and some properties of the modified coatings such as heat-resistance, hardness, surface roughness, and tightness are investigated depending on the laser output parameters.     

氧化锆增韧HA/ZrO2功能梯度涂层的TEM分析

利用净能量控制的PRAXAIR4500型等离子喷涂系统,在钛合金基体上制备出HA/ZrO2功能梯度涂层,采用HTEM、XRD、SEM等对涂层过渡层ZrO2相的结构特征进行分析.结果表明:(1)富锆的过渡层存在ZrO2 3种晶型,主要以四方氧化锆为主,含有少量的立方氧化锆及微量的单斜氧化锆和CaZrO3,单斜氧化锆的出现说明材料内发生了四方氧化锆向单斜氧化锆马氏体相变,这种马氏体相变有利于提高HA材料的韧性;(2)生物活性功能涂层的富锆过渡层致密,与钛合金基体结合紧密,纯羟基磷灰石的表面层具有典型的多孔结构特征,整个涂层沿垂直基体方向从过渡层致密结构向表面层多孔结构过渡;涂层的这种结构特征有利于改善功能梯度涂层的综合性能,提高涂层与基体的结合强度,其结合强度达到48.6MPa.     

Temperature-dependent emissivity of coatings produced from mixtures of BaCO3 and TiO2 powders and ZrO2 micro- or nanoparticles

We have determined temperature-dependent emissivity of coatings produced from annealed mixtures of BaCO₃ and TiO₂ powders and ZrO₂ micro- or nanoparticles. The results demonstrate that the best coatings have been obtained using ZrO₂ microparticles.     

Effects of ZrO2 addition on phase stability and photocatalytic activity of ZrO2/TiO2 nanoparticles

ZrO₂/TiO₂ nanoparticles with various Zr/Ti ratios (0–0.9) were prepared by a polymer complex solution method (PCSM). The prepared samples were characterized using transmission electron microscopy (TEM), the Brunauer, Emmett & Teller (BET) method, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The ZrO₂/TiO₂ photocatalyst showed a high specific area and small crystal size. The XRD pattern for the Zr/Ti = 0.1 sample indicated that the addition of ZrO₂ stabilized the anatase phase of TiO₂ up to 800 °C. The photocatalytic activity of Zr/Ti = 0.1 sample was higher than that of the TiO₂ sample and commercially available Degussa P25. The high photocatalytic activity can be attributed to stronger adsorption in the visible light region, higher specific area, smaller crystal size and increased surface OH groups.     

ZrO2及ZrO2:CdS薄膜的制备和表征

利用ｓｏｌ－ｇｅｌ方法合成了ＺｒＯ_２薄膜,并通过在ＺｒＯ_２薄膜中复合ＣｄＳ纳米粒子成功地制备了ＺｒＯ_２：ＣｄＳ薄膜．制得的ＺｒＯ_２薄膜透明并具有较好的光透射性,而ＺｒＯ_２的含量及膜厚是影响其光透射性的主要因素．分散在ＺｒＯ_２：ＣｄＳ薄膜中的ＣｄＳ纳米粒子为六方相结构,并具有较好的分散性,其平均尺寸为４～６ｎｍ．实验结果表明：ＺｒＯ_２颗粒的晶化会对薄膜的光学性能及表面形貌产生影响,但ＣｄＳ的形成可以抑制薄膜表面ＺｒＯ_２颗粒的晶化,从而得到较为平滑的薄膜．     

Electrochemical ZrO2 and Al2O3 coatings on SiC substrates

SiC was electrochemically coated with ZrO₂ and with Al₂O₃ from 0.1 m aqueous solutions of metal-nitrate-hydrates with ethanol added. Amorphous zirconia and alumina coatings were formed with current densities from 10 to 70 mA cm^–2, and deposition durations of 1–60 min. The as-deposited coatings contained microcracks caused by drying shrinkage. Sintering of zirconia at 900 °C for 1 h and of alumina at 1200 °C for 2 h in air was accompanied by crystallization to a mixture of tetragonal and monoclinic phases in the former and to -alumina in the latter. The absence of intermediate phases between the coatings and the substrates and the good adherence of the sintered coatings indicate the high-temperature stability of these coatings.     

Mechanical treatment of TiO2 and ZrO2 oxide mixtures

The mixed ZrO2-TiO2 system (5-50 wt% of ZrO2) has been studied to investigate the influence of the mechanical treatment on its physicochemical properties depending on the composition, time of milling (5, 10 and 20 min, r.p.m. 82) and temperature (400, 550 and 700 degrees C). Samples were characterized by Raman spectroscopy, X-ray powder diffraction, Scanning Electron Microscopy coupled with Energy Dispersion X-ray analyzer, High Resolution-Transmission Electron Microscopy and nitrogen adsorption porosimetry. Results show that srilankite (TiZrO4) phase has been produced. No influence of the milling time and temperature on the phase composition is observed. The presence of zirconia increases the thermal stability of anatase phase up to 700 degrees C hindering the anatase rutile phase transformation.     

Nano-crystallization and surface analysis of electrolytic ZrO2 coatings on Co-Cr alloy

Zirconia coatings were formed on Co-Cr substrates by electrolytic deposition. The microstructure of electrolytic zirconia-coated films on Co-Cr substrates was examined. According to the results of ESCA, the bonding energies of ZrO₂ coating surface layer which changed with the annealing temperature from 400 °C, 500 °C to 600 °C are attributed to amorphous (a), tetragonal (t) and monoclinic (m) structure, respectively. The X-ray diffraction (XRD) of the coatings on the Co-Cr substrates annealed at 400, 500 and 600 °C revealed the major crystallization from m through t and then to m+t. However, TEM observations clearly showed that the interface layer of the coatings were nanosize crystallites, first the formation of tetragonal and monoclinic ZrO₂ structures. These different phase transformations are mainly due to the different surface energy of ZrO₂ coating in air, in bulk or on Co-Cr alloy. © 2001 Kluwer Academic Publishers     

TiO2/ZrO2复合陶瓷膜的性能研究

采用反相微乳液法制备TiO2/ZrO2复合微乳液,并以其作为前驱体制得TiO2/ZrO2复合膜。研究了复合膜的机械性能、表面形貌及杀菌性能。由扫描电子显微镜观察到TiO2/ZrO2的复合膜中微粒以棒状形式分布。杀菌实验测试结果表明其对大肠杆菌有很好的杀菌效果,灭菌率达98%~99%。     

Microstructure and phase composition of ZrO2-CeO2 thermal barrier coatings

The microstructure and phase composition of zirconia plasma-sprayed thermal barrier coatings containing 12 to 25 wt% ceria addition have been investigated. Coatings containing less than 20 wt% CeO₂ are composed of a monoclinic and retained metastable transformable tetragonal phase due to the constraint developed by the small crystal size. This phase transforms readily under moderate thermal stresses. Compositions greater than 20 wt% CeO₂ are composed only of a metastable non-transformable tetragonal, tz′ structure, resistant to transformation under thermal or mechanical stresses. The microstructure of this phase shows microstructural similarities to the high-yttria t′-phase in the ZrO₂-Y₂O₃ system, such as transformation twins and anti-phase boundaries. This suggests that the phase observed in the ZrO₂-CeO₂ system forms by a similar mechanism.     

Cast aluminium alloy containing dispersions of TiO2 and ZrO2 particles

Up to 4 wt% of ultrasonically-pretreated titania and zirconia particles (5m average size) were dispersed in Al-11.8 wt% Si-1 wt% Mg alloy castings. The technique employed to prepare the cast composites involved mechanically mixing pretreated oxide particles in aluminium alloy melts in the presence of magnesium, followed by casting the resulting mix in permanent moulds. Pretreatment of the oxide particles consisted of agitating the particles in acetone by ultrasonic vibrations to cause the disintegration of agglomerates and the removal of adsorbed water molecules from the particle surfaces. Infra-red (i.r.) spectroscopy of powders showed desorption of water molecules from oxide surfaces by ultrasonic pretreatment in acetone. Ultrasonic pretreatment of oxide particles before their incorporation into the melt and presence of magnesium in the melt were found to be necessary to disperse TiO₂ and ZrO₂ particles in molten Al. Microscopic studies of the composites indicated dispersed TiO₂ and ZrO₂ particles which exhibited a reaction zone at the periphery of the particles, and microprobe X-ray elemental analysis confirmed preferential segregation of magnesium at the particle-matrix interface. The composites exhibited an increase in hardness as a result of dispersions of titania and zirconia particles, while the tensile-strength values of composites were comparable with that of the base alloy.     

Synthesis of ZrO2 and TiO2 nanocrystalline powders by hydrothermal process

In present work, nanocrystalline zirconia and titania were synthesized by hydrothermal treatment of zirconyl ZrO(NO₃)₂ and titanyl TiO(NO₃)₂ nitrates aqueous solutions and amorphous gels of the corresponding hydroxides. The hydrothermal synthesis was performed in a wide range of temperatures (150–250 °C), concentration of starting solutions (0.25–0.5 M) and duration of the process (from 10 min to up to 24 h). The hydrothermal treatment at high pressure about 2.0–4.0 GPa was also carried out. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and BET. Particle sizes, morphology and properties of the products were investigated. The influence of hydrothermal synthesis conditions on ZrO₂ and TiO₂ phase compositions were established.     

Ultrasonically Activated Hydrothermal Synthesis of Fine TiO2 and ZrO2 Powders

Fine TiO₂ and ZrO₂ powders were prepared by hydrothermal synthesis at 150 and 250°C (10 min, 1 h, 3 h) from aqueous titanyl and zirconyl salts and amorphous titanyl and zirconyl hydroxide gels with and without ultrasonic activation. The synthesized materials were characterized by x-ray diffraction, scanning and transmission electron-microscopic techniques, and nitrogen capillary adsorption measurements. The results demonstrate that ultrasonic activation of the hydrothermal process markedly accelerates the crystallization rates of the amorphous titanyl and zirconyl hydroxides and raises the content of thermodynamically stable phases in the reaction products. It is also shown that hydrothermal treatment of amorphous cobalt(II) hydroxide leads to its crystallization, whereas ultrasonic–hydrothermal treatment results in partial Co(II)-to-Co(III) oxidation, yielding a mixture of Co(OH)₂ and Co₃O₄.     

纳米二氧化钛/硅胶光催化剂的制备与性能研究

采用溶胶 凝胶法在硅胶载体上制备了纳米二氧化钛 ,研究载体表面负载二氧化钛的结构、表面形态及其光催化性能。实验发现 ,包覆在硅胶表面的二氧化钛大小为 2 0～ 30nm ,且分布均匀 ,晶型为锐钛矿相 ,以甲基橙作为降解对象研究所制备样品的光催化性能。