Hydrothermal preparation of nanosized cubic ZrO2 powders

Journal of Materials Science Letters -     

Crystallization studies of ZrO2−SiO2 composite gels

Composite ZrO₂−SiO₂ powders were prepared using a gel route. Morphological and crystallographic features of ZrO₂ particles formed during the heat treatment, and the particle sizes of the composites have been investigated. The following polymorphic changes have been observed during the heat treatment: amorphous → metastable-cubic/tetragonal ZrO₂ → tetragonal ZrO₂ → monoclinic ZrO₂. SiO₂ crystallizes above 1273K. The martensitic transformation of ZrO₂ (t → m) was observedin situ, when exposed to a high-energy electron beam. These results are important in the production of ZrO₂-toughened ceramics of controlled microstructure.     

氧化锆对聚丙烯非等温结晶动力学的影响

以不同含量的氧化锆(ZrO2)作为成核剂对聚丙烯进行改性,通过差示扫描量热(DSC)方法研究改性聚丙烯的非等温结晶动力学,对所得数据分别用修正Avrami方程、Jeziorny法进行处理。实验结果表明:氧化锆的加入使聚丙烯在较高的温度下就可以产生结晶现象,氧化锆具有明显的成核作用;氧化锆的加入并未改变聚丙烯的成核和生长机理,但降低了聚丙烯的结晶活化能。     

Formation and hot isostatic pressing of ZrO2 solid solution in the system ZrO2-Al2O3

In the system of ZrO₂-Al₂O₃, cubic ZrO₂ solid solutions containing up to 40 mol% Al₂O₃ crystallize at low temperatures from amorphous materials prepared by the simultaneous hydrolysis of zirconium and aluminium alkoxides. At higher temperatures, they transform into tetragonal solid solutions. Metastable ZrO₂ solid solution powders containing 25 mol% Al₂O₃ have been sintered at 1000–1150 °C under 196 M Pausing the hot isostatic pressing technique. The solid solution ceramics consisting of homogeneous microstructure with an average grain size of 50 nm exhibited a very high fracture toughness of 23 MN m ^–1.5. They have been characterized by X-ray diffraction and electron probe surface analyses.     

Preparation and properties of cubic ZrO2 stabilized with Ni(II)

Samples of cubic stabilized ZrO₂ have been prepared by the code-composition of nickel nitrate and zirconyl nitrate at 500°C. A comparison of the stability towards reduction of the bulk NiO and the Ni(II) in the cubic stabilized ZrO₂ deomstrates the influence of the stabilization of cubic ZrO₂ with Ni(II).     

Control the polymorphism and morphology of calcium carbonate precipitation from a calcium acetate and urea solution

Two metastable calcium carbonate polymorphs, rod-like aragonite and spherical vaterite are selectively formed in this study. Aragonite rods were synthesized from a calcium acetate (Ca(AC)₂) and urea (CO(NH₂)₂) solution under a given condition. In contrast, the addition of polyacrylamide (PAM) and oleic acid results in the formation of spherical vaterite. The morphology, size and crystal structure were characterized by means of Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and X-ray diffraction (XRD). The results show that PAM and oleic acid can be used as additives to select the polymorph from aragonite and vaterite. The contact angle of the modified products reached 112.49°. We have succeeded in surface modification of particles in situ at the same time.     

Determination of the monoclinic, tetragonal and cubic phases in mechanically alloyed ZrO2-Y2O3 and ZrO2-CoO powder mixtures by Raman spectroscopy

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Crystal growth of tetragonal ZrO2 in the glass system ZrO2-SiO2 prepared by the sol-gel process from metal alkoxides

Glasses in the system ZrO₂-SiO₂ containing 40 to 60 mol % ZrO₂ were prepared by the sol-gel process from metal alkoxides. Tetragonal ZrO₂ was precipitated by heat treatment at 800 and 1200° C, and its crystal growth was measured by differential thermal and X-ray diffraction analyses. At 800 to 900° C, tetragonal ZrO₂ crystals grew three-dimensionally and the activation energy for growth was calculated as about 680 kJ mol⁻¹. On the other hand, the secondary growth of tetragonal ZrO₂ at 1000 to 1200° C followed the cube-root-of-time law. The activation energy for secondary growth was about 380 kJ mol⁻¹. It is suggested that the diffusion of Zr⁴⁺ ions is the rate-limiting process for the secondary crystal growth of tetragonal ZrO₂.     

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.     

正交实验优化ZrO2包覆钛白粉工艺研究

采用L9(34)正交实验优化实验方案,以六偏磷酸钠(SHMP)为分散剂,滴加速率、分散剂用量、包膜量、体系pH值作为实验变量,研究ZrO2包覆对金红型石钛白粉性能的影响。通过Nano-zs电位仪(zeta)、扫描电子显微镜(SEM)、傅里叶红外(FT-IR)、透射电子显微镜(TEM)、物理漆膜紫外老化实验的检测,对金红石钛白粉包覆前后的性能进行比较,得到ZrO2包覆的优化试验条件。结果表明,其在滴液速率为5滴/min,分散剂的用量为0.1%,包膜量为2%,体系pH值为8.5～9.0条件下,经过包膜过后的金红石型钛白粉化学性质稳定,能有效屏蔽其光化学活性,其吸附性、分散性、耐候性较好。     

煅烧工艺对溶液燃烧合成超细ZrO2粉末的影响

以硝酸锆-尿素为原料,采用溶液燃烧合成(SCS)法制备了超细ZrO2粉末,着重研究了后续煅烧处理对合成的ZrO2粉末结构、尺寸和团聚程度的影响.结果表明,利用SCS法可以合成超细ZrO2粉末,对之进一步进行煅烧处理,可明显降低合成产物中残留有机物的含量,并改善合成粉末的分散性;在700℃煅烧1.0h的条件下,可以获得分散性好,粒径小(＜200nm)的ZrO2粉末.     

Solid solutions of metastable tetragonal ZrO2 and Ce3ZrO8 in the system ZrO2-CeO2

In the system ZrO₂-CeO₂, metastable t-ZrO₂ solid solutions containing up to 30 mol% CeO₂ crystallize at temperatures of 385–430 °C from amorphous materials prepared by the hydrazine method. Crystalline Ce₃ZrO₈ solid solutions are formed in as-prepared powders between 30–75 mol % CeO₂. The variation of the lattice parameters of both solid solutions is determined as a function of CeO₂ content. The value of the lattice parameter of pure Ce₃ZrO₈ (cubic) is a = 0.5342 nm. Detailed characterization of the Ce₃ZrO₈ powder has been performed. Crystallite size and particle size are strongly dependent on the heating temperature. Specific surface areas do not drop below 40 m²g^–1 until the heating temperature is above 1000°C.     

An approximate 2-D solution for the shear-induced strain fields in eigenstrained cubic materials

Summary An approximate analytical 2-D solution for the strain field components ₁₁, ₁₂ and ₂₂ occurring in a cubic material due to a coherently bonded shear eigenstrained inclusion of cylindrical geometry was obtained by means of Continous Fourier Transforms (CFT). A Discrete Fourier Transform (DFT) based numerical model was used in order to test the validity of the results. For the case where the cylindrical inclusion and the surrounding media are elastically homogeneous and the orientation of their principal crystal axes are the same, a correlation between the analytical and numerical models is demonstrated, both for strongly and weakly anisotropic materials. Moreover, the strain fields within the inclusion are shown to be of homogeneous isotropic type. Finally, an expression for the closed-form strain energy of two cylindrical inclusions at arbitrary radius and angle was derived, and then used to determine the minimum energy configuration for the system.Dedicated to Professor Krzysztof Wilmanski on the occasion of his 60th birthday     

Synthesis of dispersed ZrO2 nano-laminae composed of ZrO2 nanocrystals

Dispersed ZrO₂ nano-laminae were synthesized at low temperature using zirconium oxynitrate and polyvinyl pyrrolidone (PVP) as reaction materials. High-resolution transmission electron microscopy (HRTEM) of individual ZrO₂ nano-laminae showed that each piece of ZrO₂ nano-laminae was assembled by large numbers of ZrO₂ nanocrystals. The bulk dispersed ZrO₂ nano-laminae could be observed in situ from scanning electron microscopy (SEM) images. The results of X-ray diffraction (XRD) showed that the crystallographic phase of ZrO₂ nano-laminae was cubic ZrO₂. Experiments indicated that the morphologies and phase composition of ZrO₂ nano-laminae were affected by the calcined temperature. PVP plays an important role in the formation process of dispersed ZrO₂ nano-laminae.