不同形貌超细碳酸锶粒子制备研究进展

对目前国内外不同形貌超细碳酸锶粒子的制备情况做了简要的综述.重点介绍了球状、针状、纺锤状、片状、哑铃状、橄榄状等不同形貌超细碳酸锶粒子的制备方法.最后对制备过程中晶形控制剂对粒子形貌进行调控的机理做了初步的探讨.     

Phase transformation of 316L stainless steel from wire to fiber

In this work, quantitative crystalline phase analysis of 316L stainless steel from wire to fiber using a multi-pass cold drawing process was studied using the Rietveld whole XRD profile fitting technique. The different diameters of the fibers: 179, 112, 75, 50, 34, 20, and 8 μm, were produced from an as-received wire with a diameter of 190 μm. The crystalline phases were identified using MDI Jade 5.0 software. The volume fractions of crystalline phases were estimated using a Materials Analysis Using Diffraction software. XRD analysis revealed that the crystal structure of as-received wire is essentially a γ-austenite crystalline phase. The phase transformation occurred during the 316L stainless steel from wire to fiber. Three crystalline phases such as γ-austenite, α′-martensite, and sigma phase of the fine fiber were observed. A cold drawing accelerates the sigma phase precipitates, particularly during the heat treatment of the fiber.     

Phase transformation in Cu-Cr-Zr-Mg alloy

After solid solution treatment, the effects of aging processes on the microstructure and electrical conductivity of Cu-Cr-Zr-Mg lead frame alloy were investigated in order to determine the phase transformation and the time-temperature-transformation (TTT) behavior. The results show that aged at 470 °C the fine precipitation of an ordered CrCu₂(Zr,Mg) phase is found in copper matrix as well as fine Cr and Cu₄Zr, aged at 550 °C the phase CrCu₂(Zr,Mg) is decomposed into Cu₄Zr and Cr phase, aged at 600 °C the precipitates is bcc Cr only. The phase transformation kinetics equation was deduced from the Avrami empirical formula based on the linear relationship between the electrical conductivity and the volume fraction of the phase transformation.     

Allotropic phase transformation of pure zirconium by high-pressure torsion

Pure Zr is processed by high-pressure torsion (HPT) at pressures in the range of 1–40 GPa. A phase transformation occurs from α to ω phase during HPT at pressures above 4 GPa while the total fraction of ω phase increases with straining and saturates to a constant level at higher strain. This phase transformation leads to microstructural refinement, hardness and strength enhancement and ductility reduction. Lattice parameter measurements confirm that c for α phase is expanded about 0.6% by the presence of ω phase. The temperature for reverse transformation from ω to α phase increases with straining and thus, straining under high pressure increases thermal stability of ω phase. The ω phase obtained by HPT is stable for more than 400 days at room temperature.     

Preparation,characterization and dielectric behaviour of some yttrium doped strontium stannates

Samples of Sr_{(1− 3x/2)}YxSnO₃ are prepared by usual solid state reaction route. X- ray diffraction studies confirm the formation of single cubic perovskite single phase. The dielectric constant and dielectric loss at 1 kHz were measured in the temperature range from room temperature up to -150†C. The dielectric constant decreases and losses increase with increased yttrium content in the samples. The percentage porosity and unit cell parameters are also calculated for the samples.     

Effects of hydrogen on phase stability of ytterbium doped strontium cerates

The effect of hydrogen on the phase stability of both SrCe_0.95Yb_0.05O_3 − α, (SCYb-5) powder and disk samples in both dry and wet hydrogen atmospheres was investigated. It was found that decomposition of the perovskite phase was especially evident in the disk samples treated in a dry hydrogen atmosphere, probably due to reduction of the tetravalent cerium ions to trivalent cerium ions in the sample. It was interesting to find that the extent of the decomposition of the perovskite phase was most influenced by the status (i.e. either disk or powder form) of the SCYb-5 samples, rather than the temperature or the extent of the reducing atmospheres. The findings of this study indicate that relaxation kinetics may play an important role in the phase stability of perovskite materials.     

Phase transformation and thermomechanical characteristics of stretched polyvinylidene fluoride

Phase transformation and thermomechanical characteristics of the polyvinylidene fluoride (PVDF) are investigated using a microtesting machine and a thermomechanical analyzer. The phase transformation from the - to β-phase of the PVDF resulted from increased PVDF chain length caused by the stretching procedure. The results show that the phase transformation changed due to increased stretching ratios with smaller changes for stretching ratios over 4. Young's modulus along the stretching direction was higher than that along the transverse of stretching. The thermomechanical curve variation can be divided into two parts: one part is a gradual slope before about 50 °C, and the other is similar to exponential growth. Thermomechanical change, thermal elongation, and expansion greatly influence the stretching ratios of 5 in the stretching direction. The higher stretching ratio easily causes the shrink influence of the material due to the higher cohesion of the amorphous regions. Therefore, the observed results can provide useful information to optimize for piezoelectric or pyroelectric PVDF applications.     

微裂纹对相变陶瓷的相变条件及强度的影响

相变临界条件的研究是相变增韧的关键，材料内大量存在的微裂纹是影响相变陶瓷性能的重要因素。本文用作者改进的等效夹杂理论，研究相变陶瓷中微裂纹对材料强度的影响，建立在外载作用下的相变临界条件。通过Ａｌ_２Ｏ_３／ＺｒＯ_２陶瓷的三点弯曲实验，验证了本文理论模型的合理性。     

Phase transformation behavior of porous NiTi alloy fabricated by powder metallurgical method

Nickel titanium shape memory alloys (NiTi-SMAs) were successfully produced from elemental Ni/Ti powders by powder metallurgical method and then subjected to age treatment. Microstructure was examined by SEM and XRD and phase transformation temperatures were measured by dilatometric method. The phase transformation temperatures increased with both duration and temperature of the age treatment. The porous product exhibited desirable shape memory effect.     

Mechanical and optical studies on pure and nitro doped 4-hydroxyacetophenone

Single crystals of pure and nitro doped 4-hydroxyacetophenone (NLO material) were grown by slow cooling technique. The single crystals were subjected to studies of Vicker's microhardness. The Vicker's hardness increases with the increase in applied load. The UV cut off wavelength of the grown crystals has been measured as about 280 nm from the optical transmission spectra of the samples. Chemical etching has also been carried out.     

Si-B-O系BST玻璃陶瓷制备及介电弥散研究

采用硝酸钡、硝酸锶、钛酸丁酯、正硅酸乙脂和硼酸三正丁脂为原料的溶胶凝胶方法制备了Si-B-O系BaxSr1-xTiO3玻璃陶瓷。通过差热分析(DTA)、热失重(TG)、X射线衍射(XRD)分析Si-B-O系BST玻璃陶瓷超细粉体合成过程及其相结构变化。采用X射线衍射(XRD)、扫描电子显微镜(SEM)描述Si-B-O系BST玻璃陶瓷烧结体的相结构和显微组织结构变化。阻抗分析仪测量Si-B-O系BST玻璃陶瓷的-50～100℃介电温谱。实验结果表明：Si-B-O系BST玻璃陶瓷粉体的相结构为立方钙钛矿相结构,其合成温度为700℃．不存在第二相。Si-B-O系BST玻璃陶瓷的烧结温度低于传统工艺。Si-B-O系BST玻璃陶瓷的显微结构呈细晶结构。Si-B-O系BST玻璃陶瓷的介电常数ε随着烧结温度升高而增大．介电损耗tgδ随测试温度的增加而降低。随着晶粒平均尺寸的减小．Si-B-O系BST玻璃陶瓷样品的介电峰变低．平坦．宽化．存在介电峰弥散化的现象。     

Phase transformation and grain growth of doped nanosized titania

The influence of altervalent cation doping of TiO₂ on its phase transition and grain growth has been investigated. It is shown that dopants like Fe³⁺, Si⁴⁺, V⁵⁺, Ru³⁺ and Ni²⁺ affect the phase transition temperature of the titania host, and that significant variation is observed for silicon doping. Iron titanium oxide and nickel titanium oxide phases were found in the iron-doped and nickel-doped system, respectively, at elevated calcination temperatures, while other doped systems only show the modifications of anatase and rutile at the observed range of calcination temperature and dopant content. Compared with the pure TiO₂, grain growth is arrested for the iron-doped and silicon-doped systems, and this tendency is especially distinct in the silicon-doped system.     

Growth and characterization of pure and lithium doped strontium tartrate tetrahydrate crystals by solution-gel technique

The effect of lithium ion as dopant on the size and transparency of strontium tartrate tetrahydrate (SrC₄H₄O₆·4H₂O) crystals are presented in this paper. Growth of single crystals of undoped and lithium doped strontium tartrate tetrahydrate by controlled diffusion of strontium nitrate into the gel charged with tartaric acid at room temperature are narrated. The lithium ion enhances the size and transparency of the doped crystals. The crystal structure of the compound was confirmed by X-ray diffractometry and dopant concentration with ICP-atomic emission spectrometer system. Thermal decomposition of the grown crystals is investigated by TGA and DTA studies. The FTIR spectra of pure and doped crystals are recorded and analysed. Kurtz powder technique has been used to test SHG efficiency of the crystals.     

Phase transformations—a physicist’s perception

Echoing a recent remark by Prof. Ramaseshan, a perspective review is made of the field of phase transformation, highlighting areas that might appeal to physicists. Prominent in this category are the study of ground state structures, the study of phase diagrams and the study of kinetic phenomena. Enumeration of ground state structures calls for inputs from group theory as well as reliable potentials, and physicists are therefore well equipped to make significant contributions. The theoretical analysis of phase diagrams (concerning which much experimental information already exists) raises challenging questions in equilibrium statistical mechanics. Since the problems map to Ising models of varying complexity and their generalizations, there are also very interesting connections to magnetism. Lately, computer simulation has added a new dimension, opening up fresh vistas both for theory and experiments. The study of kinetics belongs to the newly emerging area of non-equilibrium statistical mechanics. The focus being ontemporal phenomena, physicists can play a key role, particularly through the application of various types of relaxation spectroscopy. On the theoretical side too there are challenging problems, especially on account of the dominance of nonlinearities. Indeed if one is bold enough, one could even speculate on possible universalities underlying the complex microstructures invariably seen in late-stage evolution. In short, though the subject of phase transformations has thus far been nursed predominantly by metallurgists, there is enough room for physicists to make an independent entry and to make distinctive contributions. This paper was originally prepared for the 60th birthday volume of Prof. S Ramaseshan.     

Thermodynamic Functions and Phase Transformation of Metal Nanocrystals

1.IntroductionNanocrystalline materials have attracted increasingscientific interests since they emerged in the late80s',be-cause of their unusual physical and chemical propertiesthat are normally attributed to the ultrafine grains.Thespecial properties of nanocrystalline materials are essen-tially connected with both thermodynamics and dynam-ics of the formation of nano materials.However,it hasshown that traditional thermodynamic and phase trans-formation models cannot satisfactorily describe…     

Phase transition and PTCR effect in erbium doped BT ceramics

In this work the dielectric behaviour and main features of the phase transition of BaTiO₃ and Ba_0.99Er_0.01TiO₃ ceramics were carefully investigated. The temperature and frequency dependences of the dielectric properties of erbium doped BaTiO₃ ceramics were measured in the 25–225 °C and 100 Hz to 10 MHz ranges, respectively. From this study, a dielectric anomaly in the ferroelectric–paraelectric phase transition of the Ba_0.99Er_0.01TiO₃ ceramic was observed. The features of the samples phase transition were analysed by using Curie–Weiss, Santos–Eiras’ and order parameter local phenomenological models. In the BaTiO₃ system, all models showed a normal phase transition, while was not possible to establish the character of the phase transition in the Ba_0.99Er_0.01TiO₃ system. The relaxation parameters of conductive processes for the study ferroelectric materials, analysed in the time domain, did not show any influence on the ferroelectric–paraelectric phase transition. Finally, it was demonstrated that the anomaly observed on the phase transition of the erbium doped BaTiO₃ ceramics is associated with the processes that results in the PTCR effect.     

A new type face-centered cubic zirconium phase in pure zirconium

So far,only two orientation relationships (OR) between hexagonal close-packed (HCP) (α phase) and face-centered cubic (FCC) structures in zirconium and titanium alloys have been reported.Here a new type FCC phase (named γphase) with OR:< 11(2)0 >αll< 100 >γ and {0001}αll{002}γ was observed for the first time in annealed pure zirconium by means of transmission electron microscopy (TEM) technique.The α→γphase transformation can be accomplished via expansion along[1(1)00]direction and slip of Shockley partial dislocation with 1/3[1(1)00]on (0001) basal planes.