Structural modifications in phillipsite-rich tuff induced by thermal treatment

A phillipsite-tuff from the South of Tenerife (Canary Islands) has been treated at several temperatures between 150 and 600°C, and the induced structural changes have been studied by different techniques: FTi.r., XRD, d.g.t.—d.s.c., and porosimetry. Results show an aluminum migration toward the surface, creating amorphous zones and new—OH groups. The pore size and the zeolite framework undergo a reduction, and the β angle of the unit cell rotates as a consequence of the heating.     

Structural modifications induced by ion implantation in metals and polymers used for orthopaedic prostheses

Abstract

Ti–6Al–4V titanium alloy, AISI 316L stainless steel, and UHMW (ultrahigh molecular weight) polyethylene are commonly used as friction materials in orthopaedic joint prostheses. The most interesting property of the titanium alloy is its high corrosion fatigue resistance. However, its friction and wear behaviour is unsatisfactory, even when rubbing against a soft material such as polyethylene; it cannot be used without a surface treatment. The 316L stainless steel has superior friction and wear characteristics, but its mechanical properties are inferior and crevice corrosion is often associated with wear. The UHMW polyethylene wears and flows. Wear is related to the surface properties, whereas creep is linked to the bulk mechanical properties. Ion implantation is a surface treatment mainly used in industry for increasing the wear resistance of metals, such as in cutting tools, and for changing the electrical or optical properties of ceramics and polymers. In the present work, the technique is applied to orthopaedic materials, to improve their surface properties and to increase the lifetime of the prostheses. The treatment does not deteriorate the bulk characteristics of the materials. As far as metals are concerned, structural modifications are produced in a thin layer of <1 μm thickness. They depend on the implantation parameters, namely, nature of the ions, energy, dose, and temperature, and are analysed using glow discharge spectrometry and grazing incidence X-ray diffraction. For polymers, ion implantation leads to two different effects: a modification of the first atomic layers, which induces an increase in wettability, and a variation of the structure at greater depths, which influences the mechanical properties. These effects are analysed using specific methods such as electron spectroscopy for chemical analysis, electron spin resonance, and attenuated total reflectance infrared spectroscopy.

MST/1689     

Structural modifications simulated by virtual distortions

A numerical strategy for the simulation of structural modifications by virtual distortions is proposed. Two cases of structural modification are considered: the first concerns modifications of material distribution, and the second modifications of local constitutive relations (e.g. unilateral constraints for stresses or deformations). A formaulation of the fundamental equations of the simulation method is presented. These equations are applicable to the general structural modification problem of a truss-like structure. Then numerical algorithms which refer to particular applications, such as progressive collapse analysis or the analysis of structures with gaps, are discussed. The versatility of the method is illustrated with a number of examples, and the computational advantages of structural modification by the virtual distortion method are discussed.     

Structural and spectroscopic modifications of nanocrystalline zinc oxide films induced by swift heavy ions

Structural and spectroscopic modifications of nanocrystalline (nc) ZnO films induced by Swift heavy ion (SHI) irradiation is reported. Films were irradiated at incremented ion fluences. Structural study reveals that the nanocrystals become more oriented at low fluences, while a release of strain and decrease in grain size is observed at high fluence. The surface morphology study also shows a decrease in crystallite size and agglomeration of grains at high fluence. On the other hand micro-Raman and Fourier transform infrared (FTIR) results show that the longitudinal optical (LO) mode is strengthened and red shifted, while the transverse optical (TO) mode get dampened at high fluence. But the amorphization of crystallites was not observed under the used irradiation conditions. The observed structural and spectroscopic modifications are explained in terms of high density of lattice defects and disorder created by dense electronic excitations induced by SHI irradiation.     

Structural and spectroscopic modifications of nanocrystalline zinc oxide films induced by swift heavy ions

Structural and spectroscopic modifications of nanocrystalline (nc) ZnO films induced by Swift heavy ion (SHI) irradiation is reported. Films were irradiated at incremented ion fluences. Structural study reveals that the nanocrystals become more oriented at low fluences, while a release of strain and decrease in grain size is observed at high fluence. The surface morphology study also shows a decrease in crystallite size and agglomeration of grains at high fluence. On the other hand micro-Raman and Fourier transform infrared (FTIR) results show that the longitudinal optical (LO) mode is strengthened and red shifted, while the transverse optical (TO) mode get dampened at high fluence. But the amorphization of crystallites was not observed under the used irradiation conditions. The observed structural and spectroscopic modifications are explained in terms of high density of lattice defects and disorder created by dense electronic excitations induced by SHI irradiation.     

抽空涂晶法合成A型分子筛膜及渗透汽化性能研究

采用抽空涂晶二次生长法在管状α-Al2O3基膜上合成了具有高选择性、高渗透量的A型分子筛膜.XRD结果表明,分子筛膜晶相中只有A型分子筛存在;SEM表明,基膜表面覆盖了一层致密连续的分子筛膜.考察了A型分子筛膜的渗透汽化性能,结果表明,在温度为323K和343K下,当原料液中异丙醇的质量分数为95%时,其水/异丙醇分离系数都大于10000,渗透量分别为1.27kg/(m2·h)和1.74kg/(m2·h).     

渗透汽化脱水分子筛膜的制备与应用研究

开发了擦涂-浸渍涂晶法和亚微米晶种诱导制备NaA分子筛膜技术,有效地提高了膜的成品率、缩短了合成时间,获得了适合规模化生产的制膜工艺。通过分子模拟的方法,对有机溶剂和水在分子筛膜中的传质机理进行了探讨。对NaA分子筛膜在体系中的水热、酸碱和盐稳定性进行了系统地研究,提出了相应的预处理工艺,并设计建造出渗透汽化工业应用装置,实现了长时间稳定运行。     

Structural dynamic modifications via models

Structural dynamic modification techniques attempt to reduce dynamic design time and can be implemented beginning with spatial models of structures, dynamic test data or updated models. The models assumed in this discussion are mathematical models, namely mass, stiffness, and damping matrices of the equations of motion of a structure. These models are identified/ extracted from dynamic test data viz. frequency response functions (FRFs). Alternatively these models could have been obtained by adjusting or updating the finite element model of the structure in the light of the test data. The methods of structural modification for getting desired dynamic characteristics by using modifiers namely mass, beams and tuned absorbers are discussed.     

亲水性沸石膜在异丙醇脱水中的应用及其耐酸性研究

采用二次生长法,在α-Al2O3陶瓷管上制备亲水性NaA、T型、ZSM-5沸石膜,采用SEM对其进行表征.比较3种亲水性膜在异丙醇/水体系的渗透汽化性能,考察其在不同的料液温度下对异丙醇的分离效果.通过优化膜合成液中Si/Al和F-/Si的摩尔比、合成时间等条件,提高ZSM-5沸石膜的渗透汽化性能.分析考察膜的耐酸性能,结果显示ZSM-5沸石膜具有良好的耐酸性;将ZSM-5沸石膜在pH为5.8的酸性溶液浸泡10天后,用于97%的乙酸乙酯/水体系中渗透汽化脱水,渗透液水含量可达99.59%,渗透通量可达0.12kg/(m2·h),分离因数高达7 894.     

沸石分子筛膜苛刻环境有机物脱水的研究进展

苛刻环境酸性条件下有机物的脱水在工业上有重大需求.尽管NaA沸石分子筛膜渗透蒸发在中性温和条件下乙醇等有机物脱水已经实现了工业化,但沸石分子筛膜有机酸的脱水或强酸性条件下(pH<3)的有机物的脱水在国际上刚刚起步,面临的关键技术问题是沸分子筛膜的耐酸性和膜的通量极低.对国际上酸性条件下有机物脱水沸石膜的研究现状进行了简要的概述和分析,介绍了功能化修补法高性能MOR沸石膜的研制等,及我们在这领域所做的各种尝试和取得的成果,指出沸石膜微结构的调控是高性能乙酸脱水分离膜制备的关键,对未来发展予以展望.     

Structural modifications of the superconducting phases on Bi system by electron beam irradiation

Superconducting samples of the Bi(Pb)-Sr-Ca-Cu-O system have been irradiated in transmission electron microscopy (TEM) to investigate the effect of a relative high fluence of electrons with 75 and 100 keV energy on the microstructure of the material. The diffraction pattern images show a dramatic change from very uniform lattice spots atab crystalline planes to a circular pattern corresponding to damage and breaking of the materials in very small crystallites.     

Modifications of the phosphate coatings microcrystalline structures induced by dehydration and rehydration processes

Bare and electrogalvanized steel sheets were subjected to phosphatation in three different phosphatation baths. The aim of the work was to characterize and to compare the behaviour of pure hopeite, phosphophyllite and manganese modified hopeite crystals during dehydration and rehydration processes. Scanning electron microscopy, thermal analysis and X-ray diffractometry were employed to study the obtained phosphate coatings. Thermogravimetric analysis showed that all the considered phases underwent the total loss of two water molecules above 150° C. X-ray diffraction measurements showed the formation of bihydrated phases which appear very similar independently from the use of the phosphatation bath. After exposure to a hydrating environment only the pure hopeite bihydrated crystals underwent a rehydration process which led to the tetrahydrated phase and consequently to a decreased paint-phosphate adhesiveness. On the contrary both the bihydrated phosphophyllite phase and the bihydrated manganese modified hopeite phase revealed their inability to return to the completely hydrated crystal and consequently improved paint adhesion.     

High performance dehydration of ethyl acetate/water mixture by pervaporation using NaA zeolite membrane synthesized by vacuum seeding method

High quality NaA zeolite membranes were prepared by vacuum assisted secondary growth. At the first stage in which NaA powder was synthesized, increasing the aging time led to formation of impure and smaller crystals. However, at the aging time of 48 h, pure NaA zeolite particles with average particle size of 1.5 μm were obtained. In the second stage, the outer surface of porous α-Al₂O₃ tubular supports were seeded by vacuum method using 1.5 μm NaA particles. The most stable and uniform seeded layer was obtained at seeding time and suspension concentration of 90 s and 5 g L⁻¹, respectively. Then, 6 h of secondary growth of the zeolite layer on the seeded surface was carried out at 373 K three times. The XRD and SEM results showed the formation of a uniform and dense layer of pure NaA zeolite with an average thickness of 45 μm. Dehydration experiments were conducted on ethyl acetate/water mixtures with 2 wt% water content. The average total fluxes were 0.147, 0.208, and 0.315 kg m⁻² h⁻¹ at 303, 313, and 323 K, respectively. The separation factor was 163,000. This parameter did not change with temperature and it was due to very close activation energies of ethyl acetate and water.     

Study of structural transformations in potassium-exchanged zeolite A induced by thermal and mechanochemical treatments

Thermal transformations of potassium-exchanged zeolite A and the X-ray amorphous material obtained by ball milling the potassium-exchanged zeolite A were investigated by different methods, such as differential thermogravimetric analysis (DTA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Controlled heating of crystalline, potassium-exchanged zeolite A causes a phase transformation in the sequence: [0.22 Na2O, 0.78 K2O]·Al2O3·2SiO2·3.48 H2Oamorphouskalsilite+kaliophilite, while the heating of mechanochemically amorphous potassium-exchanged zeolite A results in its transformation into a mixture of kalsilite and kaliophilite. The differences in the pathways of the transformation processes are discussed in terms of the structural properties of the starting materials.     

Hydrogen induced catalysis by silver-exchanged zeolites: transformation of ethylbenzene over AgY zeolite

Catalytic activity of AgY at 473 K is greatly enhanced by the presence of hydrogen. Activity in the presence of hydrogen is much higher than that observed for HY, where the presence of hydrogen has no effect. The effect caused by hydrogen is reversible. When hydrogen is removed from the system, activity decreases. Activity is restored by the re-introduction of hydrogen into the system. This shows that hydrogen is reversibly chemisorbed to form protons in the zeolite. It is suggested that the interconversion of hydrogen molecules and protons is related to the redox property of the small silver clusters.     

Structural transformation induced by nitrogen implantation in thin metal films

High dose nitrogen implantation was carried out in gadolinium, cobalt, aluminium and copper thin films to study the implantation-induced phase formation. It is concluded that the presence or absence of an equilibrium nitride after implantation is directly related to the structural correlation between the metal matrix and the nitride. The formation of a nitride would be retarded or even inhibited if the required structural transformation is difficult to achieve. These results are believed to be attributable to the transient thermodynamic and kinetic conditions during ion irradiation.     

Analysis of the collective behaviour of evaporated gold nuclei: modifications induced by electric fields

The experimental results on the collective behaviour of gold nuclei on (100) KCl substrates are summarized in order to demonstrate that the repulsive forces between nuclei can be modified by the application of an electric field in the plane of the film. An analysis of the radial distribution of nuclei gives direct evidence of the role of an electric field in the kinetics of coalescence.