Microwave synthesis and physical characterization of tin(II) phosphate glasses

Tin phosphate glasses in the SnO–P₂O₅ binary diagram have been prepared by using a domestic microwave-heating device. Microwaves provide an extremely facile and automatically temperature-controlled route to the synthesis of glasses due to the specific dielectric properties of each chemical composition. Typical melting time is no longer than 10 min, limiting the oxidation of Sn²⁺ and the melt can be quenched into glass. The glass transition temperature increases with the SnO content confirming the depolymerization of the vitreous network, as expected by the relative fraction of the different Q ⁿ structural units deduced from NMR experiments. Concerning the mechanical properties, the Vickers hardness and the fracture toughness decrease while the thermal expansion coefficient and the different elastic moduli remain constants. These results confirm that those characteristics are not very sensible to structural considerations. On the contrary, the chemical durability of Sn₂P₂O₇, determined from the weight loss method, is 300 times higher than that of Sn(PO₃)₂. Furthermore, Sn₂P₂O₇ is the only glass composition that exhibits a devitrification phenomenon leading to the low-temperature phase of the crystalline tin(II) pyrophosphate.     

Anti-corrosive mechanism of poly (N-ethylaniline)/sodium silicate electrochemical composites for copper: Correlated experimental and in-silico studies

Poly (N-ethylaniline) (PNEA) composites with varying silicate content were fabricated on copper through a novel electropolymerized strategy in acidic solution.Thickness,compactness,conductivity and adhesive strength of the composite (PNEA-10Si) were optimized as silicate content reached 10 mM.Electrochemical,morphological and solution analyses were employed to evaluate the protective performance of PNEA and PNEA-10Si coatings for copper in 3.5 ％ NaCl solution.Results of electrochemical analyses indicated that as-prepared coatings retarded the oxygen reduction process efficiently for copper in 3.5 ％ NaCl solution,drained corrosion current density and elevated interfacial charge transfer resistance.Due to favorable barrier effect,compact structure and low porosity index,PNEA-10Si composite exhibited superior anti-corrosive performance,which was more tolerant than PNEA during long-time immersion.PNEA-10Si coated sample exhibited a stable topography after 144 h immersion with the minimum concentration of released ions revealing the improved protection capacity.Electronic/atomic-multiscale calculations were conducted to clarify the deposition and protection mechanism of as-prepared coatings.Outcomes of density functional theory corroborated that silicate is stabilized in the PNEA layer via electrostatic force;and immobile silicate positively contributed to the charge transfer barrier of the composite.Molecular dynamics simulations evidenced that the favorable compatibility between PNEA and silicate facilitated polymer deposition and confined in-situ ions diffusion.     

An experimental study on HC290 and a commercial liquefied petroleum gas (LPG) mix as suitable replacements for HCFC22

This paper presents an experimental study on the performance of hydrocarbon refrigerants, namely propane and a liquefied petroleum gas (LPG) mix as suitable replacements for the widely used refrigerant HCFC22 in refrigeration and heat pump applications. A cylinder of commercially available LPG from New Zealand market was obtained for this study. The composition of the specific LPG mix (by mass fraction) was propane (HC290)—98.95%, ethane (HC170)—1.007%, iso-butane (HC600a)—0.0397% and other constituents in small proportions. Experiments were carried out in a laboratory heat pump test facility with maximum condenser capacity of approximately 15 kW. Condensing temperatures were held constant at 35, 45 and 55°C, while evaporating temperatures were varied over a wide range from − 15 to + 15°C. All tests were carried out at constant degree of superheat (about 1 K) and subcooling (about 8 K). All appropriate precautions were observed against any leaks or fire.The analysis revealed that the hydrocarbon refrigerants performed better than HCFC22 but with a small loss of condenser capacity. The mass flow rate and compressor discharge temperature were found to be significantly lower than HCFC22. The performance of the specific LPG mix tested was found to be better than HC290 at higher condensing temperatures but poorer at a lower condensing temperature. No adverse effects were found with the LPG mix despite the presence of little moisture (less than 0.01%) in its composition. The study reveals that LPG of the tested composition (i.e. predominantly a mixture of propane, ethane and iso-butane) can be an excellent refrigerant in heat pump/refrigeration applications.     

Thermal shock and thermal fatigue study of ceramic materials on a newly developed ascending thermal shock test equipment

A test equipment was designed to study thermal shock and thermal fatigue of ceramic materials subjected to fast heating (ascending). The equipment was designed to generate thermal stress in a test specimen by heating one surface of it by an oxy-hydrogen flame while cooling the opposite surface. The sample cracked when thermal stress exceeded its mechanical strength. The in situ crack formation was detected by an acoustic emission system coupled to the set up. The hot zone temperature was measured by an infra red pyrometer. The equipment was also designed to run thermal fatigue test cycles in automatic mode between two selected temperatures. The temperature and thermal stress distribution in the test specimen were modelled using finite element software. The effect of temperature distribution of the top and bottom surfaces on thermal stresses was studied. It was observed that the thermal stress is very sensitive to the temperature distribution on the top surface and maximum near the periphery of the top surface. This was in agreement with the experimental results in which the cracks were originated from the periphery of top surface. It was also observed that the failure temperature was higher for thicker samples.     

Optical and esr spectra of vanadium (IV) in different simple germanate,phosphate and borate glasses

The optical and esr spectra of some Na₂O-GeO₂, Na₂O-P₂O₅, Na₂O-CaO-P₂O₅ and Na₂O-Al₂O₃-B₂O₃ glasses containing vanadium(IV) have been studied; these spectra have been analyzed by assuming that vanadium(IV) is present as the vanadyl ion in a ligand field of C_4V symmetry. It has been found that in Na₂O-GeO₂ and Na₂O-P₂O₅ glasses the covalency in the in-plane V-O δ-bonds increases, and the degree ofπ-bonding with the vanadyl oxygen decreases, with increasing Na₂O content of the glass; the rate of change being greatest in the region 15 to 20 mol % Na₂O for the Na₂O-GeO₂ series and around 50 mol % in the Na₂O-P₂O₅ series. In the Na₂O-CaO-P₂O₅ glasses the covalency in the in-plane V-O δ-bond decreases andπ-bonding with vanadyl oxygen increases on substitution of CaO for Na₂O in the glass. Gradual addition of Al₂O₃ in three different Na₂O-B₂O₃ glasses did not cause any significant change in covalency either in the δ or in theπ-bonding. These changes have been discussed in terms of possible structural units in these glasses.     

Enhancement of Goos-H(a)nchen Shift with Cascade Optical Waveguides

前期的工作已经证明,由于共振效应和渗透深度的增加,利用毫米尺度对称金属包覆波导和自由空间耦合技术,可获得毫米量级的古斯-汉欣(Goos-H(a)nchen)位移.本文在此基础上,利用一对对称金属包覆波导组成级联型结构,研究了这种结构中古斯-汉欣位移的增强效应.实验结果表明:当激光波长变化43 pm时,由CCD探测器测量得到的古斯-汉欣位移达到了2 215 μm,约为单级波导古斯-汉欣位移的2倍,实验结果与理论推导完全一致.     

Optical correlators with (-k)th-law nonlinearity: optimal and suboptimal solutions

A computer simulation of nonlinear correlators with (-k)th-law nonlinearity has been implemented. The nonlinearity is applied to the input-image power spectrum, with either a matched filter or a phase-only filter representing the reference object. Optimal correlators (with an exactly known power spectrum of the background-image component) and suboptimal correlators have been studied in order to establish potential limits and achievable figures for the correlator's discrimination capability in a target location in a cluttered background. For the suboptimal correlators, different values of the nonlinearity index k have been investigated for two methods of the image's power-spectrum estimation and for different degrees on the limitation of the nonlinearity's dynamic range. The results show that the nonlinear correlators promise significant improvement in the correlator's discrimination capability and provide important information for evaluating the practical aspects of the correlator's design.     

Assessment of forming parameters influencing spring-back in multi-point forming process: A comprehensive experimental and numerical study

Like all sheet metal forming methods, one of the main characteristics of parts formed by multi-point forming is dimensional deviation caused by elastic recovery that is known as spring-back. In this paper the effects of material property, sheet thickness and anisotropy ratio along with process parameters such as elastic layer thickness, elastic layer hardness and number of punch elements on spring-back are studied utilizing finite element simulations and experimental tests. Experimental tests are carried out under various conditions by forming V-shaped and Sin-shaped geometries. Aluminum alloy 3105, stainless steel 304 and pure copper were used as sheet materials for experiments. Likewise, black rubber with shore A hardness of 50 and polyurethane with hardness of 65 and 85 were allocated as elastic layers. The Abaqus® commercial code is employed for finite element simulations. The definition of yield behavior of utilized sheet materials is fulfilled by using three yield criteria of Barlat-89, Hill-48 and Von-Mises. Since the Barlat-89 is not adopted in Abaqus, VUMAT and UMAT user defined subroutines are provided and integrated with explicit simulation of forming process and implicit simulation of spring-back phenomenon respectively. The results indicate that parameters such as material property, blank thickness and anisotropy affect spring-back in multi-point forming. Also the thickness and hardness of elastic layers are novel ideas that should be considered in order to minimize the spring-back. In general, using the elastic layer with minimum possible thickness and greater hardness beside the maximum number of pins leads to minimum spring-back.     

A new type of polytetrafluoroethylene prosthesis (Mycro Mesh): an experimental study

Comparisons were made of the tissue response to the implantation of two different polytetrafluoroethylene prostheses: Soft Tissue Patch (STP) and Mycro Mesh (MM). A 7 × 5 cm prosthesis of STP (n=12) or MM (n=12) was implanted into a defect of the same size (involving all layers except skin) created in the anterior abdominal wall in 24 New Zealand rabbits. The prostheses were anchored to the recipient tissue, in direct contact with the intestinal loops and connective tissue. After 14, 30, 60 and 90 days, groups of six implants were studied macroscopically and samples were taken to be processed by light microscopy, scanning electron microscopy (SEM), immunohistochemical studies and tensiometry. All animals were valid for the study. In three cases STP implants presented very loose adhesions in the peripheral zones corresponding to the sutures. They were also observed on three MM implants, in the area of the perforations. Light and scanning microscopy revealed the formation of a capsule of scar tissue surrounding both types of prosthesis. At day 90, bridges of connective tissue had formed in the perforated areas of MM. Good vascularization was established in the areas of recipient tissue corresponding to both implants. The macrophage reaction to both biomaterials was maximal at 14 days, after which it progressively decreased until day 90. Tensile testing revealed no significant differences between the two biomaterials. It is concluded that (a) behaviour in the peritoneal interface is similar in the two prostheses, (b) both biomaterials become encapsulated rather than integrated into the recipient tissue, (c) the foreign body reaction does not determine the success or failure of the implants, (d) The perforations of the MM prosthesis do not increase its resistance to stress, or at least not after 90 days of implantation into rabbit abdominal wall.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Mechanical properties and structure of a new commercial SiC-type fibre (Tyranno)

An initial evaluation of a new titanium-doped polymer-pyrolysis SiC fibre, Tyranno (Ube Industries, Ltd) showed a narrow distribution of diameters with a mean of 8.5m; average tensile strengths 3 G Pa, nearly independent of gauge length in the 1 to 4cm range; Weibull parameterm 7.3; and mean Young's modulus 170 G Pa. Heat treatment at 1300 to 1350° C in N₂ appreciably reducedS, m andE; and X-ray diffraction showed that significant crystallite growth as well as some Si₃N₄ formation had occurred. Tyranno fibre properties are compared with those of the well-known Nicalon SiC fibre.     

Optical absorption of nickel (II) in Na2O-NaCl-B2O3 and Na2O-NaBr-B2O3 glasses

The optical absorption spectra of nickel(II) have been studied in Na₂O-NaX-B₂O₃ glasses X = Cl or Br); the absorption bands have been interpreted in terms of Ligand Field Theory. In halide-free B₂O₃-rich glasses nickel(II) is octahedral, and halide substitution is accompanied by the formation of a tetrahedral nickel(II)-oxide-halide complex. In alkali-rich glasses nickel(II) is square planar and/or tetrahedral and no halide substitution can be observed. It is suggested that the halide ions are unable to substitute for oxygen in the predominantly covalent nickel(II)-oxygen bonds of the complex formed in basic glasses.     

Piezoelectric behaviour of PZT doped with calcium: a combined experimental and theoretical study

An experimental and theoretical study on the piezoelectric behaviour of PZT doped with a range of calcium ion concentrations is presented. A systematic study of the effect on the piezoelectric properties of PZT doped with various concentrations of CaO at constant sintering temperature and sintering time was carried out. The remanent polarization, planar coupling factor and frequency–thickness constant increase with calcium concentration. Ab initio perturbed ion calculations show that the lattice energy decreases with calcium addition for both tetragonal and rhombohedral phases of PZT. This revised version was published online in November 2006 with corrections to the Cover Date.     

Oscillation of absorption bands of Zn(1-x)Mn(x)S clusters: an experimental and theoretical study

Electroporation of synthetic vesicles is utilized for the preparation of molecular size uncapped Zn(1-x)Mn(x)S clusters. The absence of caps permits (i) continued growth of the Zn(1-x)Mn(x)S clusters formed, (ii) the assessment of their true absorption spectra unaltered by stabilizing ligands, and (iii) the previously inaccessible live observation of the growth of the clusters in the molecular size regime. Upon cluster growth, the UV spectra exhibit novel, time-dependent, oscillation of red and blue shifts of the characteristic absorption band. The structure and electronic properties of Zn(N-1)MnS(N) clusters with N = 1-9 are calculated using the first-principles DMol(3) package. On the basis of similarities between the oscillating trend of the experimentally observed absorption spectra and that of the calculated highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap of Zn(N-1)MnS(N) clusters with N = 1-9, the wavelengths of the sequential spectral peaks can be assigned to Zn(2)MnS(3), Zn(3)MnS(4), Zn(4)MnS(5), Zn(6)MnS(7), and Zn(8)MnS(9), respectively. Our results demonstrate that both the cluster size and the composition can be used to tune the optical properties.     

Optical profilometry of poly(methylmethacrylate) surfaces after reshaping with a scanning photorefractive keratectomy (SPRK) system

A prototype frequency-quintupled Nd:YAG laser was used with a scanning system to create, on poly(methylmethacrylate) (PMMA) blocks, ablations corresponding to a correction of 6 diopters of myopia by photorefractive keratectomy. The topography of the ablated samples was measured with an optical profilometer to evaluate the smoothness and accuracy of the ablations. The ablation depth was larger than expected. With a 50% to 70% spot overlap, large valleylike variations with a maximum peak-to-peak amplitude of 20 μm were observed. With an 80% spot overlap, the rms surface roughness was 1.3 μm, and the central flattening was 7 diopters. This study shows that optical profilometry can be used to determine precisely the ablation per pulse and the smoothness and accuracy of surface ablations. Knowing the exact ablation per pulse is necessary to produce a smooth and accurate corneal surface by scanning photorefractive keratectomy.     

Kinetic study of the reaction between copper(I) chloride and commercial silicon or silicides

The reaction of CuCl with silicon containing as impurities Al, Fe, Ca and Ti or with some silicides (Si₂Ca, Si₂Fe, Si₂Ti) has been investigated in the temperature range 250–310 °C. For the reaction between CuCl and commercial Si, it has been found that at 282 °C, the aluminium promotes the reaction between Cu₃Si and CuCl while its rate of consumption is greatly decreased by the presence of iron impurity. The combined action of these two impurities improves the quantity of the copper-silicon alloy formed. In the presence of silicides, the reaction with CuCl leads to copper formation with a high degree of dispersion.     

A study of cadmium mercury telluride (CMT) thin film structures: some physical observations and characteristics

Polycrystalline thin film structures of the form Cd_1?x Hg _x Te (0 ≤ x ≤ 0.5) were obtained on ultrasonically cleaned glass substrates in an alkaline medium (pH≈ 10 ± 0.2) at 80^°C. The forerunner solutions were obtained from the equimolar solutions of CdCl₂, HgCl₂ and 0.33 M-refluxed Na₂TeSO₃. The preparation parameters such as temperature, pH, deposition time and speed of mechanical stirring were optimized. The as-prepared samples were tightly adherent to the substrate support, less smooth, diffusely reflecting and were analysed for composition. It appeared that incorporation of Hg²⁺ in the lattice of CdTe replaced divalent Cd²⁺ predominantly. However, a small amount of Te^2? replacement by Hg²⁺ ions has also been observed at higher levels of Hg in CdTe (> 0.1 mol. %). The samples were then characterized optically to determine the absorption coefficient, mode of optical transition and the optical bandgaps. The estimated band-gap decreased, typically from 1.51 to 0.83 eV as Hg content in CdTe was increased from 0 to 0.5. The dc electrical conductivity measurements were made in the temperature range from 300 to 550 K and it was observed that the conductivity increased rapidly up to x = 0.1 and thereafter remained more or less the same. The thermopower measurements showed n-type conduction of these films. Both carrier concentration (n) and mobility (μ) were computed from these studies and found to be dependent on the working temperature and the film composition. The surface morphologies of these as-grown layers were then observed via a scanning electron microscope. CdTe crystals are more or less crystalline spherical and hexagonal prismatic in shape whereas HgCdTe samples appear glassy and show hexagonal prismatic whiskers, some less frequent forms of needles.     

Interface structure of deposited GaSb on GaAs (001): Monte Carlo simulation and experimental study

The growth of GaSb thin films by MBE on GaAs (001) is investigated experimentally, using TEM, and theoretically, using KMC simulations. The atomic scale mechanisms inherent to the growth are discussed and described in the KMC model in which the strain is introduced through an elastic energy term based on a valence force field approximation. We observe that the first two monolayers of the deposited films form strained three-dimensional clusters, but further deposition induces film relaxation and rough 3D growth with valley formation presenting (111) facets with unstable bottoms. We show that the roughening morphology and creation of grooves during growth are in agreement with experimental TEM observations.