Millimetre-sized hollow spheres of lead zirconate titanate by a sol-gel method

Hollow spheres of lead zirconate titanate (PZT) [chemical formula Pb(Zr_0.52Ti_0.48)O₃)], with outer diameter of 1–2 mm and a wall thickness of about 100 m, were fabricated by gellation of a PZT sol inside solid polymer spheres and then burning the polymer out. Monomodally sized polyacrylamide spheres, with diameter 1.40–1.90 mm, were soaked in a PZT sol, prepared by dissolving Pb(NO₃)₂, zirconiumn-butoxide and titanium isopropoxide inN, N-dimethylformamide. The absorbed sol was then gelled beneath the surface of the polymer sphere by the action of NH₃. Upon calcination of the spheres at 850 °C for 4 h in air, hollow spheres of pure PZT perovskite phase (as identified by X-ray diffraction patterns) were obtained. The density of the hollow spheres was 1.13gcm^–3, while that of the wall of the spheres was 3.10g cm^–3. The scanning electron microscopic examination of the broken spheres showed that the inner surface of the spheres contained rib-like structures, which provided strength to the hollow spheres. The planar coupling factor,k _p, of six hollow spheres, placed at a close-packed arrangement in a plane, was 0.22, indicating the possibility of fabrication of low-density transducer arrays.     

Flow behavior in surface-modified microchannels with polymer nanosheets

The paper describes water flow behavior in surface-modified microchannels. We prepared straight-type microchannels which had rectangular cross sections with four different combinations of microchannel surface wettability; cleaned glass substrates served as hydrophilic microchannel walls and the microchannel walls coated with polymer Langmuir–Blodgett (LB) films were used as hydrophobic surfaces. The polymer LB films were successfully transferred onto glass substrates by vertical dipping method. The flow rates and the water meniscus shape strongly depended on the microchannel surface wettability. The decrease in flow rate with the increasing number of hydrophobic (polymer LB film) surface was attributed to the higher adhesion energy of hydrophobic surface. The Reynolds number was also characterized to be in the order of 10^− 1, implying a specific feature of microchannel; laminar flow.     

Preparation, structure and mechanical properties of all-hemp cellulose biocomposites

All-hemp (Cannabis Sativa L.) cellulose composites were prepared by a mechanical blending technique followed by hot pressing and water–ethanol regeneration. The alkali treated fibres were ground and sieved to a size ranging from 45 μm to 500 μm. Introduction of fibres into 12% w/v cellulose N-methyl-morpholine-N-oxide (NMMO) solution was performed with low solution viscosity at 100 °C. The solid mixtures were cut and heat pressed between heated glass and PTFE plates at 85 °C to obtain a flat smooth-surfaced composite sheet of approximately 0.2 mm thickness. The cellulose was regenerated in a 50:50 water–ethanol mixture that subsequently removed NMMO and stabilizer (Irganox 1010, Ciba) from the composite. FTIR and X-ray diffraction measurements were performed to investigate the structural change of cellulose from fibre into partially regenerated composite. Composition and thermal stability of composites were investigated using thermogravimetry. A broadening of the scattering of the main crystalline plane (0 0 2) and a depression of the maximum degradation temperature of fibre were observed. The observations revealed a structural change in the fibres. The mechanical properties of composites depended on size, surface area, crystallinity and the structural swelling of fibres.     

The fracture stress of float glass

A fracture test [1] which uses concentrically loaded square plates supported near their corners has been used to measure the fracture stress of float glass. The plates were 102mm square and 5.98mm thick. The maximum displacement at fracture was less than 0.4mm. Under these circumstances it has been shown that use of a linear finite element solution for the stress distribution and the plate deflections is justified. The glass plates had greater edge damage than had the alumina plates tested in an earlier investigation. In order to secure an adequate proportion of failures in the central plate region, it was necessary to move the supports inwards towards the centre of the plate. This reduced the ratio of the maximum edge stress to the maximum stress in the plate. Batches of plates were tested with loading circle diameters of 7.5 and 25mm, to measure volume effects, with the side of the plate that had been in contact with the liquid tin in tension. Median ranking was used in the statistical analysis and edge failures were treated as suspensions, it being assumed that the minimum fracture stress of the central region of the edge-fractured plates was the plate centre stress at the fracture load. The Weibull modulus was determined by a linear regression in which extreme members of the population were given reduced weighting using the relationship of Faucher and Tyson [3]. The average fracture stresses were 147.2 and 107.3 N mm^–2 for the 7.5 and 25 mm loading circles, respectively, and the Weibull moduli were 4.49 and 5.44. These data are shown to agree well with Weibull statistics. Tests using a 7.5 mm diameter loading circle on plates with the non-tin side in tension gave a significantly higher average fracture stress of 242.1 N mm^–2, confirming the fact that the non-tin side has a higher strength.     

Failure mechanism of optically transparent solids subjected to a local thermal laser pulse

Experimental data on the failure mechanism of glass plates subjected to a millisecond pulse of focused laser light are presented. It is established as a result of investigation of the failure kinetics of irradiated glass plates that their failure is caused by an increase in gas pressure in the cavity formed at the focal point of the light-collecting lens. This failure mechanism of glass differs from that described earlier for the case of the irradiation of a glass plate by a nanosecond pulse of laser light, according to which the glass fails as a result of the development of a high-amplitude acoustic pressure wave near the front surface of the irradiated plate. The failure mechanism described for the glass plates agrees with a thermodynamic failure model of transparent solids.Translated from Problemy Prochnosti, No. 4, pp. 88–93, April, 1993.     

The effect of α1 plates on the martensitic transformation and shape memory effect in a β Cu–Zn alloy

The martensitic transformation and shape memory effect (SME) in a β Cu–Zn alloy containing various amounts of α₁ plates have been investigated. The results showed that the characteristic temperature of martensitic transformation decreased as the isothermal aging time increased. The crystal structure, twin relationships between martensite variants, and characteristics of martensitic transformation of the β Cu–Zn alloy were not affected by the existence of α₁ plates. However, the α₁ plates were distributed homogeneously in the parent phase and functioned as grain boundaries, hindering the progress of martensite variants, and reducing the effective grain size of the parent phase and the size of self-accommodating plate groups formed upon cooling. In addition, the strain recovery due to the SME decreased as the isothermal aging time increased (the quantity of α₁ plate increased) and/or imposed prestrain increased. Nevertheless, the SME mechanism in the β Cu–Zn alloy containing α₁ plates was not affected by the presence of the α₁ plates.     

Metal oxide–chitosan based nanocomposite for cholesterol biosensor

Metal oxide [cerium oxide (NanoCeO₂)]–chitosan (CH) nanocomposite film has been fabricated onto indium-tin-oxide (ITO) coated glass plate to immobilize cholesterol oxidase (ChOx) via physiosorption for cholesterol detection. Electrochemical studies reveal that the presence of NanoCeO₂ in CH–CeO₂ nanocomposite results in increased electroactive surface area for ChOx loading resulting in enhanced electron transport between ChOx and electrode. The ChOx/CH–NanoCeO₂/ITO bioelectrode exhibits interesting characteristics such as detection range of 10–400 mg/dL, detection limit of 5 mg/dL, response time of 10 s, low K_m value of 3.5 mg/dL and value of regression coefficient of 0.994.     

Oxygen inhibition of autopolymerization of polymethylmethacrylate–glass fibre composite

The aim of this study was to determine the thickness of the unpolymerized surface layer of autopolymerizing polymethylmethacrylate (PMMA) and PMMA–glass fibre (GF) composite. Powder-to-liquid (P/L) ratios of 10 : 8, 10 : 9 and 10 : 10 by weight of the commercial PMMA was tested and the E-glass fibre weave was used as filler in the PMMA–GF composite. The resin was polymerized between two glass plates at 55°C in air under an air pressure of 300 kPa. Five samples were polymerized for each test group. The inhibition depth was measured by a light microscopic technique with polarized light. The inhibition depth was affected by the P/L ratio of the PMMA: the mean inhibition depth of the unfilled PMMA with the P/L ratio of 10 : 10 was 248.6 m, while it was 175.4 m in PMMA with the P/L ratio of 10 : 8 (p=0.044). The inhibition depths were higher in the PMMA–GF composite than in the plain PMMA, which was explained by an inadequate impregnation of the GF weave with the PMMA resin. The results suggest that improper impregnation of the fibre product with autopolymerizing PMMA resin can cause oxygen inhibition of the polymerization reaction which should be taken into account when fibre products are clinically used.     

Novel bioresorbable and bioactive composites based on bioactive glass and polylactide foams for bone tissue engineering

Bioresorbable and bioactive tissue engineering scaffolds based on bioactive glass (45S5 Bioglass®) particles and macroporous poly(DL-lactide) (PDLLA) foams were fabricated. A slurry dipping technique in conjunction with pretreatment in ethanol was used to achieve reproducible and well adhering bioactive glass coatings of uniform thickness on the internal and external surfaces of the foams. In vitro studies in simulated body fluid (SBF) demonstrated rapid hydroxyapatite (HA) formation on the surface of the composites, indicating their bioactivity. For comparison, composite foams containing Bioglass® particles as filler for the polymer matrix (in concentration of up to 40 wt %) were prepared by freeze-drying, enabling homogenous glass particle distribution in the polymer matrix. The formation of HA on the composite surfaces after immersion in phosphate buffer saline (PBS) was investigated to confirm the bioactivity of the composites. Human osteoblasts (HOBs) were seeded onto as-fabricated PDLLA foams and onto PDLLA foams coated with Bioglass® particles to determine early cell attachment and spreading. Cells were observed to attach and spread on all surfaces after the first 90 min in culture. The results of this study indicate that the fabricated composite materials have potential as scaffolds for guided bone regeneration.     

The effects of back plate materials on perfect cone formation in impact-loaded soda-lime glass

In order to investigate the possibility of processing brittle materials by ball impact, the effects of back plate materials on cone crack formation in glass plate by impact with small spheres were evaluated experimentally. Crack morphologies developed in soda-lime glass with back plate materials of Polyurethane, PMMA and Aluminum were investigated as a function of impact velocity. Back plate materials were more effective in producing perfect cones than unbacked glass plates. In the case of PMMA, perfect cone was formed over a larger velocity range. The velocity range over which perfect cones were formed was influenced by both the thickness and the material of the back plates. By the proper selection of back plate materials, the application of this punching process to brittle materials in industrial technology is expected.     

Investigation of failure of composite materials by the method of deformation luminescence in a broad velocity range of loading

The article presents a way of investigating failure of materials with the aid of the method of deformation luminescence (DL) and describes the results of tests with specimens of laminated glass reinforced plastic with reinforcing structure (O₂; ±60) and (±30; 90₂) in static and dynamic tension. Diagrams are plotted of the change of intensity of DL and stress ₁₁ vs. time at a speed of impact 0.5 and 1 m/sec, and also under static loading at the rate of 3 mm/min. It is shown that static and dynamic tension of laminated glass reinforced plastic is accompanied by DL expressing the jumpwise nature of step-by-step failure of the material.Translated from Problemy Prochnosti, No. 9, pp. 48–52, September, 1991.     

A novel carbon-based nanocomposite plate as a counter electrode for dye-sensitized solar cells

This study develops cost effective and high performance composite conductive plates for use in dye-sensitized solar cells (DSSCs). Composite plates with various graphite contents at a constant carbon nanotube (CNT) loading were prepared by bulk molding compound (BMC) process. Results show that the bulk electrical resistance of the composite plate gradually decreases from 6.7 mΩ cm to 1.7 mΩ cm as the graphite content increases, which is due to the formation of efficient electronic conducting networks. For DSSCs, the composite plates may be suitable substitutes for the conductive glass plates in the counter electrodes substrates of DSSCs. Results reveal that composite plates at the optimum level (80 wt.% graphite loading) provide lower cell resistance, lower preparation cost and higher cell performance than common conductive glass plates. Therefore, in order to decrease the cost of the cells and to maintain good cell performance, this graphite-like composite plate prepared by the BMC process is a promising substitute component for DSSCs.     

Preparation and characterization of plasticized polymer electrolytes based on the PVdF-HFP copolymer for lithium/sulfur battery

PVdF-TG-LiX polymer electrolytes comprised of polyvinylidene fluoride (PVdF)-hexafluoropropylene (HFP) copolymer, tetra(ethylene glycol) dimethyl ether as plasticizer, LiCF₃SO₃, LiBF₄ and LiPF₆ as lithium salt and acetone as solvent have been prepared by solvent casting of slurry that mixed PVdF-HFP copolymer with acetone and salt using a ball-milling technique, which was performed for 2 and 12 h with a ball-to-material ratio of 400:1, and their electrochemical and thermal properties were studied. The ball-milled PVdF-TG-LiX polymer electrolytes have higher ionic conductivity as well as lower glass transition temperature and melting points than the magnetically stirred one. The PVdF-TG-LiPF₆ polymer electrolytes prepared by ball-milling, for, 12 h, in particular, resulted in a maximum value in the ionic conductivity, which was 4.99×10^–4 S cm^–1 at room temperature. The ball-milled PVdF-TG-LiX polymer electrolytes were introduced into Li/S cells with sulfur as cathode and lithium as the anode. The first specific discharge capacities with discharge rate of 0.14 mA cm^–2 at room temperature were about 575 and 765 mA h g–cathode^–1 for magnetic stirring and 12 h ball milling.     

Molecular orientation of nonlinear optical polymer nanosheets on silica nanoparticle monolayer studied by optical waveguide spectroscopy

The paper describes molecular orientation of nonlinear optical (NLO) polymer monolayer transferred onto a sphere-shaped silica nanoparticle monolayer using optical waveguide spectroscopy. Structurally well-defined hybrid polymer nanoassemblies were constructed through bottom-up approaches: Langmuir–Blodgett technique and immersion method. Silica nanoparticles (SiO₂ NPs, 40–50 nm diameter) were immobilized on a quartz waveguide using cationic polymer Langmuir–Blodgett films (nanosheets) as a template. The SiO₂ NPs took a uniformly distributed monolayer formation without any aggregates, which minimizes light scattering. This allows us to gain reproducible absorption spectra of dye molecules embedded in polymer nanosheet monolayer on the nanoscale rough surface using optical waveguide spectroscopy. The NLO polymer nanosheets containing disperse red 1 (DR) were transferred onto the SiO₂ NP monolayer. The polarized absorption spectra were obtained; the s-light absorption was larger than the p-light absorption, indicating that polymer nanosheets are wrapped around SiO₂ NPs so that DR moieties undergo molecular disorientation not to form H-aggregates. This method provides us with useful information on structure–property relationship between nanoshaped inorganic nanoparticle and organic functional molecules in hybrid nanoassemblies.     

橡胶/环氧树脂复合补强胶片的制备及性能研究

以丁腈橡胶、天然橡胶及环氧树脂共混制备高分子合金,采用压延法与玻璃纤维布复合成汽车用补强胶片。通过扫描电镜、热分析对高分子合金进行表征,用弯曲强度表征补强胶片对钢板的增强作用,用剪切强度表征丁腈橡胶/天然橡胶/环氧树脂复合材料与钢板的粘接性能。     

Effect of glass–ceramic microstructure on its in vitro bioactivity

Two routes were used to obtain a glass–ceramic composed of 43.5 wt % SiO₂ – 43.5 wt % CaO – 13 wt % ZrO₂. Heat treatment of a glass monolith produced a glass–ceramic (WZ1) containing wollastonite-2M and tetragonal zirconia as crystalline phases. The WZ1 did not display bioactivity in vitro. Ceramizing the glass via powder technology routes formed a bioactive glass–ceramic (WZ2). The two glass–ceramics, WZ1 and WZ2, were composed of the same crystalline phases, but differed in microstructure. The in vitro studies carried out on WZ2 showed the formation of an apatite-like layer on its surface during exposure to a simulated body fluid. This paper examined the influence of both chemical and morphological factors on the in vitro bioactivitity. The interfacial reaction product was examined by scanning and transmission electron microscopy. Both instruments were fitted with energy-dispersive X-ray analyzers. Measurements of the pH made directly at the interface of the two glass–ceramics were important in understanding their different behavior during exposure to the same physiological environment.     

Electron field emission properties of electro-deposited diamond-like carbon coatings

Field emission studies were carried out on diamond-like carbon films deposited by an electro-deposition technique onto SnO₂-coated glass substrates. A mixture of acetic acid and water was the electrolyte. The films are compact with surface roughness 10 nm. Work function (φ) values obtained from the Fowler–Nordheim model varied between 15 and 214 meV, while the field factor (β) varied between 4 and 700. The critical field was found to vary between 2 and 28 V/μm.     

Influence of the non-bridging oxygen groups on the bioactivity of silicate glasses

The effect of the composition and bonding configuration of the bioactive silica-based glasses on the initial stage in vitro bioactivity is presented. Information of the IR active Si–O groups of glass in the system SiO₂–P₂O₅–CaO–Na₂O–K₂O–MgO–B₂O₃ was obtained by fourier transform Infrared (FTIR) spectroscopy. Two different bands associated to non-bridging oxygen stretching vibrations (Si–O–1NBO and Si–O–2NBO) and a gradual shifting of the bridging oxygen stretching vibration (Si–O) have been observed and evaluated. Both effects are attributed to a decrease of the local symmetry originating from the incorporation of alkali ions into the vitreous silica network. The Si–O–NBO(s)/Si–O(s) absorbance intensity ratio increases with a gradual incorporation of the alkali ions (diminution of SiO₂ content) following a linear dependence up to values close to 50 wt % of SiO₂. In vitro test analysis by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA) showed a correlation between the amount and type of the non-bridging oxygen functional groups and the growth of the silica-rich and CaP layers. It was found that a minimum concentration of Si–O–NBO bonds in the glass network is required in order to have an efficient ion exchange and dissolution of the silica network. Finally, the bioactivity of the glass is favored by the presence of the Si–O–2NBO groups in the glassy network. The role of these functional groups in the dissolution of the silica network through the formation of silanol groups and the adsorption of water is discussed.     

In vitro evaluation of borate-based bioactive glass scaffolds prepared by a polymer foam replication method

Borate-based bioactive glass scaffolds with a microstructure similar to that of human trabecular bone were prepared using a polymer foam replication method, and evaluated in vitro for potential bone repair applications. The scaffolds (porosity = 72 ± 3%; pore size = 250–500 μm) had a compressive strength of 6.4 ± 1.0 MPa. The bioactivity of the scaffolds was confirmed by the formation of a hydroxyapatite (HA) layer on the surface of the glass within 7 days in 0.02 M K₂HPO₄ solution at 37 °C. The biocompatibility of the scaffolds was assessed from the response of cells to extracts of the dissolution products of the scaffolds, using assays of MTT hydrolysis, cell viability, and alkaline phosphatase activity. For boron concentrations below a threshold value (0.65 mM), extracts of the glass dissolution products supported the proliferation of bone marrow stromal cells, as well as the proliferation and function of murine MLO-A5 cells, an osteogenic cell line. Scanning electron microscopy showed attachment and continuous increase in the density of MLO-A5 cells cultured on the surface of the glass scaffolds. The results indicate that borate-based bioactive glass could be a potential scaffold material for bone tissue engineering provided that the boron released from the glass could be controlled below a threshold value.     

Optical Measurement of the Non-linear Focusing of Sound in Liquid Helium 4

We have measured the amplitude of 1MHz acoustic waves focused in liquid helium 4. Our resolution is 10 nanoseconds in time and 15 micrometers in space. The waves are focused onto a flat glass plate. We measure the reflection of light at the glass/helium interface, which depends on the refractive index of the liquid, consequently on its density which we could measure with an accuracy of ±10 ^–4 g/cm ³ . At large amplitude, strong non-linear effects are observed, in good agreement with a numerical calculation.