Development of a procedure for spherical alginate–boehmite particle preparation

Herein we describe a versatile new strategy for producing spherical solid particles with 2 mm in size using integrated gelling process. The method involves the formation of spherical droplets by using a peristatic pump device and shaping the droplets in a liquid calcium chloride solution. The shape and size of these calcium alginate macroparticles depend strongly on the calcium solution concentration. The shaping mechanism of the macroparticles and the impact of the experimental conditions on particle shape and size are investigated. This method has the following features: (1) A new level of control over the shapes of the particles is offered. (2) The procedure can be scaled up to produce large numbers of particles. (3) The final porous structure of the developed particle can be designed for a specific application (adsorption, catalysis).     

Effect of γ-irradiation on the physical and mechanical properties of chitosan powder

In this study, locally produced chitosan powder was irradiated with pre-determined doses of γ-ray (Co-60) of 10 kGy, 25 kGy, 50 kGy and 100 kGy respectively. The properties of both chitosan powder and the chitosan film were examined and compared with unradiated chitosan. Physical characteristic of the irradiated powder and film was studied using stereo microscope. It was observed that the γ-ray induces a noticeable colour tone intensity change to the chitosan. Further investigation using Fourier Transformed Infrared Spectroscopy (FT-IR) analysis has confirmed that the chain scission reaction was occurred as a result of γ-ray exposure through the depolymerization mechanisms. Interestingly, the degree of deacetylation (DD) of chitosan measured using FT-IR showed a negligible effect due to the exposure of γ-ray radiation. Further investigation on the viscosity average molecular weight (M_v) showed a reduction of M_v from 577 kD of pure chitosan to 458 kD, 242 kD, 159 kD and 106 kD for 10 kGy, 25 kGy, 50 kGy and 100 kGy of γ-radiated chitosan respectively. In addition, the tensile strength and elongation at break showed a similar decreasing trend with increasing dosage of γ-ray.     

Influence of sulphur on the microstructure and properties of Ag–Cu–Zn brazing filler metal

Abstract

The effect of sulphur on the microstructure and properties of Ag45–Cu30–Zn25 brazing filler metal was investigated. Under the given experimental conditions, the sulphuration products mainly consisted of CuS, ZnS, Ag₂S, Cu₂S and Ag₃CuS₂. These sulphides not only distributed on the surface but also diffused into the interior of the filler metal and cut apart the matrix thereby significantly damaging the tensile strength of the filler metal from 658 to 283 MPa. The corresponding fracture characterisation turned from ductile fracture to brittle fracture. The sulphides existed as solid particles, which hinder the spreading of the liquid filler metal and the spreading area dramatically decreased from 317?09 to 18?55 mm², which indicates that the filler metal rarely wets the base metal.     

Influence of the elastic stress relaxation on the microstructures and mechanical properties of metal–matrix composites

Role of the residual stresses on the mechanical properties of metal–matrix composites is studied. It is shown that the stress relaxation can be responsible for the morphologies and spatial distribution of precipitates. Direct measurements of the residual stress is also emphasized and the influence of dislocations in the accommodation process and during interface crossing is exemplified.     

Influence of the combined addition of Y and Nd on the microstructure and mechanical properties of Mg–Li alloy

Y and Nd are simultaneously added into Mg–5Li–3Al–2Zn alloy. It is found that there exist the phases of α-Mg, AlLi, Al₁₁Nd₃ and Al₂Y in the alloys. When the contents of Y and Nd are 1.2% and 0.8%, respectively, the grain is the finest with an average size of 30 μm, and the tensile strength of the alloy reaches 231 MPa, the elongation reaches 16%. When the ratio of Y to Nd is 1.2:0.8, there is a synergistic strengthening effect.     

Influence of humidity on the scratch behavior of polystyrene–acrylonitrile random copolymers

The effect of exposure to a humid environment on the scratch behavior of a set of model polystyrene–acrylonitrile (SAN) random copolymers was investigated over a period of 10 days. Linear increasing load scratch tests were performed according to ASTM D7027/ISO 19252. The critical loads for the onset of key scratch deformation mechanisms like periodic micro-cracking, plowing, and scratch visibility were used as metrics for evaluating scratch resistance. The scratching coefficient of friction was evaluated, as well. It was found that, in general, the scratch resistance decreases during the first few days of moisture exposure, but then experiences a degree of recovery upon saturation. It is proposed that the initially absorbed moisture causes plasticization, making the surface weaker until saturation where the water molecules gather together on the surface to impart a degree of lubrication and consequently improve the scratch resistance. Implications of moisture absorption on the scratch behavior of polymers will be discussed.     

Effect of substrate type, dopant and thermal treatment on physicochemical properties of TiO2–SnO2 sol–gel films

Thin nanocrystalline TiO₂–SnO₂ films (0–50 mol% SnO₂) were prepared on quartz and stainless steel substrates by sol–gel coating method. The obtained films were investigated by XRD, Raman spectroscopy and XPS. The size of the nanocrystallites was determined by XRD–LB measurements. We ascertained that the increase of treatment temperature and concentration of SnO₂ in the films favour the crystallization of rutile phase. The substrate type influences more substantially the phase composition of the TiO₂–SnO₂ films. It was established that a penetration of elements took place from the substrate into the films. TiO₂ films deposited on quartz substrate include a Si which stabilizes anatase phase up to 600 °C. The films which are deposited on stainless steel substrate and treated at 700 °C show the presence of significant quantity of rutile phase. This phenomenon could be explained by the combined effect of Sn dopant as well as Fe and Cr, which also are penetrated in the films from the steel substrate. The titania films doped up to 10 mol% SnO₂ on stainless steel possess only 12–17 nm anatase crystallites, whereas the TiO₂–(10–50 mol%) SnO₂ films contain very fine grain rutile phase (4 nm).     

Influence of Ni–Cr substitution on the magnetic and electric properties of magnesium ferrite nanomaterials

The effect of variation of composition on the structural, morphological, magnetic and electric properties of Mg_1?xNi_xCr_xFe_2?xO₄ (x = 0.0–0.5) nanocrystallites is presented. The samples were prepared by novel polyethylene glycol (PEG) assisted microemulsion method with average crystallite size of 15–47 nm. The microstructure, chemical, and phase analyses of the samples were studied by the scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray fluorescence (ED-XRF), and X-ray diffraction (XRD). Compositional variation greatly affected the magnetic and structural properties. The high-field regimes of the magnetic loops are modelled using the Law of Approach (LOA) to saturation in order to extract information about their anisotropy and the saturation magnetization. Thermal demagnetization measurements are carried out using VSM and significant enhancement of the Curie temperature from 681 K to 832 K has been achieved by substitution of different contents of Ni–Cr. The dc-electrical resistivity (ρ^RT) at potential operational range around 300 K is increased from 7.5 × 10⁸ to 4.85 × 10⁹ Ωcm with the increase in Ni–Cr contents. Moreover, the results of the present study provide sufficient evidence to show that the electric and magnetic properties of Mg-ferrite have been improved significantly by substituting low contents of Ni–Cr.     

Sintering behavior and effect of ternary additions on the microstructure and mechanical properties of Ni–Fe-based alloy

The sintering behavior and effect of ternary additions on the microstructure and mechanical properties of Ni–Fe-based alloy were investigated, with the ternary additions Al, Co, Cr, Mo, Ta, and Ti. The effect of the different ternary additions was more obvious when comparing Ni40Fe10X (X?=?Al, Ti) and the rest of the alloys, with the former having better density and hardness than the latter. Sintered densities close to theoretical (≥98%), excluding Ni40Fe10Mo, were achieved. Interestingly, the visible porosity regions in all the samples were very small in agreement of the high sintered densities observed. The shrinkage rate was similar for all the alloys, and three peaks were observed, the first two peaks merged, and overall all the peaks were indicative of the phenomena responsible for good densification. The hardness measurement revealed that samples with poor homogeneity and those with clusters of ternary element addition in the microstructure had no hardness improvement compared to the base binary alloy. For alloys with Al, Cr, and Ti, fracture surface SEM morphology revealed the intergranular fracture of the grains and the ductile tearing of the binding phase, typical dimple structure of a ductile material; therefore, the mechanical properties of these samples are improved, while the rest of the alloys were characterized with peeling of very fine spherical particles and varying grain size and consequently compromising its mechanical properties.     

Influence of high-pressure torsion and hot rolling on the microstructure and mechanical properties of aluminum–fullerene composites

In this study, we investigate the impacts of working process, high-pressure torsion (HPT) and hot rolling (HR) on the microstructure and mechanical performance of aluminum-based nanocomposites containing fullerenes. HPT caused severe plastic deformations that generate numerous dislocations and lattice strains, and this stimulated the formation of aluminum carbides (Al₄C₃) and reduced the hardness during heat treatment. In contrast, the HRed specimens experienced dynamic recovery, and their initial dislocation densities and lattice strains were lower than those of the HPTed specimens. Thus, the HRed composites formed supersaturated aluminum phases as well as aluminum carbides during the heat treatment. The supersaturated phases provided high-density dislocations and severe lattice strains, resulting in an increase in the hardness during the heat treatment. This comparison suggests that the mechanical properties of aluminum–fullerene composites can be controlled by working processes in practical situations.     

Study of preparation and properties on solid superacid sulfated titania–silica nanomaterials

Solid superacid sulfated titania–silicon (SO₄²⁻/TiO₂–SiO₂) nanocatalysts were prepared by the chemical method. The structure and the properties of the catalysts were examined by using XRD, BET, DTA and IR spectroscopy. Acidity properties of the catalysts were tested by Hammett indicator. Catalytic activity of the catalysts was evaluated by the reaction of glycerin with acetic acid in toluene. The optimum calcination temperature of the catalysts is 450 °C. The specific surface area of the catalyst is 550 m²/g. The conversion rate of acetic acid is 91.4% when the TiO₂ content of the catalyst is 13.8 wt.%.     

Influence of notch radius and microstructure on the fracture behavior of Al–Zn–Mg–Cu alloys of different purity

The influence of notch radius on the fracture behavior of two high-strength Al–Zn–Mg–Cu alloys with different Fe content in the T73 condition was investigated. The fracture toughness tests were performed on non-fatigue-precracked notched bending specimens with different notch radii ranged from 0.15 mm to 1.0 mm. The obtained data were interpreted using the concept of Notch Fracture Mechanics combined with finite-element method (FEM) calculations. It was found that both alloys are very sensitive to the notch radius. The fracture toughness increases with increasing notch radius. For a given notch radii, the increase in fracture toughness is more significant for the more pure alloy. The fracture behavior of investigated alloys with respect to microstructural features and their relation with the fracture micromechanisms were analyzed.     

The fabrication of nanocomposites via calcium phosphate formation on gelatin–chitosan network and the gelatin influence on the properties of biphasic composites

A novel biodegradable polymer–ceramic nanocomposite which consisted of gelatin (Gel), chitosan (CS), and calcium phosphate (CaP) nanoparticles was prepared based on in situ preparation method. The fabricated biocomposites were characterized by FTIR, X-ray diffraction (XRD), transmission electron microscopy (TEM) as well as scanning electron microscope with X-ray elemental analysis (SEM-EDX). The characterization results confirmed that the crystalline calcium phosphate nanoparticles were mineralized in polymeric matrix and the interaction between Ca2+ in calcium phosphate and functional groups in polymers molecular chains was formed. XRD result showed that in addition to hydroxyapatite (HA), Brushite (BR) and tricalcium phosphate (β-TCP) particles also were formed due to lack of complete penetration of the basic solution into the polymeric matrix. However, SEM image indicated that the polymeric matrix has the controlling role in the particle size of calcium phosphate. The size of particles in three component composites was about 100 nm while in two component composites proved to be more in μm size. TEM observation supported SEM results and showed that the three component composites have calcium phosphate nanoparticles. The elastic modulus and compressive strength of the composites were also improved by the employment of gelatin and chitosan together, which can make them more beneficial for surgical applications.     

Influence of retrogression and reaging on microstructure and properties of 8090 Al–Li alloy

Abstract

An investigation was made into the influence of a retrogression and reaging treatment on the microstructure, tensile properties, and stress corrosion cracking resistance of 8090 Al–Li alloy. The results show that retrogression of the material at 230°C for 40 min or 325°C for 1·5 min, and then reaging to the peak aged condition, can result in an improved combination of tensile strength and stress corrosion cracking resistance. Through retrogression and reaging treatment, the alloy almost achieves the strength of the peak aged state and the stress corrosion cracking resistance of the overaged state. Transmission electron microscopy indicates that the δ′ phase dissolves during retrogression and reprecipitates during reaging, thus increasing the strength. The T₂ phase precipitates and grows during both retrogression and reaging, which results in the increase of stress corrosion cracking resistance.

MST/1670     

Influence of short glass fibres and weldlines on the mechanical properties of injection-moulded acrylonitrile–styrene–acrylate copolymer

The present study investigated the dependence of various mechanical and fracture properties on the volume fraction, f, of reinforcing glass fibres in acrylonitrile–styrene–acrylate (ASA) copolymer. The addition of glass fibres enhanced the ultimate strength and modulus as measured in both tension and flexure but reduced the total work of fracture. The elastic modulus was not affected by the loading mode. The ultimate strength in flexure was found to be always greater than in tension by a factor of about 1.3. Both properties were found to be a linear function of f following the rule of mixtures:Pc=Pff+Pm(1–f)where Pc is the measured property for the composite, Pf and Pm are the corresponding values for the fibre and the matrix, respectively, and is the overall efficiency of the reinforcing fibres. Addition of glass fibres to ASA polymer reduced both the notched and the unnotched impact strengths. Linear elastic fracture mechanics were used to determine values of the fracture toughness and the strain energy release rate. The fracture toughness did not change significantly with f, whereas the strain energy release rate decreased with increasing f. The presence of weldlines in the specimens had an adverse effect on all tensile properties except for the elastic modulus. The weldline integrity parameter for the modulus was between 1 and 0.95, and for strength it was between 0.87 and 0.20, decreasing linearly with increasing f. © 1998 Kluwer Academic Publishers     

Influence of Y on the phase composition and mechanical properties of as-extruded Mg–Zn–Y–Zr magnesium alloys

The influence of Y on the microstructure, phase composition and mechanical properties of the extruded Mg–6Zn–xY–0.6Zr (x = 0, 1, 2, 3 and 4, in wt%) alloys has been investigated and compared by optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer and tensile testing. The increase in Y content has shown grain refinement effects on the microstructure morphologies of the extruded alloys. However, when the content of Y exceeds 2.2 wt%, the grain refinement effect of the Y is not obvious any more with the increase of the Y content. The quasicrystal I-phase (Mg₃YZn₆), face-centred cubic structure W-phase (Mg₃Y₂Zn₃) and a long period stacking ordered (LPSO) X-phase (Mg₁₂YZn) can precipitate in different ranges of Y/Zn ratio (in at.%) when the Y content in the Mg–Zn–Y–Zr alloys is varied. Comparison of the mechanical properties of the alloys showed that the different ternary Mg–Zn–Y phases have different strengthening and toughening effects on the Mg–Zn–Y–Zr alloys in the following order: X-phase > I-phase > W-phase > MgZn₂.     

Influence of La–B–Zn glass on the sintering and microwave dielectric properties of Ca–Nd–Ti ceramics

The effects of La₂O₃–B₂O₃–ZnO (LBZ) glass on the sintering behaviors, phase structures, microstructures and the microwave dielectric properties of perovskite type Ca_0.6Nd_0.26TiO₃ (CNT) ceramics were studied. It indicates that the LBZ glass has an obvious effect on lowering the sintering temperature without damaging the microwave dielectric properties of the CNT ceramics. Small amounts of LBZ glass significantly lowered the sintering temperatures of CNT ceramics and obtained excellent microwave dielectric properties. However, too much LBZ glass is leading to inferior dielectric properties. The CNT ceramics doped with 3 wt% LBZ can be well sintered at 975 °C for 4 h and shows good properties: ε_r = 87.87, Q × f = 8132 GHz (f = 3.3 GHz), τ_f = +244.63 ppm/°C.     

Influence of crystallization time on microstructures and dielectric properties of tungsten–bronze glass–ceramics

A glass with a composition of 22.5SrO–22.5BaO–15Nb₂O₅–40SiO₂ (mol %) was prepared by a melt-quenching method and then heat-treated at 950 °C for different crystallization time. Microstructure observations were carried out using scanning electron microscope and dielectric properties were measured by a LCR meter. The experimental results show that volume fraction of the crystalline phase increased, dielectric constant maximum enhanced, and Curie temperature shifted as the crystallization time is prolonged. The decrease in the Curie temperature for the sample crystallized at 950 °C for 1 h is considered to be caused by the clamping effect from the glass matrix or small compositional fluctuation. Impedance spectroscopy has been employed to study the polarization contributions arising from the glass and crystalline phases in the glass–ceramics for different crystallization time. With the increase in crystallization time, the magnitudes of impedance and modulus as well as the relaxation frequency changed significantly. The activation energy calculated from the relaxation frequency increased for the glass phase due to a denser network structure, while the crystalline phase showed a slight decrease implying there is no change in its polarization mechanism.