In situ fabricated metal-carbide with core–shell structure for high impact-toughness iron-matrix composite

A series of metal-carbide (Ta–TaC, Nb–NbC and W–WC) with core–shell structure for iron-matrix composites are fabricated by in situ solid-phase diffusion. Results show that the formation of metal-carbide with a rod-shaped core–shell structure, in which the metal-rod surface was covered with a carbide shell layer, in the iron- matrix after in situ solid-phase diffusion. The TaC, NbC, and WC shell layers are in situ synthesised by the diffusion of carbon atoms from the iron-matrix onto the surface of the Ta, Nb, and W rods, respectively. Metallurgical integration occurs between metal-carbide and iron-matrix. The metal-carbide-reinforced iron-matrix composites show excellent impact resistance, and the shell-layer hardness is extremely high.     

In situ preparation of a SiC–TiB2 composite and its wear fracture mechanism at high temperatures

Journal of Materials Science - The unsatisfactory high-temperature performance of commonly used silicon carbide (SiC)-based ceramics calls for a novel approach for their reinforcement. We present...     

The preparation and mechanical properties of carbon–carbon/lithium–aluminum–silicate composite joints

Silica carbide modified carbon cloth laminated C–C composites have been successfully joined to lithium–aluminum–silicate (LAS) glass–ceramics using magnesium–aluminum–silicate (MAS) glass–ceramics as interlayer by vacuum hot-press technique. The microstructure, mechanical properties and fracture mechanism of C–C/LAS composite joints were investigated. SiC coating modified the wettability between C–C composites and LAS glass–ceramics. Three continuous and homogenous interfaces (i.e. C–C/SiC, SiC/MAS and MAS/LAS) were formed by element interdiffusions and chemical reactions, which lead to a smooth transition from C–C composites to LAS glass–ceramics. The C–C/LAS joints have superior flexural property with a quasi-ductile behavior. The average flexural strength of C–C/LAS joints can be up to 140.26 MPa and 160.02 MPa at 25 °C and 800 °C, respectively. The average shear strength of C–C/LAS joints achieves 21.01 MPa and the joints are apt to fracture along the SiC/MAS interface. The high retention of mechanical properties at 800 °C makes the joints to be potentially used in a broad temperature range as structural components.     

In situ synthesis of gold–polyaniline composite in nanopores of polycarbonate membrane

In situ one-step chemical synthesis route for the preparation of a gold–polyaniline composite in nanopores of polycarbonate (PC) membrane is reported. PC membrane, which was placed in a specially designed two-compartment cell, separated the aqueous solution of aniline from HAuCl₄ solution. Concentration gradient across the membrane caused movement of AuCl₄ ⁻ and anilinium ions in the pores of polycarbonate membrane. Nanopores in PC membrane acted as reaction vessels where aniline and HAuCl₄ were allowed to mix together, and the redox reaction between aniline and HAuCl₄ led to the formation of gold–polyaniline composite. The gold–polyaniline composite in PC membrane was characterised by EDXRF, XRD, UV–Vis spectroscopy, FTIR and TEM. Peak broadening in XRD suggests that Au particles formed in the membrane are nanocrystallites and average crystallite size is (24 ± 4) nm. TEM studies show that gold nanoparticles are randomly dispersed in polyaniline clusters formed in the nanopores of PC membrane. Characterisation results show that the surfaces of the PC membrane exposed to HAuCl₄ and aniline have significantly higher concentrations of Au nanoparticles and polyaniline, respectively.     

Synthesis of water-compatible surface-imprinted composite microspheres with core–shell structure for selective recognition of thymopentin from aqueous solution

A novel water-compatible surface-imprinted core–shell microsphere, which had multiple non–covalent interactions with template molecule, was successfully prepared by the surface grafting polymerization method in acetonitrile–water systems with thymopentin as template through ionic liquid-functionalized polyethyleneglycolmethacrylate-co-vinylimidazole microsphere as the matrix. The average diameter of matrix was 1 μm ± 20 nm and the thickness of imprinted layer was about 50 nm. The results of static adsorption experiments indicated that ionic liquid-functionalized molecularly imprinted microspheres showed the good adsorption capacity and specific recognition for template peptide. The binding-isotherm analysis showed that Langmuir isotherm models gave a good fit in the range of concentrations, suggesting that there was only one kind of binding site in imprinted layer. Measurements of the binding kinetics revealed that surface-imprinted composite microspheres reached peptide-adsorption equilibrium in 60 min and the maximum adsorption capacity for TP5 was 38.4 mg g^?1. The effects of pH, salt concentration, and temperature on the adsorption capacities were investigated. The microspheres were found to have a high specificity for TP5 with little affinity for BSA and Hb. Finally, the core–shell microspheres can be reused with only 15.6 % decrease in TP5 adsorption capacity after six times.     

Preparation of alginate–CaCl2 microspheres as resveratrol carriers

Resveratrol-loaded calcium alginate microspheres for prolonged drug release were prepared by ionic gelation of alginate with calcium chloride (CaCl₂). Further, resveratrol-loaded calcium alginate microspheres were developed using two concentrations of alginate (0.5 and 1 % w/v) and CaCl₂ (0.5 and 1 M) and an encapsulator equipped with a 300-μm nozzle. The mean particle size of the microspheres was between 175.52 and 244.03 μm, and an encapsulation efficiency (EE) of over 95 % was observed. FTIR spectroscopy indicated a polyelectrolyte interaction between alginate and CaCl₂; alginate microsphere thermograms were analyzed by differential scanning calorimetry. X-ray diffraction shows the crystalline change of microspheres by cross linking. The release profiles and EE increased depending on the CaCl₂ concentration, and a slow initial burst release was observed on freeze-dried microspheres. These results indicate that resveratrol-loaded calcium alginate microspheres can be used as a potential resveratrol delivery system in the food industry.     

In situ stir cast Al–TiB2 composite: processing and mechanical properties

Abstract

Elemental Ti and B powders of stoichiometric composition were mixed and added to molten aluminium. In situ TiB₂ particles were formed in the aluminium melt. On casting, an Al–TiB₂ composite was produced. Despite the presence of the Al₃Ti phase associated with the Al–Ti–B ternary system, the in situ TiB₂ particles, with sizes of 1–3 µm formed in the composite was able to yield an improvement of 57% increase in tensile strength, 66% in yield strength and 22% in modulus in an Al–15 vol.-%TiB₂ composite. The extent of improvement in these properties depended on the volume fraction in the composite. Fractography showed a texture of dimples seated with hexagonal TiB₂ particles indicating retention of high ductility in the composite, despite the fact that the predominance of the coarse Al₃Ti in the composite had led to premature rupturing.     

Simulated strength and structure of carbon–carbon reinforced composite

The atomistic simulations of carbon nanotube (CNT) – carbon reinforced composite material are reported. The studied composite samples are obtained by impregnating certain amounts of CNTs (3,3) and (6,6) into a pristine graphite matrix. The addition of CNTs is found to be of significant usefulness for the CNT–reinforced composites, since it allows to achieve extreme lightness and strength. Being impregnated into graphite matrix, CNTs are able to increase the critical component of its initially highly anisotropic Young modulus by 2–8 times. The linear thermal expansion coefficients do not exceed 10⁻⁶ to 10⁻⁵ K⁻¹, making this material applicable for novel aviation and space vehicles. The degree of dispersion of CNTs within graphite matrix is found to drastically influence composite properties.     

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).     

Influence of the preparation procedure and chitosan type on physicochemical properties and release behavior of alginate–chitosan microparticles

Background: The potential for use of chitosan-treated alginate microparticles as a vehicle for oral phenytoin delivery has not been thoroughly exploited. Aim: We studied the influence of preparation procedure and chitosan type on physicochemical properties and release behavior of alginate-chitosan microparticles. Method: The total number of 24 microparticles formulations prepared by varying contents of calcium gelling ions and varying contents and type of chitosan was examined. As an additional variable, two different hardening times (1 and 24 hours) were employed. Possible interactions of components, surface morphology of microparticles as well as release profile of phenytoin were studied. Results: Both series of formulations with regard to hardening times, irrespective of the chitosan type and/or concentration employed appeared to be highly loaded with the model drug (above 90%). The drug release studies showed that the kinetics of phenytoin cannot be straightforwardly predicted based on the molecular weight of chitosan alone. On the other hand, prolonging the hardening time from 1 to 24 hours had significantly improved phenytoin kinetics, and gave rise to a formulation with the liberation half-time of about 2.5 hours. Conclusion: This study showed that the latter formulation is eligible for further modifications aimed at improving the regularity of phenytoin absorption.     

Nicotine–magnesium aluminum silicate microparticle surface modified with chitosan for mucosal delivery

Magnesium aluminum silicate (MAS), a negatively charged clay, and nicotine (NCT), a basic drug, can interact electrostatically to form microparticles. Chitosan (CS) was used for the surface modification of the microparticles, and a lyophilization method was used to preserve the original particle morphology. The microparticles were characterized in terms of their physicochemical properties, NCT content, mucoadhesive properties, and release and permeation across porcine esophageal mucosa. The results showed that the microparticles formed via electrostatic interaction between MAS and protonated NCT had an irregular shape and that their NCT content increased with increasing NCT ratios in the microparticle preparation solution. High molecular weight CS (800 kDa) adsorbed to the microparticle surface and induced a positive surface charge. CS molecules intercalated into the MAS silicate layers and decreased the crystallinity of the microparticles, leading to an increase in the release rate and diffusion coefficient of NCT from the microparticles. Moreover, the microparticle surface modified with CS was found to have higher NCT permeation fluxes and mucoadhesive properties, which indicated the significant role of CS for NCT mucosal delivery. However, the enhancement of NCT permeation and of mucoadhesive properties depended on the molecular weight and concentration of CS. These findings suggest that NCT-MAS microparticle surface modified with CS represents a promising mucosal delivery system for NCT.     

Thermomechanical behaviour of a copper–chromium in situ composite

Abstract

The mechanical response of an in situ copper–chromium composite was investigated over a range of temperatures by means of tensile and isothermal creep tests. Scanning electron microscopy was used to characterise the extent, type, and distribution of damage. It was found that the failure mechanisms fell into distinct regimes. At cryogenic temperatures damage tended to occur in the form of reinforcement fracture. Around room temperature, very little damage was observed in the composite. At temperatures of about 400°C, extensive damage was again observed in the form of reinforcement failure and cavitation. Further increase in the test temperature resulted in a transition from a local to a global load sharing, with damage distribution becoming more homogeneous. These experimental observations were rationalised by considering the relative extent of deformation within the two phases as a function of temperature.     

In situ high-temperature X-ray and neutron diffraction of Cu–Mn oxide phases

Copper–manganese oxides were analyzed by in situ high-temperature powder neutron and X-ray diffraction to investigate their crystal structure. Cu–Mn spinel was found to form a continuous solid solution with cubic symmetry between Mn₃O₄ and Cu₂MnO₄. A high-temperature phase with approximate composition Cu₅Mn₄O₉ was shown to have hexagonal symmetry. The cation distribution and lattice parameters of Cu–Mn spinel were resolved through Rietveld refinement of in situ neutron diffraction data. The results demonstrated that the Cu ion has a lower octahedral site preference than manganese ions, and quenching is not a reliable method to determine the equilibrium structure in the system.     

In situ production of Fe–VC and Fe–TiC surface composites by cast-sintering

Using a new cast-sintering technique, iron-base surface composites reinforced by VC and TiC particles which were produced in situ and consisting of self-lubricant graphite and chromium-carbide, were sintered on the surface of cast steel during casting. The structure and composition of the surface composites were studied with the help of a SEM, an electron probe and XRD. From the outside in of the iron-based surface composites, the concentration of V and Ti was relatively stable and consistently retained a high level, while the concentration of Cr and Ni took on a gradient distribution and decreased gradually. The fine particles of VC and TiC measuring between 1 and 3 μm in diameter were uniformly dispersed in their matrices, and there was a perfect metallurgy-bond between the surface composite layer and the master-alloy. Under the condition of dry slipping with a heavy load, the Fe–VC and Fe–TiC surface composites offer virtually unique wear-resistance.     

Process and mechanical properties of carbon/carbon–silicon carbide composite reinforced with carbon nanotubes grown in situ

A hierarchical C_f/C–SiC composite was fabricated via in situ growth of carbon nanotubes (CNTs) on fiber cloths following polymer impregnation and pyrolysis process. The effects of CNTs grown in situ on mechanical properties of the composite, such as flexural strength, fracture toughness, crack propagation behavior and interfacial bonding strength, were evaluated. Fiber push-out test showed that the interfacial bonding strength between fiber and matrix was enhanced by CNTs grown in situ. The propagation of cracks into and in fiber bundles was impeded, which results in decreased crack density and a “pull-out of fiber bundle” failure mode. The flexural strength was increased while the fracture toughness was not improved significantly due to the decreased crack density and few interfacial debonding between fiber and matrix, although the local toughness can be improved by the pull-out of CNTs.     

In vitro and in vivo biocompatibility of graded hydroxyapatite–zirconia composite bioceramic

To obtain bioceramics with good osteoinductive ability and mechanical strength, graded hydroxyapatite–zirconia (HA–ZrO₂) composite bioceramics were prepared in this work. The biocompatibility of the bioceramics was investigated in vitro based on acute toxicity and cytotoxicity tests and hemolysis assay. Results showed the studied graded HA–ZrO₂ had little toxicity to mouse and L929 mouse fibroblasts. Also, hemolysis assay indicated a good blood compatibility of the bioceramics. Based on the results of in vitro tests, animal experiments were performed on white New Zealand rabbits by implantation into hip muscles and femur. It was found that the graded HA–ZrO₂ composite bioceramics exhibited superior osteoinductive ability, which may be a promising bioceramics implant.     

Strength and damage tolerance of composite–composite joints with steel and titanium through the thickness reinforcements

Today’s aeronautic, automotive and marine industry is in demand of structurally efficient, low weight alternatives for composite–composite joints which combine the advantages of low weight input of adhesively bonded joints and high damage tolerance of through the thickness bolted joints. In the present work, composite–composite joints are reinforced through the thickness by thin metal inserts carrying cold metal transfer welded pins (CMT pins). The influence of pin alignment and type of pin on the damage tolerance of single lap shear (SLS) composite–composite joints is investigated. The use of titanium reinforcements is evaluated and compared to stainless steel reinforced, adhesively bonded and co-cured specimens. A detailed analysis of the stress–strain behavior is given and the stiffness and energy absorption of the SLS joints during tensile loading is assessed. The results show that joints reinforced with CMT pins absorb significantly higher amounts of energy, when compared to adhesively bonded and co-cured joints.     

Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon–carbon composite and TiBw/Ti–6Al–4V composite joint

Carbon–carbon composite (C–C composite) and TiB whiskers reinforced Ti–6Al–4V composite (TiB_w/Ti–6Al–4V composite) were brazed by Cu–Ni + TiB₂ composite filler. TiB₂ powders have reacted with Ti which diffused from TiB_w/Ti–6Al–4V composite, leading to formation of TiB whiskers in the brazing layer. The effects of TiB₂ addition, brazing temperature, and holding time on microstructure and shear strength of the brazed joints were investigated. The results indicate that in situ synthesized TiB whiskers uniformly distributed in the joints, which not only provided reinforcing effects, but also lowered residual thermal stress of the joints. As for each brazing temperature or holding time, the joint shear strength brazed with Cu–Ni alloy was lower than that of the joints brazed with Cu–Ni + TiB₂ alloy powder. The maximum shear strengths of the joints brazed with Cu–Ni + TiB₂ alloy powder was 18.5 MPa with the brazing temperature of 1223 K for 10 min, which was 56% higher than that of the joints brazed with Cu–Ni alloy powder.