Synthesis and mechanical properties of Cu-based bulk metallic glass composites containing in-situ TiC particles

Cu-based bulk metallic glass matrix composites (BMGMCs) containing in-situ TiC particles were fabricated successfully. The yield and fracture strength increased from 1930 MPa, 2250 MPa to 2210 MPa, 2500 MPa, respectively. The ductility was improved and the hardness was also enhanced by 25%. The fracture mechanism was investigated in detail. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Superconductivity in metal-mixed ion-implanted polymer films

Ion implantation of normally insulating polymers offers an alternative to depositing conjugated organics onto plastic films to make electronic circuits. We used a 50 keV nitrogen ion beam to mix a thin 10 nm Sn/Sb alloy film into the subsurface of polyetheretherketone and report the low temperature properties of this material. We observed metallic behavior, and the onset of superconductivity below 3 K. There are strong indications that the superconductivity does not result from a residual thin film of alloy, but instead from a network of alloy grains coupled via a weakly conducting, ion-beam carbonized polymer matrix. (c) 2006 American Institute of Physics.

Physicochemical characterisation, drug polymer dissolution and in vitro evaluation of phenacetin and phenylbutazone solid dispersions with polyethylene glycol 8000

Poor water solubility leads to low dissolution rate and consequently, it can limit bioavailability. Solid dispersions, where the drug is dispersed into an inert, hydrophilic polymer matrix can enhance drug dissolution. Solid dispersions were prepared using phenacetin and phenylbutazone as model drugs with polyethylene glycol (PEG) 8000 (carrier), by melt fusion method. Phenacetin and phenylbutazone displayed an increase in the dissolution rate when formulated as solid dispersions as compared with their physical mixture and drug alone counterparts. Characterisation of the solid dispersions was performed using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). DSC studies revealed that drugs were present in the amorphous form within the solid dispersions. FTIR spectra for the solid dispersions of drugs suggested that there was a lack of interaction between PEG 8000 and the drug. However, the physical mixture of phenacetin with PEG 8000 indicated the formation of hydrogen bond between phenacetin and the carrier. Permeability of phenacetin and phenylbutazone was higher for solid dispersions as compared with that of drug alone across Caco-2 cell monolayers. Permeability studies have shown that both phenacetin and phenylbutazone, and their solid dispersions can be categorised as well-absorbed compounds.

Transition metal ion coordination in hydrophilic polymer membranes

The research described within this thesis is concerned with the investigation of transition metal ion complexation within hydrophilic copolymer membranes. The membranes are copolymers of 4-methyl-4'-vinyl-2,2'-bipyridine, the 2-hydroxyethyl ester of 4,4'- dicarboxy-2,2'-bipyridine & bis-(5-vinylsalicylidene)ethylenediamine with 2-hydroxyethyl methacrylate. The effect of the polymer matrix on the formation and properties of transition metal iron complexes has been studied, specifically Cr(III) & Fe(II) salts for the bipyridyl- based copolymer membranes and Co(II), Ni(II) & Cu(II) salts for the salenH2- based copolymer membranes. The concomitant effect of complex formation on the properties of the polymer matrix have also been studied, e.g. on mechanical strength. A detailed body of work into the kinetics and thermodynamics for the formation of Cu(II) complexes in the salenH2- based copolymer membranes has been performed. The rate of complex formation is found to be very slow while the value of K for the equilibrium of complex formation is found to be unexpectedly small and shows a slight anion dependence. These phenomena are explained in terms of the effects of the heterogeneous phase provided by the polymer matrix. The transport of Cr(III) ions across uncomplexed and Cr(III)-pre-complexed bipyridyl-based membranes has been studied. In both cases, no Cr(III) coordination occurs within the time-scale of an experiment. Pre-complexation of the membrane does not lead to a change in the rate of permeation of Cr(III) ions. The transport of Co(II), Ni(II) & Cu(II) ions across salenH2- based membranes shows that there is no detectable lag-time in transport of the ions, despite independent evidence that complex formation within the membranes does occur. Finally, the synthesis of a number of functionalised ligands is described. Although they were found to be non-polymerisable by the methods employed in this research, they remain interesting ligands which provide a startmg pomt for further functionalisation.

Transition metal ion co-ordination in hydrophilic polymer membrane

This thesis is concerned with the investigation of transition metal (TM) ion complexation with hydrophilic membranes composed of copolymers of 4-vinyl pyridine & 4-methyl-4'vinyl- 2,2'-bipyridine with 2-hydroxyethyl methacrylate. The Cu(II), CoCII) & Fe(II) complexes with these coordinating membranes were characterised by a variety of techniques, in order to assess the effect of the polymer on the properties of the complex, and vice versa. A detailed programme of work was instigated into the kinetics of formation for the polymer-bound tris(bipyridyl) iron(II) complex; the rate and extent of complex formation was found to be anion-dependent. This is explained in terms of the influence of the anion on the transport properties and water content of the membrane, the controlling factor in the development of the tris-complex being the equilibrium concentration of Fe(II) in the gel matrix. A series of transport studies were performed with a view to the potential application of complexing hydrogel membranes for aqueous TM ion separations. A number of salts were studied individually and shown to possess a range of permeabilities; the degree of interaction between particular metal-ion:ligand combinations is given by the lag-time observed before steady-state permeation is achieved. However, when two TM salts that individually display different transport properties were studied in combination, they showed similar lag-times & permeabilities, characteristic of the more strongly coordinating metal ion. This 'anti-selective' nature thus renders the membrane systems unsuitable for TM ion separations. Finally, attempts were made to synthesise and immobilise a series of N ,0-donor macrocyclic ligands into hydrogel membranes. Although the functionalisation reactions failed, limited transport data was obtained from membranes in which the ligands were physically entrapped within the polymer matrix.

Mechanical properties and the evolution of matrix molecules in PTFE upon irradiation with MeV alpha particles

The morphology, chemical composition, and mechanical properties in the surface region of α-irradiated polytetrafluoroethylene (PTFE) have been examined and compared to unirradiated specimens. Samples were irradiated with 5.5 MeV 4He2+ ions from a tandem accelerator to doses between 1 × 106 and 5 × 1010 Rad. Static time-of-flight secondary ion mass spectrometry (ToF-SIMS), using a 20 keV C60+ source, was employed to probe chemical changes as a function of a dose. Chemical images and high resolution spectra were collected and analyzed to reveal the effects of a particle radiation on the chemical structure. Residual gas analysis (RGA) was utilized to monitor the evolution of volatile species during vacuum irradiation of the samples. Scanning electron microscopy (SEM) was used to observe the morphological variation of samples with increasing a particle dose, and nanoindentation was engaged to determine the hardness and elastic modulus as a function of a dose. The data show that PTFE nominally retains its innate chemical structure and morphology at a doses <109 Rad. At α doses ≥109 Rad the polymer matrix experiences increased chemical degradation and morphological roughening which are accompanied by increased hardness and declining elasticity. At  α doses >1010 Rad the polymer matrix suffers severe chemical degradation and material loss. Chemical degradation is observed in ToF-SIMS by detection of ions that are indicative of fragmentation, unsaturation, and functionalization of molecules in the PTFE matrix. The mass spectra also expose the subtle trends of crosslinking within the α-irradiated polymer matrix. ToF-SIMS images support the assertion that chemical degradation is the result of a particle irradiation and show morphological roughening of the sample with increased a dose. High resolution SEM images more clearly illustrate the morphological roughening and the mass loss that accompanies high doses of a particles. RGA confirms the supposition that the outcome of chemical degradation in the PTFE matrix with continuing irradiation is evolution of volatile species resulting in morphological roughening and mass loss. Finally, we reveal and discuss relationships between chemical structure and mechanical properties such as hardness and elastic modulus.

Composites take off without a parachute

The review is devoted to the cost effectiveness of composite materials applications as compared with their high performance characteristics. The use of reinforced plastics, ceramic matrix and metal matrix composites reinforced by carbon and graphite fibers in aerospace industry is considered. Until recently, the two major drivers for the application of composites in engines have been weight reduction and performance improvement. As shown, today a major challenge to be met by the industry is cost reduction.

The effect of microstructure on the fracture toughness of a metal-matrix composite

The fracture behaviour and plane strain fracture toughness, KIC, of four 8090-based metal-matrix composites containing 20 weight % SiC particles, 3, 6 and 23 μm in diameter, has been evaluated as a function of matrix ageing condition. Toughness values are found to be almost independent of reinforcement size. Ageing at 170°C results in a monotonic decrease in toughness with increasing strength up to the peak condition, with no subsequent recovery in toughness on overageing. However, unlike reinforced 8090, the composites are not found to be susceptible to intergranular embrittlement on overageing. The observed trends are found to be independent of reinforcement size. These findings are explained in terms of the strength, work hardening behaviour and nature and distribution of void-nucleating particles in the matrix. © 1993.

Failure in composite materials

The economic and efficient exploitation of composite materials in critical load bearing applications relies on the ability to predict safe operational lives without excessive conservatism. Developing life prediction and monitoring techniques in these complex, inhomogeneous materials requires an understanding of the various failure mechanisms which can take place. This article describes a range of damage mechanisms which are observed in polymer, metal and ceramic matrix composites.

Recovery of glass fibre and carbon fibres from reinforced thermosets by batch pyrolysis and investigation of fibre re-using as reinforcement in LDPE matrix

A semi-batch pyrolysis process was used to recover samples carbon fibre and glass fibre from their respective wastes. The mechanical properties of the recovered fibres were tested and compared to those of virgin fibres, showing good retention of the fibre properties. The recovered fibres were then used to prepare new LDPE composite materials with commercial and laboratory-synthesized compatibilizers. Mild oxidation of the post-pyrolysis recovered fibres and the use of different compatibilizers gave significant improvements in the mechanical properties of the LDPE composites; however some of the manufactured composites made from recovered fibres had properties similar to those made from virgin fibres.

Thermo-oxidative stabilization of poly(lactic acid) with antioxidant intercalated layered double hydroxides

Two antioxidant modified layered double hydroxides (AO-LDHs) were successfully prepared by theintercalation of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (IrganoxCOOH) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) in the layered structure of LDH. It was foundthat by anchoring the phenolic moieties to the LDH layers the antioxidant power is retained in the caseof Trolox, and even amplified in the case of IrganoxCOOH. A small amount of the two AO-LDHs wasincorporated into poly(lactic acid), PLA, by solution mixing and melt extrusion. The thermo-oxidativestability of the composites was compared with that of the neat PLA and PLA containing free AOs. SECanalysis indicates that, after a controlled period of ageing, both the AO-LDHs protect the PLA fromchain scission. The oxidation induction time (OIT, DSC) at 230 °C shows also the beneficial effects ofthe presence of the functional filler in the polymer matrix. Further, results from a preliminary migrationtest suggest that the AO species have a low tendency to migrate away from the AO-LDHs embedded inthe polymer matrix thus keeping the AO protected inside the nanofiller layers thereby remaining activefor a longer time.

Plasma and cold sprayed aluminum carbon nanotube composites: Quantification of nanotube distribution and multi-scale mechanical properties

Carbon nanotubes (CNT) could serve as potential reinforcement for metal matrix composites for improved mechanical properties. However dispersion of carbon nanotubes (CNT) in the matrix has been a longstanding problem, since they tend to form clusters to minimize their surface area. The aim of this study was to use plasma and cold spraying techniques to synthesize CNT reinforced aluminum composite with improved dispersion and to quantify the degree of CNT dispersion as it influences the mechanical properties. Novel method of spray drying was used to disperse CNTs in Al-12 wt.% Si prealloyed powder, which was used as feedstock for plasma and cold spraying. A new method for quantification of CNT distribution was developed. Two parameters for CNT dispersion quantification, namely Dispersion parameter (DP) and Clustering Parameter (CP) have been proposed based on the image analysis and distance between the centers of CNTs. Nanomechanical properties were correlated with the dispersion of CNTs in the microstructure. Coating microstructure evolution has been discussed in terms of splat formation, deformation and damage of CNTs and CNT/matrix interface. Effect of Si and CNT content on the reaction at CNT/matrix interface was thermodynamically and kinetically studied. A pseudo phase diagram was computed which predicts the interfacial carbide for reaction between CNT and Al-Si alloy at processing temperature. Kinetic aspects showed that Al4C3 forms with Al-12 wt.% Si alloy while SiC forms with Al-23wt.% Si alloy. Mechanical properties at nano, micro and macro-scale were evaluated using nanoindentation and nanoscratch, microindentation and bulk tensile testing respectively. Nano and micro-scale mechanical properties (elastic modulus, hardness and yield strength) displayed improvement whereas macro-scale mechanical properties were poor. The inversion of the mechanical properties at different scale length was attributed to the porosity, CNT clustering, CNT-splat adhesion and Al 4C3 formation at the CNT/matrix interface. The Dispersion parameter (DP) was more sensitive than Clustering parameter (CP) in measuring degree of CNT distribution in the matrix.

Plasma And Cold Sprayed Aluminum Carbon Nanotube Composites: Quantification Of Nanotube Distribution And Multi-Scale Mechanical Properties

Carbon nanotubes (CNT) could serve as potential reinforcement for metal matrix composites for improved mechanical properties. However dispersion of carbon nanotubes (CNT) in the matrix has been a longstanding problem, since they tend to form clusters to minimize their surface area. The aim of this study was to use plasma and cold spraying techniques to synthesize CNT reinforced aluminum composite with improved dispersion and to quantify the degree of CNT dispersion as it influences the mechanical properties. Novel method of spray drying was used to disperse CNTs in Al-12 wt.% Si pre-alloyed powder, which was used as feedstock for plasma and cold spraying. A new method for quantification of CNT distribution was developed. Two parameters for CNT dispersion quantification, namely Dispersion parameter (DP) and Clustering Parameter (CP) have been proposed based on the image analysis and distance between the centers of CNTs. Nanomechanical properties were correlated with the dispersion of CNTs in the microstructure. Coating microstructure evolution has been discussed in terms of splat formation, deformation and damage of CNTs and CNT/matrix interface. Effect of Si and CNT content on the reaction at CNT/matrix interface was thermodynamically and kinetically studied. A pseudo phase diagram was computed which predicts the interfacial carbide for reaction between CNT and Al-Si alloy at processing temperature. Kinetic aspects showed that Al4C3 forms with Al-12 wt.% Si alloy while SiC forms with Al-23wt.% Si alloy. Mechanical properties at nano, micro and macro-scale were evaluated using nanoindentation and nanoscratch, microindentation and bulk tensile testing respectively. Nano and micro-scale mechanical properties (elastic modulus, hardness and yield strength) displayed improvement whereas macro-scale mechanical properties were poor. The inversion of the mechanical properties at different scale length was attributed to the porosity, CNT clustering, CNT-splat adhesion and Al4C3 formation at the CNT/matrix interface. The Dispersion parameter (DP) was more sensitive than Clustering parameter (CP) in measuring degree of CNT distribution in the matrix.

Tratamento de argila montmorilonítica para a produção de nanocompósitos poliméricos com retardo de propagação de chama

Compared to conventional composites, polymer matrix nanocomposites typically exhibit enhanced properties at a significantly lower filler volume fraction. Studies published in the literature indicate t hat the addition of nanosilicate s can increase the resistance to flame propagation in polymers. In this work, a treatment of montmorillonite (MMT) nano clay and the effect of its ad dition o n flame propagation characteristics of vinyl ester were studied. The resea rch was conducted in two stages. The first stage focused on the purification and activation of the MMT clay collected from a natural deposit to improve compatibility with the polymer matrix . Clay modification with sodium acetate was also studied to improve particle dispersion in the polymer. The second step was focused on the effect of the addition of the treated clay on nanocomposites ’ properties. Nanocomposites with clay con tents of 1, 2, 4 wt. % were processed. T he techniques for the characterization of the clay included X - ray fluorescence (XRF), X - r ay d iffraction (XRD), thermogravimetric a nalysis (TGA), d ifferential scanning c alorimetry (DSC) , s urface area (BET) and Fourier transform infrared spectroscopy (FTIR). For t he characterization of the nanocomposites , the techniques used were thermogravimetric a nalysis (TGA) , differential scanning c alorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) , scanning electron mi croscopy (SEM), transmission electron m icroscopy (TEM), and the determination of tensile strength, modulus of elasticity and resistance to flame propagation. According to the results, the purification and activation treatment with freeze - drying used in thi s work for the montmorillonite clay was efficient to promote compatibility and dispersion in the polymer matrix as evidenced by the characterization of the nanocomposite s . It was also observed that the clay modifica tion using sodium acetate did not produce any significant effect to improve compatibilization of the clay with the polymer. The addition of the treated MMT resulted in a reduction of up to 53% in the polymer flame propagation speed and did not affect the mechanical tensile strength and modulus o f elas ticity of the polymer, indicating compatibility between the clay and polymer. The effectiveness in reducing flame propagation speed peaked for nanocomposites with 2 wt. % clay, indicating that this is the optimum clay concentration for this property. T he clay treatment used in this work enables the production of vinylester matrix nanocomposites with flame - retardancy properties .

Swellable polymer films containing Au nanoparticles for point-of-care therapeutic drug monitoring using surface-enhanced Raman spectroscopy

Large (10 × 10 cm) sheets of surface-enhanced Raman spectroscopy (SERS) active polymer have been prepared by stabilising metal nanoparticle aggregates within dry hydroxyethylcellulose (HEC) films. In these films the aggregates are protected by the polymer matrix during storage but in use they are released when aqueous analyte droplets cause the films to swell to their gel form. The fact that these "Poly-SERS" films can be prepared in bulk but then cut to size and stored in air before use means that they provide a cost effective and convenient method for routine SERS analysis. Here we have tested both Ag and Au Poly-SERS films for use in point-of-care monitoring of therapeutic drugs, using phenytoin as the test compound. Phenytoin in water could readily be detected using Ag Poly-SERS films but dissolving the compound in phosphate buffered saline (PBS) to mimic body fluid samples caused loss of the drug signal due to competition for metal surface sites from Cl^- ions in the buffer solution. However, with Au Poly-SERS films there was no detectable interference from Cl^- and these materials allowed phenytoin to be detected at 1.8 mg L^-1, even in PBS. The target range of detection of phenytoin in therapeutic drug monitoring is 10-20 mg L^-1. With the Au Poly-SERS films, the absolute signal generated by a given concentration of phenytoin was lower for the films than for the parent colloid but the SERS signals were still high enough to be used for therapeutic monitoring, so the cost in sensitivity for moving from simple aqueous colloids to films is not so large that it outweighs the advantages which the films bring for practical applications, in particular their ease of use and long shelf life.