Dependence of surface free energy on molecular orientation in polymer films

Abstract

Surface free energy of mechanically drawn polycarbonate films was determined using contact angle measurements and shown to increase with orientation. The increase in polymer film surface free energy was attributed to increased polymer chain packing during orientation, supported by film density measurements, which provides enhanced intermolecular interactions. Surface free energy can therefore be increased by, or used to predict, polymer orientation.

Appl. Phys. Lett. DOI: 10.1063/1.3691186

Stress Delocalization in Crack Tolerant Electrospun Nanofiber Networks

Abstract

The fracture toughness of a noncontinuum fibrous network produced by electrospinning polyamide 6 nanofibers is investigated. The mechanical properties of the nanofiber network is observed to be independent of various incorporated macroscopic crack lengths, resulting in an apparent increase in fracture toughness with increasing crack length as evaluated using conventional fracture mechanics. Strain mapping of the nanofiber network indicates stress delocalization mechanisms operating around these macroscopic cracks in the network. The deformation behavior of the nanofiber network will therefore depend on the volume of fibers being loaded in the network and not the number of fibers in the cross-sectional width defining continuum sample mechanics. These results indicate a propensity for both the synthetic electrospun nanofibrous network in this work and potentially other nanofibrous networks to resist failure from macroscopic cracks incorporated within the material.

ACS Applied Materials and Interfaces, 2011, 3 (6), pp 1991–1996

Ferroelectric Domain Structures and Electrical Properties of Fine Grained Lead-Free Sodium Potassium Niobate Ceramics

Abstract

J. American Ceramic Society, in press (2011)

Improving Tensile Strength and Toughness of Melt Processed Polyamide 6/Multiwalled Carbon Nanotube Composites by In Situ Polymerization and Filler Surface Functionalization

Abstract

The effect of processing method and condition on the dispersion status of multiwalled carbon nanotubes (MWCNTs), and mechanical properties of the MWCNT/polyamide 6 (PA6) composites are investigated. Different melt processing conditions are used to dilute the master batch produced by melt process or in situ polymerization. Both MWCNTs and carboxyl group functionalized MWCNTs (MWCNTs-COOH) are compounded with PA6 at different loadings (0.1, 0.25, 0.5, and 0.75 wt %) to study the effect of chemical modification of MWCNTs on the mechanical properties of the final composites. It is demonstrated that chemical modification of MWCNTs has a positive effect on the strength of the composites as an increase of 5-10 MPa was observed. More importantly, a near 5 MPa increase in strength and more importantly, a maximum of 138% increase in strain at break were observed for the composites produced by in situ polymerization, indicating a toughening and strengthening effect of CNT on the composites.

JOURNAL OF APPLIED POLYMER SCIENCE Volume: 120 Issue: 1 Pages: 133-140 Published: APR 5 2011

High Strength Nano-grained and Translucent Hydroxyapatite Monoliths via Continuous Hydrothermal Synthesis and Optimized Spark Plasma Sintering

Abstract

The synthesis of high-strength, completely dense nanograined hydroxyapatite (bioceramic) monoliths is a challenge as high temperatures or long sintering times are often required. In this study, nanorods of hydroxyapatite (HA) and calcium-deficient HA (made using a novel continuous hydrothermal flow synthesis method) were consolidated using spark plasma sintering (SPS) up to full theoretical density in ~5 min at temperatures up to 1000°C. After significant optimization of the SPS heating and loading cycles, fully dense HA discs were obtained which were translucent, suggesting very high densities. Significantly high three-point flexural strength values for such materials (up to 158 MPa) were measured. Freeze-fracturing of disks followed by scanning electron microscopy investigation revealed selected samples possessed sub-200 nm sized grains and no visible pores, suggesting they were fully dense.

Acta Biomaterialia, 7, 791-799 (2011).

Investigation into the Structural, Morphological, Mechanical and Thermal Behavior of Bacterial Cellulose after a Two-Step Purification Process

Abstract

Bacterial cellulose (BC) is a natural hydrogel, which is produced by Acetobacter xylinum (recently renamed Gluconacetobacter xylinum)e in culture and constitutes of a three-dimensional network of ribbon-shaped bundles of cellulose microfibrils. Here, a two-step purification process is presented that significantly improves the structural, mechanical, thermal and morphological behaviour of BC sheet processed from these hydrogels produced in static culture. Alkalization of BC using a singlestep treatment of 2.5 wt.% NaOH solution produced a two-fold increase in Young’s modulus of processed BC sheet over untreated BC sheet. Further enhancements are achieved after a second treatment with 2.5 wt.% NaOCl (bleaching). These treatments were carefully designed in order to prevent any polymorphic crystal transformation from cellulose I to cellulose II, which can be detrimental for the mechanical properties. Scanning electron microscopy and thermogravimetric analysis reveals that with increasing chemical treatment, morphological and thermal stability of the processed films are also improved.

Accepted in Bioresource Technology

Contribution of Electrical Conductivity, Dielectric Permittivity and Domain switching in Ferroelectric Hysteresis Loops

Abstract

Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity, electric conductivity and domain switching in current-electric field curves. At the same time, it is shown how those contributions can affect the shape of the electric displacement — electric field loops (D–E loops). The effects of frequency, temperature and microstructure (point defects, grain size and texture) on the ferroelectric properties of several ferroelectric compositions is reported, including: BaTiO3; lead zirconate titanate (PZT); lead-free Na0.5K0.5NbO3; perovskite-like layer structured A2B2O7 with super high Curie point (Tc); Aurivillius phase ferroelectric Bi3.15Nd0.5Ti3O12; and multiferroic Bi0.89La0.05Tb0.06FeO3. This systematic study provides an instructive outline in the measurement of ferroelectric properties and the analysis and interpretation of experimental data.

J. Advanced Dielectrics, 1, 107-118 (2011)

Enhanced Wetting Behavior at Electrospun Polyamide Nanofiber Surfaces

Abstract

Nanofibers of polyamide have been synthesized using electrospinning processes and their wetting properties determined directly from a nanoscale Wilhelmy balance approach. Individual electrospun polyamide nanofibers were attached to atomic force microscope (AFM) tips and immersed in a range of organic liquids with varying polar and dispersive surface tension components. AFM was used to measure nanofiber-liquid wetting forces and derive contact angles using Wilhelmy balance theory. Owens-Wendt plots were used to show a considerable increase in the polar component of the surface free energy of the polyamide nanofibers compared with bulk film of the same polymer. Chemical surface analysis of the polyamide nanofibers and films using X-ray photoelectron spectroscopy provided evidence for enhanced availability of polar oxygen groups at the electrospun nanofiber surface relative to the film. Our results therefore confirm chemical group orientation at the electrospun polyamide nanofiber surface that promotes availability of polar groups for enhanced wetting behavior.

Publication Date (Web): February 18, 2011
Copyright © 2011 American Chemical Society

Thermodynamic effects of linear dissipative small deformations

Abstract

This paper presents a phenomenological model of dissipative losses manifested as heat transfer effects in small linear deformations of solid continua. The impetus is the need for a unified theory characterizing heat transfer effects (called “stretching calorimetry” in the literature) on the mechanics of deformations from a macroscopic point of view, overcoming the fragmentary description of these thermodynamic effects in the available literature. The model is based on derivation of mathematical expressions that quantify the contribution of the heat transfer effects and of the mechanical work in small linear deformations. The formulation has been developed by considering the Gibbs’ free energy and the entropy functions of the body under deformation and applying the energy balance to the continuum. The model has been compared to available experimental data of measurements of such heat effects in linear deformations (“stretching calorimetry”) of a broad range of materials. Results are presented by illustrating force-elongation values under the Hooke’s law, the proposed model, and the experimental data. The calculated model results show excellent agreement with the reported experimental data, for all the different classes of materials considered.

JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY Volume: 100 Issue: 3 Pages: 941-947 Published: 2010

The synergistic performance of multiwalled carbon nanotubes and sepiolite nanoclays as flame retardants for unsaturated polyester

Abstract

The synergistic effect on the thermal decomposition and heat release rate (HRR) in particular the peak heat release rate (PHRR) of unsaturated polyester (UP) resin blended with multiwalled carbon nanotubes (MWNTs) and sepiolite nanoclay was investigated using thermal gravimetric analysis (TGA), pyrolysis combustion flow calorimetery (PCFC) and the cone calorimetery. Initial microcalorimeter findings established a synergistic effect for ternary system comprising a 10:0.5 wt% mixture of sepiolite:MWNT, respectively, which resulted in a 40% reduction in heat release capacity (HRC). This result was also confirmed within the well-established cone calorimeter by a 50% reduction in PHRR in contrast to unfilled UP. The mechanism behind this reduction is thought to be due to the bridging of the MWNTs between the sepiolite clay needles, creating a tight protective surface layer that reduces the MLR. TGA also confirmed the advantage of such a ternary system through a 36∘C shift in the onset decomposition temperature and an 11% increase in residual char.

Fire and Materials. v. 35, p. 157–169. DOI: 10.1002/fam.1044

Preparation of High-Performance Conductive Polymer Fibers through Morphological Control of Networks Formed by Nanofillers

Abstract

A general method is described to prepare high-performance conductive polymer fibers or tapes. In this method, bicomponent tapes/fibers containing two layers of conductive polymer composites (CPCs) filled with multiwall carbon nanotubes (MWNT) or carbon black (CB) based on a lower-melting-temperature polymer and an unfilled polymer core with higher melting temperature are fabricated by a melt-based process. Morphological control of the conductive network formed by nanofillers is realized by solid-state drawing and annealing. Information on the morphological and electrical change of the highly oriented conductive nanofiller network in CPC bicomponent tapes during relaxation, melting, and crystallization of the polymer matrix is reported for the first time. The conductivity of these polypropylene tapes can be as high as 275?S?m-1 with tensile strengths of around 500?MPa. To the best of the authors' knowledge, it is the most conductive, high-strength polymer fiber produced by melt-processing reported in literature, despite the fact that only ~5?wt.% of MWNTs are used in the outer layers of the tape and the overall MWNT content in the bicomponent tape can be much lower (typically ~0.5?wt.%). Their applications could include sensing, smart textiles, electrodes for flexible solar cells, and electromagnetic interference (EMI) shielding. Furthermore, a modeling approach was used to study the relaxation process of highly oriented conductive networks formed by carbon nanofillers.

Advanced Functional Materials, v 20, n 9, May 10, 2010, p 1424-1432. DOI: 10.1002/adfm.200902207.

Bacterial cellulose–poly(vinyl alcohol) nanocomposites prepared by an in-situ process

Abstract

Bio-nanocomposites were prepared by an in-situ growth process through the direct addition of poly(vinyl alcohol) (PVA) into the Acetobacter xylinum inoculated medium and compared with composites made by impregnation of bacterial cellulose (BC) gels with a PVA solution. Mechanical property tests showed that the presence of PVA in the BC acts as a plasticizer, interrupting hydrogen bonding between cellulose fibrils within the BC network. This resulted in a reduction in Young's modulus and an increase in toughness compared to pure BC sheet, especially for in-situ grown samples. Interestingly, the small amount of added PVA turns the BC sheet into optical transparent nanocomposite films with excellent mechanical properties.

Materials Letters, v 64, n 8, Apr 30, 2010, p 901-904. DOI: 10.1016/j.matlet.2010.01.042

Effective Reinforcement of Carbon Nanotubes in Polypropylene Matrices

Abstract

This study describes an attempt to mechanically reinforce polypropylene (PP) using multi-wall carbon nanotubes (MWNTs) through a melt compounding process followed by hot-pressing and solid state drawing. The effect of a high density polyethylene (HDPE) coating on MWNTs and melt flow index (MFI) of PP on the dispersion of MWNTs and composite properties are studied by means of mechanical tests, transmission electron microscopy (TEM), scanning electron microscope (SEM), differential scanning calorimetry (DSC), and wide angle x-ray diffraction (WAXD). Highly orientated composite tapes are prepared to fully utilize the properties of MWNTs in uniaxial direction. Highly aligned MWNTs are shown by SEM, while highly oriented polymer chains are characterized by WAXD. Composite theory is used to analysis the results and indicates that effective reinforcement of PP by MWNTs is highest at relatively low filler content and draw ratios.

Journal of Applied Polymer Science, 2010, v 118, n 1, p 30-41.

Effective Modulus of Single and Multi-walled Carbon Nanotubes in Melt-compounded Polycarbonate Nanocomposites

Abstract

This study compares the reinforcing efficiency of multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) in polycarbonate (PC) films processed using melt-compounding followed by hot-pressing. The effect of carbon nanotube (CNT) type on composite properties is studied by means of dynamic mechanical analysis (DMA). Composite theory is used to analyse the results. It is found that, despite the good dispersion and interfacial interactions reported in the literature for PC/CNT nanocomposites, SWNTs and MWNTs efficiently reinforce PC only at nanofiller contents below 0.3 wt.% and 0.5 wt.%, respectively. Nevertheless, effective moduli of CNTs (in particular SWNT) close to the theoretical values were achieved for low nanofiller content.

Advanced Composites Letters. v. 19, issure 5, p. 169–174. DOI

Biodegradable composites based on poly (ε-caprolactone) and bacterial cellulose as a reinforcing agent

Abstract

Bacterial cellulose (BC) pellicles produced from Acetobacter xylinum culture were used as a reinforcing agent for biodegradable composites with poly(e-caprolactone) (PCL) as a matrix. BC prepared in both particulate bacterial cellulose (PBC) and fibrous freeze-dried bacterial cellulose (FBC) states was melt-compounded with PCL. Thermal analysis was carried out using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical properties were assessed by tensile tests and dynamic mechanical analysis (DMA) and morphological analysis by scanning electron microscopy (SEM). Results showed a significant improvement in mechanical properties of PCL through the addition of both PBC and FBC, with the latter giving better mechanical properties compared with PBC. PCL/FBC composites, based on high-aspect ratio cellulose nanofibres, showed higher tensile strength and strain at break than particulate PCL/PBC while modulus was similar for both types of composites.

Journal of Biobased Materials and Bioenergy, 4, 1-7

A Novel Route for Processing Co-Cr-Mo Orthopaedic Alloys

Abstract

Spark plasma sintering has been used for the first time to prepare the ASTM F75 cobalt-chromium-molybdenum (Co-Cr-Mo) orthopaedic alloy composition using nanopowders. In the preliminary work presented in this report, the effect of processing variables on the structural features of the alloy (phases present, grain size and microstructure) has been investigated. Specimens of greater than 99.5 per cent theoretical density were obtained. Carbide phases were not detected in the microstructure but oxides were present. However, harder materials with finer grains were produced, compared with the commonly used cast/wrought processing methods, probably because of the presence of oxides in the microstructure.

J. Royal Society Interfaces, 7(52), 1641-5 (2010)

Effects of Point Defects on Thermal Depoling Behavior of Bismuth Layer-Structured Ferroelectric Ceramics

Abstract

Effect of point defects on the thermal depoling behavior of bismuth layer-structured ferroelectric Bi2WO6 (BW) and Sr2Bi4Ti5O18 (SBT) ceramics was investigated. Point defects in BW ceramics formed defect dipoles that interacted with the ferroelectric domain structure. These defect dipoles produced pinched polarization-electric field (P-E) hysteresis loops and an irreversible reduction in d33 after annealing below 200°C. They became decoupled and randomized above 200°C, and the d33 of BW became stable with increasing temperature from 200°C up to its Curie point. SBT ceramics with low defect concentration showed symmetric P-E hysteresis loops and good piezoelectric stability with increasing temperature.

J Applied Physics, 108, 096101 (2010)

High temperature lead-free relaxor ferroelectric: Intergrowth Aurivillius phase BaBi2Nb2O9–Bi4Ti3O12 ceramics

Abstract

Intergrowth BaBi2Nb2O9–Bi4Ti3O12 (BaBi6Ti3Nb2O21) Aurivillius phase ceramic has been found to be a relaxor ferroelectric (RFE) with the highest reported temperature of the maximum of the dielectric permittivity (Tm) of all of the known RFE systems. Dielectric characterization revealed that it has two dielectric anomalies. The first one is a frequency independent broad dielectric constant peak at ∼280°C, while the second anomaly shows relaxor behavior at 636°C (100 kHz). There is obvious frequency dispersion of dielectric response at room temperature, which is in agreement with dielectric properties of a typical relaxor. Ferroelectric hysteresis loops and a measurable value of piezoelectric constant d33 confirmed the ferroelectric nature of BaBi6Ti3Nb2O21 ceramics. The piezoelectric response remained even after annealing at temperatures above 636°C.

JAP, 107, 104111

Highly Conductive Low Nickel Content Nano-composite Dense Cermets from Nanopowders Made via a Continuous Hydrothermal Synthesis Route

Abstract

Homogenously doped and mixed yttria stabilized zirconia, YSZ (with 3 and 10 mol% Y2O3 known as 3YSZ and 10YSZ) and NiO/10YSZ co-precipitates (nominally corresponding to 7, 12, 24, 30, 35 and 45 vol.% Ni metal), were synthesized using a continuous hydrothermal flow synthesis (CHFS) system which uses a stream of superheated water at 450 °C and 24.1 MPa as a reaction medium to cause rapid precipitation of metal oxide nanoparticle co-precipitates from a mixed metal salt solution. All products were obtained directly from the outlet of the CHFS reactor as a slurry, which was then cleaned and freeze-dried prior to further processing. The highly crystalline nano-powdered products were characterized using a range of analytical methods, including: powder X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), Raman spectroscopy and BET surface area measurements. Spherical primary particles of 10YSZ and 3YSZ were observed under the TEM and found to be 5.0 ± 0.8 nm (range 3.2–6.3 nm) and 6.2 ± 1.4 nm (range 3.3–8.4 nm) in size, with measured BET surface areas of 160.6 and 241.7 m2 g−1, respectively. Sintering of the nano-powder co-precipitates was performed via spark plasma sintering (SPS) at 1100 °C for 1 min, leading to densities of ca. 98% for 10YSZ and ca. 96% for Ni/10YSZ cermets (all NiO was converted into Ni due to the reducing atmosphere of the SPS). The 24% Ni/10YSZ cermet was subjected to focused ion beam tomography, which allowed the 3D arrangement of the conducting Ni metallic network of the dense cermet to be elucidated, and showed that a complete 3D network of Ni existed throughout the dense cermet disk. Electrical conductivity tests showed that the samples exhibited higher than expected electrical conductivity (for such low metal content), e.g., the 24 vol.% Ni-containing sample achieved an electrical conductivity of not, vert, similar 200 S cm−1 at the fuel cell operating temperature, which corresponds to an effective conductivity of not, vert, similar 117 S cm−1 if a porosity of 30% were to be introduced.

Solid State Ionics, 181, 827-824 (2010)

Microstructure and electrical properties of Aurivillius phase (CaBi2Nb2O9)1-x(BaBi2Nb2O9)x solid solution

Abstract

The microstructures and electrical properties of Aurivillius phase ferroelectric solid solutions of (CaBi2Nb2O9)1-x(BaBi2Nb2O9)x (0≤x≤1) have been studied. X-ray diffraction analyses revealed a bismuth layered structure for all compositions. Scanning electron microscope images showed randomly oriented and platelike grain morphology. The Curie point Tc or the maximum permittivity temperature Tm decreased with increasing x. The (CaBi2Nb2O9)1-x(BaBi2Nb2O9)x ceramics exhibited a ferroelectric–paraelectric phase transition at small x values (x≤0.5), whereas a relaxor behavior was observed at high x values (x≥0.8). The d33 value of CaBi2Nb2O9 ceramics was enhanced by Ba2+ doping on the A-sites (x≤0.3). A combination of high d33 values and high Tc points (>700 °C) suggests that compositions with x≤0.3 could be good candidates for high-temperature piezoelectric applications. The composition with x=0.8 is a relaxor ferroelectric with Tm around 320 °C at 1 MHz.

J. Applied Physics, 108, 014109 (2010).

Piezoelectric Strontium niobate and Calcium Niobate Ceramics with Super-High Curie Points

Abstract

The perovskite-like layer structured strontium niobate (Sr2Nb2O7) and calcium niobate (Ca2Nb2O7) are good candidates for high-temperature piezoelectric applications because of their high Curie points. Single-phase dense Sr2Nb2O7 and Ca2Nb2O7 ceramics with grain-oriented microstructures were prepared by spark plasma sintering using a two-step method. The Lotgering orientation factors were 0.86 and 0.70 for Sr2Nb2O7 and Ca2Nb2O7, respectively. The Tc of Sr2Nb2O7 and Ca2Nb2O7 were measured as 1327±5°C and above 1525°C, respectively. The dielectric, piezoelectric, ferroelectric properties, and direct-current electrical conductivity are higher along the directions perpendicular to the pressing direction compared with parallel. The piezoelectric constant d33 for Sr2Nb2O7 was 2.8±0.2 pC/N.

J. American Ceramic Society, 93, 1409-1413 (2010)

Stability of Nanocrystalline Spark Plasma Sintered 3Y-TZP

Abstract

Spark plasma sintered 3Y-TZP has been investigated with respect to hydrothermal ageing and grinding. The sintering was performed between the temperatures of 1,100 and 1,600 °C for a soaking time of 5 minutes and the resulting materials were obtained with grain sizes between 65 to 800 nm and relative densities between 88.5 to 98.8%. Experiments on hydrothermal ageing in water vapour at 131 °C, 2 bars during 60 hours shows that phase stability is retained, elastic modulus and hardness of near surface region measured by nanoindentation does not change in fine grain (<200 nm) materials, in spite of porosity. In ground specimens, very small amount of transformation was found for all grain sizes studied.

Materials, 3, 800-814 (2010)

Structural and Chemical Stability of Multiwall Carbon Nanotubes in Sintered Ceramic Nanocomposite

Abstract

The structural and chemical stability of multiwall carbon nanotubes (MWNTs) in ceramic nanocomposites prepared by spark plasma sintering was studied. High resolution electron microscopy, X‐ray diffraction and Raman spectroscopy were used to evaluate any degradation of the MWNTs. They were found to be well preserved in alumina after sintering up to 1900°C/100 MPa/3 min. In boron carbide, structural degradation of MWNTs started from ∼1600°C when sintered for 20 min. Multiwall carbon nanotubes maintained their high aspect ratio and fibrous nature even after being sintered in boron carbide at 2000°C for 20 min. However, no Raman vibrations of MWNTs were observed for nanocomposites processed at temperatures 2000°C, which indicates that they were severely degraded. Structural preservation of MWNTs in ceramic nanocomposites depends on the ceramic matrix, sintering temperature and dwell time. Multiwall carbon nanotubes were not preserved for matrices that require high sintering temperatures (>1600°C) and longer processing times (>13 min).

Advances in Applied Ceramics, 109, 240-245 (2010)

The Sintering and Grain Growth Behaviour of Ceramic-CNT Composites

Abstract

The sintering and grain growth behaviour of alumina + 2, 3.5 and 5 wt.% carbon nanotubes (CNTs) and alumina + 2 wt.% carbon black nanocomposites prepared by Spark Plasma Sintering (SPS) were studied. The addition of CNTs to ceramics produces a large reduction in the sintering temperature required for their complete densification and a significant grain size refinement by a previously unreported mechanism. The CNTs form a strong entangled network around the grains, which constrains the normal and abnormal grain growth. An alumina/alumina + 2 wt.% CNT/alumina laminate structure was prepared to demonstrate directly the large grain-growth retardation effect of CNTs. These effects open up the possibility of using CNTs as a sintering aid to control the sintering behaviour and microstructures of ceramics in bulk, laminate and functionally gradient (FGM) form.

Composite Science and Technology, 70, 947–952 (2010)

Fabrication and Property Prediction of Conductive and Strain Sensing TPU/CNT Nanocomposite Fibres

Abstract

In this study, thermoplastic polyurethane (TPU) fibres containing multi-walled carbon nanotubes (MWNTs) and fabricated via an extrusion process were demonstrated to possess a tuneable level of electrical conductivity. A simple approach based on the time–temperature superposition applied to the electrical conductivity of carbon nanotube (CNT) percolating in a thermoplastic polyurethane (TPU) melt was also developed to predict the conductivity of the nanocomposite fibres. The observation of Arrhenius dependence of zero-shear viscosity and the assumption of simple inverse proportionality between the variation of conductivity, due to network formation, and viscosity allow a universal plot of time variation of conductivity to be composed, which is able to predict the conductivity of the extruded fibres. The same TPU/CNT fibres were also demonstrated to possess good strain sensing abilities, which makes them good candidates for applications in smart textiles.

J. Mater. Chem. 2010. DOI: 10.1039/c0jm01827a

Low temperature consolidated lead-free ferroelectric niobate ceramics with improved electrical properties

Abstract

There is a concerted effort to develop lead-free piezoelectric ceramics. (Na0.5K0.5)NbO3 based ceramics have good electrical properties, and are potential replacement materials for lead zirconate titanate piezoelectric ceramics. In this work a commercial powder based on (Na0.5K0.5)NbO3 with an initial particle size of ~260 nm was consolidated by Spark Plasma Sintering (SPS). To avoid volatilization high mechanical pressures were used to minimize the densification temperature. It was found that under a uniaxial pressure of 100 MPa, fully densified compacts can be prepared at 850 oC. Ceramics densified at such a low temperature demonstrate an unusually high remanent polarization (30 mC/cm2) and high d33 (146pC/N). The improved ferroelectric properties are ascribed to the homogeneous, dense and submicron grained microstructure achieved.

Keywords

In press, Journal of Materials Research

Synergistic reinforcement of highly oriented polypropylene tapes by sepiolite nanoclay

Abstract

This paper presents the study of highly oriented nanocomposites tapes based on isotactic polypropylene (PP) and sepiolite clay, obtained by a solid state drawing process. Sepiolite is a needle-like nanoclay and has already shown good mechanical reinforcement capabilities in several polymeric matrices. The intrinsic one-dimensional (1D) character of sepiolite allows its exploitation in 1D objects, such as oriented polymer fibres and tapes, where this nanofiller is uniaxially oriented upon drawing, along with the alignment of the polymer chains. A synergistic increase in mechanical properties will be presented, for tapes drawn as much as 20 times and for filler loadings less than 2.5 wt.%, which can not be explained by simple micromechanical composite models. Mechanical performances will be intimately related to the dispersion state of the nanoclays in polypropylene (PP), the rheological properties of the nanocomposites and the polymer crystallinity.

Macromolecular Materials and Engineering, v 295, n 1, Jan 2010, p 37-47. DOI: 10.1002/mame.200900156

Electrically Conductive Alumina-Carbon Nanocomposites Prepared by Spark Plasma Sintering

Abstract

Carbon nanotubes (CNTs) and carbon black were added to alumina to convert it into a good electrical conductor. Alumina–CNT and alumina–carbon black nanocomposites were fabricated by Spark Plasma Sintering (SPS). The electrical conductivity of alumina–CNT nanocomposites was found to be four times higher as compared to alumina–carbon black nanocomposites due to the fibrous nature and high aspect ratio of CNTs. The electrical conductivity of alumina–CNT nanocomposite increased with increasing grain size due to increasing density of CNTs at the grain boundaries. This effect was not observed for alumina–carbon black nanocomposite due to the particulate geometry of the carbon black.

J. European Ceramic Society, 30, 153-157 (2010)

Aluminium trihydroxide in combination with ammonium polyphosphate as flame retardants for unsaturated polyester resin

Abstract

The thermal and reaction to fire characteristics of a flame retardant unsaturated polyester resin (UP) ternary system are presented here. Thermal gravimetric analysis showed an improved thermal stability between 200-600 °C with the addition of ammonium polyphosphate (APP) and aluminium trihydroxide (ATH) formulation. Cone calorimetry tests indicated that ATH is more efficient than calcium carbonate at delaying the ignition time, lowering the carbon monoxide yield and lowering the peak heat release rate (PHRR). However the addition of APP and ATH to the formulation failed to demonstrate any significant synergistic effect at reducing the PHRR.

Express Polymer Letters. 2009. 3. No 11. p. 743-751.

Piezoelectric Ceramics with Super-High Curie Points

Abstract

High-temperature piezoelectric sensing technology is of major importance to the chemical and material processing, automotive, aerospace, and power generating industries. Ferroelectric polycrystalline ceramics have the advantages over piezoelectric/ferroelectric single crystals of lower cost and the possibility to control, by compositional modifications and processing, their properties. The perovskite-like layer structured (PLS) Nd2Ti2O7 and La2Ti2O7 have possibly the highest Curie points of any materials. Their piezoelectric properties have only been characterized using single crystal samples. Despite more than 30 years of extensive effort, there is still no report on the ferroelectric and piezoelectric properties of their polycrystalline ceramics. To pole these ceramics at high electrical field, highly textured, dense ceramics with high dc electrical resistivity are necessary. The ferroelectric and piezoelectric properties of lead-free Nd2Ti2O7 and La2Ti2O7 grain-oriented ceramics prepared by Spark Plasma Sintering (SPS) using a two-step method was reported for the first time here. The Tc of Nd2Ti2O7 and La2Ti2O7 are 1482?5 ?C and 1461?5 ?C, respectively. The measured piezoelectric constant of the textured La2Ti2O7 was d33 = 2.6 pC/N. These results now open up the possibility of studying the ferroelectric/piezoelectric properties of the PLS family of ceramics with super-high Curie points.

Journal of the American Ceramics, In press, 2009

Stability of multiwall carbon nanotubes in ceramic nanocomposite sintering

Abstract

Carbon nanotube (CNT) and alumina dispersions were prepared separately in dimethylformamide (DMF) and ethanol by ultrasonication. The colloidal stability of the dispersions was monitored and a particle size analysis was performed to evaluate the size range of the agglomerates after different times. DMF was found to be a much more effective dispersant than ethanol for making stable, homogeneous CNT and composite dispersions. Alumina–CNT (4.65 vol%) nanocomposites were sintered in a spark plasma sintering (SPS) furnace. DMF dispersions produced homogeneously distributed and agglomerate-free CNT–alumina nanocomposites with higher electrical conductivity as compared to nanocomposites prepared using ethanol.

Advances in Applied Ceramics, accepted, 2009

Prediction of yield and long-term failure of oriented polypropylene: Kinetics and anisotropy

Abstract

The time-dependent yield and failure behavior of off-axis loaded uniaxially oriented polypropylene tape is investigated. The yield and failure behavior is described with an anisotropic viscoplastic model.A viscoplastic flow rule is used with an equivalent stress, based on Hill’s anisotropic yield criterion, and the Eyring flow theory combined with a critical equivalent strain definition. This model is based on factorization of the rate and draw ratio dependence and is capable of quantitatively predicting the rate, angle and draw ratio dependence of the yield stress as well as time-to-failure in various off-axis tensile loading conditions characterized solely from the transverse direction.

Journal of Polymer Science Part B: Polymer Physics, 47, (2009) 2026-2035

Oriented UHMW-PE/CNT composite tapes by a solution casting-drawing process using mixed-solvents

Abstract

Ultra-high molecular weight polyethylene/multi-wall carbon nanotube (UHMW-PE/MWNT) composites have been prepared by a novel approach which involves the use of a mixture of solvents during the gelation process. By combining one of the best known organic solvents for nanotubes, N,N-dimethylformamide (DMF) with xylene and use this mixed-solvent in the gelation/crystallisation process for UHMW-PE/MWNT composite fabrication, an attempt is made to improve the dispersion of carbon nanotubes in UHMW-PE. The obtained films were drawn to obtain highly oriented tapes, which were characterized in terms of electrical and mechanical properties. The conductivity of the drawn tapes is maintained at 10-4 S/m at draw ratio 30, two orders of magnitude higher than the minimum level required to provide electrostatic discharge. Although the mechanical properties are compromised by use of DMF and MWNTs, the Young’s modulus still remains at 25 GPa, in comparison with 35 GPa for pure UHMW-PE tape at draw ratio 30.

European Polymer Journal, Volume 45, Issue 10, October 2009, Pages 2741-2748

A novel concept for highly oriented carbon nanotubes composite tapes or fibres with high strength and electrical conductivity

Abstract

A new concept is described for the creation of multifunctional polymer nanocomposite tapes (or fibres) that combines high stiffness and strength with good electrical properties and a low percolation threshold of carbon nanotubes (CNTs). The concept is based on a bicomponent tape (or fibre) construction consisting of a highly oriented polymer core and a conductive polymer composite (CPC) skin based on a polymer with a lower melting temperature than the core, enabling thermal annealing of these skins to improve conductivity through a dynamic percolation process while retaining the properties of the core and hence those of the tape (or fibre). The percolation threshold in the CPC skins of the highly drawn conductive bicomponent tapes could be decreased from 5.3 to 1.1 wt.-% after annealing.

Macromolecular Materials and Engineering, V 294, Issue 11, 2009 Pages 749 - 755

All-poly(ethylene terephthalate) composites by film stacking of oriented tapes

Abstract

Self-reinforced polymer or all-polymer composites have been developed to replace traditional fibre reinforced plastic (FRP) with good interfacial adhesion and enhanced recyclability. Poly(ethylene terephthalate) (PET) is one of the most attractive polymers to be used in these fully recyclable all-polymer composites, in terms of cost and properties. In this work, all-PET composites were prepared by film stacking of oriented PET tapes. A processing temperature window was determined by a series of tests on PET tapes and co-PET films, including DSC and T-peel tests. Tensile properties of PET tape, co-PET film and all-PET composites are reported and compared with a commercial co-extruded PURE® polypropylene tape. The effect of compaction temperatures and pressures on tensile properties of all-PET composites was investigated to explore the optimum processing parameters for balancing good interfacial adhesion between tapes and residual tensile properties of PET tapes.

Composites Part A: Applied Science and Manufacturing, Volume 40, Issue 11, November 2009, Pages 1747-1755

Grain-size effect on the roperties of Aurivillius phase Bi3.15Nd0.85Ti3O12 ferroelectric ceramics

Abstract

Aurivillius phase, bismuth layer structured ferroelectric Bi3.15Nd0.85Ti3O12 (BNdT) ceramics with average grain sizes from 90 nm and high densities (>97%) were fabricated by spark plasma sintering. Decreasing grain size produced a diffuse ferro–paraelectric phase transition and a decrease in the Curie point. Compared with BNdT ceramics with grain sizes of micrometre scale, nanograined BNdT ceramics exhibit a depression of the dielectric maximum at the Curie point, enhanced dielectric constant from room temperature to 350 °C and dramatically decreased losses. Although ferroelectric switching was greatly inhibited in nanograined ceramics, both ferroelectric and piezoelectric measurements still clearly showed that BNdT ceramics with 90 nm average grain sizes are ferroelectrically switchable. This is the first reported evidence that nanoscale Aurivillius phase ceramics are ferroelectrically active.

Nanotechnology, vol.20, p385708, 2009

Textured high Curie temperature piezoelectric ceramics prepared by Spark Plasma Sintering

Abstract

The Curie point, Tc, of a ferroelectric sets the upper temperature limit for their application as piezoelectrics. Some Aurivillius phase and perovskite-like layer structured (PLS) materials are good candidates for high temperature piezoelectric applications because of their high Tc. The Aurivillius phase CaBi2Nb2O9 and PLS Sr2Nb2O7 were sintered by ordinary sintering and/or Spark Plasma Sintering (SPS). All of the materials were single phase and their grains were plate-like. Their density was greater than 95%. The SPSed ceramics had grain-oriented textured structures. The Curie point of CaBi2Nb2O9 was measured as 943?5 °C. Ferroelectric switching in CaBi2Nb2O9 was observed at room temperature. The d33 of the textured CaBi2Nb2O9 materials was nearly three times that of conventionally sintered materials. The Curie Point of Sr2Nb2O7 was measured as 1327?5 °C. Ferroelectric and piezoelectric (2.8 pC/N) properties were observed for SPSed textured Sr2Nb2O7 ceramics.

Keywords:

Advances in Applied Ceramics, in press, 2009

Piezoelectric Bi2WO6 Ceramics Prepared by Spark Plasma Sintering

Abstract

Single-phase bismuth tungstate (Bi2WO6) ceramics with high relative density (99%) were fabricated by spark plasma sintering. Ferroelectric, dielectric, and piezoelectric properties of Bi2WO6 ceramics were investigated. Almost saturated polarization– electric field (P–E) hysteresis loops with a remanent polarization (Pr) of B16.1 °C/cm2 and a coercive field (Ec) of 3.7 kV/mm were obtained. Curie point and second phase transition temperatures were observed at 937 °C and 665 °C, respectively. The average piezoelectric constant (d33) of this high Curie point ceramic is 15?0.2 pCN_1

J. American Ceramic Society, In press 2009

Fabrication and Properties of Dense Ex Situ Magnesium Diboride Bulk Material using Spark Plasma Sintering

Abstract

High density ex situ magnesium diboride bulks were synthesized from commercial MgB2 powder using spark plasma sintering under a range of applied uniaxial pressures between 16 and 80 MPa. The microstructure was characterized using x-ray diffraction, scanning electron microscopy, polarized optical microscopy, Vickers hardness measurements, and density measurements using the Archimedes method. By combining these data with those for other bulk samples we have developed a correlation curve for the hardness and density for magnesium diboride for relative densities of 60–100%. The superconducting properties were determined using magnetization measurements. Comparison to samples of significantly higher porosity indicates a positive correlation between magnetization critical current density and bulk density for magnesium diboride bulks up to around 90% density. Above this level other microstructural processes such as grain growth begin to influence the critical current density, suggesting that full elimination of porosity is not necessary to obtain high critical current density. We conclude that the best superconducting properties are likely to be obtained with a combination of small grain size and minimal porosity.

Superconductor Science and Technology, vol.22, p095003, 2009

Piezoelectric and Ferroelectric Properties of Bismuth Tungstate Ceramics Fabricated by Spark Plasma Sintering

Abstract

Single phase bismuth tungstate (Bi2WO6) ceramics with high relative density (>99%) were fabricated by spark plasma sintering (SPS). Ferroelectric, dielectric and piezoelectric properties of Bi2WO6 ceramics were investigated. Almost saturated polarization-electric field (P-E) hysteresis loops with a remanent polarization (Pr) of ~16.1 ?C/cm2 and a coercive field (Ec) of ~3.7 kV/mm were obtained. Curie point and second phase transition temperatures were observed at 937?5 oC and 665?5 oC, respectively. The average piezoelectric constant (d33) of this high Curie point ceramic is 15? 0.2 pCN-1.

Journal of the American Ceramics, In press, 2009

The effect of Nd substitution on the electrical properties of Bi3NbTiO9 Aurivillius phase ceramics

Abstract

The effect of Nd substitution on the microstructures and electrical properties of Aurivillius phase ferroelectric Bi3NbTiO9-based ceramics has been studied. All of the Bi3-xNdxNbTiO9 (0<= x<= 1) ceramics are ferroelectrics. The Curie point Tc decreased with increasing Nd doping content x. The Bi3-xNdxNbTiO9 ceramics exhibited a sharp ferroelectric-paraelectric phase transition at small x values (x = 0.6), whereas a diffuse phase transition was observed at higher x values (x = 0.8). Both the piezoelectric constant d33 and DC electrical resistivity of Bi3NbTiO9 ceramics were greatly enhanced by Nd substitution on the A-sites. The improved properties can be attributed to the fact that Nd substitution depressed the generation of oxygen vacancies. A combination of high d33 values, high resistivity, and high Tc points (> 700 °C) suggests that the Bi3-xNdxNbTiO9 ceramics with x = 0.6 could be good candidates for high temperature piezoelectric applications.

J Appl. Phys. In press, 2009

Electrically conductive alumina - carbon nanocomposites prepared by Spark Plasma Sintering

Abstract

Carbon nanotubes (CNTs) and carbon black were added to alumina to convert it into a good electrical conductor. Alumina–CNT and alumina–carbon black nanocomposites were fabricated by Spark Plasma Sintering (SPS). The electrical conductivity of alumina–CNT nanocomposites was found to be four times higher as compared to alumina–carbon black nanocomposites due to the fibrous nature and high aspect ratio of CNTs. The electrical conductivity of alumina–CNT nanocomposite increased with increasing grain size due to increasing density of CNTs at the grain boundaries. This effect was not observed for alumina–carbon black nanocomposite due to the particulate geometry of the carbon black.

J. Eur. Ceram. Soc. In press, 2009

High-temperature ferroelectric phase transition observed in multiferroic Bi0.91La0.05Tb0.04FeO3

Abstract

A single-phase Bi0.91La0.05Tb0.04FeO3 polycrystalline ceramic was fabricated by spark-plasma-sintering the precursor powder prepared by a sol-gel method. Temperature-dependent properties of polycrystalline Bi0.91La0.05Tb0.04FeO3 were characterized by x-ray diffraction, dielectric, and piezoelectric measurement. The x-ray diffraction results revealed a phase transition near 700 °C. Especially, temperature-dependent dielectric behavior demonstrated that there was a dielectric abnormal peak at about 697 °C, in addition to those two well-known dielectric abnormal peaks at 337 °C (Néel temperature) and 831 °C (Curie temperature). The observations, together with thermal depoled behavior, suggest a ferroelectric-ferroelectric phase transition from R3c to Pbnm at around 700 °C.

Appl. Phys. Lett., vol.95, p012909, 2009

Non-Isothermal Stamp Forming of Continuous Tape Reinforced All-Polypropylene Composite Sheet

Abstract

This paper describes the thermoforming behaviour of a self-reinforced composite based on co-extruded polypropylene (PP) tapes. In contrast to traditional continuous woven glass fabric reinforced polypropylene (GF/PP) materials, where the sole mode of deformation is either inter- or intraply shearing, all-PP composites have an additional mode of deformation as here the fibres (or in this case tapes) can still be deformed. The importance of this additional deformation mode is investigated in a range of stamping experiments in combination with 3D strain mapping experiments. Non-isothermal thermoforming experiments revealed that all-PP woven fabric laminates based on flat tapes deform in a different manner to traditional GF/PP. Although the main mode of deformation of both all-PP and GF/PP for the investigated dome parts was intraply shearing, a much lower energy was required to deform the all-PP laminate. Whenever possible, deformation of the tape by drawing should be avoided as it requires higher energy which may lead to higher residual stresses in the final part. However, tape drawing may prove an essential benefit when complex shapes are involved.

Composites: Part A (2008), doi: 10.1016/j.compositesa.2008.05.014

Effect of A site substitution on the properties of CaBi2Nb2O9 ferroelectric ceramics

Abstract

The effect of A-site substitution on the piezoelectric coefficient, high-temperature dc resistivity, and thermal depoling behaviour of Aurivillius phase CaBi2Nb2O9 ferroelectric ceramics was investigated. Ceramics with the general formula of Ca1-xMxBi2Nb2O9, where M=Na, (Na,Ce), (Na,La), and La, were prepared by conventional solid-state sintering. All the ceramics were single-phase ferroelectrics with high Curie points (>900C). The doped ceramics, Ca0.9Na0.1Bi2Nb2O9, Ca0.9 (NaLa)0.1Bi2Nb2O9, Ca0.95La0.05Bi2Nb2O9, and Ca0.9La0.1Bi2Nb2O9, had improved resistance to thermal depoling compared with Ca2Bi2Nb2O9 and were stable up to 8001C. The donor dopants increased the dc electrical resistivity, while the acceptor dopants decreased it. The donor-doped Ca0.95La0.05Bi2Nb2O9 had a higher piezoelectric constant (d33512.8 pC/N) compared with CaBi2Nb2O9 (d3355.8 pC/N), and its electrical resistivity was higher than 10^6 ohm.cm at 600C. These properties suggest that doped CaBi2Nb2O9 ceramics might be good candidates for high-temperature piezoelectric applications.

J. Am. Ceram. Soc., Vol.91, 2989-2932, 2008

Dimethylformanide: an effective dispersant for making ceramic-carbon nanotube composites

Abstract

Carbon nanotube (CNT) and alumina dispersions were prepared separately in dimethylformamide (DMF) and ethanol by ultrasonication. The colloidal stability of the dispersions was monitored and a particle size analysis was performed to evaluate the size range of the agglomerates after different times. DMF was found to be a much more effective dispersant than ethanol for making stable, homogeneous CNT and composite dispersions. Alumina–CNT (4.65 vol%) nanocomposites were sintered in a spark plasma sintering (SPS) furnace. DMF dispersions produced homogeneously distributed and agglomerate-free CNT–alumina nanocomposites with higher electrical conductivity as compared to nanocomposites prepared using ethanol.

Nanotechnology vol.19, p195710, 2008

The effect of texture on the properties of Bi3.15Nd0.85Ti3O12 ceramcis prepared by spark plasma sintering

Abstract

Bi3.15Nd0.85Ti3O12 ceramic, which is a three-layer ferroelectric Aurivillius phase, was prepared by spark plasma sintering. The effect of texture on the anisotropy of dielectric, ferroelectric and piezoelectric properties was studied. X-ray diffraction showed that samples perpendicular to the hot-pressing direction had a–b-axis preferred texture, whereas, samples parallel to hot-pressing direction had c-axis preferred orientation. The dielectric constant, remanent polarization and piezoelectric constant of samples with orientation close to a-axis are larger than those of samples with orientation close to c-axis. Their Curie points are all about 410 ?C

Mater. Sci. Eng. A, vol.475, p92-95, 2008

Luminescence of Sr2SiO4-xN2x/3:Eu2+ phosphors prepared by spark plasma sintering

Abstract

Spark plasma sintering _SPS_ was employed to synthesize Sr2SiO3.5N0.333:Eu2+, Sr2SiO3N0.667:Eu2+, and Sr2SiO2N1.333:Eu2+ for use in white light emitting diodes _LED_ lightings. The SPS technique enabled a complete, rapid synthesis of these phosphors with ease, whereas it is difficult to produce nitridosilicate phosphors by any other conventional synthesis methods. The photoluminescent _PL_ spectrum of Sr2SiO3.5N0.333:Eu2+ had two emission peaks, one at 420 and the other at 526 nm. There existed a single peak at 529 nm in the case of Sr2SiO3N0.667:Eu2+. The PL spectrum of Sr2SiO2N1.333:Eu2+ also had two peaks, one at 529 and the other at 600 nm. Even though the exact structure was not identified, it was revealed that the X-ray diffraction pattern of Sr2SiO3.5N0.333:Eu2+, Sr2SiO3N0.667:Eu2+, and Sr2SiO2N1.333:Eu2+ was consistent with the PL data. The phosphor with the highest nitrogen content, Sr2SiO2N1.333:Eu2+, showed a broad emission band spanning almost the entire visible range, which may work best if coupled with either UV or blue LEDs.

J Electrochemical Soc. Vol.155, P58, 2008

Biocomposites based on Bacterial Cellulose and Apple and Radish Pulp

Abstract

Bacterial cellulose (BC) pellicles obtained from an Acetobacter xylinum culture were disintegrated using mechanical methods to be used as reinforcement to produce biocomposite sheets with Apple and Radish pulp. The nano size disintegrated BC pellicles were blended with micro size apple and radish pilp in the wet state and then got pressed to produce paper_like sheets. Thermal analysis was carried out by thermo gravimetric analysis (TGA). Mechanical properties were assessed by Quasi-static tensile tests and dynamic mechanical analysis (DMA). High tensile moduli were obtained (up to 8GPa) and a nearly linear dependence of Young’s modulus on the BC volume fraction was observed. Morphological characterization of biocomposite sheets and fracture surfaces performed by scanning electron microscopy (SEM) revealed the structure of the disintegrated cellulose network and the failure mechanisms of the biocomposites.

International Polymer Processing XXII (2007) 5

The effect of temperature and strain rate on the mechanical properties of highly oriented polypropylene tapes and all-polypropylene composites

Abstract

The creation of highly oriented, co-extruded polypropylene (PP) tapes allows the production of recyclable “all-polypropylene” (all-PP) composites, with a large temperature processing window and a high volume fraction of highly oriented PP (>90%). The wholly thermoplastic nature of these ‘self-reinforced’ composites implies that the mechanical performance may vary with temperature. This paper describes the mechanical performance of all-PP composites by measuring the mechanical properties of highly oriented PP tapes and subsequent all-PP composites at a range of temperatures by static and dynamic testing methods. The time–temperature equivalence of all-PP composites is investigated by creating mastercurves of dynamic modulus and tensile strength. A comparison of the performance of these composites with commercial glass fibre reinforced polypropylene composites is included.

Composites Science and Technology 67 (2007) 2061–2070

Dielectric, piezoelectric and ferroelectric properties of grain-orientated Bi3.25La0.75Ti3O12 ceramics

Abstract

By dynamic forging during Spark Plasma Sintering (SPS), grain-orientated ferroelectric Bi3.25La0.75Ti3O12 (BLT) ceramics were prepared. Their ferroelectric, piezoelectric, and dielectric properties are anisotropic. The textured ceramics parallel and perpendicular to the shear flow directions have similar thermal depoling behaviors. The d33 piezoelectric coefficient of BLT ceramics gradually reduces up to 350 °C; it then drops rapidly. The broadness of the dielectric constant and loss peaks and the existence of d33 above the permittivity peak, Tm, show that the BLT ceramic has relaxor-like behavior.

J. Appl. Phys. Vol.102, p104107, 2007

Firing up on all cylinders

Carbon nanotubes have high aspect ratios (length/diameter), so that they percolate or form a conductive network for electrons at very low loadings (typically well below one per cent weight when added to materials such as polymers or ceramics. Carbon nanotubes are essentially nanowires that transport electricity and thermal energy through the matrix in which they are embedded. Another advantage of their high aspect ratio or one-dimensional character is that highly anisotropic materials can be produced. Nanoforce Technology Ltd has developed proprietary processing routes to produce ceramic and polymer composites with one- and two-dimensional electrical conductivity. By controlling the alignment of the CNTs during processing, it is possible to produce materials that are highly electrically insulating in one direction, but good conductors in perpendicular directions.

Materials World, Vol. 15, No. 10 pp. 24-25, 2007

Use of an ARAMIS system to measure the motion of bone segments in two different distal radial fracture fixation systems

Abstract

The ARAMIS system is a non-contact three dimensional measuring system based on the triangulation of directional bundles, which are used to calculate the position of object points. A high contrast surface pattern is applied to the specimen surface, illuminated and two cameras are used to follow the motion of object points and thus the strain, displacement or relative motion of points or segments are calculated. The only requirement is to be able to apply and view a high contrast pattern on the object of interest.

Journal of Biomechanics 2006 (39) S525