A novel route for processing cobalt–chromium–molybdenum 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.

Multiscale hybrid micro-nanocomposites based on carbon nanotubes and carbon fibers

Abstract

Amino-modified double wall carbon nanotube (DWCNT-NH2)/carbon fiber (CF)/epoxy hybrid micro-nanocomposite laminates were prepared by a resin infusion technique. DWCNT-NH2/epoxy nanocomposites and carbon fiber/epoxy microcomposites were made for comparison. Morphological analysis of the hybrid composites was performed using field emission scanning electron microscope. A good dispersion at low loadings of carbon nanotubes (CNTs) in epoxy matrix was achieved by a bath ultrasonication method. Mechanical characterization of the hybrid micro-nanocomposites manufactured by a resin infusion process included three-point bending, mode I interlaminar toughness, dynamic mechanical analysis, and drop-weight impact testing. The addition of small amounts of CNTs (0.025, 0.05, and 0.1 wt%) to epoxy resins for the fabrication of multiscale carbon fiber composites resulted in a maximum enhancement in flexural modulus by 35%, a 5% improvement in flexural strength, a 6% improvement in absorbed impact energy, and 23% decrease in the mode I interlaminar toughness. Hybridization of carbon fiber-reinforced epoxy using CNTs resulted in a reduction in Tg and dampening characteristics, presumably as a result of the presence of micron-sized agglomerates.

The sintering and grain growth behaviour of ceramic – carbon nanotube nanocomposites

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.

Microstructural evolution during high-temperature oxidation of Ti2AlN ceramics

Abstract

Microstructural evolution of Ti2AlN ceramics during high-temperature oxidation in air has been revealed by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM), and energy-dispersive spectroscopy (EDS). After oxidation below 1200 ºC, layered microstructures formed on Ti2AlN surfaces containing anatase, rutile, and a-Al2O3. Above 1200 ºC, more complex layered microstructures formed containing Al2TiO5, rutile, a-Al2O3, and continuous void layers. With increasing temperature, anatase gradually transformed to rutile, and TiO2 reacted with a-Al2O3 to form Al2TiO5. Based on these microstructural observations, an oxidation mechanism for Ti2AlN ceramics is proposed.

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

Sparking Advanced Ceramics

Abstract

Ceramics are normally processed by consolidating powders using sintering at high temperatures. The time required for this process is usually measured in hours because of the slow rate of heating/cooling of the furnaces used. Spark plasma sintering (SPS), as it is commonly known, is a rapid sintering process, where the cycle can be completed in minutes. This generates the possibility of making ceramics with new microstructures and properties. Queen Mary University of London and its spin-out company, Nanoforce Technology Ltd, are working to exploit SPS technology in the UK.

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.

Laser melting of spark plasma sintered zirconium carbide: thermophysical properties of a generation IV very high temperature reactor material

Abstract

Commercial ZrC0.96 powder (ABCR, Karlsruhe, Germany) was densified by spark plasma sintering to greater than 96% relative density at temperatures of 1900-2180°C, applied pressures of 40-100 MPa, and soak time of 6-30 min. Effects of process parameters on microstructure were assessed by ceramography. High temperature (>2000 °C) was more instrumental in full densification than was high pressure, and excessive ramp rate resulted in high residual porosity. Grain coarsening was promoted by prolonging the isothermal dwell. Laser heating was used to melt sintered ceramics, as part of a novel thermal analysis technique for probing extremely high temperature phase transformations. Temperatures well in excess of the expected melting temperature of ZrC and up to 4000 K were achieved. The feasibility of the technique for detecting melting transitions in zirconium carbide was demonstrated, and solidus and liquidus temperatures within 50-80 K of predicted values were measured. Post-melting analysis of laser-melted specimens revealed dendritic microstructure and composition consistent with single phase ZrC.

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

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 oC/ 100 MPa/ 3 min. In boron carbide, structural degradation of MWNTs started from ~1600 oC 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 oC for 20 min. However, no Raman vibrations of MWNTs were observed for nanocomposites processed at temperatures >2000 oC, 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 oC) and longer processing times (>13 min).

Advances in Applied Ceramics, 109 (2009) 240-245

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 (> 700oC) suggests that the Bi3-xNdxNbTiO9 ceramics with x = 0.6 could be good candidates for high temperature piezoelectric applications.

Journal of Applied Physics, in press, 2009

a) E-mail address:

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.

Journal of the European Ceramic Society 30 (2010) 153–157

Hot pressed and spark plasma sintered zirconia/carbon nanofiber composites

Abstract

Zirconia/carbon nanofiber composites were prepared by hot pressing and spark plasma sintering with 2.0 and 3.3 vol.% of carbon nanofibers (CNFs). The effects of the sintering route and the carbon nanofiber additions on the microstructure, fracture/mechanical and electrical properties of the CNF/3Y-TZP composites were investigated. The microstructure of the ZrO2 and ZrO2–CNF composites consisted of a small grain sized matrix (approximately 120 nm), with relatively well dispersed carbon nanofibers in the composite. All of the composites showed significantly higher electrical conductivity (from 391 to 985 S/m) compared to the monolithic zirconia (approximately 1×10-10 S/m). The spark plasma sintered composites exhibited higher densities, hardness and indentation toughness but lower electrical conductivity compared to the hot pressed composites. The improved electrical conductivity of the composites is caused by CNFs network and by thin disordered graphite layers at the ZrO2/ZrO2 boundaries.

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

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

Abstract

J Appl. Phys. In press, 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