Dielectric behaviors of PHBHHx–BaTiO3 multifunctional composite films

Multifunctional polymeric composites were investigated for potential use in high energy storage capacitors and tissue engineering. The polymeric composites were fabricated by employing biodegradable polyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), as the matrix. Ferroelectric BaTiO₃ ceramic powders were added to the composites as fillers. The dielectric spectroscopy of the composites was measured over a wide frequency range (10⁰–10⁷ Hz) from −100 to 60 °C. The composition dependent dielectric behavior was modeled by a self-consistent effective medium theory. A percolation threshold of 0.367 was observed in the composites. The glass transition relaxation of the composite was also discussed by comparing the popular Vögel–Fulcher–Tammann law with a new glass model. The composites show attractive ferroelectricity and piezoelectricity for biomedical applications.     

Electrical,mechanical and thermal properties of polyvinyl chloride composites filled with aluminum powder

In this work, the electrical, mechanical and thermal properties of polyvinyl chloride (PVC) composites filled with different content of aluminum powder varying from 0 to 40 wt.% have been prepared. The dielectric properties of these composites were investigated in the frequency range 100 Hz–100 kHz at temperature range from 30 to 98 °C. The percolation threshold concentration, which is the concentration after which the conductivity increases many orders of magnitude with very little increase in the filler content for PVC/Al composites depends upon the measuring temperature, whether it is below or above the glass transition of the polymer matrix. The highest value of the electrical conductivity, σ, of the composites was found to be in the order of 10⁻⁸ S cm⁻¹, this value recommend such composites to be used in electrostatic dissipation applications as the range of conductivity for such application should be in the range of 10⁻⁵–10⁻⁹ S cm⁻¹.     

Nanocomposites based on MWCNT and styrene–butadiene–styrene block copolymers: Effect of the preparation method on dispersion and polymer–filler interactions

Composites of Kraton-D® 1102 BT (a styrene–butadiene–styrene block copolymer) and multi-walled carbon nanotubes (MWCNTs) were prepared by melt mixing. The composites were characterized by electrical conductivity measurements (Coleman’s method), mechanical properties (DMA and stress–strain tests), thermal stability (thermogravimetry) and morphology of dispersion (SEM). Finally, the resulting composites were compared with those made by the solution casting method. The results showed a strong influence of the preparation methodology on the final properties of the composites due to changes in morphology. Composites prepared by casting showed a higher electrical conductivity than extruded ones; the composites with 6 wt.% of MWCNT prepared by extrusion presented conductivity of the same order of magnitude as the composite with 1 wt.% of MWCNT prepared by casting – 10⁻³ to 10⁻⁴ S cm⁻¹. However, the extruded samples presented better mechanical properties than the casting ones.     

Synthesis of (1 − x)Ca2/5Sm2/5TiO3-xLi1/2Nd1/2TiO3 ceramic powder via ethylenediaminetetraacetic acid precursor

(1 − x)Ca_2/5Sm_2/5TiO₃-xLi_1/2Nd_1/2TiO₃ (CSLNT) ceramic powder was prepared by a liquid mixing method using ethylenediaminetetraacetic acid (EDTA) as the chelating agent. TG, DTA, XRD and TEM characterized the precursors and derived oxide powders. When x = 0.3, perovskite CSLNT was synthesized at 1000 °C for 3 h in air. The CSLNT (x = 0.3) ceramics sintered at 1200 °C for 3 h show excellent microwave dielectric properties of ?_r = 99, Q_f = 6200 GHz and τ_f = 9 × 10⁻⁶ °C⁻¹.     

Hot working behavior and processing map of a γ-TiAl alloy synthesized by powder metallurgy

Powder metallurgy technique has been explored to synthesize a titanium aluminide alloy with the composition 46Ti–46Al–4Nb–2Cr–2Mn by mixing of elemental powders followed by hot isostatic pressing (HIP). The microstructure of the compact revealed the formation TiAl solid solution in addition to a Nb-rich phase. Cylindrical specimens from the HIP’ed billets were compressed at temperatures and strain rates in the ranges of 850–1050 °C and 0.0001–10 s⁻¹. A processing map has been developed on the basis of flow stress data at different temperatures and strain rates, which revealed that the alloy may be hot worked in the range 925–1050 °C and 0.0001–0.01 s⁻¹. Kinetic analysis of the flow stress data yielded a stress exponent of 4.4 and apparent activation energy of 387 kJ/mole which is close to that for self-diffusion of Al in γ TiAl.     

Hot compressive deformation behavior of a new hot isostatically pressed Ni–Cr–Co based powder metallurgy superalloy

The hot compressive deformation behavior of a new hot isostatically pressed Ni–Cr–Co based powder metallurgy (P/M) superalloy was studied in the temperature range of 950–1150 °C and strain rate range of 0.0003–1 s⁻¹ using Gleeble-1500 thermal simulator. The dynamic recrystallization-time–temperature (RTT) curve was developed and the constitutive equation of flow stress during hot deformation was established. The results show that the flow stress decreases with increasing deformation temperature and decreasing strain rate. The flow stress represents as the characteristic of dynamic crystallization with the increasing of strain at the deformation temperatures lower than 1100 °C and strain rates higher than 0.0003 s⁻¹. The beginning time of dynamic crystallization has no linear relationship with deformation temperature in the condition of strain rate lower than 0.01 s⁻¹. Besides, the experiments verify that the hyperbolic sine model including the variable of strain reflects the changing law of flow stress during the hot deformation process.     

Microstructures and improved wear resistance of 3D needled C/SiC composites with graphite filler

Three-dimensional (3D) needled carbon/carbon (C/C) composites with a lowest porosity of 15.6% were achieved after 1 cycle of impregnation by phenolic resin slurry containing graphite filler, hot-pressing curing and pyrolysis. Carbon/silicon carbide (C/SiC) composites were obtained by liquid silicon infiltrating C/C composites. The aim was to incorporate cost effectiveness and excellent performance of C/SiC braking material. Using filler content not exceeding 30 wt% in the slurry promised undamaged C/C segments in C/SiC composites. The linear wear rate of C/SiC using 30 wt% filler was 0.33 μm side⁻¹ cycle⁻¹ and displayed a fourfold decrease; its weight wear rate was 2.46 mg side⁻¹ cycle⁻¹ and minus 171%, compared with the previously reported values of C/SiC without filler, at a braking velocity of 28 m/s. Its friction coefficients and friction stability coefficients appeared relative insensitive to changes in braking velocities and displayed higher values at high braking velocities compared with the previous values.     

High-performance composites based on all-aromatic liquid crystal thermosets

In this study, a new high-performance liquid crystal ester-based thermoset for composite applications was investigated. All-aromatic liquid crystalline thermosets (LCTs) are a promising class of polymers that offer a unique combination of properties such as solvent resistivity, high modulus, high strength, low coefficient of thermal expansion and high after cure glass-transition temperatures (T_g ? 150 °C). Fully cured LCTs offer superior thermo-mechanical properties over high-performance thermoplastic polymers such as PPS, PEEK and PEI. For this study we used a 9000 g mol⁻¹ ester-based LCT based on cheap and readily available monomers, i.e. 4-hydroxybenzoic acid (H), isophthalic acid (I) and hydroquinone (Q), abbreviated by us as HIQ-9. Composite panels prepared from T300 carbon fiber (5-harness satin weave) showed in-plane shear strength of 154 MPa and an in-plane shear modulus of 3.7 GPa. The tensile strength and modulus were measured to be 696 MPa and 57 GPa, respectively. A post-mortem inspection showed that the interfacial strength was excellent and no delamination was observed in the test specimen. Preliminary results show that LCT-based composites exhibit a better combination of (thermo) mechanical properties over PPS and PEI-based composites.     

Dynamic properties of pultruded natural fibre reinforced composites using Split Hopkinson Pressure Bar technique

The paper presents results on dynamic mechanical properties of jute, and kenaf fibre reinforced composites at various strain rates using compression Split Hopkinson Pressure Bar technique. The stress–strain curves for both pultruded natural fibre reinforced composites at strain rates of nearly 1400 s⁻¹ are illustrated and then compared with statically determines stress–strain curve (1.0 × 10⁻³ s⁻¹). Results show that the strain rate does affect the value of dynamic compressive properties of both pultruded natural fibre composites. Higher dynamic compression modulus and 2.5% flow stress were recorded for higher strain rates as compared to lower strain rate over the range of strain rates investigated. Under dynamic loading, jute fibre reinforced composites recorded the highest value of dynamic response in terms of compression modulus, 2.5% flow stress and compressive strength than that of kenaf fibre reinforced composites. In addition, kenaf fibre reinforced composites is more severely damaged as compared to jute fibre reinforced composites for all tested strain rate.     

Study on properties of CaO-SiO2-B2O3 system glass-ceramic

Low temperature co-fired ceramic (LTCC) is prepared by sintering a glass selected from CaO-SiO₂-B₂O₃ system, and its sintered bodies are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that the optimal sintering temperature for this glass-ceramic is 820 °C for 15 min, and the major phases of this material are CaSiO₃, CaB₂O₄ and SiO₂. The glass-ceramic possesses excellent dielectric properties: ?_r = 6.5, tan δ < 2 × 10⁻³ at 10 MHz, temperature coefficient of dielectric constant about −51 × 10⁻⁶ °C⁻¹ and coefficient of thermal expansion about 8 × 10⁻⁶ °C⁻¹ at 20-400 °C. Thus, this material is supposed to be suitable for the tape casting process and be compatible with Ag electrode, which could be used as the LTCC materials for the application in wireless communications.