Apatite wollastonite–poly methyl methacrylate bio-composites

Bio-composites consisting of sol–gel processed apatite wollastonite (AW) glass ceramics and poly methyl methacrylate (PMMA) were prepared by hot compaction method. Density of the composites decreased with increase in PMMA content, while, biaxial flexural strength (BFS) was 21 MPa for 20 wt.% PMMA and beyond which it decreased. A correlation between phase compositions of AW glass ceramics with BFS was attempted from the XRD results. In vitro bioactivity of the composites in a simulated body fluid (SBF) showed the formation of spherical globules on the surface within 7 days of soaking as observed by environmental SEM. Thin film XRD and EDX measurement confirmed these globules to be bone like apatite with Ca/P ratio 1.53 and FTIR measurement showed the corresponding peaks for phosphates. Results indicated the bone bonding ability of the composites by forming a surface apatite (calcium phosphate) layer in SBF and the growth increased with increase in soaking durations. ICP measurement of the remaining SBF after 7, 14 and 21 days soaking of samples was found to be in good agreement with the EDX analysis results.     

High‐strength and low‐stiffness composites of nanoclay‐filled thermoplastic polyurethanes

In this study, bulk polymerized clay‐tethered thermoplastic polyurethane (TPU) composites were synthesized that offered much improved tensile strength with negligible changes in tensile modulus. These composites contained intercalated, tethered layered silicate particles and were synthesized by mixing low molecular weight prepolymer chains containing unreacted –NCO groups with reactive layered silicate clay followed by catalyzed chain extension reaction with butanediol. The molar ratio of –NCO and –OH functional groups in the composite was varied between 1.0 and 1.2. It was found that an appreciable amount of –NCO groups was consumed in reaction with moisture present in the clay and some in quaternary ammonium ion‐catalyzed dimerization and trimerization. Composites with –NCO to –OH molar ratio 1.1 provided the best improvement in mechanical properties—the composite with 5 wt% clay provided a 60% increase in tensile strength and 50% increase in strain at break, while the tensile modulus increased only by 15% over TPU. POLYM. ENG. SCI., 45:1532–1539, 2005. © 2005 Society of Plastics Engineers     

Application of hydrophilic ionic liquid treatment to the morphological observations of hydrated porous ceramic green bodies

In this study, a simple and convenient method for observing the surface morphology of hydrated porous ceramic green bodies is proposed. The porous hyrdoxyapatite (HAp) green body was prepared by a gelcasting process and was dried in a humid chamber from 90 to 50% relative humidity at 25 °C before subsequent treatment with a hydrophilic ionic liquid (IL). The surface morphology of the IL-treated porous HAp green body was observed using FE-SEM. The results showed that the pore morphology and microstructure of the HAp green body was readily observable without evidence of charging. The as-prepared sample showed pores approximately 300–600 μm in diameter, which gradually contracted to approximately 200–400 μm upon drying in the humid chamber. Following sintering at 1000 °C, the pores had further contracted to approximately 100–300 μm. The IL binds with the surrounding water to prevent the sample from drying in vacuum and acts as a conductive media, allowing the HAp ceramics to be observed in the electron microscope. In comparison to the micro-focused X-ray CT analysis, the fine pore structure (less than 100 μm) could only be observed using FE-SEM when the porous body had also been subjected to the IL treatment.     

Structural and dielectric properties of Bi1−xSrxMnO3 (0.40≤x≤0.55)

In order to study the effect of Sr substitution on structural and dielectric properties of Bi_1−xSr_xMnO₃ (0.40≤x≤0.55) compounds were synthesized by the solid state reaction method. The as-prepared samples were characterized by X- ray diffraction (XRD) and dielectric measurements to correlate structural changes with dielectric properties. The XRD data were further analyzed by the Rietveld refinement. The highest dielectric constant was observed in Bi_0.55Sr_0.45MnO₃ and Bi_0.5Sr_0.5MnO₃ systems (∼10⁶) mainly because of orientation polarization. The charge ordering temperature decreases with increasing Sr concentration in Bi_1−xSr_xMnO₃ systems.     

Structural,Thermal, and Electrical Study of Bi0.5Sr0.5MnO3

Solid oxide fuel cell (SOFC) is considered as a potential candidate for clean and efficient alternate energy source. Efforts are being made to reduce their operating temperature for SOFCs commercialization. However, the reduction in operating temperature increases the polarization effect in the existing cathodes. In the present study, Bi_0.5Sr_0.5MnO₃ was synthesized and studied for its structural, thermal, and electrical properties. Bi_0.5Sr_0.5MnO₃ was synthesized by conventional solid state reaction method. The as-prepared sample was characterized by x-ray diffraction, scanning electron microscope, thermogravimetric analysis, dilatometer and impedance spectroscopy. The Rietveld refinement results confirm that Bi_0.50Sr_0.50MnO₃ shows the tetragonal symmetry with p4 mm space group. Scanning electron microscopy study shows that the distribution of grains is uniform and the grains are well connected to each other due to better sinterability of the samples. The dilatometric curve shows linear behavior up to 600°C and after that becomes steeper. This can be due to the loss of lattice oxygen at higher temperatures and creation of oxygen vacancies. The thermal expansion coefficient of the system is ～8.9 × 10^?6 °C^?1 and total conductivity of the sample is ～4.78 × 10^?3 S/cm.     

Effect of Praseodymium on Electrical Properties of BiFeO3 Multiferroic

Polycrystalline samples of Bi_1?x Pr _x FeO₃ (BPFO) (x = 0, 0.05, 0.1, 0.15) were synthesized by a solid-state reaction technique. Preliminary x-ray structural analysis confirmed the formation of a single-phase compound of BPFO. Scanning electron micrographs recorded at room temperature on pellet samples showed: (i) a uniform distribution of grains on the surface of the samples (with fewer voids) and (ii) reduction of grain size with increasing Pr content of the BPFO samples. Detailed studies of the impedance and electrical modulus of the materials, carried out in a wide range of frequency (1 kHz to 1 MHz) at different temperatures (25°C to 400°C), have provided many interesting results including a significant decrease in loss tangent, structural stability, etc. The variation of the alternating-current (ac) and direct-current (dc) conductivity with inverse absolute temperature follows an Arrhenius relation. The decrease in leakage current and the negative temperature coefficient of resistance behavior with increasing Pr content of BPFO are important observations of this work.     

Design methodology for battery powered embedded systems — In safety critical application

Battery powered embedded system can be considered as a power aware system for a safety critical application. There is a need of saving the battery power for such power aware system so that it can be used more efficiently, particularly in safety critical applications. Present paper describes power optimization procedure using real time scheduling technique having a specific dead line guided by the model based optimum current discharge profile of a battery. In any power aware system ‘energy optimization’ is one of the major issues for a faithful operation.     

Simulated body fluid (SBF) adsorption onto a-SiC:H thin films deposited by hot wire chemical vapor deposition (HWCVD)

Hydrogen amorphous silicon carbon (a-SiC:H) film deposited by the Hot Wire Chemical Vapor Deposition (HWCVD) technique on silicon substrates were soaked in simulated body fluid (SBF). Characterization of the film with different soaking durations in SBF was carried out by Fourier Transform Infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and contact angle measurements. It was found that the relative amounts of carbon in the a-SiC:H film surface decreases with increase in soaking period. XPS results showed the adsorption of Ca and Mg on the a-SiC:H surface. This indicates the formation of negatively charged surface possibly due to formation of silanol groups or dissolution of carbon to SBF confirming the bioactivity of the material. Contact angle decreased from 74° to 65° during 30 days of soaking in the body fluid. Present study is an attempt to observe the interaction of a-SiC:H film prepared by HWCVD technique with the body environment for its future suitability as artificial heart valve and stent coating materials.     

Apatite Wollastonite–Titanium Biocomposites: Synthesis and In Vitro Evaluation

The present paper discusses the consolidation of apatite wollastonite (AW) glass ceramic/titanium composites with various percentages of Ti (5–40 wt%) in an argon atmosphere, and, evaluation of the sintered properties and bioactivity in simulated body fluid (SBF). The sintered density of the composites was found to increase with an increase in Ti content and was found to be in the range of 2.25 (5 wt% Ti)–2.70 g/cm³ (40 wt%) as compared with those of sintered AW (2.06 g/cm³) and Ti (4.5 g/cm³). Biaxial flexural strength of the composites was found to be in the range of 13–45 MPa. X-ray diffraction studies of the sintered AW/Ti composites showed Ti phases (TiPO₄+CaTiO₃+Ti₂O₃) and wollastonites (CaSiO₃+MgSiO₃+CaMgSiO₄) as dominating phases. In vitro bioactivity of the composites was studied by soaking the composites in SBF for 7, 14, and 21 days, and the sample surfaces as well as the remaining SBF were analyzed to study the interaction between the material and SBF. The results indicated that the growth of phosphates increased in about 7 days of soaking in SBF, after which a steady state was reached, confirming the samples to be bioactive.