Effect of carbon black loading on fluoroelastomer–solvent interactions

An analysis of the molecular transport of organic liquids into fluoroelastomer membranes containing varying amounts of carbon black has been undertaken by the sorption–desorption gravimetric method. The variation in carbon black loading and temperature showed a significant effect on their transport characteristics. Diffusion coefficients were calculated from Fick's equation. Experimental sorption–desorption results were analyzed in terms of concentration profiles obtained from a solution of Fick's equation as well as by a numerical method based on the finite difference technique. Arrhenius activation parameters were estimated from the temperature-dependent diffusion and permeation data. The results of this study are discussed in terms of polymer–solvent interactions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:815–825, 1998     

In vitro analysis of the wear,wear debris and biological activity of surface-engineered coatings for use in metal-on-metal total hip replacements

Extremely low wear rates have been reported for metal-on-metal total hip replacements, but concerns remain about the effects of metal ion release, dissolution rates and toxicity. Surface-engineered coatings have the potential to improve wear resistance and reduce the biological activity of the wear debris produced. The aim of this study was to examine the wear and wear debris generation from surface-engineered coatings: titanium nitride (TiN), chromium nitride (CrN) and chromium carbon nitride (CrCN) applied to a cobalt-chrome alloy (CoCr) substrate. The coatings were articulated against themselves in a simple geometry model. The wear particles generated were characterized and the cytotoxic effect on U937 macrophages and L929 fibroblasts assessed. The CrN and CrCN coatings showed a decrease in wear compared to the CoCr bearings and produced small (less than 40 nm in length) wear particles. The wear particles released from the surface engineered bearings also showed a decreased cytotoxic effect on cells compared to the CoCr alloy debris. The reduced wear volumes coupled with the reduced cytotoxicity per unit volume of wear indicate the potential for the clinical application of this technology.     

Variation of crystal structure,magnetization, and dielectric properties of Nd and Ba co-doped BiFeO3 multiferroics

Multiferroics having composition Bi_0.80Nd_0.20-xBa_xFeO₃ were prepared to investigate the effect of doping on crystal structure, magnetic, and dielectric properties. The Rietveld refinement deduces the formation of mixed structural symmetry. With larger content of Nd, crystal structure consisting of major rhombohedral R3c and minor orthorhombic Pnma has been accomplished. The fraction of rhombohedral phase has been found to increase with doping of Ba up to x = 0.10. At composition x = 0.15, the orthorhombic phase Pnma disappears, and there is evolution of triclinic phase P1 in place of it. The mixed structure now accomplished contains ≈61% rhombohedral R3c and rest 39% triclinic P1. In solely Ba-doped sample (ie, at x = 0.20), the fraction of rhombohedral R3c phase again rises and attains ≈92% fraction of the structure along with rest triclinic P1 phase. The M-H loops depict enormous enhancement in magnetic properties with increasing doping of Ba. Dielectric constant (ε′) and dielectric loss (tan δ) both were found to increase with doping of Ba. The anomalies present in the dielectric constant and dielectric loss with temperature may be regarded to the hopping conduction of e⁻ between Fe³⁺ and Fe²⁺ and their interaction with oxygen vacancies.     

Fatigue Fracture of a Compressor Disc of an Aeroengine

There was an accident to a single engine aircraft. From the eye and ear witness accounts, it was established that the accident occurred because of engine failure. After preliminary examination of the wreckage of the crashed engine, a few suspected components were identified for detailed laboratory investigation. The objective was to establish the primary failure in the engine. While majority of the engine components submitted for laboratory analysis showed secondary damages due to either crash impact forces or post-accident fire, the fracture pattern in one of the compressor disks was different from other components of the engine. Fractographic study revealed that the failure of the disk was by fatigue mechanism. Subsequent investigation showed that the fatigue fracture of the compressor disk was the first in the chain of events that led to the engine failure. This finding was further substantiated through fracture mechanics calculations.     

Characterisation of wear particles produced by metal on metal and ceramic on metal hip prostheses under standard and microseparation simulation

The failure of metal on polyethylene total hip replacements due to wear particle induced osteolysis and late aseptic loosening has focused interest upon alternative bearings, such as metal on metal implants. A recent advance in this field has been the development of a novel ceramic on metal implant. The characteristics of the wear particles generated in this low-wearing bearing have not been previously determined. The aims of this study were to characterise metal wear particles from metal on metal and ceramic on metal hips under standard and adverse (microseparation) wear conditions. Accurate characterisation of cobalt-chrome wear particles is difficult since the reactive nature of the particles prevents them from being isolated using acids and bases. A method was developed to isolate the metal wear particles using enzymes to digest serum containing lubricants from metal on metal and ceramic on metal hip simulations. High resolution scanning electron microscopy was then used to characterise the wear particles generated by both metal on metal and ceramic on metal implants under standard and microseparation wear conditions. The wear particles isolated from all simulations had a mean size of less than 50 nm with a rounded and irregular morphology. No significant difference was found between the size of wear particles generated under any conditions.     

A microwave route for the synthesis of nanoflakes and dendrites-type beta-ln2S3 and their characterization

In this article, a simple microwave route was applied for the synthesis of nanoflakes and dendrite-type beta-indium sulfide (In2S3) in high yield (> 97%), using a homogeneous mixture of indium(lll)chloride and thiourea in an ethylene glycol (EG)/polyethylene glycol (PEG400) solvent. The reaction was conducted in a simple domestic microwave oven (DMO). Powder X-ray diffraction (XRD), low resolution and high resolution transmission electron microscopy (LRTEM and HRTEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDS), were applied to investigate the crystallinity, structure, morphology, and composition of the In2S3 nano-materials. Both the as-synthesized and calcined In2S3 products were a body-centered tetragonal (bct) phase, observed by XRD and HRTEM. The length and width of the resulting nanoflakes were in the range of 70-600 nm and 4-10 nm, respectively. The optical band gap of the powder was determined by diffuse reflectance spectroscopy (DRS) and was found to be 2.44 eV. The electronic properties of the products were studied by measuring the optical absorption spectra using photoacoustic spectroscopy. The band gap calculated by this method was found to be 2.52 eV. A possible mechanism for the formation of nanoflakes/dendrites-type In2S3 was also discussed.     

Reactive oxygen species driven angiogenesis by inorganic nanorods

The exact mechanism of angiogenesis by europium hydroxide nanorods was unclear. In this study we have showed that formation of reactive oxygen species (H(2)O(2) and O(2)·-) is involved in redox signaling pathways during angiogenesis, important for cardiovascular and ischemic diseases. Here we used single-walled carbon nanotube sensor array to measure the single-molecule efflux of H(2)O(2) and a HPLC method for the determination of O(2)·- from endothelial cells in response to proangiogenic factors. Additionally, reactive oxygen species-mediated angiogenesis using inorganic nanorods was observed in transgenic (fli1a:EGFP) zebrafish embryos.     

Digitally controlled oscillator design with a variable capacitance XOR gate

A digitally controlled oscillator (DCO) using a three-transistor XOR gate as the variable load has been presented. A delay cell using an inverter and a three-transistor XOR gate as the variable capacitance is also proposed. Three-, five- and seven-stage DCO circuits have been designed using the proposed delay cell. The output frequency is controlled digitally with bits applied to the delay cells. The three-bit DCO shows output frequency and power consumption variation in the range of 3.2486-4.0267 GHz and 0.6121-0.3901 mW, respectively, with a change in the control word 111-000. The five-bit DCO achieves frequency and power of 1.8553-2.3506 GHz and 1.0202-0.6501 mW, respectively, with a change in the control word 11111-00000. Moreover, the seven-bit DCO shows a frequency and power consumption variation of 1.3239-1.6817 GHz and 1.4282-0.9102 mW, respectively, with a varying control word 1111111-0000000. The power consumption and output frequency of the proposed circuits have been compared with earlier reported circuits and the present approaches show significant improvements.