Fatigue Behavior of Vitallium-2000 Plus Alloy for Orthopedic Applications

Vitallium-2000 Plus alloy is one of the important metallic biomaterials having excellent biocompatibility as it is free from nickel, vanadium, and beryllium elements that could cause potential allergic problems to patients. In this study, the high cycle fatigue behavior of continuous cast vitallium-2000 Plus alloy was investigated using rotation bend fatigue tests at 50 Hz frequency and at room temperature apart from tensile studies. A series of tests were carried out at varying stresses, and the S-N curve was obtained from regression of the test data. The endurance limit was determined as 387 MPa, which is very good for a cast alloy. This increase in fatigue property (compared to the previous version of this alloy) is primarily due to the presence of nitrogen that is added during continuous casting process and also that of the other alloying elements. Tensile test was also performed as per the ASTM standard to evaluate its static properties. The fracture morphology was investigated using scanning electron microscope to study the mechanisms of fracture. It was established that the primary mechanism of fracture was by microvoid nucleation and coalescence, typical of a ductile material that is significant for a cast alloy. The experimentally determined values of endurance limit, yield strength, tensile strength, and percent elongation provide evidence that vitallium-2000 Plus cast alloy has very good fatigue, tensile properties, and increased formability without fracture, allowing for excellent adjustability during its application.     

Isospecific polymerization of vinyl ethers with titanium catalysts containing modified tridentate anionic donor ligands

BACKGROUND: Stereo‐regulated polymerization of vinyl ethers (VEs) assumes significance because of its elegance and the resultant unique polymer properties. Although several Lewis acid catalysts polymerize VEs with good control of molecular weight, achieving stereo‐regularity is quite challenging. There are literature reports of a few catalyst systems capable of producing highly isotactic poly(vinyl ether) (PVE) only at lower temperatures with the polymer becoming atactic with an increase in reaction temperature. Hence innovating new catalyst systems which can produce highly stereo‐regular PVEs with high molecular weight at ambient temperature is quite challenging. RESULTS: We used two different titanium pre‐catalysts (1‐TiCl₂ and 2‐TiCl₂) for the polymerization of VEs. These pre‐catalysts in combination with methylaluminoxane (MAO)/borate polymerized VEs in higher conversions. Highly isotactic poly(n‐butylvinyl ether) (PBVE; 75% dyad isotactic ratio) was obtained with 1‐TiCl₂/MAO at ambient temperature. CONCLUSION: We synthesized unimodal and highly isotactic PBVE with molecular weights of the order of 10⁵ g mol^?1 using the non‐metallocene‐type single‐site catalyst system 1‐TiCl₂/MAO even at ambient temperature. The symmetry around the metal centre in the pre‐catalyst and the polymerization temperature played a major role in controlling the stereo‐regularization of the olefin inserted. Copyright © 2009 Society of Chemical Industry     

Gel permeation chromatography for characterization of graft copolymer

Summary The present paper describes the grafting of vinyl monomers onto cellulose nitrate in non-aqueous medium using benzoyl peroxide as a catalyst. The complete separation of the homopolymers and graft copolymer was carried out by selective solvent extraction. The graft copolymer was characterized by IR spectra. The GPC was used as a technique to differentiate between homopolymer, polymer mixture, polyblend, and graft copolymer.     

Styrene butadiene rubber/aluminum powder composites—mechanical,morphological and electrical behaviors

Different weight fractions of aluminum (Al) powder viz., 10, 20, 30, 40, 50, 60 and 70 phr were incorporated into styrene butadiene rubber (SBR) matrix. The Al powder filled and vulcanized SBR composites have been characterized for mechanical properties such as tensile strength, tensile modulus and surface hardness. A drastical improvement in tensile strength and tensile modulus with increase in filler content of the composites was noticed. The electrical properties such as dielectric constant, tan delta and dielectric loss were measured for all the four compositions. The effect of volume fraction (0–70 phr) of conducting filler, frequency (100 kHz–30 MHz), temperature (25–75°C) and relative humidity on dielectric constant, dielectric loss and tan delta values of the composites were studied.     

Dynamics of growth and weight transitions in a pediatric cohort from India

Background  

There is paucity of information regarding time trends of weight status in children from rapidly developing economies like India. The aim of the study was to analyse the dynamics of growth and weight transitions in a cohort of school children from India.     

Synthesis and characterization of aromatic-alipathic polyamides containing tetraphenylthiophene units into the backbone

Summary Aromatic-aliphatic polyamides were prepared from 2, 5-bis(4-carboxyethylcarbonylphenyl)-3,4-diphenylthiophene (BCDT) with few commercial diamines by using Yamazaki's phosphorylation reaction. The polymers were obtained in good yields and were characterized by solubility tests, viscosity measurements, IR spectroscopy, thermal analysis and X-ray diffraction studies. These polyamides had inherent viscosities in the range of 0.35 to 0.70 dl/g and were amorphous in nature. All the polyamides were readily soluble in solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidinone, N,N-dimethylformamide, nitrobenzene, hexamethylphosphoramide, m-cresol, sulphuric acid and did not lose weight below 300°C in air. NCL Communication No:-4815     

Formation of BaCrO4 NanoCrystallites within Thermally Evaporated Sodium Bis-2-Ethylhexyl-Sulfosuccinate and Stearic Acid Thin Films

This paper describes the growth of barium chromate (BaCrO₄) nanocrystallites within thermally evaporated thin films of stearic acid (StA) and sodium bis-2-ethylhexyl-sulfosuccinate by a process of Ba²⁺ ion entrapment followed by in situ reaction with CrO₄²⁻ ions. Dense spherical assemblies of BaCrO₄ nanocrystallites of very uniform size (∼50 nm) were obtained within the two different host matrices. The spherical assemblies were composed of smaller (ca. 5–10 nm size) BaCrO₄ crystals indicating that efficient size control over crystal size may be exercised by the matrix. Contact angle measurements of the BaCrO₄–StA and BaCrO₄–sodium bis-2-ethylhexyl-sulfosuccinate films indicated that they were hydrophobic, thus pointing to the possible role of hydrophobic interaction between the StA and sodium bis-2-ethylhexyl-sulfosuccinate monolayer-covered BaCrO₄ crystals in the assembly process.     

Solid-state spun fibers and yarns from 1-mm long carbon nanotube forests synthesized by water-assisted chemical vapor deposition

We report continuous carbon nanotube (CNT) fibers and yarns dry-drawn directly from water-assisted chemical vapor deposition (CVD) grown forests with about 1-mm height. As-drawn CNT fibers exist as aerogel and can be transformed into more compact fibers through twisting or densification with a volatile organic liquid. CNT fibers are characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman microscopy, and wide-angle X-ray diffraction. Mechanical properties and electrical conductivity of the post-treated CNT fibers are investigated. The resulting fibers show the work of rupture of 30 J/g and DC electrical conductivity of 5.0 × 10⁴ S/m.     

Effective Suppression of Conducted Electro Magnetic Interference in DC-DC Boost Converter Using Field Programmable Gate Array Based Chaotic Pulse Width Modulation Switching

Abstract—In recent years, electro-magnetic interference on DC-DC converters is seen as serious problem as it limits the capability of the DC-DC converter. It is popular to use analog circuits to suppress electro-magnetic interference; however, a cheap analog circuit suffers from numerous drawbacks, including inaccurate pulse generation, carrier frequency limitation, and degraded performance due to aging. Conversely, high-performance digital circuits are capable of providing accurate pulses compared to analog circuits. In this article, a field-programmable gate array is used to generate accurate chaotic pulse-width modulation pulses for DC-DC converters. A spread spectrum technique based on randomized carrier frequency modulation with fixed duty ratio is proposed for gating pulse generation, implemented using a field-programmable gate array for electro-magnetic interference suppression. A hardware prototype is built in the laboratory for the proposed method and tested. The performance of the proposed method estimated through simulation study is validated via experimental results.