Selection of the optimum electrolyte composition and flow rate for machining a particular high alloy steel

Conventional methods employed for machining flame cut surfaces of alloy steel castings present many difficulties, mainly breakage of tool tips which makes the process uneconomical. In this paper D.L. Pramanik and A. Chattopadhyay have chosen the electrochemical (ec) method to machine these surfaces. The present work has been designed to deal with the problem in such a way so as to be useful for a broad spectrum of applications. Efforts have been made to select the optimum electrolyte and operating conditions to produce low overcut and a good surface finish     

Metabolizable Semiconducting Polymer Nanoparticles for Second Near‐Infrared Photoacoustic Imaging

Photoacoustic (PA) imaging in the second near‐infrared (NIR‐II) window (1000–1700 nm) holds great promise for deep‐tissue diagnosis due to the reduced light scattering and minimized tissue absorption; however, exploration of such a noninvasive imaging technique is greatly constrained by the lack of biodegradable NIR‐II absorbing agents. Herein, the first series of metabolizable NIR‐II PA agents are reported based on semiconducting polymer nanoparticles (SPNs). Such completely organic nanoagents consist of π‐conjugated yet oxidizable optical polymer as PA generator and hydrolyzable amphiphilic polymer as particle matrix to provide water solubility. The obtained SPNs are readily degraded by myeloperoxidase and lipase abundant in phagocytes, transforming from nonfluorescent nanoparticles (30 nm) into NIR fluorescent ultrasmall metabolites (≈1 nm). As such, these nanoagents can be effectively cleared out via both hepatobiliary and renal excretions after systematic administration, leaving no toxicity to living mice. Particularly these nanoagents possess high photothermal conversion efficiencies and emit bright PA signals at 1064 nm, enabling sensitive NIR‐II PA imaging of both subcutaneous tumor and deep brain vasculature through intact skull in living animals at a low systematic dosage. This study thus provides a generalized molecular design toward organic metabolizable semiconducting materials for biophotonic applications in NIR‐II window.     

Crystallization and oxidation resistance properties of boron modified silicon oxycarbides derived from polymeric precursors by sol–gel method

Boron modified silicon oxycarbides (SiBOCs) were prepared from sol–gel derived pre-ceramic polymeric gels followed by pyrolysis at 950 °C under nitrogen. As-prepared SiBOC was found to be amorphous in nature and partially crystallized to SiO₂ at 1500 °C. The effect of boron incorporation on the crystallization of SiBOC was studied and the result revealed that the tendency to crystallization decreased with increasing boron content. This is due to the formation of Si–O–B bridges at higher temperatures, which retards the crystallization of SiO₂, evidenced from FTIR studies. SiBOC also exhibited excellent oxidation resistance ability at high temperature.     

Low-Temperature Preparation of Nanocrystalline Lead Zirconate Titanate and Lead Lanthanum Zirconate Titanate Powders Using Triethanolamine

Nanocrystalline lead zirconate titanate (PZT) powders, with a Zr:Ti ratio of 60:40, have been prepared from a solution of triethanolamine (TEA) and Ti⁴⁺, Zr⁴⁺, and Pb²⁺ ions. The metal ions were in solution through complex formation with TEA. The soluble metal-ion–TEA complex formed the precursor material when it was completely dehydrated. Heat treatment of the precursor at 450°C resulted in single-phase PZT powders. The precursor and the heat-treated powders have been characterized by using thermal analysis and X-ray diffractometry (XRD) studies. The average particle size, as measured from X-ray line broadening and transmission electron microscopy studies, was ∼20 nm. PZT powders modified with 3 mol% of lanthanum (PLZT) also were prepared through this route and were investigated via XRD studies. The dielectric constants of the PZT and PLZT powders were 12475 and 11262, and their corresponding Curie temperatures were 362° and 315°C, respectively.     

Numerical study of rich catalytic combustion of syngas

The rich catalytic combustion of syngas/air mixtures over platinum has been investigated numerically in a two-dimensional circular channel using steady simulations and detailed hetero-homogeneous chemistry. The channel dimensions are representative of a catalytic monolith. Simulations have been conducted in the pressure range of 1–10 bar and Φ = 3–5 with varying inlet velocities, residence time, H₂/CO ratio and CH₄ percentage. Detailed kinetic studies including the reaction path diagram (RPD) in a plug flow reactor have also been conducted to understand the kinetic interactions between H₂, CO, and CH₄. It has been observed that the homogeneous reaction rates are significant at higher pressures and cannot be neglected, although they were highly localized. The channel temperature significantly affected the relative conversion of H₂ and CO. The kinetic coupling between H₂ and CO oxidation was studied and the reason for the differential consumption of O₂ by the reactants was addressed by analyzing the reaction pathways. The residence time in the channel affected the species oxidation and four operation regimes were identified. Both the water-gas shift reaction and the reverse water-gas shift reaction were observed under varying conditions of pressure and equivalence ratio. The effect of H₂/CO ratio has also been investigated. The present study shows that rich catalytic combustion of syngas is fundamentally different from lean combustion.     

Characterization of Nanocrystalline Bismuth Telluride (Bi2Te3) Synthesized by a Novel Approach Through Aqueous Precursor Method

Bi₂Te₃-based alloys are currently best-known, technologically important thermoelectric materials near room temperature. In this paper, nanocrystalline Bi₂Te₃ was synthesized by an aqueous solution technique based on the reaction between the aqueous solution of Bi-ethylenediamine tetraaceticacid (EDTA), TeO-EDTA, and NaBH₄ at room temperature. NaBH₄ was used as a reducing agent. TeO-EDTA was prepared from TeO₂ after satisfactory purification. The sample purity was examined by selected area energy dispersive X-ray analysis. The products were characterized by X-ray diffraction and high-resolution transmission electron microscopy by which the particle morphologies and size were studied. The particle size ranges from 60 to 90 nm.     

Preparation of Nanosized Rutile TiO2 from an Aqueous Peroxotitanate Solution

A new facile method for direct preparation of well-crystallized rutile TiO₂ nanoparticles without any ionic impurities was reported. The nanosized TiO₂ was prepared by aging a peroxotitanate solution at 100°C for 0–12 h, formed by reaction of H₂O₂ and titanium tetraisopropoxide (TTIP). The method involves hydrolysis of TTIP and simultaneous digestion of hydrolyzed precipitates, and hydrothermal treatment into crystalline phases. It was found that the TTIP/H₂O₂ molar ratio in the preparation of peroxotitanate as a precursor for TiO₂ was crucial in the formation of a rutile phase. Transmission electron microscope observation for sols showed rod-like shapes with average particle sizes of around 100 nm in the elongated direction.     

Processing and properties of nano‐ and macro‐hydroxyapatite/poly(ethylene‐co‐acrylic acid) composites

Hydroxyapatite (HAp)/poly(ethylene‐co‐acrylic acid) composites have been synthesized by a solution‐based method, using nanosized (n‐HAp) and coarse hydroxyapatite (c‐HAp) particles, respectively. X‐ray diffraction study has indicated the development of compressive and tensile stresses in composites because of the thermal expansion mismatch between the particles and polymer matrix. Fourier transform infrared absorption spectra and thermal analysis have showed the presence of strong interfacial bonding between the particles and polymer. The surface roughness and the homogeneous dispersion of HAp particles in the polymer matrix have been observed by scanning electron microscopy. A comparison in mechanical properties between composites prepared with n‐HAp and c‐HAp particles, respectively, has been studied. Nanosized particles contribute excellent improvement of mechanical properties of the composites rather than the coarse particles. The uniform dispersion of HAp particles, followed by the improvement in mechanical properties of the composite, provides a means of preparing HAp/polymer composites for low load‐bearing implant applications. POLYM. COMPOS., 27:633–641, 2006. © 2006 Society of Plastics Engineers     

Progress of key strategies in development of electrospun scaffolds: bone tissue

There has been unprecedented development in tissue engineering (TE) over the last few years owing to its potential applications, particularly in bone reconstruction or regeneration. In this article, we illustrate several advantages and disadvantages of different approaches to the design of electrospun TE scaffolds. We also review the major benefits of electrospun fibers for three-dimensional scaffolds in hard connective TE applications and identify the key strategies that can improve the mechanical properties of scaffolds for bone TE applications. A few interesting results of recent investigations have been explained for future trends in TE scaffold research.     

Effect of photocatalytic activities of nano-sized copper molybdate (CuMoO4)-doped bismuth titanate (Bi2Ti4O11) (CMBT) alloy

Different compositions of [CuMoO₄]_x-doped Bi₂Ti₄O₁₁ nanophotocatalyst (x = 0.05, 0.1, 0.5) have been prepared by chemical precursor decomposition (CPD) method using triethanolamine (TEA) and HNO₃. Cu(II) is one of reactive species on the catalyst surface and Mo(VI) ion helps to generate charge compensation of lattice having poor catalytic properties. The photocatalytic properties based on the prepared samples for photodecolorization of thymol blue (TB) solutions are examined by Hg-lamp. The crystal structures of the prepared nano-powders are characterized by XRD, EDAX, UV-vis spectra, specific surface area (BET), and HRTEM analyses. The average particle size of copper molybdate-doped bismuth titanate ranges 32 ± 5 nm measured from TEM. Results show doping of copper molybdate of 5 mol% with bismuth titanate can significantly increase the photoactivity of bismuth titanate compared all the compositions studied except degussa P25 titania. The observed increased photocatalytic activity of copper molybdate-doped bismuth titanate ((CuMoO4)_x(Bi₂Ti₄O₁₁)_1−x; CM_xBT_1−x) is attributed to the strong absorption of OH groups at the surface of the catalyst.