Silicon Nitride Films Deposited by RF Sputtering for Microstructure Fabrication in MEMS

In the present work, we report silicon nitride films deposited by a radio- frequency (RF) sputtering process at relatively low temperatures (<260°C) for microelectromechanical system (MEMS) applications. The films were prepared by RF diode sputtering using a 3-inch-diameter Si₃N₄ target in an argon ambient at 5 mTorr to 20 mTorr pressure and an RF power of 100 W to 300 W. The influence of the film deposition parameters, such as RF power and sputtering pressure, on deposition rate, Si-N bonding, surface roughness, etch rate, and stress in the films was investigated. The films were deposited on single/double-side polished silicon wafers and transparent fused-quartz substrates. To explore the RF-sputtered silicon nitride film as a structural material in MEMS, microcantilever beams of silicon nitride were fabricated by bulk, surface, and surface-bulk micromachining technology. An RF-sputtered phosphosilicate glass film was used as a sacrificial layer with RF-sputtered silicon nitride. Other applications of sputtered silicon nitride films, such as in the local oxidation of silicon (LOCOS) process, were also investigated.     

Use of HPLC to monitor olefins,dienes, and aromatics in the dehydrogenated products of higher n-paraffins

The linear higher olefins are generated through catalytic dehydrogenation of long-chain linear paraffins. During the catalytic dehydrogenation, a variety of dienes and aromatics are also formed. These side products not only cause coking of the catalyst, but also hamper in the reaction course of olefins with other substrate. A method has been developed based on the High-Performance Liquid Chromatography with Refractive Index detection for simultaneous estimation of olefins, dienes, and aromatics in the catalytic dehydrogenated product of model compound decane. The application of method for monitoring of the dehydrogenated stream from C10-C14 n-paraffins has also been discussed.     

Low temperature thermal ageing embrittlement of austenitic stainless steel welds and its electrochemical assessment

The low temperature thermal ageing embrittlement of austenitic stainless steel welds is investigated after ageing up to 20,000 h at 335, 365 and 400 °C. Spinodal decomposition and G-phase precipitation after thermal ageing were identified by transmission electron microscopy. Ageing led to increase in hardness of the ferrite phase while there was no change in the hardness of austenite. The degree of embrittlement was evaluated by non-destructive methods, e.g., double-loop and single-loop electrochemical potentiokinetic reactivation tests. A good correlation was obtained between the electrochemical properties and hardening of the ferrite phase of the aged materials.     

The role of niobium carbide in radiation induced segregation behaviour of type 347 austenitic stainless steel

The effect of niobium carbide precipitates on radiation induced segregation (RIS) behaviour in type 347 stainless steel was investigated. The material in the as-received condition was irradiated using double-loop 4.8 MeV protons at 300 °C for 0.43 dpa (displacement per atom). The RIS in the proton irradiated specimen was characterized using double-loop electrochemical potentiokinetic reactivation (DL-EPR) test followed by atomic force microscopic examination. The nature of variation of DL-EPR values with the depth matched with the variation of the calculated irradiation damage (dpa) with the depth. The attack on grain boundaries during EPR tests was negligible indicating absence of chromium depletion zones. The interface between niobium carbide and the matrix acts as a sink for point defects generated during irradiation and this had reduced point defect flux toward grain boundaries. The attack was noticed at a few large cluster of niobium carbide after the DL-EPR test at the depth of maximum attack for the irradiated specimen. Pit-like features were not observed within the matrix indicating the absence of chromium depletion regions within the matrix.     

The Practice of Dialysis in the Developing Countries

There are few organized data on the practice of dialysis in developing countries, mostly because of a lack of renal registries. The economic, human, and technical resources required for long-term dialysis make it a major economical and political challenge. Most countries do not have not well-formed policies for treatment of end-stage renal disease. The dialysis facilities are grossly inadequate, and there are no reimbursement schemes to fund long-term dialysis. Hemodialysis units are mostly in the private sector and consist of small numbers of refurbished machines. Water treatment is frequently suboptimal, and this problem has led to a number of complications. Hepatitis B and C infections are widespread in dialysis units. Continuous ambulatory peritoneal dialysis (CAPD) seems to be the ideal dialysis option for patients living in remote areas, but high costs preclude its widespread usage. The Mexican experience suggests that even after it becomes affordable, CAPD needs to be used judiciously. Inadequate dialysis, infections, and malnutrition account for the high mortality among the dialysis population in developing countries. Acute peritoneal dialysis using rigid stylet-based catheters is the main form of dialysis in remote areas. Pediatric dialysis units are almost nonexistent. A significant lack of resources exists in developing countries, making the provision of highly technical and expensive care like dialysis a challenge.     

Failure analysis of cupronickel evaporator tubes of a chilling plant

Pin-hole leakage was observed in a number of 90/10 cupronickel evaporator tubes of a chilling plant which was in service for about 6 years. Chilled water is cooled from 12 °C to 7 °C which flows inside the evaporator tubes, while the OD side has LiBr environment. The failure investigation of the failed tubes revealed greenish/blackish uniform deposits together with some spots where localized thick deposits on the ID surfaces were present. Underdeposit corrosion beneath these thick deposits was the primary reason for failure of the tubes. Intergranular corrosion was also observed underneath the thick deposits. The ID surface of the failed tubes confirmed the presence of wide variety of deposits, e.g. carbonates, silicates, phosphates, and sulphur-bearing compounds. The stagnant conditions under the thick deposits alter the chemistry inside the crevices thus formed. The altered chemistry conditions caused rapid corrosion (and intergranular attack) on the cupronickel tubes. Remedial measures that may be undertaken to prevent future occurrence of the problem are addressed.     

Flow accelerated corrosion: Experience from examination of components from nuclear power plants

Flow accelerated corrosion (FAC) has affected a large number of components made from carbon steel in the secondary as well as primary circuits of light water reactors worldwide. This is primarily a corrosion process enhanced by (electro) chemical dissolution and mass transfer, rather than a mechanical process. It has caused rupture of all sizes of pipelines as well as other components carrying either single phase water or two phase (wet steam) flow. It is reported to be the only mechanism that has significant potential for large leaks in the secondary circuit. This paper describes the observations from examination of a number of components that were affected by FAC in Pressurized Heavy Water Reactors in the past 5 years. Failure analysis done on the 10% feed water line, non-return valve (NRV) in the auxiliary feed water system and on the affected pipeline components from the secondary water system of various reactors has been described in this paper. The surface features observed (the signature pattern of FAC) on the inner surfaces of the pipelines affected by FAC in the primary and the secondary circuits of nuclear reactors have been described. Signature patterns of FAC, on components severely affected by single phase FAC (scallops) and on components affected by dual phase FAC (tiger striping) are recorded and reported. Components where FAC degradation had just initiated showed that the patterns were not well defined. The signature patterns became evident only after the degradation had occurred to a large extent. FAC like features were not seen in stainless steel components in the secondary side. Case studies showing that thinning of carbon steel components is not always attributable to FAC in the secondary circuit of the reactors are also described and reasons of these thinning illustrated to show the importance of establishing the cause of each thinning case. The paper also discusses if the size of the scallops is possible to be correlated to the FAC rate.     

Energy Efficient Model for Recovery from Multiple Nodes Failure in Wireless Sensor Networks

Wireless Personal Communications - Connectivity among deployed sensor nodes in wireless sensor network (WSN) is essential for collection and transmission of sensed data. In harsh environmental...     

Synergic effect of vanadium trichloride on the reversible hydrogen storage performance of the MgMgH2 system

Vanadium trichloride (VCl₃) is one of the best catalysts for the hydrogenation-dehydrogenation MgMgH₂ system. X-ray photoelectron spectroscopy (XPS) has shown that VCl₃ reduced to metallic vanadium during ball milling along with MgH₂. The in-situ-formed metallic vanadium doped over the MgH₂ surface which has shown an excellent catalytic effect on hydrogenation-dehydrogenation of the MgMgH₂ system. The catalyzed surface reduced the activation energies of hydrogenation-dehydrogenation reactions and correspondingly on-set hydrogenation-dehydrogenation temperatures. The microstructural analysis has also shown an excellent grain refinement property of VCl₃ which reduced the crystallite size of MgH₂. The decreased crystallite size decreases the diffusion path length of hydrogen and increases the active surface area which eventually enhances the hydrogenation-dehydrogenation kinetics of MgMgH₂.