Iranian Journal of Materials science and Engineering
Volume:6 Issue: 2, Jun 2009

The risks of alternating current (AC) corrosion and overprotection increasingly demand new criteria for cathodically protected pipelines. To assess the risk of AC corrosion، new cathodic protection (CP) criteria have been proposed based on DC/AC current densities measurements using coupons. The monitoring system designed for this project was based on the instant-off method، with steel coupons simulating coating defects on a buried pipeline. The problems associated with the instantaneous off-potential measurements have been attributed to a non-sufficient time resolution. In present study، it has been possible to determine the de-polarisation of steel coupon within a few milliseconds after disconnecting the coupon from the DC/AC power source، by increasing data acquisition rate. For this، a monitoring system was developed in order to measure the IR-free potential together with the DC/AC current densities. The monitoring system was utilized for both laboratory experiments and site survey to study the mechanism and the condition of AC corrosion، its mitigation and more importantly to define new CP criteria.

In this paper، a DRIE process for fabricating MEMS silicon trenches with a depth of more than 250 m is described. The DRIE was produced in oxygen-added sulfur hexafluoride (SF6) plasma، with sample cooling to cryogenic temperature using a Plasmalab System 100 ICP 180 at different RF powers. A series of experiments were performed to determine the etch rate and selectivity of the some masking materials such as resists، and metal (Al). Experiments show that different materials have different etch rates، but for the Al mask، an etch rate of 5. 44x10-3 nm/min was achieved، that exhibits very stronger resistance against RIE than resists. By controlling the major parameters for plasma etch، an etch rate of 2. 85 microns per minute for silicon and a high selectivity of 5. 24x105 to the Al etch mask have been obtained. A 90 min etching experiments using etching gas SF6 of 60 standard cubic centimeters per minutes (sccm) with oxygen (13 sccm) were performed by supplying RF power of 5 W to an ICP of 600 watts، and silicon etching process with a depth of 257 m was demonstrated. Our experiments show that Al is the best mask material for very deep trenches in silicon.

of activator and total molar ratios of Nacomposition exhibiting the highest 28-day compressive strength. Mixtures exhibiting the highest compressive strength were studied for their molecular structure using laboratory technique of Fourier transform infrared spectroscopy. Results obtained confirm that changes in chemical composition and curing condition can result in variations in degree of silicon substitution by aluminum in the second coordination sphere. Hydrothermal curing affects the molecular structure so that by increasing the hydrothermal curing temperatures، a lower degree of silicon substitution by aluminum in the second coordination sphere is observed. The molecular structure of the studied inorganic polymeric binde is composed of Si-O-Si chains bonded to Al-O and Si-O units creating two and three dimensional networks. In this paper، the effects of chemical composition and curing conditions on molecular structure of2/Na2O molar ratio2O/Al2O3، and H2O/Al2O3 were changed to determine the optimum chemical

materials can be fabricated by sintering of W-Cu composite powders. In this research W 20%wt Cu composite powders was synthesized via a co-precipitation method. Precipitate obtained from a mixture of copper nitrate and ammonium paratungstate (APT) in distilled water contained W-Cu compounds. This precipitate was washed، dried and calcined at 550 of dried precipitate powder was determined by thermogravimetry (TG)، differential thermal analysis (DTA) and X-ray diffraction (XRD). The sintering of the reduced powders was investigated as a function of temperature. Relative density of more than 98% obtained for the powders sintered at 1200 close to theoretical calculations. The hardness of the sintered powders was 320 Vickers. W-Cu composites are widely used as contacts، heat sinks and electro discharge electrodes. These kinds of°C in air and then reduced in H2 atmosphere in order to convert to W-Cu powders. The calcination temperature°C. The corresponding electrical conductivity was too

the changes of BET surface area of a mineral substance during intensive grinding process. Validity of the proposed model was tested by the experiments performed using a natural chalcopyrite mineral as well as the published data. It was shown that the model can predict the experimental results with a very good accuracy and can be used to predict what may happen under the similar experimental conditions. Based on experimental observations، a model has been developed to describe the effect of grinding time on

transition and heat affected zones formed during surface remelting (in order to improve wear resistance) with TIG process has been investigated. Relationship between various TIG parameters and thickness of remelted and heat affected zones revealed that a high concentrated heat energy is imposed by TIG process which makes it a proper option for focused surface treatment. Based on microstructural examinations five areas with different microstructure and microhardness were identified within the surface area. Graphite flakes were totally dissolved within the first area leading to the transformation of denderitic austenite to plate martensite and the formation of ledeburite within interdenderites. The main feature of the second area, resulted from the presence of graphite flakes, was the local melting with a gap in the vicinity of graphite flakes and that of third area was the formation of finer and denser martensite plates closer to the graphite flakes compared with those formed at a further distance. In the fourth layer there is a mixture of martensitic and pearlitic matrix while the matrix of fifth layer has no change of microstructure. In this study the effect of graphite flakes present in a pearlitic grey cast iron on the microstructure of melted,

fabricated. Modifications carried out in different parts of the old system in order to control most of the growth parameters with more accuracy. The fabricated system was used to grow sapphire single crystals with almost 10 mm in diameter and 50 mm in length. The crystallinity and structure of the grown crystals were characterized by computer aided single crystal X-ray diffraction technique. A Verneuil system, more sophisticated than a conventional one, has been designed and