مجله مواد نوین
سال پنجم شماره 1 (پیاپی 17، پاییز 1393)

In this paper، diffusion bonding of dense alumina bodies using hydride nanopowders mixture as the interlayer was investigated. Mixture of aluminum hydride and magnesium alanate was synthesized via mechano chemical activation process. Aluminum and magnesium chloride and lithium alanate were used as precursors. Products of milling process were consisted of nano sized alane and Mg alanates. Alumina bodies were diffusion boned at 300، 350، 400، and 450 ْC، under pressure of 20 Mpa for 30 min dwelling time using custom designed induction hot press. Dissociation of hydride mixture interlayer during diffusion bonding process produced in-situ nanosized alloyed aluminum and aluminum-magnesium intermetallic without any surface oxides. Combination of stoichiometric and non-stoichiometric spinel، oxide، and free metal structures were formed during bonding process. The highest bond strength was about 196 MPa via formation of Mg-Al spinel oxide during bonding at 450ْC.

In this research، nanocrystalline TiB2-TiC powder was fabricated by new method which named MACS (Microwave-Assisted Combustion Synthesis). Powder mixture consists of 3Ti+B4C was milled via a planetary mill up to 9 h. Then، from milled powder with different milling time، the pellets was shaped with diameter equal 10 mm for MACS process and synthesized by home microwave device with power of 1100W. The effects of milling time was also considered. Synthesized samples were characterized by XRD and SEM analysis. The results of above analysis showed increasing of the milling time to 9 h the synthesis of desired phases (TiC and TiB2) was associated with greater success and the amount of the side products and intermediate compounds reach to minimum in the final product. This phenomenin was confirmed by TEM images. Also، with increasing of milling time from 1 to 9 h the required time for synthesis of samples reduces from 3 min to 35 sec.

The aim of this research is to establish an aluminum foam with suitable cover In this research، after preparation and brushing، commercial pure aluminum sheets with dimensions 200×100×1 mm3 of they were stacked with 2 wt% of TiH2 powder. Then sheets were rolled by ARB method up to 4 passes with 50% reduction in each pass. They are treat different temperatures of 500-650 °C and diffrent times of 10-20 min for foaming. The effect of temperature and holding heat treated. The density and porosity of the foam was measured by tests based on Archimedes. The results showed that the produced foams have higher porosity at temperatures close to the melting temperature of aluminum and at hoding time of 10 min. The produced foams were welded by friction stir welding at different rotational speeds of 560-1100 rpm at constant advancing speed of 25 mm/min. Invesstigation of welded sections of the foam showed that a suitable joints with acceptable properties is achieved by FSW. Furtheremore، the weld stir zone hardness of the foam rises by increasing rotational speed.

In this paper، the effect of variation of surface chemical properties in second phase and ultrasound wave was investigated on the dispersity of carbon nanotube in Polyethylene matrix composites. In order to examine both parameters on tensile properties of composites، standard tensile sample of PE/CNT composite was prepared. The results indicated that the addition of untreated carbon nanotube to PE matrix increased the strength of composite، but there is significant drop in elongation as severe agglomeration. The formation of functional group، covering by stearic acid، and ultrasound wave control the dimension of agglomerated carbon nanotubes، and improve the dispersity of second phase in matrix. For example، The increment of 12% in strength، and 82% decreasing in elongation was detected for untreated carbon nanotube/ PE composite compare to pure Polyethylene. Also the effect of functional group and ultrasound wave cause to increase in 17% strength and to decrease 70% in elongation. Finally stearic acid group on the surface of Carbon nanotube result in 15% augmentation in strength and 60% drop in elongation compare to PE. Besides the results showed that it is not necessary to used ultrasound wave to improve the dispersity of CNT coated with SA in PE composite.

Stress corrosion cracking behavior of X52 pipeline steel was investigated in a near neutral pH solution by slow strain rate test، potentiodynamic polarization and surface analysis technique. Potentiodynamic polarization tests were performed at fast and slow potential sweep rates، to simulate crack tip and crack wall roles in the SCC process. The results showed that the dominant mechanism of SCC at relatively low and moderate applied potentials is anodic dissolution mechanism. While، at more cathodic applied potentials hydrogen based mechanism was the dominant one.

FAC is known more than 30 years in the word. It’s occurrence in deferent types of nuclear، steam and combined cycle power plants has been reported. With attention to this antiquity، the methods for it’s control or obviation، is important. In this essay single phaseFlow Accelerated (assisted) Erosion-Corrosion in High Pressure economizer tubes (HP-ECO) of Boiler Unite 1 at Kerman Combined Cycle Power plant، investigate with visual، dimensional and macrostructure check on damaged carbon steel tubes. The results show that the tube’s thickness is less than standard value، no damage to tube’s macrostructure (Ferrite-Perlite) and erosion corrosion occurrence. The most important factors due to FAC is water chemical condition، first harp design، materials properties (mechanical and metallurgical) used in harp and thermodynamic and hydrodynamic condition of fluid. In this essay un expected tube failure protect with chemical control of water (pH & O2) and change of tubes materials.

One of the most important methods for protection of the metals against corrosion especially in acid media is the use of inhibitors. Acid solutions are generally used in several industrial processes، such as HCl. Copper has a wide range of industrial applications due to its good mechanical and electrical properties. Although copper and its alloys are generally known to be good corrosion resistant materials، they still suffer different forms of corrosion depending on the service environment، which limits greatly their application in practice. One effective approach that can be taken to solve this problem is surface modification using Self Assembled Mono layers (SAM). SAMs provide a flexible and simple system that act as an insulating film and prevent chloride penetration to surface. In this report، two new synthesis Schiff base، N،N''- bis (salicylidene) -1،3 propanediamine and N،N''- bis (4-methoxysalicylidene) -1،3 propanediamine، has been proposed as new corrosion inhibitors. These two inhibitors where self-assembled on copper and their corrosion inhibition performance in 0. 5 M HCl solution was investigated by using polarization curves and electrochemical impedance spectroscopy (EIS) methods. The polarization measurements suggest that the SAMs act as mix inhibitors and suppressed both the anodic and cathodic reaction. Increasing curves diameter in the impedance measurements showed that the SAMs act as good inhibitors. The results from polarization and impedance measurements are in good agreement and show inhibition efficiency gradually increase by increasing concentration. Login methoxy groups in the benzene ring of the Schiff inhibition efficiency increases that could result from the electron donors effects and the effects of the hydrophobic group.

Duplex stainless steels has had a variety of usage in the chemical، petrochemical، oil and gas industries because of the adequate mechanical properties and high corrosion resistance. In this article، corrosion rate and mechanical properties of welded duplex stainless steel (2205) has been analyzed using for different heat input of 0. 86، 0. 91، 1. 02، 1. 12 kJ/mm. welding process carried out using reverse Pole GTAW process. The corrosion resistance in 3. 5% of NaCl solution was evaluated by potentiodynamic polarization tests for weld deposit and heat affected zone (HAZ) at room temperature. The results indicated that for heat input 1. 12، 1. 02، 0. 91، 0. 86 kJ/mm the corrosion rate are 0. 230، 0. 004، 0. 009، and 0. 034 (mm/yr) respectively. Decreasing the heat input causes the ferrite volume content of weld deposit of the samples to increase which the correspondence between the theoretical and experimental results of this article has been indicated by studying the effects of this parameter on the corrosion rate and mechanical properties. The sample No. 1 having Max. Heat input possesses Max. Corrosion rate. The results also show that the sample No. 2 with heat input of 1. 02 kJ/mm، have an optimum condition of corrosion rate and creating proper mechanical properties for welding the 2205 stainless steel.

porous nano-sic with high specific surface can be used as catalyst support and also for optimisation of the sic body sintering processes. in this paper،first micropore zeolite zsm-5 was synthesized to synthesis of porous sic Then ZSM-5 zeolite/furfuryl alcohol nanocomposite was carbonized in argon atmosphere at 900˚C with the retention time of 6 hours at the maximum temperature. ZSM-5 zeolite/obtained carbon nanocomposite was mixed with fine-grained magnesium according to the stoichiometry reaction and was put at 800˚C with the retention time of 6 hours. Porous carbons resulting from ZSM-5 synthesized zeolite molds، clinoptilolite natural zeolite and MCM-48 mesoporous were also synthesized to determine the amount and type of carbon. ZSM-5 zeolite/carbon nanocomposite was synthesized with different stoichiometry ratio of magnesium and stoichiometry ratio of different carbons and In the next step، the prepared samples were mixed with carbon black and was put at two different temperatures، 650 and 800˚C with the retention time of 6 hours at the maximum temperature under argon atmosphere. Finally، the samples were subjected to pickling operations. ZSM-5 zeolite، ZSM-5 zeolite/carbon nanocomposite، synthesized precursor carbons and obtained SiC were characterized by various techniques such as X-RAY Diffraction، Thermogravimetric، Scanning Electron Microscope، Fourier Transform Infrared Spectroscopy and X-ray Fluorescence. Comparison of XRD data of samples synthesized by ZSM-5 zeolite/carbon nanocomposite and CMK-1 carbon with other samples showed that the use of carbon with high surface area (CMK-1 carbon) is associated with increased SiC phase.

This study investigates the effect of a Schiff base، namely Bis (N-(2-2aminoethylamino) ethanol) -2-Hydroxy-5-methoxybenzaldehyde) cobalt (III) chloride on corrosion inhibition of mild steel in 0. 5 M HCl. Potentiodynamic polarization was applied to study inhibition efficiency. It was found that the percent of inhibition efficiencies (IE%) and surface coverage (θ) increase with an increases in the concentrations of inhibitor. Quantum chemical studies obtained theoretical results of complex and ligand and also shows superiority of complex over the corresponding ligand. FTIR observations of the mild steel surface confirmed the formation of protective film and the synergy effect of ions on the metal surface. The scanning electron micrographs (SEM) images are taken and examined in order to support our findings.