مجله مواد نوین
سال سوم شماره 1 (پیاپی 9، پاییز 1391)

Mold powders are mainly composed of oxides such as SiO2، CaO، Al2O3، Na2O، along with F- and carbon. One of components of mold powders is F-،which is utilized in chemical composition of mold powders for lubricating and controlling viscosity between solidified steel shell and copper mold. However، emission of F-through compositions such as HF (g) causes health and environmental problems. The purpose of this research is elimination of F- from chemical composition of a high speed lubricating powder used in continuous casting in steel industries. In addition، the effects of substitut compound upon viscosity is investigated. Groove viscometer test and image analysis were used to compare produced powders and used powder molten viscosity. X-ray diffraction، emission electronic microscope and spectroscopic analysis of scattered energy were used also for evaluation the crystalline behavior. The results of the study showed that Portland cement clinker could be an appropriate substitution for Wollastonite in the basic composition of mold powders. In addition، using TiO2 of about 3 wt% and hematite of about 3 wt% (surplus to the existing hematite in the chemical composition of Portland cement clinker)، a fluorine-free sample was prepared having viscosity near to that of the molten main powder. Considering produced phases such as Perovskite and Fayalite، it can be concluded that this is a fluorine-free sample which is believed to be an appropriate substitution for the main powder being currently used in continuous casting of steel due to its similarity in viscosity and crystallization to those of the molten main powder.

The lifetime management of repaired gas pipelines with Fiber Reinforced Plastics (FRP)، especially when the probability of leakage is expectable، is an important technical-economic factor of repair system. This work is concerned with the evaluation of hydro test performed on repaired metallic gas pipelines with FRP. The goal is to assess the role of external composite repair system on structural integrity of pipelines، based on experimental investigations. Hydro tests were executed on one meter composite repaired pipeline sections containing artificial through hole at 6’oclock orientation. The repair systems were designed according to ISO-24817 and Hydro tests simulated by ABAQUS finite element method. The results showed the ability of the repaired pipeline to withstand the pressures up to 1. 5 times of the design pressure. The applicability of this type of repair system was demonstrated by means of simulation and experimental results which showed that this technique can be used in repair of gas line ever in worst conditions.

Electrodeposition provides a cost-effective means of producing fully dense nanocrystalline (10-100nm in grain size) metals، alloys and metal-matrix composites. Zn nano-structured coatings were prepared from an acidic zinc sulphate bath. The influence of the current density، the surfactant Sodium Dodecyl Sulphate and grain refiner (Saccharin) on structural and morphological characteristic of the coatings were investigated. The characterization of the samples was made by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the zinc nano-structured coatings in the presence of SDS، approached a homogeneous، spherical and fine morphology by increase of current density and saccharin concentration.

Phosphate coatings are in the hydrated state because of they are formed in aquatic environment and therefore when these coatings are exposed to high temperatures such as paint oven، the chemical stability of such coatings especially dehydration behavior is of great concern. Thus، phosphate layer applied on the surface should be dried، by application of non – aquase organic or powder organic coatings until thermal stability of phosphate coatings، and removal of their structural water during exposing the samples in the furnace not result in the loss of paint quality. In this article، the effect of heat treatment at different temperatures of 120، 180، 250، 280، 350 °C on the weight loss and corrosion behavior of zinc phosphate coating formed on the surface of plain carbon steel was investigated. The results showed that heat treatment of phosphate coating at 120 °C improved protective behavior because of the loss of structural water. But increasing temperature to 180 °C and higher، decreased the corrosion resistance.

In this study، for the first time، accumulative roll bonding were used to produce Al/Brass composite. Commercial pure Aluminum with 200 micron thickness was used as matrix and brass 70/30 with thickness of 100 and 200 microns were selected as agent till 7 passes. The mechanical properties and microstructure were investigated using the tensile and microhardness test. Scanning electron microscope. analysis shows that rolling caused fracture of hard phase of brass and distribut it in Al matrix، also a more uniform phase distribution has been produce in composite. The mechanical behavior of composite with 100 micron brass is not increased from that of pure Al due to insufficient bonding between the layers. While the strength and microhardness of composite with 100 and 200 micron brass shows no regular changes according to increases in passes and there is an optimum pass number in relation to the value in strength. Ductile fracture surfaces in tensile test were observed.

So far، most of the researches have examined the production process and its effect on the properties of epoxy nanocomposites and there is little informations on the nanocomposite with vinyl ester polymeric matrix. However، vinyl ester is one of the highly used resins in composite industry. In recent years، adding reinforcements with small dimensions (especially in nanoscale) has been proposed as a solution to improving the properties. In nanocomposites، due to diffusion of polymer chains into the nanoparticles and establishment of an appropriate bond with them، improvment of the properties can be expected. The aim of this research was to manufacture and investigate of tensile behavior of vinyl ester/titanium dioxide nanocomposites. Nanocomposite samples were produced by melt mixing technique and with content of 1، 2. 5 and 5 weight percent of TiO2 nanoparticles. In addition، BYK-C8000 was added to the mixture as polymeric coupling agent. At first، the influence of production parameters on the properties of vinyl ester/1%wt. TiO2 nanocomposite was evaluated and then with selecting the optimum conditions and fixing the manufacture parameters، the effect of nanoparticles content on the properties of the samples was studied. Tensile behavior of nanocomposite was evaluated by uniaxial tensile test. Results indicate that by increasing in TiO2 content in the polymer matrix، the Young''s modulus steadily increases; while the strain-to-break of nanocomposites is reduced compared to the pure specimen.

The purpose of this study is decoration of cabon nanotube with TiO2 nanoparticles using wet chemical method and investigation the stability of its nanofluid. To do this، multiwalled carbon nanotubes and TiCl4 were used as precursor of TiO2 nanoparticles. The decoration were systematically characterized using transmission electron microscopy (TEM). The effect of acid treatment and decoration on structure of carbon nanotube were investigated by the use of Raman spectroscopy. Zeta potentials were used to obtain the stability of suspensions containing raw، acid treated and decorated carbon nanotubes. The TEM image showed the successful attachment of TiO2 nanoparticles on the outer surface of carbon nanotubes. Raman spectroscopy verified the increasing of defects on the structure of acid treated and decorated carbon nanotubes. Zeta potential results confirms that modified carbon nanotubes with TiO2 nanoparticles and functionalized groups have better stability in the fluids.

In the present study، the microstructure of dissimilar welds of AISI 347austenitic stainless steel to ASTM A335 low alloy steel by using gas tungsten direct current arc welding process with a negatively charged electrode (DCEN) was investigated. For this purpose، two filler metals، ER309L and ERNiCr-3، were used. After welding، the microstructure of the different zones of each joint، including weld metals، Heat affected zone (HAZ)، interface and unmixed zones (UMZ) were evaluated by using optical microscope (OM). The (SEM) equipped (EDS) were used to investigate the precipitates and fracture of different samples. The microstructure of base and weld metals were evaluated by using OM. The fracture surfaces was investigated by (SEM) equipped to (EDS). The microstructural evaluations showed that a two-phase structure، consist of dendritic and inter-dendritic regions with primary austenite solidification was observed in ERNiCr-3 (filer metal)، and a primary skeleton-shaped ferrite in austenitic matrix was observed in the 309L (filer metal). The epitaxial growth was observed in interface between 347austenitic stainless steel and two filler metals and a narrow zone was observed in interface between A335low alloy steel and filler metals، and also the coarse grains occurred in HAZ zone of both weld metals. Also، the impact toughness and fractography of samples were investigated. The maximum impact energy obtained in to the ERNiCr-3 (filer metal) specimens. Finally، it can be noted that for the joints between the AISI 347 austenitic stainless steel and A335low alloy steel، the ERNICr-3 filler material provides the optimum qualities.