Showing 758 results for Type of Study: Research Paper
Saghafian Larijani H., Rainforth W. M.,
Volume 1, Issue 3 (9-2004)
Abstract
An AI-7wt%Si-5vol%TiCp was worn against a cast iron disc in a tri-pin-on-disc machine, under dry sliding conditions at the sliding speed of 0.24 m/s and applied loads of 6, 20 and 40 N/pin. Stress-strain (σ-ε) curves were constructed by measuring the microhardness and the equivalent strain gradients in near surface regions on the cross-sectional surface prepared parallel to sliding direction.It was shown that, both the magnitude of plastic strains and the depth of plastic deformed zones increased with the applied load. The material exhibited considerable work softening in addition to work hardening at the highest applied load. The softened layer placed just beneath the mechanical mixed layer (MML), was mostly covered with the fine fractured eutectic Si and TiC fragments most of which were associated with microcracks at Al/Si and Al/TiC interfaces. The results were discussed in terms of some of the current work hardening models.
Tavakoli A. H., Goudarzi M.,
Volume 1, Issue 3 (9-2004)
Abstract
The synthesis of advanced materials from low cost minerals concentrates is a new field of study that has great potential applications. In this paper, the effect of milling time on the temperature of initiation and amount of carbothermic reduction of ilmenite has been investigated. The stoichiometric molar ratio (1:4) of ilmenite to graphite was mixed and mechanically activatedfor 30-70 hours at room temperature. Then homogenized mixture heated for one hour at 1000-1400°C in coal reducing atmosphere. The results show that complete conversion of ilmenite to Fe and TiC can not be achieved in the unmilled powder at 1400°C, while with milling of mixture for 30 hours, complete reduction of ilmenite to Fe and TiC at 1400° C was observed. With increasing milling time from 30 to 70 hours the temperature of complete reduction decreases from 1400 to 1200° C. Leaching of final product in HCI 3% solution dissolve Fe but leave pure titanium carbide intact. Determination of TiC unit cell size from X-ray diffraction pattern shows that unit cell size of synthesized TiC is less than stoichiometric one, which suggests that some oxycarbide phases (TiCxO1-x), is present into the final product.
Bafghi M. Sh., Adeli M., Mohammadi Nikoo H.,
Volume 1, Issue 3 (9-2004)
Abstract
Two commercial methods are used for the production of strontium carbonate:1) Direct conversion of Celsetite to strontium carbonate by hot sodium carbonate,2) Carbothermic reduction of celestite with coal followed by water leaching of strontium sulfide(SrS) and its conversion to strontium carbonate.The present study has been made on the carbothermic reduction of celestite ores of Varamin (Iran) mines. Effects of temperature, time, pellet size, particle size of celestite ore, pellet compactness and type of reducing agent have been studied. In the range of 800-1100°C, reduction rate increases notably with temperature, which may mean that the reduction is predominantly chemical controlled. Activation energy of around 22.5 kcal/mol supports the idea of chemical control mechanism. Further support for this postulation is provided by the following facts:1) Increasing rate with carbon reactivity (graphite, coal, and charcoal)2) Small dependency of rate on pellet compactness.3) Small dependency of rate on pellet size
Rand B., Ramos V. P. S., Ahmed A. S.,
Volume 1, Issue 3 (9-2004)
Abstract
Some of the scientific principles underlying the role of carbon and graphite in graphitic refractories are considered, with emphasis on the graphite phase. The highly anisotropic nature ofgraphite is a key factor in its ability to modify the properties of oxide refractories, resulting in the potential for anisotropy in the subsequent graphitic composite, depending upon the fabrication conditions. The thermal and mechanical properties are considered for model alumina-graphitecomposites first with no anti-oxidant additives in the formulation to reveal the intrinsic effect ofthe graphite phase and then effects of silicon as a typical additive are examined. The behaviour is modified considerably when the extent of ceramic bonding in the materials is increased through the reactions of silicon with the gaseous atmosphere and with the constituents in the refractory. Finally, a brief consideration of the structure and properties of typical binder phases is presented.
Lee W.e.,
Volume 1, Issue 3 (9-2004)
Abstract
Penetration and dissolution mechanisms are reviewed for predominantly single-phase oxide, two phase oxide and oxide-carbon composite refractories by liquid silicate slags. Theoretical models of these processes, as well as static (sessile drop, dipping and crucible) and dynamic (rotating finger and rotary slag) experimental tests, along with their practical limitations are considered. Direct (congruent or homogeneous) attack is controlled by the reaction rate at the slag-refractory interface or the rate of diffusive transport of species to it through the slag leading to active corrosion. Indirect (incongruent or heterogeneous) attack is controlled by diffusive transport through the slag or through a new solid phase, which forms at the original slagrefractory interface. This may lead to passive corrosion. Examples of direct and indirect attack in a range of refractory/slag systems are described highlighting the critical influence of the composition and hence viscosity of the local liquid slag adjacent the solid refractory. Penetration and corrosion can be controlled either through the local slag composition via the refractory or the bulk slag or by microstructural control of the refractory by e.g. internal generation of dense layers or external deposition/generation of passive coatings, so-called in situ refractories.
Javadpour J., Sakhaii K., Masihiyanpour A.a.,
Volume 1, Issue 4 (12-2004)
Abstract
Thin sheets of hydroxyapatite were fabricated by tape casting process. The non-aqueoustape casting formulation was optimized by adjusting the concentration of organic additivesspecially those of binder and plasticizer in the slurry. The optimized slurry was cast on a glasscarrier using a designed laboratory scale doctor blade. Following a binder removal stage, thetapes were sintered at different temperatures in air atmosphere. Heat treatment at 1250 °C led tothe formation of a dense microstructure as was evidenced by the scanning electron microscopy.
Attar E., Babaei R., Homayonifar P., Asgary K., Davami P.,
Volume 1, Issue 4 (12-2004)
Abstract
During mold filling, molten metal can only advance as quickly as the air inside thecavity is expelled. In this work an analytical model describing air flow is developed based on aincompressible flow theory. Air pressure has serious effects upon the filling behaviour such assurface profile and filling time. In this work a new mathematical model is proposed for calculationthe air pressure during the mold filling. A single phase computational fluid dynamic code based onthe SOLA-VOF algorithm used for prediction the fluid flow. Air discharged through the vents ismodelled by ideal gas assumption, conservation of mass equation and Bernoulli law. A newalgorithm was developed to interpolates the air pressure on the surface cell. The creation of airback pressure was correlated with sizes of vents and pouring basin height. In order to verify thecomputational results a series of experimental test was conducted. Comparison between theexperimental data and simulation results has shown a good agreement.
Karaminezhaad M., Maghsoudi A.a., Nozhati R., Sakhaei A.,
Volume 1, Issue 4 (12-2004)
Abstract
A large number of reinforced concrete structures subjected to chloride ions. Two basicapproaches for preventing corrosion of reinforcing steel embedded in concrete are: Increasing theconsolidation of concrete and using different coating on rebars. In present research steel rebarsare coated in different ways: a) 40 µm of zinc electroplated on steel rebar b) Zinc powder withepoxy paste (zinc rich). The rebars were placed in a macrocell design according to ASTM G109-92. Concrete operations were done with mixture designs of high and normal strength concrete.The results show corrosion decrease of zinc coated rebars.
Fotoohi B., No Parast M., Oliazadeh M.,
Volume 1, Issue 4 (12-2004)
Abstract
Gold deposits are varied regarding their geological and geochemical settings. Hence,their processing methods must be best organized for achieving the desired recovery of preciousmetals. In this research, two types of hard-rock gold ores, each with specific characteristics fromKouh-zar region (south of Damghan city) were subjected to mineral processing tests at thelaboratory scale. The reference (head) samples of both veins contained on average 3.5-4.5 ppmgold. According to mineralogical investigations no observable gold particles reported even inSEM analyses except for rare over-micrometer gold particles locked in the silica matrix.Therefore, the major (invisible) gold supposed to exist in sulfides" crystal structure. Flotationapplied to recover the gold interlocked within sulfides. The highest grades achieved were 49.2ppm @ R=77.61% for Baghu samples and 57.0 ppm @ R=61.00% for Darestan samples gold inthe sulfide concentrates. In the cyanidation diagnostic tests the optimum conditions of pH,particle size, cyanide concentration and leaching time were determined for both ores. High goldrecoveries (> 95%) were achievable for Baghu samples for the pH conditions between 10.5 and11, and cyanide and hydrated lime consumptions of 0.6 and 2.5 grams per kilogram of orerespectively. As it had been expected, direct cyanidation of Darestan samples (containing up to1.5% copper), couldn"t be established as an efficient procedure (due to cyanide consumption ofabout 20 times higher than for Baghu tests to achieve similar recoveries) and the preliminarycopper removal phase was determined as a necessity for better recovery of gold.
Akbar Zadeh A., Salari M.,
Volume 1, Issue 4 (12-2004)
Abstract
AA3004 alloy is widely used in can making. The major concern in the production of canbodies is earing, which develop by high planar anisotropy of rolled sheet. Balance ofrecrystallisation and rolling textures together with a uniform and fine grain microstructure canminimize the earing. The effects of finish rolling temperature (FRT) on planar anisotropy,microstructure, texture development and mechanical properties of sheet have been analyzedIncreasing the FRT resulted in promotion of cube and G texture in hot rolled sheet. Lower |ΔR| ofthe final sheet with higher FRY, i.e. the lower planar anisotropy, is accompained with a balance ofrolling and recrystallisation orientations.
Rigaud M.,
Volume 1, Issue 4 (12-2004)
Abstract
At first, trends in the steel industry are briefly reviewed, taking into consideration bothmanagerial and technical issues. As a consequence of this review, the importance of electricfurnace technology and of secondary metallurgy is being underlined. The same sequence iffollowed to describe the refractory industry. Specific issues concerning the latest developments oncarbon-containing castables, in steelmaking ladles, are described, as an illustration of what mayoccur.
Mirfakhraee B., Eshraghi H., Sar Poulaki H.,
Volume 2, Issue 1 (3-2005)
Abstract
Effect of MgO addition on reaction sintering of aluminium titanate was investigated using equimolar Al2O3 and TiO2 after firing the samples at 1400 C for four hours. Results showed that MgO addition enhanced the sintering process by magnesium aluminates formation, which led to lower porosity and improved densification of the samples. Physical and mechanical properties showed that samples containing 5 wt% MgO was the optimum composition.
Aneziris C.g., Borzov D., Schmidt G.,
Volume 2, Issue 1 (3-2005)
Abstract
Improved structures of MgO carbon bonded materials due to new binder systems and due to the application of electrical currents during operation have been achieved for advanced applications in the secondary metallurgy and during near net shape metal casting.
Yahosseini M.r.s., Simchi A., Varahram N., Davami P.,
Volume 2, Issue 1 (3-2005)
Abstract
In the present work, a model was proposed to predict the thermal history during rapid solidification (RS) of metal droplets in the gas atomization process. The classical theory of heterogeneous nucleation was based on Newtonian heat flow and enthalpy method. Solving the governing numerical equations by the finite difference method (FDM) gave up the opportunity of analyzing the temperature-time history of the droplets during cooling in the RS process. Here, cooling in the liquid state, nucleation and recalescence, segregated solidification, eutectic solidification and cooling in the solid state were considered. To verify the model, the gas atomization of Al-4.5% Cu alloy was studied and the results were compared with the Shukla's model [1]. Convincing agreement was obtained between the predicted undercoolings and the experimental results reported previously.
Pakshir M., Amini R.,
Volume 2, Issue 1 (3-2005)
Abstract
Anodes are critical component of cathodic protection systems. As part of this effort, three different anodes were tested in a cathodic protection system that was designed and constructed to prevent further corrosion of reinforced concrete. This anodic system includes an electrically conductive coating composition applied in fluid form over an outer surface of the concrete mix. The composition further includes a predetermined amount of electrically conductive carbon material (coke, carbon black, graphite) uniformly distributed in the epoxy resin (as a binder) whereby the coating composition has a predetermined value of resistively. This investigation attempts to find the best type and optimum content of conductive carbon filler in poxy coating, to ensure optimal anode working parameters for marine environments (basically marine and sewer environments) and if any of the coating systems tested in this study excel over the other. In this study, electric and electrochemical parameters of three layer (with average coating thickness of 300µm) coke-epoxy, carbon black-epoxy and graphite-epoxy conducting paints (with different amount of filler) have been determined during long-term anodic polarization (70 days) in a seawater solution. During this test, on the basis of impedance measurements, the electrical resistances of these coatings have been calculated every 14 days. if conductive paints exhibit good electric and electrochemical stability, they will be attractive for cathodic protection of reinforced concrete.
Dehghanian C., Saremi M., Mohammadi Sabet M.,
Volume 2, Issue 1 (3-2005)
Abstract
The synergistic behavior of molybdate and phosphate ions in mitigating the corrosion of mild steel in simulated cooling water was evaluated performing potentiodynamic polarization and impedance spectroscopy tests. Phosphate and molybdate showed a synergistic effect on corrosion inhibition of steel in simulated cooling water. The observed reduction in anodic and cathodic current densities could be the consequence of incorporation of both phosphate and molybdate ions in forming a protective layer on the surface. The charge transfer resistance of the protective layer formed on steel surface was much greater in presence of both ions in solution than that when each inhibitor used alone.
Kharazi Y.h.k., Divandari M.,
Volume 2, Issue 1 (3-2005)
Abstract
The mold-filling behavior in the casting of aluminum alloy (A413) using lost foam casting (LFC) was explored. The effects of gate numbers, type of gating and casting thickness on the filling behavior were evaluated. Although, unlike convectional casting process, the gating system showed little effect onfilling ability, casting thickness created a greater effect on the mold filling. In contrast with convectional casting process, the mold filling seems to be controlled by castinggeometry as a consequence of combined influence of heat and mass transfer. The melt used to enter from the first gate instead of last gate which is in contrast with convectional casting process.
Mehryab A., Arabi H., Tamizifar M., Seyedein S.h., Razazi M.a.,
Volume 2, Issue 1 (3-2005)
Abstract
In this research, the mechanism of joining three sheets of metals, i.e. brass-steel-brass, by cold roll welding process has been studied. For this purpose, the two surfaces of steel sheets were roughened with stainless steel wire brush by different amounts, then the brass sheets were put on both sides of the steel sheets, before they were subjected to cold roll process. During rolling, peaks of the asperities on the surfaces of the steel sheet were pressurized, i.e. deformed, much more than that of trough. Hence, more hardening due to formation of higher dislocation density in the peaks regions were detected in comparison to the trough regions. Therefore, due to the differences in the amounts of work hardening occurred during cold rolling in the peaks & trough of the scratches and also due to the nature of the rough surfaces of the steel sheets, which causes the smooth surface of soft brass sheets laied over the rough surface of the steel sheet to be shappend according to the profile of the steel sheet scratches during cold rolling, mechanical locking occurred at the interface of brass & steel sheets. In addition, while the extrusion of brass took place through cracks within the surface of hardend peaks and metal bonding occurred on the contact points of the brass sheet & the vergin steel. Therefore, it seems two mechanisms were in operation is making a suitable joining between the sheets. One was a locking mechanism due to the roughness of the steel sheets & the other was bonding mechanism due to the bonding between the peak points of the scratches &soft brass surface. The strength of the bonded points in the interface were later increased by annealing the composite, so that by annealing the samples within the 500-900°C range for aperiod of 1 1/2 hr the interface strength increase substantially. The results of peeling test indicated that the interface strength of the samples annealed at 700°C or more increased so much that the brass sheet toms during peeling & the fracture did not pass through the interface.
Eftekhari-Yekta B., Marghussian V.k.,
Volume 2, Issue 2 (6-2005)
Abstract
The effect of precipitation of ?.qss. and gahnite phases during heat treatment of glass frits in the ZnO-Al2O3-SiO2 system on the mechanical property of resulting glass-ceramic specimens were investigated. It was shown that gahnite glass-ceramics had higher bend strength and toughness values than ?.qss. ones. The results are attributed to the higher modulus of elasticity as well as higher thermal expansion coefficient of gahnite relative to the residual glass phase.
Paydar M.h., Fadaei R., Shariat M.h.,
Volume 2, Issue 2 (6-2005)
Abstract
Copper coated SiC powders having three different amounts of copper, in the range of 20-60 wt%, were prepared via electroless coating process. The produced composite powders were uniaxially cold compressed and sintered at different temperatures and times under protective atmosphere. It was found that composite Cu/SiC powders and a relatively dense copper matrix composite with a uniform distribution of SiC reinforcing particles imbedded in copper matrix can be fabricated via electroless coating method followed by conventional cold pressing and sintering process. The results also show that SiC particles have a poor wettability with copper and so liquid phase sintering of the Cu/SiC composite powders did not enhance densification of the samples. Regarding this fact, optimum sintering temperatures, which depends on copper content, was determined to be in the range of 1050-1080?C.
