Showing 23 results for Temperature
P. Delshad-Khatibi, F. Akhlaghi,
Volume 28, Issue 1 (6-2009)
Abstract
Solid Assisted Melt Disintegration (SAMD) is a relatively new method for producing metallic powder particles in which the kinetic energy transferred from a rotating impeller to the melt via a solid medium causes melt disintegration. These droplets are then solidified and separated from the media to obtain metallic powder particles. In the present study, sodium chloride (NaCl) was used to produce Al-6wt%Si powder particles. A specified amount of NaCl was introduced into the aluminum alloy melt and the slurry was stirred following a specified time-temperature regime to disintegrate the molten alloy into droplets. This blend was quenched in water to solidify Al powder particles and to dissolve NaCl in water. The Al powder particles were then collected, washed, dried, and subjected to laser particle size (LPS) analysis and scanning electron microscopy (SEM). The effects of different time-temperature regimes on the size and morphology of the resultant Al-6wt%Si powder particles were investigated and the optimum conditions for obtaining the finest spherical particles were established. It was concluded that the finest and most spherically shaped Al powder particles could be produced by stirring the slurry at 690 °C for 5 min followed by water quenching.
S. R. Bakhshi, M. Salehi, H. Edris, G. H. Borhani,
Volume 29, Issue 1 (6-2010)
Abstract
In this study, Mo-14Si-10B and Mo-57Si-10B (at%) elemental powders were separately milled using an attritor mill. Mechanically alloyed powders were agglomerated and annealed. Then, powders of Mo-Si-B as alloyed (with composites) and agglomerated (without composites) were plasma sprayed onto plain carbon steels. The samples, both coated and non-coated, were subjected to isothermal oxidation tests. Metallurgical characteristics of powders and coatings were evaluated by SEM and XRD. Plasma-sprayed Mo-Si-B coatings (with phases of MoSi2, Mo5Si3, MoB and Mo5SiB2) greatly improved the oxidation resistance of the plain steel substrates, but plasma-sprayed Mo-Si-B coatings (without any phases) did not significantly improve the oxidation rate of substrates. Also, the kinetics and composition of the oxide-scale have been found to depend on the alloy composition.
H.r. Salehi, S.m.r. Khalili,
Volume 30, Issue 2 (12-2011)
Abstract
In the present work, thermal and mechanical behaviors of phenolic resin are investigated. This polymer can be used as a matrix for carbon-carbon composites. To find out the best heating process, five different cycles are used for curing the polymer and flexural strength of the specimens are obtained. The cycle with maximum strength is used for the next steps. Then, the oxidation behavior of specimens is studied at different temperatures. The results show that the polymer can withstand temperature about 350°C without significant weight changes. Carbonization of phenolic resin is studied by four different cycles at 1100°C. Oxidation of carbon obtained from carbonization cycle is analyzed extensively and shows no weight change until 550°C. The microstructure of specimens is also investigated by SEM. By additining SiC micro particles to phenolic polymer, the strength change is achieved.
M. Mashhadi, A. Abdollahi, Z. Nasiri,
Volume 33, Issue 2 (3-2015)
Abstract
In this study, ZrB2-HfB2 composite was produced by pressureless sintering method. MoSi2 B4C and SiC particles were used as reinforcement. ZrB2 powder was milled in planetary ball mill apparatus and then reinforcement particles were added to the milled powder. The composite powders were then CIPed and sintered at 2100oC and 2150oC. Scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDS), flexural test, and resonance frequency method were used to compare the added particle effects on mechanical properties and pressureless sintering behavior of ZrB2-HfB2 composite. The analysis showed that the ZrB2-HfB2-MoSi2-SiCnano composite displays the largest gain in flexural strength. Furthermore, increasing the sintering temperature leads to an increase in flexural strength of samples.
Zahra Omidi, Saeed Reza Bakhshi, Ali Ghasemi,
Volume 33, Issue 3 (3-2015)
Abstract
Silicon nitride has attracted a considerable attention because of its excellent properties such as high-temperature strength, good oxidation resistance, high corrosion resistance, good thermal shock resistance, high creep resistance and good thermal and chemical stability. There are several different fabrication methods for synthesizing Si3N4 particles. Such methods are mostly costly and kinetically slow and require lengthy heat treatment. In this study, Si3N4 compounds were synthesized by means
of mechanical milling. In the mechanical milling route,Si powder (≤99.0%) was milled under nitrogen gas for 25 h and heated at various temperatures 1100-1200-1300 and 1400 C for 1 h at the nitrogen atmosphere at a rate of 200 ml/min. Silicon powder was also annealed under a similar condition in order to evaluate the impact of milling process on the low temperature synthesizing of Si3N4. Phase identification and microstructural characteristics of products were evaluated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The Fourier transform infrared spectroscopy and thermal analysis were used for characterization of the formed bands and thermal treatment of the sample, respectively. The obtained results exhibited that Si3N4 powder was fully formed with two kinds of morphologies including globular particles and wire with a width of 100–300 nm and length of several microns at sintering temperature of 1300 C. This was confirmed by the Si–N absorption bonds in the FTIR trace. Based on XRD results, 25 h milling reduced temperature of reaction remarkably in comparison with direct nitridation of Si powders for 1 h. With an increase in the reaction temperature, the Si3N4 samples had a phase transformation 𝛂→𝛃, and variation of the morphology followed the vapor–liquid -solid mechanism.
R. Tajalli, H. Baharvandee, H. Abdizadeh,
Volume 33, Issue 3 (3-2015)
Abstract
In this research, ZrC nano particles were synthesized by self-propagating high temperature (SHS) using the mixed powder of ZrO2-C-Mg and NaF or NaCl diluent. The effect of different proportions of raw materials, milling time, composition
of the diluent and also pickling on the synthesis of ZrC was investigated. Optimal amounts of magnesium and sodium fluoride for the synthesis of ZrC were 2.8 and 2 mol, respectively. Milling process of 120 minutes decreased the diffusion gap of raw material and increased the combustion reaction progress. XRD and SEM analysis showed that the NaF diluent more than NaCl caused a reduction in the size of the particles of ZrC and increased the progress of the combustion reaction. Synthesized samples were subjected to pickling in order to remove impurities of MgO by 37% HCl, and distilled water was used to wash off NaF and NaCl residues. ZrC particle size of different samples were in the range of 50-90 nm.
S.t. Mohammadi Benehi, S. Manouchehri, M.h. Yousefi,
Volume 35, Issue 3 (12-2016)
Abstract
Magnesium-manganese ferrite nanopowders (MgxMn1-xFe2O4, x=0.0 up to 1 with step 0.2) were prepared by coprecipitation method. The as-prepared samples were pressed with hydrolic press to form a pellet and were sintered in 900, 1050 and 1250˚C. Scanning Tunneling Microscope (STM) images showed the particle size of powders about 17 nm. The X-ray patterns confirmed the formation of cubic single phase spinel structure in samples sintered at 1250˚C. Substituting Mg2+ with Mn2+ in these samples, the lattice parameter decreased from 8.49 to 8.35Å and magnetization saturation decreased from 74.7 to 21.2emu/g. Also, coercity (HC ) increased from 5 to 23Oe and Curie temperature (TC ) increased from 269 to 392˚C. Samples with x= 0.2, 0.4, 0.6 sintered at 1250 ˚C, because of their magnetic properties, can be recommended for hyperthermia applications and for phase shifters.
M. Pourkarimi, B. Lotfi, F. Shahriari Nogorani,
Volume 35, Issue 4 (2-2017)
Abstract
In this study, creation of a silicon aluminide coating on IN738LC nickel-based superalloy has been investigated, using co-deposition process. Thermochemical calculations indicated the possibility of obtaining a silicon aluminide with NH4Cl activated pack powder at 900°C, in order to achieve coating with desirable structures. Two powder mixtures with nominal compositions of 7Si-14Al-(1-3) NH4Cl-Al2O3 (wt. %) and 16Si-4Al-(1-3) NH4Cl-Al2O3 (4 and 0.5 Si/Al ratios, respectively) were used. According to the results, both coatings showed multi-layered structures containing AlNi2Si as dominant phase. In coating created by pack powder with Si/Al ratio of 0.5, a porous and brittle layer of NiSi was formed on the surface which deteriorated the mechanical properties of coating to some extent. It was found that inward diffusion of Al was dominant at the first stage, while afterward, inward diffusion of Si led to conversion of NiAl phase to AlNi2Si and, finally, to NiSi phase. Eventually, the sample coated by Si/Al=4, showed superior microstructural characteristics, containing desirable AlNi2Si phase without undesirable brittle NiSi phase.
M. Mottaghi, M. Ahmadian,
Volume 36, Issue 1 (6-2017)
Abstract
In this research, the wear behavior of commercial grades of WC-10wt%Co (H10F), WC-40vol%Co and WC-40vol%FeAl-B composites with different amounts of boron from zero to 1000 ppm has been investigated by the pin on disk test method at high temperature. The wear tests were done under load of 40 N, a distance of 100 m and at ambient temperature, 200 ̊C and 300 ̊C. Wear surfaces were examined by scanning electron microscopy. The results showed that the wear resistance of all composites decreased with increasing temperature. The boron free WC-40vol%FeAl composite showed the lowest wear resistance at all ranges of temperature. In the presence of boron up to 500 ppm in iron-aluminide matrix, the high temperature wear resistance of these composites improves and the wear mechanisms changes from particle pullout into abrasive state. The toughness enhancement of these composites and plasticity enhancement of iron aluminide in the presence of boron, leads to better link of the interface of FeAl matrix and tungsten carbide particles, and thus increases the wear resistance of these composites. WC-40vol% FeAl-500ppmB composite has a higher wear resistance at high temperature than WC-40vol% Co and commercial WC-10wt% Co.
S. R. Hosseini, M. Barati, E. Maghsoudi,
Volume 36, Issue 1 (6-2017)
Abstract
The aim of the present research is calculation and determination of the temperature distribution in the oxy-gas source line heating process for application in the steel plates. Analytical method was used to calculate the temperature distribution by solving mathematical equations. The temperature distribution was determined with numerical method using MATLAB software. A computerized numerical control line heating apparatus was used for carrying out the processes. ITI thermograph camera was used to measure the temperature. The effect of torch distance, gas flow and torch speed on the temperature distribution at the upper and lower surfaces of plate were evaluated. The changes of temperature distribution were achieved at torch speeds of 120, 200 and 300 mm/min, gas flow of 10, 9 and 8 lit/min and torch distances of 30, 40 and 50 mm. Calculated and measured maximum temperatures reached to 900, 810 and 720 K, and 885, 785, 690 K, at torch speeds of 120, 200, 300 mm/min, respectively. The calculated and measured maximum temperatures at gas flow of 10, 9, 8 lit/min are attained to be 900, 810 and 750 K, and 885, 795 and 740 K, respectively. Maximum calculated and measured temperatures at torch distance of 30, 40 and 50 mm are accomplished to be 900, 880 and 810 K and 885, 840 and 790 K, respectively.
F. Z. Akbarzadeh, M. Rajabi,
Volume 36, Issue 4 (3-2018)
Abstract
In this study, the composite material with composition of MgH2-10 wt% (25Ce-75Ni) has been prepared by co-milling of magnesium hydride powder with Ce-Ni alloy produced by vacuum arc remelting method. The effect of milling time and additive on magnesium hydride structure, i.e. crystallite size, lattice strain and particle size, and also hydrogen desorption properties of obtained composite were evaluated and compared with pure milled MgH2. It has been shown that the addition of 25Ce-75Ni alloy to magnesium hydride yielded a finer particle size. As a consequence, the desorption temperature of mechanically activated MgH2 decreased from 340 °C to 280 °C for composite 1(5 h mechanical alloying) and to 290 °C for composite 2 (15 h mechanical alloying). Further improvement in the hydrogen desorption tempreture of composite 1 can be related to finer particle size and higher Mg2NiH4 phase value, which corresponded with calculated enthalpy results.
S. Ghadiri, A. Hassanzadeh-Tabrizi,
Volume 37, Issue 1 (6-2018)
Abstract
In this study, the synthesis of nano-porous calcium magnesium silicate was performed and studied to improve drug properties and drug release. This synthesis was carried out by using the tetraethyl ortho silicate precursor (TEOS) and the Cetyltrimethyl ammonium bromide surfactant (CTAB) in a sol-gel alkaline environment; and the product was heat treated at 600° C and 800° C temperatures. The purpose of this study is to investigate the effect of the calcination temperature on the potential for ibuprofen release by the production produced compound. The product was studied using X-ray diffraction patterns (XRD), Nitrogen adsorption / desorption, Fourier-transform infrared spectroscopy (FTIR), ultraviolet spectroscopy (UV) and Transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). The results of Nitrogen absorption-desorption assay showed a surface area of 42-140 m2 /g The drug release after 240 hours showed that the calcite sample had a lower release at 600 ° C, temperature that which was is due to the smaller size of the cavities and the more surface area, as compared tothan the other specimens. Also, calcium and magnesium elements increased the loading capacity, and createcreating a suitable substrate for for the slower drug release. Overall, This this study showed that nano-porous magnesium silicate calcium has had the ability to load and release the ibuprofen and can could be, therefore, used as a modern drug delivery system in the bone tissue engineering field.
Z. Jarrahi, Sh. Raygan, M. Pourabdoli,
Volume 37, Issue 4 (3-2019)
Abstract
In this study, boron containing Cu-12wt%Al-4wt%Ni shape memory alloy was prepared by mechanical alloying, pressing and rolling. In this regard, 20 and 40 hour-milled powder was compacted and changed to the bulk alloy by cold pressing, sintering, rolling, heat treatment and quenching. Phase structure, micro-structure, micro-hardness, and transformation temperatures of the prepared samples were studied. It was found that increasing the milling time from 20 to 40 hours led to the rise of the starting temperature of martensite transformation (Ms) from 254 to 264°C. Also, the results showed that adding 0.5 wt.% B decreased the Ms temperature to 211°C and enhanced the micro-hardness from 154 (for the sample without B) to 193 vickers. These alternations were attributed to the fine structure caused by Boron rich precipitations. Moreover, two martenistic transformations with different structures were formed due to the non-homogeneity of the Al concentration in the matrix, which appeared in the form of two different transformation temperatures (Ms) in the Differential Scanning Calorimetry curves.
N. Alirezaei Varnosfaderani, S. E. Mousavi Ghahfarokhi, M. Zargar Shoushtari,
Volume 38, Issue 3 (12-2019)
Abstract
In this paper, W-type SrCo2Fe16O27 hexaferrite nanostructures were synthesized by sol-gel auto-combustion method. Effect of annealing temperature on the structural, magnetic and optical properties of these SrCo2Fe16O27 nanostructures was investigated. In order to determine the annealing temperature of samples, the prepared gel was examined by thermo-gravimetric and differential-thermal analyses. Morphology and crystal structure of the prepared samples were characterized by field emission scanning electron microscopy and X-ray diffraction pattern. Based on X-ray diffraction results, at annealing temperature of 1000 °C, the maximum amount of main phase formed. A planar morphology was spectroscopy for the synthesized samples through scanning electron microscope images. Fourier transform infrared analysis was used to confirm the synthesis of the main properties obtained of samples were measured by the vibrating sample magnetometer and the results showed that by increasing temperature, magnetic saturation increases. Moreover, optical properties of samples were investigated by ultraviolet–visible absorption and photoluminescence spectroscopies. The result of measurements of the energy gap approximately is same in the ultraviolet- visible and photoluminescence spectroscopes and also the energy gap is constant with increasing temperature.
M. Emami, Sh. Hayashi,
Volume 38, Issue 3 (12-2019)
Abstract
The outer surface of heat exchanger tubes that work under fluidized bed waste or biomass incineration is exposed to severe high-temperature erosion-corrosion (E-C). To evaluate the behavior and enhance the service life of the tubes, the real service conditions ought to be simulated in the laboratory. In this study a test rig with a fluidized bed of hot sand was designed and manufactured to expose nickel-based SFNi4 alloy to high-temperature E-C. In order to increase the corrosiveness of the environment, the silicon oxide sand was mixed with 0, 0.5 and 1 wt.% of a mixture of NaCl and KCl salts with 1:1 molar ratio. The erosive conditions of the environment were changed by altering air flow rate from 20 to 25 L/min and changing the sand incident angle from 45 to 90 degrees. The rate of material removal was calculated by measuring the thickness of each sample before and after the test. After each experiment, the surface and cross-section of specimens were studied using SEM and EDS analysis. Finally, the optimum E-C parameters to ensure actual industrial conditions were obtained.
M. Emami, S. Hayashi,
Volume 39, Issue 3 (12-2020)
Abstract
High-temperature erosion-oxidation behavior of nickel-based alloys containing 0-7 wt.% Mo in fluidized bed waste incineration conditions was studied. A stream of hot condensed air with a flow rate of 25 L/min caused hot silica sand (700 °C) mixed with 0.5 wt.% of chloride salts to hit the specimens for 250 h. By removing the erosive factor, the high-temperature oxidation behavior of the alloys in air and air-chlorine atmospheres was studied at 520 and 560 °C for 100 h. Mass gain measurement due to oxidation followed by thickness loss measurement in the erosion-oxidation tests showed that an increased Mo content led to improved oxidation resistance as a result of reduced scaling rate. However, under simultaneous oxidation and erosion conditions, the lower oxidation rate of the alloy with 7 wt.% Mo caused rapid removal of the protective scale and a reduction in erosion-oxidation resistance of the alloy. Under these conditions, the alloy with 3 wt.% Mo showed the smallest removal rate. Microscopic observations and XRD analysis confirmed formation of Cr2O3/NiCr2O4 scales on the surface. Mo-free alloy with lowest oxidation resistance showed a higher erosion-oxidation resistance. However, the high oxidation rate of this alloy led to a severe Cr-depletion and internal oxidation in subsurface region.
F. Mostafaee Heydarloo, M. Morakabati, H. Badri ,
Volume 39, Issue 3 (12-2020)
Abstract
The aim of this study was to investigate the suitable temperature range for hot deformation of three medium carbon Ni-Cr-Mo low alloy steels by hot tensile and hot torsion tests. Hot tensile tests were carried out in the te,prature range of 850-1150°C at a constant strain rate of 0.1 s-1 until fracture. Then, the tensile flow behavior, hot ductility and microstructural evolution of the steels were studied. Hot torsion tests were performed in the temperature range of 1200-780°C at strain of 0.1 with strain rate of 1s-1. The effect of titanium and niobium on the mean flow stress and the non-recrystallization temperature were investigated. The tensile test results showed that dynamic recrystallization was the dominant mechanism at temperatures above 950°C in the base steel and temperatures above 1050°C in the microalloyed steels. The results of hot torsion tests showed that the non-recrystallization temperatures of the base, Ti containing and Nb containing steels were 1070°C, 1069°C and 1116°C, respectively. Finally, the suitable hot deformation temperature range to achieve optimum mechanical properties in the base and Ti containing steels obtained as 950-1070°C and that of Nb containing steel obtained as 950-1100°C.
S. N. Hosseini, F. Karimzadeh, M. H. Enayati,
Volume 39, Issue 4 (2-2021)
Abstract
The bare and pre-oxidized AISI 430 pieces were screen printed by copper ferrite spinel coatings. Good bonding between the coating and the substrate was achieved by the reactive sintering process of the reduced coating. The energy dispersive X-ray spectroscopy (EDS) analysis revealed that the scale is a double layer consisting of a chromia-rich subscale and an outer Cu/Fe-rich spinel. The results showed that the spinel protection layer not only significantly decreased the area specific resistance (ASR), but also inhibited the subscale growth by acting as a barrier to the inward diffusion of oxygen. ASRs of 19.7 and 32.5 mΩ.cm2, much lower than that of the bare substrate (153.4 mΩ.cm2), at 800 °C after 400 h oxidation were achieved for the bare and pre-oxidized copper ferrite spinel coated samples, respectively. Excellent, stable ASR (20.5 mΩ.cm2) was obtained with copper ferrite coating after 600 h of exposure at 800 °C. The high electrical conductivity of CuFe2O4 and its doping by Mn, the growth reduction of Cr2O3 oxide scale and the good coating to substrate adherence are proposed to be responsible for substantial improvement in electrical conductivity.
I. Forooghi , M. Mashhadi,
Volume 39, Issue 4 (2-2021)
Abstract
Due to their unique features, Ultra-High Temperature Ceramics (UHTCs) have potential applications in aerospace, military and industry. ZrB2-SiC composite as one of these ceramics has been at the center of researches due to its attractive mechanical, thermal and oxidation resistance. In this study, the effect of ZrC addition on pressureless sintering behavior, mechanical, microstructural and thermal properties of ZrB2-SiC nanocomposite were investigated. For this purpose, micron-sized ZrB2 and ZrC powders and nano-sized SiC powder were used. ZrB2-20vol% SiC nanocomposites with addition of (3, 6, 9, 12, 15) vol% ZrC were sintered by pressureless sintering method at 2100 ºC. The results showed that the addition of ZrC improved relative density, hardness and fracture toughness of ZrB2-20vol% SiC nanocomposite. Optimum properties were obtained in a sample containing 12 vol% ZrC and the relative density, hardness and fracture toughness of this sample were reported to be 99.01%, 16.95 Gpa and 5.43 Mpa.m0.5, respectively. Thermal analysis of the samples showed that by adding ZrC, thermal diffusivity of this nanocomposite reduced. The highest thermal diffusivity at room temperature equaled 35.3 mm2 /s and was obtained for ZS composite.
E. Mohagheghpour, R. Gholamipour, M. Rajabi, M. Mojtahedzadeh Larijani,
Volume 40, Issue 3 (11-2021)
Abstract
In this study, the amorphous carbon thin films were deposited by ion beam sputtering deposition method on the glass and Ni–Cu alloy substrates. The structural evolution of amorphous carbon and its correlation with the kinetic energy of carbon atoms during the growth of thin film was investigated. The effect of substrate material, deposition temperature, and ion beam energy on the structural changes were examined. Raman spectroscopy indicated a structural transition from amorphous carbon to diamond-like amorphous carbon (DLC) due to an increase in deposition temperature up to 100°C and ion beam energy from 2 keV to 5 keV. The size of graphite crystallites with sp2 bonds (La) were smaller than 1 nm in the amorphous carbon layers deposited on Ni-Cu alloy. The results of residual stress calculation using X-ray diffractometer (XRD) analysis revealed a decreasing trend in the tensile residual stress values of the amorphous carbon thin films with increasing the ion beam energy.
