نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 46 (پاییز 1397)

In this study, the effect of several industrial protective coatings such as alkyd base primer, zinc rich primer and polyamide primer coatings in compassion with the surface paints comprising alkyd, polyamide and polyamine were investigated. For evaluating corrosion and durability of concrete properties, strength of mixture, electrochemical impedance spectroscopy (EIS) and pull of test was accomplished. The outcomes significantly demonstrated EIS method performs an excellent response to corrosion analysis of coating upon the rebar. Beside, in harsh media the two parts of isocyanide-acrylic coating with a surface resistance approximately 7.3 GΩ.cm2 shows the best manner

Ni-Cr-Al-Hf alloys containing 0, 0.1, 0.2 and 0.4 wt.% Hf were produced and their isothermal oxidation behavior and electrical resistance has been investigated in air for 75 h at the temperature of 1000 °C. Microstructures of the oxidized samples were examined using scanning electron microscopy (SEM) and electrical resistance was measured. The samples showed different microstructures, and oxidation behavior depending on their chemical composition. The results indicated that the sample containing 0.4 wt.% Hf had the lowest weight gain, while the weight gain of the sample without Hf was the highest. An external scale of spinel overlying a region of internal oxides precipitates formed on Ni-12Cr-4.5Al. Conversely, an external Al2O3 formed on the samples containing Hf additions. In absence of Hf, Cr2O3 was the major scale that formed on surface. The improvement in the oxidation resistance is believed to be due to the transition between the internal and external oxidation of aluminum, adherent and protective Al2O3 oxide layer on the surface of the Ni-12Cr-4.5Al-0.4Hf alloy. It was found that the scale adhesion can be affected by mechanical keying at the alloy/scale interface resulting from the pegs’ formation during oxidation. Higher electrical resistance of Alloy without Hf is due to higher thickness of oxide scale formation on surface and sample with 0.4 wt.% Hf showed lowest electrical resistance due to thinner scale of Al2O3.

The purpose of this study is synthesised of functionalized polycaprolactone and polyethylene glycol diacrylate based scaffold in the presence of hydroxyapatite (HA) particles and investigated of mechanical and biological properties of scaffolds. . At the first step, PCL diol was acrylated with acryloyl chloride and confirmed using fourier transform infrared (FTIR).Then, the scaffolds were synthesized by radical crosslinking reaction of polycaprolacton acrylate and polyethylene glycol diacrylate (PEGDA) in the presence of hydroxyapatite (HA) particles and particulate technique with sodium chloride. The prepared samples were characterized using techniques such as scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and dynamic mechanical thermal analysis (DMTA). Results show that increasing the ratio of PEGDA to polycaprolactone diacrylate (PCLDA) led to increase of tan δ peak and decrease of compressive modulus of the network, respectively. It was found that the incorporation of HA particles with the polymer matrices resulted in an increased of compressive modulus and a decrease of tan δ peak. Cytocompatability of the scaffolds were assessed by direct contact test and staining cell. Results indicated no toxicity, and cells attached and spread on the pore walls offered by the scaffols. Thus, the results indicated that the PCLDA/PEGDA/HA scaffolds have the potential of being used as promosing substrates in bone tissue engineering.

In the present research, a quantitative approach was employed to investigate the mechanical properties of ultrafine grained 6061 aluminum alloy after different cycles of accumulative roll bonding (ARB) process. In this regard, the yield strength of samples was modelled based on the microstructural parameters extracted from x-ray diffraction (XRD) patterns and micrographs using corresponding mathematical equations. The microstructural features and mechanical properties of samples were analyzed by transmission electron microscopy (TEM) and uniaxial tensile test, respectively. The density of stored dislocations was calculated from XRD patterns by famous Williamson-Hall equation. Microstructural characterizations revealed that ultrafine grains as well as non-shearable precipitates were formed gradually by increasing the number of ARB cycles. The yield strength of ARBed samples was increased by increasing the number of cycles and reached to 278 MPa after third cycle. The grain refinement mechanism was the dominant strengthening mechanism in one cycle ARBed sample, contributing a strength increment estimated to about 95 MPa and its positive role was increased continuously by increasing the number of cycles. Also, the experimentally determined yield strength was in reasonable agreement with theoretically determined yield strength from strengthening mechanisms.

In the present work the two microalloyed steel (X65 and X70 ) used in oil and gas transition pipeline, was obtained as a hot rolled plate with accelerated cooling. First, weld heat affected zone thermal cycles, according to four-wire tandem submerged arc welding process were analyzed. The Baehr 805A/D dilatometer was used for weld heat affected zone thermal cycles’ simulation. The thermal cycles simulated process for heated region involved heating the steel specimens to the peak temperatures of 950, 1150 and 1350 °C and transformation behaviour and microstructure is investigated. By analyzing the dilatometry results, continuous heating diagram, austenite grain growth and austenite formation kinetics were investigated. Austenite formation modeling was done using Johnson- Mehl- Avrami- Kolmogorov (JMAK) classic equation. The parameter n was found to be relatively independent on temperature (or heating rate); While the parameter k is strongly dependent to temperature, phase fraction transformed and austenite grain growth

Activated carbon is a porous material which has found extensive applications in separation and purification processes. Special properties of this material such as high specific surface area, highly porous structure, and high absorption capacity have resulted in its utilization in numerous industries. The purpose of this research is the production of activated carbon from waste olive stones using the chemical activation method. Phosphoric acid was used to chemically activate the olive stones, and a reductive atmosphere was applied in the heating stage instead of inert gas atmosphere. The effect of such parameters as acid concentration and activation temperature on the product properties were investigated. The products were characterized using XRD, SEM, and BET analysis. It was found out that the production of high-quality activated carbon is possible without the need for an inert heating atmosphere. It was also concluded that the concentration of the soaking solution highly affects the properties of activated carbon, especially its specific surface. The optimum conditions for obtaining the highest specific surface in the activated carbon (1194.94 m2/g) were determined to be 85 wt.% concentration of acid soaking solution, and heating temperature of 500°C.

In the present paper, ZrB2-SiC was developed by pressureless sintering method and SiC powder at nano and micro-sized scale was used as reinforcement phase. In order to produce composite samples, the primary powders were milled and blended in planetary ball mill apparatus with rotational speed of 200rpm and then processed using hot pressing (70ᵒC and 70MPa), cold isostatic press (200MPa), Pyrolysis (1000ᵒC) and sintering (2150ᵒC). The values of relative density and porosity of samples were measured to evaluate the effect of presence of micro-sized SiC and SiC nano particles simultaneously on the pressureless sintering behavior of ZrB2-SiC. In order to compare the microstructure and mechanical properties of samples Scanning Electron microscopy (SEM), equipped with EDS spectroscopy, XRD analysis, hardness and toughness tests were used. The results show that as the volume percentage of nano SiC decreases to 15 vol.%, the hardness, toughness, relative density and shrinkage initially increase and then decrease.

Metal foams are a relatively new class of materials. They provide a high energy absorption ability, large surface to volume ratio, and a high stiffness to weight ratio because of the existence of porosity in their structure. One of the most applicable metal foams is nickel foam used as catalysts, filters, and silencers in different industries. In this work, Ni foam has been prepared by electrodeposition technique on a polyurethane sponge substrate. The produced foams were sintered at 600℃ and 1000℃ in the neutral atmosphere to eliminate organic substrate and increase their ductility. EDX analysis showed that carbon atoms have diffused into Ni deposition during sintering at 600 ℃, and also the samples sintered at 1000 ℃ have oxidized. The pressure tests indicated that the samples were ductile after the sintering process. By increasing ductility, plateau strength will reduce from 4.79 MPa to 3.6 MPa and 1.65 MPa for the samples sintered at 600℃ and 1000℃, respectively. Obtained results showed that heat treatments didn’t have any effects on the densification strain, but energy absorption reduced from 1.51 MJ/cm2 to 1.21 MJ/cm2 and 0.55 MJ/cm2 for the sintered samples at 600℃ and 1000℃, respectively.

The objective of this study was to prepare crystalline poly (L-lactic acid) (PLLA)/multiwall carbon nanotube (MWCNT) nanocomposite films using solvent vaporization method, for nerve regeneration applications. Ultrasonic energy and heparinization of MWCNTs were used in order to effective dispersion of the carbon nanotube in the PLLA matrix. The effect of fundamental system parameters including carbon nanotube types and concentrations on morphology of the films was studied by Scanning Electron Microscopy (SEM). Transmission Electron Microscopy (TEM) was carried out for characterization of nanotubes’ dispersion in PLLA. Contact angle and zeta potential measurements were used to investigate the hydrophilicity and negative surface charge of the films. In vitro studies were also conducted by using murine P19 cell line as a suitable model system to analyze neuronal differentiation over a 2-week period. SEM and immunofluorescence staining were used to confirm the cells attachment and differentiation on the films. Obtained results indicate that films containing heparinized multiwall carbon nanotubes (HMWCNTs) were quite acceptable for nerve regeneration and enhanced the nerve cell differentiation and proliferation.

In this study, the microstructural properties and hardness of Friction Stir Welded (FSWed) of high strength low alloy API X70 steel at the presence of titanium dioxide (TiO2) particles were investigated. In this regard, a homogeneous mixture of TiO2 and X70 steel powders were inserted into the weld groove before applying FSW. The FSW method was applied on HSLA X70 with and without addition of titanium oxide (TiO2) particles. The optical microscopy and Vickers microhardness measurements were employed to evaluate the microstructure and hardness of the different weldments zones. The results showed that the hardness of various zones in the weldment are strongly depended on the microstructure which is affected by heat input and stiring action. In addition, the TiO2 particles were homogenously dispersed in the stir zone of TiO2-doped weldment and subsequently has changed the microstructure and hardness. In particular, a transition from an acicular ferrite (AF) dominant microstructure with a hardness value of 300 HV to a polygonal ferrite (PF) dominant microstructure with a hardness value of 180 HV was observed by moving from top surface region to near root region.

In this research study, the coating of titania particles on the SrFe12O19/SiO2 composite was successfully accomplished by the sol-gel process. For this purpose, first, the strontium hexaferrite particles were prepared by co-precipitation route with Fe3+/Sr2+ molar ratios of 11 and 12 and subsequent calcination treatment. The formation of single phase strontium hexaferrite particles, as hard magnetic cores of the composite, was attained in the molar ratio of Fe3+/Sr2+=12 after calcination at 950 °C. In the next step, the silica coating of hexaferrite particles was performed using the tetraethyl orthosilicate (TEOS) precursor via the Stöber method. In the end, the covering of titania particles on the SrFe12O19/SiO2 composite was carried out by utilizing titanium n-butoxide (TNBT) precursor. The as-prepared composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and vibrating sample magnetometry (VSM) analyses. The results confirmed the core/shell/shell structure of the synthesized SrFe12O19/SiO2/TiO2 composite. The analysis of the magnetic properties showed that saturation magnetization (Ms) of strontium hexaferrite powder was obtained as 58 emu/g. After the successive coating of SiO2 and TiO2 shells, this amount has reached to 56 emu/g and 37 emu/g, respectively.

In this paper, nano-composite powder of TiO2 and multi-walled carbon nanotubes (CNTs) was synthesized by in-situ sol-gel method. The effect of processing parameters of benzyl alcohol, H2O and CNT content (1 and 10 wt.%) on the prepared powder morphology was investigated. The samples were characterized via field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis. Firstly, the influence of calcination stage on the powders structure was evaluated. XRD results showed amorphous structures for the composite powders before calcination and the dominant structure of anatase TiO2 after calcination treatment. FESEM results showed a non-uniform and agglomerated morphology without benzyl alcohol. Furthermore, addition of Tetrabutyl-orthotitanate solution to the initial solution containing H2O as the hydrolysis agent resulted in finer powder microstructure with uniform coating of TiO2 on CNTs due to slower hydrolysis reaction. The effect of CNTs on the morphology depends on percent of CNTs. Also, composite powder with higher particle size was formed with the decrease of CNT content from 10 to 1 percent which is attributed to the decreased and less accessible surface area to TiO2 particles formation.

In this research work, the synthesis of hybrid silver (Ag) and copper oxide (CuO) was carried out by solvo/hydrothermal-microwave process in the deionized water (H2O), ethanol (C2H6O) and ethylene glycol (C2H6O2) solvents and the effects of solvent type on structural and optical properties were studied. The obtained samples were characterized by X-ray diffractometer (XRD), scanning and transmission electron microscopies (SEM and TEM), photoluminescence (PL) and absorption spectroscopies (UV-Vis). The XRD study of the samples showed presence of Ag (Cubic) and CuO (Monoclinic (phase in the obtained materials. Elemental analysis (EDS) showed presence of Ag, Cu, and O in the samples. Electron microscopes images revealed non-regular and impacted samples of Ag and CuO. The intensity of emission band of synthesized nanostructures in ethanol and ethylene glycol were reduced and it was observed a shift in the absorption edge towards lower wavelength (blue shift) in compared with synthesized samples in deionized water.

Lanthanum hexaaluminate (LaMgAl11O19) as a new thermal barrier coating due to the properties and superior features is selected as a preferred composition instead of yttria -stabilized zirconia (YSZ) Composition. In this paper, synthesis of this composition by solid state reaction method was investigated then it was prepared to coat by atmospheric plasma spraying (APS) method. Scanning electron microscope with X-ray microanalysis (SEM-EDS), differential thermal analysis (TGA/DTA), X-ray diffraction (XRD) were used to characterize of the synthesized powder, granules and free standing as-sprayed LaMgAl11O19 coating. In this research first, α-Al2O3 powder was used as a raw material. The results showed that this material was not suitable for the synthesis of this compound. Therefore γ-Al2O3 powder was used. As a result of that, a single phase compound with plate-like morphology was formed and the synthesis temperature was 1330 Cº. Also α-Al2O3, LaAlO3 and MgAl2O3 compounds were formed at 850-1100 ºC that the final phase transformation was occurred due to reaction between these three compounds.
From the phase analysis results, it can be concluded that the main role of γ -Al2O3 phase in structure is to reduce the synthesis temprature of MgAl2O4 spinel phase to a temperature of less than 1100 ºC.
Also chemical analysis results of granules and APS coating with optimal parameters indicated the existence of single phase structure and the second phase was not found.