مجله مواد نوین
سال نهم شماره 3 (پیاپی 35، بهار 1398)

The effect of 0.2, 0.5 and 1.0 wt% Ca additions on the microstructure and creep behavior of an Mg‒6Al‒1Zn‒0.7Si cast alloy was investigated by indentation creep test under constant loads of 5 and 15 N and at temperatures in the range of 448–523 K. The microstructural examination of alloys was conducted using electron microscopy (SEM), and X‒ray diffraction (XRD). Results showed that addition of Ca enhances hardness and the thermal stability of the alloys. It was found that AZ61‒0.7Si‒1.0Ca had the best creep resistance among three tested alloys. The main cause of enhancing mechanical properties of Ca-containing alloys was the change in the morphology of Mg2Si phase from Chinese script to polygonal shape, with formation of CaSi2 and CaMgSi phases. Stress exponents of all alloys showed two different regimes in creep tests. In the low stress regime, n-values of about 4–7 and activation energies of about 95 kJ/mol, introduce pipe-diffusion-controlled dislocation viscous glide as the controlling creep mechanism. In the high stress regime, however, stress exponents of about 11–14 and activation energies of about 135 kJ/mol, suggest that deformation mechanism is dislocation climb with some sort of back stress, similar to those noted in dispersion strengthening alloys.

In this paper the effect of using zinc oxide and copper oxide dyes on the corrosion behavior of concrete sewer pipes in Marvdasht city which were applied by spray and brush on the inner surfaces of the pipes were investigated. 9 pipes were used in the sewage network. Four tubes were coated with copper oxide and four tubes were coated with zinc oxide. One tube was considered as a control tube. After painting, pipes were placed in the sewage flow for 217 days. To determine the amount of aerobic and non-aerobic bacteria in the sewage system, daily, weekly and monthly bacterial counting was performed. The results showed that the production of sulfide by SRB in coated tubes is reduced up to 100% compared with uncoated tube. Also, ocular studies showed that the sludge formed on zinc oxide containing pipes was much thinner and smaller than the unpolluted tube and was used in copper oxide-containing tubes to form a layer of sludge. It was narrower on the coating of zinc oxide. The results showed that sewage is domestic. The atomic absorption test was performed to determine the amount of copper and zinc ions entering the paint into the sewage. The results showed that the amount of heavy metals entering the effluent is less than the standard and therefore do not cause toxicity.

Among NiTi base high temperature shape memory alloys, NiTiHf alloys seem to be more attention, because of their high transformation temperatures, good thermal stability and lower price in comparison with other shape memory alloys. Recovery strain and recovery ratio of this alloys in comparison with binary NiTi alloys is less. One of methods for improvement of recovery strain is thermomechanical treatment. In this research, the Ni50Ti40Hf10 shape memory alloy was casted by vacuum arc melting and after homogenization, specimens were cold rolled and annealed. By bending test, applied strain from 2.6 to 5.4 carried out on specimens and then amount of recovery strain and recovery ratio were measured. The result showed that with increasing applied strain, the amount of recovery strain increased. In all of cold rolled samples until 3% applied strain, recovery is complete 100% but in applied strain above this amount due to occurrence of slip deformation, recovery is less than 100%. In cold rolled specimens, due to increasing of hardness and also strength, recovery strain in comparison with casting specimen increased. Maximum recovery strain in casting specimen, was amount of 5 with 87% recovery ratio and with applying 10% and 20% rolling, recovery strain to 5.25 and 5.28 and also recovery ratio to 92% and 93.6% increased.

A facile synthesis of novel flower-like NiCo2O4 was developed based on an electrochemical method and subsequent calcination method. The synthesis involved the co-electrodeposition of a bimetallic (Ni,‏Co) hydroxide precursor on a Ni foam support and subsequent thermal transformation to spinel mesoporous NiCo2O4. The coating was evaluated using scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and electrochemical cyclic voltammetric (CV) test. The smart combination of NiCo2O4 nanostructures and Ni foam showed a promising synergistic effect or capacitors with greatly enhanced performance. The porous foam and NiCo2O4 can provide a large surface area and accelerated the diffusion of the active species. According to XPS results, The combination of cobalt and nickel anions in NiCo2O4 afforded binary redox couples of Co2+/Co3+ and Ni2+/Ni3+ that will largely enhance the capacitive properties. This novel material exhibited a high specific capacitance of 2196 F/g at a scan rate of 5mV/s within a -3/0 mA/cm2 current density. The CV curve confirmed the pseudocapacitor behavior of the electrode. The good electrochemical performances suggested that these unique hierarchical (SEM results) NiCo2O4 could be promising materials for energy and environmentally related applications.

The needs of the human communities and industry to build low weight, high strength and durable structures have increased the demand for composite materials, including sandwich structures. In this case sandwich panels are used in situations requiring high mechanical strength, low weight, sound insulation and thermal insulation properties. In this study, carbon nanotubes-reinforced composite honeycomb sandwich panels, were constructed using silicone molding. To determine the role of carbon nanotubes on the compressive and bending behavior of sandwich panels, a different weight percentage of this material (0/025, 0/05. 0/075) was added to the epoxy resin. Also, different thicknesses (5mm, 2/5mm) were tested to determine the role of core wall thickness on the compressive and bending behavior of sandwich panels. The results showed that the compressive strength of honeycomb panels has a direct relation with the increase in the percentage of carbon nanotubes and also the thickness of the wall. The Compressive strength of Sandwich panels increased from 42/06 up to 54/32 MPa with increasing carbon from 0/025 up to 0/075 nanotubes. The compressive strength of sandwich panels with 5 mm honeycomb wall thickness and reinforced with 0/025, 0/05 and 0/075 weight percent of carbon nanotubes compared to sandwich panels with 2.5 mm honeycomb wall thickness were respectively 2/38, 2/15 and 2.17 times. also the flexural strength of 5-mm honeycomb wall thickness and reinforced with 025/0, 0/05 and 0.075% weight percent of carbon nanotubes compared to sandwich panels with 2.5 mm honeycomb wall thickness, were respectively 3, 2.66 and 2.7 times.

In this research, in order to coating pentaerythritol tetranitrate (PETN) particles, estane compound and nano-pigment of red Lithol rubine B 57:1 (NLR) were used. After structural studies of nanocomposite by infrared (FT-IR) and field emission scanning electron microscopy (FESEM), Taguchi statistical design method was used to investigation and optimization of optical reflectance of nano-composite at 532 nm. The effect of four factors of estane concentration, NLR concentration, stirring speed and ultrasonic bath temperature in three levels on optical reflection was investigated and analysis of variance (ANOVA) showed that NLR concentration with the participation of 79.36 percent had highest effect. Optimal conditions to achieve a minimum light reflectance were obtained of estane 5 wt%, NLR 7 wt%, stirring speed 400 rpm and ultrasonic bath temperature of 50°C. The lowest light reflectance by analyzing the data variance for optimum conditions was estimated 4.97 ± 1.67. The mean experimental result for optical reflectance of the synthesized nano-composite under optimum conditions was 5.90 percent. Follows, thermal behavior and vacuum stability of the optimal sample was investigated that the results show that the melting point temperature and decomposition of nano-composite are not different compared to the pure PETN Indicating the compatibility of NLR and estane with PETN.

In this paper, the rheological behavior of SiC suspensions, fabricated via gel-casting method, and the influence of this behavior on the mechanical properties of the sintered samples were studied. To prepare castable and stable SiC suspensions, the rheological behaviour of the suspensions was characterized and optimized. To this aim tetramethylammonium hydroxide as dispersant, acrylamide as monomer, methylenebisacrylamide as cross linker, ammonium persulfate as initiator and tetramethylethylenediamine as catalyst were used. The results indicated that for obtaining stable SiC suspensions with suitable viscosity, 0.4 wt% dispersant of tetramethylammonium hydroxide, the pH of 10.5 and mixing time of 24 h were required. It should be noted that this suspension was electrosterically stable and the presence of the monomer acrylamide decreased the viscosity. The results showed that in the optimal ratio of methylenebisacrylamide cross linker to acrylamide monomer the highest strength was obtained. The flexural strength of the gel cast bodies was 231 MPa.

Hydroxyapatite nanoparticles using planetary ball mill with a stoichiometric ratio of Ca / P = 1/67 were synthesized. For this reason two different approaches were adopted to synthesize the hydroxyapatite nanoparticles: insitu synthesis by mechanical activation method and mechanochemical method. For both methods the initial material of CaCO3 and CaHPO4.2H2O with a molar ratio of 2: 3 were used under the same milling conditions. After optimizing the parameters in the mechanochemical method the milling operation was done for 5 hours under argon atmosphere using a stainless steel milling vial. According to the STA results the heat treatment was done at 500 C for 3 hours with a heating rate of 10 C/min. For the insitu synthesis method the milling was done under argon atmosphere for 15 hours and the hydroxyapatite nanoparticles were obtained insitu and without any heat treatment. In order to characterize the formation of hydroxyapatite phase, X-ray diffraction analysis was used. Furthermore field emission scanning electron microscopy was used to determine the particle size and particle size distribution. According to the experiments, it was shown that increasing the milling time resulted in the decomposition of CaCO3 at low temperature and the increased chemical activation of the initial CaHPO4. 2H2O and CaCO3 powders. The decrease in the particle size and crystallite size caused an increase in the diffusibility and decrease in the reaction temperature of the mixed milled powder. As a result of these events, the hydroxyapatite nanoparticles obtained from both methods had a hexagonal structure with spherical morphology.

Lead-free [(Ba0.85Ca0.15)1-xCex/2](Zr0.1Ti0.9)O3 (BCCexZT) piezoceramics were synthesized using conventional solid-state ceramic processing. Sintering was carried out in the temperature range of 1350 - 1450 °C for 4 h. The microstructure and phase composition were investigated by scanning electron microscopy and X-ray diffraction. Polarization and strain measurements were done using a modified Sawyer-Tower circuit and a commercial aix-PES piezoelectric evaluation system was used to record the variations of polarization and strain with temperature. The addition of CeO2 decreased the Curie temperature of BCZT to near room temperature and consequently a high permittivity value was obtained at room temperature. Additionally, the temperature dependence of strain and polarization showed that electrostrictive coefficients calculated from the unipolar and bipolar loops were approximately the same. Since the Curie temperature of BCCe0.025ZT is shifted to around room temperature, 90-100% of induced polarization and strain is attributed to the electrostriction effect. The highest electrostrictive coefficients of Q33= 0.063 m4/C2 and M33=3.4E-16 m2/V2 were obtained for BCCe0.025ZT ceramics with 2.5 mol% Ce, which are higher than the corresponding values in previous reports and make this composition as a candidate for electrostrictive applications.

Today, the use of nanoparticles in aluminum composite materials has attracted researchers due to their superior effects on mechanical and physical properties. Due to the poor wettability of the nanoparticles by the metal during the casting and the high ratio of the surface to the volume of the nanoparticles, it is difficult to achieve uniform distribution of the particles in the interior. In the manufacturing process, nanoparticles tend to form cluster particle masses. The mass of nanoparticles has undesirable effects on mechanical properties, including strength and resilience of the composite. In this study, stir casting process for composite manufacturing with different amount of mixed powder containing of nano Si3N4, AlMg and Al2O3 was used. For better distribution of particle reinforcement, cold rolling was used. In order to characterize the composite, microstructural, mechanical and phases studies properties were used. FESEM tests on mixture of aluminum and nanoparticles showed that after ball milling, particles are in nanometric size. Mechanical and optical result show that optimum of reinforcement is 0.5 % w.t. It is notable that the higher yield stress of the composite samples does not reduce the elongation significantly, when compared to monolithic aluminum.

In present study closed cell aluminum A356 metal foam used as sandwich panel core with aluminum surface sheets. Then the uniaxial compressive plastic behavior and three-point bending behavior of foam slab and sandwich panel were studied. According to force-cross head displacement curves of compressive and three-point bending tests, the absorbed compressive and bending energy were calculated and by analyzing structure and metallography of cell walls, the deformation mechanism was estimated. Foam’s structure; in compressive test; showed same crushing behavior of cell walls for foam slabs and sandwich panels. However, sandwich panels showed two different behaviors due to core structure of foam in three-point bending test. First one was plastic hinges and U shape bending, around compression mandrel in three-point bending test and the other one was tearing of bottom face sheet of sandwich panel. Hence the absorption energy of sandwich panel and slab foams were calculated. The results show that sandwich panel and slab foam have almost same compressive strength. Also sandwich panel bending strength was 5.3 times greater than slab foam. However, absorbed energy in the longitudinal plastic deformation up to 7.38 % strain for slab foam was greater than sandwich panel. However, characteristic absorb energy during three-point bending test and according to disruption of panel structure mode showed that sandwich panel failure with plastic hinges had higher characteristic absorption energy.

In this study, double oxide nanopowders with perovskite type La0.9Sr0.1FeO3 were synthesized by sol-gel method in 750 ˚C for 6 hours. Two factors of citric acid and cetyltrimethyl ammonium bromide (CTAB) were used as a complex agent and surfactant, respectively. The crystalline characterization, morphology, specific surface area, and grain size of nanoparticles were investigated using a series of analytical analyzes such as XRD, SEM, DLS, BET. The X-ray diffraction pattern (XRD) showed that after the calcination, only the pericardial phase with perovskite structure was formed. The obtained material was studied by scanning electron microscope (SEM) and its morphology and particles size range was analyzed. The microstructure of the samples was studied by DLS analysis. By the BET analysis, the porosity of the nanopowder was measured and pores diameter about 75 nm were resulted. After identification and characterization of CTAB-synthesized perovskite, methylene blue dye removal process was investigated. In this process, various parameters such as time, adsorption concentration, dye concentration and pH were studied. By studying and comparing removal percent and adsorption kinetic was revealed that the synthesized nanoparticles were suitable for removal of methylene blue dye.