Journal of Environmental Friendly Materials
Volume:6 Issue: 2, Summer-Autumn 2022

Geopolymers can be mentioned as a new class of green cement adhesives. Geopolymers have recently been introduced as a greener alternative to conventional Portland cement (OPC) with the potential to minimize the negative environmental consequences of OPC such as carbon footprint and energy consumption. In this experimental study, the effects of different alkaline activating solutions on compressive, tensile, and indirect flexural strength, water absorption, and acid resistance of bentonite-based geopolymer concrete (GPC) were investigated. Also in this study, a new type of alkaline activator was used. In this study, GPC samples made from bentonite were produced and baked at 90 ° C. The results showed that the addition of NaOH to the mixture after 3 minutes of mixing KOH and Na2SiO3 with dry components (1/3 of the total mixing time) increases the compressive, tensile, and flexural strength and we also see that with this new method, water absorption capacity and the amount of weight loss of geopolymer concrete samples are reduced in acidic conditions.

Metal corrosion is the main phenomenon in different industries and destructive effects of this chemical phenomenon cause a lot of costs annually. While corrosion causes a little mass decrease in structure, brings about a dramatic reduction in mechanical strength and fatigue life of corroded materials. Hence, health monitoring of a structure can make aware of structure status at any time and prevents from harmful consequences. Structural Health Monitoring based on Electromechanical Impedance is one of the real-time monitoring techniques that could recognize damage on a structure by using an electromechanical coupling of piezoelectric materials, immediately. On the other hand, due to high frequency used in this method, small defects in the early stages will be detected. In this paper, Structural Health Monitoring based on Electromechanical Impedance was applied in an aluminum cantilever beam to recognize the corrosion and evaluate the capability of the Electromechanical Impedance method in detecting corrosion. Furthermore, the standard deviation of the mean square root has been chosen as the main metric, that it increases as the defect size increases. Afterwards, Experimental results were compared with health monitoring theory based on the Electromechanical Impedance and more energy method. Subsequently, the experimental results represent this method efficiency in the immediate monitoring of damage caused by corrosion in an aluminum cantilever beam. Besides, the possibility of pinpointing the defect by using this way has shown a good relationship between the place of damage and damage metric.

Inert Gas Tungsten Arc Welding (GTAW) process is one of the most widely used welding processes in which material is prone to stress corrosion cracking (SCC). Stress corrosion indicates cracking due to combined effect of stress and corrosion. Many rupture incidents have occurred due to this type of cracks. Effect of ultrasonic waves were studied on GTAW welded SS316L metal, in this paper. Two samples were healed by post weld ultrasonic treatment, two samples by post weld heat treatment and two were considered as control samples with no post treatment. Residual stress of all six pieces were measured by XRD method. Afterwards, samples were placed in corrosion environment. Results show that residual stress was decreased to 54.3% using heat treatment whereby this decreased to 58.7% by ultrasonic waves. It was also shown that untreated samples cracked after 720 hours, while no crack was seen in post weld ultrasonic treated samples.

Nickel-based superalloys are one of the main components of fixed and moving blades of land and air gas turbines. Susceptibility of substrate and coating during Rene80 superalloy coating with IN625 was investigated by laser cladding method. For this purpose, the substrate was selected under two conditions of casting and solution heat treatment. Microstructural studies showed that the coating, despite maintaining its hardness due to NbC carbide and Ni2(Cr,Mo) phases, did not form cracks and pores. However, in the coating-substrate interface and heat affected zone of the casting sample, cracking occurred due to the high absorption of process stresses by MC carbide (TiC) and γ´ phase as well as partial melting of these two phases. However, in the case of heat treatment, due to the dissolution of these phases and the low hardness of the substrate, the conditions of non-stress absorption and stress release further reduced the sensitivity to cracking.

The main minerals containing chromium are chromite mineral compounds. Ferrochrome is divided into three groups: high carbon, medium carbon and low carbon. Chromite mineral has a cubic lattice and belongs to spinel category. In the present study, Fe-Cr-C three-component diagrams are presented along with chemical compounds of ferrochromium. In the following, the extraction of high carbon ferrochromium is further investigated. Fe-Cr-C ternary diagrams confirm that Cr3C2 decomposition at temperatures below 1600°C in minerals with 60 wt% Cr and 8 wt% C results in Cr7C3 composition. Finally, a solution to reduce the most toxic chromium ion (Cr6+) in the leachate of the extraction process is presented. Cr6+ is the most toxic species among its different oxidation states. Cr6+ is also toxic to aquatic animals, plants, and bacteria. Cr3+ is 100 times less toxic than Cr6+. In humans and in small quantities, chromium is an essential nutrient required for sugar and lipid metabolism, but in excess it may cause cancer and allergic skin reactions.

The joints of dissimilar materials are widely used in industrial applications due to their technical and beneficial advantages. The dissimilar combination of aluminum and copper is generally difficult for fusion welding. This is because of formation of undesired intermetallic phases which reduces electrical conductivity in the joint interfaces. Therefore, in order to restrict these limitations solid states welding methods such as explosive welding have been suggested. Hence, in this research the effect of explosive welding parameters on microstructure, mechanical and electrical properties were investigated. Stand-off distance and thickness of explosive material were taken as the variable parameters which were affect the microstructure, mechanical and electrical properties. After conducting the Explosive welding process, Microstructural investigations using Optical and Scanning Electron Microscope which is equipped with Energy Dispersive Spectroscopy was performed. Also, for investigation of mechanical properties, hardness test was done. The results of microscopic investigations demonstrated that with increasing the thickness of explosive material, the joint interface was transformed from linear to wavy appearance. Also, the results showed that the Al-Cu interface had a higher hardness in comparison to the hardness of Al and Cu. Evaluations showed that forming the CuAl and CuAl2 intermetallic phases in the joint interface are the reason for increasing the hardness. Electrical resistance values of 0/3, 0/55, 0/38 and 0/40 mS/cm were obtained for Al-1050, Cu, Al-Cu joint interface of A and B samples.

In this research, the effect of sulfuric acid electrolyte temperature on the surface properties of anodizing coating of 6061 aluminum alloy is investigated. For this purpose, anodizing was done in sulfuric acid environment and 4 different temperatures (-5°C, 5°C, 15°C and 25°C) on 6061 aluminum alloy. Characterization the structure and chemical composition of the coatings by the use of low-angle X-ray diffraction (GIXRD) and Energy-dispersive X-ray spectroscopy (EDS) results showed that the coatings have a non-crystalline structure with aluminum hydroxide as a result of atmospheric hydration of the anodized samples. The results of roughness measurement and Scanning electron microscope (SEM) images indicated that the porosity increased due to the higher corrosive power of sulfuric acid at higher temperatures. Examining the changes of anodizing flow over time determined that higher temperatures of the anodizing solution causes an increase in the anodizing flow and the dissolution rate of the coating. For this reason, the thickness and hardness of the samples, which have a direct relationship with the rate of dissolution and flow, decreased significantly with increasing temperature.

In this article, using the method of dislocation distribution and separation of variables, the mechanical fracture behavior of a thin rectangular plane made of piezoelectric material with limited length and width containing several cracks under out-of-plane mechanical and in-plane electrical loading is investigated. It is assumed that the behavior of the elastic medium is linear and the surfaces of the cracks are smooth. At first, the governing equations of the problem are solved according to the boundary conditions, and then the components of stress and electrical displacement in the body without cracks under external loading at the hypothetical crack location are presented. Then, according to Buckner's principle, the stress field obtained in the main problem and using the dislocation distribution method, the equations for analyzing the problem of several cracks are presented. By solving these equations and obtaining the distribution functions of dislocations, it is possible to obtain the stress and electric displacement factors at the tips of cracks. In this article, examples are given to verify the results and also to investigate the effects of the length, arrangement and interaction between the cracks on the field intensity factors.