مجله مواد نوین
سال چهاردهم شماره 1 (پیاپی 51، بهار 1402)

 The purpose of this research is solid state recycling of 3000 and 5000 series aluminum alloy scrap to produce aluminum nano-crystalline powder by mechanical milling without using process controlling agent. In this regard, aluminum used beverage cans (UBCs) which consist of lid (alloy 5182) and the monolith part (alloy 3004) of the body (thin) and bottom (thicker).

To achieve disintegration mechanism, lid part, body and bottom of monolith part are separated each other because of diverse constituent of Al series and different thickness. The three parts individually were decoated then cut into the small chips (app. 8 mm). The chips were mechanically ball milled at different times up to 104 hours under argon atmosphere. The ratio of ball to powder was 10 to 1.   

The lid part chips are crushed faster than the monolith part chips, and, resulting in a finer powder. According to the PSA results, the D90 of the lid powder is less than 150 micrometers; while D90 of the body and bottom powders are more than 150 micrometers. This result can be used on an industrial scale to separate the constituent elements of crushed UBCs from each other. The smallest D90 values of lid, body and bottom powders, which obtained after 72, 80 and 80 h as optimum milling time, are 109, 258 and 391, respectively. Also, their flowability were 57.8, 59.3 and 61.1 s/50 g, as well as the apparent density were 1.38, 1.43 and 1.46 g/cm3, respectively.

In this research, the effect of different sources of magnesium oxide and the effect of CaO/MgO ratio, as the main oxides that activate the reactions during wall tile firing, on the path of transformations and the formation of useful phases such as Anorthite, Diopside, and Wollastonite, and the reduction of the destructive phase of Gehlenite and free quartz was studied.

Three groups with 12% wt. of calcium carbonate - as the main source of CaO supply - and different weight percentages (5, 7 and 10%) from local soils supplying MgO in Iran (Zanjan talc, Boroujard talc and Abdol-Abad dolomite) were built. After forming with a press, the mixtures were sintered in a fully industrial process and in a fast firing furnace. By means of X-ray diffraction test and with the help of Rietveld refinement method which was carried out in Maud software, the weight percentage of the forming phases of the final microstructure was quantitatively calculated.

In the samples containing talc, with the increase of the weight percentage of talc and the decrease of CaO/MgO ratio, the weight percentage of Anorthite and Gehlenite phase increased and the Diopside phase decreased. Also, the coefficient of thermal expansion and moisture expansion test decreased by decreasing the ratio of CaO/MgO. In samples containing dolomite, increasing the weight percentage of CaO oxide, despite the acceptable weight percentage of MgO oxide, led the tendency of the structure towards the formation of more calcium aluminosilicates such as Anorthite and Gehlenite. The extreme increase of Gehlenite phase (6% wt.) caused a large increase in thermal expansion coefficient (8.35 x 10-6 units/degree Celsius) and moisture expansion percentage (0.12%) in the sample with 10%wt. dolomite.

In this research, at first, glass ceramic with the same composition as 45S5 glass ceramic was synthesized by solid state method from soda lime glass waste. Then, by substituting calcium fluoride instead of calcium oxide with different weight percentages, the bioactivity behavior of these glasses and also their mechanical strength were investigated

Phase analysis of the samples after calcination was done by X-ray diffraction. The bioactivity of the samples was investigated by immersing them in the simulated body solution for different periods of time and then scanning the surface of the samples with a scanning electron microscope to observe and compare the sediments formed. The sediments formed on the surface of the samples were also identified by X-ray diffraction analysis at small angles. After that, the density and compressive strength of the samples after sintering were determined by Archimedes method and pressure test, respectively.

X-ray diffraction diagrams of glass samples subjected to calcination at different temperatures showed the crystalline phases of Na2Ca2Si3O9 and CaNaPO4, which indicates the transformation of the calcined samples into glass-ceramics. X-ray diffraction analysis of the samples with different percentages of calcium fluoride that were calcined at a temperature of 800°C showed the Ca5F(PO4)3 phase in addition to the previous crystalline phases. In fact, with the addition of calcium fluoride to the samples, the fluorapatite phase has been formed.Phase analysis of sediments formed on the surface of the samples after placing them in simulated body fluid determined the phases of fluorapatite Ca5F(PO4)3, hydroxyapatite Ca5(PO4)3 (OH) and calcium ultra-phosphate Ca2P6O17 which have the characteristic of biocompatibility with the body.The results showed that the synthesis of glass ceramics by the solid-state method from waste glass was successful and by substituting calcium fluoride instead of calcium oxide, the bioactive properties and compressive strength of the samples increased.

Due to the outstanding high-temperature mechanical properties, precipitation-hardening nickel-based superalloys are capable of working in high-temperature conditions in the harsh environment. One of the applications of these alloys is the use in the hot part of gas turbines, which can be used as rotor and stator blades. The properties of these alloys after high-temperature (800-950°C) long-term operation have changed dramatically, including oxidation, severe local deformations, creep and fatigue, and microstructure. The mentioned damages can strongly affect the reliability of the operation of these components.  

In this research, damage mechanisms and microstructural properties of GTD-111 superalloy as a precipitation-hardening nickel base superalloy are investigated. Hence, the blade airfoil operated for 75,000 hours was used as the alloy under high-temperature conditions and the root section was used as the unexposed alloy. Characterization of the exposed alloy was carried out by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray energy dispersive spectroscope (EDS). In order to assess the damage mechanism, the radiography X-ray test (RT) and fluorescence penetration inspection (FPI) were used.   

Based on the finite element analysis results, the blade airfoil experienced a high temperature condition about 800-925°C. The non-destructive tests results showed that some damages such as spallation of thermal barrier coating, local deformation, local oxidation, tip rubbing and discoloration. The microstructure observation results demonstrated that there are considerable changes in the microstructure features such as the decomposition of MC carbide, coarsening and spheroidization of primary γ′, dissolution of secondary γ′, and formation of huge deleterious topological closed packed (TCP) phases located in interdendritic regions which profoundly impact its mechanical properties. Based on the results obtained from the transmission electron microscope (TEM), dislocations have been observed in the γ channels and the γ-γ' interface. It is worth mentioning that due to the low stress level, the density of dislocation in the γ′ phase, which can be in the form of SFE and APB, is limited. Microstructural observations indicated severe structural deterioration after 75,000 hours of turbine operation. The main structural degradation that can lead to a sharp decrease in mechanical properties at high temperature and consequently a sharp decrease in reliability is the change in the size and morphology of precipitation hardening phases γ' and the continuity of brittle carbide phases in the grain boundaries of GTD-111 alloy.

Ilmenite is considered the most important source of titanium and its oxide and is usually processed by sulfate, chloride, and smelting processes. In all these processes, incomplete removal of iron combined with titanium is the main problem. In order to improve iron removal, pre-processing of ilmenite by carbothermic reduction processes is a solution used in the industry. Considering the technical and environmental problems of carbothermic, replacing coke by hydrogen, is a new method that brings significant advantages in the subsequent separation processes.

In this research, Kahnuj ilmenite concentrate is first characterized through physical, chemical, and structural analysis techniques. Gas reduction of the ilmenite pellets using pure hydrogen gas was performed, and then reduction products subjected to further characterization. The reduction degree was calculated based on the weight loss after the reduction process. Samples were characterized using optical microscopy, electron microscopy, X-ray diffraction analysis, and energy-dispersive X-ray spectroscopy.

The Kahnuj ilmenite concentrate is composed of the FeTiO3 as the main phase, hematite, and a partial sphene phase within the ilmenite grains. Mn and Mg found in the chemical analysis of the concentrate led to incomplete separation of iron oxides in ilmenite.In this research, a maximum reduction degree of 76% is achievable at a reduction temperature of 1100 °C. With an increase in the reduction temperature, metallic iron diffused out the ilmenite structure and accumulated around the particles. With an increase in the reduction time, the aggregation of the pseudobrookite phase, occurred in the center of the ilmenite particles.

Water flooding is one of the methods of enhanced oil recovery in which formation water is injected into the oil reservoir. Calcium carbonate deposition is one of the challenges in the field of water flooding and oil production. It leads to a reduction in oil production due to deposition on reservoir rocks and the path of oil movement.

The use of chemical additives, especially hydrophilic polymers, has been widely studied to prevent calcium carbonate deposition. In this study, a ternary hydrophilic polymer was used to investigate the inhibitory effect on calcium carbonate scale in the formation water of an Iranian oil reservoir. The optimal concentration of this polymer, considering its inhibitory performance coefficient in formation water, was determined to be 800 milligrams per liter based on the calcium ion concentration. This optimal concentration was then used for subsequent experiments. Temperature studies on the inhibitory performance of this polymer showed that at reservoir temperature (75 degrees Celsius), 800 milligrams/lit of this ternary polymer demonstrated good performance. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were used to study the physical mechanisms involved in preventing calcium carbonate deposition.

SEM results showed that calcium carbonate crystals, in the form of stable calcite with a regular uniform structure before the presence of the inhibitor, became heterogeneous and smaller in size after adding the polymer, disrupting their structure. On the other hand, XRD analysis indicated that adding this ternary polymer could significantly inhibit the growth of calcium carbonate crystals and prevent the transformation of vaterite into calcite. Additionally, aragonite crystals are dispersed in the water and washed away by the water flow.