Advanced Materials Research Vol. 829

Abstract: The properties of Ni-P composite coatings are related to the microstructure evolution by co-deposition of phosphorus, particle incorporation and subsequent annealing. This study focuses primarily on the effect of phosphorus content in the electrolyte on the incorporation of sub-micron diamond particles in order to understand the complex influence of Ni/Ni₃P crystallization and particle embedment on Martens hardness.

Abstract: There is a growing interest for investigation of free-volume type defects in SPD-processed ultrafine-grained materials. In the present work, excess free volume in pure Fe prepared by shaped rolling is studied by high-resolution differential dilatometer as well as Archimedes method. The results show the formation of excess volume with increasing deformation strain. The volume fraction of free volume detected by dilatometer is below the evaluation of Archimedes method maybe because of the existence of void in the deformed metal. Microstructural study by field emission type scanning electron microscope confirms the presence of voids.

Abstract: In the present study, NiAl nanostructure intermetallic produced by mechanical alloying process was investigated. Pure Al and Ni powders with the ratio of 50 at.% were mixed and milled in a planetary ball mill for different milling times in the range of 8 to 128 hours. The milled powder particles were investigated by XRD technique and scanning electron microscope. Williamson-Hall equation was employed to calculate lattice strains and crystallite sizes. The results showed that NiAl intermetallic formed after some milling times. The observation of flame or explosion in the vial just after the uncovering of it, in some cases, showed intense interaction between Al and Ni atoms after homogenization during milling. After longer milling time no flame and explosion was observed while NiAl intermetallics had been formed. Therefore, NiAl intermetallics were formed under different conditions with different structures and properties. The crystal sizes of obtained NiAl particles were less than 10 nm. The hardness changes in particles and also their internal strains were affected by milling operation at early stages of milling but they were mainly affected by transformation process of (Ni,Al) solid solution into intermetallic NiAl at longer milling times.

Abstract: In the present work, at first, nanoTiO₂ particles in anatase form were effectively surface modified via reacting with NCO groups of 4,4-methylenediphenyl disocyanate (MDI). Secondly, a solution of azobisisobutyronitrile (AIBN) (0.1 g) in inhibitor-free styrene (10 g) was poured into a 150 mL flask containing poly (vinyl alcohol) (PVA) suspending agent (0.1 g) in deionized water (60 mL) under N₂ flow, while stirring. The reaction mixture was then heated to 80 °C, and stirred for another 1 h. Next, it was divided to two portions; one for the synthesis of pure PS, and the other for the synthesis of PS/TiO₂ nanocomposites. Each aqueous portion was individually mixed with dichloromethane in a separating funnel. For PS/TiO₂ nanocomposites, the organic phase was charged with nanoTiO₂ particles (MDI-treated and/or untreated) (0.05 g), and then fully homogenized using ultrasonic homogenizer. Methanol non solvent was eventually used to precipitate the products. All samples involving pure PS, PS/surface modified TiO₂ nanocomposite, and PS/surface unmodified TiO₂ nanocomposite were thoroughly washed, filtered, and dried in vacuum at 50 °C for 12 h. From SEM images a core-shell relation could be clearly detected between the nanoTiO₂ particles and PS matrix. Meanwhile, the surface modified TiO₂ was dispersed into the PS matrix with better homogeneity compared to that of unmodified one. Undoubtedly, beside the surface modification factor, PVA suspending agent as an effective nanosized particle stabilizer, too, played a basic role in this high homogeneity. Also, FT-IR and XRD analyses led to promising results.

Abstract: nano Al₂O₃ powders have been synthesized by a solution combustion method (SCS) using glycine as a fuel and ammonium nitrate as an extra oxidizer. The effectiveness and influence of oxidizer/fuel ratio and the water contetnt of the solution on the crystallite size and characteristics of alumina particles was investigated respectively. As-synthesized powders were γ-alumina due to calcination of samples at 900 ^̊C for 2 hours. Also, Results demonstrated that the alumina nanoparticles obtained from φ=1.8 had crystallite sizes around 65 nm which is less than other values of φ, due to evolution of larg amounts of gases which inhibits grain growth and less adiabatic temperature during the process. Also, it was concluded that the more the water content of the solution, the less the crystallinity and crystallite sizes of the products as a result of decreased adiacatic temperature.

Abstract: Recently, friction stir processing (FSP) was developed as an effective method to modify microstructural and mechanical properties of materials. During process, a rotating tool is inserted in a plate, providing frictional heating and mechanical mixing. In this investigation, the effect of annealing heat treatment on the microstructure characteristics of the nugget zone was investigated during friction stirs processing (FSP) of the pure copper. Plate with 4 mm thickness was friction stir processed at constant traverse speed of 45 mm/min and tool rotation speed of 700 rpm. Samples were processed in various annealing conditions. Results showed that by increasing the annealing duration from 45 to 180 minutes at annealing temperatures of 600°C and 800°C, the grain size and the hardness value of samples significantly decreased. At annealing temperature of 1000°C samples were exposed to extra heat, grains started to coarsen and hardness decreased. Ultrafine-grained microstructure in FSP samples was achieved using annealing heat treatment at annealing temperature of 600°C.

Abstract: Bismuth oxide, due to its low melting point was selected as filler for joining alumina to alumina using Transient Liquid Phase (TLP) method. For this purpose a thin layer of bismuth oxide was placed as an interlayer between the ceramic bodies. To study the effect of time and temperature on the mechanical properties of the joined samples, the joining tests were carried out in 900, 1000 and 1100°C for various times. The mechanical properties of the joined samples were measured using shear testing method. To investigate the microstructure of the joining area, the cross section ofthe joints were studied using scanning electron microscope (SEM) and X-ray diffraction method. The results showed that longer joining times results in higher mechanical properties of the joints. The highest joint strength of about 80 MPa was obtained for the sample joined in 900°C for 10hour.

Abstract: SnS₂ nanoparticles were prepared by heat treatment of SnS nanoparticles at 300 °C under N₂ atmosphere for 1hour. SnS nanoparticles have been synthesized by chemical precipitation method. As synthesized SnS nanoparticles, for determining the optimal temperature, were heated at various temperatures; 100, 150, 200, 250 and 300 °C N₂ atmosphere for 1hour. The products are characterized by X-ray diffraction (XRD) , ultraviolet visible (UV-vis) absorbance spectra and photoluminescence (PL). XRD and optical absorption studies show an increase in particle size with increasing heat treatment temperature from 100 to 200 °C . However, a large decrease in the nanoparticle size along with transforming from SnS to SnS2 is observed at 300 °C.In addition, the optical properties of al samples , including both UV-vis absorption and emission spectra showed a blue shift as the particles size decreased.

Abstract: The major problem associated with application of aluminum titanate is decomposition to Al₂O₃ and TiO₂ oxides during heat treatment (in the range of 900-1280 °C ). In the present study, a stable compound of magnesium aluminum titanate ceramics (Mg_0.6Al_0.8Ti_1.6O₅) has been successfully synthesized with a straightforward non hydrolytic sol-gel process using inorganic metal compound. The raw materials were MgCl₂.2H₂O, AlCl₃, TiCl₄, and citric acid that were dissolved in ethanol. Prepared gel was dried at 120 °C and calcined at various temperatures using microwave heating. The results of X-ray Diffraction (XRD) and Simultaneous Thermal Analysis (STA) demonstrate that the direct crystallization of mono-phase magnesium aluminum titanate from fluffy precursor at a temperature below aluminum titanate decomposition temperature range is feasible. The formation of crystalline Mg_0.6Al_0.8Ti_1.6O₅ phase starts at about 400 °C. Also, Field Emission Scanning Electron Microscopy (FESEM) study and BrunauerEmmettTeller (BET) analysis represent the nanometric size of the mesoporous particles. The average particle size and specific surface area of powders were lower than 20 nm and more than 98 m²g^-1, respectively, at low temperatures.

Abstract: Copper oxide nanoparticles have been received attraction due to their unique properties and potential future applications. In present work nanostructure Copper (II) oxide (CuO) spherical nanoparticle synthesized by solution combustion method and the influence of different fuel and condition on the properties of CuO particle was investigated. Crystalline phase and size indicated by applying XRD and particle size distribution studied further using DLS. Scanning electron microscopy (SEM) was used for morphological study and EDAX analysis shows composition of CuO particles. Nanostructure of copper (II) oxide particle studied further by Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) applied for detail study on crystalline structure of particles.