Papers by Keyword: SEM

Abstract: In the present investigation Aluminum matrix composites (AMMCs), Al7075 Alloy as matrix metal and Al₂O₃/SiC particles (2-8%) with an average particulate size of 20, 50 nm as strengthened material have been processed by the stir casting method. For the counter surface wear testing, a computerized pin on a wear tester was used as EN31 (58-60 HRC) steel disc and composite pin. The wear rate for the matrix metal and composites in terms of weight loss per unit sliding distance, friction coefficient, and volume loss were achieved. The composite results show better resistance to wear than matrix metal. SEM was used to investigate the microstructural characterization of worn surfaces. Sample weight loss was calculated and the change in cumulative wear loss at a sliding distance was uniform both for metal matrix as well as for composites. The wear speed for composites was also noted to be small compared to the metal matrix. In addition, experiments have shown that, with the increasing weight fraction of Al₂O₃/SiC and the coefficient of friction increases with increasing sliding velocity and weight fraction of Al₂O₃/SiC, the wear rate reduces. The wear characteristics (wear rate, coefficient of friction and wear loss) were better than those of other composites and the matrix metal with 6wt% Al₂O₃/SiC composites.

Abstract: The paper presents the results of the study of fragments of the electric engine rotor shafts of the air-cooled units in order to establish the causes of its destruction. Chemical composition, type of the fracture, macro-and microstructure, as well as the mechanical properties of the metal are studied. Structural and technological factors contributed to the destruction are identified.

Abstract: To date, dye-sensitized solar cells (DSSCs) based on TiO₂ nanoparticles have been widely investigated due to their high conversion efficiency. However, constructing TiO₂ into a structure of nanorods with a high aspect ratio is difficult to be achieved. On the other hand, nanorod/nanowire arrays may provide some advantages, such as an efficient pathway for electron transport and a larger surface area for dye absorption. ZnO is one kind of metal oxides that can be formed into nanorods easily with various methods. Here, we reported our works on the preparation of ZnO nanorods and investigate its DSSC performance. We found that the cell performance was very affected by the diameter of the nanorods, which may then indicate that charge transfer and charge extraction processes are more effective in the cell with a smaller nanorod diameter.

Abstract: In this paper, the specific wear rate (SWR) and the coefficient of friction (CoF) of steel embedded glass/epoxy hybrid composites were examined and compared. Experiments were carried on the pin-on-disc machine on different types of composite materials like plain composite (steel volume 0%) and hybrid composites (steel volume 5% and 10%) pressed against a rotating steel disc (EN 31). Composites were fabricated using the hand-lay-up method. The volume percentage of steel pin/pipe varied from 0 to 10% and glass fiber from 50 to 60%, while the percentage of epoxy was kept 40% stable. The experiments were carried out on a group of samples for duration 20 minutes for different loads of 70N, 80N, 90N, 100N, and 110N with a varying sliding distance of 1000 m, 1250 m, 1500 m, 1750 m, and 2000 m. The results show that the SWR and CoF vary with different load and sliding distance. In general, CoF rises for some time of rubbing, and then it remains constant for the rest of the testing time. The results obtained show that the SWR and CoF increase with increasing sliding distance and load for all the composites. However, SWR and CoF decrease as an increase in the volume percentage of steel. An SWR of hybrid composite is observed to be reduced by 28.02% and 45.98% with an increasing percentage of steel by 5% and 10% respectively. CoF of hybrid composite is observed to be reduced by 14.11% and 24.02% with an increasing percentage of steel by 5% and 10% respectively. At last, the worn surfaces of the hybrid composites were studied through a Scanning Electron Microscope (SEM). Shallow and fine grooves appeared on the worn surfaces of hybrid composites at low loads and cracks were found in large quantities at high load which increased weight loss.

Abstract: Corrosion behavior of three carbon steels with increasing galvanized coating thickness of 5.6, 8.4 and 19.2 μm named as T₁, T₂ and T₃, respectively, was studied by immersion test, potentiodynamic polarization and electrochemical impedance spectroscopy in freely aerated 3.5% NaCl solution. The major phase in the corrosion product of all the samples after immersion test was found to be zincite, as determined by X-Ray Diffraction and Fourier Transform Infrared Spectroscopy techniques. The corrosion product on sample T₁was well adhered and was compact in most regions. Samples T₂ and T₃ showed porous and non-adherent growth of corrosion product. Corrosion rates were found to increase with increasing coating thickness. The impedance provided by the coating as well as the substrate was the highest for the sample with thinnest coating (T₁). The early exposure of the underlying steel in sample T₁ resulted in higher corrosion resistance, which was probably due to the combined effect of zinc corrosion products and Fe-Zn alloy layer. Higher amount of protective γ-FeOOH as well as compact corrosion product could have also improved the corrosion resistance of sample T₁. Although the average uniform corrosion resistance was higher for T₁, the localized pitting corrosion was also observed, probably due to the thin galvanized layer.

Abstract: Aluminium alloys are having lightweight, high strength, good corrosive resistance, and toughness. In this paper, A7075/B4C/SiC Hybrid Composites fabricated with different wt. % of reinforcement materials by using stir and squeeze casting process. The SEM Microstructure have shown that uniform distribution of reinforcement particles in the A7075 matrix reinforced with 1 % wt. % B4C and 1 % wt. % SiC. The Mechanical properties of A7075/B4C/SiC Hybrid Composites were studied Composite A7075/B4C/SiC reinforced with 1 % wt. B4C and 1 % wt. SiC has shown more compressive and tensile strength compared to base alloy. The compressive strength of the composite increased 39.73 % and the tensile strength is increased 36.67 % compared to base alloy. From the dry sliding wear studies, the Composite with 1 B4C wt. % have shown less weight loss and coefficient of friction at all conditions due to the uniform distribution of the micro-particles within the matrix surfaces. Worn surface morphology has revealed that severe wear of A7075 base alloy became mild wear by preparing composite with 1 % wt. SiC, 0.5 wt. % B4C and then mild wear became less wear with shallow grooves by increasing reinforcement weight percentage of B4C from 0.5 to 1.

Abstract: The material of FA Nagan Raya (FANR) is the alternative base material in geopolymer generated from the power plantation, Nagan Raya, Acheh, Indonesia. It was recorded that the volume of FANR material is abundant in the landfill so that it impacted on the environment. It was due to there was no investigation to evaluate the waste of FANR to be a material in the concrete. This study interested to evaluate the material of FANR to be a base material in the geopolymer referring to the analyses of XRF, XRD, SEM, FTIR, and TGA. The results showed that the material of FANR was rich in Si and Al content that contributed to the mechanical properties. While the chemical content of Ca contributed to the setting time in the geopolymer system. The XRD analysis showed that the FANR particle and binder of a geopolymer were categorized as the crystalline material. It was supported by the FTIR analysis that showed the good chemical bond of Si-O-Si and Si-O-Al. The SEM analysis showed that the particle shape of FANR was a sphere with the misty surface. This particle shape caused the absorption of a more alkaline solution to maintain the workability in the fresh geopolymer. It was supported by the analysis of TGA that showed more water in the FANR geopolymer binder. It concluded that the material of FANR is eligible to be used as the base material in the geopolymer system.

Abstract: Dolomite is one of the commonest minerals that abound in the formation of a number of geological conditions. And it is found in abundance in eastern Algeria, especially Ain Mlila-Wilaya of Oum El Bouaghi-Algeria. The analyzed sample of raw dolomite has been by various physical-chemical techniques. The constituents of these carbonates are Ca, Mg, C, O, Al, Si, Fe, Ba, F, and Sr, analysis by XRD, and Raman, show that in addition to CaMg(CO₃)₂, we may have calcium carbonate. The Photoluminescence analysis characterizes the intrinsic and extrinsic defects of this carbonate. Differential thermal analysis reveals the different transformations of this mineral during heating. Indeed several stages including the elimination of water, the departure of CO₂, the formation of MgO, and finally the formation of CaO.

Abstract: Fe-10wt% La (OH)₃ composite powders have been fabricated by ball milling, under argon atmosphere for milling periods of 0, 5 and 10 h, respectively. Changes in structural, morphological, thermal and magnetic properties of the powders during mechanical alloying and during subsequent annealing have been examined by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM). XRD results: showed the formation of new phases (Fe and LaFeO3 perovskite) created through the ball milling. The results showed that the crystalline size of ball milled powders decreased with increasing the milling time. In fact, after 10 h of ball milling, La (OH)₃ changes from nanostructure in amorphous structure. The magnetic measurements display a distinct saturation magnetization and coercivity.

Abstract: This work focuses on investigating the behavior of micro and nanoFe₂O₃ in concrete through the study of microscopy, compressive strength and flexural strength. Seven mixes of concrete are prepared. Three of which include micro Fe₂O₃ comprising 1%, 3% and 5% as partial substitutions of cement weight and the other three mixes containing 1%, 3% and 5% nanoFe₂O₃ as a partial substitutions of cement weight, as well as the reference mix. SEM study exhibits that the microstructure of sample produced with micro Fe₂O₃ show more uniformity and dense compared with reference sample. However, existence of micro cracks in the microstructure in mixes with micro Fe₂O₃ is clear especially with increasing micro Fe₂O₃ content to 3% and 5%. In mixes with nanoFe₂O₃, the new shapes of needle like crystals and flower like crystals can be distinguished. The presence of these types of crystals in thrives amount approve that nanoFe₂O₃ producing new phases of gel. Hence, the microstructure of samples is condensed, and with the increasing of nanoFe₂O₃ content the microstructure is completely compacted. The results of compressive strength and flexural strength showed that the mechanical properties are related to microstructure properties. When micro Fe₂O₃ is used, the mechanical properties drop obviously. While, the mechanical properties are improved in mixes containing nanoparticles in comparison with the control mix.