Hu Zheng-Fei; Yao Chen; Mo Fan
Abstract
Metallurgical bonding aluminum foam sandwich (AFS) was fabricated by specially designed method of solder pre-coating via hot-dip and heat-press assisted with vibration. Peeling test and three-point bending test were performed to investigate the joints strength and flexural strength of the AFS. The results ...
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Metallurgical bonding aluminum foam sandwich (AFS) was fabricated by specially designed method of solder pre-coating via hot-dip and heat-press assisted with vibration. Peeling test and three-point bending test were performed to investigate the joints strength and flexural strength of the AFS. The results show that the joints have steady mechanical properties, and the joint fabricated with ultrasonic vibration has much higher peeling moment and flexural strength than that prepared only by hot-press. Microstructure observations of the joints indicate a good metallurgical bonding between Al face sheet and foam core was achieved. The seam of AFS fabricated by hot-press assisted with ultrasonic vibration looks more compact and the bonding interface fused together firmly. The bonding faces of aluminum sheet and foam core are obviously corroded by melt ZnAl alloy and an obvious interdiffusion took placed during hot-dip process and hot-press, so the chemical compositions in the diffusion transitional zone are continuous. However the seam of the AFS fabricated only by hot-press has visible macro-defects, and the worse is its bonding interface fused together partially, which severely degrades the bonding strength.
Giorgos Papadimitropoulos; Maria Vasilopoulou; Nikos Vourdas; Dimitris N. Kouvatsos; Kostas Giannakopoulos; Stella Kennou; Dimitris Davazoglou
Abstract
Tantalum pentoxide films were deposited on Si substrates at room temperature, by heating metallic filaments at temperatures below 600 o C, at a pressure of 1 Torr in O2 environment. This deposition method can be applied for all metallic oxides having higher vapor pressure than the corresponding metal. ...
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Tantalum pentoxide films were deposited on Si substrates at room temperature, by heating metallic filaments at temperatures below 600 o C, at a pressure of 1 Torr in O2 environment. This deposition method can be applied for all metallic oxides having higher vapor pressure than the corresponding metal. These (hwTa2O5) films were composed by amorphous material (as revealed by XRD measurements) and were found to be highly transparent within the range 350-1000 nm. Spectroscopic ellipsometry measurements have shown that the real part of the refractive index (n) of hwTa2O5 films depends on the deposition time and has a value below 1.5. As shown by scanning electron microscopy (TEM) measurements, these grains were composed by others with dimensions near 5 nm and with voids between them. The above microscopy measurements explain the high porosity of hwTa2O5 films. Moreover, hwTa2O5 films were also characterized by XPS and UPS measurements and the stoichiometric composition of the deposited films was determined.
T. S. K. Raunija; R. K. Gautam; S.C. Sharma; A. Verma
Abstract
The main objective of the work was to rapidly prepare high density short carbon fiber reinforced randomly oriented C/C composite by coupling the processes. The C/C composite was fabricated by coupling two processes. In primary high pressure HP method, medium density C/C composite was prepared by mixing ...
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The main objective of the work was to rapidly prepare high density short carbon fiber reinforced randomly oriented C/C composite by coupling the processes. The C/C composite was fabricated by coupling two processes. In primary high pressure HP method, medium density C/C composite was prepared by mixing the exfoliated carbon fibers and PMP with distilled water; moulding of the slurry; drying of the green cake; hot-pressing of the preform and finally carbonizing the compact. In secondary low pressure ITC method, the medium density C/C composite was densified by SMP in three repeated cycles to obtain high density. The composite was characterized for microstructure, density, porosity, hardness, flexural strength, compressive strength and permeability. The results showed that the coupling of primary method with secondary method resulted in fine microstructure, high density (1.70 g/cm 3 ), excellent mechanical properties (flexural strength 77 MPa and compressive strength 161 MPa) and reduced porosity & permeability.
Preetam Singh; K. M. K. Srivatsa; Sourav Das
Abstract
Polycrystalline Si (Poly-Si) film with highly crystalline nature, and having most of the grains in the range of 50-100 µm has been grown over biaxially textured Ni-W substrate by Hot-wire chemical vapor deposition technique, using a single buffer layer of CeO2 thin film. This result has been achieved ...
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Polycrystalline Si (Poly-Si) film with highly crystalline nature, and having most of the grains in the range of 50-100 µm has been grown over biaxially textured Ni-W substrate by Hot-wire chemical vapor deposition technique, using a single buffer layer of CeO2 thin film. This result has been achieved for the SiH4 source gas diluted to 95% with added H2 gas, and for the substrate temperature of 840±10oC and a deposition pressure of 40 mTorr. XRD analysis shows that the Poly-Si films have grown with (111) and (200) orientations. Raman studies reveal that a crystalline volume fraction of 95.3% has been achieved. The imaginary part of pseudo dielectric function, <ε2>, as extracted from ellipsometric data, shows two prominent shoulders at energy positions 3.4 eV and 4.2 eV corresponding to the optical absorption of crystalline Si, indicating a high crystallinity of the Poly-Si film. SEM micrograph shows that the grown Poly-Si film is following the morphology and grain size as that of biaxially textured Ni-W substrate. SIMS analysis of the total multilayer structure shows a formation of very sharp interfaces, with no diffusion between Si and Ni, indicating that a single buffer layer of CeO2 is sufficient to avoid the formation of nickel silicide while growing Si over Ni substrate. Thus, these results are very encouraging for the fabrication of Poly-Si film based solar cells with increased efficiency by minimizing the undesired recombination of charge carriers at grain boundaries.
Ronald Machaka; Bonex W. Mwakikunga; Elayaperumal Manikandan; Trevor E. Derry; Iakovos Sigalas
Abstract
Despite hot pressing being the most popular method of consolidating B6O powder, the Raman spectrum of polycrystalline hot-pressed B6O was until now poorly understood. Yet, recent reports have contributed to the understanding of only high-pressure and high-temperature sintered B6O. Using an automated ...
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Despite hot pressing being the most popular method of consolidating B6O powder, the Raman spectrum of polycrystalline hot-pressed B6O was until now poorly understood. Yet, recent reports have contributed to the understanding of only high-pressure and high-temperature sintered B6O. Using an automated method for subtraction of the fluorescence background from Raman measurements, the first- and second-order Raman spectra of B6O and their dependence on the wavelength of the excitation line from a green Argon ion (Ar + ) laser are reported. Our results confirm the existence of observable highly resolved first- and second-order Raman modes measured at ambient conditions using a green Ar + ion laser as the source of excitation. We also extend our study to present a comparative analysis of our recovered first-order Raman spectra and previously reported first-order Raman spectra other α-rhombohedral boron type based ultra-hard boron-rich ceramic materials. The results show an overall good agreement.
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