In this work, a simple, fast and efficient route is presented for the metal (such as Pt, Rh, etc.) nanocrystal synthesis and deposition on carbon nanotubes (CNTs) in ionic liquids (ILs) via microwave heating. In this method, inorganic salts (such as H2PtCl6.4H2O, RhCl3.2H2O, etc.) dissolved in ILs, 1,1,3,3-tetramethylguanidinium trifluoroacetate or 1,1,3,3-tetramethylguanidinium lactate, were reduced to metal nanoparticles by glycol with the aid of microwave heating, and the produced metal nanoparticles could be decorated on CNTs in the presence of CNTs in ILs. The resulting nanomaterials were characterized by means of transmission electron microscopy and X-ray diffraction. It was demonstrated that the homogeneously dispersed Pt nanocrystals with the size of 2-3 nm were obtained using H2PtCl6.4H2O as precursor, and they deposited on CNTs with the similar size when CNTs was present in ILs. This technique also can be extended to fabricate other noble metal nanocrystals (including Rh, Au, etc.) and corresponding CNT composites.
Annealing characteristics of a nanostructured copper alloy processed by accumulative roll-bonding (ARB) were studied. A nano-grained Cu-Fe-P alloy processed by 8 cycles of the ARB was annealed at various temperatures ranging from 100 to 400 degrees C for 0.6 ks. The sample still showed an ultrafine grained (UFG) structure up to 250 degrees C, however above 300 degrees C it began to replace by equiaxed and coarse grains due to an occurrence of the conventional static recrystallization. The hardness of the annealed copper decreased largely above 300 degrees C. These annealing characteristics of the UFG copper alloy were compared to those of a high purity copper.
The effect of mechanical alloying (MA) on the formation of MnSi1.73 thermoelectric compound was investigated. Due to the observed larger loss of Si relative to Mn during MA, the starting composition of Mn-Si was modified to MnSi1.83 and MnSi1.88. Sintering was performed in a spark plasma sintering (SPS) machine up to 600-800 degrees C under 50 MPa. The single phase MnSi1.73 has been obtained by MA of MnSi1.88 mixture powders for 200 h. It is also found that the grain size of MnSi1.73 compound analyzed by Hall plot method is reduced to 40 nm after 200 h of milling. Additionally, X-ray diffraction data shows that the SPS compact from 200 h MA powders consolidated at 600 degrees C consists of only nanocrystalline MnSi1.73 compound with a grain size of 90 nm.
The mechanical alloying process has been studied on the Cu-Mo system, the atomic pair of which is characterized by a positive heat of mixing of +19 kJ/mol. The EXAFS and X-ray diffraction measurements have been employed to analyze the structural changes taking place during milling. Two phases mixture of nanocrystalline fcc-Cu and bcc-Mo with a grain size of 10 nm has been formed by MA of Cu30Mo70 powders for 200 hours. The structural analysis based on the EXAFS spectra revealed that bcc and fcc crystal structure clearly do not change around Mo and Cu atoms up to 200 h of milling, respectively. Studies of the thermodynamical considerations by DSC analyses confirmed that the alloying does not occur even after 200 hours of MA in Cu-Mo system.
A mixture of elemental Cr-Si powders has been subjected to mechanical alloying (MA) at room temperature to prepare CrSi2 thermoelectric compound.The MA powders were sintered at 800-1000 °C Cunder 60 MPa using spark plasma sintering (SPS) technique. Due to the observed larger loss of Si relative Cr during ball milling, the starting composition was modified to Cr30Si70, Cr31.5Si68.5 and Cr33Si67 to get a single phase of CrSi2 compound. The single phase CrSi2 has been obtained by MA of Cr31.5Si68.5 mixture powders for 70 h and subsequently sintered at 1000 °C. X-ray diffraction data shows that the SPS compact sintered at 1000 °C consists of only nanocrystalline CrSi2 compound with a grain size of 250 nm. The value of Seebeck coefficient of CrSi2 compound increases with temperature and reaches maximum value of 245 µV/K at 300 °C.
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