Papers by Keyword: Mechanical Activation (MA)

Abstract: The iron-based composite ceramic powder Fe-WC is produced by ball milling with synthetic tungsten mine and graphite. The process is accomplished through mechanical activation and reductive diffusion of the reactant powders during the milling process. The products are analyzed by means of XRD, DTA and EPMA. The results approved that the reaction does not carry through completely when the milling time is less than 8h. However, the composite powder of Fe and WC is gained by annealing from powders milled under 180V of the milling machine. The apparent activation energy of the reductive reaction is gradually decreased with the extending of milling time by mechanical activation.

Abstract: Powder of Ti-46at%Al alloy was synthesized through mechanical activation (MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using spark plasma sintering (SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti₃Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Abstract: Powder of Ti-46at%Al alloy was synthesized through mechanical activation (MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using spark plasma sintering (SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti₃Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Abstract: Powder of Ti-46at%Al alloy was synthesized through mechanical activation (MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using spark plasma sintering (SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti₃Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Abstract: Powder of Ti-46at%Al alloy was synthesized through mechanical activation (MA) and then sintered and concurrently consolidated in a short sintering time of 900 s by using spark plasma sintering (SPS) process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti3Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering (MASPS) within a very short period of time.

Abstract: This study was concerned with the effects of mechanical activation (MA) on structural characterization for neutral leach residue of zinc calcine (NLR) and kinetics of indium extraction from NLR in sulphuric acid. The X-ray diffraction (XRD) analysis showed that MA caused the decrease in crystalline phase and increase in lattice distortion. The activation time, reaction temperature and H₂SO₄ concentration had positive effect on indium extraction from NLR. The activation energies of the unactivated, milled for 30 and 60 min NLR samples calculated for indium extraction were 39.3, 32.1, and 30.4 kJ/mol, respectively, which indicated that MA increased the leaching kinetics of indium extraction from NLR. The empirical orders of the unactivated, activated for 30 and 60 min samples for extracting indium with respect to H₂SO₄ concentration were 0.52, 0.51, and 0.51, respectively.

Abstract: A lower-temperature and cost-efficient way is developed to produce Fe-TiC powders. Fe-TiC is produced by means of mechanical activation -reductive diffusion with ilmenite and graphite. The feasibility of this method and the kinetics of the carbothermic reduction are studied with both natural ilmenite and synthetic ilmenite, respectively. The result approved that Fe-TiC powder could be produced by this new technique; moreover, the particles were prominently diminished in size and activated after ball milling. No obvious reactions were detected when ball milling time was less than 8h by EPMA and XRD; however, the mixed powder of Fe and TiC was obtained after annealing for different time intervals. The kinetic study showed that the apparent activation energy of the reductive reaction decreased gradually with milling time due to mechanical activation, but this effect weakened after ball milling for 6h. As ascertained experimentally, the optimum ball milling time was between 4h and 6h.

Abstract: In this research carbothermal reduction of mechanical activated hematite (Fe2O3), anatase (TiO2) and graphite (C) mixture was investigated. Mixture of raw materials with composition of Fe-20vol%TiC was mechanically activated in a planetary ball mill with different milling time (0h-60h) in argon atmosphere. X-ray diffraction (XRD) results showed the intensity of Fe2O3 reduced with milling time. The activated powders were pressed using cold pressing under a constant pressure (100MPa) and heat treated at 1100°C for sintering in a vacuum furnace. The increase in milling time resulted in the formation of iron (Fe) and titanium carbide (TiC) phase as confirmed by XRD result.

Abstract: Using Mechanical Activation it is possible to obtain small grain size and good homogeneity in a ceramic piece. For ZnO varistor devices Mechanical Activation appears to be a good fabrication technique, since good homogeneity and small grain sizes are advantageous microstructural features. The typical formulation is composed by ZnO, Bi2O3, Sb2O3, CoO, MnO2 and Cr2O3 as raw materials, and during sintering, several dissolutions and reactions to form pyrochlore and spinel phases occur. When Mechanical Activation is applied to the entire formulation, it is difficult to know what processes are being mechanically activated due to the complexity of the system. The aim of the present work was to clarify how the mechanical activation is taking place in a typical ZnO varistor formulation. The methodology consisted in the formation of all possible combinations of two out of the five oxides above mentioned and to apply mechanical activation on the mixture of each pair of powders. The results showed that systems containing Bi2O3 are prone to react during mechanical activation. Also, reduction reactions were observed in MnO2. In addition, the powder mixture corresponding to the whole formulation was milled in a planetary mill, pressed and sintered, and varistor devices were fabricated. Improvement in the nonlinearity coefficient and breakdown voltage was observed.

Abstract: The high-energy milling uses the mechanical energy to activate chemical reactions by developing structural changes in the powder particles. High-energy milling with an acceleration of 28g was applied for the mechanical activation of the aluminium and silicon nitrides mixture with yttria additive. The activated powders showed the significant damage of the crystal structure and limited formation of a solid solution. Sintering of the activated precursor demonstrated higher ability for densification and started at 300 °C lower temperature in comparison to the standard mixture. The phase evolution during sintering was dependent on the starting composition and degree of powder activation.