Milled Powder Mixture Research Articles

Microstructure and properties of NiAl/TiC composite synthesized by spark plasma sintering of mechanically activated elemental powders

In this study, NiAl/TiC0.95 composite was synthesized by reactive spark plasma sintering of mechanically activated elemental powders. The microstructure and properties of activated powders and sintered samples were evaluated. The elemental powders were milled after different milling times and as-mixed and 10 h milled powder mixtures were sintered by the reactive spark plasma sintering method. The phase and the microstructure changes were evaluated by x-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy, respectively. The XRD pattern of 0 h milled powder after sintering showed that Ni3Al, Ni2Al3 beside NiAl and TiC0.75 formed. While after the sintering of 10 h mechanically activated powder, the Ni3Al and Ni2Al3 were eliminated and NiAl remained with TiC0.95. The nanoindentation result of the SPSed sample showed a hardness of 12.2 ± 0.1 GPa with an elastic modulus of 25.0 ± 0.5 GPa.

Effects of Mg and MgO Nanoparticles on Microstructural and Mechanical Properties of Aluminum Matrix Composite Prepared via Mechanical Alloying

Aluminum-based composites reinforced with ceramic particles have been used for many applications because of their high hardness, good wear resistance, low weight, and low thermal expansion coefficient. The Al-MgO/Mg composite was prepared in the present study. The effects of milling time and amounts of initial Mg and MgO were studied on the properties of the composite. The milled powder mixtures were subsequently analyzed by the XRD and SEM tests. Crystal sizes and internal strains were calculated using XRD data and the Williamson-Hall equation. The hardness of samples was measured by the Vickers method. The results showed that the lattice parameter significantly increased by increasing the amount of Mg. During the milling, the crystallite size, and simultaneously internal strain and hardness increased by increasing amounts of Mg and MgO. The results also showed that the effects of Mg on the composite properties were higher than MgO particles.

Microstructure and property relationship between Al-4.5Cu alloy and Al-4.5Cu-Al2O3 composite developed by mechanical alloying

The present work aims to fabricate an alloy (Al-4.5Cu) and a composite (Al-4.5Cu-Al 2 O 3 ) with the help of the mechanical alloying method. As compared to the high-temperature melting and casting process, mechanical alloying is a solid-state synthesis process, which requires low temperature for the synthesis of alloy and composite through powder metallurgy route. A high energy planetary ball mill mechanically alloy the Al, Cu, and Al 2 O 3 powders for 10 h with 200 revolutions per minute to milled the alloy and composite powder mixture. Then the milled powder mixtures are compacted in a single punch die compaction machine and then sintered at 550 and 660 °C for 1hr. XRD analysis of the sintered alloy and composite predicts the formation of a new phase, i.e., CuAl 2 . A comparative study of density, hardness, and compressive strength values of the alloy with the composite depicts that the un-sintered and sintered composite have better properties (density, hardness, and compressive strength) due to the presence of Al 2 O 3 and CuAl 2 . With increasing the sintering temperature from 550 to 660 °C, the properties further enhanced for both the alloy and composite.

Synthesis of Ni-Cr-B-Si-Fe-based interlayer alloy for transient liquid phase bonding of Inconel 718 superalloy by mechanical alloying process

A Ni-Cr-B-Si-Fe-based filler alloy powder has been synthesized by mechanical alloying technique in a high-energy ball mill to join Inconel 718 (IN 718) by transient liquid phase (TLP) bonding. The structural analysis of the synthesized alloy powders was done by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), field emission transmission electron microscope (FETEM), and laser particle size analyzer (LPSA). Thermal characterization was done by differential scanning calorimetry (DSC). The particle size of 60-h milled powders was found to be 15.4 μm and exhibits equiaxed shapes. Analysis of results reveals that during the milling process, elemental powder mixture gradually transforms to a nano-crystalline non-equilibrium face-centered cubic structured (FCC) Ni (Cr, Fe, Si, B) solid solution alloy. For the powder after 60-h milling, the crystallite size measured by XRD was found to be 4.0 nm. The lattice constant of nickel in the milled powder mixture decreased up to 5 h of milling and increased with a further increase in milling time. Dissolution of Si, B, Cr, and Fe into the Ni matrix resulted in the change of lattice constant of the alloy powder. The DSC result of 60-h milled powders reveals an endothermic peak at 1023.5 °C, which is attributed to the melting of the alloy powder. The activation energy of the milled powder reduced with milling time; as a result, the diffusivity of the elements in the filler metal increased. The activation energy of the 60-h milled alloyed powders was found to be 2714.67 KJ/mol. IN 718 superalloy was joined by the TLP bonding process. The microstructure of the TLP-bonded IN 718 joints showed three distinct zones in the bond area. Increasing the bonding temperature from 1050 to 1100 °C resulted in a 21% increase in the shear strength of TLP-bonded IN 718 alloy.

High Performance Cu Matrix Nanocomposite Fabricated Through Spark Plasma Sintering of Cu and Cu-Coated CNT

In this paper, the effects of Cu coating of carbon nanotube (CNTs) as reinforcement on structural, microstructural, physical and mechanical properties of Cu–3 wt%CNT nanocomposite were investigated. CNTs were coated by Cu using the electroless technique for 1 and 2 h. Bulk nanocomposite samples were produced by spark plasma sintering of a mechanically milled powder mixture of Cu and CNT. Kinetic study showed a nucleation and growth mechanism for the Cu coating process. Microstructural characterization showed that the coated CNTs dispersed more homogeneously in the powder mixture. Results also revealed that 1 h coating of CNTs led to the higher relative density and thermal properties. The coating process increased 62 Brinell hardness (BHN) in hardness, 14% IACS in electrical conductivity for Cu–CNT nanocomposite. Transmission electron microscopy analysis showed a strong bonding between CNT and Cu matrix within the distinguishable interface. About 20 MPa increase in shear strength of nanocomposite was observed by 1 h coating of CNTs. Also, the fracture surfaces exhibit changes in the mode of fracture by well-bonded CNTs with the Cu matrix. The coefficient of thermal expansion and thermal distortion parameter revealed 12.7 ppm/k and 0.037 ppm.m/w for the sample including 1 h coated CNT, respectively.

Magnesium-based composites reinforced with graphene nanoplatelets as biodegradable implant materials

Magnesium (Mg) and its alloys are considered promising biodegradable implant materials because of their strength and ability to degrade naturally in the body. However, pure Mg degrades rapidly in the physiological environment which adversely affects its mechanical integrity before sufficient bone healing. In this study, a high energy ball mill was used to disperse 0.5 wt% zirconium (Zr) and 0.1 wt% GNPs in Mg powders. Ball milled powder mixtures were then cold pressed under 760 MPa into green compacts and sintered in an argon atmosphere at 610 °C for 2 h. Results indicated that the addition of Zr and GNPs to the Mg matrix significantly enhanced its compressive yield strength by 91% and reduced the corrosion rate by 48% and 68% in electrochemical polarization test and hydrogen evolution test, respectively, compared to pure Mg. The contributions of various strengthening mechanisms to the compressive yield strength of MMNCs were quantitatively predicted in conjunction with validation via experimental results. This study demonstrates the potential of GNPs as effective reinforcement in fabrication of MMNCs with improved mechanical and corrosion properties.

Synthesis of Ni–TiC Composite by Ball Milling and Heat Treatment of NiO/TiO2/C Powder Mixture

In this study, a Ni–TiC composite was synthesized by the carbothermic reduction of activated NiO/TiO2/C powder mixture. The effect of 0-, 2-, 5-, and 10-h ball milling of the sample on the reduction process was investigated. Results of XRD pattern from milled samples showed that no reaction occurred between NiO, TiO2, and carbon due to milling. FESEM images for samples milled for 2, 5, and 10 h revealed the fine distribution of the brittle oxide particles in the matrix of graphite, as a ductile phase. Particle size reduction was also noticeable, especially in the case of oxide particles. By increasing the milling time, agglomeration of particles was also observed. Results of the thermogravimetry analysis of milled and un-milled mixtures showed the onset temperature of reduction for NiO decreased from 867 °C in the un-milled sample to 582, 571, and 560 °C in samples activated for 2, 5, and 10 h, respectively. Also, the onset temperature of the reduction of TiO2 decreased from 1029 for the sample milled for 2 h to 1019 and 1004 °C for samples milled for 5 and 10 h, respectively. The XRD pattern of the heat-treated milled powder mixture for 1 h under vacuum proved that Ni–TiC composite was formed at 1100 °C. It was found that bulk Ni–TiC composite could be synthesized by the heat treatment of activated powder at 1300 °C. Formation of TiC quadrilateral particles as reinforcement in the continuous matrix of Ni was evident at this temperature. Furthermore, the best morphology with the most appropriate particle size distribution was observed in the sample milled for 2 h.

Development of dense Al2O3–TiO2 ceramic composites by the glass-infiltration of porous substrates prepared from mechanical alloyed powders

In this work bio-composites were obtained by infiltrating porous alumina–titania (Al2O3–TiO2) substrates with a lanthania-rich (La2O3) glass. Al2O3–TiO2 substrates were fabricated using high-energy milled powder mixtures of two different compositions with molar ratios of 3:1 and 1:1, uniaxial compaction under 100 MPa and sintering at 1300 °C - 2 h or 1400 °C - 2 h. The high energy milling process of the powders resulted in homogeneous, extremely fine mixtures. For comparison, as-received Al2O3 and TiO2 powders were also mixed at a proportion of 3:1 and sintered at 1600 °C - 2 h. The sintered substrates presented α-Al2O3 and β-Al2TiO5 (aluminium titanate) as crystal phases and relative densities ranging between 65.5 ± 2% and 69.4 ± 1.2% of the theoretical density. These porous substrates were infiltrated with a lanthania containing glass at a temperature of 1140°C-2h. The resulting ceramic composites exhibited high density, varying between 94 to 99% of the theoretical density, Vickers hardness ranging between 895 ± 14 HV and 1036 ± 33 HV, fracture strength ranging between 218 ± 28 MPa and 254 ± 18 MPa and a fracture toughness (KC) higher than 2.6 MPam1/2. Phase analysis of the infiltrated substrates by X-ray diffraction indicated the decomposition of aluminium titanate into alumina and titania besides the formation of lanthanum borosilicate, LaBSiO5. In addition, all compositions studied presented non-cytotoxic behaviour and low chemical solubility, inferior to 75 μg/cm2.

Nonlinear Electrical Properties of ZnO-V2O5 Based Rare Earth (Er2O3) Added Varistors

The densification, microstructure and nonlinear electrical properties of ZnO-V2O5-MnO2-Nb2O5 varistor ceramics have been investigated with different amounts (0–2 mol.%) of Er2O3 addition. The ball milled powder mixtures have been sintered at 900°C, 1100°C and 1300°C for 1 h. The microstructure shows the presence of ZnO grains as the primary phase with secondary phases like Zn3(VO4)2, ErVO4, Zn4V2O9, Er- and Mn-rich in the intergranular layers. Generation of ErVO4 and Er-rich secondary phases at triple points and grain boundaries is found to inhibit grain growth resulting in the significant reduction of ZnO grain size, although this slightly diminishes the densification process. At a particular sintering temperature, the size of ZnO grains gets reduced over ten times when Er2O3 addition is increased from 0 mol.% to 2 mol.%. The nonlinear electrical property of the varistors improves with Er2O3 addition up to 0.5 mol.% and further addition (1–2 mol.%) does not appear to be beneficial in the chosen sintering temperatures. For varistors sintered at 1100°C, average ZnO grain size reduces from 10.8 μm in Er2O3 free sample to 7.2 μm in 0.5 mol.% Er2O3 added sample; this, in turn, significantly improves nonlinear electrical properties. The breakdown field increases from 1588 V cm−1 to 2585 V cm−1 with concurrent enhancement of nonlinear exponent value from 16 to 26 when Er2O3 concentration is raised from 0 mol.% to 0.5 mol.%.

Microstructure and properties of WC-17Co cermets prepared using different processing routes

WC-17Co cermets were prepared using three different processing routes. An as-ball milled powder mixture (BMPM) and pre-solid solution treatment powder (PSTP) were used as feedstock. Sinter-hot isostatic pressing (SHIP) and high-velocity oxy-fuel (HVOF) thermal spraying were used as consolidation methods. The microstructure and properties of the WC-17Co cermets prepared using the BMPM-SHIP, PSTP-SHIP, and PSTP-HVOF routes were characterized and systematically compared. Solid-solution strengthening of the Co binder phase accounted for the higher hardness and lower fracture toughness (KIC) of the cermets produced using the PSTP-SHIP and PSTP-HVOF routes compared with those of the BMPM-SHIP-produced cermet. Moreover, the SHIP method yielded WC grains featuring an equilibrium truncated triangular prism morphology, which were faceted compared to the round-edged WC grains prepared using HVOF. Owing to the formation of a dense protective tribofilm on its surface, the cermet prepared using the BMPM-SHIP route exhibited the lowest wear rate of 0.13 × 10−7 mm3/(Nm), while the wear rates of the cermets prepared using PSTP-SHIP and PSPT-HVOF were 0.24 × 10−7 and 0.96 × 10−7 mm3/(Nm), respectively.

Formation mechanism and phase transformations in mechanochemically prepared Al2O3-40wt% ZrO2 nanocomposite powder

ABSTRACTZirconia dispersed alumina nanocomposite powder has been synthesized by mechanochemical technique using inorganic reagents. The reactions were designed in a way to achieve 40wt% zirconia. Differential thermal analysis (DSC)/Thermogravimetric (TG), Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction study (XRD) along with Rietveld analysis was applied at different stages to obtain information on phase transformations and mechanisms in the temperature range of 400–1300 °C. The analysis revealed that Al2O3 and ZrO2 do not form by direct displasive reactions. In this system the CaO present in the milled powder mixture absorbs the HCl formed by the hydrolysis of the AlCl3 and ZrCl4 powders present in the milled powder mixture and helps in the completion of the reactions. The milled ZrCl4 and AlCl3 powders initially convert into amorphous Zr(OH)4 and crystalline bayerite (Al(OH)3) phases at 350 °C respectively and later decompose to their respective oxides at different stages upon the subsequent heat treatment. Upon heating, the intermediate hydroxide phases lose water and convert to nanostructured powders. The following phase transformations sequences are suggested for the aluminum and zirconium powders:The formed hydroxide phases and the phase transformation sequences for the alumina and zirconia powders obtained by this method is different from individually prepared alumina and zirconia powders reported by others. This finding is due to the effect of milling the powders together.

Mechanically activated combustion synthesis of Ti3AlC2/Al2O3 nanocomposite from TiO2/Al/C powder mixtures

Ti3AlC2/Al2O3 nanocomposite powder was synthesized by mechanical-activation-assisted combustion synthesis of TiO2, Al and C powder mixtures. The effect of mechanical activation time of 3TiO2-5Al-2C powder mixtures, via high energy planetary milling (up to 20 h), on the phase transformation after combustion synthesis was experimentally investigated. X-ray diffraction (XRD) was used to characterize as-milled and thermally treated powder mixtures. The morphology and microstructure of as-fabricated products were also studied by scanning electron microscopy (SEM) and field-emission gun electron microscopy (FESEM). The experimental results showed that mechanical activation via ball-milling increased the initial extra energy of TiO2-Al-C powder mixtures, which is needed to enhance the reactivity of powder mixture and make it possible to ignite and sustain the combustion reaction to form Ti3AlC2/Al2O3 nanocomposite. TiC, AlTi and Al2O3 intermediate phases were formed when the initial 10 h milled powder mixtures were thermally treated. The desired Ti3AlC2/Al2O3 nanocomposite was synthesized after thermal treatment of 20 h milled powder and consequent combustion synthesis and FESEM result confirmed that produced powder had nanocrystalline structure.

Synthesizing Core-Shell Heterostructures for SOFCs Using a Solution Precipitation Method

In the last three decades, solid oxide fuel cells (SOFCs) have garnered significant interest for viable distributed power generation systems. In this work, we focus on the cathode in SOFCs, where oxygen reduction occurs in two steps—adsorption and electronation, and surface/bulk diffusion to incorporation sites. Transition metal oxides such as strontium-doped lanthanum manganite (LSM) and strontium-doped cobalt iron oxide (LSCF) have been used as cathode materials, however both individually lack the key characteristics to successfully complete oxygen reduction. Furthermore, the accumulation of chromium (chromium poisoning) on SOFC cathodes is known to significantly hinder the performance of the cells. Incorporating core-shell hetero-structures as the cathode material could alleviate this problem: effectively combining the functionalities of both materials, and providing a nanoscale protection from Cr poisoning with a shell such as Cr-doped LSM (LSCM). However, synthesizing core-shell cathode structures previously has proved difficult requiring multiple steps, resulting in non-uniform core-shell structures. In this work we propose utilizing a molten salt synthesis process to create core-shell structures with precise composition with relative ease. The core is synthesized using high-temperature calcination and ball milled with the precursors of the target shell material. The milled powder mixtures are added to a LiCl-KCl eutectic melt to form core-shell hetero-structures via heterogeneous nucleation. Prior results have shown the successful formation of LSM and LSCF using the molten salt synthesis, along with the formation of core-shell LSCF-LSM hetero-structures. Synthesis temperatures dropped from the conventional 1000 ºC to 500 ºC, with dwell times as low as 10 minutes. Furthermore, SOFC cathodes consisting of LSCM were found to have stable polarization resistances, whereas the polarization resistance in LSM cathodes steadily increased. This result provides a strong motivation to further explore LSCM as a shell for core-shell cathodes to ensure protection from chromium poisoning. In essence, this work demonstrates an inexpensive method to synthesize core-shell cathodes that can simultaneously provide high power densities and low rates of degradation arising from Cr-poisoning. Figure 1

Low temperature sintered magneto-dielectric ferrite ceramics with near net-shape derived from high-energy milled powders

Nanosized Ni0.70Zn0.25Co0.05Fe1.90Mn0.02O4 ferrite ceramics were fabricated from high-energy ball milled powder mixtures with various ratios of Fe2O3/Fe as starting materials, in order to achieve magneto-dielectric materials with near net shape behavior for practical applications. The ferrite ceramics were obtained by sintering the milled powder compacts at 800 °C for 4 h, with a linear expansion of less than 4% as compared to the green pellets. The ceramics had an average grain size of less than 200 nm. The real part of relative permittivity decreases with increasing percentage of Fe2O3 used in the starting mixtures. The sample from the powder mixture with 50% Fe2O3 exhibits promising magneto-dielectric properties at frequencies of up to 90 MHz, which can be used for miniaturization of antennas at very high frequency (VHF) band.

Recycling of waste Ti machining chips by planetary milling: Generation of Ti powder and development of in situ TiC reinforced Ti-TiC composite powder mixture

The present paper reports the synthesis of in-situ TiC reinforced Ti-TiC composite powder mixture from waste Ti chips by high energy planetary milling. First, we synthesize Ti powder from waste Ti chips by planetary milling for 2.5 h and then Ti and graphite powder mixtures (Ti/C weight ratios of 100/6 and 48/12) are milled for 12 h to obtain in-situ TiC reinforced Ti-TiC composite. The both milled Ti and Ti-TiC composite powder mixtures are characterized by XRD, SEM, FESEM and TEM. It has been found that Ti powder of size 5–10 μm with crystal size of 10–20 nm are obtained after 2.5 h of milling. Faster rate of formation of TiC is evident from XRD spectra at high Ti content (Ti/C weight ratio = 100/6) than low Ti content (Ti/C weight ratio = 48/12). The contamination issue during synthesis of Ti powder and also during milling of Ti and graphite are discussed. It has also been observed that rate of oxidation reduces during milling of Ti + graphite than milling of pure Ti chips as graphite forms a layer around Ti particle and prevents oxidation. An average particle size of 5 μm is obtained after milling Ti + C powder mixture for 12 h (Ti/C weight ratio 48/12), whereas average size of 15 μm is obtained for Ti/C weight ratio of 100/6.

Formation of Al/(Al13Fe4 + Al2O3) Nano-composites via Mechanical Alloying and Friction Stir Processing

Combination of mechanical alloying and friction stir processing was used for the fabrication of Al/(Al13Fe4 + Al2O3) nano-composites. Pre-milled hematite + Al powder mixture was introduced into the stir zone generated on 1050 aluminum alloy sheet by friction stir processing. Uniform and active milled powder mixture reacted with plasticized aluminum to produced Al13Fe4 + Al2O3 particles. Al13Fe4 intermetallic showed elliptical shape with a typical size of ~ 100 nm, while nano-sized Al2O3 exhibited irregular floc-shaped particles that formed clusters with the remnant of iron oxide particles in the fine recrystallized aluminum matrix. As the milling time (1-3 h) of the introduced powder mixture increased, the volume fraction of Al13Fe4 + Al2O3 particles increased in the fabricated composite. The hardness and ultimate tensile strength of the fabricated nano-composites varied from 54.5 to 75 HV and 139 to 159 MPa, respectively; these are much higher than those of the friction stir processed base alloy (33 HV and 97 UTS). The highest hardness and strength were achieved for the nano-composite fabricated using the 3-h milled powder mixture; hard nano-sized reaction products and fine recrystallized grains of Al matrix had major and minor roles on enhancing these properties, respectively.

The Effect of Powder Ball Milling on the Microstructure and Mechanical Properties of Sintered Fe-Cr-Mo-Mn-(Cu) Steel

Abstract The effect of ball milling powder mixtures of Höganäs pre-alloyed iron Astaloy CrM, low-carbon ferromanganese Elkem, elemental electrolytic Cu and C-UF graphite on the sintered structure and mechanical properties was evaluated. The mixing was conducted using Turbula mixer for 30 minutes and CDI-EM60 frequency inverter for 1 and 2 hours. Milling was performed on 150 g mixtures with (in weight %) CrM + 1% Mn, CrM + 2% Mn, CrM + 1% Mn + 1% Cu and CrM + 2% Mn + 1% Cu, all with 0.6%C. The green compacts were single pressed at 660 MPa according to PN-EN ISO 2740. Sintering was carried out in a laboratory horizontal furnace Carbolite STF 15/450 at 1250°C for 60 minutes in 5%H2 – 95%N2 atmosphere with a heating rate of 75°C/min, followed by sintering hardening at 60°C/min cooling rate. All the steels were characterized by martensitic structures. Mechanical testing revealed that steels based on milled powders have slightly higher mechanical properties compared to those only mixed and sintered. The best combination of mechanical properties, for ball milled CrM + 1% Mn + 1% Cu was UTS 1046 MPa, TRS 1336 MPa and A 1.94%.

EBSD investigation of Al/(Al13 Fe4 +Al2 O3 ) nanocomposites fabricated by mechanical milling and friction stir processing.

The application of ball-milling for reactant powders (Fe2 O3 +Al) to form in situ nanosized reaction products in the stir zone of 1050 aluminium alloy was examined and the evolution of microstructure, grain boundaries and microtexture of the fabricated Al/(Al13 Fe4 +Al2 O3 ) nanocomposite was investigated. The mean matrix grain size of the fabricated nanocomposites by the combination of ball milling and friction stir processing were found to be ∼3.2, 3.1 and 2.1 μm for 1, 2 and 3 h milled powder mixtures, respectively. The fraction of high-angle grain boundaries increased markedly in the stir zone indicating the occurrence of dynamic restoration of the aluminium matrix. This was also associated with increasing of the fraction of low ∑CSL boundaries. In addition, the fraction of high-angle grain boundaries increased as the reaction product increased. The developed textures were compared with the most important deformation and recrystallisation texture components of cubic close packed structure. Some of the main texture components formed due to the restoration of aluminium in the stir zone of the material with no powder addition were CubeND {001}<310>, BR {236}<385> and R (or retained S{123} <634>); these are usually found in the rolled materials. However, the presence of nanosized reaction products in the fabricated nanocomposite changed the texture components to the dominant Goss {011}<100>, P {011}<122> and R{124}<211> textures.

Simultaneous synthesis and densification of nanocrystalline magnesium silicide compound by spark plasma sintering

Magnesium silicide (Mg2Si) is considered as a promising candidate among semiconducting materials for thermo-electric energy harvesting at medium functional temperature range (room temperature – 600°C) due to its light weight, good thermo-physical properties and economically inexpensive. However, synthesis of pure Mg2Si compound through conventional metallurgical processes are found to be a difficult task. The present investigation reports on the simple and robust attempt to fabricate nanocrystalline Mg2Si bulk compound from mechanically milled nanostrutured Mg-Si powder mixture by self-propagating high temperature synthesis (SHS) in spark plasma sintering (SPS). X ray diffraction and trasnsmission electron microscopy (TEM) analysis confirms the phase formation and structural features of Mg2Si compound by SPS. Energy dispersive X-ray absorption spectroscopy (EDAX) mapping reveals the homogenous distribution of constituent elementals and an estimated stochiometry. Differential thermal analysis (DTA) study confirms the lowering of recrystallization and combustion temperatures of milled Mg-Si powder mixture. It is understood that SPS temperature and pressure plays a crucial role in the reaction and densification kinectics in Mg2Si formation of theoretical density. The fabricated nanocrystalline Mg2Si exhibits n type semiconducting behavior and superior power factor (thermo-power) of 11.160μW/cm-K2 at 300°C.

Solid state synthesis of Bi 0 . 4 Sr 0 . 6 FeO 3 − δ powder for SOFC applications

We report on the synthesis of Bi0.4Sr0.6FeO3 powder with cubic structure by solid state reaction (mechanical milling and calcination) from Bi2O3, SrCO3 and Fe2O3 stoichiometric ratios. Milled powder mixtures were heat treated between 775∘C and 825∘C for 30 and 60 min in oxygen atmosphere and characterized by X-ray diffraction (XRD), impedance as well as Mossbauer spectroscopy. The cubic phase of Bi0.4Sr0.6FeO3 was successfully obtained in samples milled for only 2 h and a subsequent calcination at 800∘C. Irrespective of milling time, heat treatments at lower temperatures (775∘C) still show spurious phases such as Sr0.23Bi0.76O1.1 (30 min) and Sr0.53Bi1.72O3 (60 min). Impedance spectroscopy show high values (105–109) Ω indicating strong structural bond between the atoms of the system and activation energies for the strontium ion around 04 eV. These results show a single dynamic behavior in a range from 1 to 2*105 Hz enabling data adjustment and analysis to a RC circuit. Conductivity results normally show a behavior that obeys the universal law of Jonscher’s relaxation (σ = σDc + αωn) with values for the exponent n (0.8 < n < 1) typical in these structures. Mossbauer spectrometry measurements reveal that the hyperfine magnetic field of the precursors and milled powders corresponds to hematite 512 T. After the thermal treatment of the samples, the mean hyperfine field decreases to 489 ± 0.5 T showing the Bi and Sr atoms diffusion, (non- magnetic) in Fe2O3. While the result of isomer shift corresponds to a Fe+3 oxidation state irrespective of the heat treatment.