Mechanochemical synthesis and characterization of xIn2O3��(1???x)��-Fe2O3 nanostructure system

Indium oxide-doped hematite xIn₂O₃·(1 ? x)??-Fe₂O₃ (x = 0.1?C0.7) nanostructure system was synthesized using mechanochemical activation by ball milling and characterized by XRD, simultaneous DSC?CTGA, and UV/Vis/NIR. The microstructure and thermal behavior of as obtained system were dependent on the starting In₂O₃ molar concentration x and ball milling time. XRD patterns yielded the dependence of lattice parameters and grain size as a function of ball milling time. After 12 h of ball milling, the completion of In³⁺ substitution of Fe³⁺ in hematite lattice occurs for x = 0.1, indicating that the solid solubility of In₂O₃ in hematite lattice is extended. For x = 0.3, 0.5, and 0.7, the substitutions between In³⁺ and Fe³⁺ into hematite and In₂O₃ lattice occur simultaneously. The lattice parameters a and c of hematite and lattice parameter a of indium oxide vary as a function of ball milling time. The changes of these parameters are due to ion substitutions between In³⁺ and Fe³⁺ and the decrease in the grain sizes. Ball milling has a strong effect on the thermal behavior and band gap energy of the as-obtained system. The hematite decomposition is enhanced due to the smaller hematite grain size. The crystallization of hematite and In₂O₃ was suppressed, with drops of enthalpy values due to the stronger solid?Csolid interactions after ball milling, which caused gradual In³⁺?CFe³⁺ substitution in hematite/In₂O₃ lattices. The band gap for hematite shifts to higher energy value, while that of indium oxide shifts to lower energy value after ball milling.     

Transformation behavior and thermal stability of Al-based systems prepared by ball milling

Transmission electron microscopy, X-ray diffraction, scanning electron microscopy, differential thermal analysis, and differential scanning calorimetry were used to investigate the transformation behavior of (Al_0.88Ni_0.08Co_0.04)_100−x,Zr_x, (wherex = 0 to 5 at. %) alloys during ball milling, and the thermal stability during the reverse process of return to equilibrium. The results have shown that the crystalline to amorphous transformation occurs only in compositions containing Zr. Mechanical grinding is shown to easily amorphize the Al₃Zr compound which enters in equilibrium with the fcc-Al and (Co, Ni)₂Al₉ phases for the compositions studied. The formation of an amorphous phase at the fcc-Al and Co₂Al₉ grain boundaries leads to a wetting transition, and with decreasing grain size the initially nanostructured Al₈₈Ni₈Co₄ alloy was found to progressively transform to an amorphous alloy. The crystallization temperature, the activation energy, and the crystallization enthalpy increase, while the melting temperature of the quaternary alloys decrease with increasing Zr substitution up to 5 at. %.     

Formation of metastable solid solutions of boron in nickel under mechanochemical synthesis from Ni-B and Ni-Nb-B mixtures

Using high-energy ball milling of Ni₈₇B₁₃ and Ni_{87 ? x} Nb _x B₁₃ component mixtures (x = 7, 10, 12, 14) for 2 h, nanocrystalline alloys containing fcc solid solutions of Ni〈B〉 and Ni〈Nb,B〉 were obtained. According to the results of X-ray analysis, oversaturated solid solutions of Ni〈B〉 are interstitial solutions; those of Ni〈Nb,B〉 are substitutional solutions or mixed substitutional-interstitial solutions. Upon heating of the alloys, exothermal effects appear on differential scanning calorimetry (DSC) curves; they are attributed to decomposition of metastable solid solutions and to crystallization of the amorphous phase appearing in mechanical alloying. After heating to 720°C, the Ni₈₇B₁₃ alloy contained stable phases of Ni and Ni₃B; the Ni₇₅Nb₁₂B₁₃ alloy contained a τ phase (Ni₂₁Nb₂B₆) and a metastable solid solution of Ni〈Nb〉.     

Thermal and structural study of nanocrystalline Fe(Co)NiZrB alloys prepared by mechanical alloying

Three nanocrystalline alloys, Fe_75−x Co _x (Ni₇₀Zr₃₀)₁₅B₁₀ (x = 0, 10, and 20), were synthesized from elemental powders in a planetary high-energy ball mill. Their microstructure, magnetic properties, and thermal stability were characterized by X-ray diffraction, transmission M?ssbauer spectroscopy, transmission electron microscopy, scanning electron microscopy, induction coupled plasma, vibrating sample magnetometry, and differential scanning calorimetry. After 80 h of milling, the nanocrystallites size of alloys is in the range 6–10 ± 1 nm. The lattice parameter decreases when increasing (decreasing) milling time (Fe content). Furthermore, the thermal stability of the nanocrystalline phase increases when increasing Co concentration. The activation energy of the main crystallization process, between 275 ± 8 and 311 ± 10 kJ mol⁻¹, is associated with grain growth. Slight contamination from milling tools and milling atmosphere was detected. Minor differences were detected after M?ssbauer analysis.     

Synthesis and characterisation of nanostructured FeCo alloys

Nanocrystalline Fe_(1?x)Co _x (x = 0.12, 0.5, 0.6) mixtures have been prepared by mechanical alloying using a planetary ball mill under several milling conditions. The alloying process between the elemental powders and the microstructure changes of the prepared samples have been investigated using X-ray diffraction (XRD) and ⁵⁷Fe Mössbauer spectrometry. The XRD patterns refinement on the mechanical alloying products according to the Rietveld method (Maud software) reveals the allotropic transformation of Co from fcc to hcp form and the progressive dissolution of Co into the α-Fe lattice as a function of both Co concentration and milling conditions. The grain size values of the obtained powders reaches a nanometer scale of about 10 nm. Mössbauer results show that the beginning of the solid state reaction between Fe and Co elemental powders depends on the milling conditions. After 24 h of milling, the average hyperfine magnetic fields values of Fe₈₈Co₁₂, Fe₅₀Co₅₀ and Fe₄₀Co₆₀ mixtures are consistent with a disordered and an ordered FeCo solid solution, respectively.     

Structural and Magnetic Properties of Nanostructured Pr0.75 Y 0.25Co5 Powders Obtained by Mechanical Milling and Subsequent Annealing

Pr_0.75 Y _0.25Co₅-based as-cast alloys were processed by high-energy ball milling to obtain nanostructured powders with high coercivity. The powders obtained after 4 h of milling exhibited nearly amorphous behavior in X-ray diffraction patterns. DSC scans of the as-milled powders indicated a process of crystallization by broad, exothermic transition peak at 503 °C. Annealing of the milled powders at 850 °C for 2.5 min in high vacuum produced fine grains of size ranging 15–30 nm with optimal microstructure and hard magnetic properties. Magnetic measurements of the annealed powders evaluated a high intrinsic coercivity, _i H _c of 9.3 kOe, and a remanence ratio, M _r/ M _max of 0.72. The magnetic hardening was attributed to higher anisotropy field of the powders and microstructural uniformity achieved by the processing methodologies.     

Ti-based amorphous alloys with a wide supercooled liquid region

Ti-Cu-Ni-Co quaternary amorphous alloys produce by melt spinning were found to have a wide supercooled liquid region before crystallization, though no glass transition was observed in Ti-Cu binary amorphous alloys. The largest temperature interval of the supercooled liquid region (ΔT_x) is as large as 90 K for Ti₅₀Cu₂₅Ni₂₀Co₅.There is a tendency for ΔT_x to increase with an increase in storage modulus and with a decrease in loss modulus. It is therefore presumed that the increase in ΔT_x for the multicomponent amorphous alloy is due to the suppression of crystallization for the supercooled liquid resulting from the increase in viscosity.     

Mechanochemical synthesis of sodium tungsten bronze nanocrystalline powders

Nanocrystalline powders of sodium tungsten bronze Na_xWO₃ (x∼0.88) have been prepared by mechanochemical process using starting materials of Na pieces and WO₃ powders in a planetary ball mill. The synthesis reactions proceed with increasing milling time and are almost completed after 44 h. Phase-pure nanoparticles of Na_xWO₃ with average size of 17 nm were directly obtained after a simple washing process to remove the by-product of Na₂WO₄. The resistivity was measured in the temperature range from 77 to 300 K. The sample displays semiconducting behavior and can be characterized by three-dimensional variable-range hopping. The mechanochemical process seems to be an attractive route to fabricate tungsten bronzes because of several advantages such as easy preparation, less cost, operating at low temperature and suitability for a large-scale production.     

Calorimetric studies of non-isothermal crystallization in amorphous Cu x Ti100−x alloys

The present paper reports the composition dependence of pre-exponential factor and activation energy of non-isothermal crystallization in amorphous alloys of Cu _x Ti_100?x system using differential scanning calorimeter (DSC) technique. The applicability of Meyer-Neldel relation between the pre-exponential factor and activation energy of non-isothermal crystallization for amorphous alloys of Cu-Ti system was verified.     

Influences of milling media on the fabricating process and thermoelectric properties of silicon germanium alloys

In this work, Si₈₀Ge₂₀P₂ alloys were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). SiO₂ and ZrO₂ were taken as milling media respectively to investigate the effect of milling media on the fabricating process and the thermoelectric properties of SiGe alloys. The results show that, compared with the zirconia ball, though the agate one contains less kinetic energy, the solid solution of SiGe taken it as the milling media forms more quickly and at the same time has smaller average grain size through the whole milling time. The solid solution of Ge to Si crystal of samples under ZrO₂ media remains stably around 98% and is much higher than that of specimens with agate as the media. In the sintering process, the previous application of ZrO₂ easily causes the enrichment of elementary P and the loss of Si and leads to serious deviation from the original stoichiometric proportion of the compounds which is beneficial to the following machining and finally does harm to the thermoelectric properties of the Si₈₀Ge₂₀P₂ alloys.     

Calorimetric and optical study of amorphous Se85 − xTe15Bix glassy alloy

Bulk samples of Se_85 − xTe₁₅Bi_x (where x = 0, 1, 2, 3, 4, 5) glassy alloys are obtained by melt quenching technique. Differential scanning calorimetric (DSC) technique has been applied to determine the thermal properties of Se-rich Se_85 − xTe₁₅Bi_x glassy alloys in the glass transition and crystallization regions at four heating rates (5, 10, 15, 20 K min^− 1). The glass transition temperature (T_g) and peak crystallization temperature(T_p) are found to shift to a higher temperature with increasing heating rate. With Bi addition, the value of (T_g)increases. (T_p) is found to increase as Bi is introduced to the Se-Te host, however further increase in Bi concentration is responsible for the reduction of. Thin film of bulk samples are deposited on glass substrate using thermal evaporation technique under vacuum for optical characterization. Optical band gap is estimated using Tauc's extrapolation and is found to decrease from 1.46 to 1.24 eV with the Bi addition.     

Chemical bond approach to activation energy of crystallization in some Se-Ge-M (M = Bi, In) chalcogenide glasses

The crystallization kinetics of glassy Se_78−xGe₂₂Bi_x (0 ≤ x ≤ 10) and Se_80−xGe₂₀In_x (0 ≤ x ≤ 15) alloys has been studied by an isothermal method. For this purpose, conductivity measurements are done during isothermal annealing at various temperatures between the glass transition and crystallization temperatures. Avrami's equation is used to calculate the activation energy of crystallization (E_c). The composition dependence of E_c in these alloys has been discussed using chemical bond approach.     

Structure and phase composition of oxide dispersion strengthened fcc alloys prepared via strong deformation in the Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe-Ni-M (M = Ti,Zr) systems

Deformation-induced Fe 2 dissolution in fcc Fe-Ni-M (M = Ti, Zr) alloys has been studied by Mössbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. The results indicate that high-pressure shear deformation in Bridgman anvil cells and ball milling lead to dissolution of the low-stability oxide Fe₂O₃ in the fcc matrix and the formation of metallic solid solutions and secondary oxides of the alloying elements. This enables preparation of oxide dispersion strengthened Fe-Ni alloys and grain size reduction of the fcc matrix. The formation of secondary oxides occurs more actively during ball milling than during high-pressure shear deformation because of the more significant local heating of the mixture and the larger specific surface area and higher reactivity of the powder.     

Hydrogen sorption enhancement in cold-rolled and ball-milled CaNi<Subscript>5</Subscript>

The effect of cold rolling and ball milling on the hydrogen sorption properties of CaNi₅ was investigated with a special emphasis on the first hydrogenation. We compared cold rolling for 5, 12, and 25 rolling passes in the air with ball milling in argon for 30 and 60 min. Results show that 15 min of ball milling had a positive effect on the first hydrogen absorption, but further milling to 60 min made the sample almost impermeable to hydrogen. Cold rolling had a positive effect on first hydrogenation. We found that cold rolling greatly reduces the particle size as well as the crystallite size. We also found that dehydrogenation under 5 kPa of hydrogen at 323 K was not complete. Two partially hydride phases remained: CaNi₅H and Ca₂Ni₇H _x .     

XRD, Magnetic and M?ssbauer Spectral Studies of?Ag x Ni1?x Fe2O4 Ferrite Nanoparticles

Nanophase Ag _x Ni_1?x Fe₂O₄ (x=0,0.2) ferrites were prepared by glycothermal method. The NiFe₂O₄ (x=0) nanosized sample was also produced by high-energy ball milling for comparison of properties. Structural investigations of the samples were carried out by X-ray diffraction. The experiment reveals that pure Ag-Ni ferrite materials with grain sizes of about 8 nm can be obtained after annealing at relatively low temperature of about 500?°C. The nanosized compounds produced by glycothermal reaction indicate superparamagnetic behavior. A higher value of coercive field (910 Oe) is observed in x=0 milled sample with similar particle size. The zero field cooled (ZFC) and field cooled (FC) magnetization measurements reveals spin glass like behavior of the nanosized compounds.     

Mechanical alloying of Fe-B alloys

Mechanical alloying (MA) of Fe-B alloy systems using a conventional ball mill has been performed. The structure change of Fe_100?x B _x for the composition range 10≤x≤90 has been investigated using X-ray diffractometry, thermal analysis, transmission electron microscopy, scanning electron microscopy and Mössbauer spectroscopy. According to the X-ray diffraction analysis, the sequences of transformation have been classified into three groups,x≤20, 25≤x≤35 andx≥50 for Fe_100?x B _x . The amorphous phase whose composition is nearlyx=30, first appeared for the whole composition range. This amorphous phase changed into a tetragonal Fe₂B-like compound on further milling for 1000 h. On further milling of thex= 50 sample, the Fe₂B compound phase disappeared and orthorhombic FeB compound appeared.     

Ball milling of Co70 Fe8Si9B13 amorphous ribbon,crystallized ribbon and a mixture of pure crystalline powders

Co₇₀ Fe₈ Si₉B₁₃ amorphous ribbon, crystallized ribbon and a mixture of pure crystalline powders were mechanically alloyed by milling and nanocrystalline structures were obtained. The structural changes were monitored By X-ray diffraction and differential scanning calorimetry measurements. The thermal behaviour on heating the alloys prepared by ball milling was studied and the influence of the high-energy ball milling on the resulting phases was found.     

Structural Transformations during the Mechanochemical Synthesis and Heating of Co–Al Alloys

X-ray diffraction analysis and differential scanning calorimetry are used to follow the structural changes induced in cobalt by high-energy ball milling and the processes involved in the mechanochemical synthesis (MCS) of Co–Al alloys containing 3, 10, 20, and 50 at % Al. The results demonstrate that short-term (2–3 min) high-energy milling of cobalt, consisting, as a rule, of two phases, hcp and fcc, causes the high-temperature (fcc) phase to disappear. Longer term milling leads to the reverse, hcp-to-fcc phase transformation. This milling-induced transformation is attributable to the increase in the probability of stacking faults, which attains 20%. Similar structural changes occur in the initial stages of MCS at Al contents from 3 to 20 at %. The formation of fcc Co_{1 – x} Al _x solid solutions (x < 0.5) is accompanied by an increase in the probability of stacking faults. The presence of Al stabilizes stacking faults in hexagonal cobalt and accelerates the transition to the cubic phase, which dissolves the aluminum. The milling of a mixture containing 20 at % Al leads to the formation of a solid solution and, at intermediate milling times, CoAl. The latter phase disappears at sufficiently long milling times. Mechanical alloying of an equiatomic mixture (Co + 50 at % Al) yields phase-pure CoAl. Heating of the MCS alloys to 720°C stabilizes the Co_{1 – x} Al _x solid solution and the intermetallic phase CoAl. Heating to 720°C after medium-term milling leads to the formation of the metastable phase Co₃Al (L1₂ type), which disappears at higher temperatures.     

Structural disorder of ball-milled,nanosized, Fe-doped SnO<Subscript>2</Subscript>: X-ray diffraction and Mössbauer spectroscopy characterization

Structural characterization of nanosized Fe-doped semiconducting oxide SnO₂ is reported. Samples of Sn_1?x Fe _x O_2?y (with x ranging from 0.11 to 0.33) were processed in a planetary ball mill, subsequently HCl-washed to eliminate metallic iron impurities introduced by the milling tools, and characterized by X-ray diffraction and Mössbauer spectroscopy. Results showed that Fe enters the host matrix randomly replacing Sn in octahedral sites regardless of iron concentration. It has been found the presence of oxygen deficient iron sites attributed to the stoichiometric unbalance of precursor materials used in the milling process. It is known that structural features like particle size and residual microstrain are highly affected by the milling process. Values of average particle sizes as calculated by Scherrer’s method alone decreased with increasing Fe concentration. This result was shown, by means of the Williamson-Hall correction method, to be misleading as a large degree of microstrain is expected for mechanically milled powders. In fact, corrected values of average particle sizes turned out to be reasonably homogeneous regardless of iron content and milling time with no consistent trend. Residual microstrain, on the other hand, was found to increase with iron content giving way to the conclusion that broadening of diffraction peaks are mostly due to increasing microstrain as a function of iron doping and milling time. Williamson-Hall analysis also showed a large degree of particle size inhomogeneity. Milling of undoped SnO₂ showed that this inhomogeneity is due mostly to doping as opposed to milling.     

Thermal stability and thermoelectric properties of Mg2Si0.4Sn0.6 and Mg2Si0.6Sn0.4

Compounds of Mg₂Si_1?x Sn _x are environmentally friendly, inexpensive and high-efficiency thermoelectric materials for energy conversion in the temperature range 300–550 °C. In this study, the thermal stability is investigated of fine powders and sintered pellets of the compounds Mg₂Si_0.4Sn_0.6 and Mg₂Si_0.6Sn_0.4 by heating the samples from room temperature to ~400 °C in air, while measuring powder X-ray diffraction patterns. The diffractograms of the pellets show no significant changes upon heating for several hours, while the powder samples show increasing emergence of a Mg₂Sn-rich, Mg₂Si_1?x Sn _x phase, and other impurities upon heating for only several minutes. This is attributed to the larger amount of surface area in the powder samples. The appearance of the Mg₂Sn-rich phase is most pronounced for the Sn-rich composition. In addition, the thermal expansion coefficients were extracted from the powder diffraction patterns. All materials have been synthesized by induction-melting followed by ball milling and spark plasma sintering. The thermal conductivity, Seebeck coefficient, electrical resistivity and Hall carrier concentrations have been measured from room temperature to 400 °C on the pellets.