Crystallization kinetics of metallic glasses

In this study, the temperature-heating rate diagram of the main crystallization process of two metallic glasses, Fe₇₄Ni_3.5Mo₃B₁₆Si_3.5 and Fe₄₁Ni₃₈Mo₃B_18, was obtained from one experimental differential scanning calorimetry (DSC) scan and the knowledge of their activation energy as determined by an isoconversional method. A good concordance was observed between the diagram curves obtained by calculation (isoconversional approach) and the experimental data, which verifies the reliability of the method and the validity of the kinetic approach in these alloys.     

The effect of Nb and Ni addition on crystallization behavior of amorphous–nanocrystalline Fe–Cr–B–Si alloys

The crystallization behavior of amorphous Fe–Cr–B–Si alloys in the presence of Ni and Nb elements was the goal of this study. In this regard, four different amorphous–nanocrystalline Fe₄₀Cr₂₀Si₁₅B₁₅M₁₀ (M=Fe, Nb, Ni, Ni_0.5Nb_0.5) alloys were prepared using mechanical alloying technique up to 20 h. Based on the achieved results, in contrast to Fe₅₀Cr₂₀Si₁₅B₁₅ alloy, the amorphous phase can be successfully prepared in the presence of Ni and Nb in composition. Although the crystallization mechanism of prepared amorphous phase in different alloys was the same, the Fe₄₀Cr₂₀Si₁₅B₁₅Nb₁₀ alloy showed higher thermal stability in comparison with other samples. The crystallization activation energy of this amorphous alloy was estimated about 410 kJ mol^?1 which was much higher than Fe₄₀Cr₂₀Si₁₅B₁₅Ni₁₀ (195.5 kJ mol^?1) and Fe₄₀Cr₂₀Si₁₅B₁₅Ni₅Nb₅ (360 kJ mol^?1) samples. The calculated values of Avrami exponent (1.5 < n < 2.2) indicated that the crystallization process in different alloying systems is the same and to be governed by a three-dimensional diffusion-controlled growth.     

Annealing and Crystallization of Fe40Ni40P14B6 Glassy Alloy. A DSC study

In this paper a DSC study is reported of the behavior of Fe₄₀Ni₄₀P₁₄B₆ alloy produced by rapid quenching. The experimental results show that relaxation phenomena can be studied directly from the DSC curves. From these experiments, the spread of the E _c values in the literature is attributed to differences in the quenching rates and the presence of variable number of quenched-in nuclei. It is also shown that the microstructure (number and size of crystals) of the non-isothermally devitrified metallic alloy changes with the heating rate; this is a consequence of the shift of crystallization temperatures and, therefore, of the change of the ratio of nucleation and crystal growth rates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Non-isothermal crystallization kinetics of recycled PET-Si3N4 nanocomposites

Poly(ethylene terephthalate) (PET) is an important industrial material and has been widely applied in consumer products. Due to its slow crystallization rate, nanoparticles are incorporated into PET to function as heterogeneous nucleating agents. In this study, the non-isothermal crystallization behavior of recycled PET-silicon nitride (Si₃N₄) nanocomposites was investigated by differential scanning calorimetry (DSC). In the general analysis of the non-isothermal crystallization curves, it was found that the Si₃N₄ nanoparticles could effectively accelerate the nucleation of PET, but the crystal growth rate was slowed down when the Si₃N₄ content was more than 1 wt%. This might be attributed to the interaction between the PET chains and the surface-treated Si₃N₄ nanoparticles. Results obtained from Avrami and Mo treatments agreed well with the general analysis. Application of the Kissinger method and isoconversional method of Flynn-Wall-Ozawa also showed that Si₃N₄ nanoparticles had a good nucleation effect on the crystallization of PET, and the crystal growth was hindered by Si₃N₄ when the particle loading is higher than 1 wt%.     

Thermal analysis of two Fe-X-B (X=Nb,ZrNi) alloys prepared by mechanical alloying

The alloys, Fe₆₀Ni₁₄Zr₆B₂₀ and Fe₈₅Nb₉B₆, were produced by mechanical alloying. The formation of the nanocrystallites (about 40 nm) was detected by X-ray diffraction. Furthermore, a slight oxygen presence (<3 at.%) was found by induced-coupled plasma and EDX microanalysis. After milling, calorimetry scans show low temperature recovery process and several crystallization processes related with the crystal growth and reordering of the crystalline phases. The apparent activation energies, 360 and 290 kJ mol^-1, were determined by the Kissinger method. A mass increase (about 1 mass%) was detected by thermogravimetry. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytically active electrodes in the redox processes of oligomeric peroxides

The catalytic activity of different electrodes (Pt, glassy carbon, and amorphous metal alloys Al_87.0Y_5.0Ni_8.0, Fe_78.5Ni_1.0Mo_0.5Si_6.0B_14.0, and Fe_73.1Cu_1.0Nb_3.0Si_15.5B_7.4) in the redox processes of polyfunctional oligomeric peroxides based on vinylacetate, 3-tert-butylperoxy-3-phenylbutylmethylmethacrylate and maleic anhydride and vinylacetate, 3-tert-butylperoxy-3-methylbutylmethacrylate and maleic anhydride was evaluated by potentiometry and cyclic voltammetry. It was established that amorphous metal iron-based Fe_73.1Cu_1.0Nb_3.0Si_15.5B_7.4 and Fe_78.5Ni_1.0Mo_0.5Si_6.0B_14.0 electrodes manifested a high electrocatalytic activity comparable with that of a platinum electrode in the redox processes of polyfunctional oligomeric peroxides.     

Investigation of core-excited BK quantum yield spectra of amorphous and crystalline Fe40Ni40P14B6 alloys

X-ray quantum yield spectra from the BK edge in amorphous and crystalline Fe₄₀Ni₄₀P₁₄B₆ alloys are presented. ESCA core level binding energies were also measured. The quantum yield spectra are discussed together with calculated densities of states. A good coincidence between band structure calculations and experimental results is obtained. A small structure at absorption onset is interpreted as due to oxidation products at the sample surface. Crystallization effects after heating of the compound are discussed.     

Mechanism and kinetics of crystallization of α-Fe in amorphous Fe81B13Si4C2 alloy

The non-isothermal crystallization of α-Fe from Fe₈₁B₁₃Si₄C₂ amorphous alloy was investigated. The kinetic parameters of crystallization process were determined by Kissinger and Kissinger–Akahira–Sunose (KAS) methods. It was established that the kinetic parameters of transformation do not change with the degree of crystallization in the range of 0.1–0.7. The kinetic model of the crystallization process was determined using the Malek's procedure. It was established that the primary crystallization α-Fe phase from amorphous alloy can be described by Šesták–Berggren autocatalytic model with kinetic triplet E_a = 349.4.0 kJ mol⁻¹, ln A = 50.76 and f(α) = α^0.72(1 − α)^1.02.     

Thermal evolution of ferromagnetic metallic glasses

A traditional TG apparatus was modified by placing two permanent magnets producing a controlled magnetic field (TG(M): Magneto Thermogravimetry). This technique proved to be useful to study both structural relaxation and crystallisation of ferromagnetic metallic glasses. Results obtained for the amorphous alloys Fe₄₀Ni₄₀P₁₄B₆ and Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅, are reported in this paper. Structural relaxation can be evaluated by measuring changes in Curie temperature induced by thermal treatments. Crystallisation in TG(M) is detected through a change in the measured apparent mass (difference between the sample mass and magnetic force driving it upward). These results were confirmed by DSC analysis. Whether the obtained crystalline phase is ferromagnetic, it can be identified through its Curie temperature, measured by TG(M). In fact the value of 770°C measured as Curie temperature of crystallised Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅led to conclude that the only ferromagnetic crystalline phase is a-Fe. These hypothesis was confirmed by XRD analysis, showing that the first crystallisation yields to a-Fe nanocrystals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of Ni content on Fe–Nb–B alloy formation

In this work three alloys, Fe₇₄Nb₆B₂₀, Fe₆₄Ni₁₀Nb₆B₂₀ and Fe₅₄Ni₂₀Nb₆B₂₀, were obtained by mechanical alloying to analyze the influence of Ni content on Fe–Nb–B alloy formation. Structural analysis by X-ray diffraction (XRD) confirms that partial substitution of Fe by Ni favours the formation during milling of a more disordered structure. Furthermore, thermal stability study was performed by differential scanning calorimetry (DSC) because thermally induced structural changes can affect soft magnetic behaviour. After 40 h of milling time, all DSC curves show several exothermic effects on heating associated to structural relaxation and crystallization. All alloys present a crystallization process with associated activation energy values ranged between 238 and 265 kJ mol^–1 related to the crystalline growth of the bcc-Fe rich phase. In alloys with Ni, a second crystallization process appears at temperatures over 500°C with activation energies 397 (10% Ni alloy) and 385 kJ mol^–1 (20% Ni alloy) probably associated to the nucleation and crystalline growth of a new phase.     

Crystal structure and magnetism of the FexNi8-xSi3 materials, 0 ≤ x ≤ 8

The crystal structure and magnetic properties of the materials Fe_xNi_8-xSi₃ with 0 ≤ x ≤ 8 have been investigated to estimate any possible magnetocaloric effect and compare it to that in known magnetocalorics. Two structural ranges could be identified in this system by X-ray and neutron diffraction. The structure of the samples with 0 ≤ x ≤ 4 is related to the trigonal structure of Ni₃₁Si₁₂. Doubled c lattice parameters compared to the one in Ni₃₁Si₁₂ are observed in the samples with x = 2 and x = 3. The average structure of Fe₂Ni₆Si₃ has been determined by X-ray single-crystal diffraction. The compounds with the compositions 5 ≤ x ≤ 8 crystallize in cubic Fe₃Si-type structure. Magnetic measurements have shown that the compound Fe₃Ni₅Si₃ displays a phase transition close to room temperature. However, its magnetocaloric effect is much smaller than the one in the promising magnetocaloric materials.     

Effect of different inorganic filler over isothermal and non-isothermal crystallization of polypropylene homopolymer

In this study, the effect of several inorganic fillers: silicon oxide (SiO₂), nanoclay (C20A), alumina (Al₂O₃), and calcium carbonate (CaCO₃) on the crystallization behavior of polypropylene were analyzed for composites with fixed filler content (5 mass%) prepared by intensive mixing following by compression molding. In addition, for calcium carbonate, which produces the highest increase on toughness, PP grafted with maleic anhydride (PP-g-MA) was added to enhance the compatibility. In that case, different content of particles was used (from 5 to 20 mass%) and the synergic effect of both incorporations was demonstrated. For this purpose, isothermal and non-isothermal crystallization tests were carried out in the bulk (by differential scanning calorimetry). In addition, the spherulitic growth was studied (by optical microscopy). Different models were used to predict the relative degree of crystallinity and several parameters were analyzed. All results indicate that whereas alumina and calcium carbonate acted as nucleating agents, silica and nanoclay displayed an opposite behavior. The full models that take into account the different parameters during cooling under isothermal and non-isothermal conditions were used to construct continuous cooling transformation and time temperature transformation diagrams. Both kind of diagrams provide a fundamental tool to understand the crystallization behavior of studied composites and are useful to determine the processing conditions.     

Iso-conversional kinetic study of non-isothermal crystallization in glassy Se98Ag2 alloy

The crystallization kinetics of glassy Se₉₈Ag₂ alloy is studied at different heating rates (5, 10, 15, and 20?K?min^?1) using differential scanning calorimetric technique. Endothermic and exothermic peaks are obtained at glass transition (T _g) and crystallization temperature (T _c). Four iso-conversional methods (Kissinger?CAkahira?CSunose (KAS), Flynn?CWall?COzawa (FWO), Tang and Straink) were used to determine the various kinetic parameters (crystallization temperature T _?? , activation energy of crystallization E _??, order parameter n) in non-isothermal mode.     

Passivity characteristics on Ni(Cr)(Fe)SiB glassy alloys in phosphate solution

Passivity characteristics of three nickel-metalloids glassy alloys (Ni_92.3Si_4.5B₃₂, Ni_82.3Cr₇Fe₃Si_4.5B_3.2 and Ni_75.5Cr₁₃Fe_4.2Si_4.5B_2.8) and the immersion time effect on the corrosion resistance were carried out by AC and DC electrochemical methods and SEM and XPS analyses. The study also focused on the effect of H₃PO₄ concentration and its role on the corrosion rate, passivation ability of nickel base glassy alloys surface. The present investigation revealed (i) corrosion resistance of Cr-free alloy shows pseudo passivity at all examined H₃PO₄ concentrations, (ii) high corrosion resistance of Cr contains alloys due to the formation of protective layer of chromium oxyhydroxide on the surface which acts as a diffusion barrier against alloy dissolution, (iii) the negative resistance observed in the case Ni_75.5Cr₁₃Fe_4.2Si_4.5B_2.8 alloy revealed the sudden transition of metal/solution interface from a state of active dissolution to the passive state.     

New Phosphides with Transition and Rare-Earth Metals and Their Crystal Structures

Abstract

The interaction between components in systems M-M′- P (M -Zr, Hf, Nb, Mo, W, Mn, Re; M′-V, Cr, Fe, Co, Ni, Cu), Ln-{Fe, Co, Ni, Cu}-P (Ln-rare-earth metals) and M-{Si, B}-P (M-Cr, Mo, W, Mn, Re, Co, Ni, Cu) have been investigated and isotermal sections for 47 ternary systems have been built. 98 new phosphides have been synthesized and the crystal structure for 76 has been determined. The structures of new compounds belong to the known structure types, such as MgCu₂, Mg₆ Cu₁₆ Si₇, TiNiSi, Zr₂ Fe₁₂P₇, Hf₂ CO₄ P₃, CeAl₂ Ga₂, ZrFe₄Si₂, Nb₄ CoSi, Mo₅ SiB₂, MgZn₂, HfCuSi₂. The structures of several phosphides represent the new types: Nb₂P, α-Ni₈P₃, Zr₂Ni_l-xP, Tb,_1?xNiP, SmNi₄P₂, Nd₃Ni₇P₅, Ni₃,₃₆Si₁,₇₆P₆, Mo₂Ni₆P₃, Re_0,6, Ni_0,4P · The obtained experimental data allowed us to make the following conclusions:     

Kinetic studies of the crystallization process of glass-ceramics based on basalt

The crystallization kinetic of the basalt glass ceramic of the oxide composition, (%): SiO₂ − 50.82; Al₂O₃ − 12.05; Fe₂O₃ − 9.28; CaO − 15.48; MgO − 11.08; Na₂O+K₂O − 1.14; TiO₂ − 0.15, with addition of 10% TiO₂ as nucleating agent has been studied using thermal analysis under non-isothermal conditions. In this order, the non-isothermal DTA curves were obtained at different heating rates between 4 and 20°C min⁻¹ in the temperature range of 25–1000°C using a Derivatograph-C (MOM, Hungary). The kinetic parameters of the crystallization process were calculated on the basis of Ozawa-Flynn-Wall, Friedman, Budrugeac-Segal and non-parametric kinetic methods.     

Non-isothermal crystallization kinetics of Ti<Subscript>20</Subscript>Zr<Subscript>20</Subscript>Hf<Subscript>20</Subscript>Be<Subscript>20</Subscript>(Cu<Subscript>50</Subscript>Ni<Subscript>50</Subscript>)<Subscript>20</Subscript> high-entropy bulk metallic glass

The crystallization transformation kinetics of Ti₂₀Zr₂₀Hf₂₀Be₂₀(Cu₅₀Ni₅₀)₂₀ high-entropy bulk metallic glass under non-isothermal conditions are investigated using differential scanning calorimetry. The alloy shows two distinct crystallization events. The activation energies of the crystallization events are determined using Kissinger, Ozawa and Augis–Bennett methodologies. Further, we observe that similar values are obtained using the three equations. The activation energy of the initial crystallization event is observed to be slightly small as compared to that of the second event. This implies that the initial crystallization event may have been easier to be occurred. The local activation energy (E(x)) maximizes in the initial stage of crystallization and keeps dropping in subsequent crystallization process. The non-isothermal crystallization kinetics are further analyzed using the modified Johnson–Mehl–Avrami (JMA) equation. Further, the Avrami exponent values are observed to be 1.5 < n(x) < 2.5 for approximately the entire period of the initial crystallization event and for most instances (0.1 < x < 0.6) of the second crystallization event, which implies that the mechanism of crystallization is significantly controlled by diffusion-controlled two- and three-dimensional growth along with a decreasing nucleation rate.     

Magnetic investigations on AlB2 type structures

Magnetic measurements over a temperature interval 6°–630°K show that the effective paramagnetic moments in Gd₃Si₅, Dy₃Si₅, and Tb₃Si₅ are those of the tripositive rare-earth ions, and these materials are either antiferromagnets or have spiral configurations. In NdSi_1.6Ni_0.4 the effective magnetic moment is due to Nd⁺³ only. NdSi_1.6Fe_0.4 shows a complex magnetic structure. LaSi_1.6Ni_0.4 and LaSi_1.6Fe_0.4 are Pauli paramagnets.     

Polypropylene Crystallization in an Ethylene-propylene-diene Rubber Matrix

The effect of the incorporation of an amorphous immiscible polymer (ethylene-propylene-diene- terpolymer) on the PP crystallization kinetics and thermodynamics is investigated by thermal analysis. The results of the investigation have shown that EPDM acts as a nucleant agent. A marked decrease of the half time of PP crystallization, τ_1/2 , as well as a sensible increase of the overall crystallization rate, K _n , has been observed in the presence of EPDM. Moreover, at any crystallization temperature, a minimum of τ_1/2 , is obtained at 25% EPDM content in the blend. The Avrami model has been successfully applied to describe the crystallization kinetics of the blend. The kinetic curves obtained under non-isothermal conditions confirm the results obtained under isothermal conditions and demonstrate the nucleant action of the EPDM phase on the PP crystallization. This revised version was published online in July 2006 with corrections to the Cover Date.     

The electrochemical properties of Al–Si–Ni alloys composed of nanocrystal and metallic glass for lithium-ion battery anodes

Melt-spun Al_75?X Si₂₅Ni _X (X?=?2, 4, 7, and 10?mol%) alloys were investigated as anode materials for lithium-ion batteries. The Al₆₈Si₂₅Ni₇ anode showed a maximum capacity of 840?mA?h?g^?1 at the fifth cycle and maintained 661?mA?h?g^?1 after 40 cycles with a high coulumbic efficiency of 93%. The specific capacity increased as the decrease in the Ni content during the first 20 cycles, but the cycle performance became poorer. For the Al₆₅Si₂₅Ni₁₀ anode, the specific capacity increased slowly as the cycles increased and reached 370?mA?h?g^?1 after 40 cycles. When the Al₆₈Si₂₅Ni₇ ribbons were annealed, their initial capacity became higher, but much poorer cycle performance and low coulumbic efficiency occurred. Except Al₆₅Si₂₅Ni_10, the AlLi compound could be detected in the anodes after lithiation. However, the capacity faded rapidly due to the formation of excessive AlLi in the Al₇₃Si₂₅Ni₂ and annealed Al₆₈Si₂₅Ni₇ anodes. The experiments revealed that the as-quenched ribbons consisted of the nanoscaled α-Al, metallic glass and α-Si, and their fractions were dependent on the Ni content. The α-Al was a supersaturated solid solution of Si and Ni in fcc-Al. For the as-quenched Al₆₈Si₂₅Ni₇ ribbons, the α-Al grains were embedded in the amorphous matrix. It can be understood that metallic glass can store Li, and the supersaturated solid solution can store Li even more easily compared with other known Al–Si-based alloys. A conclusion can be drawn that the microstructure that the nanoscaled α-Al embedded in the metallic glass matrix is beneficial to improve the structure stability, restrain serious structural evolution, and limit the volume variation and pulverization during electrochemical cycles.