Crystallization kinetics of Ti20Zr20Cu60 metallic glass by isoconversional methods using modulated differential scanning calorimetry

The study of crystallization kinetics of amorphous alloys has been a matter of great interest for material researchers for past few decades, since it provides information about the kinetic parameters i.e., activation energy of crystallization and the frequency factor. These kinetic parameters can be calculated by model-free isoconversional methods. Isoconversional methods allow calculating the activation energy as a function of degree of conversion, α. Hence, these methods provide accurate results for multistep processes like crystallization. Model-free methods are categorized as linear and non-linear isoconversional methods. Linear methods are further classified as linear differential and linear integral isoconversional methods. In present work, we have used these isoconversional methods to study the effect of non-linear heating rate, employed by modulated differential scanning calorimetry (MDSC), on the non-isothermal crystallization kinetics of Ti₂₀Zr₂₀Cu₆₀ metallic glass. For Ti₂₀Zr₂₀Cu₆₀, MDSC curves clearly indicate a two-step crystallization process. Both crystallization peaks were studied based on the modified expressions for isoconversional methods by non-linear heating rate. The term corresponding to non-linearity comes out to be (A _T ω/2β)². The effect of non-linear heating rate on measurement of kinetic parameters by isoconversional methods is studied. The activation energy of crystallization is calculated for Ti₂₀Zr₂₀Cu₆₀ metallic glass for various degrees of conversion by linear integral isoconversional methods i.e., Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose, and also with Friedman method which is a linear differential isoconversional method.     

Thermodynamics of Zr<Subscript>52.5</Subscript>Cu<Subscript>17.9</Subscript>Ni<Subscript>14.6</Subscript>Al<Subscript>10</Subscript>Ti<Subscript>5</Subscript> bulk metallic glass forming alloy

Recently, multicomponent glass forming alloys have been found which exhibit extraordinary glass forming ability and cooling rates of less than 100 K/s are sufficient to suppress nucleation of crystalline phases and consequently bulk metallic glass (BMG) is formed. The undercooled melts of BMG systems have high thermal stability in the undercooled region. Therefore, it is interesting to study the thermodynamics of such materials. This article investigates the thermodynamic behavior of a BMG system namely Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ by estimating the Gibbs free energy difference ΔG, entropy difference ΔS, enthalpy difference ΔH between the undercooled liquid and corresponding equilibrium crystalline solid phase, in the entire temperature range from T _m to T _K. Glass forming ability (GFA) of this system has been investigated through various GFA parameters indicating the degree of ease of glass formation.     

Photocatalytic decolouration,degradation and disinfection capability of Ag2CO3/ZnO in natural sunlight

In this study, a series of hybrid Ag₂CO₃/ZnO composites were synthesised via a simple precipitation route and investigated for discolouration-degradation of Methylene Blue and disinfection of Escherichia coli in natural sunlight. It was observed that the photonic efficiency of discolouration was more than 6 times that of the conventionally popular TiO₂, under experimental conditions; 100% Total Organic Carbon reduction was observed in 30 ?min and 32% disinfection in an hour. This upswing in the performance is attributed to favourable modulation of the dynamics of charge transfer. The photocatalysts were characterized by X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, Brunauer, Emmett and Teller and Ultraviolet–Visible-Near-InfraRed Spectroscopy. An equitable photocatalyst functional mechanism has also been proposed on the basis of Tauc plot and scavenging experiments. The effect of influencing parameters has also been investigated and reported in terms of photonic efficiency. Since the entire study is carried out in direct sunlight, it inherently supports realizable solar energy applications in wastewater treatment.     

Kinetics of crystallization of Zr52Cu18Ni14Al10Ti6 metallic glass

Metallic glasses have received considerable attention in comparison to normal metallic materials due to their superior physical and mechanical properties. These systems possess large under cooled region, ∆T (∆T = T _x − T _g where, T _x is crystallization temperature and T _g is glass transition temperature) and hence increased thermal stability against crystallization. Due to this, the study of their crystallization kinetics is important and interesting. It is interesting because of the fact that, crystallization becomes multi-step process due to several components present in these systems. In this paper, we report the experimental investigations of crystallization of Zr₅₂Cu₁₈Ni₁₄Al₁₀Ti₆ glassy alloy system, which is among the best non-beryllium containing glasses, using differential scanning calorimetry (DSC). The crystallization, as expected, consists of multiple steps. Interestingly, the peak heights of these steps vary with heating rate. At lower heating rates, first peak is most prominent and subsequently diminishes with increase in heating rate with last peak prominence visible at highest heating rate. Both, iso-kinetic and iso-conversional methods of analysis of kinetics of crystallization have been used to evaluate the activation energy and Avrami exponents and consistent results are obtained.     

Study of kinetics of glass transition of metallic glasses

In this study, the kinetics of glass transitions of Ti₅₀Cu₂₀Ni₃₀ and Fe₆₇Co₁₈B₁₄Si₁ metallic glasses are studied using thermal analysis technique, i.e., differential scanning calorimetry, by means of continuous heating of the sample at various heating rates. In the present study, based on the heating rate dependence of glass transition temperature (T _g), the activation energy (E) of the glass transition region is determined by two most frequently used approaches, i.e., Moynihan's method and Kissinger's equation. The fragility index, m, is also calculated using T _g, which is a measure of glass-forming ability of the given system. The result shows that the fragility index, m, of the given systems is <16. This indicates that the given systems are strong liquids with excellent glass-forming ability.