On the study by D.S.C. of the unexpected ice melting at 0°C of emulsified aqueous saline solutions

Firstly, the behavior of droplets (Φ ≈ 1μm) of aqueous saline solutions dispersed within an emulsifying medium and subjected to steady cooling and heating is described. Droplets undergo freezing around a temperature T¹(x) and partial ice melting and total salt melting at the eutectic temperature T_E. This melting is followed by progressive melting of the remaining ice which ceases when the equilibrium temperature (T_e(x)) ice ⇆ solution is reached. Between T_e and T¹ the droplets are undercooled. Secondly, the results obtained when water crystallization occurs versus time at a fixed temperature _C, such as T¹(x) < > _C < T_e(x) are reported. During heating following crystallization at Θ_C, an unusual ice melting at 0° and/or ice melting ending at T & >; T_e(x) is noticed on the thermogram obtained by differential scanning calorimetry of the emulsion. This shows that pure ice or at all events less concentrated solutions must be present within the emulsion. A possible mechanism of crystallization at Θ_C is proposed.     

Effect of the Heating Rate on Crystallization Kinetics of Mg84Ni12.5Y3.5 Amorphous Ribbons

Crystallization kinetics of Mg₈₄Ni_12.5Y_3.5 amorphous ribbons produced by the melt-spinning method, was studied by DSC analysis and X-ray diffraction. The effect of heating rate (from 2 to 240 K min^–1) was investigated in the temperature range from 298 to 673 K. The results showed that the crystallization process took place in two stages: a) crystallization of part of the amorphous matrix to an intermediate phase and hcp-Mg, and b) transformation of the intermediate phase and the remaining amorphous material to Mg₂Ni+Mg (solid solution of Y in Mg). Increasing the heating rate from 2 to 240 K min^–1 results in increases of the temperature difference between the two-step crystallization of the first stage transformation processes from 33 to 56 K and in increases of the temperature difference between the two-stage transformation from 62 to 97 K.This revised version was published online in November 2005 with corrections to the Cover Date.     

Intercalation von Metallnitraten in Graphit. IV. Die Reaktion von wasserfreiem Kupfer(II)-nitrat mit Graphit

Intercalation of Metal Nitrates in Graphite. IV. Reaction of Anhydrous Copper (II) Nitrate with Graphite By heating of Cu(NO₃)₂ and Cu(NO₃)₂ · N₂O₄ with graphite (160–200°C, 1–8 d) samples of stage 4, 5, and 6 of Cu(NO₃)₂ graphite were obtained, which were characterized by X-ray powder diffraction and chemical analysis. 4^th stage: I_c = 2030 pm, C:Cu ≈ 40:1. 5^th stage: I_c = 2365 pm, C:Cu ≈ 50:1. 6^th stage: I_c = 2700 pm, C:Cu ≈ 60:1. The intercalate thickness was found to be 690 pm. Heating with Cl₂ yields the corresponding stages of CuCl₂ graphite.     

Effect of Heating Rate on Crystallization Kinetics of Amorphous Al91La5Ni4 Alloys by DSC

Crystallization kinetics of Al₉₁La₅Ni₄ amorphous ribbons produced by a melt-spinning method were studied by DSC analysis and X-ray diffraction. The effect of heating rate (from 4 to 200°C min^-1) was investigated in the temperature range from 298 to 700 K. Increases the heating rate from 4 to 200°C min^-1 resulted in increases of the temperature difference between the two stages of the transformation process: crystallization of Al and crystallization of the Al compounds from 148.9 to 167.4 K. The apparent activation energies for the first step, related to Al crystallization, and to the second step related to crystallization of Al₄La and Al₃Ni, were found to be 161±9 and 199±10 kJ mol^-1, respectively. The results indicate the possibility of tailoring the heating treatment to produce the required fraction of the amorphous phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of formation of nano-quasicrystals and crystallization kinetics of Zr-Al-Ni-Cu metallic glass

The formation of nano-quasicrystals on isothermal annealing of melt-spun ribbons of Zr_69.5Al_7.5Ni₁₁Cu₁₂ metallic glass has been investigated using transmission electron microscopy (TEM). The crystallization study of this metallic glass has been carried out using differential scanning calorimetry (DSC) in non-isothermal (linear heating) mode. It exhibits two-stage crystallization where the first stage corresponds to the precipitation of icosohedral nano-quasicrystalline phase. This has been confirmed with the help of TEM investigations. The crystallization parameters like the activation energy (E _c) and frequency factor (k ₀) have been derived using the Kissinger peak shift analysis. The activation energies for the first and second crystallization peak are found to be 278 and 295 kJ mol^–1, respectively. The frequency factors obtained for the two peaks are respectively 7.16·10¹⁹ and 1.42·10²⁰ s^–1. E _c, k ₀ and the Avrami exponent (n) have also been derived by fitting the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation for the transformed volume fraction (x) to the crystallization data. JMAK results of E _c for the first and second crystallization peak turn out to be 270 and 290 kJ mol^–1 respectively. However, k ₀ and n are found to be heating rate dependent as reported in similar studies. The values of n for the first crystallization stage ranges between 1.66 and 2.57 indicating diffusion-controlled transformation in agreement with earlier reports.     

Crystallization kinetics of amorphous Fe75−xAgxSi9B16

The influence of Ag admixtures on the crystallization process of amorphous Fe-Si-B alloys of the series Fe_75−xAg_xSi₉B₁₆ (x=0, 1, 2, 3 and 4) was studied by differential scanning calorimetry (DSC) measurements at different heating rates. Two exothermic peaks were observed in the DSC trace when the Ag content was 2-4 at.% and one when it was 1 at.%, respectively. The activation energy was calculated both with Kissinger’s and isoconversional Flynn, Wall and Ozawa methods. The possibility of analysis with the JMA model using the Avrami plot was investigated for the third stage of crystallization.     

Radiochemical separation of 109Cd from a silver target

A radiochemical separation method was developed for the separation of ¹⁰⁹Cd from a ^nat.Ag target (6.6 g, pressed into a 19 mm disc). The method comprised of two stages. In the first stage, after dissolution of the target in nitric acid, silver was separated from Cd by precipitation into the metallic form using 20 g of Cu turnings for the reduction of Ag⁺ ions. In the second stage, ¹⁰⁹Cd in the filtrate, that contained trace amount of silver and substantial quantity of Cu(I), was purified by use of a Bio-Rad AG1-X10 anion-exchange resin. The ion-exchange chromatography employed a column with (1.6 cm i.d. and 4 cm length) with a flow rate of 2 ml/min throughout the separation. ¹⁰⁹Cd was quantitatively recovered from the first stage and the recovery yield from the ion-exchange chromatography was greater than 96%. 2M HCl containing H₂O₂ was used for the adsorption of ¹⁰⁹Cd and elution of Cu. ¹⁰⁹Cd was eluted by 50 ml 1M HNO₃. The concentrations of stable isotopes of Ag and Cu in the final solution (5 ml 0.05M HCl) were measured by an ICP-OES method and found to be <1 ppm.     

Melting kinetics of it-polypropylene crystals over wide heating rates

Melting kinetics of it-polypropylene crystals has been examined over wide heating rates of 0.6 K min^?1?10⁴ K s^?1 using a standard DSC and a fast-scan DSC. With fast-scan DSC, we have an access to the melting of crystals obtained at low temperatures, which are susceptible to re-organization at the heating rates applicable with standard DSC. It is clearly discernible that the appearance and disappearance of multiple melting peaks are strongly influenced by the applied heating rates and dependent on the crystallization temperatures. By examining the heating rate dependence of superheating of melting, we have determined the melting points of as-grown crystals formed under wide crystallization temperatures.     

Thermal stability and crystallization kinetics of Se–Te–Sn alloys using differential scanning calorimetry

The present article deals with the differential scanning calorimetric (DSC) study of Se?CTe glasses containing Sn. DSC runs are taken at four different heating rates (10, 15, 20 and 25?K?min^?1). The crystallization data are examined in terms of modified Kissinger, Matusita equations, Mahadevan method and Augis and Bennett approximation for the non-isothermal crystallization. The activation energy for crystallization (E _c) is evaluated from the data obtained at different heating rates. Activation energy of glass transition is calculated by Kissinger??s relation and Moynihan theory. The glass forming tendency is also calculated for each composition. The glass transition temperature and peak crystallization temperature increases with the increase in Sn % as well as with the heating rate.     

Non-isothermal crystallization kinetics of poly(trimethylene terephthalate)/poly(ethylene 2,6-naphthalate) blends

The glass-transition temperature and non-isothermal crystallization of poly(trimethylene terephthalate)/poly(ethylene 2,6-naphthalate) (PTT/PEN) blends were investigated by using differential scanning calorimeter (DSC). The results suggested that the binary blends showed different crystallization and melting behaviors due to their different component of PTT and PEN. All of the samples exhibited a single glass-transition temperature, indicating that the component PTT and PEN were miscible in amorphous phase. The value of T_g predicted well by Gordon-Taylor equation decreased gradually with increasing of PTT content. The commonly used Avrami equation modified by Jeziorny, Ozawa theory and the method developed by Mo were used, respectively, to fit the primary stage of non-isothermal crystallization. The kinetic parameters suggested that the PTT content improved the crystallization of PEN in the binary blend. The crystallization growth dimension, crystallization rate and the degree of crystallinity of the blends were increased with the increasing content of PTT. The effective activation energy calculated by the advanced iso-conversional method developed by Vyazovkin also concluded that the value of E_a depended not only on the system but also on temperature, that is, the binary blend with more PTT component had higher crystallization ability and the crystallization ability is increased with increasing temperature. The kinetic parameters U^* and K_g were also determined, respectively, by the Hoffman-Lauritzen theory.     

Study of non-isothermal crystallization of amorphous Cu<Subscript>50</Subscript>Ti<Subscript>50</Subscript> alloy

The crystallization kinetics of amorphous Cu₅₀Ti₅₀ has been studied using differential scanning calorimetry (DSC) under non-isothermal conditions. The curves at different linear heating rates (2, 4, 8 and 16 K min^–1) show sharp crystallization peaks. The crystallization peak shifts to higher temperatures with increasing heating rate. The Kissingers method of analysis of the shift in the transformation peak is applied to evaluate the activation energy (E _c). The KJMA formalism, which is basically developed for isothermal experiments, is also used to obtain E _c and the Avrami parameter (n).The DSC data have been analysed in terms of kinetic parameters, viz. activation energy (E _c), Avrami exponent (n) and frequency factor K ₀ using three different theoretical models. It is observed that the activation energy values derived from KJMA approach and modified Kissinger equation agree fairly well with each other. The activation energy values obtained from normal Kissinger method, and Gao and Wang expression underestimate the activation energy.The financial support provided by All India Council for Technical Education (AICTE), New Delhi (Govt. of India) is gratefully acknowledged.     

CRYSTALLIZATION AND MULTI-MELTING BEHAVIOR OF POLY (ETHYLENE TEREPHTHALATE) MODIFIED BY SODIUM SALT OF 5-SULPHO-ISOPHTHALIC ACID

The crystallization kinetics of the copolyester, poly(ethylene terephthalate) (PET) modified by sodium salt of 5-sulpho-isophthalic acid(SIPM), was investigated by means of differential scanning calorimeter. The experimental results and polari-microscopy observation all showed that the introduction of SIPM did not affect the nucleation of crystallization. Within the temperature range between their glass transition temperature T_θand melting point T_m, the crystallization rate of the copolyester sample decreased with increasing content of SIPM. The relative crystallization rate constant Z of SIPM/DMT (dimethyl terephthalate) 4mol % sample was about 1% pure PET's Z value. For isothermal crystallized copolyester samples, DSC heating curves displayed multi-melting behavior. This was interpreted by molecular weight fractionation during crystallization and premelting-recrystallization mechanism. This interpretation showed why the second melting point T_(m2) will change according to Hoffman-Weeks(H-W) equation and the first melting point T_(m1) will increase with increasing SIPM. The principal cause of these phenomena is the high temperature crystallization rate decreases rapidly with increasing SIPM.     

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.     

Crystallization study of Na-Gd phosphate glass using non-isothermal DTA

Na-Gd phosphate glasses doped with Ce³⁺ are intensively studied due to their high intensity radioluminescence. Crystallization kinetics of glass with nominal composition of NaGd(PO₃)₄ was investigated using non-isothermal DTA at heating rates between 10 and 115 K min⁻¹ and evaluated by the Kissinger and Ozawa peak methods. The activation energy for crystallization was determined for heating rates lower than 72 Kmin⁻¹ as 789.91 and 802.77 kJ mol⁻¹ by using the Kissinger and Ozawa methods, respectively. Formation of nuclei, their dimensions and movement of the crystallization front were observed using isothermal optical thermomicroscopy.     

Pyrolysis of pine needles: effects of process parameters on products yield and analysis of products

Pyrolysis of pine needles was carried out in a semi-batch reactor. The effects of pyrolysis parameters such as temperature (350–650 °C), heating rate (10 and 50 °C min^?1), nitrogen flow rate (50–200 cm³ min^?1) and biomass particle size (0.25–1.7 mm) were examined on products yield. Maximum bio-oil yield of 43.76% was obtained at pyrolysis temperature of 550 °C with a heating rate of 50 °C min^?1, nitrogen flow rate of 100 cm³ min^?1 for biomass particle size of 0.6 < d _p < 1 mm. The characterization of pyrolysis products (bio-oil, bio-char) has been made through different instrumental methods like Fourier transform infrared spectroscopy, gas chromatography–mass spectrometry, nuclear magnetic resonance spectroscopy (¹H NMR), X-ray powder diffraction, field emission scanning electron microscope and Brunauer–Emmett–Teller surface area analysis. The empirical formula of the bio-oil and bio-char was found as CH_1.47O_0.36N_0.005 and CH_0.56O_0.28N_0.013 with heating value of 26.25 and 25.50 MJ kg^?1, respectively. Results show that bio-oil can be potentially valuable as a renewable fuel after upgrading and can be used as a feedstock for valuable chemicals production. The properties of bio-char reveal that it can be used as solid fuels, as a cheap adsorbent and as a feedstock for activated carbon production.     

Thermal Behavior and Non-isothermal Decomposition Reaction Kinetics of NEPE Propellant with Ammonium Dinitramide

Thermal decomposition behavior and non‐isothermal decomposition reaction kinetics of nitrate ester plasticized polyether NEPE propellant containing ammonium dinitramide (ADN), which is one of the most important high energetic materials, were investigated by DSC, TG and DTG at 0.1 MPa. The results show that there are four exothermic peaks on DTG curves and four mass loss stages on TG curves at a heating rate of 2.5 K·min^?1 under 0.1 MPa, and nitric ester evaporates and decomposes in the first stage, ADN decomposes in the second stage, nitrocellulose and cyclotrimethylenetrinitramine (RDX) decompose in the third stage, and ammonium perchlorate decomposes in the fourth stage. It was also found that the thermal decomposition processes of the NEPE propellant with ADN mainly have two mass loss stages with an increase in the heating rate, that is the result of the decomposition heats of the first two processes overlap each other and the mass content of ammonium perchlorate is very little which is not displayed in the fourth stage at the heating rate of 5, 10, and 20 K·min^?1 probably. It was to be found that the exothermal peak temperatures increased with an increase in the heating rate. The reaction mechanism was random nucleation and then growth, and the process can be classified as chemical reaction. The kinetic equations of the main exothermal decomposition reaction can be expressed as: dα/dt=10^12.77(3/2)(1?α)[?ln(1?α)]^1/3 e^{?1.723×104/T}. The critical temperatures of the thermal explosion (T_be and T_bp) obtained from the onset temperature (T_e) and the peak temperature (T_p) on the condition of β→0 are 461.41 and 458.02 K, respectively. Activation entropy (ΔS^≠), activation enthalpy (ΔH^≠), and Gibbs free energy (ΔG^≠) of the decomposition reaction are ?7.02 J·mol^?1·K^?1, 126.19 kJ·mol^?1, and 129.31 kJ·mol^?1, respectively.     

123 Phases in Ce-La-Nd-2Cu-Mg-O and Ce-2Nd-2Cu-Mg-O samples

We show that the substitution of lanthanum by neodymium, whose oxide melts at a temperature 500°C lower than La₂O₃, appreciably facilitates the synthesis of 123 phases with their Cu(1) positions fully or selectively substituted by magnesium. 123 phases with unit cells doubled in plane ab (phases “336”) and with compositions close to Ce₂(La_1.4Nd₂Ba_0.6){ Cu _3.4 ²⁺ Cu _0.6 ³⁺ } [Mg₂]O₁₆ (a = b = 0.5498(5) nm, c = 1.6425(8) nm), and Ce₂(La_1.7Nd₂K_0.3){ Cu _3.4 ²⁺ Cu _0.6 ³⁺ } [Mg₂]O₁₆ (a = b = 0.5498(5) nm, c = 1.6488(8) nm), and Ce₂(Nd_3.4Ba_0.6){ Cu _3.4 ²⁺ Cu _0.6 ³⁺ } [Mg₂]O₁₆ (a = b = 0.5474(5) nm, c = 1.6425 nm), where the parentheses indicate the Ba positions, the braces indicate the Cu(2) positions, and the brackets indicate the Cu(1) positions, were synthesized using modified nitrate technology at 810°C in flowing oxygen. The existence of Cu³⁺ in the Cu(2) positions endows the phases with electrical conductivity. The conductivity versus temperature curves show the semiconductor trend. The samples do not experience superconducting transitions up to 60 K.     

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.     

Alkynylhalocarbenes. 2. Generation of (alkyn-1-yl)-chlorocarbenes by basic solvolysis of 1,1-dichloro-2-alkynes and their reaction with olefins: Synthesis of 1-chloro-1-alkynylcyclopropanes

1,1-Dichloro-2-alkynes R¹CCCHCl₂ (4a–g; R¹=Me, n-Pr, c-Pr, t-Bu, Ad, Nor, Ph) were synthesized with yields of 50–75% by chlorination with PCl₅ of formylacetylenes (3a–g), prepared by oxidation of propargyl alcohols (1a–d) with CrO₃·Py·HCl complex or acidolysis of propargyl acetals (2a–c) in the presence of catalytic quantities of pyridine; the corresponding alkynylchlorocarbenes, R¹CCCCl (5a–g) were generated from them with powdered KOH in a two-phase system or t-BuOK. The latter were trapped by olefins with formation of 1-chloro-1-alkynylcyclopropanes (6a–t) with yields of up to 90%.See [1] for Communication 1.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1128–1135, May, 1992.     

Preparation,Properties and Thermal Decompositions of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) Complexes of 2,5-dichlorobenzoic Acid

Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 2,5-dichlorobenzoates were prepared and their compositions and solubilities in water at 295 K were determined. The IR spectra and X-ray diffractograms of the obtained complexes were recorded. The complexes of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) were obtained as solids with a 1:2 molar ratio of metal to organic ligand and different degrees of hydration. When heated at a heating rate of 10 K min^-1, the hydrated complexes lose some (Co, Zn) or all (Ni, Cu, Cd) of the crystallization water molecules and then decompose to oxide MO (Co, Ni) or gaseous products (Cu, Zn, Cd). When heated at a heating rate of 5 K min^-1, the complexes of Ni(II) and Cu(II) lose some (Ni) or all (Cu) of the crystallization water molecules and then decompose directly to MO. This revised version was published online in July 2006 with corrections to the Cover Date.