查看更多>>摘要：In this work, the isothermal and non-isothermal crystallization kinetics of two polyamides, a polyamide-based hot melt adhesive with the trade name of Technomelt PA 6910 and a copolymer of PA 6 and PA 66, are studied using Fast Scanning Calorimetry (FSC) and Differential Scanning Calorimetry (DSC). While both of these materials exhibit good performance as feedstocks for material extrusion additive manufacturing, their crystallization behavior and kinetics differ substantially. Technomelt PA 6910 crystallizes much slower than the PA 6/66 due to the lower density of hydrogen bonding within Technomelt PA 6910's structure. The low glass transition temperature encourages room temperature crystallization of Technomelt PA 6910. PA 6/66 is a random copolymer whose faster crystallization is attributed to a high density of hydrogen bonding accompanied by a sheet-like structure of the hydrogen bonding within the melt, which favors high-temperature crystallization. The kinetic results from this study enable coupling the crystallization kinetics of these materials with thermal models for processing techniques including material extrusion additive manufacturing.
查看更多>>摘要：In recent years, dimethylphenol has played an important role in industrial production. The demand and application of dimethylphenol will increase greatly with the continuous advancement of the internationalization process. Solid-liquid equilibrium (SLE) is fundamental for the separation process design, the SLE data of dimethylphenol plays an important role in designing the melting and crystallization separation process. The SLE data of mixtures of 2,6-dimethylphenol (2,6-DMP), 3,5-dimethylphenol (3,5-DMP) and 2,5-dimethylphenol (2,5-DMP) were determined by differential scanning calorimetry (DSC). The crystallographic analysis of eutectic mixtures was analyzed by FTIR. The experimental results show that all the systems studied in this paper exhibit eutectic behavior. SLE data was correlated with Wilson and NRTL models and a satisfactory correlation was obtained. The study provided reliable and accurate data for separating the mixtures of 2,6-dimethylphenol, 3,5-dimethylphenol and 2,5-dimethylphenol. These SLE data are of great significance for the process development and process optimization of dimethylphenol.
查看更多>>摘要：The pyrolysis process was a promising technology for the clean, efficient and resource utilization of iron-based waste catalysts containing wax (IWC) produced from Fisher-Tropsch synthesis. In this study, TG and Py-GCMS were used to investigate the pyrolysis characteristics of IWC. The results showed that the main pyrolysis temperature range of IWC was 200-500 degrees C, attributed to the decomposition of wax. Iron species in IWC were converted to Fe metal at >500 degrees C and slightly promoted the pyrolysis of wax. The tar components produced at low temperature were mainly alkanes of C21+ and C-11-C-20, but linear alpha olefins of C-5-C-20 and few dienes at higher temperature. It was also concluded that some aromatics were also produced from IWC especially at above 700 degrees C. TG and kinetic analyses demonstrated that pyrolysis of IWC occurred in a three-stage reaction with activation energy in the range of 126-331 kJ/mol. A possible pyrolysis mechanism of IWC was also proposed.
查看更多>>摘要：Co-Cr-Mo (CCM) alloys, which are used in biomedical implants, are currently produced by additive manufacturing, for which accurate modeling of the process is required to attain the desired thermophysical properties of the melts. For the purpose of modeling, the density, surface tension, and viscosity of two CCM melts of distinct carbon content (0.05 and 0.25% by mass) were measured using an electrostatic levitation technique. The temperature dependence of both density and surface tension of the melts were assumed to be linear, whereas that for viscosity was assumed to have Arrhenius form, from which the activation energy corresponding to the viscous flow of each CCM melt was obtained. Using the Szyzkowski model along with our present and previous results, the influence of the partial pressure of oxygen on the surface tension of the two CCM melts was evaluated. No substantial difference in surface tension and viscosity between these melts was found.
查看更多>>摘要：Strontium cobaltite containing equimolar amounts of Sr and Co was produced by heating the mixture of SrCO3 and Co3O4 starting materials with a mole ratio of 1:0.333 under dynamic air atmosphere. The chemical reactions occurred during heating were determined and the intermediate and final products obtained at each critical temperature were characterized using TG/DTA-MS, ICP-OES, XRD and FT-IR analytical techniques. The volumetric analysis method (iodometric titration) and carbonation process were carried out to determine the oxygen stoichiometry of strontium cobaltite. It was determined by thermal analysis results that pure SrCO3 and Co3O4 were decomposed to SrO and CoO final products, respectively. Sr6Co5O15-beta was formed by solid-state reaction between SrO and Co3O4 and by gaining O-2 from air. Sr2Co2O5-delta was produced at elevated temperatures by solid-state reaction between Sr6Co5O15-beta and Co3O4 by releasing O-2. At temperature where the decomposition of SrCO3 is not completed and the decomposition temperature of Co3O4 is reached, firstly the formation of Sr6Co5O15-beta and then Sr2Co2O5-delta takes place with CoO instead of Co3O4 . Strontium cobaltite releases oxygen from its structure during heating as the temperature increases in the air atmosphere and it gains oxygen during cooling as the temperature decreases. Sr2Co2O5-delta is converted firstly to Sr6Co5O15 and CoO and then CoO reacts with O-2 to form Co3O4 when cooled to the mom temperature from the temperature it was obtained.
查看更多>>摘要：The thermal decomposition of double complex compounds (DCC) [Co(NH3)(6)][Cr(CNS)(6)] and [Ni(NH3)(6)](3)[Cr (CNS)(6)](2) in air, argon and hydrogen atmospheres has been investigated. The nature and properties of the decomposition products were studied. It was found that the decomposition products of [Co(NH3)(6)][Cr(CNS)(6)] in air in the range 500-700 degrees C are CoSO4, and at 700-900 degrees C - CoCr2O4 and Co2CrO4, in argon up to 500 degrees C - unidentified amorphous phases, and above 500 degrees C - cobalt and chrome sulfides, in a hydrogen atmosphere mixture of metals and sulfides. The initial decomposition products of [Ni(NH3)(6)](3)[Cr(CNS)(6)](2) in air are intermediate metal sulfides, and the final products are nickel sulfates and chromates; in an argon and hydrogen atmosphere - nickel and chromium sulfides. The gaseous products in argon are, respectively, nitrogen, carbon and sulfur dioxides, ammonia, ammonium rhodanide, CS2, and hydrogen sulfide. In a hydrogen atmosphere, thiocyanate undergoes hydrogenation to form ammonia, hydrogen sulfide, methane, and other hydrocarbons.
查看更多>>摘要：The kinetics of the ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) initiated by 1.0 mol% of tin(II) chloride (SnCl2) and zinc(II) chloride (ZnCl2) was completely investigated by the differential scanning calorimetry (DSC) technique. The fast method to determine the activation parameters such as activation enthalpy (Delta H-not equal) and activation entropy (Delta S-not equal) was successfully developed basing on the transition state theory and isoconversional method. From Friedman isoconversional method, the values of activation energy (E-a) for the ROP of epsilon-CL initiated by SnCl2 (36.2 +/- 1.5 to 40.8 +/- 1.5 kJ/mol) were lower than ZnCl2 (51.9 +/- 2.8 to 62.3 +/- 2.8 kJ/mol). From Starink isoconversional method, the E-a values for the ROP of epsilon-CL initiated by SnCl2 (32.3 +/- 1.1 to 35.8 +/- 1.1 kJ/mol) were also lower than ZnCl2 (59.2 +/- 0.8 to 62.1 +/- 0.8 kJ/mol). By using the compensation parameters, the reconstructed monomer conversion function (f(alpha)) was fitted with the Avrami-Erofeev nucleation model (A2, f(alpha) = 2(1-alpha)[-ln(1-alpha)](1/2)). The values of frequency factor (A) for the ROP of epsilon-CL with SnCl2 and ZnCl2 were 4.3 x 10(3)(to) 1.6 x 10(4) min(-1) and 2.1 x 10(5) to 5.3 x 10(5) min(-1), respectively. From the developed rate equation, the values of Delta H-not equal and Delta S-not equal could be conveniently determined from dynamic heating. The obtained Delta H-not equal values for the ROP of epsilon-CL initiated by SnCl2 and ZnCl2 were similar to the E-a values. The Delta S-not equal values for the transition state of the ROP of epsilon-CL initiated by SnCl2 (-152.0 to -161.7 J/mol.K) were lower than ZnCl2 (-129.6 to -153.1 J/mol.K). The kinetics and the stability of transition state information demonstrated that the reactivity of SnCl2 in the ROP of epsilon-CL was higher than ZnCl2. The mechanism of the ROP of epsilon-CL with SnCl2 and ZnCl2 was proposed through a classical coordination-insertion mechanism. From poly(e-caprolactone) (PCL) synthesis via solvent-free polymerization, SnCl2 acted as the highly effective initiator than ZnCl2. The highest number average molecular weight (M n ) of PCLs obtained from the SnCl2 and ZnCl2 initiator were 1.8 x 10(5) g/mol and 3.6 x 10(4) g/mol, respectively. The effectiveness of the slow ZnCl2 initiator in the production of high molecular weight and %yield of PCL could be improved by increasing the synthesis temperature. These SnCl2 and ZnCl2 compounds acted as a powerful initiator for the synthesis of PCL. The obtained results from this work were useful for understanding the transition state formulation in the ROP of other cyclic esters with various initiating systems that still in our attention and would be described in our future work.
Mukhametzyanov, Timur A.Fatkhutdinova, Alisa A.Schick, Christoph
14页
查看更多>>摘要：Calorimetric step-scan curves of the reversible protein denaturation were modeled numerically. The quasi-equilibrium denaturation regime can be realized if the duration of isothermal steps is long enough so that the system is able to settle to equilibrium. We show the changes in the real and imaginary parts of the complex heat capacity during the denaturation process depending on the kinetic regime of denaturation. The practical application of the step-scan method for denaturation of lysozyme in water has revealed the negative temperature coefficient of the excess heat capacity of lysozyme. In the case of denaturation of lysozyme in glycerol studied by fast scanning calorimetry, the step-scan technique can be used to improve the quality of the baseline and reveal a heat capacity step after during denaturation.
NSTL
Elsevier