Differential Scanning Calorimeter Heating Research Articles

Effect of Homogenization Process on Microstructure of Al–Zn–Mg–Cu Aluminum Alloys

Herein, the best homogenization process of 466.5 °C × 36 h + 490 °C × (14–26.4 h) that can completely eliminate the coarse phases σ[Mg(Zn, Al, Cu)2] and S(Al2CuMg) in the Al–Zn–Mg–Cu aluminum alloy is developed. The homogenization process is determined by the method of calculation phase diagram, and the experimental verification. It is shown in the results that, first, in the microstructure of the as‐cast alloys, the crystal structure of the σ[Mg(Zn, Al, Cu)2], Al7Cu2Fe, and Mg2Si phases is determined. Second, during the homogenization process, the σ[Mg(Zn, Al, Cu)2] phase dissolves and also transforms into the S(Al2CuMg) phase. Most importantly, the dissolution temperature range of the σ[Mg(Zn, Al, Cu)2], S(Al2CuMg), and Al7Cu2Fe phases is determined from 472.56 to 476.36 °C, from 484.09 to 485.39 °C, and from 540.18 to 547.23 °C, respectively. At best homogenization process, the residual Al7Cu2Fe phase area fraction ranges from 1.28 ± 0.16% to 1.60 ± 0.18%. In addition, dispersed η(MgZn2) phase precipitates in supersaturated Al‐matrix during differential scanning calorimeter heating. And, the concentration differences between the grain center and the eutectic of structure of Zn, Mg and Cu regression equations are established, which can provide some reference for the design of experimental parameters, thus reducing the experimental workload.

Effects of Proportion of BF3-MEA on Curing Properties of AG-80/DDS Resin System

Through differential scanning calorimeter (DSC), the systematic analysis is carried out on the issues including: the curing properties of the resin system composed of 4,4’-diaminodiphenylmethane epoxy resin (AG-80), 4,4’-diaminodiphenylsulfone (DDS) and boron trifluoride monoethylamine complex (BF3-MEA); the effect imposed by the varying content of BF3-MEA on the temperature, extent and rate of reaction; and the effect imposed by the varying DSC heating rates on the curing properties of the AG-80/DDS/BF3-MEA resin system. In the meantime, Ti0, Tp0 and Tf0 are derived, and the curing regimes of the three proportioning schemes are determined accordingly. The gel time of the AG-80/DDS/BF3-MEA resin system is measured through the gel drawing method, and the effect of the BF3-MEA content on the gel time is assessed, so as to determine that 0.7 times of the gel time shall be the pressure time for the forming of composite materials. Furthermore, tests are carried out on the mechanical properties of the resin cast and the carbon fiber composite materials prepared through the three proportioning schemes. The results have shown that when the content of BF3-MEA is 2%, the AG-80/DDS/BF3-MEA resin system outperforms the other proportioning schemes in terms of the curing process and the processability of its composite materials. Besides, the comprehensive mechanical properties of the resin cast and the carbon fiber composite are better.

Experimentally Implementing the Linear Nonisothermal Equation for Simultaneously Obtaining D- and z-Values of Salmonella Senftenberg in Skim Milk with a Differential Scanning Calorimeter

For bacteria with log-linear thermal inactivation kinetics in food, D-values are obtained in multiple isothermal inactivation experiments at different temperatures, and the z-value is obtained from these D-values. In a previous work, the cumulative lethality integral was mathematically solved in closed form when temperature in the food increased linearly with time. The solution revealed that each nonisothermal experiment could yield both D- and z-values, eliminating the need for getting multiple D-values to get a z-value. The present study reports on the first experimental implementation of this method of obtaining D- and z-values for Salmonella Senftenberg suspended in skim milk for which a differential scanning calorimeter (DSC) provided the required constant heating rate. The resulting D- and z-values were compared with those obtained from an isothermal method with capillary tubes. No significant differences in z-values were found between the two methods. The D-values also agreed but only after correcting the nonisothermal value for temperature lag in the DSC caused by the large sample size required. A 5 K/min heating rate was used in this comparison. Other rates were also investigated: 1, 3, 7.5, and 10 K/min. Although D- and z-values should be independent of DSC heating rate, heating rates of 1 and 10 K/min yielded values that were significantly different from the others; therefore, these rates cannot be recommended for use in this nonisothermal method.

Complex Phase Behaviors and Structural Coexistence of Natural Gas Hydrates Containing Large-Molecule Guest Substances

The complex phase behaviors and structural coexistence of natural gas hydrates (NGHs) that contain large-molecule guest substances (LMGSs) were examined for their significance in the exploration and exploitation of NGHs as well as natural gas storage and transportation. Methylcyclopentane (MCP) and 2,2-dimethylbutane [neohexane (NH)] were chosen as LMGSs, and the simplest composition of NGHs and natural gas was simulated by a gas mixture of CH4 (90%) + C2H6 (10%). The coexistence of structure II (sII) and structure H (sH) hydrates in the CH4 + C2H6 + LMGS + water mixtures was revealed by 13C nuclear magnetic resonance (NMR) and powder X-ray diffraction (PXRD). CH4 and LMGSs were captured in sH, whereas CH4 and C2H6 were enclathrated in sII. Endothermic heat flow curves, which were obtained by a differential scanning calorimeter (DSC), and pressure (P)–temperature (T) traces exhibited two-step dissociation of formed gas hydrates (sH dissociation followed by sII dissociation). The experimental results for the PXRD patterns, 13C NMR spectra, phase equilibria, DSC heating curves, and P–T traces clearly demonstrated that the CH4 (90%) + C2H6 (10%) + LMGS + water mixtures formed both sII hydrates and sH hydrates and that the final hydrate structure at equilibrium dissociation points was sII.

Effects of amylose chain length and heat treatment on amylose–glycerol monocaprate complex formation

Aqueous mixtures of amylose with different chain lengths (DP 23–849), which had been enzymatically synthesized or isolated from potato and maize starches, and glycerol monocaprate (GMC, 5:1 weight ratio) were analyzed by using a differential scanning calorimeter (DSC). The mixtures were thermally treated (first DSC scan: 20–140°C, 5°C/min and prolonged heat treatment: 100°C for 24h) and its effect on the amylose–GMC complex formation was analyzed by DSC and X-ray diffractometer. The amylose, especially short ones, readily associated in the dispersion forming the amylose–amylose crystals but the presence of GMC inhibited the crystal formation. The longer amylose had the greater possibility for the complex formation with GMC, and the prolonged heat treatment facilitated the amylose–GMC complex formation. Both type I and type II complexes were formed during quenching after the initial DSC heating. However, only the type II complexes were formed after the prolonged heat treatment with improved crystallinity and thermostability.

Phase transformations in Al–Mg–Zn alloys during high pressure torsion and subsequent heating

The structure, phase composition, and their thermal evolution were studied in case of ternary Al–Zn–Mg alloys before and after high-pressure torsion (HPT) in Bridgman anvils. The as-cast non-deformed alloys contained the fine particles of Mg32(Al,Zn)49 (τ phase), MgZn2 (η phase), AlMg4Zn11 (η′ phase), and Mg7Zn3 phases embedded in the matrix of Al-based solid solution. During heating in differential scanning calorimeter (DSC), all these phases dissolved around 148 °C. The τ nanoparticles coherent with (Al) matrix-formed instead around 222 °C. HPT of the as-cast alloys strongly refined the grains of (Al) solid solution from 500 μm to 120–150 nm. The particles of τ, η, η′, and Mg7Zn3 phases fully dissolved in the (Al) matrix. During the following DSC-heating, particles of η phase appeared and grew. Their amount became maximal around 166 °C. The growth of η phase in the fine-grained HPT-treated alloys instead of τ phase in the coarse-grained ones is explained by the shift of the (Al) + η/(Al) + η + τ/(Al) + τ lines in the Al–Zn–Mg ternary phase diagram due to the grain boundary (GB) adsorption. At 166 °C the η phase formed the continuous flat layers in numerous (Al)/(Al) GBs. This corresponds to the complete GB wetting by the η phase. Other (Al)/(Al) GBs contain separated lenticular η particles (incomplete GB wetting). Increasing the temperature from 166 to 320 °C led to the disappearance of the completely wetted (Al)/(Al) GBs. In other words, the transition from complete to the incomplete wetting of (Al)/(Al) GBs by the η phase proceeds between 166 °C and 320 °C.

Microstructure and solidification behaviour characterisation of phosphorus and boron doped IN718 superalloy

The additions of 0·022–0·025 mass-% phosphorus and 0·010–0·012 mass-% boron could enhance the creep properties and increase the service temperature of IN718 superalloy markedly. However, the as cast microstructure and solidification behaviour of modified IN718 with P and B additions are not completely recognised. In the present paper, differential scanning calorimeter (DSC) technique accompanied by scanning electron microscope and electron probe microanalysis characterisation is applied to understand the effects of P and B additions. It is found that P and B additions may promote the formation of big blocky Laves phase and result in the existence of B bearing phase enriched in Nb and Mo. In the meantime, another endothermic peak appearing before the Laves phase peak in the DSC heating curve is related to the melting of the B bearing phase. After the thermodynamics calculation, this new endothermic peak detected may be involved with the melting of M3B2. Furthermore, the endothermic peak appears before the Laves phase peak in the DSC heating curve, suggesting that the incipient melting temperature is greatly reduced as a result of P and B additions. In addition, both melting and solidification temperature ranges are significantly widened, indicating that the solidification process becomes more complex for the P and B doped IN718 superalloy.

Estudo do reprocessamento de polietileno de baixa densidade (PEBD) reciclado do processamento de extrusão de filmes tubulares

O mercado de reciclagem para os polímeros termoplásticos encontra-se atualmente em acentuada ascensão. Os materiais reciclados são vistos como materiais de propriedades inferiores em relação ao material virgem. O presente trabalho avaliou as características viscoelásticas e térmicas do polietileno de baixa densidade (PEBD) reciclado. As amostras foram reprocessadas até dez vezes em condições extremas de processamento (300 °C/80 rpm) em uma extrusora monorosca, a fim de avaliar modificações estruturais nas suas propriedades. Foram realizadas análises de reometria oscilatória de placas paralelas e calorimetria exploratória de varredura (DSC). A partir das análises de reometria oscilatória foram calculados espectros de relaxação e retardação pelo programa de regularização não-linear (NLREG) e através das análises de DSC no primeiro aquecimento foram calculados os parâmetros cinéticos pelos métodos de Avrami e Freeman-Carroll. Os resultados do estudo reológico demonstraram que as amostras reprocessadas acima de quatro vezes apresentaram aumento da viscosidade complexa e dos módulos de armazenamento e perda, além de fenômenos de relaxação e retardação mais largos. Entretanto, os termogramas de DSC e os parâmetros cinéticos de fusão demonstraram que o PEBD estudado manteve sua estabilidade térmica, independentemente da modificação de suas características viscoelásticas.

Metastable phases in Gallium–Indium eutectic alloy particles and their size dependence

In this paper, submicrometer-sized Ga–In eutectic alloy particles were dispersed into polymethylmethacrylate (PMMA) matrix by ultrasonic vibration and sedimentation method. The solidification and melting processes of Ga–In eutectic alloy particles were studied by differential scanning calorimeter (DSC). Four endothermal peaks with the onset temperature located at 16, −11, −22, and −27 °C were observed in DSC heating curves, which corresponded to the melting process of the stable Ga–In phase α-Ga(In) and three metastable phases of β-Ga(In), δ-Ga(In) and γ-Ga(In), respectively. The stable phase α-Ga(In) can only be formed when the size of alloy particle was larger than 0.58 μm. Conversely, metastable phases β-Ga(In), δ-Ga(In) and γ-Ga(In) are mainly formed. The result shows that phase structures in Ga–In eutectic alloy are size dependent.

Effect of surface modification of nanosilica on crystallization, thermal and mechanical properties of poly(vinylidene fluoride)

Composites were prepared by solution blending ploy(vinylidene fluoride) (PVDF) and nanosilica which modified by different organic modifiers. Infrared analysis showed that the crystalline structure of PVDF was changed by the addition of RNS-A (silica with amino terminated group), while similar crystalline structure as pure PVDF was observed for composites with DNS-0 and DNS-2, unmodified silica and alkyl terminated group silica, respectively. With differential scanning calorimeter (DSC) and dynamic mechanic thermal analysis (DMTA) techniques, crystalline structure, thermal, and mechanical properties of the composite films were examined. As the DSC results showed, addition of SiO2 would lead to the increased cooling crystallization temperature (Tc), implying that SiO2 nanoparticles could act as nucleating agents, however the degree of crystallinity of PVDF was not elevated significantly. In the complementary modulated DSC curves, multi-melting peaks associated with non-reversing portion were observed and were explained from the viewpoint of melting-recrystallization in the DSC heating scan. In addition, dynamic mechanical properties as well as the thermal stability of the composites are also influenced by SiO2. As manifested by the corresponding DMTA and thermogravimetric analysis (TGA) results, a strong interaction should exist between PVDF and SiO2 nanoparticles.

Model of cold crystallization of uniaxially oriented poly(ethylene terephthalate) fibers

The differential scanning calorimeter heating curves of uniaxially oriented poly(ethylene terephthalate) (PET) fibers with three peaks were analyzed by using a newly proposed equation. The diffusion-controlled crystallization theory is suitable for describing cold crystallization of uniaxially oriented PET fibers. A crystallization model was proposed based on the kinetic parameters obtained. The model embraces the three sub-processes of crystallization corresponding to different growth geometries. The first sub-process corresponds to the nucleation of ordered molecular segments or the radial growth of preformed nucleus, resulting in the shorter bundle-like entities. The second sub-process corresponds to further growth of the bundle-like crystallites along chain direction, resulting in the longer bundle-like entities. The third sub-process corresponds to the three-dimensional growth of crystallites relating to the random segments, resulting in the spherical entities.

Direct observation of a concealed glass transition in a Mg–Ni–Nd metallic glass

Glass transition and crystallization behavior of Mg75Ni10Nd15 metallic glass has been studied by a temperature-modulated differential scanning calorimeter (TMDSC) and a normal differential scanning calorimeter (DSC). The truly vitreous state of the as-spun Mg75Ni10Nd15 alloy was confirmed by the direct observation of the glass transition through TMDSC measurements, which was not perceptible in the normal DSC heating scans. It was concluded that the glass transition signal was concealed by the relatively strong concurrent signal of the primary crystallization. This was further confirmed by the fact that the glass transition was revealed by both TMDSC and DSC for the samples with negligible heat release from the primary crystallization.

Correction of intensities for preferred orientation in neutron-diffraction data of NiTi shape-memory alloy using the generalized spherical-harmonic description

Analysis of quantitative texture (crystallographic preferred orientation, PO) in polycrystalline materials is of interest not only because the PO gives errors in quantitative phase analysis, but also because it can affect the results of structure determination from powder diffraction data. In the present study, texture characterization of the polycrystalline Ni-rich NiTi shape-memory alloy (SMA) of nominal composition 50.14 atomic percent nickel has been carried out using the BT-1 high-resolution, fixed-wavelength, 32-detector powder diffractometer at the NIST Center for Neutron Research. Data were collected along the differential scanning calorimeter (DSC) heating curve. The results obtained from Rietveld refinement with the generalized spherical harmonic (GSH) description for all neutron diffraction data sets show that the weight percentages for monoclinic and cubic phases during the phase transition are consistent with the DSC heating curve.

Phase transformation behaviors of prestrained TiNi shape memory alloy fibers under the constraint of a hard substrate

The phase transformation behaviors of prestrained TiNi shape memory alloy (SMA) fibers under the constraint of a hard substrate were explored. By means of measuring the deformation of the substrate, it was found that the temperature when the recovery stress is generated upon second heating is much lower than that upon the first heating. The results of the differential scanning calorimeter (DSC) measurements indicated that after the first constrained heating–cooling process, the oriented martensite (M) in the TiNi alloy divided into two sorts of martensite, the deformed martensite (M1) and the inheriting deformation martensite (M2). The start temperature of the transformation from inheriting deformation martensite M2 to parent is lower than that of the transformation from oriented martensite (M) to parent. Therefore, upon the second heating the recovery stress generated at the lower temperature corresponds to the transformation from inheriting deformation martensite M2 to parent. The phase transformation behavior upon the third heating–cooling process is similar to the second one due to the almost identical DSC heating and elongation curves.

New Precipitate Phase in Pd and Ni Rich Ti-Pd-Ni Shape Memory Alloys

The decomposition behavior and morphology of new precipitate in Pd and Ni rich Ti-Pd-Ni high temperature shape memory alloys have been studied by differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). The precipitate is formed in Ti 48 Pd 52-X NiX alloys with X = 11 to 36 at%Ni. The precipitate appears with exothermic peak about 650 to 700 K and resolves with endothermic peak with about 740 to 780 K in DSC heating curve for the quenched alloys. The both peak temperatures increase with increasing Ni concentration. The shape of precipitate changes from cuboid to oval sphere shapes with increasing Ni concentration. The electron diffraction patterns of the precipitate are characterized by 1/4{111} superlattice reflections in B2 reciprocal space. The Ti 48 Pd 31 Ni 2 alloy aged under constrained condition at 673 K for 36 ks shows reversible shape memory effect during thermal cycling between room temperature and 523 K.

BEHAVIOR OF A LIQUID CRYSTAL POLYMER AFTER ELONGATION FLOW TREATMENT

Crystallization behavior of a liquid crystal copolyester of 4-hy-droxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) after an elongation flow treatment was investigated by differential scanning calorimeter (DSC), polarized light microscopy (PLM), and an instrument capable of generating elongation flow. DSC heating scans of the elongation flow treated samples exhibit an additional high temperature endothermic peak, suggesting that the high degree of molecular orientation achieved by elongation flow results in a formation of new kind of crystalline structure. The annealing effect including different temperature and time on such stretched samples has also been studied.

Dynamic analysis of the melting behavior of polymers showing polymorphism observed by simultaneous DSC/X-ray diffraction measurements

The melting behavior of isotactic poly(propylene) (iPP) and poly(vinylidene fluoride) (PVDF), which contained several crystal modifications, was measured by simultaneous differential scanning calorimeter (DSC)/wide angle X-ray diffraction (WAXD) measurements. The DSC heating curve of iPP showed at least two endothermic peaks and one exothermic peak. These peaks were assigned to melting of β- and α-modifications of iPP and melt-recrystallization of α-modification which occurred immediately after starting the melting of β-modification. The DSC heating curve of a polymer blend of PVDF/poly(methylmethacrylate) (PMMA) (PVDF content was 80 wt%) showed three endothermic peaks, which were assigned to melting of I(β), II(α) and III(γ)-modifications of PVDF, respectively. The prepared PVDF/PMMA blend film originally contained these three modifications.