A calorimetric study of phase evolution in a WE43 Mg alloy

A DSC investigation has been performed on a Mg–RE–Y–Zr (RE=rare earth) technical alloy WE43. Hardness trend during isothermal treatments has been correlated to the calorimetric traces evolution and to the forming β phases with its precursors. Oversaturation of solute elements occurs at temperatures higher than 150±C, on cooling at room temperature after the anneals. Activation energies, found under non-isothermal conditions on artificially aged samples, suggest a slow transformation velocity, while the hardness response is relatively fast.     

DSC analysis of the precipitation reaction in AA6005 alloy

DSC analysis is applied to investigate the precipitation reaction in the AA6005 extrusion alloy for different heat treatment practices often presented in commercial production. The quenching practice is shown to have a big impact on the response of the AA6005 alloy to an artificial ageing treatment. The range of β″ precipitation is displaced to lower temperatures in samples quenched in air following the solution treatment. This acceleration, however, does not produce a favorable effect on age hardening capacity since much of the solute Mg and Si is removed from the solid solution before the principal hardening phase can precipitate. The DSC results are in good agreement with the age hardening curves. Natural ageing before artificial ageing promotes clustering activities during a subsequent thermal exposure and produces a strong delay in β″ precipitation.     

DSC study of precipitation in an Al-Mg-Mn alloy microalloyed with Cu

Power compensation differential scanning calorimetry (DSC) has been employed to detect and analyse precipitation reactions in an Al-1.3Mg-0.4Mn and an Al-1.3Mg-0.4Mn-0.07Cu alloy in which very small amounts of precipitate, less than 0.3 at.%, are expected to form. Due to the very small heat effects, baseline instability and drift significantly interfere with the measurements. After repeated experiments and careful baseline correction it is demonstrated that in the Cu containing alloy, ageing at 170 °C causes the appearance of two endothermic effects: for 2 days ageing a small dissolution effect appears at about 230 °C, whilst for 7 and 21 days ageing a dissolution effect peaking appears at about 300 °C. The temperature range of the latter is consistent with S phase dissolution.     

The use of DSC in describing the structure evolution of an AlZnMg alloy

Summary The potential of DSC in suggesting modifications of thermal treatments of Al alloys to increase mechanical properties is described. Significant results can be obtained from calorimetric evolution after a series of annealings, even without a direct observation of the microstructure. The role of a reference baseline is discussed. The Guinier-Preston (GP) zones formation, dissolution or transformation is followed, and their relevance for the microhardness increase is shown, for an AlZnMg alloy of technical interest. Multi-stage thermal treatments have been confirmed to be beneficial. A secondary precipitation occurs at room temperature after annealing at temperatures at which primary precipitation is almost complete.     

DSC calibration in the study of shape memory alloys

The unusual mechanical properties (i.e. shape memory effect and superelasticity) of shape memory alloys (SMA) rely on the thermoelastic martensitic transformation (TMT) which is a first-order solid-solid, non-diffusive phase transition, athermal in character. Differential scanning calorimetry (DSC) is often used as a convenient method of investigating the thermal properties ofSMAs. The common practice of standard temperature calibration, required for a correct instrument performance, is here critically discussed in relation to the study of both the direct exothermic transformation on cooling, and the reverse endothermic transformation on heating in a NiTiSMA. The DSC results show that, with the standard temperature calibration, the instrument is calibrated on heating but un-calibrated on cooling. A general method is advanced to overcome this problem, intrinsically related to the dynamic character of DSC.     

DSC Analysis of the precipitation reactions in the alloy AA6082

The deformation introduced during the sample preparation had a high impact on the response of the alloy AA6082 to heating in the DSC cell. The DSC curve was strikingly different when DSC samples of this alloy were punched after the solution treatment. Dislocations introduced by punching have annihilated the quenched-in vacancies and have suppressed clustering initially. Dislocations have also provided heterogeneous nucleation sites for the GP-1 zones that readily grew to become stable nuclei for the β" phase owing to the enhanced atomic transport. β" as well as the β' precipitation kinetics were thus accelerated leading to a substantial change in the DSC peak arrangement. Deformation introduced during sample preparation by gentle grinding alone, on the other hand, did not suffice to alter the precipitation sequence, producing a DSC curve very similar to that obtained with samples punched before the solution treatment.     

DSC study of precipitation processes in Cu-Co-Si alloys

Using differential scanning calorimetry (DSC) the precipitation processes of supersaturated solid solutions of three Cu-Co-Si alloys containing the same atomic cobalt content were investigated. Thermoanalytical and previous studies, reveal that the decomposition begins with cobalt clustering which initiates the precipitation of the Co₂Si stoichiometric particles, which in turn dissolves after further heating. Volume fractions are unequivocally determined by the amount of cobalt present in these alloys. It is infered that surplus silicon atoms retained in the solution increase the reaction rate and dispersity of precipitate structure. Kinetic parameters were obtained by a convolution method based in the Mehl-Johnson-Avrami (MJA) formalism. The lower activation energy associated with cobalt clustering is attributed to the contribution of quenched-in vacancies. Superimposed to the MJA formalism and adaptative spherical diffusion model was used for Co₂Si precipitation with particle size as a disposable parameter. This model further confirmed that as silicon content increases particle dispersity becomes more pronounced. Such results are also infered from a three dimensional diffusion dissolution model previously developed which adjusts quite well to such process in the present cases. Age hardening experiments are in line with all previous results obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hydrogen determinations in a zirconium based alloy with a DSC

In the present work a method to measure hydrogen concentrations in zirconium-based alloys was developed measuring simultaneously both, the temperature of terminal solid solubility, T_TSSd, and the hydride dissolution heat, Q_δ→α, using a differential scanning calorimeter (DSC). The hydrogen concentration measured with that technique, [H]_Q, and the values obtained with a standard hydrogen gas meter, [H]_HGM, shows a linear relation: [H]_Q = (1.00 ± 0.03)[H]_HGM| + (9.2 ± 8.0) with a correlation factor of 0.99 in the entire solubility interval in the αZr phase, from 15 to 650 wt. ppm-H. The mean enthalpy value determined with two different criteria for T_TSSd and Q_δ→α measurements is  kJ/mol H. The present method is specially appropriate for alloys where a partition of the overall hydrogen concentration in two phases exists. It is applicable to all hydride forming metals which ideally follows the van’t Hoff law.     

DSC analysis of the effect of processing technique on the dissolution/precipitation reactions in a hypereutectic Al−Si alloy

In the present study, the effect of primary processing route on the dissolution and precipitation reactions in a commercial Al?Si alloy (designated as A390) is investigated using differential scanning calorimetry (DSC). The Al?Si alloy selected for the present investigation was processed using conventional casting and spray atomization and deposition routes. The results of differential scanning calorimetry conducted on the as-processed samples indicated no significant dissolution reaction for the as-cast A390 alloy when compared to the similar results obtained for as-spray atomized and deposited samples. However, the thermal analysis conducted on the solutionized cast and spray deposited samples exhibited no significant difference in the kinetics of precipitation reactions. The results of the differential thermal analyses were finally rationalized in terms of observed microstructural features.     

A study of PBT/PC blends by modulated DSC and conventional DSC

Two poly(butylene terephthalate)/polycarbonate (PBT/PC) blends with different formulations were analyzed by modulated DSC (MDSC) and conventional DSC to determine differences in crystallization behavior. A significant difference (30°C in cold crystallization temperature) between the two samples was detectable by MDSC while no significant difference was seen by conventional DSC. That indicatesthe total heat flow from MDSC is not always equivalent to the heat flow from conventional DSC as we have assumed or seen before. The reason has not been fully understood, but may be related to unusual nucleation and crystallization induced by modulation. Alternative conventional DSC methods were developed and compared to the MDSC results.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThe authors like to thank Drs. Bernhard Wunderlich and Robert Gallucci for helpful discussion, David Shaker and Mary Parsonage for some DSC experiments. Technical support from TA Instruments is also greatly appreciated.     

Anodic growth of self-ordered magnesium oxy-fluoride nanoporous/tubular layers on Mg alloy (WE43)

In the present work we show that self-ordered nanotubular and nanoporous magnesium oxy-fluoride structures can be grown on a magnesium-based alloy when anodized in a non-aqueous (ethylene glycol) HF electrolyte. The morphology of the surface structures varies with applied potential and anodisation time. Tubular and porous structures with different sizes and orientation can be grown.     

Mg65Cu25Gd10和Mg65Cu20Zn5Gd10基大块非晶合金的制备及其力学性能

利用铜模喷注法可以制备出直径为5 mm的Mg65Cu25Gd10的非晶合金,将Mg65Cu25Gd10的Cu用Zn部分代替后,制备出的Mg65Cu20Zn5Gd10合金的非晶形成能力（GFA）并未得到提高。在室温下,Mg65Cu25Gd10的非晶合金有很高的强度,而在玻璃转变温度附近,在温度大于403 K时,.ε=5×10^-4s^-1和2.5×10^-4s^-1两种应变速率下的流变应力小于100 MPa,塑性很好,非常适合塑性成型。     

A modulated DSC study on the stress oscillation phenomenon in a syndiotactic polypropylene

The static loading-induced stress oscillation (SO) in syndiotactic polypropylene (sPP) was studied by modulated differential scanning calorimetry (TMDSC). Samples were taken from the initial necked, premature and mature SO oscillation ranges, respectively, and the related calorimetric responses were compared to those of the bulk material. It was established that necking caused some decrease in the crystallinity. In addition, necking resulted in cold crystallization that was assigned to a polymorphic transition (from all-trans to helical conformation) based on literature results. The TMDSC response was practically the same for necked samples with and without SO. A model was proposed to explain SO. The model assumes the presence of a network (similar to that of semicrystalline thermoplastic elastomers), which is highly stretchable and fails by sudden voiding at the intersections of shear micro bands intermittently.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermodynamic properties of cycloketones: A DSC study

In this paper, we describe the study of the thermodynamic properties of all cycloketones, from cyclobutanone to cyclododecanone, through DSC measurements in order to reveal possible new glassy crystalline phases. This work presents revised phase diagrams of the four previously known plastic crystals of the series, namely cyclohexanone, cycloheptanone, cyclooctanone, and cyclononanone. In particular, it has been shown that the last three crystals exhibit two phase sequences, a stable one and a metastable one, which could be attained through reproducible heat treatments. Contrary to what could be expected by comparison with the cyclo-alcohol series, only two compounds, namely cyclooctanone and cyclononanone, exhibit glassy crystalline phases. Finally, the thermodynamic data related to the various phase transitions of all these compounds have been determined.     

DSC study of melting and glass transition in gelatins

In the range from –50° to +130°C, the temperature dependence of the heat capacity for different kinds of gelatins with water contents of from 2 to 95% was studied by the DSC method. It was shown that, in all studied cases, metastable collagen-like structures are formed in gels or crystalline gelatins, with thermodynamic parameters depending on the formation conditions. The characteristic properties of the glass transitions in amorphous gelatins and crystalline gelatins with different melting heats and different contents of the ordered phase were established. Special attention is paid to the structural properties of free and bound water. The dependence of the glass transition temperatureT _g on the bound water content was shown to be of general applicability for many denatured biopolymers. Free water in gelatins, in distinction to the bound water, does not act as a plasticizer, but forms a rigid matrix inhibiting the glass transition.

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Zusammenfassung Mittels DSC wurde im Bereich –50° bis +130°C die Temperaturabhängigkeit der Wärmekapazität für verschiedene Arten von Gelantine mit einem Wassergehalt von 2 bis 95% untersucht. Es wurde gezeigt, daß in allen untersuchten Fällen metastabile kollagenähnliche Strukturen in Gelen oder kristallinen Gelantinen gebildet werden, deren thermodynamische Parameter von den Bildungsbedingungen abhängen. Es wurden die charakteristischen Eigenschaften der Glasumwandlungen in amorphen Gelantinen und kristallinen Gelantinen mit unterschiedlichen Schmelzwärmen und einem unterschiedlichen Gehalt an geordneter Phase bestimmt. Spezielle Aufmerksamkeit wurde den strukturellen Eigenschaften von freiem und gebundenem Wasser gewidmet. Es wurde gezeigt, daß die Ab-hängigkeit der GlasumwandlungstemperaturT _g vom Gehalt an gebundenem Wasser generell für viele denaturierte Biopolymere anwendbar ist. Im Unterschied zu gebundenem Wasser fungiert freies Wasser in Gelatinen nicht als ein Weichmacher, bildet aber eine starre Matrix, die die Glasumwandlung verhindert.

     

Effect of a bioactive curcumin derivative on DPPC membrane: A DSC and Raman spectroscopy study

Interactions of dimethoxycurcumin (1) a lipophilic bioactive curcumin derivative with dipalmitoyl phosphatidylcholine (DPPC) were investigated. The thermodynamic changes caused by (1) and its location into DPPC lipid bilayers were monitored by differential scanning calorimetry and Raman spectroscopy. The results reveal that (1) influences the thermotropic properties of DPPC lipid membrane causing abolition of the pretransition and broadening of the phase-transition profile and slightly decreases the T_m at increasing concentrations. The Raman height intensity ratios of the peaks I_2935/2880, I_2844/2880 and I_1090/1130 are representative of the interaction of (1) with the alkyl chains and furnish information about the ratio between disorder and order that exists in the conformation of the alkyl chain. The intensity changes of the peak at 715 cm⁻¹ indicates interaction between the choline head group and (1). The Raman spectroscopy results are in agreement with the thermal analysis results. Biologically active lipophilic molecules such as (1) should be studied in terms of their interaction with lipid bilayers prior to the development of advanced lipid carrier systems such as liposomes. The results of these studies provide information on the membrane integrity and physicochemical properties that are essential for the rational design lipidic drug delivery systems.     

Enzymatic Hydrolysis of Soy Protein Isolates. DSC study

The aim of this work was to analyze the possible use of differential scanning calorimetry (DSC) as a method to study the process of protein modifications during enzymatic hydrolysis. Results of the enzymatic hydrolysis of soy protein showed significant differences in the values of maximum deflection temperature (T _p), heat of reaction (ΔH), and width at half peak height (ΔT _1/2), between DSC curves corresponding to the substrate, or zerotime of hydrolysis, and those of the hydrolysates obtained by the action of cucurbita and pomiferin enzymes. DSC curve changes mentioned were explained by the use of gel-filtration chromatography, denaturing electrophoresis and surface hydrophobicity of the hydrolysis products obtained at 30 min of reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Energetic and Kinetic Evaluations Conducted in a Quasi-Binary Cu−1 at% Co2Si Alloy Through DSC

By means of differential scanning calorimetry (DSC) the precipitation process from a supersaturated solid solution of Cu−0.65 at% Co−0.33 at% Si (Cu−1 at% Co2Si) was investigated. On the basis of enthalpimetric calculations it was found that the decomposition begins with cobalt precipitation. Clustering of atoms of cobalt initiates the precipitation of silicon, and particles of the stoichiometric Co2Si composition are finally formed. Kinetic parameters were obtained by a convolution method based on the Mehl–Johnson–Avramiformalism. Their values are all in agreement with the experimentally observed behavior displayed by DSC traces. Decay kinetics of cobalt and silicon matrix during simulated isothermal calculations using DSC data reveals good agreement with similar computed results reported in literature. Precipitate dissolution obeys quite well to a three-dimensional diffusion kinetic law previously developed. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Numerical Model of a Two-pan Heat Flux DSC

A numerical program has been written to treat a heat-flux DSC. The model operates in two modes. In the first,experimental data is used as input and the enthalpy is calculated as a function of the sample temperature rather than the sample thermocouple temperature. This allows accurate enthalpies and transition temperatures to be obtained without smearing. In the second mode, enthalpy is used as an input and the responses of the calorimeter are calculated. Using this mode it is possible to investigate the effects of sample size, heating rate and alloy composition. Non-equilibrium effects and difficulty in nucleation can also be included. This revised version was published online in July 2006 with corrections to the Cover Date.     

DSC study on the motor protein myosin in fibre system

We have examined by DSC the complexes of myosin with actin in fibre system in the absence of nucleotides and the intermediate state of ATP hydrolysis by mimicking stable complex with myosin and ADP and beryllium fluoride in muscle fibres. Comparing the DSC results with other structural analogues of phosphate P_i leads the conclusion that the AM.ADP.BeF_x complex favours the AM.ADP.P_i complex in fibre system. The deconvolution of DSC scans resulted in four transitions, the first three transition temperatures were almost independent of the intermediate state of the muscle, the last transition temperature was shifted to higher temperature, depending on the actual intermediate states of ATP hydrolysis. In AM.ADP.V_i state the transition temperature at the second and third transitions (actin binding domain and myosin rod) varied only slightly, whereas the last one (the fourth transition) shifted markedly to higher temperature depending on the ternary complex, e.g. in case of ADP plus BeF_x it was 77.7 °C, the highest value in weakly binding state of myosin to actin. The sum of calorimetric enthalpies of the first and last curves was practically constant, but their fractions depended on the state of the muscle. In strongly binding state of myosin to actin (rigor, ADP state) the fraction of the first transition was much larger, than the last one, whereas in weakly binding state of myosin to actin, the fraction of the first transition decreased at the expense of the last one. It supports also the view that these transitions are parts of the same portion of the myosin molecule.