During Differential Scanning Calorimetry Research Articles

Degradation of mechanical properties of MgO-spinel bricks after pre-treatment in hydrogen-containing atmospheres at different temperatures

The current climate policy raises targets to reduce CO2 emissions, i.a. by using “green” hydrogen as a power source. However, the resulting water vapor-containing atmosphere raises uncertainties regarding its impact on the properties of refractory materials during their production and application. Therefore, this study investigates the effect of pre-treatment of unsintered MgO-spinel bricks with flue gas from firing with hydrogen, natural gas and a mixture of both at different temperatures followed by sintering in an industrial furnace as well as during differential scanning calorimetry (DSC). While the splitting tensile strength of the bricks was unaffected for a pre-treatment at 200°C, the samples pre-treated with hydrogen at 600°C revealed a decreased strength of about 14.5% compared to those pre-treated with natural gas at 600°C. DSC results indicated that, besides brucite formation, the formation of additional phases (probably magnesium-silicates) also play a non-negligible role for this strength degradation.

Effect of ECAP processing on distribution of second phase particles, hardness and electrical conductivity of Cu−0.81Cr−0.07Zr alloy

The effect of equal-channel angular pressing (ECAP) processing at room temperature and 300 °C on the distribution of the second phase particles and its influence on hardness and electrical conductivity of the commercial Cu−0.81Cr−0.07Zr alloy were investigated. Microstructural characterization indicated that the area fraction of coarse Cr-rich particles decreased after ECAP processing. This reduction was attributed to the Cr dissolution induced by plastic deformation. The electrical conductivity of the alloy decreased by 12% after 4 ECAP passes at room temperature due to the increase of electrons scattering caused by higher Cr content in solid solution and higher density of defects in the matrix. These results were supported by the reduction of the Cu lattice parameter and by the exothermic reactions, during differential scanning calorimetry (DSC) analysis, observed only in the samples subjected to ECAP processing. Aging heat treatment after ECAP processing promoted an additional hardening effect and the complete recuperation of the electrical conductivity, caused by the re-precipitation of the partially dissolved particles. The better combination of hardness (191 HV) and electrical conductivity (83.5%(IACS)) was obtained after 4 ECAP passes at room temperature and subsequent aging at 380 °C for 1 h.

Effect of Li2O on melt crystallization of CaO–SiO2–CaF2 based glasses

This paper presents the effects of Li2O on the kinetics and structural aspects of the Cuspidine (Ca4Si2F2O7) crystallization behavior of CaO–SiO2–CaF2 glass (basicity 1.7). In order to elucidate the crystallization characteristics during differential scanning calorimetry (DSC) measurements, the kinetic parameters have been determined using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The crystallization rate constant and negative activation energy thus calculated indicated that the limiting step of crystallization was nucleation. Also, Raman spectroscopy and Solid-state MAS NMR spectroscopy analyses indicated that lithium could interact with fluorine, thereby disturbing the interaction between calcium and fluorine. This retards Cuspidine nucleation at the initial stage of melt crystallization. These findings on CaO–SiO2–CaF2-based glass lubricants can be used to optimize essential properties such as viscosity and crystallization temperature during continuous casting of steels.

Insights into the starch gelatinization behavior inside intact cotyledon cells

In this work, detailed structural changes of starch within intact cotyledon cells during differential scanning calorimetry (DSC) heating (water: cells ratio of 4:1, v/w) were investigated. Intact cotyledon cells containing raw starch granules from three legumes were isolated and used as materials, followed by simulate DSC heating up to different designated temperatures based on those gelatinization profiles of cells. The swelling power, solubility and gelatinization transition parameters of raw cells were significantly lower than pure starches. Upon simulate heating, all the starches inside intact cells were considered to maintain more amounts of crystalline and double-helix structures than pure starch counterparts. Meanwhile, the starch granules were not completely disrupted even heating up to 15 °C above conclusion temperature (Tc + 15 °C) for intact cells. The results showed clearly that the presence of intact cell wall exerts significant retarding or restricting effects on the process of starch gelatinization.

High-Resolution Electron Microscopy and Kinetic Studies of Precipitation Hardening Reactions in Cast Al-5.8Zn-2.2Mg-2.5Cu

Precipitation age hardening (T6) response of Al-5.8Zn-2.2Mg-2.5Cu alloy in near-net-shaped cast condition was investigated. Cast samples were manufactured using the controlled diffusion solidification (CDS) technology combined with a metallic mold tilt pour gravity casting process. This study was conducted using (1) non-isothermal aging during differential scanning calorimetry (DSC) experiments and (2) isothermal aging during which transient bulk and micro-hardness measurements taken at four aging temperatures of 343, 393, 433 and 473 K. A detailed microstructural investigation combined with a quantitative image analysis was carried out on both DSC and hardness specimens using high-resolution electron microscopy (HREM) and energy-dispersive spectroscopy (EDS) elemental mappings. Hardness measurements were analyzed using a kinetic modeling approach (single state variable combined with a kinetic equation that is valid for the Al-Zn-Mg-Cu alloys). The results confirm the formation of hardening phases of GP zone, intermediate hardening metastable phase η′ and equilibrium phase η. The results of calorimetric measurements, electron microscopy and selected area diffraction patterns are in good agreement and confirm transient precipitation/dissolution sequences. A mean value of activation energy $$Q_{\text{A}}$$ of 75 kJ/mol was evaluated for combined bulk diffusion rate of alloying elements during precipitation of strengthening phases within Al matrix.

Ex situ and in situ TEM investigations of carbide precipitation in a 10Cr martensitic steel

An ex situ approach combining fast quenching experiments in a dilatometer and postmortem microstructural observation in transmission electron microscopy (TEM) has been used to observe the dynamic microstructure change during differential scanning calorimetry (DSC) ramping of an Fe–10Cr–0.15C (wt%) alloy fabricated from high-purity components. The DSC measurements reveal two exothermic events at temperatures about 270 and 600 °C in a heating process. The two events were discerned by TEM investigations on specimens interrupted during thermal ramping in a dilatometer. It is found that precipitation and growth of M3C carbide occurred first in a temperature range between 200 and 400 °C, following the Bagaryatskii orientation relationship. Subsequently, M7C3 carbides precipitate on prior martensitic laths boundaries in a temperature range between 500 and 700 °C at the expense of M3C. M23C6 carbides were found precipitating on the interface between M7C3 and matrix at approximately the same time with the precipitation of M7C3. The obtained results are also compared with an in situ TEM heating experiment, and differences between the two approaches are discussed.

Understanding water retention behavior and mechanism in bio-char

Bio-char has been applied to soil as an amendment to improve soil water holding capacity due to its porous nature. In this study the behavior of water in bio-char was investigated for better understanding mechanisms of water retention by bio-char. Bio-chars with different structures were prepared by partial gasification of peanut shell (PT) and palm kernel shell (PKS). It was observed that the BET surface area and total pore volume of bio-char increased with gasification conversion. Water holding capacity and water adsorption rate showed a direct correlation with micropore volume of bio-char, suggesting that physical structure of bio-char played a key role during interaction with water. These results indicated that partial gasification is a promising method for production of bio-char suitable for soil remediation. Two types of freezable water i.e. freezable free water (FFW) and freezable bound water (FBW) were directly detected in bio-char samples during Differential Scanning Calorimetry (DSC) analysis. The phase transition temperature of freezable bound water correlated well with pore size distribution of bio-chars. The presence of non-freezable (NFW) water in bio-char was also confirmed from the difference between total water content of samples and the sum of FFW and FBW. The amount of FFW showed an indirect correlation with micropore volume of bio-chars, suggesting that FFW is present in macropores. However, an opposite trend was observed for FBW and NFW in bio-chars, indicating that these two types of water were present in micropores. The low-temperature XRD results were used to define the boundary between the freezable and non-freezable water in bio-char samples.

Effect of dislocations and residual stresses on the martensitic transformation of Cu-Al-Ni-Mn shape memory alloy powders

The behaviour of the martensitic phase transformation of a Cu-Al-Ni-Mn shape memory alloy was studied for as-atomized and heat-treated powders. X-ray diffraction, microscopy techniques and thermodynamic calculations were used to understand the different transformation behaviour observed during differential scanning calorimetry (DSC) analysis. Two overlapped transformation peaks were observed in the DSC curves for the as-atomized powder. After annealing, the peaks progressively became only single peak when the annealing temperature and time were increased. No difference in phase formation and microstructure was observed by X-ray diffraction and scanning electron microscopy when compared as-atomized and annealed powders, although transmission electron microscopy analyses showed that the as-cast powders had more dislocations trapped in the microstructure than the annealed samples. Considering the experimental results and thermodynamic considerations, it was concluded that the smooth double peak effect in the as-atomized powders occurred due to a different state of internal stresses and elastic energy accumulation during forward transformation. The absence of this effect after heat treatment shows that the internal stresses and defects were annihilated after annealing, changing the elastic energy accumulation and the transformation behaviour. Understanding the martensitic transformation on Cu-Al-Ni-Mn powders is important considering the potential use of powder metallurgy processing route.

Study of the Solidification of AS Alloys Combining <i>In Situ</i> Synchrotron Diffraction and Differential Scanning Calorimetry

In situ synchrotron diffraction experiments were performed during Differential Scanning Calorimetry (DSC) of AS31, AS33 and AS35 alloys. The samples were encapsulated in stainless steel crucibles during the measurement using an empty crucible as the reference. The samples were heated up to 680°C, melted and solidified in the beginning of the experiment in order to fill the crucible. This short cycle was followed by three subsequent cycles between 400°C and 680°C with 5, 10 and 20 K/min heating and cooling rates with 5 min of holding time in the molten state. The diffraction patterns were recorded every 6 s during the DSC program by a Perkin-Elmer XRD 1622 Flatpanel detector including an acquisition time of 3 s and the collection of reference images. The endothermic and exothermic peaks are in correlation with the dissolution and formation of new diffraction patterns, respectively. During cooling from the liquid state, first, α-Mg dendrites solidify, followed by the formation of Mg2Si and Mg17Al12 intermetallics. The results are correlated with those obtained by thermodynamic simulations performed with the software Pandat.

Development of heat resistant Pb-free joints by TLPS process of Ag and Sn-Bi-Ag alloy powders

TLPS (Transient Liquid Phase Sintering) process is a candidate method of heat-resistant bonding, which makes use of the reaction between low-melting temperature powder of Sn-Bi base alloys and reactive powder of Ag. During heat treatment above the melting temperature of a Sn-Bi base alloy, the molten Sn-Bi reacts rapidly with solid Ag particles, which results in the formation of heat-resistant intermetallic compound (IMC). In this study, the TLPS properties between Sn-17Bi-1Ag (at.%) powder with its liquidus temperature of 200?C and pure Ag powder were investigated. During differential scanning calorimetry (DSC) measurement, an exothermic reaction and an endothermic reaction occurred, which correspond to the formation of the e-Ag3Sn IMC phase and the melting of the Sn-17Bi-1Ag alloy, respectively. After the overall measurement, the obtained reactant consists of the Ag3Sn-IMC and Bi-rich phases, both of which start melting above 250?C, with a small amount of the residual Sn-Bi eutectic phase. These results suggest that the TLPS process can be applied for Pb-free heatresistant bonding.

Gelatinization, Pasting, and Gelling Properties of Sweetpotato and Wheat Starch Blends

ABSTRACTSweetpotato starch is high yielding but has very limited uses. It is possible to expand its application by blending it with other starches to obtain novel properties. In this study, functional properties of the blends of native sweetpotato starch with native, acid‐thinned, and hydroxypropylated wheat starch were studied at different ratios (75:25, 50:50, 25:75). The swelling factor, extent of amylose leaching, pasting, and gel textural properties of the blends were nonadditive of their individual components, and could be mathematically modeled by quadratic equations in relation to the ratios. Two peaks during pasting were observed for some starch mixtures studied by Rapid ViscoAnalyser (RVA). The gelatinization and retrogradation enthalpies (ΔH) of the blends were additive of their individual components and could be modeled by linear equations. All starch mixtures exhibited two peaks during differential scanning calorimetry (DSC) scan for gelatinization, but a single peak for retrograded starches. This study may provide basis for formulation of mixtures using starch from diverse sources to develop more natural starch systems with a range of physicochemical properties.

Monitoring dehydration kinetics using simultaneous thermal and spectral methods

AbstractThe dehydration kinetics of theophylline monohydrate is a two‐stage process. The first stage involves loosening of the crystal water followed by a second stage in which the water evaporates from the sample. During differential scanning calorimetry (DSC) measurements, the kinetics of the two stages can be dramatically altered because of the sample environment and DSC pan type. In‐depth understanding of how the sample environment alters the dehydration process and the kinetics involved requires more than DSC experiments alone. This paper describes the use of a novel, simultaneous thermal and spectral technique to monitor the dehydration kinetics of theophylline monohydrate. The analysis of the results obtained on the combined DSC‐near‐infrared and DSC‐Raman equipment clearly detects the two stages of the dehydration process and the polymorphic structural changes that take place. The combined technique provides a powerful method to monitor the dehydration of hydrous systems. Copyright © 2010 John Wiley & Sons, Ltd.

Solid state chemistry of proteins IV. what is the meaning of thermal denaturation in freeze dried proteins?

This research addresses the thermodynamic significance of the denaturation endotherm observed during differential scanning calorimetry (DSC) scans of proteins in dry formulations, such as freeze dried solids. Human growth hormone formulations are the chosen representative examples. We employ observations of denaturation temperature, glass transition temperature, and the differences between estimated molecular mobilities to argue that unfolding is under partial thermodynamic control. Further, unfolding during a DSC scan is simulated using a three state kinetic model, which is a two state unfolding model followed by aggregation. Kramers-type rate constants are used, where the preexponential term is dominated by viscous forces. Simulation results are in qualitative agreement with experiment, and clearly show that while the denaturation endotherm is impacted by irreversibility, caused by nonzero scan rate and aggregation, the position of the endotherm peak is changed only slightly. Thus, the denaturation peak is a good approximation for the thermodynamic denaturation temperature. Using data for denaturation temperature, heat of denaturation, and heat capacity of denaturation, free energy versus temperature curves were calculated. We find that even formulations with added saccharides are thermodynamically unstable near ambient temperature; significant denaturation in the solid state is prevented by low mobility.

RARE-EARTH DOPED POTASSIUM LEAD BROMIDE MID-IR LASER SOURCES FOR STANDOFF DETECTION

The single crystal growth of KPb 2 Br 5 by vertical Bridgman technique using in-house processed zone refined PbBr 2 and KBr with rare-earth terbium doping has been studied. The grown moisture resistant crystals (1.5 cm diameter and 10 cm length) have shown high promise for low phonon energy room temperature solid-state laser applications in the longer side of mid-IR (4-15 µm) due to their high storage lifetimes, wide tunability, and excellent optical quality. The processed crystals are highly transparent ( T = ≥80%) in the 0.4-25 µm spectral region. Repeated melting-freezing cycles during differential scanning calorimetry (DSC) experiments did not reveal any appreciable variation in the melting point or phase transitions, which is indicative of their excellent thermal stability. The emission spectra pumped with a 2 µm source show broadband emissions with peak wavelength of 3 µ m (7 F 4→ 7 F6), 5µ m (7 F 5→ 7 F 6) and 7.9µ m (7 F 4→ 7 F 5). The KPb 2 Br 5: Tb laser crystals will be highly useful for standoff detection of incoming chemical and biological threats using unique infrared absorption signatures.

Water and the glass transition temperature of organic (caramel) glasses

The glass transition temperature (Tg) of sugar-related glasses is close to room temperature and here we report the affect of water concentration on the Tg of caramel–water mixtures. Based on viscosity measurements, thermal analysis and X-ray diffraction (XRD) experiments we have investigated the occurrence of the Tg during differential scanning calorimetry (DSC) runs on cooling (down to ∼170K) and heating cycles of the caramel glasses and caramel–water mixtures. The caramel–water mixtures are viscous melts with Newtonian rheology. Their melts bear a resemblance to a silicate melt which do not deviate from Vogel–Fulcher–Tammann (VFT) equation fit as the glass approaches Tg. The DSC measurements did detect low temperature transitions in caramel–water mixtures and the Tg of the dried caramel glass sample. If crystallization is avoided on cooling to ∼170K then a glass transition and devitrification of the mixture will occur on heating the sample from ∼170K up to the ambient room temperature. The detectability of the glass transition depends on the cooling rate and water concentration.

Calorimetric evidence for frictional self-adaptation of TiAlN/VN superlattice coatings

TiAlN/VN superlattices are potential candidates for dry machining due to their high hardness and excellent tribological properties. It has been reported that VN easily oxidizes at relatively low temperatures and forms V 2O 5 having lubricious properties. The aim of this work is to investigate the effects of vanadium oxides on tribological properties of TiAlN/VN superlattices at high temperatures. During differential scanning calorimetry (DSC) in an argon/oxygen atmosphere it was found that the coatings oxidize at approximately 450 °C. Melting and boiling point of the formed oxides could be determined by DSC to approximately 635 °C and 1400 °C, respectively. It was observed by DSC and X-ray diffraction that the melting phase, a V 2O 5 containing oxide, transforms into a VO 2 containing oxide causing the loss of the liquid phase. Dry sliding tests showed that up to 500 °C the friction coefficient increases from 0.55 to 0.95. It drops to approximately 0.18 at 700 °C and remains there as long as a liquid surface oxide is present. If most of V 2O 5 is converted into lower-oxidized vanadium the friction coefficient increases to a steady state value of approximately 0.55 at 700 °C. The results obtained show that addition of VN to hard coatings has high potential to achieve a low friction effect due to the formation and melting of a V 2O 5 containing oxide, in addition to its conversion into easily shearable lower-oxidized vanadium phases.

Influence of gamma radiation on potato starch gelatinization studied by differential scanning calorimetry

The paper presents a study of the influence of the conditions applied during differential scanning calorimetry (DSC) measurements (concentration and heating rate) on the possible detection of the differences between gelatinization occurring in both non-irradiated and irradiated potato starch with a dose of 20 kGy. Differences in gelatinization of irradiated and non-irradiated potato starch during DSC analysis was attributed to the radiation induced destruction of crystalline ordering. This was confirmed by studies of the samples irradiated to very high doses (446 and 600 kGy), and by comparing with the effect of grinding. Changes of starch properties caused by radiodepolymerization—contrary to those caused by grinding—influences gelatinization behaviour much more than the WAXS crystallinity in solid state.

Amylose-lipid Complex, Physicochemical Properties and the Effects of Different Variables

This work deals with the effect of different electrolytes, and low molecular weight solutes such as glycerol and urea on the melting of 1-α-lysophosphatidilcholine(AM-LPC) complex. Thermal stability changes can be interpreted by the action of solutes on water structure, according to the Hoffmeister series or, sometimes, to the specific action of those electrolytes and solutes on starch. A similar effect is observed in the formation of the dissociate AM-LPC complex during differential scanning calorimetry (DSC) cooling runs, where the solutes studied decreased the dissociation enthalpy of the AM-LPC complex with no significant trend. The glass transition temperatures (Tg) and the effect of water content on the amylose were determined. The particular value of Tg for the dry AM-LPC complex was 430 K. Tg values obtained were related to the weight fractions of the pure components of means of three models, two of which were fitted to the experimental data to obtain constants with a physical meaning.

Dipole–dipole interaction directed liquid crystalline polymers. I. Aliphatic poly(carbonate‐sulfone)s based on 1,3‐bis(3‐hydroxypropylsulfonyl)propane

AbstractAliphatic poly(carbonate‐sulfone) homo‐ and copolymers were prepared from 1,3‐bis(3‐hydroxypropylsulfonyl)propane (Diol‐333) and various alkanediols. The copolymers are random in nature since they were prepared by melt copolymerization. Both the homopolymer and the copolymers exhibited multiple reproducible first‐order transitions during differential scanning calorimetry (DSC) heating scans, but most of them exhibited only single exotherm during cooling scans. Typical schlieren textures were observed when these polymers were cooled from their isotropic melts. The copolymers have wide‐angle x‐ray diffraction (WAXD) patterns almost identical to that of the homopolymer except in the low‐angle spacing, indicating their packing in the crystalline domain in similar. DSC, cross‐polarized optical microscopy, and WAXD revealed that these polymers were smectic liquid crystalline at room temperature. Since aliphatic poly(carbonate‐sulfone)s are flexible linear polymers with no rigid rod components, the liquid crystalline phase formation is probably directed by the dipole–dipole interactions between sulfone groups in adjacent chains. © 1994 John Wiley & Sons, Inc.

Surface effects on phase transition behaviour and thermal polymerisation of long-chain compounds in micro DSC measurements

The surface effects of the aluminium sample pan on the melting behaviour of stearic acid and also on the phase transition behaviour and thermal polymerisation of N-octadecyI acrylamide during differential scanning calorimetry (DSC) were investigated. The surface effects in the micro DSC measurements can be classified into two types. In the case of stearic acid, when the weight of sample was smaller than 0.01 mg, the molar heat of fusion estimated from the peak area in the first heating curves increased abruptly up to two or three times the normal value (64.3 kJ mol −1); however, in the second heating curves obtained with samples stored for a long time after the first heating at room temperature, the molar heat of fusion tends to decrease. In contrast, in the DSC curves for N-octadecyl acrylamide with sample weights of around a milligram, an endothermic peak for melting appeared at 75°C, followed by a broad exothermic peak for thermal polymerisation ranging from 115 to 155°C; when the sample weight is smaller than a critical value of around 0.2 mg, the thermal polymerisation and also the polymorphic transition are suppressed strongly. The surface effects are attributed to the strong interaction, such as chemisorption, of the polar head group with the surface of the pan which restricts the conformational freedom of the functional groups.