Direct Calorimetric Measurements Research Articles

Thermodynamics of acidic dissociation of ammonium ion in concentrated aqueous solutions of ammonium nitrate

Based on pH-metric measurements, the equilibrium constants for ammonia protonation at 298.15 K and ionic strengths I = 5–9, supported by ammonium nitrate, were calculated. Using direct calorimetric measurements, the enthalpies of this process were determined at 288.15, 298.15 and 303.15 K and I = 5–9 and its full thermodynamic parameters were calculated. The sharp increase in exothermicity and decrease in entropy of this process observed at high ionic strengths are explained by decrease in the contribution of desolvation of reagents in the region of deficiency of solvent molecules and the influence of association of ions of background electrolyte. The obtained thermodynamic characteristics of ammonia protonation clearly indicate that a change in solvation state of reaction participants at high ionic strengths changes the nature of this reaction.

Effect of the Nature of Supporting Electrolyte on the Thermodynamic Parameters of the Stepwise Dissociation of Glycyl-D-Phenylalanine in Aqueous Solution

The thermal effects of acidic and basic dissociation of glycyl-D-phenylalanine dipeptide at a temperature of 298.15 K and ionic strengths of solution of 0.5, 0.75, and 1.0 M against the background of different supporting electrolytes were calculated from the results of direct calorimetric measurements performed on a calorimeter with an isothermal shell and automatic recording of the temperature–time curve. The influence of the nature of supporting electrolytes NaCl, NaClO4, NaNO3, KNO3, and LiNO3 on the thermal effects of stepwise dissociation of the dipeptide is considered. The standard thermal effects of ionization of glycyl‑D‑phenylalanine in two steps were found by extrapolation to zero ionic strength. The standard changes in thermodynamic functions (enthalpy, entropy, and Gibbs energy) in the acidic and basic dissociation of g-lycyl-D-phenylalanine dipeptide were calculated.

Next-gen approach to the combined micro/macro-scopic measurements of crystal growth in chalcogenide thin films: The case of Se90Te10

Crystal growth in 1 µm Se90Te10 thin films deposited on a variety of substrates was studied by means of a novel combination of direct microscopic and calorimetric measurements. Differential scanning calorimetry (DSC) was used to explore the macroscopic manifestation of the crystal growth in as-deposited Se90Te10 thin films, revealing the native-like crystal growth behavior (very close to that of the bulk glass) in the films deposited on the polymeric foil. The optical microscopy determined the following sequence for the crystal growth rates ur in the thin films deposited on different substrates: urwhite glass> urSiO2 glass> >urKapton. This finding is perfectly consistent with the calorimetric data, and can be explained by the combined influences of the Na+ ions migrating from the white glass substrate to the thin film/substrate interface, and by the compressive stresses arising from the large difference between the thermal expansion coefficients of Se90Te10 and the inorganic glasses. Conformation of the calorimetric and microscopic data was validated by the description of both datasets in terms of a single set of parametrized equations based on the combination of the temperature-resolved screw-dislocation growth model and the macroscopic nucleation-growth model. The novel approach to the crystal growth research in chalcogenide thin films was introduced, demonstrating its unprecedented accuracy, robustness and overall comprehension. All major aspects of this novel approach were discussed in detail, including the necessity to consider not only the substrate properties but also the associated process of structural relaxation that may significantly alter the crystal growth near glass transition.

Ternary nickel(II) complexes with histidine and glycylglycylglycine in solution

Potentiometric, calorimetric and photometric studies of mixed-ligand complexes of nickel(II) ion with histidine (His) or glycine (Gly) and glycylglycylglycine (GGG) have been carried out in aqueous solution at 298.15 K and ionic strength I = 0.5 (KNO3). The existence in solution of a number of heteroligand complexes of the compositions NiHisGGGHn (n = -2, -1, 0, 1), NiHis2HnGGG (n = 0, 1), as well as NiGlyGGGHn (n = -2, -1, 0) and NiGly2GGG (charges are omitted). Direct calorimetric measurements made it possible to obtain reliable values of heat effects of mentioned above processes. Possible coordination modes of tripeptide and amino acid residues in mixed-ligand complexes are discussed on the basis of comparative analysis of thermodynamic data on complex formation.

Preparation of Sb2Se3-based ceramics and glass-ceramics from native thin films deposited on Kapton foil

Amorphous Sb2Se3 thin films (200–1500 nm) deposited on Kapton foil were crystallized in controlled environment using the method of direct calorimetric measurement of thin films. X-ray diffraction was used to determine the intensity of the 1D (Sb4Sb6)n ribbons preferential orientation in dependence on the processing conditions: film thickness, energy flux during the pulsed laser deposition (PLD), heating rate, low and high temperature annealing. Lower PLD energy flux combined with higher deposited film thickness (1500 nm) led to increased orientation in the [2 2 1] direction, which is favorable for thin film solar cells application. Raman spectroscopy showed that thermally induced crystallization produces oxide-free Sb2Se3 thin films. Description of the crystallization kinetics led to very accurate kinetic predictions for the isothermal annealing conditions suitable for preparation of glass-ceramics with defined amount of crystalline phase – the predictions were accurate to ∼10% of the true (experimentally determined) value.

Forces maintaining the DNA double helix

Despite the common acceptance that the enthalpy of DNA duplex unfolding does not depend on temperature and is greater for the CG base pair held by three hydrogen bonds than for the AT base pair held by only two, direct calorimetric measurements have shown that the enthalpic and entropic contributions of both base pairs are temperature dependent and at all temperatures are greater for the AT than the CG pair. The temperature dependence results from hydration of the apolar surfaces of bases that become exposed upon duplex dissociation. The larger enthalpic and entropic contributions of the AT pair are caused by water fixed by this pair in the minor groove of DNA and released on duplex dissociation. Analysis of the experimental thermodynamic characteristics of unfolding/refolding DNA duplexes of various compositions shows that the enthalpy of base pairing is negligibly small, while the entropic contribution is considerable. Thus, DNA base pairing is entropy driven and is coupled to the enthalpy driven van der Waals base pair stacking. Each of these two processes is responsible for about half the Gibbs energy of duplex stabilization, but all the enthalpy, i.e., the total heat of melting, results from dissociation of the stacked base pairs. Both these processes tightly cooperate: while the pairing of conjugate bases is critical for recognition of complementary strands, stacking of the flat apolar surfaces of the base pairs reinforces the DNA duplex formed.

English

Despite the widely spread acceptance that the enthalpy of DNA duplex unfolding does not depend on temperature and is greater for the CG base pair held by three hydrogen bonds than for the AT base pair held by only two hydrogen bonds, direct calorimetric measurement has shown that the enthalpic and entropic contributions of both base pairs are temperature dependent and at all temperatures they are greater for the AT base pair. The larger enthalpic and entropic contributions of the AT base pair result from water that is fixed by this pair in the minor groove of DNA and is released at duplex dissociation, while their dependence on temperature results from hydration of the apolar surfaces of bases that become exposed upon duplex dissociation. Analysis of the obtained thermodynamic characteristics of unfolding/refolding of the DNA duplexes of various compositions shows that the enthalpic contribution of base pairing is negligibly small, while the entropic is considerable. Thus, the DNA base pairing is the entropy driven process but it is conjugate with the bases stacking that is the enthalpy driven. The last is responsible for about 50% of duplex stabilizing Gibbs energy and for almost 100% of its enthalpy, that is for the total heat of DNA melting. Key words: DNA, stability, hydrogen bonding, base stacking, hydration.

Use of isothermal titration calorimetry to study various systems

Isothermal titration calorimetry (ITC) is a technique that allows precise measurements and a complete thermodynamic description of association, interaction or binding processes. This review will address uses of ITC in studies of self-assemble of monocomponent systems and interacting systems in broad spectrum. It also focuses on use of ITC on conformational study, thermodynamic study, reaction kinetics, adsorption phenomena, etc. ITC studies on the association of different monocomponents such as surfactants and polymers to provide quantitative information on different thermodynamic functions associated with micellization / association (Gibbs energy, enthalpy and entropy). Studies on binding isotherm by ITC provide a comprehensive description of the interaction process. Emphasis will be given to analyze the rapid reaction kinetics with new models. This review stresses the importance of using direct calorimetric measurements to obtain and report accurate thermodynamic data, even in complex systems. These data, whenever possible, should be confirmed and verified with other techniques

VO2-based switchable radiator for spacecraft thermal control

Direct calorimetric measurements of a solid state passive switchable radiator for spacecraft thermal control have been performed in a simulated space environment. Dynamic emissivity control is provided by the thermochromic phase change in a multilayer VO2 thin film based resonant absorber. The measured radiated power difference between 300 K and 373 K was 480 W/m2 corresponding to a 7× difference in radiative cooling power. We present theoretical and experimental radiator values for both normal and hemispherical as well the optical properties of VO2 as determined via infrared spectroscopic ellipsometry.

Energetics of hydration on uranium oxide and peroxide surfaces

Abstract

Thermochemical study of tetravalent metal sulfate tetrahydrates: A4+(SO4)2(H2O)4 (A4+ = Zr, Ce, U)

The syntheses, characterization, and calorimetric measurements of enthalpies of formation of four tetravalent metal sulfate tetrahydrates (A4+(SO4)2(H2O)4 (A4+ = Zr, Ce, U): α-Zr(SO4)2(H2O)4, α-Ce(SO4)2(H2O)4, β-Ce(SO4)2(H2O)4, and β-U(SO4)2(H2O)4) are reported. Direct calorimetric measurements showed that the formation enthalpies of these compounds from the corresponding oxides correlate with the eightfold coordination radius of the tetravalent cations. An energetic slope change is observed between the α- (Fddd) and β- (Pnma) forms and is consistent with previously reported studies.

TiO2 Surface Engineering to Improve Nanostability: The Role of Interface Segregation

Nanoparticle stability against coarsening is one of the keys to allow better exploitation of the properties of nanoscale materials. The intrinsically high interfacial energies of nanoparticles constitute the driving force for coarsening, and therefore can serve as targets to design materials with improved thermal stability. In this study, we discuss the surface engineering of TiO2 nanocatalysts for artificial photosynthesis by exploiting the spontaneous segregation of Ba2+ ions to the interfaces of TiO2 nanocrystals. Ba2+ is a strong candidate for photoelectrocatalytic reduction of CO2 and its effects on interfacial energies lead to a remarkable increase in thermal stability. By using a systematic lixiviation method, we quantified the Ba2+ content located at both the surface and at grain boundary interfaces and combined with direct calorimetric measurements of surface energies and microstructural studies to demonstrate that Ba2+ excess quantities directly impact coarsening of TiO2 nanocatalysts by creatin...

Structural and thermodynamic limits of layer thickness in 2D halide perovskites

In the fast-evolving field of halide perovskite semiconductors, the 2D perovskites (A')2(A) n-1M n X3n+1 [where A = Cs+, CH3NH3+, HC(NH2)2+; A' = ammonium cation acting as spacer; M = Ge2+, Sn2+, Pb2+; and X = Cl-, Br-, I-] have recently made a critical entry. The n value defines the thickness of the 2D layers, which controls the optical and electronic properties. The 2D perovskites have demonstrated preliminary optoelectronic device lifetime superior to their 3D counterparts. They have also attracted fundamental interest as solution-processed quantum wells with structural and physical properties tunable via chemical composition, notably by the n value defining the perovskite layer thickness. The higher members (n > 5) have not been documented, and there are important scientific questions underlying fundamental limits for n To develop and utilize these materials in technology, it is imperative to understand their thermodynamic stability, fundamental synthetic limitations, and the derived structure-function relationships. We report the effective synthesis of the highest iodide n-members yet, namely (CH3(CH2)2NH3)2(CH3NH3)5Pb6I19 (n = 6) and (CH3(CH2)2NH3)2(CH3NH3)6Pb7I22 (n = 7), and confirm the crystal structure with single-crystal X-ray diffraction, and provide indirect evidence for "(CH3(CH2)2NH3)2(CH3NH3)8Pb9I28" ("n = 9"). Direct HCl solution calorimetric measurements show the compounds with n > 7 have unfavorable enthalpies of formation (ΔHf), suggesting the formation of higher homologs to be challenging. Finally, we report preliminary n-dependent solar cell efficiency in the range of 9-12.6% in these higher n-members, highlighting the strong promise of these materials for high-performance devices.

Characterization of a precast hemp concrete. Part I: Physical and thermal properties

Hemp concrete is seen as a possible solution for addressing the energy, health and comfort issues of sustainable buildings, thanks to its hygrothermal properties and environmental qualities. This paper aims to determine the physical and thermal properties of an industrial prefabricated hemp concrete block based on hemp shiv and a lime-metakaolin binder. When available, distinct measurement methods were applied and confronted on this precast material in order to evaluate the impact of the experimental procedure on the results. Concerning air permeability, the present study shows that a measurement method initially intended for regular concrete can be adapted to the specific behaviour of highly permeable material such as hemp concrete. The thermal conductivity was measured with a guarded hot plate and a hot wire. Hot wire measurements on different moist states of the material allowed the self-consistent scheme to be applied for the evaluation of the thermal conductivity as a function of the humidity. Two direct measurement methods, differential scanning calorimetry (DSC) on the components and use of a Calvet calorimeter on the hemp concrete, and one indirect method, through effusivity measurement, were adopted for evaluating the specific heat capacity of the material. The original method proposed using DSC was shown to be as accurate as direct calorimetric measurement. The direct measurement methods gave similar results while the indirect one led to a much lower value. A comprehensive analysis of the measurement values available in the literature on hemp concretes confirmed this trend.This first paper highlights the significant influence of the testing method on the determination of the thermal properties of a precast hemp concrete, especially on the heat capacity measurement. This result emphasizes the need for a large inter-laboratory experimental campaign, applied to bio-aggregate based concrete, in order to form the basis of recommendations for adequate physical and thermal characterization methods for these bio-based building materials. A second part of this study will investigate the hydric properties of the same material.

Direct measurements of laser absorptivity during metal melt pool formation associated with powder bed fusion additive manufacturing processes

Direct calorimetric measurements are used to study the effective optical absorptivity at 1070 nm laser wavelength for bulk and powder-coated discs of industrially relevant metals. Effective absorptivity is plotted as a function of nominal laser power from 30 up to 600 W for scanning velocities of 100, 500, and 1500 mm/s. The absorptivity versus power curves of the bulk materials typically shows a reduction in effective absorptivity until the beginning of the formation of a keyhole-type surface depression that is associated with an increased absorption of the laser light in the growing keyhole until a saturation value is reached. For powders, an additional plateau of higher absorptivity can be observed for low laser power, until the curves qualitatively collapse when full melting of the powder tracks is achieved. It is shown that, under conditions associated with laser powder-bed fusion additive manufacturing, absorptivity values can vary greatly, and differ from both room temperature powder layer measurements and liquid metal estimates from the literature.

Direct calorimetric measurements in a PBII and deposition (PBII&D) experiment with a HiPIMS plasma source

We report on direct calorimetric probe measurements in a plasma based ion implantation and deposition (PBII&D) system, using HiPIMS as plasma and deposition source. The combination of ion implantation and physical vapor deposition is a versatile system which allows successive and simultaneous coating, doping or cleaning of a substrate surface in a complex, finely adjustable system. Due to the pulsed nature of both processes, the delay between HiPIMS and PBII pulse is a crucial parameter which can be used to effectively tune the process according to the required needs. Since the delay defines at what time during the HiPIMS period the PBII pulse is applied to the substrate, it can also be utilized to obtain time resolved information about the ion density in the substrate's environment.To allow direct calorimetric measurement of a high voltage pulsed substrate, a common passive thermal probe (PTP) was modified utilizing a fiber optic temperature sensor. With this probe, the effect of PBII voltage, substrate distance and pressure, on the energy flux and ion current towards the PBII substrate was investigated as a function of the delay between HiPIMS and PBII pulse. The results were successfully compared to a basic model and revealed important information regarding substrate position, process pressure and the effect of secondary electrons in this combined system.

In situ absorptivity measurements of metallic powders during laser powder-bed fusion additive manufacturing

The effective absorptivity of continuous wave 1070nm laser light has been studied for bare and metal powder-coated discs of 316L stainless steel as well as for aluminum alloy 1100 and tungsten by use of direct calorimetric measurements. After carefully validating the applicability of the method, the effective absorptivity is plotted as a function of incident laser power from 30 up to ≈540W for scanning speeds of 100, 500 and 1500mms−1. The effective absorptivity versus power curves of the bulk materials typically show a slight change in effective absorptivity from 30W until the onset of the formation of a recoil pressure-induced surface depression. As observed using high-speed video, this change in surface morphology leads to an increase in absorption of the laser light. At the higher powers beyond the keyhole transition, a saturation value is reached for both bare discs and powder-coated disks. For ≈100μm thick powder layers, the measured absorptivity was found to be two times that of the bare polished discs for low-laser power. There is a sharp decrease when full melting of the powder tracks is achieved, followed by a keyhole-driven increase at higher powers, similar to the bare disc case. It is shown that, under conditions associated with laser powder-bed fusion additive manufacturing, absorptivity values can vary greatly, and differ from both powder-layer measurements and liquid metal estimates from the literature.

Adsorption enthalpy of lead(II) and phenol on coals and activated carbon in the view of thermodynamic analysis and calorimetric measurements

Comparison among adsorption enthalpies of thermodynamic analysis and these of direct calorimetric measurements is reported for sorption of lead(II) and phenol on natural coals and activated carbon. Thermodynamic calculations came out from developments of equilibrium adsorption isotherms recorded at 303K, 333K and 353K. Standard adsorption enthalpies ΔH0 were calculated from temperature dependences of equilibrium constants of adsorption Ka, with values of Ka being evaluated directly from experimental data and from fitted courses of the Langmuir and Freundlich isotherms. In addition, dependences of isosteric enthalpy on surface coverage were evaluated. Values of the exothermic enthalpies (ranging from −6kJmol−1 to −50kJmol−1) were obtained, however exclusive endothermic effect for lead(II) adsorption on a sample of natural coal (24kJmol−1) was also ascertained. Direct calorimetric measurements using flow and immersion techniques then proved that all the studied adsorptions proceed with exothermic effects from −2kJmol−1 to −42kJmol−1. It was found that experimental adsorption enthalpies correspond better to mean isosteric enthalpies in the interval 0–1molkg−1 of the surface coverages than to the standard adsorption enthalpies ΔH0 of the thermodynamic calculations.

Differential Heat of Adsorption and Isosteres.

Heat of adsorption is a basic thermodynamic property extensively used not only for understanding thermal effects and heat management in industrial gas storage and separation processes but also for development and validation of adsorption models and materials force fields. Despite a long history of theoretical studies and a vast experimental literature, controversies often arise in the thermodynamic analysis of heat effects due to various assumptions used to describe gas adsorption and inconsistencies between direct calorimetric measurements and isosteric heat obtained from various adsorption isotherms. Here we present a rigorous theoretical procedure for predicting isosteric heat without any assumption about the geometry of porous adsorbents or operating conditions. Quantitative relations between the differential heat and various isosteres have been established with the grand-canonical Monte Carlo simulation for gas adsorption in amorphous as well as crystalline porous materials. The inconsistencies and practical issues with conventional methods for the analysis of the heat effect have been clarified in the context of the exact results for model systems. Via the resolution of a number of controversies about heat analysis, we hope that the new theoretical procedure will be adopted for both fundamental research and industrial applications of gas adsorption processes.

Facilely synthesized meso-macroporous polymer as support of poly(ethyleneimine) for highly efficient and selective capture of CO2

Poly(ethyleneimine) (PEI) impregnated adsorbents are promising alternatives to amine-based liquid absorbents for post-combustion capture of CO2. A current challenge is to identify meso- and/or macroporous supports with large pore volumes that can be facilely synthesized from a cost-effective approach as supports for PEI. In this work, hierarchically nanoporous poly(divinylbenzene) (PDVB) is synthesized through a one-step polymerization of readily available divinylbenzene (DVB) under solvothermal conditions without use of any template or catalyst. The synthesized PDVB is found to have abundant meso-macropores, as well as a large pore volume. Subsequently, a series of PEI-impregnated PDVB sorbents is prepared and their performance for the selective adsorption of CO2 is investigated. The PEI-PDVB composites are found to exhibit promising CO2 capacities and exceptionally high CO2/N2 selectivities. The strength of CO2 adsorption is experimentally determined by direct calorimetric measurements. The PEI-PDVB composites show excellent stability under both dry and humidified sorption conditions during extended adsorption-desorption cycles. Based on the results obtained, these PEI-PDVB composites are identified as sorbents with significant potential for application in practical CO2 capture from industrial gas streams.