Calorimetric Investigation Research Articles

A calorimetric and thermodynamic investigation of zinc and cadmium hydrous selenites

A calorimetric and thermodynamic investigation of three hydrous selenites, ZnSeO3·2H2O, ZnSeO3·H2O and CdSeO3·H2O, was undertaken. All three phases were synthesized by mixing of aqueous solutions of zinc and cadmium nitrates, accordingly, and sodium selenite and characterized by XRD powder diffraction, energy dispersive X-ray microanalysis, inductively coupled plasma mass spectrometry and thermal analisys methods. The low-temperature heat capacity of ZnSeO3·2H2O, ZnSeO3·H2O and CdSeO3·H2O were measured using adiabatic calorimetry between 5 and 324K, and the third-law entropies were determined. Values of molar third law entropy Sm°(298K, ZnSeO3·2H2O, cr.)=179±1J·K−1·mol−1, Sm°(298K, ZnSeO3·H2O, cr.)=150±1J·K−1·mol−1, Sm°(298K, CdSeO3·H2O, cr.)=171±1J·K−1·mol−1 were calculated. The expanded uncertainties for Sm° are given at the 0.95 confidence level (k≈2). The enthalpies of formation for ZnSeO3·H2O, ZnSeO3·2H2O and CdSeO3·H2O were determined using H2SO4-solution calorimetry giving ΔfHm° (298K, ZnSeO3·2H2O, cr)=−1238±2kJ·mol−1, ΔfHm°(298K, ZnSeO3·H2O, cr)=−931±2kJ·mol−1, ΔfHm°(298K, CdSeO3·H2O, cr)=−906±2kJ·mol−1. The expanded uncertainties for ΔfHm° are given at the 0.95 confidence level (k≈2). The Gibbs energy of formation for ZnSeO3·2H2O, ZnSeO3·H2O and CdSeO3·H2O at T=298K, 1atm have been calculated on the basis on ΔfHm° and ΔfSm°: ΔfGm°(298K, ZnSeO3·2H2O, cr.)=−1035±2kJ·mol−1, ΔfGm°(298K, ZnSeO3·H2O, cr.)=−790±2kJ·mol−1 and ΔfGm°(298K, CdSeO3·2H2O, cr.)=−768±2kJ·mol−1. The expanded uncertainties for ΔfGm° are given at the 0.95 confidence level (k≈2). Smoothed Cp,m°(T) values between T=0K and T=320K for ZnSeO3·2H2O(cr.), ZnSeO3·H2O(cr.) and CdSeO3·H2O(cr.) are presented along with values for Sm° and the functions [Hm°(T)−Hm°(0)] and [Gm°(T)−Hm°(0)]. These results motivate a re-evaluation of the natural conditions under which selenites, and selenates replace selenides, and sulfides in the oxidation zones of sulfide ore deposits or upon weathering of technologic waste. The values of ΔfG° for ZnSeO3·2H2O, ZnSeO3·H2O and CdSeO3·H2O were used to calculate the Eh–pH diagrams of the Zn–Se–H2O and Cd–Se–H2O, systems. These diagrams have been constructed for the average contents of these elements in acidic waters of the oxidation zones of sulfide deposits. The behavior of selenium, zinc, and cadmium in the surface environment have been quantitatively explained by variations of the redox potential and the acidity-basicity of the mineral-forming medium. Precisely these parameters determine the migration ability of selenium compounds and its precipitation in the form of various solid phases.

Thermal and calorimetric investigations of titania–silica composites

The paper presents the studies of effects of TiO2 amount differentiation on the structural and thermal properties of titania–silica complex oxides prepared by chemical vapor deposition of TiCL4 onto the Si-40, Si-60, and Si-100 silica gels. The mesoporous materials, characterized by a varied pore structure with highly developed surface and large pore volume, were obtained. The porous structure of materials under investigations was characterized by the low-temperature nitrogen adsorption–desorption method as well as by power spectral density calculated from the calorimetric investigations of water confined in the pores. Moreover, the thermodesorption of water using the quasi-isothermal thermogravimetry was used to characterize their thermal and surface properties. The adsorbed water layers and the concentration of weakly and strongly bound water as well as the surface free energy on the adsorbent–water interfaces were calculated. It was stated that the increase of titania content causes a gradual decrease of specific surface area and has a significant effect on the porous structure formation. The water thermodesorption from the surface proceeds in few stages because of the porosity created by TiO2. The decrease in the total surface free energy (Δ GΣ) can be observed with the increasing TiO2 content. The largest Δ GΣ value at the adsorbent/strongly bound water interface is exhibited by the adsorbents of Si-100 series. The lowering of the freezing/melting points of water contained in the pores of the studied materials is strongly connected with their porous structure.

A calorimetric and thermodynamic investigation of the synthetic analogue of chalcomenite, CuSeO3·2H2O

Thermophysical and thermochemical calorimetric investigations were carried out on the synthetic analogue of chalcomenite. The synthesis of CuSeO 3 ·2H 2 O was realized from copper nitrate and sodium selenite solutions heated to 80 °C for 2 to 3 h. The precipitate was characterized by X-ray powder diffraction, X-ray fluorescence, IR spectroscopy, and Raman spectroscopy. The low-temperature heat capacity of CuSeO 3 ·2H 2 O was measured using adiabatic calorimetry between 5 and 323 K, and the third-law entropy was determined. A value of S °(298 K, CuSeO 3 ·2H 2 O, cr) = 181.0 ± 1.0 J/(K mol) was obtained with an uncertainty of 0.5%. The enthalpy of formation of CuSeO 3 ·2H 2 O was determined by solution calorimetry with H 2 SO 4 solution as the solvent, giving Δ f H °(298 K, CuSeO 3 ·2H 2 O, cr) = −1035.3 ± 4.9 kJ/mol. The Gibbs energy of formation for CuSeO 3 ·2H 2 O at T = 298 K, 1 atm can be calculated on the basis on Δ f H ° (298 K) and Δ f S °(298 K): Δ f G °(298 K, CuSeO 3 ·2H 2 O, cr) = −835.3 ± 5.3 kJ/mol. Smoothed C p °( T ) values between T = 0 K and T = 320 K for CuSeO 3 ·2H 2 O (cr) are presented along with values for S ° and the functions [ H °( T ) – H °(0)]and[ G °( T ) – H °(0)]. These results motivate a re-evaluation of the natural conditions under which selenites and selenates replace selenides, and sulfides in the oxidation zones of sulfide ore deposits or upon weathering of technologic waste. The value of Δ f G ° for CuSeO 3 ·2H 2 O was used to calculate Eh–pH diagrams of the Cu–Se–CO 2 –H 2 O system. The behaviour of selenium and copper in the surface environment has been quantitatively explained by variations of the redox potential and the acidity–basicity of the mineral-forming medium. Precisely, these parameters determine the migration ability of selenium compounds and their precipitation in the form of various solid phases.

Experimental evaluation and modeling of thermal conductivity of tetrafunctional epoxy resin containing different carbon nanostructures

This study attempts to investigate the thermal conductivity behavior of epoxy nanocomposites containing different types of nanofillers, such as 1‐D Multiwall Carbon Nanotubes (MWCNTs) and 2‐D predominant shape of Exfoliated Graphite nanoparticles (EG) at loading level from 0.25 to 3% wt. For all the analyzed epoxy nanocomposites calorimetric investigation shows that EG nanoparticles accelerate the curing process of the epoxy resin. Thermal conductivity measurements show that this acceleration is directly related to the better heat conduction obtained through the incorporation of EG in the epoxy matrix. The thermal conductivity of epoxy nanocomposites filled with EG, unlike of epoxy nanocomposites containing MWCNTs, increases significantly with increasing content of nanofiller. An increase in thermal conductivity of ∼ 300% has been detected for a filler percentage of only 3%wt of EG.The application of Deng‐Zheng micromechanical model has proven to be very effective in predicting analytically the thermal conductivity of the analyzed nanocomposites. POLYM. ENG. SCI., 57:779–786, 2017. © 2017 Society of Plastics Engineers

Calorimetric Investigation of Anomalous Heat Production in Ni–H Systems

It has been claimed that Ni–H systems produce excess heat for long periods of time. We have performed experimental calorimetric investigations of this phenomenon. The experimental setup consisted of a ceramic reactor with nickel powder inside it, a heater, hydrogen loading system and calorimeter. Nickel powders with different grain size were used because of their large surface area. Hydrogen pressure varied from 0.5 to 2.5 atm. Temperature varied from 25 to 800◦C. Different methods of input power were used in order to investigate possible effects of high amplitude magnetic pulses. The experimental runs lasted from 4 to 50 h. Experiments did not show any evidence of excess heat within the accuracy of measurement.

A calorimetric investigation of A2[(UO2)2(WO5)O] compounds with A = K, Rb and Cs and calculated phase relations in the K2WO4-UO3-H2O and K2MoO4-K2WO4-UO3-H2O systems

A calorimetric and thermodynamic investigation of three alkali-metal uranyl tungstates of general formula A2[(UO2)2(WO5)O], with A=K, Rb and Cs, was undertaken. All three phases were synthesized by high-temperature solid-state reaction of a mixture of the respective alkali-metal nitrates and tungsten (VI) and gamma uranium (VI) oxide. The synthetic products were characterized by X-ray powder diffraction and X-ray fluorescence methods. The enthalpy of formation of the three phases was determined using HF-solution calorimetry giving ΔfHm°(T=298K, K2[(UO2)2(WO5)O], cr)=−4185±8kJ·mol−1, ΔfHm°(T=298K, Rb2[(UO2)2(WO5)O], cr)=−4185±10kJ·mol−1, and ΔfHm°(T=298K, Cs2[(UO2)2(WO5)O], cr)=−4198±9kJ·mol−1. Their low-temperature molar heat capacity, Cp,m°, was measured using adiabatic calorimetry from T=9 to 329K for K2[(UO2)2(WO5)O], from T=9 to 321K for Rb2[(UO2)2(WO5)O] and from T=6 to 320K for Cs2[(UO2)2(WO5)O]. The respective molar third law entropy at T=298.15K, Sm°, was calculated giving 380±1J·K−1·mol−1 for K2[(UO2)2(WO5)O], 406±1J·K−1·mol−1 for Rb2[(UO2)2(WO5)O] and 419±1J·K−1·mol−1 for Cs2[(UO2)2(WO5)O]. These new calorimetric results, combined with literature data, have been used to calculate the Gibbs free energy of formation, ΔfGm°, for all the studied phases giving: ΔfGm° (T=298K, K2[(UO2)2(WO5)O], cr)=−3914±8kJ·mol−1, ΔfGm° (T=298K, Rb2[(UO2)2(WO5)O], cr)=−3915±10kJ·mol−1 and ΔfGm° (T=298K, Cs2[(UO2)2(WO5)O], cr)=−3926±9kJ·mol−1. Smoothed Cp,m°(T) values between 0K and 320K are presented along with the values for Sm° and the functions [Hm°(T)−Hm°(0)] and [Gm°(T)−Hm°(0)] for all three phases. The phase relations of various solid phases and solution complexes in the K2WO4-UO3-H2O and K2MoO4-K2WO4-UO3-H2O systems with and without CO2 at T=298K were calculated using a Gibbs energy minimization approach. The results show that there is no uranium-containing solid phase stable at pH<2.2 in either CO2-free or CO2-bearing systems. Here, uranium (VI) is bound in solution complexes. Various solid phases are stable from pH 2.2 to pH 10 in the CO2-free system, but at pH>10 and in the presence of CO2 no solid is present.

Calorimetric investigation on three-ring chain ethylene-bridge liquid crystalline compounds with terminal odd carbon chain

The stabilities and the phase transition sequences of two ethylene-bridge fluorinated liquid crystals have been examined using the differential scanning calorimeter; and the repeatability and reliability for these phase transitions also have been verified. Furthermore, we report molar heat capacities of these two fluorinated liquid crystals measured using a Quantum Design physical properties measurement system with specific heat option within the temperature range from 1.9 to 300 K. The heat capacities of these two compounds increase with the temperature increasing, and no thermal anomalies have been found in the entire temperature region; and also the heat capacity values of 5-BB2B-F are larger than those of 3-BB2B-F due to the molecular weight difference even though they are homologous. The experimental data have been fitted to a function of T with a series of theoretical and empirical models for the proper temperature ranges. Thermodynamic function values \(C_{\text{p,m}}^{0} ,\Delta_{ 0}^{{\text{T}}} S_{\text{m}}^{\text{o}}\) and \(\Delta_{ 0}^{\text{T}} H_{\text{m}}^{\text{o}}\) at T = (0.5–300) K have been calculated based on these fitting results. The standard molar heat capacities, entropies and enthalpies of 3-BB2B-F and 5-BB2B-F at 298.15 K and 0.1 MPa have been determined to be \(C_{\text{p,m}}^{\text{o}}\) = (450.02 ± 4.50) J K−1 mol−1 and (478.08 ± 4.78) J K−1 mol−1, \(S_{\text{m}}^{\text{o}}\) = (443.91 ± 4.44) J K−1 mol−1 and (486.85 ± 4.87) J K−1 mol−1 and \(H_{\text{m}}^{\text{o}}\) = (66.47 ± 0.66) kJ mol−1 and (72.66 ± 0.73) kJ mol−1, respectively.

Binding interaction of phenothiazinium dyes with double stranded RNAs: Spectroscopic and calorimetric investigation

RNA targeting through small molecules is an emerging and promising therapeutic route that necessitates identification of small molecules that can selectively target specific RNA structures. In this context a comparative study of the interaction of two phenothiazinium dyes thionine (THN) and toluidine blue O (TBO) with three double stranded RNA polynucleotides (ds RNAs) viz. poly(I).poly(C), poly(A).poly(U) and poly(C).poly(G) was conducted by various biophysical techniques. A higher binding of THN with poly(I).poly(C) over poly(A).poly(U) and poly(C).poly(G) was observed. The intercalative binding and RNA induced fluorescence quenching of the dyes through a static mechanism was confirmed by viscosity studies and steady state polarization anisotropy experiments. Binding induced structural perturbation in the RNA polynucleotides was confirmed from circular dichroism spectroscopy. DSC and thermal melting experiments confirmed that the binding resulted in strong thermal stabilization. The binding affinity of THN with poly(I).poly(C) was the highest followed by that to poly(A).poly(U) and poly(C).poly(G). The trend was the same for TBO also, but THN bound stronger than TBO. The binding of the dyes was characterized by strong negative enthalpy changes with minimum positive entropy changes indicating typical intercalative interaction. The results presented here may be useful to design new types of RNA binding antitumor, antibacterial and anticancer agents.

Assessing the hyperthermic properties of magnetic heterostructures: the case of gold-iron oxide composites.

Gold-iron oxide composites were obtained by in situ reduction of an Au(III) precursor by an organic reductant (either potassium citrate or tiopronin) in a dispersion of preformed iron oxide ultrasmall magnetic (USM) nanoparticles. X-ray diffraction, transmission electron microscopy, chemical analysis and mid-infrared spectroscopy show the successful deposition of gold domains on the preformed magnetic nanoparticles, and the occurrence of either citrate or tiopronin as surface coating. The potential of the USM@Au nanoheterostructures as heat mediators for therapy through magnetic fluid hyperthermia was determined by calorimetric measurements under sample irradiation by an alternating magnetic field with intensity and frequency within the safe values for biomedical use. The USM@Au composites showed to be active heat mediators for magnetic fluid hyperthermia, leading to a rapid increase in temperature under exposure to an alternating magnetic field even under the very mild experimental conditions adopted, and their potential was assessed by determining their specific absorption rate (SAR) and compared with the pure iron oxide nanoparticles. Calorimetric investigation of the synthesized nanostructures enabled us to point out the effect of different experimental conditions on the SAR value, which is to date the parameter used for the assessment of the hyperthermic efficiency.

Differential Scanning Calorimetry Tests of Epoxy and Polyester Composites Reinforced with Giant Bamboo Fibers

Despite the benefits associated with the use of natural fibers instead of synthetic ones as composite reinforcement, there are still some limitations to their application. Among the disadvantages associated with natural fibers stands the low thermal resistance. This imposes restrictions to the composite utilization when it is exposed to temperatures above 100 oC. For one point, the hydrophilic nature of lignocellulosic fibers causes absorption of water, but at high temperatures this water is lost, what produce pores and flaws in the composite polymer matrix. Moreover, the fiber cellulose, hemicellulose and lignin are degraded at higher temperatures. The objective of the present work was to conduct a comparative differential scanning calorimetric investigation between polyester and epoxy matrixes composites incorporated with different volume fractions of giant bamboo fibers. A substantial loss of mass was found up to 120 oC. The DSC curves revealed a variation in the enthalpy as a function of the giant bamboo fiber fractions and the corresponding polymeric matrix.

Calorimetric Investigations of Oriented Polypropylene Tapes and Self‐Reinforced Composites

SummaryDifferential scanning calorimetry (DSC) is a commonly applied method of determining various physical properties of thermoplastic polymers. Analyzing DSC melting and crystallization curves it is possible to verify whether the macromolecules orientation occurs in fibers, films and self‐reinforced polymer composites (SRC). This paper presents the comparison of the results of calorimetric investigations of polypropylene (PP) single polymer composites (SRC) with the investigations of constrained PP tape samples additionally annealed before the measurement. The program of thermal treatment resembled temperature changes in the mold during SRC production by hot compaction method. The results confirmed a substantial influence of compression molding pressure on the melting process of oriented PP reinforcement used in the production of single polymer composites.

Calorimetric and Electromotive Force Measurements of Al-Li-Zn Liquid Solutions

The solution calorimetry and electromotive force methods were used for the study of the mixing enthalpy and partial excess Gibbs energy of the Al-Li-Zn liquid solutions. Calorimetric investigations were conducted for solutions with the ratio of XLi/XAl and XLi/XZn = 0.8/0.2 and at the temperatures of 942 and 978 K, respectively. The electromotive force studies were performed at two temperatures: 873 and 923 K by the titration technique and for dilute solutions. Based on the data of the mixing enthalpy change and the partial excess Gibbs energy of Li available in the literature, together with that obtained in these studies, the ternary interaction parameters were elaborated. The comparative analysis of the experimental mixing enthalpy change generally showed a good agreement with the values calculated based on different models. The observed deviations between the experimental and the calculated values were, for most of the experimental data, lower than 1 kJ/mol. The experimental partial excess Gibbs energy of Li showed a satisfactory agreement with that modeled on the basis of the ternary parameters elaborated in this work.

Calorimetric investigations of UPb3 compound

Interaction of uranium based metallic fuels and lead coolant can lead to formation of intermetallic compounds of U-Pb system. To understand U-Pb interactions, it is important to know thermodynamic properties of intermetallic compounds present in this system, UPb3 and UPb. In the present work, enthalpy increment, heat capacity and enthalpy of formation of UPb3 intermetallic compound were determined. The enthalpy increment was determined by high temperature Calvet calorimeter and heat capacity was determined using DSC. The heat capacity data was used to calculate thermodynamic parameters of the compound as a function of temperature. The enthalpy of formation at 843K was determined using successive precipitation method, by direct reaction calorimetry. The enthalpy of formation at 843K, from Pb(l) and U(l), was −28.9kJat-mol−1 and after adjusting enthalpy increments of pure elements and compound, the enthalpy of formation of the compound at 298K, from Pb(s) and U(α) was found to be −20.0kJ at-mol−1.

Spectroscopic and calorimetric investigations on the binding of phenazinium dyes safranine-O and phenosafranine to double stranded RNA polynucleotides

RNA targeting through small molecules that can selectively bind specific RNA structures is an important current strategy in therapeutic drug development. Towards this strategy a comparative study on the interaction of two phenazinium dyes, safranine-O and phenosafranine to double stranded RNAs, poly(I).poly(C), poly(A).poly(U) and poly(C).poly(G) was performed. Spectrophotometric and spectrofluorimetric studies revealed non-cooperative binding of the dyes to the duplex RNA with binding constants of the order 105M−1 with a higher affinity of safranine-O to poly(I).poly(C) followed by poly(A).poly(U) and poly(C).poly(G). Anisotropy and fluorescence quenching results confirmed an intercalation mode of binding for the dyes on these RNAs. Binding induced conformational changes in the RNA polynucleotides were revealed from circular dichroism data. Thermal melting study and DSC experiments demonstrated stabilization of dye-RNA complexes. Calorimetric studies revealed that the binding was accompanied by a large positive entropy term with a small negative enthalpy contributions. Significant hydrophobic forces in the complexation of the double stranded RNAs with the dyes were confirmed from the negative heat capacity changes. Enthalpy-entropy compensation was also observed in the binding. Parsing of the Gibbs energy suggested a larger non-electrostatic contribution in all the cases. The results presented here may be helpful to design new types of RNA-based therapeutic agents.

A comparative spectroscopic and calorimetric investigation of the interaction of amsacrine with heme proteins, hemoglobin and myoglobin

The binding of the anilido aminoacridine derivative amsacrine with the heme proteins, hemoglobin, and myoglobin, was characterized by various spectroscopic and calorimetric methods. The binding affinity to hemoglobin was (1.21 ± .05) × 105 M−1, while that to myoglobin was three times higher (3.59 ± .15) × 105 M−1. The temperature-dependent fluorescence study confirmed the formation of ground-state complexes with both the proteins. The stronger binding to myoglobin was confirmed from both spectroscopic and calorimetric studies. The binding was exothermic in both cases at the three temperatures studied, and was favored by both enthalpy and entropy changes. Circular dichroism results, three-dimensional (3D) and synchronous fluorescence studies confirmed that the binding of amsacrine significantly changed the secondary structure of hemoglobin, while the change in the secondary structure of myoglobin was much less. New insights, in terms of structural and energetic aspects of the interaction of amsacrine with the heme proteins, presented here may help in understanding the structure-activity relationship, therapeutic efficacy, and drug design aspects of acridines.

Calorimetric investigation of the concentration dependent enthalpy change around semicongruent melting CaCl2·6H2O

In this study, the impact of a deviation from the stoichiometrically correct hydrate concentration of a salt hydrate on the melting enthalpy is investigated exemplarily via 10 samples of CaCl2+H2O around semicongruent melting CaCl2·6H2O by using differential scanning calorimetry (DSC). While the melting enthalpy of CaCl2·6H2O is determined to be (185±19)Jg−1, a trend of decreasing melting enthalpy with increasing deviation in the CaCl2 concentration from CaCl2·6H2O is observed. Three out of the 10 samples of CaCl2+H2O were measured via DSC and T‐History. The determined enthalpy changes agree within the standard deviation of the DSC measurements. However, the value of the enthalpy change determined for consecutive heating cycles of the same sample via T-History is more stable than for consecutive heating cycles measured via DSC. This observation is attributed to the different sample volume of DSC and T-History and indicates a volume dependent behaviour of semicongruent melting CaCl2·6H2O. Statistical investigations into the high randomness of measured values for the melting enthalpy of consecutive heating cycles of CaCl2·6H2O were conducted via DSC. These reveal a strong negative correlation between the crystallisation temperature of CaCl2·4H2O and the melting enthalpy determined for the succeeding heating cycle. By adding 1wt% of Sr(OH)2·8H2O as nucleating agent for CaCl2·6H2O, the crystallisation of CaCl2·4H2O in the DSC measurements is suppressed and reproducible values for the melting enthalpy of consecutive heating cycles are obtained.

Calorimetric investigation on the interaction of proflavine with human telomeric G-quadruplex DNA

The interaction of an acridine dye, proflavine, with human telomeric G-quadruplex DNA was characterized by isothermal titration calorimetry and differential scanning calorimetry. The equilibrium constant of binding was deduced to be (1.36±0.09)·106M−1 at T=298.15K. The binding reaction was driven by both negative enthalpy and positive entropy contributions. The equilibrium constant decreased and the reaction became increasingly enthalpy driven with rise in temperature. However, the standard molar Gibbs energy change exhibited only marginal alterations suggesting the occurrence of enthalpy–entropy compensation. Negative heat capacity values were also obtained from the temperature dependence of enthalpy change. Parsing of the standard molar Gibbs energy using the salt dependent calorimetric data revealed that the binding was dominated by non-polyelectrolytic forces which remained virtually unaltered with changing salt concentration. Proflavine binding also significantly enhanced the thermal stability of G-quadruplex DNA against thermal unfolding.

Optical non-linearity tuning in Ca8-xPbxMBi(VO4)7 whitlockite-type systems

Ca8-xPbxMBi(VO4)7, M2+ = Mg2+, Zn2+ (0 ≤ x ≤ 1.5) and M2+ = Ca2+, Cd2+ (0 ≤ x ≤ 2) solid solutions with whitlockite-type structure have been prepared by solid state reactions in the form of powders and ceramics. Ferroelectric phase transitions (FPT) are revealed in the cause of dielectric, calorimetric and temperature second harmonic generation (SHG) investigations. It is found that ferroelectric Curie points in solid solutions decrease with x from 1000–1070 K to 730–800 K. The intensity of SHG firstly increases with x and then decreases, the highest SHG signal belongs to Ca7PbCdBi(VO4)7 and Ca6.5Pb1.5CdBi(VO4)7. Variation of Pb2+ concentration is shown to have a minor influence on the coherence length, therefore the SHG augmentation in solid solutions is attributed to optical nonlinear coefficient <d>. The structure of Ca6.5Pb1.5MgBi(VO4)7 is resolved and crystal structure changes in solid solutions are analyzed. The results are interpreted in view of site occupancy by two- and trivalent cations and their influence on formation of spare space essential for Pb2+ and Bi3+ non-bonded electrons stereo-activity in whitlockite-type crystal structures. For the first time contribution to optical nonlinearity from VO43− anionic groups in different positions is also discussed.

Thermal Stability of Materials for Thin-Film Electrochemical Cells Investigated by Thin-Film Calorimetry

ABSTRACTPhase transformation enthalpies are determined using the recently developed measurement technique Thin-Film Calorimetry (TFC), which is based on piezoelectric resonators vibrating in thickness shear mode. They are applicable up to at least 1000 °C. To the best of our knowledge, no comparable TFC systems for such high temperatures exist.The experimental part is divided into two subsections. The first is addressed to a thermodynamic investigation on piezoelectric langasite crystals (LGS, La3Ga5SiO14) which are the key component of the TFC system. The specific heat capacity is measured on LGS crystals of three different manufacturers. It ranges from about 0.45 J g-1 K-1 at 40 °C to about 0.60 J g-1 K-1 at 1000 °C. Thereby, deviations of up to 5 % between the different crystals are detected. Thermal diffusivity data for Y-cut LGS crystals are determined as well. Here, a constant decrease with temperature is detected ranging from 0.48 mm2 s-1 at room temperature to 0.38 mm2 s-1 at 700 °C.The second part presents thin-film calorimetric investigation on thin films of the family Li-Ni-Mn-Co-Al-Oxide (NMC/NMCA). These cathode materials are investigated and compared when annealed in ambient air or 0.5 % H2/Ar up to 860 °C. Three stoichiometries are chosen: Li(Ni1/3Mn1/3Co1/3)O2, Li(Ni0.6Mn0.2Co0.2)O2, and Li(Ni0.6Mn0.2Co0.15Al0.05)O2. The samples show three or four phase transformations. In air, the samples crystallize in the range of 250-350 °C. In 0.5 % H2/Ar, the transformations occur at higher temperatures. Especially in air, stoichiometric NMC crystallizes at lower temperatures compared to Ni-rich compositions. Additional doping with Al enhances the thermal stability which shifts all phase transformations to higher temperatures in both atmospheres.

Structure of the Interfacial Region in Adsorbed Poly(vinyl acetate) on Silica

We performed a combined calorimetric and molecular modeling investigation of poly(vinyl acetate) (PVAc) on silica to characterize the intermolecular interactions and the behavior of the adsorbed polymer. From temperature-modulated differential scanning calorimetry experiments, different regions of thermal activity suggested a gradient of mobility in the adsorbed polymer. Polymer segments in more direct contact with silica (tightly bound) showed a significantly elevated and broadened glass transition relative to the bulk polymer, while polymer further away (loosely bound) showed only a slightly elevated transition relative to the bulk polymer. A thermal transition for PVAc at the air interface (more-mobile) was also observed and was at lower temperatures than the bulk polymer. Density profiles from molecular dynamics studies suggested a structure of the adsorbed polymer similar to that experimentally observed. These studies were consistent with the presence of a motional gradient in the polymer segments, a...