Measuring Heat Effects Research Articles

Influence of Composition on Energetic Properties of Copper Oxide – Aluminum Powder Nanothermite Materials Formed by Electrophoretic Deposition

AbstractWe investigated the reactions in composite thermite layers consisting of Al, CuO, and Cu2O nanoparticles formed by electrophoretic deposition on a titanium substrate. The composition determined the reaction propagation rates and heat effects in oxygen and oxygen‐free atmospheres. It was found that a stable self‐propagating exothermic reaction in the aluminum‐copper oxide layer takes place in the range of 50–80 wt.% of Al. The maximum values of the measured heat effects also fell in this range. At the same time, the calculation following the stoichiometry of the reaction shows the optimal range of the Al amount is 10–20 wt.%. To explain this fact, we proposed a model based on calculating the probability of contact between Al and CuO particles depending on the average particle size and their concentration. The model is based on the calculation of solid angles, which means that the exact value of the contact area does not play a decisive role in this case.

Impact of summer heat on mortality and years of life lost: Application of a novel indicator of daily excess hourly heat

BackgroundPrevious studies have widely assessed heat-mortality relationships across global regions, while the epidemiological evidence regarding the heat effect on years of life lost (YLL) is relatively sparse. Current investigations using daily mean data cannot take hourly temperature variation into consideration and may underestimate heat effects. We developed a novel indicator, daily excess hourly heat (DEHH), to precisely evaluate the potential heat effects on mortality and YLL. MethodsHourly data on temperature and daily information, including concentrations of air pollutants, relative humidity, and records of all registered deaths were obtained in Wuhan, China during the warm seasons (May–September) of 2009–2012. DEHH, developed in this study, is defined as daily total hourly temperatures that exceed a specific heat threshold. By performing time series regression analyses, we assessed the changes in daily mortality and YLL per interquartile range (IQR) increase in DEHH across different lag days. ResultsThe heat threshold evaluated by the Akaike Information Criterion for DEHH calculation is 30 °C (92th percentile of whole-year mean temperature distribution). Daily average DEHH was 13.9 °C, with an IQR of 19.9 °C. Linear exposure-response curves were found between DEHH and two health outcomes. Generally, heat effects lasted for 2–3 days and DEHH at lag 0–1 was most strongly associated with increased mortality and YLL. The effects were especially remarkable for stroke and ischemic heart disease mortality. Most intense effect on YLL was found in non-accidental deaths (20.11, 95% confidence interval: 8.90–31.33) at lag 0–1. More DEHH-related mortality and YLL from cardiovascular deaths were observed among males. People aged 0–74 years and males suffered more from YLL burden due to high temperatures. ConclusionsOur study demonstrated that DEHH may be an alternative indicator to precisely measure heat effects on daily mortality and YLL. Further DEHH-based evidence from large scale investigations is needed so as to better understand heat-associated health burden and improve public response to extremely high temperatures.

Rye (Secale cereale) supernumerary (B) chromosomes associated with heat tolerance during early stages of male sporogenesis.

Rye supernumerary (B) chromosomes have an accumulation mechanism involving the B subtelomeric domain highly enriched in D1100- and E3900-related sequences. In this work, the effects of heat stress during the early stages of male meiosis in 0B and +B plants were studied. In-depth cytological analyses of chromatin structure and behaviour were performed on staged rye meiocytes utilizing DAPI, fluorescence in situ hybridization and 5-methylcytosine immune labelling. Quantitative real-time PCR was used to measure heat effects on the expression of the Hsp101 gene as well as the 3·9- and 2·7-kb E3900 forms in various tissues and meiotic stages. Quantitative real-time PCR established that heat induced equal up-regulation of the Hsp101 gene in 0B and 2B plants, with a marked peak in anthers with meiocytes staged at pachytene. Heat also resulted in significant up-regulation of E3900-related transcripts, especially at pachytene and for the truncated 2·7-kb form of E3900. Cytological heat-induced anomalies in prophase I, measured as the frequency of anomalous meiocytes, were significantly greater in 0B plants. Whereas telomeric sequences were widely distributed in a manner close to normal in the majority of 2B pachytene cells, most 0B meiocytes displayed abnormally clustered telomeres after chromosome pairing had occurred. Relevantly, bioinformatic analysis revealed a significantly high-density heat responsive cis regulatory sequence on E3900, clearly supporting stress-induced response of transcription for the truncated variant. Taken together, these results are the first indication that rye B chromosomes have implications on heat tolerance and may protect meiocytes against heat stress-induced damage.

An improved sensor for electrochemical microcalorimetry, based on lithiumtantalate.

We have developed a pyroelectric sensor for electrochemical microcalorimetry, based on LiTaO3, which provides unprecedented sensitivity for the detection of electrochemically induced heat effects. Deterioration of the heat signal by electrostriction effects on the electrode surface is suppressed by a multilayered construction, where an intermediate sapphire sheet dampens mechanical deformations. Thus, well textured thin metal films become viable candidates as electrodes. We demonstrate the sensor performance for Cu underpotential deposition on (111)-textured Au films on sapphire. The sensor signal compares well with a purely thermal signal induced by heating with laser pulses. The high sensitivity of the sensor is demonstrated by measuring heat effects upon double layer charging in perchloric acid, i.e., in the absence of electrochemical charge- or ion-transfer reactions.

A microcalorimeter for measuring heat effects of electrochemical reactions with submonolayer conversions

We present a microcalorimeter for measuring heat effects during electrochemical reactions with conversions down to a few percent of a monolayer, referenced to the electrode's surface atoms. The design uses a thin pyroelectric polymer foil for temperature measurement at the backside of a thin electrode, similar to the concepts pioneered by the groups of D. A. King and Ch. T. Campbell for UHV adsorption microcalorimetry. To establish intimate thermal contact between electrode and sensor and utmost sensitivity, the free standing sensor and electrode foils are pressed together by air pressure, acting on the electrochemical cell. Pyroelectric temperature sensing is combined with pulsed electrochemistry, where the electrochemical heat is released on a time scale of about 10 ms, which is long enough for thermal equalization of the electrode-sensor assembly but short enough to avoid significant heat loss into electrolyte and cell compartment. As examples heat effects upon Ag deposition and dissolution as well as the electron transfer reaction of [Fe(CN)(6)](4-)/[Fe(CN)(6)](3-) are presented. The latter reaction was also employed for the calibration of the calorimeter.

Microcalorimetry of Electrochemical Reactions at Submonolayer Conversions

We measured heat effects upon underpotential deposition or dissolution of a fraction of a monolayer of Cu on a Au surface. Temperature changes due to electrochemical reactions were pyroelectrically detected at the backside of a 100μm thin polycrystalline Au electrode. Pulsed electrochemical deposition or dissolution during 10ms intervals prevented significant loss of heat into the electrolyte on that time scale. The combination of both,i.e., pulsed electrochemical reactions at a thin electrode with low heat capacity, leads to unprecedented sensitivity. In addition, we compare the experimental temperature transients with the temperature evolution simulated for our experimental setup. Interferences stemming from mechanical deformation of the electrode foil due to potential-induced surface stress are also discussed.

Mass-Elastic Band Thermodynamics: A Visual Teaching Aid at the Introductory Level

Five spontaneous isothermal processes arising from combinations of enthalpy and entropy changes can be presented in a visual manner to students being introduced to chemical thermodynamics. The five spontaneous processes illustrated are (a) purely energy changes and entropy changes in the system due to a falling mass and contracting ideal elastic band, respectively, and (b) three remaining processes derived from the coupling of a mass and elastic band together. The five spontaneous processes initially appear identical in that the basic components of each system are hidden from view. However, based on hypothetical measurements of q obtained first when each process occurs irreversibly (qirr) and then repeated performing maximum work, or reversibly (qrev), the systems and the processes occurring within them can be readily distinguished. The distinction arrived at from the values of q is readily confirmed when covers are removed revealing the inner workings of each system. The demonstration helps students appreciate how measured heat effects obtained under appropriate conditions are employed to obtain the changes in the thermodynamic parameters that are associated with the spontaneous events. Analogies can then be drawn between these mass-elastic band processes and common spontaneous molecular events such as chemical reactions and phase transitions.

A calorimetric setup for measuring heat effects of processes in solutions

A calorimetric setup was developed to determine the heat effects of chemical processes in solutions with a sensitivity of ∼10−5 K and an accuracy of temperature control in the thermostat of better than ±0.001 K. The performance of the calorimeter was tested by measuring the heat effects of solution of 1-propanol (m = 0.02–0.08 mol/kg), potassium chloride (m = 0.01–0.73 mol/kg), and L-phenylalanine (m = 0.0008–0.03 mol/kg) in water at 25°C.

Calorimetric investigations of hydrogen bonding in binary mixtures containing pyridine and its methyl-substituted derivatives. I. The dilute solutions of water

Enthalpies of solution of water in pyridine and its methyl derivatives were investigated at T=298.15 K with a titration calorimeter. The effects of solution are exothermic and increase in the following order: pyridine <3-methylpyridine <4-methylpyridine <2-methylpyridine <2,6-dimethylpyridine <2,4,6-trimethylpyridine. As expected, the negative enthalpies of solution are fairly large, especially those for pyridine derivatives with a methyl group in the ortho position, due to the formation of hydrogen bonds between water and amine. Thus, the energy of the N⋯H–O bond, strengthened by the ortho methyl group, overcomes the hindering effect of that group. The experimental results were correlated with the association energies of the 1:1 (water+amine) complexes and with the net charges on the nitrogen atom reported in the literature. Although semi-quantitative agreement between the correlated quantities is fairly good, a simple model based on the hydrogen bond interactions was found to be too simple to account for the measured heat effects.

Calorimetric investigations of liquid Ge-Te and Si-Te alloys

The heats of solution of Ge and Te in liquid Ge-Te alloys and of Si in liquid Si-Te alloys were determined in a heat flow calorimeter at different temperatures. The excess enthalpies were calculated from the measured heat effects. In addition the heats of formation of liquid Ge-Te alloys were measured at 1203 K. The associate model was used to describe the thermodynamic functions. Minima of the enthalpy curves in the Ge-Te and Si-Te systems at 1213 K were found at 57 mol.% Te and −11.2 kJ mol−1 and at 62 mol.% Te and −22.3 kJ mol−1 respectively. A temperature dependence of the excess enthalpies was only observed in the Ge-Te system below about 1093 K. The enthalpies of the Si-Te system exhibited an almost linear temperature dependence.

Some applications of enthalpimetric detection in flow injection analysis

A flow injection manifold is described based on a flow-through arrangement of thermistors for measuring heat effects of chemical reactions. Temperature changes down to 10−3 °C can be measured reproducibly. The working range for the determination of a component is dependent on the reaction enthalpy and can vary from 10−3 to 10 mol/l for acids and bases, from 10 to 1000 ppm for e.g., alkylhydroperoxides. Sample frequencies up to 150 samples per hour can be realized.

Methods of investigation determining coefficients Kν and a for oligomers using liquid chromatography

Gel-chromatography, viscometry and measurement of heat effects of condensation were used to determine coefficients K ν and a in the Mark-Kuhn-Houwink equation for three standard oligomers based on buta-1,3-diene, for use in analysing chromatographic results. It was possible to use a universal calibration dependence for determining M n of narrow oligomer fractions in the range of molecular weights of 10 3 to 10 4. Satisfactory convergence was observed between M n by measuring heat effects of condensation and using gel-chromatography combined with viscometry.

Heats of dilution of polyacrylic acid at various degrees of ionization

The heats of dilution of polyacrylic acid at four constant degrees of ionization (α = 0, 0.25, 0.50, and 1.00) have been measured in the concentration range 0.6–0.002 monomolal. The heat of dilution for pure acid (α = 0) is positive in the investigated concentration range, whereas it is negative for partially neutralized acid (α = 0.25 and 0.50). For completely neutralized add, for sodium polyacrylate (α = 1), the measured heat effects are exothermic at concentrations above about 0.05 monomolal. while below 0.05 M they become endothermic. The experimental results have been evaluated with the help of a previously developed theoretical treatment based on the cell model.

Thermal investigations of biopolymer solutions and scanning microcalorimetry

1. Introduction The interest in thermal investigations of bio- polymers in solution has greatly increased recent- ly. This is connected firstly with the rise of a number of problems in the physico-chemistry of macromolecular solutions, the solution of which requires direct data on thermal effects of tem- perature variation, and, secondly, by the increase of technical possibilities in this field and the appearance of a new measuring technique - scan- ning microcalorimetry. Though the possibilities of modern scanning microcalorimetry are still insufficiently known, since only a limited number of laboratories have had the equipment at their disposal and the published reviews [l-8] were too laconic, the possibility of direct measurement of the most important thermodynamic parameters - heat capacity, enthalpy and entropy as a function of temperature, the most fundamental physical vari- able, is, naturally, attractive. Primarily it is of interest to those dealing directly or indirectly with the problems of intramolecular cooperative transformations of biopolymers, the stability of their space structures and the intramolecular in- teractions, and interactions with the solvent which ultimately determine the structures and structural transformations of biopolymers in solu- tion. The aim of this review is to explain the principle of scanning microcalorimetry and to outline its practical possibilities. To this end we have summarized all the main results obtained up to now in thermal studies of individual macro- s140 molecules in solution. Therefore, a whole range of other studies such as thermal investigations of dry preparations [9,10], thermal investigations of the solvent state in solution [ 1 l-131 are not included. The difficulty is that the study of thermal properties of individual macromolecules in solu- tion and of the processes related to their intra- molecular transformations must be carried out on diluted solutions (<l%) in which the effects of intermacromolecular interactions are negligible. However, in such solutions the measured heat effects themselves are very small, especially against the background of the heat continuously introduced into the system. Thus, the heat capacity of a biopolymer in 0.3% solution is only a one thousandth part of the total heat capacity of the solution. Therefore, superprecise methods of heat capacity determination. over a wide temperature range are necessary. The diffi- culty is, however, aggravated by the fact that even very dilute solutions of biopolymers have a high viscosity change with temperature. This com- pletely excluded the use precise calori- meters usually used for measuring the heat capac- ity of liquids (see [14] ), since stirring was obli- gatory in such equipment. With solutions of high and inconstant viscosity this led to undeter- minable thermal effects which considerably ex- ceed the thermal effect to be determined, The first measurement of heat connected with macromolecular transformations in solutions - gelatin gel melting - was made in 1962 [ 151 with a specially elaborated vacuum adiabatic ab-

Heats of the helix-coil transitions of the poly A-poly U complexes.

AbstractThe heats of the conformational transitions of poly (A + U) and poly(A + 2U) were determined in a twin‐cell differential thermal analysis microcalorimeter capable of measuring heat effects of 25–35 meal, in reactions of this type, with a precision of about 3%. The dependence of these heats on the concentration of Na+ and K+ was studied and was found to be interpretable with fair success by a simple phenomenological argument which employs the concept of binding of counterions to polyelectrolytes.

A Thermopile for Microcalorimetry

In the study of the thermodynamics of solutions it is desirable to measure heat effects (of the order of 0.001 cal.) which occur during the dilution of dilute solutions. In the Lange-type calorimeter a thermopile of approximately 1000 junctions is used differentially. For this purpose a thermopile has been constructed using constantan-Chromel-P couples mounted in a sheet of Micarta, 5′′×10′′×516′′, and electrically insulated with a Vinylite resin which has an insulation resistance greater than 25 megohms. This instrument appears to offer somewhat better behavior than previously used units with respect to stability, sensitivity, and rapidity of response to temperature changes. The thermopile consists of two sections of equal numbers of junctions which are connected in parallel to a Leeds and Northrup HS galvanometer in series. At a scale distance of nine meters the sensitivity of the system is 0.25 microdegree per mm. Since one liter of diluent (water or dilute solution) is contained in each half of the calorimeter, this corresponds to a mean sensitivity of 2.5×10−4 cal./mm, with a probable error of the mean of ±0.03×10−4 cal./mm. The heat conductivity constant of the calorimeter is 0.004 min.−1 and that of the thermopile is 0.03 min.−1. Measurements with the present thermopile of the heats of dilution of sodium chloride solutions agree satisfactorily with wellestablished values.