Determination of crystallization enthalpies of some organic peroxides by a differential isothermal calorimeter

We developed a method for determination of the crystallization enthalpy of organic substances in a heat-conducting calorimeter at a temperature close to 298 K. Crystallization was conducted in the MID-200 calorimeter using an ampoule technique. The volume of ampoules, which contain the supercooled liquids, was approximately 0.2 cm3. The residual pressure was 650 Pa to lessen the heat loss. A few crystals of the material under investigation were employed as the crystallization centers. Based on the results of the experiment, the crystallization enthalpies of dicumyl peroxide, peroxyoctanoic acid and di-tert-butylperoxy isophthalate were determined. The vaporization and sublimation enthalpies of peroxyoctanoic acid were assessed using an ampoule method in the calorimeter. It was established that dicumyl peroxide which was supercooled 14 K below the fusion temperature exhibited a 20% increase in crystallization enthalpy as compared with that calculated from the difference between vaporization and sublimation enthalpy. At the same time, the crystallization enthalpy of peroxyoctanoic acid supercooled by 5 K was equal to that calculated from the difference between vaporization and sublimation enthalpy within the limiting experimental error. The received data show that the proposed method is promising for determining the heat of crystallization of liquids that are able to exist in a supercooled state during some time.

Effects of Temperature on Lifespan of Drosophila melanogaster from Different Genetic Backgrounds: Links between Metabolic Rate and Longevity

Despite many studies of the aging process, questions about key factors ensuring longevity have not yet found clear answers. Temperature seems to be one of the most important factors regulating lifespan. However, the genetic background may also play a key role in determining longevity. The aim of this study was to investigate the relationship between the temperature, genetic background (fruit fly origin), and metabolic rate on lifespan. Experiments were performed with the use of the wild type Drosophila melanogaster fruit flies originating from Australia, Canada, and Benin and the reference OregonR strain. The metabolic rate of D. melanogaster was measured at 20 °C, 25 °C, and 28 °C in an isothermal calorimeter. We found a strong negative relationship between the total heat flow and longevity. A high metabolic rate leads to increased aging in males and females in all strains. Furthermore, our results showed that temperature has a significant effect on fecundity and body weight. We also showed the usefulness of the isothermal calorimetry method to study the effect of environmental stress conditions on the metabolic activity of insects. This may be particularly important for the forecasting of impact of global warming on metabolic activity and lifespan of various insects.

Estimation of microbiological contamination of maize seeds using isothermal calorimetry

The storage of maize seed intended for industrial purposes in foil silo bags is associated with microbiological contamination of the material by bacteria and fungi. This results in the loss of a part of the raw material or its deterioration and causes financial losses. In this paper, the relationship between the number of microorganisms colonizing maize seeds as well as changes in heat flow has been proved. For this purpose, the heat flow and total metabolic heat emission values (total heat) were analyzed. Calorimetric measurements of seed samples were made using the TAM III isothermal calorimeter. The seed samples with the same heat flow curves shape were homogenized, and microbial DNA was isolated from them. The quantitative real-time polymerase chain reaction (qPCR) was performed for detecting the main group of microorganisms colonizing maize seeds. It has been shown that in the case of seeds less affected by Bacillus and fungi (including yeast), the heat flow (in the range of 0–360 min) has a falling shape, while for more infected it grows almost linearly. The more infected maize seeds also show significantly higher values of total heat emission. The described research can be used to quickly assess the degree of seed contamination.

An Early-age Evaluation of Thermal Cracking Index of Heavy Concrete Applying for Airport Pavement

Industrial waste management has been an integral part of many countries in the world, including in Vietnam. In which, bottom ash (BA) has been used as a pozzolanic additive in compositions of the heavy concrete applying for airport concrete pavement (ACP), which allows reducing the hydration heat, the cost, and the thermal cracking of the concrete during the construction process. The purpose of this study is to summarize the experimental laboratory results of the heavy concrete samples containing 35 % BA sourced from a thermal power plant in Vietnam. The mechanical and thermal properties of the heavy concrete samples were determined at different curing ages. Besides, the heat of cement hydration during the preparation of the heavy concrete in the laboratory was measured using a "TAM AIR" isothermal calorimeter. Moreover, the Midas civil computer software based on the finite element method was used to analyze the temperature field and thermal cracking index of the ACP at the early ages. As the results, the heavy concrete had the respective thermal conductivity and the average of specific heat of 1.1 W/(m.°C) and 878.35 J/(kg.°C). Moreover, the value of thermal cracking index indicates that no cracking occurred on the ACP at the early ages. Furthermore, the results of the present study can be considered as a useful reference source for future projects that are associated with the construction of the ACP.

Effect of boron-containing aggregates on setting and hardening of Portland cement mortars

Multicomponent cement-based composites are known as versatile structural materials for enhanced radiation shielding. The use of selected elements, like boron, cadmium, or rare earth elements, provides an increased neutron shielding capacity. Because of profusion, reasonable costs and large cross-section for neutron capture, boron containing minerals are suggested as aggregates for radiation shielding concrete. Despite many advantages, boron additives may act as cement setting retarders. Uncontrolled setting and hardening is not acceptable in radiation shielding concrete technology. In this work we present results from isothermal calorimetry measurements on cement mortars with boron-containing aggregates. Four types of boron aggregates were used in the studies: colemanite, ulexite, borax and boron carbide. Based on calorimetric curves, the beginning of setting time was determined. Additionally early mortar strength was investigated and linear relationship between the heat generated in the isothermal calorimeter and the early compressive strength has been observed. The use of isothermal calorimetry allowed us to estimate the limits for the content of boron compounds to be used cement mortar.