Study of Crack Sensitivity of Peritectic Steels

By comprehensively considering both the high temperature mechanical properties and peritectic transformation during peritectic steel solidification, the strain εCth is proposed to evaluate the crack sensitivity of peritectic steels produced in the brittle temperature range in the present work. The zero ductility temperature (ZDT) and the zero strength temperature (ZST) of Fe–C–0.32Si–1.6Mn–0.01P–0.015S steel under nonequilibrium conditions by taking the effect of the peritectic transformation on the solute segregation into account were calculated by the CK microsegregation model (Clyne–Kurz model) and were compared with the measured data. The comparison results show that this model can well simulate the nonequilibrium solidification process of peritectic steel. Then, based on the calculation of the CK microsegregation model, the strain during the peritectic phase transformation in the brittle temperature range (ZDT < TB < LIT) was calculated under nonequilibrium conditions. The results show that the calculated strain is in good agreement with the actual statistical longitudinal crack data indicating that the strain can therefore be used to predict the crack sensitivity of peritectic steels effectively.

Evaporation of a liquid sessile droplet subjected to forced convection

Experiments on measuring the rate of evaporation of liquid sessile droplets into air show that the rate of evaporation increases in the presence of forced convection flows. However, data on the effect of convection on evaporation are often contradictory and should be clarified. The paper presents a numerical analysis of evaporation from the surface of a water droplet subjected to forced convection in the gas phase. The drop is located on a smooth horizontal isothermal substrate; the mode with constant contact angle is considered. The shape of the drop has axial symmetry, the same for the velocities and pressure. Forced convection compatible with the symmetry conditions are represented by flows directed downward along the axis of the system and diverging along the sides near the drop and the substrate. The mathematical model is constructed for evaporation controlled by diffusion in the gas phase and takes into account surface tension, gravity, and viscosity in both media, buoyancy and Marangoni convection. The results indicate the existence of the mutual influence of liquid and gaseous media. Thus, a drop vibrates under the influence of movements in the atmosphere, which generates a density wave in the gas: the drop «sounds». The magnitude of the velocity in a liquid is 50 times less than the characteristic velocity in air. It is found that the evaporation rate does not change in the presence of forced convection flows, which contradicts most of the experimental works. The reason for the discrepancies is supposed to be the appearance of nonequilibrium conditions at the boundary of the condensed phase: under these conditions, the evaporation regime ceases to be diffusional.

Quantification of fast molecular adhesion by fluorescence footprinting

Rolling adhesion is a unique process in which the adhesion events are short-lived and operate under highly nonequilibrium conditions. These characteristics pose a challenge in molecular force quantification, where in situ measurement of these forces cannot be achieved with molecular force sensors that probe near equilibrium. Here, we demonstrated a quantitative adhesion footprint assay combining DNA-based nonequilibrium force probes and modeling to measure the molecular force involved in fast rolling adhesion. We were able to directly profile the ensemble molecular force distribution in our system during rolling adhesion with a dynamic range between 0 and 18 pN. Our results showed that the shear stress driving bead rolling motility directly controls the molecular tension on the probe-conjugated adhesion complex. Furthermore, the shear stress can steer the dissociation bias of components within the molecular force probe complex, favoring either DNA probe dissociation or receptor-ligand dissociation.

EXCESSIVE ENERGY OF DETONATION NANODIAMONDS

Алмазы детонационного синтеза (ДНА) отличаются набором уникальных свойств, связанных с существенно неравновесными условиями их получения. Исследование их свойств продолжает оставаться актуальным в последние годы. Наноалмазы находят применение в полировальных составах, при модификации каучуков, резин, полимеров, металлов, создании новых композиционных материалов, в качестве добавок к топливу, адсорбентов и катализаторов, в биологии и в медицине. Интерес представляет энергетическая насыщенность наноалмазов. В данной работе проведено теоретическое и экспериментальное исследование избыточной энергии алмазов детонационного синтеза. Доказано, что ДНА обладают избыточной энергией по сравнению с природными и синтетическими алмазами. Рассмотрены возможные источники возникновения избыточной энергии. Исследованы образцы ДНА, полученные в различных условиях синтеза. На основе данных по термогравиметрическому анализу образцов ДНА представлены результаты анализа избыточной энергии образцов и ее зависимости от площади удельной поверхности частиц. Площадь удельной поверхности порошков получена методом БЭТ. Установлено, что чем больше поверхность частиц, тем больше тепла затрачено на её получение и выделилось при сжигании. Однако зависимость избыточной энергии от площади удельной поверхности частиц обратная. Экспериментально полученные нами величины плотности избыточной энергии на 1-2 порядка выше теоретически полученных значений для природных алмазов и для наноалмазов, что подтверждает наличие большой избыточной энергии ДНА. Такое свойство детонационных наноалмазов может найти применение в новых технологиях, в частности, при использовании наноалмазов в роли сорбентов. Detonation synthesis diamonds (DNDs) are distinguished by a set of unique properties associated with substantially nonequilibrium conditions for their production. The study of their properties continues to be relevant in recent years. Nanodiamonds are used in polishing compositions, in the modification of rubbers, polymers, metals, the creation of new composite materials, as additives to fuel, adsorbents and catalysts, in biology and medicine. The energy saturation of nanodiamonds is of interest. In this work, a theoretical and experimental study of the excessive energy of detonation synthesis diamonds is carried out. It has been proven that DNDs have excessive energy in comparison with natural and synthetic diamonds. Possible sources of excess energy are considered. Samples of DND obtained under various synthesis conditions have been investigated. Based on the data on thermogravimetric analysis of DND samples, the results of the analysis of the excessive energy of the samples and their dependence on the specific surface area of ​​the particles are presented. The specific surface area of ​​the powders was obtained by the BET method. It was found that the larger the surface of the particles, the more heat is spent on its production and released during combustion. However, the dependence of the excessive energy on the specific surface area of ​​the particles is inverse. The experimentally obtained values ​​of the excessive energy density are 1–2 orders of magnitude higher than the theoretically obtained values ​​for natural diamonds and for nanodiamonds, which confirms the presence of a large excess excessive of DND. This property of detonation nanodiamonds can find application in new technologies, in particular, when nanodiamonds are used as sorbents.

Chemistry Under Shock Conditions

Shock loading takes materials from ambient conditions to extreme conditions of temperature and nonhydrostatic stress on picosecond timescales. In molecular materials the fast loading results in temporary nonequilibrium conditions with overheated low-frequency modes and relatively cold, high-frequency, intramolecular modes; coupling the shock front with the material's microstructure and defects results in energy localization in hot spots. These processes can conspire to lead to a material response not observed under quasi-static loads. This review focuses on chemical reactions induced by dynamical loading, the understanding of which requires bringing together materials science, shock physics, and condensed matter chemistry. Recent progress in experiments and simulations holds the key to the answer of long-standing grand challenges with implications for the initiation of detonation and life on Earth. Expected final online publication date for the Annual Review of Materials Science, Volume 51 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Direct measurements of the RHeq in salt mixtures including the contribution from metastable phases

Accelerated salt-induced deterioration occurs by frequent changes across the equilibrium relative humidity (RH eq ). Therefore, knowledge of the actual RH eq of a salt mixture has a major impact on preventive conservation to ensure that the relative humidity (RH) does not cause a salt phase transition and in situ desalination as the dissolution of salt is the essential criterion to enable transport of salt (ions) in materials. For decades, it has been possible to determine the RH eq in salt mixtures with the user-friendly, thermodynamic-based ECOS-Runsalt software. However, the ECOS-Runsalt model is challenged by the influence of kinetics along with some limitations in regard to possible ion types and combinations. A dynamic vapor sorption (DVS) instrument is used for the direct measurement of RH eq and to deduce knowledge on the physicochemical nonequilibrium process related to the phase changes in salt mixtures. The experimentally measured RH eq values in this study of NaCl-Na 2 SO 4 -NaNO3, NaNO 3 -Na 2 SO 4 , NaCl-NaNO 3 , NaCl-Na 2 SO 4 , and (NH 4 ) 2 SO 4 -Na 2 SO 4 are in agreement with values from the literature. A comparison with thermodynamically calculated results makes it probable that the phase transition for some salts is significantly influenced by nonequilibrium conditions. The present work bridges some of the existing gaps in regard to accuracy, including the effects of kinetics and the possible ions and combinations that may be found in situ. The proposed method makes it possible to determine a more representative RH eq in relation to real conditions for the improved treatment of salt-infected constructs.