On the application of Laplace pressure in the science of sintering

An equation of the Laplace pressure derived using the Gibbs thermodynamic method have been discussed and the correct applications of the equation have been substantiated. It has been shown that the expression is applicable only to macrovolumes for the description of surfaces with a constant curvature, but not to the description of nanodisperced systems and surfaces with variable curvature. The expression of the Laplace pressure applicable to a crystal and the cavity limited by a surface of any geometrical shape have been derived

Thermodynamics of the nanoparticle consolidation

Thermodynamic functions have been derived that describe the processes of nanoparticle consolidation in solid-mobile phase two- and three-phase dispersed systems. An expression for the shrinkage pressure in a two-phase dispersed system has been deduced, which allows one to calculate stresses generating in the bulk of heterophase composite materials in the course of the nanoparticle consolidation. On the strength of these thermodynamic functions criteria have been suggested that allow one to predict the structure of a nanocomposite material

Thermodynamics of the formation of mesostructures in nanodispersed composite materials

Two models of the formation of mesostructures in nanodispersed composite materials are considered. According to the first model, a mesoelement is formed of coarsely dispersed compositions as an inclusion in a nanodispersed composite body. The second model considers a mesoelement being formed from nanoparticles as an inclusion in the volume of a coarsely dispersed composite body. Depending on the class of composite materials used to produce mesoelements and a composite body, their composition and structure are defined by the liquid phase migration (or absence of the migration) as well as diffusion flows of the components

Thermodynamics of the formation of composite material structures. A review

Composite material structures at nano-, micro-, and meso- levels have been examined. The application of the Gibbs and Hill thermodynamics has allowed researchers to give the physical interpretation of the Laplace pressure for composite materials; to derive the thermodynamic functions describing the particles consolidation; to establish the new phenomenon, namely, metal melt imbibition (MMI), and to define its acting forces, to establish the criterion that allows to determine a direction of a liquid phase migration in a composite body, as well as to predict the final structure of composite materials. For the description of composite material structure, which forms under extreme conditions, it has been necessary to use the nonequilibrium thermodynamics. At the extreme conditions the Prigogine concept of local equilibrium is promising.Изучена структура композиционных материалов на нано-, микро- и мезоуровнях. Используя термодинамику Гиббса и Хилла, исследователи дали физическую интерпретацию давления Лапласа для композиционных материалов; получили термодинамические функции, описывающие процесс консолидации частиц; установили новое явление – поглощение металлических расплавов спеченными композиционными телами (phenomen MMI), определили его движущие силы; обосновали критерий, который позволяет определить направление миграции жидкой фазы в композиционных телах; предсказать окончательную структуру композиционных материалов. Для описания структуры композиционных материалов, которые формируются в экстремальных условиях, предложено применять неравновесную термодинамику. Для этих условий перспективной является концепция локального равновесия, разработанная И. Пригожиным.Вивчено структуру композиційних матеріалів на нано-, мікро- і мезорівнях. Використовуючи термодинаміку Гіббса і Хілла, дослідники дали фізичну інтерпретацію тиску Лапласа для композиційних матеріалів; одержали термодинамічні функції, що описують процес консолідації часточок; виявили нове явище – поглинання металевих розплавів спеченими композиційними тілами (phenomenon MMI) та визначили його рушійні сили; обґрунтували критерій, який дозволяє визначити напрямок міграції рідкої фази в композиційних матеріалах та прогнозувати кінцеву їх структуру. Для опису структури композиційних матеріалів, яка формується в екстремальних умовах, запропоновано застосовувати нерівноважну термодинаміку. Для цих умов перспективною є концепція локальної рівноваги, яка розроблена І. Пригожиним

Thermodynamics of formation liquid interlayers in composite materials

Composite materials consisting of refractory particles and a low-melting binder have been studied. In a composite body the process of the liquid outflow from a capillary into the body bulk have been described in terms of thermodynamics. An equation for the variation of the Helmholtz free energy of a microdispersed system during this process has been derived and the conditions, under which the liquid interlayers are either stable or unstable in the bulk of a composite body, have been established.Изучены композиционные материалы, состоящие из тугоплавких частиц и легкоплавкой связки. Процесс обнажения жидкого капилляра путем миграции жидкости из капилляра в объем тела описан в терминах термодинамики. Получено выражение для изменения свободной энергии Гельмгольца микродисперсной системы при протекании этого процесса и определены условия, при которых жидкая прослойка является устойчивой или нестабильной в объеме композиционного тела.Вивчені композиційні матеріали, які складаються з тугоплавких частинок і легкоплавкої зв'язки. Процес оголення рідкого капіляра шляхом міграції рідини з капіляра в об’єм тіла описаний у термінах термодинаміки. Отримано вираз для зміни вільної енергії Гельмгольца мікродисперсної системи при протіканні цього процесу і визначені умови, при яких рідкий прошарок є стійким або нестабільним в об’ємі композиційного тіла

Thermodynamics of processes of consolidation of an assembly of dispersed particles and deconsolidation of a polycrystalline body

Thermodynamic functions that describe the processes both of consolidation of an assembly of dispersed particles and deconsolidation of a polycrystalline body are considered. Expressions have been derived for the shrinkage pressure, which arises from the consolidation of particles, and the migration pressure, which arises from deconsolidation of a polycrystalline body. The values of the shrinkage and migration pressures are described in terms of structure parameters of a composite body (particle size and shape, phase composition, values of surface tension at the solid-solid and solid-moving phase interfaces)

Formation of mesostructure in WC-Co cemented carbides: A review

The author considers potential lines in the formation of mesostructures in cemented carbides, analyzes the existing technologies of the formation thereof, describes physical and mechanical properties of cemented carbides with mesostructure and shows the efficiency of such cemented carbides in metal working and rock destruction tools

Thermodynamics of the consolidation of nanoparticles and a macrowparticle

The thermodynamic study of the particle consolidation process in a system consisting of nanoparticles, inclusions of macroparticles, and mobile phase (gas, vapor, liquid) has been conducted. The thermodynamic functions describing this process have been derived. The conditions have been established, under which the process of consolidation proceeds to the end; the conditions, under which the process does not take place in terms of thermodynamics; and the conditions, under which only certain phases consolidate. It has been shown that in this system there are diffusion flows of the substance from nanoparticles to the macrophase. The conditions have been defined, under which a nanoparticle or a group of nanoparticles can be in an equilibrium state and maintain the size and shape arbitrarily long

Some features of mass transfer in composite materials

The paper deals with the process of mass transfer in a two-phase system which consists of a mobile phase (a liquid or a gas) and dispersed particles forming a spacial structure, i.e. a skeleton. It is shown that in systems like this the process of the mobile phase transfers is greatly affected by forces generated at both interfaces and particle boundaries. These forces are responsible for new regularities of the mass transfer in dispersed systems, in particular, a spontaneous increase in an intensive variable is a possibility