A model for second-stage liquid-phase sintering with a partially wetting liquid

Gessinger, Gernot H.; Fischmeister, H. F.; Lukas, Hans Léo

doi:10.1016/0001-6160(73)90082-5

Cited by 60 publications

(33 citation statements)

References 8 publications

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“…No model accounts for this complexity. A similar treatment by Gessinger et al [127,128] assumed the liquid layer wets the grain boundary with a small dihedral angle, giving essentially the same sintering shrinkage as Kingery. Solid-state diffusion by grain boundary diffusion in the grain contact is another densification mechanism.…”

Section: Densificationmentioning

confidence: 96%

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Review: liquid phase sintering

2009

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Liquid phase sintering (LPS) is a process for forming high performance, multiple-phase components from powders. It involves sintering under conditions where solid grains coexist with a wetting liquid. Many variants of LPS are applied to a wide range of engineering materials. Example applications for this technology are found in automobile engine connecting rods and high-speed metal cutting inserts. Scientific advances in understanding LPS began in the 1950s. The resulting quantitative process models are now embedded in computer simulations to enable predictions of the sintered component dimensions, microstructure, and properties. However, there are remaining areas in need of research attention. This LPS review, based on over 2,500 publications, outlines what happens when mixed powders are heated to the LPS temperature, with a focus on the densification and microstructure evolution events.

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Section: Densificationmentioning

confidence: 96%

“…39c [127,128]. The contact zone enlarges to change the grain shape with simultaneous shrinkage of the grains.…”

Section: Densificationmentioning

confidence: 99%

Review: liquid phase sintering

2009

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“…The driving force is usually described in terms of the effect of capillary pressure on the grain-boundary formation process. [172][173][174] The capillary forces contemplated result from the menisci at liquid-vapor interfaces between contacting particles that drive sintering by pulling particles together. An important concept is that, despite the compressive force induced across particle contacts, enough of the liquid-forming material must remain adsorbed at the boundaries to provide the high boundary diffusion required to account for enhanced rates of densification via grain-boundary formation.…”

Section: (7) Equilibrium Intergranular and Surficial Filmsmentioning

confidence: 99%

Origins and Applications of London Dispersion Forces and Hamaker Constants in Ceramics

French

2000

Journal of the American Ceramic Society

260

100

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The London dispersion forces, along with the Debye and Keesom forces, constitute the long-range van der Waals forces. London's and Hamaker's work on the point-to-point dispersion interaction and Lifshitz's development of the continuum theory of dispersion are the foundations of our understanding of dispersion forces. Dispersion forces are present for all materials and are intrinsically related to the optical properties and the underlying interband electronic structures of materials. The force law scaling constant of the dispersion force, known as the Hamaker constant, can be determined from spectral or parametric optical properties of materials, combined with knowledge of the configuration of the materials. With recent access to new experimental and ab initio tools for determination of optical properties of materials, dispersion force research has new opportunities for detailed studies. Opportunities include development of improved index approximations and parametric representations of the optical properties for estimation of Hamaker constants. Expanded databases of London dispersion spectra of materials will permit accurate estimation of both nonretarded and retarded dispersion forces in complex configurations. Development of solutions for generalized multilayer configurations of materials are needed for the treatment of more-complex problems, such as graded interfaces. Dispersion forces can play a critical role in materials applications. Typically, they are a component with other forces in a force balance, and it is this balance that dictates the resulting behavior. The ubiquitous nature of the London dispersion forces makes them a factor in a wide spectrum of problems; they have been in evidence since the pioneering work of Young and Laplace on wetting, contact angles, and surface energies. Additional applications include the interparticle forces that can be measured by direct techniques, such as atomic force microscopy. London dispersion forces are important in both adhesion and in sintering, where the detailed shape at the crack tip and at the sintering neck can be controlled by the dispersion forces. Dispersion forces have an important role in the properties of numerous ceramics that contain intergranular films, and here the opportunity exists for the development of an integrated understanding of intergranular films that encompasses dispersion forces, segregation, multilayer adsorption, and structure. The intrinsic length scale at which there is a transition from the continuum perspective (dispersion forces) to the atomistic perspective (encompassing interatomic bonds) is critical in many materials problems, and the relationship of dispersion forces and intergranular films may represent an important opportunity to probe this topic. Am. Ceram. Soc., 83 [9] 2117-46 (2000 Centennial FeatureThe London dispersion force is retarded at large separations, where the transit time of the electromagnetic interaction must be considered explicitly. Novel phenomena, such as equilibrium surficial films and bimodal wettin...

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“…Representing soil PSD in terms of statistical PDF, and considering aggregate deformation and porosity loss in wet soils as a solid diffusion process [Gessinger et al, 1973], enables modeling soil pore space changes as evolution of soil PDF governed by external forcing and soil deformation processes. A well-developed theory already exists for representing stochastic diffusion processes by the Kolmogorov forward equation or the FPE [Gardiner, 1985;Hara, 1984].…”

Section: Fokker-planck Equation (Fpe)mentioning

confidence: 99%

Stochastic model for posttillage soil pore space evolution

Or¹,

Leij²,

Snyder³

et al. 2000

Water Resources Research

107

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Abstract. Tillage operations disrupt surface layers of agricultural soils, creating a loosened structure with a substantial proportion of interaggregate porosity that enhances liquid and gaseous exchange properties favorable for plant growth. Unfortunately, such desirable soil tilth is structurally unstable and is susceptible to change by subsequent wetting and drying processes and other mechanical stresses that reduce total porosity and modify pore size distribution (PSD). Ability to model posttillage dynamics of soil pore space and concurrent changes in hydraulic properties is important for realistic predictions of transport processes through this surface layer. We propose a stochastic modeling framework that couples the probabilistic nature of pore space distributions with physically based soil deformation models using the Fokker-Planck equation (FPE) formalism. Three important features of soil pore space evolution are addressed: (1) reduction of the total porosity, (2) reduction of mean pore radius, and (3) changes in the variance of the PSD. The proposed framework may be used to provide input to hydrological models concerning temporal variations in near-surface soil hydraulic properties. In a preliminary investigation of this approach we link a previously proposed mechanistic model of soil aggregate coalescence to the stochastic FPE framework to determine the FPE coefficients. An illustrative example is presented which describes changes in interaggregate pore size due to wetting-drying cycles and the resulting effects on dynamics of the soil water characteristic curve and hydraulic conductivity functions. IntroductionThe tilled "plow layer" of agricultural soils plays a crucial role in determining crop productivity and transport of gas, The primary objective of this study was to develop a framework for modeling posttillage evolution of soil PSD based on coupling of stochastic formulation with physically based process models. We propose the use of the forward Kolmogorov 1641

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A model for second-stage liquid-phase sintering with a partially wetting liquid

Cited by 60 publications

References 8 publications

Review: liquid phase sintering

Review: liquid phase sintering

Origins and Applications of London Dispersion Forces and Hamaker Constants in Ceramics

Stochastic model for posttillage soil pore space evolution

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