Sintering of particles

Sintering of particles occurs when one heats a system of particles to an elevated temperature. It Is caused by an interaction of particle surfaces whereby the surfaces fuse together and form a solid mass. It Is related to a solid state reaction In that sintering is governed by diffusion processes, but no solid state reaction, or change of composition or state, takes place. The best way to illustrate this phenomenon is to use pore growth as an example. 

The relation between two temperatures, T and 7), required for equal degrees of sintering of particles of diameters D and Z)2 is... 

Film Assembly Using Particles 18.2.1 Simple Sintering of Particles... 

An alternative to stochastic reconstruction of multiphase media is the reconstruction based on the direct simulation of processes by which the medium is physically formed, e.g., phase separation or agglomeration and sintering of particles to form a porous matrix. An advantage of this approach is that apart from generating a medium for the purpose of further computational experiments, the reconstruction procedure also yields information about the sequence of transformation steps and the processing conditions required in order to form the medium physically. It is thereby ensured that only physically realizable structures are generated, which is not necessarily the case when a stochastic reconstruction method such as simulated annealing is employed. 

Sintering The combination of temperature, pressure, and friction effects can result in the sintering of particles, so that the limits between them are no longer evident [46,87],... 

Many nanopartide preparations lack suffident stability (above. Fig. 11.5) to allow the ordered assembly of two-dimensional or three-dimensional materials and structures, in which the particles are dosely packed, without the onset of uncontrolled aggregation (agglomeration). To overcome this problem, the partides must be rendered chemically stable, for example by ligand stabilization, also to avoid degradation processes such as partial oxidation or undesired sintering of particles [11.6]. 

Finally, it has been demonstrated that particle aggregation depends on the interparticle distance (which would correlate with surface coverage in bulk systems) with pronounced aggregation observed on TiC if the interparticle distance is around 30 nm, while no sintering took place if particles were separated by 80 nm [126, 127]. Later, it was demonstrated that sintering of particles on flat supports depends on the support pretreatment, regardless of whether the particles were fabricated using physical vapor deposition (i.e., via gas phase under UHV) or were premade chemically [128]. 

In this case the paint does dry solely by evaporation of liquids. The polymer is fully formed in the can and, when free of solvent, is relatively hard and not sticky. During the drying process there is no chemical change in the polymer. If it was dissolved in the liquid solvents of the paint, then it remains soluble in those solvents. If it was carried as an emulsion or colloidal dispersion, it is not soluble in the liquid carrier, but it is soluble in other solvents, because it is a linear polymer. More is said about the sintering of particles of linear polymer into a continuous film in Chapter 11. 

Because ball milling reaches a limit, it is impossible to make very fine particles by this method. Therefore, growing particles from vapor or solution phases has been the preferred approach to making fine dispersions. This growth method is also attractive because the particles can be controlled in shape, and can also be grown to the same size, which is useful in many applications. For example, sintering of particles is eased if the particles are nearly equal in diameter. Such fine, equal particles cannot be produced by comminution. In this section we discuss the several processes which have been developed for growing particles. 

Particle size is an important element in the performance of an HTCC system. Fine particle size enhances densification although submicron particles are often difficult to disperse effectively. A basic description of the effect of particle size on the sintering of particles is captured in Herring s scaling law that describes an exponential dependence of sintering time on particle diameter [21] ... 

Various strategies were developed in the past for the synthesis of perovskite-structured oxides (Table 3.1). Of these, the choice of a particular method depends on the type of application expected. For catalytic applications, specific surfece area and crystal structure play crucial roles. Hence, the synthesis of these materials for catalytic applications always focused on obtaining crystalline materials with high values of specific surface area. The oldest method for the synthesis of perovskite-structured mixed metal oxides is the ceramic method. In this method, thoroughly mixed precursors (oxides, hydroxides, or carbonates) of the metals are calcined at elevated temperatures (>800 °C) for several hours. The surfece area of thus synthesized perovskites was, however, found to be less than 5m /g [5,30]. The high temperature used in solid-state reactions, for perovskite crystallization, results in the sintering of particles, which in turn leads to a large... 

Frenkel Model - A model developed by Russian scientist Frenkel to describe coalescence/sintering of particles of metals and plastics. See the following references for more information Thermoplastics, Mascia, L., Materials Eng., 2" ed., Elsevier Applied Science, NY, 1989 and Lontz,J. E, in Fundamental Phenomena in the Material Sciences, Vol. 1, L. J. Borris and H. H. Hansner (eds.). Plenum Pres, New York, p. 37, 1964. 

Answer No, we have not seen any evidence of grain boundary sliding. In powder metallurgy we are generally concerned with particles smaller than 50 p. For sintering of particles of this size I believe that dislocation motion is important at least in the early stages of sintering. The final elimination of the pores may be due to diffusional flow processes. 

---