Particle fusion

In the case of solid interfaces which are in the form of coarse powders, cavitation collapse can produce enough energy to cause fragmentation and activation through surface area increase. For very fine powders the partides are accelerated to high velocity by cavitational collapse and may collide to cause surface abrasion (Fig. 3.5). For some metal powders these collisions generate sufficient heat to cause particle fusion. 

A number of techniques for assessing PVC fusion are reviewed. Additional methods were developed for investigating different levels of structure. Optical methods are used for grains and primary particle fusion. Thermal analysis investigates molecular behaviour and is used to monitor compound processing temp. 14 refs. 

Because of the importance of controlling the solid-state properties a great deal of interest has been generated around understanding the role of water in the formulation since water can act as a plasticizer that will deteriorate both chemical (i.e.. protein degradation) and physical (i.e., particle fusion, cake collapse, crystallization) stability. How dry this formulation needs to be depends on the glass transition of the formulation relative to the storage conditions and the so called zero temperature (55). 

Fig. 1. Electron micrograph of a large particle carbon black showing particle fusion into primary structure aggregates as distinguished from overlap...

Figure 6.19 Mechanism of particle fusion during extrusion of PVC.

During ram extrusion (Section 5.4.4), the molten particles are forced into contact with each other. Polyethylene chains diffuse across the particle boundaries, and, with time, a strong bond develops. The UHMWPE however retains a memory of its particle structure, especially when calcium stearate was used prior to the late 1990s—the stearate coats the particles before processing, and it makes the interfaces more visible when micro-tomed slices are examined in an optical microscope (Fig. 6.22a). There are parallels with PVC particle fusion, but it is not possible to use shear flow to disrupt the UHMWPE boundaries. 

Zachariades A.E. 1985. The effect of powder particle fusion on the mechanical properties of ultra-high molecular weight polyethylene. Poly Engr Sci 25 747-750. 

S. Shahid, K. Nijmeijer, S. Nehache, I. Vankelecom, A. Deratani, D. Quemener, MOF-mixed matrix membranes precise dispersion of MOF particles with better compatibility via a particle fusion approach for enhanced gas separation properties. Journal of Membrane Science 492 (2015) 21—31. 

In the SEM element mapping of the aluminum, silicon, and calcium on a fly ash particle fusion point, calcium was found to be in a high concentration (see Fig. 30.13). This indicates that the high Ca content of the coal used results in fusion of small fly ash particles, leading to agglomeration and resulting in industrial problems encountered. 

When an amorphous component is exposed to high temperature and/or relative humidity above glass transition temperature (Tg), the amorphous system transforms to a rubbery state. Molecules in rubbery state are mobile and can form interparticle bridges or form particle aggregates, often resulting in particle fusion (Descamps and Palzer 2007). This effect of particle fusion can be magnified in amorphous solid dispersion particles with large surface area (Matteucci et al. 2007 Alonzo et al. 2011 Shah etal. 2013). 

Face-selective polymer adsorption can also lead to the formation of onedimensional particle aggregate arrays without the particle fusion of the individual nanoparticles that takes place during oriented attachment. This was demonstrated for silicalite nanoparticles, which self-assembled to chains after selective PDADMAC adsorption [254]. 

It forms an insufficient steam flow through the foam particles. Fusion of the foam particles in the box wall is significantly worse. More disadvantages of this construction are a poorer filling behavior and mostly longer cycle times. 

The only known mechanism that could cause such an inversion is a state of extremely high pressure [9], We conjecture that the unit ratio oi Z/N coupled with high pressure describes ideal conditions for the build-up of 300 nuclides of 100 elements by a-particle fusion in massive stellar objects, explaining conditions (a) and (b). 

Calcination is a process to improve the electrical properties or whiteness of kaolin. Much of the platy kaolin character is changed from the crystalline to an amorphous form. Removal of the hydroxyls as water causes considerable shrinkage, and some particles fusion necessitates grinding of the product. Calcining of kaolin at 1,100 °C leads to considerable shrinkage and causes some of the books to open (split of the plate layers), but the finer particles fuse with the larger to yield a generally lower surface area. 

To prevent erosion To protect against fouling To prevent particle fusion To protect against corrosion... 

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