Particle shape, etching

The impact of thermal etching on the equilibrium shapes of supported particles. It is clear that particle shape and surface structure are a function of the identity of the gas. 

Hot-Drawn ABS Polymer. Draw ratios were varied between 1.0 and 2.9. In order to determine the extent of orientation produced during drawing, specimens were sectioned and etched the shapes of the initially spherical rubber particles are a measure of orientation (8). In general, the effective draw ratios calculated from particle shapes were close to the actual draw ratios. 

Fig. 4. SE images of organic polymer binders (a, b) in the primaiy form as dispersion and (c, d) coalesced in silicone resin coatings, a, b Typical particle shape of the primaiy latex particles after rapid diying in a vacuum, c, d Plaster/paint samples etched with 10% HNO3. c Plan view of a coalesced polymer binder of a silicone resin plaster and d cross-section of of a polymer film partly covering a clay mineral particle within a silicone resin emulsion paint.

The electrochemical etch profile is determined by the local current intensity gradients at the silicon interface. This technique is both extremely controllable and reproducible, and allows the manufacture of particles with characteristic sizes in the micron range and monodisperse in terms of both particle and pore size. The particle shapes attainable are Umited by the 3-D patterns achievable through the combination of photolithographic techniques and the characteristic profile of the electrochemical etch. 

Pores with a very regular, linear shape can be produced by the track-etch method (Quinn et al. 1972). Here a thin layer of a material is bombarded with highly energetic particles from a radioactive source. The track left behind in the material is much more sensitive to an etchant in the direction of the track axis than perpendicular to it. So etching the material results in straight pores of uniform shape and size with pore diameters ranging between 6 nm and 1200 nm. To avoid overlap of pores only 2-5% of the surface can be occupied by the pores. This process has been applied on polymers (e.g. Nuclepore membranes) and on some inorganic systems like mica. Membranes so obtained are attractive as model systems for fundamental studies. 

Optical examination of etched polished surfaces or small particles can often identify compounds or different minerals hy shape, color, optical properties, and the response to various etching attempts. A semi-quantitative elemental analysis can he used for elements with atomic number greater than four by SEM equipped with X-ray fluorescence and various electron detectors. The electron probe microanalyzer and Auer microprobe also provide elemental analysis of small areas. The secondary ion mass spectroscope, laser microprobe mass analyzer, and Raman microprobe analyzer can identify elements, compounds, and molecules. Electron diffraction patterns can be obtained with the TEM to determine which crystalline compounds are present. Ferrography is used for the identification of wear particles in lubricating oils. 

The important point to recognize is that the etch rate of surfaces subjected to energetic particle bombardment (bottom surfaces) will be larger than the etch rate of surfaces not subjected to this bombardment (sidewalls) because of the ion-assisted (or electron-assisted) gas-surface chemistry. The relationship between the shape of an etched profile and the dependence of the etch rate on ion bombardment is shown in... 

To etch away silica, carbonization product samples were treated with a mixture of concentrated sulfuric and hydrofluoric acids (5 drops of H2S04 and 1 mL of HF), boiled dry and washed with water. From the precipitate obtained were prepared dispersions in acetone, which were used to determine the size and shape of particles on a JEM100CX-II transmission electron microscope by a commonly used procedure[10]. 

Figures la, lb, lc, and Id show transmission electron micrographs of the blends with 5, 10, 20, and 25 wt% PST, respectively. PC forms the continuous phase and PST is dispersed as spherical particles without any aggregation. The observed oval shape of the dispersed particles results from the deformation of the specimens during ultramicrotome sectioning. Their normal spherical shape is evident from scanning electron micrographs of the etched fracture surface of these blends (Figure le).

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