Chemical resistance isotropic

Rimplast materials from Petrarch are silicone/thermoplastic IPNs that combine the warpage and wear resistance properties of silicone with nylon, thermoplastic polyurethane, or styrene/butadiene block copolymers. The combination of properties these IPNs possess make them suitable for high quality, high tolerance gear and bearing applications that can benefit from the addition of internal lubrication and isotropic shrinkage of silicone to the fatigue endurance and chemical resistance of crystalline resin, while processability still remains the same. 

The structure of cubic boron nitride is of the zincblende (or sphalerite) type which is similar to that of diamond and p-SiC and is characterized by extremehardness and excellent chemical resistance. It is shown in Fig. 12.3. Note the similarity with Fig. 7.1 of Ch. 7. This structure is relatively simple in the sense that it is essentially isotropic, in contrast with the pronounced anisotropy of hexagonal boron nitride. It can be visualized as a stacking of puckered infinite 111 layers or as two face-centered interpenetrating cubic sublattices, one consisting entirely of boron atoms and the other entirely of nitrogen atoms.I l... 

The glassy carbon electrode (a patented material) is particularly suitable for non-aqueous solvents. Its main properties are that it is isotropic, impermeable to gases, resistant to chemical attack and has high conductivity. 

Once the resist has been patterned, the selected regions of material not protected by photoresist are removed by specially designed etchants, creating the resonator pattern in the wafer. Several isotropic (etching occurs in all directions at the same etch rate) and anisotropic (directional) etching processes are available. Wet chemical etching is an isotropic process that... 

Figure 1. Cross sections of films etched with liquid or plasma etchants. The isotropic profile is the result of zero overetch and can be generated with liquid or plasma etch techniques. The anisotropic (vertical) profile requires plasma or dry-etch processes. W is the width of the resist pattern. (Reproduced from reference 2. Copyright 1983 American Chemical Society.)...

When pitch binder is pyrolyzed during the carbon bake operation, it is converted from an isotropic liquid, with no structural order, to a liquid-crystal (called mesophase) having a layered structure which is finally converted to layers of carbon atoms in a hexagonal lattice of graphite crystallites. These crystallites of binder coke become more disordered and crosslinked into a more-isotropic coke as the pitch QI content increases. Such moderately-isotropic coke, in contrast to highly-anisotropic microstructure (10), is preferred binder coke because it forms both physical and chemical bonds between filler coke particles which are stronger and more oxidation-resistant (8,9). 

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