Thermal etching

Plasma etching is a quick and effective etching method for revealing the microstructure of ceramics based on silicon nitride (Chatfield 1983 O meara (1986) Taffner 1990). It makes possible a clear representation of grain boundaries, grain boundary 

Etching is performed in plasma etching systems, which are also known as tunnel reactors or cold incinerators . Fig. 30 shows the schematic structure of such a system. 

Reaction gas Gas pressure High-frequency energy consumption of capadtor Reflected power Etching time 

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C2.18.3.1 EXPERIMENTAL STUDIES OF THERMAL ETCHING REACTION KINETICS AND DYNAMICS... 

Fig. 1. SEM photomicrograph of polished and thermally etched section of Norton SG sol—gel alumina abrasive grain.

Figure 6.12 Grain boundary after polishing (a) and after the subsequent thermal etching (b).

Figure 6.13 Surface of thermally etched La0.5Sr0.5Fe0.5Co0.5O3> a polycrystalline ceramic material.

FIGURE 3.13 SEM micrographs taken from (a) a fractured cross-section of an LSM/3YSZ specimen after heat treatment at 1500°C, and (b) the polished and thermally etched cross-section of an LSM/3YSZ specimen after heat treatment at 1400°C. (From Jiang, S.P. et al., J. Euro. Ceram. Soc., 23 1865-1873, 2003. With permission.)... 

The most common cause of it is the neglect of 3-dimensional effects as compared with those in two dimensions. Thus, all stresses in a loaded wire or ribbon are disregarded in the shrinkage method, Section III. 1. The work of deformation leading to rupture is a bulk effect which does not receive its due consideration in the calculation of fracture energy, Section III.3. Bulk deformations associated with thermal etching, Section III.4, demand more attention than was alloted to them by many scientists. The method of bubbles, Section III.5, is invalid both because of the above neglect (that is, that of the volume stresses around the bubble) and because of another popular error, namely an erroneous treatment of capillary pressure Pc. 

From a knowledge of the absorption coefficient aeff and the threshold fluence Fth, the value of the photochemical contribution to the etch rate, Fph0to> can calculated and subtracted from the measured hole depth for any given fluence. The difference, which according to this model is the thermal etch rate Fthermai will be modeled by Eq. (5) by rewriting it as... 

The above definitions are somewhat different from those given in earlier publications. In earlier studies, thermal etching has been defined to be etching that takes place in nonreactive or mildly reactive gases or under vacuum. Catalytic etching has been defined to be any etching process that takes place in... 

Leroux and Raub (10) performed a detailed study of the etching of silver and silver alloys in oxygen and hydrogen at elevated temperatures. They were the first to propose that thermal etching is kinetically controlled. Specifically, they suggested that faceting results from differences in the rate of evaporation from different planes and that evaporation rates are influenced by adsorbed species. 

According to a second class of model, thermal etching is driven by a need to reduce total surface free energy. According to this theory, faceting will take place even in the absence of any net weight loss. The first to suggest a model of... 

Experiments conducted by the same group for the thermal etching of silver in an oxygen atmosphere suggest that evaporation of metal plays little role in the thermal etching process. The thermodynamic model appears to best explain the observations. That is, identical faceted surfaces formed both in the case of suppressed and free evaporation. 

Extensive theoretical work in support of both models of thermal etching was produced before 1970. The theoretical basis for the thermodynamic model was the concept of reduction in total surface energy by the preferential formation of low-energy, low-index planes. The true equilibrium shape of a crystal is the shape with the lowest surface energy, as noted by Curie (36) and Gibbs (37). The thermodynamic models provide no information regarding the process of surface rearrangement. 

There was also a great deal of modeling of transport processes in support of the kinetic model of thermal etching. The basis of these models is that differences in chemical potential lead to mass transport via a number of mechanisms. It is important to note that these models treat the surface as a continuum and do not involve atomic-level mechanisms. 

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. 

The impact of thermal etching on metal transport and hence particle dispersion. Metal can be transported by a number of different gases. In some... 

Historically, catalytic etching has been a poorly understood phenomenon, and it has not always been clearly distinguished from thermal etching. Moreover, the largest number of studies have focused on platinum (3, 27, 34, 124-130) although the catalytic etching of silver (122, 131, 132), copper (16, 28, 133), nickel (134), and some platinum alloys (51, 121, 135-138) has also been investigated. 

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