And mechanical instability

There are of course other causes for exit beam misalignment other than simply the process of optical retardation by mirror scanning. The overall alignment integrity of the cube-corner/beamsplitter/cube-corner module as well as its optical relationship to the collimated input beam from the NIR source, and the collinear HeNe laser are all critical. The thermal and mechanical instability of this whole assembly is roughly a function of its volume. Small compact FTIR modulators will perform better in process analytical... 

The most popular of the electrodes used in reductive electrochemical detection utilise an electrode consisting of mercury deposited as a thin film on a gold substrate. This design overcomes the problems of vibration and mechanical instability observed with the older design of mercury drop electrodes. 

In 8.1 we derive the thermal and mechanical stability criteria for closed systems, and in 8.2 we apply those criteria to pure substances. In pure substances only thermal and mechanical instabilities are possible diffusional instabilities never occur because pure substances caimot exhibit concentration gradients. Then in 8.3 we derive the diffusional stability criteria for open systems, and in 8.4 we apply those... 

Internal Sn diffusion process Pure Sn or dilute Sn alloys with Cu or Mg are incorporated in the initial rod composite after processing into wire form the NbsSn phase is formed by a diffusion-reaction process with the Nb filaments. However, due to the low melting point of Sn and its low yield stress, the processing cannot use hot extmsion and the drawing processes can readily lead to inhomogeneous deformation and mechanical instabilities. 

From a purely practical point of view, the use of insoluble catalysts has important attractions, in particular the ease of separating the catalyst from reactants and products, which opens up the possibility of the use of flow reactors. Less obviously, greater selectivity in catalytic function can sometimes be achieved [4], Set against this, there are some practical disadvantages, such as the high cost of the materials, and their thermal and mechanical instability, which is especially marked for organic ion exchange resins. 

Because the metal dissolution is an anodic process, for example, Fe(s) Fe +(aq) + 2e , the current of the process is assumed to be positive. When potential increases from Mez+zMe lo f (passivation or Flade potential), the current is increasing exponentially due to the electron transfer reaction, for example, Fe(s) -> Fe +(aq) + 2e", and can be described using Tafel s equation. At a E the formation of an oxide layer (passive film) starts. When the metal surface is covered by a metal oxide passive film (an insulator or a semiconductor), the resistivity is sharply increasing, and the current density drops down to the rest current density, 7r. This low current corresponds to a slow growth of the oxide layer, and possible dissolution of the metal oxide into solution. In the region of transpassivation, another electrochemical reaction can take place, for example, H20(l) (l/2)02(g) + 2H+(aq) + 2e, or the passive film can be broken down due to a chemical interaction with environment and mechanical instability. Clearly, a three-electrode cell and a potentiostat should be used to obtain the current density-potential curve shown in Figure 9.3. 

The Ni-cermet with either stabilised zirconia, most often yttria stabilised zirconia (YSZ), or doped ceria has so far been the most successful anode in SOFCs in spite of the many problems associated with this electrode. The main reason for this is the excellent catalytic and electrocatalytic property of Ni for steam reforming of natural gas and for electrochemical oxidation of H2 and CO. These properties have been so good that they have overshadowed several drawbacks such as the sensitivity to sulphur poisoning and mechanical instability in case of redoxing. Furthermore, the electrode is fully reversible, i.e. works equally well in fuel cell and in electrolysis mode. 

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