Thermal cycling conditions, nickel

Comparison of ACAs with Hard and Soft Fitters. Kishimoto and coworkers reported (15) ACA pastes using two different fillers Au-coated rubber particles (soft) and nickel particles (hard). The ACAs were used to bond a flip chip with Au plated bumps to a board with copper metallization. With the application of pressure, the soft particles were brought into contact with surface pads and were deformed, which lowered this contact resistance. The hard particles, however, deformed the bumps and pads, and thus were also in intimate contact with the surfaces to help reduce this contact resistance. Their study showed that their choice of both hard and soft flllers in ACA materials had similar voltage-current behavior, and both exhibited stable contact resistance values after 1000 cycles of thermal cycling and 1200 h of 85°C/85% RH aging conditions (15). 

Metal Supported-Solid Oxide Fuel Cells (MS-SOFC) represent a promising new design for fuel cells which may overcome the limitations of anode-supported cells (such as poor thermal cycling resistance and brittleness. Nickel phase re-oxidation upon exposure to transient uncontrolled conditions) due to the much better mechanical properties of the support that is represented by a porous thick metal substrate, the thickness of the ceramic layers (anode/electrolyte/cathode) being in the order of 10-50 pm, only. In addition, in this design (Fig. 1), the replacement of the thick Ni/YSZ cermet with ferritic stainless steel leads to several benefits in term of fabrication cost and safety. 

There are a number of other surface finishes used in the industry, such as Electroless Nickel Electroless Palladium Immersion Gold (NiPdAu), Immersion Silver, Immersion Gold, Immersion Tin, OSP and Electrolytic Nickel Gold. There are reliability and process trade offs with each surface finish. That is why it is recommended that strain/strain rate characterization and thermal cycling be performed for each set of surface finish before it is selected for the specific end-use conditions in which it will be used. The industry test methods used to evaluate different surface finishes are outlined in detail in the next chapter. 

A low O2 condition is produced at a corrosion interface in the presence of protective scales, and complex corrosion reactions such as chlorination, sulfidation and oxidation occur below the corrosive deposit layer. Thick scales have pores and cracks due to temperature fluctuations and the vaporization of chlorides. As the thickness increases, the scales easily peel off from the surface. In particular, severe thermal cycles or increased gas velocities due to soot blowing accelerate the breakdown and spalling of the scale. Also, as a result of continuously repeated variations of gas conditions on the scales, the balance of chlorination, sulfidation and oxidation reactions at the corrosion interface and in the scales is forced to be changed by the penetration of O2. An increase of the partial pressure of O2 ( /qj ) temporarily halts the chlorination and sulfidation reactions. Therefore, a multi-layered scale stracture is produced. The presence of multi-layered oxides formed by corrosion resistant elements such as chromium, nickel, aluminum, silicon and molybdenum increases the protective effect of the scales against the... 

FCC catalysts are deactivated via several mechanisms," which all result in a loss in activity and a change in yield selectivity Catalyst will age, meaning change chemical and physical structure due to the (hydro) thermal conditions during the 10,000 to 50,000 reaction and regeneration cycles it will endure. The catalysts can also be poisoned, whereby the active sites are covered by coke and/or polars (nitrogen) that neutralize the catalytic activity or by metals (vanadium, nickel, sodium) which can destroy or alter the activity. 

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