Bimetallic plates

The passive CPS consists of absorber elements in 12 fuel assemblies of the first core zone and 36 fuel assemblies of the second core zone. The passive absorber rods are kept in the same position below the core as the active absorber rods using special triggers that are bimetallic plates made of steel of ferritic-martensitic and austenitic grades with differing coefficients of thermal expansion. The trigger is installed on top of the fuel assembly central tube. When coolant temperatures at the fuel assembly outlet exceed 900 K, the thermal deformation of a trigger reaches its critical value leading to release of the shaft and flow up of the passive absorber rod. 

The main incoming mate coniacts are generally made ot copper or brass and are cither hotted or damped on die vertical bus. Since tlic bus is generally of aluminium. Ihe coniacts may form a bimelaltic join wilh Ihe busbars and cause corrosion and pilling of ibe melal. This may result in a failure of the joinl in due course. To mininii/e rnelal oxidation and bimetallic corrosion, the conlacls must be silver plated. 

Bimetallic corrosion of nickel-iron alloys may be of significance in welding operations. Ni-45 Fe alloys are used as filler materials in the welding of cast irons but the favourable area relationship of weld metal to base plate... 

Additional metal layers can create bimetallic corrosion cells if discontinuities appear in service. The layer of copper beneath cadmium plate on aluminium (using a zincate plus cuprocyanide deposit technique) can cause corrosion troubles. When aluminium is plated with nickel and chromium, rapid service corrosion in the zinc layer causes exfoliation. 

An industrial standard method has been developed to test the lightfastness of polymers in accelerated test equipment [103]. The apparatus consists of a quartz-xenon tube with a special optical filter between the light source and the specimen to produce light that resembles window glass-filtered daylight [104], Samples are mounted at a specific distance from the arc and are supported on a frame which revolves around the arc 1 to 5 times per minute for uniform exposure. A blower unit in the base provides a flow of air which makes it possible to maintain a black panel temperature of 45°C, measured by a black panel thermometer which is positioned at level with the samples. A black panel unit consists of a bimetallic thermometer mounted on a steel frame. Both faces of the frame plate and also the stem of the thermometer are coated with a heat-resistant glossy black enamel. The relative humidity level in the exposure cabinet is closely controlled. 

Sivavec TM, Mackenzie PD, Horney DP. Effect of site groundwater on reactivity of bimetallic media deactivation of nickel-plated granular iron. 213th National Meeting, San Francisco, CA, American Chemical Society 1997 37(1) 83—85. 

In the case of mixed Ag/Pd nanoparticles, shown in the previous section, the TEM measurements pointed out the importance of palladium clusters lying on the Ag nanoparticle surface in promoting the catalytic hydrogenation of adsorbed nitroderivatives. When bimetallic particles are immobilized on quartz plates by... 

The molecular cluster [Ph4P]2[Ru5PtC(CO)i5] was used as a precursor for nanoparticle catalysts [14], The substrates with the layer of mesoporous silica were dried at 200°C in vacuum. The deposition of bimetallic clusters was achieved by immersing the substrates in ether-dichloromethane or ether-THF suspension (3 ml) containing 5 mg (2.8 pmol) of the precursor. This process was carried out for two days after which the plates were washed with diethylether and dried in vacuum. The impregnated plates were subsequently heated (either in vacuo or in air) at 200°C to decarbonylate the molecular cluster leading to the formation of anchored naked metallic nanoparticles. 

Monometallic systems based on Pt, Pd, Rh, Co, Cu, and also some bimetallic systems, Pt-Ag, Pt-Sn, Pd-Rh, Pt-Pb, have been developed, using a similar electrochemical deposition process [48-55]. Due to its important electrocatalytic behaviour, particles of platinum were mainly considered [48,54-66], but also bimetallic Pt-based systems, such as Pt-Ag [46], Pt-Ru [67-69] and Pt-Sn [53,68-70]. Dispersion of palladium particles was also carried out [47,71-73] and bimetallic Pd-Rh and Pd-Pt particles were also obtained [74], Deposition of nickel and copper into polypyrrole films from standard plating baths was considered recently, and observed by the Electrochemical Quartz Crystal Microbalance technique [75,76]. 

Bimetallic corrosion and other forms of corrosion continued to cause service failures. In 1962, a report was sent to the British Ministry of Defense stating that a copper alloy end plate had fallen off a seawater evaporator in a submarine because the steel bolts with which it was secured had effectively dissolved through galvanic action. In 1982, the nose wheels failed on two Royal Navy Sea Harriers that had returned from the Falklands War. Studies showed that the galvanic action was responsible for the corrosion that occurred between the magnesium wheel alloy and its stainless steel bearing. 

The normal thickness of coating is 5-25 jjim and has low frictional properties, making it an ideal surface on fasteners which reduces the tightening torque and prevents jamming. It also provides an effective barrier to prevent bimetallic reaction between steel fasteners and aluminium, e.g. where parts are fixed to an aluminium framework. Cadmium-plated surfaces can be easily soldered without the use of corrosive fluids. 

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