Alloys substitutional

Bulk Ag-Al alloys, containing up to 12 a/o Al, were electrodeposited from melt containing benzene as a co-solvent. Examination by x-ray diffraction (XRD) indicated that the low-Al deposits were single-phase fee Ag solid solutions whereas those approaching 12 a/o were two-phase, fee Ag and hep i>-Ag2Al. The composition at which ti-Ag2Al first nucleates was not determined. The maximum solubility of aluminum in fee silver is about 20.4 a/o at 450 °C [20] and is reduced to about 7 a/o at room temperature. One would expect the lattice parameter of the fee phase to decrease only slightly when aluminum alloys substitutionally with silver because the... 

Stainless steel generally withstands polluted sea water and polluted brackish water better than copper-base alloys. Substituting an austenitic stainless screen for silicon-bronze trash racks has resulted in greatly improved service at a west coast power plant. Normally stainless steel screens, because of the crevices involved (where the wires cross), are not recommended for use in sea water. This alteration of the usual corrosion mechanism, presumably related to the hydrogen sulfide content of polluted sea water, needs to be studied. 

Fig. 20.7. Lattice parameter vs temperature for SmS alloys substituted with different trivalent rare earth ions (left) and for Smi, GdjS alloys (middle and right). The abrupt changes in the lattice parameter are due to first-order but isostructural phase transition. To be noted is the anomalous thermal expansion (right figure) of Smi jGd,S alloys (from Jayaraman et al., 1975a).

Alloying. Substitutional alloying is another method of improving the resistance of tantalum to hydrogen embrittlement. Small alloy additions of about 1-3% of molybdenum or rhenium substantially decrease the corrosion rate and hydrogen embrittlement of tantalum in concentrated sulfuric acid at 250°C. ... 

In the case of the AB5 class of alloys, substitutions have improved the aUoy as follows - ... 

When encountered as a pigment, it may be the synthetic analogue, copper zinc carbonate, rosasite type q.v.), rather than the mineral itself This is produced in a similar manner to copper carbonate hydroxides ( verditer ) hut with brass, a Cu-Zn alloy, substituted for copper as the starting material. Other occurrences of this type of replacement are known, such as is seen through the presence of tin in Egyptian blue q.v.) when a bronze (a Cu-Sn alloy) was used. 

There are two different types of alloys, substitutional and interstitial. 

Prevention. Dezincification can be prevented by alloy substitution. Brasses with copper contents of 85% or more resist dezincification. Some alloying elements also inhibit dezincification (e.g., brasses containing 1% tin). Where dezincification is a problem, red brass, conunercial bronze, inhibited admiralty metal, and inhibited brass can be successfully used. 

Attack by graphitic corrosion is reduced by alloy substitution (e.g., use of a ductile or alloyed iron rather than gray iron), altering the environment (raise the water pH to neutral or slightly alkaline levels), the use of inhibitors, and avoiding stagnant water conditions. 

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