Aluminum and chromium were deposited simultaneously onto the nickel-base alloy Ren~ 80 H using a pack-cementation process. The pack mixtures contained a Cr-A1 source alloy and the activator salts tested were NaC1, NH4C1, YC13.6H20, and mixtures of CrC13 9 6H20 and NaC1 + NH4C1. Two deposition temperatures of 1100 and 1120~ were studied. Only aluminum deposited in packs activated by NaC1, only chromium deposited in packs activated by CrCI~ 9 6H20 or NH~C1, and both metals deposited simultaneously in packs activated by YC13 9 6H~O or NaC1 + NH~C1 mixtures containing no more than 2 weight percent (w/o) NH4C1. The effects of varying the relative amounts of NaC1 and NH4C1 in the mixed-activator packs, together with the Cr-A1 alloy composition, on the type of coating obtained were also investigated. In all cases, the tendency to deposit chromium was related to the calculated equilibrium partial pressure ratio Pc~e12/(P~cl + P~c12) and the magnitude of Pere~2. Codeposition of the two metals occurred when this ratio was between ca. 0.01 and 0.1. Adjustments to pack compositions were used to control chromium concentrations in the product coating, and a maximum chromium level of 25 w/o was achieved.
This chapter describes the use of carbon dioxide at high pressures as an alternative for the extraction of bioactive compounds in a more sustainable way, addressing some of its physicochemical properties, such as pressure, temperature, density, solvation, selectivity, and its interaction with the solute when modified by other solvents such as ethanol and water. This extraction process is considered chemically "green," when compared to conventional extraction processes using toxic organic solvents.
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