Why aren't nickel and silver soluble in each other?

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Hume–Rothery rules seem to be moderately satisfied for nickel to readily dissolve in silver. Silver has a radius of 144, valence of 1 and an electronegativity of 1.93. Nickel has a radius of 124, valence of 2 and an electronegativity of 1.91. Both elements have a fcc crystal structure. I read that nickel and silver are poorly soluble in liquid phase. Is this information incorrect?
 

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  • #2
sophiecentaur
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Is this information incorrect?
Thanks for that question.
You seem to be right, which surprises me, bearing in mind the number of alloys containing both that are available and quite often used. But , as the man says, they are made in a fancy way because solubility of Nickel in Silver is only 0.15% in the liquid phase.

One reason for my surprise is that "Nickel Silver" was a common material for cheap shiny items but it contains no actual Silver.
 
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Hume–Rothery rules seem to be moderately satisfied for nickel to readily dissolve in silver. Silver has a radius of 144, valence of 1 and an electronegativity of 1.93. Nickel has a radius of 124, valence of 2 and an electronegativity of 1.91. Both elements have a fcc crystal structure. I read that nickel and silver are poorly soluble in liquid phase. Is this information incorrect?
The difference in atomic radiuses of Ag and Ni is 16%, over 15% threshold defined in Hume-Rothery rules.
Also, different valency mean silver (lower valency metal) is relatively soluble in nickel (by about 3% looking on binary phase diagram) but solubility of nickel in silver is suppressed.
 
  • #4
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First, Nickel Silver is a corrosion resistant alloy of Copper and Nickel long used in seagoing vessels and steam boilers.
Second, you folks are confusing solid solution solubility rather than liquid miscibility. Liquid Metals are mixable in any proportion (not counting Tl, Pb, Bi, Sb) BUT metals do form compounds with each other and carbides etc. that vie for the solute.
Background. Tin and Lead form an alloy, solder, that a single liquid. However on cooling, separates into individual Lead only and Tin only domains as seen by microscopic examination. Plated Nickel-Tin forms one crystalline structure. Electroplated Tin-Lead is made of microscopic crystals of Tin and Lead. And Lead is added to many alloys because it separates out as soft lead crystals that aid metal machinability. Some alloys are intermetallic compounds, or solid solutions of intermetallic compounds (solder dissolves group Ib metals (Cu, Ag, Au) as M3Sn dissolved in Sn). Some intermetallic formation is exothermic, and can occur in solid metal at RTP as diffusion can be quite rapid in the solid state (formation of Cu3Sn from circuit copper and Tin in solder). Group VIIIa metals (Fe, Co, Ni; Re, Rh, Pd; Os, Ir, Pt) all form alloys with each other. Silver can alloy seamlessly with Palladium (5% Silver doesn't affect Palladium's Hydrogen transport capability). and Palladium is mostly mined as a byproduct of Nickel mining, as they are chemically close.
 
  • #5
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The difference in atomic radiuses of Ag and Ni is 16%, over 15% threshold defined in Hume-Rothery rules.
Also, different valency mean silver (lower valency metal) is relatively soluble in nickel (by about 3% looking on binary phase diagram) but solubility of nickel in silver is suppressed.
I've come to assume the difference in atomic radiuses is the cause . That and it seems nickel is rather immobile, even in copper alloys. Also I thought higher valency metals tend to dissolve in the lower valency metal.
 

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