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

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Discussion Overview

The discussion revolves around the solubility of nickel in silver, particularly focusing on the factors influencing their interaction in both liquid and solid states. Participants explore the implications of the Hume-Rothery rules, atomic radii, valency, and the nature of alloys.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants note that the Hume-Rothery rules suggest nickel should dissolve readily in silver, given their similar crystal structures and atomic properties.
  • Others highlight that despite the theoretical expectations, nickel's solubility in silver is very low, approximately 0.15% in the liquid phase.
  • One participant points out that while silver is relatively soluble in nickel, the reverse is not true, indicating a suppression of nickel's solubility in silver.
  • Another participant emphasizes the distinction between solid solution solubility and liquid miscibility, mentioning that liquid metals can mix in any proportion but may form compounds that affect solubility.
  • Some participants discuss the implications of atomic radius differences and valency on solubility, suggesting that the 16% difference in atomic radii may be a contributing factor to the observed low solubility.
  • There is mention of the historical use of nickel silver as a material, which contains no actual silver, adding to the complexity of the discussion.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement regarding the factors influencing solubility. While some acknowledge the theoretical framework provided by the Hume-Rothery rules, others challenge the applicability of these rules in this specific case, leading to an unresolved discussion on the solubility of nickel in silver.

Contextual Notes

Participants note limitations in their discussion, including the dependence on definitions of solubility and the complexity of alloy formation, which may not be fully captured by the Hume-Rothery rules alone.

Samson4
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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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Samson4 said:
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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Samson4 said:
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.
 
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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.
 
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trurle said:
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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