Talk:Rose's metal

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density?

Latest comment: 6 years ago1 comment1 person in discussion

heard this was a relatively high density metal - close to silver perhaps? can't find any source for this, maybe depends on the exact constitution — Preceding unsigned comment added by 96.20.246.219 (talk) 04:02, 19 August 2018 (UTC)Reply

Eutectic?

Latest comment: 5 years ago3 comments3 people in discussion

In what way is Rose's Metal non-eutectic? It seems like it's melting temperature is significantly lower than any of it's constituents. Unless I'm misunderstanding what Eutetic means in this context? --Xpyder (talk) 21:30, 2 May 2019 (UTC)Reply

Roses metal: 98 °C, 208 °F
Bismuth: 271.5 °C, 520.7 °F
Lead: 327.46 °C, 621.43 °F
Tin: 231.93 °C, 449.47 °F

What does "eutectic" mean? It's used regularly and inconsistently. One meaning (the broader one) is that it's any mixture of the constituents, such that the melting point is lowered. Another, narrower, meaning is that it's the particular proportion to give the lowest melting point. There are many eutectic systems (just look at solder) where the range is useful, not just the very lowest temperature combination. Without checking the whole diagram for bismuth-lead-tin, it's hard to know if Rose's metal is the very lowest. Several of these (the Cerro- range) are not only "quite low melting", but they also have features like accurate dimensional stability.

I think (from a quick check) that the eutectic for this system is Bi 35.7% Pb 28.6% Sn 35.7%, which is a bit different from Rose's metal. It's also (assumedly) cheaper than Rose's (less bismuth, which is the most expensive), so I presume that there's some other non-eutectic reason for Rose choosing this precise ratio (maybe the minimal shrinkage). Andy Dingley (talk) 22:39, 2 May 2019 (UTC)Reply

Eutectic (meaning "good melting"), simply means the melting point and freezing point are the same temperature. This means a rapid transition from liquid phase to solid on cooling. A common example is in the tin/lead alloy commonly used for soldering in electronics applications. Using the (cheaper) 50/50 solder there is a "pasty" phase as it solidifies, and if there is any movement between the surfaces being joined during this period the result is an unreliable joint, and the solidified solder has a dull surface. It is easier to achieve a reliable joint (with a shiny surface) using 65/35 solder, which is close to the eutectic ratio. Other compositions are taking over due to lead toxicity, but that's a different story. Doug butler (talk) 22:29, 4 December 2019 (UTC)Reply

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