Liquidus question?

[Mike W1]

A recent post referred to this term and I've often wondered but never asked. Just exactly how would you determine the liquidus of a particular alloy? For instance in a 10# Lee pot you can see the alloy start to melt on the top and I'd assume it's gonna be a bit hotter in the bottom of the pot. My TC is down there about 1/2" from both side and bottom so it's reading down there. Is liquidus the moment the top is completely fluid or is there something else one should be observing? I've noticed the term used to calibrate a thermometer but have never pursued it that way for lack of understanding.

[JSnover]

Liquidus is just the temperature at which any element turns from a solid to a liquid. It doesn't happen all at once.

[jsn]

There was an article in the NRA Cast Bullet publications from some years ago, and they referenced watching the melted alloy "freeze" or turn solid with a thermometer in it to determine the melt point.

Is this what you're refering to?

[Mike W1]

There was an article in the NRA Cast Bullet publications from some years ago, and they referenced watching the melted alloy "freeze" or turn solid with a thermometer in it to determine the melt point.

Is this what you're refering to?

I "think" it is. Maybe I'd better dig that article out and read it again. Obviously didn't understand it the first time I read it.

[Cowboy_Dan]

Most alloys will have a slushy phase between full solid and full liquid. They will start to melt at one tempreture, this is called the solidus, the highest tempreture with no liquid. Tempreture will continue to climb until it reaches liquidus, the lowest tempreture at which the alloy has no solid portion. It is near impossible to tell when liquidus is reached by looking at the pot, but the tempreture climb will stall at liquidus as all of the solid bits melt. The same is true for solidus as the alloy freezes.

[BNE]

Liquidous is the temperature that a specific mix or alloy is completely liquid. No "slush", all liquid.

Another useful term is "Eutectic". Eutectic is the alloy / mix that has the lowest melting point.

The diagram below is a Binary Phase diagram. The "All Liquid" section is the "liquidous" or all melted section. Basically you find the % Pb and the %Sn of your mix and then as you heat that mix, the mix will be all liquid (Completely melted) above that line.

186779

[Shiloh]

Liquidus for a pure metal is within a few degrees. With an alloy it will be at a larger temp range, and will a vary from batch to batch.

SHiloh