[Amps] current threads about silver solder and resoldering

[Roger (K8RI)]

On 9/2/2012 12:15 PM, Manfred Mornhinweg wrote:
> Bill,
>
>> I recalled that the ratios of lead and tin atoms had to be an integer
>> to for the lowest melting point.
>
> But that's not right either! I hate to be so overly teacherish in this
> thread, but facts remain facts!

I don't know about the others, but I appreciate jogging this old memory

73

Roger (K8RI)


>
> In all possible compositions of tin-lead alloys, only one single ratio
> is eutectic. Exact ratios of atoms such as 1:1, 2:1, 1:2, are NOT
> eutectic, and fully melt at a higher temperature than the eutectic mix.
>
> Have a look at these two web pages for more detailed information, or
> google for phase diagrams of tin lead solders or other alloys.
>
> http://www.ami.ac.uk/courses/topics/0244_tsm/index.html
>
> http://spaceflight.esa.int/impress/text/education/Solidification/Phase_Diagrams.html
>
>
> Note that the eutectic point of tin-lead is given as 61.9/38.1, rather
> than the conventional 63/37. That's why there is so much 60/40 solder
> around. The 63/37 solder is only marginally better. The reason to use
> 63/37 rather than 61.9/38.1 is in the inability to make an absolutely
> homogeneous alloy, and the fact that the pasty phase is shorter if the
> mix deviates from the eutectic point toward the tin side, then if it
> does toward the lead side. So, if the tolerance of an alloy happens to
> be 2%, it's likely that a nominal 63/37 mix will statistically end up
> having a shorter pasty range than a nominal 61.9/38.1 mix.
>
> Manfred
>
> ========================
> Visit my hobby homepage!
> http://ludens.cl
> ========================
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>