Please give detailed explanations for your answers, Thanks. For the Sn-Pn phase

Question

Please give detailed explanations for your answers, Thanks.

For the Sn-Pn phase diagram shown determine what concentration of Pb should be used in the following cases: a. Electronics - solder for circuit boards Desirable characteristics: - has rapid transformation between solid and liquid (i.e. doesn't become mushy) does not become too hot and damage components b. Plumbers Solder - used to weld lead water pipes Desirable characteristics: must not melt at maximum temperature of water (100°C) - must be able to mold it in place around the pipe must be cheap (note: Pb is cheaper than Sn) C. Miniature Train Engine Solder - to connect pipes to engine Desirable characteristics: must not melt until 250°C (max. design engine temp. is 200 °C but it may get hotter)

Explanation / Answer

case A : electronic solder for circuit board.

the melting point of the alloy should be very lo so that it can easily melt and perform the task.

and for that purpose eutectic mixture is always considered the best.

so we should go for 38.1% Sn alloy of Sn-Pb.

case B: welding lead water pipe

here the content of lead should be high so that alloy can easily mi with the lead pipe.

and also given that the alloy should not melt upto 100 C, so the obvious choice is 2.5 % Sn and 97.5% Pb alloy.

it has melting point above 150 C

case C: to connects pipes to engine

here as per the given requirement that i melting point should be above 250 C,

so by given phase iagram this situation is possible for more than 90 % Sn alloy of Sn -Pb alloy

so take 90% sn alloy

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