Traditionally tinlead mixtures have been used as solder but

Traditionally, tin-lead mixtures have been used as solder, but these are being phased out because of health concerns over the lead. This is especially the case when the solder is used to join water pipes where the water is used for drinking. Now non-lead solders have been developed as sager replacements. What kinds of alloys are likely developed to be used as soldering materials? Explain. Is eutectic composition suitable for this application, why or why not.

Solution

Generally for the purpose of Drinking water we use Copper pipes. So, for Welding the copper pipe traditionally Tin (Sn) was used. Tin in it\'s pure form makes a very weak joint. The most suitable metal to be used with Tin was Lead (Pb). They are mixed in a 50/50 ratio. Since Lead is a very heavy metal and has got a lot of issues related to the Health if Consumed, can led to the death of the person. Some other are tin-zinc for joining aluminium, lead-silver for strength at higher than room temperature, cadmium-silver for strength at high temperatures, zinc-aluminium for aluminium and corrosion resistance, and tin-silver and tin-bismuth for electronics.

Effects of these metals on health created a need of changing the whole technique of joining the copper pipes. Brazing is used for developing joints of higher strength and resistance. For this purpose, filler metals stronger than those composed primarily of tin must be used. However, this increased strength generally comes from filler metals made of materials that melt at higher temperatures. The brazing temperatures for most of the brazing alloys used to joint copper piping systems (BCuP and BAg alloys see below) are roughly between 1,150°F/621°C and 1,550°F/843°C.

The most commonly used brazing filler metal types, used to join copper tube and fittings fall into two distinct categories:

1-) BCuP Alloy (pronounced b-cup) -
Here B means Brazing
Cu Means Copper
P means Phosphorus.

A BCuP brazing alloy is primarily a copper-phosphorous brazing alloy that may contain from 0%-30% Silver (Ag).

2-) BAg Alloy (pronounced bag) -
Here B means Brazing
Ag means Silver
While there are other elements found in BAg alloys besides silver, the majority of BAg alloys may contain silver content of anywhere between 24% and 93%.

Answer 2-) Yes, A eutectic composition is suitable to use when applied to soldering as the liquidus and solidus temperatures are the same, so there is no plastic phase, and it has the lowest possible melting point. Having the lowest possible melting point minimizes heat stress on electronic components during soldering. And, having no plastic phase allows for quicker wetting as the solder heats up, and quicker setup as the solder cools.