Lead-antimony alloys ::

By far the biggest use of lead-antimony alloys is in batteries. Trends have varied over the years. At one time, antimony levels of around 10% were common but the current generation of lead-acid batteries has a much lower level.

Lead-antimony alloys with antimony contents of between 1 and 12% are used widely in the chemical industry for pumps and valves on chemical plants and in radiation shielding both for lining the walls of X-ray rooms and for bricks to house radioactive sources in the nuclear industry.

The addition of antimony to lead increases lead's hardness and therefore its resistance to physical damage without greatly reducing its corrosion resistance.

Solders ::

There are four main methods of joining material together: mechanical joining (bolts, rivets etc), adhesive joining, welding and soldering. Welding is joining under the influence of heat and/or pressure using the base metal itself to form the joint, whereas soldering employs a third metal applied in the molten state to wet the two solid surfaces and join them on solidification.

Solders are classified according to their working temperatures. At the highest end of their working temperature range are brazing alloys. Below these are the medium temperature hard solders and lastly the soft solders and fusible alloys which have the lowest melting points.

Soft solders are largely lead-tin alloys with or without antimony while fusible alloys are various combinations of lead, tin, bismuth, cadmium and other low melting point metals. Varying the tin content varies both the melting temperature and the melting characteristics.

A eutectic soft solder with 38% lead and 62% tin melts completely at 183^oC to a free flowing liquid which will easily penetrate minute openings. It is therefore used for making close joints between hard metals and in situations where minimum heat is required because of the presence of heat sensitive components. A 70% lead, 30% tin solder melts over the range 183^oC to about 255^oC. Between these temperatures the alloy is "pasty" and may be manipulated to a desired contour in car body filling or for wiped joints on lead pipes and cables. Lead-rich solders containing very little tin are used for such applications as soldering parts of car radiators where the temperatures reached in service require that the solder has a higher melting point so that the joint strength is maintained.

A substantial proportion of solder is used in electrical or electronic assemblies. The advances made in these industries have made it essential to devise fast and highly automated methods of soldering. Printed circuit assemblies are now soldered by passing them across a standing wave of continuously circulating molten solder.

Lead for radiation shielding ::

Lead and its alloys in metallic form and lead compounds are used in various forms of radiation shielding. Their high densities meet the primary requirement of a shielding material and in certain shielding applications lead's high atomic number is also important. The ease with which lead can be worked is of added value. The shielding of containers for radioactive materials is usually metallic lead. Radioactive materials in laboratories and hospitals are usually handled by remote control from a position of safety behind a wall of lead bricks and X ray machines are normally installed in rooms lined with sheet lead. Lead compounds are a constituent of the glass used in shielding partitions to permit safe viewing and lead powder is incorporated into plastic and rubber sheeting as a material for protective clothing.