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Researchers Getting the Lead Out of Electronics
alphadogg writes "Researchers at the University of Maryland say they have discovered a material to replace lead, a potential environmental hazard, in electronics products. The material, bismuth samarium ferrite (BSFO), was found by researchers in the university's A. James Clark School of Engineering. It can be used in products such as biomedical imaging devices and inkjet printers, and if implemented commercially could keep lead out of landfills and the ecosystem, they say. While manufacturers have developed replacements for lead in many products, until now no commercial replacement existed for lead zirconate titanate (PZT) — the material of choice for transducers, actuators, sensors and microelectromechanical systems used in common electronic devices, the university says."
Bismuth isn't radioactive
Toxicology can be full of (un)pleasant surprises; but the list of elements involved is promising. Bismuth is a widely accepted nontoxic substitute for lead in applications where similar mechanical properties are needed, and is a component of certain medicines. Iron is generally unproblematic. I'm not sure about Samarium, though our wikipedia overlords say "low to moderate toxicity". Since one of its isotopes has internal medical applications, there are probably some toxicological data out there.
We'll need to test the compound itself, to be sure; but it probably beats lead.
Lead is NOT a good shield against cosmic rays. Fast charged particles cause a strong bremsstrahlung (braking radiation) in lead. That's also how X-Rays machines work - fast electrons are slammed into targets made of lead or tungsten.
High-density polyethylene, water or paraffin work much better for cosmic rays shielding.
Now, lead is great against gamma-rays. But they are not the principal danger of cosmic rays.
It's all about cross section, which roughly depends on the incoming particle's energy being close to the energy of a bound state in the atoms of the material that is to absorb the radiation. The density contributes an overall factor to the calculation. Also, led is nasty when charged particles are involved (electrons, probably protons), because they will rapidly decelerate and create brehmstrahlung, so you've traded a charged particle which is easy to deflect with an X ray, which is not easy to reflect. My wife uses plexiglass shields in her lab for this reason, because it gracefully absorbs beta radiation.
And I had never realized this, but our local landfill is positively brimming with discarded medical scanning equipment. I might try to scavenge some of this, but all the discarded MRI machines are clumped together by some unseen force.
Might want to reconsider that.
As an engineer working on lead-free solder development for electronics, the problems that can arise are specific to the application. The industry has developed a number of different alloys that perform under specific conditions. Instead of just choosing a tin-lead solder that works pretty much everywhere, developers need to understand the types of reliability stresses their product will see and choose the best alloy to meet those requirements. For example lead-free solders that work well in a thermal cycling environment tend to not perform as well under shock conditions. From an assembly side of things, a lot of the problems arise from using old SnPb equipment and materials for soldering joints using leadfree solders. Different reflow temperatures, wetting characteristics, and oxides, means that you just can't use the same old eutectic flux and soldering iron and expect the same quality of results.
Lead-free solders aren't necessarily problematic, they just require a little more understanding to properly use.
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