Aluminum Sorting with X-ray or LIBS? SciAps has the answers

Karen Marzloff LIBS, Scrap Metal & Alloys, XRF

We wrote about this in The Whole Story, but here’s the quick version.

XRF

The SciAps XRF is the better choice for most aluminum alloys. The X-250 is easier to use, more forgiving, and better on a variety of curved and irregular shaped objects, especially because of the vast improvements we’ve made measuring Mg and Si with XRF. For most aluminum alloy analysis, the SciAps XRF is the only choice for these reasons:

1) Our XRF now measures Mg as low as 0.25% in 1-2 seconds. This means even very similar alloys like a A356 vs A 357 or 3003/3004/3005 or 2014/2024 can be sorted very quickly with XRF.

2) And XRF is better on the transition and heavy metals (Cr, Ni, Mn, Fe, Cu, Zn, Pb, etc.) than is LIBS.

3) And most certainly XRF for stainless and high temps. No LIBS gun will ever do as well on Ni, Cr, Mo, Co, etc. than a good XRF.

4) The XRF also costs less.

The SciAps LIBS is more precise and repeatable than the simple LIBS-based sorters on the market. We use a higher-powered laser (about 30x more energy in the laser pulse), and we use an argon purge via a small canister in the handle, rather than air.  For aluminum alloy analysis, we recommend the SciAps LIBS for the following scenarios:

1) If you must measure lithium (Li) in aluminum alloy; XRF cannot measure Li.

2) If you must measure tramp beryllium (Be) in copper or aluminum alloys, or tramp boron (B) in aluminum alloys or B in nickel alloys.

3) If you want to separate steels by carbon content or stainless by L and H grades.

4) If you just don’t want to deal with having an X-ray radiation device and the regulatory headaches of such.

Our position on the two technologies is that XRF is generally the better sorting choice, even for aluminum alloys, than any LIBS, with a few exceptions described below.

We recommend SciAps XRF because of the vast improvements we’ve made measuring Mg and Si. Historically, they’ve been the weak point of XRF, and to properly sort Al alloys it would require 30+ seconds of testing.  That is just too slow.  Our XRF now measures Mg as low as 0.25% in 1-2 seconds.  This means even very similar alloys like a A356 vs A 357 or 3003/3004/3005 or 2014/2024 can be sorted very quickly with XRF.  And XRF is better on the transition and heavy metals (Cr, Ni, Mn, Fe, Cu, Zn, Pb, etc.) than is LIBS.

So in summary — faster measurements on Mg and Si with our XRF means we generally recommend XRF over LIBS even for Al alloys.  And most certainly XRF for stainless and high temps.  No LIBS gun will ever do as well on Ni, Cr, Mo, Co, etc. than a good XRF.

For LIBS, the SciAps Z more precise and repeatable than the simple LIBS-based sorters on the market for two reasons. First, we use a higher-powered laser (about 30x more energy in the laser pulse). Second, we use an argon purge via a small canister in the handle.  Without going too deep into technical detail, optical emission spectroscopy has been done for over 50 years with argon purge because it delivers about 10x the signal compared to operating in air. Handheld LIBS is optical emission technology, just with a laser instead of a spark source.  We use argon purge; the low-end LIBS sorters use air.

We recommend the LIBS as a niche application for the following scenarios:

  • If you must measure lithium (Li) in aluminum alloys, LIBS is the way to go.  XRF cannot measure Li.
  • If you must measure tramp beryllium (Be) in copper or aluminum alloys, or tramp boron (B) in aluminum alloys or B in nickel alloys (unusual but the Colmalloys have 1-5% B.
  • If you want to separate steels by carbon content or stainless by L and H grades.
  • If you just don’t want to deal with having an X-ray radiation device and the regulatory headaches of such (varies by state).

There are two caveats to point out regarding the above rules of thumb for LIBS.

First, a lithium-silver (Li-Ag) complex is used to alloy lithium into the aluminum alloy. So Al alloys with Li also have 0.1-0.5% (typically) Ag.  X-ray sees this Ag easily. So you could say that anytime you measure Ag in an Al alloy, there is likely lithium present, too.

A similar approach exists for beryllium copper alloys. The alloying complex is Be+Co (cobalt). So you almost always see 0.1-0.2% Co when Be is present in Cu alloys.  Many scrap processors have for years used Co in copper as a flag for beryllium copper.

Still — the only surefire way to confirm presence of Li in Al alloys and Be in copper alloys is with LIBS, since X-ray cannot measure them directly.



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