Would be interested what is your experience/preference for epoxy resin for embeding mineral separates. Especially with the adhesion of very small grains (below 100 micron) in the resin during polishing. I have used 3 resins in the past:
Buehler Epoxicure - smells like a hell, rather soft, viscous when mixed, easily etched by acetone
Struers Epofix - hard, less viscous
Araldite 2020 - hard, least viscous of all
The reason Im asking is the recent experience with some very small zircon grains jumping off the Araldite resin during polishing and lasering. I do not think this was happening with Epofix resin before. Any of you have any experience? It would be greatly appreciated.
Jiri
Many thanks Ewa, this is great! I mean it is good to hear that the failure may not be on my side. We used Epofix in Bergen and after coming back to Prague they were suggested here to use Araldite - it has indeed nicely low viscosity but the adhesion seems to be an issue. From the two - Epofix and Specifix - which one would you use (has better adhesion or lower viscosity)?
Jiri
How are your grains affixed before you pour the epoxy, or are they loose?
We use Bueller Epothin that we mix 2:1. It does not need to heated, but we do to help with mixing and to allow bubbles to rise (80 C). In this setting it is fairly thin and can be poured. Heat obviously speeds up curing (12-24 hr) (enough to polish). We do not have grains moving (on double side sticky tape), but I suppose type of tape may matter. You may consider making sure grains are well affixed to tape before you pour (push down with fine tweezers).
Thanks John, Im basically doing the same thing - when I used Buehler, I also heated the resin a bit to make it less viscous and get out bubbles (I even immersed the beaker with heated resin to ultrasonic bath for a second to push out the bubbles). After that I had better experience with Struers Epofix but maybe Buehler Epothin is better that Buehler resin we used.
Dear Jiri,
We use Araldite and do not have any problems with grains droping out. May-be the problem is not so much type of resin but probably film of air around thin grains, which prevents sticking. Heating is one way to oust the air, but we have better experience with vacuuming. If the grains are well sticked to the type than the air will get out completely after a few careful repetitions of vacuuming and the grains will be completely cemented in the resin.
Thank you Mirka, yes that would certainly be good but we do not have gadget for vacuuming the samples as far as I know. Strangely this was not problem for Epofix but it is for Araldite. It mostly only happens to grains with size of ca 50 micron and smaller, ca 100 micron and bigger are OK.
Yes, Jiri, that is why I assume that trapped air around grains is the problem due to higher viscosity of the Araldite. Do you have any vacuum pump? Some time ago, we simply used dessicator with tubus, connected it to the pump with rubber or plastic tube and manually regulate vacuum by opening and closing the valve on the tubus to prevent the resin spilling over. Another chance is to make the resin less viscous by deluting it with a little acetone, but in this case you have to wait a few days the resin to reach proper hardnes (acetone to evaporate) before polishing. Best regards.
Thank you Mirka, we can also use the carbon coating machine - that makes proper vacuum. Thank you again!
Just a bit of an update - new zircon mounts with variable grain size (from 40 up to 1000 micron) behave well in Epofix resin - almost no lost during polishing and I treat the samples quite rough :-)