The very best source, by far, for technical information on fluxes and slags in general is STILL Professor Clarence Jackson's Fluxes and Slags in Welding, available at the Welding Research Council as Bulletin #190. Originally written in 73 it is slightly dated in that asbestos is not used anymore, and in a few other details. But it is remarkably solid to this day and is a foundation document for virtually everything we know of fluxes and slags. Every time I turn its dog eared pages I learn something.
TWI has some excellent reports on SAW fluxes and slags. I'd suggest trying the resource library at the Hobart Institute in Troy Ohio. Talk to Marty Baker. Class lady. You can get the WRC Bulletins there too.