- #1
glassyeyed
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I'm looking at a glass "recipe" that heats the raw ingredients to melt at 1550C. This seems to present a problem in that the raw ingredients include:
Al2O3: melting point = 2072 C
MgO: melting point = 2852 C
And even SiO2 (the primary ingredient) has a melting point (range) of 1600-1725 C .
So I'm puzzling over how this can possibly work. Yet apparently it does work, as this is a real recipe.
I can blindly go ahead and do it, but would really like to understand how & why this can be.
I understand that impure crystals have lower melting points. But in searching these forums (and the web in general) I can find no discussion of deltas that big -- (MgO melting a full 1300 C lower than its pure MP?). It seems... surprising.
[Furthermore, the recipe seems to assume no such requirement of impure ingredients.]
So I figure I must be missing something. Probably something very fundamental.
My only idea is that maybe those higher-melting-point ingredients are not really melting. Maybe they are just dissolving in the lower-melting-point SiO2 liquid? (But even then, 1550C doesn't seem quite high enough to melt the SiO2 -- though with impurities, I guess it could.)
Is that it? Or am I indeed missing something?
Thanks much!
Al2O3: melting point = 2072 C
MgO: melting point = 2852 C
And even SiO2 (the primary ingredient) has a melting point (range) of 1600-1725 C .
So I'm puzzling over how this can possibly work. Yet apparently it does work, as this is a real recipe.
I can blindly go ahead and do it, but would really like to understand how & why this can be.
I understand that impure crystals have lower melting points. But in searching these forums (and the web in general) I can find no discussion of deltas that big -- (MgO melting a full 1300 C lower than its pure MP?). It seems... surprising.
[Furthermore, the recipe seems to assume no such requirement of impure ingredients.]
So I figure I must be missing something. Probably something very fundamental.
My only idea is that maybe those higher-melting-point ingredients are not really melting. Maybe they are just dissolving in the lower-melting-point SiO2 liquid? (But even then, 1550C doesn't seem quite high enough to melt the SiO2 -- though with impurities, I guess it could.)
Is that it? Or am I indeed missing something?
Thanks much!