Low Temperature Melting of Glass at High Pressure

[phazzoo]

I have heard from an unreliable source that borostix/borobars are manufactured using a technique allowing them to be melted at low temperatures. I have heard temperatures as low as 300-400 degrees Celsius. These low melting temperatures are achieved by using very high pressures. I know that, according to the rules of thermodynamics, the melting temperature of a material can be decreased using high pressure if the phase transition results in a volume decrease. I don't understand enough to know if this concept can be applied to the creation of borostix. Does anybody know anything about this? I would be curious to hear what other people think. Thanks, this place is awesome.

[Abe Fleishman]

Hey Phazzoo I used to work for a company based in England that made pressed glass\ Borostixs. This is how they make them.
1. you take your glass and pigment\stain and add them to a spray dryer mixing tank that is filled with water at almost 150f-200f.
2. add carbon wax to the tank, this is used as a binder for the glass.
3. the glass, stain and the wax are then dryed to make a homoganized batch of powder.
4. the glass is then pressed in to the shape needed
5. then the glass is put in to a sentering furnace where the glass gets to almost 1900f this is how the glass becomes solid.
6. then presto you got borostixs.
Give me a call and I can tell you all about the process.
Peace
Abe NS\PC OG
866-684-6986

[Greymatter Glass]

Sounds like Abe's got the process pretty well spelled out....

but to answer your question... yes it would be possible, I think. I doubt it would be cost effective, but it could be done.

Commercial diamonds are made like that..... the original process used hardend steel plates to crush a sheet of graphite laced with crushed diamond "seeds" under many tons of pressure.

If you have acess to 2" tool steel plates and some hard moly bolts and heavy banding you can make your own in a kiln at around 2400F from what I've heard - never tried it myself.

anyways... to sinter glass under pressure would be a similar process. You'd clamp down the molds to several hundreds, maybe thousands of tons of pressure while cool. This is accomplished with basic hydraulic or pnuematic rams and hard alloy molds. Then heat the mold to near the fusing point of the glass. The added pressure should lower the melting point a bit and sinter the glass.

never heard of it in in practice anywhere... but I could see it would work. I think just heating an open mold to the fusing point is a more time and enery efficient process.

-Doug

[Abe Fleishman]

Good points Doug.
Preeure heating is very exspensive I looked in to it at one point and I stopped after I heard the cost.
Peace Abe
PC\NS OG

[Greymatter Glass]

well... a pressure cooker for getting colors that rely on barometric pressures shouldn't be too exsepnsive... but yeah, the pressure sintering is not a cheap process. It's used for making the highest quality diamond tools - they're fusion sintered under pressure and heat, instead of being plated into place with electroformed tin or nickel, they are pressed into the crystal matrix of the tool steel itself. they're usyally plated with nickel or chrome after that anyways, but that's not what holds them in place.

Some ceramic blades are fusion sintered as well.

It's usually used in processes where heat alone would not work for whatever reasons. If you press 2 pieces of similar crystaline materials together with enough pressure at a certain point they will fuse into a single piece from pressure alone. the pressure causes internal molecular friction which allows migration of atoms from surface to surface, eventually homogenizing and forming one cohesive unit. It can be done with glass, metal, ceramics, some stones, carbon, salts, all kinds of stuff.

in the case of glass, heat alone if usually sufficient, but if you needed to make crushed glass / frit filters, then you'd want to fusion sinter them so you get even porosity. That's about the only glass product I can think of off hand that's commonly sintered under pressure.

I could see how it might have some impact on the batching of color to take the batch to an extremely high pressure... in terms of crystal formation..... but any re-heating would distroy whatever effect you'd get anyways.

maybe striking certain colors under pressure.... but that would be dangerous and expensive to build a 50k psi vessel around a kiln.

...and I just realized I'm about 2 weeks late in getting one built for free.... oh damn....


gonna be another 3 years now.

-Doug

[Swampy]

At the other end of the scale; isn't float glass poured onto a bath of molten tin and all this inside a vaccuum chamber?

So then following your chain of thought, the float glass would be hotter than regular melting point of float glass?