RogueRose
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Boro glass vs Quartz - both are SiO2 so how are they different?
I've been confused since I read about quartz being able to handle higher temps and when I researched it I found that both sillica dioxide and quartz
are both SiO2 - so how do they differ? I read that the boro has a lower % of SiO2 as it has boron in it and quartz has a much higher purity over all.
Are pieces (flasks, beakers, etc) made of the same material just the quartz has less (if any) boron, or is a special SiO2 used for quartz?
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Elemental Phosphorus
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Borosilicate contains boron oxides but is mostly comprised of silicon dioxide with just a few percent of B2O3, quartz is pure SiO2. SiO2 is much
tougher against high heat, but borosilicate is cheaper. Borosilicate is fine for normal heating and lab use.
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Deathunter88
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Quartz glassware is truly amazing, you can dunk a piece of it red hot into cold water and it won't break.
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Texium
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Thread Moved
27-3-2017 at 10:39 |
Amos
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Borosilicate glassware isn't desirable over quartz, but it is much cheaper to make due to the boron oxides acting as a flux to reduce melting and
working temperatures. Also consider that while silica from ordinary sources such as sand or natural quartz may be used by borosilicate makers, fused
quartz glassware usually uses high-purity chemically derived silicon dioxide.
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PirateDocBrown
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Borosilicate is about 13% B2O3, 1-2% Al2O3, 4% or so Na2O, and the rest SiO2.
Of course fused quartz is 100% SiO2.
By contrast, regular flint (soda-lime) glass that windows and bottles are made of is 7-14% CaO, 9-15% Na2O, sometimes small amounts of MgO and Al2O3,
and the rest SiO2.
Naturally, such widely different compositions mean great differences in thermal expansion coefficients.
Borosilicate is under 4 ppm per degree change, while flint runs 6 to 9 ppm/K.
Fused silica is a whole different ball game, it's about 0.5 ppm/K. In addition, it has considerably higher strength, so it can withstand what thermal
strain there is.
Why don't we use it much in the lab, then? In a word: cost. Making it requires very high temperatures, and you have to make sure the silica does not
crystallize upon cooling. Naturally, it cannot be lampworked into custom equipment, either. So it's mostly reserved for high-heat applications.
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RogueRose
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Quote: Originally posted by PirateDocBrown  | Borosilicate is about 13% B2O3, 1-2% Al2O3, 4% or so Na2O, and the rest SiO2.
Of course fused quartz is 100% SiO2.
By contrast, regular flint (soda-lime) glass that windows and bottles are made of is 7-14% CaO, 9-15% Na2O, sometimes small amounts of MgO and Al2O3,
and the rest SiO2.
Naturally, such widely different compositions mean great differences in thermal expansion coefficients.
Borosilicate is under 4 ppm per degree change, while flint runs 6 to 9 ppm/K.
Fused silica is a whole different ball game, it's about 0.5 ppm/K. In addition, it has considerably higher strength, so it can withstand what thermal
strain there is.
Why don't we use it much in the lab, then? In a word: cost. Making it requires very high temperatures, and you have to make sure the silica does not
crystallize upon cooling. Naturally, it cannot be lampworked into custom equipment, either. So it's mostly reserved for high-heat
applications. |
Great info here! Thank you. Can you explain what you mean by the part I put in bold?
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XeonTheMGPony
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It means you can't use alcohol lamps and such to bend tubing, to task.
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PirateDocBrown
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Borosilicate can be worked into useful shaped using equipment found in a typical glassblowing shop.
Fused silica cannot, due to its high softening point, out of reach for a typical glassblower.
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PirateDocBrown
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While that is true, "lampworking" here is a term of art, meaning worked with a higher temperature flame than a mere alcohol lamp. What's meant is the
typical setup used by lab glassblowers, with a convective air/fuel (propane or butane, NG doesn't have a very high flame temp) torch.
In the absence of anything better, I often lampwork with a Burnz o Matic propane torch.
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Chemetix
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So long as you have oxygen as part of the torch setup, quartz can be worked just like boro in a flame....you just need more of it. Bigger torch tips
and more flame than what you would use for the same job in boro. The real trick with quartz is the right eyeware, welders tinted glasses can be used
so long as it's a heavier tint. Quartz goes white hot at working temperature and the glare is intense. The only other trick with working with quartz
it getting used to it's toffee like consistency. It's sticky and firm, and slow to work.
Actually once you have got the hang of working under these conditions, the advantage is that it's hard to crack due to lack of annealing, which is all
but guaranteed with soda glass, and a crap shoot with boro.
A final word on quartz is that the finished job is messy, you end up with with a white coating of SiO2 as nano spheres over the area being worked.
There's a trick to removing it with a flame, but again, it's slow.
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Morgan
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I was wondering what the process was/venture a guess for making this cristobalite surface treatment on quartz?
"For high temperature applications Heraeus offers quartz
glass tubes as HSQ® 400 with better temperature stability
(less sagging). These tubes have been impregnated with
an agent to trigger cristobalite formation. The crystal layer
supports the glass, resulting in significantly lower sagging
of the tube."
**HSQ®400: Higher aluminium content on the outer surface due to chemical stabilization coating.
"Tubes made of these materials can be stabilized with a special surface treatment. Stabilization is achieved by including a thin (approx. 20 μm)
uniform layer of cristobalite to form on the outer tube surface upon its first exposure to elevated temperature."
https://en.wikipedia.org/wiki/Cristobalite
As an aside I've some large rocks of black obsidian like the one pictured in the Wiki above but didn't know cristobalite would form on it.
"It is possible to rapidly quench thin particles of quartz glass from over 1000 °C by plunging them into cold water without breakage. However, it is
important to realize that the thermal shock resistance depends on factors other than CTE such as surface condition (which defines strength) and
geometry. The various types of fused silica and fused quartz have nearly identical CTE’s and thus can be joined together with no added risk of
thermally induced breakage."
https://www.heraeus.com/en/hca/fused_silica_quartz_knowledge...
[Edited on 19-12-2020 by Morgan]
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BromicAcid
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Our company glass shop used to repair quartz labware although they didn't do straight fabrication themselves. I talked to one of the head people down
there and had them contact me when they did some quartz work because I was willing to make the two hour round trip just to say I saw it. One word -
Bright! Heating the quartz hot enough to work, bright white light unlike regular borosilicate. Very cool. As Chemetrix pointed out, you get
dusting. I personally didn't notice anything but one of the reasons pointed out for me for them not doing more work is the air handling / ventilation
requirements. Glad I got to see it since we have stopped working with quartz in house since then.
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Morgan
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Going off topic, the quartz nano spheres dust mention brought to mind this glass getting caught up in the wind, kind of interesting if you haven't
seen it.
Pele's hair
https://youtu.be/COADsCTSzT4
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rockyit98
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i won't recommend it but its possible.
even BSi glass can be heated with out cracking it's susceptible to cracking after fact, NileRed had to destroy his set of beakers because thermal
stress in them kept suddenly breaking after his microwave experiment. Link to it-https://www.youtube.com/watch?v=tGqVMbAQhBs
[Edited on 20-12-2020 by rockyit98]
"A mind is a terrible thing to lose"-Meisner
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