'pyrex' Vs. Borosilicate. Lab Grade Pyrex

[RSullivan]

 

This post is not intended to start a discussion on 'Is Pyrex safe'.

This is simply intended to be informational.

If you are happy with your Pyrex containers more power to you!

 

I am a newbee.

 

Thanks to Dave 

('Vodkaman' http://www.tackleunderground.com/community/user/14497-vodkaman)

for suggesting I look at laboratory supplies for a container I was

looking for. 

 

While I was shopping I asked myself 'What is Pyrex' and found it to be

nothing more than a trademark. The term 'Pyrex' pretty much has nothing 

to due with the material and characteristics of a 'Pyrex' container.

 

We all understand that damage to the structural integrity of a 

Pyrex container (cracks, scratches, constant heating / cooling)

can cause the container to fail. We also understand that rapid

and extreme temperature changes to the Pyrex container can also cause

a failure to the container.

 

These failures can sometimes be catastrophic (i.e. 'exploding').

 

Caution: This information is gathered from the Internet!

 

Here is the Wiki page for Pyrex:

https://en.wikipedia.org/wiki/Pyrex

 

Here is the wiki page for borosilicate:

https://en.wikipedia.org/wiki/Borosilicate_glass

 

Some information on exploding Pyrex:

http://www.snopes.com/food/warnings/pyrex.asp

 

 

Synopsis:

1.) Pyrex was trademarked and manufactured by Corning from 1915-1997.

2.) Coring manufactured Pyrex from borosilicate glass.

3.) Starting in 1998 Corning licensed the brand name 'Pyrex' to various companies

    (The largest: World Kitchens, LLC).

4.) Domestically (U.S) all of these licencees seem to manufacture 'Pyrex' from 

    from soda-lime glass, not borosilicate glass.

5.) Non-domestically (Europe, The manufacturer seems to be ARC International) 

    borosilicate glass still seems to be used for 'Pyrex' branded products.

6.) World Kitchen claimed the moved from borosilicate to soda-lime glass was

    dues to the fact that soda-lime glass was cheaper to produce and has a 

    higher mechanical strength(*) (more resistant to breakage when dropped).

7.) Soda-lime glass IS NOT HEAT RESISTANT. This leads to the increase in the 

    potential for breakage from heat stress.

8.) IN 2010 Consumer reports investigated Pyrex branded containers breaking at high 

    temperatures and found it to be due to the use of World Kitchen branded Pyrex

    manufactured with tempered flint glass.

 

So, just because it says 'Pyrex' one really has no idea what it is manufactured 

from.

 

It seems that almost all 'lab grade' Pyrex is still manufactured from 

borosilicate. Myself being over cautious, am ordering lab grade (borosilicate)

Pyrex beakers from a laboratory supply house. My rational:

1.) If I drop or bang the borosilicate container I will know it.

    The container will be 'suspect' to me, but this would also be true

    for a soda-lime based container. Either way I would probably throw the 

    container away rather than risk an explosion / shattering.

2.) I would be far less fearful integrity degradation with a 

    borosilicate container due to micro cracks developing from repetitive

    heating and cooling.

 

(*)

Mechanical strength (Young's Modulus):

Soda-lime:    72 (Container)

borosilicate: 64

 

So borosilicate is in fact more 'fragile' than soda-lime, but it seems

pretty close to me.

 

Mechanical strength is not the same thing as 'hardness'.

 

 Knoop hardness:

 Sodium Chloride (Table Salt):     18.2

 Soda-Lime Glass:                 490

 borosilicate Glass:              470

 

So it does not seem possible that salt can scratch

Soda-lime or borosilicate Glass? Being a newbee I am wondering how

people are ending up with 'scratched' Pyrex containers?

 

Temperature differential:

Soda-Lime glass.    99 degrees Fahrenheit.

Borosilicate glass: 330 degrees Fahrenheit.

 

The low Temperature differential seems to be what causes micro-cracks

in soda-lime glass (repetitive heating / cooling). Eventually liquid

will get into the micro-cracks which is the major cause of exploding 

containers.

 

 

[Vodkaman]

Quite an eye opener - good work.

DAve

[MonteSS]

People still use Pyrex/glass cups.

 

Norpro silicone is where its at

[Ccfish]

I think the scratches come from stirring with metal utensils.

[mark poulson]

Thinner walls adjust to differential heating more quickly, so there is less heat/cool stress with a thin walled glass beaker.

[camrynekai]

Nice info!!!!