Soft Glass

Soft Glass

Borosilicate Glass -- A Brief History

From the laboratory standpoint, there are three main types of glass used today; borosilicate, quartz and soda lime or flint glass.

What is borosilicate glass, how is it different from other glasses, and why is it used so widely in laboratory research?

History

The formation of glass and glass products goes back to the beginnings of recorded history.

The invention of borosilicate glass is usually credited to Otto Schott, a renowned late 19th century German glassmaker. It was apparently first sold under the name "Duran" in Europe in 1893. In the United States, "Pyrex" became synonymous with borosilicate glass after Corning Glass Works inventor Joe Littleton introduced it to the English speaking world in 1915.

Though borosilicate glass was at first widely used for kitchen glassware, thermometer glass and railroad lanterns, there are now very few companies using it for that purpose, simply because it is more difficult to produce, and hence more expensive. And in the kitchen, the costs to the consumer more or less outweigh the benefits gained. There are, however, several small companies in the U.S. and abroad still offering colored borosilicate glass for the art glass market, and that market is still viable because of the durability and flexibility of borosilicate glass. It is also easy to work at low temperatures.

Because borosilicate glass melts at a higher temperature than other silicate glass, it was more complicated to bring into industrial production, and new techniques were required. New burners, using oxygen and natural gas, were developed. And for the most part, the manufacturing process has remained the same for the past 100 years or so. Borosilicate, because of its wide temperature range, strength and chemical  resistance, became "The Glass" for the laboratory.

The unofficial U.S. "capital" of glass blowing is Vineland, NJ. The reason Vineland got this distinction is very simple: The first production factory in the U.S. started just a few miles away in 1723. It was located there because of the proximity of necessary natural resources such as sand, seashells, and the evergreen trees of the New Jersey Pinelands. And of course, the subsequent proliferation of manufacturing firms and jobs in the area brought large numbers of glassblowers to the area, where they have remained throughout the years. The glassblowing techniques were handed down from grandfather to father to son.

Nowadays, very few glass companies actually "melt" borosilicate glass in the U.S.,  even in Vineland. Instead, virtually all area companies, such as Chemglass, Ace Glass, Wilmad-Lab Glass and Kimble-Kontes, are fabricators, purchasing "blanks" from large firms like Schott, Corning and Kavalier Glassworks and creating custom laboratory glassware such as round-bottom flasks, distillation apparatus, condensers, and much more.

Physical Characteristics

While "soft" glass is traditionally made from sand, sodium carbonate and calcium carbonate. Thus the name "soda lime". Boron is added to a much purer type silica sand in the manufacture of borosilicate glass. The composition of borosilicate glass is generally about 80%% silica, 10% boron oxide, 8% sodium oxide, 8% potassium oxide, and 1% aluminum oxide.

Borosilicate glass used in labware has a very low thermal expansion coefficient (32.5-33), which is about 1/3 that of "soft" glass. This reduces material stress caused by changes in temperature, and hence, the glass is more resistant to breakage. It is NOT invincible, though -- it will break or crack if dropped or otherwise impacted. Fortunately, it is much more likely to crack or snap rather than to shatter. It has a softening point (at which the glass may slump under its own weight) of 800°C is where glass blowers normally work it. The annealing point (the temperature at which residual strain or stress will relieve itself) at around 560°C.

Under "normal" laboratory conditions, borosilicate glass can withstand extended temperatures of around 230-240°C. For very short-term use, it will generally survive temperatures around 400°C. But the absolute maximum operating temperature for the formed glass is 450°C. Temperature changes from very hot to very cold should be also be avoided -- a maximum thermal shock differential of 160°C should be observed.

Borosilicate glass is very resistant to chemical corrosion, which makes it perfect for laboratory use. It can handle extremely volatile chemicals, and even nuclear waste! Everything has an Achillies heal and for borosilicate glass, it is flourines. Hydroflouric acid will etch borosilicate glass.

About the Author

Chuck Carney is Marketing Director at Ace Glass Incorporated, Vineland, NJ.

Does anyone drive the glass-topped Renault MeganeCC that THE ROOF DOES NOT LEAK?

My 4 year old beautiful sexy Renault MeganeCC leaks from somewhere where the door-seals and the doors meet. The problem became evident soon after purchase, and I read a lot of reviews, most of which complained about the roof leaking. For those of you who would like to answer this question and do not know this model - it is not the one with the soft top. The glass roof folds into the boot.

It would be interesting to know just how many of these models are being used that dont have leaking roofs. Thank you.

I'm afraid this is a very common problem. Peugeot 206/307cc's and the Ford Focus have been plagued by the same fault! I work in the motor trade and have yet to hear of a totally dry CC car!
I don't know if you bought the car new but you should have been able to claim it as a warranty fault.
I know one mechanic who was sent to Peugeot Head office to be trained specifically to deal with this!

Noah and the Whale Soft Glass