The Science Times section (Tuesday, July 7) of the NY Times has a very interesting article on how material chemists and engineers are studying and altering the molecular structure of the various types of glass to use them in new and unique ways. Students in the Forensic Science course at Bronxville High School examine many of the different types of glass discussed in this article and learn how to distinguish them (using density and refractive index) when found at a possible crime scene. Our students examine samples of soda glass, lead crystal glass, borosilicate glass, tempered glass and laminated glass.
Today's article describes the difference between tempered glass and laminated glass in simple terms and explains glass as an amorphous solid that is strengthened (tempered) by compressing the outer atoms using heat or chemical means. The advantage of tempering a piece of glass is that more tensile force is needed for cracks to appear/grow. Also this additional force and the imbalance created between the outer compressional forces and the inner tensile forces of tempered glasses make it break into many smaller pieces which are less likely to cause injury. This is why tempered glass is used to form the side and rear windows of automobiles. The article talks about Prince Rupert's drop as an illustration of this process. Laminating glass adds additional strength by using adhesives and polymer sheets to join glass layers together. Laminated glass is used to form the windshields of automobiles.
The article introduces the reader to ways in which engineers and scientists re-examine and test the structure of glass to make this ancient material stronger and less expensive to produce.
Links: Science Times Article NY Times Slide Show of Structural Uses of Glass You Tube Video of Prince Rupert's Drop You Tube Video of Annealing Glass (Explains how stress in glass is relieved)