Microscopic Cracks Spoil The Transparency Of Glass, Nano-Researchers Find

A fundamental discovery about the behavior of cooling glass could have a significant impact on the glass- and plastic-making industries, say researchers at Lehigh University.

Himanshu Jain, Diamond chair and professor of materials science and engineering at Lehigh, says the breakthrough was made possible by a combination of nanoscopic science and an old-fashioned kitchen recipe.When molten glass is blown rapidly to make articles of desired shape, Jain's group found, its outermost surface, measuring a few nanometers in thickness, sustains microscopic fractures when it comes into contact with air. One nanometer equals one one-billionth of a meter.

These fractures are microns or nanometers in width and thus too small to be seen with the unaided eye, says Jain. But when they are exposed to an aggressive solution, such as a dishwashing soap, the cracks etch out, spread and begin to dissolve faster than the rest of the glass, leaving behind a dirty look that can not be cleaned away.

In reality, says Jain, the dirty look is merely light that is scattered by the numerous microscopic cracks.

Jain's group described their findings in an article titled "Inhomogeneous evolution of a glass surface via free, rapid expansion" in the Oct. 6, 2003, issue of Applied Physics Letters.

Previously, says Jain, scientists and glass-makers had assumed that under force molten glass expanded in a uniform manner and that finished glass was a chemically durable, homogeneous material.

Jain has spent more than two decades studying the unorganized arrangements and unpredictable movements of atoms in glass's non-crystalline structure.

Several years ago, he was asked by Unilever to figure out why, after being washed in a dishwasher, some wineglasses acquire a lined, milky look that can not be removed by further cleanings.

To solve the puzzle, Jain, his graduate student Anju Sharma, and Unilever collaborator Joseph O. Carnali, turned the prevailing assumptions about the properties of glass on their head and hypothesized that the surface of molten glass was solid and thus prone to cracking.

"We had to come up with a hypothesis because, using the traditional assumption that the surface was behaving like a liquid, we could not understand everything about the corrosion of the glass," he said.

With help from his 12-year-old daughter, Isha, Jain designed a home experiment to test his hypothesis.

The Jains started their experiment with a cooking pot. Using an Internet recipe for making hard candy, known by scientists as sucrose glass, they boiled a mixture of water and sugar, which mimics the molecular behavior of the soda and silica that are the main ingredients of commercial glassware.

When the hot syrup reached the consistency of viscous glass, Jain and his daughter used an empty ballpoint pen to simulate the blowing of glass.

When they studied the microstructure of the sucrose glass surface in detail, the Jains found tiny cracks, indicating that the surface had expanded not in a uniform fashion, like a liquid would, but in a non-uniform manner, as a solid would.

Encouraged by this initial observation, the Lehigh researchers conducted more sophisticated experiments in laboratory, blowing real glass and characterizing its expanding surface with electron microscopy.

"No one had imagined that the top nanometer or two of the surface was a solid," Jain said. "Our lab experiments had proved our hypothesis. Only the top of the surface fractured; the rest of the glass remained very homogeneous."

One factor contributing to the formation of the tiny cracks on the nano-surface, says Jain, is the fact that there is a very high temperature gradient at the glass surface.

Jain conducted his experiments using sucrose glass and real glass, but he believes plastics will behave similarly, although to a lesser degree, as plastic products are formed at lower temperatures.

"This is a quality-control issue for manufacturers," he said. "For nano-researchers, the lack of homogeneity on the nano-scale could be a serious problem that would need to be resolved as nanotechnology enters the market place."

600450 Microscopic Cracks Spoil The Transparency Of Glass, Nano-Researchers Find glassonweb.com
Date: 14 October 2003
Source: Sciencedaily.com

See more news about:

Others also read

Local quality glass producer Emirates Glass Limited has won contracts to supply 68,000 square metres of its high quality EmiCool glass to five major projects in Dubai.
Southwall Technologies Inc. (Nasdaq:SWTX), a global developer, manufacturer and marketer of thin-film coatings for the electronic display, automotive glass and architectural markets, today announced that on Dec. 18, 2003, it secured an agreement for a new bank loan guarantee and equity financing package of up to $7.5 million from Needham & Company, Inc., its affiliates and Dolphin Asset Management.
Praxair, Inc. (NYSE: PX) today announced that its subsidiary Praxair Canada Inc.'s specialty gases plant in Paris, Ontario, Canada, is one of Praxair's first specialty gases plants in North America to complete the upgrade to ISO 9001:2000, the latest ISO 9000 standard for quality.
KUB Malaysia Bhd has accepted an offer from Nippon Sheet Glass Co Ltd (NSG) to acquire its 15% stake in Malaysian Sheet Glass Bhd (MSG) for RM32.6 million in cash, or RM2.68 per share.
Co-Ventures in Glass Containers (CVIGC, Ltd.) of Tampa, Florida, USA and Micro-Tek Canada, Inc. Of Toronto, Canada are excited to announce the beginning of a long term joint venture to combine their extensive experiences and resources to offer the Glass Container Industry globally a best value alternative for all their outsourcing needs in manufacturing, operations and technical assistance agreements, specifically targeted to the smaller manufacturers who have found the larger service companies to be cost and profit prohibitive.The principals of the two companies have found a global need for smaller glass companies who require excellent technical resources to properly compete within the industry without the high costs of employing their own staffs or outsourcing their requirements to the larger service companies whose own operating costs and overhead are substantial.
China's largest automobile glass maker Fuyao Glass Industry Group Co, Ltd, won its case against the dumping ruling of the US Department of Commerce (DOC).

Add new comment