Glass: characterising with precision and efficiency

Glass can possess a quite diverse array of characteristics, depending on what ingredients one uses to modify it. A new process now makes the analysis of glass characteristics easier - up to five-times faster than predecessor methods, this process only requires 20 per cent of the material. Researchers will demonstrate the process at the Glasstec trade fair from October 23 to 26 in Düsseldorf.

At home, in the car or with industrial processes – glass is a universal material. Its properties are so extraordinary that frequently there are no alternatives to this material. Take, for example, high-temperature fuel cells, in which layers of ceramics and metals are alternately attached to each other - to ensure no explosive hydrogen escapes, the metal and ceramic layers must be firmly bound to each other, and the seam must be sealed tight.

Only glass, specifically solder glass, can accomplish this type of seal. But how does glass behave at such high temperatures? To what extent does it enlarge? Until now, this question was investigated using a push rod, which pushes from the glass onto a cylinder. If the glass heats up, then it expands and pushes back against the push rod. Were the glass to become molten, however, then it adheres to the push rod and renders it unusable. Even if seeking to create glass with new qualities, scientists need reliable, efficient and simple methods in order to investigate the characteristics of the glass.

Researchers from the Fraunhofer Institute for Silicate Research ISC in Wertheim, in southwestern Germany, have just developed a thermooptical measuring device that makes the comprehensive characterisation of glass possible. ''With our system, we can study all glass characteristics simultaneously for the first time ever – and that on a laboratory scale, in other words, with minimal sample material,'' says Dr. Andreas Diegeler, head of the Center of Device Development at ISC. This system consists of an oven that a CMOS camera ''looks into.'' This camera enables the researchers to observe the glass during the entire heating process.

The centerpiece for glass characterisation is the maximum bubble pressure module, which the scientists can use to measure the viscosity and the surface tension of the glass under molten conditions. The principle behind this concept? The glass is heated in a crucible made of quartz glass.

Since quartz glass has a higher melting point (about 1600 degrees Celsius) than other glass, the quartz glass crucible remains solid while the study glass slowly melts in it. A quartz glass capillary – in other words, a pipette with an inner diameter of one to three millimeters – is dipped, on a fully-automated basis, into the molten glass through a hole in the roof of the oven. A precisely defined volume of glass is likewise blown on a fully-automated basis through this pipette into the glass melt.