Glass Ceramics & Composites

  SEM image of a glass ceramic Copyright: GHI

Glass ceramics are used in many fields of application in our daily lives due to their highly adjustable material properties. Among other things, the coefficient of thermal expansion, the strength and the optical properties can be controlled by the formation of one or more crystalline phases. The properties of the glass-ceramic depend on the properties and the proportion of the crystalline phase in the glass-ceramic.

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Malte Sander

Glass Ceramics & Composites

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+49 241 80 94967

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Intrinsic Functionalized Glass Ceramics

Glass sample placed inside of a plate capacitor Copyright: GHI Glass sample placed inside of a plate capacitor with schematic drawing of diffusion channels.

The crystallization of glass enables to adjust material properties such as the thermal expansion coefficient, strength or optical properties. Changes in the properties depend on the individual properties and proportion of the crystalline phase in the glass ceramic. Through the establishment of chemical gradients or the alignment of crystals by means of an electric field before or during the crystallization process, anisotropic properties should be induced in the material, allowing the glass ceramic to be functionalized. In the field of basic research, a new understanding of ion diffusion in glasses and glass-ceramics as well as crystallization should be obtained. In addition, the results should be used to produce glass ceramics with specific properties such as high strength, a defined coefficient of thermal expansion and defined surfaces.

 

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Jonas Hugo Hildebrand

Glass ceramics & composites

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+49 241 80 94976

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Influence of cold plasma on glass ceramics

Corona discharges at several wire tips Copyright: GHI Corona discharges at several wire tips over a glass sample. The glass rests on a grounded plate electrode.

The nucleation and crystallization behavior of glasses can be influenced and controlled in a variety of ways, for example by adding nucleating agents. However, external factors such as a defined furnace atmosphere or the application of an electric field during the ceramization process also have an effect on crystallization. Influencing glass properties by applying an electrical field at elevated temperatures (also known as thermal poling) can be done in various ways, for example by placing a glass between two capacitor plates. Another possibility is the so-called corona poling. Here, high electrical voltages of several thousand volts are applied to electrode tips and a corona discharge generates a plasma in the furnace chamber. Depending on the polarity of the applied voltage, negatively or positively charged ions are present, which cause different effects on the glass surface. Due to the open electrode configuration, there is also the possibility of interaction between glass and atmospheric components in the E-field. The effects of E-fields and different atmospheres on the structure and thereby changed mechanical properties of glass ceramics are to be investigated in an ongoing research project in order to be able to functionalize thse materials specifically for their application.

 

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Marin Bilandzic

Glass Ceramics & Composites

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+49 241 80 95396

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Laser Processing of Glasses and Glass Ceramics

Surface image of a sample Copyright: GHI Laser-scanning image of a sample

Glass can be machined by many different methods. A new type of method is the processing of glass using laser techniques. Depending on the choice of the laser source, laser parameterization and the selected glass compositions, different applications can be realized. By the adjustment and selection of the optimal material-laser interactions, various machining processes such as laser drilling and cutting, laser soldering, laser welding, laser polishing or complex 3D machining processes can be achieved. Thus, the fields of application are very widespread. Currently, the department is focusing on the ablative laser processing of dental glass ceramics in order to reduce the expensive tool wear of existing CAD-CAM systems. A further research project deals with the polishing of glasses and glass ceramics in order to reduce the surface roughness by means of optical finishing.