Search Results
Mechanical properties of microstructurable glasses
Microstructurable glasses of the system Li2O-Al2O3-SiO2 are objects of research at the Ilmenau Technical University, Department of Glass- and Ceramics Technology. These glasses also contain alkali oxides and dopants. The dopants are important for the microstructuring. Main directions of research are: the special glass materials, structuring technologies, joining processes and applications. The glasses can be structured with a photolithographic process. This process consists of the following steps: UV exposure, thermal treatment and etching. Using this standard process and variations it is possible to make through structures (e.g. holes), structures with a defined depth, structures with various depths and three-dimensional structures without undercut. Different glass sheets can be joined with a thermal process. Depending on the thermal expansion coefficient glass/metal compounds may be realized by microelectroplating. Deformable structures are very important for applications in the field of measurements and sensors, microgripping technique and microactuators. It is thus necessary to characterize the mechanical properties of these glass structures.
UV laser radiation for microstructuring of photostructurable glasses
Photostructurable glasses are important materials for applications in microsystems. They enable structures with high aspect ratios and a high dependability of mechanical, optical and chemical properties in a large range of temperatures. The exposure of photostructurable glasses to UV laser radiation, as a rapid prototyping technique, is an alternative method to the exposure by a mask aligner. Α photostructurable glass (FS21) was exposed to UV laser radiation of the wavelengths 248, 308 and 355 nm. Investigated was the influenee of the exposure parameters wavelength of laser radiation and energy density on structuring results such as crystallization depth, lateral geometry of crystallized areas, structure of crystallized areas and etch angle for single pulse exposure.
Forming of noncircular cross-section SiO2 glass fibers
Silica glass fibers with triangular and rectangular cross-sections have been produced by two different means, namely preform drawing and powder extrusion. For the preform drawing method, silica glass rods were machined and polished to yield preforms with the desired cross-sections. These were then heated to temperatures in excess of 1600°C and drawn to fibers with approximately 265 μm × 265 μm × 265 μm triangular and 275 μm × 100 μm rectangular cross-sections exhibiting tensile strengths between 300 and 400 MPa and bending radii smaller than 50 mm. For the extrusion route, a silica nanopowder was compounded at ≈ 150°C with a polyethylene-based binder and extruded at similar temperatures through dies with the desired exit cross-section. The fibers were debound by thermally decomposing the binder and sintered at 1100°C to yield amorphous glass fibers with approximately 205 μm × 205 μm × 205 μm triangular and 275 μm × 90 μm rectangular cross-sections. Although the two manufacturing processes are radically different, both involve flow of a fluid with a temperature-dependent viscosity and this dictates that shape trueness (i.e. flat faces and sharp corners) is a function of the drawing and extrusion rates and the temperature during drawing and sintering.
Fabrication of SiO2 glass fibres by thermoplastic extrusion
The fabrication of silica glass fibres by thermoplastie extrusion of nanosize and micron SiO2 powders has been investigated. The powders were mixed with a binder system, compounded for 3 h at 150 °C, and finally extruded through a die with a 500 μm-diameter die land. After debinding the green fibres at 500 °C, these were sintered for 1 h at 1100°C under air to yield glassy and crack-free silica fibres with a final diameter of 400 μm. The effect of the two different particle size distributions as well as the influence of varying powder loading (between 38 and 58 vol.%) on the rheological properties of the feedstocks were analysed using capillary rheometry. The debinding and sintering behaviour was also investigated using mercury intrusion porosimetry, thermal gravimetrie analysis and dilatometry.
Processing techniques for photostructurable glasses
Photostructurable glasses have been known for a long time. Through miniaturization they can be used as micromechanical components, e.g. sensors, grippers, additional components for analytical Instruments, microactuators, fluid and optical components, and numerous other applications. At the Technical University of Ilmenau (Department of Glass and Ceramic Technology) various photostructurable glasses have been developed in the last decade. Additionally, many process-technical investigations were carried out. As a result of these investigations specific parameters were determined creating a basis for the conception of a modular system for the fully automated production of micromechanical glass components. The modular system consists of three modules for the main steps of the process: exposure module, curing module and etching module. Additionally there is a cleaning process integrated in a separate part of the exposure module. The application of the glass wafers is realized by an input magazine, the processed wafers are placed in an output magazine. The system is calculated for small and medium-sized companies and the processing of 10 000 wafers per year.
Electromagnetic stirring of glass melts using Lorentz forces - Experimental results
The question as to whether it is possible to stir glass melts using electromagnetic (Lorentz) forces has been controversially discussed in the past. Α series of accurate experiments is reported in which the buoyancy driven motion of a directly electrically heated glass melt in a cylindrical crucible has been modified by applying an external alternating magnetic field. Using temperature measurements directly in the melt it is demonstrated for the first time that the Lorentz force created in the melt leads to a homogenization of the temperature and density distributions because of an enhancement of the flow. Moreover, evidence is provided for an improvement of the glass homogeneity. The feasibility analysis provides rational possibilities for the application of magnetic fields for electromagnetic flow control in glassmaking processes.