Entwicklung eines Verfahrens zur kontrollierten Expansion von feinstdispersen Perlit-Rohsanden
Research output: Thesis › Doctoral Thesis
The main focus of this multi-annual research work was the development of a process to expand finely dispersed perlite sands by means of a purely electrically heating system in order to achieve a controlled expansion. This process, referred as Bublite-process, should complement the Bublon®️-process, which was already successfully introduced into the market by Bublon GmbH (situated in Gleisdorf, Austria), in terms of extending the processable grain size range towards finer fractions (< 100 µm). The present work is divided into seven chapters, which can be assigned into three main parts: The first part, which is described in chapters 3 and 4 (with a brief introduction and task description in chapters 1 and 2), deals with the mineral perlite in different perspectives. Based on chemical and thermal analysis, it was explained that the water content has significant influence on the viscosity of the glassy structure of perlite, during the heating and expanding process. It is estimated that the water causes a decrease of around 102 Pa s, whereby the expansion becomes possible at all. Also, the variance of the SiO2-content (approx. 2 %) has a significant influence on the viscosity. By means of a microprobe with spatial resolution, inhomogeneous distributions of alkali-elements within the grain were found. The shapes of the distributions remind of those from splinter-like fragments, which are typical for perlite, when crushed. This may implicate a link, explained by a weakened structure at the respective spots. Additionally, conventional expansion processes and with Bublon®️-/Bublite-Spheres comparable products, which are listed as follows, are discussed, showing a potentially broader use of this product. •Cenospheres from black coal power plants •Foamed glass beads from recycled glass •Hollow glass beads •Expanded clay granulates To produce the mandatory fine and narrow grain fraction for the Bublite-process on an industrial scale, it was found that a tumbling screen is the most efficient way to do so if meshes are kept open, by the means of ultrasonic declogging systems. Laboratory trials showed that pretreating the raw perlite of Turkish origin to remove unexpandable particles will not lead to satisfying results. The second part of the research work is described in chapters 5 and 6. It summarizes the designing, erecting and commissioning stages of the Bublite-testing unit, as well as the trials of the functionality of this expansion furnace. The dispersing unit was identified to be the most critical part of the process. For its correct design, CFD-simulations were performed. Three different configurations were built and examined in the trials, of which two configurations used a multiple-deflector-plate-diffusor as a basis. The third configuration used a so-called suction-pocked-solution. Preheating the dispersing air for reducing convectional cooling of the perlite grains proved to be indispensable for good expansion results. In the third part, which can be found in chapter 7, the properties and possible applications of the expanded perlite granulates are discussed. It was also observed that there is quadratic correlation between mechanical compressive strength and the bulk density. In order to achieve higher qualities of the expanded granulate in terms of lower densities, density separation is to be considered the most promising method, if compared to magnetic and electrical separation. It was also examined, how the expanded perlites would perform as lightweight functional filler granulate in polymers. It could be observed that by adding the filler to the polymer in an injections molding process, the Young’s modulus (max. 58 %) and the elongation at break (max. 42 %) could be increased significantly. It was also observed that warping and shrinkage behavior of 3D-printed (FDM) parts was improved when Bublite-granulate was added to the compound.
|Translated title of the contribution||Development of a process for the controlled expansion of finely dispersed perlite raw sands|
|Publication status||Published - 2019|