TY - JOUR A1 - Hildebrand, Jörg A1 - Hecht, Kerstin A1 - Bliedtner, Jens A1 - Müller, Hartmut T1 - Laser Beam Polishing of Quartz Glass Surfaces JF - Physics Procedia N2 - The laser beam is a small, flexible and fast polishing tool. With laser radiation it is possible to finish many outlines or geometries on quartz glass surfaces in the shortest possible time. It's a fact that the temperature developing while polishing determines the reachable surface smoothing and, as a negative result, causes material tensions. To find out which parameters are important for the laser polishing process and the surface roughness respectively and to estimate material tensions, temperature simulations and extensive polishing experiments took place. During these experiments starting and machining parameters were changed and temperatures were measured contact-free. KW - Laser KW - Quarzglas KW - Polieren KW - Berührungslose Messung KW - Temperatur KW - Laser; quartz glass; polishing; temperature; residual stress; simulation; contactless measurement Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170418-31366 UR - http://www.sciencedirect.com/science/article/pii/S1875389211001350 SP - 452 EP - 461 ER - TY - JOUR A1 - Hildebrand, Jörg A1 - Hecht, Kerstin A1 - Bliedtner, Jens A1 - Müller, Hartmut T1 - Advanced Analysis of Laser Beam Polishing of Quartz Glass Surfaces JF - Physics Procedia N2 - The laser beam is a small, flexible and fast polishing tool. With laser radiation it is possible to finish many outlines or geometries on quartz glass surfaces in the shortest possible time. It’s a fact that the temperature developing while polishing determines the reachable surface smoothing and, as a negative result, causes material tensions. To find out which parameters are important for the laser polishing process and the surface roughness respectively and to estimate material tensions, temperature simulations and extensive polishing experiments took place. During these experiments starting and machining parameters were changed and temperatures were measured contact-free. The accuracy of thermal and mechanical simulation was improved in the case of advanced FE-analysis. KW - Laser KW - Berührungslose Messung KW - Polieren KW - Empfindlichkeit KW - Quarzglas KW - laser; contactless measurement; quartz glass; polishing; temperature; residual stress; simulation; sensitivity Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170418-31372 UR - http://www.sciencedirect.com/science/article/pii/S1875389212025667 SP - 277 EP - 285 ER - TY - JOUR A1 - Partschefeld, Stephan A1 - Tutal, Adrian A1 - Halmanseder, Thomas A1 - Schneider, Jens A1 - Osburg, Andrea T1 - Investigations on Stability of Polycarboxylate Superplasticizers in Alkaline Activators for Geopolymer Binders JF - Materials N2 - Calcined clays are interesting starting materials to be used as SCMs (supplementary cementitious materials) in cements or to be converted to geopolymers by activation with a high alkaline activator. The adjustment of the properties in the fresh state, especially regarding the consistency of these binders, is almost exclusively achieved by the addition of water, since commercially available superplasticizers seem to be ineffective in low-calcium geopolymer systems. The aim of this study was a systematic investigation of various PCE (polycarboxylate ester/ether) superplasticizers (methacrylate ester PCE: MPEG, isoprenol ether PCE: IPEG, methallyl ether PCE: HPEG) with respect to their stability in different alkaline activators (NaOH, KOH, sodium and potassium silicate solutions). The effectiveness of superplasticizers (SPs) in low-calcium geopolymer binders was verified by rheological tests. Size exclusion chromatography was used to investigate if structural degradation of the superplasticizers occurs. The investigated PCE superplasticizers showed a thickening effect in the low-calcium geopolymer system. Depending on the alkalinity of the activator solution, a degradation process was detected for all the PCEs investigated. The side chains of the PCEs are cleaved off the backbone by basic ester and ether hydrolysis. The highest degree of degradation was found in sodium and potassium silicate solutions. In alkaline hydroxide solutions, the degradation process increases with increasing alkalinity. KW - Geopolymere KW - Verflüssigung KW - metakaoline KW - superplasticizer KW - polycarboxylate ether KW - OA-Publikationsfonds2023 Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20231026-64809 UR - https://www.mdpi.com/1996-1944/16/15/5369 VL - 2023 IS - Volume 16, issue 15, article 5369 SP - 1 EP - 14 PB - MDPI CY - Basel ER - TY - JOUR A1 - Tutal, Adrian A1 - Partschefeld, Stephan A1 - Schneider, Jens A1 - Osburg, Andrea T1 - Effects of Bio-Based Plasticizers, Made From Starch, on the Properties of Fresh and Hardened Metakaolin-Geopolymer Mortar: Basic Investigations JF - Clays and Clay Minerals N2 - Conventional superplasticizers based on polycarboxylate ether (PCE) show an intolerance to clay minerals due to intercalation of their polyethylene glycol (PEG) side chains into the interlayers of the clay mineral. An intolerance to very basic media is also known. This makes PCE an unsuitable choice as a superplasticizer for geopolymers. Bio-based superplasticizers derived from starch showed comparable effects to PCE in a cementitious system. The aim of the present study was to determine if starch superplasticizers (SSPs) could be a suitable additive for geopolymers by carrying out basic investigations with respect to slump, hardening, compressive and flexural strength, shrinkage, and porosity. Four SSPs were synthesized, differing in charge polarity and specific charge density. Two conventional PCE superplasticizers, differing in terms of molecular structure, were also included in this study. The results revealed that SSPs improved the slump of a metakaolin-based geopolymer (MK-geopolymer) mortar while the PCE investigated showed no improvement. The impact of superplasticizers on early hardening (up to 72 h) was negligible. Less linear shrinkage over the course of 56 days was seen for all samples in comparison with the reference. Compressive strengths of SSP specimens tested after 7 and 28 days of curing were comparable to the reference, while PCE led to a decline. The SSPs had a small impact on porosity with a shift to the formation of more gel pores while PCE caused an increase in porosity. Throughout this research, SSPs were identified as promising superplasticizers for MK-geopolymer mortar and concrete. KW - Geopolymere KW - Metakaolin KW - Superplasticizer Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20210804-44737 UR - https://link.springer.com/article/10.1007%2Fs42860-020-00084-8 VL - 2020 IS - volume 68, No. 5 SP - 413 EP - 427 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Partschefeld, Stephan A1 - Wiegand, Torben A1 - Bellmann, Frank A1 - Osburg, Andrea T1 - Formation of Geopolymers Using Sodium Silicate Solution and Aluminum Orthophosphate JF - Materials N2 - This paper reports the formation and structure of fast setting geopolymers activated by using three sodium silicate solutions with different modules (1.6, 2.0 and 2.4) and a berlinite-type aluminum orthophosphate. By varying the concentration of the aluminum orthophosphate, different Si/Al-ratios were established (6, 3 and 2). Reaction kinetics of binders were determined by isothermal calorimetric measurements at 20 °C. X-ray diffraction analysis as well as nuclear magnetic resonance (NMR) measurements were performed on binders to determine differences in structure by varying the alkalinity of the sodium silicate solutions and the Si/Al-ratio. The calorimetric results indicated that the higher the alkalinity of the sodium silicate solution, the higher the solubility and degree of conversion of the aluminum orthophosphate. The results of X-ray diffraction and Rietveldt analysis, as well as the NMR measurements, confirmed the assumption of the calorimetric experiments that first the aluminum orthophosphate was dissolved and then a polycondensation to an amorphous aluminosilicate network occurred. The different amounts of amorphous phases formed as a function of the alkalinity of the sodium silicate solution, indicate that tetrahydroxoaluminate species were formed during the dissolution of the aluminum orthophosphate, which reduce the pH value. This led to no further dissolution of the aluminum orthophosphate, which remained unreacted. KW - Geopolymere KW - geopolymer KW - berlinite KW - sodium silicate solution KW - alumosilicate KW - OA-Publikationsfonds2020 Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20210122-43378 UR - https://www.mdpi.com/1996-1944/13/18/4202 VL - 2020 IS - Volume 13, issue 18, article 4202 SP - 1 EP - 16 PB - MDPI CY - Basel ER -