TY - JOUR A1 - Sturm, Patrick A1 - Greiser, Sebastian A1 - Gluth, Gregor A1 - Jäger, Christian A1 - Brouwers, H.J.H. T1 - Degree of reaction and phase content of silica-based one-part geopolymers investigated using chemical and NMR spectroscopic methods JF - Journal of materials science N2 - One-part geopolymers were synthesized from two different silica materials (a silica-rich residue from chlorosilane production and a commercial microsilica) and sodium aluminate at three different SiO2/Al2O3 ratios and a nominal water/solids ratio of 0.5. The degree of reaction of the silica in the cured geopolymers (i.e. the fraction of silica dissolved to form aluminosilicates and minor products) was determined using two different methods: chemical attack with HCl to dissolve the reaction products and evaluation of peak areas of 29Si MAS NMR spectra. It was found that the degree of reaction of the silica decreases with increasing the silica content of the starting mix, and that it is almost constant after 1 day of curing and almost independent from the kind of starting silica. From the results of the NMR-based method, the mean SiO2/Al2O3 ratio of the reaction products (aluminosilicates and minor products) can be estimated to be ca. 2.0, nearly independent of the starting composition of the geopolymers. The dissolution method is biased, but of sufficient precision to be useful for following changes of the degree of reaction. Major crystalline phases in the cured geopolymers are zeolite A and/or hydrosodalite. Depending on the starting composition, the relative amounts of these zeolites vary; additionally, sodalite (only for the residue from chlorosilane production with >1 wt% Cl-), faujasite, and zeolite EMT can appear in the geopolymers. The 29Si and 27Al MAS NMR results indicate mainly Si(4Al) and Al(4Si) sites, in line with the presence of zeolite A, hydrosodalite, sodalite, and geopolymeric gel of comparatively low SiO2/Al2O3 ratio. KW - Geopolymers KW - One-part mix KW - 29Si MAS NMR KW - 27Al MAS NMR KW - Silica KW - Degree of reaction PY - 2015 DO - https://doi.org/10.1007/s10853-015-9232-5 SN - 0022-2461 SN - 1573-4803 VL - 50 IS - 20 SP - 6768 EP - 6778 PB - Springer Science + Business Media B.V. CY - Norwell, Mass. AN - OPUS4-33826 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Greiser, Sebastian A1 - Sturm, Patrick A1 - Gluth, Gregor A1 - Hunger, M. A1 - Jäger, Christian T1 - Differentiation of the solid-state NMR signals of gel, zeolite phases and water species in geopolymer-zeolite composites JF - Ceramics International N2 - Geopolymer-zeolite composites were synthesized using a silica-rich industrial byproduct from chlorosilane production and sodium aluminate. Pastes were cured at 80 °C and 80% RH, and subsequently dried in two different climates: at 23 °C and 50% RH, and under vacuum. 1H MAS, 23Na MAS and 29Si MAS NMR and XRD measurements were performed after the drying procedures as well as after subsequent aging. Zeolite Na-A was found beside traces of faujasite-type zeolite and zeolite EMT as major crystalline phases in the cured composites; the fraction of geopolymeric gel in the reaction products was determined to be ~18% on a molar basis. Various water species could be distinguished using 1H MAS and 1H-29Si CP MAS NMR, applying rotorsynchronized echo experiments. The largest fraction of the pore water resides in the α-cages of the zeolite Na-A and in the geopolymeric gel; in addition, water exists in the β-cages of the zeolites and adsorbed at sodium ions. The water species in α-cages and in the pores of the geopolymeric gel exhibit slightly different chemical shifts of 4.7 ppm and 4.9 ppm, respectively, in the 1H MAS NMR spectra. Changes of the water content in the geopolymer pores of differently dried samples were observed and led to slightly varied chemical shifts in the 29Si MAS NMR spectra too. Measurements after more than 500 days revealed no significant aging effects of the composites, which confirm their chemical stability. KW - Geopolymers KW - Aluminosilicate inorganic polymers KW - Zeolite Na-A KW - Spectroscopy KW - Drying PY - 2017 DO - https://doi.org/10.1016/j.ceramint.2016.11.004 SN - 0272-8842 VL - 43 IS - 2 SP - 2202 EP - 2208 PB - Elsevier AN - OPUS4-38694 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sturm, Patrick A1 - Gluth, Gregor A1 - Jäger, Christian A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten T1 - Sulfuric acid resistance of one-part alkali-activated mortars JF - Cement and Concrete Research N2 - One-part alkali-activated (geopolymer) mortars based on three different silica-rich starting materials and sodium aluminate, with and without ground granulated blast furnace slag (GGBFS) addition, were tested regarding sulfuric acid resistance according to DIN 19573:2016-03 (70 days at pH = 1). Corresponding pastes were characterized by XRD, SEM, chemical analysis, 29Si MAS NMR and 1H-29Si CPMAS NMR after water storage and after acid exposure. The mortars exhibited a high resistance against sulfuric acid attack, with the best ones conforming to the requirements of DIN 19573:2016-03. The analytical results showed that this was due to precipitation of silica gel at the acid-mortar interface, which formed a mechanically stable layer that protected the subjacent mortar and thus inhibited further degradation. The addition of GGBFS decreased the acid resistance via formation of expansive calcium sulfate phases. KW - Alkali activated materials KW - Acid resistance KW - Nuclear magnetic resonance KW - One-part geopolymers PY - 2018 DO - https://doi.org/10.1016/j.cemconres.2018.04.009 SN - 0008-8846 VL - 109 SP - 54 EP - 63 PB - Elsevier Ltd. AN - OPUS4-44722 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gluth, Gregor A1 - Sturm, Patrick A1 - Greiser, Sebastian A1 - Jäger, Christian A1 - Kühne, Hans-Carsten ED - Wang, J. ED - Kriven, W. ED - Fey, T. ED - Colombo, P. ED - Weber, W.J. ED - Amoroso, J. ED - Fahrenholtz, W.G. ED - Shimamura, K. ED - Halbig, M. ED - Kirihara, S. ED - Wu, Y. ED - Shurgart, K. T1 - One-part geopolymers and aluminosilicate gel-zeolite composites: factors influencing microstructure and engineering properties T2 - Proceedings of the 42nd International Conference on Advanced Ceramics and Composites: Ceramic Engineering and Science Proceedings Volume 39, Issue 3 N2 - Mixing and curing of geopolymers and related alkali-activated materials without storage and handling of highly alkaline solutions possesses advantages regarding safety and economic viability. One possible approach is to produce these materials from solid silica feedstocks and solid sodium aluminate, and subsequent mixing with water. We present a comparison between geopolymers and aluminosilicate gel-zeolite composites synthesized by this route from different silica feedstocks (by-product silica from chlorosilane production, microsilica, rice husk ash) and with different SiO2/Al2O3 ratios, using results from XRD, NMR, SEM, thermal analysis, mechanical and acid resistance testing. The use of rice husk ash favors formation of a fully amorphous geopolymer with high strength. Utilization of the other silica feedstocks leads to formation of aluminosilicate gel-zeolite composites, the amount and kind of zeolites depending on the feedstock and the SiO2/Al2O3 ratio. These composites show beneficial dehydration behavior, viz. no distinct dehydration step of thermal strain, with the phase assemblage after heating to 1000°C controlled by the starting composition. Mortars produced from both, the geopolymers as well as the composites, exhibit high resistance to sulfuric acid attack, making them promising materials for the construction and the repair of industrial and sewer structures. T2 - 42nd International Conference on Advanced Ceramics and Composites CY - Daytona Beach, FL, USA DA - 21.01.2018 KW - Alkali-activated materials KW - One-part geopolymers KW - Sulfuric acid resistance KW - High-temperature resistance PY - 2019 DO - https://doi.org/10.1002/9781119543381.ch17 VL - 39 IS - 3 SP - 183 EP - 196 PB - John Wiley & Sons AN - OPUS4-47282 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Greiser, Sebastian A1 - Gluth, Gregor A1 - Sturm, Patrick A1 - Jäger, Christian T1 - 29Si{27Al}, 27Al{29Si} and 27Al{1H} double-resonance NMR spectroscopy study of cementitious sodium aluminosilicate gels (geopolymers) and gel-zeolite composites JF - RSC Advances N2 - The influence of starting materials and synthesis route on the properties and the structure of cementitious sodium aluminosilicate gels is not fully understood, partly due their amorphous nature and the fact that they often contain residual reactants, which can make the results of single-pulse NMR spectroscopy applied to these materials difficult to interpret or ambiguous. To overcome some of these limitations, 29Si{27Al} TRAPDOR NMR as well as 27Al{29Si} and 27Al{1H} REDOR NMR spectroscopy were applied to materials synthesized by the one-part alkali-activation route from three different amorphous silica starting materials, including rice husk ash. The latter led to formation of a fully amorphous sodium aluminosilicate gel (geopolymer), while the materials produced from the other silicas contained amorphous phase and crystalline zeolites. Application of the double-resonance NMR methods allowed to identify hydrous alumina gel domains in the rice husk ash-based material as well as significantly differing amounts of residual silica in the three cured materials. Four-coordinated Al existed not only in the aluminosilicate gel framework but also in a water-rich chemical environment with only a small amount of Si in proximity, likely in the alumina gel or possibly present as extra-framework Al in the aluminosilicate gel. The results demonstrate how the employment of different silica starting materials determines the phase assemblage of one-part alkali-activated materials, which in turn influences their engineering properties such as the resistance against chemically/biologically aggressive media. KW - Alkali-activated materials KW - Solid-state NMR KW - Aluminium hydroxide KW - Rice husk ash PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-469353 DO - https://doi.org/10.1039/C8RA09246J SN - 2046-2069 VL - 8 IS - 70 SP - 40164 EP - 40171 PB - Royal Society of Chemistry AN - OPUS4-46935 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -