TY - JOUR A1 - Yao, Dongxu A1 - Xia, Y. A1 - Zuo, K.-h. A1 - Zeng, Y.-P. A1 - Jiang, D. A1 - Günster, Jens A1 - Heinrich, J.G. T1 - Gradient porous silicon nitride prepared via vacuum foaming and freeze drying N2 - Gradient porous silicon nitride (Si3N4) was fabricated by a novel vacuum foaming and freeze drying process. Aqueous Si3N4 slurries were foamed at vacuum pressure of 50–90 kPa, the green body was obtained by the freeze drying process, a gradient pore structure with porosities of 72–90% was achieved after pressureless sintering at 1680 °C. The porosity was increased with decreasing vacuum pressure. The pore structure consists of large pores (~100 μm) on top, medium pores (~45 μm) on the wall of the large pores, and small pores (~0.7 μm) in the matrix. Such gradient porous Si3N4 with macro- and micro-pores has potential application as high temperature filters. KW - Silicon nitride KW - Graded PY - 2015 U6 - https://doi.org/10.1016/j.matlet.2014.11.067 SN - 0167-577x SN - 1873-4979 VL - 141 SP - 138 EP - 140 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-35177 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yao, Dongxu A1 - Xia, Y. A1 - Zuo, K.-h. A1 - Jiang, D. A1 - Günster, Jens A1 - Zeng, Y.-P. A1 - Heinrich, J.G. T1 - Porous Si3N4 ceramics prepared via partial nitridation and SHS N2 - Porous Si3N4 ceramics were prepared via partial nitridation and self-propagating high temperature synthesis (SHS) process. Raw Si and additive Y2O3 were mixed and molded under 10 MPa into a compact, the compact was partial nitridation at 1300 °C to form a porous Si/Si3N4, and then it was buried in a Si/Si3N4 bed for SHS to obtain porous Si3N4 with rod-like β-Si3N4 morphology. The processing combined the advantages of the nitridation of Si and SHS with low cost, low shrinkage and time saving. Porous Si3N4 with a porosity of 47%, a strength of 143 MPa were obtained by this method. KW - Si3N4 KW - Strength KW - Porosity PY - 2013 U6 - https://doi.org/10.1016/j.jeurceramsoc.2012.08.033 SN - 0955-2219 SN - 1873-619X VL - 33 IS - 2 SP - 371 EP - 374 PB - Elsevier CY - Oxford AN - OPUS4-31282 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yao, Dongxu A1 - Xia, Y. A1 - Zuo, K.-h. A1 - Jiang, D. A1 - Günster, Jens A1 - Zeng, Y.-P. A1 - Heinrich, J.G. T1 - The effect of fabrication parameters on the mechanical properties of sintered reaction bonded porous Si3N4 ceramics N2 - Porous silicon nitride ceramics were prepared via sintered reaction bonded silicon nitride at 1680 °C. The grain size of nitrided Si3N4 and diameter of post-sintered ß-Si3N4 are controlled by size of raw Si. Porosity of 42.14–46.54% and flexural strength from 141 MPa to 165 MPa were obtained. During post-sintering with nano Y2O3 as sintering additive, nano Y2O3 can promote the formation of small ß-Si3N4 nuclei, but the large amount of ß-Si3N4 (>20%) after nitridation also works as nuclei site for precipitation, in consequence the growth of fine ß-Si3N4 grains is restrained, the length is shortened, and the improvement on flexural strength is minimized. The effect of nano SiC on the refinement of the ß-Si3N4 grains is notable because of the pinning effect, while the effect of nano C on the refinement of the ß-Si3N4 grains is not remarkable due to the carbothermal reaction and increase in viscosity of the liquid phase. KW - Porous ceramics KW - Silicon nitride KW - Reaction bonding KW - Anisotropic grain growth KW - Ceramic PY - 2014 U6 - https://doi.org/10.1016/j.jeurceramsoc.2014.06.018 SN - 0955-2219 SN - 1873-619X VL - 34 IS - 15 SP - 3461 EP - 3467 PB - Elsevier CY - Oxford AN - OPUS4-32542 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Provis, J. L. A1 - Arbi, K. A1 - Bernal, S. A. A1 - Bondar, D. A1 - Buchwald, A. A1 - Castel, A. A1 - Chithiraputhiran, S. A1 - Cyr, M. A1 - Dehghan, A. A1 - Dombrowski-Daube, K. A1 - Dubey, A. A1 - Ducman, V. A1 - Gluth, Gregor A1 - Nanukuttan, S. A1 - Peterson, K. A1 - Puertas, F. A1 - van Riessen, A. A1 - Torres-Carrasco, M. A1 - Ye, G. A1 - Zuo, Y. T1 - RILEM TC 247-DTA round robin test: mix design and reproducibility of compressive strength of alkali-activated concretes N2 - The aim of RILEM TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ is to identify and validate methodologies for testing the durability of alkali-activated concretes. To underpin the durability testing work of this committee, five alkali-activated concrete mixes were developed based on blast furnace slag, fly ash, and flash-calcined metakaolin. The concretes were designed with different intended performance levels, aiming to assess the capability of test methods to discriminate between concretes on this basis. A total of fifteen laboratories worldwide participated in this round robin test programme, where all concretes were produced with the same mix designs, from single-source aluminosilicate precursors and locally available aggregates. This paper reports the mix designs tested, and the compressive strength results obtained, including critical insight into reasons for the observed variability in strength within and between laboratories. KW - Alkali-activated materials KW - Alkali-activated slag KW - Compressive strength KW - Concrete KW - Mix-design PY - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-489131 SN - 1359-5997 SN - 1871-6873 VL - 52 IS - 5 SP - Article Number 99 PB - Springer Nature AN - OPUS4-48913 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hu, H.-L. A1 - Zeng, Y.-P. A1 - Zuo, K.-H. A1 - Xia, Y. A1 - Yao, Dongxu A1 - Günster, Jens A1 - Heinrich, J. A1 - Li, S. T1 - Synthesis of porous Si3N4/SiC ceramics with rapid nitridation of silicon N2 - Porous Si3N4/SiC ceramics were prepared with Si and SiC as raw materials, Y2O3 as sintering additive and ZrO2 as nitrided catalyst through a rapid nitration process. The nitriding rate as a function of temperature and duration was investigated. The porous Si3N4/SiC ceramics with 8 wt% monoclinic ZrO2 addition that was nitrided at 1400 °C for 2 h exhibited the highest nitridation degree of 95%. The experimental results also demonstrated that the reciprocal formation of ZrO2 and ZrN can effectively enhance the level of nitridation by suppressing the melting of silicon in micro-regions. The effects of nitriding time on the mechanical properties of the specimens with ZrO2 as a catalyst was also studied. After nitrided at 1400 °C for various durations from 2 to 8 h, the porous Si3N4/SiC ceramics with the properties of a porosity over 39.8%, a flexural strength over 88.9 MPa and a linear shrinkage lower than 0.6% were achieved. The systematic investigation reveals the catalytic mechanism of ZrO2 in the synthesis of Si3N4/SiC ceramics. KW - Si3N4 PY - 2015 U6 - https://doi.org/10.1016/j.jeurceramsoc.2015.06.028 SN - 0955-2219 SN - 1873-619X VL - 35 IS - 14 SP - 3781 EP - 3787 PB - Elsevier Ltd. CY - Oxford AN - OPUS4-34956 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hu, H.-L. A1 - Zeng, Y.-P. A1 - Xia, Y. A1 - Yao, Dongxu A1 - Zuo, K.-H. A1 - Günster, Jens A1 - Heinrich, J.G. T1 - Rapid fabrication of porous Si3N4/SiC ceramics via nitridation of silicon powder with ZrO2 as catalyst N2 - Porous Si3N4/SiC ceramics were rapidly prepared with Y2O3 as sintering additive and ZrO2 as nitrided catalyst, using Si and SiC as starting powders. Porous Si3N4/SiC ceramics with 5 wt% ZrO2 addition showed a complete nitridation and good mechanical properties (with a high porosity of 34.96%, flexural strength of 150±4.2 MPa, linear shrinkage of 0.02%). It was revealed that the reciprocal formation of ZrO2 and ZrN effectively enhanced nitridation by inhibiting the melting of silicon in micro-regions. KW - D. ZrO2 KW - Rapid nitridation KW - Si3N4/SiC porous ceramics PY - 2014 U6 - https://doi.org/10.1016/j.ceramint.2013.11.098 SN - 0272-8842 SN - 1873-3956 VL - 40 IS - 5 SP - 7579 EP - 7582 PB - Ceramurgia CY - Faenza AN - OPUS4-30295 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gluth, Gregor A1 - Arbi, K. A1 - Bernal, S. A. A1 - Bondar, D. A1 - Castel, A. A1 - Chithiraputhiran, S. A1 - Dehghan, A. A1 - Dombrowski-Daube, K. A1 - Dubey, A. A1 - Ducman, V. A1 - Peterson, K. A1 - Pipilikaki, P. A1 - Valcke, S. L. A. A1 - Ye, G. A1 - Zuo, Y. A1 - Provis, J. L. T1 - RILEM TC 247-DTA round robin test: carbonation and chloride penetration testing of alkali-activated concretes N2 - Many standardised durability testing methods have been developed for Portland cement-based concretes, but require validation to determine whether they are also applicable to alkali-activated materials. To address this question, RILEM TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ carried out round robin testing of carbonation and chloride penetration test methods, applied to five different alkali-activated concretes based on fly ash, blast furnace slag or metakaolin. The methods appeared overall to demonstrate an intrinsic precision comparable to their precision when applied to conventional concretes. The ranking of test outcomes for pairs of concretes of similar binder chemistry was satisfactory, but rankings were not always reliable when comparing alkali-activated concretes based on different precursors. Accelerated carbonation testing gave similar results for fly ash-based and blast furnace slag-based alkali-activated concretes, whereas natural carbonation testing did not. Carbonation of concrete specimens was observed to have occurred already during curing, which has implications for extrapolation of carbonation testing results to longer service life periods. Accelerated chloride penetration testing according to NT BUILD 443 ranked the tested concretes consistently, while this was not the case for the rapid chloride migration test. Both of these chloride penetration testing methods exhibited comparatively low precision when applied to blast furnace slag-based concretes which are more resistant to chloride ingress than the other materials tested. KW - Alkali-activated materials KW - Durability KW - Carbonation KW - Chloride penetration KW - Concrete PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-504045 SN - 1359-5997 SN - 1871-6873 VL - 53 IS - 1 SP - 21 PB - Springer Nature AN - OPUS4-50404 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -