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1. Formation and stability of gismondine‐type zeolite in cementitious systems

   https://doi.org/10.1111/jace.17572  

   Okoronkwo, Monday U.; Mondal, Sukanta K.; Wang, Bu; Ma, Hongyan; Kumar, Aditya (November 2020, Journal of the American Ceramic Society)

   Abstract Microcrystalline zeolites of the gismondine family are often reported in alkali‐activated and blended cement systems. However, little is known about gismondine's compatibility with other cementitious phases to determine stability in long‐term phase assemblage. Experimental studies were conducted to investigate the compositional field of gismondine stability in the lime‐alumina‐silica‐hydrate systems, with a particular focus on understanding the compatibility of gismondine with other cement phases such as C‐S‐H, ettringite, monosulfate, strätlingite, katoite, gypsum, calcite, portlandite, alkali, silica, and aluminosilicate phases. Results show that gismondine‐Ca forms readily at ~85°C in high aluminosilicate compositions; and persists in the presence of calcite, gypsum, ettringite, katoite solid solution, low Ca tobermorite‐like C‐S‐H, silica and aluminosilicate phases, at 20‐85°C. However, gismondine‐Ca reacts with: (a) monosulfate, producing ettringite‐thaumasite solid solution; (b) portlandite, forming tobermorite‐like C‐A‐S‐H gel and siliceous katoite at >55°C; (c) aqueous NaOH, generating gismondine‐(Na,Ca), a garronite‐like zeolite P solid solution; and (d) strätlingite leading to the conversion of strätlingite to gismondine indicating the metastability of strätlingite with respect to gismondine at 55°C. The outcomes are discussed to provide insights into the long‐term phase assemblage of relevant cement systems such as lime‐calcined clay, alkali‐activated materials, and potentially ancient Roman concrete. 

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2. Assessing the Precision and Accuracy of Foraminifera Elemental Analysis at Low Ratios

   https://doi.org/10.1029/2024GC011560  

   Lu, Wanyi; Guo, Weifu; Oppo, Delia W (October 2024, Geochemistry, Geophysics, Geosystems)

   Abstract The minor and trace element compositions of biogenic carbonates such as foraminifera are important tools in paleoceanography research. However, most studies have focused primarily on samples with element to calcium (El/Ca) ratios higher than the El/Ca range often found in benthic foraminifera. Here, we systematically assess the precision and accuracy of foraminifera elemental analysis across a wide range of El/Ca especially at relatively low ratios, using a method on a Thermo Scientific iCAP Qc quadrupole Inductively Coupled Plasma Mass Spectrometer (ICP‐MS). We focus on two benthic foraminifera species,Hoeglundina elegansandCibicidoides pachyderma, and prepared a suite of solution standards based on their typical El/Ca ranges to correct for signal drift and matrix effects during ICP‐MS analysis and to determine analytical precision. We observe comparable precisions with published studies at high El/Ca, and higher relative standard deviations for each element at lower El/Ca, as expected from counting statistics. The overall long‐term analytical precision (2σ) of theH. elegans‐like consistency standard solutions was 6.5%, 4.6%, 5.0%, for Li/Ca, Mg/Ca, Mg/Li, and 6.4%, 10.0%, 4.2% for B/Ca, Cd/Ca, Sr/Ca. The precision forH. elegans‐like Mg/Li is equivalent to a temperature uncertainty of 0.5–1.1°C. Measurement precisions were also assessed based on three international standards (one solution and two powder standards) and replicate measurements ofH. elegansandC. pachydermasamples. We provide file templates and program scripts that can be used to design calibration and consistency standards, prepare run sequences, and convert the raw ICP‐MS data into molar ratios. 

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3. Effect of particle size distribution of metakaolin on hydration kinetics of tricalcium silicate

   https://doi.org/10.1111/jace.16467  

   Lapeyre, Jonathan; Ma, Hongyan; Kumar, Aditya (April 2019, Journal of the American Ceramic Society)

   Abstract The focus of this study is to elucidate the role of particle size distribution (PSD) of metakaolin (MK) on hydration kinetics of tricalcium silicate (C₃S–T₁) pastes. Investigations were carried out utilizing both physical experiments and phase boundary nucleation and growth (pBNG) simulations. [C₃S + MK] pastes, prepared using 8%_massor 30%_massMK, were investigated. Three different PSDs of MK were used: fine MK, with particulate sizes <20 µm; intermediate MK, with particulate sizes between 20 and 32 µm; and coarse MK, with particulate sizes >32 µm. Results show that the correlation between specific surface area (SSA) of MK's particulates and the consequent alteration in hydration behavior of C₃S in first 72 hours is nonlinear and nonmonotonic. At low replacement of C₃S (ie, at 8%_mass), fine MK, and, to some extent, coarse MK act as fillers, and facilitate additional nucleation and growth of calcium silicate hydrate (C–S–H). When C₃S replacement increases to 30%_mass, the filler effects of both fine and coarse MK are reversed, leading to suppression of C–S–H nucleation and growth. Such reversal of filler effect is also observed in the case of intermediate MK; but unlike the other PSDs, the intermediate MK shows reversal at both low and high replacement levels. This is due to the ability of intermediate MK to dissolve rapidly—with faster kinetics compared to both coarse and fine MK—which results in faster release of aluminate [Al(OH)₄⁻] ions in the solution. The aluminate ions adsorb onto C₃S and MK particulates and suppress C₃S hydration by blocking C₃S dissolution sites and C–S–H nucleation sites on the substrates’ surfaces and suppressing the post‐nucleation growth of C–S–H. Overall, the results suggest that grinding‐based enhancement in SSA of MK particulates does not necessarily enhance early‐age hydration of C₃S. 

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4. Structure and morphology of calcium-silicate-hydrates cross-linked with dipodal organosilanes

   https://doi.org/https://doi.org/10.1016/j.cemconres.2020.106076  

   Moshiri, A. (July 2020, Cement and concrete research)

   Coupling of organic and inorganic chemistry presents a new degree of freedom in nano-engineering of thermo-mechanical properties of cement-based materials. Despite these vast technological benefits, molecular scale cross-linking of calcium-silicate-hydrate (C-S-H) gel with organic molecules still presents a significant challenge. Herein, we report experimental results on sol-gel synthesis, structure and morphology of nanocrystalline C-S-H cross-linked with dipodal organosilanes. These novel organic-inorganic gels have layered turbostratic molecular structure with similarities to C-S-H precipitating in hydrating cement paste. The organic molecules' chain length controls the interlayer spacing, which shows little to no shrinkage upon dehydration up to 105 °C. However, the structure gets distorted in the basal crystallite plane, in which dimer and trimer Si-polyhedra structures condense on a 2D hexagonal Ca-polyhedra layer. Cross-linked C-S-H gels display plate-like morphology with tendency toward stacking into agglomerates at the larger scale. If successfully realized in cement environment, e.g. high concentration seed, such novel organic-inorganic C-S-H gels could potentially provide cement-based matrices with unique properties unmatched by classical inorganic systems. 

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5. Propane dehydrogenation over extra-framework In( i ) in chabazite zeolites

   https://doi.org/10.1039/d1sc05866e  

   Yuan, Yong; Lobo, Raul F. (March 2022, Chemical Science)

   Indium on silica, alumina and zeolite chabazite (CHA), with a range of In/Al ratios and Si/Al ratios, have been investigated to understand the effect of the support on indium speciation and its corresponding influence on propane dehydrogenation (PDH). It is found that In 2 O 3 is formed on the external surface of the zeolite crystal after the addition of In(NO 3 ) 3 to H-CHA by incipient wetness impregnation and calcination. Upon reduction in H 2 gas (550 °C), indium displaces the proton in Brønsted acid sites (BASs), forming extra-framework In + species (In-CHA). A stoichiometric ratio of 1.5 of formed H 2 O to consumed H 2 during H 2 pulsed reduction experiments confirms the indium oxidation state of +1. The reduced indium is different from the indium species observed on samples of 10In/SiO 2 , 10In/Al 2 O 3 ( i.e. , 10 wt% indium) and bulk In 2 O 3 , in which In 2 O 3 was reduced to In(0), as determined from the X-ray diffraction patterns of the product, H 2 temperature-programmed reduction (H 2 -TPR) profiles, pulse reactor investigations and in situ transmission FTIR spectroscopy. The BASs in H-CHA facilitate the formation and stabilization of In + cations in extra-framework positions, and prevent the deep reduction of In 2 O 3 to In(0). In + cations in the CHA zeolite can be oxidized with O 2 to form indium oxide species and can be reduced again with H 2 quantitatively. At comparable conversion, In-CHA shows better stability and C 3 H 6 selectivity (∼85%) than In 2 O 3 , 10In/SiO 2 and 10In/Al 2 O 3 , consistent with a low C 3 H 8 dehydrogenation activation energy (94.3 kJ mol −1 ) and high C 3 H 8 cracking activation energy (206 kJ mol −1 ) in the In-CHA catalyst. A high Si/Al ratio in CHA seems beneficial for PDH by decreasing the fraction of CHA cages containing multiple In + cations. Other small-pore zeolite-stabilized metal cation sites could form highly stable and selective catalysts for this and facilitate other alkane dehydrogenation reactions. 

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