Solid-state MAS NMR Research Articles

Effect of cation in sodium/potassium-based geopolymer coatings for the fire protection of steel structures

Common geopolymers (GPs) are activated by alkaline solutions of potassium (K) or sodium (Na). Although both properties have been extensively investigated, comparative studies on their fire resistance are still lacking. In this research, Na/K-based GPs were applied as fire-protective steel coatings. Their fire protection was evaluated by a fire test named “burn-through”. When the Aluminum/Silicon (Al/Si) molar ratio equaled 0, both GPs showed intumescence (expansion upon heating) during the fire test. The final maximum temperatures of the protected steel plate (TS) were as low as 309/335°C for Na/K-GP. However, with Al/Si=0.54, K-based GP (TS=410°C) exhibited intumescence and better fire protection than Na-based GP (TS=587°C) which even cracked. Physico-chemical properties of the GP samples were characterized before and after the fire test, including electron probe micro-analysis, dynamic mechanical analysis, and 29Si solid-state MAS (CP) NMR. Material softening was proved to come from the consumption of Si (Q2) and caused the following intumescence. Such structure was formed in K-based GP regardless of Al/Si ratio while Si (Q2) atoms were only present in Na-based GP at low Al/Si ratio. It is therefore proven that K-based GP is more appropriate to protect steel than Na-based GP, due to its intumescent property, especially when the Al/Si ratio is high.

Influence of anionic silica forms in clear sodium silicate precursors on metakaolin geopolymerisation via 29Si and 27Al MAS-NMR and microstructural studies

A number of synthesis parameters directly influence the degree of reticulation/geopolymerisation of metakaolin exposed to alkaline solutions of sodium hydroxide and/or sodium silicate. In the latter case, a sodium silicate solution can be depolymerised by the introduction of an appropriate amount of NaOH. The effects of the ageing of the activator solution on the reticulation of metakaolin-based geopolymers are quantified for the first time in this work. We studied the anionic species of the sodium silicate solution with the addition of NaOH made just before the preparation of the paste, 24 h or 7 days before. These three ageing periods cause a significant difference in the Si-bearing species in solution, as demonstrated by nuclear magnetic resonance on 29Si. The effect of these anionic species on the reticulation/polymerisation of metakaolin at room temperature was demonstrated by solid-state 27Al and 29Si MAS-NMR, the chemical stability in various solutions (deionised water, HCl, HNO3, H2SO4), and X-ray diffraction on geopolymer powders before and after immersion in acids. Compressive strength before and after the immersion in acidic media was an additional measurement to assess the overall structural stability of the 3D polymerised network of the final dense ceramic-like product. Ageing of the activator solution affected the chemical stability of the hardened geopolymers accompanied by a slight to severe reduction in strength after leaching in HNO3 or HCl and in H2SO4, respectively. The quantitative MAS-NMR description of the Si and Al coordination in the geopolymers was correlated with the chemical stability where the formulations with the higher number of Q4(0Al) and Q4(1Al) for the silicon species were more resistant (lower number of Na+ compensating for Al+3 to be exchanged with H+). The formulations with higher Al content in the structure, i.e. higher number of Q4(3Al) silicon species showed higher mechanical stability. These results show that the timing of the preparation of the alkaline activator is essential for a correct mix design.

Organic template-free synthesis of CHA zeolite by hydrothermal conversion of magadiite with the assistance of seeds and an investigation of crystallization mechanism

This study aims to explore the process of pure CHA zeolite production by a hydrothermal magadiite transformation method, with the chemical formulation of 36 NaOH: 40 SiO2: Al2O3: 400H2O, running for 7 h at 80 °C with 12 wt% seeds. Considering various synthesis factors such as NaOH/SiO2, temperature, and seeds dosage etc., XRD, SEM, FT-IR, Solid-state MAS NMR and ESI-MS were applied to investigated to discuss the transformation behavior and mechanism in both solid and liquid phase. The results indicated that the changes of secondary building units had a formation sequence progresses from 6 R s to D6Rs, and oligomers in liquid phases would take part in the formation of CHA framework. In conclusion, the study demonstrates a novel pathway for the highly efficient and green synthesis of CHA zeolite via seed-assisted hydrothermal conversion of magadiite.

Mixed Metal Amide-Hydride Solid Solutions for Energy Storage Applications

Metal amide-hydride materials have been extensively studied for usage in energy applications, especially as solid electrolytes for all-solid-state batteries and as hydrogen storage. In specific cases, the formation of mixed metal amide hydride solid solutions promotes fast hydrogen sorption kinetics and tune the thermodynamics, allowing hydrogen absorption/desorption below 150 °C in hydrogen storage systems. In addition, these intermediates, such as Li2(BH4)(NH2) or Li4(BH4)(NH2)3 are potentially ionic conductors that can be used as solid electrolytes for solid-state batteries’ applications. In this work, a series of M-N-H solid solution structures based on mixed MNH2-MH materials of Group 1 elements (M = K, Rb, Cs and their combinations), such as KNH2-KH, KNH2-RbH, RbNH2-KH, RbNH2-CsH, RbNH2-CsNH2, etc., are reported. The results obtained by experimental determination (e.g., ex-situ XRD / in-situ synchrotron powder X-ray diffraction, IR, 1H 2D solid-state MAS NMR, QENS) and theoretical calculations (e.g., molecular dynamics calculations) confirm the formation of mixed metal amide hydride solid solutions associated with an exchange between both anionic (NH2 - and H-) and cationic species (K, Rb and Cs). These structurally disordered solid solutions exhibit high ionic conductivity compared to the pure materials, e.g., mixed RbNH2-CsNH2 shows an ionic conductivity in the range of 4×10-5 S×cm-1 at 373 K compared to that of pure RbNH2 and CsNH2 (< 10-7 S×cm-1 at the same condition). Although this solid solution exhibits only moderate ionic conductivity, it offers the possibility of tuning the functional and physical properties of mixed metal amide-hydrides by structural modification.

Temporal effects on the micro- and nano-structural cement-slag pastes subjected to microwave curing over 7 years

This study examines the changes in the micro- and nano-structures of microwave-cured cement and slag pastes over 7 years. The properties of aged samples were compared with those of young pastes made from the same mixtures. Both young and aged samples were analyzed by XRD, DTA-TG, SEM-EDX, and Solid-state MAS NMR of 29Si and 27Al. It is found that, in addition to the usual components (C-S-H, calcium hydroxide, monosulfoaluminate, trisulfoaluminate, and hydrotalcite-like phases (HT)), the aged samples contained calcium magnesium aluminate hydrate and gibbsite (AH3). Over time, some HT or AH3 integrated into the C-S-H nanostructure as additional layers. These findings suggest that microwaves accelerate the general hydration processes in cement due to thermodynamic effects and selectively activate reactions in the aluminate components. This discovery highlights the potential for using microwaves to manipulate cement reactions.

Origin of Reactivity Trends of an Elusive Metathesis Intermediate from NMR Chemical Shift Analysis of Surrogate Analogues.

Olefin metathesis has become an efficient tool in synthetic organic chemistry to build carbon-carbon bonds, thanks to the development of Grubbs- and Schrock-type catalysts. Olefin coordination, a key and often rate-determining elementary step for d0 Schrock-type catalysts, has been rarely explored due to the lack of accessible relevant molecular analogues. Herein, we present a fully characterized surrogate of this key olefin-coordination intermediate, namely, a cationic d0 tungsten oxo-methylidene complex bearing two N-heterocyclic carbene ligands─[WO(CH2)Cl(IMes)2](OTf) (1) (IMes = 1,3-dimesitylimidazole-2-ylidene, OTf-triflate counteranion), resulting in a trigonal bipyramidal (TBP) geometry, along with its neutral octahedral analogue [WO(CH2)Cl2(IMes)2] (2)─and an isostructural oxo-methylidyne derivative [WO(CH)Cl(IMes)2] (3). The analysis of their solid-state 13C and 183W MAS NMR signatures, along with computed 17O NMR parameters, helps to correlate their electronic structures with NMR patterns and evidences the importance of the competition among the three equatorial ligands in the TBP complexes. Anchored on experimentally obtained NMR parameters for 1, computational analysis of a series of olefin coordination intermediates highlights the interplay between σ- and π-donating ligands in modulating their stability and further paralleling their reactivity. NMR spectroscopy descriptors reveal the origin for the advantage of the dissymmetry in σ-donating abilities of ancillary ligands in Schrock-type catalysts: weak σ-donors avoid the orbital-competition with the oxo ligand upon formation of a TBP olefin-coordination intermediate, while stronger σ-donors compromise M≡O triple bonding and thus render olefin coordination step energy demanding.

Supramolecular Solid Complexes between Bis-pyridinium-4-oxime and Distinctive Cyanoiron Platforms.

The structural features and optical properties of supramolecular cyanoiron salts containing bis-pyridinium-4-oxime Toxogonin® (TOXO) as an electron acceptor are presented. The properties of the new TOXO-based cyanoiron materials were probed by employing two cyanoiron platforms: hexacyanoferrate(II), [Fe(CN)6]4- (HCF); and nitroprusside, [Fe(CN)5(NO)]2- (NP). Two water-insoluble inter-ionic donor-acceptor phases were characterized: the as-prepared microcrystalline reddish-brown (TOXO)2[Fe(CN)6]·8H2O (1a) with a medium-responsive, hydrochromic character; and the dark violet crystalline (TOXO)2[Fe(CN)6]·3.5H2O (1cr). Complex 1a, upon external stimulation, transforms to the violet anhydrous phase (TOXO)2[Fe(CN)6] (1b), which upon water uptake transforms back to 1a. Using the NP platform resulted in the water-insoluble crystalline salt TOXO[Fe(CN)5(NO)]·2H2O (2). The structures of 1cr and 2, solved by single-crystal X-ray diffraction, along with a comparative spectroscopic (UV-vis-NIR diffuse reflectance, IR, solid-state MAS-NMR, Mössbauer), thermal, powder X-ray diffraction, and microscopic analysis (SEM, TEM) of the isolated materials, provided insight for the supramolecular binding, electron-accepting, and H-bonding capabilities of TOXO in the self-assembly of these functionalized materials.

Synthesis and Structural Analysis of High-Silica ERI Zeolite with Spatially-Biased Al Distribution as a Promising NH3-SCR Catalyst.

Erionite (ERI) zeolite has recently attracted considerable attention for its application prospect in the selective catalytic reduction of NOx with NH3 (NH3-SCR), provided that the high-silica (Si/Al > 5.5) analog with improved hydrothermal stability can be facilely synthesized. In this work, ERI zeolites with different Si/Al ratios (4.6, 6.4, and 9.1) are synthesized through an ultrafast route, and in particular, a high-silica ERI zeolite with a Si/Al ratio of 9.1 is obtained by using faujasite (FAU) as a starting material. The solid-state 29Si MAS NMR spectroscopic study in combination with a computational simulation allows for figuring out the atomic configurations of the Al species in the three ERI zeolites. It is revealed that the ERI zeolite with the highest Si/Al ratio (ERI-9.1, where the number indicates the Si/Al ratio) exhibits a biased Al occupancy at T1 site, which is possibly due to the presence of a higher fraction of the residual potassium cations in the can cages. In contrast, the Al siting in ERI-4.6 and ERI-6.4 proves to be relatively random.

Changing the reaction pathway of the CaAl2 oxidation using ball milling.

As previously shown, CaAl2 can be oxidized using elemental O2 to form CaAl2O4. This reaction, however, proceeds via Ca12Al14O33 and elemental Al as intermediates which are subsequently transformed into the stoichiometric reaction product. High-energy ball milling is known to decrease the crystallite size of a material and to significantly produce defects enabling different reaction pathways compared to a highly crystalline bulk material. In this subsequent study, a different oxidizing agent (H2O) as well as the ball milling behavior of CaAl2 and the consecutive oxidation via elemental O2 were studied. While the use of H2O as the oxidizing agent showed only minor differences in the reaction products, ball milling of CaAl2 decreases, as expected, the crystallite size of the material and introduces defects. This is visible both in the powder X-ray diffraction patterns and in the 27Al solid-state MAS NMR spectra. In the subsequent steps, the ball milled material was oxidized in an STA system. Already 5 min of ball milling significantly changes the energy pattern of the reaction. Powder X-ray diffraction studies on the oxidized material clearly indicate that a different reaction pathway occurs. Samples ball milled for 180 min even get pyrophoric.

Elucidating metal composition–coking relationships and coke formation pathways during gas-phase oxydehydration of glycerol over clay mineral-supported Mo-V-O catalysts

Catalyst deactivation by carbon deposition (coking) remains a major obstacle in many important industrial processes, such as catalytic gas-phase oxydehydration of glycerol. Understanding the chemical nature and development of coke species during the time-on-stream (TOS) of the catalytic solids is therefore crucial for mitigating the extent of coking and in the design of regeneration process of the coked catalysts. In this study, multiple analytical techniques, including SEM, XRD, FTIR, Raman, GC-MS, XPS, and 13C solid-state MAS NMR were employed to gain insights into the coking behavior of acid-activated montmorillonite (HMMT) supported Mo-V-O catalysts with modulated metal ratios, along with soluble and insoluble coke compositions and their evolution over time. Insoluble coke was comprised of polycyclic aromatic compounds with 5 or more fused-benzene rings containing different types of oxygen-bonded groups, such as −OCH3, −COOH, −CHO, and −OH. The major chemical constituents of soluble coke were mononuclear aromatic derivatives (i.e., xylenes, 2,4-di-tert-butylphenol, and 1-hydroxycyclohexyl phenyl ketone) and paraffinic hydrocarbons with 12–18 carbon atoms. The latter coke species is thought to be formed via the deoxygenation of linear oligoglycerols. The insights presented in this study may aid in understanding the carbon deposition process during gas-phase oxydehydration of glycerol for improved design of supported Mo-V-O catalyst materials with high coking resistance.

Stability of Quadruple Hydrogen Bonds in an Ionic Liquid Environment.

Hydrogen bonds (H-bonds) are highly sensitive to the surrounding environments owing to their dipolar nature, with polar solvents kown to significantly weaken H-bonds. Herein, the stability of the H-bonding motif ureidopyrimidinone (UPy) is investigated, embedded into a highly polar polymeric ionic liquid (PIL) consisting of pendant pyrrolidinium bis(trifluoromethylsulfonyl)imide (IL) moieties, to study the influence of such ionic environments on the UPy H-bonds. The content of the surrounding IL is changed by addition of an additional low molecular weight IL to further boost the IL content around the UPy moieties in molar ratios of UPy/IL ranging from 1/4 up to 1/113, thereby promoting the polar microenvironment around the UPy-H-bonds. Variable-temperature solid-state MAS NMR spectroscopy and FT-IR spectroscopy demonstrate that the UPy H-bonds are largely present as (UPy-) dimers, but sensitive to elevated temperatures (>70°C). Subsequent rheology and DSC studies reveal that the ILs only solvate the polymeric chains but do not interfere with the UPy-dimer H-bonds, thus accounting for their high stability and applicability in many material systems.

Interlayer, gallery-engineered graphene oxide using selective protection of mono-Boc-ethylenediamine as anode for sodium ion batteries

The enormous demand for Lithium urges researchers to look for alternatives. Sodium can play a critical role in a plethora of rechargeable batteries as they are more abundant, economical, have better safety characteristics, and have similar power delivery possibilities. In this work, we established the intercalation of the sodium ions in between selectively functionalized graphene oxide (GO) layers for a Na-ion battery with enhanced performance. GO was functionalized by reacting with N-Boc-ethylenediamine (EnBoc) which resulted in the formation of amino alcohol moieties offering three coordination sites for sodium ions. This synthetic approach led to the formation of Na-GO-EnBoc material by increasing the interlayer d-spacing from 9.7 Å to 13.17 Å (2θ = 6.7 deg.) which facilitated more Na+ ions to intercalate efficiently in between GO nanosheets. The insertion of sodium ions on the surface of intercalated GO-EnBoc nanosheets was performed by the precursor sodium perchlorate in ethylene carbonate. The resultant Na-GO-EnBoc material was characterized by using solid state MAS NMR, XPS, XRD, IR, Raman, and microscopy. The analysis suggested different types of Na+ ions on the interlayer gallery which was also substantiated by DFT calculations. The coin cell fabricated with Na intercalated GO-EnBoc-based anode exhibited a consistent reversible capacity of 170 mAhg−1 at 25 mAg−1 rate, suggesting the promise of Na-GO-EnBoc for building future rechargeable batteries.

Polyacrylic acid tethered onto the surface of vinyl functionalized silica nanoparticles for flexible hydrogel electrolytes of sodium ion hybrid supercapacitors

Hydrogel electrolytes, where water solvents and salts are confined in the porous networks of polymeric or inorganic solids, are attractive because they can resolve technical challenges of liquid electrolytes such as leakage, water decomposition, and mechanical instability. Herein, we demonstrate polyacrylic acid tethered onto the surface of vinyl functionalized silica nanoparticles (PAA-VSNP) hydrogel electrolytes through a sol-gel and radical polymerization process. The synthesis chemistry, the associated chemical structure, and the morphology of PAA-VSNP hydrogel electrolytes were comprehensively characterized analyzing FTIR, XPS and 13C and 29Si solid-state MAS NMR spectroscopies. The resulting PAA-VSNP hydrogel electrolytes were mechanically stable as verified by the stretchability up to 1122.75% of original length as well as ionically conductive as demonstrated by higher ionic conductivity of 20.23 mS cm−1 and lower activation energy of 0.106 eV than those of PVA counterparts. Integrating this PAA-VSNP hydrogel electrolytes with activated carbon and Na3V2(PO4)3/carbon composite and, flexible sodium ion hybrid supercapacitors (AC//PAA-VSNP //NVP@C SHSC SHSC) full cells could be fabricated. The as-fabricated AC//PAA-VSNP//NVP@C SHSC achieved a long-term cyclability over 4000 cycles and flexibility, delivering the larger energy and power densities 86.95 W h kg−1 and 19.94 kW kg−1 than those of AC//PVA//NVP@C and other works using hydrogel electrolytes.

The relationship between chemical structure of perfluorinated sulfonic acid ionomers and their membrane properties for PEMEC application

Polymer electrolyte membrane electrolyzer cells (PEMECs) has been confirmed as a prototype electrochemical system that is effective in converting water into hydrogen and oxygen under the application of electricity. Among the core components of PEMEC, the polymer electrolyte membrane (PEM) determines critically an overall electrochemical performance of the PEMEC. Ideally a PEM system should exhibit a complex transport behavior of small molecules (e.g., gases and ions) while mediating flows of ions in the cell; it should exhibit high proton selectivity while serving as a gas barrier to hydrogen and oxygen to increase current efficiency, which are in turn vital factors in determining an effectiveness when the electric energy is used for water electrolysis. Until now, perfluorinated sulfonic acid (PFSA) ionomers have been extensively used as PEM materials in water electrolysis while in generating hydrogen and oxygen gases simultaneously in high purity. In this study we have examined the chemical structure of PEM membranes derived from various types of PFSA ionomers by employing solid-state 19F MAS NMR. Subsequently, a structure-property-performance correlation was sought in accordance with the chemical structure, the dispersion characteristics, and membrane properties of PFSA ionomers. Furthermore, the effects of the membrane morphology as well as the ionomer packing characteristics on proton conduction and hydrogen transportation were investigated. Lastly, the membrane properties exerted by varying the chemical architectures and equivalent weight (EW) values of PFSA ionomers in PEMEC were confirmed. 3 M 725 membrane, which has the highest concentration of sulfonic acid groups in the hydrated state, has the highest proton conductivity. In addition, it showed the best water electrolytic cell performance via the synergistic effect with low gas permeability obtained as a result from the short side chain structure.

Unravelling the dynamic crosslinking mechanism in polyborosiloxane

This study offers a comprehensive investigation into the mechanism behind the dynamic crosslinking of polyborosiloxane (PBS). Despite this material being well known for over 70 years, the origin of PBS's unique viscoelastic properties has been a topic of debate in the literature. Through combined FTIR and solid-state 29Si and 11B MAS NMR analyses, this study provides evidence that the formation of Si–O–B dynamic covalent bonds, along with their associative exchange with neighboring hydroxyl-bearing species (free silanol, water, alcohol, etc.), drives the gelation and viscoelastic behavior of PBS. Results show no indication of hydrogen or dative bonding, instead the low energy barrier for formation and breakage of Si–O–B bonds allows for easy exchange at room temperature. Moreover, the study finds that the viscoelastic properties of PBS can be adjusted by the choice of boron B–O functionality, leading to n-functional dynamic crosslinking through Si–O–B bonds. This research provides a clear understanding of the mechanism of dynamic crosslinking in PBS, resolving long-standing controversies in the field.

The effect of ZnO on the structural and radiation shielding properties in borophosphate glasses

In this work, the influence of ZnO content in the structural and radiation shielding parameters of zinc borophosphate glass were studied. The glass batch was prepared by using the melt-quenching technique. The structural analyses have been carried out using XRD, Raman spectroscopy, 11B and 31P solid state MAS NMR. Density and glass transition temperature (Tg) were measurements and band gap were determined. XRD confirms the non-crystalline nature of the prepared samples. Changes in the structural characteristics with composition are associated with a replacement of BO4 by BO3 units and the replacement of PO4 phosphorous units by PO4−1 and PO4−2 units, leading to an increase of the average number of non-bridging oxygen (NBO). Density values revealed an increase of up to 43% and Tg shows reduction followed by stability with the replacement of P2O5 by ZnO. Band gap energies were measured as a function of ZnO content. Photon interaction parameters of the zinc borophosphate glasses have been investigated by the mass attenuation coefficient (MAC), half value layer (HVL), and mean free path (MFP). For radiation in the X-ray range (40 KeV), the MAC value for glass is 887% higher than for concrete and the HVL decreases almost four times, from 20 to 6 mm thickness, with the increase of ZnO content. The rise in ZnO content also improves all radiation attenuation parameters and the results reported here show that zinc borophosphate glasses present better results than ordinary concrete and is comparable to lead-based glasses. These characteristics make this glass system an excellent choice as a high-energy ionizing radiation attenuator.

Highly active sulfonic ionic liquid modified heteropoly acid composite catalysts for efficient production of ethyl palmitate

Highly active inorganic-organic composite catalysts were synthesized by incorporating Keggin-type tungstophosphoric acid (H3PW12O40; HPW) with SO3H-functionalized ionic liquids (SFILs), which were prepared by integrating chloromethylated polystyrene (CP) resin, piperazine (PI) and 1.3-propane sultone, as primary sources. The [CPPI-SO3H]nH3−nPW12O40 (n = 1.0–3.0) catalysts were characterized by XPS, SEM, FT-IR, XRD, TG-DTA, TEM, and solid-state 31P MAS NMR. These HPW-SFIL composite catalysts were found to be highly stable and possess ultra-strong Brønsted acidity, desirable self-separation properties, and catalyst reuse for production of biodiesels through esterification of palmitic acid (PA) and ethanol (EtOH). On the basis of the Box-Behnken design (BBD), further process optimization using response surface methodology (RSM) over the [CPPI-SO3H]2.0H1.0PW12O40 catalyst led to the optimized experimental conditions: EtOH/PA = 7.7 mol/mol, catalyst amount = 4.4 wt%, reaction time = 2.5 h, reaction temperature = 363 K, accompanied by an ethyl palmitate yield of 97.2%, in excellent agreement with the predicted value. The catalyst was highly stable, retaining a 94.7% yield after six consecutive running cycles. Moreover, a kinetic study performed under optimal reaction conditions revealed an apparent reaction order of 1.40 and an active energy of 14.80 kJ mol−1.

Post-acquisition correction of NMR spectra distorted by dynamic and static field inhomogeneity of cryogen-free magnets

Post-acquisition correction of NMR spectra is an important part of NMR spectroscopy that enables refined NMR spectra to be obtained, clean from undesirable out-phasing, broadening and noising. We describe analytical and numerical mathematical methods for post-acquisition correction of NMR spectra distorted by static and dynamic magnetic field inhomogeneity caused by imperfections of main superconducting coils and the cold head operation, typical for cryogen-free magnets. For the dynamic inhomogeneity, we apply a variant of the general reference deconvolution method, complemented with our mathematical analysis of spectral parameters. For the static inhomogeneity, we apply the method of a delayed Fourier transform, also supported with our analytical calculations. We verify our approach by correction processing of high-field experimental liquid-state 1H NMR spectra of water and ethanol as well as solid-state 13C MAS NMR spectra of adamantane and obtain good results for both static and dynamic field distortions. This work complements our previous work on instrumental suppression of dynamic distortions caused by the cold head operation. The results presented contribute well to the general field of processing NMR spectra and serve towards a more extensive use of cryogen-free magnets in high-resolution NMR spectroscopy.

Cryogen-free 400 MHz (9.4 T) solid state MAS NMR system with liquid state NMR potential

We show that the temporal magnetic field distortion generated by the Cold Head operation can be removed and high quality Solid-State Magic Angle Spinning NMR results can be obtained with a cryogen-free magnet. The compact design of the cryogen-free magnets allows for the probe to be inserted either from the bottom (as in most NMR systems) or, more conveniently, from the top. The magnetic field settling time can be made as short as an hour after a field ramp. Therefore, a single cryogen-free magnet can be used at different fixed fields. The magnetic field can be changed every day without compromising the measurement resolution.

A novel alkali-activated cement from mineral admixture, superabsorbent polymers, and alkali-doped carboxylate glass

In this paper, we introduce a novel approach for the targeted delivery of concentrated alkali required for activation of aluminosilicate-based cements, which avoids exposure to caustic solutions on site. The solid alkali, encapsulated within a water-soluble glass (alkali-doped carboxylate glass) is dry blended with mineral admixtures (ground granulated blast slag and fly ash) and water saturated superabsorbent polymers (SAP, being the only source of mix water in this study). The solubility of alkali-doped carboxylate glasses (ACG) was characterized. The hydration of ground granulated blast slag (GGBS) and fly ash (FA) with different curing times were monitored by SEM, XRD, FT-IR and solid-state MAS NMR, which showed the co-existence of calcium aluminum silicate hydrate (C-A-S-H) gel and sodium aluminosilicate hydrate (N-A-S-H) gel in the hydration products. The mechanical properties of AAC were tested, and the compressive strength of AAC (using ACG as alkali activator, water saturated SAP as water source) reached over 40 MPa after curing for 28 days.