27Al Nuclear Magnetic Resonance Spectroscopy Research Articles

Monitoring the Geopolymerization Reaction of Geopolymer Foams Using 29Si and 27Al MAS NMR

This study aims to investigate the geopolymerization reaction of geopolymer foams produced with three different foaming agents: aluminum powder, zinc powder, and hydrogen peroxide. The geopolymerization reaction of geopolymer foam was monitored using the 27Al and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy technique. 27Al MAS-NMR was used to monitor the reaction at an early stage, while 29Si and 27Al MAS-NMR analyses were employed at specific time intervals of 3, 6, 10, 15, and 28 days to examine the changes that occurred in the formed gel over time. We discussed in detail how the type of foaming agent used and the duration of the reaction both influence the quantity of gel formed and the amount of remnant fly ash. Our findings indicate that the type of foaming agent used affects the formation and structure of the gel, with aluminum powder leading to the highest gel formation. Additionally, the duration of the reaction plays a significant role in determining the quantity of remnant fly ash, with longer reaction times resulting in decreased fly ash content. This study sheds light on the relevance of understanding the role of foaming agents in the geopolymerization reactions of geopolymer foams and the influence of reaction time on the formed gel properties.

Fluorine in Complex Alumino-Boro-Silicate Glasses: Insight into Chemical Environment and Structure.

Fluorine incorporation into silicate glasses is important for technical fields as diverse as geophysics, extractive metallurgy, reconstructive dentistry, optical devices, and radioactive waste management. In this study, we explored the structural role of fluorine in alkaline alumino-borosilicate glass, with increasing amounts of fluorine up to 25 mol % F while maintaining the glass composition. Glasses were characterized by X-ray diffraction (XRD), 27Al and 19F magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and electron probe microanalysis. Results showed that essentially all F was retained; however, between 12 and 15 mol % F (∼3.6 and 4.5 wt % F), excess fluorine partitions to CaF2 and then NaF and Na-Al-F crystalline phases. Even prior to crystallization, there exist five distinct F sites, three of which evolve into crystalline phases. The two persistent glassy sites likely involve [4]Al-F-Ca/Na local structures. We propose a general understanding of the expected chemical shift of 19F NMR in systems containing Al, Ca, and Na.

Geopolymers made using organic bases. Part I: Synthesis and atomic structure

AbstractGeopolymers can act as a facile forming route to aluminosilicate ceramic composites due to being processed as fluids rather than as powders. However, the compositions available via typical alkali geopolymers are limited by the presence of alkali cations, introduced by the alkali silicate solution precursors. In order to expand the ceramic compositions that are accessible by geopolymer processing, this study explored the use of three strong organic bases (guanidine, tetramethylguanidine [TMG], and tetramethylammonium hydroxide [TMAOH]) as alternatives to inorganic alkali hydroxides in geopolymer synthesis. Silicate solutions were able to be produced with all three bases and favorable silica speciation was identified in the guanidine and TMG silicate solutions. Monolithic bodies were produced using guanidine and TMAOH, while no TMG samples hardened. By 27Al and 29Si nuclear magnetic resonance spectroscopy and powder X‐ray diffraction, the guanidine samples were determined to be structurally similar to those made using sodium hydroxide and hence can be called geopolymers, while the solids made with TMAOH were not structurally similar to sodium geopolymers and contained one or more unknown phases. This study has demonstrated that geopolymers can be made using organic bases rather than alkali hydroxides and that the speciation of dissolved silica alone does not indicate that an organic base silicate solution will be reactive.

Effect of addition of LiAlSiO4 on microstructure, phase composition, and electrical properties of Li1.3Al0.3Ti1.7(PO4)3–based solid electrolyte

Li1.3Al0.3Ti1.7(PO4)3 (LATP) NASICON-type ceramic, due to its high bulk conductivity, is believed to be one of the most appropriate material for application as solid electrolyte in all-solid-state lithium-ion batteries. However, its highly resistant grain boundaries strongly limit the total ionic conductivity. Therefore, in this work, an attempt has been made to overcome this problem by introducing a Li-ion conducting additive LiAlSiO4 (LASO) to LATP base matrix in order to provide more conduction paths for lithium ions between grains. The properties of Li1.3Al0.3Ti1.7(PO4)3–xLiAlSiO4 (0.02 ≤ x ≤ 0.1) composite system were studied by means of: high-temperature X-ray powder diffractometry (HTXRD), 6Li, 27Al, and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), scanning electron microscopy (SEM), and impedance spectroscopy (IS) methods. The obtained ceramic LATP–LASO materials exhibited high values of bulk conductivity, above 10−3 S/cm, and good total conductivity, exceeding 10−4 S/cm. The factors responsible for the enhancement, but also for the deterioration of total conductivity, i.e. microstructure and grain boundaries, are identified and discussed in this work.

The solid solution in the system NaMgAl(SO4)3–KMgAl(SO4)3

We synthesized six samples in the compositional field NaMgAl(SO4)3–KMgAl(SO4)3 in 20 mol% increments from pure Na to pure K compounds. We investigated them by Powder X-Ray diffraction, 23Na, and 27Al Nuclear Magnetic Resonance spectroscopy. The results confirm NaMgAl(SO4)3 as a unique phase identical to a presumed new mineral found in the fumaroles of Eldfell and Hekla volcanoes in Iceland. It tolerates less than 10 mol% K substitution for Na. There exists a compositional gap to approximately Na0.65K0.35MgAl(SO4)3 from where a solid solution extends to KMgAl(SO4)3. The mineral koryakite [NaKMg2Al2(SO4)6] is a member of the latter solid solution series. The crystal structures of all (Na,K)MgAl(SO4)3 phases are akin to NASICON (NA Super Ionic CONductor). NaMgAl(SO4)3 has R3¯c\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R\\overline{3}c$$\\end{document} symmetry and a disordered distribution of Mg and Al among the octahedral sites with only one unique site for the alkali atom. The members of the solid solution have R3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R\\overline{3}$$\\end{document} symmetry with ordered Mg–Al distribution and two unique alkali sites with different preferences for Na and K. In the crystal structure, the coordination of Na and/or K is trigonal antiprismatic, and these share bases with two octahedral Mg (Na) or Al (K) coordinations. These polyhedra are arranged in columns parallel to [001] and interconnected by SO4 tetrahedral groups. The alkali atoms from a column lie in the same (001) layers as the octahedrally coordinated atoms from the three neighboring rows. On the same level, parallel to (001), there are gaps in the other three neighboring columns forming channels containing Na+ or K+ ions.

Highly Efficient Decomposition of Perfluorocarbons for over 1000 Hours via Active Site Regeneration.

Tetrafluoromethane (CF4), the simplest perfluorocarbon (PFC), has the potential to exacerbate global warming. Catalytic hydrolysis is a viable method to degrade CF4, but fluorine poisoning severely restricts both the catalytic performance and catalyst lifetime. In this study, Ga is introduced to effectively assists the defluorination of poisoned Al active sites, leading to highly efficient CF4 decomposition at 600°C with a catalytic lifetime exceeding 1,000 hours. 27Al and 71Ga magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) showed that the introduced Ga exists as tetracoordinated Ga sites (GaIV), which readily dissociate water to form Ga-OH. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density function theory (DFT) calculations confirmed that Ga-OH assists the defluorination of poisoned Al active sites via a dehydration-like process. As a result, the Ga/Al2O3 catalyst achieved 100% CF4 decomposition keeping an ultra-long catalytic lifetime and outperforming reported results. This work proposes a new approach for efficient and long-term CF4 decomposition by promoting the regeneration of active sites.

Developing Innovative Cement Composites Containing Vine Shoot Waste and Superplasticizers.

The expansion of the construction industry requires large quantities of construction materials; therefore, the utilization of alternative raw materials that reduce the environmental impact and enhance the quality of the construction materials has received increasing interest. The comparative performance of 1% Dynamon SR3 or Dynamon SR41 superplasticizers on the properties of cement paste with 1 wt.% vine shoot waste addition (VSW) was investigated after 28 days using Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), and solid-state 27Al and 29Si nuclear magnetic resonance (NMR) spectroscopy. VSW does not delay the formation of calcium hydroxide and C-S-H and a slight decrease of the -OH band in samples containing superplasticizers, suggesting that free lime is converted to carbonates. The highest degree of crystallinity was remarked for the samples with superplasticizers. The structure of the cement paste with VSW and superplasticizers was corroborated with mechanical properties, showing increased strength in using VSW and superplasticizers. The results showed that adding 1% VSW and superplasticizers does not change the performance of the cement paste but reduces the water-cement ratio. The combination of VSW and superplasticizers led to cement composite with improved structural and mechanical properties suitable for construction.

Effect of mixing metakaolins: Methodological approach to estimate metakaolin reactivity

Geopolymers are obtained from an alkali silicate solution and aluminosilicate sources. The source commonly used geopolymer is metakaolin. The chemical composition, extraction site or calcination process of metakaolin influence its reactivity and thus the properties of the consolidated samples. This work focused on clarifying how the properties of aluminosilicate-based raw materials evolve when different metakaolin sources are mixed. The study involved mixing different metakaolins to evaluate their physico-chemical properties. The different samples were characterized by measuring their granulometry, wettability and zeta potential. Structural data were obtained from X-ray diffraction and 27Al nuclear magnetic resonance spectroscopy. It appears that the properties of the mixtures can be expressed as a function of different parameters. Granulometric properties directly depend on the quantity of each source, wettability is related to the amount of available amorphous aluminum in the sources, and zeta potential is strongly influenced by the source with the highest amount of siliceous-based impurities. This methodological approach can be applied to geopolymer synthesis.

A multi-faceted structural, thermodynamic, and spectroscopic approach for investigating ethanol dehydration over transition phase aluminas.

Understanding the role that the surface of a material plays in the mediation of a chemical reaction at the atomic level is paramount to the optimization and improvement of catalytic materials. While this area of research has matured over several decades, few techniques are sensitive enough to directly examine and differentiate the behavior of molecular adsorbates during the course of the chemical reaction with a substrate. In this study, a combined approach which involves structural characterization techniques, volumetric adsorption, temperature programmed desorption, and inelastic neutron scattering (INS) was used to investigate the mechanism of ethanol dehydration on the surface of transition phase aluminas. The alumina samples employed were extensively characterized using X-ray diffraction, solid-state 27Al nuclear magnetic resonance spectroscopy, and thermogravimetric analysis with differential scanning calorimetry. A high-precision volumetric adsorption apparatus was used to characterize the surface area and to controllably dose ethanol onto the surface of the aluminas. A modified temperature programmed desorption (TPD) method which samples the molecular composition of the vapor at discrete temperatures in a closed cell is described. INS results were used to confirm adsorption of ethanol on γ- and θ-alumina and show the reaction of ethanol and subsequent formation of ethylene as a function of temperature. The TPD and INS results affirm that the dehydration reaction and subsequent formation of ethylene on both γ- and θ-aluminas occur rapidly at 300 °C, though ethanol is still observed on θ-alumina indicating fewer active sites. These results demonstrate the value of a multi-faceted characterization approach, featuring INS, towards providing a detailed understanding of the ethanol dehydration mechanism on θ-alumina and further provide the basis for extending this approach to other systems in heterogeneous catalysis and areas where molecule-substrate interactions are poorly understood.

Use of Vine Shoot Waste for Manufacturing Innovative Reinforced Cement Composites

Due to the current concern with the environmental impacts produced by the construction industry, many studies have been conducted to capitalize on the advantages of waste to develop sustainable materials. The study reports an innovative, non-conventional cement-based composite material containing 10 wt.% vine shoot waste, representing a step forward toward the use of this lignocellulosic waste. The investigations were carried out using scanning electron microscopy with energy dispersive X-ray analysis, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and solid-state 27Al and 29Si nuclear magnetic resonance spectroscopy. The addition of vine shoot waste to the cement paste increases the amount of hydration products (calcium silicate hydrate (CSH), calcium hydroxide (CH), calcium carbonate (CaCO3) and ettringite), leading to a more compact and dense structure. The structural characterization techniques also confirmed the formation of a higher amount of hydration products in the case of vine shoot waste added to the cement paste.

Formation of C[sbnd]S[sbnd]H and M[sbnd]S[sbnd]H gels in alkali-activated materials based on marl by-products from phosphate mines

Marls present high volume of phosphate waste rocks that are chemically inert, but their disposal creates diverse environmental issues. This study aims to evaluate the reuse of white marls from phosphate mines as a precursor to produce Alkali-Activated Materials (AAM). White marls containing palygorskite clay were calcined up to 850 °C. The alkali activation process involved the use of calcined marls (as a precursor) and NaOH:Na2SiO3 as activators. Marls features were identified by X-ray Diffraction, X-ray Fluorescence, Fourier-transform infrared spectroscopy and Thermo-gravimetric analysis. In addition, the dissolution of Al and Si species from the marl was studied for different Sodium hydroxide concentrations and calcination temperatures. Furthermore, the compressive strength of elaborated AAM was measured, and selected samples were characterized using several methods including Solid-state 29Si – 27Al Nuclear Magnetic Resonance spectroscopy and Scanning Electron Microscopy. The XRD and NMR results indicated the co-precipitation of CSH and MSH with the presence of low amount of C/N-(A)-SH explained by the content of aluminum in marl. This result was confirmed by EDX and FTIR analysis. While the optimum compressive strength of 38 MPa was obtained for AAM based on calcined marl at 750 °C. This study results revealed that marls waste rocks could be used as a precursor for the formulation of AAM in construction applications.

Structure of diopside, enstatite, and magnesium aluminosilicate glasses: A joint approach using neutron and x-ray diffraction and solid-state NMR.

Neutron diffraction with magnesium isotope substitution, high energy x-ray diffraction, and 29Si, 27Al, and 25Mg solid-state nuclear magnetic resonance (NMR) spectroscopy were used to measure the structure of glassy diopside (CaMgSi2O6), enstatite (MgSiO3), and four (MgO)x(Al2O3)y(SiO2)1-x-y glasses, with x = 0.375 or 0.25 along the 50 mol. % silica tie-line (1 - x - y = 0.5) or with x = 0.3 or 0.2 along the 60 mol. % silica tie-line (1 - x - y = 0.6). The bound coherent neutron scattering length of the isotope 25Mg was remeasured, and the value of 3.720(12) fm was obtained from a Rietveld refinement of the powder diffraction patterns measured for crystalline 25MgO. The diffraction results for the glasses show a broad asymmetric distribution of Mg-O nearest-neighbors with a coordination number of 4.40(4) and 4.46(4) for the diopside and enstatite glasses, respectively. As magnesia is replaced by alumina along a tie-line with 50 or 60 mol. % silica, the Mg-O coordination number increases with the weighted bond distance as less Mg2+ ions adopt a network-modifying role and more of these ions adopt a predominantly charge-compensating role. 25Mg magic angle spinning (MAS) NMR results could not resolve the different coordination environments of Mg2+ under the employed field strength (14.1T) and spinning rate (20kHz). The results emphasize the power of neutron diffraction with isotope substitution to provide unambiguous site-specific information on the coordination environment of magnesium in disordered materials.

Thermal activation of palygorskite for enhanced fluoride removal under alkaline conditions

Fluoride contamination of groundwater is a global environmental problem. Based on adsorption treatment strategies, magnesium-based materials have shown potential for defluoridation of this water source. In this research, we calcined raw palygorskite (RPAL), a natural magnesium-rich clay, at different temperatures (100–1000 °C), to examine the defluoridation performance. The evolution of the morphology, physical-chemical properties, and crystal structure was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and 27Al and 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy. Palygorskite calcined at 200 °C (CP200) had F− uptake of ∼1.6 mg F−/g within a neutral-to-basic pH region of F-contaminated groundwater (e.g., pH 7–9), which is 5–6 times larger than that for RPAL. Additionally, CP200 and CP400 exhibited comparatively greater adsorption performance for fluoride removal compared with activated alumina (AA) under alkaline conditions (e.g., 1.5–3 times at pH ≥ 9). The dependence of fluoride uptake by the calcined samples appeared to be related to major changes in the crystal structure of palygorskite, particularly the dehydration of zeolite waters and partially coordinated water within pores. The exposed > MgOH2 groups at tunnel edges may play an important role in fluoride removal, especially at elevated pH. The higher stability under alkaline conditions and the lower sensitivity to pH compared with AA demonstrated the potential of calcined palygorskite as an effective magnesium-based clay for the remediation of fluoride contamination of groundwater.

Effect of CaF2 and Li2O on structure and viscosity of low-fluoride slag for electroslag remelting of rotor steel

The structure and viscosity of CaF2-CaO-Al2O3-B2O3-SiO2-Li2O slag with varying CaF2 and Li2O contents were investigated by Raman spectroscopy, 27Al, 29Si and 11B magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and rotating cylinder method, respectively. The relative fraction ofQAl2 significantly increases, the fractions ofQAl3 andQAl4 decrease with increasing the CaF2 or Li2O content. Aluminum exists in the form of four-coordinated aluminum (AlⅣ) corresponding to AlO4 and a small amount of AlO3F. The fraction ofQSi0 species increases at the expense ofQSi1,QSi2(1Al) andQSi2 with increasing the CaF2 or Li2O content. B is present in the form of BⅢ, besides 0.57% of BIV in the glass with 14.69mass% CaF2. The relative fraction of T0 increases and T1 decreases as the CaF2 or Li2O content is increased. The degree of polymerization of aluminosilicate and borates decreases with increasing the CaF2 or Li2O content, which is consistent with the results of viscosity and viscous activation energy.

Modifications in hydration kinetics and characteristics of calcium aluminate cement upon blending with calcium sulfoaluminate cement

The present study explores the modifications in hydration kinetics and characteristics of calcium aluminate cement (CAC) upon blending with calcium sulfoaluminate (CSA) cement. CAC was replaced with CSA cement at 0, 30, 50, 70, or 100 wt%. The hydration properties of the samples were evaluated and characterized by X-ray diffraction, thermogravimetric analysis, 27Al nuclear magnetic resonance spectroscopy, compressive strength tests, isothermal calorimetry, autogenous shrinkage measurements, and thermodynamic modeling. The test results indicated that the incorporation of CSA cement altered the hydration pathway of the CAC clinkers, promoting the formation of AFm phases over katoite. In addition, the addition of CSA cement increased the compressive strength development and reduced the total hydration heat release. In contrast, the occurrence of heat release rate peak was advanced by the addition of CSA cement. Furthermore, the CSA cement compensated for the autogenous shrinkage development of the samples, reaching almost no volumetric movement in the sample with 50% CSA cement.

Variation in Phosphorus Speciation of Sewage Sludge throughout Three Wastewater Treatment Plants: Determined by Sequential Extraction Combined with Microscopy, NMR Spectroscopy, and Powder X-ray Diffraction.

The variation in phosphorus (P) speciation of sewage sludge throughout three wastewater treatment plants (WWTPs) was obtained by combining sequential P extraction with optical and scanning electron microscopy (SEM), chemical analyses, powder X-ray diffraction (PXRD), and 27Al and 31P nuclear magnetic resonance (NMR) spectroscopy. The WWTPs combine chemical P removal (CPR) and enhanced biological P removal (EBPR) and were compared to understand the effect of iron (Fe) dosing with and without codosing of aluminum (Al) and thermal hydrolysis on the P speciation. 31P NMR showed comparable inorganic orthophosphate (ortho-P, 53-60% of total P) and organophosphate (organic-P, 37-45%) in primary sludge, whereas polyphosphate (poly-P, 23-44%) from poly-P accumulating organisms (PAOs) was mainly observed in the secondary sludge. Inorganic ortho-P (90-98%) dominated after anaerobic digestion, which degraded poly-P and most organic-P. The inorganic ortho-P was mainly Fe bound P (Fe-P), especially after anaerobic digestion (71%). Codosing of Fe and Al led to two comparable fractions: Fe-P (38%) and P sorbed on amorphous Al (hydr)oxides (38%). Vivianite was identified in all samples by microscopy and chemical extraction but was PXRD amorphous in 12 out of 17 samples. Thus, vivianite may be more common in sewage sludge than previously known.

Effect of Ammonium Salts on the Conductivity and Current Efficiency of Dimethyl Sulfone-Aluminum Chloride Electrolytes

In this study, we investigated the effects of ammonium chloride (NH4Cl) and tetramethylammonium chloride (TMAC) on the conductivity and current efficiency of dimethyl sulfone (DMSO2)-aluminum chloride (AlCl3) electrolyte. When NH4Cl and TMAC were added independently, the conductivity of the electrolyte increased, which was attributed to a decrease in the electrolyte viscosity. 27Al nuclear magnetic resonance (NMR) spectroscopy showed that chloride addition reduced the ratio of solvated Al3+ ions. This occurred because Al3+ and Cl− dissociated from chloride and formed AlCl4 −, which increased the amount of non-solvated DMSO2 species, consequently decreasing the electrolyte viscosity. NH4Cl improved the plating appearance even when added in small amounts; however, when added in relatively high concentrations, the conductivity increased, while the current efficiency decreased significantly. Conversely, TMAC did not induce a significant decrease in the current efficiency up to an addition amount of 0.1 mol. The electrolyte with the co-addition of TMAC and a small amount of NH4Cl showed increased conductivity while minimizing the decrease in current efficiency. Also, good results in the appearance and purity of the plating film were obtained.

Sintering, hardness and cation inversion of nanocrystalline Beryllium – Magnesium aluminate ceramics

Beryllium-magnesium aluminate (Be0.1Mg0.9Al2O4 and Be0.2Mg0.8Al2O4) nanoparticles are synthesized by a coprecipitation method and sintered using Spark Plasma Sintering (SPS) to achieve near full density ceramics with grain sizes at the nanoscale. The sintered nanoceramics display grain sizes ranging from 14 to 33 nm, which are analyzed for optical transmission, Vickers hardness, and cation site inversion. When compared to Be-free MgAl2O4 nanoceramics, both Be0.1Mg0.9Al2O4 and Be0.2Mg0.8Al2O4 show transmissions ∼30% lower at wavelength in the infrared range. The samples show a Vickers hardness of ∼19.2 GPa with no apparent dependence on grain size. These values are consistently lower to those reported for beryllium-free MgAl2O4 spinel with similar grain size. 27Al and 9Be Nuclear Magnetic Resonance (NMR) spectroscopy reveals that beryllium does not have a significant effect on cationic site inversion in the spinel and, similar to beryllium-free MgAl2O4, inversion remains solely a function of grain size. The results indicate beryllium ions form solid-solutions with MgAl2O4 spinel structure and do not alter the grain boundaries significantly enough to influence the mechanical properties of nanocrystalline ceramics.

Characterization and Optimization of AZO Nanoparticles as Coatings for Flexible Substrates toward High IR Reflectivity.

Energy consumption by air-conditioning is expansive and leads to the emission of millions of tons of CO2 every year. A promising approach to circumvent this problem is the reflection of solar radiation: Rooms that would not heat up by irradiation will not need to be cooled down. Especially, transparent conductive metal oxides exhibit high infrared (IR) reflectivity and are commonly applied as low-emissivity coatings (low-e coatings). Indium tin oxide (ITO) coatings are the state-of-the-art application, though indium is a rare and expensive resource. This work demonstrates that aluminum-doped zinc oxide (AZO) can be a suitable alternative to ITO for IR-reflection applications. AZO synthesized here exhibits better emissivity to be used as roofing membrane coatings for buildings in comparison to commercially available ITO coatings. AZO particles forming the reflective coating are generated via solvothermal synthesis routes and obtain high conductivity and IR reflectivity without the need of any further post-thermal treatment. Different synthesis parameters were studied, and their effects on both conductive and optical properties of the AZO nanoparticles were evaluated. To this end, a series of characterization methods, especially 27Al-nuclear magnetic resonance spectroscopy (27Al-NMR) analysis, have been conducted for a deeper insight into the particles' structure to understand the differences in conductivity and optical properties. The optimized AZO nanoparticles were coated on flexible transparent textile-based roofing membranes and tested as low-e coatings. The membranes demonstrated higher thermal reflectance compared with commercial ITO materials with an emissivity value lowered by 16%.

Structural dependence of crystallization in phosphorus‐containing sodium aluminoborosilicate glasses

AbstractThe article reports on the structural dependence of crystallization in Na2O–Al2O3–B2O3–P2O5–SiO2‐based glasses over a broad compositional space. The structure of melt‐quenched glasses has been investigated using 11B, 27Al, 29Si, and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, while the crystallization behavior has been followed using X‐ray diffraction and scanning electron microscopy combined with energy dispersive spectroscopy. In general, the integration of phosphate into the sodium aluminoborosilicate network is mainly accomplished via the formation of Al–O–P and B–O–P linkages with the possibility of formation of Si–O–P linkages playing only a minor role. In terms of crystallization, at low concentrations (≤5 mol.%), P2O5 promotes the crystallization of nepheline (NaAlSiO4), while at higher concentrations (≥10 mol.%), it tends to suppress (completely or incompletely depending on the glass chemistry) the crystallization in glasses. When correlating the structure of glasses with their crystallization behavior, the MAS NMR results highlight the importance of the substitution/replacement of Si–O–Al linkages by Al–O–P, Si–O–B, and B–O–P linkages in the suppression of nepheline crystallization in glasses. The results have been discussed in the context of (1) the problem of nepheline crystallization in Hanford high‐level waste glasses and (2) designing vitreous waste forms for the immobilization of phosphate‐rich dehalogenated Echem salt waste.