29Si Nuclear Magnetic Resonance Spectra Research Articles

Effect of lithium concentration on the network connectivity of nuclear waste glasses

Structure of borosilicate glasses with varying Li2O contents were investigated using Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), employing 6Li, 11B, 23Na, 27Al and 29Si nuclei. 11B MAS NMR revealed that increasing Li2O contents result in formation of [BO4]− sites at the expense of BO3. 11B{6Li} and 27Al{6Li} dipolar heteronuclear multiple quantum correlation (D-HMQC) NMR revealed Li as a charge compensator for anionic tetrahedral sites with increased Li. 11B{6Li} J-coupling mediated HMQC NMR suggested the possible association of Li with non-bridging oxygens on Q2 and Q3 sites, indicating its dual role in the glass network. 29Si and 23Na MAS NMR spectra showed depolymerisation of the silicate network and shortening of Na-O bond lengths with increased Li. NMR results are supported by Raman spectroscopy and thermal analysis that indicate depolymerisation of the silicate network and a reduction in glass transition temperature at higher Li content.

Probing oxide-based glass structures by solid-state NMR: Opportunities and limitations

This Primer critically reviews the possibilities and limitations of probing the short-range structure of an oxide-based glass by routine magic-angle spinning (MAS) or triple-quantum MAS (3QMAS) nuclear magnetic resonance (NMR) experiments. We briefly outline the structural features of oxide-based glasses and the basics of solid-state NMR. Besides suggesting guidelines for selecting favorable experimental conditions and important considerations for recording high-quality MAS NMR spectra amenable for subsequent analysis, we review options for extracting NMR observables and their distributions from spins-1/2 as well as half-integer spin quadrupolar nuclei. Considering that the isotropic chemical shift remains the primary probe of local structure by MAS NMR, we thoroughly review its dependence on the short-range oxide-based glass parameters from the viewpoint of a very simple and intuitive but qualitative model. The utility of deconvolutions of notably 29Si and 31P MAS NMR spectra are discussed critically. We also suggest alternative yet qualitative analysis options that are available whenever MAS NMR spectral deconvolutions are not warranted without additional information, which incidentally applies to a majority of modern multicomponent glasses.

Coal fly ash to Y zeolite of great purity and crystallinity: A new and green activation method of combined in situ microwave and ultrasound

Highly crystalline and pure Y (FAU) zeolite were synthesized from coal fly ash (CFA) using a combined in situ microwave and ultrasonic irradiation-assisted method, improving the extraction efficiency of silicon and aluminum from coal fly ash with limited energy usage relative to conventional microwave or ultrasound methods. Significant improvement in the combined method was evident following activation in 4 mol/L sodium hydroxide solution for 1 h at 100°C whereby 39.80 wt% conversion of CFA was attained along with 70.26 mol.% conversion of Si and 68.03 mol.% conversion of Al. Solid-state 29Si and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were used to investigate the framework chemical coordination environment, while the temperature-programmed desorption of NH3 (NH3-TPD) and pyridine-Fourier transform infrared (Pyridine-FTIR) spectra were employed to quantitatively detect the acidity and types of acid sites of the sample. The Si to Al ratio (SAR) of the as-obtained CFA-based Y zeolite was 4.65 with a specific surface area of 916.10 m2/g, leading towards excellent CO2 adsorption (107.14 cm3/g at 0 °C). Furthermore, the thermocatalytic performance of the CFA-Y sample was analyzed in the conversion of cumene, with high silica commercial ultra-stable Y (USY) zeolite as a reference.

Recycling light-emitting-diode waste quartz sand and stone sludge for the synthesis of amine grafted mesoporous humidity control material

This article proposes a cost-effective development method to recycle two types of waste material (i.e., light-emitting-diode (LED) waste quartz and stone sludge) to produce mesoporous materials. The proposed method is simple yet effective. Extraction of the precursor liquid from the silicon and aluminum sources respectively contained in the waste quartz and stone sludge is based on the alkali fusion method, and the mesoporous material is synthesized after the hydrothermal reaction. The novelty of this work lies in our functionalization of Mobil Composition of Matter No. 41 (MCM-41) through amine group grafting (AGG-MCM-41). The results show that the structure of the mesoporous MCM-41 grafted by the amine functional groups remains orderly. The 29Si nuclear magnetic resonance spectrum confirmed that the supported surface of the MCM-41 features a large number of silanol groups, which verifies that modification of the amine functional group improved the effect. The results show that when the addition amount of amine functional group is 5 vol% (when relative humidity = 95%), the highest equilibrium moisture content of the material is 26.5 kg/kg. The wet performance of the material was studied, and it was proved that 5.0-AGG-MCM-41 complies with the standard of Japanese Industrial Standard (JIS A 1475) (equilibrium moisture content>5 m3/m3). The research results also show that the optimal equilibrium moisture content is more than 44 times that of metal-organic frameworks humidity pump. Therefore, the synthesized AGG-MCM-41 offers excellent humidity control performance in the practical application of building materials as it narrows the indoor humidity fluctuation spontaneously without any energy consumption. This creates new opportunities for smart indoor humidity control. The amine-group-grafted MCM-41 effectively reduces the shortcomings of high energy consumption, high costs, and insufficient space caused by mechanical dehumidifiers. In addition, the production of AGG-MCM-41 from LED waste and stone sludge achieves 100% recycling. Transformation of two problematic industrial byproducts into humidity-conditioning materials with beneficial technical and environmental properties represents a significant contribution towards the goals of sustainable development.

Time-varying structure evolution and mechanism analysis of alite particles hydrated in restricted space

Restricted space could lead to the structure evolution of calcium silicate hydrate (C–S–H) especially during the later hydration stage, which essentially affects the strength and durability of Portland cement based materials. In order to get insights into the effect of restricted space on C–S–H microstructure, the alite powders were pressed into discs for hydration. The pre pressing treatment provides a relatively denser microstructure, which simulates the restricted space during the late hydration of alite or cement. The structure of hydrates grown in restricted space was revealed by Fourier transform infrared spectra, Raman spectra, 29Si nuclear magnetic resonance spectra, scanning electron microscope and energy dispersive X-ray spectroscopy. The results show that restricted space leads to the formation of unstable Ca–O bonds and Si–O bonds in early hydrates, and influences the silicate chains in C–S–H by the formation of high polymerized hydrates (Q3 silicates) at early stage. The content of Q3 silicates in the hydrates of restricted space is the highest at 7 d and then decreases, which is opposite to the control with the lowest Q3 silicates content at 7 d and the highest content at 28 d. The hydrates which form at 28 d show a remarkable higher chemical shift of Q3 sites and a lower Ca/Si ratio than that of the control. The findings indicate that the restricted space may lead to stress, which rearranges the nanostructure of C–S–H and induces a varied structure in Q3 silicates of C–S–H. This work lies a theoretical foundation for exploring the structure evolution of C–S–H in cement concrete after long service.

Behavior of hydrates in cement paste reacted with silicate-based impregnant

In order to improve the durability of concrete structures, silicate-based impregnant have been used, but the chemical interaction mechanism is not clear. Silicate-based impregnant react with calcium hydroxide, which is formed during the process of cement hydration, and form compounds similar to a calcium silicate hydrate (C–S–H). This paper performs reaction experiments by Ca/Si ratio, and solid state nuclear magnetic resonance (NMR) and X-ray powder diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy are conducted for observing chemical changes of cement paste with silicate-based impregnants. Based on the results of XRD, reduction of monosulfate phase was observed as well as the formation of C–S–H (tobermorite-like phase). 29Si and 27Al NMR spectra also correspond with the XRD results. Further, possibility of both Al/Si substitution and formation of a structure close to C-(A)-S-H (C–S–H containing Al) were observed. Therefore, silicate-based impregnant formed not only new C–S–H reacting with calcium hydroxide, but also influenced other hydrates.

Chemical-physical and mineralogical characterization of ceramic raw materials from Moroccan northern regions: Intriguing resources for industrial applications

Five natural ceramic raw materials from three north-west Moroccan regions (Berrechid, Tiflet and Kemmiset), which are used in the ceramic industry, have been studied with the aim to devise other possible uses or optimize the mixture and thermal conditions for manufacturers. Chemical-physical and mineralogical characterization techniques (XRD, ESEM, FTIR, CEC, TGA, BET, etc.) have been applied either to compare the bulk, grinded (the fraction used in ceramic industry) and sieved materials or to understand their changes upon heating, at temperatures comparable with those applied in ceramic industry. The data indicate that the bulk and sieved materials do not show relevant differences. All the samples are composed for at least 20% wt of quartz, accompanied by a different amount of phyllosilicates. The Tiflet material has a higher content in calcite and dolomite, together with amount of feldspar, which makes this material of particular interest for ceramic industry. Feldspar is used in ceramic industry as fluxing agent inducing early vitrification, increasing the firing shrinkage and decreasing the firing temperatures. The 29Si and 27Al solid state nuclear magnetic resonance spectra recorded before and after heating evidenced the presence of new phases formed by the dehydroxylation and decarboxylation processes. The mineral transformations upon heating were studied also for the clays fraction by in-situ XRD technique.

The influence of sapphire substrate silicon carbide sludge on structural properties of metakaolin‐based geopolymers

AbstractThis study investigated a geopolymerization system focused on the effects of the solid‐to‐liquid ratio (S/L) were ranging from 0.4 to 1.0, which produces geopolymers with various silicon carbide sludge (SCS) replacement levels (0–40 wt. %). The results indicated that the silicon carbide sludge metakaolin‐based (SCSMB) geopolymers increased S/L ratios from 0.8 to 1.0, reducing initial and final setting times. Flexural strength of SCSMB geopolymers of the SL ratio of 0.4 increased rapidly from 1.31 to 1.70 MPa during the early stage of curing (1–14 days). For SCSMB geopolymers with 10–40% SCS replacement, peak of SiOSi bonds for geopolymers at 524 cm−1 shifted to a higher wavenumber of 527 cm−1. 29Si nuclear magnetic resonance (NMR) showed that SCSMB geopolymer with an SCS replacement ratio of 10% increased S/L ratios from 0.8 to 1.0 (56 days) and increased the fractions of Q4(3Al; 38.2%–38.4%), Q4(2Al; 28.7%–31.7%), and Q4(1Al; 13.7%–14.6%). Moreover, the peak in 29Si NMR spectra shifted to the right side (higher frequency), indicating that an increased number of aluminum tetrahedrons coordinated with silicon tetrahedrons. SCSMB geopolymers with 10% SCS replacement and an S/L ratio of 1.0 yielded highly favorable mechanical characteristics and microstructure.

A new peak fitting method for 1D solid-state 29Si NMR spectra based on singular spectrum analysis

[Formula: see text]Si Nuclear Magnetic Resonance (NMR) can measure the molecular structure of silicate in oilfield reinjection water. However, noise in [Formula: see text]Si NMR spectra (NMRS) affects the determination of silicate molecular structure type. To solve this problem, a new peak fitting method (Two-step Greedy-Singular Spectrum Analysis-Gaussian Fitting Method, TSG-SSA-GFM) is proposed in this paper. This method first uses TSG to determine the embedding dimension, then uses SSA to determine the characteristic peak position. Finally, GFM is used to calculate the molar ratio of characteristic peaks. The results show that TSG can quickly determine the embedding dimension and reduce computation by at least 50% vs. the global ergodic method. The mean deviation of characteristic peak positions determined by SSA is 0.07 ppm, while Discrete Wavelet Transform (DWT) and Empirical Mode Decomposition (EMD) cannot determine characteristic peaks of [Formula: see text]Si NMRS containing overlapping peak. The average [Formula: see text]-squared of Gaussian fitting of [Formula: see text]Si NMRS is 98.4% while Lorentzian is 90.6%. Therefore, this study provides an important method for quantitative analysis of [Formula: see text]Si NMRS.

A peak fitting method for 29Si nuclear magnetic resonance spectra based on singular spectral analysis

Solid-state 29Si Nuclear Magnetic Resonance (NMR) is commonly used in the detection of silicate molecular structure. However, noise in 29Si NMR spectra (NMRS) disturbs the judgment of characteristic peak, thereby affecting the determination of molecular structure types of silicates. A method of peak fitting based on Singular Spectrum Analysis (SSA) is proposed in this paper accordingly. SSA is adopted to determine the position of characteristic peaks and Gaussian fitting model (GFM) is applied to fit characteristic peak in the method, thereby realizing a quantitative analysis of 29Si NMRS. When SSA is applied, the embedding dimension m determines its accuracy. However, the methods for determining m, such as correlation dimension (GP) and False Nearest Neighbors (FNN), often fail because of the differences in the shape of 29Si NMRS. Therefore, two-step greedy (TSG) is proposed to determine the embedding dimension m in the paper. The accuracy of TSG can be respectively improved by 350.7% and 366.8% compared with GP and FNN according to example verification, and the method can accurately determine the embedding dimension m. The peak fitting method (TSG-SSA-GFM) is formed by combining TSG, SSA, and GFM. The experimental results show that the average error of the characteristic peak location is 0.09ppm, and goodness of fit is 99.75%. The method has good accuracy. Therefore, the study provides an important method for the quantitative analysis of 29Si NMR.

Deconvolution method of 29Si MAS NMR spectra applied to homogeneous and phase separated lanthanum aluminosilicate glasses

The structural and microstructural properties of both homogeneous and phase separated lanthanum aluminosilicate (La2O3-Al2O3-SiO2 i.e. LaAS system) glasses were investigated. The microstructural observations and the structural characterization by X-ray Diffraction and by Nuclear Magnetic Resonance have highlighted the role of aluminum to favor a homogeneous vitreous aluminosilicate network by a high-level of Al/Si intermixing. A qualitative and simplified structure description is proposed from 29Si nuclear magnetic resonance spectra assignment according to Qn(mAl) species by controlling the deviation of chemical parameters. According to this approach, a homogeneous distribution of non-bridging oxygen in the aluminosilicate network and Al-O-Al linkages are considered for homogeneous glasses with high Al/Si atomic ratio. Phase separated samples are characterized by a low Al/Si atomic ratio inducing spinodal or nucleation/growth phase separation according to the depolymerization level. Homogeneity degree of the samples is discussed according to the intermixing level between silicon tetrahedra and aluminum polyhedra as a function of the proportion of Qn and Qn(mAl) species.

SiAlOC glasses derived from sol-gel synthesized ladder-like silsesquioxanes

The main aim of this study was to describe both the formation process of SiOC glasses doped with Al3+ cations and the resulting differences in their structures in comparison with undoped silicon oxycarbide glasses. A novel material was formed by means of the sol-gel method with the application of alkyl-substituted alkoxysilanes and a butoxy derivative of aluminum (Al(OC4H9)3) as a source of Al3+ ions. After the synthesis of a sol, the material was treated with a two-step thermal processing including aging (70 °C) and annealing (800 °C). As a result, yellowish xerogel (aging) and black glasses (annealing) were obtained and subjected to structural investigation, including X-ray diffraction (XRD), middle infrared spectroscopy (MIR), Raman, electron dispersive spectroscopy (EDS), and nuclear magnetic resonance (NMR) methods. The obtained results were compared to corresponding findings for SiOC glasses, obtained with the same experimental procedure. An additional thermogravimetric analysis (TGA) study was carried out for the xerogel in order to determine its thermal behavior in a protective atmosphere up to 1000 °C. The resultant mass loss curve was much smoother for the Al-doped material, indicating the beneficial impact of Al3+ addition on the formation process. XRD and spectroscopic (MIR, Raman, magic angle spinning (MAS) NMR) research revealed the formation of an amorphous silsesquioxane xerogel with a slightly modified ladder-like structure, and silicon oxycarbide glasses successfully doped with Al3+ ions, after aging and annealing, respectively. Moreover, NMR studies confirmed the introduction of aluminum into the glass network, based on the presence of Q4(1Al) and [AlO4] species in the 29Si and 27Al MAS NMR spectra, respectively. Additionally, the results from EDS and Raman spectroscopic studies suggested the partial release of free carbon phase from the glass network because of cationic substitution and ordering influence of Al3+ cations on the glass structure.

Introduction of Al into the HPM-1 Framework by In Situ Generated Seeds as an Alternative Methodology

An alternative method for the introduction of aluminum into the STW zeolitic framework is presented. HPM-1, a chiral STW zeolite with helical pores, was synthesized in the pure silica form, and an aluminum source was added by in situ generated seeds. Displacements of the peak positions in the Al samples were found in the X-ray diffractograms, indicating the possible incorporation of the heteroatom into the framework. Using an analysis of the 29Si and 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra, we concluded that the aluminum was effectively introduced into the framework. The (AlTETRAHEDRAL/AlOCTAHEDRAL) ratio and its textural properties were studied to explain the catalytic ethanol conversion results at medium temperatures. The sample with the lowest Si/Al ratio showed the best results due to its higher surface area and pore volume, in comparison to those observed for the sample with the highest Si/Al ratio, and due to its higher bulk tetrahedral aluminum content, in comparison to the intermediate Si/Al ratio sample. All catalysts were selective to ethylene and diethyl ether, confirming the presence of acidic sites.

Enhancements and mechanisms of nanoparticles on wear resistance and chloride penetration resistance of reactive powder concrete

In this paper, nano-SiO2 (NS), nano-TiO2 (NT) and nano-ZrO2 (NZ) at contents of 1% and 3% were adopted to improve the wear resistance and chloride penetration resistance of reactive powder concrete (RPC) with room temperature cuing or heat curing. The modification mechanisms of nanoparticles on RPC properties were investigated through X-ray powder diffraction analysis, thermogravimetric analysis, scanning electron microscopy observation and 29Si Nuclear Magnetic Resonance spectra analysis. Research results show that the wear resistance and chloride penetration resistance of RPC incorporating with nanoparticles are significantly improved because the addition of NS/NT/NZ can modify the microstructures of RPC. The abrasion loss per unit area of 3 wt% NZ filled RPC with heat curing is increased by 48.46% compared with the control RPC. The chloride diffusion coefficient of RPC containing 3 wt% NT, 1 wt% and 3 wt% NZ with room temperature curing can be decreased to 0. The heat curing is more beneficial to improve the wear resistance of RPC containing NS/NT/NZ than room temperature curing, while room temperature curing is more effective to improve the chloride penetration resistance.

29Si NMR Chemical Shifts in Crystalline and Amorphous Silicon Nitrides.

We investigate 29Si nuclear magnetic resonance (NMR) chemical shifts, δiso, of silicon nitride. Our goal is to relate the local structure to the NMR signal and, thus, provide the means to extract more information from the experimental 29Si NMR spectra in this family of compounds. We apply structural modeling and the gauge-included projector augmented wave (GIPAW) method within density functional theory (DFT) calculations. Our models comprise known and hypothetical crystalline Si3N4, as well as amorphous Si3N4 structures. We find good agreement with available experimental 29Si NMR data for tetrahedral Si[4] and octahedral Si[6] in crystalline Si3N4, predict the chemical shift of a trigonal-bipyramidal Si[5] to be about −120 ppm, and quantify the impact of Si-N bond lengths on 29Si δiso. We show through computations that experimental 29Si NMR data indicates that silicon dicarbodiimide, Si(NCN)2 exhibits bent Si-N-C units with angles of about 143° in its structure. A detailed investigation of amorphous silicon nitride shows that an observed peak asymmetry relates to the proximity of a fifth N neighbor in non-bonding distance between 2.5 and 2.8 Å to Si. We reveal the impact of both Si-N(H)-Si bond angle and Si-N bond length on 29Si δiso in hydrogenated silicon nitride structure, silicon diimide Si(NH)2.

NMR crystallography of zeolites: How far can we go without diffraction data?

Nuclear magnetic resonance (NMR) crystallography-an approach to structure determination that seeks to integrate solid-state NMR spectroscopy, diffraction, and computation methods-has emerged as an effective strategy to determine structures of difficult-to-characterize materials, including zeolites and related network materials. This paper explores how far it is possible to go in determining the structure of a zeolite framework from a minimal amount of input information derived only from solid-state NMR spectroscopy. It is shown that the framework structure of the fluoride-containing and tetramethylammonium-templated octadecasil clathrasil material can be solved from the 1D 29 Si NMR spectrum and a single 2D 29 Si NMR correlation spectrum alone, without the space group and unit cell parameters normally obtained from diffraction data. The resulting NMR-solved structure is in excellent agreement with the structures determined previously by diffraction methods. It is anticipated that NMR crystallography strategies like this will be useful for structure determination of other materials, which cannot be solved from diffraction methods alone.

Nanocomplexes of Magnesium Phenylsiloxanes - Moleculer Structere and Properties

Polyphenylsiloxanes containing magnesium (polymagnesiumphenyl siloxanes) with Si:Mg ratios of 1:1.5 and 1:2 have been synthesized by the exchange reaction in a mixture of benzene (toluene)–dimethyl sulfoxide with yields of 58 and 72%, respectively. The composition and structure of the synthesized polymers have been studied by the methods of positron annihilation spectroscopy (PAS), X-ray diffraction analysis (XRD), 29Si nuclear magnetic resonance (NMR), and infrared spectroscopy (IR). The cross-section surface area (S) (by the Miller–Boyer method) and coherent scattering regions (CSR) volumes have been calculated based on the XRD data. The PAS data allowed calculating the specific volumes of Ps and e+ “traps”. The T3 and T2 signal areas in 29Si NMR spectra enabled us to determine the structure of the unit cell of polymagnesiumphenyl siloxanes (PMgPS). As was demonstrated by the electron microscopy, PMgPSs were in the form of spherical particles of a radius of 50–120 nm. The polymers physical–chemical characteristics were determined from nitrogen adsorption. Based on the specific adsorption area, the radii of spherical particles in a densely packed layer, whose size depends proportionally on the specific polarization potential and the specific area, have been calculated. The calculated size values for spherical particles are similar to those found by the method of electron microscopy. An assumption on a fractal structure of spherical particles has been made on the basis of the calculated data, and data of scanning electron microscopy.

Waterborne acrylic resin modified with glycidyl methacrylate (GMA): Formula optimization and property analysis

Novel waterborne acrylic resin modified with glycidyl methacrylate (GMA) was successfully synthesized via homogeneous solution polymerization in isopropyl alcohol followed by solvent exchange with water. Aminopropyltriethoxysilane (KH-550), a silane coupling agent that can crosslink with resin and iron base material, was used as curing agent for solidifying this GMA modified resin. The cured mechanism of the coating was also investigated by 29Si nuclear magnetic resonance (29Si NMR) spectra and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The waterborne acrylic resin was sprayed on the iron base material and cured by KH-550 for 30 min at 100 °C to form the desired coating. The GMA and KH-550 were found to significantly decrease the curing temperature of this two-component waterborne resin. The thermal property of the coatings with different GMA loadings was investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The GMA enhanced the thermal stability of the coatings from 100 to 400 °C. The modification of GMA was found to reinforce significantly the mechanical properties of the coatings. The tensile strength of coating modified with 15 wt% GMA got a 78.65% improvement compared to that of unmodified resin. The surface hydrophobicity of the coatings does get affected by this modification. The contact angle got increased from 87.72°of the unmodified resin coating to 99.51°of coating modified with 15 wt% GMA. This work opens a new way to synthesize high performance waterborne acrylic resin and reports on the anti-flash corrosion of waterborne coatings on the iron base material surface.

Facile synthesis and characterization of a novel silica-molybdenum disulfide hybrid material

To improve the dispersion of MoS2 in polymer matrix, a facile synthesis approach was developed in this study through a synergetic effect between two kinds of nanofillers with different dimensionality. The nanohybrids based on two dimensional (2D) MoS2 and 0D silica nanospheres were fabricated by in situ growth method without any surfactants. Characterizations of the hybrid materials were done by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Solid-state 29Si nuclear magnetic resonance (NMR) spectra, transmission electron micrographs (TEM) and scanning electron microscopy (SEM). The TEM and SEM results demonstrated that the dispersibility of MoS2 was greatly improved and the agglomeration was suppressed, with the introduction of silica nanospheres.

Structural and Topological Evolution in SixSe1-x Glasses: Results from 1D and 2D 29Si and 77Se NMR Spectroscopy.

The coordination environments of Si and Se atoms and their connectivity in binary SixSe1-x glasses with 0.05 ≤ x ≤ 0.33 are investigated using a combination of one- and two-dimensional 29Si and 77Se nuclear magnetic resonance (NMR) and Raman spectroscopy. The high-resolution correlated isotropic and anisotropic 29Si and 77Se NMR spectra allow for the identification and quantitation of a variety of Si and Se environments. The results suggest that the structure of these glasses are characterized by a network with essentially perfect short-range chemical order, but with strong clustering at the intermediate range. Initial addition of Si to Se results in cross-linking of Se chain segments with nanoclusters of corner- and edge-shared SiSe4/2 tetrahedra. These clusters percolate via coalescence near x ≥ 0.2 to finally form a low-dimensional network with high molar volume, at the stoichiometric composition (x = 0.33) that is composed of chains of edge-sharing tetrahedra cross-linked by corner-shared tetrahedra. This structural evolution is shown to be consistent with the compositional variation of the glass transition temperature and the molar volume of these glasses.