Isomorphic substitution and the hydration behavior of alinite cement

Zn and/or Fe substituted alinite cement was synthesized using reagent grade chemicals, and its formation and hydration behavior were investigated. Mg, which is known to be essential for alinite formation, was completely replaced by Zn. XRD, FT-IR, and ²⁹Si MAS NMR results indicated that a Zn substituted alinite was a nearly single phase and was easy to grind compared to Mg-alinite. In addition, partially or fully Zn substituted alinite had superior hydration characteristics, and NMR results showed that most of the alinite was hydrated after 100 days. Fe substitution of Al was not effective for alinite formation and its hydration properties were similar to Mg-alinite. Cl⁻ ions leached out during alinite hydration, but the exsolution of Zn and Fe was below the detection limit.     

Characterization by solid-state NMR and selective dissolution techniques of anhydrous and hydrated CEM V cement pastes

The long term behaviour of cement based materials is strongly dependent on the paste microstructure and also on the internal chemistry. A CEM V blended cement containing pulverised fly ash (PFA) and blastfurnace slag (BFS) has been studied in order to understand hydration processes which influence the paste microstructure. Solid-state NMR spectroscopy with complementary X-ray diffraction analysis and selective dissolution techniques have been used for the characterization of the various phases (C₃S, C₂S, C₃A and C₄AF) of the clinker and additives and then for estimation of the degree of hydration of these same phases. Their quantification after simulation of experimental ²⁹Si and ²⁷Al MAS NMR spectra has allowed us to follow the hydration of recent (28 days) and old (10 years) samples that constitutes a basis of experimental data for the prediction of hydration model.     

Solid state NMR investigation of silica aerogel supported Fischer–Tropsch catalysts

The Fischer–Tropsch (F–T) catalyst is the critical component for the F–T synthesis of a variety of hydrocarbons from syngas. Fischer–Tropsch cobalt, iron and ruthenium catalysts supported on silica aerogel have been prepared using a combination of sol–gel chemistry and vapor phase deposition methods. Solid state NMR spectroscopy, a very powerful technique for analyzing the structure and dynamics of various materials, was employed in the study of these F–T catalyst systems. The silica aerogel supported F–T catalysts have been investigated using both solid state ²⁹Si and ¹³C NMR methods. The silica aerogel's tetrahedral sub-unit structure and the influence of the loaded metal compounds have been observed. Three types of Si(O_1/2)₄ tetrahedral unit structure (Q₂, Q₃ and Q₄) are clearly resolved in the silica aerogel samples. The calcining process and the loading of metal compounds produce line broadening in the ²⁹Si spectra sufficient to prevent clear resolution of the three distinct Q_n spectral lines, but the broadened spectra indicate that the three Q sub-unit structures are still present. The ferrocene and ruthenocene molecules used in the vapor phase deposition method exhibit a rapid exchange within the silica aerogel support similar to what one would expect in the gas or liquid state.     

Structure and mechanical properties of aluminosilicate geopolymer composites with Portland cement and its constituent minerals

The compressive strengths and structures of composites of aluminosilicate geopolymer with the synthetic cement minerals C₃S, β-C₂S, C₃A and commercial OPC were investigated. All the composites showed lower strengths than the geopolymer and OPC paste alone. X-ray diffraction, ²⁹Si and ²⁷Al MAS NMR and SEM/EDS observations indicate that hydration of the cement minerals and OPC is hindered in the presence of geopolymer, even though sufficient water was present in the mix for hydration to occur. In the absence of SEM evidence for the formation of an impervious layer around the cement mineral grains, the poor strength development is suggested to be due to the retarded development of C-S-H because of the preferential removal from the system of available Si because geopolymer formation is more rapid than the hydration of the cement minerals. This possibility is supported by experiments in which the rate of geopolymer formation is retarded by the substitution of potassium for sodium, by the reduction of the alkali content of the geopolymer paste or by the addition of borate. In all these cases the strength of the OPC-geopolymer composite was increased, particularly by the combination of the borate additive with the potassium geopolymer, producing an OPC-geopolymer composite stronger than hydrated OPC paste alone.     

Alkali activation of a novel calcium‐silicate hydraulic binder with CaO/SiO2 = 1.1

A quasi‐amorphous low‐calcium‐silicate hydraulic binder, with an overall CaO/SiO₂ (C/S) molar ratio of 1.1, was produced. This cementitious material was then hydrated with aqueous solutions containing 3 wt% alkalis (either NaOH, Na₂CO₃ or Na₂SiO₃). The evolution of the hydration processes of the samples were monitored by compressive strength testing, XRD, FTIR, ²⁹Si and ²⁷Al MAS NMR, isothermal calorimetry and TGA. It was found that the nearly exclusive hydration product formed was a C‐S‐H phase with a semi‐crystalline structure. More importantly, the paste prepared with the Na₂SiO₃ solution developed compressive strength values similar to those of ordinary portland cements (OPC) with faster early age kinetics. In addition, the isothermal calorimetry results indicated that these new hydraulic binders present much lower heat of hydration values compared with a traditional OPC. The results presented here open the possibility of producing cement with a compressive strength comparable to that of OPC but with lower CO₂ emissions during the production process and with lower hydration heat related problems during the production of concrete structures.     

The role of Al in C-S-H: NMR, XRD, and compositional results for precipitated samples

X-ray diffraction, compositional analysis, and ²⁹Si and ²⁷Al MAS NMR spectroscopy of Al-substituted tobermorite-type C-S-H made by precipitation from solution provide significant new insight into the structural mechanisms of Al-substitution in this important and complicated phase. Al occurs in 4-, 5-, and 6-coordination (Al[4], Al[5], and Al[6]) and plays multiple structural roles. Al[4] occurs on the bridging tetrahedra of the drierkette Al-silicate chains, and Al[5] and Al[6] occur in the interlayer and perhaps on particle surfaces. Al does not enter either the central Ca-O sheet or the pairing tetrahedra of the tobermorite-type layers. Al[4] occurs on three types of bridging sites, Q³ sites that bridge across the interlayer; Q² sites that are charge balanced by interlayer Ca⁺², Na⁺, or H⁺; and Q² sites that are most likely charge balanced by interlayer or surface Al[5] and Al[6] through Al[4]-O-Al[5,6] linkages. Although the data presented here are for relatively well-crystallized tobermorite-type C-S-H with C/S ratios ≤ 1.2, comparable spectral features for hydrated white cement pastes in previously published papers[30], [31] and [32] [M.D. Andersen, H.J. Jakobsen, J. Skibsted, Incorporation of aluminum in the calcium silicate hydrate (C-S-H) of hydrated Portland cements: a high-field ²⁷Al and ²⁹Si MAS NMR investigation Inorg. Chem. 42 (2003) 2280-2287; M.D. Andersen, H.J. Jakobsen, J. Skibsted, Characterization of white Portland cement hydration and the C-S-H structure in the presence of sodium aliminate by ²⁷Al and ²⁹Si MAS NMR spectroscopy, Cem. Concr. Res. 43 (2004) 857-868; M.D. Andersen, H. J. Jakobsen, J. Skibsted, A new aluminum-hydrate phase in hydrated Portland cements characterized by ²⁷Al and ²⁹Si MAS NMR spectroscopy, Cem. Concr. Res., submitted for publication.] indicate the presence of similar structural environments in the C-S-H of such pastes, and by implication OPC pastes.     

Effects of Al/Na and heat treatment on the structure and properties of glass ceramics from molten blast furnace slag

Glass ceramics with different Al/Na molar ratio from blast furnace slag were prepared using conventional melting-casting method. The structure and properties of glasses or glass ceramics were investigated by DSC, Raman, MAS NMR, XRD, and SEM. The DSC results indicated that the thermal stability (ΔT = T_c-T_g) and crystallization temperature (T_c) of the parent glass firstly increased and then decreased when Al/Na exceeded 1.21. The Raman and ²⁷Al MAS NMR spectra analysis revealed that [AlO₆] increased positively with Al₂O₃/Na₂O. The calculation of Qⁿ ([SiO₄] units with bridging oxygen atoms number of n) suggested an obvious decline of (Q⁰+Q²)/(Q¹+Q³) and that [SiO₄] mainly existed in the form of Q¹ when Al/Na exceeded 1.21, which accorded closely with T_c variation. The crystallization results determined by XRD showed that as Al/Na increased, the main crystal phase was transformed from akermanite to gehlenite and nepheline disappeared. Glass ceramics with Al/Na of 1.48 nucleated at 780 °C for 2 h and crystallized at 880 °C for 3 h exhibited the maximum value of flexural strength. Orthogonal experiment (L9(3⁴)) were carried out to investigated the optimum heat treatment of glass ceramics with a Al/Na of 1.48. The analyses indicated that nucleation time variation has little influence on the flexural strength, and the optimum heat treatment was determined as 760 °C – 1 h–900 °C – 1 h and the flexural strength was characterized as 81.310 MPa.     

Bis(perfluoro-2-n-propoxyethyl)diacyl peroxide initiated homopolymerization of vinylidene fluoride (VDF) and copolymerization with perfluoro-n-propylvinylether (PPVE)

Vinylidenefluoride (VDF) has been homopolymerized and copolymerized with perfluoro-n-propylvinylether (PPVE) using bis(perfluoro-2-n-propoxyethyl)diacyl peroxide (BPPP) as the initiator in CF₂ClCFCl₂. The polymers obtained were characterized with ¹⁹F NMR and ¹H NMR spectroscopy, DSC and TGA. The ¹⁹F NMR spectra were used to determine the polymer microstructures and end groups. Both PVDF and poly(VDF–PPVE) were terminated on both chain ends by CF₃CF₂CF₂OCF(CF₃)∼ arising from the decomposition of the initiator. The concentration of end groups was used to assess the molecular weight of the polymers. Using the Fine–Ross method, the reactivity ratios of both monomers were determined (r_VDF ∼ 1.06, r_PPVE ∼ 0). The T_g of poly(PPVE) (−10.3 °C) was determined using the T_gs of VDF/PPVE copolymers with different compositions and the Flory–Fox equation. A new method to produce a modified PVDF or VDF copolymer for powder coatings with higher thermal stability was also developed.     

Miscibility and hydrogen bonding in blends of poly(vinyl acetate) with phenolic resin

The miscibility of phenolic resin and poly(vinyl acetate) (PVAc) blends was investigated by differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FT-IR) and solid state ¹³C nuclear magnetic resonance (NMR). This blend displays single glass transition temperature (T_g) over entire compositions indicating that this blend system is miscible in the amorphous phase due to the formation of hydrogen bonding between hydroxyl groups of phenolic resin and carbonyl groups of PVAc. Quantitative measurements on fraction of hydrogen-bonded carbonyl group using both ¹³C solid-state NMR and FT-IR analyses result in good agreement between these two spectroscopic techniques. According to the proton spin-lattice relaxation time in the rotating frame (T_1ρ^H), the phenolic/PVAc blend is intimately mixed on a scale less than 2-3 nm. Furthermore, the inter-association equilibrium constant and its related enthalpy of phenolic/PVAc blends were determined as a function of temperatures by infrared spectra based on the Painter-Coleman association model.     

B NMR of boron-doped graphite as the negative electrode of a lithium secondary battery

Boron-doped graphite used as a negative electrode for a lithium rechargeable battery is known to have higher discharge capacity than undoped graphite. Herein, the graphites were mixed with 1, 2.5, 5, and 7 wt.% of boron carbide during the graphitizing process. The structural states of boron in those boron-doped graphites were successfully identified by solid-state ¹¹B NMR spectroscopy. For 1 wt.% sample, all boron atoms were at substitutional sites, as evident by the second-order quadrupole broadened ¹¹B NMR line having a quadrupole coupling constant, Q_CC=3.36(2) MHz. The NMR results show evidence of excess boron atoms recrystallizing as boron carbide during the graphitizing process which is in agreement with XRD data. Agreement of experimental results with computer simulated data indicate that the substitutional sites in boron-doped graphites were observed for the first time.     

Spectroscopic analysis of poly(bisphenol A carbonate) using high resolution C and H NMR

Quantitative structural and end-group analysis of poly(bisphenol A carbonate) (BPA-PC) was carried out and number average molecular weights (M_n) were determined using 125.76 MHz ¹³C and 500.13 MHz ¹H nuclear magnetic resonance (NMR) spectroscopy. BPA-PC with a wide range of end-group ratios (0.26-2.83) and number average molecular weights (1500-9000 g/mol) was synthesized using melt transesterification by changing the initial monomer (bisphenol A and diphenyl carbonate) ratios and reaction conditions. Results of the NMR analysis for the melt-polymerized samples were compared with those of a commercial BPA-PC with a M_n of 16,000 g/mol. It was demonstrated that NMR spectroscopy is a very selective and accurate method not only for quantification of both phenolic and phenyl chain end-groups but also in the structural analysis of main chain groups. Extremely small concentrations of end-groups (∼0.02 per repeating unit) were analyzed. In addition, NMR spectroscopy was found to be an excellent tool for detecting residual monomer and the presence of the reaction byproduct (phenol). The molecular weights that were determined using NMR end-group quantification agreed well with the molecular weights measured by gel-permeation chromatography (GPC).     

Miscibility and morphology in crystalline/amorphous blends of poly(caprolactone)/poly(4-vinylphenol) as studied by DSC, FTIR, and C solid state NMR

The miscibility and morphology of poly(caprolactone) (PCL) and poly (4-vinylphenol) (PVPh) blends were investigated by using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and ¹³C solid state nuclear magnetic resonance (NMR) spectroscopy. The DSC results indicate that PCL is miscible with PVPh. FTIR studies reveal that hydrogen bonding exists between the hydroxyl groups of PVPh and the carbonyl groups of PCL. ¹³C cross polarization (CP)/magic angle spinning (MAS)/dipolar decoupling (DD) spectra of the blends show a 1 ppm downfield shifting of ¹³C resonance of PVPh hydroxyl-substituted carbons and PCL carbonyl carbons with increasing PCL content. Both FTIR and NMR give evidence of inter-molecular hydrogen bonding within the blends. The proton spin-lattice relaxation in the laboratory frame, T₁(H), and in the rotating frame, T_1ρ(H), were studied as a function of the blend composition. The T₁(H) results are in good agreement with thermal analysis; i.e. the blends are completely homogeneous on the scale of 50-80 nm. The T_1ρ(H) results indicate that PCL in the blends has both crystalline and amorphous phases. The amorphous PCL phase is miscible with PVPh, but the PCL crystal domain size is probably larger than the spin-diffusion path length within the T_1ρ(H) time-frame, i.e. larger than 2-4 nm. The mobility differences between the crystalline and amorphous phases of PCL are clearly visible from the T_1ρ(H) data.     

Crystallization behavior and melt structure of typical CaO–SiO2 and CaO–Al2O3-Based mold fluxes

Crystallization behavior and melt structure of two typical mold fluxes A (CaO–SiO₂-based) and B (CaO–Al₂O₃-based) for casting high-aluminum steel were investigated using double hot thermocouple technology (DHTT), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results suggest that the crystallization temperature of Flux B is higher, and its crystallization incubation time is shorter compared with Flux A. The precipitated phase in Flux A is CaSiO₃, whereas BaAl₂O₄ and Ca₂Al₂SiO₇ form in Flux B. The structure analyses suggest that the degree of polymerization of Flux A is larger than that of Flux B. In addition, the major structural units of Flux A are Si–O–Si, Q₀^Si, Q₁^Si, Q₂^Si and Q₃^Si, but those of Flux B are mainly aluminate (Al–O–Al, Al–O^-), aluminosilicate (Al–O–Si) and silicate units (Q₀^Si, Q₁^Si, Q₂^Si and Q₃^Si). These different melt structures are the main reasons why the precipitated phases in these two mold fluxes are different, and the crystallization ability of Flux A is weaker than Flux B.     

Hydrations and water properties in the super salt-resistive gel probed by FT-IR

The so-called “Super Salt-Resistive Gel”, i.e., poly(4-vinyl phenol) (P4VPh) hydrogel, of different water contents (H = 95-40%) was prepared by crosslinking with different amounts of ethylene glycol diglycidyl ether (EGDGE). FT-IR spectroscopy was used to investigate the hydration and hydrogen bond (HB) properties of water in the gel samples. The OH stretching band around 3300 cm⁻¹ was deconvoluted into four sub-bands. On the basis of the relative band area and the peak wave number, it was suggested that HB of water in the gel is most stabilized when the acidic proton of the phenol residue is intact, being free from the chemical crosslinking. Difference spectra for the water band obtained in the presence of salts suggested that only sulfate systems specifically affect polymer hydrations in the gel phase. The sulfate systems were also specific in the perturbation on the main chain CH₂ stretching band; namely, with increasing the salt concentration, the peak showed a significant blue shift, which means that the hydrophobic hydration is stabilized by the typical salting-out divalent anion. All the experimental results on the FT-IR spectroscopy for the P4VPh hydrogel seem to be consistent with our previous ¹H NMR data on the water T₂ (Sakai Y, Kuroki S, Satoh M. Langmuir 2008; 24:6981-7.) as well as the specific stabilization of water (HB and hydration) in the gel that has been suggested on the basis of the swelling behavior.     

The hydration of reactive cement-in-polymer dispersions studied by nuclear magnetic resonance

The behaviour of two novel cement-in-polymer (c/p) dispersions, namely cement-in-poly(vinyl acetate) and cement-in-poly(vinyl alcohol) upon exposure to water at room temperature was investigated by a combination of various NMR methods. The swelling, cracking, and the water ingress were monitored non-destructively using ¹H single point imaging. The hydration of the cement matrix was investigated using ²⁹Si NMR whilst ¹³C CPMAS NMR spectra allowed the quantification of the kinetics of the hydrolysis reaction of poly(vinyl acetate) into poly(vinyl alcohol). The polymer controls the rate of water ingress and swelling which in turn determines the behaviour of the c/p dispersions upon exposure to water. For the cement-in-poly(vinyl alcohol), the rates of water ingress and swelling are much faster than the hydration of the clinker whilst for the cement-in-poly(vinyl acetate) the slow rates of the two processes allow the formation of a cementious matrix which assures the stability of the sample.     

Miscibility and intermolecular specific interactions in blends of poly(hydroxyether of bisphenol A) and poly(4-vinyl pyridine)

The blends of poly(hydroxyether of bisphenol A) (phenoxy) with poly(4-vinyl pyridine) (P4VPy) were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. The single, composition-dependent glass transition temperature (T_g) was observed for each blend, indicating that the system is completely miscible. The sigmoid T_g-composition relationship is characteristic of the presence of the strong intermolecular specific interactions in the blend system. FTIR studies revealed that there was intermolecular hydrogen bonding in the blends and the intermolecular hydrogen bonding between the pendant hydroxyl groups of phenoxy and nitrogen atoms of pyridine ring is much stronger than that of self-association in phenoxy. To examine the miscibility of the system at the molecular level, the high resolution ¹³C cross-polarization (CP)/magic angle spinning (MAS) together with the high-power dipolar decoupling (DD) NMR technique was employed. Upon adding P4VPy to the system, the chemical shift of the hydroxyl-substituted methylene carbon resonance of phenoxy was observed to shift downfield in the ¹³C CP/MAS spectra. The proton spin-lattice relaxation time T₁(H) and the proton spin-lattice relaxation time in the rotating frame T_1ρ(H) were measured as a function of the blend composition. In light of the proton spin-lattice relaxation parameters, it is concluded that the phenoxy and P4VPy chains are intimately mixed on the scale of 20-30 Å.     

Synthetic aspects and characterization of polypropylene-silica nanocomposites prepared via solid-state modification and sol-gel reactions

A new route is developed by combining solid-state modification (SSM) by grafting vinyl triethoxysilane (VTES) with a sol-gel method to prepare PP/silica nanocomposites with varying degree of adhesion between filler and matrix. VTES was grafted via SSM in porous PP particles. Bulk polymerization under similar experimental conditions as in SSM resulted in homopolymerization of VTES. However, SEC and NMR experiments showed that VTES was grafted as a single monomeric unit in the amorphous phase of PP with the possibility of VTES-polymer grafting during SSM. Silica-like nano-particles were synthesized in-situ by the sol-gel method. Magic-angle spinning (MAS) ²⁹Si NMR spectra showed that the chemical building blocks of the silica-like clusters are of Q³ and Q⁴ type. MAS ²⁹Si NMR and FT-IR spectroscopy showed that the grafted VTES becomes part of the in-situ formed silica particles. No decrease in molecular weight of PP was observed, indicating that chain scission is marginal compared to melt modification. The morphology of the nanocomposites as observed by ATR-FTIR microscopy showed a uniform dispersion of grafted VTES as well as in-situ formed silica. TEM and SEM demonstrated that the in-situ formed silica particles are nearly spherical and have sizes in the range of 50-100 nm.     

Effect of Processing Variables on the Solution Characteristics of γ-Glycidoxypropyltrimethoxysilane (γ-GPS)

The effects of the hydrolysis and condensation processes on the molecular structure of γ-glycidoxypropyltrimethoxysilane (γ-GPS) in aqueous solutions were investigated using Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy and FT-Raman spectroscopy. Hydrolysis was characterized by monitoring the production of methanol and the decrease in concentration of SiOCH₃ groups in 1% solutions of deuterium oxide using proton NMR. The production of methanol and loss of methoxy groups in 25% solutions of γ-GPS in water was characterized using Raman spectroscopy. Hydrolysis was found to be a very rapid process, whose rate could be increased or decreased by altering the pH of the solution. NMR spectroscopy showed that hydrolysis was complete in a 1% γ-GPS solution in deuterium oxide after 34 minutes. Raman spectroscopy also showed hydrolysis to be rapid and complete in a 25% solution of γ-GPS in water after 1 hour. Condensation, on the other hand, took a relatively long time to occur. In the NMR spectra, condensation was observed by the broadening of peaks due to the protons on the carbon atom adjacent to the silicon atom. In the Raman spectra, condensation was characterized by the disappearance of the SiOH band near 725 cm^?1 and the development of an SiOSi band near 600 cm^?1. In addition to the proton NMR, Si-29 NMR was used to characterize the silane in 10% solutions of γ-GPS in water. The Si-29 NMR showed oligomer growth with respect to time. The oligomer growth was correlated with mechanical test results.     

Structural characterization of TiO2–P2O5–CaO glasses by spectroscopy

The structure of glasses with composition x TiO₂·(65 ? x) P₂O₅·35 CaO (x = 0–30 mol%) has been studied and their glass transition temperature, Raman and NMR spectra have been analysed.For TiO₂-free glass two phosphate species have been identified as Q² and Q³. Increasing TiO₂ content in glass compositions results in the disappearance of the Q³ and Q² species and in the formation of, mainly, pyrophosphate structure, Q¹.In calcium titanophosphate glass with higher TiO₂ content the structure consists of a distorted Ti octahedral linked to pyrophosphate unit through P–O–Ti bonds. In these glass series the structural cohesion increases with TiO₂, although a depolymerization in the original P–O–P network occurs.The study of these glasses and the understanding of their structural characteristics can give a valuable contribution for the clarification of their degradation behaviour namely in biological environments.