Characterization of white Portland cement hydration and the C-S-H structure in the presence of sodium aluminate by Al and Si MAS NMR spectroscopy

The effects of hydrating a white Portland cement (wPc) in 0.30 and 0.50 M solutions of sodium aluminate (NaAlO₂) at 5 and 20 °C are investigated by ²⁷Al and ²⁹Si magic-angle spinning (MAS) NMR spectroscopy. It is demonstrated that NaAlO₂ accelerates the hydration of alite and belite and results in calcium-silicate-hydrate (C-S-H) phases with longer average chain lengths of SiO₄/AlO₄ tetrahedra. The C-S-H phases are investigated in detail and it is shown that the Al/Si ratio for the chains of tetrahedra is quite constant during the time studied for the hydration (6 h to 2 years) but increases for higher concentration of the NaAlO₂ solution. The average chain lengths of “pure” silicate and SiO₄/AlO₄ tetrahedra demonstrate that Al acts as a linker for the silicate chains, thereby producing aluminosilicate chains with longer average chain lengths. Finally, it is shown that NaAlO₂ reduces the quantity of ettringite and results in larger quantities of monosulfate and a calcium aluminate hydrate phase.     

A new aluminium-hydrate species in hydrated Portland cements characterized by Al and Si MAS NMR spectroscopy

Recent ²⁷Al MAS NMR studies of hydrated Portland cements and calcium-silicate-hydrate (C-S-H) phases have shown a resonance from Al in octahedral coordination, which cannot be assigned to the well-known aluminate species in hydrated Portland cements. This resonance, which exhibits the isotropic chemical shift δ_iso = 5.0 ppm and the quadrupole product parameter P_Q = 1.2 MHz, has been characterized in detail by ²⁷Al MAS and ²⁷Al{¹H} CP/MAS NMR for different hydrated white Portland cements and C-S-H phases. These experiments demonstrate that the resonance originates from an amorphous or disordered aluminate hydrate which contains Al(OH)₆³⁻ or O_xAl(OH)_6-x^(3+x)− units. The formation of the new aluminate hydrate is related to the formation of C-S-H at ambient temperatures, however, it decomposes by thermal treatment at temperatures of 70-90 °C. From the experiments in this work it is proposed that the new aluminate hydrate is either an amorphous/disordered aluminate hydroxide or a calcium aluminate hydrate, produced as a separate phase or as a nanostructured surface precipitate on the C-S-H phase. Finally, the possibilities of Al³⁺ for Ca²⁺ substitution in the principal layers and interlayers of the C-S-H structure are discussed.     

Aluminum Incorporation in the C–S–H Phase of White Portland Cement–Metakaolin Blends Studied by 27Al and 29Si MAS NMR Spectroscopy

The composition and structure of the calcium‐silicate‐hydrate (C–S–H) phases formed by hydration of white portland cement–metakaolin (MK) blends have been investigated using ²⁷Al and ²⁹Si MAS NMR. This includes blends with 0, 5, 10, 15, 20, 25, 30 wt% MK, following their hydration from 1 d to 1 yr. ²⁹Si MAS NMR reveals that the average Al/Si ratio for the C–S–H phases, formed by hydration of the portland cement–MK blends, increases almost linearly with the MK content but is invariant with the hydration time for a given MK content. Correspondingly, the average aluminosilicate chain lengths of the C–S–H increase with increasing MK content, reflecting the formation of a C–S–H with a lower Ca/Si ratio. The increase in Al/Si ratio with increasing MK content is supported by ²⁷Al MAS NMR which also allows detection of strätlingite and fivefold coordinated aluminum, assigned to AlO₅ sites in the interlayer of the C–S–H structure. Strätlingite is observed after prolonged hydration for MK substitution levels above 10 wt% MK. This is at a somewhat lower replacement level than expected from thermodynamic considerations which predict the formation of strätlingite for MK contents above 15 wt% after prolonged hydration for the actual portland cement–MK blends. The increase in fivefold coordinated Al with increasing MK content suggests that these sites may contribute to the charge balance of the charge deficit associated with the incorporation of Al³⁺ ions in the silicate chains of the C–S–H structure.     

Characterisation of acid-treated bentonite. Reactivity, FTIR study and 27Al MAS NMR

Acid-treated bentonite shows a catalytic activity towards decomposition of isopropanol due to overall acidity whereas the selectivity accounts for the nature of its acid sites. The examination of the IR spectra using different basic probes such as 2,6-dimethylpyridine, pyridine and CD₃CN shows the presence of various types of acid sites. The Lewis acid sites, considered to be the most abundant, are well characterised by pyridine and CD₃CN adsorption. In contrast, lutidine adsorption reveals both the existence of Brønsted acid sites and the presence of hydroxyl groups characteristic of beidellite. The potential site created by Al in tetrahedral layers is confirmed by using ²⁷Al MAS NMR.     

Experimental studies and thermodynamic modeling of the carbonation of Portland cement,metakaolin and limestone mortars

The carbonation of Portland cement, metakaolin and limestone mortars has been investigated after hydration for 91 days and exposure to 1% (v/v) CO₂ at 20 °C/57% RH for 280 days. The carbonation depths have been measured by phenolphthalein whereas mercury intrusion porosimetry (MIP), TGA and thermodynamic modeling have been used to study pore structure, CO₂ binding capacity and phase assemblages. The Portland cement has the highest resistance to carbonation due to its highest CO₂ binding capacity. The limestone blend has higher CO₂ binding capacity than the metakaolin blends, whereas the better carbonation resistance of the metakaolin blends is related to their finer pore structure and lower total porosity, since the finer pores favor capillary condensation. MIP shows a coarsening of the pore threshold upon carbonation for all mortars. Overall, the CO₂ binding capacity, porosity and capillary condensation are found to be the decisive parameters governing the carbonation rate.     

Nitridation of silicon powder studied by XRD, 29Si MAS NMR and surface analysis techniques

The nitridation of elemental silicon powder at 900–1475 °C was studied by X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), XRD, thermal analysis and ²⁹Si MAS NMR. An initial mass gain of about 12% at 1250–1300 °C corresponds to the formation of a product layer about 0·2 μm thick (assuming spherical particles). XPS and XAES show that in this temperature range, the surface atomic ratio of N/Si increases and the ratio O/Si decreases as the surface layer is converted to Si₂N₂O. XRD shows that above 1300 °C the Si is rapidly converted to a mixture of α- and β-Si₃N₄, the latter predominating >1400 °C. In this temperature range there are only slight changes in the composition of the surface material, which at the higher temperatures regains a small amount of an oxidised surface layer. By contrast, in the interval 1400–1475 °C, the ²⁹Si MAS NMR chemical shift of the elemental Si changes progressively from about −80 ppm to −70 ppm, in tandem with the growth of the Si₃N₄ resonance at about −48 ppm. Possible reasons for this previously unreported change in the Si chemical shift are discussed. ©     

Characterization of flame-retarded polymer combustion chars by solid-state 13C and 29Si NMR and EPR

We report here on the results of our continuing effort to study the flame-retardant mechanism of silica gel and potassium carbonate. These additives reduce the flammability of a wide variety of common polymers such as polypropylene, nylon, polymethylmethacrylate, poly(vinyl alcohol), and cellulose. In an effort to determine how these additives reduce polymer flammability, we have used electron paramagnetic resonance spectroscopy and solid-state ¹³C and ²⁹Si nuclear magnetic resonance spectroscopy to characterize the combustion chars or residues. These data indicate that, in the case of poly(vinyl alcohol), the additives do not change the type of char formed, but they do change the rate of char formation relative to the rate of fuel generation. We also found that, using only CP/MAS ¹³C NMR, there can be significant intensity distortions which complicate interpretation, if the char is hydrogen depleted and contains paramagnetic centres. © 1998 John Wiley & Sons, Ltd.     

Hydrolysis and condensation mechanisms of a silane coupling agent studied by 13C and 29Si NMR

The mechanisms of hydrolysis and condensation of a silane coupling agent, γ-methacrylo-xypropyltrimetoxysilane (γ-MPTS) were investigated by the use of both ¹³C and ²⁹Si nuclear magnetic resonance (NMR) spectroscopies. The NMR peaks of the hydrolyzed monomer and condensed polymer were assigned readily. The rate of hydrolysis and condensation of γ-MPTS was dependent on water content. On the basis of the time-dependent behavior of these peaks, the mechanisms of hydrolysis and condensation were clear.     

The application of 29Si and 27Al solid state n.m.r. spectroscopy to characterising minerals in coals

Solid state ²⁹Si and ²⁷Al n.m.r. spectroscopy has been applied to mineral concentrates (termed low temperature ashes) from different coals to provide information on their mineralogy. In the ²⁹Si n.m.r. spectra, two well resolved signals were observed in each case corresponding to silicate in quartz and in clays. The nuclear relaxation rates of the quartz components were found to be long and to vary between different samples. Measurement of the relative intensities of the two signals as a function of time allowed for nuclear relaxation, however, and permitted the values of the relative proportions of silicon as quartz and clay to be obtained in most cases. These agreed well with values obtained by X-ray diffraction (XRD) plus X-ray fluorescence (XRF). The ²⁹Si n.m.r. data also provided some information on the nature of clays in coals. Combined with ²⁷Al n.m.r. measurements, discrimination between kaolinite and illite clay components was possible by distinguishing aluminium in octahedral and tetrahedral coordination sites. Again, reasonable agreement with XRD and XRF was observed. The results show the potential and some limitations of solid state n.m.r. for such analytical application to coals.     

Characterization of Aluminum in Cation-Exchanged NH4NaY and USY Zeolites by 27Al MAS NMR Spectroscopy

The effects of cations on the local electromagnetic environments of catalytic sites in Y-zeolites are studied as a function of cation type and concentration. Quadrupolar coupling parameters measurable using ²⁷Al MAS NMR at multiple field strengths, provide a window to study aluminum’s local electronic structure. Quadrupolar parameters calculated for framework tetrahedral aluminum are related to cation concentration and Brønsted acidity for potassium-, zinc-, and lanthanum-exchanged NH₄NaY and USY zeolites.     

Evolution of Mineralogical Phases by 27Al and 29Si NMR in MK‐Ca(OH)2 System Cured at 60°C

The evolution of the metastable phases in metakaolin/Ca(OH)₂ systems cured at high temperatures, remains mostly unknown, newer techniques may now help to establish both the kinetic mechanism of the pozzolanic reaction and the thermodynamic stability of the main hydrated hexagonal phases: Stratlingite (C₂ASH₈) and tetra calcium aluminate hydrate (C₄AH₁₃). For this reason this work examines the kinetics of the pozzolanic reaction in the MK/Ca(OH)₂ system over 123 d at 60°C using nuclear magnetic resonance spectroscopy (²⁷Al and ²⁹Si NMR). The results obtained by ²⁷Al and ²⁹Si NMR show that during the first 30 h, the metastable phases C₂ASH₈ and C₄AH₁₃, coexist with the cubic phase (C₃ASH₆) obtained directly from the pozzolanic reaction. The gel C–S–H is clearly identified after 21 h of reaction, whereas at shorter times the C–S–H bands overlap those with the unreacted metakaolin ones. After 123 d of pozzolanic reaction, the first signs of the cubic phase are detected, a consequence of the conversion reaction of the metastable phases, and a phenomenon not previously identified.     

硅酸盐水泥熟料中A矿包裹物、方镁石、还原矿物及煤灰沉落的岩相观察

本文通过岩相观察水泥熟料中的一些非主要矿物,如A矿包裹物、方镁石、还原矿物,对熟料中煤灰沉落点的B矿区域也做了观察,通过观察总结了这些次要矿物的存在形态,并对形成原因及关联的工艺含意进行了分析,观察这些非主要矿物对判断煅烧工艺状况、了解煅烧进程具有一定的帮助。     

Assignment of 13C NMR chemical shift and microstructure of copolymers of 2-chloroethyl vinyl ether-maleic anhydride and n-butyl vinyl ether-maleic anhydride

Summary The chemical shift in the ¹³C NMR spectra of copolymers of 2-chloroethyl vinyl ether (CEVE) and maleic anhydride (MA), and of n-butyl vinyl ether (BVE) and MA is assigned. It is found that both copolymers are made of completely alternating monomer unit sequences and that the proportion of cis linkage configuration at the cyclic MA units is 45 % and 47 % in the CEVE-MA copolymer and in the BVE-MA copolymer, respectively. Depending on the relative orientation of the cyclic anhydride group, quasi “isotactic” and quasi “syndiotactic” tacticity are considered, with quasi “syndiotactic” diads shielding the vinyl ether carbons more effectively. Received: 19 April 1999/Accepted: 17 June 1999     

13C CP/MAS NMR studies on the curing characteristics of phenol formaldehyde resin in the presence of nano cupric oxide and surfactants

The effect of nano cupric oxide (CuO) in combination with surfactants on the curing characteristics of phenol formaldehyde (PF) resin analyzed using solid ¹³C CP/MAS NMR, including the bonding strength of plywood prepared by modified resin, was investigated in this study. The results showed that nano CuO alone improved the cure of PF resin. The intensity of the functional groups of the PF mixture was maintained during the curing process as sodium lignosulfonate was simultaneously introduced. Furthermore, nano CuO and alkane surfactant together modified the PF resin conformation. The shear strength of the plywood showed that the addition of nano CuO (1%) alone or in combination with alkane surfactant (0.55%) or sodium lignosulfonate (0.55%) to the PF resin mixture was effective. And this approach met the important criteria for its application in the manufacture of plywood. POLYM. COMPOS., 35:113–117, 2014. © 2013 Society of Plastics Engineers     

水泥生料硅铁铝钙的快速分析方法

1 前言 水泥生料中SiO2、Fe2O3、Al2O3、CaO的测定,是对水泥生料进行率值控制的重要依据,它对确保水泥产品质量,意义十分重大。众所周知,在生产控制分析中,要求整个分析快速准确,方可达到及时调整配方、提高产品质量的目的。目前,水泥生料的分析主要有仪器分析法和传统的化学分析法两种。大     

n-Butane conversion on sulfated zirconia: in situ 13C MAS NMR monitoring of the kinetics of the 13C-label scrambling and isomerization

The kinetics of the conversion of ¹³C-labeled n-butane adsorbed on sulfated zirconia (SZ) were monitored by in situ ¹³C MAS NMR spectroscopy. Rate constants of n- to isobutane isomerization and of the ¹³C-isotope scrambling from the primary to the secondary carbon atoms in n-butane were determined. The monomolecular scrambling of the ¹³C-label in adsorbed n-butane has an activation energy of 17 ± 3 kcal mol^–1 and occurs faster than the bimolecular process of n-butane isomerization which has an activation energy of 15.1 ± 0.2 kcal mol^–1. The transfer of the selective ¹³C-label from the primary to the secondary carbon atom in the adsorbed n-butane seems to consist of two reaction steps: (i) a hydride abstraction by SZ leading to the formation of sec-butyl cations and (ii) a label scrambling in the sec-butyl cations. This two-step process with the formation of sec-butyl cations as intermediate increases the apparent activation energy for the ¹³C-label scrambling, which is almost twice as large compared with the activation energy for carbon scrambling of sec-butyl cations in a superacidic solution.     

Temperature dependence, 0 to 40 °C, of the mineralogy of Portland cement paste in the presence of calcium carbonate

Thermodynamic calculations disclose that significant changes of the AFm and AFt phases and amount of Ca(OH)₂ occur between 0 and 40 °C; the changes are affected by added calcite. Hydrogarnet, C₃AH₆, is destabilised at low carbonate contents and/or low temperatures < 8 °C and is unlikely to form in calcite-saturated Portland cement compositions cured at < 40 °C. The AFm phase actually consists of several structurally-related compositions which form incomplete solid solutions. The AFt phase is close to its ideal stoichiometry at 25 °C but at low temperatures, < 20 °C, extensive solid solutions occur with CO₃-ettringite. A nomenclature scheme is proposed and AFm-AFt phase relations are presented in isothermal sections at 5, 25 and 40 °C. The AFt and AFm phase relations are depicted in terms of competition between OH, CO₃ and SO₄ for anion sites. Diagrams are presented showing how changing temperatures affect the volume of the solid phases with implications for space filling by the paste. Specimen calculations are related to regimes likely to occur in commercial cements and suggestions are made for testing thermal impacts on cement properties by defining four regimes. It is concluded that calculation provides a rapid and effective tool for exploring the response of cement systems to changing composition and temperature and to optimise cement performance.     

Study on the geometric structure of poly[1-(trimethylsilyl)-1-propyne] by 13C and 29Si NMR spectroscopies

Summary The geometric structure of poly[1-(trimethylsilyl)-1-propyne] was investigated by ¹³C and ²⁹Si NMR spectroscopies. According to ¹³C NMR, the geometric structure varied with polymerization catalysts. NbCl₅ was inferred to produce more cis-rich polymer than TaCl₅. On the other hand, polymerization conditions such as solvent, temperature and cocatalyst hardly affected the geometric structure. The cis contents of polymers bearing bulkier substituents (-SiMe₂-nC₆H₁₃,-SiMe₂-CH₂SiMe₃) prepared with TaCl₅ were similar to that of poly (TMSP) with TaCl₅.     

The Effect of Alkali Ions on the Incorporation of Aluminum in the Calcium Silicate Hydrate (C–S–H) Phase Resulting from Portland Cement Hydration Studied by 29Si MAS NMR

The incorporation of aluminum in the calcium–silicate–hydrate (C–S–H) phases formed by hydration of three different white Portland cements has been investigated by ²⁹Si MAS NMR. The principal difference between the three cements is their bulk Al₂O₃ contents and quantities of alkali (Na⁺ and K⁺) ions. ²⁹Si MAS NMR allows indirect detection of tetrahedral Al incorporated in the silicate chains of the C–S–H structure by the resonance from Q²(1Al) sites. Analysis of the relative ²⁹Si NMR intensities for this site, following the hydration for the three cements from 0.5 d to 30 weeks, clearly reveals that the alkali ions promote the incorporation of Al in the bridging sites of the dreierketten structure of SiO₄ tetrahedra in the C–S–H phase. The increased incorporation of Al in the C–S–H phase with increasing alkali content in the anhydrous cement is in accord with a proposed substitution mechanism where the charge deficit, obtained by the replacement of Si⁴⁺ by Al³⁺ ions in the bridging sites, is balanced by adsorption/binding of alkali ions in the interlayer region most likely in the near vicinity of the AlO₄ tetrahedra. This result is further supported by similar ²⁹Si MAS NMR experiments performed for the white Portland cements hydrated in 0.30M NaOH and NaAlO₂ solutions.