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1.
A systematic density functional theory investigation on C2Au
n
+ (n = 1,3,5) and C2Au
n
(n = 2,4,6) indicates that gold atoms serve as terminals (–Au) in the chain-like Cs C2Au+ (C=C–Au+) and D∞h C2Au2 (Au–C≡C–Au) and as bridges (–Au–) in the side-on coordinated C2v C2Au3
+ ([Au–C≡C–Au]Au+) and Cs C2HAu2
+([H–C≡C–Au]Au+). However, when the number of gold atoms reaches four, they form stable gold triangles (–Au3) in the head-on coordinated C2v C2Au4 (Au–C≡C–Au3) and the side-on coordinated C2v C2Au5
+ ([Au–C≡C–Au]Au3
+). Similar –Au3 triangular units exist in the head-on coordinated C2v C2HAu3 (H–C≡C–Au3) and D2d C2Au6 (Au3–C≡C–Au3). The existence of stable –Au3 triangular units in small dicarbon aurides is significant and intriguing. The high stability of Au3 triangles originates from the fact that an equilateral D3h Au3
+ cation possesses a completely delocalized three-center-two-electron (3c–2e) σ bond and therefore is σ-aromatic in nature.
The extension from H/Au analogy to H/Au3 analogy established in this work may have important implications in designing new gold-containing catalysts and nano-materials. 相似文献
2.
B. Zapata J. Balmaseda E. Fregoso-Israel E. Torres-García 《Journal of Thermal Analysis and Calorimetry》2009,98(1):309-315
Thermal degradation of orange peel was studied in dynamic air atmosphere by means of simultaneous TG-DSC and TG-FTIR analysis.
According to the obtained thermal profiles, the orange peel degradation occurred in at least three steps associated with its
three main components (hemicellulose, cellulose and lignin). The volatiles compounds evolved out at 150–400 °C and the gas
products were mainly CO2, CO, and CH4. A mixture of acids, aldehydes or ketones C=O, alkanes C–C, ethers C–O–C and H2O was also detected. The E
α on α dependence reveled the existence of different and simultaneous processes suggesting that the combustion reaction is
controlled by oxygen accessibility, motivated by the high evolution low-molecular-mass gases and volatile organic compounds.
These results could explain the non-autocatalytic character of the reactions during the decomposition process. 相似文献
3.
Michito Shiotsuka Naoki Nishiko Yasushi Tsuji Noboru Kitamura Satoru Onaka Katsuya Sako 《Transition Metal Chemistry》2010,35(2):129-135
A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh3)–Au–C≡C}2-phen, has been synthesized from Au(PPh3)Cl (PPh3 = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh3)–Au–C≡C}2-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed 3
π–π* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline,
3,8-bis{(PPh3)–Au–C≡C}2-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh3)–Au–C≡C}-phen, and 3-ethynylphenanthroline, 3-{(PPh3)–Au–C≡C}-phen was observed. The absorption bands assignable to the π–π*(C≡Cphen) transition and phosphorescent emission assignable to the metal-perturbed 3
π–π* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT. 相似文献
4.
Limin Han Guangbin Zhang Ning Zhu Ruijun Xie Quanling Suo Meihua Luo Linhong Weng 《Journal of Cluster Science》2010,21(4):789-801
Two novel bimetallic complexes, [Cr(CO)3(η
6-C6H5)–C≡C–C6H4–Fc] (Fc = C5H5FeC5H4] (1) and [Cr(CO)3(η
6-C6H5)–C ≡ C–Fc–C(CH3)2–Fc] (3), were synthesized by the Sonogashira coupling reaction. By using of (1) and (3) as ligands to react with Co2(CO)8, two others novel polymetallic complexes, [Cr(CO)3(η
6-C6H5){Co2(CO)6-η
2-μ
2-C≡C–}–C6H4–Fc] (2) and [Cr(CO)3(η
6-C6H5){Co2(CO)6-η
2-μ
2-C≡C–}Fc–C(CH3)2–Fc] (4) were obtained. Four carbonyl complexes were characterized by elemental analysis, FT-IR, NMR and MS. The molecular structures
of complexes (1), (2) and (4) were determined by single crystal X-ray diffraction. The interactions among the ferrocenyl,
Cr(CO)3 and Co2(CO)6-η
2-μ
2-C≡C– units were investigated by cyclic voltammetry. 相似文献
5.
Alexander Konkin Frank Wendler Frank Meister Hans-Klaus Roth Albert Aganov Oliver Ambacher 《Cellulose (London, England)》2007,14(5):457-468
Degradation processes of N-methylmorpholine-N-oxide monohydrate (NMMO), cellulose and cellulose/NMMO solutions were studied by high performance liquid chromatography (HPLC)
and electron spin resonance (ESR) spectroscopy. Kinetics of radical accumulation processes under UV (λ = 248 nm) excimer laser
flash photolysis was investigated by ESR at 77 K. Beside radical products of cellulose generated and stabilized at low temperature,
radicals in NMMO and cellulose/NMMO solutions were studied for the first time in those systems and attributed to nitroxide
type radicals ∼CH2–NO•–CH2∼ and/or ∼CH2–NO•–CH3∼ at the first and methyl •CH3 and formyl •CHO radicals at the second step of the photo-induced reaction. Kinetic study of radicals revealed that formation and recombination
rates of radical reaction depend on cellulose concentration in cellulose/NMMO solutions and additional ingredients, e.g.,
Fe(II) and propyl gallate. HPLC measurements showed that the concentrations of ring degradation products, e.g., aminoethanol
and acetaldehyde, are determined by the composition of the cellulose/NMMO solution. Results based on HPLC are mainly maintained
by ESR that supports the assumption concerning a radical initiated ring-opening of NMMO. 相似文献
6.
Jian-Long Xia Wei-Cheng Xiong Gang Chen Guang-Ao Yu Shan Jin Sheng-Hua Liu 《Transition Metal Chemistry》2009,34(4):389-393
Abstract Formal [2 + 2 + 2] addition reaction of [Cp*Ru(H2O)(NBD)][BF4] (NBD = norbornadiene) with 4,4′-Diethynylbiphenyl generates [C9H9-η6-C6H4(RuCp*)–C6H4(RuCp*)-η6-C9H9][BF4]2. The reaction of [Cp*Ru(H2O)(NBD)][BF4] with 1,4-diphenylbutadiyne generates the unusual [2 + 2 + 2] additional organic compound Ph–C≡C–C9H8–Ph in addition to the organometallic compound [Cp*Ru(η6-C6H5–C≡C–C≡C–Ph)][BF4]. [C9H9-η6-C6H4(RuCp*)–C6H4(RuCp*)-η6-C9H9][BPh4]2 is generated after the reaction of compound [C9H9-η6-C6H4(RuCp*)–C6H4(RuCp*)-η6-C9H9][BF4]2 with Na[BPh4]. The structure of this compound was confirmed by X-ray diffraction. A possible approach to form Ph–C≡C–C9H8–Ph and [Cp*Ru(η6-C6H5–C≡C–C≡C–Ph)][BF4] is suggested.
Graphical Abstract Formal [2 + 2 + 2] addition reaction of [Cp*Ru(H2O)(NBD)]BF4 (NBD = norbornadiene) with 4,4′-Diethynylbiphenyl generates [C9H9-η6-C6H4(RuCp*)–C6H4(RuCp*)-η6-C9H9][BF4]2. The reaction of [Cp*Ru(H2O)(NBD)][BF4] with 1,4-diphenylbutadiyne simply generates unusual [2 + 2 + 2] additional organic compound Ph–C≡C–C9H8–Ph in addition to the organometallic compound [Cp*Ru(η6-C6H5–C≡C–C≡C–Ph)][BF4]. [C9H9-η6-C6H4(RuCp*)–C6H4(RuCp*)-η6-C9H9][BPh4]2 is generated after the reaction of compound [C9H9-η6-C6H4(RuCp*)–C6H4(RuCp*)-η6-C9H9][BF4]2 with Na[BPh4]. The structure of this compound was confirmed by X-ray diffraction. And the possible approach to form Ph–C≡C–C9H8–Ph and [Cp*Ru(η6-C6H5–C≡C–C≡C–Ph)][BF4] was suggested.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Abdulhamid Hamza 《Structural chemistry》2010,21(5):939-945
The molecular conformations of jet-cooled 2-methylindan (2MI) and 2-phenylindan (2PI) have been studied using resonant-enhanced
two-photon ionization spectroscopy in combination with ab initio calculations. Both axial (2MIax) and equatorial (2MIeq) conformers of 2MI have been observed. A 2MIeq/2MIax conformer ratio of 2.3 was estimated at 298 K, leading to the energy difference,
\Updelta E = E 2 \textMI\textax - E 2 \textMI\texteq \Updelta E = E_{{ 2 {\text{MI}}_{\text{ax}} }} - E_{{ 2 {\text{MI}}_{\text{eq}} }} , of 0.49 kcal/mol. Ab initio calculations predicted three stable conformers of 2PI: two equatorial conformers (2PIeq0 and 2PIeq90), and one axial conformer (2PIax). Only the axial conformer of 2PI (2PIax) was experimentally observed. The indan ring of 2PIax is slightly more planar than the indan rings of the two equatorial conformers of 2PI because of the intramolecular Csp2–H/π interactions in 2PIax. The equatorial conformers of 2PI relax to the more stable axial conformer because of the high pre-expansion temperature
(383 K), and relatively low barrier (1.68 kcal/mol) to axial–equatorial interconversion. The barrier (2.33 kcal/mol) to axial–equatorial
interconversion in 2MI is high enough to prevent conformational relaxation at the pre-expansion temperature of 298 K. Intramolecular
C–H/π interactions are found to be more important in determining the conformational preference of 2PI than 2MI; this can be
attributed to the higher acidity of the Csp2–H bond than that of Csp3–H bond. 相似文献
8.
In our previous studies of the crystal structure of native cellulose (cellulose I) by solid-state two-dimensional (2D) 13C–13C INADEQUATE, it was revealed that cellulose Iα contains two kinds of β-d-glucose residues (A and A′) in the unit cell and that cellulose Iβ contains another two kinds of residues (B and B′). In the present study, the sequence of residues A and A′ along the same chains in cellulose Iα and that of residues B and B′ in Iβ were investigated by 2D 13C–13C rotor-synchronized radiofrequency-driven recoupling (RFDR) experiments using, respectively, uniformly 13C6-labeled (U−13C6) bacterial cellulose and the same [U−13C6] cellulose sample after thermal treatment at 260 °C. The RFDR spectra recorded with a short mixing time (1.0 ms) showed dipolar-coupled 13C spin pairs of only the neighboring carbon of the both phases, while those recorded with a longer mixing time (3.0–15 ms) provided correlations between weakly coupled 13C spin pairs as well as strongly coupled 13C spin pairs such as neighboring carbon nuclei. In the RFDR spectrum of the [U−13C6] cellulose recorded with a mixing time of 15 ms, the inter-residue 13C–13C correlation between C4 of residue A and C2 of residue A′ and that between C3 of residue A and C4 of residue A′ were clearly observed. In the case of cellulose Iβ, however, inter-residue 13C–13C correlations between residues B and B′ could not be detected in the series of RFDR spectra recorded with different mixing times of annealed [U−13C6] cellulose. From these findings, that cellulose Iα was revealed to have the –A–A′– repeating units along the cellulose chain. For cellulose Iβ, it was revealed that the respective residues B and B′ are composed of independent chains (–B–B– and –B′–B′– repeating units) and that there are no –B–B′– repeating units in the chain. 相似文献
9.
The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by
electron diffraction at 130∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface
has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified.
Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations
resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ
energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data
to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter
values (ra in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers
are r(C–C) = 1.507(5), r(C–C)ring, av = 1.397(3), r(C–S)av = 1.814(4), r(C–N) = 1.495(4), r(N–O)av = 1.223(3), ∠(C–C–C)ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the
rotation about C–N bond, φC−N, were found to be 30.5–36.5∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φC−C = 68–118∘ and φC−S = 66–71∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds.
Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701. 相似文献
10.
Xing Chen Wen-Tao Yin Qian Huang Hong-Rong Zuo Jia-Rong Zhou Lin-Liang Yu Chun-Lin Ni Xue-Lei Hu 《Transition Metal Chemistry》2010,35(2):143-149
Two new salts, [BzTPP]2[Cu(mnt)2] (1) and [4NO2BzTPP]2[Cu(mnt)2] (2) (BzTPP+ = benzyltriphenylphosphonium and mnt2− = maleonitriledithiolate) have been prepared and characterized by elemental analyses, UV, IR, molar conductivity and single-crystal
X-ray diffraction. The single-crystal structure analysis shows that 1 crystallizes in the monoclinic space group P21/n, while 2 crystallizes in the triclinic space group P−1. The effects of weak intramolecular interactions such as C–H···O, C–H···S, C–H···N, C–H···Cu hydrogen bonds and p···π, π···π stacking interactions in the solids generate a 3D network structure. It is noted that the change in the molecular
topology of the counteraction when the 4-substituted group in the benzyl ring is changed from H to NO2 results in differences in the crystal system, space group, weak interactions and the stacking mode of the cations and anions
of 1 and 2. The magnetic susceptibilities of these salts measured in the temperature range 2.0 to 300 K show weak ferromagnetic coupling
features with θ = 2.05 × 10−2 K for 1 and 5.13 × 10−3 K for 2. 相似文献
11.
Adriana Fuliaş Titus Vlase Gabriela Vlase Nicolae Doca 《Journal of Thermal Analysis and Calorimetry》2010,99(3):987-992
The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate,
starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min−1. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min−1. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears.
These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic
analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates:
5, 7, 10 and 12 °C min−1. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a
nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion
dependence on the reaction rate and less speculative discussions on the kinetic model. All there methods had furnished very
near values of the activation energy, this being an argument for a single thermooxidative degradation at the beginning (192–200 °C). 相似文献
12.
Thermal behavior of xGa2O3–(50 − x)PbO–50P2O5 (x = 0, 10, 20, and 30 mol.% Ga2O3) and xGa2O3–(70 − x)PbO–30P2O5 (x = 0, 10, 20, 30, and 40 mol.% Ga2O3) glassy materials were studied by thermo-mechanical analysis (TMA) and differential thermal analysis (DTA). Replacement of
PbO for Ga2O3 is accompanied by increasing glass-transition temperature (263 ≤ T
g/°C ≤ 535), deformation temperature (363 ≤ T
d/°C ≤ 672), crystallization temperature (396 ≤ T
c/°C ≤ 640) and decreasing of coefficient of thermal expansion (5.1 ≤ CTE/ppm K−1 ≤ 16.7). Values of Hruby parameter were determined (0.1 ≤ K
H ≤ 1.3). The thermal stability of prepared glasses increases with increasing of concentration of Ga2O3. 相似文献
13.
Issa Yavari Nasir Iravani S. Zahra Sayyed-Alangi Rahimeh Hajinasiri 《Monatshefte für Chemie / Chemical Monthly》2009,35(1):1199-1204
Abstract
An efficient synthesis of alkyl acylcarbamodithioates by reaction of acid chlorides with ammonium thiocyanate in the presence of thiols is described. The unusually large values of 5 J FH = 12–15 Hz, observed for alkyl (2-fluorobenzoyl)carbamodithioates provide information about Ar–C–N–H torsion in these compounds. 相似文献14.
A. López-Hernández K. Venkatesan H. W. Schmalle Heinz Berke 《Monatshefte für Chemie / Chemical Monthly》2009,36(10):845-857
Abstract
Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)2Cr(dmpe)2] n+ (R = Ph, SiMe3, SiEt3, C≡C–SiMe3 n = 0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies. 相似文献15.
Qian Huang Wei-qiang Chen Xing Chen Xiao-bin Liu Jia-rong Zhou Hong-rong Zuo Lin-liang Yu Chun-lin Ni 《Transition Metal Chemistry》2009,34(7):765-771
Two new hybrid organic–inorganic salts, [BzDMAP]2[Cu(mnt)2](1) and [NO2BzDMAP]2[Cu(mnt)2] (2) ([BzDMAP]+ = 1-benzyl-4′-dimethylaminopyridinium, [NO2BzDMAP]+ = 1-(4′-nitrobenzyl)-4′-dimethylaminopyridinium, and mnt2− = maleonitriledithiolate) have been characterized structurally and magnetically. The [BzDMAP]+ or [NO2BzDMAP]+ cations (C) and the [Cu(mnt)2]2− anions (A) in 1 and 2 stack into a 1D alternating CC-A-CC-A-CC column. The Cu···N, π···π, C–H···N, C–H···O, and C–H···S weak interactions play
important roles in the molecular stacking and generate a 2D or 3D structure of 1 and 2. The magnetic susceptibilities of these salts measured in the temperature range 2.0–300 K show weak antiferromagnetic coupling
features with θ = −2.370 K for 1 and −0.222 K for 2. 相似文献
16.
Nina I. Giricheva Georgiy V. Girichev Yulia S. Medvedeva Sergey N. Ivanov Anna V. Bardina Vyacheslav M. Petrov 《Structural chemistry》2011,22(2):373-383
A combined gas-phase electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pvtz, MP2/cc-pvtz) study of molecular
structure of 2-nitrobenzenesulfonamide (2-NBSA) was carried out. Quantum chemical calculations showed that 2-NBSA has four
conformers, two of which are stabilized by intramolecular hydrogen bond. The latter (with the S–N bond in a close to orthogonal
position around the phenyl ring and differing from each other by staggered or eclipsed positions of the N–H and S=O bonds
in the SO2NH2 group) presented in a saturated vapor over 2-NBSA at T = 433 (3) K in commensurable amounts. Experimental internuclear distances (Ǻ) for the staggered conformer are (?): r
h1(C–H)av. = 1.071(9), r
h1(C–C)av. = 1.390(4), r
h1(C–S) = 1.789(8), r
h1(S=O)av. = 1.427(6), r
h1(S–N) = 1.644(6), r
h1(N–O)av. = 1.221(4), r
h1(C′–N) = 1.487(8), r
h1(N–H)av. = 1.014. Calculations at B3LYP/cc-pvtz level were performed to determine the structure and the energies of the transition
states between conformers. It was shown that the conformer structures of free molecule differ from those of a molecule stabilized
by intermolecular hydrogen bonds in a crystal. Influence of a substituent X (X = –CH3, –NO2) on conformational features of the ortho-substituted benzenesulfonamide was established. 相似文献
17.
Cyril Rajnák Ján Titi? Roman Bo?a Ján Moncol’ Zdeňka Padělková 《Monatshefte für Chemie / Chemical Monthly》2011,36(4):789-795
Abstract
A mononuclear complex [CoL2Cl2]·3.5H2O (L = 2-[(2,2-diphenylethylimino)methyl]pyridine-1-oxide) has been synthesized and characterized by X-ray structure analysis. The crystal structure confirms the formation of an interesting porous framework with channel diameters of about 8 ? through weak C–H···π and C–H···Cl interactions. The magnetic properties of this complex have also been studied, and the susceptibility and magnetization data were analyzed in terms of the spin Hamiltonian formalism. They confirm substantial zero-field splitting, D/hc = 75 cm−1. 相似文献18.
Anna Rita Campanelli Aldo Domenicano Fabio Ramondo István Hargittai 《Structural chemistry》2011,22(2):361-369
The molecular structure of triphenylsilane has been investigated by gas-phase electron diffraction and theoretical calculations.
The electron diffraction intensities from a previous study (Rozsondai B, Hargittai I, J Organomet Chem 334:269, 1987) have
been reanalyzed using geometrical constraints and initial values of vibrational amplitudes from calculations. The free molecule
has a chiral, propeller-like equilibrium conformation of C
3 symmetry, with a twist angle of the phenyl groups τ = 39° ± 3°; the two enantiomeric conformers easily interconvert via three
possible pathways. The low-frequency vibrational modes indicate that the three phenyl groups undergo large-amplitude torsional
and out-of-plane bending vibrations about their respective Si–C bonds. Least-squares refinement of a model accounting for
the bending vibrations gives the following bond distances and angles with estimated total errors: r
g(Si–C) = 1.874 ± 0.004 ?, 〈r
g(C–C)〉 = 1.402 ± 0.003 ?, 〈r
g(C–H)〉 = 1.102 ± 0.003 ?, and ∠aC–Si–H = 108.6° ± 0.4°. Electron diffraction studies and MO calculations show that the lengths of the Si–C bonds in H4−n
SiPh
n
molecules (n = 1–4) increase gradually with n, due to π → σ*(Si–C) delocalization. They also show that the mean lengths of the ring C–C bonds are about 0.003 ? larger
than in unsubstituted benzene, due to a one hundredth angstrom lengthening of the Cipso–Cortho bonds caused by silicon substitution. A small increase of r(Si–H) and decrease of the ipso angle with increasing number of phenyl groups is also revealed by the calculations. 相似文献
19.
Trilochan Swain 《Journal of Thermal Analysis and Calorimetry》2011,103(3):1111-1117
A new inorganically template metaphosphate of Co(II) complex has been synthesized and characterized by different measurements
such as DSC, FT-IR, C–H–N–O–S, ESR, TG-DTA and X-RD. Differential Scanning Calorimeter (DSC) elucidated negative specific
heat of the system and has used to evaluate some thermo dynamical constants like activation energy (E
a), frequency factor (A), enthalpy and entropy of that system. The specific heat capacity of the system is measured both in atmospheric O2 and N2 atmosphere at different heating rates of 278, 283, 293 and 298 K min−1 in room atmosphere and 288 K min−1 in N2 atmosphere. 相似文献
20.
Sara Goñi Francisca Puertas María Soledad Hernández Marta Palacios Ana Guerrero Jorge S. Dolado Bruno Zanga Fulvio Baroni 《Journal of Thermal Analysis and Calorimetry》2010,102(3):965-973
This research is part of a European project (namely, CODICE project), main objective of which is modelling, at a multi-scale,
the evolution of the mechanical performance of non-degraded and degraded cementitious matrices. For that, a series of experiments
were planned with pure synthetic tri-calcium silicate (C3S) and bi-calcium silicate (C2S) (main components of the Portland cement clinker) to obtain different calcium–silicate–hydrate (C–S–H) gel structures during
their hydration. The characterization of those C–S–H gels and matrices will provide experimental parameters for the validation
of the multi-scale modelling scheme proposed. In this article, a quantitative method, based on thermal analyses, has been
used for the determination of the chemical composition of the C–S–H gel together with the degree of hydration and quantitative
evolution of all the components of the pastes. Besides, the microstructure and type of silicate tetrahedron and mean chain
length (MCL) were studied by scanning electron microscopy (SEM) and 29Si magic-angle-spinning (MAS) NMR, respectively. The main results showed that the chemical compositions for the C–S–H gels
have a CaO/SiO2 M ratio almost constant of 1.7 for both C3S and C2S compounds. Small differences were found in the gel water content: the H2O/SiO2 M ratio ranged from 2.9 ± 0.2 to 2.6 ± 0.2 for the C3S (decrease) and from 2.4 ± 0.2 to 3.2 ± 0.2 for the C2S (increase). The MCL values of the C–S–H gels, determined from 29Si MAS NMR, were 3.5 and 4 silicate tetrahedron, for the hydrated C3S and C2S, respectively, remaining almost constant at all hydration periods. 相似文献