The Experts below are selected from a list of 17466 Experts worldwide ranked by ideXlab platform
V G Papadakis - One of the best experts on this subject based on the ideXlab platform.
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effect of fly ash on portland cement systems part ii high calcium fly ash
Cement and Concrete Research, 1999Co-Authors: V G PapadakisAbstract:Abstract A typical low-calcium fly ash was used as additive in mortar, replacing part of the volume either of Portland cement or aggregate. The development of the strength, heat, porosity, bound water, and calcium hydroxide content was measured. In aggregate replacement higher strengths were observed after 14 days, whereas in cement replacement higher strengths were observed after 91 days. The final strength gain was found to be roughly proportional to the content of active silica in the concrete volume. Bound water content and porosity results showed that fly ash reacts with calcium hydroxide, binding small amounts of water. On the basis of the experimental results, a simplified scheme describing the chemical Reactions of the low-calcium fly ash in hydrating cement is proposed. Using the Reaction Stoichiometry, quantitative expressions for the estimation of the chemical and volumetric composition of a fly ash concrete are proposed. The model expressions can be applied in mix design and concrete performance prediction.
Hubert Rahier - One of the best experts on this subject based on the ideXlab platform.
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development of inorganic polymer by alkali activation of untreated kaolinitic clay Reaction Stoichiometry strength and dimensional stability
Construction and Building Materials, 2015Co-Authors: Muayad Esaifan, Hubert Rahier, Ahmed Barhoum, Hani Khoury, M Hourani, Jan WastielsAbstract:Abstract An environmental friendly building material was developed by alkali-activation of untreated kaolinitic clay using sodium hydroxide. The Reaction was studied using differential scanning calorimetry. The chemical structure of the produced inorganic polymer was deduced from infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and scanning electron microscopy to be the tetrahydrate phase of hydroxysodalite with a Na/Al ratio of 4/3. Its strength and stability were evaluated in terms of compressive strength under dry and saturated conditions using different ratios of mixing water and NaOH. The compressive strength of dry samples ranges between 45 and 50 MPa. The wet samples after soaking in water show a strength between 20 and 25 MPa, and the wet samples after alternating cycles of drying and wetting also show a strength of 20–25 MPa.
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Low-temperature synthesized aluminosilicate glasses: Part III Influence of the composition of the silicate solution on production, structure and properties
Journal of Materials Science, 1997Co-Authors: Hubert Rahier, W Simons, B Van Mele, Monique BiesemansAbstract:The low-temperature Reaction between an aqueous sodium or potassium silicate solution and metakaolinite yields a solid aluminosilicate. The influence of the molar ratios H_2O/R_2O (between 6.6 and 21.0) and SiO_2/R_2O (between 0.0 and 2.3) of the silicate solution (R=Na or K) on the aluminosilicate's production, on the Reaction Stoichiometry and on the aluminosilicate's molecular structure is studied with differential scanning calorimetry, ^27Al and ^29Si magic angle spinning nuclear magnetic resonance (MAS NMR), cross-polarization MAS NMR, Fourier transform infrared spectroscopy and X-ray diffractometry. The Reaction Stoichiometry is determined by a one to one ratio for R/Al. H_2O/R_2O has no influence on the molecular structure of the aluminosilicate. Aluminium in the aluminosilicate is four-fold coordinated for the whole range of silicate solutions investigated. Moreover, Si and Al are homogeneously distributed and the ratio Al/Si in the aluminosilicate is the same as in the Reaction mixture if the stoichiometric one-to-one ratio for R/Al is used. If SiO_2/R_2O in the Na-silicate solution is equal to or higher than 0.8, the low-temperature Reaction yields an amorphous aluminosilicate or “inorganic polymer glass”. For smaller values of SiO2/R2O the Na-aluminosilicates are partially crystalline. Thermomechanical analysis and dynamic mechanical analysis indicate that a variation in the composition of the amorphous aluminosilicates can shift the glass transition over a few hundreds of degrees, with a minimum value of 650°C.
A L Chandrasegaran - One of the best experts on this subject based on the ideXlab platform.
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students dilemmas in Reaction Stoichiometry problem solving deducing the limiting reagent in chemical Reactions
Chemistry Education Research and Practice, 2009Co-Authors: Bruce Waldrip, David F Treagust, A L ChandrasegaranAbstract:A qualitative case study was conducted to investigate the understanding of the limiting reagent concept and the strategies used by five Year 11 students when solving four Reaction Stoichiometry problems. Students’ written problem-solving strategies were studied using the think-aloud protocol during problem-solving, and retrospective verbalisations after each activity. Contrary to several findings reported in the research literature, the two high-achieving students in the study tended to rely on the use of a memorised formula to deduce the limiting reagent, by comparing the actual mole ratio of the reactants with the stoichiometric mole ratio. The other three average-achieving students, however, generally deduced the limiting reagent from first principles, using the Stoichiometry of the balanced chemical equation. Overall, the students displayed limited confidence during problem-solving to determine the limiting reagent and to perform related computations.
Surya Prakash Singh - One of the best experts on this subject based on the ideXlab platform.
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kinetic study of oxidation of valine by n bromophthalimide in presence of iridium iii chloride as homogenous catalyst
Synthesis and Reactivity in Inorganic Metal-organic and Nano-metal Chemistry, 2010Co-Authors: Ajaya Kumar Singh, Bhawana Jain, Reena Negi, Yokraj Katre, Surya Prakash Singh, Virender K SharmaAbstract:The mechanistic study of Ir(III) chloride catalyzed oxidation of Val has been studied by by N-bromophthalimide (NBP) in aqueous perchloric acid medium at 303 K. The Reaction followed first order kinetics with respect to [NBP] and zero order kinetics with respect to [Val]. At lower concentration range of Ir(III) chloride, the Reaction followed first order kinetics while tending to zero order at its higher concentration. A negative effect was observed for [H+] and [NHP] (phthalimide) whereas variation in [Hg(OAc)2] (mercuric acetate), [Cl−], ionic strength (I) and dielectric constant of the medium did not bring about any significant change on the rate of Reaction. The rate constants observed at five different temperatures (298 K–318 K) were used to calculate the activation parameters. A plausible mechanism from the results of kinetic studies, Reaction Stoichiometry and product analysis has been proposed.
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mechanistic study of novel oxidation of paracetamol by chloramine t using micro amount of chloro complex of ir iii as a homogeneous catalyst in acidic medium
Journal of Molecular Catalysis A-chemical, 2009Co-Authors: Ajaya Kumar Singh, Reena Negi, Yokraj Katre, Surya Prakash SinghAbstract:Abstract The mechanistic study of iridium (III)-catalyzed oxidation of paracetamol has been studied by sodium N-chloro-p-toluenesulfonamide (chloramine-T) in aqueous perchloric acid medium at 308 K. The Reaction followed first-order kinetics with respect to [chloramine-T], [paracetamol] and [Cl − ] in their lower concentrations range, tending to zero-order at their higher concentrations. First-order kinetics with respect to [Ir(III)] was observed for the oxidation of paracetamol. The rate of Reaction decreased with increasing [H + ] and [p-toluene sulphonamide, PTS] were observed for the oxidation of paracetamol. The variation of the ionic strength of the medium had no significant effect on the rate of the Reaction. The first-order rate constant increased with decrease in the dielectric constant of the medium. The values of rate constants observed at five different temperatures were utilized to calculate the activation parameters. The Reaction between chloramine-T and paracetamol in acid medium exhibits 1:2 Stoichiometry. A plausible mechanism from the results of kinetic studies, Reaction Stoichiometry and product analysis has been proposed.
Carlo G Pantano - One of the best experts on this subject based on the ideXlab platform.
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pozzolanic reactivity of recycled glass powder at elevated temperatures Reaction Stoichiometry Reaction products and effect of alkali activation
Cement & Concrete Composites, 2014Co-Authors: Hamed Maraghechi, Mahsa Maraghechi, Farshad Rajabipour, Carlo G PantanoAbstract:Abstract Use of glass powder as concrete SCM or in development of lime–pozzolan binders could provide environmental and economical benefits. In exposure to an alkaline pore solution, glass powder (GP) dissolves and reacts pozzolanically with calcium hydroxide (CH). In this paper, the Stoichiometry and products of this Reaction are studied using a CH–GP binder system cured at 60 °C. TGA, selective acid dissolution, SEM/EDS, and QXRD methods are used to quantify the Stoichiometry, and characterize the Reaction products as a function of age. It is determined that approximately equal masses of CH and GP react with each other and with water to produce C–S–H. Both crystalline and amorphous C–S–H are formed, but the crystalline C–S–H is favored at later ages and higher alkalinities. NaOH-activation accelerates the Reactions. However when high alkalinity is maintained, GP continues to dissolve after complete consumption of CH, and forms alkali–silicate gels, which could be expansive and deleterious.
