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Refaat M. Mahfouz - One of the best experts on this subject based on the ideXlab platform.

  • Gamma irradiation effects on the thermal decomposition Induction Period in uranyl acetate
    Thermochimica Acta, 1999
    Co-Authors: M. A. S. Monshi, N. M. Abd El-salam, Refaat M. Mahfouz
    Abstract:

    Abstract The effect of pre-irradiation with γ -ray prior to thermal decomposition on the Induction Period of dehydrated uranyl acetate has been investigated. The results indicated that the Induction Period of the investigated salt is shortened by exposure to γ -irradiation. Specifically, the Induction Period, I , is related to the radiation dose φ as I  =  C 1  −  C 2 log  φ , where C 1 and C 2 are constants. It is concluded that pre-exposure to ionizing radiation increases the number of nuclei that are active in salt breakdown in direct proportion to the γ -dose to which the sample had previously been exposed.

  • Gamma Irradiation Effects on the Thermal Decomposition Induction Period in Hexammine Cobalt(III) Chloride
    Isotopenpraxis Isotopes in Environmental and Health Studies, 1991
    Co-Authors: Refaat M. Mahfouz
    Abstract:

    The effects of pre irradiation with γ-ray prior to thermal decomposition on the Induction Period of hexammine cobaldt (III) chloride have been investigated. The results indicated that the Induction Period of the investigated salt is shortened by exposure to γ-irradiation. Specifically the Induction Period I is related to the radiation dose by the equation I = C1 + C2 log Φ, where C1 and C2 are constants. It is concluded that pre-exposure to ionizing radiation increases the number of nuclei that are active in salt breakdown in direct proportion to the γ-dose to which the sample had previously been exposed.

Zhongmin Liu - One of the best experts on this subject based on the ideXlab platform.

  • evolution of the reaction mechanism during the mth Induction Period over the 2 dimensional fer zeolite
    RSC Advances, 2016
    Co-Authors: Zhongmin Liu
    Abstract:

    The methanol conversion reaction mechanism over HZSM-35, an ferrierite (FER)-type zeolite with 2-D channel intersections, was investigated during the Induction Period. The MTH Induction Period could be obviously shortened by co-feeding toluene or precoking the catalyst and the formation of tetramethylcyclopentenyl cation (tetraMCP+) during the Induction Period was also confirmed through 13C magic angle spinning (MAS) NMR and GC-MS experiments, suggesting the active role of aromatics. Moreover, the dual-cycle mechanism was evidently found to evolve as the Induction reaction progressed. In the early stage, both the aromatic- and olefin-based routes work efficiently and pentamethylbenzene (pentaMB) was identified as the main aromatic hydrocarbon pool (HCP) species. While in the latter stage of the Induction Period, the olefin-based route turned out to be more dominant and pentaMB as well as hexamethylbenzene (hexaMB) became the main aromatic HCP species. Despite the limited space of the channel intersections, the reactivity of aromatics with larger molecular sizes like 1-ethyl-2,3,4,5,6-pentamethylbenzene (1-E-pentaMB) and hexaMB were much higher than lower methylbenzenes which indicates that the aromatic-based cycle can also proceed on the external acid sites of the HZSM-35 catalyst.

  • Reaction Behaviors and Kinetics during Induction Period of Methanol Conversion on HZSM-5 Zeolite
    ACS Catalysis, 2015
    Co-Authors: Yingxu Wei, Zhongmin Liu
    Abstract:

    The reaction behavior in the Induction Period of the methanol to hydrocarbon (MTH) reaction over HZSM-5 (Si/Al = 19) zeolite has been investigated in a fixed-bed reactor. It is found that the Induction Period could be more than 2 h when the reaction was performed at a temperature of 255 °C and below. Meanwhile, three reaction stages can be clearly distinguished in the Induction Period: i.e., the initial C–C bond formation stage, the hydrocarbon pool (HCP) species formation stage, and the autocatalysis reaction stage. For each reaction stage, the kinetic parameters as well as the apparent activation energies have been evaluated. The HCP species formation stage is shown to be the rate-determining step. Addition of a ppm amount (molar) of benzene, toluene, or p-xylene to the methanol feed leads to a shortened Induction Period due to a lower energy barrier for both the HCP species formation and the autocatalysis reaction. A critical value of HCP species, [HCP]c, that is required for starting the autocatalysis...

  • direct observation of Induction Period of mto process with consecutive pulse reaction system
    Catalysis Communications, 2007
    Co-Authors: Yingxu Wei, Dazhi Zhang, Fuxiang Chang, Zhongmin Liu
    Abstract:

    The initial transformation of methanol over HZSM-5 catalyst was investigated by a consecutive pulse reaction system. The reactant– catalyst contact time influenced the initial methanol transformation and the performances implied methanol reaction in Induction Period or under steady-state condition. The Induction Period, in which an organic-free HZSM-5 catalyst could be transferred to a working catalyst, were directly observed. The analysis result of the product stream predicted hydrogen-deficient species deposition over catalyst surface at the beginning of MTO reaction. The hydrogen transfer level of steady-state MTO reaction also varied with reaction contact time. 2007 Elsevier B.V. All rights reserved.

  • A new phenomenon in the Induction Period of the methane dehydroaromatization reaction
    Chemical communications (Cambridge England), 2001
    Co-Authors: Lijie Men, Li Zhang, Yan Xie, Zhongmin Liu, Jiling Bai, Guohe Sha, Jinchun Xie
    Abstract:

    The Induction Period of dehydroaromatization of methane to benzene over Mo/HZSM-5 had been investigated in real-time by the resonant-enhanced two-photon ionization (RE2PI) technique; it is remarkable that there is a small amount of benzene formed in the early stage of the Induction Period; we suggest that the trace amount of benzene was caused by the reduction of the original Mo6+ ion during the Induction Period and the Mo6+ species has a slight catalytic activity for methane–benzene conversion.

Gordon Chan - One of the best experts on this subject based on the ideXlab platform.

  • end of the Induction Period in ordinary portland cement as examined by high resolution scanning electron microscopy
    Journal of the American Ceramic Society, 2008
    Co-Authors: Jonathan M Makar, Gordon Chan
    Abstract:

    The early stages of ordinary Portland cement (OPC) hydration were studied by cold field emission scanning electron microscopy and isothermal conduction calorimetry. Particular attention was paid to samples from the end of the Induction Period, where an additional peak in the tricalcium silicate hydration reaction has recently been discovered. Higher resolution images were obtained than is possible with current in situ imaging techniques, allowing for the observation of features on the 5-nm scale. The peak in the hydration at the end of the Induction Period was associated with both the formation of pores in the surface of the cement grains and the formation of nanoscale calcium silicate hydrate (C–S–H) structures on those surfaces. The effects of grinding of OPC and additions of tricalcium aluminate and tetracalcium aluminoferrite on the peak at the end of the Induction Period were also examined. The results of the study were compared with the models in the literature used to describe the causes of the Induction Period and its end.

  • End of the Induction Period in Ordinary Portland Cement as Examined by High‐Resolution Scanning Electron Microscopy
    Journal of the American Ceramic Society, 2008
    Co-Authors: J.m. Makar, Gordon Chan
    Abstract:

    The early stages of ordinary Portland cement (OPC) hydration were studied by cold field emission scanning electron microscopy and isothermal conduction calorimetry. Particular attention was paid to samples from the end of the Induction Period, where an additional peak in the tricalcium silicate hydration reaction has recently been discovered. Higher resolution images were obtained than is possible with current in situ imaging techniques, allowing for the observation of features on the 5-nm scale. The peak in the hydration at the end of the Induction Period was associated with both the formation of pores in the surface of the cement grains and the formation of nanoscale calcium silicate hydrate (C–S–H) structures on those surfaces. The effects of grinding of OPC and additions of tricalcium aluminate and tetracalcium aluminoferrite on the peak at the end of the Induction Period were also examined. The results of the study were compared with the models in the literature used to describe the causes of the Induction Period and its end.

Wen-chen Chien - One of the best experts on this subject based on the ideXlab platform.

  • Induction Period of CaCO3 interpreted by the Smoluchowski's coagulation theory
    AIChE Journal, 2005
    Co-Authors: Clifford Y. Tai, Wen-chen Chien, Jyh-ping Hsu
    Abstract:

    Smoluchowski's coagulation theory is adopted to estimate the Induction Period for the formation of the critical nuclei of CaCO3 in a supersaturated CaCl2-Na2CO3 aqueous solution. The effects of the presence of impurity and crystal seeds, degree of supersaturation and operating temperature on the Induction Period are discussed. The association coefficient between two clusters is found to depend on both the degree of supersaturation and the temperature. The estimated activation energy for the association between two clusters is about 200 J/mol, which implies that the association between two clusters is of physical nature. It is found that the increase in the Induction Period with the presence of Mg2+ may be caused by an increase in the solid-liquid interfacial energy, and a decrease in the association coefficient. Due to van der Waals attraction, the addition of crystal seeds increases the concentration of clusters near seed surface, and, thus, yields a shorter Induction Period. © 2005 American Institute of Chemical Engineers AIChE J, 51: 480–486, 2005

  • interpreting the effects of operating variables on the Induction Period of cacl2 na2co3 system by a cluster coagulation model
    Chemical Engineering Science, 2003
    Co-Authors: Chia-te Tai, Wen-chen Chien
    Abstract:

    Abstract In this article the effects of several operating variables, including supersaturation, temperature, and the presence of additive and seeds on the Induction Period of CaCO3 were studied experimentally and theoretically. In experimental, the Induction Period was measured by a conductivity method so that the Induction Period was well identified. The results show that the Induction Period increases with decreasing supersaturation and temperature. The presence of Mg2+ in solution prolongs the Induction Period and the addition of seeds reduces the Induction Period. In theoretical, a cluster coagulation model, which brings together the current nucleation models and the theories describing the behavior of colloidal suspensions, was applied to estimate the Induction Period under various operating variables. A comparison between the two results shows that the present model is a suitable one to interpret the effects of various operating variables on the Induction Period of aqueous CaCl2–Na2CO3 solution.

  • Interpreting the effects of operating variables on the Induction Period of CaCl2–Na2CO3 system by a cluster coagulation model
    Chemical Engineering Science, 2003
    Co-Authors: Chia-te Tai, Wen-chen Chien
    Abstract:

    Abstract In this article the effects of several operating variables, including supersaturation, temperature, and the presence of additive and seeds on the Induction Period of CaCO3 were studied experimentally and theoretically. In experimental, the Induction Period was measured by a conductivity method so that the Induction Period was well identified. The results show that the Induction Period increases with decreasing supersaturation and temperature. The presence of Mg2+ in solution prolongs the Induction Period and the addition of seeds reduces the Induction Period. In theoretical, a cluster coagulation model, which brings together the current nucleation models and the theories describing the behavior of colloidal suspensions, was applied to estimate the Induction Period under various operating variables. A comparison between the two results shows that the present model is a suitable one to interpret the effects of various operating variables on the Induction Period of aqueous CaCl2–Na2CO3 solution.

  • Effects of operating variables on the Induction Period of CaCl2–Na2CO3 system
    Journal of Crystal Growth, 2001
    Co-Authors: Clifford Y. Tai, Wen-chen Chien
    Abstract:

    The Induction Period is defined as the time elapsed between the creation of supersaturation and the formation of critical nuclei. A novel data acquisition system is developed in this experiment to determine the Induction Period on the desupersaturation curve. The effect of several operating conditions, including initial reagent concentration, temperature, pH, and presence of additive and seeds on the Induction Period of CaCO3 were studied experimentally. The results showed that the Induction Period decreases with an increase in initial reagent concentration, temperature, and pH of the solution. The presence of Mg2+ in solution prolongs the Induction Period. On the other hand, the presence of Na+ in solution has little influence on the Induction Period. Further, the presence of seed crystals in solution shortens the Induction Period.

Jonathan M Makar - One of the best experts on this subject based on the ideXlab platform.

  • end of the Induction Period in ordinary portland cement as examined by high resolution scanning electron microscopy
    Journal of the American Ceramic Society, 2008
    Co-Authors: Jonathan M Makar, Gordon Chan
    Abstract:

    The early stages of ordinary Portland cement (OPC) hydration were studied by cold field emission scanning electron microscopy and isothermal conduction calorimetry. Particular attention was paid to samples from the end of the Induction Period, where an additional peak in the tricalcium silicate hydration reaction has recently been discovered. Higher resolution images were obtained than is possible with current in situ imaging techniques, allowing for the observation of features on the 5-nm scale. The peak in the hydration at the end of the Induction Period was associated with both the formation of pores in the surface of the cement grains and the formation of nanoscale calcium silicate hydrate (C–S–H) structures on those surfaces. The effects of grinding of OPC and additions of tricalcium aluminate and tetracalcium aluminoferrite on the peak at the end of the Induction Period were also examined. The results of the study were compared with the models in the literature used to describe the causes of the Induction Period and its end.

  • A peak in the hydration reaction at the end of the cement Induction Period
    Journal of Materials Science, 2007
    Co-Authors: Jonathan M Makar, G.w. Chan, K. Y. Esseghaier
    Abstract:

    Although the hydration of ordinary Portland cement (OPC) and its main constitutent, tricalcium silicate (3CaO.SiO2 or C3S), have been studied for many decades, some aspects of the hydration process remain poorly understood. In particular, there is little consensus on the mechanisms related to the dormant or Induction Period. The Induction Period is a time of minimal hydration activity between the initial hydration reactions upon wetting and the later priamry tricalcium silicate reaction with water to form calcium silicate hydrate and calcium hydroxide. This letter examines the mechanisms responsible for a peak in hydration activity at the end of the Induction Period. Although occasionally seen in the literature, this peak appears absent in most reported measurements and has therefore remained unexplained.Peer reviewed: YesNRC publication: Ye