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J C Borba – One of the best experts on this subject based on the ideXlab platform.

  • Chloride penetration into concrete structures in the marine atmosphere zone relationship between deposition of Chlorides on the wet candle and Chlorides accumulated into concrete
    Cement & Concrete Composites, 2007
    Co-Authors: Gibson Meira, C Andrade, I J Padaratz, C Alonso, J C Borba
    Abstract:

    Abstract The relationship between Chlorides from marine aerosol and Chlorides accumulated into concrete is discussed in this paper. The experimental programme comprised an environmental characterisation, with climatic and Chloride deposition data, and a study of Chloride penetration into concrete based on natural exposure of specimens in a marine atmosphere zone. Results show that salt concentration in marine aerosol strongly decreases in the first meters from the sea. Chlorides present in the atmosphere can be studied using the wet candle method and correlated with Chlorides accumulated into concrete. This relationship can be represented by the equation C tot = C 0 + k d · D ac , where k d is a coefficient which depends on concrete and environmental characteristics, C tot is the average total amount of Chlorides accumulated into concrete, C 0 is the Chloride content in concrete before exposure and D ac is the accumulated dry deposition of Chlorides.

  • Chloride penetration into concrete structures in the marine atmosphere zone – Relationship between deposition of Chlorides on the wet candle and Chlorides accumulated into concrete
    Cement & Concrete Composites, 2007
    Co-Authors: Gibson Meira, C Andrade, I J Padaratz, C Alonso, J C Borba
    Abstract:

    Abstract The relationship between Chlorides from marine aerosol and Chlorides accumulated into concrete is discussed in this paper. The experimental programme comprised an environmental characterisation, with climatic and Chloride deposition data, and a study of Chloride penetration into concrete based on natural exposure of specimens in a marine atmosphere zone. Results show that salt concentration in marine aerosol strongly decreases in the first meters from the sea. Chlorides present in the atmosphere can be studied using the wet candle method and correlated with Chlorides accumulated into concrete. This relationship can be represented by the equation C tot = C 0 + k d · D ac , where k d is a coefficient which depends on concrete and environmental characteristics, C tot is the average total amount of Chlorides accumulated into concrete, C 0 is the Chloride content in concrete before exposure and D ac is the accumulated dry deposition of Chlorides.

John F Kadla – One of the best experts on this subject based on the ideXlab platform.

Douglas R Svenson – One of the best experts on this subject based on the ideXlab platform.

  • inorganic reactions in chlorine dioxide bleaching of softwood kraft pulp
    Journal of Wood Chemistry and Technology, 2006
    Co-Authors: Douglas R Svenson, Hasan Jameel, Houmin Chang, John F Kadla
    Abstract:

    Abstract A softwood kraft pulp (27 kappa) was bleached with chlorine dioxide to various end pH values. The formation of chlorite, chlorate, and Chloride was measured to quantify the amount of chlorine dioxide wasted as a function of pH during a Do (pre‐bleaching) stage. Chlorate formation increased with a decrease in final pH. Conversely, residual chlorite increased with an increase in the final pH. After 120 min of bleaching the total residual chlorite and chlorate showed that no substantial increase in residual oxidant occurs when bleaching to an end pH below 3.4. As a result, the brightness and permanganate numbers for low pH chlorine dioxide bleached pulps did not differ when bleaching to an end pH between 3.4 and 1.8. However, decreasing the pH below 3.4 did result in increased organic Chloride formation. The results are contrary to previous studies where the maximum bleaching efficiency for a D1 stage was reported to occur when the end pH was between 3 and 4.

  • The role of non-phenolic lignin in chlorate-forming reactions during chlorine dioxide bleaching of softwood kraft pulp
    Holzforschung, 2005
    Co-Authors: Douglas R Svenson, Hasan Jameel, Houmin Chang, John F Kadla
    Abstract:

    The affect of phenolic hydroxyl groups on the reaction efficiency during chlorine dioxide pre-bleaching of a softwood kraft pulp was investigated. The removal of phenolic hydroxyl groups via pulp methylation did not adversely affect the chlorine dioxide bleaching efficiency or the amount of chlorate formed during exposure to chlorine dioxide. Ion analysis of the reaction systems revealed that the formation of Chloride and chlorite ions during the bleaching process were very similar between the kraft and methylated kraft pulps. These results indicate that the kinetic rates of lignin oxidation by chlorine dioxide and its reduction products, chlorite and hypochlorous acid, are much faster than the rate of inorganic reactions leading to chlorate formation.

  • effect of ph on the inorganic species involved in a chlorine dioxide reaction system
    Industrial & Engineering Chemistry Research, 2002
    Co-Authors: Douglas R Svenson, John F Kadla, Houmin Chang, Hasan Jameel
    Abstract:

    The effects of pH on the inorganic products formed during the reaction of chlorine dioxide with an etherified lignin model compound have been studied. Analyses of the inorganic species produced during the reaction at pH 8 revealed that 2 mol of chlorite are liberated for every 1 mol of oxidized nonphenolic lignin model compound formed, consistent with two consecutive one-electron-transfer processes. In contrast, the low-pH reactions produced mostly ring oxidation products and chlorinated organic material, accompanied by increased levels of hypochlorous acid. The transient hypochlorous acid rapidly reacted with chlorite to generate Chloride ions, with a maximum Chloride formation at pH 4. Chlorate formation was shown to increase with increasing reaction pH. These results are in contrast to those previously reported for reactions with wood pulps and are explained on the basis of the slow reaction kinetics of nonphenolic lignin moieties as compared to phenolic ones, thereby enabling hypochlorous acid to reac…

Hasan Jameel – One of the best experts on this subject based on the ideXlab platform.

  • inorganic reactions in chlorine dioxide bleaching of softwood kraft pulp
    Journal of Wood Chemistry and Technology, 2006
    Co-Authors: Douglas R Svenson, Hasan Jameel, Houmin Chang, John F Kadla
    Abstract:

    Abstract A softwood kraft pulp (27 kappa) was bleached with chlorine dioxide to various end pH values. The formation of chlorite, chlorate, and Chloride was measured to quantify the amount of chlorine dioxide wasted as a function of pH during a Do (pre‐bleaching) stage. Chlorate formation increased with a decrease in final pH. Conversely, residual chlorite increased with an increase in the final pH. After 120 min of bleaching the total residual chlorite and chlorate showed that no substantial increase in residual oxidant occurs when bleaching to an end pH below 3.4. As a result, the brightness and permanganate numbers for low pH chlorine dioxide bleached pulps did not differ when bleaching to an end pH between 3.4 and 1.8. However, decreasing the pH below 3.4 did result in increased organic Chloride formation. The results are contrary to previous studies where the maximum bleaching efficiency for a D1 stage was reported to occur when the end pH was between 3 and 4.

  • The role of non-phenolic lignin in chlorate-forming reactions during chlorine dioxide bleaching of softwood kraft pulp
    Holzforschung, 2005
    Co-Authors: Douglas R Svenson, Hasan Jameel, Houmin Chang, John F Kadla
    Abstract:

    The affect of phenolic hydroxyl groups on the reaction efficiency during chlorine dioxide pre-bleaching of a softwood kraft pulp was investigated. The removal of phenolic hydroxyl groups via pulp methylation did not adversely affect the chlorine dioxide bleaching efficiency or the amount of chlorate formed during exposure to chlorine dioxide. Ion analysis of the reaction systems revealed that the formation of Chloride and chlorite ions during the bleaching process were very similar between the kraft and methylated kraft pulps. These results indicate that the kinetic rates of lignin oxidation by chlorine dioxide and its reduction products, chlorite and hypochlorous acid, are much faster than the rate of inorganic reactions leading to chlorate formation.

  • effect of ph on the inorganic species involved in a chlorine dioxide reaction system
    Industrial & Engineering Chemistry Research, 2002
    Co-Authors: Douglas R Svenson, John F Kadla, Houmin Chang, Hasan Jameel
    Abstract:

    The effects of pH on the inorganic products formed during the reaction of chlorine dioxide with an etherified lignin model compound have been studied. Analyses of the inorganic species produced during the reaction at pH 8 revealed that 2 mol of chlorite are liberated for every 1 mol of oxidized nonphenolic lignin model compound formed, consistent with two consecutive one-electron-transfer processes. In contrast, the low-pH reactions produced mostly ring oxidation products and chlorinated organic material, accompanied by increased levels of hypochlorous acid. The transient hypochlorous acid rapidly reacted with chlorite to generate Chloride ions, with a maximum Chloride formation at pH 4. Chlorate formation was shown to increase with increasing reaction pH. These results are in contrast to those previously reported for reactions with wood pulps and are explained on the basis of the slow reaction kinetics of nonphenolic lignin moieties as compared to phenolic ones, thereby enabling hypochlorous acid to reac…

Gibson Meira – One of the best experts on this subject based on the ideXlab platform.

  • Chloride penetration into concrete structures in the marine atmosphere zone relationship between deposition of Chlorides on the wet candle and Chlorides accumulated into concrete
    Cement & Concrete Composites, 2007
    Co-Authors: Gibson Meira, C Andrade, I J Padaratz, C Alonso, J C Borba
    Abstract:

    Abstract The relationship between Chlorides from marine aerosol and Chlorides accumulated into concrete is discussed in this paper. The experimental programme comprised an environmental characterisation, with climatic and Chloride deposition data, and a study of Chloride penetration into concrete based on natural exposure of specimens in a marine atmosphere zone. Results show that salt concentration in marine aerosol strongly decreases in the first meters from the sea. Chlorides present in the atmosphere can be studied using the wet candle method and correlated with Chlorides accumulated into concrete. This relationship can be represented by the equation C tot = C 0 + k d · D ac , where k d is a coefficient which depends on concrete and environmental characteristics, C tot is the average total amount of Chlorides accumulated into concrete, C 0 is the Chloride content in concrete before exposure and D ac is the accumulated dry deposition of Chlorides.

  • Chloride penetration into concrete structures in the marine atmosphere zone – Relationship between deposition of Chlorides on the wet candle and Chlorides accumulated into concrete
    Cement & Concrete Composites, 2007
    Co-Authors: Gibson Meira, C Andrade, I J Padaratz, C Alonso, J C Borba
    Abstract:

    Abstract The relationship between Chlorides from marine aerosol and Chlorides accumulated into concrete is discussed in this paper. The experimental programme comprised an environmental characterisation, with climatic and Chloride deposition data, and a study of Chloride penetration into concrete based on natural exposure of specimens in a marine atmosphere zone. Results show that salt concentration in marine aerosol strongly decreases in the first meters from the sea. Chlorides present in the atmosphere can be studied using the wet candle method and correlated with Chlorides accumulated into concrete. This relationship can be represented by the equation C tot = C 0 + k d · D ac , where k d is a coefficient which depends on concrete and environmental characteristics, C tot is the average total amount of Chlorides accumulated into concrete, C 0 is the Chloride content in concrete before exposure and D ac is the accumulated dry deposition of Chlorides.