IJE TRANSACTIONS A: Basics Vol. 29, No. 4 (April 2016) 539-545   

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S. Ghasemi Kahrizsangi, A. Nemati, A. Shahraki and M. Farooghi
( Received: February 07, 2016 – Accepted in Revised Form: April 14, 2016 )

Abstract    In this study, the effect of variety of Nano- additives doping on the hydration resistance of the MgO-CaO system was investigated. Samples were prepared from calcined dolomite and magnesite. Nano-additives that contained cations with various valences (trivalent and tetravalent) used as a dopant. The bulk density, apparent porosity and hydration resitance were studied and evaluated. Also, phase analysis of samples was conducted by using X-ray diffraction (XRD) and the microstructure investigation was done by scanning electron microscopy (SEM). The use of both additives improved the hydration resistance. However, the important role of the higher-valence cation in improvmnt of the hydration resistance of MgO-CaO materials was revealed. This behavior is believed to be due to the formation of vacancies in solid solution of CaO or MgO with higher–valence cation. Zr4+ cation form a solid solution with CaO, which reduce the Ca2+ concentration and leads to the improved hydration resistance of the MgO-CaO system. Also trivalent cation led to the formation of some low melting phases such as C2F (2CaO.Fe2O3), CF (CaO.Fe2O3), C3A (3CaO.Al2O3). The formation of these low melting point phases surrounded the CaO and MgO grain, grain-boundaries and thus promoted densification and hydration resistance of the MgO-CaO system.


Keywords    Nano-additives, trivalent and tetravalent, hydration resistance, solid solution.


چکیده    در این پژوهش تاثیر افزودنی های نانو بر مقاومت به هیدراتاسیون سیستم MgO-CaO مورد بررسی قرار گرفته است. نمونه ها با استفاده از دولومیت و منیزیت کلسینه شده، تهیه شد. از مواد نانو با ظرفیت مختلف (سه و چهار ظرفیتی) به عنوان افزودنی استفاده شد. دانسیته بالک، تخلخل و مقاومت به هیدارتاسیون نمونه ها اندازه گیری شده است. همچنین بررسی های فاز توسط دستگاه پراش اشعه ایکس و بررسی های ریزساختار ی با استفاده از SEM بررسی شده است. استفاده از هر دو نوع افزودنی موجب افزایش مقاومت به هیدراتاسیون نمونه ها شد اما نمونه های دارای افزودنی با ظرفیت بالاتر مقاومت به هیدراتاسیون بالاتری داشتند. دلیل آن تشکیل جاهای خالی در فرآیند انحلال جامد کلسیا و منیزیا با استفاده از جایگزینی یون Zr4+ در کاتیون CaO بوده است. همچنین کاتیون های سه ظرفیتی منجر به ایجاد فازهای زودگداز از قبیل C2F، CF،C3A شد که تشکیل این فازهای زودگداز با پوشش دانه های کلسیا و منیزیا و کاهش تخلخل در سیستم منجر به افزایش مقاومت به هیدراتاسیون نمونه ها شده است.


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