Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 985185, 10 pages http://dx.doi.org/10.1155/2014/985185 Research Article Characterization and Thermal Dehydration Kinetics of Highly Crystalline Mcallisterite, Synthesized at Low Temperatures Emek Moroydor Derun and Fatma Tugce Senberber Department of Chemical Engineering, Yildiz Technical University, 34210 Istanbul, Turkey Correspondence should be addressed to Emek Moroydor Derun; [email protected] Received 18 November 2013; Accepted 19 January 2014; Published 25 February 2014 Academic Editors: A. L. R. MerceandE.Mikuliˆ Copyright © 2014 E. Moroydor Derun and F. T. Senberber. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The hydrothermal synthesis of a mcallisterite2 (Mg (B6O7(OH)6)2⋅9(H2O)) mineral at low temperatures was characterized. For ∘ this purpose, several reaction temperatures (0–70 C) and reaction times (30–240 min) were studied. Synthesized minerals were subjected to X-ray diffraction (XRD), fourier transform infrared (FT-IR), and Raman spectroscopies and scanning electron microscopy (SEM). Additionally, experimental analyses of boron trioxide (B2O3) content and reaction yields were performed. Furthermore, thermal gravimetry and differential thermal analysis (TG/DTA) were used for the determination of thermal dehydration kinetics. According to the XRD results, mcallisterite, which has a powder diffraction file (pdf) number of “01-070- 1902,” was formed under certain reaction parameters. Pure crystalline mcallisterite had diagnostic FT-IR and Raman vibration ∘ peaks and according to the SEM analysis, for the minerals which were synthesized at 60 C and 30 min of reaction time, particle size was between 398.30 and 700.06 nm. Its B2O3 content and reaction yield were 50.80 ± 1.12%and85.80 ± 0.61%, respectively. Finally, average activation energies (conversion values () that were selected between 0.1 and 0.6) were calculated as 100.40 kJ/mol and 98.31 kJ/mol according to Ozawa and Kissinger-Akahira-Sunose (KAS) methods, respectively. 1. Introduction 2MgO⋅3B2O3⋅17H2O, MgO⋅3B2O3⋅3.5H2O, 2MgO⋅B2O3⋅ H2O, 2MgO⋅6B2O3⋅15H2O, and MgO⋅3B2O3⋅7H2O[6–13]. Boron most often occurs in nature as borates which can Mcallisterite is a type of magnesium borate with the chemical be classified by the kind of metal it is complexed with. formula Mg2[B6O7(OH)6]2⋅9H2O. It has the appearance of Magnesium borate minerals, which are a subclass of boron very fine aggregates and white-colorless crystals, hardness minerals, are inorganic compounds containing magnesium of 2.5 Mohs, and low water solubility. Mcallisterite reserves and boron. They are excellent additives for industry due to are found in Argentina, China, Kazakhstan, and USA; their high elasticity coefficient, heat resistance, and corro- however, in these reserves, magnesium and calcium borates sion resistance [1]. Magnesium borates have specific appli- are found in a mixture and purification is needed14 [ ]. cations in modified glass compositions, reinforcements in General hydrothermal synthesis procedures for magnesium electronic ceramics, wide band gap semiconductors, alu- borates involve the reactions of suitable raw materials at ∘ minum/magnesium matrix alloys, antiwear additives such as high temperatures such as >100 Corbydoublesaltphase thermoluminescence dosimeters, catalysts for the conversion transformation. The type of experimental procedure used of hydrocarbons, cathode ray tube screens, and X-ray screens has effects on the product’s crystal properties and size. [2–5]. In literature, there are some examples of materials’ surface Many kinds of magnesium borates having MgO⋅B2O3⋅ modification by changing the reaction temperatures and H2O compositions can be found naturally in mixture with reaction times. According to these studies, nanoscale mate- other metal borates or can be obtained in the laboratory rials can be synthesized as different crystal types [6–13, 15]. by synthetic methods. Some examples of this type of Hydrothermal processes have several advantages over borate hydrate minerals that have been synthesized are the other types of conventional synthesis processes such as 2 The Scientific World Journal 1 2 Equipment and processes (1) Batch reactor 2 ( ) Vacuum filtration∘ (3) Incubator (40 C) 1 (4) Washing ∘ 6 8 11 (5) Incubator (40 C) Streams 3 7 4 9 5 12 (1) MgO 10 (2) BA (3) MgO(s) + MB(aq) + BA(aq) 5 (4) MgO(s) (5) MB(aq) + BA(aq) + water(l) 3 (6) Water(g) (7) MB(s) + BA(s) 2 4 8 ( ) Pure ethanol(l) Abbreviations (9) MB(s) + ethanol(l) MB: magnesium borate (10) Ethanol(l) + BA(aq) BA: boric acid (11) Ethanol(g) s: solid (12) Pure MB(s) aq: aqueous l: liquid g: gas Figure 1: Synthesis procedure of magnesium borates. ∘ solid-state method in regard to energy conservation, better In this study, the low temperature (0–70 C) synthesis nucleation control, and lower temperature and pressure of of a specific kind of magnesium borate mineral, namely, operation [16, 17]. Higher reaction temperatures and longer mcallisterite, is aimed. Therefore, in literature, Derun et al. ∘ reaction times cause increases in process cost. [1] studied the magnesium borates between 80 and 100 C Dehydrations of crystalline solids represent an important and synthesized a specific kind of magnesium borate mineral, group of heterogeneous reactions. Characteristic dehydration namely, admontite. The other aim of this study is to determine features of materials should be known in order to determine the kinetic parameters (activation energy and coefficient design parameters of equipment and to decrease mass of factor) of mcallisterite mineral which was not studied before, required materials, thus reducing the transportation costs. with both Ozawa [26]andKAS[27, 28]nonisothermal The decomposition process of the hydrated boron mineral, kinetic methods. which usually involves dehydration and dehydroxylation, can be explained by the removal of crystal water from structure [5–19]. Dehydration behaviors of different types of metal 2. Materials and Methods borate minerals have been determined by thermogravimetric 2.1. Synthesis of Mcallisterite. The raw materials used in analyses such as TG/DTA [1]. synthesis were boric acid (H3BO3), which was provided from The effects of different nonisothermal kinetic methods on Kırka Boron Management Plant (ETi Mine Kırka Works) the thermal dehydration of inderite were examined by Zhu in Eskisehir, Turkey, and magnesium oxide (MgO), which et al. [7]. Changes in ulexite structure resulting from heating was provided from Merck Chemicals. H3BO3 was crushed, and the reaction kinetic parameters were studied by Ener et grinded, and sieved and MgO was used as supplied. al. [20]andTunc¸etal.[21]; their results showed that ulexite ∘ The synthesis procedure of magnesium borates is given could be turned to amorphous phase of NaB3O5 at 855 C. in Figure 1. Experiments were carried out at the reaction Waclawska [22] studied the effect of mechanical treatment on ∘ temperatures between 0 and 70 C and reaction time between phase transitions of calcium borate and colemanite and inter- 30 and 240 minutes. Each product was coded by initial letters nal structure reconstitution processes of ground colemanite. of the raw materials (M: MgO and H: H3BO3), reaction There have also been some studies regarding dehydration temperature, and reaction time. For instance, “MH-60-30” kinetics of synthesized boron compounds. Kanturk et al. [23] indicated the product synthesized at a reaction temperature studied dehydration kinetic parameters such as activation ∘ of 60 C and at a reaction time of 30 min. energy and preexponential factors of synthesized sodium metaborate tetrahydrate (NaB(OH)4⋅2H2O). Kinetic analyses of boric acid thermal decomposition were studied by ther- 2.2. Instrumental Analyses. Philips PANalytical XRD was mogravimetric analysis and different kinds of nonisothermal used for identification of reaction products. X-rays were kinetic methods were used for the calculation of parameters produced from a Cu-K tube at 45 kV and 40 mA. The ∘ [24]. Guo et al. [25] have investigated the decomposition and parameters used in the analyses were 0.030 step, 0.50 s ∘ ∘ oxidation behavior of MgB2 using TG, XRD, and SEM-EDS. time for step, 0.060 C/s scan speed, and 0–60 range. ICSD In literature, despite the extensively reported synthesis of patterns were scanned using the inorganic library built into magnesium borates, only inderite minerals’ kinetic behavior the instrument’s program. Synthesized minerals were then has been studied. To date, there have been no studies subjected to FT-IR analyses using a Perkin Elmer FT-IR regarding the kinetic behavior of mcallisterite. with universal attenuation total reflectance (ATR) sampling The Scientific World Journal 3 ∘ accessory with a diamond/ZnSe crystal. The measurement 3D surface plot of XRD score against reaction temperature ( C) −1 10 ∗32 range was 1800–650 cm ,scannumberwas4,andresolution and reaction time (min) v c −1 XRD score = distance weighted least squares was 4 cm . For further analysis, Perkin Elmer Brand Raman Station 400 F was used for Raman spectroscopy. In these analyses, the exposure time was 4 seconds and the number 100 −1 of exposures was 4. Measurement range was 1800–250 cm −1 and the data interval was 2 cm . During the experiments, 80 100% laser power was used. Surface morphologies of synthe- sized minerals were obtained using a CamScan Apollo 300 60 field-emission SEM (20 kV and magnification 20000). XRD score 40 2.3. B2O3 Analyses and Reaction Yields. Both B2O3 analyses and calculations of reaction yields were performed according 20 to Derun et al. [1]. 40 2.4. Thermal Dehydration Kinetics. Thermal dehydration 60 behavior of highly crystalline pure mcallisterite was studied 80 ∘ 100 between the temperature ranges of 20 and 720 Cwitha 120 Perkin Elmer Diamond TG/DTA. Purely obtained mcallis- 140 terite mineral was subjected to five different heating rates 160 ∘ ∘ ∘ ∘ ∘ 180 (2 C/min, 5 C/min, 10 C/min, 15 C/min, and 20 C/min) in 200 0 20 10 an inert (nitrogen) atmosphere.