Turkish Journal of Chemistry Turk J Chem (2015) 39: 1025 { 1037 http://journals.tubitak.gov.tr/chem/ ⃝c TUB¨ ITAK_ Research Article doi:10.3906/kim-1410-37 Synthesis, characterization, and electrical and optical properties of magnesium-type boracite Tu˘gba IBROS¸KA_ 1, Azmi Seyhun KIPC¸AK1, S¨ureyya AYDIN YUKSEL¨ 2, Emek DERUN1;∗, Sabriye PIS¸K_ IN_ 1 1Department of Chemical Engineering, Faculty of Chemical and Metallurgical Engineering, Yıldız Technical University, Istanbul,_ Turkey 2Department of Physics, Faculty of Arts and Science, Yıldız Technical University, Istanbul,_ Turkey Received: 17.10.2014 • Accepted/Published Online: 09.04.2015 • Printed: 30.10.2015 Abstract: Synthesis of the magnesium type of the mineral boracite (Mg 3 B 7 O 13 Cl) was studied. Several parame- ters affecting boracite synthesis were investigated. The raw materials selected were magnesium chloride hexahydrate (MgCl 2 .6H 2 O), magnesium oxide (MgO), and boron oxide (B 2 O 3). Reaction temperatures were selected between 600 ◦ C and 900 ◦ C. Moreover, three different reaction times of 4, 1, and 0.5 h were studied with the determined opti- mum molar ratio, reaction temperature, and reaction medium. Synthesized boracite characterization analyses were done by the techniques of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM). Reaction yields were also calculated. From the results of this study the magnesium type of boracite was obtained as a single phase with high XRD crystal score. Optimum conditions for the synthesis were as follows: ◦ MgCl 2 .6H 2 O to B 2 O 3 mole ratios of 5:6.5, 5:7.5, 6:6.5, 6:7.5, 7:6.5, 7:7.5; 600 C reaction temperature; 1 h reaction time; and reaction medium as air atmosphere. Reaction yields were between 58.81 1.65% and 77.49 1.86%. Some selected magnesium type of boracite minerals, electrical resistivity, and optical absorbance properties were also measured for the determination of physical properties. Key words: Magnesium-type boracite, solid-state synthesis, reaction yield 1. Introduction Magnesium borates have many advantages in the boron mineral groups including their high elasticity coefficient and heat resistance, light weight, and anticorrosive properties. 1−4 With these properties magnesium borates can be used in cathode ray tube screens, in the ceramic industry, in detergent compositions, in ferroelastic material production, in fluorescent discharge lamps as luminescent materials, in friction reducing additive manufacture, as thermoluminescent phosphor, in superconducted material production, and in X-ray screens. 5−10 There are several studies on the solid-state synthesis of magnesium-type borates in the literature. In these studies, the synthesis was conducted in a high temperature furnace. The magnesium sources mainly used were magnesium oxide (MgO), magnesium chloride hexahydrate (MgCl 2·6H 2 O), magnesium nitride hexahydrate Mg(NO 3)2·6H 2 O, and magnesium hydroxide (Mg(OH) 2), and these sources were reacted with the boron sources of boron oxide (B 2 O 3) and boric acid (H 3 BO 3). In these syntheses dehydrated magnesium borate compounds were formed. 11−16 ∗Correspondence: [email protected] 1025 IBROS¸KA_ et al./Turk J Chem ◦ Mg 2 B 2 O 5 was obtained by Qasrawi et al. at 1250 C with a 3 h reaction time using the reactants 12 ◦ Mg(OH) 2 and H 3 BO 3 [11], by Dosler et al. at 1000 C with the reactants MgO and B 2 O 3 , by Elssfah et al. at 900 ◦ C using the same reactants used by Qasrawi et al. 13 , by Li et al. 14 at 800 ◦ C using the starting ◦ materials MgCl 2·6H 2 O and NaBH 4 , by Zeng et al. at 1200 C in a vacuum for 1 h with a mixed tablet 15 of Mg(BO 2)2 . Mg 3 B 2 O 6 is another type of magnesium borate that can be synthesized via the solid-state method. This was studied by Zhang et al. with varying lengths and widths ranging between 100 and 300 nm 16 ◦ and Dosler et al. at 1300 C with the same reactants of MgO and B 2 O 3 that synthesize Mg 2 B 2 O 5 type of magnesium borate. 12 Boracite is a borate compound that contains chlorine. Boracite is generally expressed by the formul M 3 B 7 O 13 X. M represents the two valence cations of Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn, or Cd and X is the one 17 valence anion of F, Cl, Br, I, OH, or NO 3 . In some situations, X can be S, Se, or Te and M may be single valence Li. 18 In nature there are four types of boracite. These are ericaite and trembathite, with the same formulae 19;20 of (Fe,Mg) 3 B 7 O 13 Cl; chambersite (Mn 3 B 7 O 13 Cl); and congolite (Fe 3 B 7 O 13 Cl) (Mg,Fe) 3 B 7 O 13 Cl). Boracite is found with gypsum (CaSO 4 .2H 2 O), gypsum anhydrite (CaSO 4), halite (NaCl), sylvite (KCl), 21 carnallite (KMgCl 3 .6(H 2 O), kainite (MgSO 4 .KCl.3H 2 O), and hilgardite (Ca 2 B 5 O 9 Cl.H 2 O). Usually boracites were synthesized through four different methods, namely hydrothermal, pressurized mechanical, vapor transfer, and sintering flow. 20 The most widely used method was the sintering flow method. Using this method, Wang et al. synthesized the Fe{Cl type boracite. 22 On the other hand, Ju et al. studied the utilization of the flow method in boracite synthesis where they synthesized the five different halogen boracites Mn 3 B 7 O 13 Cl, Co 3 B 7 O 13 Cl, Ni 3 B 7 O 13 Cl, Cu 3 B 7 O 13 Cl, and Zn 3 B 7 O 13 I by the reaction of the transition metal halides CoCl 2·6H 2 O, NiCl 2·6H 2 O, MnCl 2·4H 2 O, CuCl 2·2H 2 O, and ZnI 2 together with H 3 BO 3 at temperatures between 240 and 300 ◦ C and reaction times between 2 and 4 days. 23 In the study by Delfino et al., Ni{Br, Zn{Br, Zn{Cl, Mn{Cl, Co{Br, Mg{Cl, and Mn{I type boracites were studied at temperatures between 475 and 540 K, along with very long reaction times of 18{60 h and high reaction pressures of 5{33 atm. 24 However, in this study only the air atmosphere was studied and the reaction yield of magnesium-type boracite was not calculated. In the literature, it is seen that the synthesis of magnesium type of boracites was not studied in detail, and that very long reaction times were employed, ranging from 2 to 4 days. Our study group conducted some preliminary research on boracite synthesis. For instance, some studies were carried out with the solid-state method, using H 3 BO 3 as the raw material along with MgO and MgCl 2·6H 2 O, but the formation of pure boracite could not be achieved. 25;26 Another solid-state method employed at 1000 ◦ C by Piskin et al. showed that at high temperatures, dehydrated type of magnesium borates were formed as the major phases. 25 In the study by Kipcak et al., the same raw materials were used as in the aforementioned study, but a lower temperature range of 500{700 ◦ C was used. The results showed that the formation of boracite started at 500 ◦ C; however, a further increase in temperature again resulted in the formation of dehydrated type of magnesium 26 borates as the major phases. Another important result obtained from these studies is that the use of H 3 BO 3 in boracite synthesis was not suitable. This study mainly focused on the solid-state rapid synthesis of magnesium type of boracites. For this aim several different parameters such as reaction temperature, reaction time, reaction atmosphere, and different types of raw materials were studied for optimization of the perfect crystal structure for magnesium type of boracites. After the synthesis, the characterization of the products was conducted using the techniques of 1026 IBROS¸KA_ et al./Turk J Chem X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM). Furthermore, with the selected magnesium type of boracite minerals, electrical resistivity and optical absorbance properties were measured. 2. Results and discussion 2.1. Raw material results In the XRD analyses, the raw materials of MgCl 2 .6H 2 O and MgO were identified as bischofite with JCPDS card number 01-077-1268 and periclase with JCPDS card number 01-087-0651. B 2 O 3 is identified as the mixture of both phases of B 2 O 3 and B 2 O with JCPDS card numbers 00-006-0297 and 01-088-2485, respectively. 2.2. XRD results of the synthesized minerals 2.2.1. Stage 1 In stage 1, set 1 and set 2 syntheses were conducted using MgO (Mo), MgCl 2 .6H 2 O (Mc), and B 2 O 3 (B) with the synthesis temperature between 600 ◦ C and 900 ◦ C in air atmosphere. From the results of this stage three different phases were obtained (Table 1). Table 1. XRD scores of the products synthesized from Mo, Mc, and B between 600 ◦ C and 900 ◦ C and 4 h of reaction time in air atmosphere (stage 1). Mole ratio 600 ◦C 700 ◦C 800 ◦C 900 ◦C Sets (Mo:Mc:B) B M S B M S B M S B M S 4:1:6.5 16 45 - 21 50 20 65 67 20 21 77 26 4:1:7.0 25 51 - 17 53 17 31 66 - 33 74 24 4:1:7.5 7 50 - 20 53 19 23 55 22 32 78 25 5:1:6.5 11 42 - 27 60 19 6 25 - 10 80 20 1 5:1:7.0 30 53 - 26 52 20 17 65 - 34 78 23 5:1:7.5 17 36 - 23 58 19 3 22 - 17 75 24 6:1:6.5 19 43 - 23 60 - 23 62 - 20 79 21 6:1:7.0 19 43 - 24 62 18 31 66 - 34 72 23 6:1:7.5 6.5 52 - 20 52 17 4 21 17 26 78 22 4:2:6.5 25 21 - 23 47 18 10 39 25 38 72 23 4:2:7.0 20 34 17 32 41 17 7 63 17 36 81 28 4:2:7.5 24 12 - 20 50 16 22 65 21 34 77 23 5:2:6.5 33 18 - 23 48 17 7 11 7.5 33 74 22 2 5:2:7.0 34 31 - 29 52 22 3 61 25 34 76 21 5:2:7.5 29 41 - 28 26 - 4 47 20 38 79 27 6:2:6.5 24 26 - 19 39 17 17 53 28 42 77 27 6:2:7.0 24 6.5 - 18 44 16 7 32 18 35 81 23 6:2:7.5 24 32 - 33 50 22 7 47 20 39 75 25 0:5:6.5 60 23 - 63 50 - 65 67 21 42 70 21 0:5:7.0 53 11 - 66 50 - 60 57 20 33 73 19 0:5:7.5 55 29 - 63 69 - 59 69 - 31 68 22 0:6:6.5 75 - - 67 27 - 66 70 - 41 34 22 3 0:6:7.0 62 51 - 65 54 - 66 67 - 26 65 24 0:6:7.5 63 52 - 69 50 - 53 72 18 19 69 8 0:7:6.5 64 3 - 69 52 - 67 72 - 44 76 - 0:7:7.0 58 6 - 66 42 - 71 64 20 52 72 22 0:7:7.5 68 - - 67 51 - 62 63 19 40 71 20 1027 IBROS¸KA_ et al./Turk J Chem These phases are 01-071-0750 JCPDS card numbered boracite (Mg 3 B 7 O 13 Cl), 00-031-0787 JCPDS card numbered magnesium borate (MgB 4 O 7), and 01-073-2107 JCPDS card numbered suanite (Mg 2 B 2 O 5).