The Synthesis and Physical Properties of Magnesium Borate Mineral of Admontite Synthesized from Sodium Borates

Magnesium borates are significant compounds due to their advanced mechanical and thermal durability properties. This group of minerals can be used in ceramic industry, in detergent industry, and as neutron shielding material, phosphor of thermoluminescence by dint of their extraordinary specialties. In the present study, the synthesis of magnesium borate via hydrothermal method from sodium borates and physical properties of synthesized magnesium borate minerals were investigated. The characterization of the products was carried out by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopies, and differential thermal analysis and thermal gravimetry (DTA/TG). The surface morphology was examined by scanning electron microscopy (SEM). B 2 O 3 content was determined through titration. The electrical resistivity/conductivity properties of products were measured by Picoammeter Voltage Source. UV-vis spectrometer was used to investigate optical absorption characteristics of synthesized minerals in the range 200–1000 nm at room temperature. XRD results identified the synthesized borate minerals as admontite [MgO(B 2 O 3 ) 3 ⋅7(H 2 O)] with code number “01-076-0540” and mcallisterite [Mg 2 (B 6 O 7 (OH) 6 ) 2 ⋅9(H 2 O)] with code number “01-070-1902.”The FT-IR and Raman spectra of the obtained samples were similar with characteristic magnesium borate bands. The investigation of the SEM images remarked that both nanoand microscale minerals were produced. The reaction yields were between 75.1 and 98.7%.


Introduction
Magnesium borates are considerable borate minerals by virtue of their high heat resistance, light weight, high elasticity coefficient, birefringent crystal structure, anticorrosion, and antiwear properties [1][2][3][4].Owing to these properties, magnesium borates have extensive usage area and application potentials.Magnesium borates can be used in ceramic industry, in superconducted material production, in detergent composition, in friction reducing additive manufacture, in fluorescent discharge lamps as luminescent material, in ferroelastic material production, in cathode ray tube screens, in X-ray screens, and as thermoluminescent phosphor [5][6][7][8][9][10].And also magnesium borates have great potential in areas of electronic ceramics reinforcement, semiconductor material synthesis, and plastics or aluminum/magnesium matrix alloy production [11,12].
The production methods of magnesium borate minerals can be divided into two by hydrothermal and thermal methods [13].In previous studies different types of magnesium borate minerals were synthesized.For the syntheses different starting materials were used.MgO and H 3 BO 3 were used by Dou et al. [1] (OH).Mg(OH) 2 and H 3 BO 3 were used by Elssfah et al. [15] for the purpose of producing Mg 2 B 2 O 5 .MgO, BI 3 , and H 3 BO 3 were selected as starting materials for synthesis of Mg 2 B 2 O 5 by Li et al. [16].Wang et al. [17] [18] for preparation of 2MgO⋅B 2 O 3 ⋅H 2 O.
The specific type of magnesium borate mineral, namely, admontite, was synthesized from MgO and H 3 BO 3 at 100 ∘ C for the reaction times of 120 and 240 minutes by Derun et al. [19].Also at their other study, Derun and Senberber [20] synthesized pure mcallisterite by using the same raw materials of MgO and H 3 BO 3 .
The common point to all previous magnesium borate syntheses by hydrothermal method was high reaction temperatures (≥100 ∘ C) and extended reaction times, where in literature hydrothermal syntheses are frequently driven in a temperature range of 100-220 ∘ C [4].Furthermore the crystallinities of the obtained minerals were not at the desired levels.
Considering different studies about preparation of magnesium borate in this study, in order to obtain the magnesium borates below 100 ∘ C reaction temperature and 120 minutes of reaction time, different combinations and mole ratios of MgCl were used as raw materials in the hydrothermal synthesis.The mole ratios of raw materials were decided from previous experiments [21].The main originality of the study is to produce magnesium borate compounds at lower temperatures and shorter reaction times, which leads to less energy consumption and time for a green chemistry approach.Another novelty of this study is the investigation and comparison of the electrical and optical characteristics of bulk and nanowires magnesium borate crystal that were investigated in the literature [16,22,23].The bulk magnesium borate crystal has a wide optical band gap of 5.44 eV according to theoretical calculation [22].
Synthesized magnesium borate minerals were characterized by using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), and differential thermal analysis and thermal gravimetry (DTA/TG).Electrical and optical properties of the different magnesium borate minerals were investigated with picoammeter voltage source and UVvis spectrometer techniques, respectively.T : H ratio of 1 : 1 : 3 throughout the analysis was selected for further experiments [19].The expected reaction schemes are shown in (1)-(4):

Preparation and Characterization of the
The distilled water used in the experiments was obtained from a "Human Power I+" water treatment system and had a conductivity value of 18.3 mΩ⋅cm.The reaction temperatures and reaction times were selected between 60-100 ∘ C and 30-240 min.The experiments were carried out in a glass reactor and the reaction temperature was set as constant by a temperature control unit.
At the end of the selected reaction times the solution was put in an incubator maintained at 40 ∘ C until the excess water evaporated and magnesium borate minerals were crystallized.Then crystallized magnesium borate minerals were washed with pure (96%) ethanol three times to separate unreacted components and byproduct of NaCl.Washed samples were dried in an incubator maintained at 40 ∘ C again.The experimental method was shown in Figure 1.
The morphological features of materials, including their structure, morphology, phase, shape, size, and distribution, are affected by their physical and chemical properties [25].CamScan Apollo 300 Field-Emission SEM was used to observe the surface textures and particle sizes of the synthesized magnesium borate minerals at 20 kV.The detector used was back scattering electron (BEI) and the magnification was set to 10000.
The commercial values of the boron minerals are evaluated from the B 2 O 3 content of these minerals.This analysis was carried out using the method reported by Derun et al. [19].
Thermal analysis of a pure admontite selected from the XRD results was studied between the temperature range of 20-720 ∘ C with a Perkin Elmer Diamond DTA/TG with a heating rate of 10 ∘ C/min in an inert (nitrogen) atmosphere.
In order to investigate and characterize the product obtained after the thermal analysis, admontite mineral was placed in a Protherm MOS 180/4 high temperature furnace with 10 ∘ C/min temperature increment to a maximum temperature of 720 ∘ C in nitrogen flowing (5 mL/min) atmosphere.After the thermal conversion, the product was analyzed by XRD with the same parameters given in Section 2.3.
Yield analysis was also carried out using the method reported by Derun et al. [19] where MgCl 2 ⋅6H 2 O was identified as the key component.Experiments were carried out in triplicate in three pure admontite minerals, which have the highest XRD scores in order to calculate the average yields and the standard deviations.The yield calculation of the biphasic samples was carried out based on the phase with the highest molecular weight.
The number of moles of product at the final stage,   , was divided by the number of consumed moles of the key reactant  to calculate the overall yield,   (5).The number of moles of  that was consumed was calculated using the initial ( 0 ) and the final (  ) moles of the reactant.The equation then becomes as follows for a batch system [19,26]: borate compounds was taken by Perkin Elmer UV-vis spectrophotometer at room temperature.In this measurement the magnesium borate compounds were dispersed in HCl solution in quartz tube (1 cm × 1 cm).

XRD Results of the Synthesized Magnesium Borates.
Synthesized minerals XRD results were given in Table 1.
It is seen from the results that the synthesized products were admontite [MgO( The XRD patterns of three pure admontite minerals, which have the highest XRD scores, were represented in Figure 2.
As it is seen from Figure 2, the five major characteristic peaks of admontite mineral are seen at all three minerals at around 7 ∘ , 17 ∘ , 23 ∘ , 29 ∘ , and 34 ∘ .The crystallographic data of synthesized magnesium borates are given in Table 2.
The obtained products for Mc-T-H experimental setup were formed in two distinct phases at all reaction temperatures and times.The higher mcallisterite scores were reached at increasing reaction temperatures.

FT-IR and Raman Spectral Analysis Results
for the Synthesized Products.The FT-IR and Raman spectra of the synthesized magnesium borate minerals were very similar  and were also in accordance with Yongzhong et al. [24].FT-IR and Raman spectra of pure admontite minerals are given in Figures 3 and 4    The analysis showed that three endothermic peaks occurred.The first peak that occurred between the temperatures of 40 and 59.47 ∘ C was the moisture.So admontite lost its crystal water via a two-step process, where in first     mineral.So in the first dehydration step there was small moisture content of 0.495%.According to the found data the dehydration steps of appeared as, which is in a mutual agreement with the study of Derun et al. [19]:

3. 6 .
Thermal Analysis Results.TG and DTG analyses of a selected (moderate reaction temperature and low reaction time) admontite which has a code of "Mc-T-B-80-60" are shown in Figure 6.

Figure 5 :
Figure 5: SEM surface morphology and the particle size of admontite minerals.

Table 1 :
XRD scores of the synthesized magnesium borate minerals.

Table 2 :
Crystallographic data of synthesized magnesium borates.

Table 3 :
B 2 O 3 contents of the synthesized magnesium borate minerals.
dehydration step the initial, peak, and final temperatures were seen as 59.47 ∘ C, 100.10 ∘ C, and 129.45 ∘ C. In the second step, initial, peak, and final temperatures were found as 129.45 ∘ C, 212.06 ∘ C, and 710.00 ∘ C. Weight decreases were 9.965% and 24.130% for the first and second steps, respectively.Total weight loss was calculated as 34.095%, which is close to theoretical structural water content (33.60%) of admontite

Table 4 :
Crystallographic data of synthesized magnesium borates.