Synthesis of M-Hexaferrites Material Based on Natural Iron Sand with Metal Co Doping Using the Coprecipitation Method

Article Info Received: August 13th, 2020 Revised: November 8th, 2020 Accepted: Novembr 16th, 2020 Abstract: The synthesis of M-hexaferrite with metal doping Co (BaFe12-3xCoxO19 ) based on natural iron sand at Ketapang beach in Pringgabaya Subdistrict, East Lombok using the coprecipitation method has been successful. The basic ingredients used in this study were natural iron sand and BariumCarbonate (BaCO3) powder, while the doping material used was Cobalt (II) Chloride Hexahydrate (CoCl2.6H2O) powder with a variety of mole fraction (X = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0). The solvent uses 37% hydrochloric acid (HCl), 25% NH4OH solution, and distilled water. The sample formed was then calcined at 200 0C, 400 0C, 600 0C, 800 0C and 1000 0C. The resulting sample shows that there is an effect of Co doping and calcination temperature in the formation of barium M-hexaferrite. The higher the mole fraction of Co doping ions and the calcination temperature, the darker the color of the powder produced.


Introduction
The use of electromagnetic waves has been widespread in various fields such as electronics, telecommunications, and information. This results in increased pollution of electromagnetic waves in the form of microwave radiation which can interfere with the environment. Electromagnetic wave radiation that exceeds the limit can disrupt the environment, especially human health (Susilawati et al‚ 2015). In response to this problem, scientists have developed absorption technology for microwave radiation. Certain types of materials can be used for this technology. One of the materials that can be used as a microwave absorbent material is Barium M-Hexaferrite (Doyan et al, 2015). Barium M-Hexaferrite (BaM) (BaFe12O19) has a hexagonal molecular structure, high saturation magnetization (78 emu/g), high coercivity field (6700 Oe) (Saidah et al, 2012). The high magnetic strength (coercivity field) causes the absorption property of BaM to be weak, making it less effective to use as a microwave absorbing material. To solve this problem, it is necessary to substitute or dop it to reduce the magnetic properties of BaM from a strong magnet to a weak magnet. BaM, which is weakly magnetic, has a wide application as an absorbent material for electromagnetic waves (Bhattacharya et al, 2014).
This research concentrates the formation of BaFe12O19 doped with metal Co with variations in doping and calcination temperature to produce BaFe12-xCoxO19 which can be used as a microwave absorber.
This study aims to determine the characteristics of Co metal dopant administration and the temperature of barium M-hexaferrite (BaFe12-xCoxO19) on phase formation.
Several methods that can be used in the manufacture of barium M-hexaferrite include the mechanical method of milling, sol-gel, and coprecipitation . Among the three methods, the coprecipitation method is a method that has a high level of purity (Susilawati et al, 2013), so that in this study a synthesis was carried out using the coprecipitation method.

Result and Discussion
Synthesis of M-hexaferrite with metal Co doping (BaFe12-xCoxO19) using the coprecipitation method includes material separation and synthesis processes. The iron sand separation process aims to separate magnetic material from natural iron sand (Susilawati et al, 2015). The natural iron sand separation process is shown in Figure 1. This process is carried out by sieving natural iron sand first to separate the sand from the gravel so that a fine texture is obtained and then separated by using a permanent magnet with a strength of 3.6 T to separate the magnetic material from natural sand then weighed and calculated the percentage of magnetic material. obtained .
The synthesis of BaFe12-xCoxO19 made from natural iron sand was carried out with variations in the mole fraction of Co doping ion (x= 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) and variations in calcination temperature (T= 200 0 C, 400 0 C, 600 0 C, 800 0 C and 1000 0 C). This process begins with dissolving the basic ingredients of natural iron sand with HCl then stirring with a magnetic stirrer on a hot plate with a temperature of 80 0 C for one hour and dissolving BaCO3 with distilled water then stirring with a magnetic stirrer on a hot plate at room temperature for two hours. Then the natural iron sand solution is mixed with BaCO3 so that it is brownishblack and added with the doping material. Furthermore, the mixture is dripped with NH4OH to obtain a homogeneous precipitate (Figure 2). The precipitate formed is filtered with filter paper then washed with distilled water until the pH is neutral (Susilawati et al, 2015). The neutral sample was then dried in an oven at 80 0 C and crushed until smooth. The next process is calcining the sample at a temperature of 200 0 C, 400 0 C, 600 0 C, 800 0 C and 1000 0 C for two hours (Figure 3).  Figure 4 shows a sample of BaFe12-3xCox (200 0 C) doping variation. In the figure, it is clear that there is a color difference in the sample caused by the doping of metal Co. The higher the mole fraction of metal Co doping, the darker the color of the resulting sample will be (Susilawati et al, 2015). This is due to the doping of metal Co, mixing the solution will produce a darker color and the volume of NH4OH needed to precipitate the sample is higher along with the increase in the mole fraction of the doping ion . Figure 5 shows the sample BaFe12-xCoxO19 calcination temperature variations. The higher the calcination temperature, the darker the color of the resulting sample. This is because the solvent used has evaporated due to the calcination process (Susilawati et al, 2019). Calcination aims to remove water content, solvents, and impurities such as CO2 from barium carbonate (BaCO3) as it will affect the purity of the sample (Susilawati et al, 2017).

Conclusion
The synthesis of barium M-hexaferrite based on natural iron sand (Ketapang Beach area, Pringgabaya District, East Lombok) was successfully carried out using the coprecipitation method. The results of the synthesis show that there is an effect of metal doping and calcination temperature in the formation of barium M-hexaferrite. The higher the mole fraction of Co doping ions and the calcination temperature, the darker the color of the powder produced.