Addition of magnesium in excess produce silicon of pure rice husk as semiconductor materials

Abstract

Rice is one of the most important cultivated plants in human civilization. Rice is also one of the main carbohydrate source the majority of the population in Indonesia. Central Statistics Agency (BPS 2012), estimates that in 2012 rice production reached 68.59 million tons, up by 2.84 million tonnes (4:13%) than in 2011. Seeing this, then it will appear in the form of agricultural waste rice husk. Most of the waste generated from the processing of rice had only burned or thrown away (Azadi et al 2010). Utilization of rice husk furnace developed by IPB since 2007, generating more waste in the form of waste rice husk (Irzaman et al 2007). Rice husk charcoal is known to contain at 95.14% silicon dioxide (Supaman et al 2010) and has the potential to produce pure silicon with a rate 40.78% (Hikmawati 2010) and 42.29% (Ahmad L 2012). This study aimed to examine the characteristics of silicon powder obtained from rice husk by chemical reduction method, which reduces the silicon dioxide using magnesium (Mg) powder to vary the ratio of the amount of silicon dioxide with magnesium and washing with a solution of HCl in the purification. Silicon dioxide and silicon obtained will be analyzed using X-Ray Difraction (XRD), Scanning Electron Microscope-Energy Distersive X-Ray (SEM-EDX), LCR meter and I-V meter. Manufacture of silicon through three (3) phases, husk charcoal, silicon dioxide and silicon. Husk charcoal through several stages. At first the rice husk is dried with the aid of sunlight with the purpose of accelerating the combustion process. Then the rice husks were weighed at 5000 grams (5 kg), entered into a husk furnace and continued with the process of burning, then the rice husk charcoal weighed. In this process produced rice husk for 1440 grams (1.44 kg). Rice husk as much as 40 grams put in porcelain dish and baked in a kiln at a temperature initially 400 °C for 2 hours, subsequent heating to temperatures of 1000 °C for 1 hour with the temperature rising rate setting by 1 °C/minutes and 5 ° C/minutes. After the ash obtained by burning weighed, then washed rice husk ash using hydrochloric acid (HCl) 3% technical which 12 mL of HCl 3% for 1 gram of technical rice husk ash, then heated over a hotplate with temperature settings 200 °C and stirred with magnetic stirrer at a speed of 240 rpm for 2 hours. Subsequently washed with hot distilled water (temperature of about 90-100 °C) repeatedly until acid-free (tested with litmus paper), and then filtered through ash-free paper. Screening results (residue separated from the filter paper) is inserted in the porcelain dish is then heated in a furnace at temperatures of 1000 °C for 1 hour with a temperature rise of 1 °C/minutes and 5 °C/minutes until the silicon dioxide remaining white. The samples were cooled in the furnace and weighed, then the result is tested SEM-EDX, LCR meter and I-V meter (Ahmad L 2012). The next process is to get silicon, silicon dioxide mixed with magnesium powder with a reductant that vary the ratio ranging from ratio 5:6 and 1:1. Once mixed, then heated in a furnace at 650 °C temperature for 1 hour. Once heated, the mixture obtained is weighed, then washed with 75 mL of HCl 3% technical. Then heated above 200 oC hotplate with temperature control and stirring with a magnetic stirrer at a speed of 240 rpm for 2 hours. Then the sample was washed again with for HCl 3% technical 300 mL, 1 hour, 240 rpm, 1 time (Hikmawati 2010). Samples were filtered and washed with hot distilled water (temperature of about 90-100 °C) repeatedly so free acid, and then dried in a furnace at a temperature of 110 °C for 12 hours (Hikmawati 2010 and Ahmad L 2012). Subsequently the variation of the stirring speed of 240 rpm, 600 rpm, 800 rpm and 1000 rpm with a large temperature and stirring the same old ie 200 °C and 2 hours. Residue was washed with hot distilled water and then filtered and dried in a 110 °C oven for 12 hours. The next process is to vary the length of time stirring the temperature variation in the reduction of silicon dioxide with magnesium is 2 hours, 3 hours and 4 hours with each variation of temperature 125 oC, 130 oC and 135 oC. Residue was washed with hot distilled water and then filtered and dried in a 110 °C oven for 12 hours. Based on the results of XRD analysis showed that the silicon dioxide structure is tetragonal with lattice constants a = b = 10.1457A dan c = 90.4578 A , while the silicon has cube structure with lattice constants a = 5.26971 A . SEM results showed that after reduction treatment chemical changes on the morphology of silicon dioxide, and it is possible there were also changes in the structure of silicon dioxide to silicon. Seen that the surface of silicon dioxide and silicon has not homogeneous. EDX results for silicon dioxide of about 76.17%-85.20% and silicon 60.87%. Analysis of electrical properties was performed using the LCR meter and I-V meter, and was known that the silicon dioxide and silicon have the characteristics of semiconductor with electrical conductivity values ranging from 10-8 S/cm, where the electrical conductivity of silicon has a value higher than silicon dioxide. The I-V meter curves showed that silicon dioxide is a diode and silicon is a resistor.