Judul: Identifikasi silika amorf dari sekam padi
Abstrak: Rice husk is an agriculture by product derived from rice milling, which is produced in a large quantity. Up to present time, rice husk is utilized for limited uses, such as for a fuel in brick production, processed to a charcoal planting medium, and burnt to ash for cleansing powder. With a certain technique, however, rice husk can be processed to produce amourphous silica. This research was aimed to find out characteristics of rice husk ash derived from incineration at different temperatures and oxidation by H2O2. This research consisted of two main steps, i.e. combustion of rice husk and identification of silica of the combustion product. Combustion of rice husk was done with both incineration and oxidation by H2O2. Incineration was run at 400°C, 500°C, 600°C, 700°C and 900°C for 5 hours. The oxidation of rice husk was run with added H2O2 30% until the entire organic compound disappeared (do not effervesce again). Identification of silica was carried out using polarization microscope, refractometer, DTA, FT-IR and XRD. In addition, identification of silica was also done for rice husk ash from common incineration, quartzsand from Pangkalanbun (Kalimantan) and for standard quartz. Chemical characteristics of rice husk, including SiO2, Al2O3, K2O, MnO, MgO, CaO, and total C was done as well. Identification with DTA showed that the silica derived from incineration of rice husk at 400°C, 500°C, 600°C, and from oxidation of rice husk with H2O2 have DTA curve that reflecting amourphous silica. In the contrary, the DTA curve of silica in the ash from incineration at 700 °C and 900°C are much more reflect DTA curve of crystallin silica. The results of identification using FT-IR and XRD showed that only silica in the ash from incineration at 900 °C showing characteristics of crystalline silica. The results revealed that incineration of rice husk at 400°C seem to be the optimum temperature to produce amourphous silica from rice husk for use as absorbent.
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Judul: Optimasi Kelajuan Suhu Annealing untuk Ekstraksi Silika dari Abu Sekam Padi serta Uji Kandungan Molekul
Abstrak: Rice husk as a byproduct of rice milling process contain a high concentration of silica ranged between 87-97%. Rice husk ash when burned at a controlled temperature (500-600°C) will produce silica that can be used for a variety of chemical processes. Silica produced from rice husk has several advantages compared to the silica mineral. Silica from rice husk has a fine grains, more reactive, can be obtained in an easy way with relatively low cost, and also supported by the availability of abundant raw materials and can be renewed. Previous research by Faiz and Muzikarno informed that the lower rate of temperature increase in the ashing process becomes more perfect. Based on this information, the researchers extract silica from rice husk ash with variation rate of increase annealing temperature (0.7°C/min and 0.9°C/min), in which this variations rate of increase in the annealing temperature is lower than previous studies. EDX results showed that the rate of increase annealing temperature 0.7oC/menit obtained 81.96% purity silica, whereas the rate of increase annealing temperature 0.9oC/min obtained 87.48% purity silica.Analysis of the samples by using FTIR showed the presence of two major functional groups in silica which is a siloxane (Si-O-Si) and silanol (Si- OH).
Keyword: Silica, Rice Husk, FTIR, EDX, Annealing

Judul: Dynamical System of Hepatitis B in Three Groups with Vaccination
Abstrak: The aim of this study is to modify the hepatitis B transmission model in three age groups involving vaccination from the model conducted by Zhoe and Zhang.The method used is to analyze the stability of the fixed point and its basic reproduction number (R_0). Performed stability analysis and numerical simulation to see population dynamics. Next, a sensitivity analysis of the parameters was carried out to see its effect on R_0. From the analysis obtained two fixed points, namely non-endemic and endemic fixed points. Non-endemic fixed points are locally asymptotically stable if R_0 <1 Meanwhile, the endemic fixed point is locally asymptotically stable if R_0 > 1. Hepatitis vaccination affects the number of susceptible population, because the more successful the vaccination, the smaller the number of susceptible populations so that the smaller the population will be infected.
Keyword: Dynamic, Hepatitis B, Vaccine, Mathematical model