Judul: Ekstrasi Silika dari Sekam Padi dengan Metode Pelarutan dan Pengendapan Silika serta Analisis EDX dan FTIR
Abstrak: Estimated amount of rice production in 2013 is 69.27 million tons. Compared to rice production in 2012 increased by 0.21 million tons. Some researchers have done the extraction of silica from rice husk through process using alkali solvent and acid precipitation of silica. The aim of this research is to extract silica using alkali solvent and to study the effects of alkali solvent toward the purity and the molecular structure of silica. The procedure of this research covers two phases namely carbonization and silica extraction of rice husk. The largest rendemen obtained is 22.59%, when 20% NaOH solution was added. The largest purity of silica (92.01%) were obtained when 20% KOH solution added with potasium and rubidium act as inpurities. FTIR spectra on 463-486 cm-1, 617 cm-1, 787-802 cm-1, and 1095-1103 cm-1 waves number show the presence of Si-O-Si (siloksan) group, as well as on 1643 cm-1 and 3448-3464 cm-1 waves number shows the existence of Si-OH (silanol) group or a molecule of water. The value of symmetry streching vibration spring constant Si-O is 948.891 – 1017.991 N/m
Keyword: Siloksan., Silica, Silanol, Rice husk, FTIR

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: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf