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: 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: 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