Judul: Sintesis Silika dari Abu Boiler Pabrik Kelapa Sawit dengan Variasi Konsentrasi Pelarut NaOH dan Waktu Ekstraksi
Abstrak: Abu boiler pabrik kelapa sawit mengandung senyawa SiO2 tinggi. Abu boiler yang digunakan dalam penelitian ini dari PKS Cikasungka PTPN VIII, Bogor. Tujuan penelitian adalah (i) mengoptimasi kondisi proses sintesis silika dari abu boiler (ii) menganalisis kadar silika hasil sintesa, dan (iii) menganalisis kinerja silika sebagai moisture absorber. Penelitian ini dirancang menggunakan Central Composite Design dan optimasi variabel menggunakan Response Surface Method (RSM). Sintesis silika dilakukan menggunakan metode sol-gel dan uji kadar silika menggunakan X-Ray Fluorescence. Kinerja silika sebagai moisture absorber juga dipelajari untuk menentukan model kinetika adsorpsi yang sesuai pada kondisi RH 32%, 64%, 75%, 85% dan 97%. Hasil penelitian menunjukkan kondisi proses optimum dengan rendemen silika tertinggi (41.17%) adalah konsentrasi pelarut 7.39 M dan waktu ekstraksi 78.13 menit. Silika gel yang dihasilkan berupa serbuk putih dengan kadar SiO2 sebesar 79.20%. Hasil penelitian menunjukkan kinetika adsorpsi uap air pada RH 64% sesuai dengan model ordo satu, adapun perlakuan lain dengan RH 32%, 75%, 85% dan 97% sesuai dengan model pseudo ordo dua. RH 32% memiliki nilai k lebih tinggi 0.086 g/g/hari daripada RH 97% sebesar 0.011 g/g/hari., Boiler ash from palm oil mill contains high SiO2 compound. The boiler ash used in this study was from PKS Cikasungka PTPN VIII, Bogor. The research objectives were to (i) optimize the conditions of silica synthesis process from boiler ash, (ii) analyze the silica content of the synthesis, (iii) and analyze the performance of silica as a moisture absorber. This research was designed using a central composite design (CCD) and the variables were optimized using the response surface method (RSM), silica was synthesis using sol-gel method and silica content was measured using XRF. The performance of silica as a moisture absorber was also studied to determine the appropriate adsorption kinetics at 32%, 64%, 75%, 85% and 97% RH conditions. The results showed that the optimum process conditions that produced the highest silica yield (41.17%) were solvent concentration of 7.39 M and extraction time 78.13 minutes. The silica gel produced is a white powder with SiO2 content of 79.20%. The results showed that the water vapor adsorption kinetics at 64% RH was simulated with a first order model, while other treatments with 32%, 75%, 85% and 97% RH were simulated with a second order pseudo model. At 32% RH had a higher k value of 0.086 g/g/day than the 97% RH of 0.011 g/g/day.
Keyword: boiler ash, adsorption kinetics, moisture absorber, optimization, silica

Judul: Sintesis dan Pencirian Nanosilika Berbahan Dasar Abu Ketel Industri Gula dengan Variasi Waktu Aging dan pH Presipitasi.
Abstrak: Boiler ash from sugar cane industry contains silica that was synthesized to nanosilica using precipitation method. Precipitation pH and aging time are parameters that have influenced to nanosilica characterization. The purpose of this research was to synthesis nanosilica from boiler ash using precipitation method, determine the effect of precipitation pH and aging time variation on the characterization of nanosilica, determine the potential application based on characterization of nanosilica. The research was consist of three stages, preparation of boiler ash, extraction silica from furnace ash, and synthesis nanosilica. Boiler ash from sugar cane industry contained 49.69% silica and furnace ash contained 78.75% silica. Nanosilica was material or compound that have multifase characterization. Increase precipitation pH would increase amount of crystal phase, diffraction peak, and intensity of diffraction peak. Increase aging time would increase intensity of diffraction peak and amount of crystal phase. Degree of crystallinity has ranges 66.397–93.530%, average of crystal size has ranges 37.772–56.867 nm, average of particle size has ranges 214.04–698.24 nm, and PDI value has ranges 0.207–0.833. Increase precipitation pH and aging time would increase amount of siloksane groups and decrease amount of silanol groups. Nanosilica has potential application as a composit of electrolyte membrane DMFC (Direct Methanol Fuel Cell), composit of addition support layer membrane ultrafiltration, filler in ship rubber air bag, filler of composit resin, and SCM (Supplementary Cementitious Material) for concrete.
Keyword: aging time, boiler ash, nanosilica, precipitation, precipitation pH

Judul: Metrik Einstein (Anti-) Self-Dual Berdimensi Empat dengan Metode Cartan
Abstrak: Gravitational field equation can be formulated in differential forms (differential geometry), which describes gravity as a manifestation of the curvature of space-time. Curvature of space-time is characterized by a metric that satisfies the gravitational field equation. With differential forms it can be formulated the (anti-) self-dual Einstein equation, which is a modification of the Cartan structure in (anti-) self-dual basis. Calculation of (anti-) self-dual metric with (anti-) self-dual Einstein equation is simpler than the calculation using Christoffel symbols.
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