The effect of alumina addition of 5-30% by weight on phase transformation and crystallisation properties of refractory cordierite ceramics prepared from amorphous rice husk silica followed by sintering treatment at temperature of 1230 • C was studied. The crystallinity and microstructure of the samples were characterised using X-ray diffraction (XRD) coupled with Rietveld analysis, scanning electron microscopy (SEM), respectively. Some physical properties include density, porosity, hardness, bending strength, and thermal expansion coefficient of the samples with different alumina additions were measured. The results show that addition of alumina promoted crystallisation of cordierite into crystalline spinel, corundum, cristobalite, in which with addition of 10-30% alumina, the cordierite phase was practically undetected. Addition of alumina was also found to increase the amount of spinel, while corundum and cristobalite decreased following alumina addition of 10-30%. The presence of spinel, corundum, and cristobalite resulted in increased of density, hardness, bending strength and thermal expansion coefficient, while for porosity, the opposite was observed. Thermal expansion coefficient of the samples with alumina addition of 15-30% reach the relatively constant value of 9.5 × 10 −6 / • C, with the main crystalline phase was spinel, accompanied by corundum and cristobalite in smaller quantities.

IntisariThis study was carried out to investigate the effect of high temperature on the functional groups, microstructure and physical characteristics of cordierite ceramics obtained from an aqueous solution of magnesium nitrate hydrate ((Mg(NO3)2.6.12H2O)), aluminium nitrate hydrate (Al(NO3)2.9.15H2O) and silica sols extracted from rice husk. The samples were sintered at temperature of 1000• C, 1200• C and 1400• C. Functional groups and microstructural characteristics of cordierite ceramics were examined by FTIR and SEM, respectivelly. FTIR study shows that the absence of the vibration bands of Na-OH, Si-OH, C-O, Si-O-Si on the samples. However, the formation of cordierite structure was dominated on this high temperature. Microstructure results confirmed the presence of irregular morphology of the solid and compact phases. In addition, the densities, shrinkage and hardness of cordierite increase significantly with increasing temperature, but porosity decreases with increasing temperature.KATA KUNCI: rice husk, cordierite, mikrostructure, sintering I. PENDAHULUANCordierite salah satu material dengan struktur silika yang bervariasi, diantaranya entatite, magnesium silicate, dengan cordierite memiliki kandungan silika paling tinggi dan stabil [1], yang secara luas telah diaplikasikan di berbagai industri seperti, industri gelas, industri keramik dan industri elektronik sebagai isolator panas dan listrik, karena memiliki kestabilan termal dan daya tahan terhadap zat kimia yang tinggi serta koefisien termal rendah [2]. Keramik cordierite dapat disintesis dari berbagai bahan baku silika mineral seperti fumed silika, kaolinite, TMOS (tetramethylortosilicate), maupun TEOS (tetraethylorthosilicate), melalui berbagai metode diantaranya, teknik reaksi padatan (solid-state reaction) [3,4], teknik sol-gel [5,6], teknik melting [7,8].Pada penelitian yang telah dilakukan terhadap karakteristik cordierite pada suhu rendah yakni 300-700• C dengan menggunakan silika sekam padi [9] menunjukkan bahwa karakteristik fungsionalitas cordierite terdiri dari Si-OH, Si-O-Al, Mg-O-Al, Na-OH, N-O, C-O dan C-H pada suhu 300• C dan 500• C, dan proses kristalisasi pembentukan cordierite melalui spinel MgAlO 2 pada suhu sintering 700• C. Sebagai tambahan, hasil analisis SEM/EDS menunjukkan bahwa mikrostruktur dengan pori dan kekerasan meningkat dengan meningkatnya suhu sintering dengan kehadiran komposisi elemen Si, Al, Mg dan O. Perubahan sifat fisis (shrinkage, porositas, densitas dan kekerasan mengalami perubahan yang signifikan pada suhu sintering 700• C. Dari penelitian awal yang dilakukan, dapat disimpulkan bahwa proses kristalisasi diantaranya pemadatan (densification), pemben- * E-MAIL: Simbiring@yahoo.com.au tukan cordierite tergantung suhu sintering dan membutuhkan energi termal yang lebih tinggi untuk mengubah struktur. Berdasarkan latar belakang yang dipaparkan di atas, untuk melengkapi informasi pembentukan cordierite maka penelitian ini dilakukan dengan tujuan untuk mempelajari pengaruh temperatur tinggi terhadap karakteristik fu...

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Titanium Dioxide (TiO2) nanofibers have been prepared using the electrospinning method. This study aims to determine the morphology and crystal structure of the TiO2 nanofibers and to determine the effect of viscosity on the morphology and crystal structure formed. This study used titanium tetraisopropoxide as a precursor, ethanol as a solvent, acetic acid as a solution stabilizer and controlled the hydrolysis reaction of the precursor, and PVP as a fiber-making material. The amount of variations of acetic acid is 2; 2.5; 3; 3.5; and 4 ml respectively. The results of the viscosity test showed that the greater the acetic acid used, the smaller the viscosity. The electrospinning process was carried out at a high voltage of 13 kV with a flow rate of 1.5 ml/hour. The fiber obtained was then calcined at 450 o C for 3 hours. The calcined sample was then analyzed using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). SEM characterization results on samples B, C, and D showed that the sample diameters were 313 ± 28 nm, 275 ± 57 nm, and 242 ± 59 nm, respectively. The results of XRD characterization on sample D showed that the resulting sample had a tetragonal crystal structure with a mixed phase between anatase and rutile. The results of TEM characterization in sample D showed the fiber diameter with a size of 68.05 nm.

Silver-doped rice husk silica composites were created using the sol-gel method. Silver nitrate and rice husks were used as the resources. The composites were sintered at 850 °C and then characterised using Fourier transform Infrared Spectroscopy (FTIR), X-ray diffractometry (XRD) coupled with a Rietveld analysis, Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM/EDS), Ultraviolet-visible (UV-vis) spectroscopy and the Brunauer-Emmett-Teller (BET) method. The obtained results indicate the significant role of the Ag concentration and that the phase transformation changed the samples' characteristics, including an increased crystallite size and absorbance. The results also showed that the Ag/SiO 2 composite with a uniform microstructure in the form of spherical Ag particles with a relatively uniform size were dominated by silver and cristobalite phases as the main phases. Meanwhile, the silver phase emerged as a dominant phase and was embedded in the silica matrix. The crystal sizes of the silver and cristobalite were found to be 40 and 20 nm, respectively. The absorbance value showed that Ag/SiO 2 works on two wavelengths of 310 and 415 nm. The obtained surface area values ranged from 5.0 -11.4 m 2 •g -1 which belongs to the mesopore criteria. Such structural and textural properties of the produced composite indicate its suitability to be used as a catalyst.