W. Widiyastuti

Photoluminescence Characteristics of Macroporous Eu-Doped Yttrium Oxide Particles Prepared by Spray Pyrolysis

The photoluminescence (PL) characteristics of ordered macroporous europium-doped yttrium oxide (Y2O3:Eu3+) particles were investigated. The submicrometer particles were prepared by spray pyrolysis using a mixture of a yttrium and europium nitrate solution and colloidal polystyrene latex (PSL) particles as the precursor. The porous particles exhibited higher PL intensity, quantum efficiency, and red-emission properties than the non-porous particles due to their porous structures. Detailed PL analysis revealed that the porous particles have unique photophysical properties, such as a 4-nm blue-shift in the charge transfer band (CTB) wavelength, and a lower symmetry ratio of 2.7, which were not found in non-porous particles with approximately the same particle and crystallite sizes.

Effect of turbulence modelling to predict combustion and nanoparticle production in the flame assisted spray dryer based on computational fluid dynamics

Flame assisted spray dryer are widely uses for large-scale production of nanoparticles because of it ability. Numerical approach is needed to predict combustion and particles production in scale up and optimization process due to difficulty in experimental observation and relatively high cost. Computational Fluid Dynamics (CFD) can provide the momentum, energy and mass transfer, so that CFD more efficient than experiment due to time and cost. Here, two turbulence models, k-e and Large Eddy Simulation were compared and applied in flame assisted spray dryer system. The energy sources for particle drying was obtained from combustion between LPG as fuel and air as oxidizer and carrier gas that modelled by non-premixed combustion in simulation. Silica particles was used to particle modelling from sol silica solution precursor. From the several comparison result, i.e. flame contour, temperature distribution and particle size distribution, Large Eddy Simulation turbulence model can provide the closest data to th...

Particle formation of hydroxyapatite precursor containing two components in a spray pyrolysis process

The particle formation mechanism of hydroxyapatite precursor containing two components, Ca(OOCCH3)2 and (NH4)2HPO4 with a ratio of Ca/P = 1.67, in a spray pyrolysis process has been studied by computational fluid dynamics (CFD) simulation on the transfer of heat and mass from droplets to the surrounding media. The focus included the evaporation of the solvent in the droplets, a second evaporation due to crust formation, the decomposition reaction of each component of the precursor, and a solid-state reaction that included the kinetic parameters of the precursor regarding its two components that formed the hydroxyapatite product. The rate of evaporation and the reacted fraction of the precursor both increased with temperature. The predicted average size of the hydroxyapatite particles agreed well with the experimental results. Therefore, the selected models were also suitable for predicting the average size of particles that contain two components in the precursor solution.

Effect of the flame temperature on the characteristics of zirconium oxide fine particle synthesized by flame assisted spray pyrolysis

Zirconium oxide fine particles were synthesized by flame assisted spray pyrolysis using zirconium chloride solution as precursor. Propane gas and air were used as a fuel and an oxidizer, respectively. The ratio of flow rate of oxidizer and fuel was maintained constant at 10:1 to ensure a complete combustion. Increasing fuel flow rate led to the increase of temperature distribution in the flame reactor. The intensity of XRD patterns increased with temperature and precursor concentration. Phase composition of zirconium oxide produced by this process consisted of monoclinic and tetragonal phases. The volume fraction of monoclinic phase of zirconium oxide increased with temperature and precursor concentration. The morphology particles observed by SEM resulted in spherical particles with size in the submicron range depending on the precursor concentration.

Enhanced Electrocatalytic Activity of Pt/3D Hierarchical Bimodal Macroporous Carbon Nanospheres

Proton exchange membrane fuel cells require electrocatalysts with a high platinum (Pt) loading, large active surface area, and favorable hydrodynamic profile for practical applications. Here, we report the design of three-dimensional hierarchical bimodal macroporous carbon nanospheres with an interconnected pore system, which are applied as an electrocatalyst support. Carbon-supported Pt (Pt/C) catalysts were prepared by aerosol spray pyrolysis followed by microwave chemical deposition. The hierarchical porous structures not only increased the dispersion of Pt nanoparticles but also improved catalytic performance. A hierarchical bimodal macroporous Pt/C catalyst with a mixture of 30 and 120 nm size pores showed the best performance. The electrochemical surface area and mass activity values of this support were 96 m2 g-1-Pt and 378 mA mg-1-Pt, respectively at a Pt loading of 15 wt %.

Hexagonal hollow silica plate particles with high transmittance under ultraviolet-visible light

Creating hollow structures is one strategy for tuning the optical properties of materials. The current study aimed to increase the optical transmittance of silica (SiO2) particles. To this end, hexagonal-shaped hollow silica plate (HHSP) particles were synthesized from tetraethyl orthosilicate (TEOS) and zinc oxide (ZnO) template particles, using a microwave-assisted hydrothermal method. The size and shell thickness of the HHSP particles could be adjusted by using different TEOS/ZnO molar ratios and different ZnO template sizes, respectively. The optical transmittance of the HHSP particles depended on the shell thickness and particle size. The highest transmittance was 99% in the ultraviolet and visible region (300–800 nm) and was exhibited by HHSP particles with the thinnest shell thickness of 6.3 nm. This transmittance was higher than that exhibited by spherical hollow silica particles with a similar shell thickness. This suggested morphology-dependent transmittance for the semiconducting material. These preliminary results illustrate the promising features of the HHSP particles and suggest their potential application in future transparent devices.

Studi Awal Desain Pabrik Metanol Dari Syngas Hasil Proses Gasifikasi Batubara Kualitas Rendah

Methyl alcohol atau methanol (CH 3 OH) adalah produk industri hulu petrokimia yang disintesis berbahan baku gas alam. Metanol digunakan sebagai pelarut, bahan pendingin, dan bahan baku perekat. Pada industri migas, metanol digunakan sebagai antifreeze dan sebagai gas hydrate inhibitor pada sumur gas alam dan pada pipa gas. Secara keseluruhan, permintaan global metanol diproyeksikan tumbuh 9,8% dari 2010 sampai 2015. Semakin menipisnya cadangan gas alam, memaksa pemilihan alternatif bahan baku pembuatan metanol, salah satu yang paling berpotensi adalah batubara kualitas rendah (low rank atau lignit). Cadangan batubara di Indonesia mencapai 21.131,84 Juta Ton per tahun 2011 dan sebagian besar berada di Kalimantan (61%), di Sumatera (38%) dan sisanya tersebar di wilayah lain. Sedangkan berdasarkan jenisnya terbagi menjadi lignit (58,6%), sub-bituminous (26,6%), bituminous (14,4%) dan sisanya adalah anthracite (0,4%). Potensi pasar yang terus meningkat dan ketersediaan bahan baku yang melimpah, menjadi faktor penting dalam perencanaaan pendirian pabrik methanol dari batubara. Pabrik metanol ini memproduksi metanol grade AA (kemurnian 99,85%) dengan kapasitas produksi 495.000 ton/tahun dan beroperasi kontinyu 24 jam selama 330 hari. Untuk produksi, dibutuhkan batubara sebanyak 1.178.760 ton/tahun, oksigen sebanyak 722.040 ton/tahun, dan steam sebanyak 396.000 ton/tahun. Bahan baku batubara dipasok dari PT. Bukit Asam, Tbk. yaitu batubara tipe 45. Pabrik metanol ini akan didirikan di Tanjung Enim, Kabupaten Muara Enim, Sumatera Selatan. Umur dari pabrik selama 10 tahun dan masa konstruksi adalah 2 tahun. Pabrik metanol ini mulai beroperasi pada tahun 2021. Proses pembuatan metanol dari batubara ini dibagi menjadi lima bagian proses utama yaitu persiapan bahan baku, gasifikasi batubara, pembersihan dan pemurnian gas sintesis (syngas), sintesis metanol, dan purifikasi metanol. Teknologi gasifikasi yang digunakan berasal dari lisensor HTW, dan proses sintesis metanol berasal dari lisensor ICI. Berdasarkan analisis ekonomi, diperoleh laju pengembalian modal (IRR) pabrik ini sebesar 13,1% pada tingkat suku bunga per tahun 9%. Sedangkan untuk waktu pengembalian modal (POT) adalah 6,32 tahun dan titik impas (BEP) sebesar 50,97% melalui cara linear. Berdasarkan aspek penilaian analisis ekonomi dan teknisnya, maka pabrik metanol dari batubara ini layak untuk didirikan.

Synthesis of ZnO-SiO2 nanocomposite particles and their characterization by sonochemical method

ZnO-SiO2 nanocomposite particles were prepared by sonochemical method under continuous ultrasound irradiation for an hour. Zinc nitrate and sodium silicate were used as zinc oxide and silica sources, respectively. Silica concentration was varied to investigate the effect of silica on the characteristics of the generated composite particles and they were also compared to ZnO particles. Morphology, crystallinity, chemical bonding analysis, photoluminescence spectra, and photocatalytic activity were characterized by scanning electron microscopy (SEM), X-Ray diffraction, Fourier Transform Infrared (FTIR), luminescence spectrophotometer, and UV-Vis spectrophotometer, respectively. Nanorod structures were observed for pure ZnO, ZnO-SiO2 particles with 250 ppm and 750 ppm silica addition during synthesis. Spherical agglomerated particles were found for particle with 0.1 M silica addition. The crystalline size and photocalytic activity decreased with the silica addition. A strongest chemical bonding for ZnO and S...

Formation of ZnO-SiO2 particle by spray decomposition method

Zinc oxide-silicon dioxide (ZnO-SiO2) nanocomposite particle have been synthesized using spray decomposition method. This method is expected to produce nanoparticle in a continuous process, producing spherical particle, and high purity product. The influence of ratio precursor concentration was investigated in this experiment to know the characteristic of ZnO-SiO2 nanocomposite. The precursors were prepared by mixing zinc acetate and silicon dioxide solution using distilled water as a solvent. Compressor nebulizer was used to atomize a precursor solution into discrete droplets. ZnO-SiO2 particle was evaluated by X-ray diffraction (XRD) and scanning electron microscope with energy dispersive X-ray (SEM-EDX) to investigate their crystal structure, morphology, and composition. Particle ZnO-SiO2 obtained from this method have hexagonal crystals, the particle shape was spherical, and have a good dispersion of ZnO and SiO2.

Computational fluid dynamic in combustion process using pulse combustor

The advantages of Pulse Combustion process than the normal combustion was presented in this research. Reviews of phenomena and mechanisms of pulse combustion was compared with normal combustion which air or fuel was streamed continuously. Multi-dimensional simulation of turbulent flow in the combustion chamber was performed by computational fluid dynamics (CFD) with ANSYS FLUENT 15.0 software. 2D illustration axis symmetry with turbulence models k-turbulence combustion reaction using Eddy Dissipation models was used to analyze this process that has a high turbulence. Propane was used as the type of fuel with flow rate of 15 L/min. the flowrate 375 L/min of air was used as oxidizer, to meet the needs of propane and oxygen ratio of 1: 5. Based on the result, pulse combustion has higher combustion efficiency than normal combustion. This result was judged from fewer fuel that was not burned. Another advantage of using pulse combustion was the back flow of tailpipe that decrease the number of unburned reactant...