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In this paper, the synthesis of silica-coated magnetite nanoparticles using a one-step electrochemical method and their application for dye removal are presented. In this method, pure iron in a dilute aqueous sodium silicate solution that served as a silica precursor was electro-oxidized. The silica-coated magnetite nanoparticles produced by this method is nearly spherical with the size of approximately 10 nm and follows the spinel structure of Fe3O4. The silica-coated magnetite nanoparticles exhibit nearly superparamagnetic properties and excellent performance to remove methylene blue from wastewater. The adsorption capacity of the nanoparticles was approximately 24.2 mg methylene blue/g adsorbent, which was much higher than that of pure magnetite nanoparticles (1.1 mg methylene blue/g adsorbent). Also, the percentage removal was higher than 90% with the initial concentration of methylene blue up to 40 mg/L. It can be regenerated and reused with an only slight reduction in percentage removal.

One of the promising solutions to overcome the liquid loading problem in natural gas production is using a foaming agent. The extreme condition in the gas well causes the foam used tends to break up. Therefore, it is required to enhance the foam stability by adding a stabilizer agent. This research aims to investigate the effect of silica nanoparticles as a surfactant stabilizer to obtain a high-stability foam using silica nanofluid. Silica nanofluid was synthesized from sodium silicate solution by the solgel method. Then, the colloidal silica was added to the surfactant solution without a coupling agent. The effects of aging time and silica concentration were investigated. The results show that the surface tension tends to increase with the increase of aging time and silica concentration but decrease in foam stability which is indicated by a decrease in the foam half-life time. The best foam stability is obtained in silica nanofluids with an aging time of 6 hours and a silica concentration of 30 ppm, which shows a foam half-life of 42 hours and can improve foam stability with several parameters representing the conditions of the gas well

Drying air inlet temperature is one of the critical variables in the microencapsulation process by spray drying. However, when spray drying is carried out at inappropriate drying air inlet temperature, it can impact the particle produced. This study presents a simulation of spray drying from a mathematical model was developed to determine the effect of drying air inlet temperature on moisture content, particle diameter, particle density, and drying air outlet temperature in the microencapsulation process of avocado seeds oil as core materials and gum arabic as wall materials. For this aim, the mathematical model was developed then simulated using a matrix laboratory (Matlab) computer program with Euler numerical method for drying air inlet temperatures of 160, 180, and 200 °C. The selected model was validated with Cotabarren’s experimental results indicating the model was acceptable. The particles’ moisture contents predicted from simulation results are 1.170, 1.049, and 0.933 kg water/kg solid for 160, 180, and 200 °C, respectively. On the other hand, the predicted particle diameters are 29.73, 29.49, and 29.23 urn for 160, 180, and 200 °C, respectively. The predicted particle densities are 1215.72, 1225.21, and 1233.25 kg/m3 for 160, 180, and 200 °C, respectively. The prediction of drying air outlet temperatures was 39.76, 41.94, and 43.89 °C for inlet air temperatures of 160, 180, and 200 °C, respectively. The proposed models’ simulation results show that the higher temperatures caused lower particle moisture content, smaller particle diameter, and higher particle density. Also, the outlet drying air temperatures were always the same as the outlet particle temperatures.

As the second most abundant bio-resource and as a byproduct of lignocellulose material processing, alkali lignin has to become a quantitative issue due to its difficulties to handle. On the other hand, lignin has high natural carbon contents, so it has the potential to act as a precursor for carbon materials. However, many previous researchers do three steps to transform it into high porous carbon: precipitation by reducing the alkaline compound, calcination to transform it into carbon, and carbon activation by adding alkaline compound again. In this study, the porous carbon material from alkali lignin in a one-step process for use as an electrode in supercapacitor and electrocatalyst is examined. The evaporation and especially carbonation temperature are studied to obtain the high porous carbon. After varying calcination temperatures, the carbon material's characterization was investigated to examine porosity, morphology, crystallinity, specific electrocapacity, and Oxygen Reduction Reaction (ORR) electrocatalyst activity. The carbon derived from Na-lignin via calcination at 700 °C had the highest electrocapacity of 168.29 F/g. The electron transformed number is 2.23, indicating that the carbon derived from Na-lignin via calcination is promising for an electrode agent of supercapacitor and electrocatalyst for ORR.

Surfaktan berfungsi menjaga kestabilan suatu emulsi agar tetap homogen, dengan cara menurunkan tegangan permukaan. Saat ini, industri yang memproduksi surfaktan di Indonesia masih menggunakan bahan baku yang berasal dari minyak bumi tak terbarukan (surfaktan sintetis). Gliserol monostearat (GMS) merupakan jenis surfaktan yang sering digunakan dan hingga saat ini belum ada pabrik gliserol monostearat yang didirikan di Indonesia. Kegunaan gliserol monostearat dalam industri misalnya sebagai pearlizing agent , emulsifier dan dispersan. Pemilihan proses untuk memproduksi gliserol monostearat perlu dianalisis agar produksi yang dihasilkan lebih optimal. Gliserol monostearat dapat diproduksi melalui dua macam proses, yaitu proses esterifikasi dan transesterifikasi. Pada proses esterifikasi, digunakan bahan baku berupa gliserol dan asam stearat menggunakan katalis asam atau basa. Sedangkan pada proses trans-esterifikasi (gliserolisis), bahan baku yang digunakan yakni trigliserida berupa tristearat dan gliserol menggunakan katalis basa. Dari studi yang telah dilakukan, proses esterifikasi lebih dipilih karena ditinjau dari aspek teknis, aspek operasi dan aspek lingkungan, proses esterifikasi lebih baik daripada proses transesterifikasi.

In this study, electrospinning technology, iodine treatment, thermal stabilizing, and carbonization processing were applied to produce lignosulfonate-based carbon nanofibers. The porous structure of the produced lignosulfonate-based carbon nanofibers primarily contained mesopores and a relatively small amount of micropores. Moreover, the increasing amount of sodium lignosulfonate (SLS) as lignin source was also studied. The diameter of fibre was impacted by the additional of SLS that may cause by the alkali content of SLS itself. In electrospun nanofiber phase, the presence of SLS reduce the specific surface area, but contrary increase the specific surface area after the nanofibers were carbonized into carbon nanofiber. Lignosulfonate-based activated carbon fibres can be used as a highly efficient adsorption and filtration material, and further development of its applications would be valuable.

Nanotechnology had been widely developed for medical application in various forms, either nanoparticles or nanofibers. One of the most attractive use is nanofibers as a wound dressing. An ideal wound dressing should have characteristics of easily sterilized, non-toxic, biodegradable, good oxygen circulation, and anti-microbial performance. Those characteristics could be obtained by using a biomaterial composite which had a good biocompatibility on human body tissues, such as chitosan and hydroxyapatite (HA). Chitosan had an anti-microbial property, while HA could increase the cell generation rate. Therefore, this work would synthesize a chitosan/HA nanofiber as a potential wound dressing via electrospinning method. HA was firstly prepared by electrolysis using alternating electrode configuration. The dope solution of chitosan/HA for electrospinning was prepared by adding polyvinyl alcohol (PVA) as a coadjutant polymer. The morphology of the obtained nanofibers was investigated by SEM. It was revealed that the nanofibers had an average diameter of 261.87 nm which was spun each other forming many pores which was good for oxygen circulation. Therefore, chitosan/HA nanofibers could be a promising material for wound dressing application.

Polyethylene glycol (PEG) was employed as a templating agent for the preparation of mesoporous silica materials starting from sodium silicate solutions using a sol–gel method. We show that PEG can serve as a structure-directing agent resulting in silica structures with pores spanning a range of 3.3–3.9 nm depending on the PEG concentration and the PEG removal method. The use of a PEG template increased significantly the surface area from 252 m2 g−1 without PEG to >340 m2 g−1 and >634 m2 g−1 when the PEG was removed by, respectively, calcination and solvothermal extraction. It appears that calcination at high temperature caused a densification of the pore structure resulting in a smaller surface area and pore diameter. The impregnation of mesoporous silica with CaCl2 significantly increased the adsorption capacity of water. At high humidity, the composite adsorbents containing approximately 42 wt.% CaCl2 yield a maximum adsorption capacity of 1.6 times their own weight and 4.4 times that of bare silica. The adsorption is physical in nature as viewed from the adsorption energy calculated by the Dubinin–Radushkevich (D–R) equation.

Hydroxyapatite (Ca10(PO4)6(OH)2) is a ceramic biomaterial which has high biocompatibility that makes it popular in the biomedical application as it can attach on human body without rejection by human immune system. Hydroxyapatite can be synthesized by various methods; one of them is electrochemical method. Synthesis of hydroxyapatite has been successfully conducted by electrochemical method using one pair of electrodes. However, the yield of hydroxyapatite produced by this pair of electrode was still low. To address those issue this research proposed synthesis of hydroxyapatite using multiple electrodes in different arrangements to improve the yield of the reaction, which were conventional and alternating arrangements. The potential value was fixed on 6 V to study the effect of electrodes arrangement on current density. Electrosynthesis of hydroxyapatite showed that multiple electrodes on alternating arrangement produced more hydroxyapatite mass and current density than the conventional arrangement. The alternating arrangement produced hydroxyapatite mass of 2.3483 g and current density of 19.32 mA/cm2, while the conventional arrangement produced 2.3157 g and 15.05 mA/cm2.

Manganese dioxide nanoparticles have been successfully synthesized by the electrolysis method using 4-pairs carbon electrode in the alternating monopolar arrangement. The advantage of the arrangement is a significant increase in the product yield compared to the single pair electrodes. KMnO4 solution in pH 0.2 and 9 were used as precursor and electrolyzed for thirty minutes at a temperature of 60 °C. The generated particles resulted from electrolysis in pH 0.2 (MnO2-A) and in pH 9 (MnO2-B) were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and nitrogen adsorption-desorption isotherms to examine their crystallinity, morphology, and the specific surface area. The α-MnO2 was observed for MnO2-A particles and amorphous for MnO2-B particles. The particles size of MnO2-A was larger than that of MnO2-B with the specific surface areas of 396 and 98 m2/g, respectively. The higher surface area of MnO2-A corresponding to the channel pore of short rod-like morphology. On the other hand, MnO2-B contributed to the spherical particles. The measurements of cyclic voltammetry (CV) were also carried out to measure their specific capacitances and their performance for oxygen reduction reaction (ORR) electrocatalyst. MnO2-A exhibited higher specific capacitance of 13.57 F/g compared to MnO2-B that only had 3.62 F/g. In addition, MnO2-A also gave better performance as ORR electrocatalyst measured in O2-saturated 0.6 M KOH resulted in 2.69 transferred electron number per oxygen molecule.

Mesoporous silica with controlled pore structure was prepared from bagasse ash as a silica source. The silica in the bagasse ash was dissolved by NaOH solution to produce sodium silicate precursor for the mesoporous silica, with or without polyethylene glycol (PEG) template. Without the PEG template, the pore structure was greatly influenced by the pH and the presence of Na+ ions. The porous silica produced in the presence of Na+ possessed higher surface area and pore diameter than those produced in the absence of Na+. The surface area and pore diameter reached approximately 525 m2 g−1 and 18 nm, respectively, when the gelation pH was 3. When the gelation pH was increased, the surface area decreased while the pore diameter increased. The use of PEG template increased significantly the surface area, which reached approximately 656 m2 g−1 when the template was removed by solvothermal extraction. Calcination at high temperature caused a densification of pore structure resulting a smaller surface area, pore diameter and pore volume. The pore diameter for all cases was greater than 4 nm, indicating that the silicas were mesoporous.

Magnetite film was successfully prepared on the mild steel surface in alkaline environment by hydrothermal electrolysis treatment. The principle of hydrothermal electrolysis is applying current directly to electrolyte solution at hydrothermal conditions. The anodizing of mild steel was conducted at temperatures of 100–200 °C and applied current densities of 0.1–0.4 A/cm2 for 5–60 min reaction time with sodium hydroxide (NaOH) as an electrolyte solution (5–15%). Magnetite film on the mild steel surface was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and cyclic voltammetry. The patterns of XRD showed that magnetite was formed dominantly in the surface of mild steel with black color. Cyclic voltammetry analysis showed that the magnetite films produced on the mild steel surface could prevent or minimize the corrosion on its surface.

The aim of this work is to evaluate the corrosion behavior of anodized stainless steel substrates coated by electrophoretic deposition (EPD) from stabilized aqueous SiO2 sol-acetic acid-isopropyl alcohol. An oxalic acid solution was used as the electrolyte in anodization processes. The effect of oxalic acid concentration and voltage of anodization on the corrosion protective properties of deposited films were evaluated. The sols for EPD were prepared by mixing of given volumes of acetic acid, isopropanol and SiO2 with the composition in molar ratio CH3COOH/isopropanol/SiO2 is 0.1938/0.5048/0.0028. The corrosion behavior of the coated substrates were studied by linear polarization and electrochemical impedance spectroscopy (EIS). Potentiodynamic studies of coating showed that the corrosions protection behavior of silica coating increase by the increase of oxalic acid concentration and voltage of anodization. This behavior was confirmed by EIS showing that the pore resistance increase by the increase of oxa...

Mesoporous silica gels were successfully produced from geothermal sludge by alkali extraction followed by acidification. The silica in the geothermal sludge was dissolved by NaOH solution to produce a sodium silicate solution, which was then reacted with HCl or tartaric acid to produce silica gels. The effects of silica concentration and pH on the silica gel properties were investigated. In addition, an improved method was proposed by incorporating two-step aging. The first aging step, which was conducted at pH 10, was used to induce Ostwald ripening to increase the size of the primary particles, and the second step was used to strengthen the gel network. Decreasing the silica concentration by diluting the as-prepared sodium silicate solution tended to increase the surface area and pore volume of the prepared silica gels. The silica gels produced by tartaric acid possessed higher surface area and pore volume than those by HCl. The surface area and pore volume reached approximately 450 m 2 g −1 and 0.8 cm 3 g −1 , respectively. When the gelation pH was decreased to 6, the surface area exceeded 600 m 2 g −1 . The first aging process increased the size and uniformity of the primary particles, which in turn increased the surface area of the particles. The pore diameter for all cases was greater than 5 nm, indicating that the silica gels were mesoporous.

High-purity magnetite (Fe3O4) nanoparticles were successfully synthesized via the electrooxidation of iron in an aqueous system using a pulsed direct current (pulsed DC). The pure iron to be electrooxidized was electroplated on a steel plate, which was then used as a sacrificial anode in the electrochemical system. The electrolyte used was demineralized water, either with or without added NaOH, which was used to vary the pH of the solution, between 7 and 10. We showed that the pulsed DC significantly enhanced the purity of the magnetite that was formed. The FeOOH impurities that are typically present when continuous DC is used were not observed. The particles produced using the proposed method were nearly spherical in shape. The size of the particles ranged from 7 to 23 nm depending on the conditions of synthesis, namely, the pulse frequency, duty cycle, and pH. The magnetite nanoparticles exhibited ferromagnetic properties, with values of saturation magnetization ranging from 18 to 55 emu/g. The results obtained from thermal gravimetric/differential thermal analysis revealed that magnetite was converted into maghemite at a temperature of approximately 200 °C and into hematite under further heating to 500 °C. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

Sulfonate-grafted silica/chitosan hybrid (SGSC) membrane has been successfully prepared by in-situ sol-gel method. In this method, grafting of sulfonate onto silica surface was carried out along with membrane formation. Silica sol, with the particle size of about 9 nm obtained from sodium silicate, and amido sulfonic acid were mixed with chitosan solution. The mixture was stirred for 30 minutes and aged at 60 °C for 8 hours. The results showed that sulfonate could be grafted onto the silica surface as indicated by the FTIR spectra. Silica loading is greatly affect the membrane characteristics including water retention, % swelling, and ionic conductivity. Water retention and % swelling decrease with the increase of silica loading. On the other hand, ionic conductivity and acid capacity increase with the increase of silica loading. The increase is related to the amount of silica that carries sulfonate groups. However, there is limitation on the silica loading where membrane cracked if the loading was greater than 1.5 g silica/g chitosan. The ionic conductivity and acid capacity of the membrane can take the values of about 4.2 x 10-6 S/cm and 1.3432 meq/g, respectively.

The purpose of this paper is to investigate the electrophoretic deposited nanosilica on stainless steel for corrosion protection. The electrophoretic deposition (EPD) was carried out by pulsed direct current (PDC) of silica sol made of sodium silicate. The amplitude and frequency of the PDC were varied in the range of 0.1-0.6 V and 30-80 Hz, respectively. The corrosion protection properties of the silica films were analyzed by Electrochemical Impedance Spectroscopy (EIS) in 2 wt% NaCl solution. The experimental results showed that the silica films exhibit good characteristics as indicated by their high pore resistance and low admittance. The silica film corrosion protection characteristics were influenced by the frequency and amplitude of PDC during preparation of electrophoretic deposition.

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.

Hydrophobic silica coating on copper (Cu) has been successfully prepared byelectrophoretic deposition (EPD) of silica sol prepared from waterglass. trimethyl chlorosilane (TMCS) was used as the modifying agent to produce hydrophobic coating by replacing the silanol groups on the silica surface with alkyl groups. The hydrophobicity was indicated by the contact angle of water droplet on the coating surface. It has been shown that TMCS concentration plays an important role in the preparation of hydrophobic coating. However, higher concentration of TMCS made the copper corroded before coated with silica due to the production of Cl-ions when TMCS reacted with water and silanol groups during electrophoretic deposition. In addition, the electricfield intensity, silica concentration and deposition time also influence the hydrophobicity of the coating. Increasing the three parameters produces silica coating with higher hydrophobicity. Thecontact angle of the silica coating can reach 130°. EIS analysis showed that the silica coating is very porous.

Carbon fibres are important materials due to their excellent properties. Carbon fibres were formed by blending Poly(vinyl alcohol) (PVA) and a high conductivity material of Acetylene black (AB). Electrospinning technique was used to fabricate PVA and AB solutions in demineralized water. Electrospinning is an efficient technique for the formation of polymer nanofibers. The effects of solution concentration and AB contents on morphological appearance and diameter of those as-spun fibres were investigated by scanning electron microscopy (SEM). Iodine treatment on the fabricated PVA/AB composite was successfully achieved in order to build up the carbonization process and retained their original fibrous structure. The mass of iodinated nanofibers at 80 °C for 24 h increased about 130 %. The mechanism of iodine uptake by electrospun PVA/AB fibres have been obtained by thermal behaviour and its morphological characteristics. It was found that iodine treatment played an important role in changing the morphological structure during the carbonization process. With the iodine treatment of PVA/AB precursor fibres successfully converted into thin carbon fibres and SEM analysis confirmed that the diameter of fibres was about 290 nm. The resulted pure fibres and iodine treatments show guarantee for production carbon fibres.

This work demonstrates the comparison techniques between conventional and rapid thermal processing (CTP Vs RTP). It is to fabricate the interlayer-free P123 carbonised template silica membranes. The aim of this work is to understand the performance of fabricated membranes for water desalination. The silica sols pH 6 were prepared from a two acid-base catalyzed sol gel method by applying tetraethyl orthosilicate (TEOS) as the precursor. Triblock copolymer of Pluronic P123 was used as the templating agent and mixed homogenously with silica sols. The mixtures were calcined in two method called CTP and RTP. CTP is a slow calcination and takes 4 hours with 1 °C min-1 for dwelling time. On the other hand, RTP is rapid technique calcined in air (1 h without dwelling time). CTP confirms higher surface area (50 % higher), porosity (34 % higher) and thinner (60 %) than RTP. RTP technique is supposed to save time, energy and cost during membranes fabrication.

Platinum-deposited titanium nitride (Pt/TiN) nanoparticle aggregates with high porosities were successfully prepared via a self-assembly-assisted spray pyrolysis method. The addition of formic acid (HCOOH) had a significant influence on the process, promoting the simultaneous formation of metallic Pt and reduction on the surface of the TiN support material. Complete reduction of the Pt/TiN nanoparticle aggregates improved the catalytic activity. The electrochemical surface area (ECSA) of Pt/TiN with HCOOH (Pt/TiNw/HCOOH) was 87.15 m2/g-Pt, which was higher than that of Pt/TiN without HCOOH (Pt/TiNw/o-HCOOH). The catalytic durability of Pt/TiNw/HCOOH was twice that of Pt/TiNw/o-HCOOH. An effective strategy for obtaining carbon-free catalysts with high activities and durabilities was identified. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2753–2760, 2013

Magnetite nanoparticles have been prepared by electrooxidation of iron in water. Surface modifications have been conducted by coating the nanoparticles with silica by a one-step synthesis in dilute sodium silicate solution. The mean size of particles was approximately 10–30 nm for the uncoated particles and 9–12 nm for the coated particles. The results obtained from thermal gravimetric/differential thermal analysis (TG/DTA) revealed that the silica layer formed by the electrochemical method was stable and could serve as a protective layer. Annealing the nanoparticles at 550 °C for 30 min converts magnetite into maghemite for the silica-coated particles, and it further converts the uncoated particles into hematite. The conversions cause the saturation magnetization to decrease for all samples.

A simple surfactant-free electrochemical method is proposed for the preparation of magnetite nanoparticles using iron as the anode and plain water as the electrolyte. This study observed the effects of certain parameters on the formation of magnetite nanoparticles and their mechanism in the system, including the role of OH − ions, the distance between electrodes and current density. We found that OH − ions play an important role in the formation of magnetite nanoparticles. Particle size can be controlled by adjusting the current density and the distance between electrodes. Particle size increases by increasing the current density and by decreasing the distance between electrodes. Particle formation cannot be favored when the distance between electrodes is larger than a critical value. The magnetite nanoparticles produced by this method are nearly spherical with a mean size ranging from 10 to 30 nm depending on the experimental conditions. They exhibit ferromagnetic properties with a coercivity ranging from 140 to 295 Oe and a saturation magnetization ranging from 60 to 70 emu g −1 , which is lower than that of the corresponding bulk Fe 3 O 4 (92 emu g −1 ). This simple method appears to be promising as a synthetic route to producing magnetite nanoparticles.

Gelatin was employed as a templating agent for the preparation of mesoporous silica materials starting from sodium silicate solutions using a sol-gel method. The silicate anions were first transformed into silicic acid by passing the solution through an H+ ion-exchange resin, then mixed with acidic gelatin solution prior to adjustment of the pH to approximately 9–10. Gelatin was removed by solvothermal Soxhlet extraction to form pores. We show that gelatin can serve as a structure-directing agent resulting in silica structures with pores spanning a range of 3–12 nm depending on gelatin concentration. Increasing gelatin concentration resulted in a larger pore size and a wider pore-size distribution. This dependence was also observed for the surface area and pore volume but only at low gelatin concentration ( 0.4 wt%). Mesoporous silica with a high specific surface area (426.6 m2 g−1), high pore volume (0.9 cm3 g−1) and large pore diameter (8.4 nm) was obtained at a gelatin concentration of 0.41 wt%. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Bipolar diffusion charging of aerosol particles has been studied theoretically using Fuchs theory. Experimental data measured by several researchers available in the published literature were used to verify the calculation results. The calculation results show that Fuchs theory has been successfully used to predict the experimental data of the charging probability of submicron aerosol particles. The combination probability of ion-particle increases with the increase of particle size, both for particle and ion with the same sign and those with the opposite sign. However the combination probability is larger if the charges of particle and ion are of the opposite sign. Generally, Fuchs theory is not too easy to deal with due to the ill-defined of all parameters used, namely ion mass and ion mobility. These cause many possibilities of parameter combination that can give a good agreement with experimental data. Thus, in order to interpret the experimental results properly, the two parameters should be measured simultaneously with aerosol measurements. Keywords: Aerosol, Bipolar Charging, Combination Probability Abstrak Pemuatan listrik difusi bipolar partikel aerosol telah dipelajari secara teoritis menggunakan teori Fuchs. Sebagai verifikasi digunakan data eksperimen beberapa peneliti yang tersedia dalam literatur yang telah dipublikasikan. Hasil perhitungan menunjukkan bahwa teori Fuchs berhasil memprediksi dengan baik data eksperimen probabilitas pemuatan listrik partikel aerosol dalam rentang ukuran partikel berukuran submikron. Probabilitas penggabungan ion-partikel semakin besar dengan semakin besarnya ukuran partikel, baik untuk partikel dan ion yang memiliki tanda yang berlawanan maupun yang memiliki tanda yang sama. Akan tetapi, probabilitas penggabungan untuk partikel dan ion yang memiliki tanda yang berlawanan memiliki nilai yang lebih besar. Pada umumnya teori Fuchs tidak terlalu mudah untuk digunakan yang disebabkan oleh tidak terdefinisikannya dengan baik semua parameter yang digunakan, yaitu massa ion dan mobilitas ion. Hal ini mengakibatkan banyak kemungkinan kombinasi parameter yang bisa menghasilkan kesesuaian yang bagus dengan data hasil pengukuran. Jadi, agar dapat menginterpretasikan hasil pengukuran dengan tepat, kedua besaran tersebut harus diukur secara serempak denganpengukuran aerosol. Kata Kunci: Aerosol, Pemuatan Listrik Bipolar, Probabilitas Penggabungan

EDTA-assisted synthesis of nanosized hydroxyapatite by electrochemical method.Synthesis of nanosized hydroxyapatite by electrochemical method has been studied. The aim of this work is to study the effects of variuos parameters on hydroxyapatite particles. The electrochemical synthesis was prepared in solution Ca2+/EDTA/PO43 at concentration 0.25/0.25/0.15 M. The solution was electrolized by using constant direct current at certain current density. There were two treatments for particles after electrosynthesized, namely without aging or aged for 3 days at 40oC. For both cases, the particles were filtered and washed by demineralized water to eliminate the impurities and unreacted reactans. Then, the particles were dryed at 40oC for 2 days. The dryed particles were characterized by X-Ray diffraction, surface area analyzer, scanning electron microscopy, Fourier transform infrared spectra and thermogravitimetric and differential thermal analysis. The results showed that nanosized hydroxyapatite were produced by electrochemical method. The produced particles were composed of needle-like or plate-like morphologies with equivalent diameter 19-143 nm. The produced particles diameters were inversely proportional to current density, duration of electroysis and EDTA concentration, and proportional to the distance between two electrodes and temperature. The product calcium phosphates types depended on the final pH of electrolysis process and aging treatment. It would tend to hydroxyapatite if pH>8 and brushite if pH8 cenderung membentuk HA, sedangkan pH

In this paper, we systematically report the synthesis of mesoporous silica xerogels in high purity from bagasse ash. The bagasse ash was chosen as the raw material due to its availability and low-price, and environmental considerations also were important. Silica was extracted as sodium silicate from bagasse ash using NaOH solution. The sodium silicate was then reacted with HCl to produce silica gel. To produce high-purity silica xerogels, three different purification methods were investigated, i.e., acid treatment, ion exchange treatment, and washing with de-mineralized water. We were able to produce high-purity silica (>99 wt.%) by washing the produced gels with either de-mineralized water or with ion exchange resin. The specific surface area of the prepared silica xerogels ranged from 69 to 152 m 2 g −1 and the pore volume ranged from 0.059 to 0.137 cm 3 g −1 . The pore radii were 3.2–3.4 nm, which indicated that the silica xerogels was mesoporous. From the adsorption characterization, it was obvious that adsorptive capacity was better for high-purity silica xerogels compared with low-purity. The maximum adsorption capacity by high-purity silica xerogel was 0.18 g-H 2 O/g-SiO 2 . Finally, we demonstrate the potential of bagasse ash for mesoporous silica production with its excellent adsorptive capacity that makes it beneficial as an environmental solution.

The complexity of flow in an agitated tank comes in part from the global change of flow pattern from one type to another alternately on a long time scale. This phenomenon is known as macro-instability (MI). In this work, it was characterized by means of flow visualization experiment and confirmed with computational fluid dynamics (CFD) simulations. The results showed various combinations of flow patterns occurring repeatedly in the whole vessel for all configurations observed. The flow patterns inside agitated tank equipped with single impeller arrangement could be classified into the radial discharge and cross-pass types for agitation with a Rushton turbine (RT) impeller, radial discharge and axial discharge for a fan turbine (FT) impeller, axis symmetric and asymmetric axial discharges for a pitch blade turbine (PBT) impeller. In case of double impeller arrangement, there were more complex variations of flow patterns due to the interaction between the flow patterns produced by the upper and lower impellers. The frequency of appearance and life time ratio of each recognized flow type was also observed in experimental and simulation works. According to the agreement between the experimental visualization and simulation in both flow pattern recognition and its characteristic, the combination of large eddy simulation (LES) and sliding mesh (SM) method is suitable for the prediction of MI phenomenon in stirred tank.

The preparation of silica nanoparticles through solid-fed flame synthesis was investigated experimentally and theoretically. Monodispersed submicrometer- and micrometer-sized silica powders were selected as solid precursors for feeding into a flame reactor. The effects of flame temperature, residence time, and precursor particle size were investigated systematically. Silica nanoparticles were formed by the nucleation, coagulation, and surface growth of the generated silica vapors due to the solid precursor evaporation. Numerical modeling was conducted to describe the mechanism of nanoparticle formation. Evaporation of the initial silica particles was considered in the modeling, accounting for its size evolution. Simultaneous mass transfer modeling due to the silica evaporation was solved in combination with a general dynamics equation solution. The modeling and experimental results were in agreement. Both results showed that the methane flow rate, carrier gas flow rate, and initial particle size influenced the effectiveness of nanoparticle formation in solid-fed flame synthesis. 2009 American Institute of Chemical Engineers AIChE J, 55: 885–895, 2009

The effects of gas flow rate on particle formation and film deposition during the preparation of silica thin film using a TEOS/O2 plasma were investigated. Particle formation and growth are suppressed with increasing gas flow rates. The film deposition rate increases with increasing gas flow rate, reaches a maximum value, and eventually decreases again. However, the uniformity of the film tends to degrade at high gas flow rates. At a high gas flow rate, some particles trapped in the sheath near the grounded electrode pass through the sheath to reach the substrate and are then embedded in the growing film. A self-consistent sheath model combined with particle force balance based on charge fluctuation was developed to explain these experimental findings qualitatively. The model reveals that charge fluctuation is a key factor for the particle to overcome the potential barrier of the negatively charged particles to pass through the sheath, eventually reaching the substrate. The model further shows that the pr...

A particle removal system based on the properties of charged particles suspended in a plasma for use in controlling particle contamination during the preparation of silicon dioxide thin films in a plasma-enhanced chemical vapor deposition reactor is described. Since the particles suspended in the plasma carry a negative charge, the application of a positive bias to a metal tube inserted into the plasma would attract negatively charged particles. The system effectively removes particles from the trap regions during operation of the plasma. Even particles as small as about 10 nm in size can be removed using this method. Films prepared using the installed particle removal system were found to be nearly free from particle contamination. This is different from the case when the particle removal system is not installed, where some particles are deposited on the film. Even though the particle removal system reduces the rate of film growth by about 40%, it is offset by theresulting clean film, which is free from particle contamination.

The effects of gas flow rate on the contamination by dust particles in an RF plasma reactor were studied experimentally. A mixture of tetraethylorthosilicate vapor, oxygen and nitrogen were fed into the reactor to fabricate SiO2 thin film. Dust particles generated in the plasma were visualized by a laser light scattering technique. Particle size was measured by a laser particle counter, and particle deposition for the film was observed by a scanning electron microscope. The dust particles were found to be trapped in a certain region in the reactor. The amount and size of the trapped particles decreased with increasing gas flow rate. The particle contamination on the film surface also decreased with increasing gas flow rate. At a high flow rate, however, dust particles embedded into the film were observed. In addition, high gas flow rate degraded the film uniformity. It is considered from the above results that a proper selection of gas flow rate is important to decrease particulate contamination as much as possible.

Particle formation and growth in a TEOS/O2 radiofrequency (rf) plasma were studied by an in situ laser light scattering (LLS) technique and ex situ scanning electron microscopy (SEM). The particles, after being generated, were located around the sheath near the electrodes. Visualization using a high-resolution video camera shows that the particles are trapped around the sheath near the powered electrode (showerhead) and are ultimately located in localized regions between the showerhead holes. Particle-free regions are present immediately below the holes and their surroundings within a certain radius. The particles form a lump cloud when a low gas flow rate is used, change to a line shape when the flow rate is increased, and finally the LLS technique can no longer detect them when high flow rates are used. The particle trapping behavior described above clearly has an influence on particle contamination on the wafer. The particles appear to grow through coagulation as shown by the SEM images of particles ta...

The occurrence time and the contribution level of particle contamination on the wafer in individual steps during plasma-enhanced chemical vapor deposition (PECVD) operation were investigated. A method was proposed to determine the occurrence time of particle contamination by making use of the capability of thermophoresis to shield the wafer from particle deposition. The level of particle contamination on the wafer was determined by a scanning electron microscopy (SEM) and the particle behavior in the reactor was observed using a laser light scattering (LLS) technique. The particles were continuously injected into the plasma reactor from the outside. Using this technique, the effect of particle size on the particle behavior can be studied with high certainty. It was found that the particle contamination occurred during the postplasma when the injected particles were trapped in the sheath region below the powered electrode. On the other hand, when the injected particles were not trapped due to a strong inertial effect of particle, the contamination occurred during plasma operation. There is a regime of operation condition in which the lowest level of contamination occurs. Most particles retained their negative charge in the postplasma as shown by their movement and deposition on the wafer in the presence of either a negative or positive dc field. The charge on these particles was determined from particle motion with high certainty using the current experimental technique.

The distribution and transport of fine particles trapped in a radio-frequency (rf) plasma-enhanced chemical vapor deposition reactor was investigated using a laser light scattering technique. Structured clouds of particles were observed at localized regions between the holes below the showerhead. Typically, at a high rate of gas flow, particles emerging from the showerhead holes overshoot the equilibrium position of the particle trap, and the particle clouds in the trap were small and thin (winding mode). At a low rate of gas flow, the particles are directly attracted to the trap locations, and large particle clouds (lumping mode) were observed. The particle number concentration of trapped particles tends to increase with increasing rf power and decrease with increasing particle size. When the gas flow rate is increased, a sharp decrease occurs at a certain flow rate.

The conductance of nitrogen gas through circular tube of finite length was measured in the continuum and transition regimes for length to diameter ratios L / D ranging from 0.045 to 33.4 and pressure ratios across the tubes P 1 / P 2 from 1.1 to 23. A numerical analysis was carried out to estimate the conductance using the continuum approach in the continuum regime and transition regime at low Knudsen number, and using direct simulation Monte Carlo (DSMC) method in the transition regime at high Knudsen number. The observed conductances were compared with the simulation and an empirical equation derived by Hanks–Weissberg. Both the experimental and simulation results show that the conductances at a constant gas flow rate increases linearly with increasing arithmetic mean pressure across the tube P av =( P 1 + P 2 )/2, irrespective of the P 1 / P 2 ratio. The observed conductances were smaller than those predicted by the Hanks–Weissberg's equation. The deviation increases with increasing gas flow rate, and with decreasing L / D ratio. It was confirmed that the deviation occurs due to the increase in the effects of inertia and expansion in the flowing gas with increasing flow rate and decreasing L / D . A semi-empirical equation was derived by substituting the Poiseuille term in the Bernoulli formula with Hank–Weissberg's equation under the condition of isothermal expansion. The proposed equation was found to be valid in the range of the continuum regime to the transition regime at low Knudsen number.

The behavior of fine particles in a low-pressure parallel plate chemical vapor deposition reactor was investigated by constructing a system that permits particle motion in the reactor to be visualized. The test spherical silica aerosol particles, which were 1.0 μm in diameter and dispersed in argon gas, were fed into the reactor from the outside and particle motion was detected by a laser light scattering method. The effect of operating conditions, such as pressure and temperature, on particle transport in the reactor was investigated. The pressure was varied from 2.0 to 4.0 Torr and the wafer-substrate plate temperature was varied over the range of 25°C to 300°C. A three-dimensional numerical simulation was performed using the commercially available computational fluid dynamics code Fluent. A detailed configuration of the reactor, including the showerhead structure was considered when investigating this mechanism. It is found, both experimentally and by numerical simulation that, when the wafer-substrate plate is not heated, the effect of pressure on particle trajectory in the space between plates cannot be observed. However, at elevated temperature, i.e. when the wafer-substrate plate is heated, the particle trajectory is apparently influenced by pressure. In addition, the effect of thermophoresis, as the result of a temperature gradient by heating of the wafer-substrate plate is very pronounced for gas pressures of both 2.0 and 4.0 Torr . The experimentally observed phenomena were satisfactorily reproduced by simulation.

Energy is a very important in modern life and need innovations to develop it. One innovation is the application of energyfor storage devices, such as batteries, capacitors, fuel cells, etc. For 30 years, the application of the NASICON (Na1+xZr2SixP3-xO12) into the NASICON gas sensor material was successfully prepared by using solid-state method. The raw materials such as SiO2, Na2CO3, ZrO2, and NaH2PO4 with a little methanol were mixed in Ballmill equipment. The silica powder was made by the extraction of bagasse ash by using sol-gel method. The x-ray diffraction patternshowedthat the result of silica extraction was amorphous and the NASICON structure wassynthesizedto bemonoclinic. The scanning electron microscopy results indicated that silica had non-uniform surface morphology and the NASICON had good surface morphology only on the form of Na3Zr2Si2PO12. The ionic conductivty of NASICON wasshown on LCR Nyquist plot of the three compositions. The highest NASICON conductivity was found inthe composition of x = 2.0, i.e. 1.142x10-8 S/m.

Electrochemical synthesis of hydroxyapatite particles was performed from a homogeneous solution of Na2H2EDTA.2H2O, KH2PO4 and CaCl2 without stirring to investigate the mechanism of hydroxyapa-tite formation. We found that OH- ions generated by water reduction at the cathode play an important role in the formation of hydroxyapatite particles. The OH- ions induce the liberation of Ca2+ ions and the dissociation of phosphoric acid, which serve as the reactants for the formation of hydroxyapatite particles. Two layers with a clear boundary were formed during electrolysis. The upper layer comprises the produced particles and the lower layer is a homogeneous solution. The produced particles were held in the region between the electrodes mainly due to the electrostatic interactions of charged particles in an electric field. The hydroxyapatite particles are agglomerates consisting of spherical particles. Aging the suspension for 24 h after electrolysis leads to the transformation of hydroxyapatite to brushite. Thus, if producing hydroxyapatite is desired, the particles should be continuously removed from the system. This method appears to be promising as a continuous process to produce hydroxyapatite parti-cles using an electrochemical method. © 2014 BCREC UNDIP. All rights reservedReceived: 10th April 2014; Revised: 25th May 2014; Accepted: 27th June 2014How to Cite: Nur, A., Setyawan, H., Widjaja, A., Lenggoro, I.W. (2014). Electrochemical Processes for the Formation of Hydroxyapatite Powders. Bulletin of Chemical Reaction Engineering & Catalysis, 9 (3): 168-175. (doi:10.9767/bcrec.9.3.6686.168-175)Permalink/DOI: http://dx.doi.org/10.9767/bcrec.9.3.6686.168-175

The objective of this work is to investigate Fe3O4/C composite as an electrochemical capacitor. Fe3O4 nanoparticles were synthesized by oxidation of iron in water using either constant direct current (CDC) or pulse direct current (PDC). Fe3O4/C composite was prepared by two methods: (1) the nanoparticles were mixed with sucrose and carbonized at 500 °C under the mixture of 5% H2 in N2, and (2) the nanoparticles were mixed with carbon black. The electrochemical performance of the composite was evaluated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The diameters of Fe3O4 particles obtained using CDC and PDC methods were approximately 18.7 nm and 20 nm, respectively. The specific surface area of composite with method (1) using PDC was 112.93 m2/g and using CDC was 111.58 m2/g, and method (2) using PDC was approximately 48.345 m2/g and using CDC was 40.77 m2/g. EIS analysis showed that the conductivity of the composite prepared by method (1) using CDC lower than that using PDC ...

Thermal insulating material was prepared by electrophoretic deposition of nanosilica from sodium silicate in a mixture of water and ethanol. The as-prepared silica powders have the surface area ranged from 138.53 to 338.81 m2/g and the pore volume from 0.57 cm3/g to 0.74 cm3/g, depending on the applied electric field intensity and the solvent composition. The thermal conductivity of the porous silicas ranged from 0.75 to 3.61 W/m⋅K., depending on the porosity of the silicas. The higher the porosity is, the lower the thermal conductivity is.