Advanced Materials Research Vol. 789

Abstract: Perovskite lanthanum manganites, especially those doped LaMnO₃ (LMO), have shown potentials for applications in magnetic electronic functional materials. Partial substitution of La ion with divalent ions or Mn ion with trivalent ions gives rise to new properties. Substituted LMO has ability for absorbing electromagnetic waves. In this paper, we report recent investigations on substituted LaMnO₃ with designated La_(1-x)Ba_xFe_0.25Mn_0.5Ti_0.25O₃ (x= 0, 0.25, 0.75, 1) compositions. Materials were prepared by mechanical alloying technique. After heat treatments at sintering temperatures 1100°C, 1200°C and 1300°C to the quasi-crystalline powders, presence of material phases were confirmed by XRD. Single phase material was obtained in samples of 0.25 x < 0.75 compositions. Mean crystallite size of sintered materials showed that crystallites were in a nanocrystalline regime. It is then concluded, during mechanically alloyed sintering powder materials, solid-state reaction and crystallisation promoted formation of particles containing nanocrystallites. Microwave absorption data showed that materials with large amount of substituted Ba ion gives broad absorption profiles. Total substitution of La by Ba ions (x=1) has significantly changed absorption profile. Smaller mean crystallite sizes indicated an increase in reflection loss value. In this report, empirical relationship between nanostructure and absorption profile of material is discussed.

Abstract: Several natural dyes have been extracted from tropical fruit shells such as Musa aromatica and Citrus medica var Lemon fruit shells. The resulting dyes have been used as sensitizer at dye sensitized solar cell (DSSC). The main pigments, which are carotenoids, was obtained by extraction and purification at dark room. Ethanol and water are used as solvents. The dyes have been characterized through UV–Vis spectrophotometer. The thin film of TiO₂ anatase has been sintered at 450°C to enhance film compactness. According to the experimental results, the DSSC conversion efficiency which has been prepared by carotenoid dye from Musa aromatica fruit shell extract is 0.21%, 0.614 V of open-circuit voltage (V_OC), 0,280 of short-circuit current density (J_SC) mA/cm², 56 μW of maximum power (P_max) and 0.43 of fill factor (FF). Then, the DSSC conversion efficiency which has been prepared by carotenoid dye from Citrus medica var Lemon fruit shell extract is 0.05%, 0.460 V of V_OC, 0.093 mA/cm² of J_SC, 14 μW of P_max and 0.44 of FF. The measurement of I-V curve demonstrated that carotenoid was potential component as sensitizer for DSSC.

Abstract: Nanocrystalline TiO₂ has been synthesized through non-aqueous sol-gel using acetic acid (HOAc) and hydrochloric acid (HCl) as a catalyst. Titanium isopropoxide (TTIP) as precursor was prepared by reaction between TiCl₄ with isopropyl alcohol (IPA) in concentration of 0.3 M. The sol-gel process employed at around 60°C using tert-butanol as solvent and HOAc was added as ligand to stabilize the reaction. Controlled hydrolysis and condensation reactions were achieved through in-taking of water molecules released from the esterification reaction of HOAc with tert-butanol. In this paper, the influence of acidic catalyst was described at the volume ratio of HOAc:HCl are 0:2 ; 1:1 and 2:0. The crystallinity and crystal phase of the samples were characterized by X-ray Diffraction and nanocrystalline TiO₂ with anatase phase was resulted. The morphology of the TiO₂ powder was analyzed by Scanning Electron Microscopy. Pore size and the BET surface area were determined by Brunauer-Emmett-Teller (BET) analysis. Nanocrystalline TiO₂ produced was applied for photoelectrode of dye-sensitized solar cell. The optical properties of the TiO₂ photoelectrodes were measured using by UV-Vis Spectrophotometer. The performance of the cell was measured using a solar simulator with light at an intensity of 50 mW/cm² generated by a xenon lamp. The best efficiency of 0.5% was achieved for active area of 0.48 cm².

Abstract: Hydroxyapatite/chitosan (HApC) composite has been prepared by precipitation method and used for removal of heavy metals (Cr⁶⁺, Zn²⁺ and Cd²⁺) from aqueous solution. The HAp and 3H7C composite with HAp:chitosan ratio of 3:7 (wt%) were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy-energy dispersive X-ray spectroscopy. The SEM results showed that HAp is spherical-shaped and crystalline, while chitosan has a flat structure. SEM micrograph of 3H7C composite reveals crystalline of HAp uniformly spread over the surface of chitosan. The crystal structure of HAp is maintained in 3H7C composite. Chitosan affects the adsorption capacity of HAp for heavy metal ions; it binds the metal ions as well as HAp. The kinetic data was best described by the pseudo-second order. Surface adsorption and intraparticle diffusion take place in the mechanism of adsorption process. The binding of HAp powder with chitosan made the capability of composite to removal of Cr⁶⁺, Zn²⁺ and Cd²⁺ from aqueous solution effective. The order of removal efficiency (Cr⁶⁺ > Cd²⁺ > Zn²⁺) was observed.

Abstract: The synthetic dyes are a refractory and poisonous material. Most of industrial textile today used the synthetic dyes that can be dangerous to the environment because of the colored wastewater produced from their processes. This study concentrates on the application of Advanced Oxidation Processes (AOPs) for synthetic dyes wastewater treatment. Photocatalysis process as one of AOPs was applied for the degradation of organic content of synthetic dyes wastewater. The reactive dye, C.I. Reactive Red 2 (RR 2) was used as the organic pollutant model at the concentration of 100 mg/l. The TiO₂ concentration of 0.05-0.4 g/ml was used as the photocatalyst. The bulk and nanosize of TiO₂ were coating on the PET plastic and the degradation of organic content was examined in the term of color and COD within 0-12 hrs under solar irradiation. By using 0.4 g/ml of bulk TiO₂, the color degradation of 88% and COD removal of 46% was achieved. Furthermore, by using 0.4 g/ml of nanosize TiO₂, the enhancement of color degradation and COD removal was observed, that is 98% and 56%, respectively.

Abstract: This report describes the preparation of gas sensors based on SnO₂ semiconductor nanostructure thin films synthesized using chemical bath deposition (CBD) technique. As the rapid demand of the gas sensors based on the semiconductor materials, there have been significant efforts to improve the performance of the semiconductors sensors. SnO₂, which has good electrical and mechanical properties, is one of the potential materials to be developed. In the present study, the SnO₂, prepared using CBD technique with stannous cloride as precursors, has nanopattern that give much SO₂ particles to access into the semiconductor surface. The resulting nanostructure SnO₂ thin films have been confirmed by X Ray Diffractions (XRD), Energy Dispersive Spectroscopy (EDS) and Scanning Electronic Micrsocopy (SEM). The as fabricated SnO₂ thin films sensors were then characterized as SO₂ gas sensors in various concentrations for several different operating temperatures. The sensors have good sensitivity as low as 30 ppm of SO₂ gas at the optimum temperature of 200⁰ C.

Abstract: The macro texture of Nb₃Sn superconductor was observed in order to identify the tendency of crystallographic orientation of such A15 compound. The Nb₃Sn samples were prepared through the powder metallurgy process with the composition of 24at%Sn-76at%Nb. The well-blended Nb-Sn powder was consolidated by means of the uni-axial compression method, while the subsequent sintering was performed at T = 700°C for t = 96 hr. The macro texture of the sintered samples was measured using D8 Advance XRD Goniometer and the corresponding results were analyzed in the form of pole figures. Preliminary results indicate that the crystallographic orientations of Nb₃Sn for both green compact and sintered samples show the strong textures in {112}-pole figures. The intensity of Nb₃Sn textures decreases from green compact sample to sintered sample, probably due to the mechanism of recovery recrystallisation following the Nb-Sn inter-diffusion process during sintering.

Abstract: Composite as main materials for ballistic applications has been developed in order to reduce density which leads to lower fuel consumption and faster mobilization. Composite is required to own high hardness and high impact strength for good ballistic performance. Particulate composites Al-7Si-Mg-Zn reinforced by SiC is designed for ballistic applications due to its light weight and high hardness. Whilst the high hardness showed brittle properties, heat treatment process is applied to this composite to reduce it. This research aims to study the effect of magnesium as alloying element to composite Al-7Si-Mg-Zn reinforced by SiC particulate which applied to precipitation hardening. Composites Al-7Si-Zn-SiC with 2, 4 and 6 wt. % Mg is solution treated at 500 oC for 1 hour, followed by ageing at 200 oC. The characterization was carried out by hardness testing, microstructure observations, SEM and EDX observations, impact testing and fractographic observations. Results showed that Mg does not affect hardness of composite by precipitation hardening. Composite with 2, 4, 6 wt. % Mg had 63.83, 62.27, 62.48 HRB on its peak hardness. Mg did not become precipitate in matrix Al-7Si-Mg-Zn because of its low diffusivity in aluminium. Mg worked as wetting agent that reduces interface tension between aluminium matrix and SiC particles in order for composite to own better interface bonding. Therefore impact testing showed significant increase of impact strength with the increase of Mg content. Composite with 2, 4, 6 wt. % Mg had 2075, 3006, 3257 J/mm2 impact strength respectively

Abstract: NiTi is alloy that has unique properties include shape memory dan superelasticity. However, it has disadvantages which cause allergic and toxicity to the body from the Ni release. In order to reduce Ni release and increase corrosion resistance an Electropolishing Pretreatment-Photoelectrocatalytic Oxidation (EP-PEO) and Advanced Oxidation Process (AOP) coating were synthesized in order to produce TiO₂. Scanning Electron Microscope (SEM) was depicted various morphologies of NiTi orthodontic wire surface. Ni release experiment in various saliva by using Inductively Coupled Plasma (ICP) was shown reducing Ni release significantly both in saliva pH 3 dan pH 6.25 in AOP coating for 2 months monitoring. This results confirmed that the Ni release was evidently decreased and the corrosion resistance significantly improved after coated with AOP.

Abstract: The development of biomaterial has reached biodegradable stage. Biodegradable means it can be degraded after certain period of time after implantation and cause no harm for the system. Degradable Biomaterial has the potential to be used as Coronary Stent to minimize the risk from thrombosis issue. Thrombosis is a symptom of body defense where will be a clots blood effect around stent area. The formation of clots blood will disturb a blood flow in artery and it will result a restenosis effect.