No abstract

Ti-6Al-4V Extra Low Interstitial (ELI) alloys have been widely used for biomedical application as implant materials due to its excellent mechanical properties and good corrosion resistance. Furthermore, mechanical properties of this alloy could be improved by heat treatment process. In this research, it has been studied the effect of heat treatment temperature on microstructure and hardness properties of casted Ti-6Al-4V ELI alloy. After calculation of material balance to obtain this alloy composition, raw materials were melted using single arc melting furnace flowed with argon gas and melted alloy was casted. Then, it was heat treated by solution treatment for around 1 hour and subsequently quenched in water as medium. Solution temperature was given with temperature variables of 850 o C, 950 o C, and 1050 o C. After that, it was aged at temperature of 500 o C for 4 hours. Microstructures were observed using optical microscope and hardness value were obtained by Vickers hardness method. The results of microstructure observation showed that it was changed after heat treatment process, especially on morphology of α and β phase. Thus, the hardness of alloy significantly increased compared with as-cast condition after heat treatment process. The optimum value of hardness was obtained at temperature of 850 o C that was 478 HVN.

The LaNi5 intermetallic phase has been extensively investigated because of its excellent properties, such as attractive hydrogen storage, medium plateau pressure, and easy activation. LaNi5 phase is generally produced by a complicated method, which involves several steps, i.e. melting, alloying, casting, softening and making them into powder. This study aimed to develop a new LaNi5 synthesis process by modifying the combustion-reduction method. In this method it is very important to produce La2NiO4, because LaNi5 is formed from the process of reducing this phase. The precursor powders La(NO3)3.6H2O and Ni(NO3)2.6H2O were reacted with distilled water as a solvent medium and mixed using magnetic stirring. The synthesis process was carried out at room temperature, 60 °C, 70 °C, and 80 °C for 10 minutes until the solution became transparent green. The solution was then dried for 2 hours at 100 °C to form a transparent green gel. The gel was calcined at a temperature of 500 °C for 2 hours, producing a black powder. The optimal black powder was then reduced using CO gas at 600 °C for 2 hours. The powder samples were characterized using XRD, FTIR, and SEM-EDX. The analysis revealed that synthesis at room temperature was the most optimal method for the reduction process because it produced the most La2NiO4, at 12.135 wt%.

Lithium-ion battery has been drawing attention from researchers due to its excellent properties in terms of electrochemical and structural stability, low cost, and high safety feature, leading to prospective applications in electric vehicles and other large-scale applications. However, lithium-ion batteries are still in charging time owing to its low conductivity, restricting its wide applications in large-scale applications. In this work, therefore, lithium lanthanum titanate (LLTO) was synthesized derived from lanthanum oxalate, as a lanthanum source, for an anode active material application in the lithium-ion batteries due its high electrochemical conductivity and pseudocapacitive characteristics. To the best our knowledge, our work is the first one to synthesize LLTO from lanthanum oxalate as the lanthanum source. Commercial lithium carbonate and commercial titanium oxide were used as the lithium and titanium sources, respectively. It was used low cost and simple solid-state reaction process to synthesize this material and performed a two-step calcination processs at 800 oC for 8 hours and 1050 oC for 12 hours under ambient atmosphere. The physical characteristics showed that LLTO possesses high purity (98.141%) and micro sized grains with abundant empty spaces between the grains. This, therefore, lead to improve electrochemical performances such as stable discharge capacity at low potential even near to zero (98.67 mAh), and a high conductivity of 2.45 × 10-2 S/cm at room temperature. This LLTO is interesting to be used as the anode active material in low potential lithium-ion battery applications.

Elektrolit berbasis serium seperti GDC10 telah banyak dikembangkan untuk aplikasi sel bahan bakar oksida padatan suhu sedang atau yang dikenal dengan Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC). Kodoping merupakan salah satu cara untuk meningkatkan konduktivitas elektrolit IT-SOFC. Tujuan dari penelitian ini adalah untuk mempelajari pengaruh penambahan kodopan neodimium (Nd) terhadap GDC10 (Ce0,9Gd0,1-xNdxO1,90) dengan rasio molar x = 0,025; 0,050; dan 0,075 terhadap sifat fisis dan elektrokimianya. Neodimium digunakan sebagai kodopan karena dapat menurunkan energi aktivasi, sehingga konduktivitas elektrolit meningkat. Metode sintesis yang digunakan adalah sol gel untuk menghasilkan serbuk GDC terdoping Nd, setelah itu serbuk dibuat pelet. Sampel dikarakterisasi dengan menggunakan X-Ray Diffraction (XRD) untuk mengidentifikasi fasa, Scanning Electron Microscope (SEM) untuk melihat morfologi dan Thermal Gravimetric Analysis (TGA) untuk melihat stabilitas termalnya. Dari hasil penelitian, kalsinasi pada suhu 700 oC selama 5 jam dan sintering pada suhu 1350 oC selama 2 jam diperoleh densitas pelet elektrolit lebih besar dari 95%. Hal ini telah memenuhi syarat sebagai elektrolit sel bahan bakar padatan yang baik. Keseluruhan sampel memiliki struktur kubik dengan ukuran kristal antara 4,26 nm hingga 4,47 nm. GDC10 terdoping neodimium dengan rasio molar x = 0,025 (GDC-Nd0,025) memiliki konduktivitas tertinggi yaitu 0,055 S/cmpada suhu 600 oC. Hasil tersebut menunjukkan bahwa kodoping dapat meningkatkan konduktivitas sel elektrolit GDC untuk aplikasi sel bahan bakar oksida padatan suhu sedang.

Gadolinium doped cerium (Ce0.9Gd0.1O1.95 or GDC10) was successfully synthesized using the solid-state method. Commercially available CeO2 and Gd2O3 powders were used as starting materials. They were mixed in a ball mill where alumina balls were added as grinding medium with the ratio to powders as of 1:2. The obtained powders were dried and then calcined at temperatures of 600, 700 and 800 °C, respectively. The objective of this research was to investigate the effects of calcination temperature on the properties of GDC10. The powders were characterized using XRF, TGA, XRD, and PSA instruments. XRF analysis shows the presence of Ce, Gd and O elements in stoichiometric composition without any impurities. XRD analysis showed single phase structure of CeO2 where the crystallite size and lattice parameter increases and decreases, respectively, as the calcination temperature increases. The smallest particle size of 647.3 nm was obtained at the calcination temperature of 600 °C. The density of all GDC10 samples sintered at 1350 °C was found to be higher than 95%. In addition, the calcination temperature also influenced the ionic conductivity where the highest obtained value was 0.0153 S.cm-1 at 800 °C for the sample calcinaed at 600 °C. The results suggest that the calcination temperature affected the properties of GDC10 for solid oxide fuel cell application.