Key Engineering Materials Vol. 860

Abstract: Amorphous carbon (a-C) film is a unique material that attracts the attention of scientists to be investigated. Nitrogen- and boron- doped amorphous carbon (a-C:N and a-C:B) have been deposited on ITO glass substrates by using nanospray method. Palmyra sugar is heated at temperature 250^o C for 2.5 hours to obtain a-C. Boric acid (H₃BO₃) and amonium hidroxide (NH₄OH) are used as the sources of boron doping and nitrogen doping. a-C:N and a-C:B are made by the variations of mole ratio for doping and amorphous carbon, that are 1:15 and 1:20. Then, these samples are dissolved into mixed dymethyl sulfoxide (DMSO) and aquades. The exfoliation process of samples has been done by applying ultrasonic cleaner for 2 hours and also centrifugated at 4000 rpm for 45 minutes. Electrical conductivity and band gap are measured by using four point probe and UV Vis. The results show that electrical conductivity increases but band gap decreases than pure a-C. Furthermore, the larger mole ratio of a:C-N and a-C:B also increases conductivity and decreases band gap, resulting between 5.5×10^-1S/cm – 6.1×10^-1 S/cm and 1.43 eV – 1.71 eV.

Abstract: Amorphous carbon films have been explored and used in a wide variety of applications. With the n-type and p-type amorphous carbon film, it can be used to make p-n junctions for solar cells. This research aims to study the structure of boron- and nitrogen-doped amorphous carbon (a-C:B and a-C:N) films. This research uses the basic material of bio-product from palmyra sugar to form amorphous carbon. Amorphous carbon was synthesized by heating the palmyra sugar at 250°C. The results of XRD showed that the doped films produce an amorphous carbon phase. PES was used to analyze the bonding state of dopants in the sample. B₄C, BC₃, and BC₂O bonds formed in a-C:B, while pyridine and pyrrolic formed in a-C:N.

Abstract: Structure of amorphous carbon can be composed of sp² (graphite), or sp³ (diamond), or a combination of both, depending on their fractions. Therefore, many researchers were exploring to use it as solar cell material. This research used the amorphous carbon of bio-product as a basic material in the form of palmyra sugar which was synthesized through the heating and doping process to produce n-type and p-type semiconductors. This research aims to analyze the effect of dopant and deposition time on electrical properties. The heating process was carried out at 250°C and the doping process was carried out by adding NH₄OH for a-C:N and H₃BO₃ for a-C:B. The deposition process was carried out by the nano-spray method using a variety of deposition time on the ITO substrate. The result of scanning electron microscopy (SEM) showed that the film thickness increased with the increase of deposition time. Besides, the result of four-point probe (FPP) showed that the dopant can increase electrical conductivity, but the film thickness did not influence it. The electrical conductivity obtained was 5x10^-1 - 6x10^-1 S/cm. And the result of further analysis, it can be concluded that electrical conductivity was still in the range of semiconducting material.

Abstract: The Zn-Mg alloy is a suitable candidate for the manufacture of biomaterials that can be excessively degraded in the human body without producing a mixture. This study was conducted with the aim to determine variations in the mechanical characteristics of Zn-Mg alloys with Mg ratio of 1%, 3%, 5%, and 7%wt, and to study variations in composition and sintering of the degradation rate of Zn-alloy Mg uses the powder metallurgy method. The synthesis results were characterized by using a defense test and obtained the best value at Zn7% Mg of 117.5 ± 25.37. The presence of MgZn₂ and Mg₂Zn₁₁ phases that were confirmed by XRD characterization could increase the material hardness. Dynamic degradation test was carried out on samples with the best mechanical properties (Zn7% Mg) with variations in compacting pressure and sintering temperature. The increase in compaction pressure and sintering temperature could reduce the degradation rate of Zn-Mg alloys. The best degradation test was obtained at a pressure of 400 MPa with a sintering temperature of 400°C of 0.70mmpy. The degradation test results were as expected because previous studies stated at the degradation rate (0.40mmpy-1.53mmpy) on statistical testing and the degradation rate (4.9-7.0) mmpy on the change policy supported for bone scaffolding applications. Scanning Electron Microscope (SEM) characterization results showed that samples with compacting pressure and low sintering temperature do not have perfect particle bonding. Samples with high compacting pressure and sintering temperature have good bonding between particles so they do not have a pore composition in the alloy.

Abstract: Magnesium alloy has been widely investigated as a biodegradable implant material owing to its unique properties to degrade spontaneously in human body fluid without causing toxicity. However, the degradation rate needs to be controlled. An effective way to lower down the degradation rate of Mg alloy is by coating with plasma electrolytic oxidation (PEO) technique. In this research, the microstructure and mechanical hardness of the PEO film formed on AZ31 were investigated. The film was prepared under a constant current of 400 A/m² in the Na₃PO₄ solution at 30°C. The voltage-time curve showed an immediate increase of current during the first 25 s before reaching a steady-state voltage of 150 V. The spark discharge revealed as white micro discharges. The film formed for 3 min exhibited a high surface roughness with a large variety of thickness in the range of 1-20 µm. The film contained pores and cracks. The big pores with diameter size 10-20 µm were formed as a result of gas entrapment, while the small pores with a radius of 1-3 µm were associated with the discharge tunnel during the PEO process. The X-ray diffraction pattern indicated that the film composed of crystalline Mg₃(PO₄)₂.

Abstract: The metastable β Ti-6Al-4V alloy has been used clinically as a permanent implant material owing to its suitable mechanical properties and biocompatibility. However, the alloying element V was accused of causing toxicity when released to human body fluid. In this work, Nb was used in the alloy to replace V. This study presents the characterization of microstructure and mechanical hardness of as-cast Ti-6Al-7Nb and after solution treatment. The Ti-6Al-7Nb alloy was fabricated by the centrifugal casting method. Solution treatment was carried out at 970°C for 1 hour, followed by oil quenching, and consecutively an aging treatment was applied at 500°C for 8 hours. The microstructure was studied by an optical microscope. The mechanical hardness was measured by microhardness Vickers. The results show that the mechanical hardness of the Ti-6Al-7Nb decreased from 396.2 to 377.2 HV as a result of the solution treatment. Reduction in the hardness was attributed to the phase transformation of α to the β phase during the solution treatment. The XRD analysis showed a reduction in the intensity of α phases at the (011), (012), and (020) planes in the alloy after the solution treatment. The results indicated that the microstructure and mechanical hardness of Ti-6Al7-Nb alloy were affected by the solution treatment.

Abstract: Fabrication of pure magnesium (Mg) disk was performed by powder metallurgy with the compaction method of spark plasma sintering (SPS). The effect of mechanical milling time on the microstructure, density, and porosity of the disk specimen was investigated. At an identical temperature, the 4 and 5 h milled specimens exhibited a nearly overlapped displacement curves during SPS, and a higher value indicating a higher densification degree than that of the 3 h milling powder. In agreement, the specimen density increased consecutively from 1.76 to 1.77 and 1.80 g/cm³ for the milling time of 3, 4, and 5 h. However, the porosity increased from 1.21% to 1.49% when the milling time increased from 3 to 4 h and further to 3.44% for 5 h milled specimens. The microstructure observation revealed that the average grain size decreased, and the pores became smaller and elongated with increasing milling time. The number of pores was higher with the gain fraction of grain boundaries. The 3 h milled specimen contained the highest atomic fraction of oxygen (21.9 at%) than that of the 4 and 5 h milled specimens (5.6 at% and 7.9 at%). The optimum milling time for obtaining high density and low porosity of pure Mg disk was 4 h.

Abstract: Hydroxyapatite (HA) is a calcium phosphate compound [Ca₁₀(PO₄)₆(OH)₂] which is non-toxic and has high biocompatibility. HA can be synthesized from natural basic ingredients with high calcium carbonate (CaCO₃) content such as chicken eggshells. Here, we reported the synthesis of HA from chicken eggshells by hydrothermal methods. The effects of temperature synthesis of 120 °C and 230 °C on the purity and crystallinity were investigated in order to get information about best synthesis temperature for producing high quality of HA. The structure and crystallinity of HA were determined by XRD and FTIR. Morphology of HA is determined by TEM, while the composition was determined by XRF, respectively. High purity samples of HA with hexagonal structure of P63/m were successfully obtained with synthesis temperature of 120 °C and 230 °C. For HA synthesized in 120°C, the purity was 97.7%, while for HA synthesized in 230 °C, the purity was 97.8%. Two types of impurities, namely Ca(OH)₂ and tricalcium phosphate (TCP) ware detected in both samples, It was also obtained the degree of crystallinity of 26.86% and 56.46% for samples synthesized at 120 °C and 230 °C, respectively. HA synthesized with at 230 °C has a higher and better crystallinity.

Abstract: Polydimethylsiloxane (PDMS) is a tamponade substance that is used as vitreous humour substitutes in vitreoretinal surgery. PDMS can be obtained from monomers of Octamethylcyclotetrasiloxane (D4) that was reacted with Hexamethyldisiloxane through polymerization reactions in a base condition. The monomers are very difficult to obtain in Indonesia, therefore another alternative monomer is needed to produce PDMS with specific properties for vitreoretinal surgery. Here, we reported the synthesis of monomer for replacing D4 through hydrolysis process of Dichlorodimethylsilane (DCMS). Furthermore, the synthesized monomer was used to produce PDMS. The process of DCMS hydrolysis assisted by KOH 0.5 M along 18 hours in reflux system. The synthesized monomer has viscosity of 171 mPas, refractive index of 1.4005 and surface tension of 17 mN/m. PDMS was produced using synthesized monomer by ring-opening polymerization. It is found that the properties of PDMS are very similar with that of commercial PDMS of 5500 cSt.

Abstract: Hydroxyapatite (HA) coating was deposited on commercially pure Ti to improve its biocompatibility as a biomedical implant material. The HA layer was deposited by the electrophoretic deposition (EPD) method. The processing parameters controlled the HA structure. In this research, the applied voltage was varied 20, 30, and 40 V to optimize a free-crack layer. The current output during EPD at 20 V was in the order of 10^-5 A/cm². A higher current density in the order of 10^-4 A/cm² was obtained at 30 and 40 V. The coating formed at 20 V was relatively free of crack. A high number of cracks began to observe in the layer formed at 30 V, while only a few cracks were revealed on the layer formed at 40 V. The average thickness of the HA layer increased slightly with applied voltage. The thickness was approximately 40±5 µm, as observed by an optical microscope. The optimum voltage to produce a thick HA layer with a small number of cracks was at 40 V.