Materials Science Forum Vol. 1000

Abstract: Nowadays, either keeping or throwing out the final product of dental cast is the most common thing to do. The waste from dentistry can be considered toxic if not handled specifically and separately to other waste. Hence, the recycling process can reduce its effect and the waste of dental casts. It can also reduce the cost of producing new high-grade dental gypsum. This paper studies the behavior of before-after recycle and heat treatment to several grades of dental gypsum that will be used as impression material or dies. As it is designed to be an impression material that will undergo heat treatment, Simultaneous Thermogravimetry and Differential Scanning Calorimetry (TGA-DSC) will be applied to understand the Phase Transformation to its mass change and the behavior to a temperature difference. The result will be validated using an experimental approach. X-ray Diffraction (XRD) and Scanning Electron Microscope will also be done to identify the crystalline phases and the surface microstructure, and it will be validated using an experimental approach as well. A range of gaps between parameter values is expected between the fresh/new dental gypsum and the recycled one. However, it is expected some similar values between the heat-treated and the fresh/new dental gypsum.

Abstract: Research about the utilization of titanium alloy (Ti-6Al-4V ELI) as implant material in the treatment of orthopedic cases had been increasing. Health problems appear due to the drawbacks of using titanium. The lack of titanium using is bio-inertness characteristic, which decreasing its bioactivity and results in low bone growth and effect for implant failure. The titanium can be modified with coating on the surface using a bioactive substance that is natural-source hydroxyapatite. Bovine-source hydroxyapatite (bovineHA) contains apatite component that is similar to human bone apatite. The coating process was carried out using particle size variation (25 μm, 63 μm, and 125 μm) of bovineHA. The electrophoretic deposition (EPD) method was applied to coat hydroxyapatite with 10 volt for 5 minutes onto the titanium surface. The result showed that different size particles have an effect on coating properties. The coating composed by particle-sized 25 μm has better surface coverage (95.89%), indicating more particle mass (particle weight 6.97x10³ μg) attached to surface material, thus resulting thick coating. The good coating characteristic using bovine-source hydroxyapatite with small particle size was expected can be used in biomedical applications due to fulfill the prerequisite of the bone implant.

Abstract: The bone scaffold is susceptible to infection in its application due to the bacteria that often appear on the surface. To prevent this phenomenon, the scaffolds need to be modified in order to provide antibacterial properties. In this study, the bone scaffold was fabricated from chitosan-collagen with the addition of zinc oxide as an antibacterial agent. There were four variables of the amount of zinc oxide added to the scaffold: 0%, 1%, 3%, and 5%. The method used was Thermally Induced Phase Separation (TIPS). From this study, a porous scaffold with a rough surface was obtained. SEM image of the scaffold showed that more zinc oxide caused smaller pore and lower porosity. Characterization with FTIR proved that the scaffold obtained from this process has the same functional group as chitosan and collagen. The DSC-TGA curve confirmed that the heating process performed on dehydrothermal treatment (DHT) did not cause degradation of the scaffold because chitosan and collagen have higher degradation temperatures than DHT temperatures. In addition, this study also proved that the addition of zinc oxide had successfully provided the scaffold with antibacterial properties in which the protection against bacteria was related to the amount of zinc oxide in direct proportion.

Abstract: Magnesium Alloys have the potential to be applied in the various fields of applications including biomaterials. Magnesium Alloys are an interesting alloy due to its high strength to density ratio. They have been proposed as a biodegradable implant material due to its friendly effect to human body compared to another alloy. Besides its good biodegradable properties, it has a disadvantage of low hardness and corrosion properties. In order to overcome this, it has been combined with other metals such as Zinc (Zn) or Copper (Cu). To increase mechanical properties, we used Carbon Nanotubes (CNT) as reinforcement. Magnesium-Zinc (Mg-xZn) CNTs composites with several compositions was prepared by using powder metallurgy and sintered in the presence of flowing Argon (Ar) gas in tube furnace. Mg-Zn Alloy with the composition of 4% and 6% of Zn and the variation of CNTs at 0.1%, 0.3 %, and 0.5% was also prepared. Hardness testing by using microvickers showed that CNTs can increase the alloy hardness which the maximum hardness is 53.6 HV. The corrosion rates as low as 175.5 mpy exhibited for the Mg-Alloy with the composition of Mg-4-Zn with 0.1 wt.% of CNTs

Abstract: This study aims to investigate the effect of the electrophoretic deposition process (EPD) of natural HA (extracted from bovine bones) with various particle size on Ti-29Nb-13Ta-4.6Zr (TNTZ) coating surfaces. HA particles were refined from bovine bone powders using planetary ball mill and then sieving to separate the particle based on its size. The maximum size according to sieving mesh size is #25 µm, #63 µm and #125 µm. The coating process was conducted by using EPD apparatus with voltage and time process 10V and 5 minutes, respectively, for each sample. The coating layer morphology was observed with Stereo Microscopy, Scanning Electron Microscopy (SEM) and the thickness was measured with Thickness Gauge. The result shows that the size of the particle determines the coating layer characteristics. The best of HA coating quality according to the implant coating standard is obtained for the 25 µm particle size with the surface coverage is 99%. The thickness is 121 µm and the ratio of chemical composition Calcium and Phosphor Ca/P) is 1,49%. These may be concluded that, on the point of view physical characteristics, natural HA from bovine bone has potential enough as a coating layer to improve the bioactivity implant for biomedical application. However, the mechanical characteristic of the layer is still needed to determine the strength of coating layer for avoiding delamination during application.

Abstract: Macroporous hydroxyapatite have been used in biomedical application especially for bone graft. The objective of this research was to study the effect of yolk addition, rate of sintering temperature rise, and rate of stirring on the physical, chemical and mechanical properties of porous hydroxyapatite prepared using protein foaming-starch consolidation method. The slurry was made by mixing the hydroxyapatite and starch powder with Darvan 821A and yolk in a beaker glass. The slurry was stirred mechanically at rate of 150 rpm for 3 hours and it poured in cylindrical mold. Subsequently the slurry was heated in air oven at 180°C for 1 hour. The dried green bodies were burn out at 600°C ended by sintering at 1250°C. The porous hydroxyapatite with average pore size in the range of 13.7-17.9 μm, porosity of 59.3-63.6 % and compressive strength of 5.17-8.2 MPa was obtained. The calculation result of response surface methodology shows that p-value < 0.05 and lack of fit > 0.05. The most effecting factor significantly was hydroxyapatite addition that followed by mixing rate and temperature rising rate of sintering. Optimum condition hydroxyapatite addition of 22 gr, mixing rate of 150 rpm and temperature rising rate of sintering of 2.8°C/minutes with the optimum value of response for pore size by 17.665 μm, porosity by 63.475% and compressive strength 5.17 MPa.

Abstract: Magnesium has been developed as a biodegradable bone implant material due to its similarity in elasticity modulus of bone. However, magnesium has a higher corrosion rate and a lower strength. Gadolinium is alloyed to magnesium in order to improve the corrosion resistance and then rolled to improve the strength due to grain refinement in rolling. Cold roll produced the finest grain, but magnesium has a poor formability. Due to this fact, warm rolling with temperature 247 – 375 oC is applied. Optical Microscope, Scanning Electron Microscope (SEM), and Energy Dispersive Spectrometry (EDS) are used for characterization. Electrochemical Impedance Spectroscopy (EIS) and Polarization test were carried out to observe the corrosion mechanism of Mg-Gd in SBF Kokubo to replicate a human body condition. The result of polarization test shows that the cross-rolled sample experienced an increase in E corr, with 0,15 and –0,048 V due to a better distribution of Gadolinium. EIS states that the single pass rolled sample has a stronger passive layer with 116 and 126 kΩ value of Rf due to a smaller grain size which resulted a fewer compression stress. The hydrogen evolution was also observed with immersion test. Keywords: uni-directional rolling, cross-directional rolling, corrosion, simulated body fluid, hydrogen evolution.

Abstract: This experiment is to investigate delamination damage of carbon/basalt/epoxy hybrid composites on the drilling manufacturing process. The damage is caused by drilling on wet and dry conditions with a twist drill size of 8 [mm], and 10 [mm] have been conducted. This experiment was carried out based on the ASTMD 5470-12 standard. Three hybrid composites have been manufactured for samples such as H₁, H₂, and H₃. Additionally, the carbon fibers reinforced epoxy composites (CFRP) and basalt fibers reinforced epoxy composites (BFRP) as experiment control had built. The aim is to assess the defect zone of carbon/basalt hybrid composite against the drilling. The examination results showed that the feed rate speed of various laminate configurations e.g., H₁, H₂, and H₃, on drilling dried between twist drill of 10 [mm] and 8 [mm] diameters are 50.5 %, 25 %, and 33.2 %, respectively. Also, adding lubricant during the drilling work has reduced peel-out and push-out effectively. The delamination defect has been the high resulted in drilling using drill 10 [mm] in wet or dry conditions. In contrast, delamination defect has occurred minimum on drilling hole using twist drill 8mm in work wet and dry condition. It has still occurred. From this research, the combination sequence of basalt and carbon fiber has the possibility to experience the delaminate damage in dry drilling processes.

Abstract: Aluminium Matrix Composites (AMCs) made by A356 as matrix and nanoAl₂O₃ as reinforced are widely used for high performance application because of light weight and alumina has good performance at high temperature. In this study, the nanoAl₂O₃ used varied from 0.1 vf-% to 1.2 vf-%, which subsequently determined the optimum point. In addition, the magnesium with 10% are added as a wetting agent between aluminium and nanoAl₂O₃ as reinforced. Stir casting process is carried out for 2 minutes and 4 minutes for the degassing process using argon gasses then pouring molten metal in to the mold at 800°C. The effect of nanoAl₂O₃ on the mechanical properties and microstructure of the composites was investigated. The result showed that the tensile strength decreased with the addition of nanoAl₂O₃ but the hardness increased. Increasing of hardness mainly caused by grain refinement, and particle strengthening which act as obstacles to the motion of dislocations. Addition of nanoAl₂O₃ as reinforced also tend to form microporosity and agglomeration which would decrease the tensile strength of composites. The optimum strength was reached by 0.5 %Vf nanoAl₂O₃ with the value of 140 MPa and hardness of 46 BHN which was supported by low porosity level. Keyword : Al A356, Al₂O₃, nanoComposite, Stir Casting

Abstract: Electric bicycles are one of the two-wheeled transportation that has been widely used. The structure of the bicycle is generally composed of several components, one of which is the frame. The frame serves to support the load on the bicycle. At present, many changes in design, geometry and bicycle-forming materials have been carried out. In general, bicycle frames are made of metal and alloy because they have good strength to support the load of the driver. Lately, the use of composites has begun to develop as a bicycle frame material, because the frame of the bicycle has become lighter but still has the strength to support the load. This paper presents a study of the structure of electric bicycles using composite material based on epoxy matrices with rami fiber reinforcement. This study used an experimental and simulation method by designing composite laminates with A(90o/90o/90o), B(90o/45o/90o), and C(45o/45o/45o) fiber webbing layout and then carried out free compressive strength (UCS), optical microscopy and simulation using ANSYS 19.0 software. The results obtained are composite laminate design with a woven fiber layout (45o/45o/45o) having the highest strength value with a compressive stress value σ=58.64 MPa in the axial compressive plane, and σ=1.539 MPa in the tangential compressive plane. Likewise, the simulation results also obtained the highest strength in the webbing design (45o/45o/45o) which is equal σ_s=58.72 MPa in the axial compressive plane and σ_s=1.531 MPa in the tangential compressive plane.