| Summary: | 碩士 === 大葉大學 === 機械與自動化工程學系 === 98 === The most commonly used porous metal material in studies of recent years refers to titanium and its alloys, because titanium and its alloys have excellent biocompatibility, biological activity, and lower elastic modulus. As a result, titanium and its alloys have been widely used in biomedical materials.
The purpose of the experiment is to achieve an amorphous alloy powder between pure elements Ti and Mo powders within the TiMo alloy system through mechanical alloying (MA). Ammonium bicarbonate (NH4HCO3) was used as the pore-forming agent for this study, and the reason being ammonium bicarbonate is characterized by its low melting point, which makes removal easier. The milling time of the experiment was set respectively as 3, 15, and 30, which were represented as BM3, BM15, and BM30 respectively. Back electron microscope showed that powder did not reach homogenization after treatment in BM3, and homogenization was only reached after BM15 and BM30 treatment. Ball-milled alloy powder was then used for making porous TiMo scaffold. It then underwent vacuum sintering in a vacuum heat treatment furnace at a vacuum of D1 Pa, sintering temperature of up to A1 ℃ that last for B1, B2, B3 and B4 hours.
In the XRD phase analysis, the porous TiMo alloy showed no sign of any pure element of titanium and molybdenum after different sintering stage. During this time it would also produce a new alloy phase β-(Ti, Mo). In terms of compressive strength, porous TiMo scaffolds of B1, B2, B3 and B4 hours were already produced under different holding temperatures. The results showed that an increase of sintering time can help to improve the compressive strength of porous TiMo scaffold. In working with the compressive strength results, the experiment then selected the alloy powder of BM15 and the porous samples sintered for B1 hours as the follow-up study on surface modification. Therefore, the group conditions of compressive strength and elastic modulus were 25.02 MPa, and 1.72 GPa respectively, very suitable for the application as an implant material for cancellous bones.
Also in the pore size distribution, the majority of them are 100-200 μm for porous samples of different milling time and different sintering stages; but after BM30 treatment, the powder particle size distribution tends to be more uniform, leading to the existence of gaps between powders after compression molding, which in turn affects the pore size differences. Therefore, we can clearly see a visibly increased number of above 400 μm aperture in BM30 treated porous samples.
After surface modification (alkali treatment and alkali water treatment) of porous samples, it was found that a mesh-like porous structure will form on specimen surface, which was identified as Na2Ti6O13 (sodium titanate hydrogel) using HR-XRD analysis. Through FE-SEM observations, it was found that alkaline water treatment produces mesh of smaller pore size than the alkali treatment. However, in order to observe the effects of pores on formation of apatite, solid specimens were used as control group. Thereafter, both solid and porous specimens were soaked in simulated body fluid (SBF). The results showed that apatite has already begun to form inside the pores in porous specimens with alkali and alkali water treatments after SBF-14 days of immersion. In the follow-up observation of 21 days immersion, it was found that on porous specimens with alkali and alkali water treatments, both inside and outside the pores was covered in apatite, although no noticeable results were seen for the solid part. But the follow-up EDS analysis revealed extremely high content of Ca and P in both alkaline and alkaline water treatments. This result showed that porous TiMo scaffolding has a better bioactivity after surface modification in terms of porous implant material.
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