This work proposes four different glass formulas derived from the SiO 2 -Li 2 O-K 2 O-Al 2 O 3 system to investigate the effect of glass composition on their crystal formations and properties. Glass LD1 was SiO 2 -Li 2 O-K 2 O-Al 2 O 3 system with the addition of P 2 O 5 and CaF 2 as nucleating agents. In Glass LD2, a slight amount of MgO was mixed in order to increase the viscosity of the melting glass. Finally, the important factor of Si : Li ratio was increased in Glasses LD3 and LD4 with compositions otherwise the same as LD1 and LD2. The results found that P 2 O 5 and CaF 2 served as a nucleating site for lithium phosphate and fluorapatite to encourage heterogenous nucleation and produce a fine-grained interlocking microstructure of lithium disilicate glass ceramics. MgO content in this system seemed to increase the viscosity of the melting glass and thermal expansion coefficient including the chemical solubility. Increasing the Si : Li ratio in glass compositions resulted in the change of the microstructure of Li 2 Si 2 O 5 crystals.
A technique combining gel-casting and freeze drying methods is introduced to prepare porous hydroxyapatite scaffolds which allow for better control of the scaffold microstructure and have improved mechanical properties. A monomeric system which is known to be a suitable gelling agent for setting ceramic suspensions into dense forms was selected to produce ceramic foams. Different concentrations of sodium lauryl sulphate solution were added into the hydroxyapatite gel suspension as a pore former. The effect of the solid content on the mechanical properties of the scaffold was also investigated. Rapid freezing with liquid nitrogen was performed according to the freeze drying technique and the porous structure and morphology of the scaffolds were analyzed by scanning electron microscopy. The mechanical properties of the hydroxyapatite scaffolds were determined by testing compressive strength using a universal testing machine. The prepared scaffolds were characterized by well-defined pore connectivity along with directional, uniform and completely open porosity. The maximum compressive strength of about 17 MPa obtained from the suspension consisted of 50% solid content with 20% concentration of sodium lauryl sulphate solution. The results show that sodium lauryl sulphate solution plays a significant role in changing the pore structure of hydroxyapaite scaffolds in systems having high solid content.
A series of TiO2 modified hydroxyapatite composites (HA/TiO2) with different compositions were prepared. Phase formations and morphologies of the obtained HA/TiO2 composite were characterised using X-ray diffraction and SEM, and their photocatalytic activities were also determined by decomposition of methylene blue solution. Filter cloths were prepared by depositing the composite on polyester non-wovens via pad dry cure, and their filtering effectiveness was examined by photocatalytic activity measurement and bactericidal test. Hydroxyapatite/TiO2 composites were successfully prepared and exhibited photocatalytic properties. With increasing ratio of anatase titania in the HA/TiO2 composite from 20 to 30 and 50%, photocatalytic activity of composite material increased such that HATi5050 composite exhibited the highest photocatalytic activity. Non-woven filters coated with HA/TiO2 composites also exhibited good photocatalytic activities. Less difference in photocatalytic activity between HATi7030 and HATi5050 coated non-woven filters was observed, compared to that in powder form. The filter coated with HA/TiO2 composite exhibited good bactericidal effect.
This study aims to improve the strength of porous BCP samples by the addition of titanium dioxide (TiO2), the well known biocompatible and strong ceramic. BCP powder with HA/TCP ratio of 70/30 (BCP7030) obtained by mixing a pure HA and β-TCP powder. TiO2 powder with 2 (BCP_2Ti), 5 (BCP_5Ti) and 10 (BCP_10Ti) %wt were added into the BCP7030 powder, then ball milled in ethanol for 6 hrs. The porous samples were fabricated by the combination of the gel-casting and freeze drying techniques. All samples were sintered at 1100°C for 2 hrs. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were used to determine crystal structures and morphology of the sintered samples, respectively. Mechanical properties and porosity of samples were measured by using the universal testing machine and Archimedess principle, respectively. XRD results showed that the phases of the undoped sample can be indexed HA and β-TCP with the ratio of 70/30 as the major phases. In BCP_2Ti, CaTiO3 was observed as a minor phase among the crystallization of HA and β-TCP with the proportion of 30:70. Meanwhile, in BCP_5Ti and BCP_10Ti, XRD patterns revealed a completely transformation of HA to β-TCP with minor phases of CaTiO3 and TiO2. The microstructure of sintered samples present highly porous structure which consisted of two-dimensional pore channels along the long axis and the short axis, which replicates the ice and pore orientation in the direction of freezing. Relatively, the porosity of the samples was increased with the amount of TiO2. Surprisingly, an additions of the TiO2 was not rather improved the mechanical strength of porous BCP7030 in this study. This might be a result of a high percentage of porosity (84%).
Biphasic calcium phosphate (BCP) ceramic is commonly used in the biomedical applications particularly as a bone substitute due to its biocompatibility and directly bond to bones. However, the mechanical strength is quite poor. Therefore, well known biocompatible and strong ceramics such as SiO2, ZrO2 and TiO2 were added to improve the strength of BCP. BCP powder with HA/TCP ratios of 70/30 (HAP7030) was obtained by controlling the calcining temperature of the mixture between a pure HA and TCP. SiO2, ZrO2 and TiO2 powder with 2, 5 and 10 %wt were mixed with the HAP7030 powder by ball milling in ethanol. The mixtures were dried, pressed and sintered at 1100°C for 2 hrs. XRD and SEM were used to determine crystal structures and morphology of the sintered samples, respectively. Physical properties and flexural strength of samples were measured. Results showed that the bending strength of HAP7030 sample was rather improved by adding TiO2 than the addition of SiO2 or ZrO2. With increasing TiO2, HAP7030 strength was superior and HAP7030 with 10 %wt of TiO2 obtained the optimum bending strength around 61 MPa. However, the addition of TiO2 induced the thermal stability of HA/TCP, in which HA completely decomposed to β-TCP in this study.
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