Study On Surface Coating And Tribological Properties Of Porous Titanium Prepared From Rice Husk

In past years,the research and application of bone implant materials have attracted extensive attention in the medical field.Porous titanium becomes the most appropriate substitute for bone implant materials with the advantages of unique pore structure and excellent biocompatibility.However,The researchers mainly focuses on the preparation process and the improvedperformance of porous titanium,but as an implant material,porous titanium hadfew research on the friction and wear for porous titanium has been made so far.Subsequently,it is necessary to study the preparation process and friction and wear of porous titanium.Porous titanium materials with porous structure were prepared by using rice husk as space-holder and titanium powder as matrix material in this paper,and the surface modification of porous titanium,the preparation of bioactive coatings and the friction and wear properties of porous titanium were studied as well.The following results can be obtained as follows:Thermodynamic and kinetic characteristics of the pyrolysis of rice husk.The rice husk was subjected to particle size control and surface removal treatment according to the bone implant material requirements for the aperture.The pyrolysis characteristics of rice husk were studied by thermodynamics and kinetics,and the carbon loss during the pyrolysis of rice husk was analyzed.The results show that the optimum process parameters of rice husk pyrolysis is obtained at 10?/min.The activation energy of rice husk pyrolysis temperature is calculated to be 12.22 kJ · mol-1 and the carbon loss is 65.3%at 300-450?.Effect of process parameters on the performance of porous titanium prepared from rice husk.The porous titanium materials with different porosity and properties were prepared by pressing pressure,sintering temperature,pore size and content of space-holder.The results show that at a pressing pressure of 300MPa,anda sintering temperature of 1300?,a rice hull particle size of 180 to 250?m and a rice husk content of 20wt.%was used to prepare an excellent porous titanium material.The porosity,compressive strength and elastic modulus were 52.8%,58.94MPa and 7.26GPa,respectively.The porous titanium material has a class-oriented pore structure and the inner wall of the pores has a long tumor-like titanium fiber.The compressive fracture mode of porous titanium exhibits brittle fracture.Effect of surface modification on the surface coating of porous titanium.In the surface modification of porous titanium,two kinds of surface modification treatment processes of acid-base treatment and alkali heat treatment are selected.The surface of the porous titanium treated with acid and alkali has a agglomerate sodium titanate deposit with a height of about 10?m,a sodium titanate needle fiber length of about 4?m,a roughness of 275.27?m,which improves porous titanium biocompatibility.With the increase of the alkali solution soaking time,the surface of the porous titanium was changed from the plush-like layer to the gel-like sedimentary layerafter the heat treatment,and finally,it becomes a dendritic-like sedimentary layer,which is beneficial for the improvement of the bonding strength of the porous titanium substrate and the active layer.Bioactivity and activation coating of porous titanium.After being immersed in simulatedbody fluids for 7 days,the needle-like sodium titanate fiber and rod-shaped hydroxyapatite activated sediment layer form on the surface of the porous titanium,the surface roughness is about 259.8?m.Rough surface is favorable for the preferred growth and improved the bonding strength between the substrate and the activating sedimentary layer which is uniformed and dense.Which not only results in the formation of chemical bond between Ca-P layer and the matrix,but also plays a role in mechanical locking.After being immersed in the simulated body fluid of the bovine serum albuminfor 7 days,the surface roughness of the porous titanium decreases and the amount of acicular sodium titanate fibers in the surface layerincreases.The addition of bovine serum albumin improves the capability of nucleation better on the surface of porous titanium,which provides a large number of nucleation sites for the deposition of calcium phosphate,make the surface of the bionic coating more compact,and improves the biological phase of porous titanium,beneficial for the adsorption of protein.As a result,bone-inducible factorcan be carried,leading to the increase on the bone conduction and bone-induced characteristics.Study on the friction and wear mechanism of porous titanium.The friction coefficient and wear rate of the three samples were studied by using porous titanium,commercial porous titanium and pure titanium prepared by rice husk as the research object.The microscopic morphology and interface element films were also compared and analyzed,the wear mechanism was determined.The results shows that the friction coefficients of the prepared porous titanium are 1.05 and 0.5 under dry friction and bovine serum,respectively,and the wear rates are 9.94×10-4mm3/m and 0.76×10-4 mm3/m.The wear mechanism is oxidative wear and abrasive wear under the dry friction condition,while the abrasive wear and adhesive wear arethe main mechanism under the bovine serum condition.