Porous titanium materials have attracted extensive attention due to their excellent physical and chemical properties, so their preparation and related properties have been studied. However, when they are used as bone implant materials, their surface inertness restricts their application in biomedicine. At present, the preparation methods for porous titanium materials include space occupation method, metal powder injection molding and resin-impregnated titanium replacement technology. It focuses on the use of ammonium bicarbonate and urea as pore-forming agents when using the space-occupying method, and compares the advantages and disadvantages of different pore-forming agents in this method. In addition, further analysis to clarify the constraints of porous titanium materials in biomedical applications due to surface inertness.
1. Preparation of porous titanium materials by pore former method
The method is to use powder metallurgy to mix the pore-forming agent with the metal powder, then remove the pore-forming agent, and then sinter in a vacuum or protective atmosphere to obtain a porous material. The method can prepare porous metal with higher porosity, and its pore shape, pore size distribution and porosity can be controlled by controlling the shape, size and addition amount of the pore-forming agent material. Common pore-forming agents include ammonium bicarbonate, urea, and sodium chloride.
1.1 Preparation of porous titanium materials by space occupation method using ammonium bicarbonate as pore-forming agent
Because ammonium bicarbonate is decomposed when heated at a lower temperature, it is used as a pore-forming agent to prepare porous materials. The decomposition of the pore-forming agent at a lower temperature can avoid the reaction between the decomposition products of the pore-forming agent and the porous material and cause foreign impurities to contaminate the matrix. Therefore, the pore-forming agent can prepare relatively pure porous materials.
1.2 Preparation of porous titanium materials by pore-forming agent method with urea as pore-forming agent
In addition, urea can be decomposed at higher temperature and can also be used as a pore-forming agent to prepare porous materials. Some scholars have found that urea can be completely removed when heated to 460 ° C through thermogravimetric analysis, but the holding time can be increased to reduce the removal of urea. temperature.
1.3 Preparation of porous titanium materials by pore-forming agent method using other materials as pore-forming agent
Water-soluble materials (such as sugar spheres and soluble salts, etc.) can also be used as pore-forming agents.
2. Other common methods for preparing porous titanium materials
2.1 Preparation of porous titanium materials by 3D printing
In addition to the above pore-forming agent method for preparing porous materials, 3D printing is also a popular method. As a method of 3D printing, selective laser melting (SLM) is used to design the model of the required specimen through 3D modeling software, and then use Selective Laser Sintering.
2.2 Preparation of porous titanium materials by organic sponge impregnation and sintering technology
The organic sponge impregnation and sintering is based on the organic sponge as the carrier, and the organic sponge is immersed in the slurry prepared by the metal, so that the organic sponge fully absorbs the slurry, then it is taken out and dried, and then sintered at high temperature. The material prepared by this method has high porosity, but the process is relatively complicated.
2.3 Preparation of porous titanium materials by metal injection molding
Metal powder injection molding is to first mix metal powder with organic binder, then heat it to maintain a molten state, inject it into the prepared mold for solidification, and then degrease to remove the binder in the formed blank, and finally sinter. The method is capable of producing small pieces of porous titanium with great design flexibility, combining the properties of powder metallurgy (such as low cost, simplicity, flexibility in choosing components) with the properties of injection molding (such as making complex parts and rapid production).
2.4 Preparation of porous titanium materials by infiltration casting combined with acid etching
Wang et al. injected titanium liquid into the wound molybdenum wire, and then etched the molybdenum wire, and the prepared porous titanium material had a porosity of 32-47%, a modulus of 23-62 GPa, and a strength of 76-192 MP.