Overview
As early as 1791, British chemist Gregor discovered titanium metal when he was studying rutile, but the extraction of elemental titanium failed repeatedly. It will become very active at high temperature, and will react with oxygen, nitrogen, carbon and other elements in the air during the refining process. It was not until 1910 that American chemist Hunter extracted metal titanium with a purity of 99.9% for the first time. Studies have shown that titanium accounts for about 0.42% of the total weight in the earth's crust, which is 16 times the total of copper, nickel, lead, and zinc. It ranks seventh in the metal world, and there are more than 70 kinds of minerals containing titanium.
The current surge in titanium production has been dubbed "the metal of the 21st century". Due to the unique physical and chemical properties of titanium metal, it has been used in aviation, medical and other fields.
Titanium has a steel-like appearance with a silver-gray luster and is a transition metal
nature
After continuous experiments, scientists finally discovered the unique physical and chemical properties of titanium. In terms of physical properties, it has a silver-white metallic luster, looks much like steel, and has a density of 4.5g/cm. , higher than aluminum but lower than iron, copper, nickel, the density is relatively small. Its strength ranks first among metals, 3 times that of stainless steel and 1-3 times that of aluminum alloys. It has a melting point of 1725°C and a boiling point of 3260°C. The latent heat of fusion is 3.75kcal/gram atom, the latent heat of vaporization is 102.5～112.5kcal/gram atom, the critical temperature is 4350℃, and the critical pressure is 1130atm. It also exhibits extremely strong corrosion resistance, low temperature toughness, and poor physical properties of electrical and thermal conductivity. In terms of chemical properties, it is a metal that is easily passivated. It is easily oxidized in air and aqueous solutions to form a stable oxidative protective film. This oxide film can even resist the effect of aqua regia. Therefore, titanium It is particularly resistant to corrosion, and because its chemical properties are very active at high temperatures, it is easy to interact with non-metals such as 0, N, H, S and halogen elements, so refining titanium metal will easily introduce impurities, which will affect the mechanical properties of titanium. performance has a certain impact. The above-mentioned physical and chemical properties of titanium determine the use, coupled with its relatively abundant reserves on the earth, so people will not waste this precious resource in vain.
Surface modification and strengthening
The surface modification of titanium is mainly to form a coating of hydroxyapatite on the surface of titanium metal, which is an important inorganic component of bone tissue and increases the bonding between biological materials and bone.
Modification of Surface Morphology Using Mechanical Methods
Change the roughness and shape of the implant surface, and promote the growth of tissue cells, so as to penetrate into the response of the cell tissue to the implant. Mainly use mechanical methods such as cutting, polishing, sandblasting to complete the cleaning of the surface and the removal of impurities.
Surface Modification Strengthening by Chemical Methods
A modification method that initiates a chemical reaction during the modification process.
(1) Chemical treatment. The oxide layer and contaminants on the titanium surface are removed by acid treatment, and the titanium surface is cleaned. The biological activity of titanium metal surface is enhanced by alkali heat treatment. This method can form relatively stable hydroxyapatite.
(2) Electrochemical treatment method. Anodizing. This chemical treatment method is relatively traditional. Through the action of an electric field, a chemical reaction occurs on the surface of the anode and a porous oxide film is formed. This oxide film is extremely small, ranging from several hundred nanometers to several micrometers, which improves the binding and wear resistance of biological materials. Micro-arc oxidation. A ceramic film is formed on the surface of titanium metal, which is an oxide film with larger pore structure and three-dimensional structure, which increases the hardness, bonding degree and wear resistance of biological materials. The purpose of electrodeposition technology is to deposit a layer of bioceramic coating on the surface of titanium, which is generated by adjusting the concentration of electrolyte and electric field strength. This method is relatively simple and efficient, and has a good effect on the biocompatibility and activity of biomaterials.
(3) Sol-gel method. It is also achieved by coating. The ingredients of the coating are used to make a sol, which is evenly covered on the surface. After the sol is volatilized, the reaction and cross-gelation occur rapidly, and the coating can be formed after drying or heat treatment. Through temperature adjustment and organic additives, the type of coating, crystallinity, pore size, etc. can be easily changed.
(4) Chemical vapor deposition. Vapor-phase chemicals produce chemical reactions on the titanium surface, and non-volatile substances are deposited to form thin films. Can improve wear resistance, corrosion resistance and biocompatibility.
(5) Biochemical modification method. Some macromolecular substances are immobilized on the surface of biomaterials to regulate cell and tissue responses. Amino acids, polypeptides, proteins, growth factors, etc. can be used. It can promote the adhesion of adhesion proteins and affect the adhesion strength and extensibility of cells.
Titanium particle reinforcement
reinforce purpose
Biomaterials need to achieve a balance between mechanical properties and the biological effects of materials. The research on composite materials provides a solution, both in terms of the bonding stress between the implant and the tissue, and in the induction of the implant to bone growth. Got good results. Titanium-based composite materials can be prepared through particle reinforcement, and now the most widely used composite materials are titanium and ceramics.
reinforcement method
(1) Strengthening of fine-grained materials. Using applied force to activate dislocations in adjacent particles, thereby affecting plastic deformation, with sufficient dislocation sources to form high-strength stress concentration fields, thereby improving the stress continuity of biomaterials
(2) Grain strengthening of sedimentary facies. The strength of the material is improved by the interaction between the dislocation and the precipitated phase of titanium and ceramics, and the particles of the precipitated phase are dispersed, which effectively hinders the dislocation movement of the composite material. After the effect of solid solution strengthening is achieved, the weakening of the plasticity of the material can be reduced. [4] Because of the biophilic properties of titanium itself and its high strength and low density, biomedical materials reinforced with titanium metal have become the main part of today's medical materials. In order to make titanium metal better used in biological materials, it is a necessary process to strengthen titanium metal. A series of titanium-based composite biological materials are prepared through surface strengthening and particle strengthening, which can greatly solve the problem of biological materials. Wear resistance, stress persistence, corrosion resistance and fatigue resistance, biological activity and biocompatibility, etc., enable titanium metal biomaterials to better perform its role in the replacement and repair of diseased and damaged tissues and organs. Development and treatment of patients by providing excellent treatment
biomaterials
Advantages and disadvantages of titanium metal as a biological material
Titanium metal biomaterial is the best choice for comprehensive performance. Titanium metal has the biggest advantage of low density, high elasticity matching with human body, and corrosion resistance, fatigue resistance, non-toxicity, and highest biocompatibility, so it has become the most widely used biological material. Titanium metal artificial joints, vascular stents, heart valves and dental implants have been widely used in clinical treatment as medical devices, and have upgraded the simple treatment of repair and orthopaedics to an alternative treatment for human diseased tissues and organs, which has greatly promoted the The degree of restoration of human function.
Disadvantages of Titanium Biomaterials
(1) It is difficult to combine with biological tissues. The bone regeneration ability of titanium metal biomaterial implants is poor, and the degree of integration with surrounding tissues is not high. There is an oxide layer on the surface of titanium, which is an inert biological material. After implantation, a layer of protein from biological solution will be adsorbed on the surface of the material to form a protein film, which will be surrounded by this layer of fibrous film, and then affect the implant and the implant. The combination of human body will also affect cell morphology and function due to cell adhesion, thereby changing cell proliferation, differentiation and gene expression. There are three binding methods between biomaterials and human tissues: morphological combination, biological combination and biological activity combination. The first two methods can easily lead to discontinuity of stress transmission. The morphological combination is only the surface of the implant and the human tissue. The mechanical locking is achieved by the biological combination, and the material-tissue combination is realized through the pores. The two combination methods do not have the continuity of stress transmission, and both easily lead to the loosening of the implant. The most ideal bonding method is biologically active bonding, which realizes the chemical bonding between the implant and the bone tissue. The implant and the bone tissue are not bonded through the intermediary of soft tissue, which realizes the long-term use of the implant in the human body. It is possible.
(2) The improvement of wear resistance. Titanium has the characteristics of poor wear resistance, and it is easy to oxidize and fail at high temperature. In the biological environment for a long time, there may be dissolution of wear particles or metal ions. Implants may accelerate corrosion due to wear, affect the surface properties of the implants, and may change its strength and various mechanical properties, and the properties of the implants themselves may degenerate. In addition, the produced abrasives can also dissolve into the surrounding tissue, which may cause inflammation and even tissue mutation, which can cause some toxic side effects and lead to implant failure. At the junction of the implant and the human body, the generation of tumor tissue may also be caused by the generation of wear objects.
(3) Solving the disadvantages of titanium metal biomaterials On the basis of retaining the original advantages of titanium metal, strengthening titanium and titanium alloys to solve biocompatibility, wear resistance, antibacterial properties, etc. can effectively improve the implantation. The use period and function of entering the body can better heal the diseased and damaged tissues and organs of patients.
application
Since the discovery of titanium, scientists have been exploring and experimenting with its application fields in order to benefit mankind and make it an important resource that contributes to the development of human civilization. Up to now, the application of titanium metal is mainly concentrated in the following fields.
Aviation and aerospace applications
At the beginning of the 20th century, people invented the airplane, which opened a new era of human aerospace. The early aircraft manufacturing materials were mainly wood, but they had the defects of brittleness, breakage and decay. With the application of aircraft in the first and second world wars, people had higher and higher requirements for the performance of aircraft, so the plasticity was good. , High-strength, easy-to-process, and light-weight aluminum alloy aircraft came into being, but aluminum alloy aircraft has the shortcomings of high temperature resistance and wear resistance. In order to solve the above problems, scientists have been looking for a metal that can replace aluminum alloys to make aircraft skeletons, so titanium entered the field of vision of aircraft manufacturers. It can be seen from the properties of titanium that titanium has low density, high thermal strength and lasting strength, low sensitivity to crack propagation under vibration load and impact load, and good corrosion resistance. The strength is comparable to that of steel, but the weight is 57% of that of steel. Therefore, it is a trend to use titanium alloys instead of aluminum alloys to manufacture aircraft. In modern aircraft manufacturing, people generally use aircraft engines and casing structures. High-strength titanium and titanium alloys to replace aluminum alloys.
At present, the proportion of aircraft mainly made of titanium alloys in the aviation field has an overwhelming advantage, especially the aircraft of the US military are mostly titanium alloy products. Such as its hypersonic reconnaissance aircraft SR-71. The mass of titanium alloy in this aircraft accounts for 92% of the total mass of the whole aircraft, and B titanium alloy is used for the first time. For another example, the fourth-generation fighter F-22 in the United States, space planes, and titanium also account for 50% to 60%. Also, the proportion of titanium in F-14, F-15, F-18 Hornet, F-117 Nighthawk, B-1 bomber, B-2 bomber is 24%, 27%, 13%, 25%, 22%, and 26%. In the weight composition of supersonic aircraft, the amount of titanium used accounts for more than 95%. Facts have proved that it is difficult to develop supersonic aircraft without using titanium alloys, because aircraft made of titanium alloys can reduce the mass of about 5t compared with aluminum alloys. Speed increased. In addition, in the development of rockets and other aero-engines, the application ratio of titanium is also increasing, generally accounting for 18% to 25% of the total weight. According to research, half of the world's titanium production is used in aero-engines upper circle
Applications in the medical field
Titanium metal is also widely used in the medical field:
First, it is widely used in tooth restoration and reconstruction. Because titanium has good corrosion resistance and human body affinity, the human body does not have allergies when it comes into contact with it, and coupled with its extremely low thermal conductivity, it can reduce the thermal stimulation to the dental pulp of the crown teeth, so it is highly favored by dentists. favor. Since the 1980s, developed countries have used titanium to repair teeth. This kind of denture made of titanium alloy is of great help to restore the function of teeth. Moreover, gloss, wear resistance and corrosion resistance all meet the requirements of permanent restorations, and are welcomed by people. At present, the research on titanium and titanium alloys has become one of the hot issues of dental alloys.
Second, it can also be used in human bone, tissue transplantation and reconstruction. In a large number of surgical operations, the transplantation, reconstruction and connection of human bones and tissues is a common occurrence. To become a replacement material for human bones and joints, it should have the following basic properties: light weight, high strength, biocompatibility, corrosion resistance, and the tissue reaction that occurs in the implanted body cannot cause deterioration of the material. The physical and chemical properties of titanium and titanium metals meet these performance requirements, which must remain functional over the expected life and not degrade when subjected to fatigue, wear, corrosion and shock loads. Therefore, using titanium to make artificial bones can not only meet the above requirements, but also according to experiments, human cells can regenerate bones and grow on them.
At present, titanium metal has been widely used in artificial bone joints, artificial bones, joint foot plates, broken bone fixators, intramedullary nails, artificial heart valves, skulls and other clinical replacement and repair. Practice has proved that the application effect of titanium is good. It was found that there were cases that were obviously excluded from the human body. Third, surgical instruments made of titanium have long become the favorite instruments of doctors. Since the development of surgical instruments, titanium has become the protagonist. The first-generation surgical instruments were mainly made of carbon steel, and the second-generation surgical instruments were made of austenitic, ferritic and martensitic stainless steel. The instruments made of titanium can effectively avoid the above problems, so there is a third generation of surgical instruments - titanium surgical instruments, which are light in weight, corrosion resistance, elasticity and softness. The first and second generation surgical instruments It can be used repeatedly after surgery, so surgical instruments made of titanium are favored by surgeons.
applications in industrial production
Since titanium has strong corrosion resistance in acid, alkali and smoke medium, it has the characteristics of good stability. For example, in the chlor-alkali industry, titanium metal is widely used as a metal anode and a titanium wet chlorine cooler, which has received very good economic results. It can be said that it is a great revolution in the chlor-alkali industry. Taking advantage of the good stability of titanium, it has become a good structural material in the process of petroleum refining and petroleum refining, and has a wide range of applications in heat exchangers, reactors, high-pressure vessels and stills. For another example, because titanium has a good gettering function as an active metal, it has become a degassing agent in the steelmaking industry, which can combine the oxygen and hydrogen that are precipitated when the steel is cooled. If a small amount of titanium ((Ti) = 0.1%) is added to the steel, the steel can be hard and elastic. Therefore, titanium has become an important alloy additive in the steel and aluminum industries. In the copper hydrometallurgy industry, titanium is widely used in the electrolysis of copper, manganese, cobalt and nickel.
