Advanced materials refer to those recently researched or under development that have exceptional performance and special functionalities. These materials are of paramount importance for the advancement of science and technology, especially in high-tech and emerging industries.
This article provides a brief introduction to some of these innovative engineering materials.
1. Optical fibers
Optical fibers, abbreviated as fibers, are optical fibers used to transmit light information. As a medium for transmitting light waves, typical fibers consist of a core with a high refractive index and a cladding with a lower refractive index. In practical applications, hundreds or even thousands of fibers are combined into a certain type of cable structure.
For long-distance transmission, optical repeaters are needed to restore light signals that gradually decrease during transmission. The two main characteristics of optical fibers are light loss and transmission bandwidth; the first determines the transmission distance, while the second governs the information capacity.
Optical fiber development is currently focused on increasing repeater-free distance, reducing losses, and moving toward super-long wavelengths and ultra-wide frequency bands. The following are some types of optical fibers that have been developed and used:
(1) Quartz Fibers
Currently, communication fibers are mainly composed of high-purity fused quartz glass. Quartz fibers are chemically stable, have a small coefficient of expansion, excellent long-term reliability and abundant resources. However, they are somewhat fragile and further reduction of light loss is limited.
(2) Plastic Fibers
The core material of plastic fibers can be polymethylmethacrylate (PMMA) and polystyrene (PS), with fiber covering materials that can be fluoresin on PMMA or PMMA on PS material. Plastic fibers have many advantages, such as excellent flexibility, high resistance to breakage, light weight, low cost and simple processing.
However, due to high transmission loss, its applications mainly focus on transmitting power and image information over short distances.
(3) Sulfide Composite Fibers
The most typical sulfide composite glass fiber is the As-S system, which has a high melting point and good processability.
(4) Halide Crystal Fibers
Halide crystal fibers include single-crystalline CsBr and CrI and polycrystalline TiBrI, among others. Crystal fibers demonstrate low loss over a wide wavelength bandwidth of 1 to 10 μm and can be used for CO gas laser transmission.
(5) Fluoridated glass
Promising materials for ultra-low-loss infrared fibers currently under study include zirconium fluoride (hafnium) silicate glass, fluoride aluminate glass, and fluoride glass composed primarily of thorium oxide and rare earth fluorides.
Among them, zirconium (hafnium) silicate glass is considered the most promising material for long-wavelength communication fibers, with characteristics such as wide wavelength range, low dispersion and good processability.
Optical fibers can be used for transmission of computer information, allowing the establishment of flexible, high-speed, large-scale computer networks for data retrieval, bank account transactions, futures contracts, and potentially long-distance transmission of holographic images . They can also be used to transmit high-intensity lasers and manufacture fiber optic sensors, among other applications.
2. Superconducting Materials
In 1911, Dutch physicist Heike Kamerlingh Onnes discovered a sudden disappearance of mercury's resistance to the temperature of liquid nitrogen, 4.2K. This phenomenon is known as superconductivity, and materials that exhibit this are called superconductors.
The state in which a superconductor enters zero resistance is called the superconducting state. The temperature at which superconductivity appears is defined as the critical temperature, denoted as T, and is measured in Kelvin (K), the thermodynamic temperature scale.
It was later discovered that if a superconductor is cooled in a magnetic field, at the point where the material's resistance disappears, the magnetic field lines are expelled from the conductor, a phenomenon known as perfect diamagnetism or the Meissner effect. Superconductivity and diamagnetism are the two main characteristics of superconductors.
Superconducting materials have applications in various fields, including energy, transportation, information, fundamental science and healthcare. For example, in power systems, superconducting energy storage is currently the most efficient storage method, and the use of superconducting transmission can significantly reduce energy loss.
Superconducting magnets, with their high magnetic fields, low energy loss and light weight, can be used for magnetohydrodynamic power generation, directly converting thermal energy into electrical energy and significantly increasing the power output of generators.
The use of superconducting tunneling can create various devices characterized by high sensitivity, low noise, fast response and low loss, suitable for electromagnetic wave detection and promoting the practicality of precision measurement and testing technologies. In computers, Josephson junction computers made of superconducting materials can perform ten high-speed calculations per second, with small size and large capacity.
The magnetic levitation effect produced between superconductors and magnetic fields can be used to create superconducting maglev trains. Furthermore, the enormous magnetic fields generated by superconductors can be used in controlled thermonuclear reactions.
3. Vibration damping materials
Vibration damping alloys are functional materials that have vibration dampening capabilities while maintaining the required structural strength. They are alloys with high internal friction, allowing rapid decay of vibrations. Depending on their damping mechanisms, vibration damping alloys can be categorized into multiphase, ferromagnetic, twinned, and discordant types.
(1) Multiphase Alloys
Multiphase alloys comprise two or more phases, generally featuring a softer second phase distributed over a harder matrix. They utilize the repeated plastic deformation of the alloy's second phase to convert vibrational energy into frictional heat for damping.
Gray cast iron with flaked graphite is the most widely used multiphase damping alloy, typically employed in machine tool bases, crankshafts, cams and so on. Al-Zn alloy is another typical multiphase damping alloy used in devices such as stereo amplifiers.
(2) Ferromagnetic Alloys
These alloys utilize the magnetostriction of ferromagnetic materials and the rotation and movement of magnetic domains during vibration to consume vibrational energy for damping. Chrome steel with 12% chromium content and Fe-Cr-Al alloys are examples of ferromagnetic damping alloys, used in steam turbine blades, precision instrument gears, etc.
(3) Twinning leagues
Twinned alloys utilize the formation of fine twinned structures during phase change, absorbing vibrational energy through the movement of twinned grain boundaries. For example, the newly developed Mn-Cu-Ni-Fe alloy in Japan can halve the amplitude in a single vibration, suitable for engine parts, engine casings, washing machine parts and so on.
(4) Dislocation Garters
Dislocation alloys absorb vibrational energy due to mutual vibration between dislocations and interstitial atoms. Mg-Zr (w Zr A alloy =6%), for example, is used in gyrocompasses for missile guidance and in precision instrument holders as control devices, ensuring their normal functioning.
Mg-MgNi alloy not only has excellent damping properties, but also high strength and low density, making it an excellent vibration damping material for the aerospace industry.
4. Low temperature materials
The most dangerous failure mode of materials at low temperatures is low-temperature brittle fracture. Therefore, materials that work at low temperatures need to have excellent low temperature toughness. Furthermore, to avoid thermal deformations caused by changes between ambient and low temperatures, these materials must have a lower coefficient of thermal expansion and good workability.
Materials used under magnetic fields at low temperatures should normally be non-magnetic. Low-temperature metal materials mainly include low-alloy ferritic steel, austenitic stainless steel, nickel steel, duplex steel, iron-nickel-based super alloys, aluminum alloys, copper alloys, titanium alloys and so on.
Based on different usage temperatures, commonly used low-temperature materials can be roughly divided into the following three categories:
(1) Materials for -40 to -100 ℃: Low temperature materials used in this temperature range are mainly low carbon steel and low alloy steel such as alloy steel with 3.5% w No and manganese steel with low carbon and aluminum content 06MnVAl, with its lowest use temperature being -130°C.
They are mainly used in petrochemical industries, refrigeration equipment, engineering structures in cold regions, gas pipelines and compressors, pumps and valves operating at low temperature.
(2) Materials for -160 to -196°C: Low temperature materials used in this temperature range are mainly for liquefied natural gas and oxygen production industries.
Types include 18-8 austenitic stainless steel, which has excellent low-temperature toughness but lower strength and higher coefficient of expansion; nickel-based low temperature steel, such as steel with 9% w No (c c <0.1%), Ni (w No =5%) -Mo (w Mo =0.2%) steel, which has high strength, good low temperature toughness, reliable weldability and is increasingly used; High manganese austenitic steel 20Mn23Al, aluminum alloy 5083, etc.
(3) Ultra-low temperature materials for -253 to -269°C: These types of materials are mainly used to manufacture containers for storing and transporting liquid hydrogen and liquid chlorine, as well as parts in superconducting devices with strong magnetic fields.
The ultra-low temperature alloys that have been developed and are under research mainly include: ultra-low temperature austenitic stainless steel formed by adding carbon and nitrogen to type 18-8 stainless steel; austenitic stainless steel with high manganese content 15Mn26Al4; Ni (w No =12%) -Ti (w Ti =0.25%), Ni (w No =13%) -Mo (W Mo =3%) steel and Ni-based alloys.
5. Shape memory materials
In contrast to ordinary materials, the distinctive feature of shape memory materials is that they retain their deformation when stress is applied at low temperatures and do not disappear after the stress is removed. However, when heated above a certain intrinsic critical temperature, the material can fully recover its pre-deformation geometric shape, as if remembering its original shape.
This phenomenon is known as the shape memory effect. Materials that exhibit this effect are called shape memory materials. Both metallic memory materials and ceramics exhibit the shape memory effect through martensitic phase transformation, while polymeric memory materials exhibit this effect due to changes in their chain structure with temperature.
Shape memory materials are primarily shape memory alloys, of which there are dozens in use today. They can be roughly divided into:
1) Nickel-Titanium (Ni-Ti) Based: Composed of nickel and titanium in an atomic ratio of 1:1, these alloys have excellent shape memory effects, high heat resistance, corrosion resistance, strength and toughness to unparalleled thermal fatigue along with excellent biocompatibility. However, the high cost of raw materials and difficult manufacturing processes make them expensive and difficult to machine.
2) Copper-based: Copper-based alloys are cheap, easy to produce, have good shape memory effects, low resistivity and good machinability. However, the shape recovery rate decreases with prolonged or repeated use, which is a problem that needs to be resolved. The most practical copper-based alloys are Cu-Zn-Al, with others including Cu-Al-Mn and Cu-Al-Ni.
3) Iron-based: Iron-based shape memory alloys have high strength, good plasticity and are cheap, gradually gaining attention. Iron-based memory alloys currently under development and research mainly include Fe-Mn-Si and Fe-N-Co-Ti.
Recently, the shape memory effect has been discovered in ceramic materials, polymeric materials and superconducting materials, each with its unique characteristics, further expanding the application prospects of memory materials.
Shape memory materials have been widely applied in aviation, aerospace, machinery, electronics, energy, medical fields and daily life. For example, an American aviation company used the shape memory effect to solve the problem of connecting difficult-to-weld oil pipes on the F-14 fighter jet.
6. Hydrogen Storage Materials
Hydrogen, being a pollution-free and abundantly available energy source on Earth, should be a primary energy source in the future. However, hydrogen storage represents a significant challenge. A functional material that can absorb and store hydrogen in the form of metal hydrides and release the stored hydrogen when needed is called a hydrogen storage material.
Hydrogen storage materials absorb hydrogen to form metal hydrides and release heat upon cooling or pressurization. On the other hand, they revert to metal and hydrogen, releasing hydrogen gas and absorbing heat when heated or depressurized. The density of hydrogen in hydrogen storage materials is 1,000 to 1,300 times that of gaseous hydrogen.
Currently, the main hydrogen storage materials under study and development include:
Magnesium-based: These materials have a large hydrogen storage capacity and are low cost. The disadvantage is that they need temperatures above 250°C to release hydrogen. Examples include Mg2Ni, Mg2Cu, etc.
Titanium-based: Titanium-based hydrogen storage alloys have strong hydrogen absorption capacity, are easily activated at room temperature, are low in cost, and are suitable for large-scale applications. Examples include binary alloys such as titanium-manganese, titanium-chromium and ternary and multi-element alloys such as titanium-manganese-chromium, titanium-zirconium-chromium-manganese, etc.
Zirconium-based: Characterized by excellent hydrogen storage properties even at temperatures above 100°C, they can absorb and release large amounts of hydrogen quickly and efficiently, making them suitable for high-temperature hydrogen storage materials . Examples include ZrCr2, ZrMn2, etc.
Rare earth-based: Rare earth hydrogen storage alloys, represented by the nickel-lanthanum alloy LaNi, have good hydrogen absorption properties and are easily activated. They release hydrogen quickly at temperatures above 40°C, but their cost is relatively high.
To reduce costs and improve performance, mixed rare earths can replace lanthanum, or other metallic elements can partially replace the multi-element hydrogen storage alloy formed by mixed rare earths and Ni.
Iron-based: The most common iron-based hydrogen storage alloy is the iron-titanium alloy. It has excellent hydrogen storage properties and is low cost, but activation is relatively difficult.
7. Magnetic Materials
Materials in nature can be classified into three types based on their magnetic properties: diamagnetic, paramagnetic and ferromagnetic. Magnetic materials are substances that possess ferromagnetism.
Magnetic materials are essential in industries such as electronics, energy, electric motors, instrumentation and telecommunications. Based on their magnetic properties, magnetic materials can be categorized into soft magnetic materials and hard magnetic materials.
Soft magnetic materials are those that are easily magnetized under an external magnetic field and easily demagnetize when the external field is removed. They are characterized by high permeability, high resistance to magnetic induction, low coercivity and minimal energy loss during magnetization and demagnetization.
There are many types of soft magnetic materials, the most common being pure electric iron, silicon steel sheets, Fe-Al alloys, Fe-Ni alloys and ferrite soft magnetic materials.
Hard magnetic materials, also known as permanent magnetic materials, are those that can generate a magnetic field without an external power supply once magnetized.
These materials are characterized by considerable coercivity and residual magnetism and are widely used in magnetoelectric instruments, loudspeakers, permanent magnet generators, and communication devices.
The hard magnetic materials currently in use and under study can be divided into metallic hard magnetic materials, ferrite hard magnetic materials, rare earth hard magnetic materials and neodymium-iron-boron hard magnetic materials.
In addition, there are some special-purpose magnetic materials, such as magnetic memory materials for recording information (manufacturing magnetic tapes, magnetic disks, etc.), materials used for recording heads, magnetic memory materials in electronic computers, and magnetic compensation materials in precision instruments.
