Silver nanowire “ink” makes paper-based printing electronic products possible

By suspending tiny metal nanoparticles in liquids, Duke scientists are developing conductive inks for inkjet printers that can print inexpensive, customizable circuit patterns on any surface virtually .

Printed electronics have been widely used on a number of devices, such as anti-theft radio frequency identification (RFID) tags that are usually found behind new DVDs. It currently has a major drawback: in order for the circuit to work, it must first be heated to fuse all of the nanoparticles into a single conductive filament, which makes it impossible to print circuits on cheap plastic or paper.

A new study by Duke University researchers shows that adjusting the shape of the nanoparticles in ink eliminates the need for heating.

By comparing the conductivity of thin films made from different shapes of silver nanostructures, the researchers found that electrons made of silver nanowires are much easier to fabricate than films made of other shapes such as nanospheres or microdisks. In fact, the flow of electrons through a film made of nanowires is so easy that they can be used in printed circuits without melting them together.

Benjamin Wiley, an assistant professor of chemistry at Duke University, said: “the conductivity of nanowires is 4000 times higher than that of commonly used silver nanoparticles that can be found on printed RFID tags. So if you use nanowires, then you don’t need to heat the printed circui to such a high temperature that you can use cheaper plastic or paper.”

Wiley added: “in addition to these silver nanowires, I really don’t think there is anything else that can be simply printed out like this. Without any post-processing, it can be directly conductive.”

Applications of these types of printed electronics may go far beyond smart packaging. Researchers envision using this technology to make solar cells, printed displays, LEDs, touch screens, amplifiers, batteries, and even some implanted bioelectronic devices.

Wiley said that silver has become a raw material for the manufacture of printed electronic materials, and many recent studies have shown the measurement of the electrical conductivity of silver nanostructure films of different shapes. However, experimental errors make it difficult to make direct comparisons between different shapes, and there are few reports that relate the conductivity of the film to the total mass of silver used, which is an important factor when using expensive materials.

“We want to eliminate any extra materials from ink, just focus on the silver content in the film and the link between the nanostructures as the only source of variation,” said Stewart, another graduate student.

Stewart uses known recipes to make silver nanostructures with different shapes, including nanoparticles, microchips, and short and long nanowires. These nanostructures are then mixed with distilled water to make a simple “ink.” He then invented a quick and easy way to make films using glass slides and double-sided adhesive tapes that can be easily found in any laboratory.

Stewart said: “We used punches to punch wells out of double-sided tape and stick it to the glass.” By adding a precise amount of ink to each well of the tape, the well was then heated to a temperature of The relatively low temperature at which the water evaporates or the relatively high temperature at which the structure begins to melt, he has obtained a variety of films for testing.

The research team said that they are not surprised that the long nanowire film has the highest conductivity. Electrons usually pass easily through a single nanostructure, but they tend to get stuck when they have to jump from one structure to the next, Wiley explained, while long nanowires greatly reduce the number of electronic “jumps.”

However, they were surprised by the intensity of this change. “The resistivity of long silver nanowire films is orders of magnitude lower than that of silver nanoparticles, and only ten times larger than pure silver,” Stewart said.

The team is now experimenting with aerosol inkjet printers to print silver nanowire inks in available circuits. Wiley said that they also want to explore whether silver-plated copper nanowires can produce the same effect, which is much cheaper than pure silver nanowires.

“King of whiskers” silicon carbide (SiC whisker) and its related toughened composites

With the rapid development of modern science and technology, the fields of aerospace, energy and other fields put forward higher requirements for the performance of structural materials. The development of new composite materials with high toughness, wear resistance, corrosion resistance and good thermal/chemical stability has become one of the hotspots in material research. Among them, whisker toughened composite materials have attracted much attention due to their excellent properties.

SiC whisker has the reputation of “king of whiskers” and has the advantages of high strength and high modulus of elasticity. The addition of silicon carbide whiskers has significantly improved the fracture toughness and flexural strength of composites. As an excellent reinforcing and toughening agent, SiC whisker toughened metal-based, ceramic-based and polymer-based composite materials have been widely used in machinery, chemical, defense, energy, environmental protection and other fields.

First, the nature of silicon carbide whiskers

SiC whisker (SiC whisker) is a highly oriented single crystal fiber with a diameter ranging from nanometer to micrometer. Its crystal structure is similar to that of diamond. There are few chemical impurities in the crystal, no grain boundaries, and few crystal structure defects. The phase composition is uniform. It has high melting point, low density, high strength, high modulus of elasticity, low thermal expansion rate, and wear resistance, corrosion resistance, and high temperature oxidation resistance. It is mainly used in toughening applications where high temperature and high strength applications are required.

The relevant indicators are shown in the following table:
Melting point: >2700 °C
Density: 3.21g/cm3
Tensile strength: 2100kg/cm2
Modulus of elasticity: 4.9×10^4kg/cm2

SiC whisker has two crystal forms of α type (hexagonal and rhombohedral structure) and β type (face-centered cubic structure), and the β type is superior to α type in all aspects. At present, only β-SiC whisker has achieved industrial scale production, so the research and use is mainly β-SiC whisker.

Second, the research and application of silicon carbide whiskers

At present, SiC whisker has been widely used to toughen metal-based, ceramic-based and polymer-based composite materials. The following is a brief introduction to the application of various fields.

1. SiC whisker toughened metal matrix composite
Under the premise of ensuring good wettability without serious interface damage and damage to whiskers, the current preparation process is more mature SiC whisker toughened aluminum matrix composites. Almost all commercial aluminum alloys can be successfully compounded with SiC whisker by die casting or powder metallurgy and have been put into practical use.

The main manufacturers of SiC whisker toughened metal matrix composite products are ACMC, Mitsubishi Electric, and US Naval Weapons Center. The products have the advantages of light weight, high strength, heat resistance, low thermal expansion coefficient and good degassing. It is used in aerospace and military fields, such as aircraft skins, airfoils, vertical tails, missiles, ultra-light space telescopes, etc. It can also be used in automobiles, machinery and other components and sports equipment.

2. SiC whisker toughened ceramic matrix composite
SiC whisker toughened ceramic materials are mainly Al2O3, ZrO2, mullite ceramics and the like. As the composite technology continues to mature, SiC whisker toughened composite materials such as Si3N4, ZrB2 and glass ceramics have emerged.

a. Al2O3 ceramic matrix composite
Alumina ceramics have the advantages of high melting point, high hardness, wear resistance and structural stability, but their strength is low. After toughening and strengthening by SiC whisker, the toughness can reach above 9MPa·m1/2, and the strength can reach 600-900Mpa.

The use of silicon carbide whiskers for further broaden the use of alumina has been applied to wear parts, cutting tools and certain components of internal combustion engines.
Among them, SiC whisker toughened ceramic cutting tool materials have excellent performance in difficulty of cutting alloys such as high-temperature alloys due to their good fracture toughness and thermal shock resistance, prolonging the service life of the tool, and the cutting efficiency is much higher than ordinary tools and have great application potential.

b. ZrO2 ceramic matrix composite
Zirconium oxide ceramics are widely used as refractories, fast ion conductors, high temperature heating elements, etc. due to their high chemical stability, high melting point, and good high temperature conductance. Due to the failure of the phase transformation toughening mechanism at high temperatures, its high temperature mechanical properties are seriously deteriorated. The addition of SiC whisker can increase its modulus of elasticity, hardness, high temperature strength and toughness, thereby expanding its application range.

At present, SiC whisker toughened ZrO2 ceramics can be applied to gas turbine rotors, turbine stator blades, various ceramic engine components, ceramic tools, wire drawing dies, bearings, etc. used above 1350 °C.

c. mullite ceramic matrix composite
Mullite ceramic has the advantages of uniform expansion, good thermal shock resistance, high hardness and low temperature creep value. It is a high-quality refractory material, but its toughness is relatively low, thus affecting its practical application.

Huang Zhengren from the Shanghai Institute of Ceramics of the Chinese Academy of Sciences used 30 vol% β-SiC whiskers to reinforce mullite. Under SPS sintering conditions, the material strength is about 10% higher than the hot pressure, 570 MPa, and the fracture toughness is 4.5 Mpam 1/2. Mullite increases by more than 100%

d. ZrB2 ceramic matrix composite
ZrB2 ceramics have the advantages of high melting point, high hardness, excellent wear resistance and chemical stability. They are typical ultra-high temperature ceramics and can be used in metallurgical industry, casting of electronic equipment and refractory metals. Due to the low toughness, it limits the further expansion of its application range. The addition of SiC whisker to the ZrB2 matrix improves the toughness of the material.

Studies have shown that when silicon carbide whiskers are added in a volume fraction of 30%, the toughness of the material can reach 6.33 MPa·m 1/2, which is 71% higher than that of pure ZrB2 ceramics, and 33% higher than that of SiC particles toughened ZrB2 ceramics. %. SiC whisker toughened ZrB2 ceramics can be used in thermal protection equipment, front compartments of supersonic aerospace vehicles, and heat-resistant components such as rocket nozzles.

e. SiC whisker toughened silicon nitride ceramics
SiC whisker toughening Si3N4 ceramics is one of the main ways to improve its fracture toughness and stability. Previous studies have shown that whisker toughening effect depends not only on the degree of whisker dispersion, whisker size and volume fraction, but also on the spatial position and orientation of whiskers.

Researchers have studied the whisker orientation in silicon nitride-based composites of SiC whiskers. When the whiskers are in the same direction and the whiskers are weakly connected to the substrate interface, the fracture toughness in this direction has a maximum value. The strength and fracture toughness were 1038 MPa and 10.7 MPa m 1/2, respectively.

A series of excellent physical and mechanical properties and chemical properties of silicon nitride ceramics have great market and application potential in high temperature structural materials, tool ceramic materials, wear resistant ceramic materials and wear resistant ceramic materials. With the deepening of whisker toughening research, the application of silicon nitride ceramics in tools, bearings, engines, insulation materials, etc. will be more perfect.

f. glass ceramic matrix composite
The addition of SiC whisker to the glass ceramic not only preserves the advantages of easy glass forming, but also increases the strength and toughness of the material by more than two times.

For example, SiC whisker toughened and reinforced bioactive glass-ceramic composites have a toughness of 4.3 MPa·m 1/2, a strength of up to 460 MPa, and a Weibull coefficient of up to 24.7, due to the non-toxicity of SiC whisker and the bioactivity of bioglass ceramics. The material has a life expectancy of more than 50 years under the stress equivalent to the flexural strength of the human body, and is the bio-ceramic material with the longest life expectancy. It can be used to prepare artificial teeth and bone repair materials and bones such as bones and joints. Tissue engineering scaffolding material.

3. SiC whisker toughened polymer composite
As a toughening and reinforcing agent for polymer materials, SiC whisker does not increase the melt viscosity, but also significantly improves the toughness and elongation of the material. It can be used to prepare parts with complex shapes, high precision and high surface finish.

Studies have shown that the addition of SiC whisker with a mass fraction of 5% in PVC can increase the toughness of the material by 50% and the elongation by more than four times. Therefore, SiC whisker is compounded with polymers such as PVC to produce composite materials with excellent properties, such as: jet engine oil tank blades, helicopter propellers, aircraft and automotive components.

Nano-tungsten oxide & titanium dioxide — new advanced nano transparent heat-insulating coating

Breif introduction:
Nano transparent thermal insulation coating is a ceramic thermal insulation water-based coating. It adopts the latest composite ceramic nano-tungsten oxide insulation material and is designed to absorb infrared infrared light. Nano transparent thermal insulation coatings are unique environmentally friendly ingredients – nano tungsten oxide liquid, titanium dioxide can remove odors in the surrounding environment, and degrade formaldehyde and other harmful substances. Nano-transparent thermal insulation coating is a new type of coating that meets the requirements and characteristics of environmentally friendly coatings.

Principle of heat insulation

The principle of thermal insulation of nano transparent thermal insulation coatings is as follows:
1 Nano transparent heat-insulating coating uses advanced production technology to make nano-tungsten oxide and TiO2 into nano-coating materials suitable for surface coating on glass, ceramic tile, metal, cement, PE, PET, PC, PP, PVC, etc. Transparent nano-tungsten oxide, which absorbs near-infrared rays and blocks ultraviolet rays;
2 Nano-tungsten oxide has stable chemical properties and small physical changes caused by external environment such as heat and humidity, so it can maintain permanent semiconductor materials, effectively block infrared radiation and ultraviolet radiation, block infrared effect by 95%, block UV The effect is up to 99%, the coating material has excellent compatibility with the substrate, the spreading and leveling performance is good, the adhesion is strong, and the long-lasting does not fall off;
3 Ceramic powder can effectively block ultraviolet light up to 99%, and can reflect more than 90% of visible light, can block infrared rays up to 92.5%, ceramic molecules can prevent excessive water vapor from entering, and allow normal amount of water molecules to pass, This greatly increases the sunscreen insulation capacity of the entire building surface;
4 Nano transparent heat-insulating coatings are safe and environmentally friendly. All components are nano-inorganic, which is a new type of environmentally friendly coating.

Characteristics:

The characteristics of nano-transparent thermal insulation coatings are as follows:

1 Thermal insulation
The nano transparent heat-insulating coating effectively blocks the infrared rays and ultraviolet rays in the sunlight from entering the room, shielding more than 99% of the ultraviolet rays, blocking the infrared rays of more than 75%, and lowering the indoor temperature by 3-5℃, so that the exposed objects can be dried. The temperature is lowered by 6-10℃.

2 transparent
After the nano transparent heat-insulating coating is applied, a micro-film layer of about 8-10 microns is formed on the surface layer of the substrate, and the visible light transmittance is as high as 70% or more, which does not affect the visual field.

3 energy saving
The effect of heat insulation and heat preservation of nano-transparent heat-insulating coatings extends the indoor and temperature-equal temperature rise and fall, reduces the number of air-conditioning cold or heat machines, and saves air-conditioning energy consumption by 25-35%.

4 Environmental protection
Nano-transparent heat-insulating coatings are water-based coatings that do not contain harmful substances such as TVOC, free formaldehyde, lead, chromium, cadmium, and mercury. They are environmentally friendly and meet the national environmental quality standards. They are a new type of environmentally friendly coating.

5 health
Nano-transparent heat-insulating coatings prevent UV rays from fading and aging of furniture, fabrics, carpets, curtains, murals, etc., and prevent UV-induced skin cancer, cataracts and other diseases.

Application range
1 The glass surface is insulated and resistant to ultraviolet rays;
2 External wall latex paint is insulated and antistatic;
3 PE, PET, PC, PP, PVC insulation, anti-static;
4 lamp cup, lampshade insulation, antistatic, etc.

Nano SiO2 is widely used in many aspects, and here are some applications of silica nanopowder in coatings.

1. Application of nano-silica SIO2 in architectural coatings
Adding nano-silica to architectural coatings can improve coating adhesion, scrub resistance, weather resistance, strength hardness, toughness, elasticity, anti-aging, anti-bacterial, anti-ultraviolet and other characteristics, significantly improve coatings’ property of self-cleaning, waterproofing, anti-seepage, anti-wear, anti-corrosion, color retention and other properties, so it has a good effect on modified exterior wall coatings.

2. Application of nano-silica in metal protective coatings
The addition of nano-SIO2 and TIO2 can increase the strength of the carbonaceous layer after the expansion of the fire retardant coating and prolong the fire resistance of the steel structure. When adding 1.5% by mass of nano-SIO2, the fire endurance of 110 min can be achieved.

3. Application of nano-silica in plastic coatings
The modified nano silica is beneficial to improve the thermal stability of the composite, delay the thermal oxidative degradation of the polyethylene, and significantly improve the flame retardant performance of the halogen-free flame retardant polyethylene. A material with better mechanical properties and flame retardancy.

4. Application of nano-silica in UV-curable coatings
Nano-silica has extremely strong UV absorption and infrared reflection properties. The spectrophotometer test shows that the absorption rate of ultraviolet light within a wavelength of 400 nm is as high as 70% or more, and the reflectance of infrared light within a wavelength of 400 nm is also more than 70%. It is added to the coating to form a shielding effect on the coating to achieve anti-UV aging and heat aging, and at the same time increase the thermal insulation of the coating.

5. Application of nano-silica in color inkjet paper coating
There are a large number of micropores and cracks on the surface of high gloss color inkjet paper. Primer can significantly improve sheet properties, and nanoscale silica provides high smoothness, absorbency, color density, and image quality.

6. Application of nano-silica in wood coatings
In the waterborne wood coating, the addition of the nano silica gel can improve the hardness of the coating film, improve the water resistance and aging resistance of the coating film, and at the same time improve the blocking resistance of the coating film. In the closed primer, the nano-silica gel has a small particle size and can be easily inserted into fine pores of wood or fiberboard. The pores are filled and sealed, and can be bonded to the substrate after drying and forming. Insoluble in water coating, which has a good sealing effect. A suitable nano-silica sol can be properly blended in the aqueous primer to accelerate the release of moisture in the primer.
It can improve the drying speed, increase the hardness of the coating film, and reduce the cost of the primer. Adding a certain nano-silica sol to the water-based topcoat has obvious improvement in water resistance, anti-blocking and hardness properties.

Application of nano gold catalyst

There are mainly three types of nanoparticles catalysts. One is to directly use metal nanoparticles as a catalyst. This type of catalysts are mainly nano-powders of noble metals (AG, PD, PT, RH, etc.), and nano-powders of base metals such as FE, CO, and also NI have also been applied as catalyst. When some noble metal nanoparticles are used as catalysts, in addition to increasing the reaction rate, they also have good selectivity, and this selectivity is related to the particle size of the nanoparticles. The second is to load the metal nanoparticles onto the porous support as a catalyst. Commonly used carriers are porous carriers such as AL2O3, SIO2, MGO, TIO2 and activated carbon, and the supported metal nanoparticles have a particle diameter of about 1-20nm. A plurality of metal nanoparticles can be simultaneously loaded or formed into composite metal nanoparticles and loaded onto the same carrier, which can further increase the selectivity of the catalyst.

Application of nano gold catalyst
Gold has been considered as a low-activity catalytic material for a long time, but when gold is dispersed to the nano scale, it exhibits high catalytic activity. Therefore, nano gold catalysts have attracted widespread attention. Nano gold catalysts and become an important representative of nano catalysis technology. Let’s select some of the ions that have been successfully applied, which are summarized as follows:

1. Catalytic CO to CO2
The research in the past 10 years shows that when the nano Au particles are loaded onto the metal oxide by deposition or co-precipitation, the catalytic activity is very high, especially in the process of catalytic oxidation of CO to CO2 at low temperature, the catalytic ability and efficiency are better than other silicon. The metal is much higher.

2. Epoxidation of propylene
Propylene Oxide PO is an important chemical raw material used primarily in the production of polyurethane and polyol raw materials. For the gas phase in which O2 and H2 are present, the supported AU nanoparticles can catalyze the propylene to PO, and the epoxidation can be completed in one step, and no other by-products other than water.

Among the single metal oxide supports, only anatase TIO2 enables gold to selectively catalyze the oxidation of propylene to propylene oxide PO.

3. Hydrogenation of unsaturated hydrocarbons
A distinct feature of nano gold catalysts is that their partial hydrogenation is very selective: in the hydrogenation of unsaturated aldehydes, when the particle size of gold nanoparticles is greater than 2 nm, the hydrogenation selectivity ratio to C===O is C=== C is 40-50% higher. In the hydrogenation of acetylene on AU/AL2O3 and acrolein on AU/TIO2 and AU/ZRO2, the catalytic activity of the gold catalyst increases as the particle size of the AU nanoparticles decreases. This means that the metal nature of gold has an important influence on the hydrogenation of unsaturated hydrocarbons.

4. Liquid phase reaction
Ethylene glycol is oxidized to an acid in a MeOH-H2O (6:4) solvent. The gold/activated carbon catalyst is more active and selective than other precious metal catalysts and is used in the cosmetic and food industries.

5. Water-gas conversion reaction
The low temperature water-gas shift reaction has a good application prospect in polymer electrolyte fuel cells and civil electric heating systems for automobiles. A significant advantage of supported nano gold catalysts is their ability to catalyze at temperatures as low as 473K.

Transparent flexible circuit based on silver nanowire conductive material

With the continuous development of technology, various transparent and flexible electronic devices have developed rapidly. However, compared with transparent flexible conductive materials, there are still many problems in the research of transparent flexible circuits. The research of many transparent flexible circuits only stays at the level of transparent substrate and opaque circuit. Recently, Professor Sun Jing of Dalian University has designed a transparent flexible circuit by using polydimethylsiloxane (PDMS) as a flexible substrate and silver nanowires (AgNWs) as a conductive material, which overcomes the previous transparent flexible circuit part. The drawback of transparency is the realization of a truly transparent transparent circuit. The related research work was published in Chemical Communications and was selected as the bottom article of the 5418, Volume 39, issue of 2018.

The researchers first performed experiments on PDMS, using the spin coating technique to spread the AgNWs solution evenly on the hydrophilically modified PDMS surface. The transmittance and resistance of the transparent flexible conductive material reached 90.86% and 3.22 Ω·sq-1, respectively. It is at the leading level in the field of transparent flexible conductive materials.

The research team used the mature microfluidic control technology to create holes with various complex patterns on the transparent flexible substrate PDMS surface, and the precision can reach micron level; then AgNWs are spread into these holes to make them high at the same time. Electrical conductivity. The transparent flexible circuit thus prepared has a strong wear resistance due to the protection of the channel to the AgNWs.

The transparent flexible circuit not only has good optical and electrical properties, but also has good mechanical properties. They used LEDs and ordinary dry batteries to test their electrical conductivity. The results showed that the conductivity was good. After the 180-degree inward and outward bending, 720-degree distortion and tensile test of the circuit, the brightness of the LEDs remained basically unchanged. change. The researchers further explored the application of the transparent flexible circuit, deposited Pd nanoparticles on the AgNWs of the circuit by electrodeposition, and used it to detect glucose. The results show that the sensor has high sensitivity to glucose detection.

The originality of this research is to solve two problems in the preparation of transparent flexible circuits: (1) to achieve a completely transparent flexible circuit; (2) to design circuit patterns as desired. The transparent flexible electrode prepared by the research is simple in preparation, controllable in quality and excellent in technical indicators, which can greatly promote the development of wearable electronic devices.

High Functional Nano White Graphite – Hexagonal Boron Nitride Nanoparticle

As one of the best heat conduction materials in ceramic materials, HBN has a structure similar to that of graphite. It has a hexagonal layer structure and is loose, lubricated, light and soft, with high processability and color. White is therefore also known as “white graphite.”
It is not only a good conductor of heat, but also a typical electrical insulator. It is an ideal high-frequency insulation, high-voltage insulation, high-temperature insulation material.

Boron nitride ceramics, composite ceramics, conductive ceramics, superhard materials, mold release lubricants, high temperature coatings, thermal conductive fillers.

1. High temperature lubricant
h-BN has excellent high-temperature lubricity. When used as a lubricant, it can be dispersed in heat-resistant grease, water or solvent. Sprayed on the friction surface, the solvent evaporates to form a dry mold, because h-BN and steel Stainless steel, aluminum, etc. are neither wet nor active, so it is often used in places resistant to molten metal corrosion, such as crucibles, boats, liquid financial pipes, etc.

2. Thermally conductive filler
BN has been widely used as a filler in thermally conductive composites to solve the problem of short-circuiting of high-resistivity materials required for thermal conductive materials to come into contact with electrical components in operation. The ultrasonically exfoliated two-dimensional boron nitride nanosheets and one-dimensional cellulose nanofibers were blended to prepare a composite with a thermal conductivity of up to 180 W/(m·K), which is the highest thermal conductivity

3. Boron nitride has a significant chemical inertness at high temperatures, allowing boron nitride(BN) coatings to protect materials such as aluminum, magnesium, zinc alloys from high temperature oxidation.
When the boron nitride coating is on a refractory material or a ceramic vessel, it can effectively protect its oxidation resistance even at a temperature of up to 1273K.

4. The ultra-high temperature mold release agent using solid lubricant boron nitride as raw material can maintain excellent lubricity and mold release property under extreme high temperature, so it is suitable for molding diamond tools, molding of high temperature hardening resin, and sintering of metal. Forming, pressing of aluminum frame, molding of glass, demoulding of die casting, etc..

5. High insulation and high thermal conductivity ceramic products
Boron nitride ceramics have good heat resistance, thermal stability, thermal conductivity, high temperature dielectric strength, and are ideal heat dissipation materials and high temperature insulation materials. Because of its good chemical stability, it is resistant to most of the molten metal. The hardness of the product is low (Mohs strength 2), so it can be machined with an accuracy of 1/100mm. It is commonly used in the manufacture of high-temperature containers for metallurgical melting, semiconductor heat-dissipating insulation parts, high-temperature bearings, thermowells, and glass forming dies.

6. Synthetic cubic boron nitride
C-BN is another common form of boron nitride, which is second only to diamonds in hardness and is also a theoretical low temperature stable phase. The use of h-BN in the participation of the catalyst, at high temperature (1800℃), high pressure (800 MPa) into a hard, such as diamond c-BN boron nitride, is currently one of the main methods of synthesizing boron nitride.

Related reading :Hexagonal Boron Nitride Nanoparticle  Hexagonal Boron Nitride

Graphene helps prevent steel from rusting

An Indian-American researcher and his partner invented a new technology that uses graphene to prevent steel from rusting.

Iron and steel rust is a big problem in the automotive industry. Although there is paint coverage, it is easy to scratch, and the bumper is coated with chromium. This process involves the addition of toxic chemicals.

In order to solve this problem, SUBA Buffalo professor of chemistry Sarbajit Banerjee and doctoral student Robert Dennis developed a polymer composite containing graphene.

Graphene is a layer of carbon atoms, it has hydrophobicity and strong conductivity. These properties make the steel contact with water and also reduce the electrochemical reaction of iron oxides that rust iron.

The two researchers added this composite coating to a varnish, applied it to steel, and then immersed it in salt water. In a typical winter climate, the mixture of salt water and salt and snow is different and a car will encounter a car, so it is very effective as a very harsh environmental avatar.

Initially, varnished steel sheets could only last in salt water for several days. However, Banerjee and Dennis can keep varnish in this environment for a month by adjusting the concentration and dispersion of added graphene.

Banerjee said that he wanted to add something to the coating that detects the pH of the water in the vicinity of the scratches and reacts with the water in a manner that seals the crack.

Although this technology still has a long way to go for commercialization, some large companies in the steel industry are also interested in participating in this research, especially Tata Steel, which has provided funding for Banerjee’s experiments. The two scientists also received $50,000 in funding from the New York State Institute of Pollution Prevention.

In a news release, Banerjee stated that the paint can be produced using the existing equipment of the local steel plant.

Unlike hexavalent chromium, used to coat bumpers and some engines, graphene is non-toxic because it is only a carbon atom and does not require the use of strong acids. It is safe throughout the process. These reasons make graphene a magic material for future electronic components.

Related reading:Carbon Material Nanopowders  Carbon Nanomaterials

Research Status and Application Progress of Polycrystalline Transparent Alumina Ceramics

Overview:

According to the definition of Japanese scholars, certain shapes of blanks, produced by using inorganic powders with a certain molding method, under a certain temperature, atmosphere, and pressure conditions, ceramics with a certain degree of transparency are sintered to be transparent ceramics. It is generally stipulated that in the case where the in-line transmittance is greater than 40%, it becomes a transparent ceramic, and some scholars also call it a translucent ceramic. Compared to the single-crystal transparent ceramics of the melting method, the sinterable transparent ceramics, due to its multi-element composition and influencing factors, have crystal structures that are composed of more than two kinds of crystals and polycrystals with irregular geometries, and are therefore called “polycrystals. Transparent ceramic.” Transparent ceramics made of high-purity alumina powder are generally polycrystalline and are called “polycrystalline transparent alumina ceramics”.

 

In 1957, some ceramics scientists from the United States, according to the principle of crystal transparency, using ceramic production methods, successfully prepared the first transparent alumina ceramic – “Lucalox”. Open up new application areas of ceramic materials, since then, the research and development of ceramic materials has entered a new stage, triggered the upsurge of research and application of transparent ceramics. With the deepening of the research and exploration of the ceramic material’s sintering aids, sintering process, crystal structure, light transmission mechanism, thermodynamic properties, and specific applications, the performance of transparent ceramics has come a long way. Nowadays, ceramic gold halides have been prepared. Transparent aluminum oxide ceramic discharge tube in the lamp, transparent zirconia ceramic lens, yttrium aluminum garnet laser transparent ceramic, magnesium aluminum spinel fairing, transparent ceramic armor, and so on.

 

First, the preparation method of polycrystalline transparent alumina ceramics

The preparation process of transparent ceramics is not much different from the preparation process of ordinary ceramics, but from the perspective of preparation technology, the preparation of transparent ceramics requires more rigorous technical means.

 

1 original powder

In the preparation of raw materials for transparent alumina ceramics, the original powder must meet the following requirements: (1) The powder has high purity and dispersibility, the purity must be higher than 99.9%; (2) the powder has good sintering Activity; (3) Powder particles have good dispersibility, can’t appear serious agglomeration phenomenon, uniform in size and can exhibit better spherical shape; powder particle size generally requires submicron or even nanometer grade, and should be α phase powder. When the original powder is self-made, α-Al 2 O 3 powder is usually prepared by pyrolysis using ammonium aluminum sulfate or ammonium aluminum carbonate.

 

2 Sintering additives

The role of the sintering aid is mainly to promote the liquid phase in the sintering process of the powder, thereby reducing the sintering temperature, inhibiting the abnormal growth of crystal particles, and shortening the diffusion path of the blowhole. When high-purity alumina powders are used to sinter transparent ceramics, a small amount of MgO (0.05-0.25wt%) is generally added as a sintering aid, which can effectively suppress abnormal grain growth.

 

3 transparent alumina ceramic sintering process

Similar to ordinary ceramics, the preparation process of the transparent ceramic material includes the synthesis of the precursor powder. In addition to the compaction molding, the heat treatment and post-processing (annealing, mechanical processing, and polishing) are included. However, the preparation process of transparent ceramics has its more stringent requirements, especially for powder synthesis and post-molding sintering processes. The sintering process of transparent alumina ceramics is generally the same as that of other ceramics, and mainly includes atmosphere and vacuum sintering, atmospheric pressure sintering, hot isostatic pressure sintering, spark plasma sintering and microwave rapid sintering, etc. Sintering in combination with hot isostatic pressing.

 

Second, the application of transparent alumina ceramics

Since the first research and preparation of transparent alumina ceramics by US doctor in the late 1950s, the research and application of transparent alumina ceramics have received extensive attention. Compared with glass, transparent alumina ceramics have higher strength, hardness and toughness, and its excellent surface abrasion resistance is also not comparable to glass; compared with single crystal materials, the preparation temperature of transparent alumina ceramics is more Low, shorter production cycle. It is precisely because of the properties of transparent alumina ceramics that it has become a research hotspot. It has been widely used in the fields of optics, special instrumentation, lighting, electronic technology, high-temperature technology, defense and military, and aerospace. application. For example, transparent aluminum oxide ceramics can be made into a light-emitting arc tube for use in high-pressure sodium lamps by utilizing light transmission, corrosion resistance, and high-temperature stability. With statistics, there are more than 70 million aluminum oxide arc tubes produced each year worldwide. In the 1990s, a Dutch company further developed the use of transparent alumina, which was used as an arc tube for metal halide lamps. The ceramic metal halide lamp exhibited good color rendering properties, high light efficiency, and long life. For more than half a century, the United States, Japan, Russia, France and other countries have made great progress in the study of transparent ceramics. In addition to preparing alumina ceramics with high light transmittance, many other transparent ceramics have been developed. The system includes oxide transparent ceramics and non-oxide transparent ceramics. As workers further explored and studied the raw material synthesis, sintering process, crystal structure, performance, light transmission mechanism, and application of transparent ceramic materials, as well as the development of science and technology, the practical application of the performance of transparent ceramics was proposed. More demanding requirements, a large number of more high-performance transparent ceramic materials came into being.

Application of nano-powder in lubrication:

Nano tin(Sn), indium(In), bismuth(Bi) powder:
The melting points of tin, indium, bismuth and their alloys are all below 300 ° C. Many organic solvents have boiling points above this temperature and can be stable for a long time, so it is easy to find a suitable reaction medium. Tin, indium and antimony nanoparticles have attracted much attention in the field of friction due to their special physicochemical properties and small particle size. The use of nanoparticles as lubricant additives is a research hotspot in the field of lubrication. Studies have shown that nanoparticles have different lubrication properties than traditional organic lubricant additives due to their composition and structural characteristics. Specifically in the following three aspects:
(1) The nanoparticles are mostly spherical, and they may act like a “ball bearing” between the frictional faces, thereby effectively improving the tribological properties of the lubricating oil;
(2) Under heavy load and high temperature, the nanoparticles between the frictional faces may be flattened to form a sliding system, thereby reducing friction and wear;
(3) Nanoparticles can be filled in the pits and damage sites on the surface of the workpiece, making it possible to repair the surface of the friction surface in situ. Metal nanoparticle lubricants combined with the combination of the above three mechanisms of nanoparticles are considered to be the most likely to be a new generation of lubricant additives.

Nano Copper(Cu) powder:
The nano-copper powder in the nano-copper powder lubricating oil additive acts as a buffer on the surface of the friction workpiece during the circulation of the oil circuit, and the nano-copper powder has better high-temperature chemical stability with respect to the organic additive, and therefore, fundamentally It solves the problem of agglomeration and carbonization which may occur in lubricating oil at high temperatures. More importantly, the nano copper powder is fine and soft, and can be filled with friction defects at any time to play a self-repairing effect. The function of nano copper lubricant additive is mainly reflected in:
1. Reduce frictional resistance, improve engine effective power and extend engine life;
2. Eliminate damage to the engine from initial start-up and save fuel consumption;
3. Improve the efficiency of the lubricating oil and ensure the power output of the engine.
Technical indicators
Experimental studies have shown that the addition of 0.1% nano-copper powder lubricant additive to the lubricating oil can reduce the friction coefficient by 30%, the wear by 34%, the fuel economy by 5%, and the average fuel consumption by 3%.

Nano boron nitride powder:
Nano boron nitride powder has excellent lubricating properties at room temperature and good lubricity in high temperature environments. It is widely used in the field of high temperature solid lubricants.

Nano Graphite powder:
Nano graphite powder belongs to layered inorganic substances, and the addition of nano-graphite lubricating oil and grease has obvious improvement in lubrication performance, high-temperature resistance, wear resistance and wear-reducing performance.
Lubricating oil and grease are used in the industrial lubrication field. However, lubricating oil and grease will reduce the lubricating effect in high temperature and high pressure environment, and nano graphite powder will be added as lubricant additive to lubricating oil and grease production. Among them, nano-graphite powder can upgrade its lubricating performance and high temperature resistance. Nano-graphite powder is made of natural flake graphite powder with good lubricity as raw material, while nano-graphite powder has nanometer-scale grain size and volume effect. , quantum effect, surface and interface effects, after research, it shows that under the same conditions of scale crystal size, the smaller the particle size of graphite powder, the better the lubrication effect.
The use of nano-graphite powder in grease is better than that in lubricating oil. Nano-graphite powder can be made into nano-graphite solid lubricating dry film, which can be used on the rolling surface of heavy-duty bearings. The coating formed by nano-graphite powder can be effective. The ground is isolated from corrosive media while providing effective lubrication.

Nano Zirconium Dioxide(ZrO2) particle:
The zirconia particles having a particle diameter of less than 100 nm can effectively improve the antiwear and antifriction properties and load carrying capacity of the lubricating oil. The tribological mechanism of nano-zirconia is deposited on the friction surface to form a lubricating film with anti-wear and anti-friction effects. It should be noted that the amount of nano zirconia added has an optimum value, and the amount of addition is too large, and the tribological properties of the lubricating oil may decrease.

Nano Silica(SiO2) particle:
The surface of the nano-silica particles contains a large amount of hydroxyl groups and unsaturated residual bonds, which can form a strong chemical adsorption film on the surface of the friction pair, thereby protecting the metal friction surface and significantly improving the friction performance of the lubricating oil.
Some studies have found that the bearing capacity of lubricating oil is greatly improved after adding nano-SiO2. When the amount of addition is 1.5, the PB value is increased by nearly one time. At the same time, it was also found that SiO2 nanoparticles as excellent lubricant additives showed excellent anti-wear and anti-friction properties, and played a certain role in repairing the wear table.