April 2019 – Silver Nanoparticles Antimicrobial,Copper Oxide Nanoparticles,Gold Nanopowder

April 30, 2019

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.

April 12, 2019

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.

April 4, 2019

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.