Posted on

Low Cost Synthesis of Silicon Carbide Nanopowders

Among modern ceramic materials, silicon carbide (SiC) and silicon nitride (Si3N4) has been successfully used in a variety of high-tech applications. SiC provides the effective combination of mechanical properties. It is widely used as an abrasive material and structure. It has high hardness, chemical inertness, than the melting temperature of the steel wear and oxidation of it for serious conditions such as high temperature sealing valve, rocket nozzle and wire drawing die and extrusion die for bearing applications because of its good wear resistance and corrosion resistance. In the tube by SiC to find its thermal properties and creep resistance of high temperature and hot electron exchange. The heating element from SiC. They can produce a high temperature of 1650 DEG C and medium in the air or inert considerable life. However, with any contact with water or hydrocarbon gas, can influence their age.

Silicon nitride has comparatively lower oxidation resistance and higher thermal conductivity than SiC. Major applications of silicon nitride are as automotive and gas turbine engine parts. It has high strength, fracture toughness and refractoriness which are required properties for ball bearings, anti-friction rollers. It performs remarkably when exposed to molten metal and/or slag.

A combined form of silicon carbide and nitride has been developed as silicon carbide grains bonded in silicon nitride matrix. This Si3N4-bonded silicon carbide is used for some critical applications where very high thermal shock resistance is required. For instance, in particular case of flame-out engine start-up, temperature reaches from ambient to 1600 °C in few seconds followed by an abrupt decrement to 900 °C in less than one second. Si3N4-bonded silicon carbide exclusively endures these conditions.

Traditional methods to produce these ceramic materials are energy intensive and hence expensive. For example, the Acheson process, which is the most widely adapted method to produce commercial-grade SiC, essentially takes 6 – 12 kWh to yield one kg of SiC. An inexpensive method, that uses low cost agro-industrial byproduct, is the pyrolysis of rice husks, first carried out by Lee and Cutler in 1975. Since then many researchers have discussed and used various process routes and modifications to obtain Silicon Carbide Nanopowders and/or silicon nitride, either in particulate or in whisker form, from rice husks.

Morphological studies on RH reveal that micron size silica particles are distributed in cellulosic part of RH. When these silica particles are made to react with carbon in biomass part of RH under specific experimental conditions, silicon carbide can result. Moreover, besides silicon carbide, modifications in process mechanism lead to formation of some other industrially useful products, viz. silicon nitride, silicon oxynitride (Si2N2O), ultra-fine silica, and solar-cell grade silicon.

Related reading: nano particles nano oxides

 

 

 

 

Posted on

Microwave hybrid synthesis of silicon carbide nanopowders

Nanosized silicon carbide powders were synthesised from a mixture of silica gel and carbon through both the conventional and microwave heating methods. Reaction kinetics of SiC formation were found to exhibit notable differences for the samples heated in microwave field and furnace. In the conventional method SiC nanopowders can be synthesised after 105 min heating at 1500 °C in a coke-bed using an electrical tube furnace. Electron microscopy studies of these powders showed the existence of equiaxed SiC nanopowders with an average particle size of 8.2 nm. In the microwave heating process, SiC powders formed after 60 min; the powder consisted of a mixture of SiC nanopowders (with two average particle sizes of 13.6 and 58.2 nm) and particles in the shape of long strands (with an average diameter of 330 nm).
The powders were prepared by a sol-gel process. Dielectric constants (ϵ′) and dielectric loss tangents (tanδ) were measured within the microwave frequency range from 4 to18 GHz. Both ϵ′ and tanδ of pure SiC nanopowder are much higher (ϵ′=40–50, tanδ=0.6–0.7) than for the doped ones over the frequency range. The dielectric parameters decreased with increasing aluminum and nitrogen contents. Infrared (IR) spectra were measured in the range from 500 to 4000 cm−1, showing that the background of pure SiC nanopowder is also much higher than for the doped ones. The possible mechanisms of these promising features of undoped SiC nanopowder are discussed.
By a simple and controlled method, that is, by electroless plating, nickel has been deposited on the surfaces of Silicon Carbide Nanopowders Energy dispersive spectrometry (EDS) spectra show that pre-treatments of the silicon carbide nanoparticles have an important influence on the effect of electroless nickel plating. Transmission electron microscopy images and EDS spectra of silicon carbide nanoparticles before and after electroless nickel plating reveal that nickel has been deposited on the surface of silicon carbide nanoparticles and the deposited nickel and silicon carbide nanoparticles are bound tightly.

Posted on

Nano silicon semiconductor light-emitting materials research

By changing the quantity of silicon rich, annealing conditions, size and density control oxidation of silicon in silicon Silicon Carbide Nanopowders. Literature that the critical temperature of silicon nanocrystals is 1000oC, and we tested to determine the critical annealing temperature for 900oC nanocrystals. On the right is via the 900oC annealing silicon rich silicon was about high resolution electron microscopy images of 30% silicon rich silicon oxide. Can clear the silicon nanocrystals. On the left corner of the electron diffraction pattern it is.

First observed by Au/ (Ge/SiO2) /p-Si superlattice structure electroluminescence. Right out of high resolution electron microscopy figure four cycle Ge/SiO2 superlattices. The bright line for the SiO2, 2.0nm thickness, Ge thickness of 2.4nm.

The growth of nano SiO2/Si/SiO2 double barrier by magnetron sputtering technique on silicon substrate (NDB) single well potential sandwich structure, the first realization of visible photoluminescence of Au/NDB/p-Si structure. Discovery of electroluminescence peak position, intensity with the nanometer silicon layer thickness (W) changes as synchronous oscillations, as shown on the right. Further tests and analyses show that the oscillation period is equal to the deBroglie wavelength of 1/2 carrier. Lighting model is explained by our group proposed electroluminescence.

For the first time based on SiO2:Si:Er film growth by magnetron sputtering has been achieved on the 1.54 m wavelength as (optical communication window) Er electroluminescence.