Basic types of ultrafine powders and prospects
1980s , gradually developed ultra-fine powder , has increasingly become the focus of national research so-called ultra-fine powder is the scale ranged between molecules, atoms and bulk materials , usually refers to small solid within 1 ~ 100nm range particles , including a variety of material particles of metal , non-metallic , organic, inorganic and biological .
With superfine material , the surface electronic structure and crystal structure has changed , resulting in a bulk material does not have the surface effect, small size effect , quantum effect and macroscopic quantum tunneling effect , so that the ultrafine powder with conventional compared with a series of excellent particulate material physical and chemical properties.
The industry due to the different uses of ultra-fine powder and preparation method , while the ultra- powder to make a different division . Currently, more consistent identity and a more reasonable division :
( 1 ) fine powder ; ( 2 ) fine powder ; ( 3 ) sub-micron powders ; ( 4 ) nanopowder
Superfine powder particle size between large 100A to 1000A said ultrafine particles ; particle size 20A to 100A in between called ultrafine particles ; 20A or less in diameter , said small ultrafine particles. Currently preparing ultrafine particles is still relatively small difficulty , so ultra-fine powder material in this section refers to a particle size of between 0.1μm 0.01μm solid particles. Thus , the ultrafine particles is between our intermediate state of matter of a large amount of atoms or molecules and between the small number of atoms or molecules composed of artificial obtained , which maintains the existing chemical substances nature and metastable atoms or a group of molecules , are thermodynamically unstable. So for their research and development is key to understanding how the transition to the microscopic world of macro world. With the high development of the electron microscope , the presence of ultrafine particles and the size and shape can be observed already very clear .
Comparison with the powder of ultrafine particles generally , have now discovered a series of unique properties, such as low melting point, high chemical activity , strong magnetic , good thermal conductivity , electromagnetic wave absorption abnormal characteristics . These changes are mainly due to the nature of the \"surface effect\" and \" volume effect\" caused . Although some of the features and applications of ultrafine particles to be further research and development, the peculiar nature of the above has opened up bright prospects for its wide range of applications .
The finer the particle size of ultrafine particles reduce the melting point of the more remarkable. Melting point of silver block is 900 ℃, the melting point of the ultrafine particles may be reduced to below 100 ℃, soluble in hot water. Nuggets melting point of 1064 ℃, and the particle size of ultrafine particles 20A melting point of only 327 ℃. Because of lower melting point can be at a lower temperature of the powder metal, alloy or compound is sintered to prepare a variety of mechanical parts , not only to save energy , reduce the difficulty of the manufacturing process, the more important is the excellent properties can be obtained components. Refractory material such as WC, SiC, BN, Si3N4 , etc. to use as a structural material , the manufacturing process requires high temperature sintering , when the ultrafine particles , can be carried out at low temperatures and without additives to obtain a high density of the sintered body . This high-performance structural materials of inorganic wider application to open up more ways to have a very good practical significance. Ultrafine particles of a diameter smaller than the larger the surface area , a corresponding increase in surface energy , high chemical activity. Whereby efficient catalysts for chemical reactions , can also be used for combustion of solid rocket fuel additive . Practice has showed that the catalyst particles ultrafine Ni alloy and Cu- Zn as the main component is made , the efficiency in terms of the hydrogenation was 10 times that of traditional organic catalyst ; solid rocket fuel , less than 1% by weight of added ultrafine particles of aluminum or nickel powder, burning calories per gram of fuel to increase about twice .
Strong magnetic properties of applications for magnetic fastest progress . Use γ a Fe203, Cr02 and metal ultrafine particles have been developed better performance ultra-high density magnetic tapes and videotapes , etc., which the recording density of the previous 10 times , and has good stability. Now open up more applications, such as new liquid colloidal magnetic fluid materials, mechanical seals , speakers and so on.
Common metals and their powder reflected light we have seen , showing a metallic luster, but the metal ultrafine particles completely lose their luster , and the finer , deeper black . This may be due to the reason of light is completely absorbed . This feature can be used as a light absorbing material in addition to the utilization of solar energy , you can also use its absorption of infrared , hot -type detector is used as coatings . Another example of ultrafine particles of iron oxide and zinc stearate, together with a dispersant to prepare a polystyrene resin film having a good visible light transmittance of the ultraviolet light has a good absorbency. If it is added to plastics , can be made of anti- UV- transparent plastic containers , transparent better than brown glass . When added to food packaging , to protect food from ultraviolet light , effectively extending the shelf life.
Posted by: Roy on Jan 22 2014Tags: Machinery Ultrafine Powder Mill Powder Mill Grinding Mill
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