Nanomaterials and nanoparticles are used in a broad spectrum of applications. Today they are contained in many products and used in various technologies. Most nanoproducts produced on an industrial scale are nanoparticles, although they also arise as byproducts in the manufacture of other materials.
Defined production and reaction conditions are crucial in obtaining such size-dependent particle features. Particle size, chemical composition, crystallinity and shape can be controlled by temperature, pH-value, concentration, chemical composition, surface modifications and process control.
Two basic strategies are used to produce nanoparticles: “top-down” and “bottom-up”. The term 'top-down' refers here to the mechanical crushing of source material using a milling process. In the 'bottom-up' strategy, structures are built up by chemical processes. The selection of the respective process depends on the chemical composition and the desired features specified for the nanoparticles.
Top-Down/mechanical-physical production processes 'Top-down' refers to mechanical-physical particle production processes based on principles of microsystem technology. The traditional mechanical-physical crushing methods for producing nanoparticles involve various milling techniques.
Milling processes The mechanical production approach uses milling to crush microparticles. This approach is applied in producing metallic and ceramic nanomaterials. For metallic nanoparticles, for example, traditional source materials (such as metal oxides) are pulverized using the high-energy ball mills. Such mills are equipped with grinding media composed of wolfram carbide or steel.
Milling involves thermal stress and is energy intensive. Lengthier processing can potentially abrade the grinding media, contaminating the particles. Purely mechanical milling can be accompanied by reactive milling: here, a chemical or chemo-physical reaction accompanies the milling process.
Compared to the chemo-physical production processes, using mills to crush particles yields product powders with a relatively broad particle-size ranges. This method does not allow full control of particle shape. Gas phase processes(aerosol processes) Gas phase processes are among the most common industrial-scale technologies for producing nanomaterials in powder or film form. Nanoparticles are created from the gas phase by producing a vapor of the product material using chemical or physical means. The production of the initial nanoparticles, which can be in a liquid or solid state, takes place via homogeneous nucleation.
– In flame reactors , nanoparticles are formed by the decomposition of source molecules in the flame at relatively high temperatures (about 1200~2200°C). Flame reactors are used today for the industrial-scale production of soot, pigment-titanium dioxide and silicon dioxide particles.
– In plasma reactors , plasma (ionized gas) provides the energy for the vaporization and for initializing the decomposition reactions.
– In laser reactors , lasers selectively heat the gaseous source material, utilizing its absorption wavelength, and decompose it to the desired product.
– In hot wall reactors , vaporization and condensation are applied. The source material is vaporized in an inert gas under low pressures (ca. 1 mbar). This removes the enriched gas phase from the hot zone. The particles created by the rapid cooling are collected on filters. Technically, hot wall reactors are used for example in producing nanoscale nickel- and iron powders.
– The chemical gas phase deposition process is used to directly deposit nanoparticles from the gas phase onto surfaces. Here, the source material is vaporized in a vacuum and condensed on a heated surface by a chemical reaction, is deposited from the gas phase into the solid final product.
Luoyang Trunnano Tech Co., Ltd (TRUNNANO) is a professional Nano Bi Powder manufacturer with over 12 years experience in chemical products research and development. If you are looking for high qualityBismuth Nanoparticles Nano Bi Powder, please feel free to contact us and send an inquiry.
