Liquid spray-liquids spray (LF-FSP) is one of the latest iterations in the production technology of flame spray powder (FSP). FSP produces a metal oxide powder from a highly volatile metal chloride gas that decomposes/oxidizes in a fire of hydrogen-oxygen to form a nano-oxide powder. However, products made from the FSP vapor phase process are limited to Al-, Ti-, Zr-, and Si-based oxides of their metal chlorides. Thus, interest in producing more complex materials requires a new methodology, LF-FSP.
LF-FSP, as found at the University of Michigan, uses metaloorganic precursors such as carboxylic metals or alkoxides, not metal chlorides. Briefly, an alcohol solution (usually ethanol) containing 1-10 wt.% Of loading of the target ceramic component as precursor is aerosol with O 2 into quartz chamber and ignited with a methane pilot torch. The initial combustion temperature runs from 1500 to 2000 Â ° C, depending on processing conditions, resulting in "soot" nanopowder. Temperatures dropped to 300-500 ° C above 1.5 m, equivalent to 1000 Â ° C extinguishes 100 μm leading to non-separated kinetic products and nanopowders. The production rate can be 200 g/h when using a wire-in-tube electrostatic precipitator operating at 10 kV. The typical powder has 15-100Ã, nm average particle size (APS) with a specific surface area of ​​30-100 m 2 /g. The LF-FSP technology can be used to produce single and mixed metal oxides easily from low-cost starting materials in one step without forming harmful byproducts such as HCl, which is formed when metal chloride is used as a precursor.
Video Liquid-feed flame spray pyrolysis
Process
Initially, metaloorganic precursors dissolved in alcohol, usually ethanol, to the desired ceramic loading. For more details on precursors, see the precursor section below. The final ceramic oxide mass can be calculated with the ceramic yield and the amount of precursor used. The production process, referred to as "shooting", broadly refers to the aerosol of the liquid solution of the dissolved precursor and burns it in a flame. The metal oxide is produced, having the final stoichiometry determined by the composition of the precursor solution.
The level of production depends on the predecessor's predecessor ceramic results; this can be understood practically as the number of metal atoms injected into the flame per liquid volume. In addition, the efficiency of particle collection is important to minimize waste and loss. The efficiency of collection is defined as the mass of powders collected through the theoretically expected mass. While "shooting", some of the powder flows into the exhaust without being deposited onto electrostatic precipitators (ESP), and during the collection of the powder carried by scrubbing it, the powder loss occurs which causes the powder mass deviation collected from the theoretically expected. value. In a laboratory setting, the production rate can range from 10 to 300 g/h, yielding uniform nanoparticles, not aggregated with APS between 15 and 100 nm. Commercially, Nanocerox holds an exclusive license for LF-FSP and can produce a quantity of 4 kg/h through a continuous process.
Normally, the solvent serves as fuel; so the cost and solubility issues lead to the use of other "cheap" ethanol or alcohol to disperse precursors. The oxygen/alcohol aerosol undergoes rapid combustion in milliseconds, oxidizing all organic components at temperatures up to 2000 ° C leaving only the metal oxyion eg, (M-O) x in the gas phase. The oxidation is then formed into clusters and sub-100 particles, as shown in Fig. 1 .
The combustion of precursors produces oxidation of ligands/adducts to produce steam which may comprise a gas metal ion and an oxyone species, which co-reacts to nucleation and grows into a metal oxide bonding group.
This cluster condenses to form the nucleus, which then grows by consuming the vapor phase species and the bonds with the oxygen available in the atmosphere. In this context, the term cluster refers to a species originally produced that is formed as a vapor. These clusters converge into nuclei, which then form stable particles.
Once formed, the cores collide to coalesce or clump where temperatures and species dictate mechanisms. Cooling changes the collision effect from coalescence to agglomeration. Rapid LF-FSP temperature drop when particles out of the flame prevent aggregate formation. The aggregate definition and its adverse effects are discussed in the profit section. Collisions that occur after the temperature drop in the agglomerates, where the particle bonds are weakened by Van der Waals forces, and they can be easily separated by ultrasonication or ball-milling.
Although there are exceptions, most artificial particles are nano sized (& lt; 100 nm) and are highly crystalline. Also, no phase separation in any particle or variation of the composition between the particles is observed, because the whole process is so fast that the particles of the atomic mixture are formed. Their properties come from flame temperatures (up to 2000 Â ° C) and high cooling rates (& gt; 500 Â ° C/s). The low residence time in the flame (the amount of time spent by metal ions in the zone of the flame) and rapid cooling lead to the formation of metastable phases and more important particles that are not aggregated, because they have no energy to coalesce and neck. The purity of the initial reactants largely encourages the purity of the final powder. Several species of carbonate may be present in the powder produced; However, the processing technique can minimize this impurity in the final product. First, the powder is dispersed in the solvent through ultrasonication and left for 8 to 12 hours, which leads to some small fraction of the larger particles, mostly carbonate, settling at the bottom. The suspension is separated from the precipitate and dried in an oven before it is ground into a powder. Thus, LF-FSP provides a robust, versatile route for single oxide powder and metal alloys in the 15-100 m size range with varying phases and morphologies from relatively inexpensive organic precursors.
Maps Liquid-feed flame spray pyrolysis
Tools
The LF-FSP apparatus has five components: aerosol generators with fluid and reservoir feed, cylinder quartz combustion chamber, Y-shaped quartz tube, four wire-in-cylinder electrostatic precipitators (ESP) connected in parallel series, and drain pipe.
Precursors, usually single or metal alloys, or carboxylates dissolved in ethanol at 1-10 wt.% Are fed into the combustion chamber through a twin, shear-height (Bernoulli) aerosol fluid generator with oxygen as an atomizing gas. The aerosol generator consists of a precursor-oriented delivery tube perpendicular to a high-speed oxygen flow tube. The aerosol twin generator provides high throughput of the precursor solution and stabilizes the flame. Two methane pilot torches made of alumina are used to power the aerosols. The next combustion results in a flame temperature of 1500-2000 Â ° C, depending on the solvent, the loading of the precursor, and the rate of aerosolization. The precursors evaporate on combustion and then convert to nanoparticles in a flame. The temperature drops to 300-500 ° C along the 1.5 m of combustion chamber, which is equivalent to 1000 Â ° C quench in <= 100 ms . This process leads to kinetic products and nanopowders that are largely unopposed.
The resulting nanopowders are collected by electrophoretic deposition in a parallel series arrangement of wire-in-aluminum electrostatic tube precipitators (ESPs). 5-10 kV direct current bias is applied between the wire and ESP wall, which induces the deposition of particles on walls and wires.
Precursors
Metal alkoxides, carboxylates such as alumates [Al (OCH 2 CH 2 ) 3 N], silatrane Si (OCH 2 CH 2 ) 3 N [CH 2 N (CH 2 CH 2 OH) 2 ], and zirconium propionate [Zr (O 2 CCH 2 CH 3 ) 2 - (OH) 2 ], commonly used, and they are dissolved in alcohol solvents such as methanol or ethanol. The solubility of precursors in alcohol is an important property, which is controlled by ligands. Too much carbon in the ligands can increase the formation of metal carbonates as a minor minor phase because large amounts of CO 2 are produced on combustion which can react with metal oxides. Too little carbon in the ligand will limit the solubility of precursors in alcohol. This process is inexpensive because metal oxides, hydroxides, carbonates or nitrates can be used as a starting point for precursor synthesis. For mixed metal oxides, one can synthesize a double alkoxide containing two metallic elements such as magnesium aluminum alkoxide double as shown in Table 1 , or simply mix various alkoxides and/or carboxylates in stoichiometric ratio.. For example, the LF-FSP product of alumina and silatrane glycolate dissolved in ethanol at a 3: 1 molar ratio is a mullite (3Al 2 O 3 o2SiO 2 ). Stoichiometry of nanopowder made through LF-FSP corresponds to its precursor.
Metal Alkoxides
One way to make metallic alkoxide precursors is through simple "one pot" synthesis. Alkoxide precursors of single or mixed metal oxides are prepared in this way. In this process, the suspension of ethylene glycol oxide metal or hydroxide with triethanolamine is heated at 200 ° C. The reaction takes place by dissolving the starting material while simultaneously removing the by-product water to form a clear solution. Excluding oxygen, hydrogen, carbon, and nitrogen, the ratio of different metal elements in alkoxides according to the stoichiometry of LF-FSP makes nanoparticles. Examples of the alkoxides already used in LF-FSP are shown in Table 1 .
Table 1. Examples of metal alkoxides.
Carboxylate metal
The carbonate or nitrate metal may be reacted with an excess of carboxylic acid (eg propionic acid) in a flask equipped with a silent head and an additional funnel. N 2 is introduced into the solution as the solution is heated to 120 ° C and maintained until all the by-products and the appropriate amount of carboxylic acid are removed with the help of N 2 flow. Additional CO byproducts CO 2 and (NO) x are produced for carbonate and nitrate of each metal. Pure carboxylates are usually ground powders to facilitate dissolution in alcohols. The table 2 gives an example of common metal carboxylates that have been used in LF-FSP.
Table 2. Examples of carboxylic metals.
Benefits
LF-FSP offers several advantages over other nanopowder production methods. The main problem in nanopowder synthesis is the use of expensive raw materials. These expensive raw materials include metal chloride precursors, which are highly corrosive. Equipment protective construction is required when using metal chloride precursors in FSP. In addition, toxic and polluting by-products need to be discarded. In LF-FSP, organometallic precursors are used which do not cause this problem. Due to the use of non-corrosive precursors, LF-FSP does not require protective equipment and the disposal of toxic byproducts. Also, organometallic precursors are low cost and easy to produce. For example, silatrane glycolate, the precursor in the production of SiO 2 through LF-FSP, can be synthesized in kilograms in one step of silica.
Another problem in nanopowder synthesis is the difficulty in controlling size, size distribution, and particle agglomeration. Conventional milling, milling, grinding, jet, crushing and micronization are used for particle size reduction. However, the particle size can not reach the nanoscale, nor the uniform shape. LF-FSP directly produces nanopowders that are not possible through grinding. A uniform particle size distribution is obtained using LF-FSP as it is a vapor phase process. For example, Al 2 O 3 nanopowders generated from LF-FSP have an average particle size (APS) of 20-150 nm with a log-normal particle size distribution.
Obtaining high-purity end products and relatively narrow size distributions is much easier than alternatives, and such powders do not require additional powder processing which can lead to the introduction of impurities. Aggregation is another key issue in nanopowder synthesis. Aggregates contain discrete primary particles with a neck. The necking particles refer to particles, which chemically bond together from the diffusion of atoms to the interface of particles in the presence of driving forces, such as heat. The formation of the neck is shown in Figure 3 . The main disadvantage of steam-fed FSPs is the formation of hard clumps in the gas phase. As a result, it causes difficulties in producing high quality bulk materials. LF-FSP greatly avoids this problem by limiting aggregation through rapid quenching.
LF-FSP can be used to produce nanopowders in commercial quantities, while other nano-powder synthesis methods have low production rates. For example, hydrothermal processing of nanoparticles in supercritical water can produce nanopowders at levels of 10-15 g/h. The production rate of nanopowders using LF-FSP is significantly greater. For example, Nanocerox can produce nanopowen up to 4 kilograms/hour using LF-FSP.
The common method of producing coated nanoparticles is primarily based on the solution phase method and sol-gel processing, which is a multi-step process. This multi-step process is inefficient in cost, time and homogeneity of the final product. Also, solvent removal is expensive. These coated nanoparticles include ZrO 2 coated Al 2 O 3 , SiO 2 coated ZrO 2 , and SnO 2 coat ZrO 2 . However, LF-FSP has the potential to provide a simple and efficient route to the production of coated nanopowder without aggregation. LF-FSP allows access to shell-core nanoparticles (ZrO 2 ) 1-x (Al 2 O 3 ) x , which can be produced in one step.
Apps
Laser app
LF-FSP can produce various nanopowders for multiple applications. Yttrium or YAG aluminum garments are treated with rare earth metals (Ce 3 , Pr 3 , or Nd 3 ) can be produced through LF-FSP, which has phosphor and laser applications. YAG is doped with rare earth metals, Nd: YAG, for example, shows the behavior of the electron pump driver. Small particle sizes of rare earth metals provide optical feedback. YAG has been studied for its high-temperature mechanical and photonic forces. The development of sintered YAG nanopowders to full density and transparency has been studied because YAG laser transparent polycrystalline lasers outperform single YAG laser crystals.
Catalysts app
Nanopowders produced from LF-FSP can be used for some catalytic applications. If the aggregate is nanocatalyst, its activity is lower due to the decrease in surface area. LF-FSP allows the production of nanocatalysts with minimal aggregation. It is well known that bimetallic and trimetallic catalysts offer enhanced properties through a single metal catalyst. Bimetal Nanocatalyst has been produced through LF-FSP. NiO-Co 3 O 4 , NiO-MoO 3 , and NiO-CuO are used for some types of catalytic reactions. For example, NiO-Co 3 O 4 nanoparticles are used as catalysts for the production of fuels and chemicals, and reduction of environmental pollution. Catalyst CeO 2 /ZrO 2 has been studied for automotive catalytic converters. Catalyst CeO 2 /ZrO 2 has been added to the catalytic system for the elimination and reduction of pollutants contained in the vehicle exhaust gas.
Composite app
The zirconia composite zirconia comprises Al 2 O 3 and ZrO 2 nanopowders, which can be produced through LF-FSP. Toughened zirconia alumina has been studied for high toughness and resistance to wear and has biomedical applications. It has the potential to produce harder and harder ceramic surfaces that can be used for ceramic hip implants. The life of the implant depends on the surface quality. Enhanced zirconia of alumina implants offers enhanced component life and more cost-effective long-term solutions.
Military applications
Alpha (?) - alumina produced with APS less than 100 m can be used to produce transparent armor. Transparent armor provides enhanced protection against ballistic threats and severe explosions. Traditional bullet proof glass can not stop the caliber of.50 caliber.50 caliber shooters.50 This aluminum-ceramic material can clearly stop the rounds of anti-aircraft guns and.50 caliber pistols. In addition, it is half the weight and bulky bullet-proof glass. In the future, this material can be incorporated in a variety of vehicles including light armored trucks to low-flying aircraft.
Self-cleaning app
Uniform Nanoparticles TiO 2 have been produced using the LF-FSP process, which has potential applications in producing self-cleaning windows, paints, interior furnishings, and aluminum linings. In addition, TiO 2 has been used for self-sterilization applications in hospitals and bathrooms. For example, Optimus Services LLC has included TiO 2 into the tiles used to cover the floor and walls of the medical operation room. TiO 2 is currently the main ingredient for self-cleaning applications due to its high photocatalytic activity, chemical inertia, mechanical properties, and low cost.
Other apps
The 3 table lists some potential nanopowders applications generated from LF-FSP.
Table 3 . Nanopowders are produced from LF-FSP and their potential applications.
References
Source of the article : Wikipedia
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