Flame spray pyrolysis process

We recently described two discoveries that offer solutions to this problem. First, a new, simple synthesis of polymeric precursors to P"-alumina made directly from NaOH, alumina and triethanolamine, TEA (2). Second, we learned to form a wide variety of ultrafine aluminosilicate ceramic powders by flame spray pyrolysis processing of these polymers. The goal of the current research program is to demonstrate that it is possible to produce reasonable quality P"-alumina shapes using these low cost precursors and powders. 

Flame spray pyrolysis (FSP) a liquid precursor solution is sprayed into the flame and ignites its combustion drives the flame process. 

Another distinguishing feature of titania prepared by flame spray pyrolysis is the draar e of anatase crystallite size with the increase of flame temperature. Generally, the increase of preparation temperature increases the crystallite size in other processes such as sol-gel method, hydrothermal method [2, 3], flame processing and conventional spray pyrolysis. The decrease of crystallite size was directly related to the decrease of particle size. Fig. 5 shows SEM and TEM images of titania particles prepared by flame spray pyrolysis. 

Strobel et al. [51] prepared barium carbonate nanoparticles (50-100 nm) by flame spray pyrolysis. The rapid quenching during the preparation process resulted in the unprecedented formation of pure monoclinic BaCOa- The as-prepared material was characterized by electron microscopy, XRD as well as by TG and DSC analyses (Figures 6 and 7). At ambient conditions the metastable monoclinic phase transformed easily into the thermodynamically stable orthorhombic BaCOs (witherite) within a few days. 

Takatori and his collaborators in Toyota Research Center were one of the first who developed and systematically studied the emulsion combustion method (ECM) [3]. This method is basically a combination of the microemulsion wet chemistry and the flame spray pyrolysis methods. In ECM, an aqueous solution of a metal salt is mixed with a fuel such as kerosene and a small amount of an emulsifier or surfactant to obtain a water-in-oil (W/O) type of emulsion. Using a spray nozzle, the solution is then atomized to produce a spray. The size of the mother emulsion droplets depends on the atomizer type and the atomization conditimis, and is on the order of 10 pm for air-assist nozzles. The size of the dispersed micro-solution droplets depends on the string process and surfactant, and is about 1 pm [3]. Figure 40.1 shows a schematic diagram of the ECM. 

Liquid-feed flame spray pyrolysis provides highly dispersed and unaggregated nanopowders with average particle sizes of 20-70 nm, which are dependent on the processing conditions. Their chemical compositions can be controlled to ppm levels... 

As per the literature, there are two types of approach vapour feed-flame spray pyrolysis and liquid feed-flame spray pyrolysis (LF-FSP). However, it is often difficult in the vapour feed process to... 

Widely used methods in the synthesis of silica nanoparticles are the sol-gel process and flame synthesis [5]. The latter is an effective synthetic route to continuously produce extremely pure nanoparticles, but in many cases the final products are agglomerated or show low reactive surfaces that make them difficult to functionalize. Nevertheless, flame synthesis is a prominent method to commercially produce silica nanopartides in powder form [6]. It is being used since decades for the production of the so-called fumed siUca, which is a filler in many applications, for example, in the pharmaceutical or polymeric business [7]. The extension of this preparation route is the so-called flame spray pyrolysis that has expanded in the last two decades to many other material compositions and is a promising rapid technique for the production of nanopowders [8]. 

Various methods are applied to the synthesis of titania particles including sol-gel method, hydrothermal method [2], citrate gel method, flame processing and spray pyrolysis [1]. To utilize titania as a photocatalyst, the formation of ultrafme anatase titania particles with large crystallite size and large surface area by various ways has been studied [4]. 

The liquid solution CCVD process does not deposit droplets (these evaporate in the flame environment) or powders as in traditional thermal spray processes. The CCVD technology is drastically different from spray pyrolysis In spray pyrolysis, a liquid mixture is sprayed onto a heated substrate, while CCVD atomizes a precursor solution into sub-micron droplets followed by vaporization of said droplets. The resulting coating capabilities and properties described hereafter qualifies CCVD as a true vapor deposition process. For example, depositions are not line-of-sight limited and achieve epitaxy, 10 nm dielectric coatings onto silicon wafers in a Class 100 clean room resulted... 

Chemical Vapor Deposition (CVD) has been defined as a materials synthesis process whereby constituents of the vapor phase react chemically near or on a substrate surface to form a solid product. With these traditional processes a reaction chamber and secondary energy (heat) source are mandatory making them different from the Combustion CVD process. Numerous flame-based variations of CVD have been used to generate powders, perform spray pyrolysis, create glass forms, and form carbon films including diamond films. 

The generic apparatus used in a vapor precursor process is very similar to that used in spray pyrolysis, except that the precursor material is introduced to the reactor as a vapor (see Figure 2.1, 2. la). If the precursor is a liquid, carrier gas is typically bubbled through it. If the precursor is a solid, then the carrier gas is often passed through a heated, packed bed of the material. The vapor-laden carrier gas then flows to a furnace reactor, where thermal decomposition of the precursor occurs and particle formation results. Product powder is collected or measured at the reactor outlet. Flame processes also fall into the vapor precursor/thermal decomposition category of gas-phase powder synthesis. The only difference is that the thermal energy is provided by combustion as opposed to an external source. 

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