Flame-based processing

Recent advances in aerosol and combustion science and engineering now allow scalable flame synthesis of mixed oxides, metal salts, and even pure metals in the form of nanoparticles and films with closely controlled characteristics [71-76]. Flame processes are classified into vapor-fed and liquid-fed, depending on the employed state of the metal precursor [77]. Liquid-fed flame processes are distinguished for their flexibility in producing materials of various compositions and morphologies that result in unique product functionalities. 

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A new flame-based process is being considered to oxidize a film on a wafer. As illustrated in Fig. 17.22, a combustible mixture flows downward from a showerhead manifold onto the wafer and the exhaust products are drawn out through an annular channel. A control system is presumed to hold the wafer temperature at a fixed temperature. The objective of the process is to deliver an atomic-oxygen number density of approximately 1015 cm-3 at the wafer surface while the wafer temperature is held at approximately Tw = 320°C. Assume the following nominal process conditions showerhead-to-... 

In this chapter, we review the spray-based powder production method, flame-based process, and CVD process for electrocatalyst powder production or direct film deposition, and describe the attributes of this process in terms of the nature of the catalyst produced, the particle size, and the influences on MEA layer structure, performance, and cost. 

Ammonia—Gas-Cured Flame Retardants. The first flame-retardant process based on curing with ammonia gas, ie, THPC—amide—NH, consisted of padding cotton with a solution containing THPC, TMM, and urea. The fabric was dried and then cured with either gaseous ammonia or ammonium hydroxide (96). There was Httle or no reaction with cellulose. A very stable polymer was deposited in situ in the cellulose matrix. Because the fire-retardant finish did not actually react with the cellulose matrix, there was generally Httle loss in fabric strength. However, the finish was very effective and quite durable to laundering. 

The model is a straightforward extension of a pool-fire model developed by Steward (1964), and is, of course, a drastic simplification of reality. Figure 5.4 illustrates the model, consisting of a two-dimensional, turbulent-flame front propagating at a given, constant velocity S into a stagnant mixture of depth d. The flame base of width W is dependent on the combustion process in the buoyant plume above the flame base. This fire plume is fed by an unbumt mixture that flows in with velocity Mq. The model assumes that the combustion process is fully convection-controlled, and therefore, fully determined by entrainment of air into the buoyant fire plume. 

Measurements showed that the amount of soot produced by the flame was affected by the mixing process between the air jet vortices, the fuel jets, and naturally entrained external air. PIV and smoke flow visualization showed that the air vortices induced strong external air entrainment into the main jet flow very close to the exit plane when the phase angle between the fuel jets and air jet were at the value for minimized soot production. When the wrong phase angle was used, i.e., that which leads to soot formation, the air vorticity coherence was reduced, the vortices appeared to develop further downstream, and the air entrainment at the flame base was significantly reduced. 

In 1892, Lewes (13, 14, 66) first proposed that acetylene is an important intermediate in combustion processes. He suggested a theory of luminosity of flames based upon its formation and subsequent incandescent decomposition. This did not prove successful as a general explanation of luminosity, but in recent years a modified version of this concept has been advocated by Porter (58, 59) and others. They suggest that acetylene is the starting point for the major reactions of carbon formation in flames and combustion. 

Since the first columns appeared in Camera Darkroom, The Darkroom Cookbook has taken on a further significance. As a photographer, educator, and writer, I put great importance on the future of the silver-based process. I have a strong desire to keep the flame alive, to pass on experience and technique to new generations of photographers. 

The most commonly used atomiser is the chemical flame, based upon the combination of a fuel gas (e.g., acetylene) with an oxidant (e.g., air or nitrous oxide). The sample solution is introduced into the flame using a nebuliser in which the passage of the oxidant creates a partial vacuum by the venturi effect and thus the sample solution is drawn up through a capillary. Thus, an aerosol is produced having a wide variety of droplet sizes. This process is shown in Fig. 2. 

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. 

We are aware of recent work by others concerning development of flame-based thin film deposition processes. However, our efforts and patents predate all of this work. Some key references ... 

The flame-based GC selective detectors derive their response from a specific flame emission (flame photometric detectors), or certain secondary ionization processes subsequent to the combustion in a flame (thermionic or alkali-flame detectors). Recent advances in the detector principles and their applications, as pertinent to biochemical uses, will now briefly be reviewed. 

Further field tests demonstrated that in spite of the excellent thermal and fire resistance, shrinking of the fabrics occurred above the glass-transition temperature which might expose the wearer to flames. Based on the results obtained in an Air Force contract at Dynatech Co., the Celanese Research Co. developed a two-stage process that reduced the shrinkage from 50 to 6%. The process was also amenable to on-line processing. The sulfonated derivative is the fiber which was marketed by the Celanese Corp. Some end uses include replacement of asbestos, thermal and chemical safety apparel, and stack gas filter bags, airline seat covers, firemen turn coats, and race car driver suits. 

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