Hot flame

The end or front of the plasma flame impinges onto a metal plate (the cone or sampler or sampling cone), which has a small hole in its center (Figure 14.2). The region on the other side of the cone from the flame is under vacuum, so the ions and neutrals passing from the atmospheric-pressure hot flame into a vacuum space are accelerated to supersonic speeds and cooled as rapid expansion occurs. A supersonic jet of gas passes toward a second metal plate (the skimmer) containing a hole smaller than the one in the sampler, where ions pass into the mass analyzer. The sampler and skimmer form an interface between the plasma flame and the mass analyzer. A light... 

At still higher temperatures, when sufficient oxygen is present, combustion and "hot" flames are observed the principal products are carbon oxides and water. Key variables that determine the reaction characteristics are fuel-to-oxidant ratio, pressure, reactor configuration and residence time, and the nature of the surface exposed to the reaction 2one. The chemistry of hot flames, which occur in the high temperature region, has been extensively discussed (60-62) (see Col ustion science and technology). 

The blue luminescence observed during cool flames is said to arise from electronically excited formaldehyde (60,69). The high energy required indicates radical— radical reactions are producing hot molecules. Quantum yields appear to be very low (10 to 10 ) (81). Cool flames never deposit carbon, in contrast to hot flames which emit much more intense, yellowish light and may deposit carbon (82). 

Figure 14-9 also shows a flowchart for analysis of wet and dry precipitation. The process involves weight determinations, followed by pH and conductivity measurements, and finally chemical analysis for anions and cations. The pH measurements are made with a well-calibrated pH meter, with extreme care taken to avoid contaminating the sample. The metal ions Ca, Mg, Na, and are determined by flame photometry, which involves absorption of radiation by metal ions in a hot flame. Ammorda and the anions Cl, S04 , NO3 , and P04 are measured by automated colorimetric techniques. 

The precipitation step may be replaced by spray drying of a homogeneously stirred solution of, e.g., nitrates [31], or by spraying the precursors into a very hot flame at about 1500-2200 °C. This method is called flame pyrolysis. 

MacEvoy. Proposed to use primers contg metallic Na and w in sep compartments. A hot flame was produced on the contact of the ingredients Ref Daniel (1902), 414... 

Its rate of deton is comparable to that of LA and its thermal stability is quite good (no weight loss at 80° for several days). It bums in air, producing a hot flame... 

If an expl is intended for use in primers, then its brisance and power may be lower than for groups (1), (2) and (3), but it should possess low sensitivity to impact and friction and should produce a hot flame in order to ignite a charge of proplnt or a deiay train... 

In the case of initiating expls, the requirements are the same as in (4) except that a hot flame is not required, but rather that it produce a shock wave strong enough to detonate a HE such as Tetryl, PETN, RDX, PA, TNT, etc... 

Acetylenes contain at least one triple bond. The triple bond is even more reactive than a double bond and, therefore, acetylene is used industrially to make other compounds used in rubber and plastics. Acetylene burns in oxygen to produce a very hot flame used for welding and metal cutting (oxy-acetylene torch). 

These needles have the disadvantage that, owing to their fineness, they tend to oxidize away readily and may also be melted if held in a hot flame for any appreciable length of time. 

The seal is made by cutting 1-cm diameter tubing to give one piece with a square end. Near the end of the other piece a spindle is drawn. The shoulder of the spindle is heated in a small hot flame so that it thickens, and then, with a fairly cool flame, the spindle beyond the shoulder is drawn out to a fine capillary about 1 mm diameter. This is heated in a very cool flame and bent first one way and then the other, as m Figure 47, II. The end is finally sealed off. The tip thus prepared is inserted into the square end of the other piece of tubing, as in Figure 47, /, and a joint is made by directing a small flame at... 

For tooling of molten Vitreosil inch Nichrome wire may be employed though if much tooling is required, then carbon rods or plates are necessary. In general, most of the operations described in earlier chapters can be modified for working with Vitreosil and, if a sufficiently hot flame is available, less manipulative skill is usually necessary because the material stays fairly viscous. 

Atomic absorption takes advantage of the fact that most of the atoms remain in the ground state, and are capable of absorbing radiation of the appropriate wavelength corresponding to Ah. Whereas a hot flame is preferred for flame photometry, a cooler flame is preferred for atomic absorption, except in cases where chemical interference may occur. 

Hot Flame Ignition - A rapid self-sustaining, sometimes audible gas phase reaction of the sample or its decomposition products with an oxidant. A readily visible yellow or blue flame usually accompanies the reaction. 

NFPA now normally refers to autoignition as the Hot Flame Ignition Temperature, as a more precise definition. Subsequently the following two additional terms are being adopted by NFPA to further refine the ignition properties of materials. The lowest temperatures at which cool flame ignitions are observed are named the Cool Flame Reaction Threshold (CFT). The lowest flame temperatures at which an exothermic gas phase reaction is noticed are named the Preflame Reaction Threshold (RTT). 

---