Oxyacetylene combustion

Oxyacetylene torches used for welding reach temperatures near 2000°C. The reaction involved in die combustion of acetylene is... 

Oxyacetylene welding torches burn acetylene gas, C2H2(g). Use the information in Table 8.2 to calculate AH° (in kilojoules) for the combustion reaction of acetylene to yield C02(g) and H20(g). 

The kinetics and mechanisms of radical reactions important in combustion chemistry are best studied under conditions in which single reactions can be isolated rather than in flames where there are multiple pathways for formation and disappearance of the radicals. Reactions of C2 are of particular importance since recent laser saturation measurements in our laboratory (1) have shown that C2 a3IIu is present in oxyacetylene flames at concentrations on the order of 1016 molecules/cm3 (approximately 0.1 torr). Although concentrations of ground state C2 in flames are unknown and cannot be measured by the same technique due to spectroscopic constraints, we expect that C2 X3 g populations are at least comparable. Because of these relatively large concentrations the reactions of both species are of considerable importance in combustion chemistry. However, until recently very little was known about these reactions due to the difficulty of producing a clean source of C2 radicals. 

Acetylene is by far the most important commercial alkyne. Acetylene is an important industrial feedstock, but its largest use is as the fuel for the oxyacetylene welding torch. Acetylene is a colorless, foul-smelling gas that burns in air with a yellow, sooty flame. When the flame is supplied with pure oxygen, however, the color turns to light blue, and the flame temperature increases dramatically. A comparison of the heat of combustion for acetylene with those of ethene and ethane shows why this gas makes an excellent fuel for a high-temperature flame. 

Have you ever seen a construction worker using an oxyacetylene torch (See Figure 14.6.) A brilliant white light comes from the torch as it cuts through steel. The intense heat that is associated with this flame comes from the combustion of ethyne, a very common alkyne. Ethyne is also known as acetylene. 

The energy necessary to weld metals with an oxyacetylene torch comes from the combustion of acetylene. 

Combustion synthesis of diamond films fi om atmospheric pressure oxyacetylene flame was first reported by Hirose in 1988.This technique, as shown schematically in Fig. 2h, has been demonstrated to be a potentially very important means of growing diamond (Table 1). In Hirose s experiments, linear growth rates of100-200 pmh were achieved. The results were then confirmed by Hanssen et al.l l In Hirose s experiments and most of those that followed, the oxyacetylene torch was typically run with... 

Acetylene gas (ethyne HC=CH) burns with oxygen in an oxyacetylene torch to produce carbon dioxide, water vapor, and the heat needed to weld metals. The heat of reaction for the combustion of acetylene is 1259 kJ/mol. (a) Calculate the C=C bond energy, and compare your value with that in Table 9.2. (b) When 500.0 g of acetylene burns, how many kilojoules of heat are given off (c) How many grams of CO2 are produced ... 

Oxyacetylene welding is used to repair metal structures, including bridges, buildings, and even the Statue of Liberty. Calculate AS° for the combustion of 1 mol of acetylene (C2H2). 

With a temperature of 3300°C, the flame of an oxyacetylene torch exceeds that obtained from any other combustible gas mixture. 

The combustion of acetylene yields energy that produces the very hot temperatures of an oxyacetylene torch. 

Alkynes are nonpolar and exhibit the same trends in boiling points and physical states as other hydrocarbons. The smallest alkyne, ethyne, is a gas. The combustion of ethyne when it is mixed with pure oxygen produces the intense heat of welding torches, as shown in Figure 2.11. As mentioned, the common name of ethyne is acetylene, so these welding torches are commonly called oxyacetylene torches. 

Over 100 million tonnes of oxygen is made each year in industry. Most of that is used to make steel, but other uses include supporting combustion and generation of high temperature (oxyacetylene cutters) and in life support, the latter in health care (oxygen tents and masks, emphysema treatment) and by divers, in aircraft and in spaceflight. 

Plasma arc-jet and oxyacetylene torch ablation tests are much more convenient for operations and with much lower cost, which therefore are often used for primary evaluations of materials about their thermal shock resistance and ablation resistance properties . The difference between these two methods is their gaseous composition and flow speed. A plasma of air may exhibit ultra high temperatures above 5000°C and high velocities of 2 Mach but with ionized air atmosphere. On the other hand, the generally used oxyacetylene torch is of combustion gaseous products of carbon mono/dioxide, water vapor, OH and active hydrocarbon species with gas velocity less than 1 Mach and temperatures above 3000°C. A HVOF torch exhibits... 

Acetylene is also used to produce high-temperature flames that are used in a variety of applications. For example, the combustion of acetylene in excess oxygen is the basis of oxyacetylene torches used for cutting and welding metals. 

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