Oxidatively-heating behavior

As stated in Preface, the oxidatively-heating behavior of a gas-permeable oxidatively-heating substance, such as sawdust, coal dust or oil-soaked lagging, is also of the TD type. Therefore, it is possible, in principle, to calculate the critical temperature for the spontaneous ignition or Tc for a heap of a gas-permeable oxidatively-heating substance such as sawdust of every wood species, having an arbitrary shape and an arbitrary size, placed in the atmosphere under isothermal conditions, by applying the reduced form of the F-K equation, i.e., Eq. (79) derived in Section 6.2, provided the value of for the shape of the substance is known. 

Early works were typically carried out using single atmosphere exposure conditions, either air (or moist air) representing the cathode side environment [124-129, 139, 142,144-162] or a reducing atmosphere simulating the anode side environment [124, 125, 127-129, 144, 145], Lately, studies have been also performed to determine the oxidation/corrosion behavior of metal and alloys under dual-atmosphere exposure conditions that closely simulate the interconnect exposure conditions during SOFC operation [154-159], The alloys studied include both Fe-Cr base FSSs and Ni or Ni-Cr base heat-resistant alloys, as well as Cr or Cr base alloys. 

Richardson and Waddams (31) found the same behavior for silica. Ground quartz particles agitated with water release some monosilicic acid molecules which form a true solution and, in addition, some very small quartz crystals which form a dispersion in water until a hydrated equilibrium surface is established. Analogous to the ferric oxide, heating the quartz to a temperature above 600° C. regenerates the anomalous solubility behavior. 

Direct study of the desorption of stearic acid from platinum and from NiO was carried out by Timmons and Zisman [10]. Their findings are shown in Table 10-5. The methylene iodide contact angle and the surface potential measurements indicate that a stearic acid monolayer adsorbed on platinum can be removed completely by heating to 130 C or by extraction with diethyl ether. But if the adsorbent is nickel oxide, heating to 150 C or extraction with diethyl ether fails to restore the original contact angle behavior or the surface potential of the adsorbent surface. 

Solution stability (to acid, base, oxidation, heat) Sobd-state stability according to ICH guidelines Electrostatic behavior Hygroscopicity Processability... 

Special Hazards of Combustion Products Produces toxic gas when heated Behavior in Fire Does not bum but supports combustion of combustible materials such as wood. May cause fire or explode on contact with other materials Igmtion Temperature (deg. F) Not flammable Electrical Hazard Data not available Burning Rate Not flammable. Chemical Reactivity Reactivity with Water Dissolves to foim nitric acid and nitric oxide. Nitric oxide reacts with air to form more nitrogen tetroxide Reactivity with Common Materials Very corrosive to metals when wet. Reacts vigorously with combustible materials such as wood Stability During Transport Stable Neutralizing Agents for Aci and Caustics Flush with water, then use soda ash or lime Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Figure 5.188 and Figure 5.189, respectively show how additives, such as flame retardants, can affect thermal-oxidative aging behavior of polycarbonates. Adding suitable stabilizers and glass fibers also influences degradation (Figure 5.190). A highly heat resistant polycarbonate exhibits higher resistance to thermal oxidation than a standard material.

Diamond behaves somewhat differently in that n is low in air, about 0.1. It is dependent, however, on which crystal face is involved, and rises severalfold in vacuum (after heating) [1,2,25]. The behavior of sapphire is similar [24]. Diamond surfaces, incidentally, can have an oxide layer. Naturally occurring ones may be hydrophilic or hydrophobic, depending on whether they are found in formations exposed to air and water. The relation between surface wettability and friction seems not to have been studied. 

Heterogeneous Catalysis. The main discovery of the 1980s was the use of titanium sihcaUte (TS-1) a synthetic zeoHte from the ZSM family containing no aluminum and where some titanium atoms replace siUcon atoms in the crystalline system (Ti/Si = 5%) (33). This zeoHte can be obtained by the hydrolysis of a siUcate and an alkyl titanate in the presence of quaternary ammonium hydroxide followed by heating to 170°C. Mainly studies have been devoted to the stmcture of TS-1 and its behavior toward H2O2 (34). The oxidation properties of the couple H2O2/TS-I have been extensively developed in... 

A good summary of the behavior of steels in high temperature steam is available (45). Calculated scale thickness for 10 years of exposure of ferritic steels in 593°C and 13.8 MPa (2000 psi) superheated steam is about 0.64 mm for 5 Cr—0.5 Mo steels, and 1 mm for 2.25 Cr—1 Mo steels. Steam pressure does not seem to have much influence. The steels form duplex layer scales of a uniform thickness. Scales on austenitic steels in the same test also form two layers but were irregular. Generally, the higher the alloy content, the thinner the oxide scale. Excessively thick oxide scale can exfoHate and be prone to under-the-scale concentration of corrodents and corrosion. ExfoHated scale can cause soHd particle erosion of the downstream equipment and clogging. Thick scale on boiler tubes impairs heat transfer and causes an increase in metal temperature. 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

Diaziridines, discovered in 1958, six years after the oxaziridines, were almost immediately realized to be structural analogs of oxaziridines. Like these they showed oxidizing properties unexpected for other classes of organic nitrogen compound. Properties in common with oxaziridines include the rearrangement to open chain isomers on heating above 100 °C (for several diaziridines), and their hydrolytic behavior in acidic media, which leads to carbonyl compounds with conservation of the hetero-hetero bond. 

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