Thermal shock and oxidation

Graham, S., McDowell, D.L., Lara-Curzio, E., Dinwiddie, R.B., Wang, H., Porter, W. (2003), Nondestructive characterization of thermal shock and oxidation-induced damage by flash diffusivity , J. Comp. Mater., 37(1), 73-87. 

Some examples of the grain-size effect in ceramics are illustrated below Ti3SiC2 was chosen as one exemplar, since this ternary compound exhibits a unique combination of properties. It is a layered material that is as machinable as graphite. At the same time, CG (100-300 pm) samples of Ti3SiC2 have been observed to be damage-tolerant, not susceptible to thermal shock and oxidation resistant. The specimens are fully dense, bulk, single-phase polycrystalline samples of Ti3SiC2. This material exhibits brittle failure characteristics at RT, but is plastic at 1,300 °C with yield points of 300 and 100 MPa under compression and flexure, respectively. 

The salient properties of this layered ternary ceramic are good damage tolerance, good machinabUity, low density and excellent thermal shock and oxidation resistance. Such unique properties make it possible to use Ti3AlC2 in structural components for high-temperature applications and as oxidation-resistant coatings. 

CrBe2 had some oxidation-resistance at 1260 °C weight gains after 100 h measured from 2 to 5.5 mg cm , depending on sample preparation. It seemed, however, very sensitive to thermal shock and oxidation-resistance was described as marginal at temperatures greater than 1371 °C. Small amounts of free Cr were detected in these samples before to testing, and the amounts increased after exposure. 

The wear and subsequent failure of a cutting tool is a complex mechanism that usually involves a number of physical and chemical phenomena. Temperatures at the tool/workpiece interface (cutting edge) may reach up to 1200°C in a very short period of time. This creates a pronounced thermal shock and promotes oxidation of the tool surface and the diffusion of metallic constituents of the tool into the chip with a resulting loss of tool strength. 

Beryllium oxide shows excellent thermal conductivity, resistance to thermal shock, and high electrical resistance. Also, it is unreactive to most chemicals. Because of these properties the compound has several applications. It is used to make refractory crucible materials and precision resistor cores as a reflector in nuclear power reactors in microwave energy windows and as an additive to glass, ceramics and plastics. 

Degradation of the fibre-matrix interface and removal of fibres. This type of damage appeared at A T= 600°C but was attributed to both thermal shock and/or oxidation effects. 

A common mistake is to use too little perchloric acid even with acid soluble materials posing no particular difficulty, there is considerable energy given off during the actual perchloric oxidation, and the acid is both consumed as oxidant and vigorously boiled off. If the total amount of acid available is insufficient, the mixture will go to dryness before the oxidation is complete and the dry residues will catch fire. True explosions on the 1—2 g sample scale are rare at this stage, but the beaker may shatter because of the thermal shock, and in any case the analysis will be ruined. 

Note that in general the nitrides and carbides of Si, with their lower thermal expansion coefficients, are more resistant to thermal shock than oxides. In theory, a material with zero thermal expansion would not be susceptible to thermal shock. In practice, a number of such materials do actually exist commercially, including some glass-ceramics that have been developed which, as a result of thermal expansion anisotropy, have extremely low a s (see Ch. 4). Another good example is fused silica which also has an extremely low a and thus is not prone to thermal shock. 

Alumina is the most important oxidic abrasion-resistant material. Metal carbides are in some ways superior to oxides with respect to hardness and melting point, but they are much more brittle than the oxides and are only used in isolated instances as wearing bodies. Silicon carbide is characterized by its low thermal expansion and high thermal conductivity and has proved to be more resistant to thermal shock than oxides. Zirconia is tougher than alumina its modulus of elasticity is only about half as large, and it is comparable with that of steel. Zirconia is therefore very suitable for compound structures with steel. At present, the applications of ceramic sintered materials in chemical plant construction are slide rings, pump parts, and slide bearings. 

Plain oxide ceramics do not enable economical machining of luckel base materials, due to their poor resistance to thermal shock and low firacture toughness. Alumina oxide with titanium-carbide, so-called mixed ceramics, was successful applied with cutting velocities up to 500 m/min for turning operations (Wiemann 2006). 

The new cements and composite based on then can be used in the coating of quartz glass tanks. In contact with glass there are used refractories made of natural baddeleyite without stabilizing oxides. The coating of this material showed good characteristics under thermal shock and quartz glass penetration resistance properties. 

Cells are fabricated on metal substrates. Compared with ceramic substrates, adoptable fabrication conditions are limited to prevent metals from being oxidized severely. Instead, metals as a main stmctural component provide many benefits such as better stability against thermal shocks and milder temperature distribution inside the stacks, etc. 

Tsyrulnikov, P.G., Kovalenko, O.N., Gogin, L.L., Starostina, T.G., Noskov, A.S., Kalinkin, A.V., Krukova, G.N., Tsybulya, S.V., Kudrya, E.N., and Bubnov, A.V. Behavior of some deep oxidation catalysts under extreme conditions. 1. Comparison of resistance to thermal shock and SO2 poisoning. Appl. Catal. A 1998,157,31-37. 

F. Monteverde and L. Scatteia Resistance to thermal shock and to oxidation of metal diborides-SiC ceramics for aerospace application. Journal of the American Ceramic Society 90, 1130-1138 (2007). 

With the advent of automobile catalytic converters, monolithic catalyst beds have been developed to convert unbumed hydrocarbons and carbon monoxide to combustion products. These oxidation reactions are highly exothermic. Thus, the catalyst is deposited only on the surface layers of the support. Other design considerations are a mechanically strong bed to withstand mechanical and thermal shock, and low pressure drop. These requirements led to monolithic catalyst beds of various configurations. 

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