Thermal matching

Since the photosensitive material and the electronics layer are very thin, the detector is mounted on a mechanical package for structural integrity. This package is thermally matched to the detector so that the detector will not be stretched or compressed during the large transition from room temperature to operating temperature. 

Reforming and Sulfur Removal - A better thermal match exists with existing reforming and sulfur removal processes. However, it should be noted the optimal nominal reformer temperature depends on the composition of the fuel. 

Thermal integration is an important aspect of the system. Figure 3a depicts a fuel cell coupled to a catalytic POX reformer. This reformer thermally matches very well with the 800°C SOFC technologies being developed. However, both the reformer and fuel cell involve exothermic oxidation reactions, and heat is in... 

These gas-phase fuel processing reactions have significantly different operating temperatures and thermal requirements (exothermic versus endothermic), so that thermal matching of the various gas streams through heat exchangers is an engineering requirement. 

Thermal drift, not a problem in UHV, is particularly troublesome for instruments operated in air or at low-temperatures without proper thermal isolation. Because the piezoelectric materials have a low thermal conductivity and are housed in materials that have been carefully thermally matched, like Macor or Invar , the whole scanner assembly will drift over a long period of time if heated or cooled, intentionally or unintentionally. A screen room or simply a cover will protect the SPM from temperature fluctuations due to air-conditioning fans cycling on and off. The low-temperature thermal isolation was discussed in the section on low-temperature designs above. 

Modern DTA instruments have the ability to change atmospheres from inert to reactive gases, as is done in TGA. As is the case with TGA, the appearance of the DTA thermal curve depends on the particle size of the sample, sample packing, the heating rate, flow characteristics inside the furnace, and other factors. Thermal matching between the sample and the reference is often improved by diluting the sample with the inert reference, keeping the total masses in each crucible as close to each other as possible. 

Solid oxide fuel cells (SOFCs) involve structures composed of multiple ceramic layers, or interleaved layers of ceramic membranes and metal interconnects. To eliminate premature mixing of fuel and air gases or leaking of these gases from interior regions of the structure, the interfaces of adjacent layers are sealed with a glass or ceramic seal. These seals must withstand the high-temperature environment of the SOFC over its lifetime. Therefore these materials must be thermally matched with the adjacent layers to minimize transient stress risers and eliminate the potential for consequent seal failure. 

A significant advantage of MCM-Si is the fact that the substrate is the same material as the ICs that will be attached to it. Therefore, it is thermally matched to the ICs, ensuring reliable contacts over extremes of temperature. 

Minor species, such as CO, result from subsequent dissociation reactions governed by thermodynamics. Of the various fuels involved, methanol is the simplest liquid-based fuel to reform due to the lack of carbon-carbon bond and low reformation temperature of only around 200°C [21]. This temperature can easily be coupled to low-temperature systems. The PAFC is almost perfectly thermally matched to the methanol reformation temperature, so that waste heat from the fuel cell can be used to drive the process. For PEFCs, some additional input heat is needed for methanol and other fuel reformation. For high-temperature fuel cells, methanol (and other fuel) reformation can be accomplished internally or externally, as discussed in Chapter 7. The reformation temperature of other fuels can be several hundreds of degrees higher than that of methanol, depending on the complexity and strength of the chemical bonds as well as the catalyst used to promote the reaction. 

SOFCo (825°C), thermally matched materials and seal-less stack printing followed by co-firing... 

Corporation (750°C) with thermally matched materials robust structure with rapid start-up deposition followed by co-sintering... 

Glass has a very low thermal expansion coefficient the materials joined with glass have to be similar in expansion or must be duetile, while staying vacuum tight. Even with best-matched materials skilled craftsmanship is asked for the joining process. 

In order to Introduce thermal effects into the theory, the material balance equations developed in this chapter must be supplemented by a further equation representing the condition of enthalpy balance. This matches the extra dependent variable, namely temperature. Care must also be taken to account properly for the temperature dependence of certain parameters In... 

Thermal ionization has three distinct advantages the ability to produce mass spectra free from background interference, the ability to regulate the flow of ions by altering the filament temperature, and the possibility of changing the filament material to obtain a work function matching ionization energies. This flexibility makes thermal ionization a useful technique for the precise measurement of isotope ratios in a variety of substrates. 

Euture appHcations may involve use of SiC as substrates for siHcon chips, making use of the high thermal conductivity of SiC and its close thermal expansion match to siHcon. The low density and high stiffness of siHcon carbides may also result in appHcations in space. One such appHcation is for space-based mirrors, making use of the high degree of surface poHsh possible on dense SiC. 

Properties. The ideal substitute should have identical or better performance properties than the CFG it replaces. The ideal CFG substitute must not harm the o2one layer, and must have a short atmospheric lifetime to ensure a low greenhouse warming potential (GWP). It also must be nontoxic, nonflammable, thermally and chemically stable under normal use conditions, and manufacturable at a reasonable pnce. The chemical industry has found substitutes that match many but not all of these cntena. 

From the colorless state it can be switched with light of short wavelength (A = 380 nm) via an electrocycHc ring opening and cis/trans rotation of one half of the molecule into a state with violet/purple color. The reverse reaction is effected by visible light (A = 580 nm). Since the system is metastable, one of the two reaction directions is matched by a rival thermal reaction, the thermoreversion. This progresses, however, in the case of benzospiropyran, at room temperature by a factor of 10 slower than the light-induced reaction. 

Decomposition of diphenoylperoxide [6109-04-2] (40) in the presence of a fluorescer such as perylene in methylene chloride at 24°C produces chemiluminescence matching the fluorescence spectmm of the fluorescer with perylene was reported to be 10 5% (135). The reaction follows pseudo-first-order kinetics with the observed rate constant increasing with fluorescer concentration according to = k [flr]. Thus the fluorescer acts as a catalyst for peroxide decomposition, with catalytic decomposition competing with spontaneous thermal decomposition. An electron-transfer mechanism has been proposed (135). 

The thermal expansivity of Ni—Fe alloys vary from ca 0 at ca 36 wt % Ni (Invar [12683-18-OJ) to ca 13 x 10 / C for Ni. Hence, a number of compositions, which are available commercially, match the thermal expansivities of glasses and ceramics for sealing electron tubes, lamps, and bushings. In addition, the thermal expansion characteristic is utilized ia temperature controls, thermostats, measuriag iastmments, and condensers. 

Single-crystal sUicon has also been employed as substrate material, particularly in multichip module (MGM)-Si appUcations. As a substrate, sUicon offers good thermal conductivity and matches the GTE of the devices mounted on it it does, however, have a relatively high dielectric constant and is very britde. 

Cases can be classified as either hermetic or nonhermetic, based on their permeabiUty to moisture. Ceramics and metals are usually used for hermetic cases, whereas plastic materials are used for nonhermetic appHcations. Cases should have good electrical insulation properties. The coefficient of thermal expansion of a particular case should closely match those of the substrate, die, and sealing materials to avoid excessive residual stresses and fatigue damage under thermal cycling loads. Moreover, since cases must provide a path for heat dissipation, high thermal conductivity is also desirable. 

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