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The 1976–1977 heating season was the coldest on record, forcing utilities throughout the Northeast and Middle West to curtail their customers severely. Based on Ohio survey data, the employment impact of these curtailments is estimated by industry and week. Several types of curtailment were used, including appeals for voluntary conservation. As these curtailments allow customers a variety of responses, the study differentiates among curtailment types and assesses the employment impact of each.The impact estimates have been used in the design of an emergency curtailment system in Ohio. They also provide useful information in non-emergency situations for utilities faced with a decision to increase capacity and to expand customer hook-ups. As capacity is usually insufficient to preclude all shortages, it is important that the cost of capacity increases be weighed against the cost of the shortages they could avoid. 相似文献
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The oxidation behaviour of four model Co? Re? Cr alloys and a commercial Co‐based alloy was investigated at 1000 °C and a low‐oxygen partial pressure of p(O2) = 10?16 bar, in order to prove the feasibility of a pre‐oxidation treatment. Under suitable conditions of the pre‐oxidation treatment, the oxidation of the highly reactive alloying element Cr is possible. All the studied alloys form a continuous and dense Cr2O3 scale on the metal surface. The transport of chromium to the surface occurs mainly from the Cr‐rich σ‐phase, which becomes completely dissolved in the surrounding matrix after long exposure times. As a result of the Cr2O3 scale, growth depletion of Cr occurs in the near surface region, leading to internal oxidation. 相似文献
6.
S. Burk B. Gorr M. Krüger M. Heilmaier H. -J. Christ 《JOM Journal of the Minerals, Metals and Materials Society》2011,63(12):32-36
High melting Mo-Si-B based alloys exhibit good mechanical properties and oxidation resistance at very high temperatures. The
alloy composition Mo-9Si-8B (at.%) shows excellent oxidation behavior between 900°C–1,300°C as a consequence of protective
silica scale formation. Below 900°C, a protective oxide layer does not form as a consequence of simultaneous and competitive
Mo- and Si-oxide formation. Macro- and microalloying strategies as well as pre-treatment prior to oxidation in air were examined
in order to determine their impact on the oxidation performance. Alloying with Cr is a suitable means for protective Cr-oxide
scale formation at intermediate temperatures; adding small amounts of reactive elements was found to have a strong impact
on the silica scale forming ability. Furthermore, the oxidation behavior can be controlled and enhanced by selective oxidation
in oxygen-deficient atmospheres prior to exposure to air. 相似文献
7.
Bronislava Gorr Franz Müller Maria Azim Hans-Jürgen Christ Torsten Müller Hans Chen Alexander Kauffmann Martin Heilmaier 《Oxidation of Metals》2017,88(3-4):339-349
The high-temperature oxidation behavior of a new family of refractory high-entropy alloys (HEAs) with compositions of W–Mo–Cr–Ti–Al, Nb–Mo–Cr–Ti–Al and Ta–Mo–Cr–Ti–Al was studied at 1000 and 1100 °C. Based on these equimolar starting compositions, the main incentive of this study was to select the most promising alloy system whose properties may then be successively improved. Despite the high amount of refractory elements, Ta–Mo–Cr–Ti–Al showed good oxidation resistance at 1000 and 1100 °C. Moderate values of mass gain and complex oxidation kinetics were observed for the W- and Nb-containing HEAs. These alloys formed inhomogeneous oxide scales possessing regions with thick and porous layers as well as areas revealing quite thin oxide scales due to the formation of discontinuous Cr- and Al-rich scales. The most promising behavior was shown by the alloy Ta–Mo–Cr–Ti–Al which followed the parabolic rate law for oxide growth due to the formation of a thin and compact Al-rich layer. 相似文献
8.
S. Majumdar D. Schliephake B. Gorr H.-J. Christ M. Heilmaier 《Metallurgical and Materials Transactions A》2013,44(5):2243-2257
The oxidation behavior of 0.2 Y-alloyed Mo-9Si-8B (at. pct) was investigated in a wide temperature range from 923 K to 1673 K (650 °C to 1400 °C). Formation of a thin yttrium-silicate scale at the outer layer along with the thick silica-rich inner layer containing Y-rich oxide inclusions was detected beyond 1573 K (1300 °C). A substantial improvement in the oxidation resistance of the alloy could be realized at 1073 K to 1273 K (800 °C to 1000 °C) with the addition of yttrium. The formation of a viscous silica-rich protective scale could prevent the permeation of MoO3 at the initial stages of oxidation at this temperature regime. The growth of the internal oxidation zone followed a parabolic rate at 1273 K to 1673 K (1000 °C to 1400 °C), and the activation energy values calculated for both the outer oxide scale and internal oxidation zone formation indicated the inward diffusion of oxygen as the dominant rate controlling mechanism. The microstructural and kinetic data obtained for internal and external oxidation indicate that yttrium-silicate scale reduces the inward diffusion of oxygen, thereby improving the oxidation resistance of the alloy at high temperatures in any oxidizing environment. 相似文献
9.
K. Esleben B. Gorr H.-J. Christ D. Mukherji J. Rösler 《Materials at High Temperatures》2018,35(1-3):177-186
AbstractThe present study focused on the influence of Ni on the microstructure and oxidation behaviour of Co–Re–Cr-based alloys. Alloys with three different Ni contents were tested in laboratory air at 800–1100 °C. A refinement and a reduction of the σ phase volume fraction as well as a change in the matrix microstructure were observed. Thermogravimetric measurements showed that the alloys with higher Ni contents possess a better oxidation resistance when exposed to higher temperatures. All alloys suffered from continuous mass loss during oxidation at 800 °C due to the formation of porous oxides scales, consisting of Co3O4, Co(Ni)O and Ni-doped CoCr2O4, which allow the evaporation of Re-oxides. At 900–1100 °C, only the alloy with 25 at. % Ni showed parabolic oxidation kinetics after a short period of transient oxidation. This is a result of the fast formation of a protective Cr2O3 layer. It was also found that exposure to air at 1000 °C leads to a phase transformation of the bulk material; an oxidation-induced formation of fine hexagonal close-packed (hcp) grains was observed near the oxide scales. It is supposed that the improved oxidation resistance of Ni-containing Co–Re–Cr alloys is a result of enhanced Cr diffusion caused by the Ni addition. The extensive formation of the fcc phase in the alloy matrix had a detrimental effect on the oxidation behaviour of the Ni-containing Co–Re–Cr-based alloys. 相似文献
10.
Franz Müller Bronislava Gorr Hans-Jürgen Christ Hans Chen Alexander Kauffmann Martin Heilmaier 《Materials at High Temperatures》2018,35(1-3):168-176
AbstractThe effect of 1 at.% Si addition to the refractory high-entropy alloy (HEA) Ta–Mo–Cr–Ti–Al on the high temperature oxidation resistance in air between 900 °C and 1100 °C was studied. Due to the formation of protective chromia-rich and alumina scales, the thermogravimetric curves for Ta–Mo–Cr–Ti–Al and Ta–Mo–Cr–Ti–Al–1Si showed small mass changes and low oxidation rates which are on the level of chromia-forming alloys. The oxide scales formed on both alloys at all temperatures are complex and consist of outermost TiO2, intermediate Al2O3, and (Cr, Ta, Ti)-rich oxide at the interface oxide/substrate. The Si addition had a slightly detrimental effect on the oxidation resistance at all temperatures primarily as a result of increased internal corrosion attack observed in the Si-containing HEA. Large Laves phase particles distinctly found in the Si-containing alloy were identified to be responsible for the more rapid internal corrosion. 相似文献