<p><strong>Abstract</strong></p><p>The behavior for MoSi<sub>2</sub> based high temperature heating elements for resistive heating has been examined in elevated temperature and low oxygen content environment. MoSi<sub>2</sub> spontaneously forms a protective SiO<sub>2</sub> scale at high temperature if the amount of oxygen in the ambient atmosphere is sufficient according to the following reaction:</p><p>5MoSi<sub>2</sub> + 7O<sub>2</sub>(g) 7SiO<sub>2</sub> + Mo<sub>5</sub>Si<sub>3</sub></p><p>If the oxygen content at a specific temperature is too low, SiO(g) is more stable than SiO<sub>2</sub> and the following reaction will occur instead:</p><p>2SiO<sub>2</sub> 2SiO(g) + O<sub>2</sub>(g)</p><p>Then surface will be Si-deplated and finally, the base material will be exposed. Si and Mo will oxidize and degas from the surface as SiO and MoO<sub>3</sub> with severe diameter reduction of the heating element as a result. It is therefore of high interest to find the relationship between the maximum element temperature and the oxygen content in the ambient atmosphere to be able to fully exploit the potential of the heating elements and also to aid and help diagnose customer complaints.</p><p> </p><p>After 14 full scale tests in a custom made atmospheric furnace, the following equation could be calculated:</p><p>p(O<sub>2</sub>) = 1.748·10<sup>0.01677·T·log(e)-10</sup></p><p>The equation gives the minimum oxygen content at a specified temperature. The equation is based on 100 hours tests at atmospheric pressure, gas flow rate of 4 liter per minute, varying temperature and varying oxygen content. Nitrogen has been used as carrier gas for the oxygen.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-121411 |
| Date | January 2010 |
| Creators | Persson, Petter |
| Publisher | Uppsala University, Materials Science |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, text |
| Relation | UPTEC Q, 1401-5773 ; 10 002 |
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