Kinetics and Mechanism of the Oxidation of Molybdenum

Simnad, Massoud T.; Spilners, Aija

doi:10.1007/bf03377603

Cited by 22 publications

(26 citation statements)

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“…Speiser and St. Pierre [6] reported on the occurrence of this mechanism. Our data with an inflection in volatilization rate near 600ºC resembles that shown by Simnad and Spilners [5]. They reported activation energies of 53.0 kcal/mole and 89.6 kcal/mole below and above 650ºC, which likely reflect the volatilization processes of MoO 2 (OH) 2(g) and (MoO 3 ) m , respectively.…”

Section: Discussionsupporting

confidence: 86%

“…Studies [1,5,6] on molybdenum at lower temperatures in high levels of oxygen report: 1) parabolic rate law at 250 to 450ºC, 2) linear behavior above 400ºC, 3) a role of MoO 2 and other oxides (MoO Z ), where 2 < Z < 3, between 450 to 650ºC, and 4) high vaporization of MoO 3 , mass loss and oxidation rates above 650ºC. We performed this study to explore conditions more typical to future fusion devices and to demonstrate predictive capabilities of a vaporization mass transport model.…”

Section: Introductionmentioning

confidence: 99%

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Oxidation and volatilization of TZM alloy in air

Smolik

Petti

Schuetz

2000

Journal of Nuclear Materials

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Section: Discussionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Oxidation and volatilization of TZM alloy in air

Smolik

Petti

Schuetz

2000

Journal of Nuclear Materials

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“…The oxidation process of rereficatroy metals has been the subject of numerious past studies and reviews. [1][2][3][4][5][6][7] It is well known that most of metals except noble metals, form tarnishing oxides layers even at low temperatures. Their reaction with oxygen at high temperature is expected to be very rapid.…”

Section: Introductionmentioning

confidence: 99%

“…air and oxygen gas) under different experimental conditions like temperature, oxygen partial pressure, duration of oxidation etc. [1][2][3][4][5][6][7] But very limited reports were published on the oxidation of metals using oxygen plasma as an oxidizing medium. It has been reported that oxygen plasma comprises positive ions, negative ions, neutrals, and many excited metastable states of oxygen molecules.…”

Section: Introductionmentioning

confidence: 99%

Oxidation of vanadium metal in oxygen plasma and their characterizations

et al. 2015

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In this report, the role of oxygen plasma on oxidation of vanadium (V) metal and the volatilization of its oxides has been studied as a function of source (V metal strip) temperature (Tss) and oxygen partial pressure (PO2). The presence of O2-plasma not only enhances the oxidation rate but also ficilitates in transport of oxide molecules from metal to substrate, as confirmed by the simultanous deposition of oxide film onto substrate. Both the oxidized metal strips and oxide films deposited on substrates are characterized separately. The structural and vibrational results evidence the presence of two different oxide phases (i.e. orthorhombic V2O5 and monocilinic V O2) in oxide layers formed on V metal strips, whereas the oxide films deposited on substrates exhibit only orthorhombic phase (i.e. V2O5). The decrease in peak intensities recorded from heated V metal strips on increasing Tss points out the increment in the rate of oxide volatilization, which also confirms by the oxide layer thickness measurements. The SEM results show the noticeable surface changes on V-strips as the function of Tss and PO2 and their optimum values are recorded to be 500 ˚C and 7.5 × 10−2 Torr, respectively to deposit maximum thick oxide film on substrate. The formation of microcracks on oxidized V-strips, those responsible to countinue oxidation is also confirmed by SEM results. The compositional study of oxide layers formed on V-strips, corroborates their pureness and further assures about the existence of mixed oxide phases. The effect of oxygen partial pressure on oxidation of V-metal has also been discussed in the present report. All the results are well in agreement to each other.

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“…Many of these studies have been oriented toward extremely high temperatures, e.g., up to 1700ºC, often under vacuum or environments with low oxygen activities [1,2,3,4]. Studies [1,5,6] on molybdenum at lower temperatures in high levels of oxygen report: 1) parabolic rate law at 250 to 450ºC, 2) linear behavior above 400ºC, 3) a role of MoO 2 and other oxides (MoO Z ), where 2 < Z < 3, between 450 to 650ºC. At temperatures above 650ºC, oxidation rates are largely influenced by the high rates of the vaporization of the various polymers of MoO 3 .…”

Section: Introductionmentioning

confidence: 99%

Oxidation, Volatilization, and Redistribution of Molybdenum from TZM Alloy in Air

Smolik¹,

Petti²,

McCarthy³

et al. 2000

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The excellent high temperature strength and thermal conductivity of molybdenum-base alloys provide attractive features for components in advanced magnetic and inertial fusion devices. Refractory metal alloys react readily with oxygen and other gases. Oxidized molybdenum in turn is susceptible to losses from volatile molybdenum trioxide species, (MoO 3 ) m , in air and the hydroxide, MoO 2 (OH) 2 , formed from water vapor. Transport of radioactivity by the volatilization, migration, and re-deposition of these volatile species during a potential accident involving a loss of vacuum or inert environment represents a safety issue. In this report we present experimental results on the oxidation, volatilization and re-deposition of molybdenum from TZM in flowing air between 400 and 800ºC. These results are compared with calculations obtained from a vaporization mass transfer model using chemical thermodynamic data for vapor pressures of MoO 3 (g) over pure solid MoO 3 and an expression for the vapor pressures of MoO 2 (OH) 2 from the literature. Calculations correlate well with experimental data. The volatilization process is dominated by MoO 3 above 550°C and by MoO 2 (OH) 2 , formed from the small ingress of water vapor, at temperatures below 550°C. Partial saturation of gaseous species of (MoO 3 ) near specimen surfaces accounts for observed reductions in volatilization rates at lower flow rates at 700ºC. We have thus demonstrated predictive capabilities of the model to account for volatilization as influenced by temperature, humidity (vapor content), and flow rate.We obtained oxidation rates (mm/h) as indicated by the recession into the base metal. These rates which accounted for the concurrent processes of oxidation and volatilization showed trends similar to other refractory metals, namely, niobium and tantalum.Deposition of MoO 3 downstream at lower temperatures was calculated with a model using saturation ratios of (MoO 3 ) m within segmented regions. Calculated locations of peak distributions and maximums within the temperature gradients generally correlate reasonable well with experimental measurements. Scanning electron microscopy showed that deposits collected in a final filter consisted of small agglomerated particles. We might expect such nucleation, growth and agglomeration of particles to result from the supersaturation of the (MoO 3 ) m upon cooling during transport. Hydroxide molecules also decompose back into MoO 3 (s) and water vapor at low temperatures. These latter two processes and increased surface areas due to extensive crystal growth from (MoO 3 ) m are plausible explanations for differences in peak height and distribution predictions between the model and experiments..The oxidation-driven mobilization data, along with activation calculations determining radioactive isotope inventories, were used to determine airborne dose rates. These calculations showed that site boundary doses from TZM alloy would be one to two orders of magnitude lower than tungsten at comparable temperatures.iii S...

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Kinetics and Mechanism of the Oxidation of Molybdenum

Cited by 22 publications

References 1 publication

Oxidation and volatilization of TZM alloy in air

Oxidation and volatilization of TZM alloy in air

Oxidation of vanadium metal in oxygen plasma and their characterizations

Oxidation, Volatilization, and Redistribution of Molybdenum from TZM Alloy in Air

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