Colmenares, C.A.

McKenzie, D.R.

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'· . ' . ... ~.: UCID -167 93 This is an informal report intended primarily for internal or limited external distribution . (The opinions and conclusions stated are those of the author and may or may not be those of the laboratory.) This report is not to be given additional external distribution or cited in external documents without the consent of the author or LLL Technical Information Department. ~ LAWRENCE LIVERMORE LABORATORY University of California/Livermore, California OXIDATION OF THORIUM IN OXYGEN, HUMID AIR, AND HUMID NITROGEN D. R. McKenzie and C. A. Co1menares May . 19, 1975 r--------------NOTICE--------------, This report was prepared as an account of work sponsor~d by the United States Government. Neither the Uruted States nor the United States Energy Re~arch and Development Administration. nor any nf lheu employees, nor any of their contractors subcontractors, or their employees, makes an; ~~nty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefu~ess of any information, apparatus, product or process diSclosed, or represents that its use would not mfringe pnvately owned rights. DISTRIBUTION OF THIS DOCUMENT UNLIMITE.Q P"P'"d fo1 U.S. A<omk Eo"gy Comm;,;oo ood" ooo""' oo. W·7405·Eog·48 ~ • DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. OXIDATION OF THORIUM IN OXYGEN, HUMID AIR, AND HUMID NITROGEN D. R. McKenzie and C. A. Colmenares Lawrence Livermore Laboratory Livermore, California (Presented at the 15th meeting of JOWOG-12, June 18-21, 1974, AWRE, Aldermaston, England) ABSTRACT The oxidation of two different grades of thorium, each with two different surface treatments, by water vapor at a pressure of 13.33 kPa has been studied in both air and nitrogen between 353 and 415 K. The dependence of the oxidation rates on the partial pressure of water vapor at 415 K was also investigated for these two grades of thorium. The oxidation of the lower-purity, arc-melted thorium was studied in 6.66 kPa oxygen between 373 and 433 K. The dependence of the oxidation rate on the partial pressure of oxygen was determined at 415 K for the arc-melted thorium. Experimental: Thorium, 1 ike many metals, corrodes when exposed to oxygen or moist gases. An understanding of the thorium water-vapor reaction and the oxidation of thorium is essential before thorium can be used in nuclear appl ica-P tions in the presence of oxygen and/or water vapor. ·:- The flow corrosion test apparatus used to test the two grades of thorium in a stream of moist gas has been previously documented. 1 It consisted of a heated test chamber capable of holding six samples suspended in the flowing test gas, a gas humidifier, and ~n analytical balance. In the static system, used for the studies in pure oxygen, the sample was suspended from a recording thermobalance 1 C. A. Colmenares, D. R. McKenzie, and T. E. Shell, J. Phys. E: .§., 1121 (1973). -2-in a thermostatically controlled test chamber. The entire system, including the thermobalance, was evacuated to 480 ~Pa before the test gas was introduced. The high-purity electron-beam-melted (EB) thorium contained less than 600 ppm impurities, while the lower-purity, arc-melted (AM) thorium contained 3500 ppm impurities. Prior to testing, the 11 degreased11 thorium samples were polished on 600-grit paper, ultrasonically cleaned for 15 min. in trichloroethylene, and then ultrasonically cleaned in ab.solute ethanol. The 11 etched 11 thorium samples were prepared by etching for 10 min. in 50 val% nitric acid, containing 0.5 val% hydro-fluoric acid, at room temperature for the EB samples and at 311 K for the AM thorium samples. Results: The reaction of thorium with water vapor, as followed by weight gain, showed three distinct regions: an initial portion, followed by an accel-erated transitional region and a final 1 inear portion. 2 The weight gain per unit surface area in the initial region was found to be proportional to a fractional power of time. However~ the weight gain in the initial region, if extended slightly, can also be approximated as a 11near function of time. We have analyzed the data both ways. The activation-energy results are presented in Table l, and the pressure exponents in Ta~le 2. The confidence 1 imits for the activation energies ' and pressure exponents were calculated using small sample statistics (t-test). J The electrical conductivity of thorium, or any material, is the product of mobility, concentration, and charge. This conductivity should be directly pro-portional to changes in concentration of the charge carriers at constant temperature, since the mobility of these charge carriers should be relatively insensitive to changes in concentration. Considering only cases where defects arising from oxidation 214th meeting of JOWOG-12, October 3-5, 1972. Union Carbide Y-12 Plant, CNC-2-698. J -3-or reduction predominate the pressure.dependences shown in Table 3 can be derived. 3 The po~sible control! i~g defects associated with the oxidation of the various grades of thorium are also 1 isted in Table 2. 3R. W. West, N. M. Tallan, and W. C. Tripp, J. Am. Ceram. So·c., !!l (12) 635-40 ( 1964) . -~ TABLE 1. Activation energies for the oxidation of thorium in oxygen, humid air and humid nitrogen. Activation energl Time Oxide Confidence Confidence Gas exponent, thickniss Mean limits, level, Thor i urn Treatment mixture (n) a m9/cm kJ/mole kJ/mole % AM Degreased Air/H 20 0.69 0.0-0.14 68.36 ±· 5.50 95 l.O 0.0-0.53 93.08 ± 2. 15 95 l. 0 2.7-8.0 72.39 ± 8.43 95 N/H20 0.67 0.0-0.27 64.32 ± 3.93 95 1.0 0.0-0.50 .92.59 ± 2.96 95 1.0 4.3-8.0 77.32 ± 4.18 c95 02 0.0-3.3 134.54 ±16.65 80 AM Etched Air/H20 0.67 0.0-0.04 54.99 ± 6.09 70 l.O 0.0-0.04 84.40 ± 19. 18 70 l. 0 2.5-8.0 67.19 ±13. 77 80 I .t" N/H20 0.33 0.0-0.06 34.67 ±13.21 70 I l. 00 0.0-0.06 94.52 ±19. 41 70 l.O 3.5-8.0 67.91 ±4.88 80 EB Degreased Air/H20 0.69 0.0-0.20 ]2.00 ± 5.48 90 1.0 0.0-0.50 99.59 ± 5.53 95 1.0 3.0-6.0 69.27 ± 6.08 90 N/H20 0.67 0.0-0.24 53.43 ± 3.43 95 1.0 0.0-0.45 73.27 ±· 7. 96 90 l.O 4.5-7.5 55.57 ±' 4.40 90 EB Etched Air/H 20 0.67 0.0-0.11 63.09 ± 5.59 90 l.O 0.0-0.20 94.21 ± 0.97 95 1.0 3.0-6.0 71.37 ± 8.92 80 N/H20 l.O 0.0-0.30 78.63 ± 12.15 60 1. 0 3.0-6.0 63.25 ± 5.30 95 a From (6W/A) = c + n Kt , where (6W/A) = weight gain/unit area, K = rate constant, t = time, and n = time exponent. ,_ 4 TABLE 2. Pressure exponents for- the oxidation of thorium in oxygen, humid air and humid nitrogen. Time Oxide Pressure exponents Confidence Gas exponent thickness Confidence level, Controlling Tno!·ium Treatment mixture (n)a ·mg/cm2 · Mean 1 imits % defect --------~------------------------~~--------~------------~----------------------~--------------------. Degreased Etched -Degreased Etched 1. 0 1.0 1.0 I. 0 1. 38 1.0 1. 0 1.0 1.0 1.0 l .. o 1.0 1.1 0.0-0.46 2.7-8.0 0.0-0.39 4.3-8.0 0.0-2.7 0.0-0.023 2.5-7.7 0.0-0.047 4.0-8.5 0.0-0.50 3.0-6.0 0.0-0.20 3.0-6.0 0.225 0.444 0.170 0.252 -0.153 0.810 0.332 0.245 0.280 0.400 0.318 0.502 0.473 ±0.029 ±0.072 ±0.090 ±0.072 ±0.036 ±0. 129 ±0.508 ±0. 116 ±0.046 ±0.067 ±0. 154 ±0.070 80 80 70 70 60 60 60 60 80 60 60 60 VTh-3, ~ O.-l, ~n=l/4 I . V T h-4 , (±) n= 1 I 5 VTh-1,<±) 0.-2, ® I VTh-3, ~) 0.-1, (f) I V0+2, 0 VTh-2, (±) VTh -3' (±) 0.- 1 , .<!;. I VTh-3,(±)-0.-1, <±) I VTh-2,(±) VTh-2' (£) VTh-1,(:±) v -1 4\ Th '~ I V1 I ., '':':·em (l:.W A) C + i<.tn, where K = rate constant, t = time, n = time exponent; (6W/A) =weight gain/ unit area. -6-TABLE 3 .. Pressure exponents for the oxidation of thorium for various possible defects under oxidation-reduction conditions Rate = K(Po2)x Predominant Pressure defect exponent v0+m, ·:~ (m I , 2) -1/4, -1/6 Th.+n, - (n 1,2,3,4) -1/2, -1/3, -1/4, -::j = I VTh-p, ~ (p 1",2,3,4) 1/2, 1/3, 1/4, 1/5 o.-q, I '+· ,!./ (q = I , 2) 1/4, 1/6 -1/5 V = vacancy, I interstitial,®= positive holes, (.:) = electrons. •. I Distribution - LLL C. F .. Bender, L-404 C. A. Colmenares, L-404 (3) K. Ernst/L. Hrubesh, L-404 W. J. Frank, L-28 . J. Frazer/ L. Rob.erts, L-40.1 W. Inouye, L-125 J. Keller, L-125 D. McKenzie, L-404 W. Nelson, L-)25 S. Root, L-401 : T. Taylor, L-404 TID ( 15) Distribution - LASL A. H. Zeltmann, CNC-2 TIC - OakRidge, TN (27) NOTICE "This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Energy Research & Development Administration, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any . information, · apparatus, product or process disclosed, or represents that its use would not infringe privately-owned rights." Printed in the United States of America Available from National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield, Virginia 22151 Price: Printed Copy $~; Microfiche $2.25 _,_ ·-·-Pages 1-50 51-150 151-325 326-500 501-1000 NTIS Selling Price $4.00 $5.45 $7.60 $10.60 $13.60 

Oxidation of thorium in oxygen, humid air, and humid nitrogen

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Oxidation of thorium in oxygen, humid air, and humid nitrogen

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