I-Ming Chou
W. Lu
Robert Burruss
Y. Zhang
L. Shang
2009
<p>Diffusion coefficients (<i>D</i>) of hydrogen in fused silica capillaries (FSC) were determined between 296 and 523 K by Raman spectroscopy using CO<sub>2</sub><span> </span>as an internal standard. FSC capsules (3.25 × 10<sup>−4</sup> m OD, 9.9 × 10<sup>−5</sup> m ID, and ∼0.01 m long) containing CO<sub>2</sub><span> </span>and H<sub>2</sub>were prepared and the initial relative concentrations of hydrogen in these capsules were derived from the Raman peak-height ratios between H<sub>2</sub><span> </span>(near 587 cm<sup>−1</sup>) and CO<sub>2</sub><span> </span>(near 1387 cm<sup>−1</sup>). The sample capsules were then heated at a fixed temperature (<i>T</i>) at one atmosphere to let H<sub>2</sub><span> </span>diffuse out of the capsule, and the changes of hydrogen concentration were monitored by Raman spectroscopy after quench. This process was repeated using different heating durations at 296 (room<span> </span><i>T</i>), 323, 375, 430, 473, and 523 K; the same sample capsule was used repeatedly at each temperature. The values of<span> </span><i>D</i><span> </span>(in m<sup>2</sup> s<sup>−1</sup>) in FSC were obtained by fitting the observed changes of hydrogen concentration in the FSC capsule to an equation based on Fick’s law. Our<span> </span><i>D</i><span> </span>values are in good agreement with the more recent of the two previously reported experimental data sets, and both can be represented by:<span class="display"></span></p><div class="formula"><span id="MathJax-Element-1-Frame" class="MathJax_SVG" data-mathml="<math class="math" xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal" is="true">ln</mi><mi is="true">D</mi><mo is="true">=</mo><mo is="true">-</mo><mo stretchy="false" is="true">(</mo><mn is="true">16.471</mn><mo is="true">&#xB1;</mo><mn is="true">0.035</mn><mo stretchy="false" is="true">)</mo><mo is="true">-</mo><mfrac is="true"><mrow is="true"><mn is="true">44589</mn><mo is="true">&#xB1;</mo><mn is="true">139</mn></mrow><mrow is="true"><mi mathvariant="italic" is="true">RT</mi></mrow></mfrac><mspace width="2em" is="true" /><mo stretchy="false" is="true">(</mo><msup is="true"><mrow is="true"><mi is="true">R</mi></mrow><mrow is="true"><mn is="true">2</mn></mrow></msup><mo is="true">=</mo><mn is="true">0.99991</mn><mo stretchy="false" is="true">)</mo></math>"><span class="MJX_Assistive_MathML">lnD=-(16.471±0.035)-44589±139RT(R2=0.99991)</span></span></div><p><span class="display"></span>where<span> </span><i>R</i><span> </span>is the gas constant (8.3145 J/mol K),<span> </span><i>T</i><span> </span>in Kelvin, and errors at 1<i>σ</i><span> </span>level. The slope corresponds to an activation energy of 44.59 ± 0.14 kJ/mol.</p><p>The<span> </span><i>D</i><span> </span>in FSC determined at 296 K is about an order of magnitude higher than that in platinum at 723 K, indicating that FSC is a suitable membrane for hydrogen at temperature between 673 K and room temperature, and has a great potential for studying redox reactions at these temperatures, especially for systems containing organic material and/or sulphur.</p>
application/pdf
10.1016/j.gca.2009.06.001
en
Elsevier
Determination of diffusion coefficients of hydrogen in fused silica between 296 and 523 K by Raman spectroscopy and application of fused silica capillaries in studying redox reactions
article