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Diffusion mechanism modeling on mesoporous tin dioxide (SnO2) as gas sensor in detecting ethanol vapor

Diffusion mechanism modeling on mesoporous tin dioxide (SnO2) as gas sensor in detecting ethanol vapor / Chai Bui Hon

Abstract Pengaruh fenomena resapan gas pada kepekaan filem tebal mesoporous timah dioksida sensor gas telah dikaji secara teori. Persamaan resapan dirumuskan di bawah keadaan mantap tindak balas kinetik tertib pertama sebagai fungsi dalam pemalar resapan Knudsen (D), ketebalan filem (L), dan kepekatan gas (𝐶𝐴𝑆) . Andaian selanjutnya bahawa dengan pergantungan suhu sensor pada pemalar kadar Arrhenius (k) dan pekali kepekaan (ɑ), satu pernyataan umum terhadap kepekaan (S) melibatkan suhu dan kepekatan gas telah diperolehi. Keputusan menyatakan bahawa kepekaan melawan suhu operasi sensor menunjukkan satu variasi graf berbentuk loceng dengan suhu optimum manakala kepekatan gas yang semakin meningkat membawa kepada peningkatan kepekaan sehingga ketepuan tercapai. Seterusnya, model transduksi gas dirumuskan di bawah keadaan tidak mantap dengan andaian bahawa resapan gas mewujudkan kealiran dalam sensor gas menggunakan prinsip elektrokimia. Model transduksi gas telah digunakan untuk menyatakan kepekatan gas sebagai satu fungsi polinomial yang melibatkan pekali resapan (D), pemalar kadar Arrhenius (k), ketebalan filem (L), masa (t), kepekatan gas sasaran (C0) dan rintangan asas sensor (R0). Kepekaan sensor memaparkan peningkatan dan mencapai kestabilan selepas beberapa minit. Keputusan menunjukkan bahawa tindak balas sensor dalam masa singkat di mana pergantungan kepekaan sensor gas pada suhu operasi dan kepekatan gas boleh disimulasikan secara tepat berdasarkan model transduksi itu. _______________________________________________________________________________________________________ Influences of gas diffusion phenomena on the sensitivity of a mesoporous thick film tin dioxide gas sensor were investigated theoretically. Diffusion equation was formulated under steady-state first order reaction kinetic as the function of Knudsen diffusion constant (D) , film thickness (L), and gas concentration (𝐶𝐴𝑆). Further by assuming that the temperature dependence of Arrhenius rate constant (k) and sensitivity coefficient (ɑ) , a general expression of sensitivity (S) involving temperature and gas concentration was derived. Results show that sensitivity versus sensor operating temperature led to a bell-shaped graph variation with an optimum temperature whereas increasing gas concentration led to an increasing sensitivity until saturation reached. On the other hand, gas transduction model was formulated under non steady-state condition assuming that diffusing gas created conductance in gas sensor using electrochemical principles. The gas transduction model was used to express the gas concentration by a polynomial function involving diffusion coefficient (D), Arrhenius rate constant (k), film thickness (L), time (t), target gas concentration (C0) and sensor baseline resistance (R0). Remarkably, the sensor sensitivity exhibits an increasing behavior and reached stabilization after few minutes. Results showed that the time-dependent transient response of gas sensor sensitivity which dependence on operating temperature and gas concentration could be simulated well based on the transduction model.

Contributor(s): Chai Bui Hon - Author Primary Item Type: Final Year Project Identifiers: Accession Number : 875005168 Language: English Subject Keywords: gas; diffusion; mesoporous First presented to the public: 6/1/2013 Original Publication Date: 1/27/2020 Previously Published By: Universiti Sains Malaysia Place Of Publication: School of Chemical Engineering Citation: Extents: Number of Pages - 93 License Grantor / Date Granted:   / ( View License ) Date Deposited 2020-01-28 16:35:01.438 Submitter: Mohd Jasnizam Mohd Salleh

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