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 (πΆπ΄π) . Andaian
selanjutnya bahawa dengan pergantungan suhu sensor pada pemalar kadar Arrhenius
(k) dan pekali kepekaan (Ι), 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.
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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 (πΆπ΄π). Further by
assuming that the temperature dependence of Arrhenius rate constant (k) and
sensitivity coefficient (Ι) , 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.