Date of Award

2016

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Science

First Advisor

Professor Kamal Alameh

Second Advisor

Devendra Maurya

Abstract

pH sensors are broadly used in chemical and biological applications. Example, Metal oxide-based pH sensors have many appealing features that include chemical resistance, insolubility, stability, outstanding mechanical strength, electrocatalyst and manufacturing technology. This thesis focuses on recent pH measurement techniques which incorporate miniaturization and optimization of the sensor and fabrication with super Nerstian pH sensitive materials. Such sensors have high sensitivity, fast response, excellent corrosion resistance, wide detection range, low hysteresis, long-term stability and good reversibility/reproducibility.

The research validates the feasibility of developing a low-cost, rugged, miniaturized ruthenium oxide (RuO2) thin-film pH sensor comprising a RuO2 on platinum sensing electrode deposited using R.F. magnetron sputtered in conjunction with an integrated thick Ag/AgCl reference electrode. Ion diffusion condition (O2:Ar ratio), electrode film thickness (50-425 nm), sensing media temperature (1.5-50 °C) and working electrode area to reference electrode area ratio, are investigated for alumina and flexible substrates. Sensitivity values ranging from of 58.50 mV/pH to 84.50 mV/pH are attained with the developed sensors, for water quality, urease, biomedical application and standard buffer solutions of pH values 4.0 and 10.0. These results are in excellent agreement with the theoretical Nernstian response. The performance and characterization of the pH sensors with regards to sensitivity, response time, pH resolution, stability and reversibility are also investigated. A feasibility study for developing a ruthenium oxide (RuO2)-based pH sensor on a flexible substrate was also investigated.

Moreover, the suitability of sensors demonstrate the concept of electrodes for monitoring engine oil acidity by adding nitric acid. Experimental results show a linear potential-versus-acid-concentration response for nitric acid concentration between 0 (fresh oil) to 400 ppm, thus demonstrating the accuracy of the RuO2 sensor in real-time operation, making it attractive for use in cars and industrial engines.

Available for download on Tuesday, April 10, 2018

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