Louis P. Martin

Investigating the Stability and Accuracy of the Phase Response for NOx Sensing 5% Mg-modified LaCrO3

Impedance spectroscopy measurements were carried out on LaCr{sub 0.95}Mg{sub 0.05}O{sub 3} (LCM) asymmetric interdigitated electrodes supported on fully stabilized 8-mol% Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} (YSZ) electrolytes. Experiments were carried out using 0-50 ppm NO{sub x}, 5-15% O{sub 2} with N{sub 2} as the balance, over temperatures ranging from 600-700 C. AC measurements taken at a constant frequency between 1-100 Hz indicated the phase response of the sensor was less sensitive to fluctuations in the O{sub 2} concentration and the baseline drift was limited. Specific frequencies were observed where the sensor response was essentially temperature independent.

Electrochemical NO x Sensors for Automotive Diesel Exhaust

New emissions regulations will increase the need for compact, inexpensive sensors for monitoring and control of automotive exhaust gas pollutants. Species of interest include hydrocarbons, carbon monoxide, and oxides of nitrogen (NO{sub x}). The current work is directed towards the development of fast, high sensitivity electrochemical NO{sub x} sensors for automotive diesel applications. We have investigated potentiometric NO sensors with good sensitivity and fast response when operated in 10% O{sub 2}. The sensors consist of yttria-stabilized zirconia substrates attached with NiCr{sub 2}O{sub 4} sensing electrodes and Pt reference electrodes. A composite NiCr{sub 2}O{sub 4}:Rh sensing electrode is shown to give significantly faster response than NiCr{sub 2}O{sub 4} alone. The exact role of the Rh in enhancing the response speed is not clear at present. However, the Rh appears to accumulate at the contacts between the NiCr{sub 2}O{sub 4} particles and may enhance the inter-particle electronic conduction. Ongoing testing of these sensors is being performed to elucidate the sensing mechanisms and to quantify cross sensitivity to, for example, NO{sub 2}.

Ultrasonic monitoring of laser damage in fused silica

The growth of a laser induced, surface damage site in a fused silica window was monitored by the ultrasonic pulse-echo technique. The laser damage was grown using 15 ns pulses of 1.053 μm wavelength light at a fluence of ∼25 J/cm2. The ultrasonic signal amplitude exhibited variations with the damage size which are attributable to the changing subsurface morphology of the damage site. The sensitivity to subsurface morphology makes the ultrasonic methodology a promising tool for monitoring laser damage in fused silica optics. This type of diagnostic capability may facilitate the safe deployment of large, high powered laser systems used in high energy and fusion research facilities.