Infrared radiation coatings were prepared by plasma spray on the copper sheet. The structure and emissivity were examined by x-ray diffraction and infrared radiant instrument, respectively. The results show that an appropriate addition of TiO 2 (5-15 wt.%) to NiO and Cr 2 O 3 leads to high emissivity of coating with (Cr 0.88 Ti 0.12 ) 2 O 3 and NiCr 2 O 4 phase. However, more (20-30 wt.%) will frustrate the formation of NiCr 2 O 4 and ultimately decrease the emissivity. Moreover, the coating prepared by plasma spray endures a long working time without emissivity decrease.

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A compact, sensitive laser-based absorption sensor for multispecies monitoring of methane (CH4), acetylene (C2H2) and ammonia (NH3) was developed using a compact multipass gas cell. The gas cell is 8.8 cm long and has an effective optical path length of 3.0 m with a sampling volume of 75 mL. The sensor is composed of three fiber-coupled distributed feedback lasers operating near 1512 nm, 1532 nm and 1654 nm, an InGaAs photodetector and a custom-designed software for data acquisition, signal processing and display. The lasers were scanned over the target absorption features at 1 Hz. First-harmonic-normalized wavelength modulation spectroscopy (f = 3 kHz) with the second harmonic detection (WMS-2f/1f) is employed to eliminate the unwanted power fluctuations of the transmitted laser caused by aerosol/particles scattering, absorption and beam-steering. The multispecies sensor has excellent linear responses (R2 > 0.997) within the gas concentration range of 1–1000 ppm and shows a detection limit of 0.32 ppm for CH4, 0.16 ppm for C2H2 and 0.23 ppm for NH3 at 1 s response time. The Allan–Werle deviation analysis verifies the long-term stability of the sensor, indicating a minimal detection limit of 20–34 ppb were achieved after 60–148 s integration time. Flow test of the portable multispecies sensor is also demonstrated in this work.

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