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The paper deals with chemical contamination monitoring in phosphate-ester-based hydraulic fluids using nondispersive infrared (NDIR) optical absorption. Our results show that NDIR monitoring allows detecting the take-up of water into such fluids and their hydrolytic disintegration as these become additionally stressed by Joule heating. Observations on the O-H stretching vibration band (3200-3800 cm −1 ) are used for determining the free water content (0-1.5%) and the Total Acid Number (0-1 mgKOH/g). Both quantities can be assessed by monitoring the strength and the asymmetry of the O-H vibration band with regard to the free water absorption band centred around 3500 cm −1 . As such optical parameters can be assessed without taking fluid samples from a pressurised hydraulic system, fluid degradation trends can be established based on regular measurements, before irreversible damage to the fluid has occurred. Therefore maintenance actions can be planned accordingly, which is very important for the airline, as unscheduled maintenance disturbs the flights organisation and often generates money loss.

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We have fabricated microthruster chip pairs-one chip with microthruster structures such as injection capillaries, combustion chamber and converging/diverging nozzle machined using the deep reactive ion etching process, the other chip with sputtered platinum (Pt) thin film devices such as resistance temperature detectors (RTDs) and a heater. To our knowledge, this is the first microelectromechanical systems-based microthruster with fully integrated temperature sensors. The effects of anneal up to 1,050°C on the surface morphology of Pt thin films with varied geometry as well as with/without PECVD-SiO 2 coating were investigated in air and N 2 and results will also be presented. It was observed that by reducing the lateral scale of thin films the morphology change can be suppressed and their adhesion on the substrate can be enhanced. Chemical analysis with X-ray photoelectron spectroscopy showed that no diffusion took place between neighboring layers during annealing up to 1 h at 1,050°C in air. Electrical characterization of sensors was carried out between room temperature and 1,000°C with a ramp of ±5 Kmin -1 in air and N 2 . In N 2 , the temperature-resistance characteristics of sensors had stabilized to a large extent after the first heating. After stabilization the sensors underwent up to eight further temperature cycles. The maximum drift of the sensor signal was observed for temperatures above 950°C and was less than 8.5 K in N 2 . To reduce the loss of combustion heat, chip material around microthruster structures was partially removed with laser ablation. The effects of thermal insulation were investigated with microthruster chip pairs which were clamped together mechanically. The heater was operated with up to 20 W and the temperature distribution in the chip pairs with/without thermal insulation was monitored with seven integrated RTDs. The experiments showed that a thermal insulation allows the maximum temperature as well as the temperature gradient within the microthruster chip pairs to be increased.