Hydrogen-Containing Ambient

Capacitance measurements were performed to investigate the 1/C versus voltage relationship. Measurements were performed at 300°C after annealing the samples in oxygen- or hydrogen-containing ambient. The curves show the same... 

To test the time response of the sensors, a 10% H2/90% Nj ambient was switched into the chamber through a mass flow controller for periods of 10,20 or 30 s and then switched back to pure Nj, Figure 5.9 shows the time dependence of forward current at a fixed bias of 2V under these conditions. The response of the sensor is rapid (< 1 s), with saturation taking close to 30 s. On switching off the hydrogen-containing ambient, the forward current decays exponentially back to its initial value. This time constant is determined by the transport properties of the test chamber and is not limited by the response of the diode itself. 

The introduction of protonic defects in oxides in hydrogen-containing ambients has been reported frequently, and has recently been reviewed by Colomban and Novak and Strelkov etal. ... 

The famous HotSpot fuel processor developed by Johnson Matthey was actually a fixed-bed reactor. Platinum and chromium catalyst were applied for the reactor, which was able to start from ambient conditions when methanol was used as the feedstock [5,472]. Through the initial methanol combustion, the reactor was preheated and then able to produce hydrogen containing reformate under autothermal conditions. 

Electrode for electrochemical oxidation reactions. In solid oxide fuel cells, hydrogen-containing fuels are oxidized by oxygen ions transported through an electrolyte to form water vapor or CO2 as the reaction products at this electrode. SOFC anodes may also act as fuel reforming catalysts when hydrocarbon-based fuels are supplied to the anodes. Electrode for electrochemical reduction reactions. In solid oxide fuel cells, oxygen in ambient air is reduced to oxygen ions at this electrode. 

Liquid ethylene oxide under adiabatic conditions requires about 200°C before a self-heating rate of 0.02°C/min is observed (190,191). However, in the presence of contaminants such as acids and bases, or reactants possessing a labile hydrogen atom, the self-heating temperature can be much lower (190). In large containers, mnaway reaction can occur from ambient temperature, and destmctive explosions may occur (268,269). 

Anhydrous hydrogen fluoride and hydrofluoric acid react with substances containing silica and silicon oxide to form silicon tetrafluoridc and fluorosilic acid. SiF, a colorless gas at ambient temperature, is liighly toxic. An equilibrium mixture of SiF in the presence of moisture also contains hydrogen fluoride and hydrofluoric acid. 

Griess has observed crevice corrosion of titanium in hot concentrated solutions of Cl , SOj I ions, and considers that the formation of acid within the crevice is the major factor in the mechanism. He points out that at room temperature Ti(OH)3 precipitates at pH 3, and Ti(OH)4 at pH 0-7, and that at elevated temperatures and at the high concentrations of Cl ions that prevail within a crevice the activity of hydrogen ions could be even greater than that indicated by the equilibrium pH values at ambient temperatures. Alloys that remain passive in acid solutions of the same pH as that developed within a crevice should be more immune to crevice attack than pure titanium, and this appears to be the case with alloys containing 0-2% Pd, 2% Mo or 2[Pg.169]

The tarnishing of copper and silver in dry air containing traces of hydrogen sulphide (Table 2.6) is another example of film growth by lattice diffusion at ambient temperatures. In these cases defects in the sulphide lattice enable the films to grow to visible thicknesses with the consequent formation of tarnish films which are aesthetically objectionable and may have a significant effect on the behaviour of the metals in particular applications, e.g. electrical contacts. 

---