Hydrogen response

Cassidy, J., Pons, S. and Janata, J., Hydrogen response of palladium coated suspended gate field effect transistor, Analytical Chemistry, 58(8), 1757,1986. 

Fogelberg, J. and Petersson, L.-G., Kinetic modeling of the H sub 2-0 sub 2 reaction on palladium and of its influence on the hydrogen response of a hydrogen sensitive palladium metal-oxide-semiconductor device, Surface Science, 350(1-3), 91,1996. 

Kim et al. have compared the hydrogen and methane sensitivity at 400-600°C of Pt and Pd-SiC Schottky diodes fabricated on n-type 6H-SiC. The Pd or Pt (<80 nm) was sputter deposited in 1-mm dots [8]. The sensitivity was measured as the change in current at a constant forward bias of 3V. The Pd-SiC Schottky diodes showed a higher sensitivity, as well as faster speed of response to both hydrogen and methane. The stability of the hydrogen response was tested for 30 days at 500°C and showed excellent results for both types of sensors. 

Also Tobias et al. reported, as already described, resistivity changes to be the main reason for the hydrogen response observed in the forward direction of the /-V characteristic of Schottky diodes with a Pt gate and an interfacial layer of TaSi [78]. 

Table I. Effect of Water Vapor on the Device Hydrogen Response Time (tt) and Recovery Time (Td) at RT...

Figure 16. Effect of water vapor on the device hydrogen response in air and recovery in air at RT. Pd/Si02 ( -1000 A)/n-Si capacitor is used. Dry air and wet air (saturated with water vapor are initial ambients, respectively.

It was found that in these reactions free hydrogen is not extracted. The results of these works allowed the authors to conclude that two processes proceeded in the reaction system dehydrogenation leading to benzene formation and hydrogenation responsible for cyclohexane accumulation. Both these reactions proceed simultaneously and are conjugated. The catalyst action is reduced to distribution of mobile hydrogen between three cyclohexadiene molecules. 

The H-NMR spectrum of I-ethyl-4-methylbenzene. The numbers above each group of peaks are the integrals and provide the relative numbers for hydrogens responsible for that group of peaks. 

Figure 6. Initial response measurements for a yttrium-hydride film (17 nm Ag/100 nm Y/20 nm Pd) to 0.45% H2 in air. The first reduction in the signal corresponds to conversion of Y metal to YH2, and subsequent cycles to increases in hydrogen content toward the tri-hydride, YH2. The response was measured in reflection (no SPR) at 700 nm. The time constant of the hydrogen response is about 5.7 seconds... 

Figure 9. Hydrogen response data as a function of time after quenching for gas metal arc welded ASTM A36 steel (0.1% H2/Ar shielding gas) using prototype fiber optic weld sensor.

Figure 11. Experimental hydrogen response curves for prototype fiber optic weld sensor (gas metal arc welded HSLA 100 steel)...

With new catalysts based on di-ether technology (5th generation catalyst, RK-Catalystand RH-Catalyst), wider melt-index ranged polymers can be produced (compare with those produced with 4th generation catalyst) due to the high hydrogen response of RK/RH-Catalyst. 

Chromocene catalyst has excellent hydrogen response for molecular weight control. 

For propylene polymerization, it has been demonstrated that the chain transfer is dependent not only on regio -but also on stereo -selectivity.412 This is in keeping with the tendency that, with catalyst systems of the type MgC /TiCU/phthalate ester-AlR3-alkoxysilane, the silanes which give the most stereoregular isotactic polymer also give relatively low hydrogen response. 

The donors present in the catalyst system play an active role in the formation or modification of isospecific sites, and the polymer molecular weight distribution depends on the relative contribution and hydrogen response (i.e., sensitivity to chain transfer with hydrogen) of each type of active site. The characteristics of different catalyst systems with regard to PP molecular weight distribution are as follows ... 

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