Hydrogen loss, atmospheric

The investigations of magnetic properties of hydrides Er2Fei4BHx, that have been carried out previously have not taken into account the hydrogen loss in the sample with temperature increase. We have used an apparatus that has allowed to measure the magnetic properties of the sample at high temperatures in hydrogen atmosphere with pressure control. 

To return now to the carbon dioxide question, early in Earth s history, degassing would have been vigorous but so would have been the return of carbon to the interior, and it is likely that the mantle cycle would have dominated (Sleep and Zahnle, 2001). Moreover, frequent meteorite impacts would have created vast quantities of basalt ejecta that would also have reacted with carbon dioxide to precipitate carbonate. Sleep and Zahnle (2001) concluded that so much carbon dioxide would have been held in the mantle that the greenhouse warming would have been small the Earth was probably heavily glaciated— the Hadean was probably a Norse ice-hell. Possibly early Hadean Earth risked loss of atmospheric carbon dioxide to the interior more than dehydration by hydrogen loss to space, though this would depend on how much methane was in the air. 

Although little water manages to pass through the cold trap, there are other sources of hydrogen in the upper air. As mentioned above, methane emissions from the surface mix upwards from the surface, as methane has no cold trap, and in the upper air photolysis leads eventually to release of H. In addition, there is a small emission of H2 from the surface, some of which will reach the upper part of the atmosphere however. Earth also sweeps up H and H2 from space. Over time, net hydrogen loss must have been limited we have kept the oceans. 

Others expect water vapor emissions in a hydrogen energy economy (assumption is that half of the present energy supply is covered by hydrogen) to be reducible down to the respective level presently given by the fossil and nuclear economy which is a 0.005 % share of the total atmospheric water cycle. In order to reach the above reduction factor, hydrogen losses need to be decreased from currently estimated 10 % over the whole chain to 2 - 3 %. Today s world energy economy emits around 20 10 kg of water per year [134]. 

Fluoroaromatics are produced on an industrial scale by diazotization of substituted anilines with sodium nitrite or other nitrosating agents in anhydrous hydrogen fluoride, followed by in situ decomposition (fluorodediazoniation) of the aryldiazonium fluoride (21). The decomposition temperature depends on the stabiHty of the diazonium fluoride (22,23). A significant development was the addition of pyridine (24), tertiary amines (25), and ammonium fluoride (or bifluoride) (26,27) to permit higher decomposition temperatures (>50° C) under atmospheric pressure with minimum hydrogen fluoride loss. 

A process based on a nickel catalyst, either supported or Raney type, is described ia Olin Mathieson patents (26,27). The reduction is carried out ia a continuous stirred tank reactor with a concentric filter element built iato the reactor so that the catalyst remains ia the reaction 2one. Methanol is used as a solvent. Reaction conditions are 2.4—3.5 MPa (350—500 psi), 120—140°C. Keeping the catalyst iaside the reactor iacreases catalyst lifetime by maintaining a hydrogen atmosphere on its surface at all times and minimises handling losses. Periodic cleaning of the filter element is required. 

A convenient method for assessing the extent of surface oxidation is the measurement of volatile content. This standard method measures the weight loss of the evolved gases on heating up to 950°C in an inert atmosphere. The composition of these gases consists of three principal components hydrogen, carbon monoxide, and carbon dioxide. The volatile content of normal furnace blacks is under 1.5%, and the volatile content of oxidized special grades is 2.0 to 9.5%. 

By the use of many commercial abrasive processes, the corrosion resistance of magnesium alloys can be reduced to such an extent that samples of metal that may lie quiescent in salt water for many hours will, after shot blasting, evolve hydrogen vigorously, and the corrosion rate, as measured by loss of weight, will be found to have increased many hundred-fold. The effect in normal atmospheres is naturally much less, yet the activation of the surface is an added hazard and is the opposite of passivation which is essential if later-applied paint finishes are to have proper durability. 

There appears to be a correlation between the mass of the planets and the mass and composition of their atmospheres. Generally, only those planets of high mass were able to retain much of their atmospheres. Nitrogen, hydrogen, and helium are probably abundant, though not yet detected, on the heavier planets. Table 25-V also reveals a considerable range in the surface temperatures of the planets. The higher temperatures on the terrestrial planets also contributed to the loss of their atmospheres. 

---