Oxygen-17, abundance availability

However, in many archaeological samples pimarane diterpenoids are often absent, and of the abietane compounds only dehydroabietic acid remains. In fact, dehydroabietic acid is present as a minor component in the fresh resins, but its abundance increases on ageing at the expense of the abietadienic acids since the latter undergo oxidative dehydrogenation to the more stable aromatic triene, dehydroabietic acid [2,18]. If oxygen is available, dehydroabietic acid can be oxidized to 7-oxodehydroabietic acid and 15-hydroxy-7-oxodehydroabietic acid. Since these diterpenoid compounds are often the dominant components in archaeological samples [95,97], they are considered characteristic for the presence of Pinaceae resins. 

For the other fuel oxygenates detailed studies on the reaction pathways are not as abundantly available in literature. However, the similarity in chemical structure implies similar reaction by-products. In the case of TAME, tert-amyl formate and tert-amyl alcohol were observed instead of fBF and fBA, and their subsequent degradation products however, acetone and methyl acetate were observed as well [117]. The attack on the methoxy group was observed to be the major pathway, corresponding to the MTBE ehmination. During the elimination of ETBE the same reaction by-products were observed as with MTBE, with the exception of fert-butyl acetate which was formed instead of fBF [30]. 

The nitrates are more economical and more abundantly available in war time and safer to handle but more difficult to initiate under comparable conditions than chlorates or p>erchlorates. They are practically equal to chlorates in usable oxygen but also release nitrogen. This is generally not objectionable in flare candles, star compositions, etc., but makes them undesirable for fully confined applications other than for pressurization. 

Starch is a renewable carbon source abundantly available from plant sources. However, it is usually hydrolysed to glucose via a two-step process, liquefaction and saccharification, before adding it into the polymer prodnction medium [26]. Kim [27] reported P(3HB) production from starch using Azotobacter chroococcum via a fed-batch fermentation. A PHA content of 46 and 20 wt% with a CDW of 54 g/1 and 71 g/1 were obtained with and without oxygen limitation, respectively. A halophilic bacterinm, Haloferax mediterrane was also reported to be able to produce P(3HB) from starch, but the strain was not favourable due to the salt required for its growth which contributed significantly to the PHA manufacturing cost. 

So they are now used only to a limited extent in the manufacture of greases and as additives to improve the oiliness of other lubricants. They have largely been replaced with cheap, more easily and abundantly available and more stable mineral oils obtained by refining of petroleum. Chemically, mineral lubricating oils are mixtures of hydrocarbons (C12 -C50), and may contain only a small amount of oxygen, present as impurity, while this element is the main constituent of fatty oils. 

Recently, metal oxides are widely being explored as photocatalysts. They have particular advantages including a naturally abundant availability, a negative band gap, and chemical stability. Moreover, the 2p orbital in the oxygen of the metal oxide is mainly contributed to the formation of the valence band of the metal oxide semiconductors which are able to oxidize water molecules [1],... 

Inadequate FW deaeration is a common cause of serious corrosion problems that affect many hundreds (if not thousands) of boiler plants of all sizes around the world. Despite the abundance of available literature advising the need to eliminate oxygen from boiler FW, inadequate deaeration continues to cause permanent waterside damage. 

---