Lower oxides, pyrophoric

All phosphoms oxides are obtained by direct oxidation of phosphoms, but only phosphoms(V) oxide is produced commercially. This is in part because of the stabiUty of phosphoms pentoxide and the tendency for the intermediate oxidation states to undergo disproportionation to mixtures. Besides the oxides mentioned above, other lower oxides of phosphoms can be formed but which are poorly understood. These are commonly termed lower oxides of phosphoms (LOOPs) and are mixtures of usually water-insoluble, yeUow-to-orange, and poorly characteri2ed polymers (58). LOOPs are often formed as a disproportionation by-product in a number of reactions, eg, in combustion of phosphoms with an inadequate air supply, in hydrolysis of a phosphoms trihahde with less than a stoichiometric amount of water, and in various reactions of phosphoms haUdes or phosphonic acid. LOOPs appear to have a backbone of phosphoms atoms having —OH, =0, and —H pendent groups and is often represented by an approximate formula, (P OH). LOOPs may either hydroly2e slowly, be pyrophoric, or pyroly2e rapidly and yield diphosphine-contaminated phosphine. LOOP can also decompose explosively in the presence of moisture and air near 150° C. 

Semipyrophoric Metals. A patented mfg process which converts metals such as Fe, Co, Ni, Cu, etc, in the form of their oxides or oxalates to a semipyrophoric form which ignites in air between 100° and 350°. The process is such that a completely pyrophoric form is not obtd. The prepn procedure may vary in several ways a) a metal (oxide) compd is converted to the pyrophoric condition as a lower oxide which is then converted into the semipyrophoric condition by slow exposure to air or dil 02 or by treatment with an 02-free gas, or b) by introducing a pyrophoric lower oxide into an organic liq, ie, methanol, eth, aldehydes or esters and either evapg the liq or working up the suspension into a semipyrophoric compn... 

The lower oxide, prepared by hydrogenation, incandesces on exposure to air. See other METAL OXIDES, PYROPHORIC MATERIALS... 

Pyrophoricity is a property of metals and oxides of lower oxidation states, including radioactive ones, in which they spontaneously ignite during or after stabilization. If the waste also contains other combustible matter, it will burn. For a waste form to be safe from spontaneously igniting, the metals and oxides of lower oxidation states must be fully oxidized. To determine whether a particular waste is pyrophoric or not, one must identify the pyrophoric components within the waste. Such identification is done by analytical methods such as X-ray diffraction. 

The acid-base reaction that forms the Ceramicrete waste forms also creates an oxidizing environment in which species of lower oxidation states are automatically converted to their fully oxidized states. Hence, pyrophoric components (such as PU2O3) should be converted to their most stable and fully oxidized forms (such as PUO2) that are no longer pyrophoric. Wagh et al. [10] have demonstrated such transformations in the Ceramicrete process by using surrogates of Pu (see the case study in Section 17.5.4). 

This conversion of actinide oxides of lower oxidation states into fully oxidized forms has a great advantage. The actinides of lower oxidation states are pyrophoric. Once converted into their fuUy oxidized form and encapsulated in the phosphate matrix, they are not spontaneously combustible and, hence, are safe for transportation and storage. Thus, because of this oxidation, the phosphate matrix removes the pyrophoricity during the stabihzation process. 

Plutonium is a very reactive metal and oxidizes readily in moist air. In finely divided form, plutonium metal is pyrophoric (Taylor 1973). Plutonium exhibits five oxidation states from plutonium(lll) to plutonium(VII). The four lower oxidation states are stable in solution and may co- exist in the same solution. Complex (coordination) compounds are formed with many of the common inorganic anions, such as plutonium nitrate (Pu(NO 3) 4). 

Several of the partially lower-alkylated derivatives of non-metal hydrides are pyrophoric in air. With other gaseous oxidants (halogens, etc.) the reaction may be explosive. The class includes the groups ... 

The combustion of Zn powder in air has been investigated (Ref 18). Owing to the higher vapor pressure of Zn compared with that of Al, ignition temps for Zn are also lower. Complete combustion of Zn powder takes place above 980° whereas the ignition temp for Al powder under the same exptl conditions is 1765° with a combustion temp of 2160—2290°. The process of self-oxidation of Zn dust is stimulated by humidity and the presence of chlorides, whereas the composition of the metallic phase, and the specific surface of the Zn dust were shown to be of minor importance in determining the pyrophoric properties (Ref 19). For a discussion of... 

Although very unreactive in massive forms, the finely divided metal may be pyrophoric, a Japanese study of this hazard has been reported [1]. Consequent upon an explosion in a tantalum dust collector, further study of powder explosion was made. Minimum ignition energies were found to be much lower than previously supposed. An oxide coating makes it susceptible to electrostatic charge generaton and discharge [2]. See entry PYROPHORIC METALS (references 3,9)... 

Pyrophoric NickeL—Nickel that has been reduced by hydrogen at temperatures below 270 C. is a black powder, pyrophoric upon exposure to ordinary air. It does not, however, burn as brilliantly as iron reduced at 440° C. If reduced at 270° to 280° C. it is oxidised by dry air or oxygen only at 350° C. Moisture facilitates the oxidation of reduced nickel, effecting it at lower temperatures. Nickelous oxide is not oxidised either by dry or by moist air within the temperature interval 220° to 480° C.5... 

When obtained at 1000° C., or if heated to this temperature after production at lower temperatures, ferrous oxide is no longer pyrophoric it does not decompose water, neither is it soluble m dilute acetic acid. 

The group 15 organoelement hydrides of the type R EHj (E = As, Sb, Bi) are highly reactive and very sensitive towards oxidation by air (see below). The methyl and ethyl derivatives are pyrophoric. However, due to the low polarity of the E—H bond these species are relatively moisture-stable (cf. x (Pauling) = H, 2.20 As, 2.18 Sb, 2.05 Bi, 2.02). In general, the (thermal) stability decreases for the central atoms in the order As > Sb > Bi. The more H atoms are present the lower is the stability of their hydrides. 

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