Pyrophoric effect

Caution Because tellurium compounds have toxic effects similar to those of arsenic compounds care should be taken not to bring tellurium tetrachloride and its reaction products into contact with the skin. Avoid breathing fumes and dust of tellurium compounds. In addition, hydrogen chloride is evolved in Step A, and pyrophoric Raney nickel is used in Step B. Therefore all manipulations described in this procedure must be carried out in an efficient fume hood. 

Investigation into the effect has been mainly devoted to reactions with red fuming nitric acid . It seems that in red fuming nitric acid a preliminary reaction results in the formation of a surface deposit of finely divided metallic titanium ignition or pyrophoricity can then be initiated by any slight impact or friction. The tendency to pyrophoricity increases as the nitrogen dioxide content of the nitric acid rises from zero to maximum solubility at about 20%, but decreases as the water content rises, the effect being nearly completely stifled at about 2% water. 

Pellets, slugs or flechettes made of U have very good powers of penetration. However, U is softer than steel so that in the process of penetrating an armored steel plate it is partially pulverized. Since in this form U is pyrophoric (self-igniting), such projectiles have an incendiary as well as a penetrating effect. According to one account of flechettes made of depleted U ... 

In order to permit safe handling and storage, TEA may be made non-pyrophoric by the addition of soluble siluents (for example, n-hexane). The diluent is expected to flash off when the flame weapon is employed rendering the basic TEA payload pyrophoric again. An effective... 

The characteristics of a metal which contribute to a good incendiary capability are not yet fully understood nor have they been completely defined. Hillstrom (Ref 64) found that pyrophoricity is related to the ratio of the oxide volume to the metal volume, a ratio above one giving rise to the popcoming effect which is... 

Pyrophoric penetrators equal in effectiveness to those containing U are reportedly provided by those containing spark sintered bodies of 49—95% W, 4—50% Zr and a binder of ductile metal such as Ni, Fe, Co or Cu (Ref 115). Even though U is the most pyrophoric of all elements, it is not expected to see use as an incendiary because of its toxicity and its great value as a nuclear fuel... 

The catalyst is washed thoroughly with 100 ml. of water and with 200 ml. of absolute methanol to remove all traces of water, after which it is transferred to the flask under nitrogen with a minimal amount of absolute methanol. To be effective the catalyst must be pyrophoric, and extreme care must be taken during this operation to prevent ignition of the methanol or ammonia. The catalyst must not be allowed to become dry or to collect on the wall of the flask above the surface of the liquid ammonia. 

Airborne particulate matter may comprise liquid (aerosols, mists or fogs) or solids (dust, fumes). Refer to Figure 5.2. Some causes of dust and aerosol formation are listed in Table 4.3. In either case dispersion, by spraying or fragmentation, will result in a considerable increase in the surface area of the chemical. This increases the reactivity, e.g. to render some chemicals pyrophoric, explosive or prone to spontaneous combustion it also increases the ease of entry into the body. The behaviour of an airborne particle depends upon its size (e.g. equivalent diameter), shape and density. The effect of particle diameter on terminal settling velocity is shown in Table 4.4. As a result ... 

Finely divided aluminium powder or dust forms highly explosive dispersions in air [1], and all aspects of prevention of aluminium dust explosions are covered in 2 recent US National Fire Codes [2], The effects on ignition properties of impurities introduced by recycled metal used to prepare dust were studied [3], Pyrophoricity is eliminated by surface coating aluminium powder with polystyrene [4], Explosion hazards involved in arc and flame spraying of the powder are analysed and discussed [5], and the effect of surface oxide layers on flammability was studied [6], The causes of a severe explosion in 1983 in a plant producing fine aluminium powder are analysed, and improvements in safety practices discussed... 

The moist sulfide readily oxidises in air exothermally, and may reach incandescence. Grinding in a mortar hastens this [1]. The impure sulfide formed when steel processing equipment is used with materials containing hydrogen sulfide or volatile sulfur compounds is pyrophoric, and has caused many fires and explosions when such equipment is opened without effective purging. Various methods of purging are discussed [2], Formation of pyrophoric FeS in bitumen tanks is considered as a cause of spontaneous ignition and explosion in the head space [3], A detailed study of formation of possibly pyrophoric sulphides from rust in crude oil tankers has been made [4],... 

Very effective heat removal (reaction control), as well as safe handling of the sometimes pyrophoric and/or air-sensitive catalysts. 

By far the most important redox reaction relative to chemical stability is the reaction between an oxidizable material and oxygen from air. The particle size and any droplets have a large effect on the combustion properties. Some substances react so rapidly in air that ignition occurs spontaneously. These so called pyrophoric compounds (white phosphorus, alkali metals, metal hydrides, some metal catalysts, and fully alkylated metals and nonmetals) must be stored in the absence of air. 

Reductions with zinc are very effective on aromatic nitro compounds using organic solvents and an acid medium at around 50-70°, No matter what kind of metal is used, good stirring is a must. After the reaction is over, the zinc is filtered off, care being taken not to let it become dry, as it is pyrophoric. Also, be careful while disposing of zinc for the very same reasons. 

Dilithiated diamine 2 was synthesized by Karsch by a two-fold metalation of N,N,N, N tetramethylmethylenediamine (TMMDA) (1). The reaction was effected in n-pentane at low temperatures, yielding the poorly soluble Af,Af -bis(fithiomethyl)-Af,Af -dimethyl-methylenediamine (2) (Scheme 1). Due to its low solubility in toluene or THE, the highly pyrophoric compound was characterized by derivatization with several electrophiles, mainly chlorosilanes. Obviously, the addition of coordinating additives, such as TMEDA, DME (dimethoxyethane) or THE, does not enhance the solubility of the dilithium compound. Interestingly, as the author comments, TMEDA is only monolithiated in modest yields by alkyllithium bases. 

For the hthiation reactions of the closely related compound 123 with w-butyllithium, a significant solvent effect was observed by Maercker and coworkers . While a two-fold lithiation process by tellurium-lithium exchange takes place in hexane, yielding highly pyrophoric 91, only a-deprotonation occurs when the reaction is effected in THF, yielding the monohthiated tellurole 124 (Scheme 45). 

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