Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Aluminium finely divided

Strong oxidising acids, for example hot concentrated sulphuric acid and nitric acid, attack finely divided boron to give boric acid H3CO3. The metallic elements behave much as expected, the metal being oxidised whilst the acid is reduced. Bulk aluminium, however, is rendered passive by both dilute and concentrated nitric acid and no action occurs the passivity is due to the formation of an impervious oxide layer. Finely divided aluminium does dissolve slowly when heated in concentrated nitric acid. [Pg.143]

Lithium aluminium hydride if carelessly manipulated may be dangerous for two distinct reasons. The material is caustic, and should not be allowed to touch the skin it is particularly important that the finely divided material should be kept away from the lips, nostrils and eyes, and consequently pulverisation in a mortar must be carried out with the mortar in a fume-cupboard, and with the window drawn down as far as possible in front of the operator. This danger from handling has however been greatly reduced, for the hydride is now sold in stated amounts as a coarse powder enclosed in a polythene bag in a metal container this powder dissolves readily in ether, and preliminary pulverisation is unnecessary. [Pg.155]

Certain metals/alloys - the alkali metals (lidiium, potassium, sodium) and even some metals/ alloys which undergo slow oxidation or are rendered passive in bulk form but which, in the finely divided state, inflame immediately when exposed to oxygen (e.g. aluminium, magnesium, zirconium). [Pg.185]

A proportion of finely divided aluminium is often added to TNT explosives in order to increase the power. As aluminium has also a sensitising effect, it is particularly useful in waterproofed compositions. Another power producing additive which is sometimes employed in large diameter charges where its slow reaction is of less disadvantage is calcium silicide. Care must be taken with this material, however, to ensure that it does not lead to sensitiveness to friction and impact. [Pg.55]

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... [Pg.27]

The finely divided mixture of metals produced by hydrogen reduction of coprecipitated bismuth and aluminium hydroxides is pyrophoric. [Pg.28]

A pyrotechnic mixture of aluminium powder with potassium perchlorate, barium nitrate, potassium nitrate and water exploded after 24 h storage under water. Tests revealed the exothermic interaction of finely divided aluminium with nitrate and water to produce ammonia and aluminium hydroxide. Under the conditions prevailing in the stored mixture, the reaction would be expected to accelerate, finally involving the perchlorate as oxidant and causing ignition of the mixture. [Pg.34]

Cans of aluminium paint contaminated with water contained a considerable pressure of hydrogen from interaction of finely divided metal and moisture [1]. Mixtures of... [Pg.38]

Thin sections of potassium or sodium usually ignite in the liquid bromide. Iron at about 650°C ignites and incandesces in the vapour [1], Interaction with finely divided aluminium or antimony is violent [2],... [Pg.120]

Trituration in a mortar with finely divided aluminium, iron, lead or mercury may be violent, carbon being liberated. [Pg.375]

Finely divided boron, tetraboron carbide, and boron-aluminium mixtures will... [Pg.1342]

Boron (finely divided forms) reacts violently with cone, acid and may attain incandescence. The vapour of phosphorus, heated in nitric acid in presence of air, may ignite. Boron phosphide ignites with the cone, acid [1], Silicon crystallised from its eutectic with aluminium reacts violently with cone, acid [2], arsenic may react violently with the fuming acid, and finely divided carbon similarly with cone, acid [3], Use of cone, acid to clean a stainless steel hose contaminated with phosphorus led to an explosion [4],... [Pg.1593]

The finely divided metal is pyrophoric, and a mixture of manganese and aluminium dusts accidentally released from a filter bag exploded violently. [Pg.1766]

At 240° C mixtures of finely divided metals (aluminium, iron, tungsten) with the peroxide ignite under high friction, and molybdenum powder reacts explosively. [Pg.1827]

Mixtures of the oxide with aluminium powder give a violent or explosive thermite reaction on heating. Finely divided sodium ignites on admixture with the oxide, and a mixture of the latter with zirconium explodes on heating. Titanium is also oxidised violently on warming. [Pg.1838]

Finely divided magnesium or aluminium hydroxides (or a 3 1 combination) are currently the best smoke suppressants. They also neutralise the acidic vapours produced from halogen-containing flame inhibiters. The more finely divide they are the more efficient they become. [Pg.109]

Of the 313 samples examined, the dust explosion hazards of finely divided aluminium, aluminium-magnesium alloys, magnesium, thorium, titanium and uranium, and the hydrides of thorium and uranium, are rated highest [1]. The... [Pg.233]

Intimate mixtures of chlorates, bromates or iodates of barium, cadmium, calcium, magnesium, potassium, sodium or zinc, with finely divided aluminium, arsenic, copper carbon, phosphorus, sulfur hydrides of alkali- and alkaline earth-metals sulfides of antimony, arsenic, copper or tin metal cyanides, thiocyanates or impure manganese dioxide may react violently or explosively, either spontaneously (especially in presence of moisture) or on initiation by heat, friction, impact, sparks or addition of sulfuric acid [1], Mixtures of sodium or potassium chlorate with sulfur or phosphorus are rated as being exceptionally dangerous on frictional initiation. [Pg.238]

Perchlorate salts react explosively when rubbed in a mortar with calcium hydride or with sulfur and charcoal, when melted with reducants, or on contact with glowing charcoal [1], Mixtures with finely divided aluminium, magnesium, zinc or other metals are explosives [2],... [Pg.324]

By reduction of aldehydes and ketones Aldehydes and ketones are reduced to the corresponding alcohols by addition of hydrogen in the presence of catalysts (catalytic hydrogenation). The usual catalyst is a finely divided metal such as platinum, palladium or nickel. It is also prepared by treating aldehydes and ketones with sodium borohydride (NaBH4) or lithium aluminium hydride (LLAIH4). Aldehydes yield primary alcohols whereas ketones give secondary alcohols. [Pg.53]

The selective hydrogenation of enones is also achieved in a process employing an aluminium-mckel system. This process is electrochemical in nature but does not use an external electron source. Dissolving aluminium is used as the reducing agent with a catalytic amount of nickel chloride present in the tetrahydrofuran solvent. Finely divided nickel is deposited on tlie aluminium and this sets up local corrosion cells. Aluminium dissolves and tlie released electrons are transferred to nickel where protons are reduced to hydrogen. The hydrogen-nickel system then reduces the alkene bond in the enone [153]. [Pg.84]

Reformatsky reactions between allyl chloride and carbonyl cortqiounds are also effected in protic solvents using aluminium and a catalytic amount of tin chloride. Finely divided tin is formed and organotin reagents are involved as intermediates. These react with the carbonyl compound releasing tin ions, which are recycled by the dissolving aluminium [189],... [Pg.136]

Electrocatalytic hydrogenation is also achieved by reaction of carbonyl compounds with aluminium and nickel(ll) chloride in tetrahydrofuran. Nickel(li) is reduced to finely divided nickel(o) which is deposited on the aluminium.This se-tsup corrosion cells where aluminium dissolves, liberating electrons which are transferred to the nickel. Protons are then reduced to hydrogen at the nickel surface. Hydrogenation of benzaldehydes to the alcohol has been effected under these conditions [206]. [Pg.364]

Surfaces of finely divided nickel also promote the formation of aniline. A practical route to tlie preparation of electrodes coaled with a finely divided metal involves electroplating nickel onto a cathode from a solution containing a suspension of finely divided Raney nickel (Ni 50% A1 50%) or Devarda copper alloy (Cu 50% A1 45% Zn 5%), Some alloy particles stick to the cathode surface which is then activated by leaching out the aluminium using hot aqueous sodium hydroxide... [Pg.378]

Thermal decomposition of iron pentacarbonyl. Very finely divided red iron oxide is obtained by atomizing iron pentacarbonyl, Fe(CO)5, and burning it in excess of air. The size of the particles depends on the temperature (580-800 °C) and the residence time in the reactor. The smallest particles are transparent and consist of 2-line ferri-hydrite, whereas the larger, semi-transparent particles consist of hematite (see Chap. 19). The only byproduct of the reaction is carbon dioxide, hence, the process has no undesirable environmental side effects. Magnetite can be produced by the same process if it is carried out at 100-400 °C. Thermal decomposition of iron pentacarbonyl is also used to coat aluminium powder (in a fluidized bed) and also mica platelets with iron oxides to produce interference or nacreous pigments. [Pg.529]

G. S. Serullas treated potassium chlorate with an excess of hydrofluosilicic acid the clear liquid was decanted from the sparingly soluble potassium fluosilicate, the soln. evaporated below 30°, and filtered through glass powder J. J. Berzelius evaporated the acid liquid mixed with finely divided silica below 30° in air, or over cone, sulphuric acid and potassium hydroxide in vacuo. The excess of hydrofluoric acid was volatilized as silicon fluoride, and the clear liquid was then filtered from the excess of silica. R. Bottger treated sodium chlorate with oxalic acid whereby sparingly soluble sodium oxalate was formed J. L. Wheeler, and T. B. Munroe treated sodium chlorate with hydrofluosilicic acid and M. Brandau treated potassium chlorate with aluminium sulphate and sulphuric acid and precipitated the alum so formed with alcohol. Chloric acid is formed in many reactions with hypochlorous and chlorous acid for example, it is formed when an aq. soln. of chlorine or hypochlorous or chlorous acid decomposes in light. It is also formed when an aq. soln. of chlorine dioxide stands in darkness or in light. A mixture of alkali chlorate and chlorite is formed when an aq. soln. of an alkali hydroxide is treated with chlorine dioxide. [Pg.300]

Direct combination of the metal and sulphur can generally be effected,1 sometimes even at the ordinary temperature. This process is of especial advantage for the preparation of sulphides which are decomposed by water, e.g. aluminium sulphide (see also p. 38). Finely divided mixtures of zinc and sulphur may be exploded by shock, heat or friction.2... [Pg.61]

Phosphorus dissolves in arsenic trichloride on warming without reaction and is deposited on cooling.8 If the mixture is heated in the presence of aluminium chloride at 130° to 150° C. for 40 minutes, a brownish-red compound of composition A1As3C13 results,9 from which, however, aluminium chloride can readily be removed by water or ammonia, leaving a residue of finely divided black arsenic. If the compound is heated to 190° C. in the absence of air, it turns black as arsenic trichloride and aluminium chloride distil off and a bright grey mixture of arsenic and arsenide remains. It has been suggested that the arsenic is co-ordinatively bound, and that the compound may be /Ass... [Pg.107]


See other pages where Aluminium finely divided is mentioned: [Pg.870]    [Pg.41]    [Pg.870]    [Pg.56]    [Pg.39]    [Pg.49]    [Pg.50]    [Pg.1375]    [Pg.1524]    [Pg.1555]    [Pg.1726]    [Pg.1739]    [Pg.1888]    [Pg.1901]    [Pg.112]    [Pg.135]    [Pg.13]    [Pg.92]    [Pg.255]    [Pg.870]    [Pg.109]   
See also in sourсe #XX -- [ Pg.320 ]




SEARCH



Divide

Divider

© 2024 chempedia.info