Two articles have appeared by Bichsel on electron microscopy ; one is concerned with an investigation of sub-grain structure in high purity aluminium , while the other is general , describing the application of oxide replica techniques and the examination of thin foils .sx The illustrations in all these papers are impressive scientifically and attractive aesthetically ; it is only a matter of time before they receive the attention of designers of wallpaper , floor coverings and similar goods .sx Single crystals continue to attract the experimenter ; McKinnon has studied the work-hardening of a super-purity aluminium crystal , and indicated that during stage =1 , that is the period of slip on ( 111 ) plane of maximum resolved shear stress , the rate of hardening is determined by the amount and type of uniformly distributed secondary slip .sx Greetham and Honeycombe have deformed single crystals of aluminium-4 .sx 5% copper given various ageing treatments after solution treatment .sx Under-aged crystals showed a marked yield point followed by a period of low hardening , while over-aged crystals and those treated at the optimum temperature , though showing no yield point , strain-hardened rapidly .sx By X-ray and metallographic study , Richards and Pugh have determined the sequences of behaviour of super-purity aluminium during rolling and annealing .sx Structures after various amounts of cold reduction are illustrated as photomicrographs and X-ray transmission patterns .sx Blade , Clare and Lamb have used levitation melting to provide ingots of zone-refined aluminium containing additions of various elements , which were then rolled to sheet for determination of recrystallisation temperatures .sx As little as 0.001 at .sx % of the addition elements was sufficient to produce most of the retardation of recrystallisation ; silicon , copper and magnesium each caused an increase of recrystallisation temperature of 50-100@ C. , while for iron , chromium and manganese a figure of c. 200@ C. is quoted .sx At temperatures varying from 195-500@ C. , Ormerod and Tegart have subjected super-purity aluminium to torsion stresses , and determined torque values which are converted to shear stress , while specimen revolutions are converted to shear strain , the two being used to draw true stress/ strain curves .sx Davies has performed stress-rupture tests on the aluminium-1% nickel alloy favoured for resistance to corrosion by high temperature water , and obtained 1,000 hour values of 0.75 at 350@ C. , 1.8 at 250@ C. , and 4.2 at 100@ C. , the units being kg/ sq .sx mm .sx ; English eyes would have preferred tons/ sq .sx in .sx Corrosion and Protection .sx No form of degeneration of metals is more insidious than corrosion , and the volume of work published on the subject is a measure of the seriousness with which it is viewed .sx Evans has produced a monumental volume of great authority on the corrosion and oxidation of metals in general , with an author index containing no less than 3,000 names .sx A fat volume , but the scribbling has been very well worth while , and as with Gibbon's work it will well outlive the author .sx Another useful book is that written by Rogers , principally for the education of naval constructors who are responsible for the maintenance of ships of war ; aluminium receives its due meed of attention , with alarming illustrations of what happens when wrong procedures are adopted , and details of correct design and practice .sx The power of the corrosive enemy must be recognised and assessed ; Great Britain has the unenviable reputation of being a particularly aggressive place .sx Ambler has found that the distribution of chloride in the British atmosphere has the same general relation to distance from the sea as in West Africa , and that the corrosion of steel and zinc bears no relation to salinity ; encouragingly , he considers that the corrosion of his aluminium specimens was so small as to give high errors on cleaning .sx A new hazard has been added to corrosion testing .sx At Llanrhystyd , Ambler's specimens were liable to be licked by cows on the landward side ; he states that this would not be expected to give low results , but this surely depends on the corrosivity of cow saliva as against the beneficial effects of regular cleaning .sx In continuing its work on the basic causes and mechanism of corrosion , the National Bureau of Standards in the U.S.A. has established that with large single crystals of high purity aluminium exposed to an acid mixture , configuration of etch pits differed according to crystallographic orientation , and the rates of attack varied radically from those observed in an alkali mixture .sx Edeleanu has studied the pitting mechanism , using 99.999% aluminium foil in sodium chloride solution , and demonstrated that the rate of attack per unit of active area inside a pit is a constant , and that changes in an external polarising current change the rate of pitting only by altering the active area .sx An electron micrograph of a pitting system illustrates effectively the frequent changes in direction of the attack .sx In a general summary of the causes of pitting and its effects , Robinson makes the cardinal point that to avoid it one must eliminate the chloride ion or inhibit it ; it is not always possible to adopt either of these admirable actions , so that pitting must sometimes be lived with and allowed for in design and selection of materials .sx Susceptibility to intercrystalline corrosion may be a less serious matter than proneness to stress-corrosion ; indeed , in the high strength Al-Zn-Mg-Cu alloys , stress-corrosion failure can occur when very little evidence of corrosive attack is to be detected .sx In developing tests for the susceptibility of this type of alloy to intercrystalline attack , Ketcham and Taylor do not mention stress-corrosion , and while their tests are no doubt of value , tests including stress application would be preferred .sx Silver is highly cathodic to aluminium , and alloys containing large additions of silver might be expected to be correspondingly low in corrosion resistance .sx This has been shown to be the case by Stadelmeier and Whitener ; in their aluminium-silver alloy , Ag;2;Al was precipitated on the grain boundaries , and in a refrigerator atmosphere samples were completely pulverised in four weeks .sx A Committee of the National Association of Corrosion Engineers has reported on its investigations of techniques applicable to the examination of aluminium corrosion products , including X-ray diffraction and fluorescence , thermal analysis , electrographic methods , spectrographic analysis , microscopic examination and quantitative and qualitative tests .sx Having purified water sufficiently for it to merit the application high-purity , the user is anxious to keep it so , and Knoedler and Gordon have assembled test data on many materials that may be used for containers , pipes , etc. , including steel sprayed with aluminium , and the same combination coated with a polyvinyl top coat .sx Commercially pure aluminium and aluminium-manganese alloy tanks were also used , and the water showed 0.035 parts per million of aluminium after 56 days' storage ; a very low proportion .sx In comparing metals for compatibility with 90% hydrogen peroxide , Bloom and his co-workers award classification 1 only to pure aluminium , certain aluminium alloys and zirconium .sx A rocket fuel rejoicing in the name of unsymmetrical dimethylhydrazine has been successfully stored in aluminium containers for three years without ill effect , as reported by Raleigh and Derr .sx Many somewhat unusual chemicals are needed in conjunction with rocket engines , and Geiger , Schuler and Mowers have discussed material selection problems in the light of present knowledge .sx Aluminium is compatible with hydrogen peroxide , nitrogen tetroxide , liquid fluorine and inhibited red fuming nitric acid , amongst other rocket chemicals .sx Aylmore , Gregg and Jepson have studied the oxides formed when aluminium is heated in dry oxygen and interpreted their results as showing crystallisation of an initially formed amorphous layer .sx Using an A.C. bridge , Lorking measured the capacity and thus the thickness of non-porous oxide films on aluminium ; chloride ions in solution increased the permeability of the film , and this was detected by potential measurements .sx Since a general air of pessimism permeates the account by Capp and Philibert about ship corrosion , their remarks about trouble with aluminium are perhaps less unacceptable ; however , they seem to be ill-informed about developments since the war in such matters as riveting and boundary bar joints , and the general avoidance of bimetallic corrosion .sx The stupid things that are still done are exemplified in an account by Brooks of a floodlight from a fishing vessel , that had castings in an aluminium alloy containing 2 1/2% copper , was bolted together with brass bolts , and employed an absorbent fibre gasket .sx It seems hardly conceivable , but these things still happen , even in the second half of the twentieth century .sx In the aircraft industry , hazards are much more fully recognised ; Heath has shown how modern aircraft design is being modified to provide access to all parts for inspection , to ensure that unobserved corrosion cannot proceed to cause a catastrophe .sx This requirement in design is , of course , most important in modern aircraft from which long service lives are expected .sx Corrosion at welds has not proved a serious problem with aluminium since the dangers of flux entrapment were eliminated by the adoption of inert gas-shielded welding methods ; however , trouble with large gas-welded cooking pans in aluminium-2% magnesium alloy described by Latimer was not due to flux residues .sx " Knife-edge " attack along the sides of the welds was shown to be associated with the coarse structure of the partially fused zone , and the presence of continuous 15b-phase on the grain boundaries of the heat-affected zones .sx This could be avoided by welding at a faster rate with less heat input , e.g. by tungsten-arc welding .sx Oldfield and Twigg investigating the staining of stainless steel tableware , tested blades in contact with galvanised iron and with aluminium in Sheffield tap water at 60@ and 100@ C. They concluded that aluminium containers are reasonably safe for trays or baskets for washing stainless steel cutlery , but galvanised iron can cause staining .sx Aluminium-magnesium-silicon alloy ( similar to H9-P ) pipe , TIG welded , and used for sour gas was inspected by Flournoy after being buried for six years without protection in a soil of sandy loam and broken caliche .sx Where failure had occurred , it was by pitting from the outside , and chlorides were detected in the corrosion product .sx This experience shows that aluminium is resistant to sour gas , and may be installed bare underground if protection is afforded at local spots of high corrosivity .sx If one keeps the anti-freeze in the cooling system of one's car from year to year , one runs the risk of corrosion of the cast-iron parts of the circuit , due to increase in acid content and reduction of inhibitor content of the cooling liquid .sx This has been shown by Collins and Higgins , who also state that the danger of corrosion of other metals by the deteriorated anti-freeze is slight ; only occasionally has slight pitting been seen with aluminium , and no corrosion necessitating replacement has resulted .sx Investigating the special case of hypereutectic aluminium-silicon alloys under conditions related to car engine cooling systems , Craig and Woods have shown that such alloys , even when coupled to copper , are corroded to a negligible extent if there are suitable inhibitors in the coolant ; in general , hypereutectic aluminium-silicon alloys are more corrosion resistant than cast iron .sx Sundararajan and Char , continuing their studies of inhibition of the corrosion of aluminium , have assessed the effects of acridine , nicotinic acid , dextrin , thiourea and tannic acid in dilute hydrochloric acid ; all were efficient .sx In a second paper these authors describe polarisation studies in acid and alkaline solutions , with thiourea and dextrin as inhibitors , and conclude that cathodic protection is possible in acid solutions in the potential range -0 .sx 55 to -0 .sx 80 V. In both these papers one meets again the curious material previously described by Sundararajan and Char , namely 92% pure aluminium , containing 3% Fe , 4% Mn , 1% Si ; doubts about decimal points return more strongly than ever .sx Using some impressive mathematics , Bauer and Eddy have compared various possible anode materials for the protection of water tanks .sx One interesting factor affecting choice is whether or not the water freezes and breaks the anode or suspension ; if it does , aluminium is used , because of its cheapness .sx Chemical conversion coatings have been summarised by Ayres , considering them principally from the point of view of corrosion resistance , which is conferred by low chemical activity and solubility .sx Wells and Pinner have surveyed recent advances in chemical and electrolytic polishing , on all relevant metals including aluminium .sx