Dilute Solutions of Aluminium in GoldAuthor(s): C. T. Heycock and F. H. NevilleSource: Proceedings of the Royal Society of London. Series A, Containing Papers of aMathematical and Physical Character, Vol. 90, No. 621 (Aug. 1, 1914), pp. 560-562Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/93389 .

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560 Messrs. C. T. Heycock and F. H. Neville.

the calculated values of the frequencies can only be regarded as confirmatory of the value inserted in the atomic heat formulae.

The following comparison shows the order of agreement between the values obtained by the two methods:-

Vm x 10-12

Metal. Al. Ag. Pb.

V,Y (specific heat) ............... 8 0 4 3 1 9 Vm (elastic constants) ......... 8-3 44 1 5

Prof. Callendar has kindly inserted a note regarding his theory of atomic heat.

Dilute Solutions of Aluminium in Gold.

By C. T. HEYCOCK, F.R.S., and F. H. NEVILLE, F.E.S.

(From the Goldsmiths' Metallurgical Laboratory, Cambridge.)

(Received June 16,-Read June 25, 1914.)

(Abstract.)

The paper deals with the solid condition of alloys containing not more

than 5 per cent. by weight of aluminium. The diagram is a concentration-

temperature diagram, the atomic percentage of aluminium being measured

horizontally from left to right, and the temperature, in degrees Centigrade,

being measured vertically. The alloys melt at varying temperatures, but below the upper line Aabcd

of the diagram they are wholly solid; we may say, approximately, that they are wholly solid below 525? C. Between this temperature and the level of

the point L there is a range of 100?. The diagram shows four compartments in this area and records the following facts:-The first area, on the left, indicates the fact that gold can dissolve rather more than 2 per cent. by

weight of aluminium to form uniform solid solutions; these we call a. With

rather more aluminium we have the complex alloys of the second area,.

containing, in addition to a, a second constituent /3. In the alloys of the

third compartment, 3 is the sole constituent, while in the fourth a new

560 Messrs. C. T. Heycock and F. H. Neville.

the calculated values of the frequencies can only be regarded as confirmatory of the value inserted in the atomic heat formulae.

The following comparison shows the order of agreement between the values obtained by the two methods:-

Vm x 10-12

Metal. Al. Ag. Pb.

V,Y (specific heat) ............... 8 0 4 3 1 9 Vm (elastic constants) ......... 8-3 44 1 5

Prof. Callendar has kindly inserted a note regarding his theory of atomic heat.

Dilute Solutions of Aluminium in Gold.

By C. T. HEYCOCK, F.R.S., and F. H. NEVILLE, F.E.S.

(From the Goldsmiths' Metallurgical Laboratory, Cambridge.)

(Received June 16,-Read June 25, 1914.)

(Abstract.)

The paper deals with the solid condition of alloys containing not more

than 5 per cent. by weight of aluminium. The diagram is a concentration-

temperature diagram, the atomic percentage of aluminium being measured

horizontally from left to right, and the temperature, in degrees Centigrade,

being measured vertically. The alloys melt at varying temperatures, but below the upper line Aabcd

of the diagram they are wholly solid; we may say, approximately, that they are wholly solid below 525? C. Between this temperature and the level of

the point L there is a range of 100?. The diagram shows four compartments in this area and records the following facts:-The first area, on the left, indicates the fact that gold can dissolve rather more than 2 per cent. by

weight of aluminium to form uniform solid solutions; these we call a. With

rather more aluminium we have the complex alloys of the second area,.

containing, in addition to a, a second constituent /3. In the alloys of the

third compartment, 3 is the sole constituent, while in the fourth a new

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Dilute Solutions of Aluminium in Gold.

constituent D appears. Like a, /3 can vary in composition, but only between narrow limits; D is probably the compound Au5Al2.

The solid /3 may be regarded as a solvent for a and D, for when the

representative point of an alloy passes, by cooling, out of the triangle bLc, then a or D crystallises from the previously uniform substance of the alloy, the form in which the D crystallises being somewhat remarkable. L is an eutectoid point, when a slowly cooled alloy falls below 524?, the

561

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Dilute Solutions (f Aluminium in Gold.

temperature of the L point, the residual /3 breaks up into a "pearlite" or eutectoid complex of a and D, the 38-phase wholly disappearing.

The above remarks apply only to alloys that have been cooled from the molten state to temperatures not below 400? C. If cooled below 400?, the

alloys with an aluminium content between 2 and 5 per cent. by weight undergo a remarkable change, they recalesce, the temperature suddenly jumping as much as 70? in the case of alloys containing 3'3 per cent. by weight of aluminium, with a smaller rise in the case of alloys with a greater or less percentage. The microscope shows that the recalescence is due to a

decomposition, or recrystallisation, of the /, or more precisely, to a reaction between the a and the D of the L eutectoid. The recalescence causes a

permanent change in structure that is unaffected by prolonged annealing at any temperature below 520?, so that the new state must be regarded as the stable one at all temperatures below 520?. The recalescence some-

times, but rarely, occurs spontaneously above 410?; but between 2'5 and 4 per cent. of aluminium it can be provoked at much higher temperatures; for example, if an ingot near L in composition be cooled from the molten

state, and at 500?, or even as high as 514? (where it is wholly solid), it be touched with a cold steel wire, the recalescence occurs with a rise of

temperature to near 5250, but never to above this point. A complete recrystallisation takes place, with partial fusion of the ingot. Such a

profound change caused in this way is somewhat remarkable. We have strong reason to think that, in all cases of recalescence, the new

substance formed is the definite compound Au4Al. The diagram we give does

not apply to the alloys containing the new substance.

562

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