Thermodynamic modeling and experimental investigation of the Al-Sb-Zn system

University of Ljubljana, Faculty of Natural science and Engineering, Department of Materials and Metallurgy, Aškerčeva 12,SI-1000 Ljubljana,

Slovenia

Al-Sb-Zn system

Grega Klančnik, Jožef Medved

E-mail:grega.klancnik@ntf.uni-lj.si

Experimental investigation:

• determination and optimization of liquidus surface inside Al-Zn-Sb system• determination of ternary – characteristic- points inside zinc rich corner• determination of pseudo-binary phase diagram Zn-AlSb• new approach of prediction of existence of two phase equilibrium (L+AlSb) inside ternary system

• etc.

• All alloys were prepared with metals of 99,99 at. % purity

• After carefully weighting the metals, they were mixed together and put into corundum crucible

• Corundum crucible was sealed with carbon cup

• Melting was done systematically and under argon

• All alloys were heated up to 850 °C and kept at temperature for hour or two,• All alloys were heated up to 850 °C and kept at temperature for hour or two,mixed with ceramic rod and cooled to the room temperature

• The established procedure was repeated again with samples (regulus) turned for 180°

Knudsen effusion method (Al-Zn) at 833 K:

In the effusion method vapor pressure is calculated from effusion velocity by an equation:

)1(12

B

KAG

kAM

RTP

ατπ +⋅⋅=

A - geometric area of the effusion orificeKA - effective area

K - Clausing factor

B - effective vaporization area

M - molecular weight of effusing moleculeR - gas constantG - weight of effused molecule and τ time

ii

i akAp

kAp =⋅0

Oelsen`s calorimetry (Al-Zn-Sb):

classic thermodynamic method

Based on the equation (2) a tangent construction for determination of –Rlnax,T was done at 1000 and 1350 K in specific section

Calculation of total excess Gibbs energy in AlSb binary system at 1000K

The calculation of total excess Gibbs energy for Al-Sb binary systemat 1000 K was done on the basis of next thermodynamic models:unary phase model, disordered solution phase model andstoichiometric compound phase model.

The term for unary phase:971320 ln)( −− +++++++= hTgTfTeTdTTcTbTaTGi

φ

Where the 0Giφ is Gibbs energy for the pure element i with structure Φ at 298.15 K.

The liquid phase is described with:

Liquidexjjii

Liquidjj

Liquidii

Liquid GxxxxRTGxGxG ++++= ))ln()ln((00

∑=

−=m

n

nji

Liquidji

nji

Liquidxs xxLxxG0

, ))(( TbaL nnLiquid

jin +=,

In the Al-Sb binary system only one stoichiometric phase appears

fjjii GGxGxG ∆++= 2010 φφφ bTaG f +=∆

Where 0Gi,jφ1,2 is Gibbs free energy of component i and j in standard states. ∆Gf represents Gibbs free energy of formation and is calculated from parameters a and b

1273 K 1073 K 873 K

System ij Ref.

Al - Zn 10466.6-3.39355T [I]

Al - Sb -13.328-5.103T 10.748+0.337T [II]

Sb - Zn -11740.942-0.1283T -427.582-0.8090855T 34440.943-33.59286T [III]

Sb - Zn-43058.4+290.880T-

37.67392TlnT

-11870.5+85.641T-

10.30928TlnT25102.1-14.005T -9302.8+2.120T -9191 [IV]

Phase a (J/mol atom) b (J/mol atom K)AlSb - 40636 15847

The optimized parameters for AlSb phase

Thermodynamic parameters of liquid Al-Sb-Zn system

[i] Y.Liu,D.Liang;A contribution to the Al-Pb-Zn ternary system;Journal of Alloys and Compounds,403,110-117,2005[ii] T.Balakumur,M.Medraj;Computer Coupling of Phase Diagrams and Thermochemistry,29,pp,24-36,2005[iii] X.J.Liu,C.P.Wang,I.Ohnuma,R.Kainuma,K,Ishida;Thermodynamic Assesment of the Phase Diagrams of the Phase Diagrams of the Cu-Sb and Sb-Zn Systems,Journal of Phase Equailibria,vol21,5,pp.432-442,2000[iv] L.A.Zabdyr;Phase equalibria in ternary Cd-Sb-Zn system;Calphad,vol21,No.3,pp.349-388,1997

Prediction methods: Chou model Toop model Muggianu model

Chou model:

Toop model:Toop model:

Muggianu model:

In all cases partial thermodynamic quantities were calculated from:

Kurnakov rule:

System with binary congruent intermetal compounds K=E=c2+1=q+1=m+1

K-numbers of eutectic planes,E-number of eutectic points,C2-number of binary intermetal phases,q-number of quasi-binary cutsm-number of saddle points

Sb-Zn binary system: three intermetal phases among two congruentAl-Sb binary system: one congruent phaseAl-Zn binary system: none

K=E=3+1=q+1=m+1 q=3,m=3,E=4

Al-Sb-Zn ternary system done by using GSM method at 1350 K

Figure 3. Zinc activities according to: (a) Chou , (b) Muggianu and (c) Toop model at 1350 K

Figure 4. (a) Antimony and (b) aluminium activities according to Chou model at 1350 K

Alloy P*kA / barcm2 P / bar xZn aZn γZn GxsZn / J/mol

AZ1 1.815*10-6 7.9497*10-4 0.051 0.115 2.254 5628AZ2 5.226*10-6 2.2889*10-3 0.199 0.331 1.663 3522AZ3 5.052*10-6 2.2177*10-3 0.237 0.32 1.350 2078AZ4 5.803*10-6 2.5417*10-3 0.305 0.365 1.196 1239Zn 1.59*10-5 0.00698 1 1 / 0

Al-Zn binary system at 833 K

Figure 5. Enthalpy space diagram (a) and enthalpy isotherm diagram (b) for Al-Sb0.1Zn0.9 section inside Al-Sb-Zn ternary system

Figure 6. Activities obtained at: (a) 1350 K and (b) 1000 K for Zn : Sb = 9:1

Experimental values determined from measured polynomials

Calculation and experimental determination of concentration fluctuations in the long wavelength Scc(0) is important tool for study segregation and /or presence of chemical order

Figure 7. Concentration fluctuations in the long wavelength Scc(0) at 1000 K and 1350 K for Al-ZnSb section in AlSb ternary system

•Scc(0) is higher than ideal values in the all measured concentration range

Existence of miscibility gap

a

Thermodynamic prediction of extension of two phase region inside ternary system at 1000 K using GSM model and TCW

Sb

Predicted liquidus surface using GSM model

Zn Al

determination and optimization of liquidus surface inside Al-Zn-Sb system

Liquidus / Liquidus / °°CC Ternary / Ternary / °°C C EutecticEutectic

SampleSample CompositionComposition ThermoCalc / ThermoCalc / DTA DTA DSCDSC DTADTA DSCDSC

AZS1AZS1 0.2Al0.1Sb0.7Zn0.2Al0.1Sb0.7Zn 695695 737737 372.3372.3 372372

AZS2AZS2 0.1Al0.1Sb0.8Zn0.1Al0.1Sb0.8Zn 654654 701701 403403 400.8400.8

AZS3AZS3 0.05Al0.1Sb0.85Zn0.05Al0.1Sb0.85Zn 612612 641641 658658 397397 398.5398.5

AZS4AZS4 0.15Al0.05Sb0.8Zn0.15Al0.05Sb0.8Zn 637637 696696 377377

AZS5AZS5 0.05Al0.05Sb0.9Zn0.05Al0.05Sb0.9Zn 590590 616616 399.5399.5

AZS7AZS7 0.025Al0.05Sb0.925Zn0.025Al0.05Sb0.925Zn 555555 574574 580580 397397 394394

E1 559.1 °C L → Sb2Zn3_T + Sb3Zn4_G + Zincblen

U1 538.44 °C L +Sb3Zn4_G → CdSb_OME + Zincblen

E2 509.29 °C L → CdSb_OME + Rhombone + Zincblen

P1 446.71 °C L + Sb2Zn3_T +Zincblen → Sb2Zn3_D

E3 409.6 °C L → HCP_Zn + Sb2Zn3_D + Zincblen

E4 380.7 °C L → FCC_A1 + HCP_Zn +Zincblen

Ternary invariant reactions in Al-Sb-Zn system:

AZS1

AlSb

η-Zn

AlSb + η-Zn + α-Al

β-Al + AlSb

Figure 1. Macrograph of AZS1B alloy

AZS2

AZS3

Phase HV 25 (AZS 1B) HV25 (AZS2) HV 25 (AZS3)η-Zn 63 53 50AlSb 84 78Sb3Zn4 / / 193

Results from measurements of microhardnes in alloys AZS1B and AZS2 are represented by table 1. The measurements were done with 25 g of load and 15 s of measurements time.The measurements were done on the Shimadzu Microhardness Tester

The AlSb in hard but also brittle phase and as, that problematic for measuring. By classical metallographic preparation the AlSb phase cracked

Figure. Phase equilibrium with four phase peritectic reaction plane at “458 °C”

Figure. Phase equilibrium with four phase eutectic reaction plane at “395 °C”

Figure. Phase equilibrium at “372 °C” with four-phase eutectic reaction plane

Al`, (β-Al)

CONCLUSIONS:

• The major influence of Sb on the constitutuon of Al-Sb-Zn alloy is confirmedTrough thermodynamic prediction methods and experimenal results

• the effect of monotectoid reaction was determined relative deep inside the system,Effect of monotectoid reaction and correlated miscibility gap in solid could explain Positive deviation of Scc(0)

• Tendency to segregation of Investigated liquid alloys is also visible when liquid ispassing monovariant linespassing monovariant lines

•According to Scc(0) AlSb is disociated already at 1000 K in specific region

• In all investigated alloys AlSb phase was found as primary phase

• Experimental results confirms to the existence of quasibinary cut η-Zn – AlSb

Thank you for attention