Surfinv1402034dalakovalo.fm

ISSN 10274510, Journal of Surface Investigation. Xray, Synchrotron and Neutron Techniques, 2014, Vol. 8, No. 2, pp. 360–363. Pleiades Publishing, Ltd., 2014.
Original Russian Text N.V. Dalakova, K.M. Elekoeva, A.Z. Kashezhev, A.R. Manukyants, A.D. Prokhorenko, M.Kh. Ponezhev, V.A. Sozaev, 2014, published in Poverkhnost'.
Rentgenovskie, Sinkhrotronnye i Neitronnye Issledovaniya, 2014, No. 4, pp. 60–63. Polytherms of Angles of Aluminum and Aluminum–Lithium
Alloy Wetting by TinBased Melts
N. V. Dalakovaa, K. M. Elekoevab, A. Z. Kashezhevc, A. R. Manukyantsb, A. D. Prokhorenkob,
M. Kh. Ponezhevc, and V. A. Sozaevb, c
aVerkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, Kharkiv, 61077 Ukraine bNorth Caucasian Institute of Mining and Metallurgy, Vladikavkaz, North OssetiaAlania, 362021 Russia cKabardinoBalkarian State University, Nalchik, KabardinoBalkaria, 360004 Russia Received April 18, 2013 Abstract—The results of an experimental study of the surface properties of the eutectic tin–aluminum alloy
are presented in this work. The temperature dependences of the wetting angles for plates of aluminum and
aluminum–lithium alloy wetted by tin and tin–aluminum eutectics are studied. Wetting thresholds at tem
peratures above 765 K are found.
changes its sign from positive in the region of 873–1473 K to negative in the region of 1473–1673 K. In Solders based on the Sn–Al eutectic with additions alloys that are richer in tin, one can observe linear ST of nickel [1] and Sn–Al–Zn peritectic [2] are success polytherms with positive or negative values of the ST fully applied for the fluxfree bonding of aluminum and its alloys with ceramic plates of integrated circuits.
In [7], based on measurements of the speed of In contrast to known solders, they do not contain pre ultrasound within the context of freevolume theory, cious metals and toxic components. Finding new ways surfacetension isotherms were calculated for eight for the lowtemperature bonding of aluminum liquidmetal aluminum systems. According to calcu requires reliable data on the surface tension in Al– lations, the Al–Sn system has a surfacetension iso lowmeltingpoint metal systems. One of the first therm with a zero deviation from additivity at 973 K.
works on experimental determination of the surface In [8], the experimental isotherms of aluminum tension (ST) of Sn–Al alloys is [3] where it was shown nitride wetting by Ge–Al and Sn–Al melts were pre that the surface tension of Al decreases with an sented, as well as the density and surface tension of the increase in the Sn content (the measurements were aforesaid alloys in the entire concentration range.
carried out in a bounded region up to 7% of tin in Thorough consideration of the capillary characteris aluminum). The ST polytherm of the Sn–Al system at tics of a melt in the study was carried out by taking into Т = 1273 K was presented in [4]. There is a large gap account available data on the thermodynamic activity in experimental data, and no data are available for a of melt components. Tin more strongly decreases the rather wide range of compositions (especially in the surface tension of aluminum than germanium. This is region of small tin concentrations).
caused not only by the lower ST value of pure tin as In [5], the Auger spectra of Al–Sn alloys with 0.14, compared to germanium but also by the higher ther 0.2, 0.3, 0.58, 2.1, and 2.6% concentration of tin in modynamic activity of tin in the aluminum melt.
aluminum at 973 K were studied. Strong segregation Thus, most studies of ST in the Sn–Al system were of tin was pronounced on the surface due to the size performed in a region that is rich in aluminum because effect and the repulsion of atoms of different types.
such alloys are often used as babbits for the car indus In [6], the large drop method was used to study the try. In this work, in connection with the lack of exper ST of the Al–Sn double system in the region of small imental data on the ST in the aluminumrich region, tin concentrations at temperatures up to 1673 K. The the polytherms of density ρ and surface tension σ of ST polytherm of the Al alloy with a Sn content of the melted Sn–Al eutectics are measured by the 0.4 at % appeared to have a zero temperature coeffi sessiledrop method and polytherms of wetting cient; the ST polytherms of alloys with a Sn content of angles θ of Al and Al + 4 at % Li alloy wetted by Sn 1.2 and 2.5 at % pass through a maximum near 1473 K, melts are studied in a wide range of i.e., the ST temperature coefficient of these alloys POLYTHERMS OF ANGLES OF ALUMINUM AND ALUMINUM–LITHIUM ALLOY Fig. 1. Polytherms of (a) surface tension and (b) density for the eutectic melt (1) Sn99.5–Al0.5 wt % and (2) pure tin [11].
Such investigations are also necessary in connec tively. The wetting was studied using 15 × 15 mm2 sub tion with the development of technologies for tin–alu strates preliminarily polished and washed in alcohol minum resistancereaction soldering [9] and for and distilled water. Measurements of θ were carried revealing the general regularities of the relationship out in a vacuum chamber with a residual pressure of between the surface properties and parameters of con 0.01 Pa. The wetting angle was determined using tact melting [10].
IMAGEJ free software [12] by averaging values of θ over the "left" and "right" halves of the drop with anerror of about 1%.
MEASUREMENT TECHNIQUE The eutectic Sn–Al alloy was prepared from tin and aluminum (99.9995 and 99.995 wt % purity, respectively) in glass ampoules in a helium atmo Experimental data testify that the density and sur sphere. During the process of melting, the melt was face tension of the eutectic alloy of the tin–aluminum intensively mixed and then crystallized. The obtained system decrease with an increase in temperature. The ingot was then used to prepare the samples. Measure results are well described by linear equations (Fig. 1): ments of ρ and σ were carried out using a graphite cup ρ = 7240.56–0.58 Т for the density and σ = 579.9– to which a drop of the studied substance was delivered 0.046 Т for the surface tension. Approximating coeffi via a quartz funnel with an extended capillary tube.
cients for these equations are also presented in the Before the beginning of the experiments, helium was table where the corresponding coefficients for pure tin introduced into the working chamber of a hightem [11] are presented for comparison. The data on pure perature installation with a watercooled casing; then, tin [11] well agree with recommended values. It is seen the chamber was evacuated to a pressure of 0.01 Pa.
from Fig. 1 that a small addition of aluminum to tin The drop was kept at the given temperature for 5 min; increases its surface tension by 30 mN/m.
the interval between successive images was 1–2 min.
The digital image of the drop profile obtained in the Figure 2 presents polytherms of wetting angles for experiment was processed using a PC via a highspeed substrates of aluminum and Al + 4 at % Li alloy (which software package [11] which permitted one to process is widely used in the aviation industry) wetted by tin and perform the optimization procedure for deter and Sn–Al eutectic melt. A pure aluminum substrate mining the surface tension of the liquid by different is not wetted by liquid tin (θ = 147°) up to a tempera methods. The measuring procedure lies in the imple ture of T = 855 K above which the wetting angle mentation of three blocks in the form of an applicationfor the Windows operating system. The imageprocessing unit reads out graphic files containing images Coefficients A, B and A*, B * of linear approximations of den of the equatorial cross section of the drop and sepa sity ρ= A – BT and surface tension σ = A* – B *T in the tin– rates the drop profile. In the computational unit, thethermophysical properties of the liquid are calculated using linear models. The output unit forms a report file of the experimental data processing.
Applying this technique allows simultaneous deter mination of ρ and σ with errors of 1% and 2%, respec JOURNAL OF SURFACE INVESTIGATION. XRAY, SYNCHROTRON AND NEUTRON TECHNIQUES Vol. 8 No. 2 2014 DALAKOVA et al.
(curve 3). Drop melting is accompanied by intense interaction with the substrate (reaction wetting) withthe formation of craters. At higher temperatures, the drop of the studied substance completely spreads overthe substrate, θ → 0 (Fig. 2).
When etching the crystallized solder in a hydro chloricacid solution, acicular structures were revealed (Fig. 3); their formation probably suppressedthe wetting of the studied substrates during the initialstage. In addition, the wetting of Al and Al + 4 at % Li plates was suppressed by oxide films on the surface ofthe drops and substrates. It is the destruction of these films in vacuum that is followed by a sharp decrease in the wetting angle. Fragments of a partially destroyed oxide film on the surface of the aluminum plate in thecase of wetting by pure tin that were found in one of the Fig. 2. Temperature dependence of the wetting angles for
parts of the substrate when studying using a PHENOM (1) pure aluminum and (2) aluminum Al + 4 at % Li alloy scanning microscope are presented in Fig. 4.
wetted by tin. (3) Wetting of the substrate of the Al + 4 at %Li alloy by the (Sn–Al)EUT melt.
To reveal the cause of the appearance of the wetting threshold, aluminum substrates with a solidified dropwere studied by electron microscopy. Preliminary sharply decreases almost to zero (curve 1). Introduc (before threshold) wetting along trenches formed by ing 4 at % Li into the Al substrate results in a decrease grain boundaries was found on the substrate. Atoms in the angle of wetting by tin by 7° (θ = 140°) up to located at these boundaries possess excess energy; temperatures of T = 810–820 K, which is followed by therefore, intergrain melt boundaries along which the a drop in the wetting angle to zero (curve 2). When the tin melt preliminarily spreads can be dissolved more Al + 4 at % Li alloy is wetted by the Sn–Al eutectic intensively at high temperatures.
melt, the wetting angles appeared to be even smaller Thus, before the wetting threshold, the wetting of (θ = 125°); however, at T = 765 K, as in the two previ trenches along grain boundaries antecedes the ous cases, the wetting threshold is observed again destruction of oxide films on the substrate and on the Fig. 3. Electronmicroscopy images of a film of the melt
crystallized on Al + 4 at % Li plate, after etching. The
Fig. 4. Fragment of a partially destroyed oxide film in the
image was taken using a PHENOM microscope with process of wetting of aluminum by tin after etching (begin ning of spread at 855 K).
JOURNAL OF SURFACE INVESTIGATION. XRAY, SYNCHROTRON AND NEUTRON TECHNIQUES Vol. 8 No. 2 2014 POLYTHERMS OF ANGLES OF ALUMINUM AND ALUMINUM–LITHIUM ALLOY drop, which makes an additional contribution to the moving force of spreading.
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When the Al + 4 at % Li alloy is wetted by the 9. N. V. Dalakova, K. M. Elekoeva, T. A. Orkvasov, and eutectic melt of the Sn–Al system, the formation of V. A. Sozaev, Poverkhnost', No. 12, 88 (2010).
acicular structures is observed; they probably suppress 10. A. A. Akhkubekov, O. M. Enaldieva, Kh. P. Zhilokov, wetting of the substrates during the initial stage T. A. Orkvasov, and V. A. Sozaev, Poverkhnost', No. 1, together with oxide films on the surface of melt drops.
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The work was carried out using equipment of the 12. A. F. Stalder, G. Kulik, D. Sage, L. Barbieri, and Center of Collective Usage of the Vladikavkaz Nanosys P. A. Hoffmann, Colloids Surf. A: Physicochem. Eng.
tems and Materials for Mining and Smelting Enterprise Aspects 286, 92 (2006).
and supported by the Ministry of Education and Scienceof the Russian Federation, project no. 16.552.11.7030.
Translated by A. Nikol'skii JOURNAL OF SURFACE INVESTIGATION. XRAY, SYNCHROTRON AND NEUTRON TECHNIQUES Vol. 8 No. 2 2014

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