Thermodynamic Assessment of Molten Bix-Sn1−x (x = 0.1 to 0.9) Alloys and Microstructural Characterization of Some Bi-Sn Solder Alloys
Abstract
:1. Introduction
2. Materials and Methods
2.1. Elaboration of the Bi-Sn Solder Alloys
2.2. Determination of Thermodynamic Functions of the Bi-Sn System
2.3. Sample Characterization
3. Results and Discussion
3.1. Thermodynamical Assessment
- -
- The values of the partial molar enthalpies of the mixture () of Bi and Sn at 600 K and 903 K, calculated based on Equation (1), are presented in Table 1.
- -
- The calculation of the values of partial molar entropies for the mixture was performed based on the following relationship (2):
- -
- The integral molar free energies () and the integral molar excess energies () at 600K and 903K have been calculated using Equations (3) and (4), and they are presented in Table 3.
Temperature 600 K | Temperature 903 K | |||
---|---|---|---|---|
XBi | [J/mol] | [J/mol] | [J/mol] | [J/mol] |
0.0 | 0 | 0 | 0 | 0 |
0.1 | −6425 | −35,620 | −602 | −9820 |
0.2 | −5802 | −32,060 | −1177 | −11,850 |
0.3 | −5292 | −28,590 | −1739 | −14,450 |
0.4 | −4906 | −21,990 | −2249 | −17,400 |
0.5 | −4679 | −18,920 | −2853 | −20,550 |
0.6 | −4672 | −16,060 | −3593 | −23,830 |
0.7 | −4946 | −13,490 | −4697 | −27,180 |
0.8 | −5674 | −11,370 | −6548 | −30,570 |
0.9 | −7157 | −10,000 | −10,530 | −33,970 |
1.0 | 0 | 0 | 0 | 0 |
- -
- The integral molar enthalpies () and integral molar excess enthalpies () at temperatures of 600 K and 903 K were calculated using Equations (5) and (6) and are presented in Table 4.
Temperature 600 K | Temperature 903 K | |||
---|---|---|---|---|
XBi | [J/mol] | [J/mol] | [J/mol] | [J/mol] |
0.0 | 0 | 0 | 0 | 0 |
0.1 | −19,960 | −18,140 | −13,050 | −17,130 |
0.2 | −11,360 | −14,020 | −8486 | −11,370 |
0.3 | −8794 | −11,410 | −5593 | −8019 |
0.4 | −6838 | −9188 | −3628 | −5280 |
0.5 | −5248 | −7031 | −2278 | −2672 |
0.6 | −3908 | −4865 | −1342 | −95 |
0.7 | −2769 | −2791 | −698 | 2391 |
0.8 | −1756 | −870 | −295 | 4616 |
0.9 | −817 | 736 | −68 | 6381 |
1.0 | 0 | 0 | 0 | 0 |
- -
- The integral molar entropies () and the integral molar excess entropies () of the alloy Bi–Sn at temperatures of 600 K and 903 K, they were calculated using Equations (7) and (8) and are presented in Table 5.
Temperature 600 K | Temperature 903 K | |||
---|---|---|---|---|
XBi | [J/mol] | [J/mol] | [J/mol] | [J/mol] |
0.0 | 0 | 0 | 0 | 0 |
0.1 | −1.189 | 1.514 | −1.175 | 1.484 |
0.2 | 0.922 | 5.082 | 0.823 | 4.784 |
0.3 | 3.850 | 8.929 | 2.954 | 7.726 |
0.4 | 6.186 | 11.781 | 5.881 | 10.690 |
0.5 | 7.469 | 13.232 | 6.841 | 12.467 |
0.6 | 7.632 | 13.228 | 6.326 | 12.563 |
0.7 | 6.726 | 11.805 | 5.765 | 10.679 |
0.8 | 4.890 | 9.051 | 3.909 | 8.611 |
0.9 | 2.606 | 5.309 | 1.806 | 4.629 |
1.0 | 0 | 0 | 0 | 0 |
3.2. Characterization of Bi-Sn Solder Alloys
3.2.1. Optical Microscopy
3.2.2. SEM-EDS Investigations
3.2.3. Structural Analysis through XRD and ED-XRFS
4. Conclusions
- -
- Microstructural variations were observed depending on the bismuth content, with structures exhibiting Sn-based matrices, Bi-based matrices, and equilibrated structures with numerous intermetallic constituents. Bismuth has an obvious effect on the formation of the alloy structure. The absence of conglomerates or clusters causing heterogeneity in chemical composition was noted. Metallic phases were uniformly distributed, and the formation of polyhedral, tetragonal, or orthorhombic compounds was observed.
- -
- The SEM-EDS characterization revealed significant changes in the structure of the elaborated alloys. It starts with a hypoeutectic structure (Bi25Sn75), and as the bismuth content is increased, a hypereutectic structure (Bi75Sn25) is reached. The formation of fine needle-shaped beta phases embedded in the alpha phase dendritic matrix is highlighted for the Bi75Sn25 alloy.
- -
- The EDP-XRFS analyses revealed that the concentrations of the main elements, Bi and Sn, can be observed with values that are very close to those calculated, as well as the presence of negligible amounts of other elements. Sample one exhibited dominant fluorescence lines of bismuth and tin, with semi-quantitative phase analysis indicating the presence of two Sn-rich phases and segregated bismuth. Sample two showed more intense fluorescence lines in the low-energy region due to increased bismuth content, with diffractometric investigations confirming the intended alloy state. Sample three closely matched the projected standard composition, with identified residual elements attributed to impurities or artifacts.
- -
- Diffractometric analysis revealed the prevalence of metallic bismuth and the formation of the Sn0.3Bi0.7 and Sn0.95Bi0.05 compounds, along with traces of metallic tin, thus demonstrating strong interactions between Bi and Sn leading to the formation of different solid solutions. The presence of SnO is undoubted, as its diffraction lines overlap with the lines of other indexed phases (Figure 14). Also, the lines of SnO2 overlap except for a line of very small intensity (Figure 13).
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Temperature 600 K | Temperature 903 K | |||
---|---|---|---|---|
XBi | [J/mol] | [J/mol] | [J/mol] | [J/mol] |
0.0 | −6.093 × 103 | −5.812 × 103 | −9.166 × 103 | −4.054 × 103 |
0.1 | −3.389 × 103 | −2.593 × 103 | −5.100 × 103 | 0.302 × 103 |
0.2 | −1.188 × 103 | −1.188 × 103 | −1.788 × 103 | 3.674 × 103 |
0.3 | 0.498 × 103 | 0.117 × 103 | 0.751 × 103 | 6.533 × 103 |
0.4 | 1.978 × 103 | 2.270 × 103 | 2.977 × 103 | 9.077 × 103 |
0.5 | 3.469 × 103 | 4.365 × 103 | 5.217 × 103 | 1.131 × 103 |
0.6 | 5.265 × 103 | 6.244 × 103 | 7.911 × 103 | 1.341 × 103 |
0.7 | 8.023 × 103 | 8.045 × 103 | 1.207 × 104 | 1.528 × 103 |
0.8 | 1.398 × 104 | 9.724 × 103 | 2.104 × 104 | 1.682 × 103 |
0.9 | 1.634 × 104 | 1.118 × 104 | 2.459 × 104 | 1.871 × 104 |
1.0 | 0 | 0 | 0 | 0 |
Temperature 903 K | ||
---|---|---|
XBi | [J/mol] | [J/mol] |
0.0 | 27.227 | 20.721 |
0.1 | 23.304 | 18.631 |
0.2 | 14.194 | 16.964 |
0.3 | 10.540 | 15.047 |
0.4 | 8.671 | 13.000 |
0.5 | 7.354 | 10.975 |
0.6 | 6.335 | 8.831 |
0.7 | 5.154 | 6.696 |
0.8 | 3.498 | 4.524 |
0.9 | 1.743 | 2.245 |
1.0 | 0 | 0 |
Sample Name 1—Bi25Sn75 Description Method—TurboQuant-Alloys | |||||
---|---|---|---|---|---|
Z | Symbol | Element | Norm. Int. | Concentration | Abs. Error |
13 | Al | Aluminum | 61.6353 | 0.0775% | 0.0014% |
15 | P | Phosphorus | 285.3130 | 0.08956% | 0.00050% |
20 | Ca | Calcium | 3071.7985 | 0.08837% | 0.0010% |
28 | Ni | Nickel | 100.9788 | 0.0527% | 0.0032% |
29 | Cu | Copper | 154.5501 | 0.0829% | 0.0032% |
50 | Sn | Tin | 30,350.5791 | 75.0850% | 0.06% |
72 | Hf | Hafnium | 105.3269 | 0.0157% | 0.0084% |
73 | Ta | Tantalum | 35.1758 | 0.0153% | 0.0024% |
74 | W | Tungsten | 63.0604 | 0.0623% | 0.0031% |
79 | Au | Gold | 534.9385 | 0.02587% | 0.0054% |
83 | Bi | Bismuth | 41,692.0316 | 24.317% | 0.003% |
Other | 0.0178% | ||||
Sum | 99.93% |
Sample Name 2—Bi50Sn50 Description Method—TurboQuant-Alloys | |||||
---|---|---|---|---|---|
Z | Symbol | Element | Norm. Int. | Concentration | Abs. Error |
13 | Al | Aluminum | 88.0285 | 0.01747% | 0.0032% |
15 | P | Phosphorus | 583.8644 | 0.02200% | 0.0010% |
20 | Ca | Calcium | 1977.1571 | 0.08571% | 0.0013% |
28 | Ni | Nickel | 84.0540 | 0.0540% | 0.0074% |
29 | Cu | Copper | 185.2806 | 0.0354% | 0.0076% |
30 | Zn | Zinc | 24.0341 | 0.01265% | 0.00094% |
40 | Zr | Zirconium | 358.2148 | 0.05063% | 0.0018% |
47 | Ag | Silver | 50.5271 | 0.0137% | 0.031% |
50 | Sn | Tin | 18,162.4573 | 50.062% | 0.05% |
51 | Sb | Antimony | 26.0649 | 0.1180% | 0.0027% |
72 | Hf | Hafnium | 89.0883 | 0.0183% | 0.021% |
74 | W | Tungsten | 76.8009 | 0.1045% | 0.0080% |
78 | Pt | Platinum | 2567.5260 | 0.034% | 0.073% |
81 | Tl | Thallium | 845.4254 | 0.0402% | 0.0062% |
82 | Pb | Lead | 506.6176 | 0.0273% | 0.0062% |
83 | Bi | Bismuth | 97,237.1198 | 49.035% | 0.01% |
Other | 0.1768% | ||||
Sum | 99.91% |
Sample Name 3—Bi75Sn25 Description Method—TurboQuant-Alloys | |||||
---|---|---|---|---|---|
Z | Symbol | Element | Norm. Int. | Concentration | Abs. Error |
13 | Al | Aluminum | 145.4822 | 0.0531% | 0.0094% |
20 | Ca | Calcium | 762.9267 | 0.06833% | 0.0019% |
28 | Ni | Nickel | 98.3900 | 0.0110% | 0.019% |
29 | Cu | Copper | 101.9181 | 0.0122% | 0.018% |
30 | Zn | Zinc | 39.4357 | 0.0354% | 0.0025% |
48 | Cd | Cadmium | 4.1658 | 0.0472% | 0.0062% |
50 | Sn | Tin | 5420.5119 | 24.9102% | 0.05% |
51 | Sb | Antimony | 13.5239 | 0.0119% | 0.0035% |
52 | Te | Tellurium | 8.0419 | 0.01203% | 0.00058% |
83 | Bi | Bismuth | 163,456.8712 | 74.7006% | 0.02% |
Other | 0.0918% | ||||
Sum | 99.95% |
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Niculescu, F.; Pencea, I.; Iacob, G.; Ghiţă, M.; Stănescu, M.-M.; Petrescu, M.-I.; Niculescu, E.-L.; Buţu, M.; Stăncel, C.-D.; Şerban, N.; et al. Thermodynamic Assessment of Molten Bix-Sn1−x (x = 0.1 to 0.9) Alloys and Microstructural Characterization of Some Bi-Sn Solder Alloys. Materials 2024, 17, 1579. https://doi.org/10.3390/ma17071579
Niculescu F, Pencea I, Iacob G, Ghiţă M, Stănescu M-M, Petrescu M-I, Niculescu E-L, Buţu M, Stăncel C-D, Şerban N, et al. Thermodynamic Assessment of Molten Bix-Sn1−x (x = 0.1 to 0.9) Alloys and Microstructural Characterization of Some Bi-Sn Solder Alloys. Materials. 2024; 17(7):1579. https://doi.org/10.3390/ma17071579
Chicago/Turabian StyleNiculescu, Florentina, Ion Pencea, Gheorghe Iacob, Mihai Ghiţă, Mariana-Mirela Stănescu, Mircea-Ionuţ Petrescu, Emanuel-Laurenţiu Niculescu, Mihai Buţu, Constantin-Domenic Stăncel, Nicolae Şerban, and et al. 2024. "Thermodynamic Assessment of Molten Bix-Sn1−x (x = 0.1 to 0.9) Alloys and Microstructural Characterization of Some Bi-Sn Solder Alloys" Materials 17, no. 7: 1579. https://doi.org/10.3390/ma17071579