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A Novel Self-Assembling Al-based Composite Powder with High Hydrogen Generation Efficiency.

Wang C, Liu Y, Liu H, Yang T, Chen X, Yang S, Liu X - Sci Rep (2015)

Bottom Line: The results indicated that the powders formed unique core/shell microstructures with cracked surfaces and (Bi, Sn)-rich phases distributed on the Al grain boundaries.The powders exhibited good oxidation resistance and reacted violently with distilled water at temperatures as low as 0 °C.The mechanisms of the hydrolysis reactions were also analyzed.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen, 361005, P. R. China.

ABSTRACT
In this study, a novel self-assembling hydrogen generation powder comprised of 80Al-10Bi-10Sn wt.% was prepared using the gas atomization method and then collected in an air environment. The morphological and hydrolysis properties of the powders were investigated. The results indicated that the powders formed unique core/shell microstructures with cracked surfaces and (Bi, Sn)-rich phases distributed on the Al grain boundaries. The powders exhibited good oxidation resistance and reacted violently with distilled water at temperatures as low as 0 °C. Furthermore, at 30 °C, the powders exhibited a hydrogen conversion yield of 91.30% within 16 minutes. The hydrogen produced by this powder could be directly used in proton exchange membrane fuel cells. The mechanisms of the hydrolysis reactions were also analyzed.

No MeSH data available.


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(a–c) SEM images of the 80Al-10Bi-10Sn wt.% powders: (a,b) surfaces, (c) cross-section; (d–g) EPMA element mappings of the cross section of the powders: (d) BSE, (e) Al, (f) Bi, and (g) Sn.
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f1: (a–c) SEM images of the 80Al-10Bi-10Sn wt.% powders: (a,b) surfaces, (c) cross-section; (d–g) EPMA element mappings of the cross section of the powders: (d) BSE, (e) Al, (f) Bi, and (g) Sn.

Mentions: The morphologies of the 80Al-10Bi-10Sn powders are shown in Fig. 1. As shown in Fig. 1a,b, the microstructures of the 80Al-10Bi-10Sn powders were characterized by cracked surfaces with linear (Bi, Sn)-rich phases spreading throughout the grain boundaries. Moreover, as can be seen in the cross-section in Fig. 1c and the electron probe microanalysis (EPMA) element mappings in Fig. 1(d–g), the powders were enveloped by a thin, discontinuous (Bi, Sn)-rich shell. According to Liu27, the Al-Bi-Sn ternary system also exhibited a liquid-phase miscibility gap (Supplementary Figures S1a and S2). During the cooling process of gas atomization, for every droplets, the parent liquid phase decomposed into the minor (Bi, Sn)-rich phase and the major Al-rich phase24. According to our previous studies, the final morphologies of core/shell microstructures of the composite powders are determined by the differences of volume fractions and the differences of surface energies between the separated phases2829. Under the fast cooling conditions of gas atomization, there exists a large temperature gradient in the droplets. Therefore, the influences of the differences of surface energies play a greater role in this case24. In order to reduce the energy of the whole powder, the (Bi, Sn)-rich phase with lower surface energies moved outward, wetting and occupying the powder surface. However, the volume of the (Bi, Sn)-rich phase was too small to entirely cover the powder surface (Supplementary Figure S1b). In addition, since the composition of the (Bi, Sn)-rich phase was very close to the eutectic composition of the Bi-Sn system27, its solidifying point was much lower than that of the Al-rich phase. As the temperature decreased, the Al-rich phase firstly solidified, while the (Bi, Sn)-rich phase remained in the liquid state and was homogeneously distributed around the grain boundaries of the outer layers of the powders. The cracked surfaces were attributed to the differences in the thermal expansion coefficients of the Al, Sn, and Bi30 (23.0 ppm k−1, 21.9 ppm k−1, and 13.2 ppm k−1 at 20 °C, respectively). Under the fast-cooling conditions of gas atomization, the Al-rich and (Bi, Sn)-rich phases on the grain boundaries shrank for different degrees, leading to the crack of the powder surface. As for the small (Bi, Sn)-rich phases distributed on the grain boundaries inside the powders, as shown in Fig. 1c, they were supersaturated from the Al-rich phase when the temperature decreased. In order to prove our assumption for the crack of the powder surfaces, powders comprised of 85Al-8.55Bi-6.45Sn wt.%, in which the compositions of Bi and Sn were located just on the eutectic one of the Bi-Sn system, were prepared using the same method. The results show that, the surfaces of the powders cracked more heavily (Supplementary Figure S3).


A Novel Self-Assembling Al-based Composite Powder with High Hydrogen Generation Efficiency.

Wang C, Liu Y, Liu H, Yang T, Chen X, Yang S, Liu X - Sci Rep (2015)

(a–c) SEM images of the 80Al-10Bi-10Sn wt.% powders: (a,b) surfaces, (c) cross-section; (d–g) EPMA element mappings of the cross section of the powders: (d) BSE, (e) Al, (f) Bi, and (g) Sn.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663537&req=5

f1: (a–c) SEM images of the 80Al-10Bi-10Sn wt.% powders: (a,b) surfaces, (c) cross-section; (d–g) EPMA element mappings of the cross section of the powders: (d) BSE, (e) Al, (f) Bi, and (g) Sn.
Mentions: The morphologies of the 80Al-10Bi-10Sn powders are shown in Fig. 1. As shown in Fig. 1a,b, the microstructures of the 80Al-10Bi-10Sn powders were characterized by cracked surfaces with linear (Bi, Sn)-rich phases spreading throughout the grain boundaries. Moreover, as can be seen in the cross-section in Fig. 1c and the electron probe microanalysis (EPMA) element mappings in Fig. 1(d–g), the powders were enveloped by a thin, discontinuous (Bi, Sn)-rich shell. According to Liu27, the Al-Bi-Sn ternary system also exhibited a liquid-phase miscibility gap (Supplementary Figures S1a and S2). During the cooling process of gas atomization, for every droplets, the parent liquid phase decomposed into the minor (Bi, Sn)-rich phase and the major Al-rich phase24. According to our previous studies, the final morphologies of core/shell microstructures of the composite powders are determined by the differences of volume fractions and the differences of surface energies between the separated phases2829. Under the fast cooling conditions of gas atomization, there exists a large temperature gradient in the droplets. Therefore, the influences of the differences of surface energies play a greater role in this case24. In order to reduce the energy of the whole powder, the (Bi, Sn)-rich phase with lower surface energies moved outward, wetting and occupying the powder surface. However, the volume of the (Bi, Sn)-rich phase was too small to entirely cover the powder surface (Supplementary Figure S1b). In addition, since the composition of the (Bi, Sn)-rich phase was very close to the eutectic composition of the Bi-Sn system27, its solidifying point was much lower than that of the Al-rich phase. As the temperature decreased, the Al-rich phase firstly solidified, while the (Bi, Sn)-rich phase remained in the liquid state and was homogeneously distributed around the grain boundaries of the outer layers of the powders. The cracked surfaces were attributed to the differences in the thermal expansion coefficients of the Al, Sn, and Bi30 (23.0 ppm k−1, 21.9 ppm k−1, and 13.2 ppm k−1 at 20 °C, respectively). Under the fast-cooling conditions of gas atomization, the Al-rich and (Bi, Sn)-rich phases on the grain boundaries shrank for different degrees, leading to the crack of the powder surface. As for the small (Bi, Sn)-rich phases distributed on the grain boundaries inside the powders, as shown in Fig. 1c, they were supersaturated from the Al-rich phase when the temperature decreased. In order to prove our assumption for the crack of the powder surfaces, powders comprised of 85Al-8.55Bi-6.45Sn wt.%, in which the compositions of Bi and Sn were located just on the eutectic one of the Bi-Sn system, were prepared using the same method. The results show that, the surfaces of the powders cracked more heavily (Supplementary Figure S3).

Bottom Line: The results indicated that the powders formed unique core/shell microstructures with cracked surfaces and (Bi, Sn)-rich phases distributed on the Al grain boundaries.The powders exhibited good oxidation resistance and reacted violently with distilled water at temperatures as low as 0 °C.The mechanisms of the hydrolysis reactions were also analyzed.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen, 361005, P. R. China.

ABSTRACT
In this study, a novel self-assembling hydrogen generation powder comprised of 80Al-10Bi-10Sn wt.% was prepared using the gas atomization method and then collected in an air environment. The morphological and hydrolysis properties of the powders were investigated. The results indicated that the powders formed unique core/shell microstructures with cracked surfaces and (Bi, Sn)-rich phases distributed on the Al grain boundaries. The powders exhibited good oxidation resistance and reacted violently with distilled water at temperatures as low as 0 °C. Furthermore, at 30 °C, the powders exhibited a hydrogen conversion yield of 91.30% within 16 minutes. The hydrogen produced by this powder could be directly used in proton exchange membrane fuel cells. The mechanisms of the hydrolysis reactions were also analyzed.

No MeSH data available.


Related in: MedlinePlus