The Au−Fe (Gold-Iron) system

Okamoto, H.; Massalski, T. B.; Swartzendruber, L. J.; Beck, Paul A.

doi:10.1007/bf02868322

Cited by 72 publications

(82 citation statements)

References 77 publications

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“…Experimental observations of the microstructure showed that the eutectoid composition is 2.3 %Au, which agrees perfectly with DTA and calculated data from the literature [14]. In addition, the influence of several processing routes on the final microstructure was studied.…”

Section: Discussionsupporting

confidence: 86%

“…Jette et al [10] found that alloys quenched from 894°C showed the ␥-Fe diffraction lines, and concluded that the transformation temperature must be below 894°C. An estimate of this temperature, according to the thermodynamic model of Okamoto et al [14], showed a value of 868°C, which is close to that of Seigle [11] and consistent with that of Jette [10]. The low eutectoid temperature of about 830°C observed by Isaac [7] is likely to be caused by supercooling.…”

Section: Figuresupporting

confidence: 77%

“…The diagram is based mainly on experimental results obtained by Raub and Walter [9] and Buckley and HumeRothery [12]. More recently, Okamoto et al assessed the phase diagram [14]. The equilibrium phases are: liquid, fcc terminal solid solutions of Au and ␥-Fe, and bcc terminal solid solutions of ␦-Fe and ␣-Fe.…”

Section: Fe-au Phase Diagrammentioning

confidence: 99%

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Gold nanostructures by directional solid-state decomposition

2006

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The trend in electronics industry towards miniaturisation is leading to increasing research focus on nano-electronic devices. For example, metal nanowires show potential for future application as connector lines in such devices. The controlled fabrication of these structures at scales beyond the current limits of lithographic techniques is of great interest. Self-assembly processes using gold nanoparticles are being extensively studied as one possible long-term solution. This study addresses a novel approach of obtaining gold nanostructures. It consists of applying directional solidification processing to eutectoid alloys in order to produce ordered structures, followed by phase separation by selective etching.The directional transformation of eutectoid alloys is a close derivation of the directional solidification of eutectics. In this case, two phases precipitate simultaneously from a high-temperature solid phase (Figure 1). When the growth properties of the two phases are sufficiently compatible, unidirectional decomposition can also produce aligned composite materials [1,2]. One of the most prominent examples of eutectoid reaction is the formation of pearlite by undercooling a Fe-C alloy in the ␥-state. Microstructures are best when the high-temperature phase is nearly singlecrystalline. Therefore, aligned eutectoids are often produced by accomplishing unidirectional solidification and unidirectional decomposition sequentially. Eutectic solidification and eutectoid decomposition, as examples of duplex crystal growth, are inherently more complex than single-phase crystal growth. The technique used in both cases is quite similar: a specimen is unidirectionally translated through a steep temperature gradient and traversed by a macroscopically planar transformation front. If adequate experimental conditions are arranged, the eutectoid reaction product is an aligned microstructure. The conditions to be met are: i) sufficiently steep gradient to avoid both nucleation before the actual position of the transformation front and coalescence afterwards, ii) a translation rate which permits the attainment of a transformation front with stationary moving conditions, i.e., as a first approximation, a lower translation rate than the maximum eutectoid growth rate.Although eutectic and eutectoid reactions are essentially the same in nature, there are some differences that must be pointed out. Firstly, eutectoid spacings are much finer than the eutectic spacings for the same growth rate, due to the lower values of diffusion coefficients in the solid state as compared to the liquid. Also, a decrease in eutectoid spacing, , with increasing growth rate, V, is generally slower for eutectoids than for eutectics. Data can again be fitted to a formula n V = const. However, whereas n = 2 fits to almost all data for eutectics, values of n ranging from 2 to 4 have been reported for eutectoids. The value n = 2 is consistent with volume-diffusion control, and n = 3 is predicted for grain-boundary-diffusion control.

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Section: Discussionsupporting

confidence: 86%

Section: Figuresupporting

confidence: 77%

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Gold nanostructures by directional solid-state decomposition

2006

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“…S.5, are based on a fully-relaxed bcc Fe unit cell, for which we allowed volumetric and shape changes. For this cell we obtained a 0 K equilibrium lattice parameter of 2.8297 Å, in agreement with reported experimental data [30]. In all slab models the positions of atoms are relaxed in all degrees of freedom.…”

Section: Dft Proceduressupporting

confidence: 72%

“…This would be in line with a description of this layer as a thin wetting film of equilibrium thickness, as long as the composition of this layer is close to that of the bulk Au-rich phase in the system. While the bulk solubility of Fe in Au at 900 C is~60 at.% [30], values of~70 at.% were measured in our previous investigations of Au/Fe particles on sapphire (annealed at the same temperature) [16]. This difference was discussed in terms of the effects of elastic energy in such particles, constrained in part by the rigid single crystal substrate, on phase equilibria.…”

Section: Classical Thermodynamicsmentioning

confidence: 97%

Encapsulation by segregation – A multifaceted approach to gold segregation in iron particles on sapphire

2016

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Gold‐Cobalt Nanoparticle Alloys Exhibiting Tunable Compositions, Near‐Infrared Emission, and High T₂ Relaxivity

Marbella

Andolina

Smith

et al. 2014

Adv Funct Materials

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We demonstrate the synthesis of discrete, composition‐tunable gold‐cobalt nanoparticle alloys (% Co = 0–100%; diameter = 2–3 nm), in contrast with bulk behavior, which shows immiscibility of Au and Co at room temperature across all composition space. These particles are characterized by transmission electron microscopy and 1H NMR techniques, as well as inductively coupled plasma mass spectrometry, X‐ray photoelectron spectroscopy, and photoluminescence spectroscopy. In particular, 1H NMR methods allow the simultaneous evaluation of composition‐tunable magnetic properties as well as molecular characterization of the colloid, including ligand environment and hydrodynamic diameter. These experiments also demonstrate a route to optimize bimodal imaging modalities, where we identify AuxCoyNP compositions that exhibit both bright NIR emission (2884 m −1cm−1) as well as some of the highest per‐particle T 2 relaxivities (12200 mm NP −1s−1) reported to date for this particle size range.

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The Au−Fe (Gold-Iron) system

Cited by 72 publications

References 77 publications

Gold nanostructures by directional solid-state decomposition

Gold nanostructures by directional solid-state decomposition

Encapsulation by segregation – A multifaceted approach to gold segregation in iron particles on sapphire

Gold‐Cobalt Nanoparticle Alloys Exhibiting Tunable Compositions, Near‐Infrared Emission, and High T₂ Relaxivity

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The Au−Fe (Gold-Iron) system

Cited by 72 publications

References 77 publications

Gold nanostructures by directional solid-state decomposition

Gold nanostructures by directional solid-state decomposition

Encapsulation by segregation – A multifaceted approach to gold segregation in iron particles on sapphire

Gold‐Cobalt Nanoparticle Alloys Exhibiting Tunable Compositions, Near‐Infrared Emission, and High T2 Relaxivity

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Gold‐Cobalt Nanoparticle Alloys Exhibiting Tunable Compositions, Near‐Infrared Emission, and High T₂ Relaxivity