US20150050183A1

US20150050183A1 - Containment of molten materials having silicon

Info

Publication number: US20150050183A1
Application number: US14/526,791
Authority: US
Inventors: Alitha Allbee; Zachary Bauer; Jeremy Beebe; Matthew Gave; Vasgen Shamamian; Randall Siegel; Joseph Sootsman; James Young
Original assignee: Dow Corning Corp
Current assignee: Dow Silicones Corp
Priority date: 2012-05-21
Filing date: 2014-10-29
Publication date: 2015-02-19
Also published as: WO2013177019A2; CN104321277A; EP2852555A2; WO2013177019A3

Abstract

Silicon eutectic alloy compositions and methods for making the same are disclosed. In one approach, a method may include using a glass carbon container to restrict contamination of the eutectic alloy melt. In an alternative approach, a method may include using a container having aluminum. The aluminum in the container may provide aluminum that is incorporated into the silicon eutectic alloy. Silicon eutectic bodies made by such methods are also disclosed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of International Patent Application No. PCT/US2013/041773, filed May 20, 2013, which claims priority to U.S. Provisional Patent Application No. 61/649,686, filed May 21, 2012, both of which are incorporated by reference herein in their entirety.

FIELD

The present disclosure is directed generally to eutectic alloys and more particularly to eutectic alloy compositions comprising silicon (Si).

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Silicon eutectic compositions are of great technological interest as structural and wear resistant components. These “castable ceramic” materials can have similar mechanical properties to certain technical ceramics, including good wear resistance, corrosion behavior, toughness, and strength. For example, Si—CrSi₂eutectic alloy composites have been studied and their mechanical properties are similar to or better than many technical ceramics. It has also been recognized that these alloys can be fabricated by melting and casting processes (see, e.g., WO 2011/022058).

SUMMARY

Described herein are methods of forming silicon eutectic alloys in containers that do not substantially contaminate a molten silicon eutectic alloy. In addition, silicon eutectic alloys and methods of fabricating silicon eutectic alloys are described according to the teachings of the present disclosure.
According to one aspect of the present disclosure, a silicon eutectic alloy composition includes a body comprising a eutectic alloy including silicon, a metallic element M_a, a metallic element M_b, and a eutectic aggregation including a first phase comprising the silicon, a second phase comprising the metallic element M_aand a third phase comprising the metallic element M_b. The second phase has a formula M_aSi₂, and the third phase has a formula M_bSi₂, the second and third phases are immiscible. The metallic element M_amay include chromium and the metallic element M_bmay include vanadium.
According to a further aspect of the present disclosure, a method of making a eutectic alloy composition includes heating a mixture including silicon and a metal to form a eutectic alloy melt in a container. The metal includes one or more metallic elements M, and portions of the container in contact with the eutectic alloy melt comprise glassy carbon. The method further includes removing heat from the eutectic alloy melt to solidify the eutectic alloy melt, thereby forming the eutectic alloy composition including silicon, the one or more metallic elements M, and a eutectic aggregation of a first phase comprising silicon and a second phase being a silicide phase.
According to one aspect of the present disclosure, a silicon eutectic alloy composition includes a body comprising a eutectic alloy including silicon, aluminum, a metallic element M_a, a metallic element M_b, and a eutectic aggregation including a first phase comprising the silicon, a second phase comprising the metallic element M_aand the metallic element M_b. The second phase is a silicide comprising a solid solution of the metallic element M_aand the metallic element M_b, and having a formula of M_a _{x l M} _b _xSi₂, where 0<x<1.
The silicon eutectic alloy composition may be advantageously used in any of a number of industries, such as by way of example chemical, oil and gas, semiconductor, automotive, aerospace, machine parts and solar industries, among others, in which a component exhibiting good fracture toughness and wear resistance is desired.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a Cr—Si phase diagram obtained from ASM Alloy Phase Diagrams Center, P. Villars, editor-in-chief, H. Okamoto and K. Cenzual, section editors, ASM International, Materials Park, Ohio, USA, 2006-2011;

FIG. 2 is an optical microscope image of rod-like reinforcement phase structures aligned perpendicular to the surface of a eutectic alloy sample prepared by directional solidification;

FIG. 3 is a differential scanning calorimetry (DSC) thermogram of heating cycles of elemental silicon in an alumina crucible indicating that with increasing cycle number and therefore time in the melt, the endothermic peak corresponding to the melting of Si was observed to shift to lower temperature and decrease in intensity;

FIGS. 4A-4B are scanning electron microscope (SEM)/energy dispersive spectroscopy (EDS) images of the alumina crucible containing silicon following temperature cycling demonstrating the presence of aluminum in the silicon;

FIG. 5 is a DSC thermogram of heating cycles of elemental silicon in an alumina crucible;

FIG. 6 is a x-ray diffraction (XRD) plot of a mixture of elemental silicon mixed with Al₂O₃after being heated to 1600° C. for one hour;

FIGS. 7A-7B are (A) DSC and (B) SEM/EDS of a Si+Cr+V mixture under temperature cycling in an alumina crucible showing evidence of incorporation of aluminum;

FIGS. 8A-8B are (A) DSC thermogram and (B) SEM images of pure silicon in a glassy carbon crucible with the lightest contrast in the SEM images being silicon, the darkest contrast being the glassy carbon, and the intermediate contrast being SiC, and the constancy of the DSC thermogram with temperature cycling indicates no observed compositional differences between cycles;

FIG. 9 is a DSC thermogram of a Si+Cr+V mixture loaded into a glassy carbon crucible, and the constancy of the DSC thermogram with cycling indicates no observed compositional differences between cycles;

FIGS. 10A-10B are DSC thermograms of Si+Cr+V mixture in glassy carbon containers;

FIGS. 11A-11B are (A) DSC thermogram and (B) XRD of larger sample portions of a Si+Cr+V mixture;

FIGS. 12A-12C are (A) melting temperature for silicon in alumina and silicon in carbon, (B) melting temperature for Si+Cr+V eutectic in alumina and in carbon, and (C) is a phase diagram of Al—Si;

FIG. 13 is a plot of EDS point-by-point analysis of at. % vanadium as a function of counts;

FIG. 14 is a schematic of a possible phase diagram of CrSi₂and VSi₂;

FIGS. 15A-15B are (A) DSC thermogram of an identical sample as that of FIG. 10A except in an alumina container and (B) a plot of fraction of Si-V eutectic composition as a function of temperature showing onset temperature of the eutectic with different amounts of vanadium; and

FIGS. 16A-16D are EDS maps of (A) composite image of vanadium, chromium, and aluminum, (B) vanadium, (C) chromium, and (D) aluminum.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. It should be understood that throughout the description, corresponding reference numerals indicate like or corresponding parts and features.
The present disclosure generally relates to silicon eutectic alloy compositions as well as methods of making a silicon eutectic alloy composition. The following specific embodiments are given to illustrate the design and use of a silicon eutectic alloy composition according to the teachings of the present disclosure and should not be construed to limit the scope of the disclosure. Those skilled-in-the-art, in light of the present disclosure, will appreciate that many changes can be made in the specific embodiments which are disclosed herein and still obtain alike or similar result without departing from or exceeding the spirit or scope of the disclosure. One skilled in the art will further understand that any properties reported herein represent properties that are routinely measured and can be obtained by multiple different methods. The methods described herein represent one such method and other methods may be utilized without exceeding the scope of the present disclosure.
Alumina (Al₂O₃) has commonly been used as a containment vessel for molten mixtures having silicon. However, molten silicon and mixtures or compositions having silicon can be highly corrosive and exhibit reactivity towards nearly every known material. It is important to select a suitable containment vessel to avoid introducing undesirable impurities into the melt.
The inventors have discovered that when alumina crucibles are used to contain melts comprising silicon, aluminum metal may be incorporated into the melt in an amount proportional to the amount of time that the mixture is held in the molten state. Glassy carbon (e.g., vitreous carbon), however, has been demonstrated to contain molten silicon and melts having silicon without the introduction of detectable impurities. Glassy carbon may therefore be advantageous for the containment of materials comprising silicon in the molten state for commercial production and also for the study of physical properties by differential scanning calorimetry (DSC).
Unexpectedly, the presence of aluminum in the eutectic alloy melt influences the miscibility of the silicide phases in the resulting eutectic alloy. For example, when an alumina crucible is used to contain molten alloys in the Si—V—Cr system, aluminum from the crucible may be incorporated into the melt and the resulting eutectic alloy may include miscible CrSi₂and VSi₂phases. However, when a glassly carbon crucible is used to ensure no aluminum contamination of the melt, CrSi₂and VSi₂phases have been found to be immiscible. Without being bound by theory, when aluminum is included in the eutectic alloy melt, at least some of the aluminum is believed to be forming a solid solution with the silicide phases resulting in a change of the lattice structure of the silicide phases which creates the miscibility of the silicide phases.
A host of other materials have also been screened for use as a crucible or container for melts comprising silicon, including graphite, boron nitride, sapphire, diamond coated graphite, silicon carbide coated alumina, silicon carbide coated graphite, and amorphous silica. Each of these materials was observed in preliminary testing to demonstrably interact with the molten silicon with unexpected results in laboratory analysis.
By way of background, general description of eutectic alloy compositions comprising silicon (Si) and a metallic element (M) are described below first. A eutectic reaction of the elements Si and M can be described as follows:
L
Si+MSi ₂, or (1)
L
M_xSi_y+MSi₂, (2)
where a liquid phase (L) and two solid phases (e.g., Si and MSi₂as in (1) or M_xSi_yand MSi₂as in (2)) exist in equilibrium at a eutectic composition and the corresponding eutectic temperature. FIG. 1 is an example phase diagram illustrating a eutectic reaction of elements silicon and chromium. In the case of a binary eutectic alloy, the eutectic composition and eutectic temperature define an invariant point (or eutectic point). A liquid having the eutectic composition undergoes eutectic solidification upon cooling through the eutectic temperature to form a eutectic alloy composed of a eutectic aggregation of solid phases. Eutectic alloys at the eutectic composition melt at a lower temperature than do the elemental or compound constituents and any other compositions thereof.
According to one aspect of the present disclosure, a silicon eutectic alloy composition may include a body having a eutectic alloy comprising silicon, a metallic element M_a, a metallic element M_b, and a eutectic aggregation. The eutectic aggregation can include a first phase comprising the silicon, a second phase comprising the metallic element M_aand a third phase comprising the metallic element M_b. The second and third phases may be immiscible
M_aand M_bmay be any metallic element M described herein. For example, M_aand M_bmay each include at least one element selected from the group consisting of chromium, vanadium, tungsten, magnesium, niobium, tantalum, titanium, molybdenum, cobalt, zirconium, hafnium, manganese, nickel, and rhenium. Furthermore, the metallic element M_amay be or include chromium and the metallic element M_bmay be or include vanadium. M_aand M_bmay be different metallic elements or different compositions of metallic elements.
The first phase may be an elemental silicon phase. For example, the elemental silicon phase may be in the form of crystalline silicon and/or amorphous silicon. The first phase may alternatively be an intermetallic compound phase. For example, the first phase may include silicon and the metallic element(s) M. The first phase may have a formula M_xSi_y, where x and y are integers. Generally, the intermetallic compound phase is different from the second phase. For example, if the second phase is a disilicide phase, x may not be 1 and y may not be 2.
The second phase or the silicide phase may be a disilicide phase. In addition, the second phase may have a formula M_aSi₂. For example, the disilicide phase may be selected from the group consisting of CrSi₂, VSi₂, WSi₂, MgSi₂, NbSi₂, TaSi₂, TiSi₂, MoSi₂, CoSi₂, ZrSi₂, HfSi₂, MnSi₂, NiSi₂, and ReSi₂.
The third phase may have a formula M_bSi₂. The second and third phases may be immiscible as a result of the having substantially no aluminum contamination. Accordingly, the eutectic alloy composition may comprise less than about 0.1 percent by weight aluminum.
Although the second and third phases are immiscible, the compositions of the second and third phases (e.g., M_aSi₂and M_bSi₂) may share common elements. For example, CrSi₂may have some vanadium in solid solution and VSi₂may have some chromium in solid solution. However, the CrSi₂phase and the VSi₂phase have different compositions and are therefore immiscible.
The eutectic aggregation may have a morphology that depends on the solidification process. The eutectic aggregation may have a lamellar morphology including alternating layers of the solid phases (e.g., first and second phases), which may be referred to as matrix and reinforcement phases, depending on their respective volume fractions, where the reinforcement phase is present at a lower volume fraction than the matrix phase. In other words, the reinforcement phase is present at a volume fraction of less than 0.5. The reinforcement phase may comprise discrete eutectic structures, whereas the matrix phase may be substantially continuous. For example, the eutectic aggregation may include a reinforcement phase of rod-like, plate-like, acicular and/or globular structures dispersed in a substantially continuous matrix phase. Such eutectic structures may be referred to as “reinforcement phase structures.”
The reinforcement phase structures in the eutectic aggregation may further be referred to as high aspect ratio structures when at least one dimension (e.g., length) exceeds another dimension (e.g., width, thickness, diameter) by a factor of by a factor of 2 or more. Aspect ratios of reinforcement phase structures may be determined by optical or electron microscopy using standard measurement and image analysis software. The solidification process may be controlled to form and align high aspect ratio structures in the matrix phase. For example, when the eutectic alloy is produced by a directional solidification process, it is possible to align a plurality of the high aspect ratio structures along the direction of solidification, as shown for example in FIG. 2, which shows an optical microscope image of rod-like structures aligned perpendicular to the surface of an exemplary Si—CrSi₂eutectic alloy sample (and viewed end-on in the image).
According to one aspect of the present disclosure, a method of making the silicon eutectic alloy where the second and third phases may be immiscible may include heating a mixture including the silicon, the metallic element M_a, and the metallic element M_b, to form a eutectic alloy melt in a container where portions of the container in contact with the eutectic alloy melt comprise glassy carbon. The method may further include removing heat from the eutectic alloy melt to solidify the eutectic alloy melt, thereby forming the body.
The elemental silicon and metallic elements can include other elements for alloying or can be a relatively high purity. As such, the elemental silicon and/or metallic elements can include a wide variety of impurities. For example, the elemental silicon and/or metallic elements can be chemical grade, metallurgical grade, solar grade, electronic grade, semi-conductor grade, or ultra-high purity. For example, the elemental silicon and/or metallic elements can have a purity of at least about 95%, at least about 99%, at least about 99.9%, or about 95% to about 99% by weight. Furthermore, the elemental silicon and/or metallic elements can include alloying elements such as iron (e.g., ferrosilicon), boron, aluminum, calcium, etc. As such, a lower purity of silicon and/or metallic elements can be a means for including alloying elements. Furthermore, the mixture may include one or more additional alloying elements.
The heating the mixture may include, for example, resistive or inductive heating. The melting together the components of the mixture may entail heating the silicon and the metallic element(s) to a predetermined temperature at or above the eutectic temperature. The mixture may also be heated to a superheat temperature such as greater than about 50° C. above the eutectic temperature. The molten silicon and the metallic element(s) may be held at the predetermined temperature for a length of time sufficient for diffusion to occur and for the melt to homogenize. For example, the mixture may be heated to the temperature for at least about 5 minutes.
The heating of the mixture may take place in a vacuum or an inert gas environment. For example, the vacuum environment may be an environment maintained at a pressure of about 10⁻⁴Torr (about 10⁻²Pa) or lower (where a lower pressure correlates to a higher vacuum). The vacuum environment may also be maintained at a pressure of about 10⁻⁵Torr (10⁻³Pa) or lower and greater than 0 Pa.
Portions of the container in contact with the eutectic alloy melt can be or comprise glassy carbon. For example, the container may have a barrier coating of glassy carbon on the surface. Glassy carbon may not substantially contaminate the eutectic alloy melt (e.g., substantially no detectable impurities). For example, the eutectic alloy melt may be substantially free of carbon from the glassy carbon. Furthermore, substantially no contamination of the eutectic alloy melt may mean that the melting point of the eutectic alloy melt does not substantially change compared to the melting point of a eutectic alloy melt having no contamination. For example, a change in the melting point of the eutectic alloy melt may be less than about 1 degree Celsius. As described in the examples below, DSC analysis can be used to measure a melting point of an alloy melt. A protective carbide phase may form between the eutectic alloy melt and the container which may prevent contamination of the eutectic alloy melt. For example, the carbide phase may comprise silicon carbide.
The method of making can further include removing heat from the eutectic alloy melt to solidify the eutectic alloy melt, thereby forming the body or eutectic alloy composition. Heat may be removed by a number of methods. For example, directional solidification of a eutectic alloy melt may be used. In addition, the eutectic alloy melt can be cooled at a variety of rates depending on desired microstructure. For example, the eutectic alloy melt may be cooled at a rate of at least about 10° C. per minute.
According to another aspect of the present disclosure, a method of making a eutectic alloy composition is provided. The method can include heating a mixture including silicon and a metal to form a eutectic alloy melt in a container comprising glassy carbon.
The metal can comprise one or more metallic elements M. The one or more metallic elements M may include at least one element selected from the group consisting of chromium, vanadium, tungsten, magnesium, niobium, tantalum, titanium, molybdenum, cobalt, zirconium, hafnium, manganese, nickel, and rhenium.
The eutectic alloy composition may include silicon, the one or more metallic elements M, and a eutectic aggregation of a first phase comprising silicon and a second phase being a silicide phase.
Unlike certain previous aspects of the present disclosure described above, aluminum may be intentionally included in the silicon eutectic alloy composition. For example, a silicon eutectic alloy composition may include a body comprising a eutectic alloy having silicon, aluminum, a metallic element M_a, a metallic element M_b, and a eutectic aggregation. For example, the eutectic alloy comprises greater than about 0.1 percent by weight aluminum, about 0.1 to about 10 percent by weight aluminum, or about 1 to about 7 percent by weight aluminum.
The eutectic aggregation can include a first phase comprising the silicon and a second phase comprising the metallic element M_aand the metallic element M_b. The second phase is a disilicide comprising a solid solution of the metallic element M_aand the metallic element M_b, and having a formula of M_a _xM_b _1-xSi₂, where 0<x<1. The component x may also be in the range where 0.01<x<0.99. As such, M_aSi₂and M_bSi₂may be miscible in the eutectic alloy. As a result, the eutectic alloy may comprise only one silicide phase. Furthermore, at least some of the aluminum in the silicon eutectic alloy composition may be in solid solution with the silicide. For example, the silicide may have about 0.1 percent by weight aluminum or at least about 0.1 percent by weight aluminum.
According to one aspect of the present disclosure, a method of making the silicon eutectic alloy where the silicide comprises the solid solution of the metallic element M_aand the metallic element M_b, and having the formula of M_a _xM_b _1-xSi₂may include heating a mixture including the silicon, the aluminum, the metallic element M_a, and the metallic element M_b, to form a eutectic alloy melt in a container where portions of the container in contact with the eutectic alloy melt comprise glassy carbon, and removing heat from the eutectic alloy melt to solidify the eutectic alloy melt, thereby forming the body.
In an alternative method, the method can include heating a mixture including the silicon, the metallic element M_a, and the metallic element M_b, to form a eutectic alloy melt in a container where portions of the container in contact with the eutectic alloy melt comprise a composition having aluminum, and removing heat from the eutectic alloy melt to solidify the eutectic alloy melt, thereby forming the body. The aluminum in the container may provide the aluminum that is incorporated into the silicon eutectic alloy.
The following examples are provided to demonstrate the effect of using containers with aluminum such as alumina and without aluminum such as glassy carbon to form silicon eutectic alloy composites.

EXAMPLE 1

Use of Alumina as Containment of Molten Silicon

A small amount (<50 mg) of elemental silicon was placed into a 70 μL-capacity alumina crucible and loaded into a DSC (Mettler TGA/DSC 1). The material was then heated to 1100° C. in less than 10 minutes and held isothermally for 5 minutes. The sample was then heated to 1550° C. at 20° C./minute, held isothermally for 5 minutes, then ramped back to 1100° C. at −20 ° C./minute, and followed by another 5 minute hold. The cycling between 1100 and 1550° C. was cycled for a total of six times. The instrument was continuously purged with argon at all times with a 70 mL/min total flow. In subsequent heating cycles, the observed onset of the endotherm corresponding to the melting of elemental silicon was observed to shift to lower temperatures and decrease in integrated intensity (enthalpy), as shown in FIG. 3.
Analysis of the material by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) along with x-ray diffraction (XRD) following this thermal program indicated the presence of elemental aluminum that had been incorporated into the bulk of the silicon. FIG. 4A is a SEM image of the alumina crucible and the silicon, and FIG. 4B is a magnified image of circled region of FIG. 4A. As shown in FIG. 5, low temperature DSC (FIG. 5) also reveals an emerging phase transition.
A mixture of elemental silicon with about 25 volume percent Al₂O₃was heated to 1600° C. for one hour. Table 4 below provides measured volume percentage of silicon, Al₂O₃, and aluminum of the mixture before (initial) and after (final) being heated. FIG. 6 is a XRD plot of the mixture after being heated.

TABLE 4

Measured volume percentage of phases before and after heating.

	Initial	Final
Phase	(vol. %)	(vol. %)

Si	83	77
Al₂O₃	17	16
Al	0	7

EXAMPLE 2

Use of Alumina as Containment for Si+Cr+V Mixture

A mixture of Si+Cr+V (81.25% of Si, 16.83% of Cr, and 1.92% of V by weight) was loaded into an alumina crucible and treated identically to the pure silicon sample of Example 1. The peak intensity was again observed to decrease and its placement was found to move towards lower temperature, as shown in FIG. 7A. This shift was again associated with the presence of elemental aluminum in the sample following the heating cycles, as seen in FIG. 7B.

EXAMPLE 3

Use of Glassy Carbon as Containment for Silicon

About 10 mg of elemental silicon was placed into a glassy carbon crucible and heat treated identically to the conditions in Examples 1 and 2. As shown in FIG. 8A, the DSC trace was observed to be nearly co-linear and changes in enthalpy and peak position were minimal. Following heating, SEM analysis indicated the presence of a silicon carbide boundary layer that separated the silicon from the glassy carbon, as seen in FIG. 8B. No evidence was observed for the presence of carbon in the bulk of the silicon, and the silicon was instead confined to the boundary layer. The constancy of the DSC thermogram probably indicates that the SiC layer is self-limiting.

EXAMPLE 4

Use of Glassy Carbon as Containment for Si+Cr+V

The same Si+Cr+V ratio used in Example 2 was loaded into a glassy carbon crucible and subjected to the same heating profile of Examples 1-3. The DSC thermogram was again nearly co-linear, as shown in FIG. 9.
Furthermore, as shown in FIGS. 10A-10B, DSC thermograms indicated multiple peaks. Larger sample portions were prepared in a vacuum induction melter (VIM) and placed back in the DSC. As shown in FIG. 11A, these VIM samples were similar to the original DSC data, and as seen in FIG. 11B, XRD of the VIM samples also showed evidence for MSi₂inhomogeneity.

EXAMPLE 5

Compositional Variability Dependent Upon Crucible Type

Both elemental silicon, as shown in FIG. 12A, and silicon eutectic alloy, as shown in FIG. 12B, demonstrate that a melting temperature decrease when an alumina container was used. However, when a carbon container was used, a drop in melting point was not observed. FIG. 12C is a phase diagram of Al—Si, which shows that aluminum forms a solid solution with silicon and as more aluminum is incorporated into the silicon, the melting temperature decreases.
With a Si+Cr+V composition (12.5 at. % V, 12.5 at. % Cr, and 75 at. % Si), EDS maps were used to conduct EDS point-by-point analysis with silicon background subtracted which indicated bimodal distribution, as shown in FIG. 13. This provided additional evidence that there is limited Cr/V solubility. Therefore, without being bound by theory, there is likely a spinodal region, as shown by the schematic phase diagram of FIG. 14, between CrSi₂and VSi₂resulting in insolubility between CrSi₂and VSi₂.

EXAMPLE 6

Use of Glassy Carbon as Containment for Si+Cr+V+Al

Similar Si+Cr+V ratio used in Example 4 but with added Al of about 3 weight percentage was loaded into a glassy carbon crucible and subjected to the same heating profile of Example 4. The DSC thermogram indicated a proposed eutectic that has four components: Si, Cr, V, and Al, as shown by FIGS. 15A-15B. EDS maps reveal a distribution of disilicides, as shown in FIGS. 16A-16D.
The present examples demonstrate that fundamentally different thermal behavior can be observed as a function of crucible material due to the incorporation of impurities. In the case of the glassy carbon, multiple overlapped peaks were observed, whereas in the case of the alumina-contained samples, single features were observed. The incorporated aluminum may therefore act as a “processing aid” that may help to homogenize the melt, particularly near the solidus and liquidus temperatures. Contrarily, glassy carbon allows for the observation of the material in what is believed to be its pure, native state.
The foregoing description of various forms of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications or variations are possible in light of the above teachings. The forms discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various forms and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

What is claimed is:

1. A method of making a silicon eutectic alloy body, the method comprising:

heating a mixture in a container thereby forming a eutectic alloy melt, wherein the mixture includes silicon and a metallic element M_a, where portions of the container in contact with the eutectic alloy melt comprise glassy carbon; and

removing heat from the eutectic alloy melt to solidify the eutectic alloy melt, thereby forming a silicon eutectic alloy body comprising having a eutectic aggregation including a first phase comprising the silicon and a second phase comprising the metallic element a, wherein the second phase has a formula M_aSi₂.

2. The method of claim 1, wherein the mixture comprises a third phase comprising the metallic element M_b, and wherein, after the removing step, the body comprising the eutectic aggregation comprises a third phase comprising the metallic element M_b, wherein the third phase has a formula M_bSi₂, and wherein the second and third phases are immiscible.

3. The method of claim 2, wherein the metallic element M_acomprises chromium and the metallic element M_bcomprises vanadium

4. The method of claim 1, wherein a carbide phase forms between the eutectic alloy melt and the container.

5. The method of claim 4, wherein the carbide phase comprises silicon carbide.

6. The method of claim 1, wherein the glassy carbon substantially does not contaminate the eutectic alloy melt.

7. The method of claim 1, wherein the eutectic alloy melt is substantially free of carbon.

8. The method of claims 1, wherein the heating the mixture comprises resistive or inductive heating.

9. A silicon eutectic alloy composition comprising:

a body comprising a eutectic alloy including silicon, aluminum, a metallic element M_a, a metallic element M_b, and a eutectic aggregation including a first phase comprising the silicon, a second phase comprising the metallic element M_aand the metallic element M_b, wherein the second phase is a disilicide comprising a solid solution of the metallic element M_aand the metallic element M_b, and having a formula of M_a _xM_b _1-xSi₂, where 0<x<1, and wherein the body comprises greater than 0.1 wt. % of the aluminum.

10. The silicon eutectic alloy composition of claim 9, wherein M_aSi₂and M_bSi₂phases are miscible in the eutectic alloy.

11. The silicon eutectic alloy composition of claim 9, wherein the eutectic alloy comprises only one silicide phase.

12. A method of making a silicon eutectic alloy, the method comprising:

heating a mixture including silicon, a metallic element M_a, and a metallic element M_b, to form a eutectic alloy melt in a container where portions of the container in contact with the eutectic alloy melt comprises a composition having aluminum; and

removing heat from the eutectic alloy melt to solidify the eutectic alloy melt, thereby forming a body comprising a eutectic alloy including the silicon, aluminum, the metallic element M_a, the metallic element M_b, and a eutectic aggregation including a first phase comprising the silicon, a second phase comprising the metallic element M_aand the metallic element M_b, wherein the second phase is a disilicide comprising a solid solution of the metallic element M_aand the metallic element M_b, and having a formula of M_a _xM_b _1-xSi₂, where 0<x<1, and wherein the body comprises greater than 0.1 wt. % of the aluminum.