How can you melt down nickel?

Question

How can nickel be melted... assuming one does not have access to an industrial facility?

Answer 1

u cant cuz it has such a high melting point and didu no the United States Mint, made new rules on December 14, 2006,  which criminalize the melting and export of cents and nickels. Violators can be punished with a fine of up to $10,000 and/or imprisoned for a maximum of five years.

Answer 2

The melting point of pure nickel is 2651° F(1455° C). This temperature is much higher than the melting points of most base metals. Yet, according to the definition of brazing, base metals must be joined at a brazing temperature below their melting points. Therefore, to braze with nickel filler metals, elements such as boron must be alloyed with the nickel to lower its melting point below that of most base metals. As shown in Figure 1(1), when alloyed with nickel, a mere 3.6 wt% boron will lower the melting point by 652° F to 1999° F (1093° C). The lower melting point allows us to use nickel-boron filler metals to braze a wide variety of metals at temperatures far below their melting points.

Although boron serves an important function in lowering the melting point of brazing filler metals, when alloyed alone with nickel, boron has some disadvantages. At 2.5-3.5 wt% boron (amounts commonly used in brazing filler metals), the binary nickel-boron alloy will be deficient in the following ways.

Low tensile strength, higher hardness

Lower corrosion resistance

Excessive fluidity when molten

Thus, there are no commercially available binary nickel-boron brazing filler metals. All nickel-based filler metals containing boron must have additional elements to enhance their physical properties.

Silicon (Si)

Another element that lowers the melting point of nickel is silicon. Approximately 11.8 wt% silicon alloyed with pure nickel will lower the melting point by 594° F (330° C). But, when alloyed alone with nickel, silicon like boron will not make a satisfactory brazing filler metal. A binary nickel-silicon alloy will exhibit low tensile strength, poor ductility and excessive fluidity.

Ni-B-Si

Although boron and silicon are both strong melting point depressants, neither one when alloyed alone with nickel will produce a satisfactory brazing filler metal. However, when alloyed together in nickel with 1.5-3.5% boron and 2.75-4.0% silicon, suitable brazing filler metals can be formed. Examples are Nicrobraz 130 (BNi-3) with a melting point as low as1900° F (1040° C) and Nicrobraz 135 (BNi-4) at 1935° F (1055°C). The silicon addition will also enhance corrosion resistance in both instances.

Phosphorus (P)

Similar to boron and silicon, phosphorus also reduces the melting point of nickel, in fact quite dramatically as shown in Figure 2(2). When alloyed with 11 wt% phosphorus, the melting point of nickel is reduced by 1035° F to 1616° F (880° C).

Unlike boron and silicon, phosphorus does produce a satisfactory brazing filler metal when alloyed alone with nickel. Phosphorus at11 wt% in nickel is Nicrobraz 10 (BNi-6). However, even though this filler metal has some satisfactory brazing characteristics and an extremely low melting point, the trade off is low strength and ductility, and greater fluidity when molten.

Chromium (Cr)

To diminish the shortcomings associated with the binary systems we have examined thus far (nickel-boron, nickel-silicon and nickel-phosphorus), chromium can be alloyed with any of these elements to add strength and corrosion resistance to the brazing filler metal. One example is Nicrobraz 150 (BNi-9) with 3.5 wt% boron, 15 wt% chromium and the balance nickel.

To maximize the benefits of the chromium addition, the time at brazing temperature can be extended (typically 40-60 minutes) to allow the boron to diffuse out of the braze joint and into the base metals being joined (diffusion brazing). The boron loss will result in a strong, corrosion resistant braze joint with a melting point higher than the original filler metal (above2500° F or 1370° C).

Another example with chromium is Nicrobraz 30 (BNi-5), which is nickel-silicon alloyed with 19 wt% chromium. This strong (64 ksi braze joints are not uncommon) corrosion-resistant brazing filler metal is used to braze a wide range of high temperature applications.

To improve a binary nickel-phosphorus filler metal, 14 wt% chromium is added to form Nicrobraz 50 (BNi-7). This addition provides three major advantages.

Increased molten viscosity

More strength and ductility

Corrosion resistance

These advantages are best realized when the brazing temperature is held at 1950° F (1065° C) for 60 minutes. This will allow the phosphorus (after doing its job to lower the melting point of the filler metal) to diffuse into the base materials and a small quantity of the phosphorus will oxidize and replenish the more ductile nickel.

Ni-B-Cr-Si

Until this point, we had only examined alloying two elements with nickel. What happens if we combine nickel, boron, silicon and chromium? Keep in mind that both boron and silicon substantially lower the melting point of pure nickel.

By alloying all three elements with nickel, we form NicrobrazLM (BNi-2) with a melting point at 1830° F (1000° C). This is particularly noteworthy because we started with pure nickel that melts at2651° F (1455° C). By alloying it with approximately 3.1 wt% boron, 7wt% chromium, 4.5 wt% silicon and also 3 wt% iron, a filler metal is forme dwith a much lower melting point.

Furthermore, if the time at brazing temperature is extended, most of the boron will diffuse out of the braze joint and into the base metals. This will result in a finished braze joint of Ni-Cr-Si-Fe with high strength, enhanced corrosion resistance and, due to the boron diffusion, a higher melting point (above 2300° F or 1260° C) than the original brazing filler metal.

Carbon (C)

Carbon is an undesirable element in most brazing filler metals. Carbon reacts with chromium to form chromium carbides, which are brittle, angular, hollow crystals that raise braze joint stress. Observations of braze joints by X-ray mapping (SEM) have shown that chromium carbides are common in joints that are not fully diffused or have wide gaps. These carbides can also tie up valuable chromium, thus lowering the corrosion resistance of the braze joint. Therefore, most nickel-based brazing filler metals have less than 0.1% carbon content.

However, there is another school of thought which attributes less influence to carbon. The claim is that although carbon may slightly decrease the melting point, increase fluidity and decrease the strength of the filler metal, in general, carbon in small amounts has minimal effect (positive or negative) on nickel-based brazing filler metals.

Iron (Fe), Copper (Cu), Tungsten (W) and Molybdenum (Mo)

Here we will briefly discuss a few additional elements which are less common than the ones examined thus far, yet worth mentioning. Iron is generally a neutral element which is inadvertently added to brazing filler metals with the addition of boron and/or silicon (ferro-silicon and low quality nickel-boron). However, iron does impart some ductility in brazing filler metals. Copper, when alloyed with nickel and chromium, enhances the corrosion resistance to saltwater environments and other aqueous media. Tungsten elevates the melting point of brazing filler metals and reduces viscosity during brazing. In diffusion brazing processes, the presence of tungsten increases the high temperature strength of the braze joint. Molybdenum increases the viscosity of brazing filler metals, adds high temperature strength and enhances corrosion resistance to aqueous media, especially when alloyed with chromium and copper.

During this examination of the elements alloyed with nickel to make many popular nickel-based brazing filler metals, we discovered that melting points, strength, ductility, viscosity and corrosion resistance are important considerations. We showed how boron, silicon and phosphorus substantially reduce the melting point of pure nickel. Chromium, when alloyed with nickel-boron, nickel-silicon, nickel-phosphorus or combinations of these elements, will improve the strength, ductility and corrosion resistance of brazing filler metals. Generally, carbon and iron are controlled neutral elements in nickel based brazing filler metals, tungsten increases the melting point and reduces viscosity, while copper and molybdenum are beneficial additions which will increase the corrosion resistance of brazing filler metals.