Information

Non toxic low melting point alloy


I am looking for an alloy with low melting temperature (< 350°C) which is not toxic when in direct constant contact with skin, food and overall in domestic environment. My application is a solder that can be used for soldering a ring.


I'm not a metallurgist, which you should probably ask… but there is this that I found:

Low Melting Fusible Alloys

Both Cadmium and Lead are toxic, but Bismuth, Indium, and Tin are not. An alloy of those might be what you're looking for. Indium raises the price-point considerably, as it's a few magnitudes more expensive than Bismuth and Tin.


Solder alloys

Solder is a metallic material that is used to connect metal workpieces. The choice of specific solder alloys depends on their melting point, chemical reactivity, mechanical properties, toxicity, and other properties. Hence a wide range of solder alloys exist, and only major ones are listed below. Since early 2000s the use of lead in solder alloys is discouraged by several governmental guidelines in the European Union, Japan and other countries, [1] such as Restriction of Hazardous Substances Directive and Waste Electrical and Electronic Equipment Directive.


Contents

Wood's metal is useful as a low-melting solder, low-temperature casting metal, high-temperature coupling fluid in heat baths, and as a fire-melted valve element in fire sprinkler systems in buildings. Medical gas cylinders in the United Kingdom have a Wood's metal seal, which melts in fire, allowing the gas to escape and reducing the risk of gas explosion.

Wood's metal is commonly used as a filler when bending thin-walled metal tubes. For this use the tubing is filled with molten Wood's metal. After this filler solidifies, the tubing is bent. The filler prevents the tube collapsing. The Wood's metal is then removed by heating, often by immersion in boiling water.

Other uses include making custom-shaped apertures and blocks (for example, electron-beam cutouts and lung blocks) for medical radiation treatment, making casts of keys that are hard to duplicate otherwise [4] [5] and making metal inlays in wood.

Wood's metal is useful in machine shops and technical laboratories when alternative means of holding delicate parts become necessary. It is used as an additional hardened layer to allow the proper gripping and machining of an object. The object is immersed in melted Wood's metal to completely or partially coat it, forming a layer from a few millimeters up to few centimeters thick, depending on how the object will be held in place. After cooling, the new assembly is clamped by conventional means. This method is most useful for one-off or limited-production workpieces, when construction of a special clamping or holding jig would neither be cost-effective nor offer maximum holding capability.

Wood's metal is also useful for repairing antiques. For example, a bent piece of sheet metal may be repaired by casting a Wood's metal die from an intact example: The low melting temperature of Wood's metal makes it unlikely to harm the original, and the damaged piece can then be clamped in the die and slowly tightened to form it back into shape.

Wood's metal has long been used by model railroad enthusiasts to add weight to locomotives, increasing traction and the number of cars that can be pulled.

Wood's metal is also used in the making of extracellular electrodes for the electro-physiological recording of neural activity. [6]

Like other fusible alloys, e.g. Rose's metal, Wood's metal can be used as a heat-transfer medium in hot baths. Hot baths with Rose's and Wood's metals are not in routine use but are employed for temperatures above 220 °C (428 °F). [7]

Wood's metal has a modulus of elasticity of 12.7 GPa and a yield strength of 26.2 MPa. [8]

Wood's metal is toxic because it contains lead and cadmium, and contamination of bare skin is considered harmful. Vapour from cadmium-containing alloys is also known to pose a danger to humans. Cadmium poisoning carries the risk of cancer, anosmia (loss of sense of smell), and damage to the liver, kidneys, nerves, bones, and respiratory system. Field's metal is a non-toxic alternative.


Bismuth Alloys

Bismuth is a white, crystalline, brittle metal with a pinkish tinge. It s the most naturally diamagnetic element and has one of the lowest values of thermal conductivity among metals. Bismuth is 86% as dense as Lead and has long been considered as the element with the highest atomic mass that is stable. It is available as commercial-grade or high purity,

Applications:

It can be used as a carbide stabilizer in the manufacturing of malleable Iron, as an additive to low-carbon steel or aluminum to improve machinability, and as a dense material for fishing sinkers. Bismuth as an alloying element can be used in the production of fusible alloys ( low melting point alloys ) and Bismuth based low temperature solders. Standard and special compositions are Bismuth alloyed with either Antimony, Cadmium, Copper, Indium, Lead or Tin.

Bismuth is offered in a variety of forms such as Ingot, Lumps, Shot, Granular, Powder, Pellets or Needles. Bismuth Alloys are available in various sizes as well including Bar, Cakes, Cast Shapes, Ingot, Granular, Shot and Sticks. Special shapes are also available.


How to Melt Aluminum

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Aluminum is one of the most heavily used metals in modern manufacturing. Its durability and plasticity make it an ideal material for multiple functions. Because of this, aluminum is a great metal for DIY forging. With the right information and materials, forging aluminum can be a fun hobby or a source of extra income.


Bismuth

Bismuth (Bi) is a silvery-white metallic element with a pinkish tint on freshly-broken surfaces. The most common bismuth minerals are bismuthinite and bismite, but most bismuth is recovered as a by-product from lead processing.

Mineral Classification

Sulfide (bismuthinite), Oxide (bismite)

Chemical Formula

Bi2S3 (bismuthinite), Bi2O3 (bismite)

Streak

Lead gray (bismuthinite), gray to yellow (bismite)

Mohs Hardness

2 (bismuthinite), 4.5 (bismite)

Crystal System

Orthorhombic (bismuthinite), monoclinic (bismite)

Color

Lead-gray to tin-white, with a yellowish or iridescent (bismuthinite) greyish green, greenish yellow to bright yellow (bismite)

Luster

Metallic (bismuthinite), dull, earthy (bismite)

Fracture

Description

Bismuth (Bi) is a silvery-white metallic element with a pinkish tint on freshly-broken surfaces. The most common bismuth minerals are bismuthinite and bismite, but most bismuth is recovered as a by-product from lead processing.

Relation to Mining

Most bismuth is produced from mines in China, Mexico and Bolivia. Only one mine in Bolivia is a primary bismuth mine in other countries bismuth is a by-product of mining other metals. Bismuth is a moderately priced metal, costing more than copper, lead, and zinc, but much less than gold or silver. In addition, an important part of world bismuth production is from the small amounts of bismuth in ores of other metals, which is recovered in Belgium and Japan from foreign ores which are shipped to those countries for smelting. The United States produces small amounts of bismuth through recycling. Recycled bismuth makes up less than 5% of U.S. consumption.

Bismuth is used in a number of very different applications. Almost none of the uses is for pure metallic bismuth. The majority is consumed in bismuth alloys, and in pharmaceuticals and chemicals. The remainder is used in ceramics, paints, catalysts, and a variety of minor applications.

Alloys of bismuth are useful for many reasons:

Bismuth and many of its alloys expand slightly when they solidify (freeze). This allows the bismuth to fill all corners of a mold to form a perfectly sharp replica of the mold or the item being replicated. This is also a valued property when used in soldering or plumbing (joining of pipes).

Many bismuth alloys have a low melting point, sometimes even below the temperature of boiling water. Thus a bismuth-alloy casting can be covered by plastic or other material to form an intricate machine part. The bismuth-alloy core is then removed by simply melting it in hot water and pouring it out. The use of low-melting bismuth alloys is widespread in sprinkler systems in buildings. When the alloy melts in fire-heated air, the sprinkler becomes unplugged, and water sprays the fire. This application accounts for over one-third of the bismuth used in the United States each year.

Bismuth metal is relatively inert and non-toxic. It has replaced toxic lead in many applications such as plumbing, bullets, birdshot, metal alloys, soldering, and other applications.

Fourthly, many bismuth alloys are relatively soft and malleable. Malleable means that a metal can be hammered into thin sheets. Bismuth is alloyed with iron to create what is known as “malleable irons.”

Bismuth compounds are used in stomach-upset medicines (hence the trademarked name Pepto-Bismol), treatment of stomach ulcers, soothing creams, and cosmetics.

Industry uses bismuth in a variety of other applications. Bismuth is a catalyst in the production of acrylic fibers. Bismuth replaces lead in some ceramic glazes and paints, because bismuth is non-toxic.


Non toxic low melting point alloy - Biology

Suppose you had a metal alloy that had the advantages of liquid mercury, but without the toxic effects?

You could make your own barometers and thermometers, and not worry about calling in a hazardous materials team to clean up after any accidents. You could simply wipe up the mess with a paper towel. You wouldn't have to worry about breathing in toxic mercury fumes, but you could still make neat little electric motors that dip into liquid metal to make their electrical connections.

Suppose further, that the metal would stick to glass, so you could paint it on glass to make your own mirrors. Or that it would stick to paper so you could draw your own electric circuits in it?


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In the photo above, I am holding two small vials of liquid metal. The vial on the right contains gallium, an element that melts at 29.76° Celsius (85.57° Fahrenheit). The vial on the left is an alloy that contains gallium, indium, and tin, and melts at -20° Celsius (-4° Fahrenheit). (Both are available in our catalog.)

The gallium is liquid because I had the bottle in my shirt pocket, next to my warm body. At normal comfortable room temperatures it is a solid.

Because gallium expands when it solidifies (unlike most metals), the vials are only filled half way. To get the solid metal out of the vial, simply warm it up in a cup of hot water until it melts.

Fun things to do with liquid metal

One fun thing you can do right away with the liquid metal alloy is make your own mirrors. All it takes is a piece of glass and a cotton swab.


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Dip the cotton swab in the vial, and twirl it around to coat it with the liquid metal alloy.


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Now rub the coated swab on the glass (in the phot we are using a glass microscope slide). The metal sticks to the glass, and makes an opaque reflective coating.


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In the photo above, I am holding the new mirror so that it reflects the view of the trees outside my window. The camera is focused on the window, so the trees and my hand are out of focus.

Being able to make your own mirrors is an advantage when the mirror you need can't be bought anywhere. For example, I needed a small lightweight mirror to glue to a speaker, so I could bounce a laser beam off of the speaker and have the music wiggle the mirror, making a pattern on the wall.


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I used the liquid metal to coat a thin glass cover slip for a microscope slide.


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The resulting mirror was very lightweight, and yet stiff, so it would remain flat while being bounced around by the speaker.


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When it is glued onto the speaker and the music turned on, the laser makes a light show on the wall. Using two speakers, and bouncing the light off of one and then off of the other, gives you two dimensions, and you can make a computer sound file that uses both stereo channels to draw pictures on the wall.

More fun things

  • Make thermometers
  • Make barometers
  • Make tilt meter seismographs
  • Make non-conductive objects conductive
  • Make electrodes that conform to varying surfaces
  • Experiment with magnetohydrodynamics
  • Wiggle it with high frequency electricity
  • Use it to conduct high energy sound
  • Replace mercury in spinning telescope mirrors

If you need a shiny surface, a dilute solution of hydrochloric acid can be placed on the surface, or you can use a light coating of mineral oil. Both will prevent the slow oxidation of the metal that occurs over time.

How does it do that?

Gallium is an element (atomic number 31, right below aluminum and just to the right of zinc in the periodic table of the elements). It starts out with a very low melting point already, but we can add some other elements to get an even lower melting point.

Right below gallium in the periodic table is indium (element 49). Just to the right of indium is tin (element 50).

When these elements are combined, their atoms bind together into a compound. The molecules of that compound do not bind to one another as much as the atoms of the original metals bound to each other. This lowers the melting point.

There are many ways to combine the three metals:

Compound Percentages Grams Ga Grams In Grams Sn
Ga14In3Sn2 62.65% Ga, 22.11% In, 15.24% Sn 97.6122 34.4454 23.742
Ga17In4Sn2 62.98% Ga, 24.40% In, 12.62% Sn 118.529 45.9272 23.742
Ga22In5Sn3 62.25% Ga, 23.30% In, 14.45% Sn 153.391 57.409 35.613
Ga25In5Sn4 62.43% Ga, 20.56% In, 17.01% Sn 174.308 57.409 47.484
Ga25In6Sn3 62.52% Ga, 24.71% In, 12.77% Sn 174.308 68.8908 35.613

Each combination will have a slightly different melting point. Which do you think has the lowest melting point? This might make a good science fair experiment.

A mixture of 76% gallium and 24% indium melts at 16° Celsius (61° Fahrenheit). Both gallium and this combination can be supercooled. That means that once melted, they can stay liquid even though they are cooled well below their melting points. Eventually a small crystal forms, and starts the whole batch solidifying, but small amounts can be kept supercooled for quite a while.

The gallium-indium alloy is more reflective than mercury, and is less dense, so it is being explored as a replacement for mercury in spinning liquid mirrors for astronomical telescopes.

When gallium is exposed to air, a thin layer of gallium oxide forms on the surface, just like what happens with aluminum, the metal just above it in the periodic table. This allows gallium alloys to "wet" almost any material, so instead of beading up, it spreads out over the surface. This property makes it good for making mirrors, and for coating objects to make them conductive.

In the same way that mercury alloys with other metals to make amalgams, gallium also alloys with other metals. When a small drop of gallium is placed on aluminum foil, for example, it will combine with the aluminum to make a liquid with a crusty surface, as in the photo below.


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The alloy eventually combines with all of the aluminum, dissolving a hole in it.


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If a drop of water is added to the resulting bead of liquid metal, the water combines vigorously with the aluminum, making a hot solution of caustic aluminum hydroxide. What is left is the original drop of gallium, with a tiny amount of aluminum dissolved in it. (Don't put that drop back in the bottle, it will contaminate the rest of the gallium).

This experiment can be done with either the gallium, or the gallium-indium-tin alloy.


Noble Gases

One group of elements, the noble gases (helium, neon, argon, krypton, xenon, and radon), forms almost no chemical compounds. Although small concentrations of the noble gases are present in the earth&rsquos atmosphere, they were not discovered until 1894, largely because they underwent no reactions. Fluorine is sufficiently reactive to combine with pure samples of xenon, radon, and (under special conditions) krypton. The only other element that has been shown conclusively to occur in compounds with the noble gases is oxygen, and no more than a couple of dozen noble-gas compounds of all types are known. This group of elements is far less reactive chemically than any other.