From the circuitry in your smartphone to the catalytic converter in your car, a family of lustrous, silvery metals plays a vital but often unseen role. These are the white metals.
White metals are an important category of metals used in various industrial applications, just as alloys are. An old use of white metals is their referencing in the antique trade for describing items suspected of containing silver but not hallmarked. As an example, the term “white metal” is used in the British fine art trade auction catalogs to refer to foreign silver items not carrying British Assay Office marks, but are however known to be silver and priced accordingly. This post will briefly introduce what white metals are, their general properties, and their applications in daily life.
What are White Metals?
The term “white metals” refers to a range of metallic elements and alloys characterized primarily by their silvery-white appearance and lustrous finish. This category is not strictly scientific but is crucial in industry and commerce, encompassing both precious and non-precious metals.
We can broadly classify white metals into two main groups:
- Precious White Metals: This group includes Silver (Ag), Palladium (Pd), and Platinum (Pt). They are valued for their exceptional corrosion resistance, high luster, and specific functional properties like excellent electrical conductivity (Silver) and powerful catalytic capabilities (Platinum, Palladium).
- Non-Precious White Metals & Alloys: This group includes various alloys where tin, lead, antimony, bismuth, and zinc are the primary components. Examples include pewter (traditionally tin-based), solders (tin-lead or lead-free alternatives), and Babbitt metals (tin- or lead-based bearing alloys). It’s important to note that modern regulations are phasing out toxic elements like lead in many consumer applications.
Historically, the term was used in contexts like the antique trade to describe items suspected of containing silver but lacking official hallmarks. While this historical usage is interesting, the modern industrial applications of white metals are far more extensive and technologically significant.
Why Are White Metals Important Today?
White metals are the unsung heroes of modern technology. Their importance stems from a combination of properties that are essential across cutting-edge industries:
- Electronics & Conductivity: Silver, for instance, boasts the highest electrical and thermal conductivity of all metals, making it indispensable in circuit boards, switches, and even advanced computing.
- Catalysis & Green Technology: Platinum and Palladium are critical components in catalytic converters, reducing harmful emissions from vehicles. They are also vital in the production of green hydrogen and other clean energy solutions.
- Jewelry & Durability: Their lustrous appearance and resistance to tarnish make metals like white gold (a gold-palladium alloy) and platinum staples in fine jewelry.
- Specialized Industrial Alloys: Tin-based white metals (like Babbitt metal) are used in bearings for their low friction, while fusible alloys are used in safety devices like fire sprinklers.
General Properties of White Metals
In general, the white metal group is known for its high densities, low melting points (hardly over 4,000 e°C), and the minimal solid solubility of the constituent alloys. Based on experimentations in the past, specific properties of this special group of metal alloys have been discovered, which also explains their importance in many applications today.
While properties vary by specific metal or alloy, white metals as a group often share several key characteristics that make them indispensable:
- Silvery-White Luster: They share a characteristic bright, reflective appearance that is highly valued for decorative and optical applications.
- Good Corrosion Resistance: Many, especially the precious white metals, resist tarnishing and oxidation exceptionally well.
- Functional Versatility: The group exhibits a wide range of melting points, hardness, and conductivity, allowing for tailored solutions from low-melting-point solders to high-temperature catalysts.
- Castability and Workability: Numerous white metal alloys are known for their excellent fluidity when molten and ease of casting, machining, and polishing.
Here are more properties of white metals based on different combinations of the constituent metals in the allotted:
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Lead-Tin Alloys
The extreme softness of pure lead prohibits its use in the pure state, but it can be hardened by adding comparatively small quantities of other metals such as tin. The “hardener” generally helps to stiffen the whole alloy structure. Pure tin is distinguished by its white color, and it is when exposed to the air. But this characteristic, according to studies, is not inhibited by additions of 10-15% of lead, and the resulting alloys are much harder and cheaper.
The addition of lead to tin also helps to increase its fluidity and castability in a molten state and its malleability and ductility in solid form. Many of the alloys of lead and tin (especially those with 40% tin) have an especially lustrous appearance. This is often explored commercially in jewelry manufacture and for making mirrors in reflectors.
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Lead-Antimony Alloys
This alloy is often used on account of its plasticity, increased hardness and resistance to chemical corrosion as compared to lead, and the ease with which it can be cast or rolled into shape. It was found that alloys that contain more than 10% antimony could not be satisfactorily led.
Arsenic, incidentally, has the same general effect on the properties of lead. Lead-antimony alloys must be rapidly cooled, lest the primary antimony crystals become forced upwards in the heavier, lead-rich melt and form an antimony-rich upper layer (called bright crust).
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Lead-Bismuth
Lead and bismuth, when mixed, yield alloys that are malleable and ductile as long as the proportion of bismuth does not exceed that of lead. Malleability and ductility decrease as the bismuth content increases. Although the bismuth-lead alloys show significant contraction (maximum at 50-50), the metal bismuth causes the opposite effect — expansion, when mixed into lead-tin alloys (a quality which is made use of commercially as casting alloys).
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Bismuth-Tin
The binary alloys of tin and bismuth are generally relatively weak and brittle, which is why they’re seldom, if ever, used industrially. Since the alloys are low melters and can be made up easily, they are often used in the lab for constant-temperature baths. Actually, the eutectic between tin and bismuth occurs at the same bismuth-content as that for lead-bismuth (58%). The tin-bismuth eutectic melts at 1350 C.
There are other alloy variations, such as cadmium and tin and cadmium and bismuth. And each has its own unique set of properties.
Applications of White Metals
The production of white metals can either follow a simple laboratory procedure or a more complex industrial process. Generally, white metals are applied in the production of the following materials:
| Application Area | Key Materials | Notes |
|---|---|---|
| Jewelry & Watches | White Gold (Au-Pd/Ni), Platinum, Sterling Silver | Provides a lustrous, tarnish-resistant, and durable alternative to yellow gold. |
| Electronics & Electrical | Silver (contacts, pastes), Tin-alloy Solders | Silver offers unmatched conductivity; lead-free solders provide reliable, eco-friendly connections. |
| Automotive Catalysis | Platinum, Palladium, Rhodium | Critical for catalytic converters, transforming harmful exhaust gases into less toxic substances. |
| Bearings & Machinery | Babbitt Metal (Sn-Sb-Cu based) | A low-friction, embeddable surface that protects heavier machinery shafts from wear. |
| Decorative Items & Pewter | Modern Pewter (Sn, Sb, Cu – Lead-Free) | Offers a malleable, attractive, and safe material for tableware, trophies, and ornaments. |
Wrapping Up
White metals have evolved far beyond their historical role in the antique trade. Today, they are critical enablers of modern technology, from the electronics we use daily to the catalytic converters that clean our air and the jewelry we cherish. As research continues, particularly in recycling and sustainable sourcing, the role of these versatile materials is set to become even more important.
Thank you for reading our article and we hope that it can help you better understand white metals. If you want to know more about metal materials, we would like to advise you to visit Stanford Advanced Materials (SAM) for more information.
