Issue 013, July 9, 2021
Patrick K. Bowen, Ph.D., R&D Manager
Precious metals and their alloys have permeated a wide array of engineering applications and market spaces. To ensure delivery of products that conform to a specific set of chemical and/or physical requirements, the most common materials are governed by agreed-upon industrial specifications. The most commonly referenced standard specifications are set by producers and users in accordance with rules set forth by ASTM International, and curated by the same organization.
Standards for nonferrous materials are curated by committees B01 through B10, and can be recognized by the prefix “B.” Selected standards that pertain to pure noble metal elements in their refined and fabricated forms are enumerated in Table 1. Particular attention should be paid to the difference between “refined” and “fabricated” materials: the former is intended to govern pure elements procured as shot or sponge; the latter governs metals wrought into a usable form, such as wire or sheet.
Table 1: Standards curated by ASTM International that pertain to selected pure noble metals.
| Metal | ASTM Designation | Applications | |
|---|---|---|---|
| Silver (Ag) | B413 | Standard Specification for Refined Silver | Fine silver is commonly used as an alloy constituent or investment vehicle. This specification contains only chemical requirements. (A companion standard for fine silver electrical contacts, B742, was withdrawn in 2019.) |
| Platinum (Pt) | B561 | Standard Specification for Refined?Platinum | Pure platinum is used in drawn wires for life sciences research applications, thin foils for fabricated electrodes, as well as controlling the quality of refined metal used in alloying. Only chemical requirements are included in this standard. |
| Gold (Au) | B562 | Standard Specification for Refined Gold | ASTM B562 frequently appears in medical device specifications, despite its original intent to control quality of refined gold. High purity gold materials are used in applications such as X-ray radiopaque fiducial markers, catheter tips, and wires consumed in the fabrication of other medical devices. |
| Palladium (Pd) | B589 | Standard Specification for Refined Palladium | This standard assures the purity of refined palladium. B589 only contains chemical requirements. |
| Palladium (Pd) | B683 | Standard Specification for Pure Palladium Electrical Contact Material | Palladium for electrical contact applications are fabricated from rod/wire and strip/sheet. Fabricated Pd materials have generous impurity tolerances compared to the refined metal (ASTM B589). This standard contains mechanical specifications for various tempers. |
Chemical requirements for each element differ between the ASTM standards in Table 1 according to producer capabilities and quality expectations of users. Elemental purities for each element, their respective standard(s), and Unified Numbering System (UNS) identifier(s) are shown in Table 2.
Table 2: Standard purity ASTM International specifications for pure precious metals and corresponding UNS numbers (†indicates no UNS number assigned at the time of writing)
| Silver (Ag) | Platinum (Pt) | Gold (Au) | Palladium (Pd) | |
|---|---|---|---|---|
| 99.50% | -- | -- | B562 | -- |
| 99.80% | -- | -- | -- | B683 |
| 99.90% | B413/P07020 | -- | -- | -- |
| 99.95% | B413/P07015 | B561/P04995 | B562 | B589/P03995 |
| 99.99% | B413/P07010 | B561 | B562 | -- |
| 100.00% | -- | -- | B562 | -- |
The aforementioned noble metal elements may be combined with other noble and base metals to create alloys of varied and well-recognized utility. Selected alloys for which ASTM specifications exist are listed in Table 3. (At the time of writing, no UNS designations have been applied to these alloys.) Because these alloys are used in engineering applications, most standards specify multiple tempers with varied mechanical properties.
Table 3: ASTM standards that pertain to selected noble metal-containing alloys produced by Deringer-Ney.
| Alloy | ASTM/UNS Designations | Applications | |
|---|---|---|---|
| Number | Title | ||
| Neyoro 28A | B477 | Standard Specification for Gold-Silver-Nickel Electrical Contact Alloy | Relatively soft alloy, highly resistant to corrosion, with low resistivity. Used in low-noise sliding electrical contacts and selected make-and-break applications. |
| Neyoro 69 | B522 | Standard Specification for Gold-Silver-Platinum Electrical Contact Alloy | Known also as Western Electric #1, this platinum-containing alloy boasts higher wear resistance and tarnish resistance than Neyoro 28A. It may be used in low energy make-and-break applications. |
| Paliney® 7 | B540 | Standard Specification for Palladium Electrical Contact Alloy | A versatile, age-hardenable palladium alloy that contains 55% noble metal by weight. A number of tempers, from annealed to fully age hardened, are specified. Commonly found in high speed signal slip rings, buckling beam integrated circuit test probes, and as contacts in corrosive environments. |
| Neyoro G | B541 | Standard Specification for Gold Electrical Contact Alloy | 80% noble metal content by weight affords this alloy extreme tarnish and corrosion resistance. A high degree of work hardenability and age hardenability make this an engineer's gold. Found in electrical contact applications where absolute reliability is needed. |
| Paliney® 6 | B563 | Standard Specification for Palladium-Silver-Copper Electrical Contact Alloy | A 45% noble alloy that is used in a wide variety of sliding electrical contacts. Some applications include throttle position sensors, slip ring brushes, and fuel level sensors. |
| Coin Gold | B596 | Standard Specification for Gold-Copper Alloy Electrical Contact Material | This soft, gold-10wt.% copper alloy is used in specialty, low-noise sliding electrical contact systems. |
| Coin Silver | B617 | Standard Specification for Coin Silver Electrical Contact Alloy | An alloy of silver and 10wt.% copper, this material offers improved hardness and arc erosion resistance when compared to fine silver. |
| Platinum-Iridium | B684 | Standard Specification for Platinum-Iridium Electrical Contact Materials | Pt-10wt.% Ir and -15wt.% Ir have gained popularity in the medical device field as tissue contacting electrodes, X-ray radiopaque interventional device components, and more. These alloys are employed in low energy make-and-break contact applications, and as electrodes in corrosion-resistant fluid flow sensors. |
| Ney 75 | B780 | Standard Specification for 75% Silver, 24.5% Copper, 0.5% Nickel Electrical Contact Alloy | A time-tested, reliable silver alloy used in wire-formed or multifilar slip ring brushes. This alloy is also used to fabricate corrosion-resistant inductors and as a braze alloy in selected applications. |
The noble metal alloys specified above may be fabricated in a wide array of physical forms including rod, wire, fine wire, strip, and foil, and are generally used at smaller dimensions than other nonferrous materials. These compositions and properties suit a wide range of applications. Bespoke material tempers may be available from, or developed by, Deringer-Ney on a custom basis for challenging applications, even while adhering to ASTM-standard compositional ranges.
Important notes: Paliney is a registered trademark and Neyoro is a trademark of Deringer-Ney Inc. “ASTM” and “ASTM International” are registered trademarks of ASTM International. Standards must be purchased directly from and used exclusively in accordance with the terms and conditions set forth by ASTM International.