spore: profile
id: palladium-silver
spore_version: 0.2
family: precious-metals
name: Palladium-silver alloys
abbreviation: Pd-Ag
role: hydrogen membrane, electrical contact and thick-film conductor alloy
category: metals
type: precious-metals
summary: |
  Palladium-silver alloys are solid solutions of silver in face-centred cubic palladium. Two families matter here. A 75 percent palladium, 25 percent silver grade passes hydrogen through thin walls, and a 1969 NASA-sponsored separator used it to cut dissolved hydrogen in fuel-cell water from 60 psia to under 0.5 psia. Palladium-rich grades serve as electrical contacts and fired thick-film conductors. Witjens et al. (2004) report that 23 at% silver is the best composition for hydrogen permeability and membrane lifetime, because it lowers the critical temperature at which two hydride phases coexist. A 2007 study found a 2.5 um Pd-25Ag membrane resisted hydrogen-induced brittleness where a pure palladium membrane fractured.
best_for: Hydrogen passage through thin walls, where silver keeps the metal from cracking (23 at% silver is the best composition per Witjens et al. 2004)
weakest_at: Hydrogen cracking when silver is too low, and silver migration in humid, biased thick-film lines (the Heraeus datasheet says palladium reduces the risk)
identity:
  formula: Pd-Ag solid solution; membrane grade 75% Pd and 25% Ag, contact grade PdAg70 listed as 30% Pd and 70% Ag
  crystal_system: face-centred cubic
  source: witjens2004
  where: Abstract (fcc Pd/Ag model with Ag atoms evenly distributed) and section 2 (fcc lattice)
tags:
  environments: []
  stresses: []
  applications:
    - habitats-and-suits
    - cryogenic-fuel
    - electronics-and-chips
properties:
  - benchmark: alpha_beta_critical_temperature
    label: Temperature below which hydride alpha and beta phases coexist, Pd-23 mol% Ag
    value: 20
    unit: degC
    scope: material
    conditions:
      composition: Pd-23 mol% Ag
      hydrogen_pressure: not stated
      wording_in_source: approximately 20 degC
    method: Statement in section 3.3 of the 2020 review, which quotes Suzuki et al. (2016) for Pd-23 mol% Ag
    status: ground
    note: The review says Ag suppresses the alpha-alpha' transition in this alloy. Witjens et al. (2004) say the same alloying lowers the critical temperature but give no number.
    source: pmc-review-2020
    where: Section 3.3 (Understanding of reverse temperature dependence), paragraph on the alpha-alpha' transition
  - benchmark: optimal_silver_content
    label: Silver content giving the best hydrogen membrane (permeability and lifetime)
    value: 23
    unit: at% Ag
    scope: material
    conditions:
      basis: atomic percent of silver in Pd-Ag hydrogen membranes
    method: Statement in the introduction of the 2004 PCCP paper, which says the optimum is well documented and cites earlier work
    status: ground
    source: witjens2004
    where: Introduction, paragraph 2 (optimal Pd/Ag membrane composition)
  - benchmark: alloy_silver_fraction
    label: Silver fraction recommended for a palladium purification alloy
    value: 25
    unit: percent (basis not stated)
    scope: material
    conditions:
      use: hydrogen purification membranes
      note_on_basis: NASA gives the figure in percent without naming a weight or atomic basis
    method: 'Statement in the introduction of NASA/TM-2019-220189: silver can approach 60 percent, and 25 percent gives a respectable balance of properties'
    status: ground
    source: smith2019-nasa-tm
    where: Introduction, paragraph 1
  - benchmark: membrane_thickness
    label: Thickness of a microfabricated Pd-25Ag membrane on silicon
    value: 2.5
    unit: um
    scope: material
    conditions:
      composition: Pd-25Ag, as named in the paper
      support: silicon
      fabrication: microfabrication
      test_range_in_source: 423 to 673 K, in situ hydrogen microscope
    method: Thickness stated in the abstract of the 2007 MRS-J paper
    status: ground
    source: zhang2007-mrsj
    where: Abstract, first paragraph
  - benchmark: density
    label: Density of the PdAg70 contact grade
    value: 10.9
    unit: g/cm3
    scope: material
    conditions:
      composition: PdAg70, listed as 30% palladium and 70% silver
      temperature: 20 degC
      temper: soft annealed (A)
    method: Value in the General Property table of an online listing for the PdAg70 alloy
    status: ground
    note: This is the contact grade, not the 75/25 membrane alloy. The listing does not name its original datasheet, so the value is unverified against the manufacturer.
    source: mfgrobots-pd30ag70
    where: General Property table, Density row
  - benchmark: elastic_modulus
    label: Elastic modulus of the PdAg70 contact grade
    value: 114
    unit: GPa
    scope: material
    conditions:
      composition: PdAg70
      temperature: 20 degC
      temper: soft annealed (A)
    method: Value in the Mechanical Property table of the same online listing
    status: ground
    source: mfgrobots-pd30ag70
    where: Mechanical Property table, Elastic modulus row
  - benchmark: ultimate_tensile_strength
    label: Tensile strength of the PdAg70 contact grade, soft annealed
    value: 310
    unit: MPa
    scope: material
    conditions:
      composition: PdAg70
      temperature: 20 degC
      temper: soft annealed (A)
    method: Value in the Mechanical Property table of the same online listing
    status: ground
    source: mfgrobots-pd30ag70
    where: Mechanical Property table, Tensile strength row
  - benchmark: yield_strength
    label: 0.2% offset yield strength of the PdAg70 contact grade, soft annealed
    value: 150
    unit: MPa
    scope: material
    conditions:
      composition: PdAg70
      temperature: 20 degC
      temper: soft annealed (A)
      offset: 0.2% (Rp0.2)
    method: Value in the Mechanical Property table of the same online listing
    status: ground
    source: mfgrobots-pd30ag70
    where: Mechanical Property table, Yield strength Rp0.2 row
  - benchmark: elongation
    label: Elongation of the PdAg70 contact grade, soft annealed
    value: 36
    unit: '%'
    scope: material
    conditions:
      composition: PdAg70
      temperature: 20 degC
      temper: soft annealed (A)
    method: Value in the Mechanical Property table of the same online listing
    status: ground
    note: Only one listing was opened for these mechanical values. A second online listing seen in search results was not opened, and its elongation was not used.
    source: mfgrobots-pd30ag70
    where: Mechanical Property table, Elongation row
  - benchmark: vickers_hardness
    label: Vickers hardness of the PdAg70 contact grade, soft annealed
    value: 55
    unit: HV
    scope: material
    conditions:
      composition: PdAg70
      temperature: 20 degC
      temper: soft annealed (A)
    method: Value in the Mechanical Property table of the same online listing
    status: ground
    source: mfgrobots-pd30ag70
    where: Mechanical Property table, Hardness Vickers row
  - benchmark: thermal_conductivity
    label: Thermal conductivity of the PdAg70 contact grade
    value: 61
    unit: W/(m.K)
    scope: material
    conditions:
      composition: PdAg70
      temperature: 20 degC
    method: Value in the Thermal Property table of the same online listing
    status: ground
    note: The same listing labels its melting point, Poisson ratio and specific heat as typical for palladium, so those values are not alloy data and are not used here.
    source: mfgrobots-pd30ag70
    where: Thermal Property table, Thermal conductivity row
  - benchmark: electrical_resistivity
    label: Electrical resistivity of the PdAg70 contact grade
    value: 15
    unit: uOhm.cm
    scope: material
    conditions:
      composition: PdAg70
      temperature: 20 degC
      unit_in_source: 1.5 x 10^-7 Ohm.m
    method: Printed as 1.5 x 10^-7 Ohm.m at 20 degC in the Electrical Property table and converted here (1 Ohm.m is 10^8 uOhm.cm)
    status: ground
    source: mfgrobots-pd30ag70
    where: Electrical Property table, Electrical resistivity row
  - benchmark: sheet_resistance
    label: Sheet resistance of a fired 25:75 Ag/Pd thick-film conductor
    value: 180
    unit: milliohms/square
    scope: material
    conditions:
      paste: C4313GSD, pre-alloyed 25:75 Ag/Pd conductor paste
      film_thickness: 12 um fired (FFT)
      firing: 850 degC peak, total cycle 30 to 60 minutes
    method: Printed as an upper limit (less than or equal to 180) in the Typical Properties table
    status: ground
    note: A paste property for a fired film, not a bulk alloy value.
    source: heraeus-c4313
    where: Typical Properties, Conductivity and Resistivity rows; Recommended Processing Guide
  - benchmark: dissolved_h2_pressure_out
    label: Dissolved-hydrogen partial pressure after a Pd-Ag separator
    value: 0.5
    unit: psia (stated as "less than")
    scope: material
    conditions:
      inlet_partial_pressure: 60 psia
      water_temperature: 75 degF
      water_flow: 10 ml per minute
      membrane: 75% palladium-25% silver alloy tubes coated with palladium black, 18 tubes, 1/8 in outer diameter, 10 mil wall
    method: NASA Tech Brief 69-10635, describing a separator built by The Garrett Corporation under contract to the Manned Spacecraft Center
    status: ground
    source: nasa-tech-brief-1969
    where: Main text, right column, paragraph beginning A separator that was fabricated
  - benchmark: operating_test_duration
    label: Operating time of the separator test unit without loss of efficiency
    value: 3700
    unit: h
    scope: material
    conditions:
      water_temperature: 75 degF
      device: 1969 fuel-cell water separator test unit
    method: 'Statement in the 1969 NASA brief: operated for more than 5 months (3700 hours) without loss of efficiency'
    status: ground
    source: nasa-tech-brief-1969
    where: Main text, right column, final sentence of the separator paragraph
corrosion:
  - environment: Hydrogen, repeated loading and unloading
    headline: Silver-rich alloy resists the cracking that breaks pure palladium
    effect: Zhang et al. (2007) report that a silicon-supported Pd-25Ag membrane showed excellent resistance to hydrogen-induced brittleness, while a pure Pd membrane fractured after a hydrogenation-dehydrogenation cycle. The test range was 423 to 673 K.
    rating: low
    conditions:
      temperature: 423 to 673 K
      form: 2.5 um membrane on silicon support
    source: zhang2007-mrsj
    where: Abstract, sentences on hydrogen-induced brittleness
  - environment: Hydrogen below the critical temperature in a palladium-rich alloy
    headline: Silver-poor patches can start the hydride cracking
    effect: Witjens et al. (2004) say that alloying with 23 at% silver lowers the critical temperature, so only one phase forms above ambient temperature and embrittlement is prevented. They also say silver-poor areas can act as crystallisation points for hydrogen embrittlement and microcracking.
    rating: moderate
    conditions:
      silver_content: 23 at% is the stated protective level
      hydrogen_pressure: not stated
    source: witjens2004
    where: Introduction, paragraphs 2 and 3
  - environment: Humid air with a DC bias across silver-rich fired lines
    headline: Palladium addition reduces silver migration in fired films
    effect: Heraeus says the very smooth fired surface of its 25:75 Ag/Pd paste greatly reduces the risk of silver migration. The datasheet gives no humidity, bias or test-method details.
    rating: low
    conditions:
      composition: 25:75 Ag/Pd
      firing: 850 degC peak
    source: heraeus-c4313
    where: Description and Key Features
  - environment: Sulfur-bearing fuel
    headline: Paste is sold for high-sulfur fuel service
    effect: Heraeus describes C4313GSD as having enriched palladium for harsh environments such as high sulfur fuel applications, with leach resistance. No sulfur test result is printed on the datasheet.
    rating: unknown
    conditions:
      composition: 25:75 Ag/Pd paste
      test_result: none printed
    source: heraeus-c4313
    where: Description, and Key Features
  - environment: Oxidation in air at elevated temperature
    headline: The review credits Pd-Ag membranes with strong resistance to oxidation
    effect: The 2020 review says Pd-Ag membranes combine high hydrogen permeability and excellent selectivity with strong resistance to oxidation and hydrogen embrittlement. It gives no oxidation rate.
    rating: low
    conditions:
      basis: qualitative statement in the review
    source: pmc-review-2020
    where: Section 3.3, first paragraph
risks:
  hazards:
    - text: 'PubChem aggregates 616 company reports for palladium: 59.3% say it does not meet GHS hazard criteria, and 31.5% classify it as a flammable solid (H228, signal word Danger). The classification depends on the supplier and the form of the metal.'
      ghs:
        - H228
      source: pubchem-pd
      where: Safety and Hazards > Hazards Identification > GHS Classification
    - text: 'Silver: PubChem aggregates 2154 company reports, with H400 (70.4%) and H410 (69.3%), very toxic to aquatic life with long-lasting effects. Some individual notifications also carry H361f (suspected of damaging fertility) and H373 (damage to organs through prolonged exposure).'
      ghs:
        - H400
        - H410
        - H361f
        - H373
      source: pubchem-ag
      where: Safety and Hazards > Hazards Identification > GHS Classification (aggregated block and individual notifications)
    - text: Palladium dust is combustible when exposed to heat or flame. Finely divided palladium (palladium black) used as a hydrogenation catalyst is usually pyrophoric.
      ghs: []
      source: pubchem-pd
      where: Hazards Summary; Fire Potential
    - text: Possible skin sensitiser. Contact dermatitis has been associated with metallic palladium, especially palladium alloys. Occupational asthma has been reported but is very rare.
      ghs: []
      source: pubchem-pd
      where: Hazards Summary; Skin, Eye, and Respiratory Irritations
  failure_risks:
    - mode: Hydrogen cracking where silver is too low
      trigger: Hydrogen cycling of a palladium-rich membrane below about 23 at% silver, where the alpha-beta transition can form
      consequence: Witjens et al. (2004) say the hydride transition creates local tension that leads to microcracking and mechanical failure. Silver-poor areas are the likely starting points.
      severity: high
      source: witjens2004
      where: Introduction, paragraphs 2 and 3
    - mode: Fracture of a thin pure palladium membrane
      trigger: Hydrogenation and dehydrogenation cycling of an unalloyed palladium membrane at 2.5 um
      consequence: The 2007 study found the pure Pd membrane fractured after one cycle, while the Pd-25Ag membrane resisted. Thin pure membranes should not be assumed to survive cycling.
      severity: high
      source: zhang2007-mrsj
      where: Abstract
    - mode: Silver migration across fine conductor lines
      trigger: Humid conditions with a DC bias across silver-rich thick-film lines
      consequence: Silver can migrate and bridge lines. Wang et al. (1994) list Ag diffusion and migration among the factors that control fired film performance. Heraeus says palladium-rich fired surfaces greatly reduce the risk.
      severity: moderate
      source: heraeus-c4313
      where: Description and Key Features; Wang et al. abstract for the factor list
  side_effects: []
  handling:
    - text: 'Storage of Heraeus C4313GSD paste: dry and cool at 2 to 23 degC, in a dark place, with the container tightly shut. Warranty is 6 months from manufacture with proper storage.'
      source: heraeus-c4313
      where: Storage and Warranty pages
    - text: PubChem reports palladium on carbon (10%) as highly pyrophoric under hydrogen and as a frequent igniter on contact with methanol, which is a significant safety risk. Keep catalyst powders away from methanol and hydrogen together.
      source: pubchem-pd
      where: Safety and Hazards > Stability and Reactivity > Reactivity Alerts (CSL reaction information)
    - text: PubChem lists explosive reaction with hydrogen and hydrogen peroxide for palladium.
      source: pubchem-pd
      where: Safety and Hazards > Safety and Hazard Properties > Explosive Limits and Potential
  mitigations:
    - text: Keep the membrane near 23 at% silver, which Witjens et al. (2004) say prevents hydride embrittlement by keeping one phase above ambient temperature.
      source: witjens2004
      where: Introduction, paragraph 2
    - text: PubChem's disposal note says to recycle unused portions and use an alternative with less exposure potential where possible.
      source: pubchem-pd
      where: Accidental Release Measures > Disposal Methods
uses:
  - application: habitats-and-suits
    device: Dissolved-hydrogen separator for alkaline fuel-cell water (1969 design)
    example: A 1969 NASA-sponsored separator of 75% palladium-25% silver tubes with palladium black was built by The Garrett Corporation to remove dissolved hydrogen from fuel-cell water. A test unit ran 3700 hours without loss of efficiency.
    source: nasa-tech-brief-1969
    where: Main text and Notes
  - application: cryogenic-fuel
    device: Hydrogen purification membranes
    example: NASA Glenn's 2019 report says palladium is commonly alloyed with silver for hydrogen purification, because only hydrogen readily passes through bulk palladium and the silver protects the membrane's strength and shape. A 25 percent silver balance is a good compromise.
    source: smith2019-nasa-tm
    where: Introduction
  - application: electronics-and-chips
    device: Silver-palladium thick-film conductor paste for fine lines and sensor tracks
    example: Heraeus C4313GSD is a screen-printable 25:75 Ag/Pd paste with a line definition of 125 um or more and a fired film of 8 to 13 um, sold for harsh environments including high-sulfur fuel sensors. Wang et al. (1994) list hybrid microcircuits, multichip modules and multilayer capacitors as Ag/Pd conductor uses.
    source: heraeus-c4313
    where: Description; Recommended Processing Guide
  - application: electronics-and-chips
    device: Relay and switch contacts for telecommunications and measurement and control
    example: The PdAg70 contact grade is used at 20 to 60 V and switching capacities up to 300 W, and is also used for potentiometers. The listing calls the alloy ductile, corrosion resistant and abrasion resistant.
    source: mfgrobots-pd30ag70
    where: Description paragraph
supply:
  - subject: Palladium (through the platinum-group metals)
    abundance: World mine production of palladium was an estimated 190,000 kg in 2024 (208,000 kg in 2023). Russia mined an estimated 75,000 kg, South Africa 72,000 kg, Canada 15,000 kg, Zimbabwe 15,000 kg and the United States 8,000 kg. US apparent consumption of palladium was an estimated 83,000 kg in 2024, with net import reliance of 36 percent.
    producers:
      - country: Russia
        share_percent: 39.5
        year: 2024
      - country: South Africa
        share_percent: 37.9
        year: 2024
      - country: Canada
        share_percent: 7.9
        year: 2024
      - country: Zimbabwe
        share_percent: 7.9
        year: 2024
      - country: United States
        share_percent: 4.2
        year: 2024
      - country: Other countries
        share_percent: 2.2
        year: 2024
    critical_lists: []
    recycling: About 120,000 kg of palladium and platinum were recovered globally from scrap in 2024, including about 45,000 kg of palladium from US automobile catalytic converters.
    substitutes:
      - Palladium has replaced platinum in most gasoline-engine catalytic converters, and about 25% of palladium can routinely be substituted for platinum in diesel converters (USGS).
    source: usgs-mcs2025-pgm
    where: World Mine Production and Reserves table; Recycling; Substitutes. Producer shares are calculated by Space Mushroom as each country's 2024e kg divided by the 190,000 kg world total, so they sum to about 99.6% because the USGS total is rounded.
  - subject: Silver
    abundance: World silver mine production was an estimated 25,000 tons in 2024 (25,500 tons in 2023). US apparent consumption was an estimated 6,400 tons in 2024, with net import reliance of 64 percent. Estimated US domestic uses in 2024 were electrical and electronics 29%, physical investment 30% and photovoltaics 12%.
    producers:
      - country: Mexico
        share_percent: 25.2
        year: 2024
      - country: China
        share_percent: 13.2
        year: 2024
      - country: Peru
        share_percent: 12.4
        year: 2024
      - country: Poland
        share_percent: 5.2
        year: 2024
      - country: Bolivia
        share_percent: 5.2
        year: 2024
    critical_lists: []
    recycling: About 1,200 tons of silver was recovered from new and old scrap in 2024, about 19% of apparent consumption.
    substitutes:
      - Aluminum and rhodium may replace silver in mirrors and reflecting surfaces, and nonsilver batteries may replace silver batteries in some applications (USGS).
    source: usgs-mcs2025-silver
    where: Salient Statistics; World Mine Production and Reserves table; Domestic Production and Use; Substitutes. Producer shares are calculated by Space Mushroom as each country's 2024e tons divided by the 25,000 ton world total (rounded), so they are approximate.
documents:
  - title: 'Witjens, Bitter, van Dillen, de Jong and de Groot: Pd L3 edge XANES of Pd/Ag-H membranes (PCCP 2004)'
    type: paper
    url: https://anorg.chem.uu.nl/people/staff/FrankdeGroot/pub/122%2004%20witjens%20pccp.pdf
    year: 2004
  - title: Review for consistent analysis of hydrogen permeability through dense metallic membranes (Membranes, PMC7345108)
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC7345108/
    year: 2020
  - title: 'NASA/TM-2019-220189: Permeation Rate Equations for Hydrogen and Deuterium in a Palladium-Silver Alloy'
    type: report
    url: https://ntrs.nasa.gov/api/citations/20190030498/downloads/20190030498.pdf
    year: 2019
  - title: 'NASA Tech Brief 69-10635: Device Separates Hydrogen from Solution in Water at Ambient Temperatures'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19690000580/downloads/19690000580.pdf
    year: 1969
  - title: Characterization of Thin Palladium-based Membranes for On-site Hydrogen Production (MRS-J 32[4], 2007)
    type: paper
    url: https://www.mrs-j.org/pub/tmrsj/vol32_no4/vol32_no4_0979.pdf
    year: 2007
  - title: 'Heraeus Electronics datasheet: C4313GSD 25:75 Ag/Pd conductor'
    type: datasheet
    url: https://pim.heraeus.com/datasheets/HET/TFM/C4313GSD.pdf
    year: 2026
  - title: 'Wang et al.: Silver-palladium thick-film conductors (Scholars Mine record 467, J. Am. Ceram. Soc., 1994)'
    type: paper
    url: https://scholarsmine.mst.edu/matsci_eng_facwork/467
    year: 1994
  - title: 'MfgRobots listing: PdAg70 alloy, soft annealed (A), contact material datasheet data'
    type: database
    url: https://www.mfgrobots.com/Article/material/metal/35366.html
    year: 2026
  - title: 'PubChem compound record: Palladium (CID 23938), GHS and reactivity sections'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23938/JSON
    year: 2026
  - title: 'PubChem compound record: Silver (CID 23954), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23954/JSON
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2025: Platinum-Group Metals'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2025/mcs2025-platinum-group.pdf
    year: 2025
  - title: 'USGS Mineral Commodity Summaries 2025: Silver'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2025/mcs2025-silver.pdf
    year: 2025
gaps:
  - No datasheet for the 75/25 membrane alloy itself was opened. The only density, melting point and resistivity values are for the PdAg70 (30/70) contact grade or are theoretical AgPd figures from search snippets, which were not used. The melting point of Pd-Ag was not found in any source opened.
  - The MfgRobots PdAg70 listing gives its melting point, Poisson ratio and specific heat as typical for palladium, so none of them are used. Mechanical values come from one listing; a second listing seen in search results was not opened.
  - 'Hydrogen solubility and permeability fit: NASA/TM-2019-220189 gives constants (4.22 and 704 K for hydrogen, 2.12 and 468 K for deuterium), but the text extraction has garbled exponents, so none are entered. Check the PDF before use.'
  - Silver migration numbers (Lin and Chan 1996; Lin and Chuang 1997) were seen in search results only and were not opened, so no migration rate is given. Wang et al. (1994) is cited only for the factors it lists.
  - No sulfide or H2S corrosion test result was found for Pd-Ag. The Heraeus claim on sulfur service has no test method printed.
  - Acid resistance (for example aqua regia or nitric acid) of Pd-Ag alloys was not sourced. PubChem covers pure palladium only.
  - Designations (UNS, EN, ASTM codes for PdAg grades) were not found in the sources consulted, so identity.designations is left out.
  - 'Critical-mineral status: the USGS silver and PGM summaries read here name no critical list, so critical_lists is empty for both. The 2026 USGS PGM summary could not be reached; 2024 estimates from the 2025 edition are used.'
  - No space-environment data (vacuum outgassing, atomic oxygen, radiation, thermal cycling) for Pd-Ag were found. The 1969 NASA brief says the separator works in air or vacuum, the only space-related statement used.
  - No production or refining route for the alloy or for Pd-Ag tubes was sourced. No prices are shown.
  - Heat-treatment and cold-work temper effects on the 75/25 grade are not sourced; the mechanical values are for the soft annealed PdAg70 listing only.
sources:
  pmc-review-2020:
    title: A Review for Consistent Analysis of Hydrogen Permeability through Dense Metallic Membranes
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC7345108/
    year: 2020
    kind: paper
    license: open access on PubMed Central; licence not checked
  witjens2004:
    title: Pd L3 edge XANES investigation of the electronic and geometric structure of Pd/Ag-H membranes (PCCP)
    id: doi:10.1039/b402540g
    url: https://anorg.chem.uu.nl/people/staff/FrankdeGroot/pub/122%2004%20witjens%20pccp.pdf
    year: 2004
    kind: paper
    license: author copy hosted by Utrecht University; publisher copyright
  smith2019-nasa-tm:
    title: Permeation Rate Equations for Hydrogen and Deuterium in a Palladium-Silver Alloy
    id: NASA/TM-2019-220189, NTRS 20190030498
    url: https://ntrs.nasa.gov/api/citations/20190030498/downloads/20190030498.pdf
    year: 2019
    kind: report
    license: public domain (NASA)
  nasa-tech-brief-1969:
    title: Device Separates Hydrogen from Solution in Water at Ambient Temperatures
    id: NASA Tech Brief B69-10635 (MSC-13335), November 1969
    url: https://ntrs.nasa.gov/api/citations/19690000580/downloads/19690000580.pdf
    year: 1969
    kind: report
    license: public domain (NASA)
  zhang2007-mrsj:
    title: Characterization of Thin Palladium-based Membranes for the Application of On-site Hydrogen Production
    id: Trans. Mat. Res. Soc. Jpn. 32[4] 979-982 (2007)
    url: https://www.mrs-j.org/pub/tmrsj/vol32_no4/vol32_no4_0979.pdf
    year: 2007
    kind: paper
    license: Materials Research Society of Japan; linked not reproduced
  heraeus-c4313:
    title: 'Heraeus Electronics: C4313GSD Conductor, Technical Data Sheet'
    id: Document HET32043-0921-2
    url: https://pim.heraeus.com/datasheets/HET/TFM/C4313GSD.pdf
    year: 2026
    kind: datasheet
    license: manufacturer document, linked not reproduced
  wang1994-thick-film:
    title: Silver-palladium Thick-film Conductors (Scholars Mine record, Journal of the American Ceramic Society, 1994)
    id: Scholars Mine record 467; publication date 1 Dec 1994
    url: https://scholarsmine.mst.edu/matsci_eng_facwork/467
    year: 1994
    kind: paper
    license: abstract read on the repository record; full text not opened
  mfgrobots-pd30ag70:
    title: 'PdAg70 Alloy, Soft Annealed (A): Premium Contact Material for Telecom and Control Applications (MfgRobots listing)'
    id: Online listing; original datasheet not named
    url: https://www.mfgrobots.com/Article/material/metal/35366.html
    year: 2026
    kind: web
    license: listing page; linked not reproduced
  pubchem-pd:
    title: PubChem compound record, Palladium (CID 23938)
    id: CID 23938; CAS 7440-05-3
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23938/JSON
    year: 2026
    kind: database
    license: public domain (NCBI); cited handbooks not reproduced
  pubchem-ag:
    title: PubChem compound record, Silver (CID 23954)
    id: CID 23954; CAS 7440-22-4
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23954/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  usgs-mcs2025-pgm:
    title: Mineral Commodity Summaries 2025, Platinum-Group Metals
    id: USGS MCS 2025, pp. 136-137 (data to 2024)
    url: https://pubs.usgs.gov/periodicals/mcs2025/mcs2025-platinum-group.pdf
    year: 2025
    kind: report
    license: public domain (USGS)
  usgs-mcs2025-silver:
    title: Mineral Commodity Summaries 2025, Silver
    id: USGS MCS 2025, pp. 162-163 (data to 2024)
    url: https://pubs.usgs.gov/periodicals/mcs2025/mcs2025-silver.pdf
    year: 2025
    kind: report
    license: public domain (USGS)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 3
  caveats: 6
  note: Written by an AI assistant on 2026-10-26. Values were read in PDF text extracted with pdftotext (NASA 2019 and 1969, USGS 2025 PGM and silver, Heraeus, Witjens 2004, Zhang 2007), in the review's HTML page (PMC7345108), in PubChem JSON (Pd and Ag) and in the MfgRobots listing HTML. The MfgRobots values are for PdAg70 and come from a listing, not the manufacturer. Three items seen only in search results (Lin and Chan 1996, Lin and Chuang 1997, the Serra 1998 DOI) were not opened and are not used.
story:
  recipe:
    line: A palladium-silver alloy is a solid solution of silver in a face-centred cubic palladium lattice. Witjens et al. (2004) model the Pd/Ag-H system on a fcc lattice with silver evenly distributed. Membrane grade is about 75 percent palladium and 25 percent silver, the same 25:75 Ag/Pd ratio as Heraeus C4313GSD paste. The contact grade PdAg70 is 30 percent palladium and 70 percent silver. No sourced production or tube-making route is given.
    parts:
      - name: Palladium
        symbol: Pd
        share: 75 percent in the membrane grade (NASA) and in C4313GSD (Heraeus); 30 percent in the PdAg70 contact grade (listing)
        role: The matrix metal. Only hydrogen readily passes through bulk palladium, which is why it is used for purification (NASA TM 2019).
      - name: Silver
        symbol: Ag
        share: 25 percent in the membrane grade (NASA) and in C4313GSD (Heraeus); 70 percent in the PdAg70 contact grade (listing)
        role: Suppresses the hydride transition that cracks pure palladium. Witjens et al. (2004) say 23 at% silver lowers the critical temperature so one phase forms above ambient.
  risk_groups:
    - title: For people
      level: 1
      verdict: Dust and catalyst powders are the concern
      lead: A solid alloy foil or tube is a low concern. Fine palladium dust and palladium black need care, and silver carries an aquatic classification.
      points:
        - label: Palladium
          line: 'PubChem''s 616 supplier reports for palladium split: 59.3% say it does not meet GHS criteria, and 31.5% classify it as a flammable solid (H228).'
        - label: Silver
          line: Silver is very toxic to aquatic life in 70.4% (H400) and 69.3% (H410) of 2154 reports. Some notifications also carry H361f and H373.
        - label: Skin
          line: Contact dermatitis has been associated with metallic palladium, especially palladium alloys. Occupational asthma has been reported but is very rare.
    - title: If it fails
      lead: The documented failure is hydrogen cracking when silver is too low. Silver migration is the second risk in fine, humid, biased circuits.
      points:
        - label: Hydrogen cracking
          line: Below about 23 at% silver, the alpha-beta hydride transition can form. Witjens et al. (2004) say the local tension leads to microcracking, and silver-poor areas are the starting points.
        - label: Thin pure Pd
          line: In the 2007 study a silicon-supported pure Pd membrane fractured under hydrogen cycling, while the Pd-25Ag membrane of the same thickness resisted brittleness.
        - label: Silver migration
          line: Heraeus says the palladium-rich fired surface of its 25:75 Ag/Pd paste greatly reduces the risk of silver migration. The datasheet gives no test details.
    - title: Handling and storage
      points:
        - label: Catalyst powders
          line: Palladium black and palladium on carbon are pyrophoric. PubChem reports ignition when Pd/C meets methanol in a hydrogen atmosphere.
        - label: Paste storage
          line: Heraeus says to store the paste dry and cool at 2 to 23 degC, in the dark, tightly shut. The warranty runs 6 months from manufacture.
        - label: Incompatibilities
          line: PubChem lists explosive reaction of palladium with hydrogen and hydrogen peroxide.
  why: Silver makes palladium usable as a hydrogen membrane. Pure palladium lets hydrogen pass and swells as it takes it up, so thin walls can crack. Witjens et al. (2004) found 23 at% silver is the best composition for permeability and lifetime, because it lowers the critical temperature for the two hydride phases. The 2007 study found a 2.5 um Pd-25Ag membrane resisted hydrogen-induced brittleness where pure palladium fractured. The contact grade PdAg70 has a density of 10.9 g/cm3, a Vickers hardness of 55 and a tensile strength of 310 MPa when soft annealed, with 36 percent elongation.
  uses:
    - where: Spacecraft fuel-cell water
      line: In 1969 a separator of palladium-silver alloy tubes coated with palladium black was built under a Manned Spacecraft Center contract to remove dissolved hydrogen from alkaline fuel-cell water. A test unit ran 3700 hours without loss of efficiency.
    - where: Hydrogen purification
      line: NASA Glenn's 2019 report says palladium is commonly alloyed with silver for purification membranes, with 25 percent silver a good balance of strength and shape-holding against hydrogen.
    - where: Thick-film circuits
      line: Heraeus's C4313GSD is a 25:75 Ag/Pd paste with a fired sheet resistance of 180 milliohms/square at 12 um. Wang et al. (1994) list hybrid microcircuits, multichip modules and multilayer capacitors as Ag/Pd conductor uses.
    - where: Contacts
      line: PdAg70 is used as a contact material in telecom and measurement relays and switches at 20 to 60 V and up to 300 W, and for potentiometers.
  can_do:
    - label: Hydrogen passage
      value: Dissolved H2 from 60 psia to under 0.5 psia
      line: The 1969 NASA-sponsored separator, made of 75% palladium-25% silver tubes, lowered dissolved hydrogen to less than 0.5 psia at 75 degF and 10 ml per minute of water flow.
    - label: Resists cracking
      value: No fracture in 423 to 673 K
      line: The 2.5 um Pd-25Ag membrane on silicon resisted hydrogen-induced brittleness across 423 to 673 K, while the pure Pd membrane fractured.
    - label: Conducting paste
      value: 180 milliohms/square at 12 um
      line: Heraeus gives a maximum sheet resistance of 180 milliohms/square for C4313GSD fired at 850 degC peak to a 12 um film.
    - label: Contact grade
      value: 15 uOhm.cm at 20 degC
      line: The PdAg70 contact grade has a listed resistivity of 15 uOhm.cm at 20 degC, which is 1.5 x 10^-7 Ohm.m as printed.
    - label: Supply
      value: 190,000 kg Pd in 2024
      line: USGS estimates world palladium mine production at 190,000 kg in 2024, with Russia at 75,000 kg and South Africa at 72,000 kg. World silver mine output was about 25,000 tons.
  compare: Pure palladium and Pd-25Ag behave differently under hydrogen cycling. In the 2007 study the pure Pd membrane fractured while the alloy resisted, and Witjens et al. (2004) tie that to 23 at% silver. The 75/25 membrane alloy and the PdAg70 contact grade differ in composition and use, so their properties are not directly comparable. The Heraeus sheet resistance is for a fired film, not for bulk metal.
  compare_rows:
    - label: Density
      benchmark: density
      scope: material
    - label: Elastic modulus
      benchmark: elastic_modulus
      scope: material
    - label: Thermal conductivity
      benchmark: thermal_conductivity
      scope: material
  handling:
    - Treat palladium black and palladium on carbon as pyrophoric; keep them away from methanol and hydrogen together.
    - Expect a possible skin sensitiser, especially with palladium alloys.
    - Store Ag-Pd thick-film paste dry and cool at 2 to 23 degC, in the dark.
    - Keep the membrane near 23 at% silver so hydrogen cycling does not crack it.
    - Recycle scrap; the USGS counts about 45,000 kg of palladium recovered from US car catalysts in 2024.
  good_for:
    - Hydrogen separation through thin walls. The 1969 separator ran 3700 hours without loss of efficiency.
    - Stable electrical contacts. PdAg70 has a listed resistivity of 15 uOhm.cm and a Vickers hardness of 55.
    - Fired conductors where silver migration matters. Heraeus says the palladium-rich surface reduces the risk.
  watch_out:
    - Hydrogen cracking when silver falls below about 23 at%. Witjens et al. (2004) describe the mechanism.
    - Silver aquatic toxicity. Silver is very toxic to aquatic life in 70.4% (H400) and 69.3% (H410) of 2154 reports.
    - Mixed grades. The 75/25 membrane alloy and the PdAg70 contact grade are different compositions with different data.
    - Supply concentration. Russia (39.5%) and South Africa (37.9%) mine most of the world's estimated 2024 palladium.
  verdict: Palladium-silver alloys are the practical answer for hydrogen membranes and palladium-rich contacts and fired conductors. Silver near 23 at% keeps the membrane from cracking, and the 1969 NASA separator and 2007 membrane data support the design. The gaps are the 75/25 alloy's own melting point and density, and any sulfide test result.