{
  "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.\n",
  "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",
    "designations": [],
    "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,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "optimal_silver_content",
      "label": "Silver content giving the best hydrogen membrane (permeability and lifetime)",
      "value": 23,
      "bound": "exact",
      "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)",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "alloy_silver_fraction",
      "label": "Silver fraction recommended for a palladium purification alloy",
      "value": 25,
      "bound": "exact",
      "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",
      "source_detail": {
        "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)"
      }
    },
    {
      "benchmark": "membrane_thickness",
      "label": "Thickness of a microfabricated Pd-25Ag membrane on silicon",
      "value": 2.5,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "density",
      "label": "Density of the PdAg70 contact grade",
      "value": 10.9,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "elastic_modulus",
      "label": "Elastic modulus of the PdAg70 contact grade",
      "value": 114,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "ultimate_tensile_strength",
      "label": "Tensile strength of the PdAg70 contact grade, soft annealed",
      "value": 310,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "yield_strength",
      "label": "0.2% offset yield strength of the PdAg70 contact grade, soft annealed",
      "value": 150,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "elongation",
      "label": "Elongation of the PdAg70 contact grade, soft annealed",
      "value": 36,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "vickers_hardness",
      "label": "Vickers hardness of the PdAg70 contact grade, soft annealed",
      "value": 55,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "thermal_conductivity",
      "label": "Thermal conductivity of the PdAg70 contact grade",
      "value": 61,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "electrical_resistivity",
      "label": "Electrical resistivity of the PdAg70 contact grade",
      "value": 15,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "sheet_resistance",
      "label": "Sheet resistance of a fired 25:75 Ag/Pd thick-film conductor",
      "value": 180,
      "bound": "exact",
      "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",
      "source_detail": {
        "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"
      }
    },
    {
      "benchmark": "dissolved_h2_pressure_out",
      "label": "Dissolved-hydrogen partial pressure after a Pd-Ag separator",
      "value": 0.5,
      "bound": "exact",
      "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",
      "source_detail": {
        "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)"
      }
    },
    {
      "benchmark": "operating_test_duration",
      "label": "Operating time of the separator test unit without loss of efficiency",
      "value": 3700,
      "bound": "exact",
      "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",
      "source_detail": {
        "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)"
      }
    }
  ],
  "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."
    }
  ],
  "media": [],
  "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."
  ],
  "story": {
    "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",
        "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.",
        "scope": "material",
        "value": "Dissolved H2 from 60 psia to under 0.5 psia"
      },
      {
        "label": "Resists cracking",
        "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.",
        "scope": "material",
        "value": "No fracture in 423 to 673 K"
      },
      {
        "label": "Conducting paste",
        "line": "Heraeus gives a maximum sheet resistance of 180 milliohms/square for C4313GSD fired at 850 degC peak to a 12 um film.",
        "scope": "material",
        "value": "180 milliohms/square at 12 um"
      },
      {
        "label": "Contact grade",
        "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.",
        "scope": "material",
        "value": "15 uOhm.cm at 20 degC"
      },
      {
        "label": "Supply",
        "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.",
        "scope": "material",
        "value": "190,000 kg Pd in 2024"
      }
    ],
    "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.",
    "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",
          "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",
          "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",
        "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."
          }
        ],
        "level": 1,
        "verdict": "Dust and catalyst powders are the concern"
      },
      {
        "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."
          }
        ]
      }
    ]
  },
  "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."
  },
  "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",
  "url": "https://spacemushroom.com/profiles/palladium-silver/"
}