Cadmium sulfide (CdS) CdS

spore: profile
id: cadmium-sulfide
spore_version: 0.2
family: ii-vi-semiconductors
name: Cadmium sulfide (CdS)
abbreviation: CdS
role: n-type window semiconductor and photoconductor
category: energy
type: solar-cells
summary: |
  Cadmium sulfide (CdS) is a yellow inorganic compound with a direct band gap of 2.42 eV and a solid density of 4.826 g/cm3, both per Wikipedia. It is the n-type window layer in CdTe thin-film solar cells, where a review gives its band gap as 2.4 eV. Its conductivity rises under light, which is why it is used in photoresistors. A NASA review of thin-film cells says CdS is no longer considered for space applications. No flight, vacuum or radiation-test record for CdS was found in the sources read.
best_for: Thin n-type window layers in CdTe thin-film solar cells, and light-sensitive resistors (photoresistors)
weakest_at: 'Cadmium toxicity: dust is the main hazard, and the supplier safety data sheet classes the compound as carcinogenic and mutagenic. No space or radiation data for CdS was found.'
identity:
  formula: CdS
  cas: 1306-23-6
  crystal_system: hexagonal (wurtzite) and cubic (zinc blende) forms
  source: cds-wiki
  where: Chembox identifiers (CAS number 1306-23-6) and structure section (hexagonal wurtzite and cubic zinc blende forms)
  designations:
    - system: Trade name
      code: cadmium yellow
      source: cds-wiki
      where: 'Applications, Pigment section: ''known as cadmium yellow'''
tags:
  environments: []
  stresses: []
  applications:
    - solar-arrays
    - electronics-and-chips
properties:
  - benchmark: density
    label: Density, solid (Wikipedia infobox)
    value: 4.826
    unit: g/cm3
    scope: material
    conditions:
      state: solid, as printed in the infobox
      temperature: not printed on the page
    method: Infobox value printed as 4.826 g/cm3, solid
    status: ground
    source: cds-wiki
    where: Infobox, Density row
  - benchmark: density
    label: Density, cubic form (PubChem)
    value: 4.5
    unit: g/cu cm
    scope: material
    conditions:
      structure: cubic (zinc blende) form
      temperature: not printed on the page
    method: Experimental property entry printed in the PubChem record
    status: ground
    source: pubchem-cds
    where: 'Experimental Properties, Density entry ''Cubic structure: 4.50 g/cu cm'''
  - benchmark: density
    label: Density, hexagonal form (PubChem)
    value: 4.82
    unit: g/cu cm
    scope: material
    conditions:
      structure: hexagonal (wurtzite) form
      temperature: not printed on the page
    method: Experimental property entry printed in the PubChem record
    status: ground
    source: pubchem-cds
    where: 'Experimental Properties, Density entry ''hexagonal structure: 4.82 g/cu cm'''
  - benchmark: density
    label: Relative density (supplier SDS)
    value: 4.82
    unit: g/mL
    scope: material
    conditions:
      temperature: 25 °C
    method: Physical and chemical properties section of the supplier SDS, item m (relative density)
    status: ground
    source: sam-cds-sds
    where: 'Section 9 (physical and chemical properties), item m, Relative density: 4.82 g/mL at 25 °C'
  - benchmark: melting_point
    label: Melting point (Wikipedia infobox, at 10 MPa)
    value: 1750
    unit: °C
    scope: material
    conditions:
      pressure: 10 MPa, as printed in the infobox note
    method: Infobox value printed as 1,750 °C
    status: ground
    source: cds-wiki
    where: Infobox, Melting point row, with note 10 MPa
  - benchmark: melting_point
    label: Melting point (AEM Deposition product table)
    value: 1750
    unit: °C
    scope: material
    conditions:
      pressure: not stated on the product page
    method: Product specification table, row 'Melting Point (°C)' printed as 1,750
    status: ground
    source: aem-cds
    where: Product specification table, Melting Point (°C) row
  - benchmark: melting_point
    label: Melting point (PubChem, approximate)
    value: 1480
    unit: °C
    scope: material
    conditions:
      basis: printed as approximately 1480 °C
    method: Experimental property entry in the PubChem record
    status: ground
    note: PubChem prints this value as approximate and disagrees with the two values above.
    source: pubchem-cds
    where: Experimental Properties, Melting Point entry
  - benchmark: melting_point
    label: Melting point (supplier SDS)
    value: 999
    unit: °C
    scope: material
    conditions:
      basis: printed as 999 °C (1,830 °F)
    method: Physical and chemical properties section of the supplier SDS, item e
    status: ground
    note: Disagrees with the Wikipedia and AEM values; the supplier does not give a test method.
    source: sam-cds-sds
    where: Section 9 (physical and chemical properties), item e, Melting point/range
  - benchmark: sublimation_point
    label: Sublimation point
    value: 980
    unit: °C
    scope: material
    conditions:
      basis: sublimes on heating; the ICSC card gives it as a sublimation point, not a boiling point
    method: Physical and chemical information section of the ICSC card, printed as 980°C
    status: ground
    source: icsc-0404
    where: Physical and chemical information, Sublimation point row
  - benchmark: band_gap
    label: Band gap, direct (Wikipedia)
    value: 2.42
    unit: eV
    scope: material
    conditions:
      gap_type: direct, as the page states
      temperature: not printed on the page
    method: Infobox BandGap value; the text reads 'direct band gap semiconductor (gap 2.42 eV)'
    status: ground
    note: Not in property-canon; a snake_case name is used.
    source: cds-wiki
    where: Infobox, BandGap row; Structure and physical properties section
  - benchmark: band_gap
    label: Band gap (CdS in a CdTe/CdS review)
    value: 2.4
    unit: eV
    scope: material
    conditions:
      basis: stated in the same sentence as the CdTe band gap of 1.45 eV
    method: Printed in the introduction of a review of CdS window layers
    status: ground
    note: Not in property-canon; a snake_case name is used.
    source: lilhare2020
    where: Section 1 (Introduction), paragraph beginning 'Since the CdTe and CdS bandgaps'
  - benchmark: refractive_index
    label: Refractive index (Wikipedia infobox)
    value: 2.529
    unit: '-'
    scope: material
    conditions:
      wavelength: not printed on the page
    method: Infobox RefractIndex value
    status: ground
    source: cds-wiki
    where: Infobox, RefractIndex row
  - benchmark: refractive_index
    label: Refractive index (PubChem, first value)
    value: 2.506
    unit: '-'
    scope: material
    conditions:
      wavelength: not printed on the page
      basis: 'printed as ''INDEX OF REFRACTION: 2.506; 2.529'''
    method: Experimental property entry in the PubChem record
    status: ground
    note: PubChem prints two values for the same entry; the second matches the Wikipedia infobox.
    source: pubchem-cds
    where: Experimental Properties, Refractive Index entry
  - benchmark: standard_entropy
    label: Standard entropy
    value: 65
    unit: J/mol K
    scope: material
    conditions:
      state: standard state (25 °C, 100 kPa), as the page states for its data
    method: Thermochemistry infobox, citing a textbook
    status: ground
    note: Not in property-canon; a snake_case name is used.
    source: cds-wiki
    where: Infobox, Thermochemistry, Entropy row
  - benchmark: molar_mass
    label: Molecular weight
    value: 144.48
    unit: g/mol
    scope: material
    conditions:
      basis: as printed in the supplier SDS for CdS
    method: Composition section of the supplier SDS
    status: ground
    note: Not in property-canon; a snake_case name is used.
    source: sam-cds-sds
    where: Section 3 (composition/information on ingredients), Molecular weight row
  - benchmark: ld50_oral
    label: Acute oral LD50, rat
    value: 7080
    unit: mg/kg
    scope: material
    conditions:
      species: rat
      route: oral
    method: Hazards infobox, LD50 row; the safety section also gives approximately 7,080 mg/kg in rats
    status: ground
    note: Not in property-canon; a snake_case name is used.
    source: cds-wiki
    where: Infobox, Hazards, LD50 row; Safety section
  - benchmark: occupational_exposure_limit
    label: OSHA permissible exposure limit, TWA as Cd
    value: 0.005
    unit: mg/m3
    scope: material
    conditions:
      basis: OSHA 1910.1027 PEL, time-weighted average, expressed as cadmium
    method: Hazards infobox, PEL row; the SDS prints the same PEL
    status: ground
    note: Not in property-canon; a snake_case name is used.
    source: cds-wiki
    where: Infobox, Hazards, PEL row
  - benchmark: occupational_exposure_limit
    label: ACGIH TLV, respirable fraction, TWA
    value: 0.002
    unit: mg/m3
    scope: material
    conditions:
      basis: TLV as TWA, respirable fraction, as the ICSC card prints it
    method: Occupational exposure limits section of the ICSC card
    status: ground
    note: Not in property-canon; a snake_case name is used.
    source: icsc-0404
    where: Occupational exposure limits, TLV (respirable fraction) line
  - benchmark: solubility_product_log
    label: Log solubility product (log Ksp)
    value: -14.36
    unit: '-'
    scope: material
    conditions:
      temperature: 25 °C
      pressure: 1 atm
    method: Other experimental properties entry in the PubChem record
    status: ground
    note: Not in property-canon; a snake_case name is used. PubChem also prints a second log K(sp) figure in its Solubility entry that is not recorded here, because it uses a different convention.
    source: pubchem-cds
    where: Experimental Properties, Other Experimental Properties entry 'log Ksp = -14.36 at 25 °C and 1 atm'
  - benchmark: oxidation_temperature
    label: Heating in air that oxidizes CdS to sulfate and oxide
    value: 700
    unit: °C
    scope: material
    conditions:
      atmosphere: air, especially in the presence of moisture
    method: Other experimental properties entry in the PubChem record
    status: ground
    note: Not in property-canon; a snake_case name is used.
    source: pubchem-cds
    where: Experimental Properties, Other Experimental Properties entry on oxidation in air
corrosion:
  - environment: Heating in air, especially with moisture
    headline: On heating in air to 700 °C, CdS oxidizes to a sulfate and then to the oxide.
    effect: PubChem reports that CdS is oxidized to the sulfate, basic sulfate and eventually the oxide on heating in air to 700 °C, especially in the presence of moisture.
    rating: moderate
    conditions:
      temperature: 700 °C
      atmosphere: air with moisture
    source: pubchem-cds
    where: Experimental Properties, Other Experimental Properties entry on oxidation
  - environment: Mineral acids
    headline: CdS dissolves in acids and releases hydrogen sulfide.
    effect: PubChem reports that CdS is soluble in concentrated or warm dilute mineral acids with evolution of H2S, and that moderately dilute nitric acid readily decomposes or dissolves it. Wikipedia gives the reaction with hydrochloric acid, which releases hydrogen sulfide.
    rating: severe
    conditions:
      basis: chemical attack, not a test of a film or coating
    source: pubchem-cds
    where: Experimental Properties, Solubility entries
risks:
  hazards:
    - text: Wikipedia prints the GHS signal word Danger for CdS with the H-phrases H302, H341, H350, H361, H372 and H413, and GHS pictograms GHS07 and GHS08.
      ghs:
        - H302
        - H341
        - H350
        - H361
        - H372
        - H413
      source: cds-wiki
      where: Hazards infobox (GHS signal word, H-phrases, pictograms)
    - text: The supplier safety data sheet (Stanford Advanced Materials, version 3.0) gives the signal word Danger with H302, H341, H350, H361, H372 and H410.
      ghs:
        - H302
        - H341
        - H350
        - H361
        - H372
        - H410
      source: sam-cds-sds
      where: Section 2, Hazards identification
    - text: PubChem's GHS summary for CID 14783 lists, for the compound, the signal word Danger with H302, H341 and H350. Its aggregated notifications also include H301 and H330 from some reports.
      ghs:
        - H302
        - H341
        - H350
      source: pubchem-cds
      where: Safety and Hazards, GHS Classification
    - text: The ICSC card classes CdS as DANGER and says it may cause cancer, may cause damage to the kidneys, bones and respiratory tract through prolonged or repeated exposure, and may cause long-lasting harmful effects to aquatic life.
      ghs: []
      source: icsc-0404
      where: Classification and labelling, According to UN GHS Criteria
  failure_risks:
    - mode: Inhalation of dust
      trigger: Powder dispersed in air during handling or weighing
      consequence: The ICSC card says a harmful concentration of airborne particles can be reached quickly when the powder is dispersed. Prolonged or repeated exposure may affect the kidneys, bones and respiratory tract, and the substance is carcinogenic to humans.
      severity: high
      source: icsc-0404
      where: Exposure and health effects section
    - mode: Oxidation on heating in air
      trigger: Heating in air, especially with moisture
      consequence: The compound is oxidized to sulfate and then oxide, which changes the material.
      severity: moderate
      source: pubchem-cds
      where: Other experimental properties entry on oxidation
    - mode: Hydrogen sulfide release on contact with acid
      trigger: Contact with mineral acids
      consequence: The compound dissolves and releases hydrogen sulfide gas.
      severity: high
      source: pubchem-cds
      where: Solubility entries
    - mode: Fire
      trigger: Heat, flame or reaction with oxidizing agents
      consequence: The ICSC card says it decomposes on burning to toxic fumes including sulfur oxides, and that as a dust it presents a moderate fire hazard.
      severity: moderate
      source: icsc-0404
      where: Fire and explosion section; chemical dangers
  side_effects:
    - text: When dispersed CdS in sulfide solution is irradiated with light, hydrogen gas is generated, according to Wikipedia.
      affects: Process chemistry of CdS suspensions
      source: cds-wiki
      where: Reactions section
  handling:
    - text: The ICSC card says to prevent dispersion of dust and avoid all contact, and to use local exhaust or breathing protection. Wear a particulate filter respirator adapted to the airborne concentration.
      source: icsc-0404
      where: Prevention and spillage disposal sections
    - text: Store separated from strong oxidants, strong acids and food, in an area without a drain or sewer access (ICSC card). The supplier SDS says keep it in a dry place.
      source: icsc-0404
      where: Storage section
    - text: 'Transport classification differs between sources. The supplier SDS prints "UN number: 3077" and "Class: 9"; the ICSC card prints "UN #: 2570" and "UN Hazard Class: 6.1".'
      source: sam-cds-sds
      where: Section 14, Transport information; ICSC 0404 Transportation section
  mitigations:
    - text: PubChem notes that processes which release cadmium fumes or dust should be enclosed and fitted with exhaust ventilation, and that workers in over-exposure situations should wear a high-efficiency particulate filter respirator.
      source: pubchem-cds
      where: Hazards Summary, first record
uses:
  - application: solar-arrays
    device: CdTe thin-film solar cells (window layer)
    example: Wikipedia says CdS is used as a thin film in some solar cells. A review of CdS window layers says N-type CdS is one of the best-known transparent window layers in CdTe heterojunction cells, and gives its band gap as 2.4 eV.
    source: lilhare2020
    where: Section 1 (Introduction)
  - application: electronics-and-chips
    device: Photoresistors (light-dependent resistors)
    example: Wikipedia says the conductivity of CdS increases when it is irradiated, which is the basis of its use as a photoresistor. The NASA Radiation Effects Design Handbook says photoconductive cells that use the bulk effect are normally made of CdS or CdSe and have no junction.
    source: cds-wiki
    where: Structure and physical properties section; NASA handbook section 6 (ntrs-1971-drennan) gives the bulk-effect statement
  - application: solar-arrays
    device: Thin-film CdS/Cu2S solar cells studied for spacecraft power (no longer a candidate)
    example: A NASA review of radiation resistance says CdS/Cu2S solar cells have shown excellent radiation tolerance, but that cells of this type are no longer considered a potential candidate for photovoltaic power generation. It states that cadmium sulfide cells had been the subject of considerable effort but are no longer considered for space applications.
    source: ntrs-1991-woodyard
    where: Section 3.1 (electron irradiation resistance) and abstract
supply:
  - subject: Cadmium
    abundance: The USGS states that the cadmium content of typical zinc ores averages about 0.03%. No crustal abundance figure for cadmium was found in the sources read.
    producers:
      - country: China
        share_percent: 41.3
        year: 2025
      - country: Korea, Republic of
        share_percent: 18.7
        year: 2025
      - country: Japan
        share_percent: 5.7
        year: 2025
      - country: Canada
        share_percent: 5.7
        year: 2025
      - country: Kazakhstan
        share_percent: 4.8
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: false
      - list: EU critical raw materials list (European Commission page)
        listed: false
    recycling: 'USGS: secondary cadmium is mainly recovered from spent consumer and industrial NiCd batteries, and CdTe solar panels are named among the scrap from which cadmium can be recycled.'
    substitutes:
      - 'USGS: batteries with other chemistries, particularly lithium-ion, can replace NiCd batteries, and cerium sulfide is used as a replacement for cadmium pigments, mostly in plastics.'
    source: usgs-mcs2026-cadmium
    where: World Refinery Production and Reserves table, 2025e (shares calculated by Space Mushroom against the printed world total of 23,000 thousand t, rounded); Recycling; Substitutes; Resources
documents:
  - title: USGS Mineral Commodity Summaries 2026, Cadmium
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cadmium.pdf
    year: 2026
  - title: 'PubChem: Cadmium Sulfide (CID 14783), GHS classification and experimental properties'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/14783
    year: 2026
  - title: 'ICSC 0404: Cadmium sulfide (ILO and WHO International Chemical Safety Card)'
    type: datasheet
    url: http://www.inchem.org/documents/icsc/icsc/eics0404.htm
    year: 2021
  - title: 'Safety Data Sheet: Cadmium sulfide (Stanford Advanced Materials, version 3.0)'
    type: sds
    url: https://samaterials.com/tds/sc/1723107280-Joy-22-cd1111.pdf
    year: 2017
  - title: Radiation Resistance of Thin-Film Solar Cells for Space Photovoltaic Power (Woodyard and Landis, NASA)
    type: report
    url: https://ntrs.nasa.gov/citations/19910009863
    year: 1991
  - title: 'Radiation Effects Design Handbook, Section 6: Solid-State Photodevices (Drennan, NASA contractor report)'
    type: report
    url: https://ntrs.nasa.gov/citations/19710023222
    year: 1971
  - title: 'Development of chalcogenide solar cells: Importance of CdS window layer (Lilhare and Khare, Opto-Electronics Review)'
    type: paper
    url: https://journals.pan.pl/Content/115768/PDF/OPELRE_28_1_D_LILHARE.pdf
    year: 2020
gaps:
  - No flight, vacuum, thermal-vacuum or radiation-test result for CdS was found. The only space-related sources are historical NASA reviews and a handbook section, and they describe the cells qualitatively.
  - The NASA radiation reviews give fluences and efficiencies in exponent or spaced-letter form, which could not be matched reliably, so those numbers were left out. Their qualitative statements are quoted instead.
  - The AEM evaporation table gives a source temperature for a vapour pressure printed with an exponent; this was left out.
  - No crustal abundance figure for cadmium was found in the sources read.
  - Sources disagree on the melting point (three values are recorded side by side), on the UN transport number, and on the aquatic hazard codes (the SDS and Wikipedia differ). Each value is kept with its source.
  - No standards designation (UNS, EN, ASTM) for a CdS grade was found; only the pigment name cadmium yellow is listed.
  - Thermal conductivity, specific heat, elastic modulus, dielectric constant and radiation tolerance numbers were not found in the sources read.
  - No humidity or long-term ageing test data for CdS films were found in the sources read.
  - Benchmark names outside property-canon (band_gap, enthalpy_of_formation, standard_entropy, molar_mass, ld50_oral, occupational_exposure_limit, sublimation_point, oxidation_temperature, solubility_product_log) are snake_case names.
  - The critical-mineral lists were checked against the official pages in this run, and cadmium was not named on either page; no figure is recorded for those lists.
sources:
  cds-wiki:
    title: Cadmium sulfide (Wikipedia article, infobox and text)
    id: CAS 1306-23-6; PubChem CID 14783; ChemSpider 7969586
    url: https://en.wikipedia.org/wiki/Cadmium_sulfide
    year: 2026
    kind: web
    license: CC BY-SA (Wikipedia)
  aem-cds:
    title: Cadmium Sulfide Pellet Evaporation Material (CdS), AEM Deposition product page
    id: AEM Deposition product listing, CdS compound evaporation material
    url: https://www.aemdeposition.com/compound-evaporation-material/cadmium-sulfide-evaporation-material.html
    year: 2026
    kind: web
    license: supplier page, cited not reproduced
  usgs-mcs2026-cadmium:
    title: 'Mineral Commodity Summaries 2026: Cadmium'
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cadmium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit-2025:
    title: About the 2025 List of Critical Minerals (USGS final list)
    id: Final 2025 List of Critical Minerals
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  ec-crm:
    title: Critical raw materials (European Commission, list under Regulation (EU) 2024/1252)
    id: Regulation (EU) 2024/1252
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    year: 2024
    kind: web
    license: European Commission web page
  pubchem-cds:
    title: PubChem compound record, Cadmium Sulfide (CID 14783)
    id: CID 14783; CAS 1306-23-6
    url: https://pubchem.ncbi.nlm.nih.gov/compound/14783
    year: 2026
    kind: database
    license: public domain (NCBI)
  icsc-0404:
    title: 'ICSC 0404: Cadmium sulfide (International Chemical Safety Card, ILO and WHO)'
    id: ICSC 0404; CAS 1306-23-6; UN 2570 as printed on the card
    url: http://www.inchem.org/documents/icsc/icsc/eics0404.htm
    year: 2021
    kind: datasheet
    license: ILO and WHO, cited not reproduced
  sam-cds-sds:
    title: 'Safety Data Sheet: Cadmium sulfide (Stanford Advanced Materials, version 3.0, revision 09/04/2017)'
    id: SAM Materials, cadmium sulfide, CAS 1306-23-6
    url: https://samaterials.com/tds/sc/1723107280-Joy-22-cd1111.pdf
    year: 2017
    kind: datasheet
    license: supplier document, linked not reproduced
  ntrs-1991-woodyard:
    title: Radiation Resistance of Thin-Film Solar Cells for Space Photovoltaic Power (Woodyard and Landis, NASA review)
    id: NTRS 19910009863
    url: https://ntrs.nasa.gov/citations/19910009863
    year: 1991
    kind: report
    license: public domain (NASA)
  ntrs-1971-drennan:
    title: 'Radiation Effects Design Handbook, Section 6: Solid-State Photodevices (Drennan, NASA contractor report)'
    id: NTRS 19710023222
    url: https://ntrs.nasa.gov/citations/19710023222
    year: 1971
    kind: report
    license: public domain (NASA)
  lilhare2020:
    title: 'Development of chalcogenide solar cells: Importance of CdS window layer (Opto-Electronics Review 28, 43-63)'
    id: Opto-Electronics Review 28 (2020) 43-63; D. Lilhare and A. Khare
    url: https://journals.pan.pl/Content/115768/PDF/OPELRE_28_1_D_LILHARE.pdf
    year: 2020
    kind: paper
    license: open access, as listed by the journal
license: CC-BY-4.0
updated: '2026-11-02'
review:
  status: draft
  method: assistant
  checked_values: 20
  unreachable: 0
  caveats: 2
  note: Written by an AI assistant on 2026-11-02 from pages read in this run. Values are as printed. Three melting-point values and two transport numbers disagree between sources and are recorded side by side.
story:
  recipe:
    line: 'CdS is cadmium sulfide: one cadmium atom and one sulfur atom per formula unit. Pigment grade is made by precipitating from soluble cadmium salts with sulfide ion, washing the precipitate, then calcining (roasting) it to the hexagonal form before milling to a powder. Thin films are made by chemical bath deposition, using thiourea as the sulfide source (Wikipedia).'
    parts:
      - name: Cadmium
        symbol: Cd
        role: Divalent cation (Cd2+) in the crystal lattice; the cadmium content is what makes the compound toxic.
      - name: Sulfur
        symbol: S
        role: Sulfide anion (S2-) that pairs with cadmium; it is released as hydrogen sulfide when the compound dissolves in acid.
  risk_groups:
    - title: For people
      level: 0
      verdict: 'Carcinogen as dust: keep dust out of the air'
      lead: CdS is a cadmium compound. The supplier safety data sheet and Wikipedia both class it as carcinogenic and mutagenic, and inhaled dust is the main route of harm.
      points:
        - label: Dust
          line: The ICSC card says a harmful concentration of airborne particles can be reached quickly when the powder is dispersed. Use local exhaust or breathing protection.
        - label: Kidneys, bones and lungs
          line: Prolonged or repeated exposure may affect the kidneys, bones and respiratory tract (ICSC card).
        - label: Exposure limits
          line: The OSHA permissible exposure limit is 0.005 mg/m3 as a time-weighted average, expressed as cadmium (Wikipedia). The ICSC card gives 0.002 mg/m3 for the respirable fraction.
    - title: If the material is heated
      lead: These are laboratory and handling facts, not field incident reports.
      points:
        - label: In air
          line: On heating in air to 700 °C, CdS oxidizes to a sulfate and then to the oxide, faster when moist (PubChem).
        - label: In a fire
          line: The ICSC card says it decomposes on burning to toxic fumes, including sulfur oxides, and that as a dust it presents a moderate fire hazard.
        - label: In acid
          line: Mineral acids dissolve it and release hydrogen sulfide (PubChem).
    - title: Handling and storage
      points:
        - label: Storage
          line: Store in a cool, well-ventilated area, separated from strong oxidants, strong acids and food (ICSC card).
        - label: Spills
          line: Moisten the spill to prevent dusting, sweep it into covered containers, and do not let it enter the environment (ICSC card).
  why: Cadmium sulfide (CdS) is a yellow II-VI semiconductor compound. It forms a hexagonal wurtzite structure, which Wikipedia calls the more stable form, and a cubic zinc blende structure. CdS is used as the n-type window in CdTe thin-film solar cells, as a photoresistor, and as a yellow pigment. For space materials the interest is largely historical. NASA reviews of thin-film solar cells describe CdS cells as having been studied for spacecraft power, and say they are no longer considered for space applications.
  uses:
    - where: Thin-film solar cells
      line: N-type CdS is used as a transparent window layer in heterojunction cells paired with p-type CdTe. A review of CdS window layers gives the band gap of CdS as 2.4 eV.
    - where: Photoresistors
      line: The conductivity of CdS increases under light, which is the basis for its use in photoresistors (Wikipedia). A NASA handbook says photoconductive cells that use the bulk effect are normally made of CdS or CdSe and have no junction.
    - where: Early space solar cells, no longer a candidate
      line: A NASA review of radiation resistance says CdS/Cu2S cells have shown excellent radiation tolerance in electron tests. It also says that cadmium sulfide cells had been the subject of considerable effort but are no longer considered for space applications.
  can_do:
    - label: Window layer
      benchmark: band_gap
      line: Works as the n-type window in CdTe thin-film solar cells, with a band gap of 2.4 eV in a review and 2.42 eV on Wikipedia.
    - label: Photoresistor
      line: Acts as a photoresistor, because its conductivity rises under light (Wikipedia).
    - label: Pigment
      line: Gives a yellow colour as a pigment; Wikipedia calls it cadmium yellow.
    - label: Acid
      line: Dissolves in mineral acids with release of hydrogen sulfide (PubChem).
  compare: 'CdS is the wide-band-gap partner in a CdTe cell. Its band gap of 2.42 eV (Wikipedia) and 2.4 eV (review) lets photons with lower energy reach the CdTe absorber, according to the review. Melting-point sources disagree, so all three values are shown with their sources: 1750 °C (Wikipedia and the AEM product table), approximately 1480 °C (PubChem) and 999 °C (supplier SDS). The density values are close: 4.826 g/cm3 (Wikipedia) and 4.82 g/mL at 25 °C (supplier SDS).'
  compare_rows:
    - label: Band gap
      benchmark: band_gap
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
  handling:
    - 'Prevent dust: the ICSC card says to prevent dispersion of dust and avoid all contact.'
    - Use local exhaust, and a particulate filter respirator adapted to the airborne concentration where dust may be present.
    - Store dry and tightly closed, away from strong oxidants, strong acids and food.
    - Keep it out of drains and the environment; the ICSC card says it is persistent and bioaccumulates in some organisms.
  good_for:
    - Thin-film window layers in CdTe cells, where a wide band gap is needed (review).
    - Photoconductive cells, where its conductivity rises under light (Wikipedia).
  watch_out:
    - 'Toxicity: a carcinogenic cadmium compound, with dust as the main exposure route.'
    - Melting point and transport classification differ between sources, so check the cited value.
    - No flight, vacuum or radiation-test result for CdS was found; the space-related sources are historical reviews.
  verdict: CdS is a historic window and photoresistor material. Its cadmium toxicity and the NASA statement that CdS is no longer considered for space applications make it a poor choice for new flight hardware.