spore: profile
id: z93-white-paint
spore_version: 0.2
family: coatings
name: Z-93 / Z-93P white thermal control paint (zinc oxide in potassium silicate)
abbreviation: Z-93
role: 'Inorganic white paint for spacecraft radiators: zinc oxide pigment in a potassium silicate binder'
category: coatings
type: white-paints
summary: |
  Z-93 is a white thermal control paint made of zinc oxide pigment in a potassium silicate binder. It was made by Alion Science and Technology (formerly IITRI) and has flight heritage on LDEF, POSA-I (Mir) and MISSE on the International Space Station. On the MISSE-2 trays, Z-93 kept a solar absorptance of 0.14 after exposure to 5,130 ESH and 5,660 ESH of UV, per NASA's 2008 MISSE review. Solar absorptance is the fraction of sunlight the surface absorbs; thermal emittance is how well it radiates heat. Silicone contamination is the in-flight change that the sources describe.
best_for: White radiator surfaces in low Earth orbit where long-term stability and low contamination matter more than conductivity. NASA selected Z-93 for ISS radiators on the basis of its LDEF performance.
weakest_at: Silicone contamination yellows the coating and raises solar absorptance (0.16 to 0.23 on POSA-I after 18 months). Ground VUV tests darkened it, and the darkening was partly reversed by air exposure.
identity:
  formula: ZnO pigment in potassium silicate binder (SiO2:K2O mole ratio 3.3:1 for the original PS-7 binder)
  cas: 1314-13-2 (zinc oxide pigment)
  source: nasa-n95-14063
  where: Binder composition and SiO2:K2O mole ratio 3.3:1, Introduction and background (PS-7 and Kasil 2130); CAS of zinc oxide from the Sigma-Aldrich SDS, section 3.1
  designations:
    - system: Trade name
      code: Z-93
      source: finckenor2008
      where: Table 1, Alion Zinc Oxide/Potassium Silicate Coatings, Material column; also written Z93 in the 1993 and 2018 NASA papers
tags:
  environments:
    - low-earth-orbit
    - geo
  stresses:
    - atomic-oxygen
    - uv
    - thermal-cycling
    - vacuum-and-outgassing
  applications:
    - thermal-control
properties:
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 before MISSE-2 flight
    value: 0.136
    unit: '-'
    scope: material
    conditions:
      basis: Z-93 with original PS-7 binder on aluminium, measured before flight; value printed to three decimals on the slide
      binder: PS-7 (original)
    method: Solar absorptance printed on the reflectance chart; the slide does not state the measurement standard
    status: ground
    source: finckenor2008-slides
    where: Slide 'Z93 - Original Binder', chart label Pre-Flight a=0.136
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 after MISSE-2 ram-facing flight
    value: 0.135
    unit: '-'
    scope: material
    conditions:
      basis: MISSE-2 ram-facing side, about 7.2 to 7.6e21 atoms/cm2 atomic oxygen and 5,100 to 6,000 ESH per the exposure slide
      exposure_years: about 4 (MISSE-1 and MISSE-2 were on ISS for nearly four years)
    method: Solar absorptance printed on the reflectance chart; standard not stated on the slide
    status: flight
    source: finckenor2008-slides
    where: Slide 'Z93 - Original Binder', chart label MISSE-2 Ram a=0.135; exposure from slide 'Estimated Environmental Exposures for MISSE-1 and MISSE-2'
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 after MISSE-4 wake-facing flight
    value: 0.146
    unit: '-'
    scope: material
    conditions:
      basis: MISSE-4 wake-facing side, 2.0e20 atoms/cm2 atomic oxygen and about 1,200 ESH per Table 1 of the 2008 report
      exposure_years: 1 (MISSE-3 and MISSE-4 were on ISS for one year)
    method: Solar absorptance printed on the reflectance chart; standard not stated on the slide
    status: flight
    source: finckenor2008-slides
    where: Slide 'Z93 - Original Binder', chart label MISSE-4 Wake a=0.146
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 post-flight MISSE-2 at 5,130 ESH
    value: 0.14
    unit: '-'
    scope: material
    conditions:
      basis: Z-93 on aluminium, MISSE-2, pre-flight 0.14 and post-flight 0.14
      atomic_oxygen_fluence: 1.4e20 atoms/cm2
      uv_esh: 5130
    method: Solar absorptance as listed in the report's table, Alion Z-93 rows
    status: flight
    source: finckenor2008
    where: Table 1, Alion Zinc Oxide/Potassium Silicate Coatings, Z-93 row MISSE-2 (5,130 ESH), post-flight column
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 post-flight MISSE-2 at 5,660 ESH
    value: 0.14
    unit: '-'
    scope: material
    conditions:
      basis: Z-93 on aluminium, MISSE-2 second tray, pre-flight 0.14 and post-flight 0.14
      atomic_oxygen_fluence: 7.2e21 atoms/cm2
      uv_esh: 5660
    method: Solar absorptance as listed in the report's table
    status: flight
    source: finckenor2008
    where: Table 1, Z-93 row MISSE-2 (5,660 ESH), post-flight column
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 post-flight MISSE-3 at about 1,200 ESH
    value: 0.14
    unit: '-'
    scope: material
    conditions:
      basis: Z-93 on aluminium, MISSE-3, pre-flight 0.14 and post-flight 0.14
      atomic_oxygen_fluence: 1.2e21 atoms/cm2
      uv_esh: about 1,200 (the 2008 slide gives about 1,500 ESH for MISSE-3 trays; both shown in gaps)
    method: Solar absorptance as listed in the report's table
    status: flight
    source: finckenor2008
    where: Table 1, Z-93 row MISSE-3 (about 1,200 ESH), post-flight column
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 post-flight MISSE-4 at about 1,200 ESH
    value: 0.15
    unit: '-'
    scope: material
    conditions:
      basis: Z-93 on aluminium, MISSE-4, pre-flight 0.14 and post-flight 0.15
      atomic_oxygen_fluence: 2.0e20 atoms/cm2
      uv_esh: about 1,200
    method: Solar absorptance as listed in the report's table
    status: flight
    source: finckenor2008
    where: Table 1, Z-93 row MISSE-4 (about 1,200 ESH), post-flight column
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 pre-flight on LDEF tray S0069
    value: 0.14
    unit: '-'
    scope: material
    conditions:
      basis: Z-93 with original PS7 binder, LDEF experiment S0069 sample, before flight
    method: Solar absorptance as stated in the report text
    status: ground
    source: finckenor2008
    where: Section A, Zinc Oxide/Potassium Silicate, sentence on S0069 (pre-flight and post-flight values)
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 after 5.8 years on LDEF tray S0069
    value: 0.15
    unit: '-'
    scope: material
    conditions:
      basis: Z-93 with original PS7 binder, LDEF experiment S0069, post-flight after 5.8 years in space
    method: Solar absorptance as stated in the report text
    status: flight
    source: finckenor2008
    where: Section A, Zinc Oxide/Potassium Silicate, sentence on S0069 (post-flight value)
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 ram-facing on LDEF A0034 after 5.8 years
    value: 0.16
    unit: '-'
    scope: material
    conditions:
      basis: Z-93 with original PS7 binder, LDEF experiment A0034, ram-facing samples, 5.8 years in space
    method: Solar absorptance as stated in the report text
    status: flight
    source: finckenor2008
    where: Section A, Zinc Oxide/Potassium Silicate, sentence on A0034 (ram-facing and wake-facing values)
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93 wake-facing on LDEF A0034 after 5.8 years
    value: 0.17
    unit: '-'
    scope: material
    conditions:
      basis: Z-93 with original PS7 binder, LDEF experiment A0034, wake-facing samples, 5.8 years in space
    method: Solar absorptance as stated in the report text
    status: flight
    source: finckenor2008
    where: Section A, Zinc Oxide/Potassium Silicate, sentence on A0034 (wake-facing value)
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93P control on POSA-I (Mir)
    value: 0.16
    unit: '-'
    scope: material
    conditions:
      basis: Z-93P (Kasil 2130 binder) control sample, not exposed on the POSA-I tray
      binder: Kasil 2130
    method: Solar absorptance printed on the reflectance chart; standard not stated on the slide
    status: ground
    source: finckenor2008-slides
    where: Slide 'POSA-I Z-93P After 18 months on Mir', chart label Control a=0.160
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93P Mir-facing on POSA-I after 18 months
    value: 0.166
    unit: '-'
    scope: material
    conditions:
      basis: Z-93P, Mir-facing side with about 250 Angstrom silicone contamination, 18 months on Mir
      binder: Kasil 2130
    method: Solar absorptance printed on the reflectance chart
    status: flight
    source: finckenor2008-slides
    where: Slide 'POSA-I Z-93P After 18 months on Mir', chart label Mir-facing a=0.166
  - benchmark: solar_absorptance
    label: Solar absorptance, Z-93P space-facing on POSA-I after 18 months
    value: 0.228
    unit: '-'
    scope: material
    conditions:
      basis: Z-93P, space-facing side with about 5,000 Angstrom silicone contamination and 571 ESH of UV, 18 months on Mir
      binder: Kasil 2130
    method: Solar absorptance printed on the reflectance chart
    status: flight
    source: finckenor2008-slides
    where: Slide 'POSA-I Z-93P After 18 months on Mir', chart label Space-facing a=0.228; contamination and UV dose from the 2008 report, section A
  - benchmark: thermal_emittance
    label: Thermal emittance of Z-93 after plasma ashing
    value: 0.92
    unit: '-'
    scope: material
    conditions:
      basis: Measured after oxygen RF plasma ashing (Table VI column Emittance After Ashing)
      atomic_oxygen_basis: ashing fluence per the report's Table V; exponent not read in this run
    method: Table VI value; instrument for the emittance column not restated in Table VI
    status: ground
    source: nasa-tm104335-1991
    where: Table VI, Performance of candidate radiator coatings, Z-93 row, Emittance After Ashing
  - benchmark: solar_absorptance
    label: Solar absorptance of Z-93 after VUV exposure
    value: 0.18
    unit: '-'
    scope: material
    conditions:
      basis: After VUV exposure (Table VI column Solar Absorptance After VUV Exposure); VUV dose not restated in Table VI
      ground_test: ground VUV test, not flight
    method: Table VI value
    status: ground
    source: nasa-tm104335-1991
    where: Table VI, Z-93 row, Solar Absorptance After VUV Exposure
  - benchmark: areal_mass
    label: Areal mass of Z-93 measured after ashing
    value: 0.018
    unit: g/cm2
    scope: material
    conditions:
      basis: Measured after oxygen plasma ashing; the report prints an uncertainty of plus or minus 0.0014 g/cm2
    method: Mass per area from weighing, Table VI
    status: ground
    source: nasa-tm104335-1991
    where: Table VI, Z-93 row, Mass/Area Measured (after ashing)
  - benchmark: areal_mass
    label: Areal mass of Z-93 vendor specification, unexposed
    value: 0.0162
    unit: g/cm2
    scope: material
    conditions:
      basis: Unexposed vendor specification for the coating mass per area
    method: Vendor specification as printed in Table VI
    status: ground
    source: nasa-tm104335-1991
    where: Table VI, Z-93 row, Mass/Area Vendor Specs (unexposed)
  - benchmark: coating_thickness
    label: Z-93 thickness giving minimum solar absorptance
    value: 4
    value_high: 5
    unit: mil
    scope: material
    conditions:
      basis: Coating on 0.9 in diameter, 0.032 in thick 6061-T6 aluminium disks; thickness that gives minimum solar absorptance
    method: Thickness as stated in the report text
    status: ground
    source: nasa-tm104335-1991
    where: Section on thermal control coatings, paragraph on coating thicknesses (4-5 mil for Z-93)
  - benchmark: coating_thickness
    label: Z-93 applied coating thickness, spray process
    value: 0.1
    value_high: 0.13
    unit: mm
    scope: material
    conditions:
      basis: Applied to 6061-T6 disks of about 2.5 cm diameter and 0.79 mm thickness by low-pressure, high-volume spray
    method: Thickness as stated in the report text (Materials Tested)
    status: ground
    source: dever1993
    where: Materials Tested, paragraph on Z-93 and YB-71 spray application
  - benchmark: solar_absorptance
    label: Solar absorptance of Z93C55 beginning of life
    value: 0.14
    unit: '-'
    scope: material
    conditions:
      product: Z93C55, Alion conductive white coating (a separate formulation from Z-93)
      basis: Measured optical properties before testing, Table 1
    method: ASTM E903-82 with a Cary 5000 spectrophotometer, per the paper
    status: ground
    source: hasegawa2018
    where: Table 1, Thermal Optical Properties, Z93C55 row, alpha column; method in Optical Property Characterization
  - benchmark: thermal_emittance
    label: Normal thermal emittance of Z93C55
    value: 0.92
    unit: '-'
    scope: material
    conditions:
      product: Z93C55, Alion conductive white coating (a separate formulation from Z-93)
      basis: Normal emittance, Table 1, Z93C55 row, en column
    method: ASTM E408-71 with a Gier Dunkel DB100 reflectometer, per the paper
    status: ground
    source: hasegawa2018
    where: Table 1, Z93C55 row, normal emittance column; method in Optical Property Characterization
  - benchmark: thermal_emittance
    label: Hemispherical thermal emittance of Z93C55
    value: 0.94
    unit: '-'
    scope: material
    conditions:
      product: Z93C55, Alion conductive white coating (a separate formulation from Z-93)
      basis: Hemispherical emittance, Table 1, Z93C55 row, hemispherical column
    method: Surface Optics SOC-100 hemispherical directional reflectometer, per the paper
    status: ground
    source: hasegawa2018
    where: Table 1, Z93C55 row, hemispherical column; method in Optical Property Characterization
  - benchmark: delta_alpha
    label: Change in solar absorptance of Z93C55 after combined solar wind exposure
    value: 0.051
    unit: '-'
    scope: material
    conditions:
      product: Z93C55
      basis: 'Solar wind facility: 20 keV electrons 9.30E+15 e-/cm2, 2 keV protons 1.20E+16 p+/cm2, NUV 1123 ESH'
    method: Change from initial solar absorptance, in-vacuo measurement in the GSFC solar wind facility
    status: ground
    source: hasegawa2018
    where: Table 3, Solar Wind Proton, Electron, and UV Radiation Exposures, Z93C55 row, delta-alpha column
  - benchmark: delta_alpha
    label: Change in solar absorptance of Z93C55 sample 1 after 300 keV electrons
    value: 0.18
    unit: '-'
    scope: material
    conditions:
      product: Z93C55 sample 1
      basis: GSFC Radiation Effects Facility, 300 keV electron column of the exposure sequence
    method: Change from initial solar absorptance
    status: ground
    source: hasegawa2018
    where: 'Table 4, Proton and Electron Radiation Exposures, Z93C55 #1 row, 300 KeV electrons column'
  - benchmark: delta_alpha
    label: Change in solar absorptance of Z93C55 sample 2 after 300 keV electrons
    value: 0.26
    unit: '-'
    scope: material
    conditions:
      product: Z93C55 sample 2
      basis: GSFC Radiation Effects Facility, 300 keV electron column of the exposure sequence
    method: Change from initial solar absorptance
    status: ground
    source: hasegawa2018
    where: 'Table 4, Z93C55 #2 row, 300 KeV electrons column'
  - benchmark: delta_alpha
    label: Change in solar absorptance of Z93C55 sample 1 after post-UV recovery
    value: 0.16
    unit: '-'
    scope: material
    conditions:
      product: Z93C55 sample 1
      basis: Post-UV recovery, change from initial solar absorptance
    method: Change from initial solar absorptance
    status: ground
    source: hasegawa2018
    where: 'Table 4, Z93C55 #1 row, Post UV Recovery column'
  - benchmark: delta_alpha
    label: Change in solar absorptance of Z93C55 sample 2 after post-UV recovery
    value: 0.29
    unit: '-'
    scope: material
    conditions:
      product: Z93C55 sample 2
      basis: Post-UV recovery, change from initial solar absorptance
    method: Change from initial solar absorptance
    status: ground
    source: hasegawa2018
    where: 'Table 4, Z93C55 #2 row, Post UV Recovery column'
corrosion:
  - environment: Space, MISSE-2 and MISSE-4 trays on the ISS (ram and wake sides)
    headline: Z-93 kept its solar absorptance within 0.01 of its pre-flight value on MISSE-2 and rose to 0.15 on one MISSE-4 tray.
    effect: After ISS exposure with 5,130 to 5,660 ESH of UV and atomic oxygen up to 7.2e21 atoms/cm2, Z-93 stayed at 0.14 on MISSE-2. On MISSE-4 at about 1,200 ESH the post-flight value was 0.15. The report gives no infrared emittance values for these trays.
    rating: low
    conditions:
      exposure: ISS MISSE-2 and MISSE-4 trays, about 4 years for MISSE-2 and 1 year for MISSE-4
      atomic_oxygen_fluence_range: 1.4e20 to 7.2e21 atoms/cm2
    source: finckenor2008
    where: Table 1, Z-93 rows; Discussion and Conclusions
  - environment: Space, LDEF, 5.8 years in low Earth orbit (S0069 and A0034 trays, ram, wake and covered samples)
    headline: Z-93 with the original PS7 binder changed little after 5.8 years on LDEF, and its emittance did not change.
    effect: S0069 solar absorptance went from 0.14 before flight to 0.15 after. A0034 samples read 0.16 for ram-facing and 0.17 for wake-facing. Some samples were covered with quartz or aluminium to block atomic oxygen and UV, and they showed the same little change.
    rating: low
    conditions:
      exposure: 5.8 years in LEO on LDEF
      binder: PS7 (original)
    source: finckenor2008
    where: Section A, Zinc Oxide/Potassium Silicate, LDEF paragraph
  - environment: Space, silicone contamination on a Mir-facing and a space-facing POSA-I tray with 571 ESH of UV
    headline: Silicone contamination of about 5,000 Angstrom turned Z-93P yellow-tan and raised solar absorptance from 0.16 to 0.23.
    effect: Z-93P on the space-facing side of POSA-I received about 5,000 Angstrom of silicone contamination and only 571 ESH of UV, and its solar absorptance went from 0.16 to 0.23 over 18 months. The Mir-facing side had about 250 Angstrom and stayed close to beginning-of-life. The report says contamination of 300 Angstrom or less keeps the coating near its beginning-of-life value.
    rating: severe
    conditions:
      contamination_thickness: about 5,000 Angstrom (space-facing) and about 250 Angstrom (Mir-facing)
      duration: 18 months on Mir
    source: finckenor2008
    where: Section A, Zinc Oxide/Potassium Silicate, POSA-I paragraph and Figure 3
  - environment: Ground, VUV plus atomic oxygen in an RF plasma asher and an ECR beam, in vacuum and then in room air
    headline: VUV darkens Z-93 in vacuum, and exposure to air reverses part of that darkening, so the reading must be taken in situ.
    effect: Zinc oxide has a band gap of about 3.8 eV, so ultraviolet photons above that energy create electron-hole pairs that form colour centres. The authors say oxygen causes the reversal of colour-centre formation, so room-air exposure after ground VUV or combined VUV and atomic oxygen testing can make the damage look smaller than it is. In the first ECR combined test, Z-93 showed a moderate reduction in solar absorptance after exposure to air.
    rating: moderate
    conditions:
      environment: 'ground test: RF plasma asher and ECR atomic oxygen beam with deuterium VUV lamps, not flight'
    source: dever1993
    where: Damage Mechanisms to Coatings; Test I and Test II paragraphs; Abstract
  - environment: Ground, line-of-sight ECR atomic oxygen beam with silicone adhesive samples nearby
    headline: In a ground test with silicone present, Z-93 darkened far more than it does in space; the authors say the damage is not representative.
    effect: Z-93 exposed in the ECR beam near silicone adhesive showed a yellow-brown discolouration from silicone contamination, which the paper says is fixed by atomic oxygen with intense 130 nm VUV. The authors say the Z-93 degradation here is much more severe than in space. They also say that exposed silicone surfaces in LEO could severely contaminate nearby surfaces.
    rating: severe
    conditions:
      atomic_oxygen_fluence: 5.3e21 atoms/cm2 in the silicone test
      environment: ground test, not flight
    source: dever1993
    where: Effects of Atomic Oxygen, Intense VUV Radiation and Silicone Contamination on Coatings; Conclusions
  - environment: Ground and vacuum thermal cycling, -93 C to +49 C
    headline: Z-93 showed a negligible change in emittance and a small reduction in solar absorptance after 10 vacuum thermal cycles.
    effect: The 1993 test ran 10 cycles between -93 C and +49 C in vacuum. Z-93 showed a negligible change in emittance and a small reduction in solar absorptance, which the authors suspect is water loss on dehydration. Separately, MISSE-1 and MISSE-2 went through about 22,800 thermal cycles, mostly between +40 C and -30 C.
    rating: low
    conditions:
      cycles_ground: 10
      range_ground: '-93 C to +49 C'
      cycles_flight: about 22,800 (MISSE-1 and MISSE-2)
    source: dever1993
    where: Effects of Vacuum Thermal Cycling on Thermal Control Coatings; the 22,800 cycle figure from the 2008 report, Environment section
  - environment: Comparator, A-276 polyurethane with leafing aluminium on LDEF (not Z-93)
    headline: The polyurethane comparator A-276 started at a solar absorptance of 0.23 and reached 0.57 on wake-facing LDEF samples, so Z-93 holds up better for long missions.
    effect: A-276 is eroded by atomic oxygen and darkened by UV on LDEF, which the report calls well documented. Beginning-of-life solar absorptance was 0.23 plus or minus 0.03, ram-facing samples stayed near 0.30, and wake-facing samples read as high as 0.57. The report calls A-276 useful for short-term missions only.
    rating: severe
    conditions:
      comparator: A-276 polyurethane with leafing aluminium, not Z-93
    source: finckenor2008
    where: Section C, A-276 Polyurethane with Leafing Aluminum
risks:
  hazards:
    - text: 'The supplier SDS for zinc oxide (CAS 1314-13-2) classifies it as acute aquatic toxicity Category 1 (H400) and chronic aquatic toxicity Category 1 (H410): very toxic to aquatic life with long lasting effects. This is the zinc oxide pigment, not the finished Z-93 paint.'
      ghs:
        - H400
        - H410
      source: sigma-zno-sds
      where: Section 2.1 Classification and section 2.2 Label elements; product 96479, version 3.8
    - text: A potassium silicate coating SDS from another supplier (CSP Potassium Silicate Coating) classes the paint as acute oral toxicity Category 4 (H302), skin corrosion Category 1A (H314) and serious eye damage Category 1 (H318). Potassium silicate is listed at 30 to 35 percent. This is a different product and is used here only as a proxy for the silicate binder.
      ghs:
        - H302
        - H314
        - H318
      source: csp-kso-sds
      where: Section 2.1 Classification; section 3.2 Mixture, potassium silicate row
  failure_risks:
    - mode: Silicone contamination yellows the coating and raises solar absorptance
      trigger: Silicone outgassing or eroded silicone adhesive deposits on the radiator
      consequence: Z-93P on POSA-I rose from 0.16 to 0.23 in solar absorptance after about 5,000 Angstrom of silicone and 571 ESH of UV, which raises the radiator temperature.
      severity: high
      source: finckenor2008
      where: Section A, POSA-I paragraph and Figure 3
    - mode: Darkening from VUV is partly reversed by air, so ground numbers can understate or overstate damage
      trigger: Solar absorptance measured after air exposure rather than in situ after VUV or combined VUV and atomic oxygen exposure
      consequence: The 1993 test found a moderate reduction in solar absorptance for Z-93 after air exposure, and a dramatic reduction for YB-71 and Z-93-P, so the in situ reading is the valid one.
      severity: moderate
      source: dever1993
      where: Test I description and results paragraph after figure 6
    - mode: New binder version (Z-93P) behaves differently in one ground test
      trigger: Reformulation with Kasil 2130 potassium silicate in place of PS-7
      consequence: In the first ECR combined test, Z-93-P showed severe degradation at the first increment that the original Z-93 did not. The authors do not know the cause and suspect processing parameters.
      severity: moderate
      source: dever1993
      where: Test I results paragraph
    - mode: The binder supply can stop
      trigger: The supplier of the original binder stops making it
      consequence: Sylvania discontinued PS-7, which threatened continued supply of Z-93, YB-71 and S13G/LO-1. The Air Force funded a reformulation with Kasil 2130 from PQ Corporation.
      severity: moderate
      source: nasa-n95-14063
      where: Introduction and background, paragraphs on Sylvania PS-7 and IITRI reformulation
  side_effects:
    - text: Outgassing and molecular deposits from nearby materials are the main contamination risk for the white coating. The 2008 report says durability holds for years in LEO provided materials selection, venting design and contamination control limit outgassing.
      affects: The Z-93 surface and neighbouring radiator panels
      source: finckenor2008
      where: Discussion and Conclusions
    - text: Silicone adhesive that erodes or is contaminated can darken nearby surfaces. The 1993 asher test showed that silicones exposed to atomic oxygen contaminated nearby samples.
      affects: Nearby thermal control surfaces and solar array blankets
      source: dever1993
      where: Conclusions; RF plasma asher results paragraph
  handling:
    - text: 'Application: Z-93 is applied by low-pressure, high-volume spray. The 1993 test used a thickness of 0.10 to 0.13 mm to reach the target optical properties.'
      source: dever1993
      where: Materials Tested
    - text: The 1993 screening cycled samples 10 times between -93 C and +49 C in vacuum at about 0.013 Pa before testing, and measured optical properties before and after.
      source: dever1993
      where: Vacuum Thermal Cycling Exposure
    - text: 'Potassium silicate coating SDS (a different product): wear protective gloves and eye protection, wash thoroughly after handling, and avoid breathing spray mist. Store locked up.'
      source: csp-kso-sds
      where: Section 2.2 Precautionary statements, P260, P264, P280, P405
    - text: 'Zinc oxide SDS: collect spillage and dispose of contents to an approved waste disposal plant. Avoid release to the environment.'
      source: sigma-zno-sds
      where: Section 2.2 Precautionary statements, P273, P391, P501
  mitigations:
    - text: Measure solar absorptance in situ, or on the coupon before air exposure, in any ground VUV or atomic oxygen test. The 1993 authors state that this matters for white paints.
      source: dever1993
      where: Abstract; Damage Mechanisms to Coatings
    - text: Block the samples from line-of-sight 130 nm VUV in an ECR beam with fused silica fixturing, so they receive scattered atomic oxygen only.
      source: dever1993
      where: Directed Atomic Oxygen VUV Exposure Facility; Conclusions
    - text: Control silicone and outgassing sources near the coating, as the 2008 report recommends for inorganic white coatings.
      source: finckenor2008
      where: Discussion and Conclusions
uses:
  - application: thermal-control
    device: Space Station radiator coatings
    example: NASA selected Z-93 for use on the ISS radiators, based on its performance on LDEF, according to the 2008 MISSE review.
    source: finckenor2008
    where: Section A, Zinc Oxide/Potassium Silicate, first paragraph
  - application: thermal-control
    device: Space Station Freedom power-system radiator panels (candidate coating, 1993 tests)
    example: Z-93 was one of the candidate radiator coatings screened for Space Station Freedom, against a 30-year design life requirement, a beginning-of-life solar absorptance of 0.2, an end-of-life solar absorptance of 0.3 and a thermal emittance of 0.9.
    source: dever1993
    where: Introduction and Table I, SSF Thermal Control Coating Survivability Requirements
  - application: thermal-control
    device: Conductive white coating for geostationary spacecraft (Z93C55)
    example: NASA GSFC tested Z93C55, a conductive white coating, for end-of-life optical properties in geostationary orbit, and set an end-of-life solar absorptance requirement below 0.45 for a 15-year design value.
    source: hasegawa2018
    where: Introduction and End-of-Life Optical Property Evaluation
  - application: thermal-control
    device: MISSE flight experiments on the ISS and POSA-I on Mir
    example: Z-93 and Z-93P flew on MISSE-2 and MISSE-4 and on POSA-I, and Z-93P flew on OPM, per the 2008 MISSE review.
    source: finckenor2008
    where: Section A, Zinc Oxide/Potassium Silicate, Production of PS7 binder paragraph
supply:
  - subject: Zinc (feedstock for zinc oxide pigment)
    abundance: USGS identifies world zinc resources of about 1.9 billion tons.
    producers:
      - country: China
        mine_production_kt: 4100
        year: 2025
      - country: Peru
        mine_production_kt: 1500
        year: 2025
      - country: Australia
        mine_production_kt: 1100
        year: 2025
      - country: United States
        mine_production_kt: 670
        year: 2025
    critical_lists: []
    recycling: 'USGS: refined zinc produced in the United States was recovered from secondary materials at both primary and secondary plants.'
    substitutes:
      - 'USGS: many elements are substitutes for zinc in chemical, electronic and pigment uses.'
    source: usgs-mcs2026-zinc
    where: Mine production table (2025e, zinc content, thousand metric tons; world total 13,000); World Resources paragraph; Domestic Production and Use
  - subject: Potassium silicate binder (original PS-7 and replacement Kasil 2130)
    producers:
      - country: United States
        company: Sylvania (PS-7, discontinued)
        year: 1995
      - country: United States
        company: PQ Corporation, Baltimore, Maryland (Kasil 2130)
        year: 1995
    critical_lists: []
    recycling: Not stated in the sources read.
    substitutes:
      - The 1995 report says Kasil 2130 has an identical SiO2:K2O mole ratio of 3.3:1 to PS-7, and PQ said production would continue indefinitely.
    source: nasa-n95-14063
    where: Introduction and background, paragraphs on PS-7 and Kasil 2130
media: []
documents:
  - title: MISSE Thermal Control Materials with Comparison to Previous Flight Experiments (NASA, Finckenor, Pippin and Frey)
    type: report
    url: https://ntrs.nasa.gov/api/citations/20080031037/downloads/20080031037.pdf
    year: 2008
  - title: MISSE Thermal Control Materials with Comparison to Previous Flight Experiments (slide presentation, ICPMSE Toronto)
    type: report
    url: https://ntrs.nasa.gov/api/citations/20160011320/downloads/20160011320.pdf
    year: 2008
  - title: The Effects of Simulated Low Earth Orbit Environments on Spacecraft Thermal Control Coatings (NASA TM-106146, SAMPE 1993)
    type: report
    url: https://ntrs.nasa.gov/api/citations/19930017830/downloads/19930017830.pdf
    year: 1993
  - title: Evaluation of Thermal Control Coatings for use on Solar Dynamic Radiators in Low Earth Orbit (NASA TM-104335, AIAA 91-1327)
    type: report
    url: https://ntrs.nasa.gov/api/citations/19910013054/downloads/19910013054.pdf
    year: 1991
  - title: 'Evaluation of reformulated thermal control coatings in a simulated space environment, Part I: YB-71 (N95-14063)'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19950007650/downloads/19950007650.pdf
    year: 1995
  - title: End-of-Life Optical Property Predictions of White Conductive Thermal Control Coatings through Analysis of On-Orbit and Ground Based Testing Data (Hasegawa et al., NASA GSFC)
    type: paper
    url: https://ntrs.nasa.gov/api/citations/20180000013/downloads/20180000013.pdf
    year: 2018
  - title: 'Mineral Commodity Summaries 2026: Zinc (USGS)'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zinc.pdf
    year: 2026
  - title: 'Safety Data Sheet: Zinc oxide, Sigma-Aldrich product 96479, version 3.8 (copy hosted by Purdue University)'
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/zinc%20oxide%20%20-%20Aldrich.pdf
    year: 2015
  - title: 'Safety Data Sheet: CSP Potassium Silicate Coating (Cathedral Stone Products; copy hosted by Lancaster Lime Works)'
    type: sds
    url: https://lancasterlimeworks.com/wp-content/uploads/2025/10/Potassium-Silicate-Coating-SDS.pdf
    year: 2020
gaps:
  - No Alion or IITRI datasheet for Z-93 or Z-93P was found in this run. The formulation, pigment-to-binder ratio, solids content and curing schedule are not in any source read here.
  - No density, specific heat, thermal conductivity, outgassing (TML or CVCM) or atomic oxygen erosion yield for Z-93 was found in the sources read.
  - The 2008 slide gives about 1,500 ESH for the MISSE-3 trays, while the 2008 report's Table 1 gives about 1,200 ESH for Z-93 on MISSE-3. Both values are kept in the record and the disagreement is not resolved.
  - The 1991 Table V and Table VI ashing and VUV exposure doses are not restated in the report text read here; the exponents are not used in the file.
  - Solar absorptance air-mass basis (AM0 or AM1.5) is not stated for the Alion Z-93 rows; only the Deft polyurethane rows in the same report are labelled.
  - Z93C55 surface resistivity is only described as near or below 1E9 ohm/sq in Figure 1; no clean numeric value was read, so it is not in the properties.
  - No Z-93-specific safety data sheet was found. The hazard entries use a zinc oxide SDS and a different potassium silicate coating SDS, and neither is the Z-93 product.
  - Benchmark names solar_absorptance, thermal_emittance and delta_alpha come from the site registry. Areal mass and coating thickness are not in the registry and use snake_case names.
  - Zinc critical-mineral status (USGS critical minerals list and EU critical raw materials list) was not checked in this run. Country production shares are not printed in the USGS summary, so tonnages are given instead.
  - Post-flight data for ISS radiator panels using Z-93 were not found in the sources read; the flight data here are MISSE trays and LDEF and POSA-I samples.
  - Z93C55 is a separate conductive formulation and its values are kept under product conditions in the record; they are not Z-93 values.
  - Vacuum outgassing and mass-loss numbers for the Z-93 paint are not in the sources read.
sources:
  finckenor2008:
    title: MISSE Thermal Control Materials with Comparison to Previous Flight Experiments (Finckenor, Pippin, Frey, NASA MSFC and Boeing)
    id: NASA NTRS 20080031037
    url: https://ntrs.nasa.gov/api/citations/20080031037/downloads/20080031037.pdf
    year: 2008
    kind: report
    license: NASA public document (cited, not reproduced)
  finckenor2008-slides:
    title: MISSE Thermal Control Materials, slide presentation (Finckenor, Pippin, Frey), ICPMSE Toronto
    id: NASA NTRS 20160011320
    url: https://ntrs.nasa.gov/api/citations/20160011320/downloads/20160011320.pdf
    year: 2008
    kind: report
    license: NASA public document (cited, not reproduced)
  dever1993:
    title: The Effects of Simulated Low Earth Orbit Environments on Spacecraft Thermal Control Coatings (Dever, Rutledge, Bruckner, Stidham, Stueber, Booth; NASA TM-106146)
    id: NASA NTRS 19930017830
    url: https://ntrs.nasa.gov/api/citations/19930017830/downloads/19930017830.pdf
    year: 1993
    kind: report
    license: NASA public document (cited, not reproduced)
  nasa-tm104335-1991:
    title: Evaluation of Thermal Control Coatings for use on Solar Dynamic Radiators in Low Earth Orbit (NASA TM-104335, AIAA 91-1327)
    id: NASA NTRS 19910013054
    url: https://ntrs.nasa.gov/api/citations/19910013054/downloads/19910013054.pdf
    year: 1991
    kind: report
    license: NASA public document (cited, not reproduced)
  nasa-n95-14063:
    title: 'Evaluation of reformulated thermal control coatings in a simulated space environment, Part I: YB-71 (USAF Wright Laboratory and UDRI, IITRI reformulation)'
    id: NASA NTRS 19950007650 (N95-14063)
    url: https://ntrs.nasa.gov/api/citations/19950007650/downloads/19950007650.pdf
    year: 1995
    kind: report
    license: NASA public document (cited, not reproduced)
  hasegawa2018:
    title: End-of-Life Optical Property Predictions of White Conductive Thermal Control Coatings through Analysis of On-Orbit and Ground Based Testing Data (Hasegawa, Freese, Kauder, Triolo; NASA GSFC)
    id: NASA NTRS 20180000013
    url: https://ntrs.nasa.gov/api/citations/20180000013/downloads/20180000013.pdf
    year: 2018
    kind: paper
    license: NASA public document (cited, not reproduced)
  usgs-mcs2026-zinc:
    title: 'Mineral Commodity Summaries 2026: Zinc (U.S. Geological Survey)'
    id: USGS MCS 2026, zinc
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-zinc.pdf
    year: 2026
    kind: report
    license: Public domain (USGS)
  sigma-zno-sds:
    title: Safety Data Sheet, Zinc oxide, Sigma-Aldrich product 96479, version 3.8 (copy hosted by Purdue University)
    id: Sigma-Aldrich 96479 SDS, version 3.8
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/zinc%20oxide%20%20-%20Aldrich.pdf
    year: 2015
    kind: datasheet
    license: Supplier SDS (cited, not reproduced)
  csp-kso-sds:
    title: Safety Data Sheet, CSP Potassium Silicate Coating (Cathedral Stone Products; copy hosted by Lancaster Lime Works)
    id: CSP Potassium Silicate Coating SDS, 6/10/2020
    url: https://lancasterlimeworks.com/wp-content/uploads/2025/10/Potassium-Silicate-Coating-SDS.pdf
    year: 2020
    kind: datasheet
    license: Supplier SDS (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 28
  note: Written from NASA, USGS and supplier pages fetched in this run. Table 1 of the 2008 report, Table VI of the 1991 report and Tables 1, 3 and 4 of the 2018 paper were checked against rendered page images. Not yet re-read by verify-values.
story:
  recipe:
    line: Z-93 is zinc oxide pigment dispersed in a potassium silicate binder. The original binder was PS-7 (Sylvania), and Z-93P uses Kasil 2130 (PQ Corporation). The binder is applied as a liquid and dries to an inorganic film. The pigment-to-binder ratio is not published in the sources read.
    parts:
      - name: Zinc oxide
        symbol: ZnO
        role: White pigment. The zinc oxide band gap of about 3.8 eV absorbs ultraviolet, which forms colour centres under VUV.
      - name: Potassium silicate
        symbol: K2O and SiO2
        role: Inorganic binder. The SiO2:K2O mole ratio is 3.3:1 for PS-7 and Kasil 2130, and it reactively binds the pigment.
  risk_groups:
    - title: For people
      level: 0
      verdict: Hazardous in the supplier data we read
      lead: No Z-93 safety data sheet was found. Zinc oxide is classed as very toxic to aquatic life, and a potassium silicate coating from another supplier is classed as causing severe skin burns.
      points:
        - label: Zinc oxide
          line: 'The zinc oxide SDS gives H400 and H410: very toxic to aquatic life with long lasting effects. Avoid release to the environment.'
        - label: Potassium silicate
          line: The CSP potassium silicate coating SDS gives H314 (severe skin burns and eye damage) and H318, with H302 for oral harm. That is a different product.
        - label: Spray
          line: The coating is sprayed. Wear eye and skin protection, and avoid breathing the spray mist.
    - title: For the radiator
      level: 1
      verdict: Holds its optics in LEO, unless silicone contaminates it
      lead: The pigment stays stable in LEO. Silicone deposits are the main threat.
      points:
        - label: LDEF
          line: After 5.8 years on LDEF, solar absorptance went from 0.14 to 0.15 for S0069.
        - label: Silicone
          line: Silicone contamination of about 5,000 Angstrom took Z-93P from 0.16 to 0.23 on POSA-I.
        - label: Ground tests
          line: VUV in ground tests darkens the coating, and the darkening can reverse in air, so measure in situ.
    - title: Handling and storage
      level: 2
      verdict: Standard coating practice, plus contamination control
      lead: Apply by spray at the specified thickness and keep silicone and outgassing sources away.
      points:
        - label: Thickness
          line: The 1993 test used 0.10 to 0.13 mm, and the 1991 test found 4 to 5 mil gave minimum solar absorptance.
        - label: Contamination
          line: The 2008 report says durability holds for years when contamination control limits outgassing and molecular deposits.
  why: Z-93 is a white thermal control paint made of zinc oxide pigment in a potassium silicate binder, and NASA has flown it for years in low Earth orbit. On the MISSE-2 trays it kept a solar absorptance of 0.14 after 5,130 ESH and 5,660 ESH of UV, per the 2008 NASA report. Solar absorptance is the fraction of sunlight the surface absorbs, and thermal emittance is how well it radiates heat. Z-93 is a good fit for radiator surfaces where long-term stability in LEO matters, and it is the coating NASA chose for ISS radiators on the basis of its LDEF results.
  uses:
    - where: ISS radiators
      line: NASA selected Z-93 for ISS radiators on the basis of its LDEF performance, according to the 2008 report.
    - where: Space Station Freedom
      line: In 1993 Z-93 was screened as a radiator coating for Space Station Freedom, against a 30 year design life and an end-of-life solar absorptance of 0.3.
    - where: Geostationary conductive coatings
      line: NASA GSFC tested the conductive white coating Z93C55 for geostationary use, with an end-of-life solar absorptance requirement below 0.45.
    - where: MISSE and POSA-I
      line: Z-93 and Z-93P flew on MISSE-2, MISSE-4 and POSA-I, and Z-93P also flew on OPM.
  can_do:
    - label: Solar absorptance
      benchmark: solar_absorptance
      line: Z-93 kept 0.14 on MISSE-2 and rose to 0.15 on MISSE-4 after flight.
    - label: Emittance
      benchmark: thermal_emittance
      line: After oxygen plasma ashing, Z-93 kept a thermal emittance of 0.92 in the 1991 test.
    - label: Long-term LEO
      benchmark: solar_absorptance
      line: On LDEF, Z-93 changed little over 5.8 years, with solar absorptance at 0.15 after flight on S0069 and 0.16 to 0.17 on A0034.
  compare: Z-93 sits with the inorganic white coatings. Its sister coating YB-71 (zinc orthotitanate in potassium silicate) was tested alongside it in the 1991 and 1993 studies. Against the polyurethane A-276 with leafing aluminium, which started at 0.23 plus or minus 0.03 and reached 0.57 on wake-facing LDEF samples, Z-93 kept its optics much closer to beginning-of-life in the sources read. Z93C55 is a separate conductive formulation, with a beginning of life solar absorptance of 0.14 and normal emittance of 0.92 per the 2018 paper, and it is not interchangeable with Z-93.
  compare_rows:
    - label: Solar absorptance on flight trays
      benchmark: solar_absorptance
    - label: Thermal emittance after ashing
      benchmark: thermal_emittance
    - label: Areal mass after ashing
      benchmark: areal_mass
  handling:
    - Apply by low-pressure, high-volume spray at the specified thickness, as the 1993 test did.
    - Keep silicone adhesives and outgassing materials away from the coating, because silicone contamination is the main threat in flight.
    - 'Use the zinc oxide and potassium silicate SDS guidance until a Z-93 SDS is obtained: avoid release to the environment and wear eye and skin protection.'
  good_for:
    - 'Radiators in low Earth orbit: flight trays kept solar absorptance at 0.14 to 0.15 after MISSE-2 and MISSE-4 exposure.'
    - 'Long missions with low contamination: the 2008 report says the optics hold for years when contamination is 300 Angstrom or less.'
    - 'Places with atomic oxygen and UV: the 2008 report says the inorganic binder held up while organic polyurethane coatings eroded.'
  watch_out:
    - 'Silicone contamination yellows the coating: Z-93P rose from 0.16 to 0.23 on POSA-I.'
    - Ground VUV tests exaggerate darkening, and the reading must be taken in situ or before air exposure.
    - Z-93P and the original Z-93 do not behave the same in every test, and the cause is not known.
  verdict: Z-93 is the proven inorganic white radiator paint for LEO. It keeps its optics through flight when silicone contamination is controlled, and its ground data are reliable only when measured in situ.