Foam Hydrogen Sulfide (H2S) Corrosion Testing: Standards, Methods and Applications

Foam hydrogen sulfide (H2S) corrosion testing evaluates the resistance of polymeric foam materials—such as polyurethane, EVA, PE, silicone and EPDM foams—to corrosive sulfur-bearing atmospheres, and quantifies their tendency to release volatile sulfur compounds that tarnish or corrode adjacent metal components. Performed in accredited third-party laboratories in accordance with recognized standards such as IEC 60068-2-43, IEC 60068-2-60, ASTM B845 and GB/T 2423.20, this testing is essential for verifying the long-term reliability of foam gaskets, cushions and sealing pads used in electronics, automotive and industrial equipment. This article explains the test principles, sample types, testing items, methods, evaluation criteria and typical applications of H2S corrosion testing for foams.

Technical Overview

Polymeric foams such as polyurethane (PU), ethylene-vinyl acetate (EVA), polyethylene (PE), silicone and EPDM are widely used as sealing gaskets, cushioning pads, vibration isolators and EMI shielding components in electronic devices, vehicles and industrial equipment. In actual assemblies, these foams are frequently in intimate contact with silver-, copper-, tin- and nickel-plated connectors, antennas, shields and flexible circuits, so their chemical compatibility with surrounding parts directly affects product reliability.

Hydrogen sulfide (H2S) is among the most aggressive corrosive gases encountered in service environments. Originating from industrial processes, fossil fuel combustion, decaying organic matter and sewer systems, it is present in ambient air at ppb-to-ppm levels and reaches much higher concentrations in petrochemical plants, pulp and paper mills, wastewater treatment facilities and livestock environments. Even trace amounts of H2S react rapidly with silver and copper to form dark sulfide films (Ag2S, Cu2S, CuS) that discolor surfaces, raise contact resistance and can ultimately cause intermittent or permanent electrical failure.

Foam hydrogen sulfide corrosion testing therefore serves two complementary objectives:

• Evaluating the resistance of the foam itself to H2S-containing atmospheres, including discoloration, embrittlement, mass change and retention of mechanical properties after accelerated exposure.
• Determining whether the foam, its compounding ingredients (sulfur-based curing agents, accelerators, flame retardants, blowing-agent residues) or its pressure-sensitive adhesive releases volatile sulfur compounds that migrate to, and corrode, adjacent metal components.

Tests are performed in programmable corrosion chambers under precisely controlled gas concentration, temperature and humidity, and are commonly carried out by accredited third-party laboratories against internationally recognized standards such as IEC 60068-2-43, IEC 60068-2-60, ASTM B845 and their Chinese counterpart GB/T 2423.20.

Testing Samples

The following foam categories are routinely submitted for hydrogen sulfide corrosion evaluation:

Polyurethane (PU) Foam

Microcellular and standard PU foams used for shock absorption, gap filling and sealing in consumer electronics. Testing focuses on residual amine catalysts, siloxane volatiles and any sulfur-bearing additives that could attack plated contacts.

EVA and PE Foam

Foamed ethylene-vinyl acetate and polyethylene sheets and tapes used as frame sealing pads, packaging inserts and thermal insulation. Peroxide crosslinking residues and adhesive layers are the primary outgassing sources investigated.

Silicone Foam

High- and low-temperature silicone foam gaskets used in lighting, battery and telecom hardware. Both platinum-cured and peroxide-cured grades are evaluated for volatile species that may tarnish silver finishes.

EPDM Foam

Sulfur-vulcanized EPDM is a classic source of sulfur emission that blackens silver-plated terminals in displays and televisions, so both sulfur-cured and peroxide-cured EPDM sealing foams are screened accordingly.

Conductive and Composite Foams

Conductive fabric-wrapped EMI gaskets, foam-core laminates and foam tapes with pressure-sensitive adhesives, where corrosion of the metallized layer or of nearby connectors must be controlled.

Sample Preparation Requirements

• Typical specimen size of 50 mm x 100 mm or 100 mm x 100 mm at supplied thickness, with a minimum of three pieces per test condition plus a retained reference sample.
• Conditioning at 23 ± 2 °C and 50 ± 5 % relative humidity for at least 24 hours in accordance with ISO 291 prior to exposure.
• Handling with powder-free gloves and clean tools to prevent contamination of the specimen surface and the metal coupons.

Testing Items

Depending on the engineering requirement, a foam H2S corrosion evaluation may include the following items:

• H2S atmosphere corrosion resistance of the foam: appearance, dimensions, mass change and surface condition after exposure.
• Volatile sulfur emission (corrosivity) screening using silver and copper coupons placed in contact with, or in close proximity to, the foam.
• Contact resistance of coupons measured before and after exposure by the four-terminal (Kelvin) method.
• Coupon mass gain per unit area as an indicator of sulfide film growth.
• Corrosion product identification by SEM/EDS, XPS or XRD to confirm sulfide formation.
• Total sulfur content of the foam determined by combustion ion chromatography or elemental analysis.
• Identification of volatile sulfur species (mercaptans, sulfides, carbonyl sulfide) by headspace GC-MS.
• Retention of functional properties after exposure: Shore hardness, tensile strength and elongation, compression set and flame-retardant performance.

Testing Methods

Static Hydrogen Sulfide Exposure Test (IEC 60068-2-43 / GB/T 2423.20)

Foam specimens and reference coupons are exposed in a sealed chamber to an atmosphere of 10-15 ppm H2S at 25 ± 2 °C and 75 ± 5 % relative humidity. Standard durations are 4, 10 or 21 days, selected according to the intended service severity. After exposure, coupons are rated visually against photographic references, contact resistance is remeasured, and the foam is inspected for discoloration and degradation. This procedure corresponds to IEC Test Kd for contacts and connections.

Sealed-Vessel Sulfur Emission Coupon Test

To screen for corrosive volatiles, the foam specimen and a polished silver or copper coupon are sealed together in a clean glass vessel and held at an elevated temperature (typically 40-80 °C) with high humidity for 24-240 hours. A blank vessel without foam runs in parallel as a control. Tarnishing of the coupon beyond the control level indicates the emission of free sulfur or sulfur-donor species from the foam, its adhesive or its additives. Many electronics manufacturers impose internal limits on total sulfur content, commonly in the low mg/kg range, based on this type of evidence.

Flowing Mixed Gas Test (IEC 60068-2-60 / ASTM B845 / GB/T 2423.51)

Where a realistic multi-pollutant environment is required, specimens are exposed to flowing gas mixtures containing ppb-level H2S together with NO2, SO2 and/or Cl2 at controlled temperature (approximately 25-30 °C) and humidity (approximately 70-75 % RH) for 4-21 days. The mixed flowing gas method reproduces the synergistic corrosion chemistry of industrial and urban atmospheres and is widely used for long-life telecom, automotive and infrastructure hardware.

Thioacetamide Tarnish Test (ISO 4538)

As a complementary laboratory method, thioacetamide vapor generates H2S in situ under high humidity, providing a controlled sulfur-bearing atmosphere for assessing the tarnish sensitivity of coupons coupled with the foam under evaluation.

Evaluation and Analysis

Results are assessed by visual classification of coupon discoloration, quantitative contact-resistance change, mass gain per unit area, and microscopic-chemical confirmation of sulfide films. Test reports document the exposure conditions, coupon materials, before-and-after data, photographic records and conformity with the applicable acceptance criteria.

Applications

Foam H2S corrosion testing supports material selection, supplier qualification and failure analysis across many industries:

• Consumer electronics: sealing and cushioning foams adjacent to silver-plated connectors, display bezels, camera modules and antenna elements in smartphones, tablets, notebooks and televisions.
• Automotive and electric vehicles: battery-pack sealing foams, in-cabin electronics gaskets and sensor module cushions governed by OEM sulfur-emission specifications.
• Telecommunications and data centers: cabinet gaskets and board-level foam cushions exposed long-term to polluted indoor and outdoor air.
• New energy systems: photovoltaic junction boxes, inverter enclosures and energy-storage modules where foams operate near plated busbars and terminals.
• Industrial and petrochemical plants: instrument and control-cabinet foams installed in H2S-rich process environments.
• Rail transit, aerospace and medical devices: interior foams, enclosure seals and components located near silver-coated optical or sensing elements.

FAQ

Why is non-metallic foam tested for corrosion?

Foams do not corrode electrochemically like metals, but they can degrade in H2S atmospheres and, more importantly, can release volatile sulfur compounds that corrode adjacent silver, copper and other sensitive metals. The test addresses both the durability of the foam and its corrosivity toward surrounding components.

What test conditions and durations are typical?

The most common protocol is IEC 60068-2-43: 10-15 ppm H2S, 25 °C and 75 % RH for 4, 10 or 21 days. Sealed-vessel coupon screening typically runs 24-96 hours, while flowing mixed gas tests run 4-21 days at ppb gas concentrations.

Which metal coupons should be used?

Silver is the most sensitive indicator of sulfide corrosion and mirrors silver-plated contacts; copper is the most widely used general indicator. Nickel, tin or gold-flashed coupons may be added to match the finishes actually present in the assembly.

What sample size and quantity are required?

Pieces of approximately 50 mm x 100 mm at the supplied thickness are usually sufficient, with at least three specimens per condition plus a retained reference sample, conditioned for 24 hours at 23 °C and 50 % RH before testing.

How are test results judged?

Acceptance criteria are normally defined by the customer or product specification. Typical requirements include no visible sulfide tarnish on the silver coupon, contact-resistance change below a stated limit, limited coupon mass gain, and total sulfur content below the specified mg/kg threshold.

How does the H2S test differ from the mixed flowing gas test?

The single-gas H2S test is faster and more severe and isolates sulfide chemistry, making it ideal for screening. The mixed flowing gas test combines several pollutants at ppb levels and better reproduces real service atmospheres, making it suitable for long-life qualification programs.

Are special safety precautions needed?

Yes. H2S is toxic and flammable even at low concentrations, so tests must be conducted by trained personnel in dedicated corrosion chambers equipped with gas monitoring, ventilation and exhaust scrubbing, as found in accredited third-party laboratories.