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Frequently Asked Questions: Surface Treatments

  1. How do I select the most appropriate treatment for my application?
  2. What are the operating temperatures for treated surfaces?
  3. What is Siltek Deactivation?
  4. What are the unique benefits of Siltek deactivation?
  5. Does anyone else offer an equivalent to Siltek deactivation?
  6. What is the maximum temperature limit for Siltek deactivated glass?
  7. Does Restek offer custom surface treatments?
  8. Will you re-deactivate my Siltek treated glass liners or treated Siltek metal liners after I clean them?
  9. How tightly can the tubing be bent?
  10. What materials can be surface treated?
  11. How will surface treatments work in my acidic environment?
  12. How thick is the Siltek layer?
  13. Are secondary deactivations available for Sulfinert treated materials?
  14. Can ferrules be treated?
  15. Why is Siltek on glass gold in color?
  16. Why do Silcosteel treated pieces have different colors?

If your question doesn’t appear on the list, you can contact Restek’s expert chemists. (Please remember to include your company name and complete mailing address. Thanks!)




  1. How do I select the most appropriate treatment for my application?

  2. The following definitions explain the various treatments currently available and their recommended applications:

    • Siltek Provides the ultimate passivation of treated surfaces, from glass to high nickel alloys of steel.
    • Silcosteel A general purpose passivation layer for steel and stainless steel.
    • Silcosteel-CR A corrosion resistant layer that increases the lifetime of system components in environments containing hydrochloric, nitric, or sulfuric acid.
    • Sulfinert A required treatment for metal components used in analyzing for parts-per-billion levels of organo-sulfur compounds.

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  3. What are the operating temperatures for treated surfaces?

  4. Maximum temperatures usually will be dictated by the construction material (glass, stainless steel, etc.), not by the surface treatment. In general, temperatures should not exceed those listed in Table I. Temperatures greater than 450°C for Sulfinert or Siltek treated surfaces or greater than 600°C for Silcosteel or Silcosteel-CR treated surfaces can be used under certain conditions. Heat treatment of parts before applying a Silcosteel or Silcosteel-CR coating extends the maximum temperature limit. Please contact technical support at (800)356-1688, ext. 4 for additional information.

    Table I
    Coatings are stable to the following temperatures in an inert atmosphere:

    Sulfinert450°C
    Siltek450°C
    Silcosteel600°C
    Silcosteel-CR600°C

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  5. What is Siltek Deactivation?

  6. Siltek deactivation (U.S. patent 6,444,326) is a passivation process that applies an inert, integral layer to components used for chromatographic analysis. Unlike traditional deactivations, it is not susceptible to cleavage or formation of active silanols and, therefore, greatly reduces bleed, and breakdown or adsorption of active components, compared to conventional surface coatings.

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  7. What are the unique benefits of Siltek deactivation?

  8. Siltek deactivation creates a unique surface with an inertness range that surpasses all other known surface deactivations used in gas chromatography. In sensitive analyses, Siltek deactivated system components provide outstanding results.

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  9. Does anyone else offer an equivalent to Siltek deactivation?

  10. No. Siltek deactivation was created exclusively by Restek (now owned by SilcoTek) and is protected by a US patent (Pat. No. 6,444,326).

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  11. What is the maximum temperature limit for Siltek deactivated glass?

  12. Maximum temperatures usually will be dictated by the composition of the glass, not by the surface treatment. The Siltek layer is stable at temperatures up to 450°C, but some glasses can soften at lower temperatures. Injection port temperatures normally are well below the Siltek maximum temperature limit, so Siltek treatment is an excellent deactivation for all injection port surfaces.

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  13. Does Restek offer custom surface treatments?

  14. For any custom coatings, Restek recommends that the customer deal directly with SilcoTek. Visit www.silcotek.com or call them at 814-353-1778.

    On January 1, 2009, the Restek Performance Coatings Division became SilcoTek Corporation, an independent company led by Restek Founder Paul Silvis and members of the Performance Coatings team. The company focuses on developing new coating technologies for the process, analytical, gas, oil and semiconductor markets.

    The creation of independent SilcoTek Corporation was part of Restek Corporation’s January 1, 2009 transition to 100 percent employee ownership under an ESOP structure. That move, which had been a part of the company’s corporate planning since its inception in 1985, was designed to ensure Restek’s stability and continued growth while maintaining its status as an independent chromatography consumables manufacturer.

    SilcoTek remains a key supplier to Restek, and Restek in turn continues to offer Siltek, Sulfinert, and Silcosteel coated products for chromatography markets.

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  15. Will you re-deactivate my Siltek treated glass liners or treated Siltek metal liners after I clean them?

  16. Restek no longer offers re-deactivation of Siltek treated glass liners. If you are interested in re-deactivation of Siltek treated glass liners, please contact SilcoTek's Customer Service department (814-353-1778 or silcod@SilcoTek.com) A minimum number of liners to be re-deactivated will be required.

    Siltek metal inlet liners are designed as inexpensive, disposable products and it is not cost effective to re-treat them. We recommend discarding them when they are no longer serviceable.

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  17. How tightly can the tubing be bent?

  18. ODMin. Bend Radius
      1/16"
    1/8"
    1/4"
    3/8"
      1" (2.5cm)
    2" (5.1cm)
    4" (10.2cm)
    6" (15.2cm)
    Yes No

    Note: If tight bends are necessary, use a treated elbow union or pre-bend the tubing and contact SilcoTek for a custom treatment.

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  19. What materials can be surface treated?

  20. Virtually all alloys of stainless steel, ceramic, and most glass materials can be treated. Some other metallic materials, such as nickel, brass, copper, and aluminum, are incompatible with the high (400°C) temperatures used in the process, and should not be treated.

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  21. How will surface treatments work in my acidic environment?

  22. Silcosteel, Sulfinert, and Siltek treated materials have improved corrosion resistance, but Silcosteel-CR surface treatment is optimized to enhance resistance to hydrochloric, nitric, and sulfuric acids. It provides a 10-fold improvement in corrosion resistance, compared to untreated stainless steel, and a 4-fold improvement compared to Silcosteel-coated stainless steel.

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  23. How thick is the Siltek layer?

  24. Depending on the item, the Siltek layer can be as much as 1,200 Angstroms thick. At this thickness, the layer exhibits a reflective silver color on treated glass surfaces or a rainbow on metal surfaces. Chromatographic performance does not depend on the thickness of the layer.

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  25. Are secondary deactivations available for Sulfinert treated materials?

  26. There are no secondary deactivations available for Sulfinert products at this time.

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  27. Can ferrules be treated?

  28. No. We have found this will consistently lead to leaking problems after coating.

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  29. Why is Siltek on glass gold in color?

  30. The color of a surface coating is an expression of the light diffraction qualities and thickness of the layer. The thickness of a Siltek layer determines the degree of darkness, secondary reflectivity, and/or final color of the item. The color can range from light golden-brown (thin coatings) to reflective silver (heavier coatings). A layer that provides a gold color is deposited on inlet liners to aid analysts in inspecting for cleanliness. Chromatographic performance does not depend on the thickness of the layer.

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  31. Why do Silcosteel treated pieces have different colors?

  32. The different colors observed on Silcosteel treated parts indicate different layer thicknesses. A blue color corresponds to a 300 to 450 Angstrom layer while a rainbow color indicates a coating of at least 1200 Angstroms.

    Colors associated with layer thickness are:

    Thick depositions used in Silcosteel-CR processes are 5µm to 20µm deep and have a silver/metallic grey appearance. The photos below show colors created by Sulfinert (left) and Silcosteel-CR (right) deposition.

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