Frequently Asked Questions

We have a Chemical Compatibility Chart that you can use for reference.

We can not recyle your filters.  However, we have used Sims Recyling for many years (https://www.simslifecycle.com/) to recycle our scrap silver. 

Q: Can silver membrane filters be sterilized with ethylene oxide (EtO)?
A: EtO sterilization is not recommended for silver membrane filters.  There is a possibility that residual acetylene in the EtO can produce explosive silver acetylide capable of detonating the EtO vapor.

A. There is no predetermined shelf life for the silver membrane. The filters should be stored sealed in the original packaging until needed.  Over time, silver compounds may form on the surface of the membrane.  Any resulting surface discoloration is essentially cosmetic and does not affect filter performance.

Q. Can silver metal membranes be cleaned?

A. Sterlitech™ Silver Membranes: Cleaning Guidelines

Sterlitech’s Silver Metal Membrane Filters can be cleaned and reused repeatedly. The membranes should be cleaned immediately after each use, and handled carefully to avoid membrane punctures and tears. Various cleaning procedures can be used, depending on the nature, type, and degree of contamination. There are four effective cleaning methods outlined below, that can be used to clean Sterlitech’s silver metal membrane filters.

Chemical Cleaning

Immerse in a strong alkaline solution, a solvent, or an acid. Do not immerse in nitric acid, sulfuric acid, or cyanide solutions.

Ignition Cleaning

Place the silver metal membrane filter in a laboratory muffle furnace for approximately ½ hour to effectively remove organic contaminants from the membrane. Do not exceed the following temperatures.

Combination Cleaning

A combination of chemical and ignition cleaning may be the best method to completely regenerate the membrane. Immerse in a 10 percent concentration of hydrofluoric acid for ten minutes, followed by ignition cleaning in a muffle furnace, following the guidelines given above. This can allow for reuse of membrane up to 10 times.

Ultrasonic Cleaning

Low intensity ultrasonics can be used to clean the silver metal membrane. The cleaning intensity and time will depend on the degree and type of contamination encountered. Do not use high intensity ultrasonics.

Q. What if my membrane is slightly discolored?

A. Although the silver metal membrane is 99.97% pure silver, the formation of extraneous compounds is possible over time. For example, silver can become tarnished, especially when the environment contains certain emissions as described below. To minimize contamination of the membrane, leave it in sealed packs. Silver compounds may form on the surface which are primarily cosmetic imperfections and do not affect the pore structure or membrane filtration performance. Examples of colored compounds that can form on the surface of the silver metal membrane are:

• Ag₂S (black)
• Agl (yellow)
• Ag₃PO₄ (yellow)
• Ag₂CrO₄ (dark red)
• AgCl (dark brown)
• Ag₂O (dark brown)
• AgBr (light yellow)

The most common compounds that form on the silver metal membrane are Ag2S and AgCl. AgCl is a photosensitive salt that can be removed by flushing the membrane with an ammonia solution. Typically, just a brief soak or dip in the ammonia solution will dissolve AgCl. Ag2S is a very stable compound and is very difficult to remove from the membrane without altering the structure. A flush with methyl or ethyl alcohol can be used to remove some of the other compounds.

These compounds should not be confused with the natural grayish white appearance of the silver metal membrane surface. This appearance is due to the microporous structure of the media which reflects light in a manner different than polished silver. The slight difference in color between the two sides of the membrane is due to the manufacturing process and is most noticeable on 3 and 5 micron pores sizes.

Q. What are the advantages of silver metal membranes over conventional membranes?

A. Sterlitech™ Silver Metal Membranes are 99.97% pure, thus unique in their ability to withstand extreme chemical and thermal stress, making them ideal for applications involving aggressive fluids and/or high temperatures. In addition, the purity of the membranes enables users to easily exclude and account for the few chemicals that react with silver, thus making test results and filtering operations more precise than available through traditional membranes.