Silver Metal Filter Membranes are pure metallic silver (99.97% pure silver) and are available with particle retention ratings of 0.45 or 0.8 microns. Silver metal membranes are used in a variety of filtration applications, and their ability to withstand extreme chemical and thermal stress makes them ideal for applications involving aggressive fluids and/or high temperatures.
Features:
- 99.97% pure silver
- High temperature resistance
- High chemical resistance
- Economical - can be cleaned & reused
- Smooth surface for particle capture and easy observation
Silver membranes are composed entirely of pure metallic silver. They combine excellent chemical resistance and high temperature characteristics with an absolute retention range of 0.45 µm or 0.8 µm.
Although silver membranes are used in a large number and variety of applications, their unique chemical and thermal stability is especially valuable for those applications involving aggressive fluids and/or high temperatures. They are ideal collection media for analysis of crystalline silica by X-ray diffraction and for analysis of organic materials by other instrumentation techniques, such as the analysis of polyaromatic hydrocarbons (PAH).
Chemical and Thermal Properties
Silver membranes have the chemical inertness and high thermal stability of pure silver. They are resistant to alcohol's, fuels and hydrocarbons, natural and synthetic oils, alkalis, cryogenics, photoresists, ethers, propellants, oxidizers, halogenated hydrocarbons, esters, and most organics and acids. Under normal conditions, the silver membrane is attacked only by cyanide solutions and nitric and sulfuric acids.
Silver membranes provide excellent filtration performance at temperatures from cryogenic up to 1022°F (550°C). They may be repeatedly autoclaved and can be sterilized with steam or hot air.
High Strength
In the manufacturing of the silver membrane, the size and orientation of the silver particles are closely controlled and uniformly deposited in sheet form. The points of contact between the silver particles are then molecular bonded into a homogeneous material that resists pore collapse even under conditions of high temperature and pressure. They can be used in low intensity ultrasonic baths without fear of loss of integrity.
Nominal Retention
The careful control of the manufacturing process yields unusually precise pore size and uniformity. Performance tests indicate that nominal particle retention is achieved as the result of simple mechanical sieving by the filter structure. Thus, particle retention by the silver membrane is independent of random electrostatic charges or other extraneous, unpredictable molecular forces.
The surface of the silver membrane is flat and smooth which allows surface capture. There is minimum background interference from the silver when using X-ray diffraction.
No Fiber Release - No Media Migration
Conventional tortuous pore membranes and other filters often shed fibers or parts of the filter material itself. With changing conditions of flow and pressure drop, pores may change in size which allow previously filtered contaminants to migrate through the filter medium and to contaminate the filtrate. In the case of silver membranes, there are no fibers, and because the silver membrane is a strong uniform porous monolithic structure where the silver particles are molecularly bonded to each other, there is no media migration.
Shelf Life
The shelf life of silver membranes is indefinite when kept in sealed packages. However, since the silver membrane is pure silver, it can become tarnished when exposed to some chemicals in the air. This is a cosmetic imperfection and the filtration properties are not affected in any way.
The most common tarnishing compounds will cause the membrane to turn black in the case of Ag2S and dark brown in the case of AgCl. AgCl is simple to remove, requiring only a rinse with an ammonia solution. Ag2S is very stable, and is difficult to remove from the membrane without altering the structure. Thus, it is important that silver membranes be kept in a sealed package.
These compounds should not be confused with the natural grayish white appearance of the silver membrane filter surface. This appearance is due to the microporous structure of the membrane, which reflects light in a different way than polished silver.
