The SPI Silver Membrane filters are so different from the more common polymer
membranes that we thought it important to lay out some of the unique and unusual
characteristics that make the silver system so attractive for so many users
Chemical and Thermal Properties
SPI Silver membrane filters have the chemical inertness and high thermal stability of pure silver. They are resistant to alcohols, fuels and hydrocarbons, natural and synthetic oils, alkalies, cryogenics, photoresists , ether, 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.
The SPI 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.
In the manufacturing of the SPI silver membrane filters, 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 molecularly 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 with no loss of integrity.
Careful control of the manufacturing process yields unusually precise pore size and uniformity. Performance tests indicate that absolute 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, allowing surface capture. There is minimal 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 allowing previously-filtered contaminants to migrate through the filter medium and to contaminate the filtrate. In the case of the 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.
High Flow Rates
The SPI Silver Membranes are very thin (0.002"/ 50 µm) and this fact, when combined with a characteristically high void volume allows for exceptionally good flow rates (and low pressure drops).
Non-Absorptive and Non-Adsorptive
Many conventional membranes will absorb or adsorb constituents out of a solution and thereby alter analytical results. This is avoided with silver membranes due to the chemical resistance and intertness of pure silver and smoothness of the interstices within the membrane. Absorption and adsorption by silver membranes is virtually nonexistent.
Minimum Fluid Holdup
The thinness, characteristic non-adsorption and non-absorption and the smoothness of the interstices of the SPI Silver Membrane filters means retention of an insignificant quantity of filtrate.
Intrinsic Bacteriostatic Nature
The intrinsic bacteriostatic property of silver does not allow the growth of bacteria and other microorganisms.
Although the initial cost of the SPI Silver Membranes is higher than conventional "single use and discard" polymeric membranes, the silver is more economical in many applications because it can be used repeatedly by chemical cleaning, ignition cleaning, plasma etching and cleaning, or a combination of the three.
Cleaning and Reuse of SPI Silver Membrane Filters
The SPI Silver Membrane filters can be cleaned and reused repeatedly, in most instances. The membrane should be cleaned immediately after each use, and handled carefully to avoid membrane punctures or tears. Various cleaning procedures can be used, depending on the nature, type, and degree of contamination. There are potentially five effective cleaning methods, depending on circumstances, that can be used to clean silver membranes:
Placing the silver membrane filter in a laboratory muffle furnace for approximately 30 minutes will effectively remove organic contaminants from the membrane. Do not exceed the following temperatures:
Retention Maximum Temperature Rating µm °C / °F -------------- ---------- 5.0 550/1022 3.0 400/752 1.2 350/662 0.8 300/572 0.45 300/572 0.2 250/482
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