|
|
Advanced R &D, Inc.
|
|
|
|
|
Advanced R & D has long been recognized as a leader in Surface Chemistry and methods and technology involving CLEANING Surfaces. This has lead to an understanding of products designed for cleaning many materials under most conditions. It has also lead to understanding CORROSION and special products designed to prevent corrosion. This brief discussion provides a clearer understanding of the importance and role of cleaning; what to look for in cleaning products, HOW , WHEN, and WHERE they might be applied and what considerations are important.:
What is a SURFACE ?
"SURFACE" is a vague
and ambiguous term but it is WHERE corrosion begins.
"SURFACE" is more explicitly described using the following
illustration. In industrial applications, the term "Surface"
is not merely a flat two dimensional plane as in mathematics. To
properly understand Surface Chemistry, Contamination, Corrosion, and
Cleaning, the term "SURFACE" must imply a degree of
thickness, often on a very microscopic scale; or molecular level.
Although surface roughness and physical shape etc. have effects,
almost all initial interactions begin at the atomic ( molecular )
scale. This chemistry dictates the performance of the surface,
corrosion, adhesion, friction, reactivity, etc. Macro features
including surface roughness, texture, shape, pits, cracks, scratches,
etc. have a more general effect in collection of debris, retention of
contaminants, formation of electrochemical centers, and abrasion. This Figure of a "Typical Surface" illustrates the four major layers found on virtually every solid surface. The chemical composition of the "Surface" is always different than the chemistry of the substrate or bulk material. The bulk material may be steel, Aluminum, brass, zinc, polypropylene, polystyrene, etc. but the surface composition is very different than this. These four layers include: 1. A BULK substrate ( such as the metal or polymer), two. A normal OXIDE layer, 3. A Prepared or intentional layer, and 4. A very outer layer that is generally unknown and not easily controlled. This outer layer is usually very rich in contaminants. On top of this contaminant layer may be additional material, such as air, water, and organic material that is not chemically attached but may eventually react. The thickness of each layer is as important as its composition.
These two figures illustrate the contaminants that
can be found on normal 'clean ' steel. The one on the left
illustrates ISS depth profile spectra showing changes in chemical
composition vs. depth. The figure on the right illustrates how these
data can be used to construct an approximation of the distribution of
various elements in this the outer layers of a surface; each row
representing one or two atomic layers.
For many metals, such as steel, the oxide layer is
about 40 to 60 Angstroms thick ( about 1/6 of one microinch; about
1/200th of a micron, or about 20 to 30 layers of atoms). The
contamination layer may be less than a complete atomic or molecular
layer or several mils thick ( more than 0.001" ). Often
contaminant layers cannot be observed visually or they may be very
thin and cause unusual discoloration.
Advanced R & D laboratory has used very
sensitive and sophisticated instrumental techniques to analyze
surface chemistry of wide range of materials for over 20 years. More
extensive explanation of these techniques is available upon request.
Through these analyses, Advanced R & D has provided much better
understanding about surface chemistry and how it affects Corrosion,
Contamination, Cleaning, and Adhesion. Many companies have used this
information to solve industrial manufacturing problems and to improve
their own products. What is SURFACE CONTAMINATION ?
The term "Contamination" is also
misleading. What is considered extremely gross contamination in one
case may be impossible to see visually. Conversely, what appears by
eye to be very crude contamination may have no measurable effect
on product performance. Yet, Surface Contamination is a major cause
for corrosion, but sometimes it may actually prevent corrosion.
................. Concentration Thickness
................. Distribution
Product Application
In general, it takes only a very thin layer of
contamination of the right type at the right concentration to
initiate corrosion, prevent adhesion, or cause discoloration. Very
sophisticated surface analysis techniques have been used in
pioneering the development of corrosion inhibitors and cleaning
products. Advanced R & D has provided much of this information.
There are four major analytical instrumental techniques commonly
considered applicable to analysis of these thin outer surface layers.
They include ISS ( Ion Scattering Spectroscopy ), SIMS ( Secondary
Ion Mass Spectroscopy), XPS ( X-ray Photoelectron Spectroscopy - also
termed ESCA ), and AES ( Auger Electron Spectroscopy). What happens DURING Cleaning of Surfaces?
Product performance depends intimately on surface cleanliness before, during, and after manufacture. Many components require cleaning before preprocessing, at several stages of processing and after final production or assembly. CONTAMINATION and / or CORROSION may start at any stage. The concept and understanding of the term "Cleaning" is often used loosely and vaguely. It is clarified below. Over the past 20 years, we have helped hundreds of companies in hundreds of different applications understand their products, their cleaning requirements, and their operations -- and their Product Failures. The following considerations apply to each product, product change, and company
Some components ( such as machined metals ) may be
severely contaminated before cleaning; some ( such as electronic
devices and medical implants ) may be extremely clean. Others may
have extremely stringent requirements for surface cleanliness after
cleaning; some may not be crucial. The same cleaning process in one
case may permit use of solutions many times for many batches; other
cases may require fresh cleaning solutions for every batch of
product. Batch cleaning will surely be different than continuous
methods. *** It is extremely difficult to clean large numbers of
parts adequately using only a single stage of cleaning. We very
strongly recommend at least a two-stage operation, especially a final
rinse containing a corrosion inhibitor.
A cleaning solution may not completely remove all
contaminants from severely contaminated components or the contaminant
may severely contaminate the cleaning solution. Likewise, when a
product is very clean to begin with, the solution may be more
effective and remain free of dissolved contaminants for much longer
use. All contaminants are not necessarily removed form the parts
being cleaned and some chemical components and contaminants in the
cleaning solution may redeposit on the surface of the parts. The
rates at which these reactions occur are dependent on the chemical
nature of the parts and the processing conditions such as
Temperature, Time, Concentrations, Agitation, Volumes, etc. ***** The FINAL STAGE of cleaning is extremely important and depends on the procedures, not just the products used by the manufacturers. As a part is removed from a solution, contaminants within the solutions may redeposit very rapidly on the parts thus reversing all efforts to remove contaminants. Even very brief exposure to air can form compounds ( from very rapid air oxidation ) that are not readily soluble in normal cleaners. Thus, immediate removal of residual cleaning solutions is very important. This may be done by immediate treatment with a second solution of water or clean compressed air. Some metals, especially cast iron and steel, corrode extremely rapidly at this stage. For some metals, the cleaner the surface the faster the initial corrosion ! ( flash rusting ). But, if the surface is not properly cleaned, severe corrosion or product failure, such as adhesive failure, may result later at greater expense. Corrosion Inhibitors should be used at this stage. WHEN do I use a Cleaner ?
One major mistake made in industrial processing is
to start cleaning a product too late in manufacturing. Contaminants
which could be eliminated from incoming supplies and raw goods are
carried all the way to the final product completion. Cleaners and
corrosion inhibitors should be used at the first possible stage of
manufacturing and throughout each stage wherever possible.
Fortunately, some cleaner's Advanced R & D has helped develop,
contain built-in corrosion inhibitors. How do I SELECT a Cleaning Product ?
Advanced R & D can provide cleaners for nearly
every application involving most metals; iron, copper, zinc, brass,
stainless steel, silver, solders, electronics, rust removers, and
others. Based on years of experience in analysis of coatings and
adhesive failures, Advanced R & D has found that poor surface
cleaning is the major cause of product failure. Hence, effective
cleaning and corrosion inhibitors must be used immediately after or
even during cleaning. And, the correct cleaner and correct
concentration must be used. As an independent consulting firm,
Advanced R & D can provide recommendations and professional
guidance in this selection. The chemical nature of contaminants on the surface dictates the requirements of the cleaner. Most organic materials can be cleaned easily with less aggressive cleaners although highly degraded organic material is extremely insoluble. Inorganic contaminants oftener require very aggressive cleaning and may even need conditions that are too harsh for practical use due to safety, toxicity, and environmental requirements. They may actually require physical cleaning. Most cleaners recommended or supplied by Advanced R & D are nonhazardous, environmental friendly, biodegradable, nitrite free, non-corrosive, and free of noxious solvents, trichloroethylene, methylene chloride, CFC's, or flammable solvents.
What are the Important "RULES TO REMEMBER" about CLEANING?
The practical " RULES " of surface cleaning are summarized below. However, each and every product and its individual components should be carefully evaluated regarding its original contaminants and final requirements. Advanced R & D has done this type of evaluation for many companies for many years.
|
|
Send
mail to AdvancedRD@aol.com
with questions or comments about this web site.
|
.................
Chemical Type Physical Type