Corrosion prevention of metals using bis-functional polysulfur silanes

A method of preventing corrosion of metals using bis-functional polysulfur silanes. The method includes providing a metal surface, and applying a treatment solution onto the metal surface. The treatment solution includes at least one hydrolyzed bis-functional polysulfur silane of the formula: ##STR1## wherein each R is an alkyl or an acetyl group, and Z is either --S.sub.x or --Q--S.sub.x --Q--, wherein each Q is an aliphatic or aromatic group, and x is an integer of from 2 to 9. A treatment solution and metal surface having improved corrosion resistance are also provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of preventing corrosion of metal 
surfaces. More particularly, the present invention provides a method of 
preventing corrosion of a metal surface which comprises applying a 
solution containing one or more bis-functional polysulfur silanes to the 
metal surface. The method is particularly useful for treating surfaces of 
zinc, copper, aluminum, and alloys of the foregoing metals (such as brass 
and bronze). 
2. Description of Related Art 
Most metals are susceptible to varying degrees and types of corrosion which 
will significantly affect the quality of such metals, as well as that of 
the products produced therefrom. Although many forms of corrosion can 
sometimes be prevented, such steps are costly and may further diminish the 
utility of the final product. In addition, when polymer coatings such as 
paints, adhesives, or rubbers are applied to the metal, corrosion of the 
base metal material may cause a loss of adhesion between the polymer 
coating and the base metal. 
Prior art techniques for improving corrosion resistance of metals, 
particularly metal sheet, include passivating the surface by means of a 
heavy chromate treatment. Such treatment methods are undesirable, however, 
because the chromate ion is highly toxic, carcinogenic and environmentally 
undesirable. It is also known to employ a phosphate conversion coating in 
conjunction with a chromate rinse in order to improve paint adherence and 
provide corrosion protection. It is believed that the chromate rinse 
covers the pores in the phosphate coating, thereby improving the corrosion 
resistance and adhesion performance. Once again, however, it is highly 
desirable to eliminate the use of chromate altogether. Unfortunately, the 
phosphate conversion coating is generally not effective without the 
chromate rinse. 
Recently, various techniques for eliminating the use of chromate have been 
proposed. These include coating the metal with an inorganic silicate 
followed by treating the silicate coating with an organofunctional silane 
(U.S. Pat. No. 5,108,793). U.S. Pat. No. 5,292,549 teaches the rinsing of 
metal sheet with a solution containing an organofunctional silane and a 
crosslinking agent in order to provide temporary corrosion protection. The 
crosslinking agent crosslinks the organofunctional silane to form a denser 
siloxane film. One significant drawback of the methods of this patent, 
however, is that the organofunctional silane will not bond well to the 
metal surface, and thus the coating of U.S. Pat. No. 5,292,549 may be 
easily rinsed off. Various other techniques for preventing the corrosion 
of metal sheets have also been proposed. Many of these proposed 
techniques, however, are ineffective, or require time-consuming, 
energy-inefficient, multi-step processes. 
Further complicating the task of preventing corrosion of metals is the fact 
that corrosion can occur by a number of different mechanisms, depending in 
large part upon the particular metal in question. Brass, for example, is 
very sensitive to corrosion in aqueous environments (particularly uniform 
corrosion), dezincification (especially in acid-chloride containing 
solutions), and stress corrosion cracking (particularly in the presence of 
ammonia and amines). Copper, and copper alloys (including brass) will 
tarnish readily in air and in sulfur-containing environments. Zinc, and 
zinc alloys, on the other hand, are particularly susceptible to the 
formation of "white rust" under humid conditions. Unfortunately, many of 
the prior art treatment methods for preventing corrosion are less 
effective on zinc, zinc alloys, copper, and copper alloys, especially 
brass and bronze, or are only effective for certain types of corrosion. 
Thus, there is a need for a simple, low-cost technique for preventing 
corrosion of metal surfaces, particularly zinc, zinc alloys, aluminum, 
aluminum alloys, copper, and copper alloys (especially brass and bronze). 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved method of 
preventing corrosion of metal surfaces. 
It is another object of the present invention to provide a treatment 
solution for preventing corrosion of metal surfaces. 
It is yet another object of the present invention to provide a method of 
preventing corrosion of metal surfaces, particularly zinc, copper, 
aluminum, and alloys of the foregoing metals. 
The foregoing objects can be accomplished, in accordance with one aspect of 
the present invention, by providing a method of treating a metal surface 
to improve corrosion resistance, comprising the steps of: 
(a) providing a metal surface; and 
(b) applying a treatment solution onto the metal surface, the treatment 
solution containing at least one bis-functional polysulfur silane which 
has been at least partially hydrolyzed, the silane comprising: 
##STR2## 
wherein (before hydrolysis) each R is an alkyl or an acetyl group, and Z 
is either --S.sub.x or --Q--S.sub.x --Q--, wherein each Q is an aliphatic 
or aromatic group, and x is an integer of from 2 to 9 (preferably 4). 
Each R may be individually chosen from the group consisting of: ethyl, 
methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl, ter-butyl and 
acetyl. It will be understood, however, that hydrolysis of the silane 
results in the R groups (at least a portion of them, and preferably 
substantially all of them) being replaced by a hydrogen atom. Each Q may 
be individually chosen from the group consisting of: C.sub.1 -C.sub.6 
alkyl (linear or branched), C.sub.1 -C.sub.6 alkenyl (linear or branched), 
C.sub.1 -C.sub.6 alkyl substituted with one or more amino groups, C.sub.1 
-C.sub.6 alkenyl substituted with one or more amino groups, benzyl, and 
benzyl substituted with C.sub.1 -C.sub.6 alkyl. One preferred group of 
silanes comprises bis-(triethoxysilylpropyl) sulfides having 2 to 9 sulfur 
atoms, particularly bis-(triethoxysilylpropyl) tetrasulfide. 
The treatment method of the present invention is particular useful for 
metals chosen from the group consisting of: zinc, zinc alloys, copper, 
copper alloys, aluminum, and aluminum alloys. Examples of such metal 
surfaces are brass, bronze, and even hot-dipped galvanized steel. 
The treatment solution also preferably includes water and a solvent, such 
as one or more alcohols (e.g., ethanol, methanol, propanol, and 
iso-propanol). The total concentration of the bis-functional polysulfur 
silanes in the treatment solution is between about 0.1% and about 25% by 
volume, more preferably between about 1% and about 5%. A preferred 
embodiment includes between about 3 and about 20 parts methanol (as the 
solvent) per each part water. 
The present invention also provides a treatment solution for preventing 
corrosion of a metal substrate comprising at least one bis-functional 
polysulfur silane which has been at least partially hydrolyzed, the silane 
of the formula: 
##STR3## 
wherein each R (before hydrolysis) is an alkyl or an acetyl group, and Z 
is either --S.sub.x or --Q--S.sub.x --Q--, wherein each Q is an aliphatic 
or aromatic group, and x is an integer of from 2 to 9. 
A metal surface having improved corrosion resistance is also provided, and 
comprises: 
(a) a metal surface; and 
(b) a silane coating bonded to the metal surface, the silane comprising at 
least one bis-functional polysulfur silane which has been at least 
partially hydrolyzed, the bis-functional polysulfur silane comprising: 
##STR4## 
wherein each R is an alkyl or an acetyl group, and Z is either --S.sub.x 
or --Q--S.sub.x --Q--, wherein each Q is an aliphatic or aromatic group, 
and x is an integer of from 2 to 9. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Applicants have found that corrosion of metal surfaces, particularly 
surfaces of zinc, zinc alloys, aluminum, aluminum alloys, copper, and 
copper alloys, can be prevented by applying a treatment solution 
containing one or more bis-functional polysulfur silanes, wherein the 
silane(s) has been at least partially hydrolyzed. The bis-functional 
polysulfur silanes which may be used to prepare the treatment solution 
include: 
##STR5## 
wherein each R is an alkyl or an acetyl group, and Z is either --S.sub.x 
or --Q--S.sub.x --Q--. Each Q is an aliphatic (saturated or unsaturated) 
or aromatic group, and x is an integer of from 2 to 9 (preferably 4). 
Each R within the sulfur-containing silane can be the same or different, 
and thus the silane may include both alkoxy and acetoxy moieties. As 
further outlined below, however, the silane(s) is hydrolyzed in the 
treatment solution, such that substantially all (or at least a portion) of 
the R groups are replaced with a hydrogen atom. In a preferred embodiment, 
each R may be individually chosen from the group consisting of: ethyl, 
methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl, ter-butyl and 
acetyl. Similarly, Q within the bis-functional polysulfur silane can be 
the same or different. In a preferred embodiment, each Q is individually 
chosen from the group consisting of: C.sub.1 -C.sub.6 alkyl (linear or 
branched), C.sub.1 -C.sub.6 alkenyl (linear or branched), C.sub.1 -C.sub.6 
alkyl substituted with one or more amino groups, C.sub.1 -C.sub.6 alkenyl 
substituted with one or more amino groups, benzyl, and benzyl substituted 
with C.sub.1 -C.sub.6 alkyl. 
Particularly preferred bis-functional polysulfur silanes include 
bis-(triethoxysilylpropyl) sulfides having 2 to 9 sulfur atoms. Such 
compounds have the following formula: 
##STR6## 
wherein x is an integer of from 2 to 9. One particularly preferred 
compound is bis-(triethoxysilylpropyl) tetrasulfide (also referred to as 
bis-(triethoxysilylpropyl) sulfane), wherein x is 4. 
Applicants have found that the above-described bis-functional polysulfur 
silanes provide unexpectedly superior corrosion protection on surfaces of 
zinc, zinc alloys, aluminum, aluminum alloys, copper and copper alloys 
(particularly brass and bronze). In addition, these sulfur-containing 
silanes protect against multiple types of corrosion, including uniform 
corrosion, dezincification and stress corrosion cracking. The corrosion 
protection provided by the methods of the present is also superior to 
conventional chromate-based treatments, and avoids the chromium disposal 
problem. 
The bis-functional polysulfur silanes employed in the present invention 
must be hydrolyzed so that the silane will bond to the metal surface. 
During hydrolysis, the alkyl or acetyl groups (i.e., the "R" moieties) are 
replaced with a hydrogen atom. While the silane should be at least 
partially hydrolyzed, the method of preparing the treatment solution of 
the present invention will generally result in substantially complete 
hydrolysis of the silane(s). As used herein, the term "partially 
hydrolyzed" simply means that only a portion of the R groups on the silane 
have been replaced with a hydrogen atom. Preferably, the bis-functional 
polysulfur silane(s) should be hydrolyzed to the extent that at least two 
(and, more preferably, substantially all) of the alkyl or acetyl groups on 
each molecule have been replaced with a hydrogen atom. 
Hydrolysis of the bis-functional polysulfur silane may be accomplished 
merely be adding the silane to an alcohol/water mixture, thereby forming 
the treatment solution of the present invention. In general, mixing the 
silane with the alcohol/water mixture will result in full hydrolysis of 
the silane (substantially all of the R groups replaced with a hydrogen 
atom). The water actually hydrolyzes the silane, while the alcohol is 
necessary to ensure adequate silane solubility and solution stability. 
Alcohol also improves the wettability when the treatment solution is 
applied to the metal surface, and reduces the time necessary for drying. 
Of course other suitable solvents may be employed in place of alcohol. 
Presently preferred alcohols are methanol and ethanol, however other 
alcohols may similarly be employed (such as propanol or iso-propanol). It 
will also be understood that more than one alcohol may be used. 
In order to prepare the treatment solution of the present invention, the 
alcohol and water should first be mixed with one another, preferably at a 
ratio of between about 3 and about 99 parts alcohol(s) per 1 part water 
(by volume), more preferably between about 3 and about 20 parts alcohol(s) 
per 1 part water. After thorough mixing, the silane(s) are added to the 
alcohol/water mixture and mixed thoroughly to ensure adequate hydrolysis. 
The treatment solution should be mixed for at least 30 minutes, and up to 
24 hours in order to ensure complete hydrolysis (substantially all of the 
R groups replaced by a hydrogen atom), thereby forming the treatment 
solution of the present invention. 
Stability of the treatment solution of the present invention may be 
enhanced (e.g., sulfur precipitation inhibited) by preparing and storing 
the treatment solution at a temperature less than room temperature (25 
deg. C), more preferably between about 0 and about 20 deg. C. It should be 
noted, however, that Applicants have demonstrated good corrosion 
prevention results even if the treatment solution is mixed and stored at 
room temperature. In addition, exposure of the treatment solution to light 
should be limited as much as possible, since it is believed that light 
will reduce solution stability. The pH of the treatment solution of the 
present invention generally need not be modified, provided that the normal 
pH of the treatment solution (between about 4 and about 4.5, in the case 
of bis-(triethoxysilylpropyl) tetrasulfide) allows for complete 
hydrolysis. Of course the pH may be adjusted as needed in order to ensure 
complete hydrolysis, such as by the addition of acetic or formic acid. 
Based upon the foregoing, it will be understood that the treatment solution 
of the present invention may simply comprise a solution of one or more 
hydrolyzed (at least partially), bis-functional polysulfur silanes (as 
described above), preferably in an alcohol/water solution. In fact, a 
preferred embodiment of the treatment solution of the present invention 
consists essentially of a solution of hydrolyzed bis-functional polysulfur 
silane(s). 
The concentration of bis-functional polysulfur silanes in the treatment 
solution should be between about 0.1% and about 25% by volume, more 
preferably between about 1 and about 5%. Concentrations higher than these 
preferred ranges are not cost-effective, since no significant improvement 
in corrosion resistance will be provided, and may lead to solution 
instability. It should be noted that the concentration of silanes 
discussed and claimed herein are all measured in terms of the ratio 
between the volume of unhydrolyzed, bis-functional polysulfur silanes 
employed in the preparation of the treatment solution (i.e., prior to 
hydrolysis), and the total volume of treatment solution components (i.e., 
silanes, water, and alcohol). In addition, these concentrations refer to 
the total amount of unhydrolyzed bis-functional polysulfur silanes used in 
preparing the treatment solution, as multiple silanes may optionally be 
employed in this treatment solution. 
Once the treatment solution has been prepared in the above-described 
manner, the metal substrate to be treated should be solvent and/or 
alkaline cleaned (by techniques well-known in the prior art) prior to 
application of the above-described treatment solution, rinsed in deionized 
water and then allowed to dry. The treatment solution may then be applied 
directly onto the cleaned metal (i.e., with no other layers between the 
metal and the treatment composition of the present invention) by either 
dipping the metal into the solution (also referred to as "rinsing"), 
spraying the solution onto the surface of the metal, or even wiping or 
brushing the treatment solution onto the metal substrate. When the 
preferred application method of dipping is employed, the duration of 
dipping is not critical, as it will generally not affect the resulting 
film thickness or performance. Nevertheless, it is preferred that the 
dipping time be between about 1 second and about 30 minutes, more 
preferably between about 5 seconds and about 2 minutes in order to ensure 
complete coating of the metal. Unlike other silane treatment methods, the 
thus-coated metal may be dried at room temperature, since no heating or 
curing of the silane coating is necessary. Typically, drying will take a 
couple of minutes at room temperature, depending in part upon how much 
water is provided in the treatment solution (as ratio of alcohol to water 
is decreased, drying time is increased). While multiple coatings may be 
applied, a single coating will normally be sufficient. 
The above treatment method has been shown to provide unexpectedly superior 
corrosion prevention, particularly on zinc, copper, aluminum, and alloys 
of the foregoing metals. As used herein, the term "copper alloy" refers to 
any alloy wherein copper is the predominant metal (i.e., no other metal is 
present in an amount greater than copper). Zinc alloys and aluminum alloys 
are similarly defined. The treatment method of the present invention is 
particularly effective for preventing corrosion of brass (zinc-containing 
copper alloys) and bronze (copper alloys which typically include tin). 
Brass, for example, is highly susceptible to corrosion, particularly 
uniform corrosion in aqueous environments, dezincification (especially in 
acid-chloride containing solutions), and stress corrosion cracking 
(particularly in the presence of ammonia and amines). Heretofore, the only 
effective corrosion prevention techniques for brass of which Applicants 
are aware is painting, or adding an additional metal to the brass during 
alloying (such as in admiralty brass). However, painting is not always 
possible or desirable, such as when the brass is used in an artistic 
sculpture, and the addition of other alloying elements is expensive. 
Applicants have found, however, that the treatment method of the present 
invention is very effective in preventing corrosion of brass (and bronze) 
without the need for an outer layer of paint. Therefore, the methods of 
the present invention are particularly useful and effective in preventing 
the corrosion of brass and bronze sculptures. 
The examples below demonstrate some of the superior and unexpected results 
obtained by employing the methods and treatment solution of the present 
invention. In all cases, the metal substrate samples were first alkaline 
cleaned using a standard, non-etching alkaline cleaner (AC1055, available 
from Brent America, Inc.). An 8% aqueous solution of the cleaner was 
heated to 70 to 80 deg. C, and the metal substrates were immersed in the 
hot solution for a period of 2-3 minutes. The substrates were then rinsed 
in de-ionized water until a water-break free surface was achieved. The 
rinsed samples were then blown dry with compressed air.

EXAMPLE 1 
In order to compare the corrosion protection provided by the methods of the 
present invention with other treatment techniques, identical brass samples 
(alkaline cleaned, cold-rolled, 70/30 brass sheet) were coated with 
solutions of 1,2-bis-(triethoxysilyl) ethane ("BTSE"), 
vinyltrimethoxysilane, and bis-(triethoxysilylpropyl) amine, as well as a 
treatment solution according to the present invention. 
The treatment solution according to the present invention was prepared as 
follows. 25 ml of water was thoroughly mixed with 450 ml of methanol (18 
parts methanol for each part water, by volume). Next, 25 ml of 
bis(triethoxysilyipropyl) tetrasulfide was slowly added to the 
methanol/water mixture, while mixing, thereby providing a silane 
concentration of about 5%, by volume. The treatment solution was mixed for 
at least an hour in order to ensure sufficient hydrolysis of the silane. 
In order to prevent sulfur precipitation, the solution was then 
refrigerated such that the temperature was reduced to about 5 deg. C. 
Refrigeration also excluded light from the treatment solution. This 
treatment solution was then applied to a sample of cold-rolled, 70/30 
brass sheet by dipping. The solution temperature was about 5 to 10 deg. C, 
and the sample was dipped for about 100 seconds. After coating, the sample 
was dried in air at room temperature. 
Comparative treatment solutions of 1,2-bis-(triethoxysilyl) ethane 
("BTSE"), vinyltrimethoxysilane, bis-(triethoxysilylpropyl) amine were 
prepared in a similar fashion. In all cases, the silane concentration was 
about 5%, and an alcohol/water solvent mix was used. In addition, the pH 
of each of each solution was adjusted, as needed, in order to ensure 
maximum hydrolysis. The pH of the BTSE and vinyltrimethoxysilane solutions 
was about 4 to about 6, while the pH of the bis-(triethoxysilylpropyl) 
amine solution was about 10 to about 11. Any needed adjustments to pH were 
accomplished using acetic acid and sodium hydroxide. Samples of 
alkaline-cleaned, cold-rolled, 70/30 brass sheet were coated with these 
solutions in the same manner described above. 
In order to simulate the corrosive environment of seawater, the coated 
samples, and an uncoated control, were partially immersed in a 3% NaCl 
solution for 1000 hours. The samples were then removed and visually 
examined for any visible signs of corrosion, including attack at the water 
line and any discoloration. The results are provided in the table below. 
______________________________________ 
Sample After 1000 hours in 3% NaCl solution 
______________________________________ 
uncoated (only alkaline 
heavy discoloration, waterline attack with 
cleaned) copper deposits present 
BTSE heavy discoloration, waterline attack with 
heavy copper deposits present 
Vinyl Silane slight discoloration, minimum deposit of 
copper at waterline 
bis-(triethoxysilylpropyl) blue copper deposits throughout the immersed 
amine region, heavy waterline attack 
bis-(triethoxysilylpropyl) no change from original appearance 
tetrasulfide 
______________________________________ 
EXAMPLE 2 
Brass samples were prepared in accordance with the methods described in 
Example 1 above. The coated samples and uncoated control were then 
immersed in a 0.2N HCl solution for 5 days in order to examine the ability 
of the treatment solutions of the present invention to prevent 
dezincification. The following results were observed: 
______________________________________ 
Sample After 5 days in 0.2 N HCl solution 
______________________________________ 
uncoated (only alkaline 
dezincification observed throughout the 
cleaned) immersed region 
BTSE heavy dezincification observed throughout the 
immersed region 
Vinyl Silane dezincification observed throughout the 
immersed region 
bis-(triethoxysilylpropyl) no change from original appearance (i.e., no 
tetrasulfide dezincification) 
______________________________________ 
EXAMPLE 3 
Three brass samples were alkaline cleaned, and a treatment solution 
according to the present invention was prepared in accordance with the 
methods of Example 1. One of the brass samples was uncoated, and therefore 
acted as a control. The uncoated sample was bent over itself (180 degrees) 
in order to provide a high stress region on the sample for simulating 
stress corrosion cracking. The second sample was coated with the treatment 
solution of the present invention in the manner described in Example 1, 
and was then bent over itself. The third sample was first bent over 
itself, and was then coated with the treatment solution of the present 
invention in the manner described in Example 1. All three samples were 
then exposed to strong ammonia vapors for a period of 18 hours. After 
exposure, the samples were visually examined for corrosion, and thereafter 
opened (i.e., "unbent"). The results provided in the table below once 
again demonstrate the ability of the treatment method of the present 
invention to prevent corrosion, and also show that the coating thus 
provided is deformable: 
______________________________________ 
After 18-hour exposure to 
Effect of opening 
Sample ammonia vapors bend 
______________________________________ 
uncoated control 
heavy darkening of the entire 
sample broke at the 
surface bend 
coated, then bent minimal darkening at edges initiation of crack at 
one end of bend 
bent, then coated minimal darkening at edges no crack initiated 
______________________________________ 
EXAMPLE 4 
Three samples of Al 2024 were alkaline cleaned in the manner described 
previously. One sample acted as the control, and was not coated in any 
manner after alkaline cleaning. The second panel was subjected to a 
standard chromate treatment, in a manner well-known to those skilled in 
the art. The third panel was coated with the bis-(triethoxysilylpropyl) 
tetrasulfide solution described in Example 1, in the manner described 
therein. 
In order to examine the formability of the coating as well as any negative 
effect of forming on corrosion performance, all three samples were deep 
drawn to a depth of about 8 mm in a cup drawing machine in order to make 
standard cups for use in Olsen testing. Since the drawing process 
necessitated the application of a lubricant to the inner surface of the 
cup, some solvent cleaning was performed (using methanol and hexane) after 
drawing in order to remove any oil contamination. The drawn samples were 
then completely immersed in a 3% NaCl solution for a period of one week, 
and the samples were then visually observed for signs of corrosion (both 
the inner and outer surfaces): 
______________________________________ 
After 1 week exposure to 3% NaCl 
Sample solution 
______________________________________ 
control (alkaline cleaned only) 
discoloration of the entire surface, 
heavier at the drawn region; pitting 
with white deposits at many points 
on the sample; edge corrosion 
chromated slight discoloration of the sample, 
heavier at the drawn region; pitting 
heavy with white deposits 
throughout the sample 
bis-(triethoxysilylpropyl) original appearance throughout the 
tetrasulfide sample, including the drawn region; 
no pitting; no edge corrosion 
______________________________________ 
The above results demonstrate that the sulfur-containing silanes used in 
the methods and treatment solution of the present invention are also 
effective on aluminum and aluminum alloys. 
EXAMPLE 5 
In order to examine the effectiveness of the methods of the present 
invention in preventing corrosion of surfaces of zinc and zinc alloys 
(including, for example, hot-dipped galvanized steel), standard titanium 
zinc panels (primarily zinc, with less than 1% titanium; available from 
Nedzinc) were alkaline-cleaned in the manner described previously. One 
panel was uncoated, while another was coated with the treatment solution 
of Example 1, in the manner described therein. These panels were then 
subjected to the Butler Horizontal Water Immersion Test (developed by the 
Butler Manufacturing Company of Grandview, Mo.). The uncoated panel 
exhibited white rust over 80% of its surface after only one day, while the 
panel treated according to the present invention showed only 5% white rust 
after 6 weeks of exposure. 
The foregoing description of preferred embodiments is by no means 
exhaustive of the variations in the present invention that are possible, 
and has been presented only for purposes of illustration and description. 
Obvious modifications and variations will be apparent to those skilled in 
the art in light of the teachings of the foregoing description without 
departing from the scope of this invention. Thus, it is intended that the 
scope of the present invention be defined by the claims appended hereto.