U.S. patent application number 14/149196 was filed with the patent office on 2014-07-10 for sinter bonded porous metallic coatings.
This patent application is currently assigned to Mott Corporation. The applicant listed for this patent is Mott Corporation. Invention is credited to Alfred M. Romano, Kenneth L. Rubow, James K. Steele, Wayne F. White.
Application Number | 20140193661 14/149196 |
Document ID | / |
Family ID | 46491007 |
Filed Date | 2014-07-10 |
United States Patent
Application |
20140193661 |
Kind Code |
A1 |
Steele; James K. ; et
al. |
July 10, 2014 |
Sinter Bonded Porous Metallic Coatings
Abstract
A composite structure includes a substrate with pores of a first
mean pore size and a coating on at least one surface of that
substrate. This coating has pores of a second mean pore size where
the first mean pore size is equal to or greater than said second
mean pore size. When the pore size of the coating is effective to
capture particulate greater than 0.2 micron, the composite may be
formed into a filter effective to remove microbes from a fluid
medium. One method to form the porous coating on the substrate
includes the steps of: (a) forming a suspension of sinterable
particles in a carrier fluid and containing the suspension in a
reservoir; (b) maintaining the suspension by agitation in the
reservoir; (c) immersing the substrate in the reservoir; (c)
applying a first coating of the suspension to the substrate; (d)
removing the substrate with the applied first coating from the
reservoir; and (e) sintering the sinterable particles to the
substrate thereby forming a coated substrate.
Inventors: |
Steele; James K.; (Rockfall,
CT) ; White; Wayne F.; (Granby, CT) ; Romano;
Alfred M.; (Hartland, CT) ; Rubow; Kenneth L.;
(Avon, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mott Corporation |
Farmington |
CT |
US |
|
|
Assignee: |
Mott Corporation
Farmington
CT
|
Family ID: |
46491007 |
Appl. No.: |
14/149196 |
Filed: |
January 7, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13364478 |
Feb 2, 2012 |
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14149196 |
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11827688 |
Jul 13, 2007 |
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13364478 |
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61439176 |
Feb 3, 2011 |
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60848423 |
Sep 29, 2006 |
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Current U.S.
Class: |
428/613 ;
210/483; 210/497.01; 427/294; 427/373; 427/601; 428/316.6;
55/529 |
Current CPC
Class: |
B01D 2239/083 20130101;
B01J 35/04 20130101; Y10T 428/12479 20150115; B01D 39/2027
20130101; B01D 2239/0654 20130101; B01J 23/42 20130101; Y10T
428/249981 20150401; B22F 5/106 20130101; Y10T 428/12042 20150115;
C22C 38/00 20130101; B01D 39/2034 20130101; B01D 39/201 20130101;
Y10T 428/13 20150115; B01D 2239/0478 20130101; B01D 2239/0258
20130101; B01J 2/18 20130101; C22C 5/04 20130101; B01J 2/006
20130101; C22C 19/056 20130101; C22C 14/00 20130101; B22F 1/0018
20130101; B01J 2/04 20130101; B22F 7/02 20130101; B22F 3/1103
20130101; B82Y 30/00 20130101; B01D 2239/10 20130101; B01D
2239/1241 20130101; B01D 2239/1216 20130101; B22F 7/002 20130101;
C23C 18/06 20130101; C22C 1/02 20130101; C23C 24/04 20130101; C23C
24/08 20130101 |
Class at
Publication: |
428/613 ;
428/316.6; 55/529; 210/483; 210/497.01; 427/373; 427/294;
427/601 |
International
Class: |
B01D 39/20 20060101
B01D039/20 |
Goverment Interests
U.S. GOVERNMENT RIGHTS
[0002] N.A.
Claims
1. A composite structure, comprising: a substrate having pores with
a first mean pore size; and a coating on at least one surface of
said substrate, said coating having pores with a second mean pore
size wherein said first mean pore size is equal to or greater than
said second mean pore size.
2. The composite structure of claim 1 wherein said substrate is
selected from materials having a Media Grade of between 0.2 and
5.
3. The composite structure of claim 2 wherein said second mean pore
size is less than 0.2 micron.
4. The composite structure of claim 3 wherein said coating pores
are effective to capture particulate greater than 0.2 micron.
5. The composite structure of claim 4 wherein said coating has a
thickness of from 20 microns to 250 microns.
6. The composite structure of claim 5 wherein said coating has a
thickness of from 30 microns to 75 microns.
7. The composite structure of claim 4 wherein said coating if a
mass of particles having an average particle size of 50 nanometers
to 350 nanometers.
8. The composite structure of claim 7 wherein said coating if a
mass of particles having an average particle size of 60 nanometers
to 200 nanometers.
9. The composite structure of claim 7 wherein said substrate and
said mass of particles are both predominantly stainless steel.
10. The composite structure of claim 7 wherein said substrate and
said mass of particles are both predominantly titanium.
11. The composite structure of claim 7 wherein said substrate and
said mass of particles are sintered.
12. The composite structure of claim 11 formed into a filter
effective to remove microbes from a fluid medium.
13. The composite structure of claim 12 formed into a flat
disk.
14. The composite structure of claim 13 formed into a tube.
15. The composite structure of claim 14 wherein said coating is on
an outward facing surface of said tube.
16. A method for forming a porous coating on a substrate,
comprising the steps of: (a) forming a suspension of sinterable
particles in a carrier fluid and containing said suspension in a
reservoir; (b) maintaining said suspension by agitation in said
reservoir; (c) immersing said substrate in said reservoir; (c)
applying a first coating of said suspension to said substrate; (d)
removing said substrate with applied first coating from said
reservoir; and (e) sintering said sinterable particles to said
substrate thereby forming a coated substrate.
17. The method of claim 16 including forming said substrate as a
tube having an interior bore and applying a vacuum to said interior
bore during said applying step.
18. The method of claim 17 including applying ultrasonic energy to
said suspension.
19. The method of claim 18 wherein a ratio of said sinterable
particles to said carrier fluid in said suspension is less than or
equal to 15 grams of sinterable particles to 1 liter of carrier
fluid.
20. The method of claim 18 wherein said first coating has a
thickness of about 10 to 25 microns, whereby shrinkage cracks
during step (e) are avoided.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This patent application is a divisional of U.S. patent
application Ser. No. 13/364,478, titled "Sinter Bonded Porous
Metallic Coatings," that was filed on Feb. 2, 2012. U.S. Ser. No.
13/364,478 is a continuation-in-part of U.S. patent application
Ser. No. 11/827,688, titled "Sinter Bonded Porous Metallic
Coatings," that was filed on Jul. 13, 2007 and also claims a
benefit to the filing date of U.S. Provisional Patent Application
Ser. No. 61/439,176, titled "Sinter Bonded Porous Metallic
Coatings," that was filed on Feb. 3, 2011. U.S. Ser. No. 11/827,688
claims priority from U.S. Provisional Patent Application
60/848,423, titled "Sinter bonded porous metallic coatings" that
was filed on Sep. 29, 2006. The disclosures of U.S. Ser. No.
13/364,478, U.S. Ser. No. 11/827,688, U.S. 61/439,176, and
60/848,423 are incorporated herein by reference in their
entireties.
BACKGROUND
[0003] 1. Field
[0004] Disclosed herein is a method to form a porous metallic
coating on a substrate. More particularly, a suspension of nanosize
particles in a carrier fluid is deposited on the substrate and
heated to evaporate the carrier fluid while sintering the particles
to the substrate.
[0005] 2. Description of the Related Art
[0006] There are numerous applications requiring a porous open cell
structure including filtration and gas or liquid flow control.
These structures are typically formed by compacting metallic or
ceramic particles to form a green compact and then sintering to
form a coherent porous structure. Particle size, compaction force,
sintering time and sintering temperature all influence the pore
size and the structure strength. When the pore size is relatively
large, such as microsize (having an average diameter of one micron
(.mu.m) or greater), the structure thickness relative to pore size
is modest for sufficient strength to be handled and utilized in
industrial applications. When the pore size is relatively small,
such as nanosize (having an average diameter of less than one
micron), the structure thickness is much greater than pore size for
sufficient strength to be handled and utilized in industrial
applications. As a result, the structure has high resistance to
passing a gas or liquid through the long length, small diameter
pores and there is a high pressure drop across the filter. Note
that for this application, the diameter is to be measured along the
longest axis passing from one side of a particle to the other side
and also passing through the particle center.
[0007] A number of patents disclose methods for depositing a porous
coating on a substrate. U.S. Pat. No. 6,544,472 discloses a method
for depositing a porous surface on an orthopedic implant. Metallic
particles are suspended in a carrier fluid. The carrier fluid may
contain water, gelatin (as a binder) and optionally glycerin (as a
viscosity enhancer). Evaporation of the water results in the
metallic particles being suspended in a gelatinous binder. Heating
converts the gelatin to carbon and sinters the metallic particles
to the substrate.
[0008] U.S. Pat. No. 6,652,804 discloses a method for the
manufacture of a thin openly porous metallic film. Metal particles
with an average particle diameter between one micron and 50 microns
are suspended in a carrier fluid having as a primary component an
alcohol, such as ethanol or isopropanol, and a binder. This
suspension is applied to a substrate and heated to evaporate the
alcohol component. A green film of microparticles suspended in the
binder is then removed from the substrate and heated to a
temperature effective to decompose the binder and sinter the
metallic particles.
[0009] U.S. Pat. No. 6,709,622 discloses a porous structure formed
by mechanical attrition of metal or ceramic particles to nanosize
and then combining the nanosized particles with a binder, such as a
mixture of polyethylene and paraffin wax to form a green part. The
green part is then heated to a temperature effective to decompose
the binder and sinter the particles.
[0010] U.S. Pat. Nos. 6,544,472; 6,652,804; and 6,709,622 are all
incorporated by reference in their entireties herein.
[0011] In addition to the thickness constraint discussed above, the
inclusion of a binder and optional viscosity enhancer may further
increase the pressure drop across a structure. During sintering,
the binder and viscosity enhancer decompose, typically to carbon.
This carbonatious residue may in whole or in part block a
significant number of pores necessitating a high pressure drop
across the structure to support adequate flow.
[0012] There remains, therefore, a need for a method to deposit a
thin nano powder layer on a substrate that does not suffer from the
disadvantages of the prior art.
BRIEF SUMMARY
[0013] In accordance with an embodiment of the invention, there is
provided a method for forming a porous coating on a substrate. This
method includes the steps of (a) forming a suspension of sinterable
particles in a carrier fluid; (b) maintaining the suspension by
agitating the carrier fluid; (c) applying a first coating of the
suspension to the substrate; and (d) sintering the sinterable
particles to the substrate. An optional step (e) is to repeat steps
(c) and (d) additional times as necessary to achieve desired
thickness and performance. It is a feature of certain embodiments
of the invention that a thin coating of a nano powder material may
be deposited onto a substrate having micropores. A first advantage
of this feature is that the microporous substrate provides strength
and structure support and the nano powder layer may be quite thin.
As a result, a nanoporous material which has sufficient strength
for handling and industrial processes is provided. Since the nano
powder layer is thin, the pressure drop across the layer is
substantially less than conventional thicker nano powder
structures.
[0014] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates in flow chart representation a method for
depositing a porous coating in accordance with an embodiment of the
invention.
[0016] FIG. 2 schematically illustrates a system for depositing the
porous coating formed in accordance with an embodiment of the
invention.
[0017] FIG. 3 schematically illustrates a system for depositing the
porous coating formed in accordance with a second embodiment of the
invention.
[0018] FIG. 4 schematically illustrates a system for depositing the
porous coating on a tube in accordance with an embodiment of the
invention.
[0019] FIG. 5 schematically illustrates a system for depositing the
porous coating on a tube in accordance with a second embodiment of
the invention.
[0020] FIG. 6 illustrates a porous tube suitable for gas flow
regulation or filtration having a porous coating in accordance with
an embodiment of the invention.
[0021] FIG. 7 is a scanning electron micrograph of a surface of the
porous coating formed in accordance with an embodiment of the
invention.
[0022] FIG. 8 is a scanning electron micrograph of a cross section
of the porous coating of FIG. 4.
[0023] FIG. 9 graphically illustrates the effect of successive
layers of the porous coating of FIG. 4 on the gas flux.
[0024] FIG. 10 illustrates a fuel cell component having a porous
coating in accordance with an embodiment of the invention.
[0025] FIG. 11 illustrates a frit for use in a liquid
chromatography column having a porous coating in accordance with an
embodiment of the invention.
[0026] FIG. 12 illustrates a catalytic surface suitable for an
industrial catalytic converter having a porous coating in
accordance with an embodiment of the invention.
[0027] FIG. 13 illustrates an adhesively bonded composite having a
porous coating effective to enhance adhesion in accordance with an
embodiment of the invention.
[0028] FIG. 14 graphically illustrates isopropyl alcohol (IPA)
liquid flow through 47 mm disk assemblies in accordance with
Example 8.
[0029] FIG. 15 graphically illustrates nitrogen flow through 47 mm
disk assemblies in accordance with Example 8.
[0030] FIGS. 16A and 16B are photomicrographs of a Media Grade 2
substrate coated with stainless steel nano particles by the process
of FIG. 3.
[0031] FIGS. 17A and 17B are photomicrographs of a tubular Media
Grade 2 substrate coated with stainless steel nano particles by the
process of FIG. 4.
[0032] FIG. 18 graphically illustrates nitrogen flow through 0.5
inch OD coated tubes in accordance with Example 11.
[0033] FIG. 19 graphically illustrates IPA liquid flow through 0.5
inch OD coated tubes in accordance with Example 11.
[0034] FIG. 20 is a photograph of a bio-pharmaceutical vent filter
in accordance with Example 12.
[0035] FIG. 21 is a photograph of small parts for sterilizing grade
filtration in accordance with Example 13.
[0036] Like reference numbers and designations in the various
drawings indicated like elements.
DETAILED DESCRIPTION
[0037] For purposes of this application, a "binder" is a carrier
fluid component that remains after the carrier fluid is transformed
from a liquid, such as by evaporation. A "viscosity enhancer" is a
liquid that when added to the carrier fluid increases the viscosity
of the carrier fluid beyond that of a primary component of the
carrier fluid. A "suspension" is a mixture of a powder in a
solvent. A "substrate" is a device or a part of a device to which
the porous metallic coatings of the invention are applied. The
substrate is typically porous, but may be solid in certain
embodiments. A "nano powder coating" is the porous coating applied
to the substrate from a powder having an average particle size of
less than 10 microns.
[0038] As illustrated in flowchart representation in FIG. 1, the
sinterable particles used to form a porous coating in accordance
with the invention are suspended 10 in a carrier fluid. The
concentration of sinterable particles is from 10 grams per liter to
200 grams per liter in the carrier fluid with a preferred
concentration being about 100 grams per liter. The sinterable
particles are typically nanosize and have an average maximum
diameter sufficiently small to remain in solution in the carrier
fluid in the presence of agitation without requiring an addition of
a binder or viscosity enhancer. The sinterable particles preferably
have an average maximum diameter of from 10 nanometers to 10
microns and more preferably have an average maximum diameter of
from 10 nanometers to less than one micron. The sinterable
particles are preferably metal or metal alloy powders but may also
be other materials such as metal oxides and ceramics as long as
such powders are capable of sinter bonding to each other and/or to
a substrate. Preferred materials for the sinterable particles
include stainless steel, nickel, cobalt, iron, copper, aluminum,
palladium, titanium, platinum, silver, gold and their alloys and
oxides. One particularly suitable alloy is HASTELLOY C276 that has
a nominal composition by weight of 15.5% chromium, 2.5% cobalt,
16.0% molybdenum, 3.7% tungsten, 15.0% iron, 1.0% manganese, 1.0%
silicon, 0.03% carbon, 2.0% copper and the balance nickel
(HASTELLOY is a trademark of Haynes Stellite Company, Kokomo
Ind.).
[0039] The sinterable particles may be a mixture of materials. For
example, a platinum powder may be mixed with 316L stainless steel,
zinc, silver and tin powders to promote better adhesion of the
coating at lower temperatures. Lower temperatures better retain the
nano structure during the sintering process. The mixed coatings may
be deposited from a suspension containing the mixture of powders
and deposited simultaneously on to a substrate. Other benefits of
applying a mixture of materials include mechanically alloying the
coating, dilute and isolated particle distributions, enhanced
bonding to the substrate at lower temperatures and controlled
Thermal Coefficients of Expansion (TCE). Under the rule of
mixtures, when 50% of component A and 50% of component B are
combined and sintered, the coating would have a TCE that is the
average of the respective TCE's of A and B. More than two
components and other ratios of components may also be utilized and
the TCE of the mixture calculated. For filter applications, such as
described below in Example 8, the coating thickness is between 20
microns and 250 microns and preferably between 30 microns and 75
microns. The particles making up the coating preferably have an
average particle size of from 50 nanometers to 350 nanometers and
most preferably from 60 nanometers to 200 nanometers.
[0040] The carrier fluid is a liquid that evaporates essentially
completely without a residue remaining dispersed in the sinterable
particles. As such, the carrier fluid is substantially free of
binders and viscosity enhancers. "Substantially free" means there
is insufficient binder to form a compact without sintering and is
nominally less than 0.05%, by volume. Preferred carrier fluids are
alcohols. A most preferred alcohol for the carrier fluid is
isopropanol (also referred to as isopropyl alcohol).
[0041] The suspension is formed in an inert atmosphere to prevent
oxidation of the particles and because nanosized metallic particles
are sometimes pyrophoric and may spontaneously ignite when exposed
to air. The coating may be a mixture of different powders in which
case these powders are first mixed in an inert atmosphere, such as
argon. Once the powders are mixed, a carrier fluid is added to form
the suspension. Nominally, equal volumes of carrier fluid and
sinterable particles are utilized. However, other volume fractions
may be used, dependant primarily on the method of deposition. While
Brownian motion will cause the nanosized sinterable particles to
remain in suspension for an extended period of time, agitation 12
is utilized to extend the period of suspension consistency. The
agitation 12 may be by any effective means to maintain carrier
fluid motion such as an impeller, ultrasonic vibration and
combinations thereof.
[0042] A substrate is then coated 14 with the suspension by any
suitable means such as spraying, rolling, dipping, use of a doctor
blade, or other method by which a thin, uniform coating thickness
of about five microns maybe deposited. As described below, a
sequence of coating and sintering may be repeated multiple times to
achieve a desired total coating thickness. The substrate may be
porous or non-porous and may have either a rough or a smooth
surface finish. The substrate is formed from a material to which
the sinterable particles may be sinter bonded.
[0043] One preferred substrate is a porous metal having a thickness
on the order of 0.1 inch and pores with an average diameter on the
order of 5 .mu.m. This substrate has sufficient strength to be
handled and to withstand the rigors of an industrial process. At
least one side of this substrate is coated with nanoporous
particles by the method of the invention to a thickness effective
to continuously coat the surface. This composite structure is
effective for filtration and gas or liquid flow control on the
nanoscale while having the strength and durability of a much
coarser structure.
[0044] One method to deposit porous coatings of the inventions
utilizes the spray system 16 schematically illustrated in FIG. 2. A
suspension 18 of sinterable particles in a carrier fluid is
retained within a reservoir, such as pressure cup 20. An impeller
22 driven by a motor 24 or other means maintains the suspension 18
by agitation. Recirculating pump 26 draws the suspension 18 from
the pressure cup 20 to a spray head 28 and returns nondeposited
suspension back to pressure cup 20 in the direction generally
indicated by arrows 30. The system 16 is pressurized from an
external high pressure source 32 such as air pressurized to 40 psi.
A positive pressure of about 1 psi is maintained in pressure cup
20. Depressing trigger 34 deposits a fine spray of suspension on a
substrate (not shown).
[0045] Shop air has proven to be an acceptable external high
pressure source. Other, more inert gases, such as nitrogen, may be
used to pressurize the spray head. The use of nitrogen should
result in less oxidation of the nano powders when spraying and
provide a more uniform gas delivery in terms of consistent
pressures and dryer gas as compared to conventional plant shop air.
While, to date, the inventors have not observed a difference
between the two gas pressurization systems, in certain application,
the use of a more inert gas should be desirable.
[0046] FIG. 2 illustrates a system for the spray coat deposition of
nano scale particles using modified, but conventional, air spray
atomization similar to that used to paint automobiles and the like.
Limitations with this technique developed when depositing nano
scale particles. These limitations included significant overspray
and impingement of the parts by a high velocity air stream. The
overspray made control of the spray area difficult and also
resulted in a large amount of wasted powder. The high velocity air
made it difficult to spray small parts as the parts would move
under the air flow.
[0047] With reference to FIG. 3, switching to ultrasonic spray
atomization avoids the limitations described above for air spray
atomization. Instead of having a spray plume of several inches in
diameter, as in air spray atomization, an ultrasonic spray nozzle
produces a very small spray plume, usually less than 0.25 inch,
resulting in much better control over where the coatings are
applied. In addition, the ultrasonic spray nozzle uses a much lower
air flow running at an air pressure range of about 5 to 60 inches
H.sub.2O (0.18 to 2.17 psi) versus a pressure of about 30 psi or
higher for conventional air spray systems. A value of 10 inches
H.sub.2O works well for most coating applications and produces a
gentle flow of air over the parts that does not push small parts
around. When larger spray patterns are desired, the part to spray
head distance is increased and, optionally, the air pressure is
increased, exemplary to between 20 and 30 inches H.sub.2O, to
better define the spray pattern at the larger distances. A full
range of 5 to 60 inches H.sub.2O for the system may likely be used
dependent on the selected spray head type, distance from spray head
to part and fluid delivery rate.
[0048] Exemplary operating parameters are 2 inches for the distance
from the spray head to the parts being coated. This results in a
spray plume diameter of about 0.375 inch on the parts. Moving the
spray head closer reduces the size of the diameter of the spray
plume and moving the spray head further away increases the spray
plume pattern size. For the system illustrated in FIG. 3, the part
to spray head distance can be adjusted from about 0.5 inch to about
12 inches. The power level of the ultrasonic spray head can be
adjusted from 0.6 to 10 Watts. The higher the value, the more
energy imparted into the spray slurry and greater levels of
atomization are achieved. A setting of 6 Watts has been found to
work well without generating too much heat at the spray head.
[0049] An additional benefit of ultrasonic atomization of the spray
slurry is that the use of ultrasonics helps to break up
agglomerates of nano particles helping to provide a smoother,
denser, and more uniform coating of nano particles. This is highly
desired for filtration applications or surface treatments where a
smooth surface is desired.
[0050] A suspension 41 of nano particles in a carrier fluid is
placed in a reservoir 43 that is continuously mixed with a
mechanical impeller 22. Fluid suspension 41 is drawn from near the
bottom of this reservoir 43 and fed into an ultrasonic inline
agitator 45. The output of the ultrasonic inline agitator 45 is fed
to the inlet of a gear pump 47. The suspension 41 is then pumped to
the input of a 3-way selector valve 49. The directionality of the
3-way selector valve 49 depends on a mode of operation.
[0051] Mode 1--Suspension 41 flow is directed to an ultrasonic
spray nozzle 51 at the desired coating fluid rate (usually 3
ml/min) when coating. Fluid line 53 is kept very short (less than 1
or 2 inches) to minimize settling and reduce the time for the
system to stabilize when the 3-way selector valve 49 is
actuated.
[0052] Mode 2--Suspension 41 flow is directed to return line 55 and
directed to the fluid reservoir 43. The flow speed is increased to
about 10 ml/min when not coating to remove any air bubbles in the
system and to minimize settling of fluid throughout the fluid
path.
[0053] The ultrasonic inline agitator 45 is placed in the fluid
path of the suspension 41 to impart highly focused ultrasonic
energy into the suspension to break up agglomerates resulting in a
more homogenous coating slurry. It uses the same technology that is
used to atomize the suspension in the ultrasonic spray head 51
described above. The use of the ultrasonic inline agitator 45
helped to solve two main issues. First, it further reduced nano
powder agglomeration in the coatings resulting in more dense and
uniform coatings. Second, locating the ultrasonic inline agitator
51 at the input to the gear pump 47 greatly reduced fluid clogging
in the gear pump 47 and provided more uniform slurry feed rates.
The typical power setting that we have been using is 4 Watts. At
this level, de-agglomeration appears to be adequate with minimal
head build up in the device. Setting the power level too high
(>6 Watts) appears to introduce cavitations in the suspension
creating air bubbles which results in air pockets in the fluid line
53. This is undesirable as these air pockets create instabilities
in the spray pattern while coating parts. In addition, if
cavitations are present, they greatly shorten the life of the
ultrasonic agitator.
[0054] One suitable ultrasonic inline agitator 45 is the Sono-Tek
Ultrasonic Inline Agitator manufactured by Sono-Tek Corporation of
Milton, N.Y. A second ultrasonic inline agitator 59 is optionally
disposed between the gear pump 47 and the 3-way selector valve 49
to further break up any agglomerates in the fluid suspension.
[0055] A suitable gear pump 47 is the Zenith C9000 Precision Gear
Pump manufactured by Zenith Pumps, Monroe, N.C. The pump dispenses
a precise volume of fluid per shaft revolution. 0.3 ml/revolution
is exemplary. A stepper motor (not shown) drives the gear pump and
utilizes RS232/485 communication and/or 4 digital I/O lines (or the
like) to program and control the gear pump 47 speed and direction.
0.125 inch compression fittings were fabricated to reduce the
volume of internal cavities at the input and outlet of the pump. In
addition, a polymer insert was installed to reduce the internal
volume of the pumps input/drive shaft, again to reduce the internal
cavities of the pump.
[0056] A suitable 3-way selector valve 49 is a pneumatically
actuated valve manufactured by Swagelok Company, Cleveland,
Ohio.
[0057] Exemplary operating steps when coating are: (1) reduce
suspension 41 flow rate to desired rate while coating; (2) turn on
ultrasonic spray nozzle 51; (3) direct suspension flow to
ultrasonic spray nozzle via the 3-way valve 49; (4) wait a preset
time for the spray to stabilize (usually less than 10 seconds); (5)
spray parts; (6) switch 3-way valve to direct suspension to return
to fluid reservoir 43; (7) turn off ultrasonic spray nozzle 51; and
(8) increase suspension fluid speed to 10 ml/min or other preset
value when not coating.
[0058] An exemplary clean up procedure is: (1) pull return line 55
from fluid reservoir 43 and pump suspension 41 fluid out of lines;
(2) replace fluid in reservoir 43 with clean isopropyl alcohol
(IPA); (3) circulate IPA through system for a couple minutes at 200
ml/min; (4) replace fluid with clean IPA and repeat above 4 times
reversing direction every other time. If next operation is going to
be a different alloy suspension, then all components will need to
be disassembled and cleaned to reduce contamination.
[0059] Referring back to FIG. 1, following coating 14, the coated
substrate is heated 36 for a time and temperature effective to
evaporate the carrier fluid and sinter 36 the sinterable particles
to the substrate. To prevent oxidation, sintering is typically in a
neutral or reducing atmosphere or under a partial vacuum. While the
sintering temperature is dependent on the composition of the
substrate and sinterable particles, for iron alloy or nickel alloy
components, a temperature from about 1,200 .degree. F. to about
1,800 .degree. F., and preferably from about 1,400.degree. F. to
about 1,600.degree. F. for a time from about 45 minutes to 4 hours,
and preferably from about 1 hour to 2 hours.
[0060] Shrinkage during the sintering process may be detected if
the coating step 14 deposits a suspension layer greater than about
10 microns. Preferably, the maximum coating thickness deposited
during one coating cycle is on the order of five microns. If a
coating thicker than 5-10 microns is desired, multiple coating
cycles may be used by repeating 38 the coating and sintering steps.
For smooth substrates, complete coverage can usually be achieved
with a single coating and sintering cycle. When the substrate is
rough and/or porous, multiple coating cycles are typically required
to achieve complete coverage. When coating a Media Grade 2 porous
substrate, typically three coating cycles are required to achieve
complete coverage. For a Media Grade 1 substrate, two coating
cycles are usually sufficient, while for a Media Grade greater than
2, several coating cycles may be required for complete coverage. A
"Media Grade" number is typically equivalent to a nominal mean flow
pore size. For example, a Media Grade 1 substrate is characterized
by a nominal mean flow pore size of 1 .mu.m and a Media Grade 2
substrate is characterized by a nominal mean flow pore size of 2
.mu.m. Most applications utilize a Media Grade 0.2 to a Media Grade
5 substrate. However, larger pore size substrates, such as Media
Grade 40 or Media Grade 100 may also be coated with the coatings
described herein.
[0061] Once a coating of a desired thickness has been applied and
sintered, either in one or multiple cycles, the coated surface may
be finished 40 by secondary operations to cause an exterior portion
of the coating to be mechanically deformed. Secondary operations
include pressing, rolling, or burnishing to achieve a desired
surface finish and/or finer pore size control.
[0062] Heating the substrates greatly reduces the number of
coating/sintering cycles needed to achieve a desired filtration
efficiency. It is believed that when the porous substrate is heated
and the coating is applied, the enhanced wicking action and
evaporation of the isopropyl alcohol (the carrier fluid for the
spray solution) creates a denser and more uniform coating. The use
of heated substrates reduces the number of cycles required to coat
the original pore structure and results is higher filtration
efficiencies with thinner nano scale coatings. In addition, when
the coatings are applied to heated substrates, the amount of time
that the coating remains as a liquid on the surface of the part is
greatly reduced, reducing the time available for the nano particles
to re-agglomerate on/in the coatings. It is felt that this also
helps to make more uniform nano scale coatings. A suitable
temperature range for heated substrates is from 100.degree. F. to
200.degree. F. with a nominal value of about 150.degree. F.
[0063] When coating the outside surface of tubes, the tubes are
placed in an oven at the desired temperature and then transferred
to the coating system prior to spray coating. In this embodiment,
no heat is applied to tubes during the coating process. Because the
tubes may cool off while transferring them from the oven to the
spray system and while coating, we usually set the oven to about
20.degree. F. higher to account for this cooling that will occur
during the coating process. An alternative is to apply infra-red
(IR) heating to the tubes while coating through the use of
explosion proof IR strip heaters to help maintain a constant
temperature of the tubes/filters while spray coating.
[0064] When coating flat components, such as disk or sheet, the
parts may be placed on a porous stainless steel plate that is
heated via a hot plate or the like. The use of a porous plate to
support the parts serves several functions. First, the composition
of the plate can be adjusted to match the alloy of the coated parts
to reduce the risk of contamination and is relatively easy to clean
and reuse. In addition the porous nature of the support plate
causes over spray to dry immediately on contact and, as a result,
there is no wicking of the coating solution to the back side of the
parts being coated giving cleaner components. Further, the
conductive nature of the porous metallic supporting plate aids in
transferring heat to and maintaining the elevated temperature of
the parts while coating. Small parts are placed directly on the hot
plate and their temperature quickly rises to the desired
temperature. Larger parts are preferably placed in a preheat oven
and then transferred to the hot stage to maintain temperature
during coating.
[0065] The temperature of the parts is monitored using a
non-contact IR thermometer to ensure the desired temperature is
attained and the parts are uniform in temperature.
[0066] FIG. 4 schematically illustrates a system for rotating a
tube 61 and drawing a vacuum while spray coating 63. This technique
appears to have a similar effect to heating the tubes. The coatings
dried very quickly due to drawing the IPA into the substrate pores
and resulted in more dense coatings. Cross section analysis of
tubes coated by this system showed some evidence of nano particles
being drawn into the near surface internal pores of the tubes. The
level of vacuum drawn on the tubes varies by the capacity of the
mechanical vacuum pump 67 and the surface area of the tube being
coated. It was observed that the levels varied between 10 inches Hg
for larger tubes and 25 inches Hg for smaller tubes. As the
thickness of the nano coating is built up on the tubes, a
noticeable increase in the vacuum level was observed suggesting
that the coarser surface pores of the substrate material are being
plugged with the deposited nano coating, reducing the air flow
through the tubes during the coating process.
[0067] An exemplary process is: (1) mechanical pump 67 draws a
vacuum to a desired negative pressure as measured by vacuum gage
69; (2) a liquid trap 71 is installed between the vacuum pump 67
and the part 61 to be coated to prevent liquids from entering the
vacuum pump 67 and causing damage; (3) a rotary air/vacuum fitting
65 is attached to the vacuum line 73 and to a first end 75 of the
tube 61 or part to be coated. An opposing second end 77 of the tube
61 is plugged 79 to force air to be drawn through the porous
surface of the tube 61; (4) tube rotation 81 about a longitudinal
axis of the tube is turned on as well as heating of the tube if
desired; (5) the spray system is enabled and the spray head 83
shuttles 85 a length of the tube 61 to coat its exterior surface;
(6) when the surface pores begin to be plugged with the fine
coating, a rise in the vacuum level of the system will be observed
via vacuum gage 69; shut down the system, remove the tube 61 and
sinter bond the applied coating; and (8) repeat until the desired
total coating thickness is reached, typically requires three
coating/sintering cycles.
[0068] FIG. 5 schematically illustrates another system to vacuum
coat a tube or other structure. A vacuum is drawn on porous tube 61
and the tube then immersed them into a diluted IPA nano powder
suspension 41 to form a nano powder cake on the surface of the tube
61. The cake was then sinter bonded to the substrate and repeated
until the desired total thickness was achieved. A typical total
thickness desired for 316L stainless steel and titanium coating is
from 25 to 100 microns to achieve sterilizing grade efficiencies.
An advantage of this technique is that the coating was only formed
on the porous substrate surfaces. No coating was applied on the
welds or attached hardware. This is an advantage as the parts look
much better and there is no waste. Metallographic cross sections
were performed on tubes coated in this manor and it was observed
that unlike the spray coated tubes with a vacuum draw described in
reference to FIG. 4 above, no penetration of the nano powder was
seen in the internal pores of the substrates by this method.
[0069] Applying coatings in this manor using a typical spray
coating slurry concentration of 100 grams of powder in 1 liter of
isopropyl alcohol, resulted in the coatings being very thick
(>50 microns) and forming shrinkage cracks during the sinter
process. Preferably, the slurry concentration is diluted to about
10 grams of powder in 1 liter of alcohol to better control the
thickness of the coating on the tube 61. As in the spraying
technique, a desired coating thickness of around 10 to 25 microns
is desired to prevent shrinkage cracks during the sintering
process. To control thickness, the vacuum level in the tube was
monitored via vacuum gage 69 and coating stopped when the vacuum
level increased (pore plugging) or the surface of the tube turned
significantly dark. The tube/filter coating was then sintered and
recoated using the same process until the desired coating thickness
is great enough to reach sterilizing grade performance.
[0070] This technique of coating tubes/filters lacks the use of
ultrasonics of the slurry and a potential for nano particle
agglomeration exists. Agglomeration may be reduced or eliminated by
applying ultrasonic energy to the suspension 41 prior to or during
part immersion.
[0071] An exemplary process is: (1) vacuum pump 67 to draw vacuum;
(2) a liquid trap 71 is installed between the vacuum pump 67 and
the part 61 to be coated to prevent liquids from entering the
vacuum pump and causing damage; (3) a vacuum fitting 87 is attached
to a first end 75 of the tube or part to be coated. The opposing
second end 77 of the tube 61 is plugged 79 to force fluid flow
through the porous surface of the tube 61 towards the tube inside
diameter; (4) the tube 61 under vacuum pressure is submersed in a
container 89 containing the nano particles in suspension 41 in
isopropyl alcohol; (5) when the surface pores begin to be plugged
with the fine coating, a rise in the vacuum level of the system
will be observed at vacuum gage 69; (6) shut down the vacuum pump
67, remove the tube 61 and sinter bond the applied coating; and (7)
repeat until the desired total coating thickness is reached,
typically requires three coating/sintering cycles.
[0072] For medical and bio-pharmaceutical markets, a sterilizing
filter, useful to remove microbes such as bacteria and viruses from
a liquid or gas medium requires a pore size of under 0.2 micron.
Typical applications for sterilizing grade filters include various
implantable devices, filters to prevent plugging of catheters (IV
filters), syringe filters, manual and automated drug delivery
devices, medical instrumentation, sparging devices for cell culture
processing, gas flow restrictor devices for gas delivery in
life-critical systems, and bio-pharmaceutical vent filters.
[0073] While the method of the invention deposits a nano power
coating from a suspension having a carrier fluid that is
substantially free of a binder, it is within the scope of the
invention to deposit the nano powder coating and then apply a
binder as a top coat over the applied coating prior to
sintering.
[0074] The invention described herein may be better understood by
the examples that follow.
EXAMPLES
Example 1
[0075] Filtration is generally performed using either cross flow or
dead ended methods. In cross flow applications, only a portion of
the filtrate is filtered in each pass while in dead ended
applications, 100% of the fluid being filtered passes through the
filter media. A process tube 42 illustrated in FIG. 6 is useful for
cross flow filtration and control of gas or liquid flow. The
process tube 42 has a porous tubular substrate 44 with relatively
large pores on the order of 5 .mu.m. A porous coating 46 having a
total coating thickness of about 25 microns and pores on the order
of 50 nanometers (nm) in diameter covers the tubular substrate 44.
A process gas or liquid 48 flows into the process tube 42. The
filtered media 50 is sufficiently small to pass through the
micropores of the porous coating 46 and exit through a wall of the
process tube 42 while the waste stream 52 exits from an outlet side
of the process tube. The process tube 42 depicted in FIG. 3 may
also be used for dead ended filtration by plugging exit end 53 of
the tube, thereby forcing all of the fluid to pass through the
tubular porous substrate 44 and the applied porous coating 46.
[0076] The process tube 42 was made with a tubular substrate formed
from each one of 316L SS (stainless steel with a nominal
composition by weight of 16-18 percent chromium, 10%-14% nickel,
2.0-3.0% molybdenum, less than 0.03% carbon and the balance iron,
equally suitable is 316 SS, same composition without the
restrictive limitation on carbon content), INCONEL 625 (having a
nominal composition by weight of 20% chromium, 3.5% niobium, and
the balance nickel, INCONEL is a trademark of Huntington Alloy
Corporation, Huntington, W. Va.), and HASTELLOY C276. The tubular
substrate had pore sizes consistent with Media Grade 2. A slurry of
HASTELLOY C276 nanopowder and isopropyl alcohol was sprayed on the
exterior wall of the tubular substrate to a thickness of between
about 5-10 microns. The coating was sintered to the substrate by
sintering at 1,475.degree. F. for 60 minutes in a vacuum furnace.
The process was repeated two additional times to achieve a total
coating thickness of about 25 microns.
[0077] FIG. 7 is a scanning electron micrograph of the nanoporous
surface at a magnification of 40,000.times. illustrating the
sintered nanoparticles and fine pores. The nanoparticles have an
average diameter of about 100 nm and the nanopores have an average
pore diameter of about 50 nm. FIG. 8 is a scanning electron
microscope at a magnification of 1,000.times. showing in
cross-section the tubular substrate 44 and porous coating 46.
[0078] The performance of the process tube 42 was measured by
determining the flux of nitrogen gas passing through the tube. The
flux was measured at room temperature (nominally 22.degree. C.)
with a 3 psi pressure drop across the tube wall. The flux units are
SLM/in.sup.2 where SLM is standard liters per minute and in.sup.2
is square inches. Table 1 and FIG. 9 illustrate the flux values for
the process tube with from 0 to 3 nano powder coating layers. The
average flux on a Media Grade 2 substrate with a total coating
thickness of about 25 microns and average pore size of about 50 nm
was 6.69 SLM/in.sup.2. This compares extremely favorably with a
conventional Media Grade 0.5 (nominal mean flow pore size of 0.5
.mu.m) process tube that has a flux of 1.87 SLM/in.sup.2 at 3
psi.
TABLE-US-00001 TABLE 1 Flux at 3 psi (SLM/in.sup.2) Coating Sample
Number Layers 1 2 3 4 5 6 Average 0 15.23 15.48 17.09 17.28 17.67
15.57 16.39 1 9.34 8.84 14.38 11.70 10.17 11.86 11.05 2 9.07 8.25
8.06 7.93 8.33 3 6.81 6.56 6.69
Example 2
[0079] FIG. 10 illustrates in cross-sectional representation a
membrane 54 useful in the production of hydrogen for fuel cell
applications. A microporous substrate 56 is coated with a
nanocoating 58 of palladium or platinum or their alloys. The
substrate pore size is on the order of from 1 to 40 microns and
more preferably from 1 to 10 microns. The coating include pores
with diameters of from about 50 nm to 10 microns. Subsequent layers
may be deposited onto the nanocoating such as by plating or layered
deposition to generate an active surface for hydrogen
generation.
Example 3
[0080] FIG. 11 illustrates a particle retention barrier 60
effective to stop aluminum oxide beads from passing through a
liquid chromatography column. The particle retention barrier 60
includes a microporous frit 62 that is typically formed from
stainless steel, HASTELLOY or titanium powders. Frit 62 has a
diameter on the order of 0.082 inch (Media Grade 0.5 to 2). A nano
powder layer 64, usually of the same composition as the frit, coats
one side of the frit 62. The barrier 60 is formed by micropipetting
or spraying a suspension of nano powder onto the surface and then
vacuum sintering.
Example 4
[0081] FIG. 12 illustrates a component 66 for improved catalytic
performance. A nano powder layer 68 of platinum or other catalytic
material coats a surface of a metal or ceramic support 70 for use
in a catalytic converter, for industrial applications and/or
automotive uses.
Example 5
[0082] FIG. 13 illustrates a nano powder coating 72 applied to a
surface of a substrate 74 to increase the surface area and provide
locking pores for a polymer adhesive 76 thereby dramatically
increasing the strength of the adhesive bond.
Example 6
[0083] An example of creating a dilute distribution of isolated
particles in a coating would be to create a 1:100 mixture of
platinum particles in a stainless steel powder and then depositing
this mixture onto a stainless steel substrate and sinter bonding.
In this example, which would apply to a catalyst coating for fuel
cell applications, one ends up with isolated platinum particles in
a stainless steel surface. Here the stainless steel powder in the
coating becomes indistinguishable from the substrate and the dilute
platinum particles from the original coating are distributed over
the surface of the substrate.
Example 7
[0084] An example of bonding stainless steel to a substrate at
lower temperatures would be to mix a lower temperature melting
powder like tin with stainless steel 316 L SS powder that has a
much higher melting temperature, coating the substrate with this
mixture, and then follow up with sintering. The lower temperature
component (tin) would diffuse at much lower temperatures than the
stainless steel thus causing sintering and bonding at lower
temperatures.
Example 8
[0085] A sterilizing filter, useful to remove microbes such as
bacteria and viruses from a liquid or gas medium requires a pore
size effective to capture microbes greater than 0.2 micron. Filter
sterilization discs were made by the ultrasonic spray deposition
process described above and their effectiveness to remove bacteria
evaluated. The operating parameters were:
[0086] 47 mm diameter disks with 1'' MG2 stainless steel filter
inserts
[0087] Heated Substrate: 150 F
[0088] Spray head speed: 50 mm/sec
[0089] Spray Head Distance: 2.5 inches
[0090] Fluid flow rate: 6 ml/min
[0091] Ultrasonic energy levels (Spray gun 6-Watts, Agitator
4-Watts)
[0092] Suspension: 100 grams of 316L SS powder in 1 liter of
IPA
[0093] 2 Spray coats, Sintered, Repeated 5 times
[0094] Sintering Temperature: 1350 F
[0095] Typical IPA bubble point >20 "Hg
[0096] Typical Water bubble point: >30 "Hg
[0097] IPA Flow Rate: 1.13 mL/min/cm.sup.2@ 10 psi
[0098] Nitrogen Flow Rate: 410 mL/min/cm.sup.2 @ 10 psi
[0099] LRV Efficiencies: >7 LRV (@ 0.2 micron particle size,
LRV=Log Reduction Value)
[0100] Microbial retention ASTM F838-05 or equivalent: Passed
TABLE-US-00002 TABLE 3 Liquid IPA Flow Data for 47 mm disk
assemblies Corrected Pressure Temp Flow Flow Flux (psi) C. (ccm)
(sccm) (mL/min/cm.sup.2) 0 0 0 0 0 2.5 20.82 1.27 1.30 0.26 5 20.90
2.69 2.75 0.54 10 21.16 5.65 5.71 1.13 15 21.18 8.85 8.95 1.77 20
21.13 11.76 11.90 2.35 25 21.09 14.88 15.08 2.98 50 20.89 30.23
30.84 6.09 See FIG. 14
TABLE-US-00003 TABLE 4 Nitrogen gas flow data for 47 mm disk
assemblies See Figure 15 Flow (SLM) Flux Pressure Disk 1 Disk 3
Disk 5 Disk 6 Disk 8 Disk 15 Avg. SLM/cm.sup.2 0 0 0.00 5 0.8 0.8
0.9 0.9 0.8 0.8 0.83 0.16 10 2.1 2 2.2 2.4 1.8 2 2.08 0.41 15 3.6
3.4 3.7 4 3.1 3.4 3.53 0.70 20 5.4 5.2 5.6 6.2 4.6 5.2 5.37 1.06 25
7.7 7.3 7.9 8.8 6.5 7.3 7.58 1.50
[0101] For microbial retention testing per ASTM F838-05, all
equipment was sterilized/disinfected prior to use. All testing was
conducted in a laminar flow hood. Prior to processing each filter,
a control was prepared by filtering a minimum of 100 mL of sterile
buffer through the test filter. One hundred milliliters of filtrate
was aseptically collected downstream of the test filter in a
sterile container. The filtrate was filtered using a microbial
retentive filter. The microbial retentive filter was placed onto
Plate Count Agar and allowed to incubate at 30.+-.2.degree. C. for
7 days. A 48 hour pre-count was performed on each filter.
[0102] After the control was processed, the test filter was
challenged with approximately 3.times.10.sup.7 to 5.times.10.sup.7
CFU/100 mL of B. diminuta. One hundred milliliters of filtrate was
aseptically collected downstream of the test filter in a sterile
container. The filtrate was filtered using a microbial retentive
filter. The microbial retentive filter was placed onto Plate Count
Agar and allowed to incubate at 30.+-.2.degree. C. for 7 days. A 48
hour pre-count was performed on each filter.
[0103] Table 2 sets out the effectiveness of the sterilizing
filters produced herein:
TABLE-US-00004 TABLE 2 CFU/100 mL Sample (CFU = Colony Forming
Units) Bacterial Retention of Description Test Control Challenge
Organism Disc #1 0 0 Pass Disc #3 0 0 Pass Disc #5 0 0 Pass Disc #6
0 0 Pass Disc #8 0 0 Pass Disc #15 0 0 Pass
Example 9
[0104] A high efficiency filter for removing impurities from a gas
or liquid medium utilizes depth filtration processes. An example of
this would be to apply a relatively thick coating on the order of
200 microns on to a supporting substrate that utilizes the depth
filtration technique to capture the very fine particulate/microbes
for this kind of filtration. To build up this thickness, several
thinner layers would be applied and sintered as described in the
application to minimize shrinkage cracks during the sintering
process.
Example 10
[0105] FIGS. 16A and 16B are cross-sectional images at
magnifications of 500 times and 1000 times, respectively, of a
Media Grade 2 substrate coated with 316L stainless steel
nanoparticles according to the method illustrated in FIG. 3. The
operating parameters were:
[0106] Heated Substrate: 150 F
[0107] Spray head speed: 50 mm/sec
[0108] Spray Head Distance: 2.5 inches
[0109] Fluid flow rate: 3 ml/min
[0110] Ultrasonic energy levels (Spray gun 6-Watts, Agitator
4-Watts)
[0111] Suspension: 25 grams of 316L SS powder in 1 liter of IPA
[0112] 2 Spray coats, Sintered, 2 additional spray coats and
sintered.
[0113] Sintering Temperature: 1425 F
[0114] Typical IPA bubble point >20 "Hg
[0115] No flow data Available
Example 11
[0116] FIGS. 17A and 17B are cross-sectional images at
magnifications of 350 times and 1000 times, respectively, of a
Media Grade 2 tubular substrate coated with 316L stainless steel
nanoparticles according to the method illustrated in FIG. 4. The
operating parameters were:
[0117] 1/2'' OD MG2 Tubes.times.5 inches long
[0118] Alloy 316L SS
[0119] Tubes heated to 160 F prior to coating
[0120] Rotation speed: 100 RPM
[0121] Spray head speed: 3 mm/sec
[0122] Spray Head Distance: 2.0 inches
[0123] Fluid flow rate: 3 ml/min
[0124] Ultrasonic energy levels (Spray gun 6-Watts, Agitator
4-Watts)
[0125] Suspension: 25 grams of 316L SS powder in 1 liter of IPA
[0126] 2 spray passes and then sintered, repeated three more
times
[0127] Total coating thickness: 30-60 microns
[0128] Sintering temperature: 1515 F
[0129] Typical IPA bubble point: >20 "Hg
[0130] Typical Water bubble point: >30 "Hg
[0131] IPA Flow Rate: 0.89 mL/min/cm.sup.2 @ 10 psi
[0132] Nitrogen Flow Rate: 590 mL/min/cm.sup.2 @ 10 psi
[0133] LRV Efficiencies 9 to 12 log @ 0.2 micron particles
FIG. 18 graphically illustrate nitrogen gas flow for 0.5 inch
outside diameter coated tubes and FIG. 19 graphically illustrates
IPA liquid flow for the same tubes.
Example 12
[0134] FIG. 20 is a photograph of a 10" Bio-Pharmaceutical Vent
Filter for Sterilizing Grade Applications made from 316L stainless
steel and nanoparticles according to the method illustrated in FIG.
4. The operating parameters were:
[0135] 21/2'' ISO Pressed Tubes or Rolled & Welded Cartridges
welded to a 226 interface flange
[0136] Alloy 316L SS
[0137] Substrate Media Grade: 2
[0138] Tubes heated to 160 F prior to coating
[0139] Rotation speed: 100 RPM
[0140] Spray head speed: 2 mm/sec
[0141] Spray Head Distance: 1.5 inches
[0142] Fluid flow rate: 5 ml/min
[0143] Air pressure 10''H.sub.2O
[0144] Ultrasonic energy levels (Spray gun 6-Watts, Agitator
4-Watts)
[0145] Suspension: 25 grams of 316L SS powder in 1 liter of IPA
[0146] 1 spray passes and then reheated to 160 F followed a second
spray coat
[0147] Spray coating and sintering cycle repeated three times
[0148] Total coating thickness: 30-75 microns
[0149] Sintering temperature: 1500 F in hydrogen
[0150] Furnace: Sinterite Belt furnace running at 6 inches/min
Example 13
[0151] FIG. 21 is a photograph of several Small Parts for
Sterilizing Grade Filtration for use in Medical devices made from
316L stainless steel and nanoparticles according to the method
illustrated in FIG. 3. The operating parameters were:
[0152] Parts: Disks and/or sleeved restrictors
[0153] Substrate material: 316L Stainless Steel
[0154] Heated Substrate: 150 F
[0155] Spray head speed: 50 mm/sec
[0156] Spray Head Distance: 2.5 inches
[0157] Fluid flow rate: 3 ml/min
[0158] Ultrasonic energy levels (Spray gun 6-Watts, Agitator
4-Watts)
[0159] Suspension: 25 grams of 316L SS 80-100 .eta.m average
particle size powder in 1 liter of IPA
[0160] 2 Spray coats, Sintered, 2 additional spray coats and
sintering cycles.
[0161] Sintering Temperature: 1425 F
[0162] Sintering Atmosphere: Hydrogen
[0163] Sintering Time: 60 minutes
[0164] The above products of Examples 12 ands 13 may be fabricated
using titanium as well. The same process is followed except we
change the materials to titanium and sinter in an Argon
atmosphere.
Example 14
[0165] This example is similar to Example 8 utilizing titanium
instead of stainless steel and the processing conditions are
slightly different. A sterilizing filter, useful to remove microbes
such as bacteria and viruses from a liquid or gas medium requires a
pore size effective to capture microbes greater than 0.2 micron.
Filter sterilization disks were made by the ultrasonic spray
deposition process previously described and their effectiveness to
remove bacteria evaluated. Here the materials of construction are
titanium which makes this filter suitable for medical uses and for
implantable applications. The operating parameters were:
[0166] 47 mm diameter disks with 1'' MG0.5titanium filter
inserts
[0167] Heated Substrate: 140 F
[0168] Spray head speed: 100 mm/sec
[0169] Spray Head Distance: 2.5 inches
[0170] Fluid flow rate: 6 ml/min
[0171] Ultrasonic energy levels (Spray gun 6-Watts, Agitator
4-Watts)
[0172] Suspension: 100 grams of titanium powderin 1 liter of
IPA
[0173] 2 Spray coats, Sintered, Repeated 4 times
[0174] Sintering Temperature: 1610 F
[0175] Typical IPA bubble point >20 "Hg
[0176] Typical Water bubble point: >30 "Hg
[0177] Microbial retention ASTM F838-05 or equivalent: Passed
Example 15
[0178] A larger flat plate useful as a sterilizing vent filter to
provide a sterile barrier between ambient air and a sterile
enclosure such as a medical transport tray was formed in accordance
with the following:
[0179] 5''.times.5''.times.062'' thick 316L stainless steel porous
plate with an average pore size about 0.5 microns.
[0180] Heated Substrate: 180 F
[0181] Spray head speed: 100 mm/sec
[0182] Spray Head Distance: 2.5 inches
[0183] Fluid flow rate: 6 ml/min
[0184] Ultrasonic energy levels (Spray gun 6-Watts, Agitator
4-Watts)
[0185] Suspension: 100 grams of 316L Stainless steel powder in 1
liter of IPA
[0186] 2 Spray coats, Sintered, Repeated 5 times
[0187] Sintering Temperature: 1550 F
[0188] Typical IPA bubble point >20 "Hg
[0189] One or more embodiments of the present invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, other embodiments are within
the scope of the following claims.
* * * * *