U.S. patent application number 11/149622 was filed with the patent office on 2005-11-10 for resistive heaters and uses thereof.
Invention is credited to Abbott, Richard C., Glenn, William A., Magnant, Gary P..
Application Number | 20050247694 11/149622 |
Document ID | / |
Family ID | 22962405 |
Filed Date | 2005-11-10 |
United States Patent
Application |
20050247694 |
Kind Code |
A1 |
Abbott, Richard C. ; et
al. |
November 10, 2005 |
Resistive heaters and uses thereof
Abstract
The present invention features a metallic resistive heater and
uses thereof. The resistive heater includes a metallic component
that is electrically conductive (i.e., has low resistivity) and an
oxide, nitride, carbide, and/or boride derivative of the metallic
component that is electrically insulating (i.e., has high
resistivity). The resistivity is controlled in part by controlling
the amount of oxide, nitride, carbide, and boride formation during
the deposition of the metallic component and the derivative.
Inventors: |
Abbott, Richard C.; (New
Boston, NH) ; Magnant, Gary P.; (Topsfield, MA)
; Glenn, William A.; (Groton, MA) |
Correspondence
Address: |
HAYES, SOLOWAY P.C.
175 CANAL STREET
MANCHESTER
NH
03101
US
|
Family ID: |
22962405 |
Appl. No.: |
11/149622 |
Filed: |
June 10, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11149622 |
Jun 10, 2005 |
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09996183 |
Nov 28, 2001 |
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6919543 |
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60253969 |
Nov 29, 2000 |
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Current U.S.
Class: |
219/469 ;
219/553 |
Current CPC
Class: |
C23C 4/12 20130101; B21B
2027/086 20130101; H05B 3/12 20130101; Y10T 29/49099 20150115; F27D
1/1636 20130101; C23C 4/123 20160101; Y02T 50/60 20130101; H01L
21/67103 20130101; C23C 4/02 20130101; B29C 45/73 20130101 |
Class at
Publication: |
219/469 ;
219/553 |
International
Class: |
H05B 003/10 |
Claims
What is claimed is:
47. A cylindrical roller comprising an outer surface, an inner
surface surrounding a hollow core, and a resistive heater
comprising a resistive layer coupled to a power source, said
resistive layer comprising a metallic component and one or more
oxide, nitride, carbide, and/or boride derivatives of said metallic
component, wherein said resistive layer has a resistivity of 0.0001
to 1.0 .OMEGA.cm, and wherein application of current from said
power supply to said resistive layer results in production of heat
by said resistive layer, wherein said resistive heater is disposed
on said outer surface or said inner surface.
48-50. (canceled)
51. A roller, comprising: a cylinder having an outer surface and an
inner surface surrounding a hollow core; and a resistive heater
coating comprising a resistive layer, where the resistive layer is
coupled to a power source, the resistive layer comprising a
metallic component and one or more oxide, nitride, carbide, and/or
boride derivatives of the metallic component, wherein the resistive
layer has a resistivity of 0.0001 to 1.0 Ohm-cm, wherein
application of current from the power supply to the resistive layer
results in production of heat by the resistive layer, and wherein
the resistive heater coating is disposed on the cylinder.
52. The roller of claim 51, wherein the resistive heater coating is
disposed on the outer surface of the cylinder.
53. The roller of claim 51, wherein the resistive heater coating is
disposed on the inner surface of the cylinder.
54. The roller of claim 51, further comprising an electrically
insulating layer located substantially between the cylinder and the
resistive layer.
55. The roller of claim 51, further comprising an anticorrosive
coating applied to the cylinder.
56. The roller of claim 51, further comprising a metal casing
affixed to the cylinder.
57. The roller of claim 51, wherein the resistive layer is formed
by a reaction of at least a portion of the solid metallic component
and a reactant gas by melting at least a portion of the solid
metallic component to form a stream of molten droplets, and
providing controlled introduction of the reactant gas to the molten
droplets, thereby combining the molten droplets and the reactant
gas, resulting in a free metal and reaction product.
58. A method of making a roller, the method comprising the steps
of: selecting a solid metallic component and at least one reactant
gas; selecting a proportion of the solid metallic component and the
at least one reactant gas to achieve a desired resistivity of a
resistive layer; promoting reaction of at least a portion of the
solid metallic component and the reactant gas by melting at least a
portion of a solid metallic component resulting in a stream of
molten droplets, and providing controlled introduction of the
reactant gas to the molten droplets, thereby combining the molten
droplets and the reactant gas, resulting in a free metal and
reaction product; depositing the combined free metal and reaction
product on a cylinder having an outside surface and an inside
surface, to form the resistive layer having the desired
resistivity; and providing power to the resistive layer.
59. The method of claim 58, wherein said reaction product is one or
more oxide, nitride, carbide, and/or boride derivatives of said
metallic component.
60. The method of claim 58, further comprising the step of applying
an anticorrosive coating to the cylinder.
61. The method of claim 58, wherein the step of depositing the
combined free metal and reaction product on the cylinder further
comprises depositing the combined free metal and reaction product
using a high velocity oxy-fuel wire spray system, titanium wire,
and nitrogen gas.
62. The method of claim 58, further comprising the step of
thermally spraying a layer of aluminum oxide to the cylinder.
63. The method of claim 58, further comprising the step of applying
at least one layer of a high-temperature sealant to the
cylinder.
64. The method of claim 63, further comprising the step of coating
the cylinder with a high-temperature silicone.
65. The method of claim 58, further comprising the step of affixing
a metal casing to the cylinder.
66. The method of claim 58, further comprising the step of
thermally spraying a metallic layer over the outside surface of the
cylinder.
67. The method of claim 58, further comprising the step of applying
an electrically insulating layer substantially between the cylinder
and the resistive layer.
68. The method of claim 58, wherein the step of depositing the
combined free metal and reaction product on a cylinder is performed
in a manner to provide the cylinder with a pattern of heating
zones.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of co-pending U.S.
Provisional Application Ser. No. 60/253,969, filed Nov. 29, 2000,
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The invention relates to the field of resistive heaters.
[0003] Thermal Spray
[0004] Thermal spray is a versatile technology for depositing
coatings of metals or ceramics. It includes systems that use powder
as feedstock (e.g., arc plasma, flame spray, and high velocity
oxy-fuel (HVOF) systems), and systems that use wire as feedstock
(e.g., arc wire, HVOF wire, and flame spray systems).
[0005] Arc plasma spraying is a method for depositing materials on
various substrates. A DC electric arc creates an ionized gas (a
plasma) that is used to spray molten powdered materials in a manner
similar to spraying paint.
[0006] Arc wire spray systems function by melting the tips of two
wires (e.g., zinc, copper, aluminum, or other metal) and
transporting the resulting molten droplets by means of a carrier
gas (e.g., compressed air) to the surface to be coated. The wire
feedstock is melted by an electric arc generated by a potential
difference between the two wires.
[0007] In flame spray, a wire or powder feedstock is melted by
means of a combustion flame, usually effected through ignition of
gas mixtures of oxygen and another gas (e.g., acetylene).
[0008] HVOF uses combustion gases (e.g., propane and oxygen) that
are ignited in a small chamber. The high combustion temperatures in
the chamber cause a concurrent rise in gas pressure that, in turn,
generates a very high speed effluent of gas from an orifice in the
chamber. This hot, high speed gas is used to both melt a feedstock
(e.g., wire, powder, or combination thereof) and transport the
molten droplets to the surface of a substrate at speeds in the
range of 330-1000 m/sec. Compressed gas (e.g., compressed air) is
used to further accelerate the droplets and cool the HVOF
apparatus.
[0009] A thermal sprayed coating has a unique microstructure.
During the deposition process, each particle enters the gas stream,
melts, and cools to the solid form independent of other particles.
When molten particles impact the substrate being coated, they
impact ("splat") as flattened circular platelets and freeze at high
cooling rates. The coating is built up on the substrate by
traversing the plasma gun apparatus repeatedly over the substrate
building up layer by layer until the desired thickness of coating
has been achieved. Because the particles solidify as splats, the
resultant microstructure is very lamellar with the grains
approximating circular platelets randomly stacked above the plane
of the substrate.
[0010] Resistive Heaters
[0011] Thermal spray technology has been used to deposit a coating
for use as a heater. A resistive heater produces heat by the
collision of electrons with the atoms of the heater material. The
rate at which heat is generated is the power, which depends on the
amount of current flowing and the resistance to the current flow
offered by the material. The resistance of a heater depends on a
material property termed "resistivity," and a geometric factor
describing the length of the current path and the cross-sectional
area through which the current passes.
[0012] Previously, resistive coatings have been deposited using
thermal spray. In one such example, metal alloys such as 80%
Nickel-20% Chrome are deposited and used as heaters. In another
example, a metal alloy in powder form is mixed with powders of
electrical insulators such as aluminum oxide prior to deposition.
The blended material is then deposited using thermal spray to form
a coating of resistive material. When nickel-chrome is deposited as
a resistive heater, however, the bulk resistivity of the layer is
still rather low, which makes it more difficult to form an element
because a long path length is required to achieve a high enough
resistance. When oxide-metal blends are deposited, large
discontinuities in the composition of resistive layer, which
produce variations in power distribution over a substrate, are
frequently present.
[0013] Molding Thermoplastic Materials
[0014] Many plastic and metal parts are manufactured by injecting
molten metal or polymer melt into a complex cavity cut into steel,
for example, aluminum automobile transmission housings or
polycarbonate computer cases. Injection-molding machinery melts a
thermoplastic powder in a heating chamber and forces it into a
mold, where it hardens. The operations take place at rigidly
controlled temperatures and intervals. In an injection molding
process, it is important to maintain a material such as
polycarbonate in a molten state as it flows into and through a mold
cavity space. Additionally, the shear stress profile of the flow of
resin must be monitored and managed to insure proper filling of the
cavity space. If the molten resin solidifies too rapidly when it
encounters a cold mold, it will not penetrate narrow cavities and
will form weak knit lines where two flows intersect. Accordingly,
much effort has been directed towards improving heat management and
flow control in the injection molding process.
SUMMARY OF THE INVENTION
[0015] The present invention features a metallic resistive heater
and uses thereof. The resistive heater includes a metallic
component that is electrically conductive (i.e., has low
resistivity) and an oxide, nitride, carbide, and/or boride
derivative of the metallic component that is electrically
insulating (i.e., has high resistivity). The resistivity is
controlled in part by controlling the amount of oxide, nitride,
carbide, and boride formation during the deposition of the metallic
component and the derivative. The resistive heater has numerous
industrial and commercial applications (i.e, production of molded
thermoplastic parts, paper, and semiconductor wafers).
[0016] Accordingly, in a first aspect, the invention features a
resistive heater that includes a resistive layer coupled to a power
source. The resistive layer includes a metallic component and one
or more oxide, nitride, carbide, and/or boride derivatives of the
metallic component. The resistivity of the resistive layer results
from the amount of the oxide, nitride, carbide, and/or boride
present in the resistive layer. Desirably, the resistive heater is
disposed on a substrate such as a mold cavity surface.
[0017] In one embodiment, the resistive layer has a microstructure
that resembles a plurality of flattened discs or platelets having
an outer region of nitride, oxide, carbide, and/or boride
derivatives of the metallic component, and an inner region of the
metallic component.
[0018] In a second, related aspect, the invention features a
resistive heater on a substrate, the heater made by a method that
includes the steps of providing a substrate, a metallic component
feedstock, and a gas including oxygen, nitrogen, carbon, and/or
boron; melting the feedstock to produce a stream of molten
droplets; reacting the molten droplets with the gas to produce one
or more oxide, nitride, carbide, or boride derivatives of the
metallic component, wherein a portion of the metallic component
reacts with the gas to produce the oxide, nitride, carbide, and/or
boride derivative of the metallic component and a portion of the
metallic component remains unreacted; depositing the unreacted
metallic component and the oxide, nitride, carbide, and/or boride
derivative of the metallic component onto the substrate to produce
a resistive layer; and connecting the resistive layer to a power
supply.
[0019] In one embodiment of the heater of the second aspect, the
melting step and the reacting step are coordinated such that the
resistive layer has a resistivity of 0.0001 to 1.0
.OMEGA..multidot.cm (e.g., 0.0001 to 0.001 .OMEGA..multidot.cm,
0.001 to 0.01 .OMEGA..multidot.cm, 0.01 to 0.1 .OMEGA..multidot.cm,
or 0.1 to 1.0 .OMEGA..multidot.cm). In another embodiment, the
molten droplets have an average diameter of 5 to 150 .mu.m, 10 to
100 .mu.m, or 20 to 80 .mu.m. In other desirable embodiments, the
method includes the additional step of applying a ceramic or
metallic layer superficial to the resistive layer, an electrically
insulating layer between the substrate and the resistive layer,
and/or an adhesion layer between the substrate and the insulating
layer.
[0020] In a third aspect, the invention features a method of
producing a resistive heater on a substrate. The method includes
the steps of providing a substrate, a metallic component feedstock,
and a gas including oxygen, nitrogen, carbon, and/or boron; melting
the feedstock to produce a stream of molten droplets; reacting the
molten droplets with the gas to produce one or more oxide, nitride,
carbide, or boride derivatives of the metallic component, wherein a
portion of the metallic component reacts with the gas to produce
the oxide, nitride, carbide, and/or boride derivative of the
metallic component and a portion of the metallic component remains
unreacted; depositing the unreacted metallic component and the
oxide, nitride, carbide, and/or boride derivative of the metallic
component onto the substrate to produce a resistive layer; and
connecting the resistive layer to a power supply.
[0021] In particular embodiments of any of the first, second, and
third aspects, the substrate is an injection mold, a roller, or a
platen for semiconductor wafer processing.
[0022] In yet another aspect, the invention features an injection
mold that includes (i) a mold cavity surface and (ii) a coating
that includes a resistive heater that in turn includes a resistive
layer coupled to a power supply, the coating being present on at
least a portion of the surface. The resistive layer includes a
metallic component and one or more oxide, nitride, carbide, and/or
boride derivatives of the metallic component. In one embodiment,
the resistivity of the resistive layer results from the amount of
the oxide, nitride, carbide, and/or boride present in the resistive
layer. Desirably, the mold includes a runner, and the coating is
disposed on at least a portion of a surface of the runner.
[0023] In still another aspect, the invention features a method of
making a molded, product. This method includes the steps of
providing an injection mold as described above; injecting a
thermoplastic melt into the mold; and cooling the melt in the mold
to form the molded product. The heated resistive heater regulates
solidification and cooling of the melt. In one embodiment, the
resistive heater is produced by the method described above.
[0024] In another aspect, the invention features a cylindrical
roller including an outer surface, an inner surface surrounding a
hollow core, and a resistive heater including a resistive layer
coupled to a power source. The resistive layer includes a metallic
component and one or more oxide, nitride, carbide, and/or boride
derivatives of the metallic component, and is disposed on the outer
surface and/or on the inner surface of the cylindrical roller.
[0025] In still another aspect, the invention features a method of
drying paper during manufacturing. This method includes the steps
of providing paper including a water content of greater than about
5% and one or more cylindrical rollers as described above; heating
the roller with the resistive heater; and contacting the paper with
the roller for a time suitable for drying the paper to a water
content of less than about 5%.
[0026] In another aspect, the invention features a semiconductor
wafer processing system including an enclosure defining a reaction
chamber; a support structure mounted within the reaction chamber,
the support structure mounting a semiconductor wafer to be
processed within the chamber; and a resistive heater including a
resistive layer coupled to a power source, the resistive layer
including a metallic component and one or more oxide, nitride,
carbide, and/or boride derivatives of the metallic component. In
one embodiment, a heater is placed on the top of the reaction
chamber such that one side (typically polished) of a wafer may be
placed adjacent to or in contact with the heater. In another
embodiment, a heater is placed on the bottom of the chamber such
that one side (polished or unpolished) of a wafer may be placed
adjacent to or in contact with the heater; In yet another
embodiment, heaters are placed on the top and the bottom of the
chamber.
[0027] In still another aspect, the invention features a method for
heating a semiconductor wafer including the steps of providing a
semiconductor wafer and a semiconductor wafer processing system as
described above; and heating the wafer with the resistive
heater.
[0028] In various embodiments of any of the foregoing aspects, the
resistive layer has a resistivity of 0.0001 to 1.0
.OMEGA..multidot.cm (e.g., 0.0001 to 0.001 .OMEGA..multidot.cm,
0.001 to 0.01 .OMEGA..multidot.cm, 0.01 to 0.1 .OMEGA..multidot.cm,
or 0.1 to 1.0 .OMEGA..multidot.cm), and the application of current
from the power supply to the resistive layer results in production
of heat by the resistive layer. Preferably, the resistive layer is
capable of generating a sustained temperature of greater than
200.degree. F., 350.degree. F., 400.degree. F., 500.degree. F.,
1200.degree. F or 2200.degree. F. In various other embodiments, the
resistive heater includes an electrically insulating layer (e.g., a
layer including aluminum oxide or silicon dioxide) between the
substrate and the resistive layer; an adhesion layer (e.g., one
including nickel-chrome alloy or nickel-chrome-aluminum-yttriu- m
alloy) between the insulating layer and the substrate, a heat
reflective layer (e.g., a layer including zirconium oxide) between
the resistive layer and the substrate, a ceramic layer (e.g., one
including aluminum oxide) superficial to the resistive layer,
and/or a metallic layer (e.g., one including molybdenum or
tungsten) superficial to the resistive layer. Desirably, the
metallic component of the resistive heater is titanium (Ti),
silicon (Si), aluminum (Al), zirconium (Zr), cobalt (Co), nickel
(Ni), or alloys or combinations thereof. Other suitable metallic
components are described herein.
[0029] A particular embodiment of the invention includes the use of
insulating layers positioned above or below the heater to insulate
the resistive layer electrically from adjacent, electrically
conductive components. Additional layers can be added to reflect or
emit heat from the heater in a selected pattern. One or more layers
can also be included to provide improved thermal matching between
components to prevent bending or fracture of different layers
having different coefficients of thermal expansion. Layers that
improve the adhesion between layers and the substrate may also be
used.
[0030] By "metallic component" is meant a metal, metalloid, or
composite thereof capable of forming an oxide, carbide, nitride,
and/or boride by reaction with a gas.
[0031] By "metallic component feedstock" is meant a metallic
component in a physical form suitable for use in thermal spraying.
Exemplary physical forms include, without limitation, wire, powder,
and ingots.
[0032] Exemplary metallic components include, without limitation,
transition metals such as titanium (Ti), vanadium (V), cobalt (Co),
nickel (Ni), and transition metal alloys; highly reactive metals
such as magnesium (Mg), zirconium (Zr), hafnium (Hf), and aluminum
(Al); refractory metals such as tungsten (W), molybdenum (Mo), and
tantalum (Ta); metal composites such as aluminum/aluminum oxide and
cobalt/tungsten carbide; and metalloids such as silicon (Si).
[0033] By "substrate" is meant any object on which a resistive
layer is deposited. The substrate may be, e.g., bare ceramic, or it
may have one or more layers, e.g., an electrically insulating
layer, on its surface.
[0034] By "thermoplastic material" is meant a material capable of
softening or fusing when heated and of hardening again when cooled.
Exemplary thermoplastic materials include metals and thermoplastic
organic polymers. A "thermoplastic melt" is the softened or molten
thermoplastic material.
[0035] By "cycle time" is meant the time elapsed between a certain
point in one cycle and that same point in the next cycle. For
example, the cycle time for injection molding is measured as the
time between injections of thermoplastic melt into a mold.
[0036] By "runner" is meant a channel that transports a
thermoplastic melt from an entrance to a mold to the cavity.
[0037] Other features and advantages will be apparent from the
description of the preferred embodiments, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 shows an illustration of an HVOF wire system 2 that
uses metal wire 4 as feedstock and combustion of fuel gases 6 for
melting the feedstock. A reactant gas 8 reacts with the molten
feedstock and transports the molten droplets to a substrate 10 to
produce a layer 12.
[0039] FIG. 2 shows an illustration of a plasma spray system 100
that uses metal powder 110 as feedstock and generates an argon
120/hydrogen 130 plasma to melt the powder. Another reactant gas
140 is supplied to the molten droplets through a nozzle 150. The
molten droplets are deposited as a layer 160 on a substrate
170.
[0040] FIG. 3 shows an illustration of a spray deposited resistive
heater designed for the inside surface of a roller 200. A resistive
layer 210 is deposited in a pattern of rings for the production of
resistive heaters that heat in parallel.
[0041] FIG. 4 shows an illustration of a cross section of an
injection mold including a resistive heater. The surface of a metal
mold 300 includes several layers: an adhesion layer 310, an
electrically and thermally insulating layer 320, a metallic
resistive layer 330, an electrically insulating and thermally
conducting layer 340, and a metal layer 350. A terminal 360,
insulated from the mold by a terminal insulator 370, connects the
resistive layer to a power supply.
DETAILED DESCRIPTION
[0042] We have discovered a metallic resistive layer (and methods
of making same) that includes a metallic component that is
electroconductive and an oxide, nitride, carbide, and/or boride
derivative of the metal component that is electrically insulating.
We have further discovered that this resistive layer, when coupled
to a power supply, functions as a heater.
[0043] To deposit a layer that will generate heat when a voltage is
applied, the layer must have a resistance that is determined by the
desired power level. The resistance, R, is calculated from the
applied voltage, V, and the desired power level, P, from:
R=V.sup.2/P
[0044] The resistance is related to the geometry of the heater
coating--the electric current path length, L, and the cross
sectional area, A, through which the current passes--and also to
the material resistivity, .rho., by the equation:
R=.rho.L/A
[0045] Therefore, to design a layer for a given power level and a
given geometry that will operate at a given voltage, one has only
to determine the resistivity of the material by:
.rho.=R A/L=V.sup.2A/PL
[0046] In the present invention, the resistivity is controlled in
part by controlling the amount of oxide, nitride, carbide, and
boride formation during the deposition of the metallic component
and the derivative.
[0047] That the resistivity is a controlled variable is significant
because it represents an additional degree of freedom for the
heater designer. In most situations, the resistivity of the heater
material, e.g., nichrome, is a fixed value. In such an instance,
the heater designer must arrange the heater geometry (L and A) to
obtain the desired power. For example, if it is desired to heat a
tube by winding nichrome wire around it, the designer must choose
the correct diameter wire for A, the cross sectional area through
which the electric current must pass, and the spacing of the
windings for L, the total path length of the electric current.
[0048] We now describe the resistive layer, its application as a
component of a coating, and its use as a resistive heater.
[0049] Metallic Components and Oxides, Nitrides, Carbides and
Borides thereof
[0050] Metallic components of the invention include any metals or
metalloids that are capable of reacting with a gas to form a
carbide, oxide, nitride, boride, or combination thereof. Exemplary
metallic components include, without limitation, transition metals
such as titanium (Ti), vanadium (V), cobalt (Co), nickel (Ni), and
transition metal alloys; highly reactive metals such as magnesium
(Mg), zirconium (Zr), hafnium (Hf), and aluminum (Al); refractory
metals such as tungsten (W), molybdenum (Mo), and tantalum (Ta);
metal composites such as aluminum/aluminum oxide and
cobalt/tungsten carbide; and metalloids such as silicon (Si). These
metallic components typically have a resistivity in the range of
1-100.times.10.sup.-8 .OMEGA..multidot.m. During the coating
process (e.g., thermal spraying), a feedstock (e.g., powder, wire,
or solid bar) of the metallic component is melted to produce, e.g.,
droplets and exposed to a gas containing oxygen, nitrogen, carbon,
and/or boron. This exposure allows the molten metallic component to
react with the gas to produce an oxide, nitride, carbide, or boride
derivative, or combination thereof, on at least a portion of the
surface of the droplet.
[0051] The nature of the reacted metallic component is dependent on
the amount and nature of the gas used in the deposition. For
example, use of pure oxygen results in an oxide of the metallic
component. In addition, a mixture of oxygen, nitrogen, and carbon
dioxide results in a mixture of oxide, nitride, and carbide. The
exact proportion of each depends on intrinsic properties of the
metallic component and on the proportion of oxygen, nitrogen, and
carbon in the gas. The resistivity of the layers produced by the
methods herein range from 500-50,000.times.10.sup.-8.OMEG-
A..multidot.m.
[0052] Exemplary species of oxide include TiO.sub.2, TiO,
ZrO.sub.2, V.sub.2O.sub.5, V.sub.2O.sub.3, V.sub.2O.sub.4, CoO,
Co.sub.2O.sub.3, CoO.sub.2, Co.sub.3O.sub.4, NiO, MgO, HfO.sub.2,
Al.sub.2O.sub.3, WO.sub.3, WO.sub.2, MoO.sub.3, MoO.sub.2,
Ta.sub.2O.sub.5, TaO.sub.2, and SiO.sub.2. Examples of nitrides
include TiN, VN, Ni.sub.3N, Mg.sub.3N.sub.2, ZrN, AlN, and
Si.sub.3N.sub.4. Desirable carbides include TiC, VC, MgC.sub.2,
Mg.sub.2C.sub.3, HfC, Al.sub.4C.sub.3, WC, Mo.sub.2C, TaC, and SiC.
Exemplary borides include TiB, TiB.sub.2, VB.sub.2, Ni.sub.2B,
Ni.sub.3B, AlB.sub.2, TaB, TaB.sub.2, SiB, and ZrB.sub.2. Other
oxides, nitrides, carbides, and borides are known by those skilled
in the art.
[0053] Gases
[0054] In order to obtain oxides, nitrides, carbides, or borides of
a metallic component, the gas that is reacted with the component
must contain oxygen, nitrogen, carbon, and/or boron. Exemplary
gases include oxygen, nitrogen, carbon dioxide, boron trichloride,
ammonia, methane, and diborane. Other gases are known by those
skilled in the art.
[0055] Thermal Spray
[0056] The resistive layers and other layers of a coating of the
present invention are desirably deposited using a thermal spray
apparatus. Exemplary thermal spray apparatuses include, without
limitation, arc plasma, flame spray, Rockide systems, arc wire, and
high velocity oxy-fuel (HVOF) systems.
[0057] A typical HVOF wire system consists of a gun or spray head
where three separate gases come together (see FIG. 1). Propane gas
and oxygen are commonly used as fuel gases, and the gas chosen as
the reactant gas is used to accelerate the molten droplets and cool
the spray nozzle in the gun. Normally, this last function is
accomplished through the use of air. The gases are fed to the spray
head through flow meters and pressure regulators or through mass
flow controllers so that there is a controlled, independent flow
for each gas. If it is desired to deliver reduced amounts of
reactant gas, it can be mixed with a nonreactant gas, for example,
argon, so that the volume and flow are sufficient to operate the
gun at appropriate velocities. The mixing may be accomplished by
flowmeters and pressure regulators, mass flow controllers, or by
the use of pre-mixed cylinders, each of which is generally known to
a practitioner skilled in the art. The feedstock, which is wire in
this case, is supplied to the gun head by means of a wire feeder
that controls the rate at which material is delivered to the gun.
The gun itself may be attached to a motion control system such as a
linear translator or multiaxis robot.
[0058] The thermal spray apparatus is desirably configured so that
a reaction gas may be injected into the molten flux stream of the
spray. For combustion systems and arc wire systems, this injection
may be accomplished by using the gas as the accelerator. For plasma
systems, if the plasma gases do not serve also as the reaction gas,
the gas may be injected using an additional nozzle (see FIG. 2).
Incorporating additional nozzles for injection of reactant gases is
also applicable to other systems.
[0059] The composition of the deposited layer may be influenced by
the type of thermal spray apparatus used. For example, droplets are
emitted very rapidly from an HVOF system in comparison to other
techniques, and these droplets are consequently exposed to
reactants for a shorter period of time and thus react with the gas
to a lesser extent. In addition, layers deposited by HVOF have
higher adhesion strength than layers deposited by other
systems.
[0060] Resistive layers may be deposited in defined patterns on a
substrate. The pattern may be defined, for example, by a removable
mask. Patterned application allows for the fabrication of more than
one spatially separated resistive layer on one or more substrates.
Patterned layers also allow controlled heating in localized areas
of a substrate.
[0061] Microstructure
[0062] The characteristic lamellar microstructure of a coating
deposited by thermal spray is a direct result of the process. The
thermal spray process creates from the feedstock a flux of molten
droplets, which are accelerated and directed towards the substrate.
The droplets, typically moving at speeds of several hundred meters
per second, impact the substrate and very rapidly cool at rates
approaching one million degrees per second. This rate of cooling
causes very rapid solidification. Nevertheless, during the impact,
the droplets deform into platelet-like shapes and stack on top of
each other as the spray head is traversed back and forth across the
substrate to build up the coating. The microstructure thus assumes
a layered configuration, with the flattened particles all aligned
parallel to the substrate and perpendicular to the line of
deposition.
[0063] If the material being deposited undergoes no reactions with
the gases present in the flux stream, then the composition of the
coating is identical to that of the feedstock. If, however, the
molten droplets react with an ambient gas during the deposition
process, the composition of the coating differs from that of the
feedstock. The droplets may acquire a surface coating of the
reaction product, which varies in thickness depending, for example,
on the rate of reaction, the temperatures encountered, and the
concentration of the gas. In some cases, the droplets react
completely; in other cases, the droplets have a large volume
fraction of free metal at their centers. The resulting
microstructure of the coating is a lamellar structure, one
consisting of individual particles of complex composition. The
coating has a reduced volume fraction of free metal with the
remainder consisting of reaction products distributed in general as
material surrounding the free metal contained in each platelet-like
particle.
[0064] When the gases that are added to the flux stream are chosen
to form reaction products, which have a much higher electrical
resistivity, then the resultant coating exhibits a bulk resistivity
that is higher than the free metallic component. In addition, when
the concentration of gas is controlled, thereby controlling the
concentration of reaction product, the resistivity of the coating
is controlled proportionately. For example, the resistivity of
aluminum sprayed in pure oxygen is higher than that sprayed in air
because there is a higher concentration of aluminum oxide in the
layer and aluminum oxide has a very high resistivity.
[0065] Spatially Variable Resistivity
[0066] The invention also provides methods for producing a coating
having a resistivity that is variable, e.g., a continuous gradient
or step function, as a function of location on a substrate. For
example, the resistivity of the layer may increase or decrease by
50, 100, 200, 500 or 1000% over a distance of 1, 10, or 100 cm. The
apparatus used includes a thermal spray gun and a gas source. The
gas source includes two or more gases that can be mixed in any
arbitrary combination. By controlling the composition of the gas
used in the thermal spray gun, the composition, and therefore
resistivity, of the coating is controlled. For example, a gradual
increase in a reactant in the gas (e.g., oxygen) leads to a gradual
increase in the resistivity of the coating. This gradual increase
can be used to produce a coating having a gradient of resistivity
on a substrate. Similarly, other patterns, e.g., step functions, of
resistivity may be formed by appropriate control of the mixture of
gases. The mixture of gases may include more than one reactive
species (e.g., nitrogen and oxygen) or a reactive and an inert
species (e.g., oxygen and argon). A computer may also be used to
control the mixing of the gases.
[0067] Applications
[0068] Coatings. Coatings on substrates can comprise resistive
layers of the invention. In addition, other layers may be present
in a coating to provide additional properties. Examples of
additional coatings include, without limitation, an adhesion layer
(e.g., nickel-aluminum alloy), an electrically insulating layer
(e.g., aluminum oxide, zirconium oxide, or magnesium oxide), an
electrical contact layer (e.g., copper), a thermally insulating
layer (e.g., zirconium dioxide), a thermally emissive coating
(e.g., chromium oxide), layers for improved thermal matching
between layers with different coefficients of thermal expansion
(e.g., nickel between aluminum oxide and aluminum), a thermally
conductive layer (e.g., molybdenum), and a thermally reflective
layer (e.g., tin). These layers may be located between the
resistive layer and the substrate (e.g., adhesion layers) or on the
side of the resistive layer distal to the substrate. Resistive
layers may also be deposited on a nonconducting surface without an
electrically insulating layer.
[0069] Heaters. A resistive layer is made into a resistive heater
by coupling a power supply to the layer. Application of a current
through the resistive layer then generates heat resistively.
Connections between the power supply and the resistive layer are
made, for example, by brazing connectors, soldering wires, or by
physical contact using various mechanical connectors. These
resistive heaters are advantageous in applications where localized
heating is desired.
[0070] A. Injection mold. One application of a resistive heater of
the invention is in injection molding. An injection mold has a
cavity into which a melt of a thermoplastic material is forced.
Once the material cools and hardens, it can be removed from the
mold, and the process can be repeated. An injection mold of the
invention has a coating containing a resistive heating layer on at
least a portion of the surface of the cavity. The resistive heating
layer may be covered with a metal layer (e.g., molybdenum or
tungsten). The purpose of placing a heater layer in the cavity of a
mold and in the conduits to that cavity is to better control the
solidification process and reduce cycle times. Heaters in close
proximity to the melt can be used to keep the melt hot so that it
flows better with less pressure, and to cool the melt during the
solidification phase in a controlled way.
[0071] B. Heated rollers. Heated rollers are used in many
industries include papermaking, printing, laminating, and paper,
film, and foil converting industries. One application of a
resistive heater of the invention is in dryers in paper
manufacturing (see FIG. 3). Paper is manufactured in several
stages, including forming, pressing, and drying. The drying stage
typically removes water remaining from the pressing stage
(typically about 30%) and reduces the water content typically to
about 5%. The drying process typically involves contacting both
sides of the paper with heated cylindrical rollers. Accordingly, a
roller for a paper dryer having a resistive heater layer may be
produced by methods of the invention. A coating containing a
resistive heater layer is deposited on the interior or exterior of
such a roller. Other coatings such as anticorrosive coatings may
also be applied. The heater may be applied in a defined pattern
through masks in the deposition step. For instance, a pattern of
zones that concentrates heat at the ends of the roller provides a
more uniform heat to the paper since the ends cool more quickly
than the center of the roller. Examples of rollers that contain
heating zones are given in U.S. Pat. No. 5,420,395, hereby
incorporated by reference.
[0072] The deposited resistive heaters may be applied to a dryer
can (or roller) used in the paper making process to remove water
from pulp. In one example, the heaters are applied to the inside
surface of a steel roller or can. First, an insulator layer of
aluminum oxide is applied by thermal spray and sealed with
nanophase aluminum oxide or some other suitable high temperature
dielectric sealant. Then, the resistive heater layer is deposited
using a high velocity oxy-fuel wire spray system, titanium wire,
and nitrogen gas. The terminals are secured to the inside of the
can by welding or threaded studs and are insulated such that
electrical power may be applied to the deposited resistive layer.
Finally, the entire heater layer is coated with high temperature
silicone or another layer of thermally sprayed aluminum oxide,
which is sealed as before.
[0073] Alternatively, the heater layer and insulator layers may be
applied to the outside surface of the dryer can and coated with a
thermally sprayed metallic layer, such as nickel. The nickel is
then ground back to the desired dimension. For smaller heated
roller applications, a metal casing may be affixed or shrunk onto
the roller with its heaters applied.
[0074] C. Semiconductor wafer processing system. Heaters are also
used in semiconductor wafer processing (see WO 98/51127, hereby
incorporated by reference). A semiconductor wafer processing system
of the invention includes a chamber, one or more resistive heaters,
and means for mounting and manipulating a semiconductor wafer. The
system may be used in wafer processing applications such as
annealing, sintering, silicidation, and glass reflow. A system
including such a heater is also useful for promoting reactions
between wafers and reactive gases, for example, oxidation and
nitridation. In addition, the system may be used for epitaxial
reactions, wherein a material such as silicon is deposited on a
heated surface in monocrystalline form. Finally, such a system
allows chemical vapor deposition of the product of a gas phase
reaction in noncrystalline form on a heated substrate.
[0075] Additional applications of the heaters of the invention are
as follows:
[0076] 1. blanket heater on pipe with metal contact layer on top
and aluminum oxide insulator on the contact.
[0077] 2. heater tip for natural gas ignitor on kitchen stove,
oven, water heater or heating system.
[0078] 3. free standing muffle tube fabricated by sprayforming on a
removable mandrel.
[0079] 4. low voltage heater coating for bathroom deodorizer.
[0080] 5. Laboratory Applications: Resistively heated coated glass
and plastic lab vessels; work trays; dissection trays; cell culture
ware; tubing; piping; heat exchangers; manifolds; surface
sterilizing laboratory hoods; self-sterilizing work surfaces;
sterilizing containers; heatable filters; frits; packed beds;
autoclaves; self-sterilizing medical bacterial and tissue culture
tools (e.g., loops and spreaders); incubators; benchtop heaters;
flameless torches; lab ovens; incinerators; vacuum ovens;
waterbaths; drybaths; heat platens; radiography pens; reaction
vessels; reaction chambers; combustion chambers; heatable mixers
and impellers; electrophoresis equipment; anode and cathode
electrodes; heating electrodes; electrolysis and gas generation
systems; desalinization systems; de-ionizing systems; spectroscopy
and mass spectroscopy equipment; chromatography equipment; HPLC; IR
sensors; high temperature probes; thermoplastic bags; cap and tube
sealers; thermal cyclers; water heaters; steam generation systems;
heated nozzles; heat activated in-line valves; shape-memory
alloy/conductive ceramic systems; lyophilizers; thermal ink pens
and printing. systems;
[0081] 6. Medical and Dental Applications: Self-sterilizing and
self-cauterizing surgical tools (e.g., scalpel blades,
forceps);-incubators; warming beds; warming trays; blood warming
systems; thermally controlled fluid systems; amalgum heaters;
dialysis systems; phoresis systems; steamer mops; ultra high
temperature incineration systems; self sterilizing tables and
surfaces; drug delivery systems (e.g., medicated steam inhaler;
thermal activated transcutaneal patches); dermatological tools;
heatable tiles; wash basins; shower floors; towel racks;.
mini-autoclaves; field heater cots; body warming systems;
[0082] 7. Industrial applications: Sparkless ignition systems;
sparkless combustion engines; bar heaters; strip heaters;
combustion chambers; reaction chambers; chemical processing lines;
nozzles and pipes; static and active mixers; catalytic heating
platforms (e.g., scrubbers); chemical processing equipment and
machines; environmental remediaton systems; paper pulp processing
and manufacturing systems; glass and ceramic processing systems;
hot air/air knife applications; room heaters; sparkless welding
equipment; inert gas welding equipment; conductive abrasives;
heater water-jet or liquid-jet cutting systems; heated impellers
and mixing tanks; fusion and resistance locks; super heated
fluorescent bulbs that use new inert gases; heatable valves;
heatable interconnects and interfaces of all types; heatable
ceramics tiles; self heating circuit boards (e.g., self-soldering
boards; self-laminating boards); fire hydrant heaters; food
processing equipment (e.g., ovens, vats, steaming systems, searing
systems, shrink wrapping systems, pressure cookers, boilers,
fryers, heat sealing systems); in-line food processing equipment;
programmable temperature grids and platens to selectively apply
heat to 2-D or 3-D structures (e.g., thermoplastic welding and
sealing systems); point pulsing heaters; battery operated heaters;
inscribers and marking systems; static mixers; steam cleaners; IC
chip heaters; LCD panel heaters; condensers; heated aircraft parts
(e.g., wings, propellers, flaps, ailerons, vertical tail, rotors);
conductive ceramic pens and probes; self-curing glazes; self-baking
pottery; walk-in-ovens; self-welding gaskets; heat pumps;
[0083] 8. Home and office applications: Heatable appliances of all
types; self cleaning ovens; igniters; grills; griddles;
susceptor-based heatable ceramic searing systems for microwaves
ovens; heated mixers; impellors; stirrers; steamers; crock pots;
pressure cookers; electric range tops; refrigerator defrost
mechanisms; heated ice cream scoops and serving ladles; operated
hand held heaters and warmers; water heaters and switches; coffee
heater systems; heatable food processors; warmable toilet seats;
towel racks; clothes warmers; bodywarmers; cat beds; instantly
heated irons; water bed heaters; washers; driers; faucets; heated
bathtubs and wash basins; dehumidifiers; hose nozzles for heated
washing or steam cleaning; platens to heat moisturized wipes;
bathroom tissue heaters; towel heaters; heated soap dispensers;
heated head razors; evaporative chilling systems; self-heating
keys; outdoor CO.sub.2 and heat generating systems for bug
attraction and killing systems; aquarium heaters; bathroom mirrors;
chair warmers; heatable blade ceiling fans; floor heaters;
[0084] 9. Whole surface geometric heaters; direct contact heaters;
pure ceramic heating systems; coated metal heating systems;
self-detecting fault systems; plasma sprayed thermocouples and
sensors; plasma spheredized bed reaction systems (e.g., boron gas
generation system for the semiconductor industry; heatable
conductive chromatographic beds and beads systems); pre-heaters to
warm surfaces prior to less costly or more efficient heating
methods; sensors (e.g., heater as part of integrated circuit chip
package);
[0085] 10. Microwave and electromagnetic applications: Magnetic
susceptor coatings; coated cooking wear; magnetic induction ovens
and range tops;
[0086] 11. Thermoplastic manufacturing applications: resistively
heated large work surfaces and large heaters; heated injection
molds; tools; molds; gates; nozzles; runners; feed lines; vats;
chemical reaction molds; screws; drives; compression systems;
extrusion dies; thermoforming equipment; ovens; annealing
equipment; welding equipment; heat bonding equipment; moisture cure
ovens; vacuum and pressure forming systems; heat sealing equipment;
films; laminates; lids; hot stamping equipment; shrink wrapping
equipment;
[0087] 12. Automotive applications: Washer fluid heaters; in-line
heaters and nozzle heaters; windshield wiper heaters; engine block
heaters; oil pan heaters; steering wheel heaters; resistance-based
locking systems; micro-catalytic converters; exhaust scrubbers;
seat heaters; air heaters; heated mirrors; heated key locks; heated
external lights; integral-heater under paint or in place of paint;
entry and exit port edges; sparkless "sparkplugs"; engine valves,
pistons, and bearings; mini-exhaust catalytic pipes;
[0088] 13.Marine applications: antifouling coatings; de-iceable
coatings (e.g., railings, walkways); electrolysis systems;
desalinization systems; on-board seafood processing systems;
canning equipment; drying equipment; ice drills and corers;
survival suits; diving suit heaters; desiccation and dehumidifying
systems;
[0089] 14. Defense applications: High temperature thermal targets
and decoys; remora heaters; MRE heating systems; weapons
preheaters; portable heaters; cooking devices; battery powered
heatable knife; noncombustion based gas expansion guns; jet
de-icing coating on wings etc; thermal fusion self destruction
systems; incinerators; flash heating systems; emergency heating
systems; emergency stills; desalinization and sterilization
systems;
[0090] 15. Signage applications: heated road signs,
thermoresponsive color changing signs; inert gas (e.g., neon)
impregnated microballoons that fluoresce in magnetic fields;
[0091] 16. Printing and photographic applications: copiers;
printers; printer heaters; wax heaters; thermal cure ink systems;
thermal transfer systems; xerographic and printing heaters;
radiographic and photographic film process heaters; ceramic
printers;
[0092] 17. Architectural applications: heated walkway mats, grates,
drains, gutters, downspouts, and roof edges;
[0093] 18. Sporting applications: heated golf club heads; bats;
sticks; handgrips; heated ice skate edges; ski and snowboard edges;
systems for de-icing and re-icing rinks; heated goggles; heated
glasses; heated spectator seats; camping stoves; electric grills;
heatable food storage containers;
[0094] In one embodiment, the heater of the present invention may
be used in an injection molding system to manage and control the
flow of the molten material throughout the mold cavity space. The
heater may be deposited as part of a coating directly on the
surface of the mold cavity area to precisely manage the temperature
profile in the moving, molten material. For some applications, the
heater may have variable resistivity across the surface of the mold
cavity area to allow for fine adjustments to the molten material
temperature gradient, thus providing precise heat flow control and
constant (or precisely-managed) viscosity and velocity of the melt
flow. Mold heat management and flow control depend on the specific
application and the type of material used.
[0095] Desirably, the heater is used in conjunction with a thermal
sensor (e.g., a thermistor or thermocouple) and/or a pressure
sensor. Direct deposit of the coating containing the heater onto
the mold cavity area can reduce or eliminate air gaps between the
heater and the heated surface, providing intimate and direct
contact for improved temperature transfer between the heater and
the heated surface.
[0096] In one example, the heater is applied to the mold cavity of
a plastics mold (see FIG. 4). First, a NiCrAlY alloy adhesion (or
bond) coat is applied to the cavity to a thickness of about 0.002"
using a High Velocity Oxy-Fuel Wire (HVOF) thermal spray system.
Next a zirconium oxide layer measuring 0.012" is applied with an
arc plasma spray system. The zirconium oxide electrically and
thermally insulates the heater from the steel mold, which is water
cooled. A resistive heater layer is applied next as a sheet or
coating of material 0.008" thick on top of the zirconium oxide. The
zirconium is deposited using a HVOF thermal spray system using
propane and oxygen for the fuel gases to melt the metal wire and
pure nitrogen as an accelerator. The nitrogen promotes formation of
zirconium nitride in the molten flux and boosts the resistivity of
the coating from 0.00007 .OMEGA..multidot.cm for pure zirconium to
0.003 .OMEGA..multidot.cm for the deposited coating. Next, a
micro-abrasive blaster using aluminum oxide media and attached to a
multiaxis machining center is used to delineate the desired heater
element pattern on the mold. Zirconium terminals are inserted at
this stage through holes machined in the mold. They are inserted to
make electrical contact with the beater layer. A second
0.015"-thick layer of ceramic electrical insulator is then applied
to the top of the heater. Aluminum oxide is chosen for this layer
because it has higher thermal conductivity than the zirconium
oxide. The aluminum oxide is applied using an arc plasma system and
is then sealed with nanophase aluminum oxide. Finally, a metal
layer of tungsten is applied to a thickness of 0.040" by arc plasma
spray and machined back to the desired dimension. The mold cavity
is completed by electroplating a layer of nickel on top of the
tungsten.
Other Embodiments
[0097] All publications and patents mentioned in the above
specification are herein incorporated by reference. Various
modifications and variations of the described method and system of
the invention will be apparent to those skilled in the art without
departing from the scope and spirit of the invention. Although the
invention has been described in connection with specific preferred
embodiments, it should be understood that the invention as claimed
should not be unduly limited to such specific embodiments. Indeed,
various modifications of the described modes for carrying out the
invention that are obvious to those skilled in thermal spraying,
coatings, thermoplastics, or related fields are intended to be
within the scope of the invention.
[0098] Other embodiments are in the claims.
* * * * *