United States Patent [19J
`Deevi et al.
`
`[54] FUNCTIONALLY STEPPED, RESISTIVE
`CERAMIC
`
`[75]
`
`Inventors: Seetharama C. Deevi, Midlothian; A.
`Clifton Lilly, Jr., Chesterfield, both of
`Va.
`
`[73] Assignee: Philip Morris Incorporated, New
`York, N.Y.
`
`[ *] Notice:
`
`The term of this patent shall not extend
`beyond the expiration date of Pat. No.
`5,498,855.
`
`[21] Appl. No.: 614,058
`
`[22] Filed:
`
`Mar. 12, 1996
`
`[51]
`
`Int. Cl.6
`
`............................. H05B 3/58; HOlC 1/012;
`H0lB 1/06; C04B 35/03
`[52] U.S. CI . .......................... 219/535; 219/539; 338/312;
`252/506; 252/516; 501/95
`[58] Field of Search ..................................... 219/535, 538,
`219/539, 542, 543, 552, 553; 338/310,
`312, 314; 29/614, 615; 252/506, 516, 518;
`501/94, 95, 97
`
`[56]
`
`References Cited
`
`U.S. PlXTENT DOCUMENTS
`
`2,406,275
`2,971,039
`3,875,476
`
`8/1946 Wej narth .
`2/1961 Westeren .
`4/1975 Crandall et al. .
`
`(List continued on next page.)
`
`FOREIGN PlXTENT DOCUMENTS
`
`1298808 12/1972 United Kingdom .
`
`OTHER PUBLICATIONS
`
`"Joining of Ceramics" by R.E. Loehman et al., published in
`Ceramic Bulletin, vol. 67 No., 2, pp. 375-380 (1988).
`"Oxidation Behavior of Silver-and Copper-Based Brazing
`Filler Metals for Silicon Nitride/Metal Joints" by R.R.
`Kapoor et al., published inJ. Am. Ceram. Soc., vol. 72 No.,
`3, pp. 448-454 (1989).
`
`I 1111111111111111 11111 1111111111 1111111111 111111111111111 IIIIII Ill lllll llll
`US005880439A
`5,880,439
`[11] Patent Number:
`[45] Date of Patent:
`*Mar. 9, 1999
`
`"Brazing Ceramic Oxides to Metals at Low Temperatures"
`by J.P. Hammond et al., published in Welding Research
`Supplement, pp. 227-232-s, (1988).
`"Brazing of Titanium-Vapor-Coated Silicon Nitride" by
`M.L. Santella published in Advanced Ceramic Materials,
`vol. 3 No., 5, pp. 457-465 (1988).
`"Microstructure of Alumina Brazed with a Silver-Copper(cid:173)
`Titanium Alloy" by M.L. Santella et al., published in J. Am.
`Ceram. Soc., vol. 73 No., 6, pp. 1785-1787 (1990).
`"New Z-direction Anisotropically Conductive Composites"
`by S. Jin et al., published in J. Appl. Phys., vol. 64 No., 10,
`pp. 6008-6010 (1988).
`"Composite PTCR Thermistors Utilizing Conducting
`Borides, Silicides, and Carbide Powders" by T.R. Shrout et
`al., published in J. Materials Science, vol. 26, pp. 145-154
`(1991).
`"Diffusional Reactions in the Combustion Synthesis of
`MoSi2 " by S.C. Deevi, published in Materials Science and
`Engineering, vol. A149, pp. 241-251 (1992).
`"Self-propagating High-temperature Synthesis of Molyb(cid:173)
`denum Disilicide" by S.C. Deevi, published in J. Materials
`Science, vol. 26, pp. 3343-3353 (1991).
`
`Primary Examiner-Teresa J. Walberg
`Assistant Examiner-Sam Paik
`Attorney, Agent, or Firm-Bums, Doane, Swecker &
`Mathis, L.L.P.
`
`[57]
`
`ABSTRACT
`
`An electrically powered functionally graded ceramic com(cid:173)
`posite heater and a functionally stepped ceramic composite
`heater useful for cigarette lighters. The electrical resistance
`heater includes discrete heating zones wherein each zone of
`the heater can be activated using an electric control module,
`and is capable of heating to a temperature in the range of
`600° C. to 900° C. using portable energy devices. The
`ceramic heater can be made by pres.sing together layers of
`differing amounts of constituents of the ceramic precursor
`material followed by secondary proces.sing steps to obtain
`discrete heating elements. The heater design can include a
`hub on one end to provide structural integrity, and function
`as a common for the heating zones.
`
`40 Claims, 14 Drawing Sheets
`
`10-2-j
`I
`
`10-3
`
`>-
`I-
`Gj2: 10-4
`(!)I-
`O:Ul
`~pj
`0:
`
`10-5
`
`108
`
`I I I l
`I 11
`I 11
`110 I I:
`
`102~
`111
`
`10-6
`
`AXIAL
`POSITION
`
`11
`I I
`I
`
`I
`I
`I
`I
`~12
`,~ I
`11
`I
`I
`
`Ex. 2015-0001
`
`

`

`5,880,439
`Page 2
`
`U.S. PKfENT DOCUMENTS
`
`3,895,219
`4,098,725
`4,110,260
`4,327,186
`4,407,971
`4,416,840
`4,449,039
`4,475,029
`4,486,651
`4,503,319
`4,528,121
`4,549,905
`4,555,358
`4,634,837
`4,697,165
`4,883,947
`
`7/1975 Richerson et al. .
`7/1978 Yamamoto et al. .
`8/1978 Yamamoto et al. .
`4/1982 Murata et al..
`10/1983 Komatsu et al. .
`11/1983 Lee et al..
`5/1984 Fukazawa et al. .
`10/1984 Yoshida et al. .
`12/1984 Atsumi et al..
`3/1985 Moritoki et al. .
`7/1985 Matsushita et al. .
`10/1985 Yamaguchi et al. .
`11/1985 Matsushita et al. .
`1/1987 Ito et al. .
`9/1987 Ishiguro et al. ........................ 219/538
`11/1989 Murase et al ........................... 219/538
`
`5/1990 Enloe et al . .............................. 29/852
`4,920,640
`9/1991 Washburn.
`5,045,237
`5,060,671 10/1991 Counts et al. .
`5,085,804
`2/1992 Washburn.
`5,093,894
`3/1992 Deevi et al ..
`5,139,594
`8/1992 Rabin.
`5,146,934
`9/1992 Deevi et al ..
`5,157,242 10/1992 Hetherington et al ..
`5,188,130
`2/1993 Hajaligol et al. .
`5,191,508
`3/1993 Axelson .................................. 361/257
`5,223,064
`6/1993 Gadkaree .................................. 501/97
`5,224,498
`7/1993 Deevi et al ..
`5,353,813 10/1994 Deevi et al ..
`5,369,723 11/1994 Counts et al. .
`5,498,855
`3/1996 Deevi et al ..
`5,530,225
`6/1996 Hajaligol ................................. 219/535
`
`Ex. 2015-0002
`
`

`

`U.S. Patent
`
`Mar. 9, 1999
`
`Sheet 1 of 14
`
`5,880,439
`
`FIG. I
`
`5
`
`4
`
`2
`
`6
`
`9
`
`'\
`
`7
`
`FIG. 2
`
`Ex. 2015-0003
`
`

`

`U.S. Patent
`U.S. Patent
`
`Mar. 9, 1999
`Mar. 9, 1999
`
`Sheet 2 0f 14
`Sheet 2 of 14
`
`5,880,439
`5,880,439
`
`10
`
`64
`
`63
`
`\
`'
`
`
`
`22
`
`17
`
`30
`
`17
`
`20
`
`50
`
`FIG. 3
`
`Ex. 2015-0004
`
`Ex. 2015-0004
`
`

`

`U.S. Patent
`
`Mar. 9, 1999
`
`Sheet 3 of 14
`
`5,880,439
`
`24
`
`31
`
`FIG. 4
`
`30i
`
`32
`
`33
`
`32
`34
`
`FIG.5
`
`FIG. 7
`
`61
`
`64
`
`63
`
`63
`
`42
`
`41
`
`42
`
`FIG.6
`
`FIG. 8
`
`Ex. 2015-0005
`
`

`

`Mar. 9, 1999
`
`Sheet 4 of 14
`
`5,880,439
`
`U.S. Patent
`
`N
`
`0)
`
`(\J
`
`Ex. 2015-0006
`
`

`

`U.S. Patent
`
`Mar. 9, 1999
`
`Sheet 5 of 14
`
`5,880,439
`
`1014
`
`10 6
`
`10 4
`
`10 3
`
`10 1
`
`10 0
`
`0
`
`~
`
`Cl)
`~
`
`10 -l
`
`e (,)
`I e .c 10 2
`+J ·s -+J
`D'l -D'l
`-«s
`-s..
`Cl) -r:.::i
`
`(,)
`
`+J
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`
`10-2
`
`10 - 3
`
`10 - 4
`
`•1
`I
`I
`I
`I
`
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`
`10-6
`
`0
`
`10
`
`20
`
`30
`
`40 50
`
`60
`
`70
`
`80 90 100
`
`Vol. ~ of Conducting Material
`Fl G. 10
`
`Ex. 2015-0007
`
`

`

`U.S. Patent
`
`Mar. 9, 1999
`
`Sheet 6 of 14
`
`5,880,439
`
`Fix Composition
`Electrical Resistivity
`Physical Properties
`
`I
`Integral Heaters
`
`J-
`
`Powder Processing
`Fix Composition, Binders,
`Sintering Aids, Surfactants,
`Rheological Fluids
`I
`Milling
`Slip Preparation
`I
`Farming Operation
`Hot Pressing, 1750°C,
`Cold lsostolic Pressing/Pre-Sinter, 1100° C
`Slip Casting/Pre-Sinter, 1100° C
`I
`Machining/Grinding
`Obtain Desired Shape
`Reduce 0.D /1.D
`I
`Sintering
`Densification to 99% +
`Heat To 1800°C, 2 Hrs
`I
`Finishing
`Diamond Grinding/Cutting
`Ultrasonic Machining
`Laser Machining
`I
`Integral Heaters
`
`FIG. I I
`
`Ex. 2015-0008
`
`

`

`d .
`r:JJ. .
`~
`~ ......
`
`11mm'90
`
`~ = ......
`
`~
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`)9
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`
`, E
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`Ul
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`
`am
`
`00 = ~
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`
`TEMPERATURE VS. ENERGY
`TEMPERATURE VS. ENERGY
`
`/ /
`
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`
`
`
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`Q
`
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`I
`
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`
`5
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`
`30
`28
`26
`24
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`
`20
`18
`16
`14
`12
`10
`8
`6
`4
`2
`
`100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950
`100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950
`TEMPERATURE (C)
`Fl G. 12
`
`.
`
`
`
`6000'910Z'XEI
`
`Ex. 2015-0009
`
`

`

`U.S. Patent
`
`Mar. 9, 1999
`
`Sheet 8 of 14
`
`5,880,439
`
`123
`
`122
`
`121
`
`FIG. 13a ",20
`
`133
`
`132
`
`:,
`
`FIG. 13b
`
`131
`
`'--
`
`130
`
`142
`
`141
`FIG. 13c
`
`140
`
`121
`
`123 133
`
`FIG. /4
`
`Ex. 2015-0010
`
`

`

`U.S. Patent
`
`Mar. 9, 1999
`
`Sheet 9 of 14
`
`5,880,439
`
`FIG. 15
`
`10-3~ - - - - - - - - - - - - - - - - -
`
`1 o-4
`
`1200° C
`
`,0
`4~~00,e
`
`en -- 1 o-5
`
`1 o-6
`
`LU
`I(cid:173)
`<(
`o:::
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`LU
`LU o::: 1 o-7
`u
`
`• FGM/PM (100&80M0Si2)
`
`,
`
`I
`
`9µ~-G -00 ~
`,'/ JZl
`(cid:127) FGM/PM (40M0Si2) ~¢
`(cid:143)
`0 M0Si2 (LANL)
`25µm ,'
`0 50MoSir50Si3N4 (LANL) CJ [~f
`.&. MoSi2-20v%SiCw (LANL)
`1 o-9 ,--.-,-r,-rrr~-r--r-T-r-r"T"T"T-r----ie----,.........-.-.-..,...,..,..1
`10 1
`102
`10°
`STRESS,MPa
`
`1 o-8
`
`FIG. 16
`10-3 =---------------------,
`
`10-4
`
`M0Si2
`1200° C
`
`10-7
`
`.&. 213MPa
`(cid:127)
`184MPa
`• 150MPa
`(cid:143)
`115MPa
`0 78MPa
`1 o-8 -r--------r--~---,e------.---.......-.......---1
`10-2
`10-1
`
`p=2 c:::::-
`
`p=S [7
`
`1/d, 1/µm
`
`en --
`
`LU
`~ 10-S
`0:::
`0...
`LU 10-6
`LU
`er:: u
`
`Ex. 2015-0011
`
`

`

`U.S. Patent
`
`Mar. 9, 1999
`
`Sheet 10 of 14
`
`5,880,439
`
`fdAC::H{)
`
`Ex. 2015-0012
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 9, 1999
`Mar. 9, 1999
`
`Sheet 11 0f 14
`Sheet 11 of 14
`
`5,880,439
`5,880,439
`
`
`
`Fig. 18
`F353 ‘33
`
`Ex. 2015-0013
`
`Ex. 2015-0013
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 9, 1999
`Mar. 9, 1999
`
`Sheet 12 0f 14
`Sheet 12 of 14
`
`5,880,439
`5,880,439
`
`
`
`
`
`EX. 2015-0014
`
`Ex. 2015-0014
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 9, 1999
`Mar. 9, 1999
`
`Sheet 13 0f 14
`Sheet 13 of 14
`
`5,880,439
`5,880,439
`
`
`
`Fig~ 20
`
`Ex. 2015-0015
`
`Ex. 2015-0015
`
`

`

`U.S. Patent
`
`Mar. 9, 1999
`
`Sheet 14 of 14
`
`5,880,439
`
`110 221
`
`I
`
`102
`
`112 106 100
`
`201 /""'
`
`10-2
`
`,o-3
`
`>-
`t-
`1--
`w>
`(!) t-
`0:: (/)
`~~
`10-5
`a::
`
`10-4
`
`10-6
`
`108
`
`21 1
`
`FIG.21
`
`108
`
`Ii I /
`I I I
`I I l
`110 111
`102:oi
`I I 1
`
`I I
`I
`I I
`I
`: 1,,2
`ti::104
`
`11
`
`AXIAL
`POSITION
`
`FIG. 22
`
`Ex. 2015-0016
`
`

`

`1
`FUNCTIONALLY STEPPED, RESISTIVE
`CERAMIC
`
`5,880,439
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`This is related to commonly assigned patent application
`Ser. No. 08/291,690 filed Aug. 16, 1994, a continuation-in(cid:173)
`part of commonly assigned patent application Ser. No.
`08/224,848, filed Apr. 8, 1994, which is a continuation-in(cid:173)
`part of commonly assigned U.S. Pat. No. 5,388,594, issued
`Feb. 14, 1995, which in tum is a continuation-in-part of
`commonly assigned patent application Ser. No. 07/943,504,
`filed Sep. 11, 1992.
`This application also relates to commonly assigned
`copending patent application Ser. No. 07/943,747, filed Sep.
`11, 1992 and to commonly assigned U.S. Pat. No. 5,060,671,
`issued Oct. 29, 1991; U.S. Pat. No. 5,095,921, issued Mar.
`17, 1992; and U.S. Pat. No. 5,224,498, issued Jul. 6, 1992;
`all of which are hereby incorporated by reference.
`1. Technical Field of the Invention
`The present invention relates generally to electrically
`powered ceramic composite heaters for devices such as
`cigarette lighters and more particularly to a tubular ceramic
`heater for use in a cigarette lighter.
`2. Discussion of the Related Art
`Previously known conventional smoking devices deliver
`flavor and aroma to the user as a result of combustion of
`tobacco. Amass of combustible material, primarily tobacco,
`is oxidized as the result of applied heat with typical com(cid:173)
`bustion temperatures in a conventional cigarette being in
`excess of 800° C. during puffing. Heat is drawn through an
`adjacent mass of tobacco by drawing on the mouth end.
`During this heating, inefficient oxidation of the combustible
`material takes place and yields various distillation and
`pyrolysis products. As these products are drawn through the
`body of the smoking device toward the mouth of the user,
`they cool and condense to form an aerosol or vapor which
`gives the consumer the flavor and aroma associated with
`smoking.
`Conventional cigarettes must be fully consumed or be
`discarded once lit. A prior alternative to the more conven(cid:173)
`tional cigarettes include those in which the combustible
`material itself does not directly provide the flavorants to the
`aerosol inhaled by the smoker. In these smoking articles, a 45
`combustible heating element, typically carbonaceous in
`nature, is combusted to heat air as it is drawn over the
`heating element and through a zone which contains heat(cid:173)
`activated elements that release a flavored aerosol. While this
`type of smoking device produces little or no sidestream
`smoke, it still generates products of combustion, and once lit
`it is not adapted to be snuffed for future use in the conven(cid:173)
`tional sense.
`Commonly assigned U.S. Pat. Nos. 5,093,894; 5,224,498;
`5,060,671 and 5,095,921 disclose various electrical smoking
`systems which significantly reduce sidestream smoke while
`permitting the smoker to selectively suspend and reinitiate
`smoking.
`U.S. Pat. No. 5,388,594, issued Feb. 14, 1995, describes
`an electrical smoking system including a novel electrically 60
`powered lighter and novel cigarette that is adapted to
`cooperate with the lighter. The preferred embodiment of the
`lighter includes a plurality of metallic sinusoidal heaters
`disposed in a configuration that slidingly receives a tobacco
`rod portion of the cigarette.
`The preferred embodiment of the cigarette of U.S. Pat.
`No. 5,388,594, issued Feb. 14, 1995, preferably comprises a
`
`5
`
`30
`
`2
`tobacco-laden tubular carrier, cigarette paper overwrapped
`about the tubular carrier, an arrangement of flow-through
`filter plugs at a mouthpiece end of the carrier and a plug at
`the opposite (distal) end of the carrier, which preferably
`limits air flow axially through the cigarette.
`The preferred embodiment of the cigarette of U.S. Pat.
`No. 5,388,594, issued Feb. 14, 1995, is essentially a hollow
`tube between the filter plugs at the mouthpiece end of the
`cigarette and the plug at the distal end. This construction is
`10 believed to elevate delivery to the smoker by providing
`sufficient space into which aerosol can evolve off the carrier
`with minimal impingement and condensation of the aerosol
`on any nearby surfaces. U.S. Pat. No. 5,388,594, issued Feb.
`14, 1995, also discloses an electrical smoking article having
`15 heaters which are actuated upon sensing of a draw by control
`and logic circuitry.
`U.S. Pat. Nos. 5,060,671 and 5,093,894 disclose a number
`of possible heater configurations, many of which are made
`from a carbon or carbon composite material formed into a
`20 desired shape. In several of the disclosed configurations, the
`heater includes a plurality of discrete electrically resistive
`heating segments that can be individually activated to pro(cid:173)
`vide a single puff of flavor to the user. For example, one
`configuration involves a radial array of blades connected in
`25 common at the center and separately connectable at their
`outer edges to a source of electrical power. By depositing
`tobacco material on each blade and heating the blades
`individually, one can provide a predetermined number of
`discrete puffs to the user. Other configurations include
`various other arrays of discrete fingers or blades of heater
`material, or various linear and tubular shapes subdivided to
`provide a number of discrete heating areas. Such configu(cid:173)
`rations of discrete heating segments may allow for more
`efficient consumption of power and more efficient use of
`35 heater and flavor-generating material.
`It has proven difficult, however, to arrange suitable heater
`materials in the above-described configurations. A suitable
`heater material must exhibit, among other things, a resistiv-
`40 ity sufficient to allow for rapid heating to operating tem(cid:173)
`peratures. It is also desirable that the heater resistance
`correspond to the energy density of the power source in
`order to minimize power consumption. Suitable heater mate-
`rials of low mass, such as those described in the above(cid:173)
`incorporated patents, must generally also be of very low
`density, however, and thus are difficult to arrange in such
`discrete heater segment configurations. Such low density
`characteristics complicate, or make impossible, assembly of
`the configurations by simple, well-known manufacturing
`50 techniques. Even after successful manufacture, such con(cid:173)
`figurations are often unacceptably fragile for use within a
`flavor-generating article. These problems can be overcome
`to some extent with the aid of highly sophisticated manu(cid:173)
`facturing techniques. However, in manufacturing the heaters
`55 which are disposable and replaceable, these techniques
`become prohibitively expensive.
`It would thus be desirable to provide a discrete heater
`configuration of suitable heater material that is sufficiently
`strong for use within a flavor-generating article without
`threat of breakage during manufacture. It would also be
`desirable to be able to manufacture such a heater with a
`discrete heater segment configuration using well-known,
`inexpensive manufacturing techniques.
`Various ceramic heating compositions are described in
`65 U.S. Pat. Nos. 5,045,237 and 5,085,804. Also, British Patent
`No. 1,298,808 and U.S. Pat. Nos. 2,406,275; 3,875,476;
`3,895,219; 4,098,725; 4,110,260; 4,327,186; 4,449,039;
`
`Ex. 2015-0017
`
`

`

`5,880,439
`
`3
`4,486,651; 4,555,358 and 4,634,837 relate to electrically
`conductive ceramic heater materials.
`
`SUMMARY OF THE INVENTION
`The invention provides an electrically powered ceramic 5
`composite heater useful for devices such as cigarette light(cid:173)
`ers. The heater includes a heating element of a functionally
`graded monolithic electrically resistance heating ceramic
`material, the heating element being adapted to receive a
`cigarette and heat a portion thereof. In a preferred
`embodiment, the heating element includes an electrically
`conductive zone such as an annular hub, with a central axis,
`and a heating zone such as a plurality of electrically con(cid:173)
`ductive blades, attached to the hub and extending from its
`perimeter in one direction parallel to the hub's central axis.
`Each of the blades can have a free end remote from the hub
`or a hub can be located at each end of the blades. The hub
`and the blades form a hollow cylinder and the hub and
`blades comprise the functionally graded monolithic electri(cid:173)
`cally resistance heating ceramic material.
`According to one aspect of the invention, the heating
`element comprises a sintered mixture having an insulative
`coating on an outer periphery thereof. The ceramic material
`preferably comprises an insulating compound or semicon- 25
`ductive metal compound A and an electrically conductive
`metal compound B. Compound A can be Si3 N4 , Al2 O3 ,
`ZrO 2 , SiC, B4 C, SiO2 , glass such as borosilicate glass,
`and/or TiO 2 . Compound B can be TiC, M0Si2 , Mo 5Si3 ,
`Ti5 Si3 , ZrSi2 , ZrB 2 , TiB 2 and/or aluminides such as iron
`aluminide, nickel aluminide and titanium aluminide. In a
`two component MoSi2-Si3N4 ceramic material, the heating
`zone can include Si3N4 in an amount of 55-65 vol. % and
`MoSi2 in an amount of 45-35 vol. %. The ceramic material
`can further comprise a reinforcing agent such as fibers or
`whiskers of SiC, SiN, SiCN, SiAlON. The ceramic material
`is preferably arranged in layers of different amounts of
`constituents (e.g., Si3 N4 and M0Si2), the amount of each
`component (e.g., Si3N4 ) varying preferably less than 20 vol.
`% between adjacent layers. Also, the layers are preferably
`hot pressed together in a single step rather than being
`individually pressed.
`The heater can have a number of desirable features. For
`instance, the ceramic material preferably heats to 900° C. in
`less than 1 second when a voltage of up to 10 volts and up
`to 6 amps is passed through the ceramic material. The
`ceramic material also preferably exhibits a weight gain of
`less than 4% when heated in air to 1000° C. for three hours.
`Each of the blades can have a resistance (R) of 0.05 to 7
`ohms, a length (L), a width (W), and a thickness (T), and the
`ceramic material has a resistivity ( a), the blade dimensions
`being in accordance with the formula R=a(L/(WxT)). Each
`of the blades can have an electrical resistance of about 0.6
`to 4 ohms throughout a heating cycle between ambient and
`900° C.
`When the heater is used in a cigarette lighter, the device
`can include a portable energy device electrically connected
`to the blades. The portable energy device can have a voltage
`of about 3 to 6 volts. In this case, each of the blades
`preferably has an electrical resistance of about 1 ohm 60
`throughout a heating cycle between ambient and 900° C.
`The heater hub can act as the common and/or negative
`electrical contact for all of the blades. Part or all of the
`blades and/or hub preferably include a coating of a brazing
`material suitable for joining ceramic material and electrical 65
`leads are preferably connected to the blades by the brazing
`material. A metal cage comprising a hub and blades can be
`
`4
`fitted against the heater hub such that the cage blades extend
`between the heater blades with air gaps having a width of
`about 0.1 to 0.25 mm being located between opposed edges
`of the cage blades and the heater blades.
`According to one aspect of the invention, the heater is
`electrically connected to a lead pin module having leads
`electrically connected to the heater blades. The heater hub
`includes at least one air passage therethrough. The free ends
`of the heater blades are supported by a lead pin module
`10 having lead pins electrically connected to the free ends of the
`heater blades, the heater hub being open and defining a
`cavity which extends along the heater blades and the cavity
`being sized to receive a cigarette containing tobacco. The
`device can further include puff sensing means and electrical
`15 circuit means for supplying electrical current to one of the
`heater blades in response to a change in pressure when a
`smoker draws on a cigarette surrounded by the heater blades.
`For instance, each of the blades can have a free end remote
`from the hub functioning to electrically connect the blade to
`20 a power and control module of the cigarette lighter with the
`hub and blades comprising the functionally graded mono(cid:173)
`lithic electrically resistance heating ceramic material. The
`cigarette is disposed in proximity to the blades so as to be
`heated by the blades.
`The invention also provides a method of making an
`electrically powered ceramic composite heater useful for
`devices such as cigarette lighters. The method includes
`forming a functionally graded ceramic material by placing
`layers of varying compositions of the ceramic material in a
`30 container and pressing the layers together. The pressed
`layers are sintered into a compact which can be machined
`into a heating element of the functionally graded monolithic
`electrically resistance heating ceramic material, the heating
`element being adapted to receive a cigarette and heat a
`35 portion thereof. The heating element can include a plurality
`of longitudinally extending and circumferentially spaced(cid:173)
`apart blades extending from one end of a cylindrical hub
`portion wherein the hub is of an electrically conductive
`composition and the blades are of an electrically resistance
`40 heating composition.
`The present invention further provides an electrically
`resistive element comprising: at least one conductive portion
`consisting essentially of a conductive ceramic component of
`MoSi2 or Mo5 Si3 ; at least one electrically resistive portion
`45 consisting essentially of the conductive ceramic component
`and an electrically insulating ceramic component. The elec(cid:173)
`trically resistive element further comprises a transitional
`portion immediately between the conductive portion and the
`resistive portion, the transitional portion comprising the
`50 conductive ceramic component and the insulating compo(cid:173)
`nent in mutual proportions such that the transitional portion
`has a resistivity of approximately 80 to 95% of a resistivity
`of the conductive portion, the insulating ceramic component
`constituting at least 15% by volume of the transitional
`55 portion.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The invention is described in conjunction with the accom(cid:173)
`panying drawings, in which like reference numerals refer to
`like parts throughout, and in which:
`FIG. 1 is a perspective view of an electrical smoking
`article which utilizes an electrically powered ceramic com(cid:173)
`posite heater in accordance with the present invention;
`FIG. 2 is an exploded view of the device shown in FIG.
`
`1;
`
`FIG. 3 is a perspective view of a ceramic heater assembly
`in accordance with the present invention;
`
`Ex. 2015-0018
`
`

`

`5,880,439
`
`5
`FIG. 4 is a perspective view of a monolithic ceramic
`heater in accordance with the present invention;
`FIG. 5 is a perspective view of an electrically conducting
`metal cage in accordance with the present invention;
`FIG. 6 is a perspective view of a fixture in accordance
`with the present invention;
`FIG. 7 is a perspective view of a retainer ring in accor(cid:173)
`dance with the present invention;
`FIG. 8 is a perspective view of a pin module in accordance
`with the present invention;
`FIG. 9 is a perspective view of a segment of a precursor
`of the heater of FIG. 4;
`FIG. 10 shows a graph of electrical resistivity vs. vol. %
`conducting material of a ceramic composite material in
`accordance with the invention;
`FIG. 11 shows a flow chart of processing steps which can
`be used to make a ceramic heater in accordance with the
`invention;
`FIG. 12 shows a typical plot of temperature vs. energy for
`composition No. 8 in Table 5;
`FIGS. 13a-c show perspective views of components of a
`heater assembly according to another embodiment of the
`invention;
`FIG. 14 shows an assembly of the components shown in
`FIGS. 13a-c;
`FIG. 15 shows a graph of creep rate versus stress for
`various ceramic materials including mixtures of MoSi2 and
`Si3 N4 ;
`FIG.16 shows a graph of grain size ofMoSi2 versus creep
`rate of the M0Si2 ;
`FIG. 17 is a photomicrograph of a five layer functionally
`graded MoSiiSi3 N4 ceramic composite in accordance with 35
`the invention;
`FIG. 18 shows a cross section of adjacent layers of 60%
`M0Si2 +40% Si3N4 and 40% M0Si2 +60% Si3 N4 ;
`FIG. 19 shows a cross section of a functionally graded
`ceramic wherein adjacent layers differ in amount of MoSi2 40
`by 40%;
`FIG. 20 is a cross section of two layers of a functionally
`graded ceramic having an upper layer of 60% MoSi2+40%
`Si3 N4 and a lower layer of 100% MoSi2 ;
`FIG. 21 is side view of a functionally stepped, ceramic 45
`heater element constructed in accordance with another pre(cid:173)
`ferred embodiment of the present invention; and
`FIG. 22 is representation of the levels of reisistvities
`associated with the differentiated portions of the ceramic 50
`heater element shown in FIG. 21.
`
`DETAILED DESCRIPTION OF IBE
`PREFERRED EMBODIMENTS
`
`The invention provides a functionally graded ceramic
`composite as a resistance heating element and as a structural
`material that can operate at or above 1200° C. with a creep
`rate lower by 5 to 6 orders of magnitude than superalloys
`such as Haynes 214, nickel aluminides and iron aluminides.
`The ceramic material will provide an electrical resistance 60
`heater that can operate up to 1400° C. with excellent
`oxidation and corrosion resistance. The heater will have a
`conducting portion for contacts, resistive portion for heating
`and insulative oxide on an outer surface thereof to prevent
`electrical shorting.
`The invention also provides a simplified arrangement of a
`ceramic heater with at least 1 ohm resistance and which can
`
`5
`
`10
`
`20
`
`6
`withstand exposure to temperatures of 1200° C. or above
`without degradation in properties. Properties can be selec(cid:173)
`tively adjusted by controlling the relative amounts of com(cid:173)
`ponents of the ceramic material. The material is preferably
`layered such that the layers have different compositions to
`provide different properties. For example, the resistivity can
`be increased in any particular layer by appropriate choice of
`constituents and/or relative amounts of the constituents of
`the ceramic material. Further, the thickness of each layer can
`be adjusted to provide optimum performance.
`MoSi2 and Mo 5Si3 (which has a higher melting point than
`MoSi2 ) provide advantages compared to other high tem(cid:173)
`perature materials. For temperature applications below
`1000° C., materials such as superalloys in polycrystal or
`15 single crystal form and aluminides and their composites
`such as TiAl, Ni3Al, and NiAl have been used. For tem(cid:173)
`perature applications above 1000° C., ceramic and ceramic
`composites have been used but such materials become brittle
`even at 1200° C. since ceramics are intrinsically brittle due
`to their covalent bonding, whereas superalloys lose their
`intrinsic strength due to the reinforcements ( e.g., y' prime
`coarsens and ultimately dissolves). Molysilicides and com(cid:173)
`posites thereof, on the other hand, are ductile at temperatures
`above 1000° C. Accordingly, as an alternative to superalloys
`25 for use at temperatures greater than 1000° C., ceramic and
`ceramic composites and suicides may be useful. MoSi2 is
`ductile due to metallic bonds between the Mo-Mo atoms
`that contribute to their electrical conductivity and are partly
`covalent thus combining the useful properties of metals and
`30 ceramics.
`Based on its open structure like other BCC materials,
`MoSi2 is expected to creep easily. Creep has been found to
`occur by cube slip on cube planes. For the dislocations (100)
`to climb, they need to move from Mo to Si to Si to Mo
`layers. From the phase diagram, since M0Si2 is essentially
`a line compound (very little solid solubility) of either Mo or
`Si, the energy of the off-site occupancy is expected to be
`very high. Hence, the diffusion of Mo or Si is essentially
`restricted to its layers. Because of restricted slip and
`restricted diffusion, grain boundaries play a dominant role in
`providing sources and sinks for the point defects. These
`contribute to significant grain size effects during creep in
`these layer materials.
`According to one aspect of the invention, a functionally
`graded ceramic composite is provided which has excellent
`oxidation resistance, electrical conductivity which can be
`tailored from metallic to semi-conductive to insulating,
`thermal conductivity which can be increased to reduce hot
`spots, thermal expansion coefficient lower than MoSi2 alone,
`enhanced creep resistance above 1200° C., and stable rein(cid:173)
`forcements can be incorporated to enhance fracture tough-
`ness. As a specific example, high contents of MoSi2 in a
`MoSi 2-Si3 N 4 composite can provide an electrical
`conductor, a mixture MoSi2-Si3N4 can provide a semi-
`55 conductor and a predominant amount of Si3N4 can provide
`an insulator. With such a functionally graded composite,
`intricate machining of the composite to form a heating
`element can be carried out with electrical discharge machin-
`ing (EDM).
`Materials comprising 100% MoSi2 and composites of
`MoSi2 with 20, 40, 60 and 80 vol. %, respectively, Si3N4
`were investigated. Process parameters evaluated included
`packing of layers, sintering temperature, and cooling rate.
`The electrical resistivity was examined by the four-probe
`65 method and the microstructure was examined by SEM,
`EDAX and TEM. Vickers hardness was measured with loads
`of 1, 10, 15, 20 and 30 kg. The flexural strength was
`
`Ex. 2015-0019
`
`

`

`5,880,439
`
`7
`determined from MOR bars. Fracture toughness was evalu(cid:173)
`ated from crack lengths of indentations. The creep rate was
`determined in tests carried out at 1200° C. or above across
`the layers and perpendicular to the layers of the functionally
`graded material. Oxidation resistance was evaluated at tem(cid:173)
`peratures of 600° -1500° C. in air. The corrosion resistance
`was investigated with various acids.
`One functionally graded material investigated included
`four layers of which an outer layer consisted of 100%
`MoSi2 , the next inner layer consisted of 60 vol. % MoSi2-40
`vol. % Si3 N4 , the next layer consisted of 40 vol. % MoSi2-60
`vol. % Si3N4 and the other outer layer consisted of 100%
`Si3 N4 .
`A six-layer functionally graded material of M0Si2-Si3 N4
`was investigated. The composite consisted of an outer layer
`of 100% MoSi2 , an adjacent layer of 80 vol. % MoSi2-20
`vol. % Si3 N4 , the next layer of 60 vol. % MoSi2-40 vol. %
`Si3 N4 , the next layer of 40 vol. % M0Si2 -60 vol. % Si3N4 ,
`the next layer of 20 vol. % MoSi2-80 vol. % Si3 N4 and the
`other outer layer of 100% Si3N4 . The thickness of each layer
`was 4--6 mm. It was found that the first five layers adhered
`extremely well but layer six could be separated from layer
`five. As such, the composite was evaluated as a five-layer
`composite by eliminating layer six.
`As a result of the investigations, it has been determined
`that a bulk functionally graded material of M0Si2-Si3 N4
`can be obtained with five layers. The gradation in amounts
`of MoSi2 between layers should preferably be no