CA2128213A1

CA2128213A1 - Electrical heating element, related composites, and composition and method for producing such products using dieless micropyretic synthesis

Info

Publication number: CA2128213A1
Application number: CA002128213A
Authority: CA
Inventors: Jainagesh A. Sekhar; Naiping Zhu
Original assignee: University of Cincinnati
Current assignee: Individual
Priority date: 1992-01-16
Filing date: 1992-12-07
Publication date: 1993-07-22
Also published as: US5565387A; US5484568A; WO1993014044A1; KR950700223A; SK85994A3; HUT70901A; JPH07507178A; EP0621859A1; US5420399A; HU9402120D0; CZ172294A3

Abstract

Electrical heating elements and related articles having oxidation resistance at high temperatures, produced by a method involving micropyretic synthesis. A composition subjected to micropyretic synthesis comprises a filler material, a reactive system capable of undergoing micropyretic synthesis, and (optionally) a plasticizer or extrusion agent. The method of preparation of articles includes slurry techniques, plastic extrusion, slip casting, or coating.

Description

W0 93/14044 212 8 2 1 ~ PCr/US92J10516 ~_~

E3A~5~1~ Q~ ~ I~I01!1 Field of th~ In~e~tioa -This in~ention uses a no~l techniqu~ to ma~e electrical hea~i~g elem~nts which may b~ us~d up to lS 1900 C. This tech~ique also provid~s new methods for ma~ufacturing ceramic composit~s, which may ~e used as both electrical heatins elements and o~idation resista~t materials.

D~scr~ptio~ of th~ Prior Art - Generally, h~ating elem~nts are mad~ from m~tals like Mo and W, and 8110y~ lik~ Fe Cr-Al ~nd ~i-Cr, SiC and m~tal silicides. Th~ alloy h~ating ~l~m~nt 25 i5 produced by melting in the electric i~duction or ~rc furnaceæ (sometimes alloys ha~e to b~ melt~d s~eral times to achieve homogeneity) and then is pres~ed or estruded. 5ilicon carbide and molybdenum disilicide heating elements ar~ made by powd~r metallurgy and have to be sintered at high temperatures and estended times in H2 and CQ
atmos.pheres. In the powder metallurgy industry, sintering i~ oft~n the most costly step of th~ total manufacturing process, esp~cially when high temperature sint~ring is involved. Melting a~d W093/140~ PCT/USs2/10S16 2iæ8~l3 1 casting are also costly~ In addition, because the manufacture of conventional materials is limited by processing, heating elements can be produced only within a predetermined resistivity range.

It is evident that the prior art methods eshibit serious disadvantages, and it is a primary o~ject of the present invention to obviate these by providing a micropyretic synthesis method and composition for production of electrical heating elements and o~idation resistant materials.

SUMMAE~ OF_THE IF~E~TIQ~

Micropyretic synthesis (also called combustion synthesis) is a technique which uses the heat release from a reac~ion for synthesis of a product. This esothermic reaction can become self-sustaining and will propagate throuqhout the reactant misture in the form of ~ combustion wave. When the combustion wave advances, the reactants are converted to the products. There are three main parameters important to the micropyretic synthesis process: (1) combustion temperature, (2) isnition temperature at whi~h a sample will become self-propagating, and (3) the velocity of wave propagation. This invention utilizes mi~ropyretic synthesis to make the desired product.

In comparison to prior art mat~ods, mic~opyretic synt~hesis provides: (i) energy-sa~ing because of the use of self-sustainin~ reactions, ~ii) simplicity, ~iii) reliability of the process, (i~) r~lative purity of the products, (v) low cost of original powders, and (vi) very low processing ~osts when WO 93/14W4 PCI/USg2/10516 1 compared to conventional methods. It is ad~antageous if a cheap powder and self-sustaining reactions can be used durin~ the preparation of electric heating elements.

According to the invention there is provided a composition comprising a fill~r mat~rial, at least one reactive system, and optionally a plasticizer (or estrusion agent). Fillers may be SiC, MoSi2, Cr2C3, WC, A1203, SiC);~, SnC~2, C, Co, Ni, rare earths, ZnO, Y203, ZrO2, Cu, N~-Co bas~d superalloys, Sb203, CuO, Fe203, GeO, Fe304, V205, F~O, Mo, Nb, Cr, Al, Si, Y, Fe, Si3N4, B, or alloys and mistures thereof.
Fillers may also be naturally occurring min~rals such as sand or clay. Th~ content of fillers may range up to 95~ (of the total weight). The reactive system comprises at least two combustible material~ which will react esothermically with one another by micropyr~tic synthesis and are present in such proportion to one another that combustion will occur when iqnited. The reactive systems and ceramic phases formed thereby may be any of thos~ in Table I. Various combinations of these combustible materials may be used. Non-stoichiometric waights ~ may also be chosen as long as combustion can be mads : ~ to occur. Th~ content of the reactive system can range from about 5% to 95% by weight of the total composition. Plasticizers or estrusion agents such as polyvinyl butyral, polyurethane, colloidal silicai 2~-5~ agueous chemical cellulose solutiont phosphoric acid, b~ntonite, fused silica and its activator, may form 0-90% of the total weiqht of the composition.

Pref~rably the composition of the invention WO93/14~ PCT/US92/10516 ~h~?.82~3 4 l c ains in weight percent based o~ the total weight, from a~out 20~ to about 85% filler material, about 15%.to about 85% r~active system, and 0% to about 25% plasticizer.
s Any one or more of the preferred range3 ~t forth above can b~ used wîth any one or more of the broad ranges for the remaini~g components indicated above.

= _ ~D ST~ICHIOM~TRIC W~IGHT~

Reactîon ~ciQh~_~

Ni+Al.NiAl ~i:68.5, Al:3l.5 3Ni~Al5Ni3Al Ni:86.7, Al:l .3 3Cr2O3~6Al~4C-2~r3C2~3Al2O3 Cr2O3:69, Al:24, C:7 20 MoO3+2Al~B-MoB~Al2O3 MoO~:69, ~l:25.9,.~:5 MoO3~2A1~2Si~MoSi2+~l2O3 MoO3O57, Al:2l, S.:~.
Ti+2B-TiB2 Ti:68.9, ~:31.l 5Ti~3Si~Ti5Si3 Ti:74, Si:26 Nb+2Al=NbAl2 Nb:63.3, Al:36.7 25 Zr+2B=ZrB2 Zr:80.8, B:19.2 Nb+2B~NbB2 Nb:81.l, B:18.9 Fe2O3+2Al-~l2O3~2Fe Fe2O3:74.7, Al:25.3 Cr2O3~2Al~Al2O3+2Cr Cr2O3:73.8, Al:26.2 ~.86~i+l.72B+l.48Al=0.86TiB2~l.48 Al Ti:41.3, B:1~.7,Al:40 30 Ti+B-TiB Ti:~l.6, B:l8.4 Hf+2B-HfB2 Hf: as . 2, B:l0.8 Ta+2B-TaB2 ~a:89.3, B:lQ.7 Ti~C-TiC Ti:~0, C:20 Ti+Ni~TiNi Ti:44.9, Ni:55.l 35 Ti~Pd~TiPd Ti:3l.0, Pd:69~0 WO 93/14044 2 1 2 ~ 2 1 ~ Pcr/US92/10516 Ti I Al=TiAl Ti: 64, Al: 3 6 Ti~Fe ITiFe Ti: 4 6 . 2, Fe: 53 ~ 8 Ti+C+O. 68Ni=TiC+0. 68Ni Ti:48, C:12, Ni:40 The proportion of combustible material to filler in the electrical heating element is critical, since the combustible content will change the composition of final products and combu~tion temperature. For instance, the combustion temperatur~ of the 10 MoO3~2A1~2Si system is as hiqh as 3300 K. It is known that the melting point of its reaction product (MoSi2) is ~293 K and that the final products may, therefor~, melt. Enough filler or diluent is thus necessar~ in order to keep the original shape of the 15 product and a crack free surface. Howe~er, too low a combustible material content will lead to low combustion temperatures so that the final product will not be well-bonded and will display wsak room temperature strenqth. Fillers have thre~ important 20 effects on the products: (1) the fillers act as diluent of the combustion process; (2) they form a part of the final composition and act as a reinforcement to the combustion product~, (for instance, MoSi2 shows very low room temperature 25 fracture toughness and low yield streng~h levels at elevated temperatures. It must therefore be reinforced by some kind of filler such as ZrO2, A12O3, SiO2, SiC, etc.); and (3) fillers may also act as sintering aids, (e.g., Y2O3 addition 30 will enhance the sintering during combustion).
Filler contents have significant effect~ on electrical resistance, room temperature fracture toughnesæ, and osidation resistance at el~vated operating temperatures of final products. In the 35 esemplary embodiments disclosed hereinaft~r filler W09~/14~ PCT/US92/1051~

~2~3 6 1 and combustion sources were chosen according to the following criteria: ~1) ad~guate mechanical strength, ~2) high osidation resistance at desiqned working temperature, (3) thermal stability between filler and combustion source at working temperature, (4) resistance to thermal shock when subject to heating and cooling, (S) slow grain growth, (6) combustion temperature, and (7) electrical resistance.

The present invention further provid~s ~ mQthod of preparing composite articles, in particular electrical heating sl~ments, comprising the ~t~ps of:
(a) blending a mîsture comprising up to 95%
by weight of a particulate filler material, between about 5~ and 95% by weight of at least one reactive system, wher~in said reactive syst~ comprise~
at least two particulate combustible - materials which will react esothermically with one another by micropyretic synthesis and are pre~nt in such proportion to ono another that combustion will occur when iqnited, up to 90~ o~ a plasticizer, and a sufficient amount of solvent in order to form a slurry;
~b) fashioning said slurry into a final desired article shape; and (c) combusting said shape by ignition at a temperature between about 150 C and .. 1250 C.
' : An electrical h~ating element or ccramic composite article in accordance with th~ invention, which may be used at temperatures upto 1900- C, WO93/14~ 212 8 21 3 PCT/US92/10516 l comprises a ceramic composite formed by ~icropyretic synthesis of a composition containing: (a~ up to 95%
by weight of a filler material; and (b) between about 5% and about 95% ~y weight of at least one reactive system, wherein said reactive system comprises at - least two combustible materials which will react esothermically with one another by micropyretic synthesis and are present in such proportion to one another ~hat combustion will occur when ignited.
. Ignition may be effected by a heat sourc~ such as a flame, laser, electron ~eam or welding electrode, or by passing the shaped article throuqh an in~uction coil or a furnace heated to ignition temperature.
DETAILED l)E$CRIP~IOI!~_ OE 1~ I~JE~TIOl!l~

Since the method of the in~entio~ per~ts preparation of compo~it~s with d~f~rent volume fractions of constituent phas~s, it is readily possible for the first time to control tha ~lectrical resistance, and th~ change in electrical resistanc~
with temperature changes. For e~ample, silicon carbîde has a negative slope of resistance ~s.
temperature, whereas ~oSi2 has a positive slope.
Judicious combination of these filler materials may thus provids a very slight change in resistance vs.
temperature. The room temperature resistivity of heating ~lements of the invention can be tailored to 3~ range from 30 ~ ohm cm to 20 ohm cm.

As will be e~ident from the compositions s2t forth her~inaft~r, the b~st known mode of carsying out the invention includes the use of the following composition~, all p~rcentages being by weight.

4~ PCT/US92/10516 2~22213 a 1 A - A filler material comprising at least one of from about 20~ to about 80~ MoSi2, up to about 30%
chromium., up to about 15% iron, up to about 6%
molybdenum, up to about 2~ titanium, up to about 1.2%
niobium, up to about 0.7% yttrium, up to about 2.5%
aluminum, up to about 10% silver, up to about 42 silicon carbide, up to about 12% Y2O3, up to about 2.5% A12O3, up to about 8% SiO2, and up to about 2.S% MgO; a reactive system comprising from about 12% to about 35% nickel, and about 3% to about 13~ aluminum; and a plasticizer which when present comprises about 8~ to about 12% of a 2.5% a~ueous chemical cellulose solution.

B - A filler material comprising at least one of from 0% to about 75% MoSi2, about 8% to about 10 SiO2, up to about 2% silicon, about 0.8% to about 40% silicon carbide, up to about 0~5% boron, up to about 8% Y2O3, and up to about 2% Si3N4; a reactive system comprising from about 7% to about 28%
Cr2O3, about 2.5% to about 10% aluminum, and about 0~7% to about 3% carbon; and a plasticizer comprising at least one of from about 4% to about 5 polyvinyl butyral, and about 8% to about 12~ of a 2.5~ aqueous chemical cellulose solution.
C - A filler material comprising at least one of from about 1% to about 50% silicon carbide, up to about 71% MoSi2, up to about 10% SiO2, up to about 10% Y2O3, up to about 10% Si3N4, up to about 0.5% BN, up to about lS chromium, up to about 1% boron, up to about 0.5~ aluminum, up to about 10S
A12O3, up to about 0.5S silicon, and up to about 7% ZrO2; a reactive system comprising from about 7S
to about 30% MoO3, about 2.5% to about 11%

WO93/14~ PCT/US92/10516 1 aluminum, and about 2.5% to about 38% silicon and up to about 11% carbon; and a plasticizer comprising at least on~ of from about 10~ to about 15% polyvinyl butyral~ about 8~ to about 15% of a 2.5~ aqueous chemical cellulose solution, about 8% to about 10%
fused silica and its activator, and about 4~ to about 10% bentonits.

D - A filler material comprising at l~aæt one of from about 35~ to about 40% silicon carbide, about 7%
to about 8% Y20~, about 1.7% tc about 2~
~1203, about 7% to a~out 8% SiO2 J and about 1.7% to about 2% MgO; a reactive system ~omp:rising from about 25~ to about 30% titanium, and about 9% to lS about 11% silicon; and a plasticizer comprising from about 8% to about 12% of a 2.5% aqueous chemical cellulose solution.

Compositions embodying th~ invention are as follows, it being u~derstood that thes~ are illustrative and not limiting:

ComPQi~ion A
Combustibl~ : Ni : 17.34 (9) 25 Al : 2.66 (q) Filler : MoSi2 : 80.0 ~g) Plasticizer : : 0 Composition ~
30Combustibl~ : Ni : 26.0 (g) ~- Al : 4.00 (9) Filler : MoSi2 : 70.0 ~g) Plasticizer : : 0 355~_~a:.L~ S
Combustible : Ni : 34.68 (q) PCT/U~92/10516 W093/14~
'3 1 Al :5.32 (g) Filler : ~oSi2 :60.0 (g) Plasticizer : : 0 Composi~ion D
- Combustible : Ni :13.70 (9) ~ 6.30 tg) Filler : MoSi2 :80.0 (g) Plasticiz~r : : 0 Con~Q~ i tion E
Combu~tibl~ 15.00 (~) Al :7-05 (Sl) Filler : MoSi2 :70.00 (9) : Cr 5.25 (cJ) : Mo 0.60 (CJ~

: Ti :1.70 (g~
: B :0.40 ~g) Plasticizer : : o CQm~osition ~
Combust~ble : Ni :27.40 ~g) Al :12.60 (g) Filler : ~oSi2 :20.00 (~) : Fe :5.30 (g) : Cr 30 (g : Mo :1.60 (g) : Nb :1.17 (g) : Y :0.67 (g) : Al :1.00 ~g) P~asticiz~r : : 0 Composition G
Combustible : Ni :24.66 (g) Al :11.34 (q) W093/14044 21282~ ~

Filler : MoSi2 :40. 00 (9) Fe 4. ao (g) Cr :18. 00 (~) Mo l. 00 (g3 : Nb :0. S0 (51) y :0 . 50 (g) Plasticizer : : 0 C~Qm~Qsition H
Conlbust~bl~ : Ni : 12 . 33 (g) Al :5. 67 (9) Filler : Mo~i2 :75. 00 (g) Fs :l. 50 (9) Cr :~. 50 (g) Al :2.50 ~9) Plasticizer : : 0 C~ompo~ltion Combusti~ Ni :12 ~, 33 (g~
Al :5. fi7 ~g3 - Filler : MoSi2 :75. 00 (S~) : Fa 3~,00 (g) Cr :2 . 50 (g) Al :l . 00 (5J) B :0 . 50 ~g) Plasticizer: : 0 GQmP~:iQn ~
Combustible : Ni :17.13 ~g) Al :7~ 88 (9) Fi l1er : MoSi2 :70 . 00 (g~

: Fe 2.50 (g) Cr l. 00 (g) Al :l . 00 (9) B :0 . 50 (~) PCr/US92/1OSI~

J~13 12 Plastici2er : O

o~oSitiQrl K
Combustible : Ni :17.13 (g) : Al :7. 88 (g) Filler : MoSi2 :75~.00 (g~
- Plasticizer : : 0 Con~bustible : Ni :13 . 70 (g) Al :6 . 30 (g~
Filler : MoSi2 :70.00 ~g) Ag : 10 . 0 (g) Plasticizer : : 0 o~DQSitio~ M
Combustible : Cr203 8. 70 (9) Al :3 . 05 (g) C :0 . B9 (9) Filler MoSi2 :75.00 ~g) - : SiOz lû . 0~ (g) S~ 0 (g) SiC :1. 00 (g) B :0.30 (g) Plasti~izer : Polyvinyl Butyral :5 . 00 (g~

Combu~tible : Cr2o3 15 . 50 (g) : Al :5 . 45 (9) C :1 . 58 (g) Filler : MoSi2 65.00 (q) SiO2 10,00 (g) si :1 . oo ~q) : Si~: 1 . 00 (g) .

PCr/US92/10516 WO93/14044 21~8~1~

B : 0 . 50 (~) Plasticizer : Polyvinyl - : Butyral :5 . oo ~5) S ~
Combustible : Cr203 :13 . 70 (g) Al :4 . 80 (g) : C :1.40 (g) Fill~r : MoSi2 :65 . 00 (9) : SiO2 :10 . 00 (9) Si :2 . 00 (g) SiC : ~ 5 (g) B : 0 . 5 ~9) Plasticizer : Poly~inyl : Butyral : 5 .

Com~ustible : MoO3 : 17.1 (g) Al : 6 . 3Q (9 6.6~ (q~
Fi ~ler : MoSi2 : 60.00 ~9) SiC : 1 . 50 (g) SiO2 : 8 . 00 (g3 Si3N4 0 . S0 (~) Plasticizer : 2 . 5% aqueous chemica 1 cellulose solution :15 . 00 (g) Comno~itio~a Q
~:ombustibl~ : MoO3 :17.10 ~g) : ~1 :6.30 ~) Si 6. 6 (~) Filler : MoSi2 :60 . 00 (g) : SiO~ :7 ~ ~) PCr/US92/10516 2~28~æ : BN : 5~ (g) Cr 0 . 70 (g) : B : 0.30 (g) SiC : l . 5 (9) Plasticizer : Poly~rinyl : - -Butyral : lO . 00 (9 Compos i t i~n R
Combustible : MoO3 : 7 . ~5 (g) : Al 3 . 00 (g) Si : 3 . 15 gg) Filler : MoSi2 : 78.00 (q) Si~2 : .4 . 80 ~9) BN 0 . 50 (9) : Cr 0 70 B :0 . 30 (9~
sic : 1 . ~ (g) Al : 0. 5 (g~
Si 0 . 5 (~) Plasticiz~r: Poly~inyl Butyral :lO. 00 (g) ~o~ppositiQn S
Combustible : MoO3 : 17. l (g~
: Al 6 . 30 (g) Si : 6. 60 (g) Filler : MoSi2 6. 00 (~) SîC :61. 50 (q) SiO2 2 . 00 (~) 3~ Si3N4 :0 . 50 ~g~
Plasticizer : 2 . 5% aqueous chemical cellulose solution : lS . 00 (9) WO 93/14044 21~ 8 2 ~ 3P~/US92J10516 CoE~po~j, q~_ ~
Con~bustibl~ : MoO3 :17.1 tg) Al :6 . 3 (g~
Si :6 . 60 (9) Filler : MoSi2 :60 . ûO (~) SiC :2 . 00 (9) Plasticiz~r : Bentonite :8 . 00 (g) om~o~ition U
Combustible : MoO3 :17.1 ~) Al :6 . 3 (I~) Si 6 . 6û (~g) Filler : MoSi2 :60 . 00 (g) Si~: :1 . 5 (l3) Si3N4 0 . S0 (~) Y;~03 3 . 00 (~) ~?lasticizer : Bentonite : 5 . 00 (g~

- 20 Combust~ ble : MoO3 :25 . 65 (g) 9 . ~15 (g) : si 9 90 (9) Filler : MoSi2 :50 . 00 ~g) sic :1.o (9) Plasticiz~r : Bentonite :4 . 00 (g~
r~ o~ie~Ol~ w Combustible : MoO3 :17.1 (~) Al :6 . 30 (~
: Si :6 . 60 (5J) F~,ller : MoSi2 :60 . 00 (g) : SiC :1.5 ~g) - : sio2 :~ . o (q) Si3N4 0 . 50 ~g) : Y203 : 3 . ~0 (5~) PCT/US9~ 516 WO93/14~W

~ Z~-~ 16 1 Plasticizer : Polyvinyl : Butyral : 15.00 (g) Combustible : MoO3 : 17.1 (g) : Al : 6.30 (y) : ~i . : 6.~0 (g) Filler : ~oSi2 : 60.00 (g) sic : ~. so (g) : SiO2 : 8.00 (5) Si3N4 0.50 (~) Plasticizer : Polyvinyl : Butyral : 15~00 (9l) Composition Y
Combustible : MoO3 : 17.1 (g) : Al : 6.30 (~) : Si : 6.60 (~) Filler : ~oSi2 : 60.00 (g) : SiC : 1.50 (~) :`
- : Zr2 : 8.00 (~
: ~i3N4 : 0~50 (~) Plasticiz~r : Polyvinyl : Butyral : 15.00 (g~

Combustible : MoO3 : 17.1 (g~
: Al : 6.30 (g) : Si 6.60 (g) Filler : MoSi2 : 60.00 ~g) .. : SiC : 1.50 (g) : S~3N4 : 0.50 (~) Plasticizer : Fused silica ~ activator : 10.00 (q) PCI`/US92/10516 w093~1~ 212~213 Combustible : MoO3 : 17.1 (9) : Al : 6.30 (g) : Si 6.60 (g) Filler : MoSi2 :60.00 ~g) - : SiC :1.50 (9) : Si3N4 :0.50 (~) : Silica 8.00 (g) Plasticiz~r : ~iquid Silica & activator : 10.00 (~) Composi~ion BB
Combustibl~ : MoO3 :17.1 (9) : Al :6.30 (9) Si :6.60 (g) Filler ; MoSi2 :60.00 (g) : SiC :1.5~
Si3N4 0.50 (g) Y2O3 3.00 ~g~
Plasticizer : Silica : (~) & activator : 10.00 ~g~

Composition CC
Co~bustible : ~oO3 :17.1 (g) : Al :6.30 ~g) : Si :6.6~ ~g~
Piller : MoSi2 :6Q.00 (9~
: SîC :9.50 (g) Si3N4 O.S0 Plasticizer : Polyvinyl Butyral : 15.00 ~9) ComDosition D~
Combustible : MoO3 :17.1 (g) : Al :6.30 (~) PCT/US~2/10516 W093/14~
, 2l~2l3 1 : Si :6.60 (g) Filler : MoSi2 :60.00 (9 : SiC :9.50 (g) Si3N4 0.50 (9) Plasticizer : ~750 Cotronics~ *
fused silica &
activator : 15.00 (g) a from Cotronics Corp., 3379 Shore Pkwy,, 1~ Brooklyn, NY 11235.

Composi~iQn EE
Combustible : MoO3 :28~0 ~y) : Al :10.50 (g) : Si :11.00 (93 Filler : SiC :40.00 (9~
Plastici~er : Bentonite : 10.00 (y) Combustible : MoO3 :22.80 (g) : Al :8.40 ~9~
: Si :8.80 ~9) Filler : Si~ :40.00 ~g) Y203 :8.00 (q) S13N4 2.00 (g) Pla~ticizer : Bentonite : 10.00 ~g) ,.

Com~ositio~ GG
Combustible : ~oO3 :22.80 ~g) ~ Al :8.40 (g~
: Si 8.80 (g) Filler : SiC :40.00 (g) ~23 :8.00 (g) Si3N4 2.00 (g~
SiO2 :1~ . 00 (g) Plasticizer : 2 . 5% a~ueGus chemical cel lulose solution : 10 . 00 (g) Composition HH
Combustible : Cr203 : 27 . 60 (g3 Al :9 . 60 (g~
C :2. 80 (g) Filler : SiC :40 . 00 (g) Y203 8 . 00 (g~
Si3N4 2 . 00 (9) SiO2 : . 10 . 00 (g) Plasticizer : 2. 5% aqueous chemical cellulose solution : 10 . 00 (g) ~==~11 20Co~bustible : ~i :34.68 (g) : Al :5.32 ~g) Filler : SiC :40.00 (g~
Y~3 :10.00 (g~
A12~3 2.00 (g~
: SiO2 6.00 (g) : MgO :2.00 (g) Plasticizer : 2~5% aqueous chemical cellulose solution : 10.00 (g) . . .
Composition J~
Co~bustible : Ni :21.67 (~) : Al :3.33 (g) -Filler : SiC :40-00 (g) Pcr/US~2/10516 Fe :15 . 00 (~) Cr :~ . 00 (g) Al :1.00 (g) Y2O3 8 . 00 (~) : ~12O3 :2.00 (g) SiO2 :6 . 00 (g) Plasticizer : 2 . 5% aqueous chemical cel lulose solu~ 10 . 00 (9) Combustible: Ti :29 . 60 (9) : Si 10.40 (g) Filler : SiC :40 . 00 ~9) Y2O3 8 . 00 ~g) A123 2 . û0 (g~
SiO2 :B ~. 00 (9) MgO :2 . 00 (g) Plasticizer : 2. 5% aqueous chemical cel lulose solution : 10 . 00 (g~

C~$ i t i~n . LI.
Combustible: Mo~3 :2Z . 80 ~9) Al :8 . ~0 ~g) Si 8 . ~0 (9) Filler : MoSi2 :10 . 00 (g) Si~: :50 . û0 ~g) Plasticizer: 2 . 5%
cel lulose in water :15.00 (9) 2 1 ~ 2 Pcr/US92/10~16 WO 93/14044 ~ .l 3 Comp~ ion MM
Combustible : MoO3 : 22 . 80 (g) Al 8 . 40 (g) Si 8. 8~ (9) Filler : MoSi;~ :10. 00 (g) SiC :40. oo (g) Plasticizer : Bentonite :10 . 00 (g) S~
Combustible : MoO3 :22 . 80 (y~
: Al : 8.40 (~) Si :8 . 8C ~g) Filler Si3N4 : 10.00 (g~l SiC :40 . OG (g) Plasticizer : Bentonite :10 . 00 (g) ~omDosi~is ~
Co~bustible : MoO3 : 19.95 ~g) : Al : 7.3S (q) Si : 7.7~ (g) 20Filler ; Y203 10.00 (g) : SiC : 40.00 (9) Plasticizer : Bentonite : 15.00 (g) 25Com~ositi~n PP
Combustible : MoO3 : 17.10 (g) : Al : 9.10 (~
: si : s.ao (q) Fîller Y2O3 10.00 (g) : S~C : 25.Q0 (~) 20.00 (9) Plasticizer : Bentonite : 10.00 (g) 9~
Combus~ible : ~qoO3 : 19 . 95 (q) .

PCr/U~92~10516 2~.82 ~

Al 7 .
Si 12 . 50 (~) Filler Y2O3 10 . 00 (g) SiC :40 . 00 ~g) Plasticizer : Bentonite : 10 . 00 (g) Compo s i t i on RR
Combustible : MoO3 : 14 . 25 (g) Al :11. 30 (g) : Si :11. 60 (g) Filler Y2O3 10 . 00 (CJ) Si~:: 40 . 00 (Cl) Plasticizer : Bentonite : 10 . 00 (Çl) Compos i t io~SS
Combustible : MoO3 : 19 . ~5 (g) Al :7 . 35 (g) : Si :7.70 (g) Filll3r Y2O3 10 . 00 (g) : SiC :25 . 00 (g) - D Mo~;i2 :2~ . 00 (q) Plasticizer : 13entonite : 10 . 00 (9) CompositiQr~ ~
Combustible : MoO3 : 17.10 (g) ~1 :9 . 0~ (g) : Si :3~40 ~g) Fi l ler Y2O3 10 . 00 ( g ) SiC :35 . 00 (g) A123 10 . 00 (g) .. : B :0 . 50 (g) Plasticizer : Bentonite : 15 . 00 (g) ~omoQsition UU
Combustible : MoO3 :17.10 (S~) P~r/uss2/losl6 WO93/14~44 212821 ~

~1 6 . 30 tq) Si :16 . 00 ~g) Filler : Y~O3 :5 . 60 (g~
SiC :35 . 00 (g) : A12O3 :5 . 00 (g) B :0 . 50 (g~
Plasticizer : Bentonit~ : 15 . 00 (g~

Combustible : MoO3: 19 . 95 (g~
Al : 7 . 35 ~g) S~ : 37.20 C : 10.50 (~
Fi ller A123 10 . 00 ~q) : B : 1. 00 (g) Plasticizer : ~entonite : 15 . 00 ~g) Proc~sæing in accordanc~ with the invent~on may inclu~e th~ followinq procedures:

Step 1. Powd~rs and polyvinyl butyral wer~
weighed according to desired eompositions.
Step 2. The weiqhed powders and pol~inyl 25 butyral w~re mised in acetone by ball milling for 2-10 hours with ZrO2 milling medîa.
i' Step 3. Th~ thin slurry was then transferred to a large glass container, driea in a 70 oYen, and solvent was allowed to evaporate.
Step 4. Dried powder was ground in a mor'car for one hour and acetone was added to thiS powder to form a thick s lurry .
- Step 5. This thick slurry was ~round for one hour to form a plastic mass.
~5 WO93/14k~ PCT/US92/10516 2~,.?,&Z~L3 1 Step 6. This plastic mass was forced through a die at high pressure (5-300 MPa) to produce wires.
Step 7. The green wire was formed into various shapes, e.g., coil, U-shape or straight.
Step 8. The wires from step 7 were dried in air for 1 hour, (these wires were no longer fle~i~le at this time), and then dried in a 70 oven.
Step 9. The wires were combusted in a furnace in air or argon atmosphere in th~ temperature range of 150 C - 1250 C.

~Q~S~
Step 1. Powders and bentonite were weighed according to desired compositions.
Step 2. The weiqhed powders and bentonite were mised in water by ball milling for 2-10 hours with Zr2 milling media.
Step 3. This thin slurry was moved to a large glass contain~r, dried in a 100 C oven, and the water was allowed to evaporate.
Step 4. Dried powder was ground in a mortar for one hour and water was added to this powder to form a thick slurry.
Step 5. This thick slurry was ground for one - 25 hour to form a plastic mass.
Step 6. This plastic mass was forced through a die at high pressure to produce wires.
Step 7. The green wire was formed into various shapes, e.q., coil, U-shape or straight.
Step 8. The wi,res from,step 7 wer~ dried in air for 2-9 hours ~these wires were no longer flesible at this ~ime), and then dried at 110 in the oven, for 2-5 hours.
Step 9. The wires were combusted in a furnace with air or argon atmosphere in the temperature range WO93/1~4 PCT/US92!10516 1 o~ lS0 - ~250 C.

Process III
Step 1. Powders and polyurethane and thinner were weighed according to desired compositions.
Step 2. The weighed powders, polyurethane and thinner were mi~ed for one half hour.
Step 3. This thin slurry was coated on a porous polyurethane polymer. Coated products were dried in air ~or about 10 minutes and then coated again;
coating thickne~s was controlled by coatin~ tims and slurry viscosity.
Step 4. Coated products were dried in air for 1-2 hours and then at a temperature of 300 C in an oven for 0.5-2 hours.
Step S. Coated products were combusted in the ran~ of 150 C - 1200 C in a furnace, or coated products from step 4 were combusted by a torch.
.:
~55~iL rQ
Step 1. Powders and col~oidal silica or phosphoric acid were w~i~hed according to desired :: compositions.
Step 2. Th~ weighed powders and silica were mised for half an hour.
Step 3. This thin slurry was coated on porous ' polymer or osidized TiB2 porous base. Coated products were drîed in air for abou~ 10 minutes and then coated aqasn; coating thickness was controlled by coating time and slurry viscosity.~
S.tep 4. Coated products were dried in air for 2 hours.
Step 5. Coated products were combusted at ~:- . 150D C - 1200 C in a furnace, or coated products from step 4 were combusted with a torch.
, wos3/l4~ PCT/US92/10516 ~ ~ 26 Step l. Powders and polyvinyl butyral were weighed according to desired compositions.
Step 2. The weished powders and polyvinyl butyral were mi~ed in ac~tone by ball milling for 2-lO hours with ZrO2 milling media.
Step 3. This thin slurry was moved to a large glass container, and dried in a 70 C oven. Acetone was allow~d to evaporate.
Step 4. Dried powder was qround in a mortar for one hour.
Step 5. This powder was pressed ~n a die to form various kinds of samples, for instanc~, sandwich samples.
Step 6. The products were combusted in a furnace with air or argon atmospher~ in the temperature range of lS0- - 1250 C.

Process VI
Step l. Powders and polyvinyl butyral w~re weighed according to desired composit~ons.
Step 2. The w~ighed powders and polyvinyl bu~yral were mised in acetone by ball millinq for 2-lO hours with a ZrO2 milling media.
Step 3. This thin slurry was moved to a large glass container, and dried in a 70 C oven. The , solvent was allowed to evaporate.
Step 4. Dried powder was ground in a mortar for ons hour, and acetone was added to this powder to 3~ form a th~n slurry.
Step 5. This thin slurry was mised m~chanically for another hour to form a slip.
Step 6. This slurry was cast in a d~ to form products with various shapes.
Step 7. Th~ sample from step 6 was dried in air ..

W093/~ 1 2 ~ 2 ~ 3 l for about lO hours, and then heated at 250 C in an oven.
Step 8. This sample was combusted in a furnace wi~h air or argon atmosphere in the temperature ran~e of 150 - 1250 C.

Process VI~
Step l. Powders were weighed aceording to desired compositions.
Step 2. The weiqhed powders were mise~ in acetone by ball millin~ for 2-lO hours with a ZrO2 milling media.
Step 3. Mised powders wers ground in a mortar for one hour.
Step 4. This powder was pressed in a die to form variaus kinds of samples, for instance, sandwich sample, dog bone shaped samples, etc.
Step 5. The products were com~u ted in a furnaca in air or ar~on atmosphere in tha temp~rature range of 150 - 1250 C.

~rQc~ VIII
Step l. U750 cotrQnies~ fused silica was ball milled for two days and then sized ~y -325 mesh sieve.
Step 2. Powders and sieved ~7S0 Cotronics~
fused silica were wei~hed according to desired compositions.
Step 3. The weighed powders and fused silica were mised in water by ball milling for 2-lO hours 30 with ZrO2 millinq media.
Step 4. The thin slurry was moved to a large glass container, dried in a 100 C o~n, and th~
water was allowed to evaporate.
Step 5. The dried powder was ground in a mortar for one hour, and liquid silica activator was added WO93/14~ PCT/US92/10516 '2~,'~.8?~3 1 to t~e powder to form a thick slurry.
Step 6. The thick slurry was ground or 30 minutes to form a plastic mass.
Step 7. The plastic mass was forced throu~h a die at high pressure to produce wires.
Step 8. The green wire was formed into various shapes, e.g., coil, U-shape or straight.
Step 9. The wires from step 8 were dried in air for 2-4 hours ~thes~ wires were no longer fle~ibl~ at this time), and dried in an oven at 110 C for 2-5 hours.
Step 10. The wires wer~ combusted in a fur~ace with air or argon at~osphere in the temperatuxe range of 750-1250 C.
1~
p~Q~SS IX
Step 1. Powders were weighed according to desired compositions.
Step 2. The weighed powders were mise~ in water by ball milling for 2-10 hours with ZrO2 milling media.
Step 3. The thin slurry was moved to a large glass container, dried in a 110 C oven, and water was allowed to evaporate.
2~ Step 4. The dried powder was ground in a mortar for one hour and 2.~ wt% chemical cellulose solution in water was added to this powder to form a thick slurry.
Step 5. This thick slurry was ground for another hour to form a plastic mass.
Step 6. This plastic mass was forced through a die at high pressure ~5-300 MPa) to produce wires.
Step 7. The green wire was formed into various shapes, e.g., coil, U-shape or straight.
Step 8. The wires rom step 7 were dried in air WO 93/1~ 2 I 2 8 21 3 PCT/USs2/10516 2g 1 for 1 hour, (~hese wires were no longer fle~ible at this time), and then dried at 100 C in an oven for 2 hours, ~nd then the oven temperature was increased to 400 C to burn the plasticizer out.
Step 9. The wires were combusted in a furnace in air or argon atmosphere in the temperature range of 700--1250 C.

Process X
Step 1. Powders were weighed accor~ing to desired compositions.
Step 2. The weighted powders were mised in water by ball milling for 2-10 hours with ZrO2 millinq media.
Step 3. This thin slurry was moved to a larg~
glass container, dried in a 100- oven, and the water was allowed to ~vaporate.
Step 4. Dried powder was ground in ~ mortar for one hour and 2.5 weight percent aqueous ch~mical 20 cellulo8~ ~olution was added to this powder to form a slurry.
Step 5. This slurry was ground for a half hour to form a homoqenous mass.
Step 6. This mass was slip cast by molding to form different shapes, e.g., cast plates, or by ~ pressinq the mass to form plates, or by working the - ~ mass with clay-sculpturing tools to obtain a shape.
, ~
Step 7. The green articles from step 6 were dried in air for 2-19 hours (these articles were no ~ 30 longer flesible at this time), and dried at 110- C in - ~ an ~ven for 2-5 hours.
, ~ ~
' Step 8. The articles were combustea in a - furnace with air or argon atmosphere in the temp~rature range of 750-1250 C.

- ~:: :

::

W093/14~ PCT/US92/10516 ~,~?J~3 ;
l Final products were prepared in accordance with the following non-limiting esamples:

Example l Composition U and Process II were used to make heating elements. The final products ~l-l0 mm wires) showed very high strength at room temperature and could be used as high temperature heating elements.
Samples were run at 1600 C for 40 hours without any degradation.

Esa~ple 2 Composition W and Process I were used to make an electrical heating element.
After combustion, the products showed escellent room temperature strength. According to this invention, this high room temperature strength comes not only from filler reaction joining amonq SiO2, MoSi2, SiC and the reac~ion product Al2O3, but also from reaction bonding between MoSi2 reaction -~ products and these fillers. It was found that an increase of the combustible ~MoO3+2Al+2Si) content up to a value of 45~ by weight of the total composition substantially enhan~ed the room ~; 25 temperature strength. But if this combustible content were more than 50% by weight, the combustion reaction would become too strong, so ~hat the final products were broken and cracks could form on the surface of the products. The adiabatic temperature of MoO3~2Al+2Si reaction is as high as 3300 ~, !
which is higher than the meltin~ point of MoSi2.
In this reaction, therefore, at least 50~ filler and plasticizer were necessary. According to this embodiment, the NoO3+2Al+2Si reaction is estremely useful in making high temperature heating elements, WO93/14~ 212 2 21 3 PCT/US92/10516 l and osidation resistance composites. In addition, the fillers such as Y2O3 and Al23' enhance sintering during combustion. It is essential, in order to obtain the best products, that different particle sizes be used in the sample. The products made from the processing were in the form o wires lmm - 10 mm in diameter or flat plate 5 mm thick.
These products could be used at high temperatures. Testing was carried out between 1200 and 1600 C. The sample surface was noted to be coated with a protective layer of SiO2 du~ to the reaction between MoSi2 and osygen. This thin quartz layer also sealed any of the pores on the surface. On account of the formation of this silica layer the product could be used at high temperatures. The wires were tested in the form of heating elements by paæsing 5-50 amps through the wires for long times and allowing the samples to attain temperatures betw~en lZ00 C and 1600- C. At 1600 C the wire ran for l00 hours without any sign of deterioration. The test was discontinued because of the terminal becoming too hot. At 1200- C the samples ran for o~er 1400 hours, and the test is still continuing. In this test the terminals were cooled with cooling water. The room temperature -- resistivity of these samples averaged 90~ ohm cm before the test and remained 90~ ohm cm after l400 hours when the test was briefly interrupted.
, E~ample 3 Process III was used to mis 70 grams Ti and 30 grams boron powder by ball milling. l00 ml polyurethane was used as a liquid media and mised with the Ti and B powder. This slurry was coated on porous polyurethane polymer 3-5 times, and then dried ..

WO 93/14044 PCI'/US92/10516 3~3 1 in air for 2 hours and 300 C oven for 1 hour, respectively. Samples were combusted in the furnace at 800 C, and osidized at 950 C for 3 hours. This formed an osidized TiB2 surface.
s E~ample 4 Eighty-seven grams of Ni powder (-100 mesh) and 13 grams of Al (-325 mesh) were mi~ed with ball millin~ in accordance with Process III. Aft~r milling, th~ mised powders wre mised with 100 ml polyurethane. This thin slurry was coated ~or 1-3 times on the surface of an o~idized TiB2 porous base. The samples were combusted at 1000- C. This porous heating element could be used as a low temperature hsater in the temperature range of 300 to 500 C.

E~ample S
Composition M and Process V wer~ used to make a sandwich sample. A sandwich sample is one which contains layers of different compositions of pressed powders or slurry. A powder misture with 69 ~rams of Cr2O3, 24 grams of Al and 7 qrams of carbon were mi~ed as a combustible source and used as the core of the sandwich. Samples were pressed into a sandwich.
After combustion, the core of the sandwich is a composite of Cr2O3 and A12O3 which are porous materials and insulators. The two outside layers were the composite resulting from Composition M.
This sample showed high stren~th for this kind of prod~uct. When used as a heating element the sample was noted to remain stable at 1300- C.

ExamPl~
Composition Y and Process I were u~ed to make WO93/l~W 2l 2~ PCT/US92/10~16 1 heating elements. The ZrO2 (partially stabilized) is advantageous in reinforcing MoSi2 since its coefficient of thermal espansion is close to that of MoSi2. It was found that partially stabilized Zr2 significantly toughened ~oSi2, and the final products could be used at temperatures up to 1600 C.

Esample 7 Compos~tion R and Process I wer~ us~d to make heating elements. The properties of the final products were comparable to those of E~ample 1.
How~ver, the combustion temperature is lower than that of Composition W used in E~ample 1.

E~am~le 8 Composition Z and Process VIII were used to make heating elements. The ~750 Cotronics~ fused silica was ball milled for 2 days to decrease the pa~ticle size to less than 40 micrometers before mising with the other powdered material. The fused silica and activator functioned very well as a plasticizer. The plastic masæ could be e~truded into shapas of various kinds. After drying in air and an oven at 110C, the samples showed good green strength. The green samples were combusted in the range of 7~0 to 1200 C. Final products eshibited escellent room temperature strength and could be used as high temperature heating elements in the range of 1000 to 1700 C.

EsamDle 9 Composition V and Process II were used to make heating elements. The combustible material comprised . 45~ by weight of the total composition. The combu~tion temp~rature was higher than that noted in WO93/140~ PCT/US92/10516 1 compositions having 40~ or less combustible material. Composition V could be ignited at relatively low temperatures, on the order of 750 -950 C. At such temperature levels crack-free products were obtained~ The final products had very high room temperature strength and could b~ used as high temperature heating elements.

~m~Q
Composition R and Process I were used to mak~
heating elements. However, estra Al and Si i~ the combustible, and Cr and B in the fillsr, were added to increase the density of the composition. It is believed that the B addition may decrease the melting point of the Si 2 in the misture, so that the products may be liquid sintered during the combustion step.

~ampl~ ll Composition E and Process ~III wsre used to make heating elements ~with omission of steps 1 and 2 since Composition E contained no plasticizer).
Samples were combusted in the temperature range of 1000 C to 1150 C. The final products showed reasonable room temperature strength and could be used as heating elements at temperatures of 500 -900 C.

Composition AA and Process VIII were used to!make high tsmperature heating elements. Pure SiO2 powd~r was used as the plasticizer, with ~750 Cotronics~ liquid silica activator. Since impurities were reduced in the final products by use of pure SiO2, the working temperature range of the h~ating . WO93/14~ PCT/US92/10516 35l elements was raised.

Example 13 Composition BB and Process VIII were used to make high temperature heating elements, again with pure SiO2 powder and "750 Cotronics~ liquid silica activator. These were found to work very well as a plasticizer. The working temperature of the heating elements was increased in comparison to products using bentonite as a plasticizerO due to reduction of the impurity phase.

xamp~e 14 Composition CC and Process I were used to make high temperature heating elements and osidation resistant composites. SiC was used (in place of SiO2) in this compo~ition as part of the filler material, and it was found that the final products could be used at temperatures as high as l700 C.

E~ample 15 Co~position DD, or ~omposition JJ, and Process X
were used to make plate-lika heating elements and oxidation resistant composite articles. Th~ final products showed improved room temperature strength and could be used as heating elements in room heaters in place of conventional alloy heating elements or ceramic heating elements. The resistivity of the element prepared ~rom Composition DD was measured at room temperature and found ~o be 0.2 ohm cm.
Average particle sizes used in the above esamples, obtained from commercially available sources, are set forth in Table II. No representation is made that these particl~ sizes are WO93/14~ PCT/US92/10516 J~

1 optimum, but they were found to be operable and hence constitute the best mode now known of carrying out the invention.

~blQ-Il Averaae Particles Sizes Ni:3~ Cr:-325 mesh (-44~m) MoSi2:3~ C:-300 mesh (-60~m) Fe:-200 mesh (-74~m) MgO:-325 m2sh (-44~m) Nb:-325 mesh (-44~m) Si:-325 me~h (-44~m) Al:-325 mesh (-44~m) Cr2O3:-325 mesh - ~-44~m) SiO2:-325 mesh (-44~m) SiC:l~
Si3N4:0.1-3~ Y23 2~
A12O3:-325 mesh (-44~m) B:Submicron, amorphous Ti:-325 mesh (-33~m) The materials made in accordance with this invention remain stable mechanically and r~main re~istant to osidation attack at high temperatures.
Consequently they may ~e also used not only as heating elements but also as materials where high temperature o~idation prevention is a service requirement. Such uses may be in furnaces, aero-space propulsion vehicles, in en~ine~ where high temperatures are produced such as jet en~ines and car engines, or for chemical and electrochemical uses.

, , ~ 35 : .

Claims

CLAIMS:

1. A composition for the preparation of composites by micropyretic synthesis having improved mechanical stability, room temperature fracture toughness, and oxidation resistance at temperatures up to 1900° C, and stable electrical conductivity, comprising:
(a) up to 95% by weight of a filler material; and (b) between about 5% and 95% by weight of at least one reactive system, wherein said reactive system comprises at least two combustible materials which will react exothermically with one another by micropyretic synthesis and are present in such proportion to one another that combustion will occur when ignited.

2. The composition according to claim 1 wherein said reactive system comprises at least one of:
Ni and Al;
Cr2O3 and Al and C;
MoO3 and Al and B;
MoO3 and Al and Si;
Ti and B;
Ti and Si;
Nb and Al;
Zr and B;
Nb and B;
Fe2O3 and Al;
Cr2O3 and Al;
Ti and B and Al;
Hf and B;
Ta and B;

Ti and C;
Ti and Ni;
Ti and Pd;
Ti and Al;
Ti and Fe;
Ti and C and Ni; or combinations thereof.

3. The composition according to claim 1 wherein said filler material comprises: SiC, MoSi2, Cr2C3, WC, Al2O3, SiO2, SnO2, C, Be, La, Co, Ni, rare earths, ZnO, Y2O3, ZrO2, Cu, Ni-Co based superalloys, Sb2O3, CuO, Fe2O3, GeO, Fe3O4, V2O5, FeO, Mo, Nb, Cr, Al, Si, Y, Fe, Si3N4, B, or alloys and mixtures thereof.

4. The composition according to claim 1 further comprising up to 90% by weight of a plasticizer.

5. The composition according to claim 4 wherein said plasticizer comprises: polyvinyl butyral, polyurethane, colloidal silica, 2%-5% aqueous chemical cellulose solution, phosphoric acid, bentonite, or fused silica and its activator.

6. The composition according to claim 5, containing from about 20% to about 85% of said filler material, about 15% to about 85% of said reactive system, and 0% to about 25% of said plasticizer by weight, based on the total weight of said composition.

7. The composition according to claim 4, wherein said filler material comprises at least one of from about 20% to about 80% MoSi2, up to about 30% chromium, up to about 15% iron, up to about 6%
molybdenum, up to about 2% titanium, up to about 1.2%

niobium, up to about 0.7% yttrium, up to about 2.5%
aluminum, up to about 10% silver, up to about 42%
silicon carbide, up to about 12% Y2O3, up to about 2.5% Al2O3, up to about 8% SiO2, and up to about 2.5% MgO; wherein said reactive system comprises from about 12% to about 35% nickel and about 3% to about 13% aluminum; and wherein said plasticizer, when present, comprises about 8% to about 12% of a 2.5% aqueous chemical cellulose solution, based on the total weight of said composition.

8. The composition according to claim 4, wherein said filler material comprises at least one of from about 8% to about 10% SiO2, up to about 75%
MoSi2, up to about 2% silicon, about 0.8% to about 40% silicon carbide, up to about 0.5% boron, up to about 8% Y2O3, and up to about 2% Si3N4;
wherein said reactive system comprises from about 7%
to about 28% Cr2O3, about 2.5% to about 10%
aluminum, and about 0.7% to about 3% carbon; and said plasticizer comprises at least one of from about 4%
to about 5% polyvinyl butyral, and about 8% to about 12% of a 2.5% aqueous chemical cellulose solution, based on the total weight of said composition.

9. The composition according to claim 4, wherein said filler material comprises at least one of from about 1% to about 50% silicon carbide, up to about 71% MoSi2, up to about 10% SiO2, up to about 10% Y2O3, up to about 10% Si3N4, up to about 0.5% BN, up to about 1% chromium, up to about 1% boron, up to about 0.5% aluminum, up to about 10%
Al2O3, up to about 0.5% silicon, and up to about 7% ZrO2; wherein said reactive system comprises from about 7% to about 30% MoO3, about 2.5% to about 11% aluminum, about 2.5% to about 38% silicon;
and up to about 11% carbon; and said plasticizer comprises at least one of from about 10% to about 15 polyvinyl butyral, about 8% to about 15% of a 2.5%
aqueous chemical cellulose solution, about 8% to about 10% fused silica and its activator, and about 4% to about 10% bentonite, based on the total weight of said composition.

10. The composition according to claim 4, wherein said filler material comprises at least one of from about 35% to about 40% silicon carbide, about 7% to about 8% Y2O3, about 1.7% to about 2%
Al2O3, about 7% to about 8% SiO2, and about 1.7% to about 2% MgO; wherein said reactive system comprises from about 25% to about 30% titanium, and about 9% to about 11% silicon; and wherein said plasticizer comprises from about 8% to about 12% of a 2.5% aqueous chemical cellulose solution, based on the total weight of said composition.

11. A method for the preparation of ceramic composite articles having improved mechanical stability, room temperature fracture toughness, and oxidation resistance at temperatures up to 1900° C, and stable electrical conductivity, comprising the steps of:
(a) blending a mixture comprising up to 95%
by weight of a particulate filler material, between about 5% and 95% by weight of at least one reactive system, wherein said reactive system comprises at least two particulate combustible materials which will react exothermically with one another by micropyretic synthesis and are present in such proportion to ane another that combustion will occur when ignited, up to 90% of a plasticizer, and a sufficient amount of solvent in order to form a slurry;
(b) fashioning said slurry into a final desired article shape; and (c) combusting said shape by ignition at a temperature between about 150° C and 1250° C.

12. The method according to claim 11, wherein said reactive system comprises at least one of:
Ni and Al;
Cr2O3 and Al and C;
MoO3 and Al and B;
MoO3 and Al and Si;
Ti and B;
Ti and Si;
Nb and Al;
Zr and B;
Nb and B;
Fe2O3 and Al;
Cr2O3 and Al;
Ti and B and Al;
Hf and B;
Ta and B;
Ti and C;
Ti and Ni;
Ti and Pd;
Ti and Al;
Ti and Fe;

Ti and C and Ni; or combinations thereof.

13. The method according to claim 11, wherein said filler material comprises: SiC, MoSi2, Cr2C3, WC, Al2O3, SiO2, SnO2, C, Be, La, Co, Ni, rare earths, ZnO, Y2O3, ZrO2, Cu, Ni-Co based superalloys, Sb2O3, CuO, Fe2O3, GeO, Fe3O4, V2O5, FeO, Mo, Nb, Cr, Al, Si, Y, Fe, Si3N4, B, or alloys and mixtures thereof.

14. The method according to claim 11, wherein said plasticizer comprises: polyvinyl butyral, polyurethane, colloidal silica, 2%-5% aqueous chemical cellulose solution, phosphoric acid, bentonite, or fused silica and its activator.

15. The method according to claim 14, wherein said solvent comprises acetone and/or water.

16. The method according to claim 14, wherein said mixture contains from about 20% to about 85% of said filler material, about 15% to about 85% of said reactive system, and 0% to about 25% of said plasticizer by weight, based on the total weight of said mixture.

17. The method according to claim 14, wherein said fashioning comprises coating said slurry onto a porous base.

18. The method according to claim 14, wherein said fashioning comprises extruding said slurry to form a wire, plate, or shaped wire.

19. An electrical heating element capable of being used at temperatures up to 1900° C comprising a ceramic composite produced in accordance with the process of claim 14.

20. A ceramic composite article having improved mechanical stability, room temperature fracture toughness, and oxidation resistance at temperatures up to 1900° C, and stable electrical conductivity, produced in accordance with the process of claim 14.

21. An electrical heating element capable of being used at temperatures up to 1300° C comprising a ceramic composite formed by micropyretic synthesis of a composition containing:
(a) up to 95% by weight of a filler material; and (b) between about 5% and 95% by weight of at least one reactive system, wherein said reactive system comprises at least two combustible materials which will react exothermically with one another by micropyretic synthesis and are present in such proportion to one another that combustion will occur when ignited.

22. The element according to claim 21, wherein said reactive system comprises at least one of:
Ni and Al;
Cr2O3 and Al and C;
MoO3 and Al and B;
MoO3 and Al and Si;
Ti and B;
Ti and Si;
Nb and Al;

Zr and B:
Nb and B:
Fe2O3 and Al;
Cr2O3 and Al;
Ti and B and Al;
Hf and B;
Ta and B;
Ti and C;
Ti and Ni;
Ti and Pd;
Ti and Al;
Ti and Fe;
Ti and C and Ni; or combinations thereof.

23. The element according to claim 21, wherein said filler material comprises: SiC, MoSi2, Cr2C3, WC, Al2O3, SiO2, SnO2, C, Be, La, Co, Ni, rare earths, ZnO, Y2O3, ZrO2O Cu, Ni-Co based superalloys, Sb2O3, CuO, Fe2O3, GeO, Fe3O4, V2O5, FeO, Mo, Nb, Cr, Al, Si, Y, Fe, Si3N4, B, or alloys and mixtures thereof.

24. The element according to claim 21, wherein said composition contains from about 20% to about 85%
of said filler material, and about 15% to about 85%
of said reactive system by weight, based on the total weight of said composition.

25. A ceramic composite article having improved mechanical stability, room temperature fracture toughness. and oxidation resistance at temperatures up to 1900° C, and stable electrical conductivity, comprising a ceramic composite formed by micropyretic synthesis of a composition containing:
(a) up to 95% by weight of a filler material; and (b) between about 5% and 95% by weight of at least one reactive system, wherein said reactive system comprises at least two combustible materials which will react exothermically with one another and are present in such proportion to one another that combustion will occur when ignited.

26. The article according to claim 25, wherein said reactive system comprises at least one of:
Ni and Al;
Cr2O3 and Al and C;
MoO3 and Al and B;
MoO3 and Al and Si;
Ti and B;
Ti and Si;
Nb and Al;
Zr and B;
Nb and B;
Fe2O3 and Al;
Cr2O3 and Al;
Ti and B and Al;
Hf and B;
Ta and B;
Ti and C;
Ti and Ni;
Ti and Pd;
Ti and Al;
Ti and Fe; or Ti and C and Ni; or combinations thereof.

27. The article according to claim 25, wherein said filler material comprises: SiC, MoSi2, Cr2C3, WC, Al2O3, SiO2, SnO2, C, Be, La, Co, Ni, rare earths, ZnO, Y2O3, ZrO2, Cu, Ni-Co based superalloys, Sb2O3, CuO, Fe2O3, GeO, Fe3O4, V2O5, FeO, Mo, Nb, Cr, Al, Si, Y, Fe, Si3N4, B, or alloys and mixtures thereof.

28. The article according to claim 25, wherein said composition contains from about 20% to about 85%
of said filler material, and about 15% to about 85%
of said reactive system by weight, based on the total weight of said composition.

29. The article according to claim 26, having a ceramic phase formed by said reactive system comprising at least one of:
NiAl;
Ni3Al;
Cr3C2 and Al2O3;
MoB and Al2O3;
MoSi2 and Al2O3;
TiB2;
Ti5Si3;
NbAl2;
ZrB2;
NbB2;
Al2O3 and Fe;
Al2O3 and Cr;
TiB2 and Al;
TiB;
HfB2;
TaB2;
TiC;
TiNi;
TiPd:
TiAl;

TiFe; and TiC and Ni.

30. The article according to claim 25, wherein said filler material comprises, in weight percent, at least one of from about 20% to about 80% MoSi2, up to about 30% chromium, up to about 15% iron, up to about 6% molybdenum, up to about 2% titanium, up to about 1.2% niobium, up to about 0.7% yttrium, up to about 2.5% aluminum, up to about 10% silver, up to about 42% silicon carbide, up to about 12% Y2O3, up to about 2.5% Al2O3, up to about 8% SiO2, and up to about 2.5% MgO; and wherein said reactive system comprises from about 12% to about 35% nickel and about 3% to about 13% aluminum.

31. The article according to claim 25, wherein said filler material comprises, in weight percent, at least one of from about 8% to about 10% SiO2, up to about 75% MoSi2, up to about 2% silicon, about 0.8%
to about 40% silicon carbide, up to about 0.5% boron, up to about 8% Y2O3, and up to about 2%
Si3N4; and wherein said reactive system comprises from about 7% to about 28% Cr2O3, about 2.5% to about 10% aluminum, and about 0.7% to about 3% carbon.

32. The article according to claim 25, wherein said filler material comprises, in weight percent, at least one of from about 1% to about 50% silicon carbide, up to about 71% MoSi2, up to about 10%
SiO2, up to about 10% Y2O3, up to about 10%
Si3N4, up to about 0.5% BN, up to about 1%
chromium, up to about 1% boron, up to about 0.5%
aluminum, up to about 10% Al2O3, up to about 0.5%
silicon, and up to about 7% ZrO2; and wherein said reactive system comprises from about 7% to about 30%
MoO3, about 2.5% to about 11% aluminum, about 2.5%
to about 38% silicon; and up to about 11% carbon.

33. The article according to claim 25, wherein said filler material comprises, in weight percent, at least one of from about 35% to about 40% silicon carbide, about 7% to about 8% Y2O3, about 1.7% to about 2% Al2O3, about 7% to about 8% SiO2, and about 1.7% to about 2% MgO; and wherein said reactive system comprises from about 25% to about 30%
titanium, and about 9% to about 11% silicon.