Carbon heat source

A carbonaceous heat source for a smoking article is provided. The heat source is designed to maximize heat transfer to a flavor bed in the smoking article. The heat source undergoes substantially complete combustion leaving minimal residual ash, has a relatively low degree of thermal conductivity and ignites under normal lighting conditions for a conventional cigarette.

BACKGROUND OF THE INVENTION 
This invention relates to a heat source used in smoking articles which 
produce substantially no visible sidestream smoke. More particularly, this 
invention relates to a carbon containing heat source for a smoking article 
which provides sufficient heat to release a flavored aerosol from a flavor 
bed for inhalation by the smoker. 
There have been previous attempts to provide a heat source for a smoking 
article. However, these attempts have not produced a heat source that is 
satisfactory for use in a smoking article such as described in copending 
U.S. patent application Ser. No. 07/223,153, filed concurrently herewith 
and now U.S. Pat. No. 4,991,606. 
For example, Siegel U.S. Pat. No. 2,907,686 discloses a charcoal rod having 
an ash content of between 10% and 20% and a porosity on the order of 50% 
to 60%. The charcoal rod is coated with a concentrated sugar solution so 
as to form an impervious layer during burning. It was thought that this 
layer would contain gases formed during smoking and concentrate the heat 
thus formed. The charcoal may or may not be activated. 
Boyd et al. U.S. Pat. No. 3,943,941 discloses a tobacco substitute which 
consists of a fuel and at least one volatile substance impregnating the 
fuel. The fuel consists essentially of combustible, flexible and 
self-coherent fibers made of a carbonaceous material containing at least 
80 percent carbon by weight. The carbon is the product of the controlled 
pyrolysis of a cellulose based fiber containing only carbon, hydrogen and 
oxygen, and which has suffered a weight loss of at least 60 percent during 
the pyrolysis. 
Bolt et al. U.S. Pat. No. 4,340,072 discloses an annular fuel rod extruded 
or molded from tobacco, a tobacco substitute, a mixture of tobacco 
substitute and carbon, other combustible materials such as wood pulp, 
straw and heat-treated cellulose or an SCMC and carbon mixture. The wall 
of the fuel rod is substantially impervious to air. 
Banerjee et al. U.S. Pat. No. 4,714,082 discloses a short combustible fuel 
element having a density greater than 0.5 g/cc. The fuel element disclosed 
in Banerjee has a plurality of longitudinal passageways in an attempt to 
maximize the heat transfer to the aerosol generator. 
Published European patent application 0 117 355 by Hearn et al. discloses a 
carbon heat source and a process for making a carbon heat source for a 
smoking article. The carbon heat source is formed from pyrolized tobacco 
or other carbonaceous material and is in the shape of a tube. The process 
for making the carbon heat source comprises three steps: a pyrolysis step, 
a controlled cooling step and either an oxygen absorption step, a water 
desorption step or a salt impregnation and subsequent heat treatment step. 
Published European patent application 0 236 992 by Farrier et al. discloses 
a carbon fuel element and process for producing the carbon fuel element. 
The carbon fuel element disclosed contains carbon powder, a binder and 
other additional ingredients as desired and is formed with one or more 
longitudinally extending passageways. The carbon fuel element is produced 
by pyrolizing a carbon containing starting material in a non-oxidizing 
atmosphere, cooling the pyrolized material in a non-oxidizing atmosphere, 
grinding the pyrolized material, adding binder to the ground material to 
form the fuel element and pyrolizing the formed fuel element in a 
nonoxidizing atmosphere. A heating step may be performed on the ground 
material after grinding. 
Published European patent application 0 245 732 by White et al. discloses a 
dual burn rate fuel element which utilizes a fast burning segment and a 
slow burning segment. 
All of these heat sources are deficient because they provide unsatisfactory 
heat transfer to the flavor bed resulting in an unsatisfactory smoking 
article, i.e., one which fails to simulate the flavor, feel and number of 
puffs of a conventional cigarette. 
It would be desirable to provide a carbonaceous heat source that will 
maximize heat transfer to the flavor bed. 
It also would be desirable to provide a heat source that undergoes 
substantially complete combustion leaving minimal residual ash. 
It still further would be desirable to provide a heat source that will 
ignite under normal lighting conditions for a conventional cigarette. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a carbonaceous heat source 
that will maximize heat transfer to the flavor bed. 
It also is an object of this invention to provide a heat source that 
undergoes substantially complete combustion leaving minimal residual ash. 
It is a still further object of this invention to provide a heat source 
that will ignite under normal lighting conditions for a conventional 
cigarette. 
In accordance with this invention, there is provided a carbonaceous heat 
source for a smoking article. The heat source is formed from charcoal and 
has one or more longitudinal air flow passageways therethrough. Each 
longitudinal air flow passageway is in the shape of a multi-pointed star. 
When the heat source is ignited and air is drawn through the smoking 
article, air is heated as it passes through the longitudinal air flow 
passageways. The heated air flows through a flavor bed, releasing a 
flavored aerosol for inhalation by the smoker. 
The heat source has a void volume greater than about 50% with a mean pore 
size of about one to about 2 microns, as measured on a mercury 
porosimeter. The heat source has a density of between about 0.2 g/cc and 
about 1.5 g/cc. The BET surface area of the charcoal particles used in the 
heat source is in the range of about 50 m.sup.2 /g to about 2000 m.sup.2 
/g. In addition, catalysts and oxidizers may be added to the charcoal to 
promote complete combustion and to provide other desired burn 
characteristics. 
There is also provided a process for manufacturing the heat source of this 
invention. The process involves three basic steps: mixing charcoal of a 
desired size with appropriate additives, molding or extruding the mixture 
into the desired shape and baking the extruded or molded material. After 
baking, the extruded or molded material may be further machined to final 
tolerances.

DETAILED DESCRIPTION OF THE INVENTION 
Smoking article 10 consists of an active element 11, an expansion chamber 
tube 12, and a mouthpiece element 13, overwrapped by cigarette wrapping 
paper 14. Active element 11 includes a carbon heat source 20 and a flavor 
bed 21 which releases flavored vapors when contacted by hot gases flowing 
through heat source 20. The vapors pass into expansion chamber tube 12 
forming an aerosol that passes to mouthpiece element 13, and thence into 
the mouth of a smoker. 
Heat source 20 should meet a number of requirements in order for smoking 
article 10 to perform satisfactorily. It should be small enough to fit 
inside smoking article 10 and still burn hot enough to ensure that the 
gases flowing therethrough are heated sufficiently to release enough 
tobacco flavor from flavor bed 21 to provide conventional cigarette flavor 
to the smoker. Heat source 20 should also be capable of burning with a 
limited amount of air until the carbon in heat source 20 is expended. 
Ideally, heat source 20 leaves minimal ash after combustion. It also 
should produce significantly more carbon dioxide than carbon monoxide upon 
combustion. Heat source 20 should have a low degree of thermal 
conductivity. If too much heat is conducted away from the burning zone to 
other parts of heat source 20, combustion at that point will cease when 
the temperature drops below the extinguishment temperature of heat source 
20. Finally, heat source 20 should ignite under normal lighting conditions 
for a conventional cigarette. 
As discussed above, heat source 20 should leave minimal residual ash after 
combustion. Residual ash tends to form a barrier to the movement of oxygen 
into the unburned carbon of heat source 20. This residual ash may also be 
pulled into flavor bed 21 or fall out of smoking article 10. Thus, 
minimizing the amount of ash left after combustion is desirable. 
It is possible to wash out ash-forming inorganic substances from charcoal 
with acid. However, this procedure would significantly increase the cost 
of heat source 20. 
Heat source 20 may be formed from hardwood charcoal or softwood charcoal. 
Typically a softwood charcoal or a hardwood charcoal yields a heat source 
that is comprised of about 89% carbon, about 1% hydrogen, about 3% oxygen 
and about 7% ash-forming inorganic substances by weight. It is desirable 
to maximize the amount of pure carbon per gram of heat source 20 to 
provide sufficient fuel. 
The charcoal may be derived from various carbon-yielding precursors such as 
wood, wood bark, peanut shells, coconut shells, tobacco, rice hulls, or 
any cellulose or cellulose-derived material that has a high carbon yield. 
These carbon-yielding precursors are carbonized using a semi-oxidizing 
process similar to that used to make wood charcoal or the bark fly ash 
process as described in U.S. Pat. No. 3,152,985. 
Preferably, a softwood charcoal is used to produce heat source 20. Softwood 
charcoal is not as dense as hardwood charcoal making softwood charcoal 
easier to burn. 
The charcoal may be activated or unactivated. Generally, activating the 
charcoal increases the charcoal's effective surface area. Increased 
effective surface area is important because this allows more oxygen to be 
present at the point of combustion, thus increasing ease of ignition and 
burning and providing minimal residue. 
As discussed previously, it is desirable to prevent too much heat from 
being lost from heat source 20 to avoid extinguishing combustion of heat 
source 20. In addition, minimizing heat loss helps maintain heat source 20 
near its combustion temperature between puffs by the smoker on smoking 
article 10. This minimizes the time necessary to raise the temperature of 
heat source 20 to its combustion temperature during a puff. This in turn 
ensures that sufficiently hot gases pass through flavor bed 21 throughout 
the puff by the smoker on smoking article 10 and thus maximizes the 
tobacco flavor released from flavor bed 21. 
The external geometric surface area of heat source 20 should be minimized 
to minimize radiative heat loss. Preferably, minimization of the external 
geometric surface area of heat source 20 is accomplished by forming heat 
source 20 in the shape of a cylinder. Conductive heat loss to the 
surrounding wrapper of smoking article 10 may be minimized by ensuring 
that an annular air space is provided around heat source 20. Preferably 
heat source 20 has a diameter of about 4.6 mm and a length of about 10 mm. 
The 4.6 mm diameter allows an annular air space around heat source 20 
without causing the diameter of smoking article 10 to be larger than the 
diameter of a conventional cigarette. 
Heat source 20 should, however, transfer as much heat as possible to flavor 
bed 21. One means of accomplishing this heat transfer is to have one or 
more longitudinal air flow passageways 22 through heat source 20. 
Longitudinal air flow passageways 22 should have a large geometric surface 
area to improve the heat transfer to the air flowing through heat source 
20. By maximizing the geometric surface area of longitudinal air flow 
passageways 22, heat transfer to flavor bed 21 is maximized. The shape and 
number of longitudinal air flow passageways 22 should be chosen such that 
the internal geometric surface area of heat source 20 is equal to or 
greater than the external geometric surface area of heat source 20. 
Preferably, maximization of heat transfer to flavor bed 21 is accomplished 
by forming each longitudinal air flow passageway 22 in the shape of a 
multi-pointed star. Even more preferably, each multi-pointed star should 
have long narrow points and a small inside circumference defined by the 
innermost edges of the star. (See FIG. 2.) In addition, maximizing the 
internal geometric surface area of heat source 20 by the use of one or 
more multi-pointed, star-shaped, longitudinal air flow passageways 22, 
results in a larger area of heat source 20 available for combustion. This 
larger combustion area results in a greater volume of carbon involved in 
combustion and therefore a hotter burning heat source. 
As discussed previously, heat source 20 should also possess low thermal 
conductivity. Low thermal conductivity is desirable because heat source 20 
should burn and transfer heat to the air flowing therethrough but not 
conduct heat to flavor bed 21. If heat source 20 conducts heat, the time 
required to promote combustion will increase. This is undesirable because 
smoking article 10 will take longer to light. Also, as discussed 
previously, heat must be maintained at the burning zone of heat source 20. 
Preferably a charcoal with a relatively low thermal conductivity is used 
to prevent the mounting structure 24 used to position heat source 20 in 
smoking article 10 from absorbing the high heat generated during 
combustion of heat source 20. Mounting structure 24 should retard oxygen 
from reaching the rear portion of the heat source 20 thereby helping to 
extinguish heat source 20 after flavor bed 21 has been consumed. This also 
prevents heat source fall-out. 
The size of the raw charcoal particles is another important consideration 
for heat source 20. The charcoal should be in the form of small particles. 
These small particles provide more carbon surface area in heat source 20 
available for combustion and results in a heat source that is more 
reactive. The size of these particles can be up to about 700 microns. 
Preferably these charcoal particles have an average particle size of about 
5 microns up to about 30 microns. Various types of mills or other grinders 
may be used to grind the charcoal down to the desired size. Preferably a 
jet mill is used. 
The BET surface area of the charcoal particles should be in the range of 
about 50 m.sup.2 /g to about 2000 m.sup.2 /g. Preferably, the BET surface 
area of the charcoal particles should be in the range of about 200 m.sup.2 
/g to about 600 m.sup.2 /g. The higher the surface area the more reactive 
the charcoal becomes because of the greater availability of carbon surface 
to react with oxygen for combustion. This is desirable because it yields a 
hotter burning heat source and less residue. 
Concomitant with the need for small charcoal particles is the need for 
enough oxygen, i.e., air, to promote combustion of the fuel. Sufficient 
oxygen is provided by ensuring that heat source 20 has a large void 
volume. Preferably the void volume of heat source 20 is about 50% to about 
60%. Also, the pore size i.e., the space between the charcoal particles, 
preferably is about one to about two microns as measured on a mercury 
porosimeter. 
A certain minimum amount of carbon is needed in order for smoking article 
10 to provide a similar amount of static burn time and number of puffs to 
the smoker as would a conventional cigarette. Typically, the amount of 
heat source 20 that is combusted is about 65 mg of a carbon cylinder which 
is 10 mm long by 4.65 mm in diameter. A greater amount may be needed 
taking into account the volume of heat source 20 surrounded by and in 
front of mounting structure 24 which is not combusted. As discussed above, 
that portion of the heat source 20 surrounded by and in front of mounting 
structure 24 will not burn because of the lack of oxygen. 
In addition to the amount of carbon, the rate of heat transfer, i.e., the 
amount of heat per weight of carbon transferred to the air passing through 
heat source 20, affects the amount of heat available to flavor bed 21. The 
rate of heat transfer depends on the design of heat source 20. As 
discussed previously, optimum heat transfer characteristics are achieved 
when the geometric surface area of longitudinal air flow passageways 22 is 
at least equal to and preferably greater than the outside geometric 
surface area of heat source 20. This may be achieved by the use of one or 
more longitudinal air flow passageways 22 each being in the shape of a 
multipointed star having long, narrow points and a small inside 
circumference defined by the innermost edges of the star. 
Heat source 20 should have a density of from about 0.2 g/cc to about 1.5 
g/cc. Preferably, the density should be between about 0.5 g/cc and 0.8 
g/cc. The optimum density maximizes both the amount of carbon and the 
availability of oxygen at the point of combustion. Theoretically the 
density can be as high as 2.25 g/cc, which is the density of pure carbon 
in its graphitic crystalline form. However, if the density becomes too 
high the void volume of heat source 20 will be low. Lower void volume 
means that there is less oxygen available at the point of combustion. This 
results in a heat source that is harder to burn. However, if a catalyst is 
added to heat source 20, it is possible to use a dense heat source, i.e., 
a heat source with a small void volume having a density approaching 2.25 
g/cc. 
Certain additives may be used in heat source 20 to either lower the 
ignition temperature of heat source 20 or to otherwise aid in the 
combustion of heat source 20. This aid may take the form of promoting 
combustion of heat source 20 at a lower temperature or with lower 
concentrations of oxygen or both. 
Sources of metal ions, such as potassium ions or iron ions may be used as 
catalysts. These potassium ions or iron ions promote combustion of heat 
source 20 at a lower temperature or with lower concentrations of oxygen 
available to the heat source than would occur in heat source 20 without 
the catalyst. Potassium carbonate, potassium citrate, iron oxide, iron 
oxalate, calcium oxalate, ferric citrate or ferrous acetate may be used. 
Other potential catalysts include compounds of molybdenum, aluminum, 
sodium, calcium and magnesium. To ensure uniform distribution of these 
additives throughout heat source 20, these additives preferably are water 
soluble. 
Iron oxide, iron oxalate or calcium oxalate may provide the added benefit 
of supplying more oxygen to heat source 20. This added oxygen may aid in 
the combustion of heat source 20. Other known oxidizers may also be added 
to heat source 20 to promote more complete combustion of heat source 20. 
As discussed previously, heat source 20 should have a minimal amount of 
ash-forming inorganic substances. However, charcoal has an ash-forming 
inorganic substance content of about 5% and the addition of metal 
catalysts increases the ash-forming inorganic substance content to about 
6% to about 8%. An ash-forming inorganic substance content of up to about 
18% is acceptable but an ash-forming inorganic substance content of up to 
about 8% is preferred. 
Heat source 20 can be manufactured according to the following process. 
First, charcoal should be ground to the desired size. As discussed 
previously, the particle size can be up to about 700 microns. Preferably 
the particles are ground to an average particle size of about 5 microns up 
to about 30 microns. 
The binder used to bind the charcoal particles together is preferably a 
two-part binder system using relatively pure raw materials. The first 
binder is a flour such as the flour of wheat, barley, corn, oat, rye, 
rice, sorghum, mayo or soybean. The highprotein (12-16%) or high-gluten 
(12-16%) flours of those listed above are preferred. Even more desirable 
is a high-protein wheat flour. The higher protein level flours are 
desirable because they increase the binding properties of the flour, thus 
increasing the strength of the finished carbon heat source. The second 
binder is a monosaccharide or disaccharide, preferably sucrose (table 
sugar). The use of sucrose reduces the amount of flour needed. It also 
aids in the extrusion of the mixture. Both of these binders form a 
relatively reactive carbon material upon carbonization. It is also 
possible to produce a carbon heat source with a one-binder system of flour 
or other known binders. 
As discussed below, varying concentrations of binders can be used, but it 
is desirable to minimize the binder concentration to reduce the thermal 
conductivity and improve the burn characteristic of heat source 20. The 
binders used are carbonized and leave behind a carbon skeleton sufficient 
to bind the carbon particles together. The carbonizing process minimizes 
the likelihood that complex products will be formed from the uncarbonized 
binders during combustion of heat source 20. 
After the charcoal is ground to the desired size, it is mixed with the 
flour, sugar, one or more burn additives, and water and mixed for a set 
period of time. In the preferred embodiment, about 4 weight percent to 
about 45 weight percent, more preferably about 7 weight percent to about 
30 weight percent, of a high protein wheat flour is used. In the preferred 
embodiment, about 1 weight percent to about 25 weight percent, more 
preferably about 5 weight percent to about 14 weight percent, of sugar is 
used. In the preferred embodiment, about 20 weight percent to about 95 
weight percent, more preferably about 50 weight percent to about 85 weight 
percent, of charcoal is used. In the preferred embodiment, up to about 8 
weight percent, more preferably about 2.7 weight percent to about 5 weight 
percent, of potassium citrate is used. Preferably iron oxide is also added 
to the mixture. In the preferred embodiment, up to about 2 weight percent, 
more preferably about 0.3 weight percent to about 1 weight percent, of 
iron oxide is used. Water is added in an amount sufficient to form an 
extrudable paste from the mixture. 
The period of time for mixing can be determined by simple routine 
experimentation. The mixing should ensure thorough distribution of the 
various substances. Preferably, if a large volume is to be mixed in a 
batch mode, mixing should be for about 15 minutes to about one hour. If a 
small volume is to be mixed in a continuous mode, for example, in a 
continuous mixing-extruder, mixing need only be performed for a few 
seconds. 
The mixture is then molded or extruded into the desired shape. Extrusion is 
preferable because this method is less expensive than molding. If heat 
source 20 is to be extruded, an extrusion aid, such as any vegetable oil 
like corn oil, may be added to the mixture about five minutes before the 
set period of time expires. The oil lubricates the mixture facilitating 
its extrusion. Various types of extruders manufactured by various 
companies can be used. A mud chamber or a continuous mixing extruder such 
as a Baker-Perkins twin-screw extruder is preferred. The extruded density 
of the mixture should be between about 0.75 g/cc and about 1.75 g/cc. 
After the mixture has been molded or extruded, it may be dried to a 
moisture content of between about 2 percent to about 11 percent, 
preferably between about 4 percent and about 6 percent. The dried, 
extruded or molded material is then baked in an inert atmosphere at a 
temperature sufficient to carbonize the binders and drive off volatiles 
from heat source 20. The charcoal may also be baked before it is mixed 
with the binder and catalyst to drive off residual organics. Typically, 
the extruded or molded material should be baked at a temperature of from 
about 500.degree. F. to about 3000.degree. F. Preferably the extruded or 
molded material is baked at a temperature of about 1400.degree. F. to 
about 1800.degree. F. The baking temperature must be high enough to drive 
off the volatiles from the extruded or molded material. However as the 
baking temperature increases, the thermal conductivity increases. As 
discussed previously, increased thermal conductivity of heat source 20 is 
an undesirable characteristic. Therefore, a compromise temperature must be 
chosen. 
The inert atmosphere in which heat source 20 is baked is preferably helium 
or argon. By using either a helium or argon atmosphere naturally occurring 
nitrogen is removed. If a nitrogen atmosphere is used, the carbon will 
react with some of the nitrogen in the atmosphere. This will result in the 
formation of nitrogen oxides when heat source 20 is burned. As discussed 
previously, preferably the predominant combustion gas transmitted to the 
smoker is carbon dioxide. 
During baking, the extruded or molded material will shrink in the range of 
about 4% to about 10%. Therefore the extruded or molded material should be 
molded or extruded to a size slightly larger than required for use as a 
heat source in order to take into account this shrinkage. 
After the extruded or molded material is baked, it may be cooled in an 
inert atmosphere to below about 200.degree. F. The extruded or molded 
material may also be cooled in an atmosphere comprised of a mixture of 
inert gases and oxygen or oxygen containing compounds. At this point, the 
extruded or molded material can then be cut to the desired length and 
ground to the final desired size for use as a heat source in a smoking 
article. The extruded or molded material can be first ground to the 
desired size and then cut to the desired length. Preferably, centerless 
grinding is used to grind the extruded or molded material to the final 
desired size. 
EXAMPLE 1 
The following mixture is blended in a Sigma Blade Mixer for approximately 
30 minutes to make an extrudable mix: 
65 g hardwood charcoal milled to an average particle size of 30 microns; 
70 g unbleached wheat flour (Pillsbury's unbleached enriched wheat flour); 
40 g sugar (Domino's pure cane sugar); 
50 g water. 
After blending, the mixture was extruded using a mud chamber type extruder 
to a size of 0.200 inches outside diameter by 24 inches long with a 
star-shaped inside passageway. The rod was then dried to a moisture level 
of about 5%. The rods were then cut or broken into 12-inch lengths, then 
packed into a stainless steel container which was flushed continuously 
with nitrogen. The container was then placed in an oven and baked to 
1000.degree. F. according to the following oven cycle: 
Room Temperature to 425.degree. F. in 3.5 hours; 
425.degree. F. to 525.degree. F. for 1.5 hours; 
525.degree. F. to 1000.degree. F. for 2 hours; 
Hold at 1000.degree. F. for 2 hours; 
1000.degree. F. to room temperature as fast as oven could cool. 
Once cooled, the rods were removed from the stainless steel box, cut to 10 
mm lengths, and used as a carbon heat source. 
EXAMPLE 2 
The following mixture is blended in a Sigma Blade Mixer for approximately 
20 minutes: 
119 grams of a softwood bark charcoal fly ash (also known as Bar Char or 
Bark Char) made by a process similar to U.S. Pat. No. 3,152,985. Before 
being used, the bark fly ash is activated by processing the bark charcoal 
through a rotor calciner with steam being injected into the calciner. The 
carbon thus obtained is then milled to 90%-325 mesh (Acticarb Industries 
brand "Watercarb" powdered activated carbon). The obtained powder is then 
jet-milled to a final average particle size of aproximately 10 to 12 
microns. 
44 grams of high-protein or high-gluten wheat flour (Pillsbury's "balancer" 
high-gluten untreated wheat flour). 
1 gram of iron oxide, less than 44 microns in particle size. 
Once blended, a solution of the following ingredients is added to the dry 
ingredients and mixed for 30 minutes: 
120 grams water; 
22 grams sugar (Domino's pure cane sugar); 
9 grams potassium citrate. 
Once mixed, 3 grams of corn oil (Mazola corn oil) were added to the mixture 
and mixed for an additional five minutes. The corn oil was used as an 
extrusion aid. 
After blending, the mixture was extruded using a mud chamber type extruder 
to a size of 0.200 inches outside diameter by 12 inches long with a 
star-shaped inside passageway. The rods were collected from the extruder 
head on V-notched grooved graphite plates for ease of processing. The 
V-notched grooved graphite plates and extruded rods were then placed in a 
stainless steel container and continuously flushed with helium. The 
container was then placed in an oven and baked to 1700.degree. F. 
according to the following oven cycle: 
Room Temperature to 425.degree. F. in 3.5 hours; 
425.degree. F. to 525.degree. F. for 1.5 hours; 
525.degree. F. to 1700.degree. F. for 2 hours; 
Hold at 1700.degree. F. for 3 hours; 
1700.degree. F. to room temperature as fast as oven could cool. 
Once cooled, the V-notched grooved graphite plates and extruded rods were 
removed from the stainless steel container. The rods were removed from the 
graphite plate, cut to 10 mm lengths, and ground to a 4.65 mm outside 
diameter. 
EXAMPLE 3 
The procedure for Example 2 was repeated, except that the softwood bark 
charcoal fly ash (also known as Bar Char or Bark Char) made by a process 
similar to U.S. Pat. No. 3,152,985, was not activated. 
EXAMPLE 4 
The procedure for Example 2 was repeated, except the rods produced were 
dried to a moisture level of 5% and placed on the conveyor belt of a 
continuous-belt baking oven, which was maintained at 1700.degree. F. and 
continuously flushed with helium or argon. 
EXAMPLE 5 
A twin-screw extruder was used to mix and continuously extrude a mixture of 
three components: (A) blended dry ingredients (9.7 lbs. of high protein or 
high-gluten wheat flour (Pillsbury's "balancer" high-gluten untreated 
wheat flour); 35.0 lbs. of carbon like that used in Example 2; and 0.29 
lbs. iron oxide, less than 44 microns in particle size); (B) a solution 
containing 17.65 lbs. of water, 4.85 lbs. of sugar (Domino's pure cane 
sugar), 2.35 lbs. of potassium citrate; and (C) 17.65 lbs. of water 
(nominal value) in a ratio of 2.55 to 1.41 to 1.0. 
The above three components were mixed and blended in the twin-screw 
extruder and extruded (adjusting the amount of water as necessary to 
achieve the proper consistency of the extruded rod) to a size of 0.195 
inches outside diameter and cut to a 12-inch length. The rod produced also 
had a star-shaped inside passageway. The rods were then dried to a 
moisture level of about 5%. The rods were then placed on V-notched grooved 
graphite plates and further processed as in Example 2. 
Thus it is seen that a carbonaceous heat source that maximizes heat 
transfer to the flavor bed, undergoes nearly complete combustion leaving 
minimal residual ash, has a relatively low degree of thermal conductivity, 
and will ignite under normal conditions for a conventional cigarette is 
provided. One skilled in the art will appreciate that the present 
invention can be practiced by other than the described embodiments, which 
are presented for purposes of illustration and not of limitation and the 
present invention is limited only by the claims which follow.