DK149606B - PROCEDURE FOR PREPARING A POROEST CARBON-CONTAINING BODY - Google Patents

Description

149606

The present invention relates to a process for preparing a porous carbonaceous body comprising the steps of: forming a liquid mixture, casting the mixture to thereby impart a certain form to the mixture, consolidating the mixture to produce a self-supporting body, and exposing it. of the pyrolysis self-supporting body, thereby transforming it into a cohesive carbonaceous object.

An important object of the invention is to obtain coherent carbonaceous bodies of considerable cross-section and with a uniformly distributed and regulated number of at least primarily interconnected pores of a fixed size.

Another important and related object of the invention is the provision of continuous porous carbonaceous bodies wherein the solid components of the body have selected size and distribution.

5 Bodies of the kind described above have many uses. They are e.g. useful as filters, electrodes, chemical absorbents, molecular sieves, membranes, catalysts and catalyst supports, chemical iron products, mechanical gaskets, bearings, electrical equipment, dental and surgical prosthetic equipment and other implants, thermal insulators and light structural elements, and they are particularly useful at very high temperatures.

Another particularly important use of the present invention takes place in the preparation of carbide-containing blanks, as described. know U.S.A. U.S. Patent Nos. 3,235,346 and 3,348,967. In this process, a porous body of carbonaceous material is permeated by a molten metal material containing one or more carbide formers. The carbide formers are then reacted with carbon in the porous body to form a single or multiple phase carbide-containing body.

Furthermore, the carbonaceous bodies of the present invention can be made to absorb other liquid and gaseous materials or otherwise modified to make them useful for further other uses and to increase their usefulness for the above-mentioned uses. Other penetrants which have been advantageously used include inorganic compounds such as halogens, borates and oxides, and polymers and other organic compounds.

A further, but more specific, object of the invention consists in the provision of novel carbonaceous bodies for the above and other applications by means of one. novel method for making such bodies.

35

For the purposes of the foregoing and for other uses for which the present carbonaceous bodies are intended, a carbonaceous body should have most or in all cases all of the following characteristics: (1) an adjustable, reproducible, spatially uniform and selectable apparent density, (2) an adjustable, reproducible, spatially uniform and selectable actual density, (5) maximum inter-pore connection, (4) an adjustable and reproducible pore size, (5) minimal pore size variation, '(6) an adjustable, reproducible, spatially uniform and selectable distribution of the solids constituting the body; (7) an adjustable and selectable size of the solids constituents and minimal variations in this size; (8) selectable reactivity with liquid metals and other penetrants; ( 9) minimum · residual gas content, (10) high strength at low and / or high temperatures, 25, x (11) maximum resistance to thermal shock, (12) ductility to accurate good tolerances in both thin and thick parts, (13) controllable shrinkage, (14) selectable catalytic activity, (15) inertness to human and other animal tissues, 35 (16) selectable elastic modulus, inelastic properties and hardness, (17) selectable wettability with various liquids, 4Q (18) selectable permeability, 4 149606 (19) selectable electrical, acoustic, optical and thermal properties, and (20) low cost.

5

Yet another important but specific object of the invention consists in obtaining novel carbonaceous bodies having the aforementioned properties and various combinations thereof by disclosing a novel method for producing such bodies.

10

All of the above properties can be readily provided in the carbonaceous bodies produced by the process of the invention. Hereby, and because of the increasing extent in which the desirable essential properties are present, the carbonaceous bodies produced in accordance with the invention differ from those made by methods known in the art.

Hitherto known methods for making carbonaceous bodies have been intended for the production of highly graphite-containing 2Q structures with maximum density and with minimum porosity by pressing, impregnation and casting methods. U.S.A. U.S. Patent Nos. 3,084,394, 3,310,611, and 3,634,569 are representative.

All three patents describe processes for making carbonaceous bodies in which cabonaceous particles are mixed with various solid and / or liquid binders and thermomechanically compressed and heated.

There are also a number of patents dealing with the manufacture of dense carbonaceous bodies by means of impregnation. The compaction and filling of the pores by liquid resin impregnation followed by carbonization is described in U.S.A. U.S. Patent No. 3,628,984. Gas phase deposition of carbon to close interconnected pores is discussed in U.S.A. U.S. Patent No. 3,084,394.

35 U.S.A. U.S. Patent No. 3,198,714 discloses a process for making thin bodies of minimal porosity by first molding to the desired shape and then heating a mixture of carbonaceous particles and a carbonaceous binder. Other literature sites describe a similar method for making dense carbonaceous bodies, and these methods include a casting step.

The dense carbonaceous bodies produced by the prior art methods lack many, not to mention most of the desirable essential properties of the carbonaceous bodies produced by the process of the invention.

In all such cases where pressing is used, it is difficult if not impossible to achieve an adjustable apparent density which is spatially uniform. The friction on the walls of the mold causes special problems in this regard, especially in the case of complicated shapes.

15

Furthermore, compressed bodies usually contain a certain amount of unrelated pores, and it is generally impossible to obtain independent control of pore size and pore size distribution for a selected apparent density.

20

Attempts have also been made to produce carbonaceous bodies which have greater porosity than can be obtained using the above methods. Only a few methods have previously been intended for the manufacture of such articles.

25

The simplest hitherto proposed method for producing a porous carbonaceous structure has consisted in pyrolysis of selected organic structures. Trees, coconut shells and other natural products and synthetic organics have been treated in this way.

30

In general, coherent bodies of considerable cross-section cannot be obtained due to the extensive destruction of the structure by the evolution of gas in the pyrolysis stage. Even if a coherent structure remains after pyrolysis, in the typical case, it will not have pores of uniform size but will contain pores of both macro and miro size. Also, in the case of natural products, uniform and strong bodies with regulated porosity can be obtained due to disparities in the starting materials.

40 6 149606 In the case of synthetic organic substances, it is only possible to prevent heavy degradation of the body if its cross-section is very thin. Accordingly, many potentially useful forms cannot be obtained by pyrolysis of synthetic organic materials.

5

Furthermore, the possibilities of controlling the amount and size of the pores formed in the body are limited. This means that bodies made by pyrolysis of synthetic materials have limited utility.

10

Another previously proposed technique for the preparation of porous carbonaceous bodies consists in the carbonization of a foamed carbonaceous material. In these methods, the foam is formed using a gaseous pore former which forms pores of macro size. An example of a method of this kind is found in U.S.A. No. 3,657,166 and uses gaseous decomposition products from certain salts of polybasic organic acids as pore formers.

The plastic foam formed according to U.S.A. No. 3,657,166,20 is partially carbonized to form elemental carbon as a coloring agent. However, only a small amount of carbon is formed, the majority of the final body being the thermoplastic starting material.

This body would not be suitable for the purposes for which the body made according to the present invention is intended. The items manufactured according to U.S.A. for example, U.S. Patent No. 3,657,166 would melt if used at high temperatures or if permeated with a molten metal, for example, by the process described in the aforementioned patents.

In the method described in U.S.A. U.S. Patent No. 3,302,999, a rigid polymer foam is formed with a haloalkylop bleaching agent and then the foam is partially oxidized and carbonized or graphitized. U.S.A. U.S. Patent No. 3,387,940 discloses a method which differs only from the method of U.S.A. No. 3,302,999 by incorporating carbon in the foam as filler. U.S.A. U.S. Patent No. 3,342,555 discloses foaming of thermosetting resins with conventional blowing agents followed by direct carbonization.

The procedure described in U.S.A. U.S. Patent No. 3,345,440 involves foaming a partially polymerized furfural alcohol with 5 urethane-forming compounds to which substantial amounts of powdered fillers such as carbon, metals and metal oxides have been added. Subsequent carbonization or graphitization of the filler-containing foam is stated to lead to a porous carbonaceous body.

10 U.S.A. U.S. Patent Nos. 3,574,548 and 3,635,676 disclose a similar method whereby foamed carbonaceous bodies are prepared from furfural alcohol resins and urethane foaming agents. The latter patent highlights one of the major drawbacks of method 5 for the production of carbonaceous bodies from foam, namely a high and uncontrollable shrinkage. In the second patent, it is proposed that this can be regulated by incorporating regulated shrinking fillers into the original foam mixture.

2Q In these processes for producing a porous structure using a gaseous pore former, the structure cannot have a large percentage of interconnected pores. Furthermore, it is difficult to achieve a high degree of pore size uniformity and to achieve a pore size of less than about 100 psi. 200 microns.

25

Another method of making porous carbonaceous bodies involves mixing a filler carbon with an organic binder, compressed with limited pressure to effect partial compression, and then pyrolysis of the organic binder. A method of this kind is described in U.S.A. patent specification no.

3171720. A variant whereby a synthetic carbon foam is formed by pressing blends of hollow, carbon-forming microspheres with organic binders is described in Carbon, Vol. 10, No. 2, 1972, p.185.

A disadvantage of the pressing method just described is the lack of interconnected pores in the body. This disadvantage is also linked to that of the U.S.A. No. 3,567,808 discloses a method in which a closed-pore material is prepared by pressing a porous filler together with organic binders. Further, porous bodies are formed by compression of carbon particles coated with liquid carbon forming resins / as disclosed in U.S.A. U.S. Patent No. 3,608,170.

5

Yet another variant of the pressing method for making porous carbon bodies is described in U.S.A. U.S. Patent No. 3,647,551¾ and involves the use of solid pore-forming materials mixed with powdery polyvinyl chloride. The mixture is pressed to the desired shape7 and the pressing is followed by removal of the pore former by melting or evaporation during carbonization or by melting, evaporation or solution after carbonization.

Certain disadvantages of the pressing method for making porous bodies have been discussed above. This process further has the same drawbacks previously described as when used to produce high density bodies.

A variant of the pressing method is described in U.S.A. No. 3,633,171, in which a sintering of loosely packed particles of thermoplastic pitch is followed by oxidation to obtain a non-melting carbon mass which can be carbonized into a porous body. Most of the disadvantages of the pressing method are also the latter method.

25

Impregnation can also be used to make porous carbonaceous bodies according to U.S.A. U.S. Patent No. 3,446,593. In the process described in this patent, a liquid resin is impregnated in a polymer foam. This is followed by curing of the resin, decomposition of the foam and carbonization of the resin. Thereby a porous body is obtained, which in structure corresponds to the original foam material. However, the method is limited to producing low density and large pore size bodies. It also requires expensive starting materials.

35

Like molding and impregnation, casting can be used to make porous as well as dense bodies. The procedure described in U.S.A. U.S. Patent No. 3,565,980 is representative of the methods employing a casting step in the preparation of porous carbonaceous bodies.

9 149606

In the method of U.S.A. U.S. Patent No. 3,565,980, candle mold is slurried into a slurry of porous particles. The molded article is dried, partially oxidized and carbonated.

It is impossible to make thick-body bodies by this method, as the liquid suspension medium must be extracted from the lollipop or slurry through the mold. The first liquid that can be extracted from the lollipop is found in the areas near the mold. When this liquid is removed, the particles in these regions 10 move closer together, thereby increasing the resistance to fluid flow - a phenomenon that is highly pronounced by the method of U.S.A. Patent No. 3,565,980 due to the small size of the pitch particles.

As fluid removal proceeds, the flow resistance increases dramatically as the path length through the areas from which the fluid was previously removed becomes longer. Accordingly, after the suspension medium has been removed from an area having only a thickness of a fraction of a cm, the resistance to further removal of the suspension liquid becomes complete for all practical purposes.

Furthermore, because of the resistance to fluid flow through the porous solid, the consolidation time is very long, even in the case of relatively thin parts. Large amounts of shrinkage also occur in the method of U.S.A. No. 3,565,980, because the initially separated solid particles are brought together when the liquid is removed. Thus, there is necessarily a large volume change during the consolidation of the solids.

30 In the method of U.S.A. Patent No. 3,565,980 furthermore, the cast articles have poor green strength after drying, since only weak surface forces hold the particles together. Furthermore, it is impossible to independently control pore size, particle size and apparent density.

35

A further known method for forming carbonaceous bodies using a casting step is described in U.S.A. U.S. Patent No. 2,431,326. In this process, furfural and furfural-furfural alcohol mixtures are treated with concentrated mineral acids, thereby precipitating carbonaceous particles which gradually combine to form a consolidated mass. This mass can be dried and then carbonized to form a porous body.

5 The method of U.S.A. Patent No. 2,431,326 also suffers from a number of disadvantages. Most carbon-forming materials, including many that are desirable because of their high carbon yields, cannot be used as the material will not be combined during treatment but simply precipitates and forms sludge.

10

Furthermore, the pore size cannot be controlled by this method.

In addition, in this method there are no measures to select and control the size of the solid components of the carbonaceous body or to maintain these components spatially uniform. In fact, if the carbon formers described in said patent are slowly cured using a dilute acid instead of a concentrated volume of equivalent volume, a very strong separation of the carbonaceous material will occur, and no a cohesive body is obtained.

Furthermore, the bodies made by said method have extremely fine pores, absorb large amounts of gas and are too reactive for penetration of liquid metals and for other applications where lower chemical reactivity is required.

Furthermore, the bodies produced by said method are relatively weak both before and after drying, also when adding glycerol to the original mixture, as stated in the patent. The ability of the heaters to withstand high temperatures in heat shock is also not satisfactory.

The casting of the blends according to said patent presents a problem, as the blends contain highly concentrated mineral-3 ^ acids, and these will corrode most materials used for molds. Alternatives such as glass are not easy to use as material for molds and will not withstand the handling necessary to remove the consolidated object from the mold.

11 149606

In the consolidation of carbon precipitated from the original mixture to form a cohesive body, the method of U.S.A. Patent No. 2,431,326 serious disadvantages. The mixtures that do not contain furfural alcohol are too long to consolidate to an appropriate strength for removal from the mold without destruction. These blends would not be suitable for commercial use, as minimal time in the mold is necessary to avoid an excessive number of molds.

If the consolidation reactions are made faster by adding furfural alcohol, as suggested in the patent, they can become almost explosively violent when carried out in large sections as heat is released during the consolidation and cannot be carried away due to the poor conductivity of the consolidate -the mass. And even in the case of less aggravated conditions, the volume of the consolidated object can be increased, causing it to become larger than when it was originally cast due to the formation of bubbles caused by the heat of reaction. Further, the heat of reaction can cause severe thermal stresses between the center and outer surface of the article to crack or cause cracking upon subsequent carbonization.

The significance of these drawbacks becomes more obvious when it becomes clear that they cannot be removed simply by setting the acid concentration. If the acid concentration is drastically lowered to decrease the reaction rate at a given furfural alcohol content, the solids will be separated and precipitated prior to consolidation.

Furthermore, if heat is added to increase the speed of the consolidation process, liquid will evaporate before the consolidation is completed, acid vapors are formed and cracks will usually appear on the surfaces where the evaporation takes place as surface tension forces contract the surface while the interior remains liquid and therefore incompressible. Similar cracks can occur during drying.

Finally, the evaporation of acid fumes during the drying or carbonization steps is also a serious drawback of the method disclosed in U.S. Patent No. 2,431,326.

12 149606

The process of the invention is characterized in that the liquid mixture is formed by admixing an organic carbon-providing binder, an optionally etherified glycol with at least one free OH group with the exception of unsubstituted ethylene glycol as liquid pore former and optionally at least one dispersant. until the mixture becomes freely flowing and macroscopically homogeneous, where the mixture, if desired, is thermally conditioned and / or at reduced pressure to form from the mixture by casting and consolidation a self-supporting body uniformly distributed therethrough containing a material which can be eliminated from the body for forming a system of uniformly distributed pores, and that said uniformly distributed material is removed from the self-supporting body before the body is subjected to pyrolysis to form said interconnected pore systems therein.

The process of the invention generally involves mixing a carbon-forming binder with said liquid pore-forming dispersant system to form a free-flowing liquid mixture comprising a selected spatially uniform distribution of constituents and a continuous liquid phase. This mixture is molded into a cavity-free mass of selected shape which is consolidated into a self-supporting body without removal of any material.

25

The materials found in the compartments · the continuous liquid phase fills are then removed from the body leaving a system of interconnected pores of selected size and spatial distribution, and the body is pyrolyzed simultaneously or thereafter to transform it into a porous continuous carbon-30 digits.

Hereby the object of the invention is achieved that the pore volume and pore size of the carbonaceous body can be independently regulated.

This particular aspect of the method according to the invention is illustrated by the following table: 35 13 149606

TABLE I

He_ 1 Hg_ 2 3 4 5

Example, truly & truly ^ ilsynela- MDP IPV

Tat) or II (g / ml) (g / ml) (g / ml) (micron) (ml / g) 3 '1.55 1.56 0.557. 4.19 1.165 2 1.80 0.636 2.54 1.015 5 4 1.00 0.85 0.154 0.881 6 1.53 1.39 0.861 0.121 0.443 8 1.41 1.36 0.968 45.9 0.294 7 1.34 1 , 40 1.031 0.011 0.258 5 1.26 1.30 1.211 0.005 0.055 10 1 Actual density determined by He-pycnometry.

2 2 Actual density determined by Hg intrusion to .4.218 kp / cm.

3 Apparent density determined by Hg.

15, - 4 Mean pore diameter from Hg porosimetry.

5 Intrusion pore volume from Hg porosimetry.

The components and treatment of the materials mentioned in Table I are described in the following Table II. Of interest is the variation in pore size that can be achieved. In the case of the materials mentioned in Table I, the pore size varies by a factor of 10,000.

Furthermore, a considerable variation in apparent density can be obtained, which in the examples in Table II goes up to a factor of more than 2. The volume of interconnected pores available for Hg has also been able to be varied by a factor of 20 in these examples.

30

The examples show a general trend towards lower pore size at finer pore size. However, this is not always the case, as evidenced by comparing Example 8 with the others. It is therefore possible to change these two factors independently.

35 14 149606

While the selectivity of pore parameters is elucidated in Table I *, no data on reproducibility are important for obvious reasons. However, a high degree of reproducibility is evident from samples in which six rods were made, as described in Example 2, Table II in separate forms. The apparent apparent density was all within 0.3% · The reproducibility of apparent density has been found to be within 0.5% in successive portions. Spatial variations within given objects have been measured to less than 0.5%.

10

Such uniformity and reproducibility, such variations in pore size and density and independent control of pore size and volume are all unique in the present process, as is the ease with which the properties of the manufactured articles can be altered.

The ability to independently regulate various parameters in the pore system is important for obvious reasons®. such as those described in the above patents.

It is also of obvious importance in other applications of the present bodies that this ability provides for easy regulation of many properties of the bodies such as density, surface area, hardness, compression and tensile strength, modulus of elasticity, etc.

In addition to the mandatory steps that culminate with the pyrolysis of the consolidated form, other optional steps can be used to change the properties of or impart additional properties to the final product. These, which will be discussed in detail below, include:

Conditioning of the moldable liquid, conditioning of. the body obtained by the consolidation step, machining and other shaping of the consolidated and pyrolyzed body, and penetration of the pyrolized body alone or with subsequent treatment of the re-penetrated body.

15 149606

Depending on the particular nature of the constituents above and other considerations such as the properties desired in the carbonaceous body, one or more optional constituents may also be used. These include: 5

Consolidating agents, fillers (solids or dispersible liquids), 10 antifoaming agents, wetting agents, and accelerators.

In Table II, certain particular embodiments have been selected from among the hundreds which have been satisfactorily performed. These methods have been selected to elucidate a wide range, both in terms of constituents and process steps.

20 16 149606 "O CO t" rH rj "3 • Λ- co m in .h id co g 5 co co in n æ q 'f3 Λ> ^ - *« ooq ^ ø ^ ooo i-; o rt σ u 0000000 ° o ° o, r-, OOOOOOOgg 1 W ooooooo SfMooo

Sen ΟΝΟ N O O) ON O fM O (M ° (S ° ^ S J'1

Pj> 1 Ng NO CMS CMS CMS CMS CMS 018 ™ ^ s ^ J, ° o ° o "i i ^ H £ -G -C £ L iJ 1 tw

Si S5 55 55 5¾ 5¾

Bgg, CM i — I CM M

01 H J2 I η λ λ ^ θϋ not in 0 0 0 0 Ο Ο 0ο ° ο S3 ^^! S rr-t 00 Γ "t- Ο O O g g r 9 S j I σ '» cr> Ον r- γ γ

^ι ^ ΐ2 S'H 3 I 1 ι I -Ρ I I L L

SP ώι-ίχΐι-ιχ: -jc ximx: χι γη Æ ^ £ η su se Si 55 "i Si Si C'SS'OO O 0 O 0 0¾¾ gyj.-He r ~ n in mmgg .¾ 3 Μ co en and a co id cd wh (ri 0 0 0 0 0 0 0 0o 0o B goo O ι-H ooogg $ .¾ in ro ro cm id id id and ci ÆO £ 0 ÆO £ 5¾ ^ ¾ K 'O oo en o no 00 g egg

Hfi'ri ro co co cd 10 i

E-ι I

8h, ¾ C C C C

5 „-r-l -H - <H -i-) ^ go εΛ εΛ ε„ „^„ <- W w ij and 0 0 0 -G Æ »G» G c_j w. p_i s æ-μ oo rr o and o oo Not -m * Not ^ Not ^ £ 3 „s g I i — ICM r-lCM IDCM CMS CMS CM 03 CM 7 * 1 CMæ H S" ο tn H Is as

pH

<D w, Λ § 5 CD S 01 O '^ Si ™ in and tn E ,.

f. «1 r-». r * '. Γ-- in JJ

8 tifi Q ι η ι ι -μ = = =

5>> 1 · Β, § ι — I I rH n C

gfrlUl S CMCTiCM CM -ri

I I

• hot ^ tr w, ih en. — i _ en, 81 Æ, O co σι en en cm ™ cm ™ CD * H [OO w-ι jo ίΤΛ FTi w ^ * », - CHO es S s vS VD t - fr r> 7

O (U -H I I I I I I I I I I

S Ό g g co o o o o g o 2 ^ CMp ^ cMCMCMCM ^ CM ™

ISLAND

I Ό g orø r- ε ε in c

ρ · Η Μ B S - g S E S J

'L? SSPSSSS7

<n c 2®- ^ ** 10 ^ S

-H-H r-l ^ oq CM CM CM CM ^ S.

S S <= s Q <3 .iEEin ^^^ - c Q * p ^ oo * £ S β § * s

zS 'XJooroooooS

m <o cn m cow cow

P-i O (D I ι ι ι ι ι I i -L

tn Pi C <n o '10 ό r- 2 Η 1 1 [- [rH rH r — 1 CM CM CM ^

CQ

l ^ rH B g g J

O! D Γ0 in lD o o o c3 o f5

C'O cnpgojuDr-iipipep ^ P

* ρΊ · Η ι ι i I I I I I I _L

CQS 5 ro m co co co co oo 2 ^ Ϊ — 1, —ΐ 1—) I — i 1—1 I — l I — I * - *

U3 f — I

I ^ SjC <“| ojm ^ Ln'X> t ^ coc '* 17 149606? Ε ιο 3 & m will« IΟ ο O' 00 CM ^ ° ® '' Ί'ο 'γΜ Ο Ο rH Ο ΓΗ Ο hm η ο Ο 0 0 0 0 Ο _

Lj to ο ο ο Ο Ο Η ο 0 0ν s. q q Q Ο Ο ΓΟ CM Ο Ο

ίίίΗ OCMOCMOCMOCMOCMO CM χί Ζ Ο CM Ο CM

Λ ° ζ ° Ζ Μ sa CM S CM ζ INS cm Ζ Γ-Ζ $ Ο Λ Λ Λ 15 0 0 0 15 15 15 15 15 15 ID L) H H ico ico ico σ σ σ> 4 -> σ '* Ρ σ' * Ρ σ ^ -Ρ C \ Ρ I -Ρ ^ § S jj I U_1 I l + _) l IH I * 4-1 I ^ I Mt 1

Sh W4J 2 ΐ s ^ 3 ό_g ^ _g £ 5 rf J2 Sri

gnS \ Ω rH kDH r-H ι-H fOH in H C? * rH CMr-tVOU

8g ij o o o o o o o o o ss s, s s s s s s s f f ° gg ^ 31 5! Ø SE SØ 3U 20 SØ 30 20 Sø C'SH'o o o o. o o o g 3 TJ (S ° ° S S m c * S ^

Ils s s s s s s ° s s i 0- H ^ g Z 4-> N1 in oy • - rn __j rrj r! N ^ pC 4S rC ÆO i p.

- * - 1 g O -H <y \ O O ^ i? H OH CMLO OH

(0 H W -U MPi Ρ Ρί Γ) (¾ Hpi Hro CNW

U) Pd e µ z ό -g .5 i2 £ j 'q, £ $ "Λ ° Ό xfo -C ^ O 0¾ X! FM l ^ O M η χ: ° ο

- HK4-> ΝΗ MIM NCM (MIM fflO ΙΛΚ ηιί NCM

Η I j, ^ I illssss s s (C> _ one O '

^ O I 4-1 O

Ζ Ό M-i Φ CM 4-1 S £ Q · § = = = = = = ^ 0) e> t 4J c i -y g fe in -Η c 2 co ή

ø4 I I

• h in O '_ _ O' - - rH O 'CM O' 01CM _ __ _ O 'O' 0c o in o oiOiOir ^ tn 01- r) P-I xtf rH CM CO VD rH "5Ρ

CJ-IrHI I I I I I I I II

OdlOJO o o o o o o o o Ζ Ό Ό cm cm cm cm cm cm cm cm cm S '-' See gEg-.e--

Hgogoorogin Eg ωίπιηοοο ^ o Γ 'co o ΟιΟιχ ^ 1 «a * r-ι ro o in ro in m1 tncrHi 1 1 1 1 1 1 ii Η -Η Φ Μ1 Μ * x * xtf O' O 'O' O ' · '

Pi-lOCM CM CM CM iH rH rH rH CM

in «5 Ο Ο E in O C§ O ID

A «a1 ro ro ro ro rH in in» h ro

Z U U I I I I I I I 111 I

2 0 0 r ~ σ 'σι σ' σ 'σι o'cmcm σι

C Ρλ C 04 r — I rH rH rH rH rHrHCN rH

In lrH Bgggggggg> S> S ο ο ο o 0 0 0 m 0

C B O '"a * x ^ ID | H rH in rH

• Η Ή I I I I I I I I I

(¾ E CM CM CM CM CM CO CO CM CM

rorororororOtHroro É in rH · __ ώωμ i — 1 cm ro xj in id p 'co cn

µ4 d i-H i-H ι-H r-H ι-H rH rH rH rH

18 149606

All temperatures in Table II are in degrees Celsius.

EXPLANATION OF NAMES

5 12- Glycerpl - technical quality.

13 - Polyfurfural Alcohol Resin - "Durez 16470", Hooker Chemical Corp.

19 - Diethylene glycol.

20 - Paratoluene sulfonic acid.

21 - Carbon powder prepared by grinding the material of Example 1. Lo 22 - Polyethylene glycol - average molecular weight 300.

23 - Glycerol borate containing 0.5 g per ml.

24 - "Triton X-100" - Nonionic Emulsifier - Water Soluble Isooctylphenoxypolyethoxyethanol, Rohm and Haas Co.

Triethylene glycol.

26 - Tetraethylene glycol.

27 - Propylene glycol.

28 - Dipropylene glycol.

32 - Furfural Alcohol Monomer, Quaker Oats Co.

33 - Phenolic Resin - "Varcum 8142", Reichold Chemicals, Inc.

2o 34 -Carbon from Example 17.

H.S. - Hand stirring.

M.S. - Mechanical stirrer.

C.M. - Epenbach type colloid mill.

R.T. - Room temperature.

25 R.P. - Decreased pressure - approx. 100 mm Hg.

Ad - Samples heated in contact with liquid absorbent media.

VAC - Vacuum - pressure less than 10 microns Hg.

Cl. - Retained fluid, g - Grams.

3ø m - Milliliter, h - hours, d - days.

Pa - apparently density.

V-C - in vacuum followed by cooling.

35

The first of the mandatory ingredients used in the process of the invention is "the carbon-forming binder". IN

The term used herein denotes the term given in quotation marks substances which, upon heating to a high temperature in a non-oxygen containing atmosphere, will lead to a solid carbonaceous residue. In order to be used for the process of the invention, the coke yield must be as large as possible while retaining the other properties which the binder must exhibit. The preferred materials provide approx. 50% carbon.

Many organic compounds which could be useful for bonding low temperature structures such as methyl methacrylates and polyethenes are unsatisfactory as they are almost completely converted to gases upon heating (their coke yield at 905 ° C is about 0.2%) . Riesz and Susman have stated in Proceedings of the Fourth Conference on Carbon, p. 609 et seq., A rather comprehensive list of coke residues for various synthetic and natural resins, and this report may be referred to for a list of organic materials which are satisfactory for the present purpose only from the point of view of the coke yield.

Furthermore, in order for a binder material to be used for the process of the present invention, it must, in addition to leading to a satisfactory coke yield, be able to be uniformly dispersed in a liquid mixture. This property is in no way possessed of all organic substances with high coke yields. Furthermore, the binder cannot be selected independently of the other constituents of the liquid mixture and must also meet other machining requirements such as those provided with the casting and consolidation steps.

3Q The binder can be dispersed by dissolving or suspending it mechanically in the liquid portion of the mixture. Fortunately, it has been found that there are a large number of binders which provide high coke yield and which can be easily dispersed either alone or by readily available dispersants. Further, as will be apparent from the following, it has been found that auxiliary dispersants can be used to effect dispersion of the binders in the liquid system, which are otherwise suitable but which are not capable of cause the necessary dispersion.

The most limiting feature necessary for the binder 5 is that there is a convenient way in which it can be bonded in a continuous network with the carbon in a spatially uniform distribution. Many organic binders suitable for this purpose are liquid resins. With regard to the liquid resins to be used, the formation of the network is effected by a 2q polymerization mechanism. In the preferred embodiments of the present invention, thermosetting polymers are used, but useful binders which are thermoplastic polymers have also been found.

Solid binders such as poly vinyl chloride, polyvinyl alcohol, polyurethane, carbon tar pitch and corn starch have also been successfully used, although liquid binders are preferred. Furthermore, low viscosity liquid binders (below 250 centipoise) are generally the most satisfactory.

20

It is desirable to use binders with a sufficiently low vapor pressure to negligible loss of binder and / or bubble formation during any heating required to condition the liquid or to consolidate the molded mixture. Although the temperatures of these steps in the preferred cases are generally below 100 ° C, the times can be long (30 hours or more), making the requirement for low vapor pressure particularly important.

Other important considerations are that the binder should be relatively non-toxic and non-corrosive, and that it should be cheaply expressed as the price per unit weight of carbon yield.

35 21 149606

Suitably, as binders in the present process, both monomers and resins are used alone or in various combinations. A large range of binder concentration has also been used.

The following are examples of binders which may be used:

Furfural.

Furfural alcohol.

10

Furfuralalkoholharpikser.

Polyvinyl chlorides.

Polyvinyl acetates.

Polyvinyl alcohols.

Polyvinylburyrater.

Starches.

Methylvinyletherpolymere.

20 Methyl vinyl ether / maleic anhydride polymers.

Polyvinyl / control mixtures.

Modified phenolic resins.

Protein Colloids (A number of protein colloids 25 are described in Swift & Company Publications PO Form C 1443 11265 and PO Form C 1756).

Mixtures of the above.

Of course, other organic substances can be used as the binders as long as they meet the criteria mentioned above.

The percentage of binder used in the liquid mixture will vary from application to application. Thus, concentrations which range from 33% to 95% by volume of the mixture have been very satisfactorily used.

22 149606

The other mandatory constituent used in the present process is the liquid pore former which is an optionally etherified glycol having at least one free OH group with the exception of ethylene glycol. A necessary condition for a satisfactory pore-forming liquid is that it alone or together with the dispersant and / or binder used in the liquid mixture is capable of forming a macroscopically uniform, continuous phase throughout the moldable liquid mixture. The liquid pore former may be in the form of a solution together with the other 10 ingredients such as when diethylene glycol is used as a pore forming liquid together with a furfural alcohol binder and "Triton X-100" as a dispersant (Examples 12-14).

"Triton X-100" referred to in the section above is a non-ionic emulsifier and wetting agent available from Rohm and Haas Co. It is a water-soluble isooctylphenoxypolyethoxyethanol containing 10 moles of ethylene oxide and is described in more detail in Technical Bulletin No. SAN 117-2 (March 1967).

A pore former which is excreted in the liquid mixture, such as ethylene glycol, used with a furfural alcohol resin and without any dispersant is not satisfactory.

The pore generator can be used to control the amount of pores in the consolidating body by adjusting its volume concentration in the original mixture. In this way, the apparent density of the body can be varied.

The density of the pyrolyzed end alloys does not decrease in direct proportion to the increase in the amount of pore formers, since the shrinkage by pyrolysis is affected to some extent by the volume of the pore forming component. However, the extent of shrinkage is readily ascertained and may be taken into account when designing the liquid molding mixture or elsewhere in the process.

35

The main function of the liquid pore former is to lower the volume concentration of carbon-forming binder in the liquid mixture. In order to perform this function satisfactorily, it must necessarily be uniformly distributed in the liquid mixture and therefore must be used in conjunction with a suitable dispersant, if it does not itself have this additional property.

It has also been found that the liquid pore former should have a high degree of solubility for the agents used to catalyze the polymerization reactions that take place in the consolidation step of the embodiments of the invention, which involve consolidation by polymerization, which condition is just met Iq by the pore formers mentioned in claim 1. This allows for a very uniform distribution of the polymerization catalyst in the moldable mixture and therefore a more uniform structure.

Also, when the consolidation is carried out by freezing, the pore former must allow the continuous phase to be formed by freezing at a reasonable temperature.

The requirements mentioned above significantly limit the pore forming materials which can be used in the process of the invention.

20 However, a number of satisfactory liquids have been found. Examples of these are listed in Table II.

The following list also lists other pore forming liquids which are examples of those used in the practice of the present invention:

Hexyleneglycol.

Ethoxytriglycol.

3Q Methoxytriglycol.

1,3-butylene glycol.

Polyethylene glycols having molecular weights above 300 "Triton X-100", as well as 35 solutions wherein one of the foregoing or one of the pore forming liquids listed in Table II is a solvent or a solute.

24 149606

In addition to being pore-forming liquids, many of the glycols of claim 1 are emulsifier-type, so that they are also excellent dispersants. By using appropriate amounts of this type of material, the same liquid can be used at double capacity as a pore-forming liquid and as a dispersant in the moldable mixtures from which the present carbonaceous bodies are prepared. Examples of these dual capacity components are included in Table II. These are:] _q Diethylene glycol.

Triethyleneglycol.

Tetraethyleneglycol.

Propylene glycol.

Dipropylene glycol.

15

The dispersant is, of course, an important component of the liquid moldable mixtures. A dispersant, as used in the present process, is as defined above a liquid which, upon mixing with the binder and liquid pore former 20, will provide a mixture having a uniform distribution of the constituents and, moreover, with a continuous phase of the kind described above. The dispersant must allow the mixture to remain in this form for any holding time which may be necessary for liquid conditioning and / or for consolidation of the mixture 25 after casting, regardless of heating. The dispersant must also be capable of uniformly dispersing fillers added to the liquid mixture.

A combination of dispersants may be desirable or necessary. The binding agents are e.g. been used in the form of a dispersed latex. However, in designing a moldable liquid mixture from a dispersion, an additional dispersant such as "Nopcosant L", which is an anionic water-soluble polymer, has been added to the mixture to ensure uniform dispersion of the ingredients. In some cases, it is possible to omit the dispersant.

In systems using propylene glycol. such as the liquid pore former and furfural alcohol binders, the dispersion is peripheral (Example 8). However, the addition of "Triton X-100! -1 also makes this type of system very stable (example li).

5

In addition to having the characteristics just discussed, the dispersant must meet the requirements of corrosion, vapor pressure, etc., which are set forth in the discussion of the other components of the moldable mixture.

10

In the exploration of various dispersants, an unforeseen and very useful result has been discovered, namely that it is possible to control the size of the pores in the final structure by controlling the concentration of dispersant. In systems using diethylene glycol and furfural alcohol binders, successively larger amounts of "Triton X-100", e.g. pore size (Example 5g12-14). In systems using propylene = glycol and furfur alcohol type binders, a similar effect was obtained.

20

A striking result also emerges when two effective dispersants are used. In a system using furfural alcohol = binder dispersed in diethylene glycol in an amount sufficient to make it both a dispersant and a pore former, the final product had a pore size of approx. four microns with a narrow size distribution (Example 1). As "Triton X-100" was added in successive larger amounts, keeping all other factors constant, the pore size steadily decreased until it reached 0.0046 microns at a volume percentage of "Triton X-100" in the dispersant - the pore-forming liquid - of 50% (Example 5). Thus, a simple setting of the ratio of starting ingredients resulted in a thousand-fold change in the measurement pore diameter.

Similar useful results can be obtained with other combinations of 35 ingredients. Polyethylene glycols are generally excellent dispersants for both furfural alcohol and its resins. One has been able to control the size of the pores by adding a large percentage of polyethylene glycol to the liquid mixture and by using higher molecular weight glycols.

26 149606

As can be seen from the foregoing, there are many liquids which can be used as dispersants in the practice of the present invention in addition to those specifically mentioned above. Other examples of dispersants are given in Table II.

5

The percentages of liquid pore former and dispersant used in the moldable compositions from which the present bodies are made can vary widely. Thus, volume percentages ranging from 5 to 91% have been successfully used.

10

It has been pointed out that a wide variety of optional ingredients can also be incorporated into the moldable mixtures used in the present process. One class of such constituents is that referred to as "fillers" or "filler constituents".

15

It is often desirable to add one or more fillers to the original mixture so that the shaped porous body will have special properties. Thus, the addition of silica or silicon to the mixture gives a body which, after pyrolysis 20 at very high temperatures, contains silicon carbide. This component gives the body hardness and resistance to oxidation.

Many metallic or metal oxides found in the carbon bodies act as catalysts for subsequent graphitization. Such 25 metallic materials can be added to the original liquid mixture by the present process to provide a graphitization catalyst in the porous body.

In the case of bodies to be used in a previously mentioned patented carbide formation process, other materials may be added to the original mixture to aid in wettability and to regulate reactivity and to add low cost alloying elements.

35

The constituents can be added in a metallic state or as oxides, sulfides, sulfates, carbides, carbonates, nitrides, nitrates, phosphides, phosphates, borides, borates, silicides, silicates, etc. The present process is actually ideally suited for the addition of most solids when a dispersant is present, usually in a large amount, which facilitates the uniform distribution of the filler (s).

The oxides which have been used as additives include CuO, 5 TiO 2> CrO 2, WO 2, Mb 2 O 2, SiO 2, NiO, Cr 2 O 2, Al 2 O 2 and

The last two of the above also act as consolidating agents, catalyzing the polymerization reactions as consolidating agents.

10

Solid carbonaceous materials are particularly useful as filler materials in the present process. The addition of high carbon substances to the original mixture can be used with particular advantage to increase overall carbon yield, to regulate the mechanical, physical and chemical properties of the carbonaceous body, to reduce shrinkage and to to provide a body with a matched pore size spectrum.

The present systems are ideally suited for the addition of solid 20 maxerials, which give high carbon yield, again because they usually contain large amounts of dispersants. Any such material, which may remain uniformly suspended, is useful, and a wide variety of substances having high carbon yields including starters, carbon black, 25 graphite species, mixed calcite compounds of graphite, polyvinyl chloride, polyvinylidene chloride, phenol formaldehyde have been used. , starch species, gilsonite, and other synthetic and natural polymers both before and after they have been carbonated to varying degrees including graphitization. Systems using fillers of the kind just described are included in the examples in Table II.

For many applications including the preparation of pervious backbones for a previously mentioned patented carbide forming process, carbonaceous fillers prepared from bodies prepared by the process disclosed herein are preferred.

149606 28

Particulate material obtained by machining, grinding or crushing the porous bodies obtained after consolidation, after conditioning and after pyrolysis has properties which make them particularly desirable filler materials. For example, by the present process, porous carbonaceous bodies which are composed of nearly spherical particles having a diameter of approx. four microns, and these can be easily separated (especially after the preceding pyro-lysis steps) and lead to an almost monodispersed spherical powder (Example 17). A body made with this powder as filler 2Q (Example 18) exhibited a very high hardness (240 HV at 10 kg) and did not crack at a load of the 50 kg sample tip.

Furthermore, the impression seemed to straighten completely. No other currently known carbonaceous material exhibits the same behavior.

15

Since bodies made by the present method have a pore size and size that can be controlled over large areas, it is possible to adapt the material to any desired pore size and bi- and other multiple pore spectra by using fillers of the above section. described species. A body having a pore size of 0.01 micron can e.g. is crushed to a 10 micron powder and used as a filler to prepare a body with 10 micron pores between the filler particles. The end product is a coherent body having an selectable volume of 10 micron pores and an independently selectable volume of 0.01 micron pores, both sets of pores being uniformly distributed within the body. Such structures have obvious advantages as catalysts and catalyst supports, filters, absorption bodies and combustion cell electrodes and in other applications where maximum accessibility to the pores is desired.

Furthermore, since there are possibilities to shape the body by the present method, macroscopic channels can be formed simultaneously with the multiple sets of pores of different sizes. The resulting cohesive structures have extremely large surface area-to-volume ratios and obvious advantages over prior art systems with large surface-to-volume ratios and must be used in finely divided particulate form.

29 1 * 9 $ 0β

The fillers added to the liquid mixture by the present process need not be solids if they are soluble or otherwise uniformly distributed in one or more of the other components and can be converted to solids in one of the subsequent process steps.

Examples of such fillers include various organometallic compounds which will be dissolved in the binder, the pore-forming liquid or dispersant such as glyceryl borate (Example 10 4), ammonium meta-tungstate dissolved in diethylene glycol, ethyl polysilicate, zirconium ethylene ethyl acetate, pre-hydrolyzed ethyl acetate r, titanyl chloride in solution, zirconium hydroxynitrate in solution, acetate zirconium chloride, basic zirconium nitrate, ammonium zirconium carbonate, tetraisopropyl titanate, and various solutions of tungsten and molybdenum.

The advantage of adding fillers in liquid form is that finely divided solids can be obtained evenly distributed throughout the body. For example, colloidal silica is made using a soluble silicate and heating the mold obtained by consolidating the molding mixture. This silica diminishes shrinkage by pyrolysis and can be converted into silicon carbide by still further heating.

Another advantage of using liquid or soluble fillers is that many of them, including a number of the above, also act as polymerization catalyst type consolidation agents.

Another constituent class which may advantageously be added to the 30 initially formed liquid mixtures in the present process are the just mentioned "consolidation agents". This designation is intended to cover any constituents added to the original mixture to consolidate the casting liquid.

35 When consolidating by freezing, the consolidating agents are not important. However, even in such cases, agents such as silver iodide may advantageously be added to the original liquid mixture to regulate freeze nucleation.

In many other systems, no consolidation agent is needed. Ionization radiation has been used to consolidate furfural alcohol-type binders. This method is advantageous in that the crosslinking can be promoted without the formation of 2 heat.

Furfural alcohol resins and other binders can also be polymerized by application of heat alone, although consolidation is progressing slowly. Furfural alcohol resin / glycol systems are e.g.

10 has been successfully consolidated by extended heating at 150 ° C.

However, a consolidation agent is usually used to promote or catalyze the polymerization in embodiments of the present invention in which consolidation is effected by this mechanism. The consolidating agent will typically be acidic in that it is known about such materials as to accelerate the polymerization of binder of furfural and other types. All the common mineral acids, various organic acids and various branded materials of unspecified composition have been successfully used as polymerization-type consolidating agents.

In many cases, it is preferred to use paratoluene sulfonic acid as a consolidating agent. This material is a solid at room temperature, but it is completely soluble in the present pore forming and preferred dispersing liquids. It can therefore be conveniently and uniformly distributed in the original mixture even at very high concentrations.

Furthermore, the disperse nature of the present liquid solution permits the use of large amounts of acid to binder (5-60 ° or more), a process which is usually not possible in prior art polymerization processes as it results in unsteady exothermic reactions. The large amounts of acid allow rapid and adjustable consolidation in furfural-alcohol and other systems, usually at temperatures of 100 ° C or lower.

149606 31

This is significantly lower than the more usual range of 125-175 ° C, which must be used to solidify resins used in prior art methods in which the acid content of the mixture must be limited to 2% or less for large cross-sectional forms. The fact that fast low temperature consolidation can be achieved has obvious advantages - e.g. the lower temperature requirements place much less vapor pressure associated and other constraints on the pore forming liquid, the dispersant and the binder.

10

As indicated above, the initial step of the present process is the mixing of the binder and pore former and any dispersants and fillers which may be used with the dispersant. lo

In this step, the constituents are formed to form a homogeneous liquid (liquid here includes materials containing solids as well as those containing only liquids) with a viscosity of less than 100 poise, so that the mixture can flow to a casting capacity. and form a mold which is free of cavities of macroscopic size without the need for pressure or vibration. The use of vibration and pressure may be undesirable because of the complexity introduced into the mixing process.

Viscosities below the above maximum can be readily obtained even with the addition of fillers in amounts of 40-60% by volume or more, especially if the preferred binders, dispersants and pore formers are used.

All else being equal, low viscosity mixtures are preferred. Low viscosities facilitate mixing and minimize bubble retention.

It is usually preferred to mix the dispersant in the glycol and then add the consolidant if one is used. The binder is then added. A definite increase in the uniformity of the final structure can be achieved by first dispersing the polymerization catalyst in the liquid portion of the original mixture and then admixing the binder.

In many cases, the volume of the glycol and dispersant will be equal to or exceed the volume of the binder. This facilitates the mixing step.

^ The above is by no means the only order in which the constituents can be incorporated into the liquid mixture. The relative volume and mutual solubility of the constituents will often make it more convenient to add the constituents in a different order.

After the mixture just described, any solids to be used are added and dispersed uniformly. The filler may be pre-wetted with the pore-forming liquid or dispersant prior to the addition of the filler to the liquid. This will often prevent air from being added in significant amounts to the preparation along with the filler.

Also, smaller amounts of ordinary foam depressants can be added at the mixing step to remove air bubbles.

20

It has been found that a common mechanical stirrer is satisfactory for mixing in most cases. A low speed colloid mill also provides an excellent uniform mixing of the liquid mixture.

25

It is often desirable before casting the liquid mixture formed at the mixing step to change the properties of the mixture in a way that will improve the quality or impart particular characteristics to the final product. Firstly, it is usually desirable to remove any air contained in the mixture during the mixing operation. Such trapped air has a particular tendency to be present in mixtures containing substantial amounts of solid fillers.

The deflection should ensure that the pores in the carbonaceous body will only be formed by the pore former. Bubbles give pores which are generally large relative to glycol-formed pores (these are 200 microns or less). Furthermore, even very small bubbles in the mixed mixture will tend to grow during subsequent steps, such as. involves heating. These bubbles are particularly prone to cause cracks during pyrolysis.

Most of the liquid mixtures used have a very low viscosity and can be easily deflated. In fact, those who have a large amount of liquid pore formers usually do not need bubbling. In addition, the dispersants used generally cause complete wetting of filler, making the viscosity of the mixture 10 the only barrier to bubble removal.

When bubbling is required, small additives of common antifouling agents are often useful. It has been found that the application of a reduced pressure (e.g., 100 mm Hg) to the liquid mixture is very effective in causing deflection. Furthermore, gentle heating can be used advantageously as long as the temperature is not high enough to cause significant polymerization and increased viscosity.

Bubbling does not impose any restrictions on the binder, pore dander and dispersant, especially if reduced pressure is used. It is desirable that these constituents have a low vapor pressure (high boiling point), as reducing the pressure on the mixture may otherwise result in loss of material from the mixture or the formation of additional bubbles.

25

By far, the most important conditioning work performed on the liquid mixture is to keep the mixture at a selected temperature when consolidation occurs by polymerization. This position of the mixture causes partial polymerization in the liquid mixture before casting.

Partial polymerization prior to casting has many pronounced advantages over using only a fully polymerized resin 35 as a starting material. First, the less polymerized binders can be mixed and deflated more easily. A further advantage of less polymerized binders is that they are less viscous and more easily dispersible. Highly polymerized furfural alcohol resins are e.g. more difficult to disperse and prevent precipitation than the low molecular weight monomer or polymer. This advantage is particularly important when the dispersion is equal on the boundary.

5 It also appears that the polymerization proceeds differently when carried out in the casting mixture rather than prior to the mixing.

In all cases, holding time can be used to affect the nature of the pyrolyzed product.

The main advantage of conditioning the moldable mixture by using holding time is that a substantial portion of the heat of polymerization can be dissipated while the mixture is still liquid by convection heat transfer. This can be increased by stirring, although stirring should be sufficiently careful not to introduce bubbles.

In conditioning, the liquid mixture can be brought to a precisely moldable consistency with a simultaneous decrease in heat which will be formed at the consolidation stage. This significantly increases the size of bodies that can be consolidated. Bodies up to 15 cents x 15 cm have been successfully consolidated with appropriate conditioning of the liquid mixture, although less complete conditioning resulted in a deferred, uncontrollable heating and expansion of the liquid cast mixture at the consolidation step.

25

Conditioning may also be used to change the pore size which will occur in the final product without changing the composition of liquid mixture or otherwise altering the process steps.

Position conditioning involves different holding times and temperatures depending on the composition of the liquid mixture, the characteristics to be imparted to it and the final product, etc.

In systems that have been studied, the liquid mixture has been maintained at temperatures ranging from -15 to 150 ° C for a period of 35 from a few minutes to several hundred hours.

Cooling the liquid mixture to a very low temperature (5 to -20 ° C) after putting it in a moldable state further lowers the reactions and allows the mixture to be stored for very long periods, which is obvious convenient. Satisfactory results have been obtained when the mixture has been stored at low temperature for six months. Furthermore, attitude at low temperatures also seems to have a favorable and significant effect on the polymerization reaction mechanism.

The free flowing mixture produced in the mixing step is molded into a mold by placing it in a container capable of accommodating the entire liquid mixture. Because of its composition and the free-flowing nature, the liquid forms a bubble- and void-free body which adheres to the shape of the container without vibration or pressure application.

Since these liquid mixtures are composed of constituents which will not corrode or penetrate into ordinary mold materials, glass, silicone rubber, various polymers, aluminum alloys, stainless steels and copper alloys are all suitable for this purpose.

Casting is followed by a consolidation step by the present method. In this step, the free-flow casting mixture is transformed into a self-supporting, physically manageable body without immersion or precipitation and without loss of material from the mold. Hereby, the present method differs from the methods employing lollipop casting, drying and similar processes and further results in the production of superior carbonaceous bodies.

The loss of material from the liquid mixture either by penetration into the mold as by lick molding or by evaporation will introduce a spatially uneven volume concentration of the components. Precipitation will also result in a spatially dissimilar concentration. Of course, spatial disparity in the consolidated material is undesirable because of the resulting lack of uniformity in the final product.

35

It is desirable, but not unconditionally, that the consolidation be done without a significant change in volume. Although a slight homogeneous shrinkage or expansion can be tolerated as no spatial disparity is introduced, the coercion that cast cores or the like may cause cracks if the linear shrinkage is too large.

149606 36

Bodies have been successfully consolidated without any easily detectable shrinkage or expansion by freezing the mold, by performing polymerization at room temperature and at temperatures below and above room temperature, and by irradiating the molding material.

^ The only structural requirement associated with the consolidation step is that the material must be capable of holding the mold in which it is molded. However, it is also highly desirable that the consolidation develop a high raw strength to facilitate removal from the mold and treatment of the cast.

10

The mechanism by which the consolidation process takes place depends on the binder selected. Mixtures using polyvinylchloride latex binders may e.g. consolidated by freezing. Other latexes which can be consolidated by this process include those described in U.S.A. U.S. Patent Nos. 3,236,788 and 3,376,158.

When a freeze-consolidable latex is used in the process, the holding time and the exact temperature below the freezing point are not critical in consolidating the liquid mixture. It has been found that, in general, freeze variables such as rate and the presence of nucleation catalysts must be in accordance with the guidelines of U.S.A. U.S. Patent No. 3,236,788.

In most of the presently preferred systems, the consolidation of the molding composition is caused by polymerization of the binder. The polymerization mechanism is not critical and will vary depending on the constituents present, the concentration, the temperature and the pressure conditions under which material is consolidated.

Part or all of the binder may be dissolved in the pore former and the dispersant at least prior to polymerization of significance, which, when e.g. furfural alcohol is used. As the polymerization proceeds by heat, time, pressure, radiation or catalyst, at least a portion of the binder is precipitated together with precipitated material which binds together to effect consolidation.

149606 37

To form a satisfactory body, the binder must remain uniformly suspended in the pore-forming dispersing liquid until consolidation has occurred. This requires that the pore-forming dispersing liquid be carefully chosen, especially since most of the usual binders are heated to a modest degree to reduce the consolidation time with a concomitant decrease in viscosity which would accelerate precipitation in the molding mixture.

Nevertheless, it has been found that there are many combinations 10 of binders, pore formers and dispersants which are satisfactory. This is evidenced by the fact that many samples have been prepared in the form of 15 cm bars with a diameter of approx.

1.9 cm from blends of widely varying nature, which at end to end control of apparent density showed less than 1/2% variation and no noticeable change in structure under the microscope.

In systems in which the dispersion is peripheral (Example 8), in the liquid mixture there is a tendency to sink below the initial liquid level, which shows that precipitation has taken place. In such cases, the lower part of the consolidated structure is more dense than the upper one. The addition of up to 5% by volume auxiliary dispersant such as "Triton X-100" was found to completely eliminate this problem with the added benefit of achieving a much finer pore structure.

25

In addition to the factors discussed above, it has been found that successful consolidation requires setting the time and temperature of the binder and the pore-forming-dispersing system. Very slow consolidation can not only result in precipitation, but also allows the formation of convection patterns in the molding mixture. These can give spatial variations in density of considerable size, causing cracks at the pyrolysis stage following consolidation.

By changing the consolidation time and temperature and the amount and type of polymerization catalyst, it is possible to correct for less than optimal binder and pore-forming dispersant properties by increasing the rate of consolidation process. However, this is not without risk, especially when large bodies are required.

149606 38

An alternative solution that completely eliminates this problem is to condition the liquid mixture before casting, as discussed above.

In the present method, the consolidated body can be pyrolyzed directly to effect pore formation and carbonization, or it may first be subjected to one or more conditioning steps.

The crushing and grinding of the present bodies provides a unique particulate material having controlled size pores in every 10 particles. In addition to using this material, as previously discussed, it has been found to provide bodies with excellent properties when re-consolidated by heat and pressure. For such 2 gene consolidation, pressures of 350 kp / cm and temperatures of 125-180 ° C have been used for a period of 10-30 minutes.

15

In the pyrolysis step of the present invention, the consolidated (and possibly conditioned) body is treated under specified time, temperature, pressure and environmental conditions to effect a depolymerization of the solids in the body, thereby increasing the percentage of carbon 20 in the body. The exact composition and structure of the solid body will change continuously in complicated ways as the heating progresses. An excellent account of the factors occurring in the pyrolysis is given by Fitzer, et al in Chemistry and Physics of Carbon, 7, p. 237 et seq., Marcel Dekker, Inc., N.Y., 1971.

The present consolidated bodies have been consolidated by generally well-known methods using maximum temperatures of 250-2400 ° C and pressures of 0.1 mm Hg to 0.7 kp / cm.

30

The heating takes place at controlled speeds, which reach between 6-43 ° C per hour in the range up to 1000 ° C. The pyrolysis is carried out in a vacuum and in flowing argon, but flowing nitrogen is preferred. Since the properties of the cohesive pyrolized body are primarily determined by the highest temperature reached, no holding time is used.

The pyrolysis is generally first carried out to ca. 700 ° C. At this temperature, the interconnected pore structure formed in the body of the pore-forming liquid will have been developed and the binder part of the body will have lost most of its constituents beyond carbon.

The carbonaceous solids comprising the continuous network. in the body will have a pore structure which is believed to comprise gap-like apertures approx. 5 A in diameter and because of the interconnected pore system in the body there is access to the openings. Accordingly, the material is prepared from liquid mixtures using binders such as furfural alcohol resins when the pyrolysis is stopped at 700 ° C (see Example 19) excellent as molecular sieves.

10

There is also pyrolysis to temperatures of approx. 700 ° C made of contiguous articles with a specific surface area of 510 m / g, which is within a range useful for absorption and catalysis.

15

The body is often heated in a second step above 700 ° C, although two-stage pyrolysis is by no means a requirement in the present process, and the bodies can be heated to temperatures greater than 700 ° C in a single step. Heating to higher temperatures tends to graphite the remaining carbon. Accordingly, the temperature used will depend at least in part on the extent to which graphitization is desired.

The degree of graphitization can also be increased by using in the original liquid mixture a filler which will catalyze the graphitization reaction. Such fillers include TiO 2> C 2 O 2, NiO, ZrO 2, ¥ 0 ^, SiO 2, Fe 2

The present novel bodies, because of their unique 3 ° structure, have important advantages as far as pyrolysis is concerned. In bodies made by many prior art methods, a substantial amount of low molecular weight hydrocarbon gases must escape from the body. This causes severe structure rupture and shrinkage, and the gas usually causes the body to crack 35 into small pieces. Even the most advanced known methods (see U.S. Patent No. 3,109,712) · require the use of one of very few resins such as phenol formaldehyde, require very long periods of pyrolysis of 30 days or more, and even then they are not in use. capable of providing bodies more than 0.6 cm thick without cracks. For this reason, massive carbonaceous bodies have so far been prepared by bonding pre-pyrolized particles with a binder which can be pyrolysed or by cumbersome lamination methods (see U.S. Patent No. 3,626,042).

The continuous pore system of the present consolidated body allows gases to easily escape during pyrolysis. It has also been possible to pyrolize bodies with cross sections up to 15 cm and 10 micron pores at a heating time of approx. 2 days to 2000 ° C without any cracks. There have also been pyrolyzed bodies of cross-section approx. 2.5 cm a pore size of less than 0.01 micron for a time of approx. 4 days up to 2000 ° C. Even larger parts with smaller pore sizes can be machined.

The pyrolyzed bodies are an excellent source of fillers having regulated properties for use in the above described process when reduced to particulate form. These materials also provide excellent results when used as fillers in metal carbon materials for sealing and bearing applications.

It is often desirable to activate carbon by heating it in a controlled atmosphere (usually carbon dioxide) for catalytic applications. The present bodies are particularly suitable for this activation, since the activating gas can readily penetrate the interior of thick parts.

At the pyrolysis stage, many of the fillers added to the original liquid mixture are reduced to metals or converted to carbides, giving bodies with properties which make them particularly suitable as catalysts and for a variety of other purposes. The bodies produced by the present method again have particular advantage in that the reduction and / or other reaction will proceed uniformly and to a more controllable extent than is otherwise possible due to the regulated interconnected pore structure.

Claims (2)

Post-treatment of the pyrolyzed bodies can also be used with particular advantage to impart to the various properties of the process according to the invention, to improve the quality or to change the properties of the bodies by virtue of their novel interconnected pore structure and their great physical strength and other mechanical properties. Consequently, the possibilities for finishing are almost unlimited. Claims. 10 --------------------- A process for preparing a porous carbonaceous body comprising the steps of: forming a liquid mixture, molding the mixture to thereby impart the mixture to a particular mold, consolidating the mixture to thereby produce a self-supporting body, and exposing it. pyrolysis self-supporting body, thereby transforming it into a coherent article of a carbonaceous nature, characterized in that the liquid mixture is formed by admixing an organic carbon-producing binder, an optionally etherified glycol with at least one free OH group, with the exception of unsubstituted ethyl -long glycol as liquid pore former and optionally at least one dispersant until the mixture becomes freely flowing and macroscopically homogeneous, where desired, the mixture is thermally conditioned and / or at reduced pressure to form a self-supporting body from the mixture by casting and consolidation. uniformly distributed therethrough in contains a material which can be eliminated from the body to form a system of uniformly spaced pores and that said uniformly spaced material is removed from the self-supporting body before the body is subjected to pyrolysis to form said interconnected pore systems therein. Process according to claim 1, characterized in that a combination of at least two dispersants is incorporated in the liquid mixture.