CA2009611A1 - Electrically conductive composition and use thereof - Google Patents

Abstract

ELECTRICALLY CONDUCTIVE COMPOSITION AND USE THEREOF
ABSTRACT

A shaped electrically conductive article which comprises an organic polymeric material and a particulate electrically conducting titanium sub-oxide.
The article may be in the shape of a film suitable for use as an anode in a cathodic protection system for the protection of steel rebars embedded in concrete.

Description

- 1 - 2(~9611 ELECTRICALLY CONDUCTIVE COMPOSITION AND USE THEREOF
The present lnventlon relates to a shaped artlcle whlch 1-~ electrlcally conductlng and whlch S comprlses an organlc polymerlc materlal and a partlculate electrlcally conductlng tltanlum sub-oxlde, to a composition from whlch such a shaped artlcle may be produced, and to uses of such an electrically conductlng shaped article.
Although the electrlcally conductlng shaped artlcle of the lnventlon has a varlety of dlfferent uses lt wlll generally be used as an electrode, and lt wlll flnd its greatest appllcatlon as an electrode in cathodlc protectlon, partlcularly when lt ls in the form of a film. The electrlcally conductlng shaped artlcle, partlcularly when ln the form of a fllm, ls especlally sultable for use in the cathodic protection of steel relnforclng bars or wlres ln concrete, herelnafter generally referred to as rebars, although lt ls to be understood that use of the shaped article ls not llmlted to use in cathodlc protectlon of rebars, nor to use in -the cathodic protection ln general.
Under normal envlronmental conditions steel rebars embedded in concrete, such as in Portland cement concrete whlch ls strongly alkaline, form a passivatlng -oxlde fllm on the surfaces Or the rebars whlch lnhlblts further corroslon of the rebars. However, corroslon of the rebars ls caused where chlorlde anlons penetrate lnto the concrete structure and cause the rebars to lose thelr protectlve passlve oxlde fllm. Such chloride anlons can be lntroduced lnto a concrete structure as a result of the use o~ deicing salts on the concrete structure, partlcularly on relnforced concrete bridge decks, but also on other relnforced concrete structures e.g. parklng garages, by the use of chlorlde-20~61~L

contamlnated aggregate ln the production of the concrete, or by the use of chlorlde-contalnlng accelerators e.g. calçlum chlorlde, ln the productlon of the concrete. Corroslon of the steel rebars may also be caused by reductlon ln the concrete alkalinlty whlch results ~rom carbonatlon o~ the concrete brought about by carbon dloxlde ln the atmosphere.
The corroslon of rebars ls a very serlous problem whlch ls very widespread and whlch ls recognlsed to be a growlng problem ln a vast number of relnforced concrete structures.
The corroslon of rebars results, at the very least, ln unslg~htly dlscolouratlon of the external surfaces of the relnforced concrete structure. However, lS corroslon of the rebars can result ln the productlon of voluminous corrosion products whlch cause spalllng or cracking of the concrete or even cause pleces of concrete to fall from the structure. In an extreme case corrosion may become so advanced as to result ln fallure o the steel rebars and collapse of the reinforced concrete structure.
Corrosion of rebars may be lnhibited or prevented by causlng the rebars to become cathodlc, that ls corroslon may be lnhlblted or prevented by 2S appllcatlon of so-called cathodlc protectlon to the rebars. There are baslcally two forms of cathodlc --protection. In one form a sacrlflclal anode ls assoclated wlth the relnforced concrete structure such that the rebars become cathodlc. The sacrlficial anode is gradually consumed durlng use and the anode necessarlly needs to be replaced perlodlcally. In another form a "permanent" anode is assoclated wlth the reinforced concrete structure and a dlrece electrlcal current is passed between the anode and the rebars whlch :35 function as a cathode. Thls latter ~orm ls the .
.

: :.... , - , ...................... ~ ... - ,................ .....

. . ,.. :., .. . .. , . .:.. -.. , ... ~,.. , ~....... , . ,. ., . " ...

3 2(~9611 so-called lmpressed current form of cathodic protection.
In thls form of cathodic protectlon the anode ls much longer lastlng than is a sacrlflclal anode and lt lS ln thls sense that the anode ls referred to as belng ~permanent".
Many cathodic protectlon systems have been proposed for use in the cathodic protectlon of rebars ln concrete, whlch systems differ malnly ln respect of the nature of the anode.
A cathodic protectlon system whlch comprlses a sacriflcial anode is descrlbed ln paper No. 41 of Corrosion 81, the International Corrosion Forum sponsored by the~ Natlonal Assoclatlon of Corroslon Engineers, ~prll 6-10, 1981, Toronto, Ontario, Canada, pages 41/1 to 41/11. The system comprlses a sacrlflclal zlnc anode, whlch may be ln the form of a rlbbon or a sheet, the zinc anode being covered by an overlay of asphaltlc concrete. A zlnc anode, whlch may be sprayed onto the concrete surface, may also be used ln an ; 20 impressed current cathodic protection system.
A cathodic protection system which comprises a permanent anode and whlch ls operated with an lmpressed current ls descrlbed in US patent 4255241. The system ; comprises flexible platlnum wire anodes which are installed in slots in the reinforced concrete, the slots belng fllled wlth carbonaceous or other conductlve backflll. The system comprises a serles of spaced apart wire anodes.
Another cathodic protectlon system which comprlses a permanent anode ls described ln European Patent Appllcatlon 0 1a6 334A. In thls publlshed patent appllcatlon there ls descrlbed a system for the cathodlc ~: protectlon of rebars ln concrete ln whlch a source of dlrect electrlcal current ls connected to the rebars, which functlon as cathodes, and to an anode whlch ls a - 4 - 2~961~

hydraullcally porous materlal whlch is permeable to water ln the llquld state and whlch ls bonded to the concrete. The hydraullcally porous materlal may be a porous ceramlc materlal, whlch may ~e ln the form of a S series of plates whlch are spaced apart from each other and whlch are electrlcally connected to each other, and the porous materlal may be an electrlcally conductlng tltanium sub-oxide or ~ormula TlOx, where x ls ln the the range 1.6~ to 1.95. The anodes, which are permeable to water ln the llquld state, allow lrrigatlon of the anode to take place such that acid whlch is formed at the anode, and thus at the lnterface between the anode and the concrete, ls removed from the concrete structure. If the acid was not removed lt could cause adverse chemical attack on the concrete.
In yet another type of cathodic protectlon system whlch comprlses a permanent anode and whlch ls sultable for cathodlc protecClon of rebars ln concrete the anode comprlses an open mesh of a fllm-formlng metal, e.g.
tltanlum, coated wlth an electrocatalytlcally active material. The mesh ls lald over a reinforced concrete structure, the anode subsequently being covered by a cementitlous layer. Such a system is described in published GB patent Appllcatlon No 2175609A.
The aforementloned cathodlc protectlon systems whlch comprlse a permanent anode are especlally sultable for use on relatlvely flat structures, for example on the surfaces of steel relnforced concrete bridge decks.
However, certaln of the systems are less sultable for use with more lrregularly shaped steel relnforced --structures, such as on the undersurfaces of reinforced brldge decks, on supportlng beams of such brldge decks, and on the plllars supportlng relnforced concrete structures. FurChermore, lnstallatlon of the cathodlc protectlon systems may not be as convenlent as m~y be zo~

deslred, for example, because of the need to cut slots lnto the surface of the concrete structure ln the case where flexible wlre anodes are to be used, or because of the need to remove the surface of the concrete in the S case where a prefabrlcated anode mesh ls to be applled to an exlsting structure. Thus, although such systems may be lnstalled reasonable easlly durlng constructlon Or a reln orced concrete structure they are not as readlly applled to such a structure after constructlon and when the need for cathodlc protectlon may have become apparent. Those cathodlc protection systems which comprlse spaced apart anodes, e.g. wires, also suffer from the.dlsadvantage that because the throwlng power of the anodes may not be very great the cathod~c lS protectlon system may have to be operated at a relatlvely high anode current denslty ln order to provlde the required cathodic protectlon of the rebars with the result that acld may be produced at the anodes at a relatlvely high concentratlon wlth a resultant adverse effect on the concrete of the structure.
G~ Patent ~ppllcatlon 2 1~0 456A describes a cathodic protectlon system whlch does not comprlse spaced apart anodes, and whlch ls sald to be sultable for use with an lrregularly shaped reinforced concrete structure, which is readlly lnstalled after construction, and whlch does not requlre the provlslon of slots or the llke ln the concrete structure. In thls publlshed patent appilcatlon there ls descrlbed a cathodlc protectlon system whlch comprlses an electrlcally conductlve fllm applied to the surface of the concrete structure and whlch serves as the anode of the system. The fllm may be applled from a palnt composltlon and thus it may readily be applled to lrregularly shaped surfaces. The palnt composltlon comprlses a llquld component, a blnder such as an epoxy 2ca96~ ~.

resln, and an electrlcally canductlve flller. The electrlcally conductlve flllers whlch are descrlbed are carbonaceous, namely, graphlte, carbon or coke breeze.
Such an anode can be expected to have good throwlng power such that the cathodlc protectlon system may be operated at current densltles whlch are lower than the current densltles whlch are requlred ln the operatlon of systems which comprlse spaced apart anodes. The anode ls also llght ln welght and, as the anode ls applled from a palnt composltlon, lt ls relatlvely easlly applled and malntalned.
The use of carbonaceous fillers, partlcularly carbon ltself, in palnt composltlons for cathodlc protectlon does however suffer from certaln dlsadvantages. For example, the carbon flller ln the applled fllm may be oxldlsed under the acldlc condltlons whlch prevall ad~acent to the fllm when the fllm functions as an anode, and also by the oxygen and chlorlne whlch are produced ln use. Furthermore, there may be carclnogenlc problems assoclated wlth the productlon and use of the carbon.
The present lnventlon relates to an electrlcally conductlng shaped artlcle, partlcularly a film, whlch ls . suitable for use in a cathodlc protectlon system, and to a compositlon from whlch such a shaped artlcle may be produced, which comprises a flller whlch ls non-carbonaceous and whlch ls chemlcally more stable .han ls carbon under the condltlons whlch prevall when the shaped artlcle is used as an anode, partlcularly as an anode ln a cathodlc protectlon system.
The present lnventlon provldes an electrlcally conducting shaped article whlch comprlses an organlc polymerlc materlal havlng a partlculate flller embedded thereln, in whlch the flller comprises an electrlcally conducting particulate tltanlu~ sub-oxlde and in whlch Z00~6~1 the flller ls present ln a proportlon such that the shaped artlcle has an electrlcal conductlvlty of at least 0.01 ohm-' cm-l.
The lnventlon also provldes a composltlon S sultable for use ln the productlon of a shaped artlcle as descrlbed, whlch comprlses a homogenous mlxture of an organlc polymerlc materlal or a precursor therefor and a partlculate flller, whlch flller comprlses an electrlcally conductlng partlculate tltanlum sub-oxlde.
In the composltlon the mlxture of organlc polymerlc materlal or precursor therefor and flller ls homogenous, that ls the flller ls evenly dlstrlbuted throughout the ~omposltlon, and the proportlon of tltanlum sub-oxlde to organlc polymerlc materlal ln the lS composltlon ls such that the electrlcal conductlvlty of the shaped artlcle produced from the composltlon ls at least 0.01 ohm~l cm-~.
The shaped artlcle may be used ln a variety of appllcatlons but it wlll generally be used as an electrode. When thc shaped artlcle ls uscd as an electrode it may be used ln appllcations other than as an anode ln a cathodlc protection system. However, a preferred form of shaped artlcle ls a fllm, especlally . where the shaped artlcle ls to be used as an anode ln a `~ 25 cathodic protection system, and ln a preferred embodiment of the composltlon of the inventlon, whlch ls --~particularly suitable for use ln the productlon of such a fllm, the composltlon is a fluld composltlon, particularly a fluld composition having a consistency sultable for appllcatlon as a palne, whlch comprises a liquid component, an organlc polymerlc materlal or a precursor therefor dlssolved or dlspersed thereln, and a particulate filler dlspersed thereln whlch comprlses an electrlcally conductlng tltanlum sub-oxlde.

_- 8 - 2~ ~6 1~

Further embodlments of the lnventlon include use of a shaped artlcle as descrlbed, partlcularly when ln the form of a fllm, as an anode ln a cathodic protectlon system, and a cathodlc protectlon system whlch comprlses a concrete structure havlng steel relnforclng bars or wlres embedded thereln, and a shaped artlcle as described, partlcularly a fllm, ln electrlcal contact wlth the structure.
We are aware of publlshed Japanese Patent Appllcatlon No 61-106414 ln whlch there ls descrlbed conductlve flne powders of titanlum oxldes, for example sub-oxldes of formula TlOx ln whlch x is ln the range 1.5 to 1.9, and use of the flne powders as conductlvity lmparting agents for supports such as electrophotographs or statlc recorders, as antlstatlc agents for fllms, flbres and magnetlc tapes, or as black plgments for plastlcs, palnts, lnks and cosmetlcs. There ls no dlsclosure ln thls publlshed applicatlon of a shaped artlcle such as a fllm havlng an electrlcal conductlvlty as hlgh as 0.01 ohm-' cm-', whlch ls the mlnlmum electrlcal conductlvlty of the shaped artlcle of the present lnventlon, nor ls there any dlsclosure of a composition from whlch such a shaped artlcle could be produced, nor ls there any disclosure in thls publlshed appllcatlon of use of the tltanlum sub-oxlde as or as part of an anode, e.g. as an anode ln a cathodic protect~on system. We are also aware of European Patent Appllcatlon 0047595-A ln whlch there ls descri~ed the use of an electrlcally conductlng tltanlum sub-oxlde TlOx, ln whlch x ls 1.55 to 1.9, as a ground bed anode ln a cathodic protectlon system, as a ground bed electrode ln the protectlon o~ oll well structures, and, when ln the form of powdered TlOX, as a conductlng back-fill for ground bed electrodes. There ls no dlsclosure ln thls appllcatlon of a shaped artlcle of an ''ti~

9 21~91611 organlc polymerlc materlal, partlcularly a fllm, contalning a tltanlum sub-oxlde, nor ls there any suggestlon of the use of such a shaped artlcle as an anode, e.g. as an anode ln cathodic protectlon.
The organlc polymerlc materlal ln the shaped article and ln the composltlon of the lnventlon may be, for example, a polyolefin, e.g. polyethylene or polypropylene, or polystyrene, or a halogen-contalnlng organlc polymerlc materlal, e.g. polyvlnyl chlorlde or a chlorlnated olefln polymer, e.g. a chlorlnated rubber.
The organlc polymerlc materlal ln the compositlon may be ln the form of a precursor therefor, that ls in the form of a polymerlsable materlal, for example a thermosettlng materlal, e.g. a polyester resln or an epoxy resln.
However, the nature of the organlc polymerlc materlal wlll depend to some extent on the lntended use of the shaped artlcle. Where, for example, the shaped article ls to be used as an anode ln cathodlc protectlon, partlcularly o~ rebars ln concrete, lt ls deslrable that the organlc polymerlc materlal ls reslstant to attack by the chemlcals produced at the anode durlng operatlon o~
the cathodic protectlon system, e.g. acid, chlorlne and oxygen. For thls reason preferred organlc polymerlc - materlals are epoxy and polyester reslns, and halogen-contalnlnq organlc polymerlc materlals, partlcularly fluorlne-contalnlng organlc polymeric materials. As ln ùse the shaped artlcle may be exposed ,- , I ~ . ! ' -to atmospherlc condltlons, e.g. when used as an anode ln a cathodlc protectlon system, lt ls desirable that ~;~ 30 the organlc polymerlc materlal ls reslstant to such condltlons, in partlcular lt 19 deslrable that the organlc polymerlc materlal ls stable In prolonged sunllght.
The shaped artlcle and the composltlon of the 35 1nventlon contaln an electrlcally conductlng partlculate 2(~ 6~

tltanlum sub-oxlde, that ls a particulate tltanlum sub-oxlde of formula TlOx ln whlch x ls less than 2.
Any value of x may be chosen provlded that the tltanlum sub-oxlde ls electrlcally conductlng, and provlded that ln the shaped artlcle lt ls posslble to achleve the deslred electrical conductlvlty. A mixture of tltanlum sub-oxldes having differing values of x may be used.
S~ecl~lcally, x ln the formula ~lOx may be ln the range 1.5 to 1.9, although x may be outslde thls range, partlcularly less than 1.5. A preferred value of x ls ln the range 1.67 to 1.9 on account of the good -electrlcal conductlvlty of the tltanlum sub-oxlde and the reslstance o~ the tltanlum sub-oxlde to attack by corroslve chemlcals, e.g. aclds. The tltanlum sub-oxlde may be predomlnantly Tl,O, and/or Tl,O,.
The partlcle slze of the titanium sub-oxide may vary over a wlde range but ln general the partlcles wlll have a size of less than 100 mlcrons, partlcularly less than 50 mlcrons. A preferred partlcle slze ls less than 10 microns or even less than 1 mlcron. The partlcle slze may be of the order of 0.1 micron or even less.
e.g. as low as 0.01 mlcron. The titanlum sub-oxide may comprlse a mixtue of partlcles of dlfferlng slzes.
The electrlcally conductlng particles of titanium sub-oxlde may have a varylng compositlon, that is the value of x ln the formula TlOx may vary wlthln a given partlcle and between dlfferent particles. Indeed it ls not necessary that the whole of a partlcle comprises -electrlcally conducting tltanlum sub-oxlde. All that ls requlred ls that the partlcles have at least a surface of electrlcally conductlng tltanium sub-oxlde; the lnterlors of the particles may comprlse electrlcaIly non-conducting tltanium dioxide. However, lt is most convenlent, for the particles to comprlse electrically ~35 conducting tltanium sub-oxide thsoughout the partlcles.

X0~61~l The proportlon of tltanlum sub oxlde to organlc polymerlc materlal ln the shaped artlcle, and ln the composltlon, should be such that the shaped artlcl~ has an electrlcal conductlvlty of at least 0.01 ohm~cm~'.
It ls generally preterred that the shaped article ha~ a hlgh electrlcal conductlvity, for example, ln order that a shaped artlcle ln the form of a thln film may be partlcularly sultable for use as an anode ln a cathodlc protectlon appllcatlon, and for thls reason lt ls preferred that the shaped article has an electrlcal conductlvity of at least 1 ohm-l cm-l, more prc~erably at least 10 ohm~' cm-'. The proportlon of tltanlum sub-oxlde whlch~ls requlred ln order to produce the desired electrlcal conductivlty ln the shaped artlcle will depend on the partlcle slze of the tltanlum sub-oxlde, on the shape of the particles, and on the electrlcal conductlvlty of the partlcles. ~owever, ln general, the proportlon of tltanlum sub-oxlde wlll be at least 10~ of tltanlum sub-oxlde by volume of organlc polymerlc material plus tltanlum sub-oxlde, preferably at least 20% by volume. The shaped article, and the composltlon, may contaln as much as B0% of tltanl~n sub-oxlde by volume of organlc pclymeric materlal plus tltanlum sub-oxlde.
: 25 In order to produce a shaped article of glven electrlcal conductlvlty the proportlon of tltanium sub-oxlde whlch ls required will be smaller where the partlcles are needle-llke or plate-llke in shape than where the partlcles are of a more spherlcal shape.
:3~ Thus, in a shaped artlcle contalnlng a glven proportlon .o~ tltanlum sub-oxide the electrical conductlvlty wlll be :~reater where the particles are needle-l~ke or ~late-llke as the area of contact.between ad~acent partlcles will be greater than is.the case where the partlcles.are more spherlcal ln.shape.

~ ~ ~9 The shaped artlcle and the composltlon may contaln partlculate flllers ln addltlon to tltanlum sub-oxlde. These addltlonal flllers may be selected ln order to lmpart sPeclflc propertles to the shaped S artlcle, ~or example, colour or relnforcement. The addltlonal flllers should be reslstant to the condltlons encountered durlng use of the shaped artlcle. - -The electrically conductlng tltanium sub-oxlde may be made, for example, by reductlon of partlculate tltanlum dloxlde. For example, partlculate tltanlum dioxide may be reduced by heating at elevated temperature ln the presence of a reduclng gas, e.g.
hydrogen or carbon monoxlde. ~lternatlvely, or ln addition, tltanlum dioxlde may ~e admlxed wlth a solld reduclng agent, e.g. titanlum, or carbon, and heated at elevated temperature. The reductlon should be effected untll the deslred value of x in the formula TlOx has been achleved. An elevated temperature of the order of 1000C may be ~equlred ln the reductlon process durlng whlch some slnterlng of the partlcles may take place.
Ir such slnterlng does take place the reduced material may subse~uently be ~round ln order to produce the deslred partlcle slze of tltanlum sub-oxlde. The ;` productlon of electrlcally conducting tltanium sub-oxldes is descrlbed, for example, in the aforementioned published European Patent Application No. 0047595 and published Japanese Patent Appllcatlon No. 61-106414. After productlon of the partlculate titanium sub-oxide it may be useful to clean the particle surfaces to remove lmpurlties therefrom.
The composltion of the lnventlon which comprises a homogenous mlxture of an organlc polymerlc material or precursor therefor and a partlculate electrically conductlng tltanlum sub-oxlde, optlonally a llquld component, and optlonally an addltlonal partlculate - 13- 2(~C~61~L

flller, may be produced by any convenlent mlxing process, although the process to be used wlll depend at least to some extent on the nature of the components of the composltlon and partlcularly on the presence or absence of a llquld component. The mlxing process whlch ls used should result ln production of a homogenous composltlon. Where the composltlon does not contaln a llquld component the composltlon may be mixed by processes whlch are conventlonal ln the plastlcs and rubber processlng art, for example, by use of a bladed mlxer, especlally such a mixer whlch lmparts high shear to the composition, by use of a twin-roll mlll, or by use~of a screw extruder. Shaplng processes whlch may be used to produce the shaped artlcle of the lnventlon lnclude calenderlng, as on a twln roll mlll, compresslon mouldlng ln a mould, ln~ectlon mouldlng and extrusion. Where the composltlon of the lnvention contalns a llquid component the mlxlng process chosen wlll depend to some extent on the proportlon of solld components ln the compositlon, that ls on the proportlon Or organlc polymeric materlal, tltanium sub-oxide, and optlonal addltlonal flller. However sultable mlxing processes will generally be ball-mllllng and mixing in a bladed mlxer. Shaping of the composition may be by ; 25 castlng lnto a mould, or by appllcatlon of the composltlon to the surface of a substrate by a palntlng technlque, for example, by applylng the composltlon by brush, roller, ot spray, followed by removal of the llquid components e.g. by causlng or allowlng the applled coatlng to dry. A fllm of lncreased thlckness may be bullt up by appllcatlon of multlple coatlngs of the composltlon to the surface of a substrate. Where the composltion of the lnventlon comprlses a llquid component the organlc polymerlc materlal or precursor therefor should be dlssolved in or dispersed ln the .:.: . .. , , . , .. , . . , ......... .. , - .. .. . . ............................ .

. . .- ~ ,. ,.. .. - . . ~ ., .. .. ,- .. ,, , , ~

- 14 - ZC~9~1~

~lquid component of the composltlon, and the particulate titanium sub-oxlde, and optlonal additlonal partlculate flller, should also be dlspersed ln the llquld component. Dlsperslon may be asslsted by use of sultable dlsperslng agents.
Where the compositlon of the lnventlon comprlses a ll~uld component the pro~ortlon of solld components in the composltlon wlll depend to some extent at least on the deslred method of shaplng of the composltlon whlch ls to be used ln order to produce the shaped artlcle.
Thus, where lt is desired to produce a fllm by a palntlng technlque the composltlon ls sultably relatlvely fluld and ln thls case the composltlon may, for example, contaln no more than 50% by volume of solld lS components, although lt ls deslrable that lt does contaln at least 10% by volume of solld components. On the other hand where the composltlon ls to be shaped by compresslng the composltlon lnto a mould the composltlon may contaln more than 50~ by volume of solld components.
The aforementloned proportlons are given by way of example only and are not lntended to be llmiting.
Where the compositlon contains a precursor for the organic polymeric material the precursor may be converted to the polymeric materlal after production of the shaped article. For example, where the precursor ls in the form of a polyester resln or an epoxy resln the precursor ln the shaped artlcle may be cured, for example by heatlng ln the presence of a suitable cross-linking agent, or hardener, respectlvely, whlch may be present ln the composltlon from whlch the shaped article has been produced.
A further embodlment Or the lnventlon ls the use of a shaped artlcle as descrlbed as an anode ln a cathodlc protectlon system. The cathodlc protectlon system comprlses a concrete structure havlng steel - 1 s - 2~(~96~

relnforclng bars or wlres embedded thereln and whlch are to be protected, and the shaped artlcle as descrlbed ln electrlcal contact wlth the structure, and a source of dlrect electrlcal current connected to the shaped S artlcle and to the relnrorclng bars or wlres, ln operatlon the bars or wlres whlch are to be protected belng cathodlc snd the shsped srtlcle belng anodlc. In a partlcular form of thls embodlment of the lnventlon the cathodlc protectlon system comprlses steel reinforclng bars or wires embedded in a concrete structure, a shaped artlcle ln the form of a fllm as hereln descrlbed on the surface of the concrete structure, and ~a source of dlrect electrlcal current connected to the relnforclng bars or wlres and to the -fllm, ln operatlon the bars or wlres belng cathodlc and the fllm anodlc. The fllm ls not ln dlrect contact wlth the bars or wlres otherwise an electrlcal short clrcult will occur.
In order to provlde protectlon to substantlally the whole of the rebars ln the concrete structure the fllm should be applled to those parts of the structure ad~acent to the rebars so that there ls only a short ~-path for the electrlcal current to travel between the fllm and the rebar.
In order to provide good dlstribution of electrlcal current to the fllm anode ln the cathodlc protectlon system the fllm may be ln electrlcal contact wlth a current dlstrlbutlng wlre, or a plurallty of such wlres. The wire or wires may be embedded ln the fllm and ln operatlon they wlll be connected to a source o dlrect electrlcal current. ~he wire or wlres may be made of platlnum or other suitable chemlcally lnert electrlcal conductor.
A sultable thlc~ness of the fllm whlch functlons as an anode ln the cathodic protectlon system ls 50 ris~

- 16 - Z~96~ ~

mlcrons to 1000 mlcrons although the fllm may have a thlckness outside thls range. A preferred fllm thlckness ls ln the range 150 to 500 mlcrons.
The fllm ls preferably porous so that products whlch are produced ln operatlon of the cathodlc . protection system, and particularly gaseous oxygen and chlorine produced by electrolysis of water and sodium chlorlde respectlvely, may escape from the concrete structure. The fllm ls thus preferably not 80 thlck as to be lmpervlous to such gaseous products, and lt ls preferably also permeable to water vapour ln order that a ~ulld-up of water at the concrete fllm interface may be prevented.
The composition of the invention, may comprise other components, e.g. colourlng matter, ln order that the fllm produced therefrom may have a deslrable appearance. Alternatlvely, or ln addltion, the fllm may be given a sultable top coat.
An embodlment of the cathodlc protectlon system of the lnventlon will be described with reference to the accompanying figure which shows in cross-sectlon a concrete beam 1 having an upper surface 2 and a lowcr surface 3, and containing steel relnforcing bars 4,5. -~ The upper surface 2 and the lower surface 3 of the beam - 25 1 are covered by coatlngs ln the form of films 6,7 respectlvely whlch comprlse partlculate titanlum - -sub-oxide in an organlc polymeric material. The fllms are electrlcally conductlng and have embedded therein platinum wires B,9. The wires B,9 are connected to the posltlve terminal of a rectifier 10 via leads 11, 12, ~ -the steel relnforclng bars 4, 5 are connected vla leads 13, 14 to the negatlve termlnal of rectlfler 10.
In operatlon a small dlrect electrlcal current ls passed between the fllms 6, 7 and the relnforclng bars 4, 5 so that the films 6, 7 are anodic and the ~ "~ ," ,", ~ . - , .. ,", ,, 17 . 2~096~
-relnforclng bars 4, 5 are cathodlc in order to prevent corroslon of the relnforclng bDrs 4, 5.

Claims (12)

1. A fluid composition suitable for use in the production of a film, and having a consistency suitable for application as a paint, comprising a liquid component, an organic polymeric material or a precursor therefor dissolved or dispersed therein, and a particulate filler dispersed therein, wherein said particulate filler comprises an electrically conducting titanium sub-oxide of formula TiOx where x is less than

2, and wherein said titanium sub-oxide is present in a quantity such that said film will have an electrical conductivity of at least 0.01 ohm-1 cm-1.

2. The composition of claim 1, wherein said film will have an electrical conductivity of at least 10 ohm-1 cm-l.

3. The composition of claim 1, wherein the proportion of titanium sub-oxide is at least 10% of titanium sub-oxide by volume of said organic polymeric material plus said titanium sub-oxide.

4. The composition of claim 3, wherein said proportion of titanium sub-oxide is at least 20% of titanium sub-oxide by volume of said organic polymeric material plus said titanium sub-oxide.

5. A composition as in claim 1, wherein said titanium sub-oxide is of the formula TiOx where x is in the range 1.67 to 1.9.

6. A composition as in claim 5, wherein said titanium sub-oxide is predominantly Ti4O7 and/or Ti5O9.

7. An electrically conducting shape article comprising an organic polymeric material having a particulate filler embedded therein, wherein said filler comprises an electrically conducting particulate titanium sub-oxide of the formula TiOx, where x is less than 2 and wherein said filler is present in a proportion such that the shaped article has an electrical conductivity of at least 0.01 ohm-1 cm-1.

8. The electrically conducting shaped article of claim 7 wherein said shaped article is a conductive film.

9. The electrically conducting shaped article of claim 7 wherein said organic polymeric material is selected from the group consisting of epoxy resins, polyester resins and halogen containing organic polymeric materials.

10. The electrically conducting shaped article of claim 7 wherein said titanium sub-oxide is of the formula TiOx, where x is in the range 1. 67 to 1.9.

11. The electrically conducting shaped article of claim 10 wherein said titanium sub-oxide is predominantly Ti4O7 and/or Ti5O9.

12. A cathodic protection system for rebars comprising a concrete structure having steel reinforcing bars or wires embedded therein, an electrically conductive film on the surface of said concrete structure and a source of direct electrical current connected to said reinforcing bars or wires in a manner such that, in operation, said film is anodic and said bars or wires are cathodic, wherein said conductive film comprises an organic polymeric material having distributed therein a titanium sub-oxide particulate having the formula TiOx, where x is less than 2, the sub-oxide being present in a proportion such that the electrical conductivity of said film is at least 0.01 ohm-1 cm-1.