CA1091862A

CA1091862A - Vermiculite rigid foam

Info

Publication number: CA1091862A
Application number: CA276,004A
Authority: CA
Inventors: Denis G.H. Ballard; Colin S. Cundy; Graham R. Rideal
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1976-04-12
Filing date: 1977-04-12
Publication date: 1980-12-23
Also published as: FI771104A; ZA772095B; SE426313B; DK158377A; AU2414477A; FR2348171A1; AU515006B2; NO145688C; NO771224L; DE2716152C2; NO145688B; NL7703870A; NO810499L; NL174452C; NZ183840A; SE7704045L; DE2716152A1; BE853367A; JPS52128918A; GB1585104A

Abstract

ABSTRACT OF THE DISCLOSURE

A process for the production of a rigid foam of vermiculite having a cellular structure composed of lamellae, the process comprises producing a suspension of the vermiculite lamellae in a liquid medium, gasifying the suspension to form a froth and removing the liquid from the froth by evaporation. The rigid foam is a useful heat resistant and heat-insulating material.

Description

lwl862 This invention relates to inorganic foams and ln particular to rigid foams of minerals.
, Accordlng to the present invention there ls provided a rigid foam comprising an inorganic S cellular structure composed of lamellae of , vermicullte.
Vermicullte ls a phylloslllcate mineral i.e. one having a layer structure. Vermlculite may be swollen by the action of aqueous salts and thereafter the structure ~" broken down (i.e. delaminated) by mechanical action . ~
into extremely thin lamellae. Other phyllosilicate , . , minerals for example hydrobiotites, or chlorite-vermlculltes also contain a substantial proportion of ,~,', 15 vermlculite layers and these also may be exfoliated ~,' ln the same or similar manner. These minerals whlch '`' contain vermiculite layers also give 'rise to thin . ,;, .
lamellae and it is to be understood that they are ;~ inc}uded ln the present lnventlon. It ls preferred ~' 20 to use the lame,l}ae"~f venm~culite,ltself for the formation of the inorganic foam of this invention.
Accordlng to a preerred aspect of the present ,- inventlon there ls provided a rlgid foam ', comprising a oellular structure having the cell walls thereo~ composed of overlapping indlvidual vermiculite lame~lae adhering together by mutually attractlve , force~. -~,` The cellular structure extends continuously and ".
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substantially uniformly ln all dimensions throughout the volume of the foam formed. The overlapplng lamellae constitute the boundary walls of each cell in the cellular structure ~o that, in the structure as a whole, the indlvldual lamellae are present ln all possible orlentatlons with respect to a glven plane of reference. Thus, the foam of the present lnvention may be dlstinguished from the heat exfollated vermicullte granules w~ich have been produced hitherto. In these heated granules a low denslty form of the mlneral is ; produced wherein, within each granule (which was a separate particle before heat-exfoli~atlon) the layers of the mineral are forced apart during the heatlng proces~ but remaln substantlally parallel to oneanother Furthermore, such a structure exists only wlthin each granule and does not extend to a co~tinuous structure between granules. This known form of low-density vermiculite is not included within the scope of ,~
the present invention.
The aforementloned individual lamellae, which may alternatively be termed platelets or flake-~, - possess for example a small dlmension of less than 0.5~m , preferably less than 0.05~m,especially less than 0.005~m and have approximately similar length or . , :
breadth dimensions of at least a hundred, preferably at least a thousand,times greater than ~hat of the .~ .
; small dimension.
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. - , '~ ' ,, : ' ' ' ' . ' The density of the foams of this inventlon lies in the range less than 0.5 g/ml and usually less than 0.15 g/ml and for especlally "light" foams the-density may be for example as low as 0.01 g/ml.
The density may be varled in several different ways, for example by incorporatlng different amounts of gas into the su~pension or by altering the solids content of the su~penslon. For a low den~lty foam the solids content may be suitably from S to 20% by weight whereas if a hlgher density foam is requlred the solids content may be lncreased to 30% w/w or more.
According to a further aspect of the present inventlon there is provided a proceQs for producing a rigid vermiculite foam comprislng the productlon of a suspenslon of vermiculite lamellae ln a liquld medlum,preferablj an agueous liguid medlum~ ga~ification of the ~u~pension to form a froth and removal of the liquld medlum from the froth by evaporation.
The swelllng and delamlnatlon of vermlculite to give aqueous dlsperslons of vermicullte lamellae has been described in several publications for example UK Patent Speciflcations Nos. 1,016,385; 1,076,786 and 1,119,305 and by Baumeister and Hahn "Micron"
, .
;:
` 7 247 (1976): the procedures dlsclosed therein are appllcable to the present invent~on. However for the formation of foams we prefer to have a surface actlve agent or a foaming agent present in the suspension prior to the gaslflcatlon of the suspension to form . ~ .
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109~86~

the froth;which term includes an expanded form of the whole suspension.
It i8 advantageous for the surface actlve agent or foaming agent to be one which ls capable of ; 5 penetrating the structure of the mlneral and thus will 3well the mlneral and allow delaminatlon to occur.
We especially prefer to use a catlonic organic salt which ls capable of undergolng lon exchange wlth the catlons present in the vermlcullte layers. Cationic surface actlve agents which are eqpecially favoured are the hydrocarbon substltuted ammonium group of surfactants. For example the substitution may be of from l to 4 hydrogen atoms on the ammonium cation by alkyl, aryl, alicyclic, or heterocyclic groups.
Examples of préferred cationic aalts are n-butyl ammonlum chloride isobutyl ammonium chloride isoamyl ammonium chloride cetyl pyrldlnium bromide ,.
cety~ trimethyl ammonium bromide .. ; ,

2-ethyl hexyl ammonium chloride dodecyl ammonium chloride , lysine monohydrochloride ornithine monohydrochloride and polypeptides in cationic form. Other types of ... .
foaming agents or foam-producing surfactants~may also be employed as additives to the suspens~on of vermiculite ~`~ lamellae,as adjuvants to other swelling agents e.g.
, .. . . . .
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alkali metal chlorides orin combination with the aforementioned cationic salts, for example long-chaln aliphatlc alcohols (e.g. cetyl alcohol), alkyl - sulphate salts, le.g- sodium lauryl sulphate) N-acyl sarcosinates and long-chain aliphatlc amine oxides ~e.g. oleyl dimethyl amine N-oxide).
An alternative class of foaming agents which may be used with advantage a~ additlves to the suspension of vermicullte lamellae are the protein type foaming agents for example water-soluble proteins (such as albumin or gelatln) or water qolubilised protein derlvatives such as hydrolysed soya bean and hydrolysed blood or feathers.
The liquid medium, if aqueous, may contain water-miscible organic liquids for example the lower alcohols or acetone. Alternatively the foam may be produced in a non-aqueous medium using suitably modified vermiculites -,~ as described in UK Patent 1,076,786.
. The gasification process may be performed by means of a release of gas or vapour ln the suspension of . .
vermicullte lamellae preferably one whlch ls substantially inert to the aqueous suspension for example air, nitrogen, argon, carbon dioxide,a hydrocarbon, chlorocarbon, .;~
-` fluorocarbon or chlorofluorocarbon. The gaslfication may - more conveniently be performed by mechanically entraining the gas in the suspension by rapid agitation -for example by rap~d churnlng or whisking of the suspension.
, Alternatively the suspension may be rapidly heated -~;
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and the foam produced by gasification due either to steam produced by evaporation of water or to liberation of gas dissolved ln the sample.
By the term rigid foam we mean a two phase - 5 dispèrslon of gas in solld, the solld phase belng an essentlally contlnuous lnorganlc cellular structure.
Small quantities of organlc materials may be present ln the foam, whlch may be elther dellberately added or lnadvertently present, but the organic materlal is not fundamental to the coheslon of the cellular structure although it may usefully modlfy the properties thereof.
On removal of water rom an aqueous disperslon of vermicullte lamellae, the lamellae come together to form a coherent fllm. Accordlngly the cell walls of the cellular structure of the present inventlon derive thelr mechanical strength largely or wholly from the self-adheslon of the flakes when water ls removed. The resultlng structure ls a non-brittle foam i.e. under atress the structure may deform without crumbllng.
The cellular vermlcullte is a useful heat-reslstant and heat lnsulatlng materlal whlch may be cast as a foam-fllllng for cavltles and voldæ or whlch ., - - may be used as a coatlng for the outslde of materials for example wood or steelwork,in both cases the vermlculite foam acting inter alia as a fire-protective layer. The vermiculite foam may be produced as a slab stock for ;.
~ubse~uent fabricatlon or other lamination. An lnner sandwich of vermiculite foam as hereln provided, , . , ., ~

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optionally bounded for example by sheets of wood-veneer, paper, asbestos, mi ca or plastic ~ or by vermiculite sheet, forms useful decorative construction panels: the vermiculite foam may be sandwiched between plaster-board or sheets of thermo-setting resin e.g.
melamine resin. The fore-going structures form useful fire-reslstant and/or souna insu~ating panels for the building industry, panels which may bé maintained at temperatures of ca.1000C without disintegration.
Sheets of vermiculite foam may be applied as facings to polyurethane foam panels by conventional lamination techniques in order to improve the fire resistance of the polyurethane foam core. The froth i.e. the gas1fied suspenslons before drylng may be con~eniently ~-~ 15 used to bond together previously formed ~ermiculite , ~
- structures e.g. sheets or slabs of foam already in drled form and so cement ~everal sheets together and build up larger structures. In a similar way the heat-,~
exfoliated vermiculite granules may be cemented together by means of thé same froth and thus a composite -structure is formed consisting of the foam of the .
present invention as a continuous cement between granules of heat-exfoliated vermiculite.
For some applications the vermlculite foam may require a water-proofing treatment for example a treatment with ammonia a~ described in our copending Canadian application Serial No. 300,521, ~iled April 5, ;~:

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The inventlon is lllustrated by the following Examples.
Exam~Ie~
1 Kg of vermiculite ore of South Africa origin known as Man~doval micron grade wa~ refluxed in 5 litres of saturated sodium chlorlde solutlon for 30 minutes.
Excess brine was decanted off and the vermlculite washed ln 5 litres of distilled water. This was followed by five separate washings of the solid with one litre aliquots of distilled water on a Buchner filter funnel.
The wet cake of vermiculite was returned to the - refluxing vessel and refluxed for two hours with 1.25mole of butyl ammonium chloride made up to five litres , volume with distilled water. After reflux, a washing procédure as descrlbed above was carried out durlng whlch a rapid expansion of the vermiculite to about six times its original volume occurred. After standing overnlght the supernatant ll~uld was decanted off and the 6 litres of swollen vermiculite ore was divided into two portions of approximately 3 lltres each and - each made up to 4 litres with distllled water ln a large beaker.
-; Each suspension was then sheared for one hour , .
using a rotary-bladed mixer dlpping into each beaker and working at 6,500 rpm. The suspenslon was maintained -near to ambient temperature by a spray of coId water , ` to the outside of each beaker. Air became entrained in the suspension of the lamellae during this process ,'~.;
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,, loals6z and a froth appeared on the surface of each suspension.
The depth of froth lncreased when the suspension was allowed to stand for 30 minutes and ca. 600 ml of foam was scraped from the suspension in each beaker.
S The foam was placed ln a mould and drled ln a well ventllated oven at 60C. A hard foam of vermiculite having a density of 0.08 g/ml was removed from the mould. The foam had adopted the peImanent shape of the mould and had acqulred a skin film o~
vermlcullte over the surface.
'1 The suspenslon of lamellae was churned at high-speed again for a period of 60 minutes and allowed ~o stand for a further 30 minutes whereupon a fresh '~ quantlty of froth appeared. The process was repeated several times and ~hereby several batches of foam wers made from the same suspen~ion. Thsse were combinsd and removsd to a mould and dried in the oven to form a solld foam of denslty 0.08 g/ml and average cell diameter 0.7 mm ,:
~ 20 Example 2 -,:
; A sample of ground vermicullte ore from the ."
~,, deposlts ln North America (Zonollte No 4) was refluxed ,` for 30 minutes in a saturated solution of sodium chloride and thoroughly washed with several portions of distilled , .. ..
- 25 water. The particles were then given a two hour reflux in an aqusous solution of n-butyl ammonium chloride -followed again by a thorough washing in distilled water.
During this second washing (which may last conveniently .
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10~1862 -between a few minutes and several hours) a pronounced swelling of the particles occurred to approx~mately six times their original wet volume. ThlS was then a sample of expanded vermlculite.
The weight ratio of the aqueous suspension of the swollen vermiculite was adjusted by removal of water by filtration until the weight ratio was approximately 10% vermicullte sollds to 90% liquid water. The suspension was placed in a high-shear mixer (manufactured by Greaves Limited) which had a blade capable of rotating at 6,500 rpm and the suspension was mechanically milled or macerated for a period of 10 minutes. During this process air was entrained in , the suspension and when the rotation of the blade was ; 15 - stopped and the suspension allowed to stand for 5 ~, minute~ several inches depth of froth was present ' above the suspenslon. The froth was taken off ~ith a knife and spread on a tray. The tray containing the froth ~ was placed in a well-ventilated oven at ca. 60C and ,t,~,., 20 and the water removed by evaporation,optionally aided , ,.: . ..
by a fan or extractor in the oven. When dry the foam , could be removed from the tray as a solld cellular vermiculite structure having a density of less than ~, 0.1 g/ml and average cell diameter of 0.5 mm.
-~ 25 Example_3 ~~~- -~ A sample of Zonolite No 4 ver~iculite was treated . . ~, as described in Example 2 the suspension being milled for 60 minutes. The density of the resultant foam was . ., .:
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109~86Z

0.035 g/ml and the average cell diameter was 0.5 mm.
ExamPle_4 _ --South Afrlcan vermiculite was expanded as described in the flrst paragraph of Example 1. After ad~ustlng the solids content of the swollen vermiculite suspension to 20~ w/w it was stirred until homogeneous and subjected to a single pass through a mill of the type known as a "rotor-in-stator" mill, runnlng at a speed of 20,000 rpm. Before passing into the shearing zone of the mill, alr was metered into the suspension at a rate of 10 litre/min. The whole suspension was converted to a thick froth which on standing overnight separated out into a lower liquid layer containing some of the larger sized vermlculite particles and another layer of wet vermicullte froth. The froth twhlch was observed to be stable for several weeks in the wet stage) was collected and dried in a wire-mesh , . . .
-- mould in a well ventilated oven at 80~. A slab of foam of dimensions 12" x 12" x 2" was formed and was ; 20 found to have the following properties:
Density 0.22 g/ml Compressive strength 0.11 MNm 2 Thermal conductivity 0.060 Wm -lR-% closed cells 12%
.
~ 25 Average cell diameter 1.5 mm .
Example 5 _

3 Kg of American vermlculite was expanded in a similar manner to that described in the flrst paragraph ; of Example 2.
.

~i. - 12 -'. . , The swollen vermiculite was then divided lnto 9 batches, each of whlch was milled for 45 minutes ln a Greaves mill, in order to produce suspensions of delamlnated vermlculite. The 9 batches were then ccmbined and the larger particles of vermiculite removed by passing the suspension through a 50 ~m sleve. The resultant "classified" suspension which contained approxlmately 5% solids by weight, was evaporated on a large heated tray to increase the solids content to 20%. Air was then beaten into the thick suspension using a culinary mixer, using the whisking attachment. An approximately two fold volume .
increase of the suspension took place and a small bubble size ~ wet foam was produced from the whole " .
'h. 15 suspension. The foam was spread on a heated tray and ~ dried overnlght to form a board 6' x 4' x l/4". The .. . .
;; dried foam had the following properties:
~ Density 0.12 g/ml ; Compresslve strength 0.30 MNm 2 , Thermal conductlvity 0.060 Wm lK 1 % closed cells 41%
Average cell diameter 0.2 mm ExamPle 6 3 Kg of South African vermiculite was expanded as described in the first paragraph of Example 1.
-~hen the expansion was complete the supernatant water ~, ,~
was decanted off and the swollen vermiculite milled in 750 ml aliguots in a domestic liquldiser for lO

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1~)9~862 minutes. The thlck, but pourable suspension was found to have solids content of 20% w/w. The suspenslon wa~ foamed using a culinary mixer as described ln Example 5. The foam was then dried in an oven at 90C overnight to form slabs of dlmensions 24" x 12" x 1/4". Several slabs were laminated using wet froth and a larger slab of dimensions 12"
x 12" x 1~" was formed and dried ln an oven. The - physical properties of the larger slab were measured as Density 0.07 g/ml Compressive strength 0.05 MN~ 2 Thermal conductivity 0.048 Wm lK 1 % closed cells 6%
Average cell dlameter 0.5 mm Exam~le 7 A non-foamed su8pension of American vermiculite (20% w/w solids con~ent~ was prepared as described in Example 5. In this case the suspension was not aerated but was placed in an oven at 140C for 3 hours, causing , 20 rapid evolution of water vapour which produced a dry foam of denslty 0.10 g/ml.
., Example 8 170 g of South African vermiculite suspension " prepared according to the method described in Example 5 , -. 25 the solids csntent adjusted to 13% w/w and placed in an "Aerosol" container which was adapted to be pressurised. A mixture of 18 g of dichloro difluoromethane and 12 g of dichloro tetrafluoroethane was forced under ' : .

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109186~

pressure into the Aerosol can and mixed with the vermiculite paste. upon activation of the ejection nozzle of the can a wet froth was applied to a tray and dried in air over a period of 24 hours. The S rigld foam of vermiculite produced was observed to have a very fine pore size (average diameter of bubbles -~ = 350~m) and a density of 0.05 g/ml.
Example 9 South African (Mandoval "micron~ grade) vermiculite (1 Kq.) was refluxed for 10 hours in a mixture of water -(4 -~.) manganese dichloride tetrahydrate (130 g.) and concentrated hydrochloric acid (0.25 ml.). The product was washed with water and then made up to a total volume ;s o~ 20 1. wlth water. Hydrochloric acid ~75 ml. lN
~, 15 801ution) and hydrogen peroxide (2 l. of 30~ solutlon) ' were then added and the stirred mixture warmed to 60C
for ~ hours whereupon the vermicullte expanded to take .~, up most of the llquld present. The mixture was then cooled, flltered, washed with water, and made up , 20 to lO l. wlth added fresh water. The resulting - suspension was divided lnto 4 equal batches and each sheared for one hour at 6500 rpm ln a 5 1. vessel wlth ~- a Greaves H5-Series mlxer (Mark III). The combined suspension was then diluted to 16 l. with water and . .
classlfied by passage through a sleve o aperture : ;,j .'! size 50 ~m to give a vermicull~e suspension containing 2.9~i by weight of solids (all water added was distilled).
The concentration of the suspension was then .

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increased to 20% by weight by evaporation of water by the application of heat, the mixture was cooled and a protein surfactant known commercially as "Nicerol" was then added at a concentration of 10%
by volume relative to the weight of the solid vermiculite and portions of the mixture beaten in a culinary mixer to form a foam. The foam when dried in a well-ventilated oven at 90C
had a density of 0.1 g/ml.
" 10 Example 10 ~' 1 Kg. of South African vermiculite was refluxed in a 20% w/w aque~us solutio~ of lithium chloride for 2 hours and after thorough washing in a Buchner funnel and standing overnight in distilled water, an eight-fold volume expansion of the orlginal ore took place.
~" Th~ mixtur,e of expanded ore and water (10% w/w of ore) ', was then mllled for 1 houF. The larger particles of vermiculite were then removed by flltration through a ",l 50~m sieve and the concentration of the suspension, / 20 ad~usted to 20% w/w by evaporatlon. A protein surfactant .i. *
,,x,, known commercially as "Nicerol" at a concentration of `"' 10% by volume relative to the weight of vermiculite - was then added and portions of the mixture beaten ~-, in a culinary mixer to form a foam. The foam when dried ln a well ventilated oven at 90C had a density of 0.1 g~ml~ ' '~ Exa~plo 11 ~---., .
~ A dried foam based on North American vermiculite ,.
'~ *Trade Mark.
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.; ~ . , ~ ~ ' ~C~9~6z was prepared as describea in Example 4 ana found to have an average size of 3.00mmand a density of O.ol g/ml.
ExamPle 12 A sample of wet foam as prepared in Example 6 was blended with granules of heat expanded vermiculite such that in the resultant blend the wet foam occupied 34% of the total volume and the granules 66% of the total volume. The blend was dried ; 10 in an oven at 90C. The resultant composite structure had a density of 0.22g/ml and a compressive strength of 0.12 MNm 2 .....
~ ExamPle 13 ~, ., , A slab of foam of dimensions 62 mm x 135 mm x 4 mm cut from the foam produced ln Example 5 havlng a density of 0.12 g/ml was placed in a furnace-at , 1000C for 10 minute~. On removal from the furnace the slab was observed not to have distorted at all visibly as a result of the intense heat, the resultant dimension-~ being 61 mm x 134 mm x 4 mm. The density ;; decreased to 0.09 g/ml and the compressive strength -- was 0.22 MNm2.
-~ These results demonstrate that the foams of this .;
invention resist heat well and therefore can be used as a fire-protective material because they have good ` dimensional stability with little loss in compressive -` strength.

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.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A rigid foam comprising a two-phase dispersion of gas in solid, the solid phase being an inorganic cellular structure composed of lamellae of vermiculite and extending continuously and substantially uniformly in all dimensions throughout the volume of the foam.

2. A rigid foam comprising a cellular structure having the cell walls thereof composed of overlapping individual vermiculite lamellae adhering together by mutually attractive forces.

3. A rigid foam as claimed in Claim 1 wherein the lamellae possess a smallest dimension not greater than 0.5 µm.

4. A rigid foam as claimed in Claim 3 wherein the lamellae have smallest dimension not greater than 0.05 µm.

5. A rigid foam as claimed in Claim 3 wherein the lamellae have length or breadth dimensions of at least one hundred times the size of the smallest dimension.

6. A rigid foam as claimed in Claim 5 wherein the lamellae have length or breadth dimensions of at least one thousand times the size of the smallest dimension.

7. A rigid foam as claimed in any one of Claims 1, 2 or 3 formed into a continuous and substantially uniform sheet or slab or foam.

8. A foam as claimed in Claim 1 having a density not greater than 0,5 g/ml.

9. A foam as claimed in Claim 8 and having a density not greater than 0.15 g/ml.

10. A process for the production of a rigid foam of vermiculite comprising the production of a suspension of vermiculite lamellae in a liquid medium; gasification of the suspension to form a froth and removal of the liquid medium from the froth by evaporation.

11. A process as claimed in Claim 10 in which the liquid medium is aqueous.

12. A process as claimed in Claim 10 wherein the gasification is performed by entraining gas in the suspension by rapid agitation.

13. A process as claimed in Claim 12 wherein the gasification is performed by whisking or beating the whole suspension into a froth.

14. A process as claimed in Claim 10 wherein the gasification is performed by intimate mixing of the suspension with a volatile liquid and evaporating the liquid in the suspension.

15. A process as claimed in Claim 10 wherein the gasification is produced by rapidly heating the suspension.

16. A process as claimed in Claim 10 wherein the suspension is classified by the removal of the coarser particles of vermiculite from the suspension prior to the gasification.

17. A process as claimed in Claim 10 wherein a surface active agent or foaming agent is present in the suspension of vermiculite lamellae.

18. A process as claimed in Claim 17 wherein the surface active agent or foaming agent is a cationic organic salt.

19. A process as claimed in any one of Claims 10, 11 or 12 wherein a foaming agent or surface active agent is added to the suspension of vermiculite lamellae prior to gasification.

20. A process as claimed in any one of Claims 10, 11, or 12 wherein during evaporation the foam is contacted with previously formed vermiculite structures, preferably in the form of rigid foam or exfoliated granules, in order to cement the solid vermiculite structures together.

21. A method of rendering articles fire resistant by applying to the exterior surface of the article a coating of a vermiculite foam as claimed in any one of the Claims 1, 2 or 3.