AU729959B2 - Sulphide of beta form and its use as a colouring pigment - Google Patents

Description

PROMRS OR TI! PSMPANATC2U OF A RE-EZTE UTAL SUJLPHIDE OF BETA FORK AND ITS USE AS A COLOURING PIGMENT S RNOUR-POUTJwC

CIIR:

The present invention relates to the use, as colouring pigment, of a rare-earth metal ouiphide of beta form and to its process of preparation.

Inorganic colouring pigments are already widely used in many industries, in particular in pa into, plastics and ceramics. In such applications, the properties, which are, inter alia, thermal and/or chemical stability, dispersibility (ability of the product to disperse correctly in a given medium), compatibility with the mediu to be coloured, intrinsic colour, colouring power and opacifying power, all constitute particularly important criteria to be taken into consideration in the choice of a suitable pigment.

most of the inorganic pigments which are suitable for applications such an above and which are actually uxsed at the present time on an industrial scale present a problem, however. This is because they generally make use of metals (ca-+ium, lead, chroiumi and cobalt in particular) whose use is becoming increasingly severely regulated, or even banned, by legislation in many countries, this being on account of 7 ~S7> xKrFO -2their supposed very high toxicity.

It is thus seen that there is a great need for novel inorganic substitution pigments.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

In a broad aspect, the present invention provides a process for the preparation of a rare-earth metal sulphide of beta form, the rare-earth metal being lanthanum, cerium, praseodymium, samarium or neodymium wherein a compound of the rare-earth metal is reacted with a sulphurizing gaseous mixture of hydrogen sulphide and carbon disulphide.

Other characteristics, details and advantages of the invention will become more evident upon reading the following description, as well as concrete, but non-limitative examples intended for its illustration.

Firstly it will be noted that the present invention applies to the preparation of a lanthanum, cerium, praseodymium, samarium or neodymium sulphide as well as mixed sulphides, that is to say sulphides of two or more rare-earth metals of the group given above. Consequently, everything described subsequently for a simple sulphide also applies to mixed sulphides.

It has been noticed that it is possible to modify the colour of the sulphide by oo oo varying the oxygen content of this sulphide. Thus, all the other process parameters otherwise being equal, a high carbon disulphide content promotes the production of sulphides with low oxygen contents, that is to say of products with lighter colours of the light Bordeaux type, for example, whereas a higher hydrogen sulphide content makes it possible to obtain products with higher oxygen concentrations and thus with darker colours.

The sulphurizing gas or mixture of sulphurising gases can be employed with an inert gas, such as argon or nitrogen.

-3- The rare-earth metal compound used for the reaction, in this second embodiment, is preferably a carbonate or a hydroxycarbonate. Mention may also be made of nitrates. A rare-earth metal oxide can also be used.

The sulphurization reaction is generally carried out at a temperature of from 600 to 1000°C, preferably 600 to 8000C, in particular at 8000C or in the region of this temperature.

The duration of the reaction corresponds to oo*** **o **o *oo *o *o the time necessary to obtain the desired sulphid.

typically from one to four hours.

On conclusion of the heating, the sulphide formed can be recovered. If it is desired to obtain a product with a finer particle size, the latter can be deagglomerated. Deagglokeratin 'under mild conditions, for example a wet milling or a milling of the air jet type wnder mild conditions, makes it possible to obtain a sulphide exhibiting, in particular, a mean aggregate size of not more than 1.5 gm.

The rare-earth metal suiphide obtained by the processes of the invention is a sulphide 'which exhibits the beta crystallographic form. Beta form, as. used herein, is understood to mean a compound of formula CeI.S 1 4O.S.. in Which X is between 0 anid 1, 0 being excluded, crystallizing in the quadratic system, I 4, 1 /acd space group.

A characteristic of the suiphide obtained by the processes of the invention is that it is composed of whole crystallites. These crystallites form aggregates and these aggregates constitute the powder in the form under which sulphide is. present. "Whole crystallite' is understood to mean a crystallite which has not been broken or shattered. Crystallites can in fact be shattered or broken during milling. Scanning electron microscopy photos of the product of the invention make it possible to show that the crystallites which constitute 'it have generally not been shattered.

F,)G

The aggregates constituting the sulphide usually exhibit a mean size of not more than 1.5 pm.

This mean size is generally not more than 1 pm and more particularly not more than 0.8 pa. Throughout the description, the characteristics of size and of particle size distribution are measured by the laser diffraction technique, using a particle sizer of the Cilas ER 850 type (distribution by volume).

It should also be noted that the sulphide obtained by the processes of the invention can be deagglomerated. It may thus not be provided directly in the form of aggregates with a mean size within the values given above. In this case, the aggregates may be agglomerated and/or slightly sintered and have a size greater than these values. Simple deagglomeration under mild conditions makes it possible to obtain aggregates with a mean size of not more than 1.5 pm or within the ranges given above.

According to a specific embodiment, the sulphide is provided in the form of a pure phase, the single beta phase as defined above.

The sulphide obtained by the processes of the invention can, in addition, exhibit a variable oxygen content. This content, expressed as weight of oxygen with respect to the weight of the entire sulphide, should not be more than 0.8%.

In the case where the rare-earth metal is cerium, the sulphide generally exhibits a Bordeaux red -6colour. According to a specific embodiment, the cerium sulphide exhibits a chromatically coordinate L* of less than 40 and a ratio of less than 0.6.

The chromaticity coordinates a* and b* are given here (and throughout the description) in the CIE 1976 system a* and as defined by the Commission Intemationale d'Eclairage [International Lighting Commission] and listed in the Recueil des Normes Francaises [Compendium of French Standards] (AFNOR), colorimetric colour No. X08-12, No. X08-14 (1983). They are determined for measurements made on products and plastics by means of a colorimeter sold by the company Pacific Scientific. The nature of the illuminate 0o is D 65 The observation surface is a circular pellet with a surface area of 12.5 cm 2 The observation conditions correspond to viewing under an aperture angle of 100. In the measurements given, the specular component is excluded.

Various alternative forms of the invention will now be described.

According to a first alternative form, the sulphide, as described above, additionally comprises a layer based on at least one transparent oxide, which layer is deposited at its surface or its periphery. Reference may also be made, as regards a product of this type consisting of such a layer to French Patent Application FR-A-2,703,999 in the name of the applicant whose teaching is incorporated herein.

This peripheral layer coating the sulphide may not be perfectly continuous or homogenous. However, preferably, the sulphides according to this embodiment comprise a transparent oxide coating layer which is unif oru and- of controlled thickness and which does not detrimentally affect the original colour of the sulphide, before coating.

"Transparent oxide' is ilnderstood to mean an oxide which, once deposited on the sulphide in the form of a more or less fine film, only absorbs light rays in the visible region to a very small extent or not at all and which does not mask,. or only very slightly mnasks, the original intrinsic coloux of the said sulphide. In addition, it should be noted that the term uoxidefl as used herein should be uuderstood'as also covering oxi&des of the hydrated type.

These oxides, or hydrated oxides, can be anorphous and/or crystalline.

Mention may more particularly be made, as examples of such oxides, of silicon oxide (silica), aluminium oxide (alumina),* zirconium oxide (zirconia), titanium oxide, zirconium silicate IrSiO, (zircon) and rare-earth metal oxides. According to a preferred alternative form, the coating layer in based on silica.

More--advantageously still, this layer is essentially, and preferably solely, compopsed of 'silica.

According to another alternative form, the sulphide can additionally comprise fluorine atom.

In this case, reference may also be made, as regards the arrangment of thxe fluorine atoms, to French Patent Application FR-A-2,706,476, 'in the name of -y the applicant whose teaching is incorporated herein.

The fluorinated sulphide can exhibit at least one of the following characteristics: -the fluorine atom are distributed along a concentration gradient decreasing frm the surface to the core of the said sulphide; the fluorine atom are mainly distributed at the outer periphery of the sulphide. Outer periphery is understood to mean, in this instance, a thickness of material, measured from the surface of the particle, of the order of a few hundreds angstroms. In addition, *main-lyn is understood to mean that more than 50% of the-fluorine atoms present in the suiphaide are found in the said outer periphery; the percentage by weight of fluorine atoms present in the suiphide does not exceed 10% and preferably the f luorine atoms are present in the f orm of fluorinated or sulphofluorinated comounds, in particular in the form of rare-earth metal fluorides or of rare-earth metal aulphofluorides (thiofluorides).

of course, the present invention also concerns the combination of embodiments which have been described above. TInls, it is possible to envisage a sulphide comprising an oxide layer and, in addition, comprising fluorine atoms.

2S Methods for the preparation of the suiphides according to these alternative forms will now be described.

For the first alternative form described above, that is to say for the suiphide exhibiting a layer of a transparent oxide, the preparation process can consist in bringing together the sulphide, as it has been obtained after the suiphurization reaction, and a precursor of the layer-forming transparent oxide, and in precipitating this oxide. The processes for precipitating the oxides and the precursors to be used are described in particular in FR-A-2,703,999.

In the case of silica, mention may be made of the preparation of silica by hydrolysis of an al-kyl silicate, a reaction mixture being formed by mixing water, alcohol, the sulphide, which is then suspended, and optionally a base, followed by the introduction of the alkyi silicate, or alternatively a preparation by reaction of the sulphide, of a silicate, of the alkali metal silicate type, and of an acid.

In the case of a layer based on alumina, the Bulphide, an aluminate and an acid can be reacted, whereby alumina is precipitated. This precipitation can' also be obtained by bringing together and by reacting the sulphide, an aluminium salt and a base.

Finally, the alumina can be formed by hydrolysis of an aluminium alkoxide.

As regards titanium oxide, it can be precipitated by introducing, into an aqueous suspension of the sulphide according to the invention. a titanium salt., such as TiCl 4 TiOCl, or TiOSO 4 on the one hand, and a bass, on the other hand. It is also possible to carry out the preparation, for example, by hydrolysis of an alkyl titanate or precipitation of a titanium Sol.

Finally, in the case- of a layer based on zirconium oxide, it is possible to carry out the preparation by cohydrolysis or coprecipitation of a suspension of the sulphide in the presence of an organometallic zirconium compound, for ezample a zirconium alkoxide, such as zirconium isopropoxide.

The process for the preparation of the sulphide according to the second alternative form, a sulphide comprising fluorine atoms, employs a fluorination.

The fluorination can be carried out according to any technique known per se bringing together the sulphide, as it has been obtained after the suiphurization reaction, and a fluorinating agent.

In particular, the fluorinatinig agen't can be liquid, solid or gaseous. Preferably, the fluorination is carried out under treatment conditions where the fluorinating agent is liquid or gaseous.

Mention may more particularly be made, as examples of fluorinating agents which are- suitable for the implementation of the treatment according to the invention, of fluorine alkali metal fluorides, amonium fluoride, rare gas fluorides, nitrogen fluoride NF,, boron fluoride

BP

3 1 tetrafluoromethane or hydrofluoric acid HF.

In the case of a treatment under a fluorinating atmosphere, the fluorinating agent can be used pure or diluted in a neutral gas, for example nitrogen.

The reaction conditions are preferably chosen so that the said treatment only brings about fluorination at the surface of the sulphide (mild conditions). In this respect, carrying out the fluorination to the core of the sulphide does not produce results which are substantially improved with respect to an essentially surface fluorination. In practice, it is possible to experimentally monitor and control the degree of progression of the fluorination reaction, for example by measuring the change in the increase in mass of the materials (increase in mass brought about by the gradual introduction of fluorine).

The fluorinating agent can more particularly be ammonium fluoride.

As has been indicated above, it is possible to envisage preparing a sulphide which combines the constituent characteristics of the various embodiments: the layer of oxide and the presence of fluorine atoms.

In order to obtain such combinations the preparation processes which have just been described are combined.

Thus, the fluorination treatment can be carried out in a first stage, and, then, in a second stage, the sulphide thus treated and a precursor of the transparent oxide are brought into contact, and the transparent oxide is precipitated on the said sulphide.

Another process can also be envisaged. In this case, in a first stage, the sulphide and a precursor of the transparent oxide are brought into contact and then the transparent oxide is precipitated on the said sulphide, and, finally, in a last stage, the fluorination treatment is carried out The sulphide of the invention such as obtained after reaction with the sulphurizing gaz or mixture can be treated in order to deposit on it a zinc gompound.This deposit can be made by reaction of a zinc precursor with aqueous ammonia or an ammonium salt. Reference may be made for this treatment to French patent application FR-A-2741629 the teaching of which is incorporated here. Some essential elements of this treatment are recalled here below.

The zinc precursor may be a zinc oxide or hydroxide which is used in suspension. This precursor may also be a zinc salt, preferably a soluble salt.

This may be a salt of inorganic acid such as a chloride, or alternatively a salt of organic acid such as an acetate.

For the deposit of the zinc compound, the sulphide, the zinc precursor, the aqueous ammonia and/or the ammonium salt are placed in contact in the presence of an alcohol. The alcohol used is generally chosen from aliphatic alcohols such as, for example, butanol or ethanol. The alcohol may in particular be introduced with the zinc precursor in the form of an alcoholic zinc solution.

According to another advantageous variant the siulphide, the zinc precursor, the aqueous ammonia and/or the ammonium salt are placed in contact in the presence of a dispersing agent. The aim of this dispersing agent is to prevent agglomeration of the particles forming the support during their placing in suspension for the treatments described above. It also makes it possible to work 12bis in more concentrated media. It promotes the formation of a homogeneous layer over all of the particles.

This dispersing agent may be chosen from the group of agents which disperse by a steric effect, and in particular nonionic organosoluble or water-soluble polymers. Dispersing agents which may be mentioned are cellulose and its derivatives, polyacrylamides, polyethylene oxides, polyethylene glycols, polyoxyethylenated polyoxypropylene glycols, polyacrylates, polyoxyethylenated alkylphenols, polyoxyethylenated long-chain alcohols, polyvinyl alcohols, alkanolamides, dispersing agents of the polyvinylpyrrolidone type and compounds based on xanthan gum.

The sulphide described has good colouring power and covering power and, for this reason, is suitable for the colouring of numerous materials, such as plastics, paints and others.

More specifically, it can be used in the colouring of polymers for plastics which can be of the thermoplastic or thermosetting type.

Mention may be made, as thermoplastic resins capable of being coloured according to the invention, purely by way of illustration, of poly(vinyl chloride), poly(vinyl alcohol) polystyrene, styrene-butadiene, styrene-acrylonitrile and acrylonitrile-butadiene-styrene copolymers, acrylic polymers, in particular poly(methyl methacrylate), polyolefins, such as polyethylene, polypropylene, polybutene or polymethylpentene, cellulose derivatives, such as cellulose acetate, cellulose acetobutyrate or ethylcellulose, or polyamides, including polyamide-6,6.

As regards the themosetting resins for which the sulphide is also suitable, mention may be made, for 13 example, of phenoplasts, aminoplasta, in particular urea-f ormaldehyde or melamine-forjsldehy.j* copolymers, epoxy resins and thermosetting polyesters.

The sulphide can. also be employed in special polymers, such as fluorinated polymers, in particular polytetrafluoroethylene polyearbonates, silicone elastomers or polyinidee.

In this specific application for the colouring of plastics, the sulphide can be employed directly in the form of powders. It is also possible, preferably, to employ it in a predispersed form, for example as a premix with a portion of the resin, or in the form of a concentrated paste or of a liquid, which mak~es it possible to introduce it at any stage in the manufacture of the resin.

Thus, the products according to the invention can be incorporated. in plastics, such as those mentioned above, in a proportion by weight generally ranging either from 0.01 to 5% (relative to the final product) or from 20 to 70%, in the case of a concentrate.

The products of the invention can also be used in the field of paints and varnishes and more particularly in the following resins: alkyd resins, the commonest of which is glyceryl phthalate resin; resins modified with long or short oil: acrylic resins derived from eaters of acrylic acid (methyl or ethyl)* and of methacrylic acid. optionally copolymerized with ethyl, 2-ethyihexyl or butyl acrylate; vinyl resins, such as poly(vinyl acetate), poly(vinyl chloride), poly(vinyl butyral) poly (vinyl formal), and vinyl chloride and vinyl acetate or vinylidene chloride copolymers; phenolic or amilnoplast resins, generally modified; polyester resins; polyurethane resins; epoxy resins; or silicone resins.

The products are generally eaployed in the proportion of 5 to 30% by weight of the paint and of 0. 1 to 5% by weight of the varnish.

In addition, the products according to the invention are also suitable for applications in the rubber industry, in particular in floor surfacing., in the paper and printing inks industry, in the field of cosmetics, and many other -non-limitative uses, such as dyes, in leathers, for finishing the latter, and laminated coatings for kitchens and other work surfaces, ceramics and glazes.

The products of the invention can also be used in the colouring of materials based on or obtained from, at least one inorganic binder.

This inorganic binder can be chosen fron, typically, hydraulic binders, air-cured binders, plaster and binders of the anhydrous or partially hydrated calcium sulphate type.

"Hydraulic binders' is understood to mean substances having the property of setting and of hardening after addition of water with the formation of is water-insoluble hydrates. The produacts of the inventioni apply very particularly to the colouring of cements and, of course, of the c;onrcretes Manufactured from these cements by addition to the latter of water, sand S and/or gravel.

In the context of the present invention, the cement can be, for example, of the aluinous type i.e.

any cement containing a high proportion either of alumina as such or of aluminate or of both. Mention may be made, as examples, of cements based on calcium aluminate, in particular those of the Secar type.

The cement can also be of the silicate type and more particularly based on calcium silicate.

Examples which may be given are Portland cements and.

in cements of this type, quick-setting or very-qujcksetting Portland cements, white cements, those which are resistant to sulphates and those coq~rising blast furnace slag and/or fly ash and/or meta-kaolin.

Mention may also be madle of cements based on calcium sulphate hemihydrate and magnesia cements, known as Sorel cements.

The products of the invention can also be used for colouring air-cured binders, that is to say binders which harden in the open air by the action of C0 2 of the calcium or magnesium oxide or hydroxide type.

Finally, the products of the invention can be used for colouring plaster and binders of the anihydrous 16 or partially hydrated calcium sulphate type (CaSO, and CaSO, 112E 2 0) The invention thus Provides Coloured compositions of a material, in particular of the plastics, paints, varnishes, rubbers, ceramics, glazes, papers, inks, cosmetic products, dyes, leathers or laminated coatings type or of the type based on or obtained from at least one inorganic binder, which comprise, as colouring pigment, a sulphide as defined above or obtained by processes of the type described above.

The following Examples further illustrate the present invention. In these Pxamples, the particle size was determined according to the abovementioneI technique. The measurement was carried out on a dispersion of the product in an aqueous solution containing 0.05% by weight of sodium hexametaphosphate which has been subj ected beforehand to treatment with an ultrasonic probe (probe with a tip with a diameter of 13 m, 20 k~z, 120 W) for 3 minutes.

EXAMPLE 1 Synthesis of Ce 1

OS,,

4 0 0 7

S,.

1 3 (light -red sulphide) Procedure: 16 g of cerium hydroxycarbonate (ce(OH)CO)), containing 70.7% of CeO., were calcined under a flow of

H

2 S (flow rate 10 1/h) and of CS, (flow rate 1.4 1/h) according to the following temperature 17 profile: temperature rise to eoo0C at the rate of VC/min, then a stationary phase of 1 hour at this temperature.

Results: 13 g of product with the f ormula given above (a single phase present according to the X-ray plates) are obtained with an oxygen content of 0.15% by mass (determined by virtue of the unit cell parameter).- The particle size obtained is 0.74 pm (a/n 0.49).

The colours, determined in the CIE Lab system, are: 38.9/36.3/16.7 The absorptions at 400 and 700 =r are as f follows: R400/R700 5.06/65.63.

g of the pigment thus synthesized are mixed in a rotating vessel wi th 2kg ofaefer~ec polypropylene ZltexO PKV 001. The mixture is then injected at 220*C using a Kapse injection moulding machine, model Protoject 10/10, with a cycle of 41 a.

The mould is maintained at a temperature of 350C.

A parallelepipedal double- thickness (2 and 4 mm) test sample is thus obtained.

It is observed that the pigment is well dispersed. The chromaticity coordinates and the absorptions, measured on the thick part of the plate, are as follows: 18 33.S/39.6/20.6 R400/R700 2.4/60.2.

EXAMPLE 2 Synthesis of 16-Ce IDS2 4

OAS

0 2 (dark-red suiphide) Procedure? 14 g of cerium hydroxycarbonate (Ce (025) Co)) containing 70.7% of CeO., were calcined under a flow of 3 2 S (flow rate 10 1/h) according to the following temperature profile: temperature rime to 8000C at the rats of 80C/min, then a stationary phase of 3 hours at this temperature.

Results: 11.2 g of product with the formula given above (a single phase present according to the X-ray plates) are obtained with an oxygen content of 0.69% by mass (determined by virtue of the unit cell parameter).

The Particle size obtained is 0.76 pm. (a/m 0.44).

The colours and the aborptione, determined in the CIE Lab system, are: 36.1/27.4/12 R400/R700 5.06/64.35.

After injection in polypropylene under the conditions of Example 1. the colours aad absorptions become: L'/afb' 29.7/31.4/16.4 R400/R700 a 2.05/59.5.

The following examples concern some products which have been submitted, after their preparation, to complementary treatment to obtain a layer of a transparent oxide, to deposit zinc or fluorine.

The treatment to deposit the layer of oxide and for the introduction of zinc is as follows.

The polyvinylpyrrolidone (PVP) is dissolved in ethanol.

The fluorinated cerium sulphide is added to this solution, then the aqueous ammonia solution and lastly the zinc precursor. The ethyl silicate is introduced continuously over two hours. After introduction of the ethyl silicate, the mixture is matured for two hours. The particles thus obtained are washed with ethanol by filtration and then dried at 50 0 C for twelve hours.

EXAMPLE 3: This example concerns the product of example 2 The reactants are used in the following proportions: g of product/kg of suspension f-CeloS 1 400o.So.2 200 Ethanol 643 Aqueous ammonia (32 100 Zinc exidd Ethyl silicate 32 PVP K10 (Aldrich company) Mw 10000 The used cerium sulphide was fluorinated beforehand as follows.

g of product are introduced into 100 ml of ammonium fluoride solution (5 by mass with respect to .f-CeioS 14 00.

8 So.2).

The pH of the mixture is brought to 8 by addition of aqueous ammonia solution and the medium is left stirring for one hour. The product is next filtered off and then dried in a desiccator under vacuum.

The product thus obtained is treated under the operating conditions given above, using aqueous ammonia.

The product obtained has the following chromatic coordinates after injection into polypropylene: L* a b* 36/20/10 EXAMPLE 4 This example concerns the product of example 1 The reactants are used in the following proportions: g of product/kg of suspension 3-Ce10S 1 40 0, 17 S 0,83 200 95 Ethanol 643 Aqueous ammonia (32 100 Zinc. oxide Ethyl silicate 32 PVP Ko1 (Aldrich company) 2 Mw 10000 The used cerium sulphide was fluorinated beforehand as follows.

of product are introduced into 100ml of ammonium fluoride solution by mass with respect to -Ce 10

S

14 0 0 17 S 0,83)- The pH of the mixture is brought to 8 by addition of aqueous ammonia solution and the medium is left stirring for one hour. The product is next filtered off and then dried in a desiccator under vacuum.

21 The product thus obtained is treated under the operating conditions given above, using aqueous ammonia.

The product obtained has the following chromatic coordinates after injection into polypropylene: 38/33/15

Claims (9)

1. Process for the preparation of a rare-earth metal sulphide of beta form, the rare- earth metal being lanthanum, cerium, praseodymium, samarium or neodymium wherein a compound of the rare-earth metal is reacted with a sulphurizing gaseous mixture of hydrogen sulphide and carbon disulphide.

2. Process according to claim 1 wherein the rare-earth metal compound is a carbonate or a hydroxycarbonate.

3. Process according to claim 1 or 2 wherein the oxygen content of the sulphide prepared is modified by varying the carbon disulphide content in the gaseous mixture.

4. Process according to any one of the preceding claims wherein the reaction is carried out at a temperature of 6000C to 8000C. Process according to any one of the preceding claims wherein the sulphide obtained after reaction with sulphurizing gas or mixture is brought into contact with a precursor of a transparent oxide such that this oxide is precipitated on the sulphide.

6. Process according to any one of claims 1 to 5 wherein the sulphide obtained after :reaction with the sulphurizing gas or mixture is brought into contact with a fluorinating agent.

7. Process according to any one of claims 1 to 6 wherein a zinc compound is deposited on the sulphide obtained after reaction with the sulphurizing gas or mixture 20 by reaction of a zinc precursor with aqueous ammonia or an ammonium salt.

8. Use as colouring pigment of a sulphide obtained by the process according to any one of the preceding claims.

9. Compositions of colored matter such as plastics, paints, varnishes, rubbers, :I ceramics, glazes, papers, inks, cosmetic products, dyes, leathers or laminated coatings type or of the type based on or obtained from at least one inorganic binder, wherein -23- they are prepared by using a sulphide obtained in the process according to claims 1 to 8. A process for the preparation of a rare-earth metal sulphide or beta form substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying examples.

11. A coloring pigment substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying examples. DATED this 21st Day of November, 2000 RHODIA CHIMIE Attorney: PAUL G. HARRISON Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS o oo o