Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-05-19
2002-07-16
Green, Anthony (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S419000, C106S436000, C106S450000, C106S461000, C106S481000, C423S263000
Reexamination Certificate
active
06419735
ABSTRACT:
This application is an application under 35 U.S.C. Section 371 of International Application Number PCT/FR98/01775, filed on Aug. 07, 1998.
The present invention relates to a composition based on a samarium sesquisulphide, to its process of preparation and to its use as colouring pigment.
Inorganic colouring pigments are already widely used in many industries, in particular in those of paints, 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 medium 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.
Unfortunately, the problem is that most of the inorganic pigments which are suitable for applications such as above and which are actually used at the present time on an industrial scale generally make use of metals (cadmium, lead, chromium and cobalt in particular) whose use is becoming increasingly severely regulated, or even banned, by legislation in many countries, this being on account of their supposed very high toxicity. Mention may thus more particularly be made, as non-limiting examples, of the case of yellow pigments of the lead chromate or cadmium sulphide type.
It is thus seen that there is a great need for novel inorganic substitution pigments.
With this aim and according to a first embodiment, the composition of the invention is characterized in that it is based on a samarium sesquisulphide, in that it exhibits a samarium purity with respect to other rare earth metals of greater than 99% and in that it comprises at least one alkali metal or alkaline earth metal element, at least a portion of which is included in the crystal lattice of the said sesquisulphide.
According to a second embodiment, the composition of the invention is characterized in that it is based on a sesquisulphide of samarium and of at least one rare earth metal which is solely trivalent and in that it comprises at least one alkali metal or alkaline earth metal element, at least a portion of which is included in the crystal lattice of the said sesquisulphide.
According to a third embodiment of the invention, the composition of the invention is characterized in that it is based on a samarium sesquisulphide, in that it exhibits a samarium purity such that the cerium content is less than 1% and in that it comprises at least one alkali metal or alkaline earth metal element, at least a portion of which is included in the crystal lattice of the said sesquisulphide.
The invention also relates to a process for the preparation of the composition according to the first embodiment, this process being characterized in that a samarium compound exhibiting a samarium purity with respect to other rare earth metals of greater than 99% and at least one compound of an alkali metal or alkaline earth metal element is reacted with a gaseous mixture of hydrogen sulphide and of carbon disulphide.
The invention also relates to the process for the preparation of a composition according to the second embodiment, this process being characterized in that a samarium compound, a compound of the trivalent rare earth metal and at least one compound of an alkali metal or alkaline earth metal element are reacted with a gaseous mixture of hydrogen sulphide and of carbon disulphide.
The invention also relates to a process for the preparation of the composition according to the third embodiment, this process being characterized in that a samarium compound exhibiting a samarium purity such that the cerium content is less than 1% and at least one compound of an alkali metal or alkaline earth metal element are reacted with a gaseous mixture of hydrogen sulphide and of carbon disulphide.
The compositions of the invention exhibit a strong yellow colour.
Other characteristics, details and advantages of the invention will become even more fully apparent on reading the description which follows and the various concrete but non-limiting examples intended to illustrate it.
The composition according to the first embodiment of the invention will now be described.
This composition is based on a samarium sesquisulphide of formula Sm
2
S
3
. It is a sesquisulphide of &ggr; type.
One characteristic of the composition according to this first embodiment is the purity of the samarium. The composition must exhibit a samarium purity, measured with respect to the other rare earth metals, of greater than 99%. This purity can be at least 99.5% and more particularly at least 99.9%.
Here and throughout the description, the purities are given as weight of oxides of the elements samarium, cerium and other rare earth metals.
Rare earth metal is understood to mean, throughout the description, the elements from the group consisting of yttrium and the elements of the Periodic Classification with an atomic number of between 57 and 71 inclusive.
It is known that samarium, from its preparation and separation processes, contains impurities which are essentially other rare earth metals. Samarium usually exhibits a purity of the order of 98.5%. Such a purity is insufficient in the context of the present invention for producing a pigment with an improved yellow colour.
The composition of the invention comprises, in addition, an alkali metal or alkaline earth metal element. The alkali metal element can more particularly be lithium or sodium. The alkaline earth metal element can more particularly be strontium or calcium. Of course, the sesquisulphide of the composition of the invention can comprise several alkali metal and/or alkaline earth metal elements and, consequently, everything which is disclosed subsequently with reference to an alkali metal or an alkaline earth metal also applies to the case where several alkali metals and/or alkaline earth metals are present.
According to another characteristic of the invention, this alkali metal or alkaline earth metal element is at least partly included in the crystal lattice of the sesquisulphide. According to an alternative form, the alkali metal or alkaline earth metal element is essentially or completely included in the crystal lattice.
The sesquisulphide of the composition of the invention can in particular possess a cubic crystallographic structure of Th
3
P
4
type, which exhibits gaps for cations in the lattice; this lacunary structure can be symbolized by giving the sesquisulphides the formula M
10.66
[]
1.33
S
16
.
According to the invention, one or more alkali metal or alkaline earth metal elements can be introduced into these cationic gaps, up to saturation or otherwise of the latter. The presence of these elements within the sesquisulphide can be demonstrated by simple chemical analysis. Moreover, X-ray diffraction analyses show that the Th
3
P
4
crystalline phase of the sesquisulphide is retained with, in some cases, modification of the unit cell parameters to a greater or lesser extent, depending both on the nature and on the amount of the alkali metal or alkaline earth metal element introduced.
The composition according to the second embodiment of the invention is based on a sesquisulphide of samarium and of at least one other solely trivalent rare earth metal. Solely trivalent rare earth metal is understood to mean a rare earth metal which can only exhibit this one valency and thus a rare earth metal which cannot change to the di- or tetravalent state. Mention may be made, by way of example of such a solely trivalent rare earth metal, of lanthanum, gadolinium or dysprosium.
The trivalent rare earth metal/trivalent rare earth metal and samarium atomic ratio can vary within a wide range. It is generally above 90%. This ratio can more particularly be at most 50%.
The composition according to this second embodiment can furthermore be prepared from a samarium exhibiting the purity mentioned in the description of the first embodiment.
For the third embodiment of the invention, the characteristic of the compos
Busnot Sylvain
Macaudiere Pierre
Green Anthony
Rhodia Chimie
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