Process for Preparing Metal Halides by the Sol-Gel Method

Europaisches Patentamt (19) European Patent Office Office europeeneen des brevets EP 0 71 3 840 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: (51) intci.6: C01F 11/20, C01F 11/22, 29.05.1996 Bulletin 1996/22 C01F 11/34, C01F 17/00, C01B9/00, C01B9/04, (21) Application number: 95420313.9 C01B9/08, C03C 17/22, (22) Date of filing: 15.11.1995 C01F5/28

(84) Designated Contracting States: (72) Inventor: Poncelet, Olivier Jean Christian, BE CH DE ES FR GB IT LI NL Kodak-Pathe F-71102 Chalon sur Saone Cedex (FR) (30) Priority: 23.11.1994 FR 9414309 (74) Representative: Fevrier, Murielle Frangoise E. (71) Applicants: Kodak Pathe, • KODAK-PATHE Departement Brevets, F-75594 Paris Cedex 12 (FR) CRT - Zone Industrielle Designated Contracting States: F-71102 Chalon-sur-Saone Cedex (FR) FR • EASTMAN KODAK COMPANY Rochester, New York 14650-2201 (US) Designated Contracting States: BE CH DE ES GB IT LI NL

(54) Process for preparing metal halides by the sol-gel method

(57) The present invention concerns a process for obtaining metal halides, in particular rare earth and/or alkali earth halides. This process consists of forming a homogeneous solution by mixing one or more rare earth and/or alkali earth halogenoalkoxides in an anhydrous organic solvent, and hydrolysing this solution. The novel materials are obtained at room temperature and are in powder, fibre, film or bulk material form.

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Printed by Jouve, 75001 PARIS (FR) 1 EP 0 713 840 A1 2

Description For example, in US patent 4 492 721, magnesium fluoride layers are obtained by the decomposition of The present invention concerns a process for ob- fluorinated organic compounds of magnesium, such as taining metal halides, in particular rare earth and/or al- magnesium trifluoroacetate. kaline earth halides, and novel materials in powder, film s US patents 5 051 278 and 5 271 956 describe a or bulk material form obtained from these metal halides. process for forming films of metal fluorides, in particular Metal halides are compounds which have been binary and ternary alkaline earth or lanthanide fluorides. known for a long time. For example, alkaline earth fluo- This process consists of forming a coating solution con- rides (group 1 1 A), 4th period transition metal fluorides or taining a non-fluorinated organometallic compound, a rare earth fluorides (group NIB) are known. These metal 10 solvent and afluorination agent and coating this solution fluorides have interesting electrical, magnetic and opti- on a support. The film thus obtained is then heated at a cal properties. temperature of approximately 500°C in order to decom- Alkaline earth fluorides have low refractive indexes, pose the products contained in the coating solution into which enables them to be used in an anti-reflective layer pure metal fluoride. In order to obtain a uniform layer, a on supports with a high reflective index. 15 temperature increase is effected with a gradient of The layers obtained from these fluorides in general around 50°C/min. have low dielectric constants, are transparent and have US patents 5 208 101 and 5 268 196 describe a excellent mechanical properties. process for forming layers comprising alkali metal or al- All these special properties mean that metal fluo- kaline earth fluorides using sol-gel technology. This rides are compounds which are advantageous for pie- 20 process consists of forming a layer on a glass substrate zoelectric, ferromagnetic or anti-ferromagnetic, electro- using a coating solution containing a light metal oxide optical, pyroelectrical or non-linear optics applications. precursor, a non-aqueous solvent and water, heating Mixed rare earth and alkaline earth metal halides the layer in order to density the layer of light metal ox- are also known as luminescent substances used for ex- ides, and exposing this densified layer at a high temper- ample to convert X-rays or gamma radiation into visible 25 ature to a gaseous current containing fluorine. The den- light. sification of the oxide layer is effected at a temperature Many publications describe the use of mixed alka- of around 500°C and the fluorination is effected at tem- line earth halides as luminescent substances, in partic- peratures of around 300°C. ular in radiographic products. In all the known processes set out above, the metal For example, European patent EP 149148 de- 30 halide layers are obtained using high temperatures, ei- scribes radiographic image recording screens which ther to vaporise the metal halides or to decompose a contain, in the storage layer, a mixed alkaline earth hal- precursor of the metal halides, or to density the base ide of general formula BaF(XY):Eu:Sr in which X and Y metal oxide layer and to halogenate this same layer. are halide atoms. These luminescent substances are All these processes enabling layers of metal halides obtained by mixing BaF2, BaCI2, BaBr2, EuF3 and SrCI 35 to be obtained have many drawbacks related to the ne- in a ball mill. The mixture is then baked red hot in a bro- cessity to use high temperatures. In particular, the mium vapour chamber for 1 to 5 hours at a temperature choice of the support for the metal halide layer is very of between 800 and 1000°C. After cooling, the product limited. In addition, at high temperature, it is very difficult is broken up, washed and then dried. In this way the to obtain homogeneous metal halide layers having con- luminescent substance described above is obtained. 40 trolled stoichiometry. This technique, which is difficult to implement, does not The object of the present invention concerns a proc- make it possible to control the stoichiometry of the final ess for obtaining homogeneous metal halides at low product. temperature, in powder, layer, fibre or bulk material It is known that thin layers of luminescent substanc- form. es can be formed by chemical vapour phase deposition. 45 The present invention makes it possible to eliminate Such layers are obtained with difficulty because of the the problems relating to the use of high temperatures. differences in vapour tension and stability of each of the For example, the process of the present invention constituents. makes it possible to obtain metal halide layers on a A process for obtaining layers of metal fluorides was much wider variety of supports, in particular organic described in US patent 3 475 1 92. Such a process con- so supports which have very little resistance to high tem- sists of coating, on a substrate, a magnesium fluoride peratures. solution in a polar solvent and heating the substrate thus The process for preparing alkaline earth and/or rare covered at between 100 and 1000°C. In this process, it earth metal halides of the present invention consists of is necessary, in order to obtain a film, to use a substrate forming a homogeneous solution by mixing one or more which is resistant to high temperatures. 55 rare earth and/or alkaline earth halogenoalkoxides in an It is known that metal fluoride layers can be ob- anhydrous organic solvent and adding to this solution a tained by the decomposition of a metal fluoride precur- quantity of water which is at least stoichiometric in order sor. to hydrolyse the halogenoalkoxides.

2 3 EP 0 713 840 A1 4

Within the scope of the invention, the halog- The rare earth alkoxides can be synthesised ac- enoalkoxides and consequently the metal halides may cording to one of the following two methods. contain one or more halogen atoms chosen from The first method consists of reacting a rare earth amongst fluorine, bromine, chlorine and iodine. chloride, for example lanthane chloride, directly with an Figure 1 is an FT-Raman spectrum of the barium 5 alkali metal alkoxide, for example a sodium or lithium fluoroalkoxide used to obtain, according to the inven- alkoxide. This synthesis has drawbacks related to the tion, barium fluoride. presence of chloride in the reaction medium. In addition, Figure 2 is an X-ray diffraction spectrum of a barium lanthanide chlorides are particularly stable chemical fluoride powder obtained by hydrolysis of the barium species which are difficult to activate, which gives rise fluoroalkoxide of Figure 1 . 10 to low reaction yields. Figure 3 is an X-ray diffraction spectrum of a euro- A second method of synthesising rare earth alkox- pium fluoride powder obtained according to the process ides consists of reacting the rare earth directly with an of the present invention. alcohol such as 2-propanol or a functionalised alcohol Figure 4 is a spectrum obtained by energy disper- such as 2-methoxyethanol. sive X-ray microanalysis, of the compound is Within the scope of the invention, it is also possible YYbBaTm0 1 Fx obtained by hydrolysis, at room temper- to use heterometal oxides obtained by mixing several ature, of a mixture of rare earth and alkaline earth fluor- homometal oxides. oalkoxides as in Example 7. According to the present invention, the rare earth or Figure 5 is the emission spectrum of the compound alkaline earth halogenoalkoxides of the invention are YYbBaTm0 -|FX in powder form excited by laser at 650 20 obtained by alcoholisation of rare earth or alkaline earth nm. alkoxides by a halogenated or perhalogenated alcohol The metal halides which can be obtained by the hereinafter referred to as a "halogenoalcohol". process of the present invention are for example halides For example, when it is desired to prepare metal of elements in group IIAsuch as beryllium, magnesium, fluorides according to the process of the present inven- calcium, strontium, barium or radium halides or halides ts25 tion, it is possible to prepare the corresponding rare of elements in group NIB, such as scandium, yttrium, earth and/or alkaline earth fluoroalkoxide by reacting lanthane and cerium, gadolinium, erbium or ytterbium one or more rare earth and/or alkaline earth alkoxides halides. For example, the metal halides which can be with a fluoroalcohol chosen from amongst obtained are barium bromide, barium fluoride, barium 1 ,1 ,1 ,3,3,3-hexafluro-2-propanol, perfluoro-tert-buta- bromofluoride, magnesium fluoride, magnesium bro- 30 nol, 2,2,2-trifluoroethanol, 2-fluoroethanol, mide, ytterbium fluoride, barium and thulium fluoride, 1,1,1,2,2,3,3-heptafluoro-4-butanol or 2,2,3,4,4,4-hex- cerium bromide, cerium (III) fluoride, europium fluoride, afluoro-l-butanol. etc. When it is desired to prepare metal bromides ac- According to the invention, mixed metal halides, for cording to the process of the present invention, it is pos- example rare earth and alkaline earth halides, can also 35 sible to prepare the rare earth and/or alkaline earth bro- be obtained. moalkoxide by reacting one or more rare earth and/or The alkaline earth and/or rare earth halides of the alkaline earth alkoxides with a bromoalcohol chosen invention are obtained from one or more rare earth from amongst 2-bromoethanol, 3-bromo-2-propanol, and/or alkaline earth halogenoalkoxides, which can be 3-bromo-2-methyl-1 -propanol or 3-bromo-2,2-dimethyl- obtained by any one of the known methods of the art. 40 1 -propanol. These halogenoalkoxides are put in solution in an an- These halogenoalkoxides can be defined by the for- hydrous solvent, which may be chosen from a large mula M(ORx)n(ORy)m in which M is a rare earth or an number of organic solvents. The preferred solvents of alkaline earth, Rx and Ry are each separately alkyl the invention are anhydrous organic solvents which are groups containing one or more identical or different hal- miscible in water, such as, for example, tetrahydro- 45 ogen atoms, and n and m are such that the sum of n furane, alcohols or ketones. and m is equal to the valency of M. The rare earth and/or alkaline earth halogenoalkox- When it is desired to obtain a metal halide contain- ides are in general obtained from the corresponding al- ing several halides, a halogenoalkoxide as defined kaline earth or rare earth alkoxide or alkoxides. above in which the groups Rx and Ry are differently hal- The preparation of the alkaline earth alkoxides may 50 ogenated is preferably used. It is also possible to use be effected by various syntheses known in the art. as a starting halogenoalkoxide a halogenoalkoxide of The easiest synthesis to implement consists of re- formula M(ORx)nXm in which M, Rx, n and m as defined acting an alcohol directly on an alkaline earth. The yield previously and X is a halogen atom. of such a synthesis depends in particular on the steric The alkaline earth halogenoalkoxides can also be hindrance of the alcohol used. The smaller the steric hin- 55 prepared by directly reacting the alkaline earth in solu- drance, the faster will be the synthesis of the alkaline tion in a polar solvent with a halogenoalcohol as defined earth alkoxides. The alcohol is preferably chosen from previously. When fluoroalkoxides are prepared, the re- amongst methanol, ethanol or propanol. action is highly exothermic, which causes a degradation

3 5 EP 0 713 840 A1 6 of the organic compounds present in the reaction medi- tion on a cellulose support makes it possible for example um. In this case, the reaction can be catalysed and must to improve the resistance to pH of such a support. be carried out under very severe anhydrous conditions. According to one embodiment, layers of metal flu- When bromoalkoxides are prepared, the reaction is not orides on a cellulose support were thus obtained. exothermic and must be catalysed by forming in situ a 5 The process of the invention also makes it possible highly reactive species such as an amidide by the addi- to obtain a material having a controlled stoichiometry tion of NH3, Et2NH or (Me3Si)2NH in the reaction medi- since it is very easy to control the metal halogenoalkox- um. ide concentration of the starting solution. In addition, According to one embodiment of the invention, in since the layers of metal halides of the invention are ob- order to prepare a mixed metal halide containing several 10 tained using perfectly homogeneous solutions, homometal elements, each of the metal halogenoalkoxides geneous metal halide layers are obtained, which is not forming part of the final composition of the metal halide the case with the prior art. are prepared separately. According to the prior art, it is known that, by hydrol- According to the invention, the hydrolysis may be ysis of metal alkoxides, metal oxides are formed. Such catalysed by means of an acid. Preferably, this acid is is a process is generally implemented at low temperature halogenated with the same halogen as the one consti- in order to form inorganic lattices of metal oxides, for tuting the final metal halide in order to avoid the pres- example polysiloxane lattices. ence of secondary products related to the counterion as- It is therefore particularly surprising that, by hydrol- sociated with the hydrogen. For example, hydrolysis of ysis of halogenoalkoxides, alkaline earth or rare earth the fluoroalkoxides was effected at a pH of less than 7, 20 halides rather than alkaline earth or rare earth oxides and preferably between 1 and 3, in the presence of hy- are obtained. drofluoric acid. Without being bound by theoretical considerations, The quantity of water used to hydrolyse the halog- it appears that the hydrolysis conditions are particularly enoalkoxides according to the invention varies in ac- important for obtaining rare earth and/or alkaline earth cordance with the type of material desired. When it is 25 halides. This is because it appears that rapid hydrolysis desired to obtain the metal halides of the invention in favours the formation of halides rather than the forma- the form of layers or fibres, hydrolysis of the halog- tion of oxides. Halogenoalkoxides, in particular fluoro- enoalkoxides is effected with a quantity of water which alkoxides, have a hydrophobic character, which brings is at least stoichiometric and less than 5 times, and pref- about the formation of micelles in the reaction medium. erably less than twice, this stoichiometric quantity. 30 Each micelle fulfils the role of a microreactor in which When it is desired to obtain powders, this quantity the hydrolysis is accelerated, which favours the forma- of water may be up to 50 times and preferably 10 to 30 tion of metal halides rather than the formation of metal times greater than the stoichiometric quantity of water oxides. for hydrolysing the halogenoalkoxides. The present invention surprisingly makes it possible 35 EXAMPLES to obtain pure rare earth or alkaline earth halides at low temperature. The process and the metal halides of the All the following reactions were carried out in an in- invention are particularly useful for manufacturing or- ert gas, at room temperature. ganic/inorganic devices in thin film, fibre or solid material The materials obtained were analysed by the fol- form. 40 lowing techniques: Within the scope of the invention, thin layers of metal halides were obtained dip-coating a support in a so- FT-RAMAN spectroscopy, which consists of irradi- lution of metal halogenoalkoxides and hydrolysing the ating a sample with a monochromatic laser and halogenoalkoxides of this layer solely by means of at- measuring the frequency of the dispersed light. mospheric moisture. The thickness of the layer can be 45 varied either by varying the initial concentration of metal X-ray diffraction, which consists of irradiating the halogenoalkoxides or by dip-coating several times the surface of a sample by means of a beam of parallel support covered with a first layer obtained according to monochromatic X-rays and studying the variation in the process of the present invention. intensity as a function of the angle of incidence. X- The supports which can be used to obtain layers 50 ray diffraction affords qualitative identification of the within the scope of the present invention can be con- crystalline material and notably determination of the ventional supports such as glass or ceramics or sup- crystalline structure. ports degradable at high temperature, such as supports made from organic polymer materials. The preferred or- Energy dispersive X-ray microanalysis spectrosco- ganic supports are supports with reactive groups at the 55 py (ED-XRMA), which enables the elements surface, for example hydroxyl groups as in cellulosic present in a sample to be identified. This identifica- supports. tion is based on the exploitation of the X-rays emit- The deposition of a metal halide layer of the inven- ted by a sample bombarded by an electron beam

4 7 EP 0 713 840 A1 8

focused on the surface, each chemical element of the reaction medium, a colourless filtrate is obtained having a characteristic line. which is concentrated and then purified by crystallisation. In this way 1.67 g of Tm(OCH2CH2OCH3)3 is ob- From the teaching of the examples described be- tained (yield 72%). low, rare earth and/or alkaline earth halides containing 5 2.1 gof 2-hexafluoropropanol is added to a solution one or more halide atoms can easily be obtained. of 1 .67 g of Tm(OCH2CH2OCH3)3 in anhydrous tetrahydrofurane. The reaction is exothermic. In this way, after EXAMPLE 1 - Synthesis of BafOCHfCFg),!? crystallisation in a mixture of anhydrous pentane and ethyl ether, 2.06 g of Tm[OCH(CF3)2]3 is obtained (yield 38 g of 2-hexafluoropropanol is added to a mixture 10 98%). consisting of 15 g of barium (0.109 moles, AldrichR) and 100 ml of anhydrous tetrahydrofurane. The mixture is EXAMPLE 5 - Synthesis of BaF? left to react for 12 hours whilst being stirred (a highly exothermic reaction). The reaction medium is filtered 5 g of barium (36 mmol) is put in solution in 50 ml and a colourless filtrate is recovered, which is then dried is of anhydrous tetrahydrofurane, and then 12.2 g of and crystallised in anhydrous hexane. In this way 48 g 2-hexafluoropropanol is added to form the barium fluor- of Ba[OCH(CF3)2] characterised by the Raman spec- oalkoxide of Example 1 . The reaction is exothermic. The trum of Figure 1 is obtained (yield 95%). reaction medium, which has become clear, is hydrolysed at room temperature by the addition of 6.48 g of EXAMPLE 2 - Synthesis of Y[OCH(CF,)olo 20 water. The hydrolysis is exothermic. In this way 6.3 g of BaF2 powder is obtained. 100 ml of freshly distilled 2-propanol is added to a Figure 2 is an X-ray spectrum of the BaF2 powder mixture consisting of 16.1 g of yttrium (0.181 moles; thus obtained. AldrichR) and 100 ml of anhydrous toluene. 13 mg of The same experiment was carried out by hydrolys- HgCI2 is then added to the reaction medium. The reac- is25 ing the reaction medium with a solution of HF and a so- tion medium is then refluxed whilst stirring for 2 days. lution of HCI04. In this case, the hydrolysis is more rapid After filtration of the medium, the filtrate is concentrated and BaF2 is obtained as before. and then purified by crystallisation in a dichlorometh- ane/toluene mixture (50/50). In this way 32 g of YsO EXAMPLE 6 - Synthesis of MgF9 (OiPr)13 is obtained (yield 72%). 30 15 g of YsO(OiPr)13 (0.0122 moles) in solution in 50 1 00 ml of absolute methanol is added to 5 g of mag- ml of anhydrous tetrahydrofurane and 27 g of 2-hex- nesium in chip form. The reaction is exothermic. A white afluoropropanol are mixed (exothermic reaction). In this suspension is thus obtained. 70 g of 2-hexafluoropropa- way Y[OCH(CF3)2]3 is obtained, which is then purified nol is then added to this suspension drop by drop in or- in anhydrous hexane (34 g, yield 95%). 35 der to form the corresponding magnesium fluoroalkoxide. The reaction is exothermic and the reaction medium EXAMPLE 3 - Synthesis of Yb[OCH(CF,)ol, clears. After eliminating the colloidal residues by filtration, the clear filtrate is hydrolysed at room temperature A mixture of 2-methoxyethanol and 2-propanol by the rapid addition of 38 g of H20. 7.9 g of MgF2 is (30/70 ml) is added to a mixture consisting of 18.3 g of 40 then obtained. ytterbium (0.105 moles, AldrichR) and 100 ml of anhydrous toluene. The reaction medium is refluxed whilst EXAMPLE 7 - Synthesis of EuFq stirring for 2 days. After filtration of the reaction medium and crystallisation of the raw product, 33 g (80%) of Yb In accordance with the method of the previous ex- (OCH2CH2OCH3)3 is obtained. 45 amples, fluorinated alcohol HOCH(CF3)2 was reacted 25 g of 2-hexafluoropropanol is added to a solution of with a europium alkoxide Eu(OCH2CH2OCH3)3. In this 20 g (0.05 moles) of Yb(OCH2CH2OCH3)3 in tetrahydro- way europium fluoroalkoxide Eu[OCH2(CF3)2] was furane (exothermic reaction). After filtration of the reac- formed, which by hydrolysis made it to obtain perfectly tion medium and crystallisation of the raw product in an- crystallised europium fluoride, at room temperature. hydrous hexane, 32 g of Yb[OCH(CF3)2]3 is obtained so50 The quantity of water used is equal to 30 times the sto- (yield 96%). ichiometric hydrolysis quantity. Figure 3 is an X-ray diffraction spectrum of the EuF3 EXAMPLE 4 - Synthesis of Tm[OCH(CFq)dq powder obtained.

A mixture of 2-methoxyethanol and 2-propanol 55 EXAMPLE 8 - Synthesis of a mixed rare earth and (7.5/7.5 ml) is added to a solution of 1 g (5.9 mmol, Aldri- alkaline earth fluoride chR) of thulium in 20 ml of toluene. The reaction medium is then refluxed whilst stirring for 2 days. After filtration 4.03 g of Ba[OCH(CF3)2]2 is added to 5 g of Yb

5 9 EP 0 713 840 A1 10

[OCH(CF3)2]3 in solution in 50 ml of anhydrous tetrahy- becomes clear. drofurane. A second solution containing 5.71 g of Yb When the barium is completely used up, the solu- [OCH(CF3)2]3 in anhydrous tetrafurane and 0.1 1 g of Tm tion is concentrated and a white solid is obtained, barium [OCH(CF3)2]3 is then added to this solution. bromoalkoxide Ba(OCH2CH2Br). The mixture thus obtained is stirred strongly for 1 5 Ba(OCH2CH2Br) was also obtained by direct alco- hour and then transferred to a Teflon reactor and hydro- holisation of Ba(OEt)2. lysed with 40 ml of water containing 0.5 ml of 40% HF. The white solid thus obtained is solubilised in etha- A very rapid increase in the viscosity of the mixture nol. Hydrolysis of the medium is then effected by the is observed, which is maintained under strong stirring addition of a quantity of water 1 0 to 30 times the stoichi- for one night. The reaction medium is then filtered and 10 ometric hydrolysis quantity. The reaction is exothermic. in this way, after drying, a white powder is obtained, the After stirring for 30 min, a white crystallised powder is structure of which was confirmed by ED-XRMA (Figure obtained. This powder was analysed by FT-RAMAN 4). spectrometry. The spectrum obtained has two very fine This powder, when it is excited by a laser with a large bands at 416 and 442 cm-1, Comparison of this wavelength of 650 nm, emits blue light, as shown by Fig- is spectrum with the spectrum obtained with BaBr2,H20 ure 5. manufactured by Aldrich shows that barium bromide has indeed been obtained. EXAMPLE 9 - Synthesis of a thin layer of BaF? fluoride The X-ray diffractometry spectrum of the powder obtained shows unambiguously the presence of a crys- A cellulose substrate (NadirR sold by Roth) is im- 20 talline phase identical to that of the commercial product. mersed in a solution of Ba[OCH(CF3)2] (0.1 M) in abso- Consequently the present process makes it possi- lute ethanol, the system being maintained under an inert ble to manufacture extremely pure hyd rated barium bro- gas. The substrate is then withdrawn and left in the open mide from the metal at room temperature. air for 5 min. Hydrolysis takes place with atmospheric moisture. 25 EXAMPLE 11 - Synthesis of SrBr9 After 5 min, the substrate is immersed into osmosed water in order to terminate the hydrolysis. 3.8 g of strontium (4.2 10~2 mol) is dissolved in 80 A layer of BaF2 is thus obtained. Such layers are ml of methanol under argon atmosphere. The reaction stable even when they are immersed in solutions having is exothermic with the release of hydrogen. When the pH values varying between 8 and 12, for several days. 30 strontium is completely used up, a crystallised white In order to measure the hydrophobia of the layers powder corresponding to Sr(OCH3)2 is recovered. of BaF2 of the invention, the wetting angle of the previ- 8 g of Sr(OCH3)2 (12.3 mmol) is dissolved under ously obtained layer and that of the cellulose substrate argon atmosphere in 60 ml of anhydrous tetrahydro- before deposition of the layer were measured: furane, and then 2 ml of 2-bromoethanol is added drop 35 by drop. Wetting angle In this way a white solid is obtained which is dissolved in 30 ml of methanol. Hydrolysis of the medium Nadir® cellulose 36 + 2 degrees is then effected by the addition of 15 ml of water. Fine 74 + 4 BaF2 layer degrees colloidal particles in suspension are thus formed. After 40 30 min of stirring, the solution is concentrated: a white The results show that the process of the present in- crystallised power is obtained. vention makes it possible to obtain hydrophobic layers This powder, analysed by FT-RAMAN spectrometry resistant to any variation in pH. and X-ray diffractometry, has a structure identical to that Tests showed that layers of variable thickness could of the commercial product SrBr2 manufactured by be obtained by modifying the concentration of starting 45 StremR. alkoxides and reimmersing the BaF2 layer in the starting alkoxide solution. EXAMPLE 12: Synthesis of BaBrF

EXAMPLE 10 - Synthesis of BaBr? 3.5 g of Ba[OCH(CF3)2]2 (7.5 mmol synthesised in so50 accordance with the method of Example 1) in solution 5.7 g of barium (41 mmol) is mixed, under argon, in 40 ml of anhydrous methanol is added to 2.9 g of Ba with 50 ml of anhydrous tetrahydrofurane, and then 4 ml (OCH2CH2Br)2 (7.5 mmol synthesised in accordance of 2-bromoethanol is added drop by drop in order to form with the method of Example 10) in solution in 40 ml of barium bromoalkoxide. The reaction is not exothermic anhydrous methanol. The reaction medium is stirred for and it is catalysed by the controlled introduction of two 55 3 hours at room temperature and then concentrated. In equivalents of hexamethyldisilazane. The reaction is ac- this way a white powder Ba(OCH2CH2Br) (OCH(CF3)2 celerated by introducing 30 ml of methanol into the re- is isolated, characterised by FT-RAMAN. action medium. The reaction medium, which is stirred, This barium bromofluoroalkoxide in solution in 20

6 11 EP 0 713 840 A1 12 ml of methanol is hydrolysed by the addition of a 0.2 M 3. Process according to Claim 1 , in which the hydrol- solution of hydrofluoric acid. The solution becomes ysis is catalysed by means of an acid. cloudy and, after concentration, a slightly coloured solid is obtained. 4. Process according to Claim 3, in which the pH of This powder is analysed by FT-RAMAN, ED-XRMA s the hydrolysis is between 1 and 3. and X-ray diffractometry. 5. Process according to Claim 1 , in which the solvent The FT-RAMAN spectrum has two bands at 212.3 is chosen from amongst tetrahydrofurane, alcohols and 238.9 cm-1, which correspond to the Ba-F or ketones. bond. 10 6. Metal halides obtainable by the process according X-ray spectrometry microanalysis confirms the to any of Claims 1 to 5, containing one or more presence of the three elements Ba, Br and F. atoms of halogens chosen from amongst fluorine, bromine, chlorine and iodine and one or more rare The diffraction spectrum is entirely comparable to is earths and/or alkaline earth metals. the reference spectrum of BaBrF crystals. 7. Method according to any of Claims 1 to 5, for pro- EXAMPLE 13: Another method of synthesising BaBrF ducing homogeneous layers of rare earth and/or alkaline earth halides, which consist of applying a 25.6 g of Me4NOH,5H20 is heated at 1 00°C in order 20 solution of rare earth and/or alkaline earth halog- to remove the water by azeotropic distillation. The an- enoalkoxides in an anhydrous organic solvent to a hydrous Me4NOH solid is then dissolved in 60 ml of an- support and placing this layer in contact with a hydrous ethanol, and then 30 g of anhydrous BaBr2 is quantity of water which is at least stoichiometric for added thereto. After stirring for half a day, a precipitate hydrolysing the halogenoalkoxides of the layer and of NMe4Br is recovered. This compound is then dis- 25 less than 5 times and preferably less than twice this solved in 9.4 ml of hexafluoropropanol. After stirring, the stoichiometric quantity. solution is filtered and the solvent is removed under vac- uum. 40 g of (CF3)CHOBaBr is thus recovered in the 8. Process according to Claim 7, in which the hydrol- form of a white solid. ysis is effected with atmospheric moisture. (CF3)CHOBaBr is solubilised in methanol and this 30 solution is hydrolysed by the addition of water. The solid 9. Process according to Claim 7 for producing layers obtained is placed in an oven at 250°C in order to elim- of rare earth and/or alkaline earth fluorides. inate any organic species still present. The heat treatment is not obligatory. The same 10. Process according to Claim 7 for producing layers product was obtained after drying at a much lower tern- 35 of rare earth and/or alkaline earth bromide. perature but for a longer time. X-ray diffraction analysis confirms that BaBrF has 11. Process according to Claim 7 for producing layers indeed been obtained. of rare earth and/or alkaline earth bromofluoride.

40 12. Film of rare earth and/or alkaline earth halides Claims obtainable by the process according to any of Claims 7 to 11, in which the support is an organic 1. Process for preparing rare earth and/or alkaline support degradable at high temperature. earth metal halides which consists of 45 13. Film according to Claim 12, in which the support is (1) forming a homogeneous solution by mixing a support having hydroxyl groups at the surface. one or more rare earth and/or alkaline earth halogenoalkoxides in an anhydrous organic sol- 14. Film according to Claim 1 3, in which the support is vent, and a cellulosic organic polymer. (2) adding to this solution a quantity of water so which is at least stoichiometric for hydrolysing the halogenoalkoxides.

2. Process according to Claim 1, in which the halogenoalkoxide comprises one or more atoms of halo- 55 gens chosen from amongst fluorine, bromine, chlorine and iodine.

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11 EP 0 713 840 A1

EMISSION SPECTRUM OF YYbBaTm0>1Fx POWDER EXCITED BY MEANS OF A LASER AT 650 nm

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NANOMETRES

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Application [Number Office E U KU r E AIN SEARCH REPORT EP 95 42 0313

lkja,uivici> is ^urNSlUEKED 1U BE RELEVANT T ■ .. vnauon oi document witn indication, where appropriate, Relevant UAa&iniAUUN U r THE of relevant passages to claim APPLICATION (Int.CI.6) YUUVtrtU JUUKNAL Ut LHIMlt, C01F11/20 /ol. 5, no. 10, 1981 GAUTHI ER-VI LLARS, C01F11/22 3ages 479-484, C01F11/34 J. L. NAMY ET AL. 'Smooth synthesis and C01F17/00 :haracterization of divalent samarium and C01B9/00 /tterbium derivatives' C01B9/04 * page 479 - page 480 * C01B9/08 C03C17/22 JOURNAL OF MATERIALS SCIENCE LETTERS, C01F5/28 /ol. 11, no. 3, February 1992 LONDON GB, Dages 152-154, XP 000248754 :. RUSSEL 'Preparation of Li F, CaF2 and 1FZ by thermal decomposition of the metal trifluoroacetates' * the whole document * IDEM ,1

V , A EP-A-0 125 721 (N.V. PHILIPS' SLOEILAMPENFABRIEKEN) * page 2, line 14 - page 5, line 2 * 1EUUNICAI. FIELDS IDEM 5-7, 121 SEARCHED (Int.CI.6) ,01 h :oib b-A-b Ubl Z/V \b. R. PAZ-PUJALT) ,2,5-7, :o3c 2 column 2, line 8 - line 19 * column 3, line 1 - column 4, line 40 *

picscui svoi vii rcpurL nas neen arawn up ror ail claims ■we vi wnjnniiii ui lib: lu 'HE HAGUE 28 February 1996 fan der Poel , W ; ui wry ur principle unaenying ine invention ) : earlier patent document, but published on, or after the filing date : particularly relevant if combined with another > : document cited in the application document of the same category : document cited for other : technological background . reasons : non-written disclosure t : member of the same : intermediate document document patent family, corresponding