GB2390092A

GB2390092A - Silane hydrolysis with rare earth metal catalysts

Info

Publication number: GB2390092A
Application number: GB0214592A
Authority: GB
Inventors: Simon Andrew Torry; Anthony Vernon Cunliffe; David Arthur Tod
Original assignee: Qinetiq Ltd
Current assignee: Qinetiq Ltd
Priority date: 2002-06-25
Filing date: 2002-06-25
Publication date: 2003-12-31
Also published as: AU2003242841A1; WO2004000851A3; AU2003242841A8; WO2004000851A2; GB0214592D0

Abstract

A process for silane hydrolysis, having a good degree of control of reaction rate and presenting mild conditions, comprises reacting together a silane having at least one hydrolysable group with water in the presence of a catalyst comprising a rare earth metal salt with a non-nucleophilic ligand. The ligand is selected from trifluoromethanesulfonate, perchlorate, oxalate, acetate and other alkanoate having a chain length of from 2 to 10 carbon atoms, hexafluoroacetylacetonate and acetylacetonate, with triflate as the preferred ligand. The rare earth metal is preferably a lanthanide, especially lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, dysprosium, erbium, thulium or ytterbium. The hydrolysis product may be used in surface treatments of materials having a superficial oxide or hydroxide layer; in one aspect the hydrolysis is carried out in the presence of the surface to be treated. The process is also useful in the production of silicon-based gels such as solvogels and alcogels.

Description

Hydrolysis of Silanes The present invention relates to processes for the

hydrolysis of silanes under 5 mild conditions and condensation of the product to form a coating on a surface to be treated. The acid and base hydrolysis of silanes is a well known reaction and proceeds via the SN2 reaction mechanism, displacing an atom or functionality 10 attached to the silicon atom to produce the silaneol. This reaction is repeated in turn for each of the hydrolysable groups attached to the silicon atom, furnishing the respective silanediol, silanetriol and silanetetraol corresponding to the number of hydrolyzable groups which are available. Such reactions are generally carried out in the presence of an effective acid catalyst and in a largely aqueous solution.

The treatment of metal surfaces with hydrolysed si}anes in this manner is a well known replacement for Cr+6 passivation coating, which has known detrimental toxicological and environmental effects. Commonly the silane used is an alkoxy silane and a surface treatment involving hydrolysis of such silanes is well known for 20 aluminiurn.

The hydrolysis and condensation of alkoxy silanes are also important reactions in a number of other industrial processes such as the formation of hard thin films on ophthalmic lenses and the formation of new hybrid sol-gel materials.

Another area which utilises alkoxysilanes is in the manufacture of aerogels, xerogels and alcogels. These are transparent materials which upon drying, have the appearance of glass, with insulation properties better than mineral wool, and which are more heat resistant than aluminium. They can be used in a variety of ways. The 30 key step in their synthesis is the hydrolysis of tetra(alkoxy)silanes, which is generally carried out under acidic or basic conditions. The silanes in this technology

- field are commonly referred to as orthosilicates, preferably the alkoxy group will

either be methoxy (TMOS) or ethoxy (TEOS).

5 A further application of the surface treatment process based on silane hydrolysis is that which is used to improve adhesive bandings, for example for rocket motor components. The use of y- glycidoxypropyltrimethoxysilane (GPS) in the pre-treatment of metal surfaces, prior to bonding with epoxy resins, improves the durability of an adhesive bond to the metal surface. However, the metal 10 involved here is often steel and acid catalysed hydrolysis of silanes in high concentrations of water is unsuitable for the surface treatment of steel, as exposure to acidified water can cause surface corrosion. The possibility of diluting the silane/water solutions by the addition of an organic solvent has been tried but found not to be feasible because it slows the rate of the hydrolysis to unacceptable levels.

The use of acidic or basic solutions is also not desirable or possible in conjunction with certain silanes having substituents which are labile under such conditions (ea. isocyanate functionalities) and this requirement consequently limits the range of silanes which can be used in silane hydrolysis treatment processes.

Lewis acids are known to promote silane hydrolysis but they generally decompose in water to form acidic solutions and so too would be considered undesirable and can be regarded in general as being of the same character as the previously discussed acidic solutions. Their use merely confirms that hydrolysis 25 depends on the presence of an effective acid catalyst and a largely aqueous solution.

The use of organometallic catalysts for the hydrolysis of silanes is known, including organotin and organotitanate compounds and Al(acac)3 (aluminium (III) acetylacetate). However, the organotin and organotitanate catalysts are insoluble in 30 water and their catalytic activity is dependent upon the initial hydrolysis of the catalyst to form an activated hydrolysed catalyst. Also they suffer from the disadvantage of readily catalysing the oligomerisation of silanes. Reaction times

when using the Al(acac)3 catalyst can be excessively long, compared to acid catalysed systems and thus, although hydrolysis can be carried out under mild conditions with this catalyst, the extended reaction times makes the use of this 5 method unsuited to industrial applications.

In most surface pre-treatment processes based on the hydrolysis of a silane, typically a 1% by mass solution of an alkoxy silane is hydrolysed by reaction in high concentrations of water and at pHs between 3 and 4.5 and used to treat a metal 10 surface. Acids and bases catalyse the hydrolysis of the alkoxy silane to a product such as the corresponding silanetriol which is then applied to the metal surface, with the result that the silanetriol undergoes condensation reactions with the metal oxide on the surface. Low concentrations of the alkoxy silane can help to minimise competing polymerization (oligomerisation) reactions of the hydrolysis product.

15 Mechanistic studies reveal that a complex co-ordination of silane species to the metal surface takes place. Under typical conditions, 2 to 5 rim or 1 to 10 monolayers of silane coating are regarded as a desirable thickness of coating for the purpose of improving adhesive bonding.

20 It is an object of the present invention to provide an improved method of silane hydrolysis, to the corresponding silanol, silanediol, silanetriol or silantetraol by catalytic means, avoiding the use of acidic or basic solutions to initiate hydrolysis. By this means interference with functionalities associated with the silane which are acid or base labile can be minimised, for example the epoxide ring in 25 GPS.

It is a further object to provide surface treatment processes for materials which possess oxide or hydroxide layers on their surfaces, particularly for metals, which processes render treated surfaces which are of a quality which is at least as 30 good as is obtained with prior art methods but which use milder treatment

conditions. Accordingly, it is a further object of this invention to provide an improved process for silane surface treatment such as will rapidly catalyse the

hydrolysis of silanes under mild conditions in the presence of a minimum amount of water, so as to avoid promoting the surface corrosion of metals, such as steel or magnesium, which are susceptible to attack in aqueous solutions under conditions of 5 high or low pH.

The applicant has now found that silane hydrolysis can be effectively catalysed in a substantially neutral solution comprised mainly of an organic solvent by the use of a rare earth metal(III) salt with a nonnucleophilic ligand.

According to a first aspect of the present invention therefore, there is provided a process for the hydrolysis of a silane having at least one hydrolysable group which comprises contacting the silane with water in the presence of a catalyst comprising a rare earth metal(III) salt with a non-nucleophilic ligand. Preferably the 1 S ligand is selected from the group comprising trifluoromethanesulfonate, perchlorate, oxalate, acetate and other alkanoate having a chain length of from 2 to 10 carbon atoms, hexafluoroacetylacetonate and acetylacetonate, but is most preferably a rare earth (III) trifluoromethanesulfonate ("triflate"). Preferably, the rare earth metal will be a lanthanide, particularly lanthanum (La), samarium (Sm), ytterbium (Yb), 20 europium (Eu) or erbium (Er). Most particularly, the catalyst will be europium (III) triflate, samarium (III) triflate, erbium (III) triflate or ytterbium (III) triflate.

Where the silane is susceptible to attack promoted by the presence of large excesses of water, the process of the invention may be carried out in an organic 25 solvent with only a minor proportion of water present, typically not more than 4% by mass. To achieve sufficient concentrations of the silane reagent and the catalyst in solution for an efficient hydrolysis process, the organic solvent will generally be a polar solvent, such as methanol, ethanol, isopropanol, acetone, acetonitrile etc. 30 The rate of silane hydrolysis using the lanthanide triflate catalysts can be modified by the appropriate choice of lanthanide metal cation, ratio of water to solvent, the solvent polarity and the reactivity of the silane. As the type of solvent

s and the amount of water present may be settled for any given process by other factors, the main determinant of the rate of hydrolysis is likely to be the choice of appropriate lanthanide metal cation. For some applications, it may be desirable that 5 the hydrolysis should proceed relatively slowly, for example when surfaces are being treated and it is desired to avoid or minimise the occurrence of oligomerisation (oligomerisation being a slow process relative to hydrolysis).

However, for other applications it will be desirable to achieve rapid hydrolysis of the silane, either because this will assist in achieving oligomerisation, such as in the 10 formation of solgels, aerogels, xerogels and alcogels, or for ease of application to surfaces which are being treated e.g. when it is necessary to spray the reacting material directly onto the surface to be treated. The ready ability to control the rate of the hydrolysis reaction according to the requirement may be appreciated to be a particular advantage of the present process over prior art hydrolysis methods.

The catalyst may, if desired, be recovered from the reaction mixture. This may be achieved by a chromatographic method, cation exchange such as a zeolite, or clay, or by conversion to an insoluble salt. In most cases, however, it is likely that it will be cheaper and simpler not to recover the catalyst.

The silanes to which the process of the invention may be applied are any silane which possesses at least one substituent group that is capable of being hydrolyzed, such as an alkoxy group, O-aryl group, a halide, carboxylate, thiol, silthian, mercaptosilane, nitrite, cyanate, peroxy, amine, silazane, diarnino, 25 perchlorate, phosphate, borate, titanate, aluminate, etc. In the case where the hydrolyzable group is an alkoxy group, the alkoxy side chain is preferably short from Cat to Co inclusive, so as not to create steric hindrance effects in the hydrolysis step. Preferably the alkoxy group is a methoxy or ethoxy group.

30 In one method of use of the process of the invention, a hydrolysed silane is generated by the process and is then used to provide a surface treatment for metals, metal alloys and non-metal complexes, possessing a superficial oxide or hydroxide

layer. Particularly suitable materials for such surface treatment include metals and alloys such as aluminium, aluminium alloys, steels, chromium and its alloys, titanium, magnesium alloys, copper, tin and brass, oxides such as alumina and also 5 non-metallics such as glass, silica, clays and talc.

In an alternative aspect of the process of the invention, hydrolysis of the silane is effected in-situ of the surface to be treated. According to this aspect, a process for treatment of a surface is provided which comprises exposing said 10 surface to a silane having at least one substituent group which is capable of being hydrolysed, in the presence of water and a catalyst comprising a rare earth metal (III) salt with a non-nucleophilic ligand. This surface treatment process is particularly suited to the treatment of steels in view of the mild conditions that may be used.

It will be appreciated that in the case of this latter process, the hydrolysis reaction may be allowed to start before the reactive solution is applied to the surface i.e the reactive solution may conveniently be prepared away from the surface but then applied immediately to it such that reaction continues in the presence of the 20 surface. Thus a reactive solution can be made up freshly from all of the constituent reagents or the solution can be pre-packaged as a two or three part solution mix, keeping the catalyst and water separate from the silane, and to apply the solution to the surface, using a spray which will draw up the two or three part solutions and mix them together during the spraying process. The silane, eg GPS, will rapidly 25 hydrolyse to the silanol, dial, and trial and these products will react directly with the surface. The rapid hydrolysis method would be suited to surfaces that cannot be easily located in a dipping tank, such as fixed structures, coverage of large areas, fixed inclined or near vertical surfaces. To achieve the desired surface treatment effect in these cases requires a higher rate of hydrolysis of the silane, which can be 30 achieved by the selection of either ytterbium (III) trifluoromethanesulfonate or erbium (111) trifluoromethanesulfonate as the catalyst.

The silanes used for surface treatment in conjunction with a process of the present invention are usually chosen from a range of specialized silanes, such as the commonly used y-glycidoxypropyltrimethoxysilane (GPS) which has three 5 hydrolyzable alkoxy functional groups and thus, on hydrolysis, forms an activated silanetriol species which then reacts to form a plurality of covalent bonds with the oxide surface. Other silanes of this type which may be used include vinyltrimethoxysilane, chloropropyltrimethoxysilane, 3-(triethoxysilyl) propyl amine, 3(triethoxysilyl)ethylene diamine, 3-(trimethoxysilyl)propyl methacrylate, 10 3-(trimethoxysilyl)propyl acrylate and 3-(triethoxysilyl)propyl thiol.

All processes for using hydrolysed silanes for surface treatment will typically involve a preliminary preparation of the surface, usually a metal or alloy surface, to remove impurities on the surface, ea. by processes of degreasing and grit 15 blasting. After this the active solution is then applied to the surface by pressure spraying or by using a material applicator such as a brush or roller or by dipping the surface into a tank which is filled with the active solution., For these methods of application, it is desired that the hydrolysis of the silane to the silaneol, dial and trial be relatively slow, typically 30 to 45 minutes. For this purpose europium(III) 20 trifluoromethanesulfonate and samarium(III) trifluoromethanesulfonate catalysts are preferred since their use gives rise to only a limited degree of oligomerisation and they will provide similar reaction times to those obtained using normal acidic conditions. Where a dipping tank is used the process may be operated as either a batch or continuous process with the reagents being replaced at the same rate that 25 they are used up.

The silane (such as typically GPS), is present in an amount of from 0.01% to 5% by mass, preferably 0.1% to 2% by mass, in the reactive solution in order to minimise the occurrence of oligomerisation. The solvent system is preferably an 30 alcohol and water mix, with the alcohol ranging from 0%-99% by mass, preferably 75%-99% by mass, and water ranging 2%-99% by mass, preferably 2-10%. The catalyst is typically present in an amount of 0.01% to 2% by mass, preferably in the

range 0.1%-0.5% to form the reactive solution. The hydrolysis reaction is generally carried out at standard atmospheric pressure and in a temperature range of 10 C to 40 C, most preferably at room temperature.

After the completion of surface treatment, the treated material is either allowed to dry at room temperature or is heated in an oven at an elevated temperature such as from 40 to 110 C, particularly around 80 C. Once dried, the material is ready for any further treatment, which is to be applied, such as the 10 application of paints or adhesives.

A further use of the process of the present invention is a method of preparing silicon based gels, which are the precursors to aerogels, xerogels and alcogels. This method comprises the hydrolysis and oligomerisation or polycondensation of a 15 silane - usually TMOS or TEOS - with a lanthanide catalyst in a water and alcoholic solvent. The effective formation of gels from silanes is best carried out at high concentrations of silane, with only minimal quantities of water and solvent required, as each mole of hydrolysed silane will produce 4 molar equivalents of solvent.

Commonly other additives, such as metal hydroxides and inert fillers, are added to 20 the solution to create desirable properties in the gel product. The formed gel encapsulates the alcoholic solvent within the pores of its network and can be dried out, if required to form either an aerogel or a xerogel.

There are many possible products resulting from the hydrolysis of Si(OR)4, 25 silanol, Si-(O-Si)4, RO-Si-(O-Si)3, (RO)2-Si-(O-Si)2 and (RO)3-Si-(OSi), where R is typically OCH3/OC2H5 or H depending on whether the species is partially or fully hydrolysed. The first step is the hydrolysis of the alkoxysilane to the silaneol, dial, trial and tetraol species and this is followed, where conditions allow, by the oligomerisation of the silanols, to form a 3D lattice. In such a condensation 30 oligomerisation reaction, it is expected that a range of silicon bridging centres will be formed. Furthermore, it will be apparent to a person skilled in the art that

careful control of the solvent to silane ratio, the rate of hydrolysis and the rate of oligomerisation will affect the respective amounts of the different silicon bridging centres and hence will allow the properties of the lattice to be adjusted as desired.

5 To produce the desired product any of the lanthanide triflate catalysts can be used to achieve the desired reaction rate, but preferably the rate of hydrolysis will be relatively fast, as previously mentioned.

The invention will now be further described with reference to the following 10 examples thereof. The rate of hydrolysis of silane in each example was followed using nuclear magnetic resonance (NMR) spectroscopy. Deuterated solvents were used during the experiments; it should be noted that the use of protonated water and solvents will cause a slight decrease in reaction rate processes due to the isotope effect. However, when comparisons are being made this effect can be ignored.

Example 1: (Comparative) Hydrolysis of GPS in water is catalysed by addition of acid or base, otherwise the rate of reaction is too slow to warrant use in an industrial process (see Table l).

Addition of ethanol or other solvent rapidly decreases the rate of hydrolysis to 20 unacceptable times. The addition of acetic acid to high ethanol to water ratio solutions, does not increase the rate of silane hydrolysis.

Table I

Mass % Mass % Mass % PH Minutes to Water Ethanol Silane 83% Conversion 99 1 Neutral 2200 99 0 1 4.3 68

99 0 1 9.0 381

4 95 1 Neutral >60000 59 40 1 Neutral 49000

Example 2: Effect of Water to Ethanol ratio on Yb(OTf)3 catalysed system Deuterated water (d2-water), deuterated ethanol (dS-ethanol) and ytterbium 5 trifluoromethanesulfonate were mixed together according to the mass ratios in Table 2. A known quantity of y- glycidoxypropyltrimethoxysilane was added to the solution and the reaction was followed using proton nuclear magnetic resonance (NMR) spectroscopy.

10 The time taken to 83% conversion was between 4 minutes and 174 minutes.

There is a clear trend that for a given catalyst, with a fixed concentration of silane, for example 0.10 mol ratio, as the water percentage increases the reaction time increases. However, at near 100% water content, the reaction times decrease 15 Further experiments were carried out using 0.20 mol ratio, effectively doubling the silane concentration, and the same effects were observed. The apparent decrease in reaction time at near 100% water content implies that a different hydrolysis mechanism could be occurring.

20 Table 2

Mol ratio Mol ratio Mel ratio Concentration Maw % Mass % Mass % Mass To Minutesto Water Silane Catalyst silane g dm-3 Water Ethanol Silane catalyst 83% Conversion 5.00 0.10 0.01 12.91 6.05 92.14 1.43 0.37 4

10.00 0.10 0.01 12.91 11.96 86.26 1.41 0.37 47

25.00 0.10 0.01 12.91 28.88 69.40 1.36 0.36 159

50.00 0.10 0.01 12.91 54.64 43.73 1.29 0.34 174

99.89 0.10 0.01 12.91 98.53 0.00 1.16 0.31 81

10.00 0.20 0.01 8.60 4.06 94.86 0.96 0.13 29

50.00 0.20 0.01 25.54 53.99 43.13 2.55 0.33 167

99.79 0.20 0.01 25.55 97.54 0.00 2.31 0.15 131

Example 3: Effect of solvent on Yb(OTfl3 catalysed system Deuterated water (d2-water), deuterated solvent and ytterbium 5 trifluoromethanesulfonate were mixed together according to the mass ratios in Table 3. A known quantity of y-glycidoxypropyltrimethoxysilane was added to the solution and the reaction was followed using proton NMR spectroscopy.

The time taken to 83% conversion was between 23 minutes and 182752 10 minutes. Although the reaction was shown to take place in THF and dioxane, for industrial purposes, high concentrations of THF and dioxane are impracticable. It should be noted that the reaction proceeds faster in a more polar solvent and the best results are in protic solvents such as ethanol and methanol.

15 Table 3

Mol ratio Mol ratio Mol ratio Concentration Solvent Mass Mass Mass Mass % Minutes to water sDane catalyst silana % % % 83% / g dm-3 Water Solvent Silane catalyst Conversion 10 0.1 0.01 12.9 EtOD 12.0 86.3 1.4 0.37 47 10 0.2 0.01 8.6 EtOD 4.1 94.9 1.0 0.13 29 10 0.1 0.01 12.9 MeOD 12.0 86. 3 1.4 0.37 58 10 0.2 0.01 8.6 MeOD 4.1 94.9 1.0 0.13 23 10 0.1 0.01 12. 9 THF 10.9 87.4 1.3 0.34 416

10 0.2 0.01 8.6 THF 3.7 95.3 0.9 0.11 2682

10 0.1 0.01 12.9 d6-Acetone 12.2 86.0 1.4 0.38 173 10 0.2 0.01 8.6 d6Acetone 4.1 94.8 1.0 0.13 267 10 0.1 0.01 12.9 ACN 12.5 85.6 1.5 0.39 142

10 0.2 0.01 8.6 ACN 4.3 94.6 1.0 0.13 124

10 0.1 0.01 12.9 dioxane 9.7 88.9 1.1 0.30 2084 10 0.2 0.01 8.6 dioxane 3. 2 95.9 0.8 0.10 18272

Example 4: Effect of silane on Yb(OTf)3 catalysed system Deuterated water (d2-water), deuterated methanol and ytterbium 5 tr'fluoromethanesulfonate were mixed together according to the mass ratios in Table 4. A known quantity of silane was added to the solution and the reaction was followed using proton NMR spectroscopy.

The time to 83% conversion was between 6 minutes and 425 minutes. All 10 the silanes underwent hydrolysis; however, vinyl trimethoxy silane and 3-

trimethoxysilyl propyl acrylate reacted rapidly within 15 minutes. The 3-

aminopropyltriethoxysilane rapidly crosslinked within an hour to form a gel like material. The kinetics of this reaction could not be followed by proton NMR spectroscopy. This example shows that the non hydrolyzable group attached to the 15 silicon atom has a great effect on the reactivity of the silane. However, for surface coating solutions it will generally be desired that the side chain should have certain specific properties and for this reason the coatings industry tends to be directed towards the use of particular silanes.

20 Table 4

Silane Mol Mel Mol Concentration Mass Mass Mass Mass j Minutesto ratio ratio ratio % D/c % % water silane Cablys Silane Water Solven Silane catalys 83% t t t Conversion _ /gum-3 1 _ Vinyl trimethoxy silane 10 0.2 0.01 8.6 6.4 92.4 0.95 0.20 11.3 3-(trimethoxysilyl) propyl 10 0.2 0.0 1 8.6 4.1 94.8 0.96 0.13 6.1 acrylate GPS 10 0.2 0.01 8. 6 4.1 94.9 0.96 0.13 28.8

Triethoxyvinylsilane 10 0.2 0.01 8.6 5.0 93.8 0.96 0.16 25.4 I riethoxysilylpropylethylen 10 0.2 0.01 8.6 4.3 94.6 0.96 0.13 31.3 ediamine dc 3 10 0.2 0.01 8.6 4.3 94.6 0.96 0.13 Gel aminopropyltriethoxysilane do 3-(triethoxysilyl)propyl 10 0.2 0.01 8.6 3. 9 95.0 0.96 0.12 425.5 isocyanate GPS (SipB) 10 0.2 0.01 8.6 4.1 94.9 0. 96 0.13 16.4 _ _ l.

Example 5: Effect of Lanthanide Series Catalyst on Hydrolysis.

Deuterated water (d2-water), deuterated ethanol and a series of lananide 5 catalysts were mixed together according to the mass ratios in Table 5. A known quantity of y-glycidoxypropyltrimethoxysilane was added to the solution and the reaction was followed using proton NMR spectroscopy.

The time to o3% conversion was between 25 minutes and 272 minutes. All 10 the lanthanide (III) (trifluoromethanesulfonate)3 catalysts were active in hydrolysing y-glycidoxypropyltrimethoxysilane. Table 5

Catalyst Mol ratio Mol ratio Mol ratio Water Silane catalyst LaTFMS 10 0. 2 0.01 PrTFMS 10 0.2 0.01 NdTFMS 10 0.2 0.01 SmTFMS 10 0.2 0.01 EuTFMS 10 0.2 0.01 GaTFMS 10 0.2 0.01 DyTFMS 10 0.2 0.01 ErTFMS 10 0.2 0. 01 TmTFMS 10 0.2 0.01 YbTFMS 10 0.2 0.01 YbTFMS 10 0.2 0.01 15 La=lantham m, Pr=prae eodymium, d=neodym,.,, , _,....

Er--erbium, Tm=thulium, yb=ynerbium TFMS=trifluromethylsulfonate

Example 6: Effect of Lanthanide Series Catalyst on Oligomerisation Deuterated water (d2-water), deuterated ethanol and catalyst were mixed 5 together according to the mass ratios in Table 6. A known quantity of y-

glycidoxypropyltrimethoxysilane was added to the solution and the oligomerisation reaction was followed using silicon-29 NMR spectroscopy (measured by the rate of loss of monomeric species).

10 Europium(lII) and samarium(III) trifluoromethanesulfonate were the least effective oligomerisation catalysts and are the preferred catalysts where it is desired to avoid or to minirnise oligomerisation, as, for example, in metal surface treatment processes. 15 Ytterbium and erbium (III) tend to promote oligomerisation and hence these catalysts are more suitable for use in crosslinked gel formation processes, such as the generation of solgels, aerogels, xerogels and alcogels.

Silicon-29 NMR measurements were performed at higher concentrations of 20 silane and lower concentrations of water. The rate of oligomerisation at 1% concentration silane will be lower than that at 10% by mass silane.

Table 6

Catalyst Mol ratio Mol ratio Mol raffo Concentration Mass % Mass % Mass % Mass a/. Half life of Water Silane catalyst silane Water Solvent Sllane catalyst silanetriol / g dm-3 / mins EuTFMS 5 0.2 0.01 94.20 21.2 1 48. 9 10.00 1.27 141 YbTFMS 5 0.2 0.01 94.24 21.2 48.8 10.00 1.31 84 ErTFMS 5 0.2 0.01 94.20 21.2 48.9 10.00 1.30 131 SmTFMS 5 0.2 0.01 94. 20 21.2 48.9 10.00 1.26 102 25 LaTFMS 5 0.2 0.01 94.20 21.2 48.9 10.00 1. 24 <80

Claims

1. A process for the hydrolysis of a silane having at least one hydrolyzable group which comprises contacting the silane with water in the presence of a catalyst 5 comprising a rare earth metal salt with a non-nucleophilic ligand.

2. A process for effecting treatment of the surface of a material having a superficial oxide or hydroxide layer, which comprises applying the product of the process of claim I to said surface.

3. A process for effecting treatment of the surface of a material having a superficial oxide or hydroxide layer, which comprises exposing the surface to a silane having at least one substituent group which is capable of being hydrolysed, in the presence of water and a catalyst comprising a rare earth metal salt with a 15 non-nucleophilic ligand.

4. A process as claimed in any of claims 1 to 3 wherein the nonnucleophilic ligand is selected from the group comprising trifluoromethanesulfonate, perchlorate, oxalate, acetate and other alkanoate having a chain length of from 2 to 10 carbon 20 atoms, hexafluoroacetylacetonate and acetylacetonate.

5. A process as claimed in claim 4 wherein the ligand is trifluoromethanesulfonate.

6. A process as claimed in any of claims 1 to 5 wherein the rare earth metal is a 25 lanthanide.

7. A process as claimed in claim 6 wherein the rare earth metal is lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, dysprosium, erbium, thulium, and ytterbium.

8. A process as claimed in claim 7 wherein the catalyst comprises samarium (III) trifluoromethanesulfonate (triflate), europium (III) trifluoromethanesulfonate (triflate), erbium(III) trifluoromethanesulfonate (triflate), or ytterbium (III) 5 trifluoromethanesulfonate (triflate).

9. A process as claimed in any preceding claim wherein the catalyst is selected to produce a desired rate of silane hydrolysis.

10 10. A process as claimed in any of the preceding claims wherein the hydrolyzable group on the silane comprises an alkoxy group, O-aryl group, halide, carboxylate, thiol, silthian, mercaptosilane, nitrite, cyanate, peroxy, amine, silazane, diamino, perchlorate, phosphate, borate, titanate or aluminate.

15

1 1. A process as claimed in claim 10 wherein the hydrolyzable group on the silane comprises at least one alkoxy group.

12. A process as claimed in claim 1 1 wherein the silane has from 2 to 4 alkoxy groups having the same or different lower alkyl substituents.

13. A process as claimed in claim 12 wherein the silane comprises vinyltrimethoxysilane, chloropropyltrimethoxysilane, 3-(triethoxysilyl) propyl amine, 3 -(triethoxysilyl)ethylene diamine, 3-(trimethoxysilyl) propyl methacrylate, 3-(trimethoxysilyl)propyl acrylate, 3(triethoxysilyl)propyl third, 25 tetraethoxysilane(TEOS), tetramethoxysilane(TMOS) ory-glycidoxypropyl trimethoxysilane (GPS).

14. A process as claimed in claim 13 wherein the silane is yglycidoxypropyl trimethoxysilane (GPS).

15. A process as claimed in any of claims 1 to 14 wherein the catalyst is typically present in an amount of from 0.01% to 2% by mass.

16. A process as claimed in any of claims 1 to 15 which is carried out in aqueous solution. 5

17. A process as claimed in any of claims 1 to 15, which is carried out in a solvent comprised of water and at least one organic solvent.

18. A process as claimed in claim 17 wherein the at least one organic solvent is methanol, ethanol, acetone, acetonitrile or isopropanol.

19. A process as claimed in claim 17 or claim 18 wherein the organic solvent is present in an amount of from 0%-99% by mass of the solvent.

20. A process as claimed 19 wherein the organic solvent is present in an amount of 15 from 75%-99% by mass of the solvent.

21. A process as claimed in claim 2 or claim 3 or in any of claims 4 to 20 when dependent thereon, wherein the material to be treated is a metal or metal alloy.

20

22. A process as claimed in claim 2 or claim 3 or in any of claims 4 to 20 when dependent thereon, wherein the material to be treated is a nonmetallic.

23. A process as claimed in claim 21 wherein the metal or metal alloy is selected from the group comprising aluminium, aluminium alloys, steels, chromium, 25 chromium alloys, titanium, magnesium alloys, copper, tin and brass.

24. A process as claimed in any of claim 23 wherein the surface to be treated is mild steel. 30

25. A process as claimed in claim 22 wherein the non-metallic is selected from the group comprising glass, silica, clays and talc.

26. A process as claimed in claim 2 or claim 3 or in any of claims 4 to 25 when dependent thereon, wherein the silane is present in an amount of from 0.01% to 5% by mass of the reaction mixture.

s

27. A process as claimed in claim 26 wherein the silane is present in an amount of from 0. 1% to 2% by mass of the reaction mixture.

28. A process as claimed in claim 26 wherein the silane is present in an amount of 10 0.01% to 5% by mass, the catalyst in an amount of from 0.01% to 2% by mass, an alcohol in an amount of from 0-98% by mass and water in an amount of from 2%-100% by mass.

29. A process as claimed in claim 28 wherein the silane is present in an amount of 15 0.1% to 2% by mass, the catalyst in an amount of from 0. l % to 0.5% by mass, an alcohol in an amount of from 75-99% by mass, water in an amount of from 2%-10% by mass.

30. A process as claimed in any of claims 26 to 29 wherein the silane is GPS.

31. A process as claimed in any preceding claim wherein the process is carried out at a temperature of from 15 to 40 C.

32. A process as claimed in claim 31 wherein the process is carried out at ambient 25 temperature.

33. A process as claimed in claim l or in any of claims 4 to 32 when dependent thereon, carried out under conditions such that a silicon-based gel is obtained.

30

34. A process as claimed in claim 33 wherein the conditions include a high ratio of silane to solvent.

35. A process as claimed in claim 33 or claim 34 wherein the catalyst and silane to solvent ratio are selected to promote formation of a siliconbased gel.

5

36. A process as claimed in claim 34 or claim 35 wherein the silane is present in an amount of 75-90% by mass, with the alcohol in an amount of from 6-22% by mass, water in an amount of from 2%-10% by mass and the catalyst in an amount of from 0.01% to 2% by mass.

10

37. A process claimed in any of claims 33 to 36 wherein the silane is tetraethoxysilane (TEDS) or tetramethoxysilane (TMOS).

38. A process as claimed in any of claims 33 to 37 wherein the catalyst is ytterbium (III) trifluoromethanesulfonate or erbium (III) trifluoromethanesulfonate.

39. A process as herein described and with particular reference to the examples.