FR2710629A1 - New process for the preparation of precipitated silica, new precipitated silicas and their use in reinforcing elastomers - Google Patents

Abstract

The invention relates to a new process for the preparation of precipitated silica which has a natural disposition towards dispersion and excellent reinforcing properties. It also relates to new silicas which are provided in the powder, substantially spherical ball or granule form, these silicas being characterised in that they have a CTAB specific surface of between 140 and 240 m<2>/g, with a high deagglomeration factor with ultrasound, a low median diameter, after deagglomeration with ultrasound, and, optionally, a pore distribution such that the pore volume resulting from the pores whose diameter is between 175 and 275 ANGSTROM represents less than 50 % of the pore volume resulting from the pores with diameters less than or equal to 400 ANGSTROM . The invention also relates to the use of the said silicas as reinforcing fillers for elastomers.

Description

New process for the preparation of precipitated silica.

new aforementioned silicas and their use

reinforcement of elastomers.

The present invention relates to a new process for the preparation of precipitated silica, precipitated silicas which are in particular in the form of powder, of substantially spherical beads or of granules, and their application.

as a reinforcing filler for elastomers.

It is known that precipitated silica has been used for a long time as a filler

reinforcing white in elastomers, in particular in tires.

However, like any reinforcing filler, it should be able to be handled on the one hand, and above all to be incorporated on the other hand, easily in the mixtures. It is generally known that in order to obtain the optimum reinforcing properties conferred by a filler, the latter should be present in the elastomeric matrix in a final form which is both the

as finely divided as possible and distributed as evenly as possible.

However, such conditions can only be achieved insofar as, on the one hand, the filler has a very good ability to be incorporated into the matrix during mixing with the elastomer (incorporability of the filler) and to disintegrate or disintegrate in the form of a very fine powder (disintegration of the filler), and o, on the other hand, the powder resulting from the aforementioned disintegration process can itself, in turn, disperse perfectly and of

homogeneous manner in the elastomer (dispersion of the powder).

In addition, for reasons of reciprocal affinities, the silica particles have

an unfortunate tendency, in the elastomeric matrix, to agglomerate between them.

These silica / silica interactions have the detrimental consequence of limiting the reinforcing properties to a level appreciably lower than that which would be theoretically possible to achieve if all the silica / elastomer interactions likely to be created during the operation of mixture, were actually obtained (this theoretical number of silica / elastomer interactions being, as is well known, directly proportional to the external surface, of the silica used). In addition, such silica / silica interactions tend, in the uncured state, to increase the stiffness and the consistency of the mixtures, thus making their processing more difficult. The problem arises of having fillers which, while being able to have a relatively large size, exhibit an aptitude for dispersion in

elastomers very satisfactory.

The object of the present invention is to obviate the aforementioned drawbacks and to solve the aforementioned problem. More precisely, its aim in particular is to propose a new process for preparing precipitated silica having, advantageously, an aptitude for dispersion (and for disagglomeration) and / or generally improved reinforcing properties, in particular which, used in as a reinforcing filler for elastomers, gives them an excellent compromise

between their different mechanical properties.

The invention also relates to precipitated silicas which are preferably in the form of powder, substantially spherical beads or, optionally, granules, and which, while having a relatively large size, have dispersibility (and to disagglomeration) very

satisfactory and generally improved reinforcing properties.

Finally, it relates to the use of said precipitated silicas as

reinforcing filler for elastomers.

Thus, one of the objects of the invention is a process for preparing precipitated silica of the type comprising the reaction of an alkali metal silicate M with an acidifying agent, whereby a suspension of precipitated silica is obtained, then the separation and drying of this suspension, characterized in that the precipitation is carried out in the following manner: (i) an initial base stock is formed comprising a part of the total quantity of the alkali metal silicate M involved in the reaction , the silicate concentration expressed in SiO2 in said starter being less than 20 g / l, (ii) the acidifying agent is added to said initial starter until at least 5% of the quantity of M20 present in said initial stock are neutralized, (iii) acidifying agent and the remaining quantity of alkali metal silicate are added to the reaction medium simultaneously, such as the quantity of silica added / quantity of silica present in the base of init tank ial (or rate of

consolidation) is between 12 and 100.

It was thus found that a very low concentration of silicate expressed as SiO2 in the initial stock as well as an appropriate consolidation rate during the simultaneous addition step were important conditions for

to give the products obtained their excellent properties.

It should be noted, in general, that the process concerned is a process for the synthesis of precipitated silica, that is to say that an acidifying agent is made to act on an alkali metal silicate M. the choice of the acidifying agent and the silicate is made in a manner well known per se. It may be recalled that, as an acidifying agent, a strong mineral acid such as sulfuric acid, nitric acid or hydrochloric acid, or an organic acid such as acetic acid, formic acid or hydrochloric acid, is generally used.

carbonic acid.

Any common form of silicates such as metasilicates, disilicates and advantageously a silicate of silicate can also be used as silicate.

alkali metal M in which M is sodium or potassium.

In general, as acidifying agent, the acid

sulfuric acid, and, as silicate, sodium silicate.

In the case where sodium silicate is used, the latter has, in general, an SiO2 / Na2O molar ratio of between 2 and 4, more particularly

between 3.0 and 3.7.

As regards more particularly the method of preparation of the invention, the precipitation is carried out in a specific manner according to the following steps. First of all, a starter is formed which comprises silicate. The quantity of silicate present in this initial yeast starter advantageously does not represent

that part of the total amount of silicate involved in the reaction.

According to an essential characteristic of the preparation process according to the invention, the silicate concentration in the initial starter is less than 20 g of SiO2 per liter. Preferably, this concentration is at most 11 g / I and,

optionally, at most 8 g / l.

The conditions imposed on the silicate concentration in the starter

initial condition in part the characteristics of the silicas obtained.

The initial starter can include an electrolyte. Nevertheless, preferably, no electrolyte is used during the preparation process according to the invention; in particular, preferably, the initial starter does not

does not include electrolyte.

The term electrolyte is understood here in its normal meaning, that is to say that it means any ionic or molecular substance which, when in solution, decomposes or dissociates to form ions or charged particles. Mention may be made, as electrolyte, of a salt from the group of salts of alkali metals and alkaline earth metals, in particular the salt of the starting silicate metal and of the acidifying agent, for example sodium sulfate in the case of the reaction of a

sodium silicate with sulfuric acid.

The second step is to add the acidifying agent to the starter.

of composition described above.

Thus, in this second step, the acidifying agent is added to said initial starter until at least 5%, preferably at least 50%, of the

quantity of M20 present in said initial starter are neutralized.

Preferably, in this second step, the acidifying agent is added to said initial starter until 50 to 99% of the amount of

M20 present in said initial starter are neutralized.

The acidifying agent can be diluted or concentrated; its normality may be between 0.4 and 36 N, for example between 0.6 and 1.5 N. In particular, in the case where the acidifying agent is sulfuric acid, its concentration is preferably between 40 and 180 g / l, for example between

60 and 130 g / l.

Once the desired value of quantity of neutralized M20 has been reached, a simultaneous addition (step (iii)) of acidifying agent and of a

amount of alkali metal silicate M such as the consolidation rate, i.e.

say the quantity of silica added / quantity of silica present in the initial yeast starter ratio is between 12 and 100, preferably between 12 and 50, in

especially between 13 and 40.

Preferably, throughout step (iii), the amount of acidifying agent added is such that 80 to 99%, for example 85 to 97%, of the amount of M20

added are neutralized.

The acidifying agent used during step (iii) can be diluted or concentrated; its normality may be between 0.4 and 36 N, for example between 0.6 and 1.5 N. In particular, in the case where this acidifying agent is sulfuric acid, its concentration is preferably between 40 and 180 g / l, for example between

and 130 g / l.

In general, the alkali metal silicate M added during step (iii) has a concentration expressed as silica of between 40 and 330 g / l, for example

between 60 and 250 g / l.

The actual precipitation reaction is complete when we have

added all the remaining amount of silicate.

It is advantageous to carry out, in particular after the aforementioned simultaneous addition, a maturing of the reaction medium, this maturing possibly by

example last from 1 to 60 minutes, especially 5 to 30 minutes.

Finally, it is desirable, after precipitation, in a subsequent step, in particular before possible ripening, to add an additional quantity of acidifying agent to the reaction medium. This addition is generally carried out until a pH value of the reaction medium of between 3 and 6.5, preferably between 4 and 5.5, is obtained. It makes it possible in particular to neutralize all the quantity of M20 added during step (iii) and to adjust the pH of the final silica to

the desired value for a given application.

The acidifying agent used during this addition is generally identical to

that used during step (iii) of the preparation process according to the invention.

The temperature of the reaction medium is usually between 60

and 98 C.

Preferably, the addition of acidifying agent during step (ii) is carried out in

an initial starter whose temperature is between 60 and 96 C.

According to one variant of the invention, the reaction is carried out at a constant temperature of between 75 and 96 C. According to another variant of the invention, the end of reaction temperature is higher than the start of reaction temperature: thus , the temperature is maintained at the start of the reaction preferably between 70 and 96 C, then the temperature is increased during the reaction in a few minutes, preferably to a value between

80 and 98 C, value at which it is maintained until the end of the reaction.

At the end of the operations which have just been described, a silica slurry is obtained which is then separated (liquid-solid separation). This separation generally consists of filtration, followed by washing if necessary. Filtration can be done by any suitable method, for example by filter

press or belt filter or rotary vacuum filter.

The precipitated silica suspension thus recovered (filter cake) is

then dried.

This drying can be done by any means known per se.

Preferably, the drying is carried out by atomization.

For this purpose, any suitable type of atomizer can be used, in particular

atomizers with turbines, nozzles, liquid pressure or two fluids.

According to a variant of the process of the invention, the suspension to be dried has a solids content greater than 15% by weight, preferably greater than 17% by weight. Drying is then generally carried out at

by means of an atomizer with turbines or, preferably, with nozzles.

The precipitated silica capable of being obtained according to this variant of the invention is generally in the form of beads substantially

spherical, preferably of an average size of at least 80 µm.

This dry matter content can be obtained directly by filtration.

using a suitable filter resulting in a filter cake of the correct content.

Another method consists, after filtration, at a later stage of the process, in adding dry matter to the cake, for example silica in powder form, so as to obtain the necessary content. It should be noted that, as is well known, the cake thus obtained is not, in general, under conditions allowing atomization.

especially because of its excessively high viscosity.

In a manner known per se, the cake is then subjected to a crumbling operation. This operation can be done by passing the cake through a colloidal or ball type mill. Furthermore, to lower the viscosity of the suspension to be atomized, it is possible to add aluminum, in particular in the form of sodium aluminate during the process as described in patent application FR-A-2536380, of which the teaching is incorporated here. This addition can

be done in particular at the time of the disintegration.

After drying, a grinding step can be carried out on the product recovered, in particular on the product obtained by drying the suspension having a dry matter content greater than 15% by weight. The precipitated silica which is then obtainable is generally in the form of a powder, preferably with an average size of at least 15 μm, in

in particular between 15 and 60 pm, for example between 20 and 45 pm.

The products ground to the desired particle size can be separated from any non-conforming products by means, for example, of vibrating sieves having appropriate mesh sizes, and the non-conforming products as well.

recovered be returned to shredding.

Likewise, according to another variant of the process of the invention, the suspension to be dried has a dry matter content of less than 15% by weight. The drying is then generally carried out by means of a turbine or nozzle atomizer. The precipitated silica which is then capable of being obtained according to this variant of the invention is generally in the form of a powder, preferably with an average size of at least 15 μm, in particular between 30 μm.

and 150 µm, for example between 45 and 120 µm.

A disintegration operation can also be carried out here.

Finally, the dried product (in particular from a suspension having a dry matter content of less than 15% by weight) or ground can, according to another

variant of the process of the invention, be subjected to an agglomeration step.

Agglomeration is understood here to mean any process which makes it possible to bind together finely divided objects in order to bring them in the form of objects of more

large size and mechanically resistant.

These processes are in particular direct compression, wet granulation (that is to say with the use of a binder such as water, silica slurry, etc.),

extrusion and, preferably, dry compaction.

When the latter technique is implemented, it may prove to be advantageous, before proceeding with the compaction, to deaerate (an operation also called pre-densification or degassing) the powdery products so as to

eliminate the air included in them and ensure a more regular compaction.

The precipitated silica capable of being obtained according to this variant of the invention is advantageously in the form of granules, of

preferably at least 1 mm in size, in particular between 1 and 10 mm.

At the end of the agglomeration step, the products can be calibrated to a desired size, for example by sieving, then packaged for their future use. The powders, as well as the beads, of precipitated silica obtained by the process of the invention thus offer the advantage, among other things, of accessing in a simple, efficient and economical manner granules as mentioned above, in particular by operations. conventional shaping, such as for example granulation or compaction, without the latter leading to degradation liable to mask, or even annihilate, the excellent intrinsic reinforcing properties attached to these powders, as may be the case

in the prior art by using conventional powders.

Other objects of the invention consist of novel precipitated silicas having a good aptitude for dispersion (and disagglomeration) and generally improved reinforcing properties, said silicas preferably exhibiting a relatively large size and generally being obtained according to l 'a

variants of the preparation process of the invention described above.

In the following description, the BET specific surface area is determined according to the BRUNAUER - EMMET - TELLER method described in "The journal of the American Chemical Society", Vol. 60, page 309, February 1938 and corresponding to

the NFT 45007 standard (November 1987).

The CTAB specific surface is the external surface determined according to the

standard NFT 45007 (November 1987) (5.12).

The DOP oil intake is determined according to standard NFT 30-022 (March

1953) by using dioctylphthalate.

The packed density (DRT) is measured according to the standard

NFT-030100.

Finally, it is specified that the given pore volumes are measured by mercury porosimetry, the pore diameters being calculated by the WASHBURN relationship with a theta contact angle equal to 130 and a gamma surface tension equal to 484 Dynes / cm (MICROMERITICS porosimeter

9300).

The ability to disperse and deagglomerate the silicas according to the invention can be quantified by means of a specific test of

disagglomeration.

The deagglomeration test is carried out according to the following protocol: the cohesion of the agglomerates is assessed by a particle size measurement (by laser diffraction), carried out on a suspension of silica previously deagglomerated by ultrasound; the aptitude for disagglomeration of the silica is thus measured (breaking objects of 0.1 to a few tens of microns). Ultrasonic deagglomeration is carried out using a VIBRACELL BIOBLOCK sonicator (600 W), equipped with a 19 mm diameter probe. The particle size measurement is carried out by laser diffraction on a

SYMPATEC particle size analyzer.

We weigh in a pillbox (height: 6 cm and diameter: 4 cm) 2 grams of silica and make up to 50 grams by adding deionized water: an aqueous suspension of 4% silica is thus produced which is homogenized for 2 minutes by magnetic stirring. The disintegration is then carried out under ultrasound as follows: the probe being immersed over a length of 4 cm, the output power is adjusted so as to obtain a deviation of the needle of the power dial indicating 20% (which corresponds to an energy dissipated by the probe tip of 120 Watt / cm2). The deagglomeration is carried out for 420 seconds. The particle size measurement is then carried out after having introduced into the tank of the particle size analyzer a volume (expressed in ml) known to the

homogenized suspension.

The value of the median diameter 050 which is obtained is all the lower as the silica exhibits a high capacity for deagglomeration. The ratio (10 × volume of suspension introduced (in ml)) / optical density of the suspension detected by the particle size analyzer (this optical density is of the order of 20) is also determined. This ratio is indicative of the level of fines, that is to say of the level of particles smaller than 0.1 μm which are not detected by the particle size analyzer. This ratio, called the ultrasonic disagglomeration factor (FD), is all the more

high that silica exhibits high deagglomeration ability.

It is now proposed, according to a first embodiment of the invention, a novel precipitated silica characterized in that it has: a CTAB specific surface (ScTAB) of between 140 and 240 m2 / g, preferably between 140 and 225 m2 / g, for example between 150 and 225 m2 / g, - an ultrasonic deagglomeration factor (FD) greater than 11 ml, preferably greater than 12.5 ml, - a median diameter (050), after ultrasonic deagglomeration, less than 2.5 pm, preferably less than 2.4 pm, for example less than

2.0 µm.

A second embodiment of the invention consists of a novel precipitated silica characterized in that it has: - a CTAB (ScTAB) specific surface area of between 140 and 240 m2 / g, preferably between 140 and 225 m2 / g, for example between 150 and 225 m2 / g, - a pore distribution such that the pore volume formed by the pores whose diameter is between 175 and 275 A represents less than 50% of the pore volume formed by the pores of smaller or equal diameters at 400 A, - an ultrasound deagglomeration factor (FD) greater than 5.5 ml, - a median diameter (50), after ultrasonic deagglomeration,

less than 5 µm.

One of the characteristics of the silica according to the second embodiment of the invention therefore also resides in the distribution, or distribution, of the pore volume, and more particularly in the distribution of the pore volume which is generated by the pores of smaller or equal diameters. at 400 A. This last volume corresponds to the useful pore volume of the fillers which are used in the reinforcement of the elastomers. Analysis of the porograms shows that the silicas according to the second embodiment of the invention are such that less than%, preferably less than 40%, of said useful pore volume consists of pores whose diameter is within the range from 175 to 275 A. Preferably, the silicas according to the second embodiment of the invention have: an ultrasonic deagglomeration factor (FD) greater than 11 ml, for example greater than 12.5 ml, and / or a median diameter (05), after ultrasound deagglomeration,

less than 4 µm, for example less than 2.5 µm.

The silicas according to the invention generally have a BET specific surface (SBET) of between 140 and 300 m2 / g, in particular between 140 and 280 m2 / g,

for example between 150 and 270 m2 / g.

According to a variant of the invention, the silicas have an SBET / SCTAB ratio of between 1.0 and 1.2, that is to say that the silicas have a

low microporosity.

According to another variant of the invention, the silicas have an SBET / SCTAB ratio greater than 1.2, for example between 1.21 and 1.4, that is to say

that silicas have a relatively high microporosity.

The silicas according to the invention have a DOP oil uptake generally between 150 and 400 ml / 100 g, more particularly between 180 and 350.

ml / 100 g, for example between 200 and 310 ml / 100 g.

The silicas according to the invention may be in the form of powder, of substantially spherical beads or, optionally, of granules, and are in particular characterized in that, while having a relatively large size, they exhibit an aptitude for deagglomeration and with remarkable dispersion and very satisfactory reinforcing properties. They thus exhibit an aptitude for disagglomeration and advantageously greater dispersion, with identical or similar specific surface area and identical size or

similar, to those of the silicas of the prior art.

The silica powders according to the invention preferably have an average size of at least 15 μm; this is for example between 20 and pm or between 15 and -60 (in particular between 20 and 45 pm) or between 30 and 150 pm

(especially between 45 and 120 pm).

The packed density (DRT) of said powders is, in

general, at least 0.17, and, for example, between 0.2 and 0.3.

Said powders generally have a total pore volume of at least

less 2.5 cm3 / g, and more particularly between 3 and 5 cm3 / g.

They make it possible to obtain a very good compromise between processing and final mechanical properties in the vulcanized state. Finally, they constitute privileged precursors for the synthesis of

granules as described below.

The substantially spherical balls according to the invention have

preferably an average size of at least 80 μm.

According to certain variants of the invention, this average size of the beads is at least 100 μm, for example at least 150 μm; it is generally at most 300 μm and is preferably between 100 and 270 μm. This average size is determined according to standard NF X 11507 (December 1970) by dry sieving and determination of the diameter corresponding to a cumulative refusal of 50%. The packed density (DRT) of said balls is, in

general, at least 0.17, and, for example, between 0.2 and 0.34.

They generally have a total pore volume of at least 2.5 cm3 / g,

and more particularly, between 3 and 5 cm3 / g.

As indicated above, such a silica in the form of substantially spherical beads, advantageously solid, homogeneous, low in dust and with good flowability, has very good aptitude for deagglomeration and dispersion. In addition, it has excellent reinforcing properties. Such a silica also constitutes a preferred precursor for the synthesis of

powders and granules according to the invention.

The dimensions of the granules according to the invention are preferably at least 1 mm, in particular between 1 and 10 mm, along the axis of their greatest dimension (length). Said granules can be in the most diverse forms. By way of example, mention may in particular be made of the spherical, cylindrical, parallelepipedal, pellet, wafer, pellet, sectional extrusion shapes.

circular or polylobed.

The packed density (DRT) of said granules is generally at least 0.27 and can range up to 0.37.

They generally have a total pore volume of at least 1 cm3 / g, and,

more particularly, between 1.5 and 2 cm3 / g.

The silicas according to the invention, in particular in the form of powder, of substantially spherical beads or of granules, are preferably prepared according to one of the appropriate variants of the preparation process according to the invention.

and described previously.

The silicas according to the invention or prepared by the process according to the invention find a particularly advantageous application in the reinforcement of elastomers, natural or synthetic, and in particular of tires. They give these elastomers an excellent compromise between their various mechanical properties, and in particular a significant improvement in their resistance to breaking and tearing, and, in general, good abrasion resistance. In addition, these elastomers are preferably subject to

reduced heating.

The following examples illustrate the invention without, however, limiting its scope.

EXAMPLE1

662 liters of a sodium silicate solution (SiO2 / Na2O molar ratio equal to 3.4) are introduced into a stainless steel reactor fitted with a propeller stirring system and double jacket heating. having

a concentration expressed as silica of 7.1 g / l.

The silicate concentration expressed as SiO2 in the initial starter is therefore 7.1 g / l. The solution is then brought to a temperature of 85 ° C. while maintaining it under stirring. The entire reaction is carried out at 85 ° C. A sulfuric acid solution, of concentration equal to 80 g / l, is then introduced therein, for 3 min and 20 s, at a flow rate of 7.3 l / min. ; at the end of this addition, the neutralization rate of the starter is 85%, i.e. 85% of the

quantity of Na2O present in the initial starter are neutralized.

The following are then introduced simultaneously, for 70 min, into the reaction medium: - a sulfuric acid solution, with a concentration equal to 80 g / l, at a flow rate of 7.3 l / min, and - a solution of sodium silicate , concentration expressed as silica

equal to 130 g / l, at a flow rate of 10.1 l / min.

During this simultaneous addition, the instantaneous neutralization rate is 92%, i.e. 92% of the amount of Na2O added (per min) are

neutralized.

The rate of consolidation, at the end of this simultaneous addition, is equal to 19.6. After introducing all of the silicate, the sulfuric acid solution is continued to be introduced at the same rate, and this for 10 min. This additional introduction of acid then brings the pH of the reaction medium to

a value equal to 4.5.

A precipitated silica slurry is thus obtained which is filtered and washed by means of a rotary vacuum filter so that a silica cake is finally recovered, the loss on ignition of which is 87% (therefore a material content dried

13% by weight).

This cake is then fluidized by simple mechanical action. After this disintegration operation, the resulting slurry is atomized by means of an atomizer

with turbines.

The characteristics of the silica P1 in powder form (in accordance with the invention) are then the following: - CTAB specific surface area 159 m2 / g - BET specific surface area 195 m2 / g - pore volume V1 represented by the pores of d <400 A 0.94 cm3 / g - pore volume V2 represented by the pores 175 A <d <275 A 0.41 cm3 / g - V2Nl ratio 44% - average particle size 60 μm The silica P1 is subjected to the disagglomeration test as as defined

previously in the description.

After disintegration with ultrasound, it has a median diameter

(05) of 1.2 µm and an ultrasonic deagglomeration factor (FD) of 12 ml.

EXAMPLE 2

662 liters of a sodium silicate solution (SiO2 / Na2O molar ratio equal to 3.4) are introduced into a stainless steel reactor fitted with a propeller stirring system and double jacket heating. having

a concentration expressed as silica of 5 g / l.

The silicate concentration expressed as SiO2 in the initial starter is therefore 5 g / l. The solution is then brought to a temperature of 85 ° C. while maintaining it under stirring. The entire reaction is carried out at 85 ° C. A solution of sulfuric acid, of concentration equal to 80 g / l, is then introduced into it for 3 min and 20 s, at a flow rate of 5.1 l / min. ; at the end of this addition, the neutralization rate of the starter is 85%, i.e. 85% of the

quantity of Na2O present in the initial starter are neutralized.

The following are then introduced simultaneously, for 70 min, into the reaction medium: - a sulfuric acid solution, with a concentration equal to 80 g / l, at a flow rate of 5.1 l / min, and - a solution of sodium silicate , concentration expressed as silica

equal to 130 g / l, at a flow rate of 7.1 l / min.

During this simultaneous addition, the instantaneous neutralization rate is 92%, that is to say that 92% of the amount of Na2O added (per min) is neutralized. The consolidation rate, at the end of this simultaneous addition, is equal to

19.5.

After introducing all of the silicate, the sulfuric acid solution is continued to be introduced at the same rate, and this for 10 min. This additional introduction of acid then brings the pH of the reaction medium to

a value equal to 4.5.

A precipitated silica slurry is thus obtained which is filtered and washed by means of a rotary vacuum filter so that a silica cake is finally recovered, the loss on ignition of which is 87% (therefore a material content dried

13% by weight).

This cake is then fluidized by simple mechanical action. After this disintegration operation, the resulting slurry is atomized by means of an atomizer

with turbines.

The characteristics of the silica P2 in powder form (in accordance with the invention) are then the following: - CTAB specific surface area 182 m2 / g - BET specific surface area 225 m2 / g - pore volume V1 represented by the pores of d _ 400 A 0.93 cm3 / g - pore volume V2 represented by the pores 175 A _ d <275 At 0.30 cm3 / g - V2N1 ratio 32% - average particle size 60 μm The silica P2 is subjected to the deagglomeration test as as defined

previously in the description.

After disintegration with ultrasound, it has a median diameter

(05o) of 2.9 µm and an ultrasonic deagglomeration factor (FD) of 14 ml.

EXAMPLE 3

The procedure is as in Example 2, except for the simultaneous addition of sulfuric acid and sodium silicate solutions. Thus: 662 liters of a sodium silicate solution (SiO2 / Na2O molar ratio equal to 3, 4) having

a concentration expressed as silica of 5 g / l.

The silicate concentration expressed as SiO2 in the initial starter is therefore 5 g / l. The solution is then brought to a temperature of 85 ° C. while maintaining it under stirring. The entire reaction is carried out at 85 ° C. A solution of sulfuric acid, of concentration equal to 80 g / l, is then introduced into it for 3 min and 20 s, at a flow rate of 5.1 l / min. ; at the end of this addition, the neutralization rate of the starter is 85%, i.e. 85% of the

quantity of Na2O present in the initial starter are neutralized.

The following are then introduced simultaneously, for 70 min, into the reaction medium: - a solution of sulfuric acid, with a concentration equal to 80 g / l, at a flow rate of 5.1 l / min, and - a solution of sodium silicate, concentration expressed in silica

equal to 230 g / l, at a flow rate of 4.1 l / min.

During this simultaneous addition, the instantaneous neutralization rate is 92%, i.e. 92% of the amount of Na2O added (per min) are

neutralized.

The rate of consolidation, at the end of this simultaneous addition, is equal to 19.9. After introducing all of the silicate, the sulfuric acid solution is continued to be introduced at the same rate, and this for 10 min. This additional introduction of acid then brings the pH of the reaction medium to a value equal to 4.5. A precipitated silica slurry is thus obtained which is filtered and washed by means of a rotary vacuum filter so that the a silica cake is finally recovered, the loss on ignition of which is 87.1% (therefore a material content

12.9% by weight).

This cake is then fluidized by simple mechanical action. After this disintegration operation, the resulting slurry is atomized by means of an atomizer

with turbines.

The characteristics of the silica P3 in powder form (in accordance with the invention) are then as follows: - CTAB specific surface area 215 m2 / g - BET specific surface area 221 m2 / g - pore volume Vl represented by the pores of d <400 A 0.93 cm3 / g - pore volume V2 represented by the pores 175 A <d <275 A 0.42 cm3 / g - ratio V2 / VN1 45% - average particle size 60 μm The silica P3 is subjected to the test of disagglomeration as defined

previously in the description.

After disintegration with ultrasound, it has a median diameter

(05) of 1.2 µm and an ultrasonic deagglomeration factor (FD) of 20 mi.

EXAMPLE 4

662 liters of a sodium silicate solution (SiO2 / Na2O molar ratio equal to 3.4) are introduced into a stainless steel reactor fitted with a propeller stirring system and double jacket heating. having

a concentration expressed as silica of 3.85 g / l.

The silicate concentration expressed as SiO2 in the initial starter is therefore 3.85 g / l. The solution is then brought to a temperature of 85 ° C. while maintaining it under stirring. The entire reaction is carried out at 85 ° C. A solution of sulfuric acid, of concentration equal to 80 g / l, is then introduced therein for 3 min and 20 s, at a flow rate of 3.9 l / min. ; at the end of this addition, the neutralization rate of the starter is 85%, i.e. 85% of the

quantity of Na2O present in the initial starter are neutralized.

The following are then introduced simultaneously, for 70 min, into the reaction medium: - a sulfuric acid solution, with a concentration equal to 80 g / l, at a flow rate of 3.9 l / min, and - a solution of sodium silicate , concentration expressed as silica

equal to 65 g / l, at a flow rate of 10.9 l / min.

During this simultaneous addition, the instantaneous neutralization rate is 92%, that is to say that 92% of the amount of Na2O added (per min) is neutralized. The rate of consolidation, at the end of this simultaneous addition, is equal to 19.5. After introducing all of the silicate, the sulfuric acid solution is continued to be introduced at the same rate, and this for 10 min. This additional introduction of acid then brings the pH of the reaction medium to

a value equal to 4.5.

A precipitated silica slurry is thus obtained which is filtered and washed by means of a rotary vacuum filter so that a silica cake is finally recovered, the loss on ignition of which is 87.1% (therefore a rate of matter

12.9% by weight).

This cake is then fluidized by simple mechanical action. After this disintegration operation, the resulting slurry is atomized by means of an atomizer

with turbines.

The characteristics of the silica P4 in powder form (in accordance with the invention) are then as follows: - CTAB specific surface area 210 m2 / g - BET specific surface area 244 m2 / g - pore volume V1 represented by the pores of d <400 At 0.89 cm3 / g - pore volume V2 represented by the pores 175 A <d <275 A 0.20 cm3 / g - ratio V2 / VN1 22% - mean particle size 60 μm The silica P4 is subjected to the test of disagglomeration as defined

previously in the description.

* After disintegration with ultrasound, it has a median diameter

(0.) of 4.1 µm and an ultrasonic deagglomeration factor (FD) of 13 µm.

EXAMPLE 5

662 liters of a sodium silicate solution (SiO2 / Na2O molar ratio equal to 3.5) are introduced into a stainless steel reactor fitted with a propeller stirring system and double jacket heating. having

a concentration expressed as silica of 5 g / l.

The silicate concentration expressed as SiO2 in the initial starter is therefore 5 g / l. The solution is then brought to a temperature of 85 ° C. while maintaining it under stirring. The entire reaction is carried out at 85 ° C. A sulfuric acid solution, of concentration equal to 80 g / l, is then introduced into it for 3 min and 8 s, at a flow rate of 5.2 l / min. ; at the end of this addition, the neutralization rate of the starter is 85%, i.e. 85% of the

quantity of Na2O present in the initial starter are neutralized.

The following are then introduced simultaneously, for 70 min, into the reaction medium: - a sulfuric acid solution, with a concentration equal to 80 g / l, at a flow rate of 5.2 l / min, and - a solution of sodium silicate , concentration expressed as silica

equal to 230 g / l, at a flow rate of 4.1 l / min.

During this simultaneous addition, the instantaneous neutralization rate is 95%, that is to say that 95% of the amount of Na2O added (per min) is neutralized. The rate of consolidation, at the end of this simultaneous addition, is equal to 19.9. After introducing all of the silicate, the sulfuric acid solution is continued to be introduced at the same rate, and this for 10 min. This additional introduction of acid then brings the pH of the reaction medium to

a value equal to 4.5.

A precipitated silica slurry is thus obtained which is filtered and washed by means of a rotary vacuum filter so that a silica cake is finally recovered, the loss on ignition of which is 86.4% (therefore a rate of matter

13.6% by weight).

This cake is then fluidized by simple mechanical action. After this disintegration operation, the resulting slurry is atomized by means of an atomizer

with turbines.

The characteristics of the silica P5 in powder form (in accordance with the invention) are then the following: - CTAB specific surface area 164 m2 / g - BET specific surface area 194 m2 / g - pore volume Vl represented by the pores of d <400 A 1.15 cm3 / g - pore volume V2 represented by the pores 175 A <d <275 A 0.70 cm3 / g - ratio V2N1 61% - average particle size 65 μm The silica P5 is subjected to the disagglomeration test as as defined

previously in the description.

After disintegration with ultrasound, it has a median diameter

(05o) of 1.2 µm and an ultrasonic deagglomeration factor (FD) of 12 mi.

EXAMPLE 6

662 liters of a sodium silicate solution (SiO2 / Na2O molar ratio equal to 3.5) are introduced into a stainless steel reactor fitted with a propeller stirring system and double jacket heating. having

a concentration expressed as silica of 5 g / l.

The silicate concentration expressed as SiO2 in the initial starter is therefore 5 g / l. The solution is then brought to a temperature of 85 ° C. while maintaining it under stirring. The entire reaction is carried out at 85 ° C. A sulfuric acid solution, of concentration equal to 80 g / l, is then introduced therein, for 3 min and 9 s, at a flow rate of 5.2 l / min. ; at the end of this addition, the neutralization rate of the starter is 85%, i.e. 85% of the

quantity of Na2O present in the initial starter are neutralized.

The following are then introduced simultaneously, for 80 min, into the reaction medium: - a sulfuric acid solution, with a concentration equal to 80 g / l, at a flow rate of 5.2 l / min, and - a solution of sodium silicate , concentration expressed as silica

equal to 230 g / l, at a flow rate of 4.1 l / min.

During this simultaneous addition, the instantaneous neutralization rate is%, i.e. 95% of the amount of Na2O added (per min) is

neutralized.

The rate of consolidation, at the end of this simultaneous addition, is equal to 22.8. After introducing all of the silicate, the sulfuric acid solution is continued to be introduced at the same rate, and this for 10 min. This additional introduction of acid then brings the pH of the reaction medium to

a value equal to 4.5.

A precipitated silica slurry is thus obtained which is filtered and washed by means of a rotary vacuum filter so that a silica cake is finally recovered, the loss on ignition of which is 86.1% (therefore a rate of matter

dry 13.9% by weight).

This cake is then fluidized by simple mechanical action. After this disintegration operation, the resulting slurry is atomized by means of an atomizer

with turbines.

The characteristics of the silica P6 in powder form (in accordance with the invention) are then as follows: - CTAB specific surface area 157 m2 / g - BET specific surface area 193 m2 / g - pore volume V1 represented by the pores of d <400 A 0.95 cm3 / g - pore volume V2 represented by the pores 175 A <d <275 A 0.42 cm3 / g - ratio V2N1 44% - average particle size 70 μm The silica P6 is subjected to the disagglomeration test as as defined

previously in the description.

After disintegration with ultrasound, it has a median diameter

(050) of 1.3 µm and an ultrasonic deagglomeration factor (FD) of 10 ml.

EXAMPLE 7

662 liters of a sodium silicate solution (SiO2 / Na2O molar ratio equal to 3.5) are introduced into a stainless steel reactor fitted with a propeller stirring system and double jacket heating. having

a concentration expressed as silica of 5 g / l.

The silicate concentration expressed as SiO2 in the initial starter is therefore 5 g / l. The solution is then brought to a temperature of 85 ° C. while maintaining it under stirring. The entire reaction is carried out at 85 ° C. A solution of sulfuric acid, of concentration equal to 80 g / l, is then introduced therein for 3 min and 30 s, at a flow rate of 5.2 l / min. ; at the end of this addition, the neutralization rate of the starter is 95%, i.e. 85% of the

quantity of Na2O present in the initial starter are neutralized.

The following are then introduced simultaneously, for 70 min, into the reaction medium: - a sulfuric acid solution, with a concentration equal to 80 g / l, at a flow rate of 5.2 l / min, and - a solution of sodium silicate , concentration expressed as silica

equal to 230 g / l, at a flow rate of 4.1 l / min.

During this simultaneous addition, the instantaneous neutralization rate is%, that is to say that 95% of the amount of Na2O added (per min) is neutralized. The consolidation rate, at the end of this simultaneous addition, is equal to

19.9.

After introducing all of the silicate, the sulfuric acid solution is continued to be introduced at the same rate, and this for 10 min. This additional introduction of acid then brings the pH of the reaction medium to

a value equal to 4.5.

A precipitated silica slurry is thus obtained which is filtered and washed using a rotary vacuum filter so that a silica cake is finally recovered, the loss on ignition of which is 86.7% (therefore a rate of matter

dry 13.3% by weight).

This cake is then fluidized by simple mechanical action. After this disintegration operation, the resulting slurry is atomized by means of an atomizer

with turbines.

The characteristics of the silica P7 in powder form (in accordance with the invention) are then the following: - CTAB specific surface area 168 m2 / g - BET specific surface area 195 m2 / g - pore volume V1 represented by the pores of d <400 A 0.94 cm3 / g - pore volume V2 represented by the pores 175 À <d <275 At 0.47 cm3 / g - ratio V2 / V1 50% - average particle size 65 μm The silica P7 is subjected to the test of disagglomeration as defined

previously in the description.

After disintegration with ultrasound, it has a median diameter

(05o) of 1.1 µm and an ultrasonic deagglomeration factor (FD) of 13 ml.

EXAMPLE 8

In a stainless steel reactor fitted with a propeller stirring system and double jacket heating, are introduced: - 626 liters of water, and - 36 liters of a sodium silicate solution (with a ratio of molar

SiO2 / Na2O equal to 3.4) having a concentration expressed as silica of 135 g / l.

The silicate concentration expressed as SiO2 in the initial starter is therefore 7.3 g / l. The solution is then brought to a temperature of 85 ° C. while maintaining it under stirring. The entire reaction is carried out at 85 ° C. A solution of sulfuric acid, of concentration equal to 80 g / l, is then introduced therein for 3 min and 30 s at a flow rate of 5.6 l / min. ; at the end of this addition, the neutralization rate of the starter is 67%, i.e. 67% of the

quantity of Na2O present in the initial starter are neutralized.

The following are then introduced simultaneously, for 70 min, into the reaction medium: - a sulfuric acid solution, with a concentration equal to 80 g / l, at a flow rate of 5.6 l / min, and - a solution of sodium silicate , concentration expressed as silica

equal to 135 g / l, at a flow rate of 8.6 l / min.

During this simultaneous addition, the instantaneous neutralization rate is%, that is to say that 80% of the amount of Na2O added (per min) is neutralized. The consolidation rate, at the end of this simultaneous addition, is equal to

16.7.

After introducing all of the silicate, the sulfuric acid solution is continued to be introduced at the same rate, and this for 10 min. This additional introduction of acid then brings the pH of the reaction medium to

a value equal to 4.5.

The reaction medium is then left to mature for 10 min (with stirring,

at 85 C)

A precipitated silica slurry is thus obtained which, after dilution with 540 liters of water, is filtered and washed by means of a rotary vacuum filter so that a silica cake is finally recovered whose loss on ignition is of

88.0% (therefore a dry matter content of 12.0% by weight).

This cake is then fluidized by mechanical and chemical action (addition of a quantity of sodium aluminate corresponding to an Al / SiO2 weight ratio of 3000 ppm). After this disintegration operation, a pumpable cake is obtained, of

pH equal to 6.4, which is then atomized by means of a turbine atomizer.

The characteristics of the silica P8 in powder form (in accordance with the invention) are then the following: - specific surface area CTAB 149 m2 / g - specific surface area BET 200 m2 / g - pore volume V1 represented by the pores of d <400 At 0.92 cm3 / g - pore volume V2 represented by the pores 175 At <d <275 At 0.50 cm3 / g - ratio V2 / V1 54% - average size of the beads 55 μm The silica P8 is subjected to the test of disagglomeration as defined

previously in the description.

After disintegration with ultrasound, it has a median diameter

(05o) of 2.3 µm and an ultrasonic deagglomeration factor (FD) of 17 ml.

EXAMPLE

By way of comparison, three silicas, with a CTAB specific surface area of between and 240 m2 / g, which can be used as reinforcing fillers for elastomers, were studied. These are: - on the one hand, two commercial silicas in powder form: - PERKASIL KS 404 powder (referenced PC1 below), sold by the AKZO Company, - ULTRASIL VN3 powder (referenced PC2 below) below), sold by the company DEGUSSA, - on the other hand, silica (referenced MP1 below), in the form of substantially spherical beads, of Example 12 of the European patent application

EP-A-0520862 (deposit no.92401677.7).

The characteristics of these silicas are collated in Table I below.

below. This table also shows, for comparison, the characteristics

silicas P1 to P8 according to the invention.

PC1 PC2 MP1 P1 P2 P3 P4 P5 P6 P7 P8 SCTAB (m2 / g) 145 155 160 159 182 215 210 164 157 168 149 SBET (m2 / g) 183 170 170 195 225 221 244 194 193 195 200 V1 (cm3 / g ) 0.76 0.93 0.90 0, 94 0.93 0.93 0.89 1.15 0.95 0.94 0.92 V2 (cm3 / g) 0.26 0.43 0.55 0 , 41 0.30 0.42 0.20 0.70 0.42 0.47 0.50 V2 / V1 (%) 34 46 61 44 32 45 20 61 44 50 54 N) Average size (pm) 12 17 260 60 60 60 60 65 70 65 55 0so (Pm) 9.45 9.9 4.3 1.2 2.9 1.2 4.1 1.2 1.3 1.1 2, 3 FD (ml) 2 , 2 2.3 6.5 12 14 20 13 12 10 13 17

TABLE I

! O

EXAMPLE 10

This example illustrates the use and behavior of silicas according to the invention and of silicas of the prior art in a formulation for industrial rubber. The following formulation is used (in parts, by weight) - Rubber S.B.R. 1712 (1) 100 - Silica 51 - Active ZnO (2) 1.81 Stearic acid 0.35

- 6PPD (3) 1.45

-CBS (4) 1.3

- DPG (5) 1.45

- Sulfur (6) 1,1 - Silane X50S (7) 8,13 (1) Styrene butadiene copolymer type 1712 (2) Zinc oxide rubber quality (3) N- (1,3-dimethyl butyl) -N'- phenyl-p- phenylene diamine (4) N-cyclohexyl 2-benzothiazyl sulfenamide (5) Diphenyl guanidine (6) Vulcanizing agent (7) Silica / rubber coupling agent (product marketed by the Company

DEGUSSA)

The formulations are prepared as follows: In an internal mixer (BANBURY type), are introduced in this order and at the times and temperatures of the mixture indicated in brackets: - SBR 1712 (to) (55 C) - the X50S and the 2/3 of the silica (to + 1 min) (90 C) - ZnO, stearic acid, 6PPD and 1/3 of the silica (to + 2 min) (110 C) The discharge of the mixer (fallen of mixing) is done when the temperature of the chamber reaches 165 C (that is to say, approximately to + 5 min). The mixture is introduced into a roller mixer, maintained at 30 C, to y

be calendered. In this mixer, CBS, DPG and sulfur are introduced.

After homogenization and three passes at the end, the final mixture is

calendered in the form of sheets 2.5-3 mm thick.

The results of the tests are as follows: 1- Rheological properties

The measurements are carried out on the formulations in the uncured state.

The results are reported in Table II below. We have indicated

the apparatus used to carry out the measurements.

TABLE II

P5 P6 P7 PC1 PC2 MP1

MOONEY consistency (1) 100 93 98 123 138 112 Minimum torque (2) 19.0 18.5 18.7 28.0 32.2 20.5 (1) MOONEY MV 200E viscometer (Mooney Large measurement (1 + 4 )) (2) MONSANTO 100 S rheometer The formulations obtained from the silicas according to the invention lead to

at the lowest values.

This reflects a greater ease of use of the mixtures prepared from the silicas according to the invention, in particular at the level of the extrusion and calendering operations often carried out during the production of tires (lower energy expenditure to put into operation. mixes, easier to inject during mixing, less swelling

in the die during extrusion, less shrinkage during calendering, etc.).

2- Mechanical properties

The measurements are carried out on the vulcanized formulations.

Vulcanization is carried out by bringing the formulations to 150 ° C. for

40 minutes.

The following standards were used: (i) tensile tests (moduli, tensile strength) NFT 46-002 or ISO 37-1977 (ii) tear strength tests

DIN 53-507

(iii) abrasion resistance tests

DIN 53-516

The results obtained are shown in Tables III and IV below.

TABLE

P5 P6 P7 PC1 PC2 MP1

100% modulus (MPa) 2.3 1.9 1.7 2.9 3.3 1.9 300% modulus (MPa) 11.1 10.3 8.5 11.7 12.2 8.3 Index of reinforcement (1) 4.8 5.4 4.9 4.0 3.7 4.4 Tensile strength (MPa) 26.4 24.5 26.0 21.1 20.9 24.4 Tear strength (kN / m) 21.0 22.5 21.0 13.7 14.0 20.0 (1) corresponds to the ratio: modulus 300% / modulus 100% These latest results show an overall improvement in the reinforcement effect conferred by the silicas according to the invention compared to silicas of

the prior art of theoretical reinforcing power yet equivalent.

On the one hand, the silicas according to the invention lead to indices of

reinforcement greater than those obtained with the silicas of the prior art, that is to say

say to a compromise between the 100% modulus and the 300% modulus very satisfactory: the silicas according to the invention lead to fairly low 100% moduli, proof of a good dispersion of the silica, and to relatively high 300% moduli , proof of a high density of silica / rubber interactions; if the silica P7 according to the invention results in a 300% lower modulus, it results in

at the same time at an extremely low 100% modulus.

On the other hand, the higher reinforcing power of the silicas according to the invention is also confirmed by the higher values obtained for the resistance to heat.

breaking and tearing.

TABLEJIV

P5 P6 P7 PC1 i PC2 MP1 Abrasion resistance (mm3) (1) 66 60 65 83 83 75 (1) the measured value is the abrasion loss: the lower it is, the better the abrasion resistance. abrasion resistance, it is noted that the abrasion loss is reduced from 10 to more than 20% compared to comparative silicas. This is a

important advantage for pneumatic application.

3- Dynamic properties

The measurements are carried out on the vulcanized formulations.

Vulcanization is obtained by bringing the formulations to 150 ° C. for

minutes.

The results are reported in Table V below. We have indicated

the apparatus used to carry out the measurements.

TABLE V

P5 P6 P7 PC1 PC2 I MP1

GOODRICH heating (C) (1) 81 80 80 81 86 85 (1) GOODRICH flexometer The heating obtained from the silicas according to the invention is relatively low.

Claims (18)

1 / A method of preparing precipitated silica of the type comprising the reaction of an alkali metal silicate M with an acidifying agent, whereby a suspension of precipitated silica is obtained, then the separation and drying of this suspension, characterized in the precipitation is carried out in the following manner: (i) an initial base stock is formed comprising a part of the total quantity of the alkali metal silicate M involved in the reaction, the silica concentration in said base stock being less than 20 g / l, (ii) the acidifying agent is added to said initial starter until at least 5% of the quantity of M20 present in said initial starter is neutralized, (iii) one simultaneously adds acidifying agent and the remaining quantity of alkali metal silicate M to the reaction medium such that the quantity of silica added / quantity of silica ratio present in the initial stock is understood between 12 and 100. 2 / A method according to claim 1, characterized in that, in step (ii), the acidifying agent is added until at least 50% of the amount of M20 present in said initial starter are neutralized. 3 / A method according to one of claims 1 and 2, characterized in that, in step (iii), acidifying agent and the remaining quantity of alkali metal silicate M are added to the reaction medium simultaneously such that the quantity of silica added / quantity of silica present in the initial stock is included between 12 and 50. 4 / A method according to one of claims 1 to 3, characterized in that, after step (iii), an additional amount of acidifying agent is added to the reaction medium, preferably until a pH value of the medium is obtained reaction between 3 and 6.5. / Method according to one of claims 1 to 4, characterized in that, throughout step (iii), the amount of acidifying agent added is such that 80 to 97% of the amount of M20 added is neutralized. 6 / A method according to one of claims 1 to 5, characterized in that said concentration of silica in said initial starter is at most 11 g / l. 7 / A method according to one of claims 1 to 6, characterized in that no electrolyte is not used. 8 / A method according to one of claims 1 to 7, characterized in that said drying is carried out by atomization. 9 / A method according to claim 8, characterized in that the dried product is then agglomerated. O / A method according to claim 8, characterized in that the dried product is then crushed, then, optionally, agglomerated. 11 / A method of preparation according to one of claims 1 to 10 of a silica precipitated, characterized in that said silica has: - a specific surface area CTAB (ScTAB) of between 140 and 240 m2 / g, - an ultrasonic deagglomeration factor (FD) greater than 11 ml, - a median diameter (05 ), after disintegration with ultrasound, less than 2.5 µm. 12 / A method of preparation according to one of claims 1 to 10 of a silica precipitated, characterized in that said silica has: - a specific surface area CTAB (ScTAB) of between 140 and 240 m2 / g, - a pore distribution such as the pore volume formed by the pores whose diameter is between 175 and 275 À represents less than 50% of the pore volume consisting of pores with diameters less than or equal to 400 A, an ultrasonic deagglomeration factor (FD) greater than 5.5 ml, a median diameter (050), after ultra-deagglomeration -sounds, less than 5 µm. 13 / Precipitated silica characterized in that it has: - a specific surface area CTAB (ScTAS) of between 140 and 240 m2 / g, - an ultrasonic deagglomeration factor (FD) greater than 11 ml, - a median diameter (0o), after disintegration with ultrasound, less than 2.5 µm. 14 / Precipitated silica characterized in that it has: - a specific surface area CTAB (ScTAB) of between 140 and 240 m2 / g, - a pore distribution such as the pore volume formed by the pores, the diameter of which is between 175 and 275 represents less than 50% of the pore volume consisting of pores with diameters less than or equal to 400 A, an ultrasonic deagglomeration factor (FD) greater than 5.5 ml, a median diameter (0.), after deagglomeration with ultrasound, less than 5 µm. / Silica according to one of claims 13 and 14, characterized in that it has a BET specific surface (SBET) of between 140 and 300 m2 / g. 16 / silica according to one of claims 13 to 15, characterized in that it has an SBET / SCTAB ratio between 1.0 and 1.2. 17 / silica according to one of claims 13 to 15, characterized in that it has an SBE-r / ScTAB ratio greater than 1.2. 18 / silica according to one of claims 13 to 17, characterized in that it has a DOP oil uptake of between 150 and 400 ml / 100 g. 19 / silica according to one of claims 13 to 18, characterized in that it is present as a powder of average size of at least 15 µm. / Silica according to one of claims 13 to 18, characterized in that it is present in the form of approximately spherical balls of average size of at least minus 80 pm. 21 / silica according to one of claims 13 to 18, characterized in that it is present in the form of granules with a size of at least 1 mm. 22 / Use as a reinforcing filler for elastomers of a silica obtained by the process according to one of claims 1 to 12 or a silica according to one of claims 13 to 21.