AU603227B2 - Process for producing fine powder of metal oxide (zirconium, hafnium and titanium) having a predetermined specific surface area or granulometry - Google Patents

Description

AU-AI-i 79368__ P T ORGANISATION MODAE E1 ZTE TUi, DEMANDE INTERNATIONALE PUBLIEE EN VERTU DU TRAITE DE COOPERATION EN MATIERE DE BREVETS (PCT) (51) Classification internationale des brevets 4 Numiro de publication internationale: WO 88/ 09307 COi1G 25/02, 27/02, 23/07 Al (43) Date de publication internation02: C0iB 13/22' 1 Lcembre 1988 (01.12.88) (21) Num~ro de la demande internationale: PCT/FR88/00247 (22) Date de d~p~t international: 16 mai 1988 (16.05.88) (31) Num~ro de la demande prioritaire: 87/05465 (32) Date de priorite: (33) Pays de priorit 18 mai 1987 (18.05.87) (71) Diposant (pour tous les Etats d~sign~s saul' US): CRI- CERAM [FR/FR]; Tour Manhattan, La De6fense 2, 6, place de l'ris, F-92400 Courbevoie (FR).

(72) Inventeurs; et Inventeurs/Dkposants (US seulement) BARRAL, Robert [FR/FR]; Lotissement Le Surville, S.-Georges-de- Commiers, F-38450 Vif DUPIN, Thierry [FR/ FR]; 5, rue Pr6-de-Treille, F-38320 Eybens (FR).

(74) Mandataire: CR05, Mireille; P~chiney, 28, rue de Bonnel, F-69433 Lyori C~dex 03 (FR).

(81) Etats disignis: AU, CH (brevet europ~en), DE (brevet europ~en), FI, FR (brevet europ~en), GB3 (brevet europ~en), JP, NO, SE (brevet europ~en), US.

Publi~e Avec rapport de recherche iternationale.

A vant l'expiration du d~lai pr~vu pour la modification des revendications, sera republi~e si de telles modifications sont re~ues.

XU.J'.P. 2 3 FEB 1989 I

AUSTRALIAN

PATENT OFFICE I_ Process for Producing (54) Title: 7ine Powder of M'lal oxide (Zirconium, Hafnium and Titanium) Having a P-redetermined Specific Surface Area or Granulometry' (54) Titre: PROCEDE D'OBTENTION DE POUDRE FINE DIOXYDE METALLIQUE (ZIRCONIUM, HAFNIUM, TITANE) AYANT UNE SURFACE SPECIFIQUE OU UNE GRANULOMETRIE PREDETERMINEE (57) Abstract Method for the direct production of a fine powder comprised of crystallites which are little or not agglomerated, of metal oxides such as zirconia, hafniumn and/or titanium oxide, having a specific surface or a grain size selected and controlled according to the particular utilization, said grain size having a mean diameter smaller than 0.2 Lm, comprising the treatment by hydrolysis of the corresponding metal tetrachloride by means of water vapor by operating at a partial pressure of tetrachloride, set at a predetermined value function of the specific surface or the gre-In size' searched for, comprised betwee.n 3 and 30 of the total pressure of the mixture of all gas components, while maintaining a molar ratio water/metai tetrachloride comprised between 2 and (57) Abrege Proc d& d'obtention directe d'une poudre Fine, compos~e de cristallites peu ou pas agglom~r~s, d'oxyde m~tallique, tels que la zircone, l'hafnone et/ou l'oxyde de titane, ayant une surface sp~cifique ou une granulom~trie choisie et contr6- 16e en vue de l'usage pr~vu, ladite granulomntrie ayant un diarnkre median inf~rieur d 0,2 lim, consistant i traiter par hydrolyse le tkrachlorure m~tallique correspondant A l'aide de vapeur d'eau en operant A une pression partielle de t~trachiorure, r_ gl~e A une valeur pr~dktermin~e fonction de la surface sp~cifique ou de la granulom~trie recherch~e, comprise entre 3 et 30 de la pression totale du melange de tous Ies composants gazeux, en maintenant un rapport molaire eau Sur t~tachlorure m~tallique compris entre 2 et "Process for Producing Fine Powder of Metal Oxide (Zirconium, Hafnium and Titanium) Having a Predetermined Specific Surface Area or Granulometry.

TECHNICAL FIELD The invention concerns a process for producing fine powder of zirconium and/or hafnium and/or titanium oxide, having a predetermined specific surface area or granulometry; the process is such that by adjusting certain operating parameters, it is possible to adjust the granulometry or the specific surface area of the powder produced to a predetermined value which is suited to the subsequent use which is to be made thereof.

STATE OF THE ART The technical ceramic industry uses powders of zirconia and/or hafnium oxide, which is also referred to as hafnia, and/or titanium oxide, for widely varying uses which each require particular characteristics on the part of the initial powder which generally is a fine powder composed of particles constituted by a single or a small number of elementary crystallites, wherein the median diameter of the particles is of the order of or less than a micron, In particular the specific surface area and the granulometry of such a powder and occasionally the residual chlorine content thereof are essential parameters of such an initial powder.

For the same type of powder, granulometry and specific surface area are generally linked: the greater the specific surface area, the finer the granulometry. However the relationship between those two parameters essentially depends on the shape factor of the particles, that is to say their state of aggregation and agglomeration. For use of those powders for the production of technical ceramics, it is necessary as stated to have fine powders with a shape factor which is as simple as possible, avoiding the presence of aggregates and agglomerates. It is therefore important for the man skilled in the art who has to provide such 2 powders to check both their granulometry and their specific surface area and to limit their state of aggregation and agglomeration.

Thus the zirconia powder for crystallogenesis must be of a BET specific surface area that is usually between 3 and 6 m2/g.

and/or Moreover zirconiaj hafnium oxide may be used as an additive by dispersion in a matrix which is itself of ceramic material for the purposes of strengthening it. In that case the specific surface area of the initial powder is between 10 and 20 m2/g. It may also be used as a base for partially or totally stabilised ceramics, in which case the specific surface areas are between 10 and 25 m2/g and the nature and/or quantity of the stabilised phase or phases obtained (tetragonal and/or cubic) depends on the granulometry. For those applications to technical ceramics, it is desirable for the granulometry to be between 2 and 0.1 pm.

arid c'f Zirconia 4 hafnium oxide may also be used as a microporous layer or as a catalyst carrier, in which case the specific surface area of the initial powder will generally be between 20 m2/g and up to at least 100 m2/g. It may be used in stable suspension (slip casting, polishing in that case, the specific surface area is generally greater than 10 m2/g and the granulometry must be suited to the nature and the viscosity of the medium in which the suspension is to be made.

Those oxides may also be involved in complex compositions obtained by chamotting and it is then necessary for their granulometry to be compatible with that of the other constituents and sufficiently fine to provide a homogenous mixture and good reactivity.

Those examples clearly show the need for the man skilled in the art to be able to provide a fine powder of zirconia, hafnium oxide or titanium oxide which has a controlled granulometry or specific surface area suited to the demands of the ceramist user.

Such a powder may be produced: i either in two steps by hydrolysis of the solid chloride i' 3 ±fZCl4 by means of steam to produce the oxychloride and then by ther.-al decomposition of the latter at elevated temperature (up to 150 0 and in an oxidising atmosphere (air) and steam.

That process results in a product which has a large specific surface area and a median granulometry which is larger than a micron. The particles obtained are generally in the form of agglomerates which are difficult or even impossible to crush to produce a submicronic powder. It also suffers from the disadvantage of giving chlorine as a by-product in the second step.

A process of that type is described in French patent No 1 209 473 (Grach), comprising two steps: water is absorbed in liquid or vapour form by zirconium tetrachloride which is maintained at a temperature, preferably 2500C, which is lower than its sublimation point 331 0 C, until a zirconyl chloride hydrate no longer containing Zr Cl 4 which is sublimable, and containing acid, is produced; the iydrate is then heated at a temperature of at least 500 0

C

going up to 15:O°C to produce ZrO 2 and the procedure can be completed by a third calcination step at 1000°C when a zirconia for ceramic use is to be produced.

ii or by treating in aqueous solution a zirconium hafnium salt, for example nitrate, sulphate, chloride by means of a base, to produce the hydroxide which is then calcined. The products obtained may be of large specific surface areas, in particular by virtue of the use of sol-gel processes, but they occur in the form of agglomerated particles of a granulometry of a median diameter which is always greater than 0.5 um, necessitating a reduction in size with the above-mentioned disadvantages due to the crushing operation.

iii or by the action at high temperature (about 1300°C) of oxygen on the tetrachloride. While that process gives submicronic powders Toe t 4 with a large specific surface area, it suffers from the disadvantages that it is not possible to control those surface areas, it uses elevated temperatures and it generates a chlorine-base effluent which it is difficult to treat prior to discarding or recycling.

iv or by a process which is similar to the foregoing and which, as described in French patent No 1 458 298, involves hydrolysing the tetrachloride in a flame in the presence of an inert gas at 1200 to 1350°C. The sublimated tetrachloride is passed into a burner with the combustible gas and the combustion-supporting agent (oxygen); the reaction takes place in the presence of an inert gas which can be recycled after scrubbing and which may thus contain chlorine which is generated in the reaction in the flame and which is not removed in the scrubbing operation.

The amounts of reactants used are such that the amount of water produced during the combustion operation permits hydrolysis of the tetrachloride; the oxygen also reacts with the tetrachloride.

Under those conditions: the gaseous effluent contains up to 10% of chlorine formed in accordance with a reaction of the following type: Zr C14 02 ZrO 2 2C12; the powder obtained is very fine (0.02 The "effective contact surface area", the significance of which is not stated and in respect of which it is not known if it can be compared to a BET surface area ranges from 175 to 190 m2/g when producing SiO0 2 Transposition of that process to the production of zirconia for example would not make it possible to foresee what would be the granulometry, specific surface area and/or appearance of the particles produced.

Besides producing a substantial amount of chlorine in its effluents, that process suffers from the disadvantage of using an elevated temperature in the flame and producing only very fine grains and specific i_ surface areas of medium value, insofar as it is possible to compare the "effective contact surface area" described to a BET specific surface area which is determined in accordance with the standard AFNOR NF-Xll-621-75-11 (AFNOR stands for "Association frangaise de Normalisation) and that it is not possible to control as desired the characteristics of the powder produced.

v Moreover DE 952254 (Degussa) describes a treatment for hydrolysis in the gaseous phase of metal tetrachloride by means of steam in the presence of an inert carrier gas. The operating conditions used, in particular the excess of water and dilution in the inert gas, are such that it is possible to regulate the size of the particles of the oxide powder 4 obtained by controlling the reaction temperature. Thus the size of the particles is of the order of around one hundred km and is not less than 20 |xm. The internal surface area is also high but, having regard to the 15 granulometries produced, that shows that the particles are necessarily severely aggregated and agglomerated.

The powders produced are moreover particularly suitable as a rubber filler and could not be used as they are as a raw material in the field of fine technical ceramics.

For such a use, it would be necessary to reduce the specific surface area thereof by a treatment (for example calcination) and/or to reduce the size of the agglomerates and aggregates by a crushing operation. Those additional operations are expensive and difficult to carry out, in particular when there is a wish to produce very fine powders which are finer than 2 pm, and they are the cause of additional harmful pollution.

OBJECT OF THE INVENTION Having regard to the above-described disadvantages and requirements, the object of the present invention is the direct production, that is to say production without crushing or other supplementary treatment, of a fine powder of metal oxide (zirconia, hafnium oxide or titanium oxide) in which the granulometry and/or BET specific surface area are adjusted as desired to a predetermined value which is selected in dependence on the use to which the powder produced is to be put, said value being achieved by setting certain operating parameters of the process to particular values.

The object of the invention is also to provide a non-polluting process which takes place in a gaseous phase at low temperature and which generates as effluent only hydrochloric acid and little chloride which is more difficult to treat and recover.

A41

H

ii~-YL-L- Another object is to provide a single-step process.

A further object is to produce a powder in which the particles are formed by one or only a small number of crystallites, which particles are not to be complex agglomerates.

In particular the process according to the invention makes it possible to produce directly, that is to say without crushing or granulometric selection methods such as sieving or the like fine powders of said metal oxides in which the granulometry is easily chosen to fall into the range from a median diameter of about 2 [im to a median diameter of less than 0.1 jim, in which case the refusal rate at 0.2 jim 0 is less than 1%.

Likewise it is possible directly to produce powders of metal oxide in oo which the specific surface area is easily chosen to lie in the range of from 3 m2/g to 110 m2/g and sometimes more.

15 DESCRIPTION OF THE INVENTION According to a broad form of the present invention there is provided a process for the direction production of a fine powder of metal oxide of zirconia, hafnium oxide and/or titanium oxide, composed of particles formed by a single or a small number of elementary crystallites, said powder also having a selected and controlled granulometryof a median diameter of less ii o 0~ 0 %e-cx 3*N/3 than about 2 jim and a BET specific surface areaAwhich is also selected and controlled, the process comprising hydrolysis in the gaseous phase at low temperature of the volatile metal tetrachloride corresponding to the oxide to be produced, said temperature being at least higher than the sublimation temperature of the Zr or Hf tetrachloride or than the vaporisation temperature of Ti tetrachloride when Zr, Hf or Ti are to be produced, by means of water vapour in the presence of an inert gas, characterized by adjusting the partial pressure of tetrachloride to a BET specific surface area, said value being between 3 and 30% of the total pressure of the initial reaction medium which is notionally reconstituted by addition of the flow rates of the gaseous reactants, while maintaining a molar ratio of water to metal tetrachloride of between 2 and 10, the granulometry of about 2 jm corresponding to the high partial pressures of tetrachloride and a granulometry of less than 0.1 jim to the low partial pressure, the large specific surface areas corresponding to the low partial pressures and the low specific surface areas to the high partial pressures.

KHK:773 W L. 7 1 1 If M represents a metal element whose chloride is volatile such as Zr, Hf and/or Ti, hydrolysis takes place in accordance with the following reaction: M C4 vap 2H2 vap M 02 solid 4HCgas at a temperature which is at least higher than the sublimation temperature of the zirconium or hafnium tetrachloride or the vaporisation temperature of titanium tetrachloride; in general it is always higher than 200°C, preferably in the range of from 300 to 800°C and more particularly in the range of from 410°C to 600°C. A temperature which falls into the high zone *010 of the range iF a favourable elemen* in regard to reducing the chlorine content in the resulting product.

In order to produce the selected granulometry and/or BET specific surface area, it is essential to adjust the amount of tetrachloride introduced to a predetermined constant value by fixing its partial pressure in the initial reaction medium which is notionally reconstituted by addition of the flow rates of gaseous reactants, including that of the inert gas, to a value which is at least equal to 0.5% of the total pressure 1 and usually between 3 and 30%, preferably between 4 and Thus: the corresponding BET specific surface area obtained, measured in accordance with the standard AFNOR-NF-Xl-621-75-11, is of a value which 9 77 KNK:773y 8 is between 3 m2/g and 110 m2/g or higher; the large specific surface areas correspond to the low partial pressures and low specific surface areas correspond to high partial pressures; the corresponding granulometry produced is between a median diameter of about 2 pn for the high partial pressures of tetrachloride and a median diameter of less than 0.1 pm, corresponding to a refusal rate at 0.2 um of less than for the low partial pressures.

In the preferred range, when the partial pressure is selected and adjusted to a value of between 25% and 4% of the total pressure, the value of the specific surface area is between 5 m2/g and 80 m2/g and the granulometry is between a median diameter of 1.5 pm and a median diameter of less than 0.1 pm, corresponding to a refusal rate at 0.2 pm of from to The amount of water vapour introduced into the reaction medium is always higher than the stoichiometry of the reaction with the U tetrachloride; the H20/tetrachloride molar ratio is usually between 2 and and preferably between 2 and 8. Its effect on the granulometry or specific surface area is such that, in regard to the greater excesses of water, finer grains are obtained, at a constant tetrachloride partial pressure. However that effect is less marked than that which is achieved by dilution of the tetrachloride.

In contrast, it is surprisingly found that it is essential to keep the amount of water vapour within the specified limits according to the invention to produce particles which are formed by a single or a small number of elementary crystallites. Indeed, if the amount of water vapour is increased beyond the specified upper limits, granulometry no longer decreases, as was envisaged, but increases and in addition the particles are no longer simple crystallites but agglomerates of crystallites which are complex and of substantial size. In that case the specific surface area may remain large although the granulometry of the powder is greater, which is contrary to that which is usually found when dealing with a k f V .9 S9 powder formed by simple or generally non-agglomerated crystallites and in w -ich, as already stated above, a fine product corresponds to a large specific surface area. That enlargement phenomenon can be explained by the fact that too great an excess of water tends to promote the formation of agglomerates and aggregates of simple crystallites which otherwise are produced by virtue of dilution of the tetrachloride.

Moreover the use of a small excess of water gives other advantages such as for example a reduction in the volume of the effluents to be treated and a smaller size for the apparatus used.

The reaction takes place in a chamber which is heated by any suitable means. The pressure in the chamber may be of any value but for practical reasons it is preferred to operate at a pressure which is close to atmospheric pressure.

Each of the reactants is introduced simultaneously into the chamber by means of a conduit which is particular thereto; those conduits preferably open into the upper part of the chamber, their respective axes may form an angle of variable value, they may be parallel or they may be coincident, in which case the two conduits are concentric. In general the ends thereof are disposed at tha same level. The way in which mixing of the reactants is effected in the chamber has an influence on the specific surface area and the granulometry of the product: if the arrangement of the conduits is such that the mixing effect is very intimate, that promotes the production of a large specific surface area and fine granulometry; conversely if a sumrnary mixing effect is produced, that promotes a small surface area and a larger grain size while remaining less than 2 ,nm.

In order to enhance the homogeneity of the mixture, it is possible to ue an agitation device, for example a blade-type agitator, within the chamber. The use of such a device also enhances the stability of the reaction and the homogeneity of the results obtained (a tight granulometric range and a constant specific surface area in a batch of iproduct).

The introduction of the reactants, tetrachloride and/or water vapour, may be divided up, that is to say one and/or the other of the reactants may be introduced into the chamber at one or more points while maintaining the desired value in respect of the tetrachloride partial pressure in the initial gaseous mixture which is reconstituted by addition of the flow rates at the different feed points. In general but without limitation, it is satisfactory to use two points of introduction per reactant and more particularly one point for the tetrachloride and tvwo points for the water vapour.

It is observed that introducing the reactants at a plurality of points makes it possible to produce a powder with a smaller specific surface area while avoiding an increase in the size of the particles beyond 2 pm and without significantly increasing the formation of agglomerates and aggregates.

That arrangement and usually that which involves introducing water vapour at two points is advantageously completed by the agitation device and is thus particularly recomrrmended for producing a powder having a specific surface area which is towards the low values or a grain size which is rather large.

The gaseous reactants may be introduced as they are, taking the necessary precautions for no condensation to occur in the interior or at the mouth of the conduits. Preferably however they are introduced by means of a carrier gas which is inert with respect to the reaction medium, generally nitrogen or, in the case of titanium oxide, oxygen or air, while observing the quantitative conditions set forth above. Thus, when large surface areas or a very fine granulometry are to be produced, that is to say when the tetrachloride partial pressure is set to a very low value, it may be necessary to use an inert gas. T~e inert gas may be introduced either with the tetrachloride or with the water vapour or with both those reactants. It also makes it easier to control the partial pressures to td 11 the selected values.

The rate of introduction of the gases which make up the reaction medium also has an effect on the intimacy of the mixing operation and must be such that the residence time of the reactants in the chamber is a few seconds, generally more than 3 seconds and preferably between 8 and seconds. That time is calculated by dividing the volume of the reaction chamber by the total flow rate of the gases including the inert gas produced by adding all of the flow rates measured at their entrance into the chamber, at the temperature of the chamber.

When the residence time is high, with all other things being equal, there is generally a trend to produce a smaller specific surface area and a larger granulometry.

Figures 1 to 3 show non-limiting examples of arrangements for the introduction of reactant and possible agitation; the significances of the reference numerals are as follows: 1 represents the reaction chamber 2 represents the point or points of introduction of the tetrachloride vapour with or without inert gas 3 represents the introduction of the water vapour with or without inert gas 4 represents a blade-type agitator represents the discharge for the gases, which is fitted with a filter f 6 represents the outlet for the powder 7 represents the outlet of the reactor towards a solid-gas separation installation.

Figure 1 shows a reactor with agitation; the tetrachloride and water vapour are introduced thereinto at a single point.

Figure 2 also shows an agitated reactor but the water vapour is introduced at two points.

u w L, ni ur, i are to ue proouceo, Dy means of water vapour in the presence of an inert gas, characterized by adjusting the partial pressure of tetrachloride to a predetermined constant value corresponding to the desired granulometry and BET specific surface area, said value being between 3 and 30% of the total pressure of the initial /2 12 In Figure 3 there is no agitation and each of the reactants is introduced at a single point.

Figure 4 represents the BET specific surface area of the powder obtained in dependence on the settings of the partial pressure of zirconium hafnium tetrachloride in the initial reaction mixture, the total pressure being atmospheric pressure. A plurality of reactant introducing devices have been used and the influence thereof on the result obtained can b' seen.

The following examples illustrate the results obtained with principally different settings for the tetrachloride partial pressures.

EXAMPLE 1 In this example the reaction chamber is of a volume of 3 litres; it is provided with a rotary blade-type agitator of the type shown in Figure 1, which rotates about its axis. The reactants are introduced by means of two pipes which are concentric with the axis, using an arrangement: of the type shown in Figure 1. The total pressure is 100 kPa, that is to say one atmosphere.

A first series of tests (90 to 93) was carried out at a temperature of 430 0 C and with a residence time of 22 seconds, using pure sublimated zirconium tetrachloride and water vapour which were introduced into the reactor by means of nitrogen. The specific surface areas and granulometry as identified by the median diameter and the refusal rate at 0.2 pm are given in the following Table which also indicates the other operating parameters and the chlorine contents produced: r -J j o

N!

TABLE 1 PRESSURE PESSURE H 2 0 1EIEC BET MEDIAN REFUSAL CHLORINE TES ZC120 rC ThIPRAU4 T: ME SURFACE DIAMETER RATE AT NTN kPa 4 kPa ratio m2/g Alm 0% by weight 11.1 27.4 2.45 430 22 40 0.1 19 3 92 17.2 77.0 4.47 430 22 24 0.16 41 91 21.3 59.8 2.81 430 22 19 <0.1 10 1.8 93 22.3 66.9 3.00 430 22 13 0.36 73 1.3 14 It can be seen that with a slight variation in the partial pressure of Zr Cl 4 from 0.11 to 0.22 atmosphere the corresponding specific surface area falls within wide limits ranging from 40 to 13 m2/g, just as granulometry increases.

By comparing 91 and 93, it can be seen that a more substantial excess of water in test 93 does not make it possible to compensate for the reduction in specific surface area and the increase in granulometry obtained by increasing the tetrachloride partial pressure.

In a second series of tests (1 to the reaction temperature and the residence time were also varied, the total pressure still being 1 atmosphere:

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4, 9 TABLE 2 PRESSUREi PRE~SSURE H 2 0 RESIDENCE BET MEDIAN REFUSAL CHLORINE TEST ZrC14 H 20 TEMPERATURE TIME SURFACE DIAMETER RATE AT CONTENT Z4 ocAREA0. u kPa kPa Molar Csec m2/g 0.2 by weight 1 5.1 25.3 5 430 1-1.5 72 40O.1 12 4 3 5.1 41.5 8.2 43,, 24 68 <0.1 11 3.4 2 5.1 39.5 7.8 570 11.7 77 c0.1 4 2 4 4.1 29.4 7.25 570 23.5 73 40.1 9 1.8 10.1 40.5 4 430 11.6 48 4 0.1 9 2.7 7 13.2 27.4 2.07 430 23.2 38 23 3.2 6I 12.2 25.3 2.08 570 11.2 47 10 1.9 8 12.2 41.5 3.42 570 23.2 47 12 16 Referring to those tables and the curve shown in Figure 4 (linking the points marked by which is drawn therefrom, it will be seen that the parameters other than the tetrachloride partial pressure have an effect of the second order on the spec Lfic surface area; it will be seen by comparing tests 2 and 4 that a longer residence tie promotes the production of a smaller BET surface area and larger granulometry.

EXA~MPLE 2 The agitated chamber is the same as in example 1, and the total pressure is also 1 atmosphere; in contrast, the arrangement has two locations at which water vapour is introduced, of the type indicated in Figure 2.

The ratio in respect of the flow rates as between the upper and lower points at which water vapour is introduced is 0.58. The results obtained were as follows: r o< TABLE 3 HO 1 PRESSURE PRESSURE 2 TEM1FP1ATURE IRESIDENCE 1 BET MEDIAN REFUSAL REFUSAL TES2 ZrCl 4 20 zc TIME SURFACE DIAMETER RATE AT RATE AT kPa kPa Molar c AE 0.2 pjm 1 an rtosec m2/g Ln by weight 1J 17.2 j 54.7 3.18 450 22 10.7 73 1.4 18 It will be seen by comparison with test 92 which is very similar that the specific surface area and granulometry obtained are substantially different, being respectively smaller and larger, because the two points at which the tetrachloride is introduced correspond to less substantial mixing of the reactants.

EXAMPLE 3 The chamber is of a volume of 450 litres. There is no agitator and the reactants are introduced by means of two pipes which open at the same level; the tetrachloride and water vapour are introduced at a single point. The results obtained were as follows: l: i Flo' ~1 TABLE 4 PESR PRSUEHO20 TMEATR EIE BET REFUSAL~ REFUSAL PRESST PRESUR 2 T0PRTR 1ESDECE SURFACE MEDIAN ATE AT RATE AT 4 2 ZrC 4 ocTIME AREA DIAMETER 02~m 1,r Molar ;m 1 u kPa kPa ratio sec m2/g 831 17.7 48.6 2.74 500 10 3.6 1.2 ic00 56 832 14.2 49.6 3.5 5010 6.8 0.78 95 39 11 11 ~j ;Izn~-; '1 The level of the results obtained is to be compared to that of preceding tests 100 and 101; it will be seen that less complete mixing (absence of agitation) makes it possible to reduce the specific surface areas and to increase granulometry.

EXAMPLE 4 This example illustrates the application of the process to the production of hafnium oxide. It was carried out in the same agitated chamber as that used in example 1, the water vapour also being introduced at a single point.

The operating parameters are as follows: Test 27 Total pressure Pressure HfCl 4 Pressure H20

H

2 0/HfCl4 Temperature Residence time 1 atmosphere 0.21 atmosphere 0.59 atmosphere 2.76 molar 495°C 22 sec.

The results obtained are as follows: BET surface area 19.4 m2/g Median diameter 0.48 pm Refusal rate at 2 um 3% Chlorine content 1.4% by weight.

EXAMPLE This example illustrates application of the process according to the invention to the production of titanium oxide from its vaporised tetrachloride. It was carried out using the arrangement employed in example 3. The operating parameters and the results obtained are set out in Table 5. The total pressure is still 100 kPa (1 atmosphere).

r i\ h r-7-

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TABLE PRESSURE PRESSURE H20 TMEAUE RSDNE BET REFUSAL TET TiCi H 0 TNEAUE RSDNE SRAE MDA AEA TS14 2 TiC1 4 TIME AREAACE MEIANRAT 2 AT ka ka Mol1ir ocsec AE IMR 2u k~a k~a ratio ~m2/q 850 13.1 78.6 6 500 12 6.9 0.8 851 23.3 69.9 3 500J 10 3.6 1.45 32 22 Thus the process according to the invention makes it possible to produce fine powders of metal oxide (principally zirconia, hafnium oxide and titanium oxide) in which the BET specific surface area and granulometry are controlled and adjusted as desired by regulating the partial pressure of the tetrachloride and the amount of water introduced to predetermined values. For example to obtain a BET surface area of greater than 60 m2/g or a fine granulometry corresponding to a refusal rate at 2 pm of less than 15%, the above-mentioned partial pressure must be adjusted to a value which is lower than 5% of the total pressure, the water/tetrachloride molar ratio being between 2 and 8 and the reaction medium preferably being agitated. Likewise, for a specific surface area which is not to exceed 10 m2/g or a granulometry corresponding to a refusal rate at 2 pm of higher than 60% or a median diameter of 0.3 to 0.4 pm, the tetrachloride partial pressure is not to be lower than 13% of the total pressure, in that case, it is preferable to introduce the tetrachloride or the water vapour at a plurality of locations, for example at two points.

It will be clearly apparent that the tetrachloride partial pressure, in association with a limited amount of water introduced, are the preponderant factors which, by keeping them to a given value in the course of the process, make it possible to produce a powder with a BET specific surface area or a granulometry of a selected value.

Claims (9)

1. A process for the direction production of a fine powder of metal oxide of zirconia, hafnium oxide and/or titanium oxide, composed of particles formed by a single or a small number of elementary crystallites, said powder also having a selected and controlled granulometry of a median diameter of less than about 2R.m and a BET specific surface area of at lease 3 in 2 /g which is also selected and controlled, the process comprising hydrolysis in the gaseous phase at low temperature of the volatile metal tetrachloride corresponding to the oxide to be produced, said temperature being at least higher than the sublimation temperature of the Zr or Hf tetrachloride or than the vaporization temperature of Ti tetrachloride when Zr, Hf or Ti are to be produced, by means of water vapour in the presence of an inert gas, characterized by adjusting the partial pressure of tetrachloride to a predetermined constant value corresponding to the desired granulometry and BET specific surface area, said value being between 3 and 30% of the total pressure of the initial ::reaction medium which is notionally reconstituted by addition of the flow rates of the gaseous reactants, while maintaining a molar ratio of water to metal tetrachloride of between 2 and 10, the granulometry of abouit 2R.m corresponding to the high partial pressures of tetrachloride and a granulometry of less than 0.lpm to the low partial pressure, the large specific surface areas corresponding to the low partial pressures and the low specific surface areas to the high partial pressures. presur ofthe tetrachloride is between 4 and 25%, the corresponding vausobtained for the BET specific surface area being between 5 m 2 /g an 8 i 2/g and for the granulometry being between a median diameter of abu .5 im and a median diameter of less than 0.lptm corresponding to a rfslrate at 0.2.tm of between 5 and

3. A process according to claim 1 or claim 2 characterised in that the reaction temperature is between 300 and 800 0 C.

4. A process according to any one of claims 1 to 3 characterised in that the molar ratio of water to metal tetrachloride is between 2 amid 8. A process according to any one of claims 1 to 4 characterised in that the reaction is carried out in the presence of a gas which is inert with respect to the reaction medium, said gas being nitrogen or, in the case of titanium oxide, oxygen or air. :901Y m i 24

6. A process according to any one of claims 1 to 5 characterised in that the reaction medium is agitated.

7. A process according to any one of claims 1 to 6 characterised in that the water vapour is introduced into the reaction chamber at a plurality of points.

8. A process according to any one of claims 1 to 7 characterized in that the residence time in the reaction chamber is greater than 3 seconds.

9. A process according to any one of claims 1 to 8 characterized in that the tetrachloride partial pressure is adjusted to a value of less than of the total pressure to produce a powder whose BET specific surface area is higher than 60 m 2 /g or whose granulometry gives a refusal rate at 2 [m of less than

10. A process according to any one of claims 1 to 8 characterized in that the pressure of the tetrachloride is adjusted to a value of higher than 13% of the total pressure to produce a powder whose BET specific surface area is less than 10 m /g or whose granulometry gives a refusal rate at 2 pim of higher than

11. A process for the direct production of a fine powder of metal oxide zirconia, hafnium oxide and/or titanium oxide, composed of particles formed by a single or a small number of elementary crystallites, said powder also having a selected and controlled granulometry of a median diameter of less than about 2 pim and a BET specific surface area which is io; also selected and controlled, substantially as herein described with reference to Example 1 and any one of Tests 90 to 93 or Tests 1 to 8, Example 2 and Test 100, Example 3 and Test 831 or 832, Example 4, or S, Example 5 and Test 850 or 851. DATED this ELEVENTH day of MAY 1990 Criceram 1 Patent Attorneys for the Applicant SPRUSON FERGUSON L r ABSTRACT PROCESS OR PRODUCING FINE POWDER OF METAL OXIDE (ZIRCONIUM, HAFNIUM AND TITANIUM) HAVING A PREDETERMINED SPECIFIC SURFACE AREA OR GRANUIk]METRY Process for the direct production of a fine powder composed of non-agglomerated or only slightly agglomerated crystallites of metal oxide such as zirconia, hafnium oxide and/or titanium oxide, with a specific surface area or granulometry selected and controlled with a view to the intended us e, said granulometry being of a median diameter of less than 0.2 comprising treating the corresponding metal tetrachloride by hydrolysis by means of water vapour, operating at a partial pressure of tetrachloride which is adjusted to a predetermined value dependent on the desired specific surface area or granulometry of between 3 and 30% of the total pressure of the mixture of all the gaseous components while maintaining a molax ratio of water to metal tetrachloride of between 2 and 4-) LI-t