Process for preparing a magnetic talcous composition, and magnetic talcous composition

Abstract

A process for preparing a magnetic talcous composition including mineral particles, referred to as magnetic talcous particles, having a non-zero magnetic susceptibility, in which, during an oxidative contacting step, talcous particles chosen from the group formed from 2:1 lamellar silicates having a zero electric charge are brought into contact with particles including at least one magnetic iron oxide chosen from the group formed from magnetite and maghemite, the magnetic particles having a mean equivalent diameter of between 1 nm and 50 nm. A magnetic talcous composition including mineral particles, referred to as magnetic talcous particles, having a non-zero magnetic susceptibility, at least 20% by weight of talcous particles and at least 0.5% by weight of magnetic particles is also described.

Claims

1. A process for preparing a composition, called a magnetic talcous composition, comprising mineral particles, called magnetic talcous particles, having a non-zero magnetic susceptibility, wherein, during a contacting step: talcous particles chosen from the group formed of the 2:1 sheet silicates having a zero electric charge and a mean equivalent diameter of from 10 nm to 300 nm are contacted with particles, called magnetic particles, comprising at least one magnetic iron oxide chosen from the group formed of magnetite and maghemite, said magnetic particles having a mean equivalent diameter of from 1 nm to 50 nm.

2. The process as claimed in claim 1, wherein the talcous particles and the magnetic particles are contacted in a liquid medium.

3. The process as claimed in claim 1, wherein, during the contacting step: an aqueous solution is prepared, talcous particles and magnetic particles are added to the aqueous solution, and the aqueous solution is removed.

4. The process as claimed in claim 1, wherein, during the contacting step: at least one precursor element of said magnetic particles is introduced into an aqueous suspension comprising talcous particles, a precipitation reaction of said magnetic particles is carried out.

5. The process as claimed in claim 2, wherein, after contacting the talcous particles and the magnetic particles in a liquid medium the talcous particles and the magnetic particles are dried, the magnetic particles and the talcous particles being in contact in a dry state.

6. The process as claimed in claim 1, wherein, during the contacting step, co-grinding of the talcous particles and of the magnetic particles in the dry state is carried out.

7. The process as claimed in claim 1, wherein the 2:1 sheet silicates having a zero electric charge are devoid of interfoliar cations and of interfoliar water molecules.

8. The process as claimed in claim 1, wherein the talcous particles have the chemical formula (Si.sub.xGe.sub.1x).sub.4M.sub.3O.sub.10(OH).sub.2 wherein: x is a number in the range of 0 to 1, and M denotes at least one divalent metal having the formula Mg.sub.y(1)CO.sub.y(2)Zn.sub.y(3)Cu.sub.y(4)Mn.sub.y(5)Fe.sub.y(6)Ni.sub.y(7) Cr.sub.y(8); each y(i) representing a number in the range of 0 to 1, and such that $\underset{i=1}{\overset{8}{.Math.}}y\left(i\right)=1.$

9. The process as claimed in claim 1, wherein the talcous particles are formed of talc Si.sub.4Mg.sub.3O.sub.10(OH).sub.2.

10. The process as claimed in claim 1, wherein said magnetic particles have a mean equivalent diameter of from 1 nm to 30 nm.

11. The process as claimed in claim 1, wherein said talcous particles have a mean equivalent diameter of from 10 nm to 200 nm.

12. The process as claimed in claim 1, wherein, during the contacting step, the talcous particles are contacted with the magnetic particles in such a manner that the ratio by mass between the magnetic particles and the talcous particles is from 0.005 to 4.

13. A composition, called a magnetic talcous composition, comprising mineral particles, called magnetic talcous particles, having a non-zero magnetic susceptibility, said magnetic talcous particles comprising: from 20 wt % to 99.5 wt % talcous particles relative to the total weight of said magnetic talcous composition, said talcous particles being chosen from the group formed of the 2:1 sheet silicates having a zero electric charge and a mean equivalent diameter of from 10 nm to 300 nm, and from 0.5 wt % to 80 wt % magnetic particles, comprising at least one magnetic iron oxide chosen from the group formed of magnetite and maghemite, relative to the total weight of said magnetic talcous composition, said magnetic particles having a mean equivalent diameter of from 1 nm to 50 nm, The ratio by mass between the magnetic particles and the talcous particles being from 0.005 to 4.

14. The composition as claimed in claim 13, wherein said magnetic talcous particles have a positive magnetic susceptibility.

15. The composition as claimed in claim 13, wherein it comprises at least 0.5 wt. % maghemite particles.

16. The composition as claimed in claim 14, wherein it comprises at least 0.5 wt. % maghemite particles.

Description

EXAMPLE 1

(1) A silico/germano-metallic gel of the formula Si.sub.4Mg.sub.3O.sub.11, nH.sub.2O is prepared and subjected to a hydrothermal treatment for 6 hours at a temperature of 300 C. Synthetic talc is thus obtained.

(2) On the one hand, a synthetic talc suspension is prepared by mixing, with magnetic stirring, 20 g of an aqueous suspension (in the form of a gel) comprising talc particles, the moisture content of which is 90% (that is to say 10 wt. % talc, relative to the total weight of said suspension), in 70 ml of distilled water. The talc particles have a mean equivalent diameter of from 20 nm to 100 nm, and in particular a thickness of approximately from 10 nm to 20 nm and a largest dimension (or particle length) of approximately 200 nm.

(3) On the other hand, an aqueous solution of iron chlorides is prepared by dissolving, with magnetic stirring, 10.81 g of iron(III) chloride hexahydrate (FeCl.sub.3.6H.sub.2O) and 3.98 g of iron(II) chloride tetrahydrate (FeCl.sub.2.4H.sub.2O) in 200 ml of distilled water. The solution is then made up with distilled water to 250 ml.

(4) 54 ml of the aqueous solution of iron chlorides are added, with magnetic stirring, to the synthetic talc suspension, that is to say the equivalent of 50 wt. % magnetite Fe.sub.3O.sub.4 relative to the talc. The solution obtained has a yellow coloration.

(5) From 3 to 5 ml of ammonia in 30% aqueous solution are then added, with magnetic stirring. Magnetite particles then form by precipitation, and the suspension assumes a black coloration. The magnetic particles have a mean equivalent diameter of from 5 nm to 30 nm.

(6) After 5 to 10 minutes of magnetic stirring, the suspension obtained is centrifuged in order to separate the particles comprising talc and magnetite Fe.sub.3O.sub.4 from a supernatant solution of ammonium chloride. The particles so obtained are dried by lyophilization.

(7) After drying there is obtained a magnetic talcous composition which comprises magnetic talcous particles comprising 66.6 wt. % talc and 33.4 wt. % magnetic iron oxide particles (that is to say magnetite Fe.sub.3O.sub.4 particles and more than 0.5 wt. % maghemite -Fe.sub.2O.sub.3 particles) relative to the total weight of the magnetic talcous composition.

(8) When a few grams of this composition comprising magnetic talcous particles are placed in a closed container made of transparent plastic and a magnet is brought up to the bottom of the container and the container is turned upside down, it is observed that the magnetic talcous particles do not fall but remain attracted by the magnet.

(9) Furthermore, the composition comprising magnetic mineral particles that is obtained has a dark-brown coloration.

EXAMPLE 2

(10) A silico/germano-metallic gel of the formula Si.sub.4Mg.sub.3O.sub.11, nH.sub.2O is prepared and is subjected to a hydrothermal treatment for 6 hours at a temperature of 300 C. Synthetic talc is thus obtained.

(11) On the one hand, a synthetic talc suspension is prepared by mixing, with magnetic stirring, 10 g of an aqueous suspension (in the form of a gel) comprising talc particles, the moisture content of which is 90% (that is to say 10 wt. % dry talc relative to the total weight of said suspension), in 70 ml of distilled water. The talc particles have a mean equivalent diameter of from 20 nm to 100 nm, and in particular a thickness of approximately from 10 nm to 20 nm and a largest dimension (or particle length) of approximately 200 nm.

(12) On the other hand, an aqueous solution of iron chlorides is prepared by dissolving, with magnetic stirring, 5.36 g of iron(III) chloride hexahydrate (FeCl.sub.3.6H.sub.2O) and 1.98 g of iron(II) chloride tetrahydrate (FeCl.sub.2.4H.sub.2O) in 100 ml of distilled water. The aqueous solution of iron chlorides is heated to 85 C. while being stirred magnetically and while nitrogen is bubbled through.

(13) 12 ml of ammonia in 30% aqueous solution are then added, with magnetic stirring. Magnetite particles then form by precipitation, and the suspension assumes a black coloration.

(14) After 5 to 10 minutes of magnetic stirring, the suspension of magnetic iron oxide obtained is centrifuged in order to separate the magnetite Fe.sub.3O.sub.4 and maghemite -Fe.sub.2O.sub.3 particles from a supernatant solution containing ammonium chloride and excess ammonia. The magnetic iron oxide composition that is recovered is washed once with distilled water and then centrifuged again. Each centrifugation is carried out at 10,000 revolutions/minute for 40 minutes. A magnetic iron oxide composition is obtained, to which there are added 400 ml of distilled water and which is subjected to ultrasound for 1 hour. The magnetic particles have a mean equivalent diameter of from 5 nm to 30 nm.

(15) 34.48 ml of the aqueous solution of magnetic iron oxide that has been prepared are added to the synthetic talc suspension, that is to say the equivalent of 20 wt. % magnetic iron oxide relative to the talc. The suspension obtained is stirred magnetically for 10 minutes at ambient temperature (25 C.).

(16) After drying there is obtained a magnetic talcous composition in suspension which comprises magnetic talcous particles having a positive magnetic susceptibility and comprising 83.4 wt. % talc and 16.6 wt. % magnetic iron oxide particles (that is to say magnetite Fe.sub.3O.sub.4 particles and more than 0.5 wt. % maghemite -Fe.sub.2O.sub.3 particles) relative to the total weight of the magnetic talcous composition.

EXAMPLE 3

(17) A silico-metallic gel of the formula Si.sub.4Mg.sub.3O.sub.ii, nH.sub.2O is prepared and subjected to a hydrothermal treatment for 6 hours at a temperature of 300 C. Synthetic talc is thus obtained.

(18) On the one hand there is prepared a synthetic talc composition composed of 1 g of talc obtained by drying an aqueous suspension recovered after hydrothermal treatment. The talc particles have a mean equivalent diameter of from 20 nm to 100 nm, and in particular a thickness of approximately from 10 nm to 20 nm and a largest dimension (or particle length) of approximately 200 nm.

(19) On the other hand, an aqueous solution of iron chlorides is prepared by dissolving, with magnetic stirring, 5.36 g of iron(III) chloride hexahydrate (FeCl.sub.3.6H.sub.2O) and 1.98 g of iron(II) chloride tetrahydrate (FeCl.sub.2.4H.sub.2O) in 100 ml of distilled water. The aqueous solution of iron chlorides is heated to 85 C. while being stirred magnetically and while nitrogen is bubbled through.

(20) 12 ml of ammonia in 30% aqueous solution are then added, with magnetic stirring. Magnetite particles then form by precipitation, and the suspension assumes a black coloration. The magnetic particles have a mean equivalent diameter of from 5 nm to 30 nm.

(21) After 5 to 10 minutes of magnetic stirring, the magnetic iron oxide suspension obtained is centrifuged in order to separate the magnetite Fe.sub.3O.sub.4 and maghemite -Fe.sub.2O.sub.3 particles from a supernatant solution containing ammonium chloride and excess ammonia. The magnetic iron oxide particles recovered are washed once with distilled water and then centrifuged again. Each centrifugation is carried out at 10,000 revolutions/minute for 40 minutes. The magnetic iron oxide particles recovered are then dried.

(22) 0.2 g of magnetic iron oxide particles is then mixed with the talc composition for 2 minutes in an agate mortar. The equivalent of 20 wt. % of magnetic iron oxide relative to the talc is thus contacted.

(23) There is obtained a composition which comprises magnetic talcous particles having a positive magnetic susceptibility and comprising 83.4 wt. % talc and 16.6 wt. % magnetic iron oxide particles (that is to say magnetite Fe.sub.3O.sub.4 particles and more than 0.5 wt. % maghemite -Fe.sub.2O.sub.3 particles) relative to the total weight of the magnetic talcous composition.