WO2015018725A1

WO2015018725A1 - Iron oxide and silicon dioxide-containing core-sheath particles having an improved heating rate

Info

Publication number: WO2015018725A1
Application number: PCT/EP2014/066458
Authority: WO
Inventors: Stipan Katusic; Harald Herzog; Peter Kress
Original assignee: Evonik Industries Ag
Priority date: 2013-08-07
Filing date: 2014-07-31
Publication date: 2015-02-12
Also published as: DE102013215498A1

Abstract

The invention relates to core-sheath particles, the core of which comprises magnetic, crystalline iron oxide, the sheath of which contains amorphous silicon dioxide, wherein in addition thereto, the sheath contains at least one non-magnetic metal oxide, or the sheath and the core each additionally contain at least one non-magnet metal oxide.

Description

Iron oxide and silica containing core-shell particles with improved heating rate

The invention relates to iron oxide and silica-containing core-shell particles with improved heating rate in the magnetic field, their preparation and their use.

WO03 / 042315 describes the use of iron-silicon oxide particles for inductive heating of adhesive composites. The particles can be obtained either via sol-gel routes or by flame pyrolysis.

In WO 2010/063557 iron-silicon oxide particles are disclosed, which can be used for inductive heating. The particles have a core-shell structure, with the iron oxide phases hematite, magnetite and maghemite as the core and an amorphous shell of silicon dioxide. The particles are prepared by reacting a mixture of silicon compounds, one of which is a monosilane, and an iron compound in a hydrogen / oxygen flame.

EP-A-2000439 discloses doped iron-silicon oxide particles having a core-shell structure, the choice of doping components being limited to those having magnetic properties. In addition, the particles have a fairly high chloride content. The particles are going through

Obtained flame pyrolysis, wherein reducing gases are introduced into different reaction zones. In WO2012 / 048985 are coated with silica-coated acicular

Disclosed iron oxide particles which may be doped with P, Si, Al, Mg, Co, K or Cr. There are no quantities and no information on the

Made connections that can be used. The doping serves to influence the particle size and shape. It is not known in which chemical form and at which point of the particle, core and / or shell, the doping component is incorporated.

The documents cited in the prior art disclose the use of iron-silicon oxide particles for inductive heating in one

magnetic or electromagnetic alternating field. Although the

Heating times could be significantly improved, it remains the goal to further reduce the heating times. It was therefore the object of the present invention to provide a material with which this goal can be achieved.

The invention relates to core-shell particles whose core magnetic, crystalline iron oxide and the shell contains amorphous silica, wherein a) the shell additionally contains at least one non-magnetic metal oxide or

b) the shell and the core additionally each contain at least one non-magnetic metal oxide.

The sum of the proportions of iron oxide, silicon dioxide and nonmagnetic metal oxide is generally at least 98% by weight, preferably at least 99 wt .-%, particularly preferably at least 99.5 wt .-%, each based on the core-shell particles.

The nonmagnetic metal oxide is preferably selected from the group consisting of aluminum oxide, calcium oxide, cerium oxide, chromium oxide, copper oxide,

Magnesium oxide, silver oxide, titanium oxide, tungsten oxide, yttrium oxide, zinc oxide, tin oxide and zirconium oxide. Particularly preferred are zinc oxide and alumina.

In the embodiment of the invention wherein both the core and the shell contain nonmagnetic metal oxides, it is understood that the nonmagnetic metal oxide may be the same or different in core and shell. Likewise, in this embodiment, the proportions of non-magnetic

Metal oxides be the same or different.

The best results in terms of the heating rate are obtained when the non-magnetic metal oxide is present in a proportion of 0.5 to 10 wt .-%, based on the core-shell particles. The distribution of this proportion to the core and the shell is not critical. Particularly preferred is a

Embodiment in which the proportion of non-magnetic metal oxide is 1.5 to 7.5% by weight. Very particular preference is given to the embodiment in which the proportion of non-magnetic metal oxide in the core and shell is in each case from 0.5 to 5% by weight, based on the core-shell particles.

The proportion of silicon dioxide in the core-shell particles according to the invention is preferably 5 to 40 wt .-%, particularly preferably 10 to 20 wt .-%. The amount of silicon dioxide in the shell of the particles according to the invention is preferably from 95 to 99.5% by weight.

The particles according to the invention are largely isolated in form

Single particles before. The individual particles have a largely spherical to bulbous form. The mean diameter of the individual particles is generally from 5 to 500 nm, preferably from 50 to 200 nm. Noble-shaped particles are not found. In addition to the isolated individual particles, three-dimensional aggregates of these particles can also be present. In these aggregates, the individual particles are firmly grown together. The proportion of aggregates is less than 50 wt .-%, preferably less than 20 wt .-%, based on the sum of individual particles and aggregates. The determination can be carried out, for example, by image evaluation of TEM images by means of suitable software, as is already known for other magnetic core-shell particles. The BET surface area of the particles according to the invention is generally 5 to 40 m ² / g, preferably 10 to 25 m ² / g.

The proportion of silicon dioxide in the core-shell particles according to the invention is preferably from 5 to 40% by weight of silica, more preferably from 8 to 25% by weight and most preferably from 10 to 20% by weight. The proportion of silicon dioxide in the shell is preferably from 70 to 95% by weight, based on the sum of silicon dioxide and metal oxide.

The case is a tight shell. Under dense is to understand that with 12 hours contact of the particle with 60 ° C with hydrochloric acid less than 300 ppm iron, hydrogen peroxide less than 10 ppm iron or a NaCl / CaC solution less than 50 ppm iron are detectable. The thickness of the shell is preferably 1 to 40 nm, more preferably 5 to 20 nm. The thickness of the shell can be determined, for example, by evaluating HR-TEM images.

The proportion of iron oxide in the core-shell particles of the invention is preferably 60 to 95 wt .-%, more preferably 75 to 90 wt .-% and most preferably 70 to 80 wt .-%. The proportion of iron oxide in the core is preferably 90 to 100 wt .-%, based on the sum of

Silica and metal oxide.

The crystalline iron oxide present in the core of the particles according to the invention may be magnetite, maghemite and hematite

Main components act. The mentioned network plane distances

correspond to these iron oxide modifications. So includes the

Lattice plane spacing of 0.20 nm and 0.29 nm maghemite and magnetite, while the interplanar spacing of 0.25 nm corresponds to maghemite, magnetite and hematite. There are no lattice plane distances detected in the HR-TEM that would have to be assigned to the doping component.

The core of the core-shell particles according to the invention preferably has a ratio (magnetite + maghemite) / hematite of 70:30 to 95: 5, particularly preferably 80:20 to 90:10, and a ratio of magnetite / maghemite of preferably 50: 50 to 90:10, more preferably 60:40 to 70:30. With these conditions, the best heating times are achieved. The composition of the core based on maghemite, magnetite and hematite can be determined This can be done by X-ray diffractometry using Co-Ka radiation in an angular range 2Θ of 10 - 100 °. Thus, Maghemit is significantly on the basis of the reflexes (1 10) and (21 1) in the front

Angular range detectable. The hematite is clearly identifiable because of the freestanding reflexes. The quantitative phase analysis is carried out using the Rietveld method, error about 10% relative.

The core-shell particles according to the invention may contain, in a boundary layer between core and shell, one or more compounds containing iron, silicon and oxygen, which in HR-TEM have a spacing of the lattice planes of 0.31 +/- 0.01 nm exhibit.

This can be done with XPS-ESCA (X-ray photoelectron spectroscopy) analysis and TEM-EDX (TEM) analysis combined with energy-dispersive X-ray analysis

[EDX]). These compounds can surround the core in the form of another shell, in addition to silicon dioxide. The thickness of this shell is 0.5 to 2 nm. This shell provides a transition region between amorphous silica shell and crystalline iron oxide core, which is a

Excellent adaptation between core and outer shell leads. It is currently believed that the phonon transport and thus the heat conduction from core to outer shell is improved by this intensive bond, which can lead to substantially higher heating rates in the application of the particles according to the invention. The core-shell particles according to the invention also have hydroxyl groups on their surface. These can react with inorganic and organic surface modification agents to form a Van der Waals interaction, ionic or covalent bond.

Suitable surface modification agents may be, for example

Alkoxysilanes, carboxylic acids, nucleic acids or polysaccharides.

Another object of the invention is a process for the preparation of the core-shell particles in which

a) containing in a first zone of a flow reactor, a mixture

a1 1) one or more iron compounds

or

a12) each one or more iron compounds and metal compounds, a2) one or more hydrogen-containing fuel gases and

a3) one or more oxygen-containing gases

ignites and reacts,

b) in a second zone of the flow-through reactor, in each case one or more silicon compounds and metal compounds are present for this reaction mixture,

c) subsequently, if appropriate, cooling the reaction mixture and separating off the solid from gaseous or vaporous substances, and

d) optionally then the solid with an agent for

Surface modification treated, where

e) iron compound, silicon compound and metal compound are oxidizable and / or hydrolyzable. The iron compound and the metal compound are preferably introduced as aerosol in the first zone. The aerosol formation can be carried out in each case from a solution, a dispersion or the substance itself in the form of a liquid in each case using a sputtering gas such as air or nitrogen and a two- or multi-component nozzle. It is also possible to generate the aerosol from a solution containing both the iron compound and the metal compound.

The silicon compound and the metal compound may also be introduced into the second zone as an aerosol together or separately. It has also proven to be the silicon compound as vapor in the second zone

contribute.

The mean droplet diameter of the aerosols is preferably less than 100 μιτι, particularly preferably less than 50 μιτι.

The iron compound used is preferably iron (II) chloride.

The silicon compound is preferably selected from the group consisting of SiCl ₄ , CH ₃ SiCl ₃ , (CH ₃ ) ₂ SiCl ₂ , (CH ₃ ) ₃ SiCl, HSiCl ₃ , (CH ₃ ) ₂ HSiCl and CH ₃ C ₂ H ₅ SiCl 2, H ₄ Si, Si (OC ₂ H ₅ ) ₄ and / or Si (OCH ₃ ) ₄ . Particular preference is given to using SiCl ₄ and / or Si (OC ₂ H ₅ ) ₄ .

The metal compound is converted to the non-magnetic metal oxide during the process. Suitable metal compounds are especially salts in the form of nitrates, chlorides and octoates, such as 2-ethylhexanoates. Likewise, organometallic compounds such as alkoxides or Acetylacetonates are used. The metal component is preferably selected from the group consisting of aluminum, calcium, cerium, chromium, copper, magnesium, silver, titanium, tungsten, yttrium, zinc, tin and zirconium. Explicit examples are: aluminum isopropylate, aluminum sec-butoxide, aluminum nitrate, copper nitrate, yttrium nitrate, silver nitrate, zinc nitrate, zirconium nitrate, calcium chloride, magnesium chloride, titanium tetrachloride,

Titanium isopropylate, zinc octoate and zirconium octoate.

In a particular embodiment of the invention, water or steam can additionally be introduced into the second zone. In this case, the water or the steam is introduced separately from the silicon compound and the metal compound. Preferably, a molar excess of water or water vapor is used. Particularly preferred may be a molar ratio of water / silicon compound of 10 to 100.

As fuel gases, hydrogen, methane, ethane and / or propane can preferably be used. Particularly preferred is hydrogen. The oxygen-containing gas used is mainly air or oxygen-enriched air. As a rule, an excess of oxygen is compared

Used hydrogen. Lambda, the quotient of fuel quantity to

Amount of oxygen, is preferably 1, 05 -1, 50th

The reaction conditions may preferably be selected so that in the first zone, the mean residence time of 10 ms to 1 s, more preferably 300 to 600 ms, and the temperature preferably 800 to 1300 ° C, more preferably 950 to 1 100 ° C, and in the second zone the mean residence time 0.1 to 10 s, more preferably 1 to 3 seconds and the temperature is preferably 400 to 900 ° C, particularly preferably 700 to 850 ° C, is. In the first zone, the

Temperature measurement 50 cm below the ignition point, in the second zone 15 cm above the uppermost point of addition in the second zone.

Suitable surface modification agents are organosilanes, silazanes or polysiloxanes. Usually these agents are sprayed onto the core-shell particles and then treated at temperatures of 120 to 200 ° C, preferably under a protective gas atmosphere, over a period of 1 to 5 hours.

Another object of the invention is a silicone rubber containing the core-shell particles according to the invention. The proportion of these particles is preferably 0.5 to 15 wt .-% and particularly preferably 3 to 6 wt .-%.

Another object of the invention is the use of the

Core-shell particles according to the invention as a constituent of

Rubber compounds, of polymer preparations, of adhesives, obtained by welding in electromagnetic alternating field

Plastic composite moldings and for the production of dispersions.

Examples

analytics

To determine the iron oxide content, the sample was homogenized in the laboratory mill and determined titrimetrically after melt digestion. The Fe (III) content is determined by means of manganometry. The content of Si and the further metal oxide components is determined by means of ICP-OES and

subsequently calculated as oxide.

The BET surface area is determined according to DIN 66131.

The determination of the core components is done by X-ray diffractometry.

(Reflection, Θ / Θ diffractometer, Co-Κα, U = 40kV, I = 35mA; Scintillation counter, simulated graphite monochromator; Angular range (2Θ) / Increment / Measurement time: 10 - 100 ° / 0.04 ° / 6s (4h)) , Using the Rietveld method, a quantitative phase analysis is carried out (error approx. 10% relative). Quantitative phase analysis is performed using set 60 of the ICDD database PDF4 + (2010). Phase analysis and crystallite size determination are performed with the Rietveld SiroQuant® program, version 3.0 (2005).

The thickness of the shell is determined by high-resolution transmission electron microscopy (HR-TEM).

The heating time from 20 ° C to 200 ° C is determined in a silicone composition. The silicone composition is obtained by adding 33 g ELASTOSIL® E50, from Momentive Performance Materials, 13 g silicone oil type M 1000, from Momentive Performance Materials, 4 g AEROSIL® 150 from Evonik and 2.5 g, corresponding to 4, 76% by weight, mixed core-shell particles by means of a SpeedMixer 2 χ 30 s and 2 χ 45 s at 3000 U / min. Subsequently, the silicone composition is applied in a thickness of about 1 mm on a glass slide. The energy input is made by induction by means of a water-cooled coil with a diameter of 80 mm. The frequency is 510 KHz, the power about 12 KW, Fives Celes GTMC 25 KW, France.

Leach Test: 0.33 g of core-shell particles in 20 ml HCl (1 mol / l) or H ₂ O ₂ (0.5 mol / l) or a solution of 8 wt% NaCl and 2 wt% CaC ^ in water are stored at 60 ° C over a period of 12 hours.

A part of the solution is subsequently analyzed for iron by means of suitable analysis techniques, for example ICP (inductively coupled plasma spectroscopy).

Examples 1 to 10 show the preparation of core-shell particles according to the invention, in which both core and shell are non-magnetic

Metal oxide included. Here, in Examples 1 to 8, the nonmagnetic metal oxide in the core and shell is the same, in Examples 9 and 10 different. Example 1 Figure 1 shows the preparation of core-shell particles according to the invention, in which only the shell contains a nonmagnetic metal oxide.

Example 1: An aerosol obtained by atomizing 4500 g / h of an aqueous solution consisting of 26.1 g of iron (II) chloride, 1.3 g of zinc nitrate and 72.6 g of water, in each case per 100 g of solution, and 3.0 kg / h nitrogen are atomized by means of a two-fluid nozzle.

The aerosol thus obtained is reacted with 8.8 Nm ³ / h of hydrogen and 19 Nm ³ / h of air, of which 15 Nm ³ / h of primary air and 4 Nm ³ / h of secondary air, in a first zone. The mean residence time of the reaction mixture in the first zone is about 540 ms. The temperature in the first zone is 979 ° C. In the stream of the reaction mixture from the first zone 410 g / h of vaporous Si (OC2H ₅ ) and one formed by means of a two-fluid nozzle

Aerosoles of 4 Nm ³ / h nitrogen and 200 g / h of a 10 weight percent, aqueous solution of Zn (NOs) 2 by two-fluid nozzle with 200l / h N ₂ given.

Separately, an additional 2.5 kg / h steam are added.

The mean residence time of the reaction mixture in the second zone is

1, 7 s. The temperature in the second zone is 808 ° C.

Subsequently, the reaction mixture is cooled and the resulting solid is deposited on a filter of the gaseous substances.

Examples 2 to 1 1 are carried out analogously to Example 1. The starting materials are shown in Table 1.

In Examples 1 to 6, aqueous solutions of the metal compounds are used in the first and second zones.

In Examples 7 to 11, an organometallic compound is used as the metal compound in the second zone. The octoates are used in the form of 2-ethylhexanoates dissolved in 2-ethylhexanoic acid, the content of octoate in the solution in each case being 50 ± 2% by weight.

Titanium (IV) isopropylate and aluminum tri-sec-butylate are used as the substance. The starting materials are also shown in Table 1.

Table 2 shows the average residence times t and the temperature T in the first and second zones. The physicochemical properties of the core-shell particles are given in Table 3.

As a comparative example, the powder of Example 6 from EP-A-2000439 is used. This is an iron-silicon mixed oxide powder doped with 1.8% by weight of manganese. The heating time from 20 ° C to 200 ° C is 15 s.

As a further comparative example, the powder of Example 10 from WO 2012/048985 is used. This is an iron-silicon mixed oxide powder doped with 1.8% by weight of phosphorus. The heating time from 20 ° C to 200 ° C is 17 s.

The core-shell particles of the invention have significantly shorter

Heating up on as a powder according to the prior art.

Table 1: Starting materials and quantities

a) Zr-2-ethylhexanoate; b) titanium (IV) isopropylate; c) η, 2-ethylhexanoate d) aluminum tri-sec-butylate;

Table 2: Mean residence time t and temperature T in zone I and zone II

Table 3: Substance parameters

Table 3: Substance parameters (continued)

a) From XRD; b) Magn = magnetite; Magh = Maghemite; Heme = hematite; c) In the alternating magnetic field; 20 ° C to 200 ° C

Claims

claims

1 . Core-shell particles whose core contains magnetic, crystalline iron oxide and its shell amorphous silica, wherein

a) the shell additionally contains at least one non-magnetic metal oxide or

b) the shell and the core additionally each at least one

contain non-magnetic metal oxide.

2. core-shell particles according to claim 1,

characterized in that

the nonmagnetic metal oxide selected from the group consisting of

Alumina, calcium oxide, cerium oxide, chromium oxide, copper oxide,

Magnesium oxide, silver oxide, titanium oxide, tungsten oxide, yttrium oxide, zinc oxide, tin oxide and zirconium oxide.

3. core-shell particles according to claims 1 to 3,

characterized in that

the non-magnetic metal oxide is present in a proportion of 0.5 to 10 wt .-%, based on the core-shell particles.

4. core-shell particles according to claims 1 to 3,

characterized in that

they contain 5 to 40 wt .-% silica.

5. core-shell particles according to claims 1 to 4,

characterized in that

they contain 60 to 95 wt .-% iron oxide.

6. core-shell particles according to claims 1 to 5,

characterized in that

the core has interplanar spacings of 0.20 nm, 0.25 nm and 0.29 nm, each +/- 0.02 nm, as determined by high-resolution transmission electron microscopy.

7. core-shell particles according to claims 1 to 6,

characterized in that

the ratio determined by X-ray diffractometry (magnetite + maghemite) to hematite is equal to 70:30 to 95: 5 and that of magnetite too

Maghemit is 50:50 to 90:10.

8. core-shell particles according to claims 1 to 7,

characterized in that

there are one or more compounds containing iron, silicon and oxygen between the core and the shell, which in the HR-TEM have a spacing of the lattice planes of 0.31 +/- 0.01 nm

exhibit.

9. core-shell particles according to claims 1 to 8,

characterized in that

they are modified by adsorption, reaction at the surface or complexation of or with inorganic and organic reagents.

10. A process for the preparation of the core-shell particles according to claims 1 to 9, characterized in that one

a) in a first zone of a flow reactor, a mixture containing a1 1) one or more iron compounds

or

a12) each one or more iron compounds and

Metal compounds

a2) one or more hydrogen-containing fuel gases and

a3) one or more oxygen-containing gases

ignites and reacts,

b) in a second zone of the flow reactor to this

Each one or more silicon compounds and metal compounds,

c) subsequently cooling the reaction mixture, if appropriate, and separating off the solid from gaseous or vaporous substances; and d) optionally subsequently adding the solid to an agent

Surface modification treated, where

e) iron compound, silicon compound and metal compound are oxidizable and / or hydrolyzable.

1 1. Method according to claim 10,

characterized in that

in the first zone, the average residence time 10 ms to 1 s and the

Temperature is 800 to 1300 ° C and in the second zone, the average residence time 0.1 to 10 s and the temperature 400 to 900 ° C.

12. The method according to claims 10 or 1 1,

characterized in that

additional water or steam is introduced in the second zone.

13. Silicone rubber containing the core-shell particles according to claims 1 to 9.

14. Use of the core-shell particles according to claims 1 to 9 as a component of rubber mixtures, as a component of

Polymer preparations, being a component of adhesives, being part of welding alternating electromagnetic fields

Plastic composite moldings, for the preparation of dispersions and for the immobilization of enzymes.