KR20070019555A - Cerium oxide powder and cerium oxide dispersion - Google Patents

Abstract

Cerium oxide powder comprising a crystalline first particle having a carbonic group and containing a cerium oxide and a carbonic acid group on the surface and in the adjacent layer, wherein

The powder has a BET surface area of 25 to 150 m ² / g and the first particles have an average diameter of 5 to 50 nm,

The layer adjacent to the first particle surface has a depth of about 5 μm nm,

The carbonic acid concentration of the layer adjacent to the surface decreases inward from the surface with the highest carbonic acid concentration,

The carbon content due to carbonate groups on the surface is from 5 to 50 area%, from 0 to 30 area% at a depth of about 5 nm in the layer adjacent to the surface,

The content of cerium oxide, calculated as CeO ₂ based on the powder, is at least 99.5% by weight and

The carbon content comprising organic and inorganic carbons is from 0.01 to 0.3% by weight, based on the powder.

Dispersion containing the powder.

Description

Cerium oxide powder and cerium oxide dispersion

The present invention relates to a powder based on cerium oxide, the preparation of the powder and the use of the powder. The invention also relates to dispersions containing such powders.

Cerium oxide is an important component of the catalyst. Moreover, cerium oxide is an important material for polishing glass and electrical components. Especially in the field of chemical mechanical polishing, the papers and patent documents contain numerous discussions that improve the properties of cerium oxide powders and cerium oxide dispersions.

Cerium oxide is usually prepared by calcination of cerium hydroxide or cerium carbonate. The calcined oxide is then comminuted and sieved.

Wet-chemical routes and gas-phase processes are also known. Cerium oxide can be prepared by the hydrothermal method, for example, as described in US Pat. No. 5,389,352. Here, the cerium (III) salt is oxidatively converted to cerium oxide which crystallizes in the form of fine particles at elevated temperatures and pressures.

Of particular interest are gas-phase processes, such as spray pyrolysis, in which the cerium oxide precursor, usually in the form of an aerosol, is oxidized in a flame. One such method is described in EP-A-1142830.

Pratsinis et al., J. Mater. Res., Vol. 17, pages 1356-1362 (2002), describe the solution of cerium acetate solution in a solvent mixture comprising acetic acid, isooctane and 2-butanol by oxidation by oxygen in an oxygen / methane flame. The production of high crystallinity cerium oxide powder by flame spray pyrolysis will be described. The solvent mixture is essential for the preparation of cerium oxide powder free of relatively coarse particles.

WO2004 / 005184A1 claims a process for producing metal oxides, in which solution droplets are prepared from solutions, which are oxidized in a flame. The solution contains at least 60% carboxylic acid as a solvent based on the one or more starting materials and the total solution.

Cerium oxide manufacturing processes comprising coarse and fine materials are known from WO01 / 36332A1. The process initiates combustion of the aerosol of cerium oxide precursor in the high temperature zone of 700-1100 K.

DE-A-10251029 describes a fraction comprising crystalline, non-aggregated particles having an average diameter of 30 to 200 nm and an average agglomerate diameter of 5 to 50 nm and a BET surface area of 15 to 200 m ² / g. An exothermic cerium oxide powder retaining a fine portion in the form of an aggregate of first particles grown to retained fine crystalline is disclosed.

EP-A-1506940 discloses polycrystalline oxidation in the form of first particle aggregates having a surface area of 70 to 150 m ² / g, an average first particle diameter of 5 to 20 nm and a protruded aggregate average diameter of 20 to 100 nm. A cerium powder and a dispersion containing such cerium oxide powder are disclosed.

Moreover, many dispersions containing cerium oxide for chemical mechanical polishing have been described.

EP-A-1203801 discloses an aqueous dispersion containing pyrogenic silicon dioxide doped with cerium oxide, wherein cerium oxide is introduced through the aerosol of the cerium salt solution or suspension and the average particle size in the dispersion is less than 100 nm. .

EP-A-133080 discloses an aqueous dispersion containing particles containing a core of doped pyrogenic lower-structured silicon dioxide, with cerium oxide not exceeding a second particle average size of 0.2 μm.

DE-B-10342826 discloses a dispersion of exothermic cerium oxide having no particles larger than 1 μm.

US 6827752 claims cerium oxide dispersions stabilized by polyacrylates.

US 6443811 claims neutral cerium oxide dispersions for weakly basic media containing cationic surface-active agents.

US 6420269 has a pH in the range from 8 to 12 and contains a dispersant, preferably a water soluble organic polymer, a water soluble anionic or nonionic surface-active agent or a water soluble amine.

A drawback of the cerium oxide dispersion according to the prior art is that satisfactory stability in the neutral to weakly alkaline range can only be achieved in the presence of additives.

It is therefore an object of the present invention to provide a dispersion that is sufficiently stable in the neutral to weakly alkaline range, which is based on cerium oxide and can be used for chemical mechanical polishing, without further additives.

Another object of the present invention was to provide a powder based on cerium oxide as a base for the dispersion. Another object was to provide a method for preparing the powder.

The present invention provides a cerium oxide comprising crystalline first particles having a carbonic group and containing cerium oxide and a carbonic acid group on and adjacent to the powder surface, wherein

The powder has a BET surface area of from 25 to 150 m ² / g,

The first particles have an average diameter of 5 to 50 nm,

The layer adjacent to the surface of the first particles has a depth of about 5 nm,

The carbonic acid concentration in the layer adjacent to the surface decreases inward from the surface with the highest carbonic acid concentration,

Carbonic acid content due to carbonate groups on the surface is from 5 to 50 area%, carbonic acid content from about 5 nm depth in layers adjacent to the surface is from 0 to 30 area%,

The content of cerium oxide, calculated as CeO ₂ based on the powder, is at least 99.5% by weight,

The content of carbon comprising organic and inorganic carbons is from 0.01 to 0.3% by weight, based on the powder.

Carbonic groups in the powders of the present invention can be detected both on the powder surface and up to about 5 nm deep. The carbonate group is chemically bonded and may exist in the following structures a-c.

Carbonated groups can be detected, for example, by XPS / ESCA analysis. To detect the carbonic acid in the layer adjacent to the surface, part of the surface can be removed by argon ion bombardment and the resulting new surface can be similarly analyzed by XPS / ESCA (XPS = X-ray photoelectron spectroscopy; ESCA = Electron spectroscopy for chemical analysis.

In the powder of the present invention, the first particles may be in isolated form or may be somewhat strongly aggregated. The first particles are preferably present in very large agglomerated form.

The powder of the invention preferably has <5 ppm sodium and <20 ppm chlorine. The elements are generally only able to withstand small amounts in chemical mechanical polishing.

Moreover, the BET surface area of the powders of the present invention for abrasive applications is preferably from 30 to 100 m ² / g, particularly preferably from 40 to 80 m ² / g.

The present invention also provides a method for preparing cerium oxide powder having a carbonic acid group, wherein

The aerosol reacts with the oxygen-containing gas at a reaction temperature of 600 ° C. to 1500 ° C., preferably 900 ° C. to 1200 ° C. in the reaction chamber, the reaction mixture is cooled and the powder is subsequently removed from the gaseous material by a filter. Separately,

An aerosol is obtained by atomization of at least one solution containing an oxidizable organocerium (III) compound dissolved in a solvent by an organic solvent or solvent mixture and at least one atomization gas,

The average droplet diameter D ₃₀ of the aerosol based on volume is from 30 to 100 μm, and the average residence time in the reaction chamber is from 0.1 to 5 seconds, where

The reaction mixture is cooled after leaving the reaction chamber by spraying water droplets on the reaction mixture,

The water droplets have an average volume-based water droplet diameter of less than 100 μm,

To generate water droplets, water is added in an amount according to the following equation

m _H2O = [cp _liq * (T _b -T ₀ ) + dh _v + cp _g * (T _e -T _b )] / 3600 * Q (I)

At this time

Q = total combustion enthalpy (KW) of all starting materials

-m _H2O = Amount of H ₂ O required to achieve the final temperature T _e (kg / h)

-T _o = Inlet temperature of water

Boiling point of water at T _b = 1 bar

-dh _v = Evaporation enthalpy of water

cp _liq = Heat capacity of water at 50 ° C

-cp _g = Heat capacity of water vapor at 150 ° C., and

T ₀ = 5-50 ° C., T _b = 100 ° C., T _e = 200-400 ° C., dh _v = 2256.7 kJ / kg, cp _liq = 4.181 kJ / kg * K and cp _g = 1.98 kJ / kg * K .

The oxygen-containing gas is generally an atmosphere or an oxygen rich atmosphere.

As the atomizing gas, an inert gas such as atmosphere, oxygen rich atmosphere and / or nitrogen may be used in the process of the present invention. Generally, atmosphere is used as the atomizing gas. The ratio of the throughput of the cerium (III) solution / amount of atomizing gas is preferably 0.1 to 25 kg / standard m ³ , particularly preferably 0.5 to 5 kg / standard m ³ . One or more two-fluid or plural fluid nozzles are particularly suitable for atomization. The atomization pressure is generally 1 to 100 bar.

In a more preferred embodiment of the invention, fuel gas is additionally added to the reaction mixture. Suitable fuel gases are, in particular, hydrogen, methane, ethane, propane, butane, natural gas. The amount of fuel gas added depends first of all on the amount of solution containing cerium (III) compound added, the composition of the solution and the Joule value. Typically the ratio of combustion gas / solution is 0.1 to 2 standard m ^{3 /} kg.

It may also be advantageous to introduce a second atmosphere in addition to the reaction chamber. In general, the amount of the second atmosphere will be present such that the ratio of the second atmosphere to the first atmosphere is 0.1 to 10.

The process of the present invention may preferably be carried out such that the ratio of oxygen in the amount of oxygen-containing gas introduced is greater than the amount necessary for complete reaction of the cerium (III) compound with the fuel gas. In particular, it is advantageous for the lambda to be ≧ 1.5, where the lambda is calculated from the sum of oxygen in the (atmosphere + if appropriate, atomization gas) / (cerium (III) compound + fuel gas), in each case mol / h to be. Very particularly preferably 2 <lambda <5.

As the organic cerium (III) compound, cerium alkoxide and / or cerium carboxylate can be used in particular. As the alkoxide, preference is given to using ethoxide, n-propoxide, isopropoxide, n-butoxide and / or tert-butoxide. As carboxylates, acetic acid, propionic acid, butanoic acid, hexanoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, octanoic acid, 2-ethyl-hexanoic acid, valeric acid, capric acid and / or laurate Compounds based on lyric acid can be used. In particular it may be advantageous to use 2-ethyl-hexanoate and / or laurate.

As an organic solvent or as a component of an organic solvent mixture, alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol or tert-butanol, ethanediol, pentanediol, 2-methyl-2, 4-pentanediol and Dialkyl ethers such as diol, diethyl ether, tert-butyl methyl ether or tetrahydrofuran, acetic acid, propionic acid, butanoic acid, hexanoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, octanoic acid, Preference is given to using C ₁ -C ₁₂ -carboxylic acids such as 2-ethylhexanoic acid, valeric acid, capric acid, lauric acid. Moreover, ethyl acetate, benzene, toluene, naphtha and / or gasoline can be used. Preference is given to using solutions containing C ₂ -C ₁₂ -carboxylic acids, in particular 2-ethylhexanoic acid and / or lauric acid.

The present invention also provides a cerium oxide powder having a carbonic group and obtainable by the process of the present invention.

The present invention also provides a dispersion containing cerium oxide powder having a carbonic acid group according to the present invention.

The liquid phase of the dispersion can be water, one or more organic solvents or water / organic solvent combinations in which the phases can preferably be mixed. The dispersion may additionally contain pH adjusters, surface-active additives and / or preservatives. However, dispersions containing surface-active additives are not beneficial. Instead, a dispersion consisting exclusively of cerium oxide powder having carbonic acid, water and optionally a pH adjuster is advantageous.

The content of cerium oxide powder containing a carbonic acid group is preferably 0.5 to 60% by weight. Particular preference is given to aqueous dispersions containing from 20 to 50% by weight, more particularly from 35 to 45% by weight of the powder of the invention. Furthermore, it is preferred that the aqueous dispersion according to the invention has a viscosity of <30 mPas, particularly preferably <20 mPas at a powder concentration of up to 40% by weight and a temperature of 23 ° C., a shear rate in the range of 1 to 1000 s ^−1. can do.

The pH of the aqueous dispersion according to the invention is preferably in the range from 3 to 8. To store the dispersion, the pH of 3 to 4 is usually adjusted by the addition of acid. Nitric acid is particularly useful for this purpose. The stability of the dispersion is particularly high in this pH range.

When aqueous dispersions are used as brighteners, the pH can be adjusted to 7-8 with, for example, ammonia or potassium hydroxide. The dispersions show satisfactory stability in this range without the presence of surface-active additives.

The average particle size d ₅₀ of the dispersion, determined by dynamic light scattering, is less than 120 nm, in particular less than 100 nm suitable for the polishing process.

Moreover, the average particle size d ₉₀ of the dispersion as determined by the dynamic light scattering method is less than 200 nm, in particular less than 150 nm is suitable for the purposes of the present invention.

The zeta potential of the dispersions of the invention is preferably at least 20 mV, in particular greater than 30 mV.

Dispersions of the invention can be prepared using dispersing devices known to those skilled in the art. Such a device can be, for example, a rotor-stator device, a high-energy grinder in which particles are crushed by collisions with each other, planetary kneaders, agitated ball grinders, vibratory ball grinders, shaking tables, ultrasonic devices or combinations of these devices. have.

Example  :

The specific surface area is measured according to DIN 66131.

Surface properties are determined by large-area (1 cm ² ) XPS / ESCA analysis (XPS = X-ray photoelectron spectroscopy; ESCA = electron spectroscopy for chemical analysis). The assessment is reported by DIN Expert Report No. of the National Institute of Physics in Tedington, England. 39, a general assessment in DMA (A) 97, and previous findings in the development-accompanied standards of the "Oberfleen-Unt Microberreihis Analisen" NMP816 (DIN) association. Furthermore, from the special literature the comparative spectra available in special cases are taken into account. The numerical value is calculated by the background difference taking into account the relative sensitivity factors of the electronic rating indicated in each case. Results are reported in area%. Accuracy is estimated as a +/- 5% correlation.

Zeta potential is measured in the pH 3-12 range using electrodynamic sound amplitude (ESA). For this purpose, a suspension containing 1% cerium oxide is prepared. Dispersion is performed using an ultrasonic rod 400W. The suspension is stirred with a magnetic high latitude, Matec. Agitated using a tube-driven pump through the PPL-80 sensor of the ESA-8000 instrument. Potentiometric titration is performed using 5 M NaOH from the starting pH value to pH 12. Back titration up to pH 4 is performed using 5M HNO ₃ . The evaluation is performed using the instrument software version pcava 5.94.

here

Zeta Potential

φ volume fraction

Δρ density difference between particles and liquid

c speed of sound in suspension

η velocity of liquid

dielectric constant of ε suspension

l G (α) l inertia correction

The dispersion was ultrasonic finger (Bandelin UW2200 / DH13G), setting 8, 100%; Prepared by sonication in water using 5 minutes. Average aggregate diameter is measured using Horiba's particle size analyzer LB-500.

Example  One:

The aerosol contains 250 kg / h of a solution containing 50% by weight of cerium (III) ethylhexanoate and 50% by weight of 2-ethylhexanoic acid (joule value of solution: 29 kJ / kg) and two fluids. It is atomized into the reaction chamber from the atomization atmosphere of 50 standard m ³ / h by the nozzle (Schlick). Here, a hydrogen / oxygen flame composed of hydrogen (40 standard m ³ / h) and the first atmosphere (1800 standard m ³ / h) is burned, and the aerosol reacts with the flame. In addition, a second atmosphere (3200 standard m ³ / h) is introduced into the reaction chamber. The residence time at the flame is about 20 ms. The flame temperature below 0.5m is 1100 ° C.

Aerosols prepared from 900 kg / h of water are subsequently injected into the reaction chamber by two fluid nozzles using an atomization atmosphere of 200 standard m ³ / h at an inlet temperature of 20 ° C. Solid output is separated from gaseous material in a filter. The reaction mixture has a temperature of 280 ° C. at this point.

The residence time of the reaction mixture in the reaction chamber is 1 s.

Examples 2-4 are carried out in a similar manner to Example 1 with the amounts shown in Table 1 and other process variables. Analytical data for the powder obtained is shown in Table 2.

XPS / ESCA analysis shows that a very pure surface is present. Elements other than Ce, C and O are not detected at all. C of carbonic acid shows a binding energy of about 289 eV.

Furthermore, the d ₅₀ and d ₉₀ values of the 1% dispersion of the powders of Examples 1 to 4 are shown in Table 2.

The particle size distribution of the powder 5% dispersion of Example 3 in water with a pH of 3.9 adjusted by HNO ₃ is d ₅₀ at 82 nm and d _{90 at} 103 nm.

The SiO ₂ surface can be polished using the dispersion according to the invention and a removal rate of 500 nm / min, preferably 1200 nm / min, in particular 1000 nm / min is achieved at a pv of 60000 N / ms.

1 and 2 show the polishing results of 0.5% dispersion of powder from Example 3 with KOH adjusted to 7.6.

1 shows the removal rate (nm / min) as a calculation function (N / ms) of contact pressure and speed.

It was also found that the motor currents measured in the polishing of SiO ₂ and Si ₃ N ₄ were different when the dispersion according to the invention was used. This can be used advantageously in STI (shallow trench isolation). The purpose of the STI is to very selectively polish SiO ₂ and stop the polishing process when the nitride layer is reached. It is known for this purpose that additives which increase this selectivity by protecting the nitride can be added to the dispersion. Surprisingly, such additives are unnecessary in the case of the dispersions of the invention.

2 shows the motor current as a function of time in seconds for SiO ₂ and Si ₃ N ₄ .

*) Cerium (III) solution;

**) 500 mm below the flame,

***) water

*) In all examples: Na <5 ppm; Cl <20 ppm;

**) at pH = 4,

***) IEP = isoelectric point;

****) when synthesized / sputtered; When sputtered: after surface removal by impingement with 5 keV argon ions for about 10 minutes

1 shows the removal rate (nm / min) as a calculation function (N / ms) of contact pressure and speed.

2 shows the motor current as a function of time in seconds for SiO ₂ and Si ₃ N ₄ .

Claims (17)

Cerium oxide powder comprising a crystalline first particle having a carbonic group and containing cerium oxide and a carbonic acid group on the surface and in a layer adjacent to the surface, wherein The powder has a BET surface area of 25 to 150 m ² / g and the first particles have an average diameter of 5 to 50 nm, The layer adjacent to the first particle surface has a depth of about 5 μm nm, The carbonic acid concentration of the layer adjacent to the surface decreases inward from the surface with the highest carbonic acid concentration, The carbon content due to carbonate groups on the surface is from 5 to 50 area%, from 0 to 30 area% at a depth of about 5 nm in the layer adjacent to the surface, The content of cerium oxide, calculated as CeO ₂ based on the powder, is at least 99.5% by weight and The carbon content comprising both organic and inorganic carbons is from 0.01 to 0.3% by weight, based on the powder. 2. The cerium oxide powder of claim 1 wherein the first particles are agglomerated. The cerium oxide powder according to claim 1, wherein the proportion of sodium is <5 ppm and the proportion of chlorine is <20 ppm. The cerium oxide powder according to any one of claims 1 to 3, wherein the BET surface area is 30 to 100 m ² / g. The aerosol is reacted with an oxygen-containing gas at a reaction temperature of 600 ° C. to 1500 ° C., preferably 900 ° C. to 1200 ° C. in the reaction chamber, and the reaction mixture is cooled, subsequently powdered using a filter from the gaseous material. Is separated, An aerosol is obtained by atomization of at least one solution containing an oxidizable organic cerium (III) compound dissolved in a solvent by an organic solvent or solvent mixture and at least one atomizing gas, The volume-based average droplet diameter D30 of the aerosol is from 30 to 100 μm, the average residence time in the reaction chamber is from 0.1 seconds to 5 seconds, A process for producing cerium oxide powder with carbonic acid, wherein the reaction mixture is cooled by injecting water droplets into the reaction mixture after leaving the reaction chamber, The water droplets have an average, volume-based water droplet diameter of less than 100 μm A process for producing cerium oxide powder, characterized in that water is added in an amount according to the following equation I to produce water droplets: m _H2O = [cp _liq * (T _b -T ₀ ) + dh _v + cp _g * (T _e -T _b )] / 3600 * Q (I) At this time Q = total combustion enthalpy (KW) of all starting materials -m _H2O = Amount of H ₂ O required to achieve the final temperature T _e (kg / h) -T _o = Inlet temperature of water Boiling point of water at T _b = 1 bar -dh _v = Evaporation enthalpy of water cp _liq = Heat capacity of water at 50 ° C -cp _g = Heat capacity of water vapor at 150 ° C, where T ₀ = 5-50 ° C., T _b = 100 ° C., T _e = 200-400 ° C., dh _v = 2256.7 kJ / kg, cp _liq = 4.181 kJ / kg * K and cp _g = 1.98 kJ / kg * K . 6. A process for producing cerium oxide powder according to claim 5, wherein the fuel gas is additionally added to the reaction mixture. The method according to claim 5 or 6, wherein the lambda is ≧ 1.5 and the lambda is in each case mol / h, which is the sum of oxygen in (atmosphere + if atomized gas if appropriate) / (cerium (III) compound + fuel gas). Process for producing cerium oxide powder, characterized in that it is calculated from the sum. Cerium oxide powder having a carbonic acid group obtainable according to any one of claims 5 to 7. Dispersion containing cerium oxide powder which has a carbonic acid group in any one of Claims 1-4 and 8. 10. The dispersion according to claim 9, wherein the components of the dispersion are cerium oxide powder having carbonic acid, water, and optionally a pH adjuster. The cerium oxide powder according to any one of claims 9 to 10, wherein the content of cerium oxide powder is 0.5 to 60% by weight. Cerium oxide powder according to any of claims 9 to 11, characterized in that the pH is from 3 to 8. The cerium oxide powder according to claim 9, wherein the average particle size d ₅₀ measured by dynamic light scattering is less than 120 nm. The cerium oxide powder according to claim 9, wherein the average particle size d _90, measured by dynamic light scattering, is less than 200 nm. The cerium oxide powder according to any one of claims 9 to 14, wherein the zeta potential of the dispersion is at least 20 mV. Use of a cerium oxide powder having a carbonic acid group according to any one of claims 1 to 4 and 8 or a dispersion according to any one of claims 9 to 15 for chemical mechanical polishing. Use of a cerium oxide powder having a carbonic acid group according to any one of claims 1 to 4 and 8 as a catalyst, as a UV absorber, as a toner component, and as a component of a fuel cell.