CA2003935A1 - Titanium dioxide, a process for its production and its use - Google Patents
Titanium dioxide, a process for its production and its useInfo
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- CA2003935A1 CA2003935A1 CA002003935A CA2003935A CA2003935A1 CA 2003935 A1 CA2003935 A1 CA 2003935A1 CA 002003935 A CA002003935 A CA 002003935A CA 2003935 A CA2003935 A CA 2003935A CA 2003935 A1 CA2003935 A1 CA 2003935A1
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- tio2
- titanium dioxide
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G23/00—Compounds of titanium
- C01G23/04—Oxides; Hydroxides
- C01G23/047—Titanium dioxide
- C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
- C01G23/0532—Producing by wet processes, e.g. hydrolysing titanium salts by hydrolysing sulfate-containing salts
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G23/00—Compounds of titanium
- C01G23/04—Oxides; Hydroxides
- C01G23/047—Titanium dioxide
- C01G23/0475—Purification
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C1/00—Ingredients generally applicable to manufacture of glasses, glazes, or vitreous enamels
- C03C1/04—Opacifiers, e.g. fluorides or phosphates; Pigments
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/60—Compounds characterised by their crystallite size
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/11—Powder tap density
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/20—Powder free flowing behaviour
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- Life Sciences & Earth Sciences (AREA)
- Inorganic Chemistry (AREA)
- Geology (AREA)
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- Environmental & Geological Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Geochemistry & Mineralogy (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Pigments, Carbon Blacks, Or Wood Stains (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
- Glass Compositions (AREA)
Abstract
TITANIUM DIOXIDE, A PROCESS FOR ITS PRODUCTION AND ITS USE
ABSTRACT OF THE DISCLOSURE
A titanium dioxide composition useful as the opacifier agent for vitreous enamels and fusion enamels comprises TiO2 in an amount of at least 87% by weight, a sulfate content of 0.45% or less by weight based on TiO2, an alkali oxide content of less than 0.5% by weight based on TiO2, a water content of less than 12% by weight based on TiO2, a BET surface of 30 to 500 m2/g, an apparent density of 0.2 to 0.8 kg/l, a primary particle size of 0.005 to 0.1 µm and a mean aggregated grain size of 30 to 500 µm and wherein the TiO2 is in amorphous form or the crystalline anatase form or a mixture of both, and the composition is prepared by adjusting an acidcontaining titanium dioxide hydrate to pH 7-13 with a base, which is then filtered and washed, and the resulting product is then spray-dried.
ABSTRACT OF THE DISCLOSURE
A titanium dioxide composition useful as the opacifier agent for vitreous enamels and fusion enamels comprises TiO2 in an amount of at least 87% by weight, a sulfate content of 0.45% or less by weight based on TiO2, an alkali oxide content of less than 0.5% by weight based on TiO2, a water content of less than 12% by weight based on TiO2, a BET surface of 30 to 500 m2/g, an apparent density of 0.2 to 0.8 kg/l, a primary particle size of 0.005 to 0.1 µm and a mean aggregated grain size of 30 to 500 µm and wherein the TiO2 is in amorphous form or the crystalline anatase form or a mixture of both, and the composition is prepared by adjusting an acidcontaining titanium dioxide hydrate to pH 7-13 with a base, which is then filtered and washed, and the resulting product is then spray-dried.
Description
2~ 9~5 TITANIUM DIOXIDE, A PROCESS FOR ITS PRODUCTION AND ITS
USE
__._ _ This inven~ion relat~s to Litanium diox;d~, to a proceC~ for its produc~ion and to i~s us~ a~ an opacifi~r in vitrQous enam~la and fuQion ~nam~ls.
BACKGROUND OF THE INVENTION
Titanium dioxide is produced as a pigment either by reaction of TiC14 with 2 or by hydrolysis of an aqueous solution of titanyl sulfate containing sulfuric acid and subsequent calcination.
In the case of the sulfate process, the titanium dioxide hydrate suspension is calcined ~or 5 to 20 hours in a rotary kiln. The deposit which accumulates during hydrolysis consists of fine particles having a specific BET
surface of 50 to 500 m2/g which undergo extensive agglomera-tion during calcination.
The agglomerates formed as a result of calcination are in the form of 0.1 to 1.0 mm diameter particles which are made up of 0.2 to 0.4 ~m primary particles. This material is unsuitable as ~linker or even as a ground pigment for incorporation in vitreous enamels or fusion enamels because it agglomerates when mixed in dry form with the other constituents of the enamel frit, resulting in incomplete and inhomogeneous dissolution of the titanium dioxide during melting of the frit.
DE-AS 1 207 363 describes a process for the production of a TiO2 product for incorporation in vitreous enamels by calcination of precipitated titanium dioxide hydrate. In this proce~s, a precipitated titanium dioxide hydrate of coar~e particle size, which consists of S to 20 ~m primary particles, is mixed with a precipitated titanium dioxide hydrate of fine particle size, which consists of primary particles mostly below 1 ~m in size, as obtained in the production of Tio2 p~gments, and the resulting mixture is calcined. ;-The disadvantage of this process is that it is extremely expensive on account of the two different L~ A 26 368 - 1 -ZO~9;~5 titanium dioxide hydrates which first have to be produced.
In addition, the disadvantage of Tio2 obtained in this way is that it is distinguished by a high apparent density of 1 to 2 kg/l and has a low specific surface of distinctly below 1 m2/g, resulting in inadequate reactivity during melting in the frit.
US 2,721,787 describes free-flowing, dust-free aggregates consisting of calcined anatase ~primary particle size 0.2 to 0.3 ~m, specific surface 4.5 to 9 m2/g) and 0.1 to 3% of an inorganic binder. These aggregates are pro-duced by spray-drying aqueous 61urries of hydroclassified titanium dioxide pigments emanating from normal pigment production at a temperature in the range from 150 to 400C.
The disadvantage of this process is that calcined titanium dioxide pigments first have to be produced and are then taken up in water to form a slurry which is then spray-dried to obtain the claimed aggregates.
DE-AS 1 202 259 describes a process for the production of Tio2 agglomerates for enamel frits in which a suitable titanium dioxide (crystallite size 0.2-0.7 ~m) is granulated with addition of a hydrolyzable metal or silicon halide.
According to Japanese patent application 85/220884, fine, spherical Tio2 particles are mixed with a Tio2 sol, spray-dried at 50C and calcined at temperatures above S00C. The Tio2 801 iS obtained from Tio2 hydrate contain-ing sulfuric acid which is neutralized with ammonia, fil-tered, washed and peptized with concentrated sulfuric acid.
The product thus produced has particle sizes of from 0.1 to 50 ~m and is used in cosmetic products, catalysts and ceramics. It is not suitable for incorporation in enamels.
Where calcination is carried out below 800~C, relatively large quantities of sulfate remain behind and give rise during firing of the enamel to rough, dull enamel surface.
At higher calcination temperatures, the powder particles are too hard so that they cannot be completely digested in Le A 26 368 2 20~1935 the frit.
GB-P 1,176,912 deseribes a finely divided a~atase having a sulfate content of 0.45 to 1.2%, based on Tio2~ a BET surface of 35 to 55 m2/g and a primary particle siæe of 0.025 to 0.05 ~m. This anatase is produced by calcination of a Tio2 hydrate eontainin~ sulfuric acid at 72S to 760C
and subsequent grinding. The produet is used in photo-graphy and in copying papers. It is not suitable for incorporation in enamels on account of its high sulfur eontent, whieh leads to rough, dull surfaces, and on aecount of its partiele fineness which causes elumping in the frit raw material mixture and, hence, incomplste dis-solution and sludge formation during melting of the frit.
Aeeording to DE-OS 1 592 428, titanium dioxide hydrate or preferably sm~ll titanium dioxide partieles are ehemie-ally treated in a liguid to promote agglomeration, the par-ticles are agglomerated to mierospheres 1 to 500 ~m in diameter and the agglomerated mierospheres are dried and ealeined. The ehemical treat~ent eomprises reaetion with a mineral aeid, an organie aeid and a base. ~he apparent density of the Tio2 powders obtained, whieh are suitable for use as eatalyst supports, is between O.8 and 1.0 g/l. ~he products are unsuitable for ineorporation in enamel beeause the individual granulate partieles become very elose-paeked and hard as a result of the chemieal treatment in conjunc-tion with the subsequent agglomeration, leading to poor and ineomplete melting in the enamel frit.
BRIEF DESCRIPTION OF THE INVENTION
Accordingly, thQ problem addres~ed by the invention was to provide a titanium dioxide suitable for use as an opacifier for vitreou~ enamels nnd fu~ion enamels.
It has now been found that the titsnium dioxide according to the in~ention ~stiafies the requiremQnts stated above. This titanium dioxide h~s a Tio2 content of > 87% by weight, a sulfste content of lesE than 0.45X by weight and preferably le~s than 0.3X by weight, based on TiO2, an alkali oxide content of less than 0.5X by weight LQ ~ 26 368 - 3 -20C~3935 and pr~ferably less th~n 0.2% by w~ight, bas~d on TiO2, a residual water conten~ of le~s than 12X by w~ight, based on Tio2, a BET surface of 30 to 500 n~/g, an apparent den-sity of 0.2 bD 0.8 kg/l, a primary particl~ ize of 0.005 to 0,1 ~m ~nd a m~an aggr~gated grain size of 30 to 500 ~m and i~ present in amorphou~ form ~nd/or a~ ~rystalline ~nst.a~e .
DETAILED DESCRIPTION OF THE INVENTION
The Tio2 contQnt of the granulate~ i~ >87% by weight, but can be increa~ed by hea~ treatment. Their ~ulfat~
content i~ le~s than 0.45X by weigh~ and preferably less than 0.3X by we;ght, based on Tio2. Higher s~lfate contents a~n~Rly affect recrys~llization of the Tio2 during firing of the enam~l and l~ad ~o irregular, dull ~namel finishes.
The total ~A~tent of alkali oxides, particularly sodium ~nd potassium oxids, i~ below O.5X by weight and preferably b~low 0.2X by weight, based on Tio2. Lary~r conten~ result in reduction~ in the opacity of ~he enamel. A recidual wat~r contQnt of up to 12X by weight, ba~d on Tio2, do~s not affect the properties of the titanium dioxide with resp~ct to ~he enamel.
Tha large BET surfac~ of 30 to 500 nF/g tBET 3urfac~
determin~d in aecordance wi~h Ger~an Indus~rial Standard, DIN 66 131, Section~6, Oc~ober, 1973; 5-point method, me~surin~ gas: ni~rogen, sdsoption at the t~mperature of ~oiling ni~rogen, one molecule of ni~rogen being as~umed ~o occupy sn ar~a of 0,162 nn~, pratr~atment: h~ting for 1 hour in a s~ream of nitrog~n at 13~ C) and th~ small primary particlo ~ize of 0.005 to 0.1 ~m re~ul~ in high reac~ivity and h~nce in excQllent digestion bahavior of the Tio2 in the enamel m~lt.
The 6pherical aggregates 30 to 500 ~m in size show satisfactory flow behavior, do not stick to the other com-~5 ponent~ of the frit during mixing and show high stability,i.e. they do not disintegrate into fine grain during the mixing process, which would result in clumping and incom-plete melting.
The aggregates are uniformly distributed in the frit during mixing and then melt completely and uniformly.
~ A 26 368 - 4 -20~9~
In the quenched frit, the particles form near zones rich in titanium dioxide which act as seed cells for recrystallization of the titanium dioxide during the initial stages of firing of the enamel. As firing of the enamel continues, anatase is almost exclusively formed in a suitable crystallite size, in isometric form and in uniform distribution, so that high reflectivity is obtained for excellent opacifying power.
In another embodi~en~, ~he ~i~anium dioxide prefer~b1y con~ins oxid~, phospha~e~ and/or ~ilica~9~ of the metals Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Zr, Zn, V, Nb, W andlor Mo andlor oxides of ~hQ e1Qments P and/or Si in a quan~i~y of from trace amount up ~o 10% by weight and preferab1y in a quantity of no more than 7X by weight, bas~d on ti~anium dioxide. For example, an addition of P205 impro~e~ the re-crystalliza~ion of Tio2 and, hencs, the opscity of the enamel whil~ an addition of W03 improYes the c~lor of the enamel. The origin~1 ~patial separation of the additive~
from the Tio2 grain is surprising1y of considerable im-portsnce to the subsequ~nt rocry~t~11iz~tion of Tio2~
the introduction of the same additive~ in the same quantity directly into the frit would ha~e a ~r wsaker Qffsc~
The titanium dioxide may additionally contain binders such as, for example, waterglass, carboxymethyl celluloses and/or polyvinyl alcohols and/or deflocculating agents such as, for example, polyphosphates and/or polyacrylates in quantities of from 0.1 to 5% by weight, based on Tio2.
The present invention also relates to a suitable pro-cess for the production of the titanium dioxide according to the invention in which precipitated acid-containing titanium dioxide hydrate is adjusted to pH 7-13 with a base, optionally heated for O.l to lO hours to a temper-ature between 40-C and the reflux temperature, filtered and washed, the excess base is optionally removed, the product is spray-dried, optionally with addition of auxiliaries, and is then optionally heat-treated at 200 to 800C and Le A 26 368 - s -20~;~935 preferably at 400 to 600C.
The object of treating the acid-containing Tio2 hydrate with a base is to convert the adhering acid completely into the corresponding salt which is subsequently washed out.
Preliminary heating of the base-treated Tio2 hydrate for 0.1 to 10 hours to a temperature between 40C and the reflux temperature promotes removal of the salt.
In one particular embodiment, the salt-containing Tio2 hydrate may be subjected to a pressure treatment before washing. This may be done, for example, by carrying out the heat treatment in a closed pressure vessel. It is also possible, for example, to use the high-pressure expansion technique in suitable apparatus.
The measures described above lead to an improvement in filtration and in the washing out of foreign salts which in turn results in an improvement in the properties of the titanium dioxide thus treated with respect to the enamel.
After filtration and washing, the excess base is preferably larqely removed again. Where sodium hydroxide and/or potassium hydroxide are used, this is done by pH
adjustment to 7-2, for example wi~h hydrochloric, nitric and/or phosphoric acid, and removal of the sodium and/or potassium salt formed by re-filtration and washing.
Measures for improving filtration and washing, such as heat or pressure treatment, may also be applied in this step.
In another preferred embodiment, ammonia is used as the base. The ammonium salt formed may also be removed by filtration and washing after pH adjustment to 7-2 with an acid. However, it may also be removed with advantage by heat treatment after spray drying at 400 to 800-C, elimin-ating the need for the second filtration cycle.
In one preferred embodiment, auxiliaries may be added in a suitable form to the washed, substantially salt-free titanium dioxide hydrate before spray drying, being present in the end product largely as oxides, phosphates and/or sili~ates of the elements Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Le A 26 368 6 20~39~5 Zi, Zn, V, Nb, W and/or Mo and/or as oxides of the elements P and/or Si in a guantity of up to 10% by weight and pref-erably in a quantity of up to 7% by weight, based on titanium dioxide.
The auxiliaries are salts of the above-mentioned metals, such as carbonates, nitra~es, chlorides, fluorides, silicates, phosphates or oxides.
Binders such as, for example, waterglass, carboxy-methyl celluloses or polyvinyl alcohols and/or defloccu-lating agents such as, for example polyphosphates, or poly-acrylates may be added to the Tio2 hydrate before calcina-tion in quantities of from 0.1 to 5% by weight.
The spray drying process takes places at a waste air temperature above 90DC and preferably above 140C. To this end, auxiliaries are optionally added to the substantially salt-free Tio2 suspension which is then introduced into the drying tower with a solids content of 2 25% by weight and preferably > 35% by weight either through a one-component or multi-component nozzle or through a centrifugal atom-izing disc. ~oth a high solids content of the feed suspen-sion and a high drying temperature in the spray dryer have a favorable effect on granule stability and hence on the processibility of the Tioz with respect to the enamel.
The Tio2 content and grain stability may optionally be increased by subsequent conditioning of the spray-dried powder at 200 to 800-C and preferably at 400 to 600C.
Precipitated titanium dioxide hydrate containing sulfuric acid with a BET surface of 50 to 500 m2/g, as obtained ~or example in pigment production by the sulfate process, is preferably used as starting material for the production process according to the invention.
The titanium dioxide according to the invention may be used as an opacifier in the production of vitreous enamels or fusion enamels.
Exa~ples 1 and 2 below are intended to illustrate the invention without limiting it in any way.
Le A 26 368 7 zo~ 9:~s An aqueous titanium dioxide hydrate suspension having a Tio2 content of 25.5% by weight, a sulfate content of 7.5%
by weight, based on Tio2~ and a BET surface of 280 m2/g is adjusted to pH 8 with sodium hydroxide, heated for 1 hour to 90C, filtered and washed free from salts, re-suspended in H2O, adjusted to pH 4 with sulfuric acid, re-filtered and washed free from salts. The filter cake, w~ich has a solids content o~ 40% by weight, is re-suspended. 0.5% by weight P2Os, based on Tio2~ is added to the suspension which is then dried in a spray dryer with centrifugal disc atom-ization at a waste air temperature of 170C.
The product obtained has a Tio2 content of 92.0% by weight, a sulfate content of 0.2% by weight, based on Tio2~
an alkali oxide content of 0.1% by weight, based on Tio2, a chloride content of 0.4% by weight, based on Tio2~ a P2O5 content of 0.5% by weight, based on TiO2, an H2O content of 6.7% by weight, based on Tio2~ a BET surface of 280 m2/g, a primary particle size of 0.01 ~m, an apparent density of 0.45 kg/l and a mean aggregated grain size of 80 ~m and is present as amorphous and crystalline anatase.
The product is non-tacky and free-flowing and shows excellent ~ixing and digestion behavior in a boron-titanium white enamel frit. High reflectivity, high opacifying power and a favorable color of the enamel finish are obtained after application and firing.
A titani~m dioxide hydrate suspension as described in Example 1 is adjusted to pH 8 with ammonia, heated for hour to 60-C, filtered and washed free from salts. The residue is taken up in water to form a 35% by weight suspension which is then dried in a spray dryer with nozzle atomiza-ation at a waste air temperature of 140~C and conditioned for 30 minutes at 500C. The product obtained has a TiO~
content of 97% by weight, a sulfate content of 0.25% by Le h 26 368 8 20~9~5 weight, based on Tio2~ an H20 content of 1.7% by weight, based on TiO2, a BET surface of 115 m2/g, an apparent density of 0.6 kg/l, a primary particle size of 0.03 ~m and a mean aggregated grain siz~ of 185 ~m and is predominantly present as crystalline anatase.
The product is non-tacky and free-flowing and shows excellent mixing and digestion behavior in a titanium boride white enamel frit. High reflectivity, high opacifying power and a favorable color of the enamel finish are obtained after application and firing.
Le A 26 368 9
USE
__._ _ This inven~ion relat~s to Litanium diox;d~, to a proceC~ for its produc~ion and to i~s us~ a~ an opacifi~r in vitrQous enam~la and fuQion ~nam~ls.
BACKGROUND OF THE INVENTION
Titanium dioxide is produced as a pigment either by reaction of TiC14 with 2 or by hydrolysis of an aqueous solution of titanyl sulfate containing sulfuric acid and subsequent calcination.
In the case of the sulfate process, the titanium dioxide hydrate suspension is calcined ~or 5 to 20 hours in a rotary kiln. The deposit which accumulates during hydrolysis consists of fine particles having a specific BET
surface of 50 to 500 m2/g which undergo extensive agglomera-tion during calcination.
The agglomerates formed as a result of calcination are in the form of 0.1 to 1.0 mm diameter particles which are made up of 0.2 to 0.4 ~m primary particles. This material is unsuitable as ~linker or even as a ground pigment for incorporation in vitreous enamels or fusion enamels because it agglomerates when mixed in dry form with the other constituents of the enamel frit, resulting in incomplete and inhomogeneous dissolution of the titanium dioxide during melting of the frit.
DE-AS 1 207 363 describes a process for the production of a TiO2 product for incorporation in vitreous enamels by calcination of precipitated titanium dioxide hydrate. In this proce~s, a precipitated titanium dioxide hydrate of coar~e particle size, which consists of S to 20 ~m primary particles, is mixed with a precipitated titanium dioxide hydrate of fine particle size, which consists of primary particles mostly below 1 ~m in size, as obtained in the production of Tio2 p~gments, and the resulting mixture is calcined. ;-The disadvantage of this process is that it is extremely expensive on account of the two different L~ A 26 368 - 1 -ZO~9;~5 titanium dioxide hydrates which first have to be produced.
In addition, the disadvantage of Tio2 obtained in this way is that it is distinguished by a high apparent density of 1 to 2 kg/l and has a low specific surface of distinctly below 1 m2/g, resulting in inadequate reactivity during melting in the frit.
US 2,721,787 describes free-flowing, dust-free aggregates consisting of calcined anatase ~primary particle size 0.2 to 0.3 ~m, specific surface 4.5 to 9 m2/g) and 0.1 to 3% of an inorganic binder. These aggregates are pro-duced by spray-drying aqueous 61urries of hydroclassified titanium dioxide pigments emanating from normal pigment production at a temperature in the range from 150 to 400C.
The disadvantage of this process is that calcined titanium dioxide pigments first have to be produced and are then taken up in water to form a slurry which is then spray-dried to obtain the claimed aggregates.
DE-AS 1 202 259 describes a process for the production of Tio2 agglomerates for enamel frits in which a suitable titanium dioxide (crystallite size 0.2-0.7 ~m) is granulated with addition of a hydrolyzable metal or silicon halide.
According to Japanese patent application 85/220884, fine, spherical Tio2 particles are mixed with a Tio2 sol, spray-dried at 50C and calcined at temperatures above S00C. The Tio2 801 iS obtained from Tio2 hydrate contain-ing sulfuric acid which is neutralized with ammonia, fil-tered, washed and peptized with concentrated sulfuric acid.
The product thus produced has particle sizes of from 0.1 to 50 ~m and is used in cosmetic products, catalysts and ceramics. It is not suitable for incorporation in enamels.
Where calcination is carried out below 800~C, relatively large quantities of sulfate remain behind and give rise during firing of the enamel to rough, dull enamel surface.
At higher calcination temperatures, the powder particles are too hard so that they cannot be completely digested in Le A 26 368 2 20~1935 the frit.
GB-P 1,176,912 deseribes a finely divided a~atase having a sulfate content of 0.45 to 1.2%, based on Tio2~ a BET surface of 35 to 55 m2/g and a primary particle siæe of 0.025 to 0.05 ~m. This anatase is produced by calcination of a Tio2 hydrate eontainin~ sulfuric acid at 72S to 760C
and subsequent grinding. The produet is used in photo-graphy and in copying papers. It is not suitable for incorporation in enamels on account of its high sulfur eontent, whieh leads to rough, dull surfaces, and on aecount of its partiele fineness which causes elumping in the frit raw material mixture and, hence, incomplste dis-solution and sludge formation during melting of the frit.
Aeeording to DE-OS 1 592 428, titanium dioxide hydrate or preferably sm~ll titanium dioxide partieles are ehemie-ally treated in a liguid to promote agglomeration, the par-ticles are agglomerated to mierospheres 1 to 500 ~m in diameter and the agglomerated mierospheres are dried and ealeined. The ehemical treat~ent eomprises reaetion with a mineral aeid, an organie aeid and a base. ~he apparent density of the Tio2 powders obtained, whieh are suitable for use as eatalyst supports, is between O.8 and 1.0 g/l. ~he products are unsuitable for ineorporation in enamel beeause the individual granulate partieles become very elose-paeked and hard as a result of the chemieal treatment in conjunc-tion with the subsequent agglomeration, leading to poor and ineomplete melting in the enamel frit.
BRIEF DESCRIPTION OF THE INVENTION
Accordingly, thQ problem addres~ed by the invention was to provide a titanium dioxide suitable for use as an opacifier for vitreou~ enamels nnd fu~ion enamels.
It has now been found that the titsnium dioxide according to the in~ention ~stiafies the requiremQnts stated above. This titanium dioxide h~s a Tio2 content of > 87% by weight, a sulfste content of lesE than 0.45X by weight and preferably le~s than 0.3X by weight, based on TiO2, an alkali oxide content of less than 0.5X by weight LQ ~ 26 368 - 3 -20C~3935 and pr~ferably less th~n 0.2% by w~ight, bas~d on TiO2, a residual water conten~ of le~s than 12X by w~ight, based on Tio2, a BET surface of 30 to 500 n~/g, an apparent den-sity of 0.2 bD 0.8 kg/l, a primary particl~ ize of 0.005 to 0,1 ~m ~nd a m~an aggr~gated grain size of 30 to 500 ~m and i~ present in amorphou~ form ~nd/or a~ ~rystalline ~nst.a~e .
DETAILED DESCRIPTION OF THE INVENTION
The Tio2 contQnt of the granulate~ i~ >87% by weight, but can be increa~ed by hea~ treatment. Their ~ulfat~
content i~ le~s than 0.45X by weigh~ and preferably less than 0.3X by we;ght, based on Tio2. Higher s~lfate contents a~n~Rly affect recrys~llization of the Tio2 during firing of the enam~l and l~ad ~o irregular, dull ~namel finishes.
The total ~A~tent of alkali oxides, particularly sodium ~nd potassium oxids, i~ below O.5X by weight and preferably b~low 0.2X by weight, based on Tio2. Lary~r conten~ result in reduction~ in the opacity of ~he enamel. A recidual wat~r contQnt of up to 12X by weight, ba~d on Tio2, do~s not affect the properties of the titanium dioxide with resp~ct to ~he enamel.
Tha large BET surfac~ of 30 to 500 nF/g tBET 3urfac~
determin~d in aecordance wi~h Ger~an Indus~rial Standard, DIN 66 131, Section~6, Oc~ober, 1973; 5-point method, me~surin~ gas: ni~rogen, sdsoption at the t~mperature of ~oiling ni~rogen, one molecule of ni~rogen being as~umed ~o occupy sn ar~a of 0,162 nn~, pratr~atment: h~ting for 1 hour in a s~ream of nitrog~n at 13~ C) and th~ small primary particlo ~ize of 0.005 to 0.1 ~m re~ul~ in high reac~ivity and h~nce in excQllent digestion bahavior of the Tio2 in the enamel m~lt.
The 6pherical aggregates 30 to 500 ~m in size show satisfactory flow behavior, do not stick to the other com-~5 ponent~ of the frit during mixing and show high stability,i.e. they do not disintegrate into fine grain during the mixing process, which would result in clumping and incom-plete melting.
The aggregates are uniformly distributed in the frit during mixing and then melt completely and uniformly.
~ A 26 368 - 4 -20~9~
In the quenched frit, the particles form near zones rich in titanium dioxide which act as seed cells for recrystallization of the titanium dioxide during the initial stages of firing of the enamel. As firing of the enamel continues, anatase is almost exclusively formed in a suitable crystallite size, in isometric form and in uniform distribution, so that high reflectivity is obtained for excellent opacifying power.
In another embodi~en~, ~he ~i~anium dioxide prefer~b1y con~ins oxid~, phospha~e~ and/or ~ilica~9~ of the metals Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Zr, Zn, V, Nb, W andlor Mo andlor oxides of ~hQ e1Qments P and/or Si in a quan~i~y of from trace amount up ~o 10% by weight and preferab1y in a quantity of no more than 7X by weight, bas~d on ti~anium dioxide. For example, an addition of P205 impro~e~ the re-crystalliza~ion of Tio2 and, hencs, the opscity of the enamel whil~ an addition of W03 improYes the c~lor of the enamel. The origin~1 ~patial separation of the additive~
from the Tio2 grain is surprising1y of considerable im-portsnce to the subsequ~nt rocry~t~11iz~tion of Tio2~
the introduction of the same additive~ in the same quantity directly into the frit would ha~e a ~r wsaker Qffsc~
The titanium dioxide may additionally contain binders such as, for example, waterglass, carboxymethyl celluloses and/or polyvinyl alcohols and/or deflocculating agents such as, for example, polyphosphates and/or polyacrylates in quantities of from 0.1 to 5% by weight, based on Tio2.
The present invention also relates to a suitable pro-cess for the production of the titanium dioxide according to the invention in which precipitated acid-containing titanium dioxide hydrate is adjusted to pH 7-13 with a base, optionally heated for O.l to lO hours to a temper-ature between 40-C and the reflux temperature, filtered and washed, the excess base is optionally removed, the product is spray-dried, optionally with addition of auxiliaries, and is then optionally heat-treated at 200 to 800C and Le A 26 368 - s -20~;~935 preferably at 400 to 600C.
The object of treating the acid-containing Tio2 hydrate with a base is to convert the adhering acid completely into the corresponding salt which is subsequently washed out.
Preliminary heating of the base-treated Tio2 hydrate for 0.1 to 10 hours to a temperature between 40C and the reflux temperature promotes removal of the salt.
In one particular embodiment, the salt-containing Tio2 hydrate may be subjected to a pressure treatment before washing. This may be done, for example, by carrying out the heat treatment in a closed pressure vessel. It is also possible, for example, to use the high-pressure expansion technique in suitable apparatus.
The measures described above lead to an improvement in filtration and in the washing out of foreign salts which in turn results in an improvement in the properties of the titanium dioxide thus treated with respect to the enamel.
After filtration and washing, the excess base is preferably larqely removed again. Where sodium hydroxide and/or potassium hydroxide are used, this is done by pH
adjustment to 7-2, for example wi~h hydrochloric, nitric and/or phosphoric acid, and removal of the sodium and/or potassium salt formed by re-filtration and washing.
Measures for improving filtration and washing, such as heat or pressure treatment, may also be applied in this step.
In another preferred embodiment, ammonia is used as the base. The ammonium salt formed may also be removed by filtration and washing after pH adjustment to 7-2 with an acid. However, it may also be removed with advantage by heat treatment after spray drying at 400 to 800-C, elimin-ating the need for the second filtration cycle.
In one preferred embodiment, auxiliaries may be added in a suitable form to the washed, substantially salt-free titanium dioxide hydrate before spray drying, being present in the end product largely as oxides, phosphates and/or sili~ates of the elements Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Le A 26 368 6 20~39~5 Zi, Zn, V, Nb, W and/or Mo and/or as oxides of the elements P and/or Si in a guantity of up to 10% by weight and pref-erably in a quantity of up to 7% by weight, based on titanium dioxide.
The auxiliaries are salts of the above-mentioned metals, such as carbonates, nitra~es, chlorides, fluorides, silicates, phosphates or oxides.
Binders such as, for example, waterglass, carboxy-methyl celluloses or polyvinyl alcohols and/or defloccu-lating agents such as, for example polyphosphates, or poly-acrylates may be added to the Tio2 hydrate before calcina-tion in quantities of from 0.1 to 5% by weight.
The spray drying process takes places at a waste air temperature above 90DC and preferably above 140C. To this end, auxiliaries are optionally added to the substantially salt-free Tio2 suspension which is then introduced into the drying tower with a solids content of 2 25% by weight and preferably > 35% by weight either through a one-component or multi-component nozzle or through a centrifugal atom-izing disc. ~oth a high solids content of the feed suspen-sion and a high drying temperature in the spray dryer have a favorable effect on granule stability and hence on the processibility of the Tioz with respect to the enamel.
The Tio2 content and grain stability may optionally be increased by subsequent conditioning of the spray-dried powder at 200 to 800-C and preferably at 400 to 600C.
Precipitated titanium dioxide hydrate containing sulfuric acid with a BET surface of 50 to 500 m2/g, as obtained ~or example in pigment production by the sulfate process, is preferably used as starting material for the production process according to the invention.
The titanium dioxide according to the invention may be used as an opacifier in the production of vitreous enamels or fusion enamels.
Exa~ples 1 and 2 below are intended to illustrate the invention without limiting it in any way.
Le A 26 368 7 zo~ 9:~s An aqueous titanium dioxide hydrate suspension having a Tio2 content of 25.5% by weight, a sulfate content of 7.5%
by weight, based on Tio2~ and a BET surface of 280 m2/g is adjusted to pH 8 with sodium hydroxide, heated for 1 hour to 90C, filtered and washed free from salts, re-suspended in H2O, adjusted to pH 4 with sulfuric acid, re-filtered and washed free from salts. The filter cake, w~ich has a solids content o~ 40% by weight, is re-suspended. 0.5% by weight P2Os, based on Tio2~ is added to the suspension which is then dried in a spray dryer with centrifugal disc atom-ization at a waste air temperature of 170C.
The product obtained has a Tio2 content of 92.0% by weight, a sulfate content of 0.2% by weight, based on Tio2~
an alkali oxide content of 0.1% by weight, based on Tio2, a chloride content of 0.4% by weight, based on Tio2~ a P2O5 content of 0.5% by weight, based on TiO2, an H2O content of 6.7% by weight, based on Tio2~ a BET surface of 280 m2/g, a primary particle size of 0.01 ~m, an apparent density of 0.45 kg/l and a mean aggregated grain size of 80 ~m and is present as amorphous and crystalline anatase.
The product is non-tacky and free-flowing and shows excellent ~ixing and digestion behavior in a boron-titanium white enamel frit. High reflectivity, high opacifying power and a favorable color of the enamel finish are obtained after application and firing.
A titani~m dioxide hydrate suspension as described in Example 1 is adjusted to pH 8 with ammonia, heated for hour to 60-C, filtered and washed free from salts. The residue is taken up in water to form a 35% by weight suspension which is then dried in a spray dryer with nozzle atomiza-ation at a waste air temperature of 140~C and conditioned for 30 minutes at 500C. The product obtained has a TiO~
content of 97% by weight, a sulfate content of 0.25% by Le h 26 368 8 20~9~5 weight, based on Tio2~ an H20 content of 1.7% by weight, based on TiO2, a BET surface of 115 m2/g, an apparent density of 0.6 kg/l, a primary particle size of 0.03 ~m and a mean aggregated grain siz~ of 185 ~m and is predominantly present as crystalline anatase.
The product is non-tacky and free-flowing and shows excellent mixing and digestion behavior in a titanium boride white enamel frit. High reflectivity, high opacifying power and a favorable color of the enamel finish are obtained after application and firing.
Le A 26 368 9
Claims (12)
1. A titanium dioxide composition which has a TiO2 content of at least 87% by weight, a sulfate content of 0.45%
or less by weight based on TiO2, an alkali oxide content of less than 0.5% by weight based on TiO2, a water content of less than 12% by weight based on TiO2, a BET surface of 30 to 500 m2/g, an apparent density of 0.2 to 0.8 kg/l, a primary particle size of 0.005 to 0.1 µm and a mean aggregated grain size of 30 to 500 µm and wherein the TiO2 is in amorphous form or the crystalline anatase form or a mixture of both.
or less by weight based on TiO2, an alkali oxide content of less than 0.5% by weight based on TiO2, a water content of less than 12% by weight based on TiO2, a BET surface of 30 to 500 m2/g, an apparent density of 0.2 to 0.8 kg/l, a primary particle size of 0.005 to 0.1 µm and a mean aggregated grain size of 30 to 500 µm and wherein the TiO2 is in amorphous form or the crystalline anatase form or a mixture of both.
2. A titanium dioxide composition as claimed in claim 1 wherein the sulfate content is less than 0.3% by weight based on TiO2.
3. A titanium dioxide composition as claimed in claim 1 wherein the alkali oxide content is less than 0.2% by weight based on TiO2.
4. A titanium dioxide composition as claimed in claim 1 which contains at least one oxide, phosphate or silicate of at least one of the metals Mg, Ca, Sr, Ba, Sn, Sb, Bi, Y, Zr, Zn, V, W and Mo, or oxides of the elements P or Si, or mixtures thereof in a quantity of up to 10% by weight, based on TiO2.
5. A process for the production of the titanium dioxide claimed in claim 1 adjusting an acid-containing titanium dioxide hydrate to pH 7-13 with a base, which is then filtered and washed, and the resulting product is then spray-dried.
6. A process as claimed in claim 5 wherein the acid-containing TiO2 hydrate contains sulfuric acid and is obtained with a BET surface of 50 to 500 m2/g after hydrolysis in pigment production by the sulfate process.
7. A process as claimed in claim 5 wherein sodium hydroxide or potassium hydroxide is the base and the excess base is after filtering and washing removed by pH adjustment to 2-7 with an acid and removal of the sodium or potassium salt formed therein by re-filtration and washing.
8. A process as claimed in claim 5 wherein after adjusting the hydrate pH the resulting mixture is heated for 0.1 to 10 hours to a temperature from 40°C to the mixture reflux temperature.
9. A process as claimed in claim 5 wherein after spray drying is at a temperature greater than 90°C.
10. A process as claimed in claim 5 wherein after spray drying the dry product is conditioned by heat treatment at 200 to 800°C.
11. A process as claimed in claim 5 wherein the base is ammonia and the excess ammonia and any ammonium salt formed are removed by heat treatment at 400 to 800°C.
12. In an improved vitreous enamel or fusion enamel containing an opacifier agent, the improvement comprises said opacifier agent being a titanium dioxide composition according to claim 1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3840195.9 | 1988-11-29 | ||
| DE3840195A DE3840195A1 (en) | 1988-11-29 | 1988-11-29 | TITANIUM DIOXIDE, METHOD FOR THE PRODUCTION AND USE THEREOF |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2003935A1 true CA2003935A1 (en) | 1990-05-29 |
Family
ID=6368083
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002003935A Abandoned CA2003935A1 (en) | 1988-11-29 | 1989-11-27 | Titanium dioxide, a process for its production and its use |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0371329A3 (en) |
| JP (1) | JPH02184527A (en) |
| AU (1) | AU4559289A (en) |
| BR (1) | BR8906003A (en) |
| CA (1) | CA2003935A1 (en) |
| DE (1) | DE3840195A1 (en) |
| FI (1) | FI895659A (en) |
| NO (1) | NO894532L (en) |
| ZA (1) | ZA899054B (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3840196C1 (en) * | 1988-11-29 | 1990-04-12 | Bayer Ag, 5090 Leverkusen, De | |
| DE4321555C1 (en) * | 1993-06-29 | 1994-09-15 | Bayer Ag | Process for producing mixed-oxide powders for denitration catalysts |
| US5527469A (en) * | 1995-06-12 | 1996-06-18 | Lawhorne; Earl R. | Method for the preparation of desulfurized titanium oxide hydrolysate of high purity |
| DE19800881A1 (en) * | 1998-01-13 | 1999-07-15 | Metallgesellschaft Ag | Energy consumption in the sulfate process for producing titanium dioxide is reduced |
| DE19806472A1 (en) * | 1998-02-17 | 1999-08-19 | Kerr Mcgee Pigments Gmbh & Co | Process and furnace for the production of TiO¶2¶ pigment using the sulfate process |
| CA2342665A1 (en) * | 2000-07-31 | 2002-01-31 | Sumitomo Chemical Company Limited | Titanium oxide production process |
| DE60223062T2 (en) * | 2001-08-22 | 2008-07-24 | Shell Internationale Research Maatschappij B.V. | CLEANING OF TITANIUM DIOXIDE |
| EP1614409B8 (en) * | 2004-06-28 | 2017-09-27 | DENTSPLY SIRONA Inc. | Opaque dental ceramic, process and use thereof |
| JP2008519750A (en) * | 2004-11-11 | 2008-06-12 | バーゼル・ポリオレフィン・イタリア・ソチエタ・ア・レスポンサビリタ・リミタータ | Production of TiO2 powder from waste liquid containing titanium compound |
| EP3175844A1 (en) | 2010-04-09 | 2017-06-07 | Pacira Pharmaceuticals, Inc. | Large diameter synthetic membrane vesicles |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2721787A (en) * | 1950-10-23 | 1955-10-25 | American Cyanamid Co | Free-flowing, nondusting titania |
| GB1176046A (en) * | 1966-12-19 | 1970-01-01 | Grace W R & Co | Preparation of Microspheroidal Titanium Dioxide. |
| US3561968A (en) * | 1968-05-22 | 1971-02-09 | Nat Lead Co | Photoreactive titanium dioxide composition |
| JPS6279841A (en) * | 1985-10-02 | 1987-04-13 | Teikoku Kako Kk | Production of inorganic spherical body |
-
1988
- 1988-11-29 DE DE3840195A patent/DE3840195A1/en not_active Withdrawn
-
1989
- 1989-11-14 NO NO89894532A patent/NO894532L/en unknown
- 1989-11-16 EP EP19890121176 patent/EP0371329A3/en not_active Withdrawn
- 1989-11-27 CA CA002003935A patent/CA2003935A1/en not_active Abandoned
- 1989-11-27 AU AU45592/89A patent/AU4559289A/en not_active Abandoned
- 1989-11-27 FI FI895659A patent/FI895659A/en not_active Application Discontinuation
- 1989-11-28 ZA ZA899054A patent/ZA899054B/en unknown
- 1989-11-29 JP JP1307864A patent/JPH02184527A/en active Pending
- 1989-11-29 BR BR898906003A patent/BR8906003A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| FI895659A (en) | 1991-05-28 |
| JPH02184527A (en) | 1990-07-19 |
| NO894532D0 (en) | 1989-11-14 |
| FI895659A0 (en) | 1989-11-27 |
| BR8906003A (en) | 1990-06-26 |
| AU4559289A (en) | 1990-06-07 |
| ZA899054B (en) | 1990-09-26 |
| EP0371329A3 (en) | 1991-03-20 |
| NO894532L (en) | 1990-05-30 |
| EP0371329A2 (en) | 1990-06-06 |
| DE3840195A1 (en) | 1990-05-31 |
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