FUMED ALUMINA POWDER WITH REDUCED MOISTURE CONTENT

Abstract

Fumed alumina powder with reduced moisture content Surface unmodified fumed alumina powder comprising less than 5% by weight of alpha-Al.sub.2O.sub.3, as determined by XRD analysis, having a numerical average particle size d.sub.50 of less than 5 ?m, as determined by SLS, and a ratio R.sub.150=KF.sub.150/BET of the water content KF.sub.150, as determined by Karl Fischer titration method after drying of the fumed alumina powder at 150? C. for 2 hours, to its BET surface area of not more than 0.0122 wt %?g/m.sup.2, preparation method and the use thereof.

Claims

1-15. (canceled)

16. A fumed alumina powder comprising: a) less than 5% by weight of alpha-Al.sub.2O.sub.3, as determined by XRD analysis; b) a numerical average particle size d.sub.50 of less than 5 ?m, as determined by static light scattering (SLS) after 120 s of ultrasonic treatment at 25? C. of a 5% by weight dispersion of the alumina in water; c) a ratio R.sub.150=KF.sub.150/BET of the water content KF.sub.150, as determined by Karl Fischer titration method after drying of the fumed alumina powder at 150? C. for 2 hours, to its BET surface area, of not more than 0.0122 wt %?g/m.sup.2; and wherein the fumed alumina powder is surface unmodified.

17. The fumed alumina powder of claim 16, wherein essentially no alpha-Al.sub.2O.sub.3 is present as determined by XRD analysis.

18. The fumed alumina powder of claim 16, wherein the BET surface area of the alumina is from 20 m.sup.2/g to 220 m.sup.2/g.

19. The fumed alumina powder of claim 16, wherein the tamped density of the alumina is not more than 250 g/L.

20. The fumed alumina of claim 16, wherein the number mean equivalent circular diameter of primary particles of the alumina d.sub.p_ECD in nanometers, as determined by transmission electron microscopy (TEM) according to ISO 21363, is at least 1100/(BET.sub.alumina surface area of the alumina in m.sup.2/g).

21. The fumed alumina powder of claim 16, wherein the alumina has a ratio R.sub.0=KF.sub.0/BET of the water content KF.sub.0 as determined by Karl Fischer titration method, to BET surface area of not more than 0.0385 wt %?g/m.sup.2.

22. The fumed alumina powder of claim 16, further comprising surface modification due to treatment with a surface treatment agent selected from the group consisting of: organosilanes; silazanes; acyclic polysiloxanes; cyclic polysiloxanes; and mixtures thereof.

23. The fumed alumina powder of claim 17, wherein the BET surface area of the alumina is from 20 m.sup.2/g to 220 m.sup.2/g and the tamped density is not more than 250 g/L.

24. The fumed alumina powder of claim 17, further comprising surface modification due to treatment with a surface treatment agent selected from the group consisting of: organosilanes; silazanes; acyclic polysiloxanes; cyclic polysiloxanes; and mixtures thereof.

25. The fumed alumina of claim 17, wherein: a) the number mean equivalent circular diameter of primary particles of the alumina d.sub.p_ECD in nanometers, as determined by transmission electron microscopy (TEM) according to ISO 21363, is at least 1100/(BET.sub.alumina surface area of the alumina in m.sup.2/g); and b) the fumed alumina has a ratio R.sub.0=KF.sub.0/BET of not more than 0.0385 wt %?g/m.sup.2.

26. A process for producing the fumed alumina powder of claim 16, comprising as step A): subjecting a surface untreated fumed alumina powder to thermal treatment at a temperature of 250? C. to 1250? C. for 5 min to 5 h, wherein: the untreated fumed alumina powder has a particle size d.sub.50 of less than 5 ?m, as determined in an aqueous dispersion by a static light scattering method after 120 s of ultrasonic treatment, and comprises less than 5% by weight of alpha-Al.sub.2O.sub.3, as determined by XRD analysis; essentially no water is added before, during or after carrying out step A); the temperature and the duration of the thermal treatment are chosen so that the BET surface area of the alumina is decreased by, at most, 23% relative to the BET surface area prior to thermal treatment.

27. The process of claim 26, wherein the fumed alumina powder produced comprises essentially no alpha-Al.sub.2O.sub.3 as determined by XRD analysis.

28. The process of claim 26, wherein the fumed alumina powder produced has a BET surface area of from 20 m.sup.2/g to 220 m.sup.2/g and a tamped density of not more than 250 g/L.

29. The process of claim 26, wherein the fumed alumina powder produced comprises: a) a number mean equivalent circular diameter of primary particles of the alumina d.sub.p_ECD in nanometers, as determined by transmission electron microscopy (TEM) according to ISO 21363, of at least 1100/(BET.sub.alumina surface area of the alumina in m.sup.2/g) and b) a ratio R.sub.0=KF.sub.0/BET of not more than 0.0385 wt %?g/m.sup.2.

30. The process of claim 26, wherein the thermal treatment is carried out while the fumed alumina powder is in motion.

31. The process of claim 26, wherein the fumed alumina powder is being moved at a rate of at least 1 cm/min during the thermal treatment step A).

32. The process of claim 26, wherein the thermal treatment is carried out in a rotary kiln.

33. The process of claim 26, further comprising as step B): surface treating the fumed alumina powder obtained in step A) with a surface treatment agent selected from the group consisting of: organosilanes; silazanes; acyclic polysiloxanes; cyclic polysiloxanes; and mixtures thereof.

34. The process of claim 33, wherein essentially no water is added before, during or after carrying out step B).

35. A composition comprising the fumed alumina powder of claim 16, wherein said composition is a paint or coating; silicone; pharmaceutical or cosmetic preparation; adhesive or sealant; toner; a component of a lithium ion battery; a liquid wherein the fumed alumina powder acts to alter the rheology properties of the liquid or as an anti-settling agent; a powder wherein the fumed alumina powder acts to improve flowability; a catalyst; a composition used in chemical mechanical planarization (CMP) applications; or a thermal insulator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0142] FIGS. 1A and 1B show transmission electron microscopy (TEM) images of starting material 2.

[0143] FIGS. 2A and 2B show transmission electron microscopy (TEM) images of thermally treated at 1200? C. starting material 2 (example 9).

[0144] FIG. 3 shows XRD image of thermally treated at 1200? C. starting material 2 (example 9).

[0145] FIG. 4 shows XRD image of thermally treated at 1300? C. starting material 2 (comparative example 3).

EXAMPLES

Analytical Methods.

[0146] Specific BET surface area [m.sup.2/g] was determined according to DIN 9277:2014 by nitrogen adsorption in accordance with the Brunauer-Emmett-Teller method.

[0147] The number of hydroxyl groups relative to BET surface area d.sub.OH [OH/nm.sup.2] was determined by reaction of the pre-dried samples of alumina powders with lithium aluminium hydride solution as described in detail on page 8, line 17 thru page 9, line 12 of EP 0725037 A1. This method is also described in Journal of Colloid and Interface Science, vol. 125, no. 1, (1988), pp. 61-68.

[0148] Tamped density [g/L] was determined according to DIN ISO 787-11:1995 General methods of test for pigments and extendersPart 11: Determination of tamped volume and apparent density after tamping.

[0149] Particle size distribution, i.e. values d.sub.10, d.sub.50, d.sub.90 and span (d.sub.90-d.sub.10)/d.sub.50 [?m] were measured by static light scattering (SLS) using laser diffraction particle size analyzer (HORIBA LA-950) after 120 s of ultrasonic treatment at 25? C. of a 5% by weight dispersion of the surface treated alumina in water.

[0150] Water content [wt. %] was determined by Karl Fischer titration using a Karl Fischer titrator.

[0151] Mean equivalent circle diameter (ECD) of the primary particles d.sub.p_ECD was determined by transition electron microscopy (TEM) analogously to ISO 21363.

[0152] X-Ray diffraction analyses (XRD) were performed by means of a transmission diffractometer from Stoe & Cie Darmstadt, Germany using CuK alpha radiation, excitation 30 mA, 45 kV, OED. For quantitative determination of alpha-Al.sub.2O.sub.3, the measured X-Ray diffraction patterns of the tested sample were compared with those of the reference samples containing 100% and 80% of alpha-Al.sub.2O.sub.3.

Starting Materials.

[0153] Fumed alumina with a BET surface area of 121 m.sup.2/g was prepared according to the description on page 35 of WO 2004108595 Al (aluminium oxide I) and used as starting material 1.

[0154] Fumed alumina with a BET surface area of 50 m.sup.2/g was prepared according to example 3 of WO 2006067127 Al and used as starting material 2. The mean primary particle size d.sub.p_ECD (mean equivalent circle diameter, ECD, of the primary particles) of the particles determined by TEM analysis was found to be 21.2 nm (=1062/BET).

Example 1

[0155] Starting material 1 was subjected to thermal treatment in a rotary kiln of ca. 160 mm diameter and 2 m length at 400? C. The mean residence time of the alumina in the rotary kiln was 1 hour. Rotational speed was set to 5 rpm resulting in a throughput of approximately 1 kg/h of alumina. Dry and filtered compressed air was fed continuously with a flow rate of ca. 1 m.sup.3/h to the kiln outlet (in counterflow to the thermally treated alumina flow) to provide preconditioned air for the convection in the tube. The process was smooth. No clogging of the rotary kiln was observed. Physico-chemical properties of the obtained thermally treated alumina are shown in Table 1.

[0156] Examples 2-4 and comparative examples 1-2 were carried out analogously to example 1 but applying thermal treatment temperatures of 700 to 1300? C. No clogging of the rotary kiln was observed in examples 2-4 at 700-1100? C., whereas in comparative example 1 (thermal treatment at 1200? C.), some clogging was observed. In comparative example 2 (thermal treatment at 1300? C.), so much clogging was observed that the experiment had to be stopped, the obtained product has not been further analyzed. Physico-chemical properties of the obtained thermally treated aluminas (except for comparative example 2) are shown in Table 1.

[0157] Table 1 shows the physicochemical properties of fumed alumina powders obtained by thermal treatment of starting material 1 (BET=121 m.sup.2/g, tamped density=52 g/L).

[0158] BET surface area, tamped density and particle size, as well the composition of crystal phases of the starting material 1 do not change much in examples 1-4, where the thermal treatment is carried out at a temperature of up to 1100? C. The total moisture content of the starting material 1 has been decreased from 4.76% down to 1.93-2.72 wt %, the content of the strongly bound water has been decreased from 1.54 wt % down to about 1 wt % in examples 1-4.

[0159] Conversely, at 1200? C. (comparative example 1) an abrupt reduction of the BET surface area (by 25.6%) and a significant increase of both the tamped density (increase by 26.9%) and the particle size, e.g. of d.sub.50 value (dramatic increase from 0.11 to 3.63 ?m), was observed (Table 1). No alpha phase of Al.sub.2O.sub.3 was observed in the XRD images of the samples from examples 1-4 and comparative example 1.

[0160] Comparative example 2 carried out at 1300? C. had to be stopped, as the used rotary kiln was congested precluding further carrying out the experiment.

Example 5

[0161] Starting material 2 was subjected to thermal treatment in a rotary kiln of ca. 160 mm diameter and 2 m length at 400? C. The mean residence time of the alumina in the rotary kiln was 1 hour. Rotational speed was set to 5 rpm resulting in a throughput of approximately 1 kg/h of alumina. Dry and filtered compressed air was fed continuously with a flow rate of ca. 1 m.sup.3/h to the kiln outlet (in counterflow to the thermally treated alumina flow) to provide preconditioned air for the convection in the tube. The process was smooth. No clogging of the rotary kiln was observed. Physico-chemical properties of the obtained thermally treated alumina are shown in Table 2.

[0162] Examples 6-9 and comparative example 3 were carried out analogously to example 5 but applying thermal treatment temperatures of 700 to 1300? C. No clogging of the rotary kiln was observed in examples 6-9, whereas in comparative example 3, a significant clogging was observed. Physico-chemical properties of the obtained thermally treated aluminas are shown in Table 2. The mean primary particle size d.sub.p_ECD (mean equivalent circle diameter, ECD, of the primary particles) of the particles obtained in example 9 determined by TEM analysis was found to be 27.6 nm (=1243/BET).

[0163] Table 2 shows the physicochemical properties of fumed alumina powders obtained by thermal treatment of starting material 2 (BET=50 m.sup.2/g, tamped density=95 g/L).

[0164] BET surface area, tamped density and particle size, as well the composition of crystal phases of the starting material 2 do not change much in examples 5-9 (FIG. 3 for example 9), where the thermal treatment is carried out at a temperature of up to 1200? C. The total moisture content of the starting material 2 has been decreased from 2.09% down to 0.98-1.25 wt %, the content of the strongly bound water has been decreased from 0.62 wt % down to about 0.45-0.55 wt % in examples 5-9.

[0165] Conversely, at 1300? C. (comparative example 3) an abrupt reduction of the BET surface area (by 24%) and a significant increase of both the tamped density (increase by 42%) and the particle size, e.g. of d.sub.50 value (dramatic increase from 0.11 to 2.48 ?m), was observed along with a significant change of the crystallographic phase composition, particularly appearance of a significant amount of alpha-Al.sub.2O.sub.3(Table 2, FIG. 4).

[0166] FIGS. 1A and 1B show transmission electron microscopy (TEM) images of starting material 2.

[0167] FIGS. 2A and 2B show transmission electron microscopy (TEM) images of thermally treated at 1200? C. starting material 2 (example 9). As it can be seen from TEM analyses, that the mean equivalent circular diameter of primary particles d.sub.p_ECD of alumina increases from 21.2 nm (starting material 2) to 27.6 nm (example 9).

TABLE-US-00001 TABLE 1 Thermal treatment of starting material 1 Sample Water Thermal tamped OH-group Al.sub.2O.sub.3 ?-phase Water content treatment BET density density phases content d.sub.10.sup.a d.sub.50.sup.a d.sub.90.sup.a content [%] after Example [? C.] [m.sup.2/g] [g/L] [OH/nm.sup.2] (XRD) [%] [?m] [?m] [?m] [%].sup.b drying.sup.c starting 121 52 9.2 ?, ? 0 0.07 0.11 0.26 4.76 1.54 material 1 example 1 400 119 47 9.0 ?, ? 0 0.08 0.15 0.37 2.72 1.02 example 2 700 118 50 8.3 ?, ? 0 0.10 0.26 0.72 2.24 0.98 example 3 1000 116 49 8.0 ?, ? 0 0.13 0.39 5.93 1.93 0.96 example 4 1100 113 51 8.2 ?, ? 0 0.13 0.46 6.86 2.30 1.00 comparative 1200 90 66 9.9 ?, ? 0 0.14 3.63 7.46 2.12 0.86 example 1 comparative 1300 example 2.sup.d .sup.adetermined by static light scattering (SLS) after 120 s of ultrasonic treatment at 25? C. of a 5% by weight dispersion of the alumina in water; .sup.bdetermined by Karl-Fischer titration; .sup.cdetermined by Karl-Fischer titration after drying of the sample at 150? C. for 2 h; .sup.dcongestion of the rotary kiln, the experiment has been stopped, the product has not been analysed.

TABLE-US-00002 TABLE 2 Thermal treatment of starting material 2. Sample Water content Thermal tamped OH-group Al.sub.2O.sub.3 ?-phase Water [%] treatment BET density density phases content d.sub.10.sup.a d.sub.50.sup.a d.sub.90.sup.a content after Example [? C.] [m.sup.2/g] [g/L] [OH/nm.sup.2] (XRD) [%] [?m] [?m] [?m] [%].sup.b drying.sup.c starting 50 95 10.0 ?, ? 0 0.07 0.11 0.21 2.09 0.62 material 2 example 5 400 48 110 9.3 ?, ? 0 0.07 0.10 0.21 1.25 0.45 example 6 700 48 113 9.4 ?, ? 0 0.09 0.24 0.50 1.17 0.49 example 7 1000 47 117 9.7 ?, ? 0 0.11 0.31 1.66 1.01 0.49 example 8 1100 47 106 9.3 ?, ? 0 0.21 0.42 3.81 1.13 0.55 example 9 1200 45 110 10.6 ?, ? 0 0.18 0.53 6.58 0.98 0.47 comparative 1300 38 135 8.3 ?, ?, ? 25 0.15 2.48 8.12 0.76 0.40 example 3 .sup.adetermined by static light scattering (SLS) after 120 s of ultrasonic treatment at 25? C. of a 5% by weight dispersion of the alumina in water; .sup.bdetermined by Karl-Fischer titration; .sup.cdetermined by Karl-Fischer titration after drying of the sample at 150? C. for 2 h.