Abstract:
A method for producing potassium-doped pyrogenic oxides involves mixing a gaseous mixture including a pyrogenic oxide precursor and an aqueous aerosol containing a potassium salt to form an aerosol-gaseous mixture which is then reacted in a flame under conditions suitable for producing pyrogenic oxides by flame oxidation or flame hydrolysis to form the potassium-doped pyrogenic oxides product. The particle product is spherical, has a BET surface between 1 and 1000 m 2 /g and a narrow distribution of particle size of at least 0.7. The doped oxides can be used as polishing material (CMP application).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention is relative to pyrogenic oxides doped by means of aerosol with potassium, to the method of their production and to their usage.  
           [0003]    2. Description of Related Art The doping of pyrogenic oxides by means of aerosol is described in DE 196 50 500. It shows how an aerosol is additionally fed into a flame in which a pyrogenic oxide is produced by flame hydrolysis.  
           [0004]    A salt of the compound(s) to be doped is in this aerosol.  
           [0005]    It was found that when potassium salts are used as doping component the structure, that is, the degree of intergrowth and also the morphology (that is, the outward image) of the primary particles, is decisively changed. According to the invention this change of the morphology begins at a potassium content of more than 0.03% by wt.  
         SUMMARY OF THE INVENTION  
         [0006]    Subject matter of the invention is constituted by pyrogenically produced oxides of metals or metalloids which oxides are doped by means of aerosol with potassium and are characterized in that the base component is an oxide that is pyrogenically produced in the manner of flame oxidation or preferably of flame hydrolysis and is doped with potassium of more than 0.03 to 20% by wt. and in that the doping amount is preferably in a range of 500 to 20,000 ppm, the doping component is a salt of potassium and the BET surface of the doped oxide is between 1 and 1000 m 2 /g.  
           [0007]    The breadth of the distribution of particle size is defined as the quotient d n /d a  with d n  as arithmetic particle diameter and d a  the average particle diameter over the surface. If the quotient d n /d a  has the value of 1, a monodisperse distribution is present. That is, the closer the value is to 1 the closer the distribution of particle size is.  
           [0008]    The close distribution of particle size, defined by the value d n /d a , assures that no scratches are caused by large particles during the chemical-mechanical polishing.  
           [0009]    The average particle size can be less than 100 nanometers and the breadth of the distribution of particle size is at least 0.7.  
           [0010]    The oxide can preferably be silicon dioxide. The pH of the doped, pyrogenic oxide, measured in a 4% aqueous dispersion, can be more than 5, preferably from 7 to 8. The BET surface of the doped oxide can be between 1 and 1000 m 2 /g, preferably between 60 and 300 m 2 /g.  
           [0011]    The (DBP number) dibutylphthalate absorption can not show any measurable end point and the BET surface of the doped oxide can be between 1 and 1000 m 2 /g.  
           [0012]    Further subject matter of the invention is constituted by a method of producing the pyrogenic oxides of metals or metalloids, which oxides are doped by means of aerosol with potassium, which is characterized in that an aerosol produced from a potassium salt solution with a potassium chloride content greater than 0.5% by wt. KCl is fed into a flame like the one used to produce pyrogenic oxides, preferably silicon dioxide in the manner of flame oxidation or preferably of flame hydrolysis, that this aerosol is homogeneously mixed before the reaction with the gaseous mixture of flame oxidation or flame hydrolysis, then the aerosol-gaseous mixture is allowed to react in a flame and the pyrogenic, potassium-doped oxides produced are separated in a known manner from the gas flow, that a potassium salt solution containing the potassium salt serves as starting product of the aerosol and that the aerosol is produced by atomization by means of an aerosol generator preferably in accordance with the gas-atomizing (two-fluid) nozzle method.  
           [0013]    The method of producing pyrogenic oxides such as, e.g., silicon dioxide is known from Ullmann&#39;s Encyclopädie der technischen Chemie, 4 th  edition, volume 21, page 464 (1982). In addition to silicon tetrachloride any liquefiable compound of silicon such as, e.g., methylmonochlorosilane can be used as starting material.  
           [0014]    DE 196 50 500 teaches a method of producing silicon dioxide doped with aerosol.  
           [0015]    In the method of the invention oxygen can be additionally added.  
           [0016]    The silicon dioxide in accordance with the invention and doped with potassium by means of aerosol exhibits a distinctly narrower distribution of particle size curve than the known silicon dioxide. It is particularly suitable for this reason for use as an abrasion means in CMP (chemical mechanical polishing). The potassium is uniformly distributed in the case of the silicon dioxide of the invention. It can not be localized on EM photographs.  
           [0017]    The pyrogenic oxides doped in this manner with potassium surprisingly exhibit spherical, round primary particles in an electron microscope image that are only slightly intergrown with each other, which is expressed in the fact that no end point can be recognized in a “determination of structure” according to the DBP method. Furthermore, highly filled dispersions with a low viscosity can be produced from these pyrogenic powders doped with potassium.  
           [0018]    Further subject matter of the invention is constituted by the use of pyrogenic oxides doped with potassium by means of aerosol as filler, carrier material, catalytically active substance, starting material for producing dispersions, as polishing material (CMP applications), base ceramic material, in the electronic industry, in the cosmetic industry, as additive in the silicon industry and rubber industry, for adjusting the rheology of liquid systems, for the stabilization of heat protection and in the paint industry. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0019]    [0019]FIG. 1 shows an EM photograph of the pyrogenic silicic acid of reference example 1 (without doping).  
         [0020]    [0020]FIG. 2 shows an EM photograph of the pyrogenic silicic acid according to example 2 doped with potassium.  
         [0021]    [0021]FIG. 3 shows the DBP curve of the powders of reference example 1 (weighed portion 16 g): The take-up of force and the measured torque (in Nm) of the rotating blades of the DBP measuring device (Rheocord 90 of the company Haake/Karlsruhe) shows a sharply pronounced maximum with a subsequent decline at a certain addition of DBP. This curve form is characteristic for known pyrogenic oxides that are not doped.  
         [0022]    [0022]FIG. 4 shows the DBP curve of the powder of the pyrogenic oxide doped with potassium in accordance with the invention (16 g weighed portion) according to example 2.  
         [0023]    [0023]FIG. 5 shows the electron microscope photograph of the powder of example 3 with an enlargement of 1:50000.  
         [0024]    [0024]FIG. 6 shows the electron microscope photograph of the powder of example 3 with an enlargement of 1:100000.  
         [0025]    [0025]FIG. 7 shows the electron microscope photograph of the powder of example 3 with an enlargement of 1:200000.  
         [0026]    [0026]FIG. 8 shows the results of the particle count of the powders of example 1.  
         [0027]    [0027]FIG. 9 shows the results of the particle count of the powders of example 1.  
         [0028]    [0028]FIG. 10 shows the results of the particle count of the powders of example 1.  
         [0029]    [0029]FIG. 11 shows the results of the particle count of the powders of example 7.  
         [0030]    [0030]FIG. 12 shows the results of the particle count of the powders of example 7.  
         [0031]    [0031]FIG. 13 shows the results of the particle count of the powders of example 7.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    The subject matter of the invention will be explained and described in detail using the following examples:  
         [0033]    A burner arrangement is used like the one described in DE OS 196 50 500.  
       EXAMPLE 1  
     Reference Example Without Doping with Potassium Salts but with Water Vapor  
       [0034]    4.44 kg/h SiCl 4  are evaporated at approximately 130° C. and transferred into the central tube of the burner with a known design in accordance with DE 196 50 500 A1. 2.9 Nm 3 /h hydrogen as well as 3.8 Nm 3 /h air and 0.25 Nm 3 /h oxygen are additionally fed into this tube. This gaseous mixture flows out of the inner burner nozzle and burns into the combustion chamber of the water-cooled fire tube. Additionally, 0.3 Nm 3 /h (secondary) hydrogen and 0.3 Nm 3 /h nitrogen are fed into the jacket nozzle surrounding the central nozzle in order to avoid cakings.  
         [0035]    Approximately 10 Nm 3 /h air is drawn from the ambient into the fire tube standing under a slight vacuum (open burner operation).  
         [0036]    The second gaseous component that is fed into the axial tube consists in this reference example of hydrogen produced by superheating distilled water at approximately 180° C. Two gas-atomizing nozzles with an atomization power of 250 g/h water function thereby as aerosol generator.  
         [0037]    The atomized water vapor is conducted with the aid of a carrier gas current of approximately 2 Nm 3 /h air through heated conduits during which the water-vapor mist turns into gas at temperatures of approximately 180° C.  
         [0038]    After the flame hydrolysis the reaction gases and the pyrogenic silicic acid produced are drawn through a cooling system by applying a vacuum and the gaseous particle current cooled off thereby to approximately 100 to 160° C. The solid matter is separated from the current of waste gas in a filter or cyclone.  
         [0039]    The pyrogenic silicic acid produced accumulates as white, fine powder. In a further step any adhering remnants of hydrochloric acid are removed from the silicic acid at an elevated temperature by a treatment with air containing water vapor.  
         [0040]    The BET surface of the pyrogenic silicic acid is 124 m 2 /g.  
         [0041]    The breadth of the distribution of the particle size is calculated as follows: 
           d   n =16.67 nm 
           d   a =31.82 nm 
         [0042]    The quotient  
         q   1     =         d   n       d   a       =     0.52   .                             
 
         [0043]    The production conditions are summarized in Table 1. The analytical data of the silicic acid obtained is indicated in Table 2.  
       EXAMPLE 2  
       [0044]    [0044] 4 . 44  kg/h SiCl 4  are evaporated at approximately 130° C. and transferred into the central tube of the burner with a known design in accordance with DE 196 50 500 A1. 4.7 Nm 3 /h hydrogen as well as 3.7 Nm 3 /h air and 1.15 Nm 3 /h oxygen are additionally fed into this tube. This gaseous mixture flows out of the inner burner nozzle and burns into the combustion chamber of the water-cooled fire tube.  
         [0045]    Additionally, 0.5 Nm 3 /h (secondary) hydrogen and 0.3 Nm 3 /h nitrogen are fed into the jacket nozzle surrounding the central nozzle in order to avoid cakings.  
         [0046]    Approximately 10 Nm 3 /h air is drawn from the ambient into the fire tube standing under a slight vacuum (open burner operation).  
         [0047]    The second gaseous component that is fed into the axial tube consists of an aerosol produced from a 12.55% aqueous solution of potassium chloride. Two gas-atomizing nozzles with an atomization power of 255 g/h aerosol function thereby as aerosol generator. This aqueous saline aerosol is conducted by 2 Nm 3 /h carrier air through externally heated conduits and leaves the inner nozzle with an exit temperature of approximately 180° C. The aerosol containing potassium salt is introduced into the flame.  
         [0048]    After the flame hydrolysis the reaction gases and the pyrogenic silicic acid produced are drawn through a cooling system by applying a vacuum and the gaseous particle current cooled off thereby to approximately 100 to 160° C. The solid matter is separated from the current of waste gas in a filter or cyclone.  
         [0049]    The pyrogenic silicic acid doped with potassium that is produced accumulates as white, fine powder. In a further step any adhering remnants of hydrochloric acid are removed from the silicic acid at an elevated temperature by a treatment with air containing water vapor.  
         [0050]    The BET surface of the pyrogenic silicic acid is 131 m 2 /g.  
         [0051]    The production conditions are summarized in Table 1. The analytical data of the silicic acid obtained is indicated in Table 2.  
       EXAMPLE 3  
       [0052]    [0052] 4 . 44  kg/h SiCl 4  are evaporated at approximately 130° C. and transferred into the central tube of the burner with a known design in accordance with DE 196 50 500 A1. 4.7 Nm 3 /h hydrogen as well as 3.7 Nm 3 /h air and 1.15 Nm 3 /h oxygen are additionally fed into this tube. This gaseous mixture flows out of the inner burner nozzle and burns into the combustion chamber of the water-cooled fire tube.  
         [0053]    Additionally, 0.5 Nm 3 /h (secondary) hydrogen and 0.3 Nm 3 /h nitrogen are fed into the jacket nozzle surrounding the central nozzle in order to avoid cakings.  
         [0054]    Approximately 10 Nm 3 /h air is drawn from the ambient into the fire tube standing under a slight vacuum (open burner operation).  
         [0055]    The second gaseous component that is fed into the axial tube consists of an aerosol produced from a 2.22% aqueous solution of potassium chloride. Two gas-atomizing nozzles with an atomization power of 210 g/h aerosol function thereby as aerosol generator. This aqueous saline aerosol is conducted by 2 Nm 3 /h carrier air through externally heated conduits and leaves the inner nozzle with an exit temperature of approximately 180° C. The aerosol is introduced into the flame and correspondingly alters the properties of the pyrogenic silicic acid produced.  
         [0056]    After the flame hydrolysis the reaction gases and the pyrogenic silicic acid produced are drawn through a cooling system by applying a vacuum and the gaseous particle current cooled off thereby to approximately 100 to 160° C. The solid matter is separated from the current of waste gas in a filter or cyclone.  
         [0057]    The pyrogenic silicic acid doped with potassium that is produced accumulates as white, fine powder. In a further step any adhering remnants of hydrochloric acid are removed from the silicic acid at an elevated temperature by a treatment with air containing water vapor.  
         [0058]    The BET surface of the pyrogenic silicic acid is 104 m 2 /g.  
         [0059]    The production conditions are summarized in Table 1. The analytical data of the silicic acid obtained is indicated in Table 2.  
       EXAMPLE 4  
       [0060]    [0060] 4 . 44  kg/h SiCl 4  are evaporated at approximately 130° C. and transferred into the central tube of the burner with a known design in accordance with DE 196 50 500 A1. 4.7 Nm 3 /h hydrogen as well as 3.7 Nm 3 /h air and 1.15 Nm 3 /h oxygen are additionally fed into this tube. This gaseous mixture flows out of the inner burner nozzle and burns into the combustion chamber of a water-cooled fire tube.  
         [0061]    Additionally, 0.5 Nm 3 /h (secondary) hydrogen and 0.3 Nm 3 /h nitrogen are fed into the jacket nozzle surrounding the central nozzle in order to avoid cakings.  
         [0062]    Approximately 10 Nm 3 /h air is drawn from the ambient into the fire tube standing under a slight vacuum (open burner operation).  
         [0063]    The second gaseous component that is fed into the axial tube consists of an aerosol produced from a 4.7% aqueous solution of potassium chloride. Two gas-atomizing nozzles with an atomization power of 225 g/h aerosol function thereby as aerosol generator. This aqueous saline aerosol is conducted by 2 Nm 3 /h carrier air through externally heated conduits and leaves the inner nozzle with an exit temperature of approximately 180° C. The aerosol is introduced into the flame.  
         [0064]    After the flame hydrolysis the reaction gases and the pyrogenic silicic acid produced are drawn through a cooling system by applying a vacuum and the gaseous particle current cooled off thereby to approximately 100 to 160° C. The solid matter is separated from the current of waste gas in a filter or cyclone.  
         [0065]    The pyrogenic silicic acid doped with potassium that is produced accumulates as white, fine powder. In a further step any adhering remnants of hydrochloric acid are removed from the silicic acid at an elevated temperature by a treatment with air containing water vapor.  
         [0066]    The BET surface of the pyrogenic silicic acid is 113 m 2 /g.  
         [0067]    The production conditions are summarized in Table 1. The analytical data of the silicic acid obtained is indicated in Table 2.  
       EXAMPLE 5  
       [0068]    [0068] 4 . 44  kg/h SiCl 4  are evaporated at approximately 130° C. and transferred into the central tube of the burner with a known design in accordance with DE 196 50 500 A1. 4.7 Nm 3 /h hydrogen as well as 3.7 Nm 3 /h air and 1.15 Nm 3 /h oxygen are additionally fed into this tube. This gaseous mixture flows out of the inner burner nozzle and bums into the combustion chamber of a water-cooled fire tube.  
         [0069]    Additionally, 0.5 Nm 3 /h (secondary) hydrogen and 0.3 Nm 3 /h nitrogen are fed into the jacket nozzle surrounding the central nozzle in order to avoid cakings.  
         [0070]    Approximately 10 Nm 3 /h air is drawn from the ambient into the fire tube standing under a slight vacuum (open burner operation).  
         [0071]    The second gaseous component that is fed into the axial tube consists of an aerosol produced from a 9.0% aqueous solution of potassium chloride. Two gas-atomizing nozzles with an atomization power of 210 g/h aerosol function thereby as aerosol generator. This aqueous saline aerosol is conducted by 2 Nm 3 /h carrier air through externally heated conduits and leaves the inner nozzle with an exit temperature of approximately 180° C. The aerosol is introduced into the flame.  
         [0072]    After the flame hydrolysis the reaction gases and the pyrogenic silicic acid produced are drawn through a cooling system by applying a vacuum and the gaseous particle current cooled off thereby to approximately 100 to 160° C. The solid matter is separated from the current of waste gas in a filter or cyclone.  
         [0073]    The pyrogenic silicic acid doped with potassium that is produced accumulates as white, fine powder. In a further step any adhering remnants of hydrochloric acid are removed from the silicic acid at an elevated temperature by a treatment with air containing water vapor.  
         [0074]    The BET surface of the pyrogenic silicic acid is 121 m 2 /g.  
         [0075]    The production conditions are summarized in Table 1. The analytical data of the silicic acid obtained is indicated in Table 2.  
       EXAMPLE 6  
       [0076]    [0076] 4 . 44  kg/h SiCl 4  are evaporated at approximately 130° C. and transferred into the central tube of the burner with a known design in accordance with DE 196 50 500 A1. 4.7 Nm 3 /h hydrogen as well as 3.7 Nm 3 /h air and 1.15 Nm 3 /h oxygen are additionally fed into this tube. This gaseous mixture flows out of the inner burner nozzle and burns into the combustion chamber of a water-cooled fire tube.  
         [0077]    Additionally, 0.5 Nm 3 /h (secondary) hydrogen and 0.3 Nm 3 /h nitrogen are fed into the jacket nozzle surrounding the central nozzle in order to avoid cakings.  
         [0078]    Approximately 10 Nm 3 /h air is drawn from the ambient into the fire tube standing under a slight vacuum (open burner operation).  
         [0079]    The second gaseous component that is fed into the axial tube consists of an aerosol produced from a 12.0% aqueous solution of potassium chloride. Two gas-atomizing nozzles with an atomization power of 225 g/h aerosol function thereby as aerosol generator. This aqueous saline aerosol is conducted by 2 Nm 3 /h carrier air through externally heated conduits and leaves the inner nozzle with an exit temperature of approximately 180° C. The aerosol is introduced into the flame.  
         [0080]    After the flame hydrolysis the reaction gases and the pyrogenic silicic acid produced are drawn through a cooling system by applying a vacuum and the gaseous particle current cooled off thereby to approximately 100 to 160° C. The solid matter is separated from the current of waste gas in a filter or cyclone.  
         [0081]    The pyrogenic silicic acid doped with potassium that is produced accumulates as white, fine powder. In a further step any adhering remnants of hydrochloric acid are removed from the silicic acid at an elevated temperature by a treatment with air containing water vapor.  
         [0082]    The BET surface of the pyrogenic silicic acid is 120 m 2 /g.  
         [0083]    The production conditions are summarized in Table 1. The analytical data of the silicic acid obtained is indicated in Table 2.  
       EXAMPLE 7  
       [0084]    [0084] 4 . 44  kg/h SiCl 4  are evaporated at approximately 130° C. and transferred into the central tube of the burner with a known design in accordance with DE 196 50 500 A1. 4.7 Nm 3 /h hydrogen as well as 3.7 Nm 3 /h air and 1.15 Nm 3 /h oxygen are additionally fed into this tube. This gaseous mixture flows out of the inner burner nozzle and burns into the combustion chamber of a water-cooled fire tube.  
         [0085]    Additionally, 0.5 Nm 3 /h (secondary) hydrogen and 0.3 Nm 3 /h nitrogen are fed into the jacket nozzle surrounding the central nozzle in order to avoid cakings.  
         [0086]    Approximately 10 Nm 3 /h air is drawn from the ambient into the fire tube standing under a slight vacuum (open burner operation).  
         [0087]    The second gaseous component that is fed into the axial tube consists of an aerosol produced from a 20% aqueous solution of potassium chloride. Two gas-atomizing nozzles with an atomization power of 210 g/h aerosol function thereby as aerosol generator. This aqueous saline aerosol is conducted by 2 Nm 3 /h carrier air through externally heated conduits and leaves the inner nozzle with an exit temperature of approximately 180° C. The aerosol is introduced into the flame.  
         [0088]    After the flame hydrolysis the reaction gases and the pyrogenic silicic acid produced are drawn through a cooling system by applying a vacuum and the gaseous particle current cooled off thereby to approximately 100 to 160° C. The solid matter is separated from the current of waste gas in a filter or cyclone.  
         [0089]    The pyrogenic silicic acid doped with potassium that is produced accumulates as white, fine powder. In a further step any adhering remnants of hydrochloric acid are removed from the silicic acid at an elevated temperature by a treatment with air containing water vapor.  
         [0090]    The BET surface of the pyrogenic silicic acid is 117 m 2 /g.  
         [0091]    The breadth of the distribution of the particle size is calculated as follows: 
           d   n =20.99 nm 
           d   a =24.27 nm 
         [0092]    The quotient  
         q   1     =         d   n       d   a       =     0.86   .                             
 
         [0093]    The production conditions are summarized in Table 1. The analytical data of the silicic acid obtained is indicated in Table 2.  
                                                                                                                                                                                 TABLE 1                           Experimental conditions in the production of doped, pyrogenic silicic acid                    Primary   O 2     H 2     H 2     N 2     Gas   KCl saline   Aerosol                   SiCl 4     Air   addit.   core   jacket   jacket   temp.   solution   amount   Air   BET       No.   kg/h   Nm 3 /h   Nm 3 /h   Nm 3 /h   Nm 3 /h   Nm 3 /h   C.   % by wt.   g/h   Nm 3 /h   m 2 /g                    Example 1 without addition of salt            1   4.44   3.8   0.25   2.9   0.3   0.3   130   Only H 2 O   250   2   124            Examples 2 to 7 with addition of salt            2   4.44   3.7   1.15   4.7   0.5   0.3   130   12.55   255   2   131       3   4.44   3.7   1.15   4.7   0.5   0.3   130   2.22   210   2   104       4   4.44   3.7   1.15   4.7   0.5   0.3   130   4.7   225   2   113       5   4.44   3.7   1.15   4.7   0.5   0.3   130   9.0   210   2   121       6   4.44   3.7   1.15   4.7   0.5   0.3   130   12.0   225   2   120       7   4.44   3.7   1.15   4.7   0.5   0.3   130   20.0   210   2   117                          
 
         [0094]    [0094]                                                                                                                     TABLE 2                           Analytical data of the doped silicic acids obtained according to       examples 1 to 7                            DBP in                           Potassium   g/100 g               pH 4%   content in   with 16 g   Bulk           BET   aqueous   % by wt.   weighed   density   Stamping       No.   m 2 /g   dispersion   as K 2 O   portion   g/l   density                    Reference example without salt            1   124   4.68   0   185   28   39            Examples with addition of potassium salt            2   131   7.64   0.44   No end   28   36                       point       3   104   7.22   0.12   No end   31   43                       point       4   113   7.67   0.24   No end   32   45                       point       5   121   7.7   0.49   No end   32   43                       point       6   120   7.96   0.69   No end   30   44                       point       7   117   7.86   1.18   No end   28   38                       point                            
         [0095]    The subject matter of the invention is explained in detail with reference made to the drawings and figures:  
         [0096]    [0096]FIG. 1 shows an EM photograph of the pyrogenic silicic acid of reference example 1 (without doping).  
         [0097]    [0097]FIG. 2 shows an EM photograph of the pyrogenic silicic acid according to example 2 doped with potassium.  
         [0098]    It can be recognized that the aggregate and agglomerate structure is changed during the doping with potassium salts and that spherical primary particles are produced during the doping that are not very intergrown with each other.  
         [0099]    The differences in the “structure”, that is, the degree of intergrowth of the particles, are expressed in clearly different DBP absorptions (dibutylphthalate absorption) and in the different course of the DBP absorption curves.  
         [0100]    [0100]FIG. 3 shows the DBP curve of the powders of reference example 1 (weighed portion 16 g): The take-up of force and the measured torque (in Nm) of the rotating blades of the DBP measuring device (Rheocord 90 of the company Haake/ Karlsruhe) shows a sharply pronounced maximum with a subsequent decline at a certain addition of DBP. This curve form is characteristic for known pyrogenic oxides that are not doped.  
         [0101]    [0101]FIG. 4 shows the DBP curve of the powder of the pyrogenic oxide doped with potassium in accordance with the invention (16 g weighed portion) according to example 2.  
         [0102]    No sharp rise of the torque with subsequent strong drop can be recognized. For this reason the DBP measuring device can also not detect an end point.  
         [0103]    [0103]FIG. 5 shows the electron microscope photograph of the powder of example 3 with an enlargement of 1:50000.  
         [0104]    [0104]FIG. 6 shows the electron microscope photograph of the powder of example 3 with an enlargement of 1:100000.  
         [0105]    [0105]FIG. 7 shows the electron microscope photograph of the powder of example 3 with an enlargement of 1:200000.  
         [0106]    The particle count by EM photography clearly shows the rather narrow particle distribution curve of the silicic acid doped by means of aerosol with potassium in accordance with the invention.  
         [0107]    Table 3 shows the results of the particle count of the powders of example 1 (reference example) by means of the EM photograph. These values are graphically shown in FIGS. 8, 9 and  10 .  
                                                           TABLE 3                           Total number of measured particles N:   5074           Particle diameter, arithmetic mean DN:   16.678   nm       Particle diameter, average over the surface DA:   31.825   nm       Particle diameter, average over the volume DV:   42.178   nm       Particle diameter, standard deviation S:   10.011   nm       Particle diameter, co-efficient of variation V:   60.027       Specific surface OEM:   85.696   qm/g       Median value numeric distribution D50 (A):   12.347   nm       Median value weight distribution D50 (g):   40.086   nm            90% span numeric distribution:   3.166 nm-36.619 nm       90% span weight distribution   12.153 nm-72.335 nm        Total span:   7.400 nm-94.200 nm                            Percent   Sum                       by   Percent   Percent by   Sum       Diameter   Number   Number   by   weight   Percent by       D   N   N %   number   ND3 %   weight %                7.400   593   11.687   11.687   0.393   0.393       10.200   1142   22.507   34.194   1.984   2.377       13.000   1046   20.615   54.809   3.761   6.138       15.800   693   13.658   68.467   4.474   10.612       18.600   498   9.815   78.281   5.245   15.857       21.400   281   5.538   83.819   4.507   20.364       24.200   193   3.804   87.623   4.477   24.841       27.000   124   2.444   90.067   3.995   28.836       29.800   86   1.695   91.762   3.725   32.561       32.600   74   1.458   93.220   4.196   36.757       35.400   62   1.222   94.442   4.502   41.259       38.200   65   1.281   95.723   5.930   47.189       41.000   37   0.729   96.453   4.174   51.363       43.800   35   0.690   97.142   4.814   56.176       46.600   30   0.591   97.734   4.969   61.145       49.400   30   0.591   98.325   5.919   67.065       52.000   16   0.315   98.640   3.725   70.789       55.000   14   0.276   98.916   3.812   74.602       57.800   15   0.296   99.212   4.741   79.343       60.600   10   0.197   99.409   3.642   82.985       63.400   7   0.138   99.547   2.920   85.905       66.200   8   0.158   99.704   3.799   89.703       69.000   8   0.158   99.862   4.301   94.005       71.800   1   0.020   99.882   0.606   94.611       74.600   3   0.059   99.941   2.039   96.649       80.200   1   0.020   99.961   0.844   97.494       88.600   1   0.020   99.980   1.138   98.632       94.200   1   0.020   100.000   1.368   100.000                  
 
         [0108]    Table 4 shows the results of the particle count of the powders of example 7 by EM photograph. These values are graphically shown in FIGS.  11  to  13 .  
                                                           TABLE 4                           Total number of measured particles N:   4259           Particle diameter, arithmetic mean DN:   20.993   nm       Particle diameter, average over the surface DA:   24.270   nm       Particle diameter, average over the volume DV:   26.562   nm       Particle diameter, standard deviation S:   5.537   nm       Particle diameter, coefficient of variation V:   26.374       Specific surface OEM:   112.370   qm/g       Median value numeric distribution D50 (A):   18.740   nm       Median value weight distribution D50 (g):   23.047   nm            90% span numeric distribution:   12.615 nm-29.237 nm       90% span weight distribution   14.686 nm-44.743 nm       Total span:    7.400 nm-55.000 nm                            Percent                           by   Sum   % by   Sum       Diameter   Number   Number   % by   weight   % by       D   N   N %   number   ND3 %   weight                7.400   1   0.023   0.023   0.001   0.001       10.200   11   0.258   0.282   0.024   0.025       13.000   233   5.471   5.753   1.051   1.075       15.800   805   18.901   24.654   6.517   7.592       18.600   1034   24.278   48.932   13.656   21.248       21.400   913   21.437   70.369   18.364   39.613       24.200   607   14.252   84.621   17.656   57.269       27.000   311   7.302   91.923   12.564   69.833       29.800   164   3.851   95.774   8.908   78.740       32.600   63   1.479   97.253   4.480   83.220       35.400   35   0.822   98.075   3.187   86.407       38.200   28   0.657   98.732   3.203   89.610       41.000   18   0.423   99.155   2.546   92.156       43.800   10   0.235   99.390   1.725   93.881       46.600   16   0.376   99.765   3.323   97.204       49.400   5   0.117   99.883   1.237   98.441       52.200   3   0.070   99.953   0.876   99.317       55.000   2   0.047   100.000   0.683   100.000