Compositions: ceramic – Ceramic compositions – Pore-forming
Reexamination Certificate
1999-03-01
2001-11-20
Sample, David R (Department: 1755)
Compositions: ceramic
Ceramic compositions
Pore-forming
C501S103000, C210S656000, C530S417000
Reexamination Certificate
active
06319868
ABSTRACT:
INTRODUCTION
The present invention relates, generally, to porous articles, and in particular to porous zirconia or zirconium-containing articles, to methods of making such articles, and to methods of using such articles. One example of the porous articles are porous particles. More particularly, the present invention relates to porous particles containing zirconia and other metallic oxides including silica in combination and to the manufacture and use of such particles. Even more particularly, the present invention relates to the use of particles containing zirconia and other metallic oxides including optionally containing silica, in separation applications, particularly in chromatographic applications. One particular aspect of the present invention relates to derivatisation processes whereby the surface of the porous zirconia or zirconium containing particles are modified and to the use of such modified particles in chemical processes, particularly in chromatographic applications.
Porous articles find use in certain applications because of their properties, such as for example, their high surface area per unit volume. Such uses include use as supports for a wide variety of chemical substances, such as catalyst supports and as chemical sorbents. Where the porosity and the pore size of the particles can be controlled, the porous particles also find particular use in chromatography applications and in chemical separation applications generally. Porous silica, one example of a porous particle, finds particular use in chromatographic applications, such as High Performance Liquid Chromatography (HPLC). However, the use of porous silica is limited by the chemical reactivity of the particles since porous silica is susceptible to reactions in alkaline media and therefore is of only limited use in applications which require resistance to alkaline attack or for operations conducted in alkaline media. Thus, there is a need for a porous material which is not susceptible to alkaline attack and can be used in alkaline media.
Another example of porous articles are organic polymers which are particularly useful in a wide variety of applications due to their pore size or to the pore sizes being readily controllable. However, at high temperatures and in certain organic solvents, or when subjected to certain mechanical stress, the organic polymers have limited strength, and can distort altering their pore sizes which in turn changes the separation characteristics of the polymers and thus reduces their effectiveness and usefulness in many applications. Disadvantages of using polymers are particularly prevalent in situations where the polymer particles are mixed with liquids, since the low density of the organic polymer particles, being similar to that of the liquids, prevents their ready separation from the liquid. In particular, low density polymeric particles are difficult to handle in fluidised beds due to the similarities of the densities of the particles and of the liquids being treated in the fluidised bed. Thus, there is a need to provide porous particles which retain their shape in a wide variety of chemical and mechanical environments in order to prolong the useful working life of the particles and to increase the variety of applications in which the particles may be used. Additionally, there is a need to provide porous particles which can be readily separated from the liquids being treated by the particles on the basis of the difference in densities of the particles and liquids.
In the past there has been a proposal to use porous zirconia particles as the support phase for chromatography applications (Rigney, Webber and Carr, Journal of Chromatography 484 (1989) 273-291). However, this proposal was not entirely successful due to the particles being unstable in some mechanical environments encountered in chromatographic applications and due to the inability to modify the surface properties of the particles. Such disadvantages arose primarily from the method used in making the particles. The present invention sets out to overcome these and other weaknesses of the particles and of the previously used method of making the particles.
Therefore, there is a need for porous particles which are resistant to alkaline attack, which are of improved strength and of high density, which can be used in a wide variety of chemical separation applications and which extend the applications in which such porous particles can be utilised by modifying the surface of the particles. It has now been discovered that it is possible to make porous zirconia which can provide improved resistance to alkaline attack, which is of good strength and has a relatively high density and which can be used in diverse chemical and mechanical environments in which hithertobefore it has not been possible to use porous zirconia particles. The improved properties result at least in part from the method of making the particles.
Porous Zirconia Particles
According to one aspect of the present invention there is provided porous zirconia particles or zirconium-containing particles in which the particles comprise a substantially continuous three dimensional interpenetrating network of interconnected pores.
Typically, the pores of the particles are of substantially constant diameter throughout their length. More typically, the pores have substantially constant diameter at the curves or bends of the pores, and at the intersection of the pores. However, it is to be noted that where two or more pores intersect, the diameter of the pores may be hanged to account for the individual pores not being exactly aligned with each other.
Typically, the zirconia or zirconium-containing particles also comprise a further component. Typically, this component is a metal oxide, such as for example silica. More typically, the particles of the present invention comprise a combination of zirconia and silica and can optionally include zircon. Preferably, there is from 1 to 100% zirconia and from 99 to 0% silica, more preferably 5-90% zirconia and 95-10% silica.
Typically, the size of the particles can be up to 200 &mgr;m or greater, preferably 5-100 &mgr;m, more preferably 5 to 80 &mgr;m and even more preferably 10-70 &mgr;m.
Preferably, the porous zirconia of the present invention comprises particles having interconnected pores of up to ;5 about 2000 Å or greater, preferably between about 20 and 2000 Å in diameter, more preferably between 200 and 1500 Å in diameter, and even more preferably, pores of between 500 and 1000 Å in diameter. However, it is to be noted that pores of up to 5000 Å or even larger are possible with some of the particles of the present invention depending on the size of the particles. When the pore sizes become too large the effectiveness of the particles in chemical separation applications reduces because the surface area of the particles is reduced.
Typically, the surface area per unit mass of the particles can be up to 100 m
2
/g, preferably 5 to 30 m
2
/g with a typical value being about 5 m
2
/g.
Typically, the surfaces of the porous zirconia particles may be modified, more typically, the outer surfaces of the particles or surfaces of the pores closer to the outer surface of the particles. More typically, the surface modification of the particles involves hydroxylation of the surface to impart a greater amount of hydroxide groups on the surface of the particles.
Even more typically, the surface modified or surface treated particles can be further modified with other functional groups. The surface modified particles find particular usefulness in chromatography applications.
It will be understood that by use of the term “zirconia” in the present specification is meant zirconia-rich compositions such as those commonly referred to in the art as zirconia compositions or compositions containing a significant proportion of zirconia or zirconium, preferably at least about 50% zirconia.
Crystallographic forms of Zirconia
Zirconia, which is also known as zirconium oxide (ZrO
2
), may exist at room temperature in
Aguilar Marie Isabel
Cheang Philip Hong Ning
Eriksson Kjell-Ove
Gani Mary Susan Jean
Hearn Milton Thomas William
Biebel & French
Monash University
Sample David R
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