Chemical Composition for Production of Hollow Spherical Glass Particles with High Compressive Strength

Abstract

A hollow spherical glass particle, comprising aluminum oxide Al.sub.2O.sub.3, silicon dioxide SiO.sub.2 and at least one metal oxide, wherein the metal oxide is selected from the group consisting of alkali metal oxides and alkaline earth metal oxides, wherein the ratio of aluminum atoms to alkali metal atoms is about 1:1 and the ratio of aluminum atoms to earth alkali atoms is about 2:1, with the proviso that the hollow spherical glass particle is free of boron.

Claims

1. A hollow spherical glass particle, comprising: aluminum oxide Al.sub.2O.sub.3, silicon dioxide SiO.sub.2 and at least one metal oxide, wherein the metal oxide is selected from the group consisting of alkali metal oxides and alkaline earth metal oxides; wherein the ratio of aluminum atoms to alkali metal atoms is about 1:1 and the ratio of aluminum atoms to earth alkali atoms is about 2:1; with the proviso that the hollow spherical glass particle is free of boron.

2. The hollow spherical glass particle of claim 1, wherein the hollow spherical glass particle comprises between about 32 wt. % and about 40 wt. %, preferably about 36 wt. %, of Al.sub.2O.sub.3, between about 38 wt. % and about 46 wt. %, preferably about 42 wt. %, of SiO.sub.2, and between about 18 wt. % and about 26 wt. %, preferably about 22 wt. %, of at least one alkali metal oxide.

3. The hollow spherical glass particle of claim 2, wherein the hollow spherical glass particle comprises between about preferably 18 wt. % and about 26 wt. %, preferably about 22 wt. %, of a mixture of K.sub.2O and Na.sub.2O.

4. The hollow spherical glass particle of claim 1, wherein the hollow spherical glass particle has a particle diameter of between about 10 and 600 microns, preferably between about 90 and 500 microns.

5. The hollow spherical glass particle of claim 4, wherein the hollow spherical glass particle has a particle diameter of between 100 and 400 microns.

6. The hollow spherical glass particle of claim 1, wherein the hollow spherical glass particle has an 80% crush strength of at least 10000 psi, more preferably at least 12500 psi, especially at least 15000 psi.

7. The hollow spherical glass particle of claim 1, wherein the hollow spherical glass particle has melting temperature of at least 1200 C.

8. A plurality of hollow spherical glass particles of claim 1.

9. The plurality of hollow spherical glass particles of claim 8, wherein the hollow spherical glass particles have a true density of between about 0.4 g/cm.sup.3 and 0.8 g/cm.sup.3, more preferably between about 0.45 g/cm.sup.3 and 0.75 g/cm.sup.3, more preferably between about 0.5 g/cm.sup.3 and 0.6 g/cm.sup.3.

10. A filler comprising the plurality of hollow spherical glass particles of claim 1.

11. Use of the filler of claim 10 in metal matrix syntactic foams.

12. A metal matrix syntactic foam comprising the filler of claim 10 and a metal and/or a metal alloy.

13. The metal matrix syntactic foam of claim 12, wherein the metal is aluminum.

14. The metal matrix syntactic foam of claim 12, wherein the metal alloy is an aluminum alloy.

Description

EXAMPLE

[0026] Three samples were prepared by mixing ingredients containing aluminium oxide Al.sub.2O.sub.3, sodium oxide Na.sub.2O, silicon dioxide SiO.sub.2 and potassium oxide K.sub.2O (for example the resulting mixture can comprise china clay, feldspar, potassium carbonate, zeolites, aluminium hydroxide, potassium or sodium silicate, porcelain) in order to achieve an atomic ratio of aluminum, silicon and either sodium or potassium or both sodium and potassium atoms of about 1:1:1, i.e. A.sub.Al:Si:(N+K)=1:1:1. This means that for each Al atom there is essentially one Si atom and essentially one Na or K atom in the mixture. For two Al atoms there are essentially two Si atoms and either essentially one Na atom and essentially one K atom or essentially two Na atoms or essentially two K atoms. In particular, in this example the mixture comprised about 36 wt. % of Al.sub.2O.sub.3, about 42 wt. % of SiO.sub.2, about 21 wt. % of Na.sub.2O and about 1% of K.sub.2O. Depending on the purity of these ingredients there might be may be impurities, i.e. other chemical compounds, present. However, the total amount of impurities (other chemical compounds) should not exceed 3-4 wt. %.

[0027] After mixing the ingredients above, the mixture can be milled in a ball mill, in order to achieve an average size of particles of at most about 5 microns. The milling can be dry or wet and can be omitted if the particle size does not have to be adjusted. Thereafter the mixture was further mixed with water and blended, in order to achieve enough flowability for subsequent spray drying. After drying in a spray dryer at the temperature of about 150-250 C., a powder with granules (particles) having an with average size of about 80-400 microns was achieved. The granules was then separated according to their size into three fractions: Fraction 1: about 80-140 microns; Fraction 2: about 140-200 microns; and Fraction 3: about 200-400 microns; all fractions having a moisture content of at least about 1% and at most 10%. After the separation step, each fraction was fed into a tube furnace with induction heating at a rate of about 1 grams/min. A graphite tube was used as a heating element and argon was used as a protective gas for providing a protected atmosphere in the furnace. The temperature in the furnace was between about 1500 and about 1800 C. Residence time of the particles in the furnace was at least 1 sec. After processing the respective granules fractions 1, 2 and 3 in the tube furnace, the resulting hollow spherical glass particles were collected 50 cm below the furnace.

[0028] As a result, three types of the hollow spherical glass particles were obtained. Their properties are summarized below.

[0029] Type 1 (resulting from Fraction 1): The hollow spherical glass particles of the first type have an essentially white color and exhibit a bulk density of about 0.43 g/cm.sup.3, a true density of about 0.75 g/cm.sup.3, a particle diameter of between about 100 micron and about 150 micron, a melting temperature of about 1200 C. and an 80% crush strength of about 15000 psi (100 Mpa).

[0030] Type 2 (resulting from Fraction 2): The hollow spherical glass particles of the second type have an essentially white color and exhibit a bulk density of about 0.38 g/cm.sup.3, a true density of about 0.6 g/cm.sup.3, a particle diameter of between about 150 micron and about 200 micron, a melting temperature of about 1200 C. and an 80% crush strength of about 12500 psi (85 Mpa).

[0031] Type 3 (resulting from Fraction 3): The hollow spherical glass particles of the third type have an essentially white color and exhibit a bulk density of about 0.32 g/cm.sup.3, a true density of about 0.5 g/cm.sup.3, a particle diameter of between about 200 micron and about 400 micron, a melting temperature of about 1200 C. and an 80% crush strength of about 10000 psi (70 Mpa).

[0032] Generally and especially within the scope of the present invention it is understood that the bulk density is not an intrinsic property of the hollow spherical glass particles and can essentially slightly change depending on how the particles are handled. Within the scope of this invention the hollow spherical glass particles have a bulk density of between about 0.3 g/cm.sup.3 and about 0.45 g/cm.sup.3.

[0033] FIG. 1 shows a microscopic image of the hollow spherical glass particles of the above example, in which the granules were not separated according to their size. Therefore, all three types (Type 1, Type 2 and Type 3) of the hollow spherical glass particles are depicted in FIG. 1. The minimal size (diameter) of the hollow spherical glass particles in FIG. 1 is about 100 microns, the maximal size (diameter) is about 400 microns.