WO2003055822A1

WO2003055822A1 - Inorganic material and method of manufacture

Info

Publication number: WO2003055822A1
Application number: PCT/GB2002/005857
Authority: WO
Inventors: Thomas Richard Jones; Richard D. Pascoe
Original assignee: University Of Exeter
Priority date: 2001-12-22
Filing date: 2002-12-20
Publication date: 2003-07-10
Also published as: GB2381268B; GB0130828D0; GB2381268A; AU2002361451A1

Abstract

A material comprises a thermally hardened mixture of a major proportion of pulverised waste or recycled glass and a minor proportion of a bonding agent is manufactured by a process comprising the steps of: (a) preparing from a waste or recycled glass powder; (b) mixing the glass powder with from 1 to 16 mass %, based on the mass of the glass powder, of a bonding agent comprising an oxide or hydroxide of an alkali or alkaline earth metal or a source of active alumina or a combination thereof; (c) adding to the mixture from 5 to 24 mass % of water, based on the mass of glass powder; (d) charging the resulting damp powder into a mould and compressing the mixture to form a desired shape; and (e) exposing the compacted shape to saturated steam at a temperature in the range of from 70°C to 200°C for a time of from 15 minutes to 48 hours.

Description

INORGANIC ATERIAL ND METHOD OF MANUFACTURE

This invention relates to a useful ceramic material which is produced from waste or recycled glass, and to a process for manufacturing said material.

In the industrial economies, the disposal of waste glass from all sources is a growing problem. Suitable landfill sites are becoming scarce, and many authorities have severely limited the type of waste that can be so dumped, or introduced landfill taxes in order to discourage such dumping of domestic and industrial waste. Some authorities pay a subsidy to organisations which can collect waste glass and put it to use. On the large industrial scale, waste glass can be recycled, far example, to the glass manufacturer, or used for aggregate in asphalt or concrete, or used as the base layer in road construction.

It is economically preferable to use waste glass to make high value products, rather than simply to use it as an aggregate which replaces quarried rock; in general, recycling any waste material into high value products is more environmentally friendly. However currently there are limited opportunities for doing this with glass. In regions remote from a glass manufacturer, it is uneconomical to transport the waste glass long distances to the glass works for re-melting. This particularly applies to the recycling of green glass bottles, in regions which do not produce wine.

Some possibilities for making relatively high value products, on the industrial scale, from waste glass have been investigated. These possibilities include: finely- ground glass as a partial substitute for Portland cement in the manufacture of concrete; using coloured waste glass aggregate in decorative concrete, giving a "terrazzo tile" effect; leaching silica from powdered waste glass, using hot sodium hydroxide solution; and sintering powdered waste glass to make a decorative ceramic material

All these potential applications have certain problems which will need to be overcome before they are commercialised on a large scale. Glass has a high sodium content (typically 14 mass % Na₂0) , but the alkali content of Portland cement, measured as Na₂0 equivalent, is often limited by regulation to 0.6 mass %. This is because high levels of alkali can, in combination with certain types of aggregate, cause alkali-aggregate reaction which causes expansive forces within the concrete. Over a period of time, the expansive forces may cause deep cracking of the concrete which then suffers accelerated deterioration.

In concrete, any aggregate composed of waste glass is liable to react with the alkali in cement (the alkali- aggregate reaction described above) and cause expansive forces. This can lead to the aggregate "popping out" of the surface of the concrete, and eventually to more general degradation.

Leaching glass with hot sodium hydroxide is an expensive process in terms of capital investment and energy usage. The products are sodium silicate solution and fine porous particles of calcium silicate. Further processing would be required, such as concentrating the dilute sodium silicate solution and washing the fine calcium silicate particles .

Likewise, sintering powdered glass into a glass ceramic is expensive in terms of capital investment and energy usage - typically the green tile is produced from the powdered glass by bonding with organic polymers, and then fired at 700 - 1,000° C.

A known synthetic calcium silicate construction material is manufactured by preparing a mixture of a particulate quartzitic silica, for example sand, containing a minor but significant proportion of particles which have been comminuted to a diameter less than 50μm, with a proportion of lime, typically about 7 mass % of lime, based on the total mass of silica. This mixture is then heat treated in steam at a temperature in the range of from 170 to 200°C, or higher, for a period of up to 24 hours. Treatment with steam at such temperatures necessitates the provision of large autoclaves which are capable of operating under pressures in the range of from 1.5 - 3.0 Mpa . (10 - 20 atm. ) , and such autoclaves are extremely expensive to build and maintain.

The object of this invention is to produce a strong and versatile ceramic material using as a starting material waste glass or recycled glass.

Accordingly, a first aspect of the present invention provides a ceramic material comprising a thermally hardened mixture of a major proportion of pulverised waste glass or recycled glass and a minor proportion of a bonding agent comprising an inorganic compound which is a chemically uncombined oxide or hydroxide of an alkali or an alkaline earth metal or a source of active alumina or any combination of two or more of said inorganic compounds.

Any type or colour of waste or recycled glass can be used, e.g. soda glass, borosilicate glass, lead glass, or glass contaminated with other metal compounds such as scrap television tubes and fluorescent light bulbs. Chopped glass fibre of any type can be added, and has the advantage of increasing the strength and toughness of the final ceramic. The glass is ground to a powder. For good results the major part of the powder particles should be substantially less than 3 mm in diameter. If glass fibre is used, it should preferably be reduced to a length of less than 5 mm, and should be substantially defibrillated.

To ensure that the powder can be pressed into a relatively dense compact, it is preferable that at least 10 mass % of the powder should consist of particles less than 50 μm in diameter. The glass ceramic can be made from powders of any reasonable particle size distribution, but in general a broad particle size distribution is preferable; the higher the proportion of particles below 50 μm in diameter, and the broader the size distribution of those particles below 50 μm, then the denser the packing. (It is well known to persons involved in manufacturing ceramics, concrete, polymer composites, coated paper etc. that optimum particle size distributions to give maximum packing can be readily calculated.) In general, the denser the packing of the glass particles, the stronger is the final ceramic product.

Ground glass of a suitable particle size distribution may be obtained by hammer milling, followed by a size separation at, for example, 200 μm or 50 μm. Alternatively, the waste glass or recycled glass may be roller milled to substantially less than 100 μm or 50 μm, or comminuted with a high pressure compaction roller mill to a size substantially less than 50 μm. It is also possible to use a roller mill or a ball mill, either in batch mode or in continuous mode (with or without an in-line particle size classifier) to give the required particle size distribution.

Preferably the bonding agent consists predominantly of calcium oxide or calcium hydroxide.

The ceramic material may be surface treated with paint, varnish, stain or metal deposition.

Alternatively, the material may be rendered hydrophobic by treatment with a silane, a siloxane, or an amine compound or by infiltration with a liquid asphaltic compound or bituminous pitch, which is then allowed to harden.

The ceramic material may be impregnated with a liquid resin which is then hardened to form a tough composite material. The ceramic material can be impregnated with the liquid resin, under vacuum if preferred. The resin is then hardened or polymerised to make a tough composite material. Examples of commercially available resins include unsaturated polyester/styrene resin, various acrylic and methacrylic resins, urethane resins, silicone resins, epoxy resins and the like.

The ceramic material may also incorporate a colouring pigment. The colouring pigment may be, for example, an iron oxide, a chromium compound, a rare earth compound, cobalt aluminate or a phthalocyanine pigment.

The ceramic material in accordance with the invention may advantageously be used to form floor, wall and roofing tiles. When the material is used to produce roofing tiles it is preferable to render the material hydrophobic by treatment with, for example, a silane, a siloxane, or an amine compound. It may be impregnated with a liquid asphaltic compound or bituminous pitch, under partial vacuum if desired.

The ceramic material may also be used to produce water- and heat-resistant wallboards, bricks, table tops, work tops, artistic and decorative items, engineering and electronic components and biological substrates.

A second aspect of the present invention provides a light weight porous insulating material comprising a ceramic material prepared by the process described in accordance with the first aspect of the invention.

It is preferable that the light weight material has a porosity of at least 40% by volume. At such porosities, the ceramic loses some strength, but is light in weight and has good heat and sound insulating properties. Therefore the light weight version of this novel ceramic can be used for insulation purposes, and as a component of light weight composite materials. On account of its porosity it can also be used as a biological support, e.g. as a medium for growing viruses or bacteria, or for supporting active molecular species in affinity chromatography .

A third aspect of the present invention provides a process for manufacturing a ceramic material comprising the steps of:

(a) preparing from a waste glass or recycled glass a glass powder having a broad particle size distribution and consisting predominantly of particles less than 3 mm. in diameter;

(b) mixing the glass powder prepared in step (a) with from 1 to 16 mass %, based on the mass of the glass powder, of a bonding agent comprising an inorganic compound which is an oxide or hydroxide of an alkali or alkaline earth metal or a source of active alumina or a combination of any two or more of said inorganic compounds; (c) adding to the mixture formed in step (b) from 5 to 24 mass % of water, based on the mass of glass powder;

(d) charging the damp powder formed in step (c) into a mould and compressing the mixture to form a desired shape; and

(e) exposing the compacted shape formed in step (d) to saturated steam at a temperature in the range of from 70 °C to 200°C for a time of from 15 minutes to 48 hours.

The source of active alumina advantageously comprises alumina trihydrate or metakaolin. The alumina reacts with the glass and the other metal hydroxides to modify the cementitious material (calcium sodium silicate) which bonds the glass particles together. Such alumina-modified cements can be more durable than simple calcium sodium silicates with respect to chemical attack by certain common acids and salts.

In step (b) , the bonding agent preferably consists predominantly of calcium oxide or calcium hydroxide. As well as calcium oxide and hydroxide, other metal hydroxides which react with glass at elevated temperatures can be used, for example sodium hydroxide, potassium hydroxide, magnesium oxide or hydroxide. They are preferably used as a blend with calcium oxide or hydroxide. If a source of active alumina is used, it may be present in a proportion of from 0 to 50 mass %, based on the mass of calcium oxide or calcium hydroxide in the bonding agent .

If the bonding agent consists predominantly of calcium hydroxide, it is preferably present in a proportion of from 2 to 12 mass %, based on the mass of glass powder, and the proportion of water added is in the range of from 5 to 20 mass %, based on the mass of glass powder. Most preferably, the bonding agent is present in a proportion of from 5 to 10 mass %, based on the mass of glass powder, and the proportion of water added is in the range of from 5 to 12 mass %, based on the mass of glass powder.

If the bonding agent consists predominantly of calcium oxide, it is preferably present in a proportion of from 1.5 to 9 mass %, based on the mass of glass powder, and the proportion of water added is in the range of from 5 to 24 mass %, based on the mass of glass powder. Most preferably, the bonding agent is present in a proportion of from 4 to 7.5 mass %, based on the mass of glass powder, and the proportion of water added is in the range of from 5.5 to 15 mass %, based on the mass of glass powder.

The powdered glass is mixed thoroughly with the powdered bonding agent and water. The water content must be sufficient to ensure that a relatively strong green compact is produced after the powder mixture is pressed in the mould. The water content must not be so great that a significant quantity of water is squeezed out during the compaction process. This technology is well known to ceramic engineers. It is not generally necessary to use additional binding agents, but if required, such binding agents (for example hydroxy methyl cellulose, carboxy methyl cellulose, acrylic latex or other polymer latex) can be incorporated into the mixture to give the required degree of green strength.

The dry powders may be pre-mixed, and the water added later, or all the ingredients may be mixed in at the same time. Suitable mixing equipment is well known to those familiar with ceramic processing, and includes hammer mills, screw extruders and various types of pelletisers. After mixing, the damp powder may be screened (sifted) through a suitable screen in order to break up large agglomerates.

The damp powder mixture is pressed into a mould. The mixture is advantageously compressed to form a desired shape at a pressure in the range of from 0.1 to 200 MPa depending on the required density of the final ceramic product.

During pressing, the air in the mould can be evacuated by a vacuum pump if required. This is particularly useful with fine powders at the higher moulding pressures.

The compression may be uniaxial (for example as in a cylinder and piston arrangement) , or isostatic (for example when the powder or initial compact is encased in a flexible membrane and subjected to hydraulic pressure in a closed vessel), or a combination of the two techniques.

The green compact is removed from the mould and placed in substantially saturated steam at a temperature between 70°C and 200°C. For temperatures above 100°C, it is necessary to increase the pressure of the steam, for example by using an autoclave. If the temperature of the steam is to be 150°C the pressure must be increased to approximately 5 atm. , and if the temperature is to be 180°C the pressure must be increased to approximately 10 atmospheres.

The residence time in steam required to convert the green compact into a hard ceramic is within the range 15 minutes to 48 hours. The longer times within this range are required at the lower temperatures, and the shorter times are required at the higher temperatures. Preferably the compacted shape is exposed to saturated steam at a temperature in the range of from 80°C to 125°C for a time of from 2 to 5 hours, since this gives a strong ceramic economically and with a reasonable residence time. At these temperatures, it is possible to use low grade waste heat as the source of steam.

During the steaming process, the added metal hydroxides and alumina (if present) react with the glassy silica and silicate species, and also with other oxides (calcium, aluminium, borate, lead etc) in the surface layers of the glass particles. A strong calcium-sodium-aluminosilicate cementitious material is formed in si tu, binding the glass particles together.

The following Examples are intended further to clarify and illustrate the invention, but should not be considered to limit the scope thereof. In the following Examples all recipes are given in terms of mass parts, unless otherwise stated.

EXAMPLE 1

90 parts of "sand", made by crushing glass bottles so that all particles are less than 3 mm diameter, was mixed with 10 parts of fine glass powder, obtained by separating the sub-150 micrometer fraction from samples of crushed glass treated in a hammer mill. The mixture was thoroughly blended with 7 parts of calcium hydroxide powder and 8 parts of water. About 10 gram of the damp mixture was pressed in a 31.5 mm diameter die with a pressure of 224 MPa. The compacted mixture, in the form of a disc, was removed from the die, placed in an autoclave, and steamed at 135°C for 1 hour. After removal from the autoclave, the cured disc was allowed to equilibrate with the atmosphere for at least 24 hours .

EXAMPLE 2

As Example 1, except 12 parts of calcium hydroxide were used.

EXAMPLE 3

As Example 1, except that the calcium hydroxide was replaced by 8 parts of sodium hydroxide.

The results of examples 1, 2, 3 are shown in Table 1 below.

Good, strong ceramic discs were produced. The bending strength of the discs was measured by the following procedure, which is known to those familiar with ceramics technology as the "ball-on-ring method".

In the 'ball-on-ring¹ method, a 31.5 mm diameter ceramic disc was placed co-axially on a ball race whose diameter (measured across the highest point of the balls) was 26 mm. A ball, 5 mm in diameter, was pressed down on the centre of the disc and the force increased until the disc cracked across or broke. The force required to break the specimen was recorded and used to calculate the bending strength. Two calculations, based on different breakage models by Timoshenko and de With respectively, were used and they gave results for the bending strength which differed by only a few percent from each other. A CK 10 test machine was used, manufactured by Engineering Systems, UK.

Table 1

EXAMPLE 4

80 parts of fine glass powder, obtained by separating the sub-150 micrometer fraction from samples of crushed glass treated in a hammer mill, was mixed with 6.4 parts of powdered calcium hydroxide and 10 parts of water. About 8 gram of the damp mixture was pressed in a 31.5 mm diameter die with a pressure of 14 MPa. The compacted mixture was removed from the die, placed in an autoclave, and steamed at 135°C for 1 hour.

After removal from the autoclave, the cured disc was allowed to equilibrate with the atmosphere for at least 24 hours .

The above procedure was repeated at different die pressures of 56 MPa and 224 MPa.

EXAMPLE 5

As Example 4, except that 2.4 parts of metakaolin powder was added to the mixture of glass, calcium hydroxide and water. The results of Examples 4 and 5 are shown in Table 2 below.

Good, strong ceramic discs were produced. The ceramic had a pleasing, smooth appearance. Bending strength was measured by the ball-on-ring method.

Table 2

EXAMPLE 6

As Example 4 except that the mixture was compacted in the die at a pressure of 0.15 MPa, thus producing a green disc of low density. The compacted mixture was removed from the die, placed in an autoclave, and steamed at 135 °C for 1 hour .

The ceramic foam was sufficiently strong to handle, it had a density of 910 kg m^"3, and a porosity of 67 volume % EXAMPLE 7

80 parts of fine glass powder, obtained by separating the sub-150 micrometer fraction from samples of crushed glass treated in a hammer mill, was mixed with 6.4 parts of powdered calcium hydroxide and 10 parts of water. About 8 gram of the damp mixture was pressed in a 31.5 mm diameter die with a pressure of 56 MPa. Discs of compacted mixture was removed from the die, placed in an autoclave, and steamed at 125 °C for either 1 hour or 2 hours.

EXAMPLE 8

As Example 7 except that 2.4 parts of metakaolin powder was added to the mixture of glass, calcium hydroxide and water, and the compacted disc was steamed at 125 °C for 1 hour.

The results of Examples 7 and 8 are shown in Table 3 below. Bending strength was measured by the ball-on-ring method.

Table 3

EXAMPLE 9 80 parts of fine glass powder, obtained by separating the sub-150 micrometer fraction from samples of crushed glass treated in a hammer mill, was mixed with 6.4 parts of powdered calcium hydroxide and 10 parts of water. About 8 gram of the damp mixture was pressed in a 31.5 mm diameter die with a pressure of 56 MPa. Discs of compacted mixture was removed from the die, and steamed in a lidded vessel at 100 °C - i.e. at atmospheric pressure - for various lengths of time.

After removal from the steam vessel, the cured disc was allowed to equilibrate with the atmosphere for at least 24 hours .

Results for the ball on ring bending strength are shown in Table 4 below.

Table 4

EXAMPLE 10

80 parts of fine glass powder, obtained by separating the sub-150 micrometer fraction from samples of crushed glass treated in a hammer mill, was mixed with various proportions of powdered calcium hydroxide (viz. 2, 4, 8 and 16 mass % calcium hydroxide based on the mass of glass) . 10 mass % of water, based on the total mass of glass and calcium hydroxide, were added. About 8 gram of the damp mixture was pressed in a 31.5 mm diameter die with a pressure of 56 MPa. Discs of compacted mixture was removed from the die and steamed in a lidded vessel at 100 °C - i.e. at atmospheric pressure - for 4 hours.

After removal from the steam vessel, the cured disc was allowed to equilibrate with the atmosphere overnight.

Results for the ball on ring bending strength are shown in Table 5 below.

Table 5

EXAMPLE 10

80 parts of fine glass powder, obtained by separating the sub-150 micrometer fraction from samples of crushed glass treated in a hammer mill, was mixed with 5.6 parts of powdered calcium hydroxide and 10 parts of water. About 8 gram of the damp mixture was pressed in a 31.5 mm diameter die with a pressure of 56 MPa. Discs of compacted mixture were removed from the die, and steamed in a lidded vessel at 80°C for various lengths of time.

Results for the ball on ring bending strength are shown in Table 6 below.

Table 6

Claims

CLAIMS :

1. A process for manufacturing a ceramic material comprising the steps of:

(a) preparing from a waste glass or recycled glass a glass powder having a broad particle size distribution and consisting predominantly of particles less than 3 mm. in diameter; (b) mixing the glass powder prepared in step (a) with from 1 to 16 mass %, based on the mass of the glass powder, of a bonding agent comprising an inorganic compound which is a chemically uncombined oxide or hydroxide of an alkali or alkaline earth metal or a source of active alumina or a combination of any two or more of said inorganic compounds;

(c) adding to the mixture formed in step (b) from 5 to 24 mass % of water, based on the mass of glass powder;

(e) exposing the compacted shape formed in step (d) to saturated steam at a temperature in the range of from

70 °C to 200°C for a time of from 15 minutes to 48 hours.

2. A process according to claim 1, wherein the source of active alumina comprises alumina trihydrate or metakaolin.

3. A process according to claim 1 or 2, wherein, in step (b) , the bonding agent consists predominantly of calcium oxide or hydroxide.

4. A process according to claim 1, 2 or 3, wherein a source of active alumina is present in a proportion of from 0 to 50 mass %, based on the mass of calcium oxide or calcium hydroxide in the bonding agent.

5. A process according to claim 3, wherein the bonding agent consists predominantly of calcium hydroxide and is present in a proportion of from 2 to 12 mass %, based on the mass of glass powder, and the proportion of water added is in the range of from 5 to 20 mass %, based on the mass of glass powder.

6. A process according to claim 5, wherein the bonding agent is present in a proportion of from 5 to 10 mass %, based on the mass of glass powder, and the proportion of water added is in the range of from 5 to 12 mass %, based on the mass of glass powder.

7. A process according to claim 3, wherein the bonding agent consists predominantly of calcium oxide and is present in a proportion of from 1.5 to 9 mass %, based on the mass of glass powder.

8. A process according to claim 7, wherein the bonding agent is present in a proportion of from 4 to 7.5 mass %, based on the mass of glass powder, and the proportion of water added is in the range of from 5.5 to 15 mass %, based on the mass of glass powder.

9. A process according to any one of claims 1 to 8, wherein the mixture is compressed to form a desired shape at a pressure in the range of from 0.1 to 200 Mpa.

10. A process according to claim 9, wherein the compression is uniaxial or isostatic, or a combination of the two techniques.

11. A process according to any one of claims 1 to 10, wherein the compacted shape is exposed to saturated steam at a temperature in the range of from 80°C to 125°C for a time of from 2 to 5 hours.

12. A ceramic material prepared by the process claimed in claim 1.

13. A ceramic material according to claim 12, wherein the bonding agent referred to in claim 1 consists predominantly of calcium oxide or hydroxide.

14. A ceramic material according to claim 12 or 13, wherein the material is surface treated with paint, varnish, stain or metal deposition.

15. A ceramic material according to claim 12,13 or 14, wherein the material is rendered hydrophobic by treatment with a silane, a siloxane or an amine compound, or by infiltration with a liquid asphaltic compound or bituminous pitch, which is then allowed to harden.

16. A ceramic material according to any one of claims 12 to 15, wherein the material is impregnated with a liquid resin which is then hardened to form a tough composite material.

17. A ceramic material according to any one of claims 12 to 16, which also incorporates a colouring pigment.

18. A ceramic material according to claim 17, wherein the colouring pigment is an iron oxide, a chromium compound, a rare earth compound, cobalt alu inate or a phthalocyanine pigment.

19. A light weight porous insulating material comprising a ceramic material according to any one of claims 12 to 18.

20. A light weight porous insulating material according to claim 19, wherein the porosity of the material is at least 40 % by volume.

21. A ceramic material as hereinbefore described with reference to the accompanying examples.

22. A process for manufacturing a ceramic material as hereinbefore described with reference to the accompanying examples.