GB2348875A - Lightweight composites containing cenospheres and a cementing agent or thermoplastic polymer - Google Patents

Abstract

Lightweight composites which may possess thermally insulating, fireproofing and/or sound proofing properties, comprise cenospheres and a cementing agent, for instance a sodium silicate solution, magnesium oxychloride, calcium sulphate, or Portland cement. Examples of their uses include as protective coatings or artificial pumice, for sanding and polishing metallic substrates and for incorporation with chemical fertilizers. Other composites comprise cenospheres and a thermoplastic polymer, for instance polystyrene, polymethyl methacrylate, polyvinyl alcohol, polyvinyl acetate or polyethylene, and may possess insulating and/ or decorative properties. In addition, table tennis bats may be made from the composite. The composites may also include exfoliated vermiculite or fly ash.

Description

LIGHTWEIGHT CERAMIC COMPOSITES (LWCC) INTRODUCTION Fireproofing of substrates, particularly metallic as in steel structures in the building industry has a long history. Essentially in the event of fire in the building, the steel structures must be prevented from reaching a temperature of above 550 C. This is to prevent the growth of grains to larger sizes, whose lower surface area to mass ratio would result in the weakening of the steel structures. The result of this weakening in the event of fire would be the collapse of the building at temperatures well below the steel's melting point.

Many industries worldwide specialise in fireproofing materials, which are for instance sprayed on the steel structures or applied as boards to provide protection against fire.

The need to keep the costs down has resulted in the use of recycled cellulose based materials as well recycled synthetic organic polymers. Gypsum, Portland cement and exfoliated Vermiculite are often used. The main disadvantage associated with most existing composites is the presence of carbonaceous organic constituents. In the event of fire and with reducing concentrations of oxygen, toxic gases such as carbon monoxide and hydrogen cyanide would be evolved. The possibility of evolution of other toxic, including small hydrocarbon molecules are also very likely as well. In many outbreaks of fire in such buildings, which are fireproofed, the occupants have died as a consequence of inhalation of toxic fumes.

ESSENTIAL TECHNICAL FEATURES OF THIS INVENTION In a first aspect this invention provides lightweight ceramic composites (LWCC), which may be used for structural purposes (e. g. the production of bricks and panels), for the construction industry. For this purpose a typical composition, preparation conditions and properties are given in examples below.

Example 1.1.

Sodium Silicate (00125) 60.0 g Cenosphere 30.0 g (Sodium silicates obtained from Crosfield Chemicals Ltd, Cenosphere from Fillite Ltd., Vermiculite from Mandoval Ltd., Magnesia from Delaniin Ltd, and Pulverized Fuel Ash, from Ash Resources Ltd.) Curing of the above was 24 hours at 50 C followed by a further 24 hours at 125 C.

Mechanical properties were recorded as follows: Modulus of Rupture (MOR) 4-6 MPa Modulus of Elasticity (Young's Modulus) E 0.4-0.6 GPa Density < 0.50 gcm~3 The resulting paste was placed in a lubricated mould and cured under various times and temperatures, in order to make samples for mechanical testing.

This invention also provides a highly thermally insulating material, which may be applied as a fireproof protection of metallic and non-metallic substrates, for example in fireproofing steel structures of the buildings.

The entire constituents of this and the following invented compositions (when as fireproofing composites) are inorganic in nature non-carbonaceous and non-combustible.

Consequently in the event of fire no toxic fume would be evolved from these materials.

When using sodium hydrogen carbonate as a minor constituent of the composition, at just below 300 C carbon dioxide and water are evolved, which will retard and cool down the fire respectively.

For this aspect of the invention, the compositions would be typically as given in examples below: Example 1.2.

Cenosphere 40.0 g Pulverized Silica Gel* 2.0 g Sodium Silicate (0079) 30.0 g *as prepared by the inventor Example 1.3.

Cenosphere 60.0 g Sodium Silicate (0079) 30.0 g Methanol 5.0 ml The above was moulded and placed in a sealed plastic bag, containing methanol (5.0 ml), and cured at 50 C during 24 hours.

Example 1.4.

Cenosphere 60.0 g Vermiculite (exfoliated flakes) 30.0 g Sodium Silicate (0079) 120.0 g The solid and dry constituents are thoroughly mixed. In the larger scale production, the dry constituents can be bagged and stored. In examples 5 and 6, upon addition of sodium silicate solution and a thorough mixing, initially a very mobile consistency is observed, however the composition will set into a solid material that can be held at 90 within one minute. The material however will remain workable for about 30 minutes.

Furthermore the optional inclusion of Portland cement in the composition is found to be convenient in some cases. Although not an essential and unique ingredient to provide room temperature curing, however it is a convenient source of silica, which allows room temperature setting by increasing the silica to sodium oxide ratio. Two examples of such compositions are given below: Examnie 1.5.

Cenosphere 40.0 g Portland Cement 20.0 g Sodium Silicate (0079) 100.0 g Example 1.6.

Cenosphere 40.0 g Portland Cement 20.0 g Sodium Hydrogen Carbonate 1.0 g Sodium Silicate (0079) 100.0 g Where sodium hydrogen carbonate is used, whilst serving as a setting agent, at temperatures above 300 C, carbon dioxide and water would be evolved to retard and cool down the fire.

The main advantage associated with the compositions as in examples: 2,5 and 6 are their ability to set at ambient temperatures, which is an important requirement when providing protection to steel structures of buildings.

Considering the composition in example one, the original density of the material when just set was 0.72 g cm~3, and when fully cured (i. e. allowing four weeks for the water content of the LWCC to reach equilibration), was recorded at 0.6g cm~3. Portland cement is used as a cheap source of silica to alter the silica to sodium oxide ratio in favor of silica and hence causing room temperature curing, as found out by the inventor. Long-term additional strength is expected as pozzolanic properties of cenosphere in the alkali medium take place.

These LWCC prepared as described herein are also used to provide thermal insulation of water pipes and containers. Thermal conductivity measurements obtained from ceramic samples prepared according to the above examples have shown typical values of around 0.1-0.004 W/M/K (thermal conductivity measurements were obtained using'Lee's Discs Method'). These recorded measurements are amongst the lowest recorded for any material.

I the second aspect of this invention, LWCC have been prepared from mixtures of Portland cement as a permanent binding agent, and Cenosphere, as the main filler.

The density of the set material, cured at room temperature has been recorded to be within the range of 0.5-0.75 gcm-3, four week after preparation, mainly depending on the percentage of the much heavier Portland cement in the composition. These LWCC benefits from the closed pores of cenosphere particles, which results in a material that would also remains afloat permanently, so long as the total saturated weight in water is kept below 1.0 gcrri 3. For this purpose the use of cement has been and must be kept to the minimum possible quantity. Although not as strong as normal concrete, either under tension or compression, this material is roughly ten times lighter.

Compositions based on the above also benefit from being a fireproofing composite for the structural protection of buildings. This includes provision of fireproofing to the steel structures in the buildings, or wherever fire protection of steel structures may be required.

For this particular purpose although not an essential ingredient, exfoliated vermiculite as well as other filler materials with fireproofing properties may be included in the composite. Furthermore inclusion of Pulverized Fuel Ash (Fly Ash), which is the main waste product of burning of coal in the coal burning power stations, provides denser, heavier, stronger, and less expensive composites, but with reduced fireproofing capabilities.

The variations of quantities of various ingredients making up the finished composites have a wide spectrum. Only as examples of workable composites, a few formulations are given below: Example 2.1.

Portland Cement 6.0 g Cenosphere 14.0 g Water 15.0 ml Portland cement and cenosphere were mixed for two minutes, using an electric mixer.

Upon obtaining a homogenous consistency, water was added in the required quantity, followed by a thorough mixing, until a homogenous consistency was obtained. This step took less than three minutes to achieve. The paste obtained, was directly applied to a steel substrate. Some quantities were placed in plastic mould. These were left at room temperature to cure. Samples were studied four days after preparation. The formulation as given above, which uses a low ratio of cement to cenosphere, would result in a material, that once set, floats on water permanently.

Example 2.2.

Portland Cement 15.0 g Cenosphere 11. 0 g Exfoliated Vermiculite 4.0 g Water 25.0 ml Composition as given in example 2.2 with much variation in the quantities of each ingredient has been formulated as a fireproofing composite for steel structural protection and with a dry density of below 0.65 g cm 3. Water is added to the thoroughly mixed dry mixture, which if required in industrial or on a much larger scales, can be prepared and stored in appropriate bags. Upon the addition of water and mixing, a paste with workable consistency results, which were applied on various substrates, including steel, or moulded, and allowed to set at room temperature. Four weeks were allowed for water in the mix to reach equilibration.

In the third aspect of this invention although strong LWCC have been prepared by the inventor, using sodium silicate with cenosphere and/or cenosphere with added fly ash, however due to a high sodium oxide ratio of soluble sodium silicates (whenever used as the cementing agent in LWCC), two major disadvantages may be encountered. The LWCC made with sodium silicate solutions in prolonged immersion, may eventually dissolve in water, resulting in the disintegration of the composites in water over time.

Furthermore, the high alkali ratios of these invented LWCC, might reduce their effective fireproofing properties above 1000 C, as the these composites will start to melt at around 1200 C. Further experiments carried out by the inventor however, have shown that higher temperatures of curing results in prolonged stability of these composites in water.

For instance upon curing to 150 C, samples of cenosphere and sodium silicate (0079, have kept their integrity in water for over 72 hours. Various curing regimes can be employed to obtain the required porosity. A'one-stage curing'at high temperatures, e. g.

120 C, would yield a highly porous composite. On the other hand a'one-stage curing at lower temperatures, e. g. 50 C, would result in a very smooth and compact composites, though much longer periods must be allowed for all the water to be driven out. However a'Multi-stage curing', at various temperatures have shown to be the most effective procedures to cure composite samples to an eventual temperature of 150 C.

POSSIBLE CURING REGIMES A. When requiring a porous LWCC for application as e. g. artificial pumice (for feet): 4 hours at 80 C, followed by 2 hours at 150 C, has proven effective.

B. When requiring a porous LWCC for application as e. g. artificial pumice (for hands): 8 hours at 50 C, 3 hours at 80 C and 2 hours at 150 C, has proven effective.

Furthermore for application as fireproofing LWCC, curing procedure (A) could be used.

For preparation of manicure and/or pedicure LWCC, curing procedure (B) could be used.

However the most important aspect of these invented LWCC has been that, when fully cured, samples of sodium silicate based LWCC were placed in a solution of magnesium chloride. Soluble sodium silicates reacted with magnesium chloride to form insoluble and thermally stable magnesium silicates, as given by the reaction below. The by-product of this reaction would be a soluble salt of sodium, (here sodium chloride), which will wash out of the composite, when immersed in water.

Here the LWCC can also be of any shape or size as they can be moulded prior to curing.

It is also possible to prepare a much larger sample, which can then be cut to the required shapes or sizes. Although the percentage of each component of the composition may vary, however the following formulations are presented below as examples.

Example 3.1.

Sodium Silicate solution (0079) 150.0 g Cenosphere 75.0 g After a thorough mixing, the LWCC is placed in a mould and cured, as described above. These composites could have potential applications as Artificial Pumice, suitable for palm of hands and sole of feet, as well as Manicure and/or Pedicure Abrasive Stones, or effective Lightweight Fireproofing Ceramics, which would not disintegrate in the presence of water. These LWCC are also entirely inorganic. A four-month trial of these composites as artificial pumice is successfully completed. A One-month continuous immersion of these composites in water have not resulted in loss of strength or disintegration, hence providing effective evidence for their potential application as e. g. artificial pumice.

Example 3.2.

Sodium Silicate solution 200.0 g Cenosphere 80.0 g Exfoliated Vermiculite 10.0 g Cenosphere and vermiculite were mixed first. Sodium silicate solution was then added, followed by a thorough mixing by an electric mixer. Upon obtaining a creamy consistency, the paste was cured, as described above. The composites are then immersed in a magnesium chloride solution, as described above. Conversion of sodium silicate to magnesium silicate would enhance the tolerance for fireproofing at higher temperatures.

Example 3.3.

Sodium Silicate solution 200.0 g Cenosphere 80.0 g Pulverized Fuel Ash 40.0 g The LWCC as given in example 3.3, would be denser, darker, stronger under compression, and cheaper to manufacture. However the fireproofing and insulation properties would suffer.

In the fourth aspect of this invention the inventor has used Sorbel cement (with properties such as non-reflection of sound), to invent LWCC with low density, fireproofing and insulating abilities but also with soundproofing properties. Cenosphere has been used as the main filler.

Combination of cenosphere as a lightweight material filled with carbon dioxide and magnesium oxychloride, (the formula below), (magnesium oxysulphate shows a similar property), has produced a lightweight, totally inorganic and insulating material with superior sound proofing features.

3 M O. M CI2. 11HO.

When produced, cenospheres as hollow spherical particles of 0.5-250 p. m in diameter are filled with CO2 (g). The best sound insulators are the gases, however amongst all the gases, carbon dioxide allows the passage of sound with most resistance. The reference below provides a comparisonl.

Carbon Dioxide 267 meter per second Air 343 meters per second Water 1469 meters per second Iron or Steel 5121 meters per second 1. The New York Science Desk Reference, Macmillan, p. 290-291,1995.

By using moulds and dyes or paint, artistic and decorative features can serve as an additional bonus. Addition of other inert materials as fillers may be possible, e. g. magnesium silicate, exfoliated vermiculite, etc. These LWCC, with a density of around half that of water, are also entirely inorganic and effective fireproofing and insulating composites as well.

The quantity of each material making up the composition of these LWCC have been based on the molar ratios of each component as given by the formula (3MgO : 1 Mi : 11 H20), and also the need for additional water to wet the cenosphere, as well as impurities of the compounds, particularly magnesia, (which is industrial grade).

Dry mixing of magnesia, cenosphere and other dry materials as fillers, (if any), were followed by the addition and thorough mixing with magnesium chloride solution with added water, prior to moulding or application on various substrates such as hard board, plasterboards, concrete surfaces, metallic substrates, or in moulds, etc. Examples of workable compositions are presented below.

Example 4.1.

Industrial grade magnesia (97%) 15.0 g Magnesium chloride solution (20% W/V) 50.0 ml Cenosphere 30.0 g Water 20.0 ml The addition and thorough mixing with water followed dry mixing of magnesia and cenosphere. Magnesium chloride solution was added last, which was followed by further mixing. The composite was then applied on various substrates, such as hard board, plasterboards, concrete surfaces and metallic substrates. Samples were also prepared in plastic moulds. The paste was then allowed to cure at room temperature.

Example 4.2.

Industrial grade Magnesia (97%) 15.0 g Cenosphere 25.0 g Exfoliated Vermiculite 5.0 g Magnesium Chloride solution (20% W/V) 50.0 ml Water 25.0 ml Following the mixing of the dry components, water and magnesium chloride solution were added respectively, followed by further mixing. The resulting paste was then placed in plastic moulds, and was then allowed to cure at room temperature. The paste can also be applied on a steel substrate for fire protection.

In the flfth aspect of this invention, the inventor has prepared LWCC with sodium silicate as the cementing agent. With this mixture various chemicals have been incorporated, which are required to leach out at a very slow rate. Within the chemical industry many chemicals as reacting agents need to be introduced to the reaction medium at a very slow rate. This aspect of the invention makes it possible for chemical reagents to be incorporated into a ceramic and porous composition and to enter the reaction medium under a controlled and slow manner as they leach out of the porous LWCC that float on the reaction medium. Although initial trials have been based on the slow leaching of chemical fertilizers from LWCC, however incorporation of any chemicals for this aspect of the invention is quite feasible. Since the use of sodium silicate in the aqueous medium is not desirable, as explained before, its conversion to insoluble magnesium silicate for this aspect of the invention has been carried out. However, as the mixing constituents reached a homogeneous consistency, they were forced through a perforated substrate and as pellets were dropped into a bath of magnesium chloride solution. This caused an immediate hardening of the LWCC, which was due to the conversion of sodium silicate to magnesium silicate. The LWCC pellets with incorporated chemicals were then removed and allowed to dry at room temperature, (or elevated temperatures if this would not chemically damage the composition of the incorporated chemical). Time of reaction in the magnesium chloride solution would depend on the size of the pellets and the concentration of the magnesium chloride solution. The entirely mineral based and inorganic composition of LWCC itself would mean that it would not take part in any reaction unless the reaction medium is highly corrosive and would result in the chemical digestion of the LWCC. The number of chemicals that can potentially be used in this system is potentially enormous. Samples made with ammonium nitrate have been prepared and are presented as examples below.

Example 5.1.

Sodium Silicate solution (0079) 15.0 g Cenosphere 7.0 g Ammonium Nitrate 5.0 g Reaction of the above results in the quick evolution of ammonia. It was therefore essential that upon obtaining a homogenous consistency, the paste as drops, were introduced to the magnesium chloride bath.

In the sixth aspect of this inventions LWCC have been prepared by the inventor using Calcium Sulfate, (Gypsum, or Plaster of Paris), as the cementing agent. Gypsum is known and applied as a cheap fireproofing and thermally insulating material on its own.

However incorporation of cenosphere or cenosphere and exfoliated vermiculite to reduce density and to enhance fireproofing and insulating properties have been the main objectives of the inventor in this aspect of the invention. Although very different formulation may be possible, however examples of workable gypsum based LWCC are presented below. The reaction, which results in the hardening of gypsum, is as given below.

Example 6. 1.

Plaster of Paris 80.0 g Water 50.0 ml Density The composition above was prepared as reference. A sample in a plastic mould was prepared.

Example 6.2.

Plaster of Paris 40.0 g Cenosphere 25.0 g Water 50.0 ml Density Plaster of Paris and cenosphere were mixed until a light grey homogenous mixture was obtained. A good consistency upon thorough mixing with water was then obtained.

Samples were prepared in a plastic mould.

Example 6.3.

Plaster of Paris 50.0 g Cenosphere 25.0 g Exfoliated Vermiculite 20.0 g Water 50.0 ml Density Mixing was carried out as in example 6.2.

All compositions in the above examples gave off heat of hydration according to the reaction as given above, and all were hard to the touch within 30 minutes. Setting was quickest in example one, and slowest in example three. These LWCC have smooth surfaces and are very soft to the touch. Use of dyes or paints are applicable in the same manner as applied on surfaces of plasters on walls.

In the seventh aspect of this invention lightweight composites (LWC), have been prepared using a large spectrum of thermoplastic polymers as binding agents and cenosphere, as the inert filler. It has been shown that the density of these materials to be well below 0.5 gcrri 3. The moderately high compressive strength of these materials (4-8 MPa), has made it possible for their preparation as very strong though extremely light decorative objects, which may find use in making engineering models and artifacts, and as impact absorbers in automobiles etc. Although not fireproofing, however these LWC have recorded to be amongst the best thermally insulating composite materials. Thermal conductivity measurements using'Lee's Disc'method, has shown a composite made from cenosphere and polyvinyl acetate to be 0.0093 WM lK-l, which is amongst the lowest thermal conductivity measured by any material.

Except when polyvinyl alcohol was used, all composite float on water, permanently.

All of the made composites can be cut and pierced with sharp objects and drilled without resulting in any damage to the composite.

Composites from cenosphere and polymethyl metacrylate have shown higher compressive strengths (6-8 MPa), and potential applicability as durable and mild abrasive materials. Similar, but not as strong products with polystyrene have also been prepared.

Relative to their very low densities, these composites have shown high compressive strengths, e. g. a composite of cenosphere and polyvinyl acetate tolerated a compressive load of 90 Kg CM before failing. They are easily prepared into any shapes or sizes as may be required. These composites can be cut and sawed, drilled and pierced with sharp objects such as pins, without resulting in any breakage or cracks.

PMMA, and PS. LWC presented slight difficulties in sample preparation due to a rapid loss of the solvent. However, these LWC shown very good properties in terms of high compressive strength, low densities and durability upon abrasion, the former a subject that has been pursued as a separate study.

LWC of PVA, on the other hand were prepared from readymade water based emulsions, resulting in homogenous pastes and composites. Safety and ease of preparation, as well as lowest recorded densities as well as impact absorption properties, has given this composite, distinct advantages. Furthermore with incorporation of dye, lightweight and decorative tiles of 0.5 cm thickness have been prepared. Considering their lightweight and good thermal insulation properties, they have a good potential to be applied as decorative and insulating tiles. These composites have already been used to invent novel table tennis bats, due to their ease of application and cheapness.

Polyvinyl alcohol LWC, although otherwise very similar in properties to polyvinyl acetate LWC, however suffers from total disintegration once immersed in water. This distinct disadvantage renders its use in moist environment undesirable.

Polyethylene LWC has shown a good compressive strengths and thermal insulation as well. A major advantage of this LWC would be the lower cost of the polymer as compared to PMMA. Preparation of this composite from the molten (soften) polymer has made its preparation via injection moulding a desirable method. However due to abrasive nature of cenosphere, suitable steel alloy (s) with higher resistance to abrasion would be required. Very strong and thin objects have been prepared.

THERMAL CONDUCTIVITY MEASUREMENTS OF THE LWCs Composition Heat Loss, H (Wm Thermal Conductivity, K (WM-'K) Cen+ PMMA 6.156 0.0069 Cen + PS 6.782 0.0085 Cen + PVA 7.636 0.0093 Cen + PE 9.427 0.0103 Cen + PVAL 7.072 0.0986 Ver + PVA 10.384 0.1139 Cen + Ver + PVA 5.982 0.0103 Cen + Ver + PMMA 9.025 0.0402 Where, Cen is Cenosphere, Ver is Exfoliated Vermiculite, and PMMA is Polymethyl Methacrylate PS is Polystyrene, PVA is Polyvinyl Acetate, PVAL is Polyvinyl Alcohol, and PE is Polyethylene.

Although the quantities of cenosphere and thermoplastic composites can vary within a wide range, however examples of workable composites that have been prepared and examined are given below: Example 7.1. Composite made from Polyvinyl Alcohol and Cenosphere.

A 20% W/V solution of polyvinyl alcohol (PVA, MW 125000, BDH) was prepared, (50 . 0 g of the polymer in 450 ml of water).

To 30. g of cenosphere 60.0 g of PVA solution was added. Upon stirring, a runny paste resulted which was place in PS. moulds, and left to cure at 55 C for 24 hours. The samples were further cured at 110 C for 24 hours. Samples were very smooth to the touch, and very strong under compression upon cooling to room temperature. The density by weighing a known volume was recorded at 0.43 gcm-3.

Upon immersion in water, within a minute the sample disintegrated completely.

Example 7.2. Composites made from Polvvinvl Acetate, (PVA) and cenosphere.

The polymer was used as ready made emulsion. Upon drying at 110 C during 24 hours, a 60% weight loss attributed to water was recorded.

To 30.0 g of cenosphere 30.0 g of PVA was added. The mixture was stirred until a creamy and homogenous consistency was achieved. The almost runny paste was poured in polystyrene moulds and placed in an oven at 55 C for 24 hours. The sampled were then demoulded and placed in an oven at 110 C to further cure during 12 hours. Upon cooling to room temperature samples were very strong under tension, and had a homogenous and smooth surfaces. A 1.0 cm3 sample was weighed at 0.3242 g; hence a density of 0.32 gcm~3 was recorded. Upon immersion in water no disintegration was observed. Upon drying the sample at 110 C, no weight loss was recorded. The sample floats on water, permanently.

Example 7.3. Composites made from Polystyrene (PS) and Cenosphere.

A 40% W/V solution of polystyrene in chloroform was prepared by dissolving 100. Og of the polymer in 400 ml of chloroform. Stirring of less than 30 minutes was required, whilst having the flask covered by a PE thin film.

To 30.0 g of cenosphere 60.0 g of PS solution was added and mixed in the fume cupboard. The viscous paste was placed in a PE mould and left in the fume cupboard to cure at room temperature for 24 hours. The samples were then demoulded, and placed in an oven at 110 C to remove the trapped solvents for 12 hours. Sampled were removed from the oven and placed in a desiccator to cool.

The density measurements were carried out by weighing a known volume of the sample and it was recorded at 0.46 gcm~3, i. e. 1.836 cm-3 weighed 0.8502 g. The sample floats on water with no signs of disintegration.

Example 7.4. Composites made from Polymethyl Metacrvlate and Cenosphere.

A 45% W/V highly viscous solution of the polymer in chloroform was prepared by dissolving 100.0 g of the polymer in 450 ml of chloroform during a 12 hours stirring whilst having the flask covered by a PE thin film.

A composite was prepared by mixing 30.0 g of cenosphere and 40.0 g of PMMA. A very tough and sticky paste was prepared and as solvents were being lost during the preparation, the paste was quickly placed in P. E mould and left in the fume cupboard to cure at room temperature for 24 hours. To remove trace quantities of solvent, a further 24-hour curing at 110 C was followed.

Upon cooling to room temperature, this composite has shown to be very strong under tension, cuts with a hand saw with ease without resulting in inward cracks. The texture is very homogenous.

Density measurements were obtained by weighing a 15 cm~3 sample. The recorded weight was 8.5030 g; hence a density of 0.567 gcrri 3 was calculated. The sample floats on water.

Example 7.5. Composites made from Polyethylene and Cenosphere.

Polyethylene HMW (15.0 g) was placed in a crucible and heated, using a hot plate until a runny consistency was achieved. 15.0 g of cenosphere was weighed and added to the molten thermoplast and mixed using a spatula, whilst continuing heating the paste. Once homogeneity was visually observed the paste was transferred to a Teflon coated aluminium moulds, and left to cool at room temperature for five minutes. To speed up the cooling and demoulding, the moulds containing the composites were placed in cool water baths. Within seconds they were demoulded. These were very strong yet thin objects. A density of 0.46 gcm-3 was recorded. The composite floats on water.

Claims (5)

1. Invention of a family of Lightweight, Thermally Insulating and/or Fireproofing and/or Soundproofing ceramic composites (LWCC) using hollow and spherical Cenosphere particles (with or without added Pulverized Fuel Ash), and a variety of cementing agents.

2. LWCC as claimed in claim 1 that may also be used as Artificial Pumice.

3. LWCC as claimed in claim 1 or 2 that may be applied as objects for sanding and polishing various substrates, e. g. metallic substrates.

4. Lightweight Composites (LWC) made from combination of thermoplastic polymers and cenosphere, may be used for decorative as well as insulation.

5. LWC as claimed in claim 4 may be used as rigid and lightweight composites.