WO2018145953A1

WO2018145953A1 - Grains comprising silica and methods of forming grains comprising silica

Info

Publication number: WO2018145953A1
Application number: PCT/EP2018/052289
Authority: WO
Inventors: Alain LE MOIGNE; Stein BERGHMAN; Francesco Ferrari
Original assignee: Sibelco Nederland N.V.
Priority date: 2017-02-13
Filing date: 2018-01-30
Publication date: 2018-08-16
Also published as: GB2559608A; GB201702314D0

Abstract

The present invention relates to grains comprising silica and methods of forming grains comprising silica.

Description

Title: Grains comprising silica and methods of forming grains comprising silica

Description of Invention The present invention relates to grains comprising silica. The present invention also relates to methods of forming grains comprising silica.

Silica fillers are used in a number of industries, including the construction industry (in mortars), the ceramics industry and the glass making industry.

A wide variety of silica fillers are currently available in the marketplace. Non- limiting examples of silica fillers sold by Sibelco^® include:

• Microsil^® M4 (D50 of 50μηπ, and D90 of 170μηπ, both measured on a Malvern MS 2000); with an Si0₂ content of 99.8% by weight (measured by X-ray diffraction).

• Microsil^® M6 (D50 of 30μηπ, and D90 of 95μηπ, both measured on a Malvern MS 2000); with an Si0₂ content of 99.8% by weight (measured by X-ray diffraction).

· Microsil^® M10 (D50 of 23μηπ, and D90 of 60μηπ, both measured on a

Malvern MS 2000); with an Si0₂ content of 99.7% by weight (measured by X-ray diffraction).

Microsil^® is produced by iron-free grinding and subsequent sieving by means of air separators. A silica sand with a Si0₂ content of over 99% is used as the raw material. Microsil^® M silica fillers are used in high-purity applications.

• Millisil^® M6 (D50 of 30μηπ, and D90 of 95μηπ, both measured on a

Malvern MS 2000); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction). illisir M10 (D50 of 23μηπ, and D90 of 60μηπ, both measured on a Malvern MS 2000); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction). isil^® is produced by iron-free grinding and subsequent sieving by means of air separators. A silica sand with a Si0₂ content of over 99% is used as the raw material. Millisil^® M silica fillers are used in ceramics, tile-glues, mortars, refractory material and investment casting, among other applications.

• Sikron^® M300 (D50 of 17μηι, and D90 of 40μηπ, both measured on a Malvern MS 2000); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction).

• Sikron^® M400 (D50 of 12μηι, and D90 of 26μηπ, both measured on a Malvern MS 2000); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction).

• Sikron^® M500 (D50 of 4μηι, and D90 of 10μηι, both measured on a Malvern MS 2000); with an Si0₂ content of 99.2% by weight (measured by X-ray diffraction).

• Sikron^® M600 (D50 of 4μηι, and D90 of 9μηπ, both measured on a

Malvern MS 2000); with an Si0₂ content of 99.2% by weight (measured by X-ray diffraction).

Sikron^® is produced by iron-free grinding and subsequent sieving by means of air separators. A silica sand with a Si0₂ content of over 99% is used as the raw material. Sikron^® M300 is the appropriate quality for glass-fibre

production. The narrow and controlled particle size distribution, chemical inertness, optical properties and hardness make Sikron® useful in heavy duty paint and coatings applications.

Silica sand of Mol M31 (D50 of 370μηπ); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction). • Silica sand of Mol M32 (D50 of 260μηπ); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction).

• Silica sand of Mol M34 (D50 of 170μηπ); with an Si0₂ content of 99.0% by weight (measured by X-ray diffraction).

Silica sand of Mol is produced, after mining, by sieving, washing and classification (by sieve). The silica sands of Mol are used as raw materials for the glass, crystal and ceramic industries, for foundries, tile glues, plasters, mortars and coatings.

• Sibelite^® M002 (D50 of 70μηπ, and D90 of 200μηπ, both measured on a Malvern MS 2000); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction).

• Sibelite^® M006 (D50 of 40μηπ, and D90 of 10Ομηι, both measured on a Malvern MS 2000); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction).

• Sibelite^® M010 (D50 of 30μηπ, and D90 of 75μηπ, both measured on a Malvern MS 2000); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction).

Sibelite^® is a high-purity silica produced from cristobalite by iron-free grinding and subsequent sieving by means of air separators. Sibelite® has a controlled particle distribution, excellent optical properties, chemical inertness and constant whiteness; used in paints and plastics.

• SilverBond^® SA 250 (D50 of 9μηπ, and D90 of 32μηι, both measured by laser diffraction on a Cilas 920); with an Si0₂ content of 99.4% by weight (measured by X-ray diffraction).

• SilverBond^® SA 300 (D50 of 6μηπ, and D90 of 15μηι, both measured by laser diffraction on a Cilas 920); with an Si0₂ content of 99.3% by weight (measured by X-ray diffraction). • SilverBond^® SA 600 (D50 of 3μηπ, and D90 of 10μηπ, both measured by laser diffraction on a Cilas 920); with an Si0₂ content of 99.2% by weight (measured by X-ray diffraction).

• SilverBond^® M50E (D50 of 21 μηι, and D90 of 58μηπ, both measured by laser diffraction on a Cilas 920); with an Si0₂ content of 99.2% by weight (measured by X-ray diffraction).

• SilverBond^® SA10S (D50 of 27μηι, and D90 of 75μηπ, both measured by laser diffraction on a Cilas 920); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction).

· SilverBond^® SA6S (D50 of 39μηπ, and D90 of 1 18μηπ, both measured by laser diffraction on a Cilas 920); with an Si0₂ content of 99.5% by weight (measured by X-ray diffraction).

SilverBond^® crystalline silica is produced from high purity quartz feedstock for manufacturing and formulation of applications which require structurally sound, chemically pure or non-reactive fine mineral fillers.

Other silica fillers sold by Sibelco^® include: Millisil^® C4, Millisil^® C6, Millisil^® C10, Millisil^® C300, Millisil^® C400, Sikron^® C500, Sikron^® C600 and Sikron^® C800.

Whilst the above discussion relates to silica fillers sold by Sibelco^®, other silica fillers sold by other companies are available in the marketplace. Silica fillers include many fine particles of silica and other materials. Fine particles are difficult to handle and use safely because they form dust which can be inhaled by humans and/or animals. Inhalation of fine silica particles is damaging to health. For example, the inhalation of fine particles of silica can cause silicosis. Fine particles in the form of dust also lead to waste during transportation and/or handling. Whilst providing silica fillers with larger particles reduces the formation of dust, the overall surface area of the silica fillers reduces and, on forming mortars or other mixtures comprising silica fillers, the particles of the silica fillers may not react with the other components of the mortars or other mixtures. This can lead to the formation of mortars or other mixtures with large particles of unreacted silica, resulting in weaker mortars.

There is a need to reduce the formation of dust from silica fillers whilst at the same time maximising the surface area of silica fillers.

The present invention relates to a grain comprising:

silica (Si0₂); and,

a binder. Preferably, wherein the silica is a silica filler.

Further preferably, wherein in the silica filler the silica is present as particles with a maximum dimension of: from 0.2μηι to 1 mm; or, from 0.2μηι to 250μηπ; or, from 1 μηι to 100μηι.

Advantageously, wherein in the silica filler the silica is present as particles with a D50 of from 4μηι to 370μηι.

Preferably, wherein in the silica filler the silica is present as particles with a D50 of from 4μηι to 200μηι.

Further preferably, wherein in the silica filler the silica is present as particles with a D50 of from 10μηι to 50μηι. Advantageously, wherein in the silica filler the silica is present as particles with a D90 of from 9μηι to 400μηι. Preferably, wherein in the silica filler the silica is present as particles with a D90 of from 9μηι to 200μηι.

Further preferably, wherein in the silica filler the silica is present as particles with a D50 of from 20μηι to 30μηι.

Advantageously, wherein the grain has a maximum dimension of from 0.05 mm to 8 mm. Preferably, wherein the silica is present as any one or more of:

Microsil^® M4, Microsil^® M6, Microsil^® M10, Millisil^® M6, Millisil^® M10, Sikron^® M300, Sikron^® M400, Sikron^® M500, Sikron^® M600, Silica sand of Mol M31 , Silica sand of Mol M32, Silica sand of Mol M34, Sibelite^® M002, Sibelite^® M006, Sibelite^® M010, SilverBond^® SA 250,

SilverBond^® SA 300, SilverBond^® SA 600, Millisil^® C4, Millisil^® C6,

Millisil^® C10, Millisil^® C300, Millisil^® C400, Sikron^® C500, Sikron^® C600, Sikron^® C800, SilverBond^® M 50 E, SilverBond^® SA 10 S and/or

SilverBond^® SA 6 S. Preferably, wherein the grain has a maximum dimension of: from 0.05 mm to 0.5mm; or, from 0.5 mm to 3 mm; or, from 3 mm to 8 mm.

Further preferably, wherein the D50, D90 and/or maximum dimension is measured on a particle size analyser.

Advantageously, wherein the D50, D90 and/or maximum dimension is measured on a Malvern MS 2000, a Malvern MS 3000, a Horiba™ Camsizer P4 or by passing the grain through a suitably sized sieve. Preferably, wherein the D50, D90 and/or maximum dimension is measured by laser diffraction; optionally, on a Cilas 920. Further preferably, wherein the binder acts to bind particles of silica together.

Advantageously, wherein the grain has a hardness of: from 0.5 MPa to 10 MPa; or, from 0.5 MPa to 5 MPa; or, from 0.75 MPa to 3 MPa.

Preferably, wherein the grain has a loss on ignition of (in weight %): from 0.5% to 5%; or, from 0.5% to 3%; or, from 0.7% to 2.5%.

Further preferably, wherein the loss on ignition (LOI) is calculated according to the following equation:

Ml - M2

LOI =

Ml

wherein, M1 is mass of the dry silica grain and M2 is the mass of the dry silica grain after heating at 450°C for 2 hours.

Advantageously, wherein the grain is for forming cement formulations and the binder comprises:

calcium lignosulfonates, sodium lignosulfonates, naphthalene sulfonate formaldehyde condensates, sulfonated melamine formaldehyde condensates, polyacrylates, polycarboxylates or water; or any combination of any two, three, four, five, six or seven of these binders.

Preferably, wherein the grain is for forming ceramic formulations and the binder comprises:

carboxymethyl celluloses, vinylic resins, acrylic resins or water; or any combination of any one, two, three or four of these binders.

Further preferably, wherein the grain comprises (in weight %):

75 to 90% silica (SiC½); and,

10 to 25% a binder;

and unavoidable impurities. Advantageously, wherein the grain further comprises:

calcium carbonate (CaC0₃); and/or,

quartz powder; and/or,

silica sand.

Preferably, wherein the grain further comprises one or more of:

quartz powder; and/or,

clay; and/or,

feldspar; and/or,

silicate zirconium; and/or,

frit; and/or,

wollastonite; and/or,

calcined alumina; and/or,

nepheline; and/or,

kaolin.

Further preferably, wherein the grain has a humidity of: less than or equal to 1 %; or, less than or equal to 0.2%. The present invention also relates to a plurality of grains comprising one or more grains according to any one of the above possibilities.

Preferably, wherein the plurality of grains have a hardness of: from 0.5 MPa to 10 MPa; or, from 0.5 MPa to 5 MPa; or, from 0.75 MPa to 3 MPa.

Further preferably, wherein the plurality of grains have a loss on ignition of (in weight %): from 0.5% to 5%; or, from 0.5% to 3%; or, from 0.7% to 2.5%.

Advantageously, wherein the loss on ignition (LOI) is calculated according to the following equation:

Ml - M2

¹⁰¹ = — Τ M.l— wherein, M1 is the mass of the plurality of the silica grains when dry and M2 is the mass of the same plurality of silica grains after heating at 450°C for 2 hours. Preferably, wherein the plurality of silica grains comprise silica filler and the silica grains produce less dust than the silica filler when dedusted.

Further preferably, wherein the amount of dust produced by the silica grains during dedusting is: from 1 .5 to 100 times lower; or, from 2 to 10 times lower; than the dust produced by the loose silica filler comprised within the silica grains.

The present invention also relates to a dry mortar mix comprising a grain according to any one of the above possibilities, or a plurality of grains according to any one of the above possibilities.

The present invention also relates to a mixture for use in the ceramics industry comprising a grain according to any one of the above possibilities, or a plurality of grains according to any one of the above possibilities.

The present invention also relates to a mixture for use in forming glass comprising a grain according to any one of the above possibilities, or a plurality of grains according to any one of the above possibilities. The present invention also relates to a method of forming a grain comprising: silica (Si0₂); and, a binder; the method comprising the steps of:

providing particles of silica;

mixing the particles of silica with a binder; and,

agglomerating the silica and the binder to form the grain.

The present invention also relates to a method of forming a grain according to any one of the above possibilities, the method comprising the steps of: providing particles of silica;

mixing the particles of silica with a binder; and,

agglomerating the silica and the binder to form the grain. Preferably, wherein the step of agglomerating the silica and the binder to form the grain occurs by plate granulation, intensive granulation or spray drying.

Further preferably, wherein the particles of silica are mixed with aqueous binder.

Advantageously, wherein the method further comprises the step of:

drying the grains by heating.

Preferably, wherein the step of drying the grains by heating occurs until the grains have a humidity lower than 0.2%.

Embodiments of the invention are described below with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a cross-section of a silica grain according to the present invention.

Some of the terms used to describe the present invention are set out below: "D50" refers to the median maximum particle dimension; it is the value of the maximum particle dimension (for example, the particle diameter in a generally spherical particle) at 50% in the cumulative distribution of the maximum particle dimension in a sample of particles; 50% of the distribution lies below the D50 value and 50% of the distribution lies above the D50 value.

"D90" refers to the value of the maximum particle dimension (for example, the particle diameter in a generally spherical particle) at 90% in the cumulative distribution of the maximum particle dimension in a sample of particles; 90% of the distribution lies below the D90 value.

"Maximum dimension" or "maximum particle dimension" refers to the longest cross-sectional dimension of any particular grain or filler particle.

"Silica filler" refers to a composition comprising at least 99.0% Si0₂ where the Si0₂ is present as particles with a maximum dimension of from 0.2μηι to 1 mm; optionally, from 0.2μηι to 250μηι.

"Binder" refers to a composition which acts to bind particles of silica filler together. Non-limiting examples of binder used in cement applications (for example when forming a dry mix mortar) include: calcium lignosulfonates, sodium lignosulfonates, naphthalene sulfonate formaldehyde condensates, sulfonated melamine formaldehyde condensates, polyacrylates,

polycarboxylates and water; and any combination of any one, two, three, four, five, six or seven of these examples. Non-limiting examples of binder used in ceramic applications include: carboxymethyl celluloses, vinylic resins, acrylic resins and water; and any combination of any one, two, three or four of these examples.

"Grain" refers to a particle comprising silica filler and binder, where the grain has a maximum dimension of from 0.5 mm to 8 mm. The choice of binder for any particular grain depends on the industry to which the grain is likely to be sold.

"Smaltobbio" is a term of art in the field of ceramics. Smaltobbio is the fusion of the words smalto (meaning glaze in Italian) and engobbio (meaning engobe in Italian). Instead of applying two layers, a first layer of engobe and a second layer of glaze, to a ceramic product, Smaltobbio is applied as a mixed formulation. Figure 1 is a schematic diagram of a cross-section of a silica grain 1 according to the present invention. The silica grain 1 of Figure 1 is generally spherical and comprises particles of silica filler 2 held together by the binder 3. The silica grain 1 of Figure 1 has a diameter s which is its maximum dimension.

In the cross-section of a silica grain 1 depicted in Figure 1 , the particles of silica filler 2 are relatively evenly spaced throughout the binder 3. In other examples, there can be clumps of particles of silica filler 2 in different areas of the binder 3.

The silica grain of Figure 1 is generally spherical. Alternatively, silica grains of the present invention can be any shape, for example the silica grains may approximate as ovoid, a cylinder, a prism, a cuboid, a cube, a pyramid, a cone or any other three dimensional shape. When used to refer to silica grains or silica filler of the present invention, the term "maximum dimension" refers to the longest cross-sectional dimension of the grain. The "maximum dimension" can be measured by passing the grain or grains through a suitably sized filter and/or on a particle sizer (for example on a Malvern MS 2000, if the grains have a maximum dimension of approximately 2mm, or a Horiba™ Camsizer P4 for grains having a maximum dimension of any value).

Methods of forming silica grains

Concrete applications

In one non-limiting example, silica grains were formed starting from Sibelco^® Sikron^® M400 silica filler.

A binder was formed by mixing water, calcium lignosulfonate (source:

Borresperse CAF from Borregaard Industries Ltd. in liquid form with 47% by weight water) and naphthalene sulfonate (source: Mapefluid N100 from MAPEI with 65% by weight water). In this non-limiting example, the binder formed was (by weight): 21 .3 % naphthalene sulfonate, 7.1 % calcium lignosulfonate and 71 .6% water.

The binder and the M400 silica filler were mixed together in a plate granulator. In this non-limiting example, the plate granulator was a Mars Mineral™ DP-14 "Agglo-Miser". In other non-limiting examples, the plate granulator is a

Grelbex PG08.

In this non-limiting example, 20.5% by weight of the binder was mixed with the M400 silica filler (79.5% by weight) in the plate granulator. This formed wet silica grains. In other examples, the amount of binder added depends on the type of silica filler: the finer the silica filler the higher the necessary relative quantity of binder. In another non-limiting example, with M6 silica filler, only 1 1 .6% by weight of the binder was mixed with 88.4% by weight of the M6 silica filler.

The wet silica grains in this example (20.5% by weight of the binder mixed with 79.5% by weight M400 silica filler) were dried by heating until the grains had a humidity lower than 0.2%. In other examples, the grains were dried by heating until the grains had a humidity of lower than 1 %. These values for humidity are given as the percentage by weight of water in the grains. Drying (to reduce the humidity) increases the hardness of the grains.

Optionally, in other examples, the dried silica grains were screened through a filter to separate silica grain particles of desired sizes.

Preparing the dried silica grains as above, without a screening step, formed silica grain particles with maximum dimensions from 3mm to 8mm. The produced dried silica grains were formed of M400 silica filler particles and held together by binder. The particle size distribution (the size referring to the maximum dimensions of the silica grain particles) of the dried silica grains formed by this example (plate granulator) are shown in Table 1 : Table 1 : Particle size distribution (plate granulator)

Generally, plate granulation forms silica grain particles with maximum dimensions from 3mm to 8mm. Alternatively, intensive granulation with a high shear mixer (for example an Eirich™ mixer, for example an Eirich™ R02 or an Eirich™ R1 1 ) provides silica grain particles with maximum dimensions from 0.5mm to 3mm.

In a non-limiting example, 18% by weight of the binder was mixed with the M400 silica filler (82% by weight) in an Eirich™ R1 1 high shear mixer. This formed wet silica grains. The wet silica grains in this example were dried by heating until the grains had a humidity lower than 0.2%.

The particle size distribution (the size referring to the maximum dimensions of the silica grain particles) of the dried silica grains formed by this example (intensive granulation) were as shown in Table 2:

Table 2: Particle size distribution (intensive granulation)

>3.15 mm 6%

Between 2 - 3.15 mm 20%

Between 1 - 2 mm 36%

Between 0.5 - 1 mm 28%

<0.5 mm 10% Further alternatively, the dried silica grains can be formed by spray drying to form silica grain particles with maximum dimensions from 0.05mm to 0.5mm. To quantify the hardness of the silica grains formed by the above method, 100 grams of the produced silica grains were sieved with high numbers of vibrations on a Haver & Boecker™ EML 200 digital T, with the highest rate of vibration, for one minute and the quantity of dust produced was noted.

Approximately, 10 grams of dust was produced from 1 00 grams of the produced silica grains. By contrast, 100 grams of dust was produced using the same test on the M400 silica filler starting material. In other words, forming the silica grains greatly reduced the formation of dust.

The re-dispersion of the silica grains produced above was tested. 10 grams of grains were added to 100 grams of water. The mixture was stirred for 30 seconds and the water was sieved to remove any remaining pieces bigger than the top cut of the silica filler used to produce the grains (63μηι for the M400 starting material). The percentage of pieces caught by the sieve was lower than 5% by weight.

The above data show that, forming silica grains from M400 in combination with the binder described above, the silica grains are hard and produce minimal amounts of dust whilst being as re-dispersible in water as the silica filler starting material.

Alternatively, in addition to the silica filler, the silica grains produced by this method can include particles of calcium carbonate. The calcium carbonate is included as an additional component for a dry mix mortar. The silica grains described above can be used to form dry mix mortars, in combination with other components required to form a dry mix mortar. Mortars were prepared using either M400 silica filler or silica grains as described above. The following data show among other things the strength of the mortar after 1 and 28 days:

Table 3: Comparison of mortars

With reference to Table 3, the same amount of M400 was included in the mortar in each case. The difference was that binder was included with the M400 in the form of silica grains in the 'silica grains' column. Including the M400 and binder together in a grain led to no loss of valuable properties of the mortar. The strength of the mortar after 28 days was in fact greater when using silica grains.

Furthermore, the silica grains have a similar rheology to the silica filler. This is shown in Table 3 by both having similar penetration of CEN diver and mortar spreading values. In order to achieve this similar rheology, the amount of water must be reduced in the mortar using the silica grains (170 grams versus 225 grams for the mortar including silica filler).

Ceramic applications

In one non-limiting example, silica grains were formed starting from Sibelco^ SilverBond^® M50E, SilverBond^® SA10S and SilverBond^® SA6S silica fillers. A binder was formed by mixing water and carboxymethyl cellulose (in this example, as sold by Lamberti S.p.A.™). In this non-limiting example, the binder formed was (by weight): 5 % carboxymethyl cellulose and 95 % water. This is an appropriate binder for ceramic applications.

The binder and the silica filler were mixed together in a plate granulator. In this non-limiting example, the plate granulator was a Mars Mineral™ DP-14 "Agglo-Miser". In other non-limiting examples, the plate granulator is a

Grelbex PG08.

In these non-limiting examples: 13.9% by weight of the binder was mixed with 86.1 % M50E silica filler; 14.5% by weight of the binder was mixed with 85.5% SA1 OS silica filler; 1 1 .2% by weight of the binder was mixed with 88.8% SA6A silica filler; in a plate granulator. In each example, this formed wet silica grains. In other examples, the amount of binder added depends on the type of silica filler: the finer the silica filler the higher the necessary relative quantity of binder.

The wet silica grains in this example were dried by heating until the grains had a humidity lower than 0.2%. In other examples, the grains were dried by heating until the grains had a humidity of lower than 1 %. These values for humidity are given as the percentage by weight of water in the grains. Drying (to reduce the humidity) increases the hardness of the grains. Optionally, the dried silica grains were screened through a filter to separate silica grain particles of desired sizes.

Preparing the dried silica grains as above, without a screening step, formed silica grain particles with maximum dimensions from 0.05mm to 8mm.

To quantify the hardness of the silica grains, 100 grams of the produced silica grains were sieved with high numbers of vibrations on a Haver & Boecker™ EML 200 digital T, with the highest rate of vibration, for one minute and the quantity of dust produced was noted. Approximately, 10 grams of dust was produced from 100 grams of the produced silica grains. By contrast, 100 grams of dust was produced using the same test on the M50E, SA10S and SA6S silica filler starting material. In other words, forming the silica grains greatly reduced the formation of dust.

The re-dispersion of the silica grains produced above was tested. 10 grams of grains were added to 100 grams of water. The mixture was stirred for 30 seconds and the water was sieved to remove any remaining pieces bigger than the top cut of the silica filler used to produce the grains. The percentage by weight was lower than 5%.

The above data show that, forming silica grains from M50E, SA10S and SA6S in combination with the binder mentioned above, the silica grains are hard and produce minimal amounts of dust whilst being as re-dispersible as the silica filler starting material.

In ceramic applications, the silica grains are combined with other components to form a glaze composition. The glaze composition can comprise one or more of: clay, feldspar, silicate zirconium, frit, wollastonite, calcined alumina, nepheline and/or kaolin, or any combination of any one, two, three, four, five, six, seven or eight of these components. A typical glaze in the ceramics industry comprises (by weight): 25% quartz,

20% clay, 17% feldspar, 13% silicate zirconium, 12% frit, 10% wollastonite and 3% calcined alumina (each amount plus or minus 10%). Providing the silica part of a glaze with the silica grains produced above resulted in a working glaze composition.

Alternatively, the silica grains can be produced with one or more of the components of the glaze added to the silica grain. Whilst the above non-limiting examples relate to silica grains formed for use in concrete and ceramic applications, silica fillers may be combined with different commercially available binders to form grains comprising silica for a multitude of applications. By mixing different binders with different silica fillers, it is possible to control the hardness, re-dispersion, setting time and mechanical properties of the silica grains and the compositions into which they are placed.

Viscosity in ceramic applications

The present inventors investigated the influence of the binder on the final properties of a glaze in a ceramics application. The silica filler was included in a typical Smaltobbio formulation. In a first test, three different silica fillers were formed into grains along with carboxymethyl cellulose (CMC) as a binder. The method of forming the grains was as described above. The grains were introduced into a Smaltobbio formulation and a slurry was formed by adding to the Smaltobbio formulation free (powder form) carboxymethyl cellulose (CMC), free (powder form) sodium tripolyphosphate (STPP) and water.

In a second test, three different silica fillers were not formed into grains. The free silica fillers were introduced into a Smaltobbio formulation and a slurry was formed by adding free (powder form) carboxymethyl cellulose (CMC), free (powder form) sodium tripolyphosphate (STPP) and water. The free (powder form) carboxymethyl cellulose (CMC), free (powder form) sodium

tripolyphosphate (STPP) and water were of the same type as in the first test.

In a third test, three different silica fillers were formed into grains along with carboxymethyl cellulose (CMC) as a binder. The method of forming the grains was as described above. The grains were introduced into a Smaltobbio formulation and a slurry was formed by adding to the Smaltobbio formulation free (powder form) sodium tripolyphosphate (STPP) and water. The free (powder form) sodium tripolyphosphate (STPP) and water were of the same type as in the first and second tests. In comparison to the first test, free (powder form) carboxymethyl cellulose (CMC) was not added to the slurry.

For all three tests the following values were measured:

- Density after milling.

- Viscosity after milling at the density of milling.

- 45 Micron Residue (only for the first test in order to check the presence of undissolved granules).

- Density of application of the glaze.

- Viscosity of the glaze at the density of application.

With each formulation, the present inventors checked the viscosity using a Ford Cup just after the milling stage and also before applying the Smaltobbio on tiles.

The Smaltobbio formulation (referred to as 'glaze' in Tables 5, 6 and 7) was the same for each test and is shown in Table 4.

Table 4: Smaltobbio formulation

^* Silica filler changed for each of the three examples for each test Table 5: First test - grains with CMC as binder + free CMC + free STPP

M50E SA10S SA6S

Dry Weight of the 150 150 150 Glaze (g)

Water Percentage (%) 45 45 45

STPP (%) 0.1 0.1 0.1

CMC (%) 0.2 0.2 0.2

Milling time (min) 50 50 50

Viscosity 62.01 61 .53 75.04 Ford cup 0 4mm

Density after mill 1815 1818 1818 (g/dm³)

45 Microns Residue 0.09 0.08 0.08

(g)

Density for Glaze 1507 1506 1506 Application (g/dm³)

Viscosity 1 1 .62 1 1 .65 1 1 .55

Ford cup 0 4mm for

Glaze Application

(sec)

Table 6: Second test - free silica filler (not formed as grains) + free CMC + free STPP

M50E SA10S SA6S

Dry Weight of the 150 150 150 Glaze (g)

Water Percentage (%) 45 45 45

STPP (%) 0.1 0.1 0.1

CMC (%) 0.2 0.2 0.2

Milling time (min) 50 50 50

Viscosity 33.63 31 .62 35.37 Ford cup 0 4mm

Density after mill 1815 1815 1818 (g/dm³)

45 Microns Residue Not measured Not measured Not measured

(g)

Density for Glaze 1506 1506 1507 Application (g/dm³)

Viscosity 1 1 .25 1 1 .18 1 1 .19

Ford cup 0 4mm for

Glaze Application

(sec)

Table 7: Third test - grains with CMC as binder + free STPP (no free CMC)

Table 5 (the first test) shows a high viscosity because the total amount of the CMC (from the silica grain and the free CMC) is high.

Comparing the first test (Table 5) and the second test (Table 6), the silica grains, added to a Smaltobbio formulation, increase the viscosity after milling of the product but do not affect the application viscosity. There was no residue of silica grains on the sieve after milling. This shows that the grains were well dispersed during the milling process.

By comparison of the second (Table 6) and third tests (Table 7), the viscosity after milling is practically the same and the application viscosity is not affected. This shows that the addition of CMC in the silica grains (in the third test) provides a similar effect as adding the free silica filler and free CMC (in the second test). From these viscosity tests, it is apparent that adding the grains comprising silica into a Smaltobbio formulation changes the rheology of milling but not the application rheology. Additionally, the silica is well dispersed during the milling process. The rheology of milling can be adjusted by reducing or removing the free CMC added to produce the glaze formulation.

Hardness testing

The hardness of different silica grains produced according to the present invention were tested. The present inventors developed a hardness test based on the crushing resistance test set out in the standard EN 13055:201 6. These tests found that, generally, forming the silica grains by intensive granulation provides a greater hardness than forming the silica grains by plate granulation.

Table 8: Hardness of different silica grains

A. M400 grain with plate granulation (% by weight):

79.5% M400 silica filler + 20.5% binder

Binder = 21 .3% naphthalene sulfonates N100 + 7.1 % lignosulfonates + 71 .6% water

B. M6 grain with plate granulation (% by weight):

88.4% M6 silica filler + 1 1 .6% binder Binder = as A

C. M50E with plate granulation (% by weight):

86.1 % silica filler + 13.9% binder

Binder = 5% dry CMC + 95 % water

The CMC used was a commercial CMC solution (Resicel™ 1282): 10% CMC + 90% water with dilution: 50% Resicel™ 1282 + 50% water. Therefore, overall 5% CMC + 95% water The silica grains A and B were found useful in concrete applications. The grains produced minimal amounts of fine dust silica and were useful in forming concrete mortars. The silica grains C were found useful in ceramic applications. The crushing resistance of the grains formed using CMC as a binder showed greater crushing resistance than silica grains A and B. The grains produced minimal amounts of fine dust silica and were useful in forming ceramic mortars. Table 9: Hardness of different silica grains

D. M50E grain with intensive granulation (% by weight) 82% M50E silica filler + 18% binder

Binder = 37% Resicel™ 1282 + 63% water (Equivalent to 3.7% dry CMC + 96.3% water)

The hardness of the silica grain D formed by this process (intensive

granulation) was relatively higher than those formed by plate granulation (A, B and C above). The present inventors found that silica grains (comprising silica and a binder) with a hardness of from 0.5 MPa to 10 MPa were particularly beneficial in minimising the generation of fine silica particles (i.e. dust) during the handling of the grains, whilst permitting the use of the silica grains in forming beneficial concrete mortars and ceramic mortars. Alternatively, silica grains (comprising silica and a binder) with a hardness of from 0.5 MPa to 5 MPa, or from 0.75 MPa to 3 MPa, were found to be beneficial.

Measuring loss on ignition

The physical properties of silica grains formed according to the present invention were further tested by measuring loss on ignition.

Non-limiting examples of silica grains were dried for 24 hours at 105°C in order to remove any water and then cooled in a desiccator. The resulting dried silica grains were weighed to provide a first mass (M1 ). The dried silica grains (M1 already measured) were then heated for 2 hours at 450°C in an oven to remove any organic matter; followed by cooling in a desiccator. The resulting grains were weighed to provide a second mass (M2). LOI (loss on ignition) at 450°C (in weight %) was calculated according to the following equation:

Ml - M2

LOI =

Ml

The lower the LOI measurement, the less organic matter there is present in the starting silica grains. Table 10: LOI of different silica grains

Table 11 : LOI of different silica grains

The present inventors observed a similar LOI result for the ceramic application grains with plate granulation and intensive granulation because they added the same quantity of dry CMC to get the same rheology. Measuring dedusting

The present inventors devised a way of measuring dedusting of silica grains according to the present invention. The dedusting was measured by passing 300g of the silica grains, or silica filler, through a funnel and into a sample holder; the narrowest portion of the funnel forming a cylinder 1 1 cm long and with a diameter of 20mm (such a funnel being used to measure the bulk density of powders in accordance with EN 196-6:2010 (E)). At different times, a device took measurements of the concentration of fine particles smaller than 10μηι in μg/m³ adjacent to the sample holder, the device being placed in the same position for all of the measurements taken. In this example, the device measuring the concentration of fine particles was a DustMate™ dust detector, as manufactured by the Turnkey™ Instruments Ltd. In a first step, the concentration of fine particles smaller than 10μηι in μg/m³ was measured in the atmosphere of the laboratory. This gave the value of dedusting at time 0s.

In a second step, 300 g of the silica grains, or silica filler, were poured through a funnel over 40 seconds into an open sample holder beneath the cylinder forming the narrowest portion of the funnel; the narrowest portion of the funnel forming a cylinder 1 1 cm long and with a diameter of 20mm. The first measurement of dust concentration was then taken 20 seconds after the silica grains, or silica filler, had been poured through the funnel into the open sample holder.

The concentration of fine particles smaller than 10μηι in the atmosphere around the open sample holder was measured after 60s (20s after the silica grains, or silica filler, had been passed through the funnel), 90s, 120s and 150s. The concentration of fine particles was measured in μg/m³ and was taken at the same location for each measurement and using the same open sample holder. Efficiency of dedusting was measured with the ratio (dust concentration of grain divided by dust concentration of filler) for each filler and at each time. Table 12: Dedusting of different silica grains

Production with a plate Dust μg/m³

granulator Time 0s 60s 90s 120s 150s

Concrete application M400 filler 1 1 977 1024 996 869

Binder (% by weight) = A. M400

21 .3% N100 + 7.1 % grain 1 1 223 205 1 68 143 lignosulfonates + 71 .6% (binder =

water 20.5%)

Ratio 4.38 4.99 5.93 6.08

M6 filler 1 1 233 880 931 869

B. M6 grain 13 14 15 15 14 (binder =

1 1 .6%)

Ratio 1 6.64 58.67 62.07 62.07

Ceramic application SA6S filler 1 1 240 854 912 843

SA6S grain

Binder (% by weight) = (binder = 13 81 129 1 14 100 50% Resicel™ 1282 + 18%)

50% water

Ratio 2.96 6.62 8 8.43 Table 13: Dedusting of different silica grains

Tables 12 and 13 show that forming silica grains according to the present invention greatly reduces the amount of dedusting compared to silica filler. These silica grains can be used to form mortars where the binders dissolve in the mortar and permit the silica filler to provide a suitable surface area for forming beneficial mortars. When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1 . A grain comprising:

silica (Si0₂); and,

a binder.

2. The grain of claim 1 , wherein the silica is a silica filler.

3. The grain of claim 2, wherein in the silica filler the silica is present as particles with a maximum dimension of: from 0.2μηι to 1 mm; or, from 0.2μηι to

250μηπ; or, from 1 μηι to 100μηι.

4. The grain of any one of claims 2 to 3, wherein in the silica filler the silica is present as particles with a D50 of from 4μηι to 370μηι.

5. The grain of any one of claims 2 to 4, wherein in the silica filler the silica is present as particles with a D50 of from 4μηι to 200μηι.

6. The grain of any one of claims 2 to 5, wherein in the silica filler the silica is present as particles with a D50 of from 10μηι to 50μηι.

7. The grain of any one of claims 2 to 6, wherein in the silica filler the silica is present as particles with a D90 of from 9μηι to 400μηι. 8. The grain of any one of claims 2 to 7, wherein in the silica filler the silica is present as particles with a D90 of from 9μηι to 200μηι.

9. The grain of any one of claims 2 to 8, wherein in the silica filler the silica is present as particles with a D50 of from 20μηι to 30μηι.

10. The grain of any one of claims 1 to 9, wherein the grain has a maximum dimension of from 0.05 mm to 8 mm.

1 1 . The grain of any one of claims 1 to 10, wherein the silica is present as any one or more of:

SilverBond^® SA 300, SilverBond^® SA 600, Millisil^® C4, Millisil^® C6, Millisil^® C10, Millisil^® C300, Millisil^® C400, Sikron^® C500, Sikron^® C600, Sikron^® C800, SilverBond^® M 50 E, SilverBond^® SA 10 S and/or

SilverBond^® SA 6 S.

12. The grain of any one of claims 1 to 1 1 , wherein the grain has a maximum dimension of: from 0.05 mm to 0.5mm; or, from 0.5 mm to 3 mm; or, from 3 mm to 8 mm.

13. The grain of any one of claims 3 to 12, wherein the D50, D90 and/or maximum dimension is measured on a particle size analyser. 14. The grain of claim 13, wherein the D50, D90 and/or maximum dimension is measured on a Malvern MS 2000, a Malvern MS 3000, a Horiba™ Camsizer P4 or by passing the grain through a suitably sized sieve.

15. The grain of any one of claims 3 to 12, wherein the D50, D90 and/or maximum dimension is measured by laser diffraction; optionally, on a Cilas

920.

1 6. The grain of any one of claims 1 to 14, wherein the binder acts to bind particles of silica together.

17. The grain of any one of claims 1 to 16, wherein the grain has a hardness of: from 0.5 MPa to 10 MPa; or, from 0.5 MPa to 5 MPa; or, from 0.75 MPa to 3 MPa. 18. The grain of any one of claims 1 to 17, wherein the grain has a loss on ignition of (in weight %): from 0.5% to 5%; or, from 0.5% to 3%; or, from 0.7% to 2.5%.

19. The grain of claim 18, wherein the loss on ignition is calculated according to the following equation:

Ml - M2

LOI =

Ml

wherein, M1 is the mass of the dry silica grain and M2 is the mass of the dry silica grain after heating at 450°C for 2 hours.

20. The grain of any one of claims 1 to 19, wherein the grain is for forming cement formulations and the binder comprises:

21 . The grain of any one of claims 1 to 20, wherein the grain is for forming ceramic formulations and the binder comprises:

22. The grain of any one of claims 1 to 21 , wherein the grain comprises (in weight %):

75 to 90% silica (SiC½); and,

10 to 25% a binder;

and unavoidable impurities.

23. The grain of any one of claims 1 to 21 , wherein the grain further comprises:

calcium carbonate (CaC0₃); and/or,

quartz powder; and/or,

silica sand.

24. The grain of any one of claims 1 to 21 , wherein the grain further comprises one or more of:

quartz powder; and/or,

clay; and/or,

feldspar; and/or,

silicate zirconium; and/or,

frit; and/or,

wollastonite; and/or,

calcined alumina; and/or,

nepheline; and/or,

kaolin. 25. The grain of any one of claims 1 to 24, wherein the grain has a humidity of: less than or equal to 1 %; or, less than or equal to 0.2%.

26. A plurality of grains comprising one or more grains according to any one of claims 1 to 25.

27. A plurality of grains according to claim 26, wherein the plurality of grains have a hardness of: from 0.5 MPa to 10 MPa; or, from 0.5 MPa to 5 MPa; or, from 0.75 MPa to 3 MPa.

28. The plurality of grains according to claim 26 or claim 27, wherein the plurality of grains have a loss on ignition of (in weight %): from 0.5% to 5%; or, from 0.5% to 3%; or, from 0.7% to 2.5%.

29. The plurality of grains according to claim 28, wherein the loss on ignition is calculated according to the following equation:

Ml - M2

LOI =

Ml

wherein, M1 is the mass of the plurality of the silica grains when dry and M2 is the mass of the same plurality of silica grains after heating at 450°C for 2 hours.

30. The plurality of silica grains according to any one of claims 26 to 29, wherein the plurality of silica grains comprise silica filler and the silica grains produce less dust than the silica filler when dedusted.

31 . The plurality of silica grains according to claim 30, wherein the amount of dust produced by the silica grains during dedusting is: from 1 .5 to 100 times lower; or, from 2 to 10 times lower; than the dust produced by the loose silica filler comprised within the silica grains.

32. A dry mortar mix comprising a grain according to any one of claims 1 to 25, or a plurality of grains according to any one of claims 26 to 31 . 33. A mixture for use in the ceramics industry comprising a grain according to any one of claims 1 to 25, or a plurality of grains according to any one of claims 26 to 31 .

34. A mixture for use in forming glass comprising a grain according to any one of claims 1 to 25, or a plurality of grains according to any one of claims 26 to 31 .

35. A method of forming a grain comprising: silica (Si0₂); and, a binder; the method comprising the steps of:

providing particles of silica; mixing the particles of silica with a binder; and,

agglomerating the silica and the binder to form the grain.

36. A method of forming a grain according to any one of claims 1 to 25, the method comprising the steps of:

providing particles of silica;

mixing the particles of silica with a binder; and,

agglomerating the silica and the binder to form the grain. 37. The method of claim 35 or claim 36, wherein the step of agglomerating the silica and the binder to form the grain occurs by plate granulation, intensive granulation or spray drying.

38. The method of any one of claims 35 to 37, wherein the particles of silica are mixed with aqueous binder.

39. The method of any one of claims 35 to 38, wherein the method further comprises the step of:

drying the grains by heating.

40. The method of claim 39, wherein the step of drying the grains by heating occurs until the grains have a humidity lower than 0.2%.

41 . A grain as hereinbefore described with reference to Figure 1 .

42. Any novel feature or combination of features described herein.