SILICON CONTAINING GRINDING AIDES FOR SLAG

Abstract: The present invention is directed to a novel grinding aid for slag and slag/clinker blends. The grinding aid is any silicon containing fluid or blends thereof. The compositions improved grinding efficiency of the slag or slag/clinker blends by reducing energy consumption during the grinding process.

Description: SILICON CONTAINING GRINDING AIDES FOR SLAG FIELD OF THE INVENTION The present invention is directed to a novel grinding aid for slag, and slag/clinker blends and the resulting cement products therefrom. BACKGROUND OF THE INVENTION The term cement is used to designate many different kinds of agents useful to bind materials together. The present invention is directed to hydraulic cements useful to form structural elements, such as roads, bridges, buildings and the like. Hydraulic cements are powder material which, when mixed with water, alone or with aggregate, form rock-hard products, such as paste, mortar or concrete. Paste is formed by mixing water with a hydraulic cement. Mortar is formed by mixing a hydraulic cement with small aggregate (e.g. sand) and water. Concrete is formed by mixing a hydraulic cement with small aggregate, large aggregate (e.g. 0.2-1 inch stone) and water. For example, portland cement is a commonly used hydraulic cement material with particular standard specifications established in the various countries of the world (See "Cement Standards of the World", Cembureau, Paris, France). Generally, hydraulic cements are prepared by sintering a mixture of components including calcium carbonate (as limestone), aluminum silicate (as clay or shale), silicon dioxide (as sand), and miscellaneous iron oxides. It is common that the mixture to be sintered contains as a component up to 80% slag. The components lose their separate identity and are chemically transformed during the sintering process. During the sintering process, chemical reactions take place wherein hardened nodules, commonly called clinkers, are formed. The granulated blast furnace slag is a cementitous material made from iron blast furnace slag. It is a non-metallic by-product of the iron industry having silicates and alumino silicates of calcium and other bases developed in a molten condition simultaneously with iron in a blast furnace at about 2700°F. After the clinker has cooled, it is then pulverized together with a small amount of gypsum (calcium sulfate) in a finish grinding mill to provide a fine, homogeneous powdery product. In certain instances other materials may be ground with the clinker or blended with the clinker to provide a particular type of hydraulic cement. A frequently added component is ' granulated blast furnace slag, pozzolans which are substituted for a portion of the expensive clinker material: This use of slag is distinguished from its use as an an optional ingredient in the sintered clinker described above. Another component which may be added to the clinker is fly ash. The slag and the clinker may be ground together, or ground separately and then blended together. In addition, ground or unground slag may be added to the clinker, then the clinker/slag blend may be ground. In clinker/slag mixtures the clinker may constitute up to 90% by weight of the composition. Slag and fly ash are generally inert and are used in cements where economy is of prime consideration and some diminution in strength is acceptable. The term "blended cement" refers to hydraulic cements having between 5 and 80% (more conventionally 5- 60%) slag as part of its composition. Products include hydraulic cements such as portland blast furnace slag cement, slag modified portland cement and the like. Due to the extreme hardness of the slag and clinkers, a large amount of energy is required to properly mill them into a suitable powder form. Energy requirements for finish grinding can vary from about 33 to 77 kWh/metric ton depending upon the nature of the slag or slag/clinker blend. Several materials such as glycols, alkanolamines, aromatic acetates, etc., have been shown to reduce the amount of energy required and thereby improve the efficiency of the grinding of clinkers. These materials, commonly known as grinding aids, are processing additives which are introduced into the mill in small dosages and interground with the clinker to attain a uniform powdery mixture. One of the major classes of grinding aids used today is the oligomers of lower alkylene glycols, such as diethylene glycol. They are used because of their availability and low cost. These glycols have had their grinding effectiveness enhanced by the inclusion of polyglycerols, lower fatty acids and sulfonated lignin (U.S. Pat. No. 4,204,877); unsaturated aliphatic acid and amines (FR 2,337,699); a C3 aliphatic acid salt and an amine (U.S. Pat. No. 3,615,785); as well as alcohols and amides (U.S. Pat. No. 5,125,976). Although the time required (and thereby energy consumed) is lessened when clinkers are ground in the presence of glycol grinding aids, the resultant powder cements do not exhibit any beneficial effect over cements formed without such grinding aid. Silicon containing grinding aids other than those of the present invention have been disclosed in the art. For example, Zadak, Zezulka and Vesely in Adsorption of Vapors of Liquid Grinding Aids on Cement Clinker (Puvodni Prace, May 7, 1971) teach that short ' trimethyl endblocked polydimethylsiloxanes can be used as grinding aids for clinker. However, this article does not disclose the use of silicone containing materials for grinding slag alone or slag blended with clinker. Silanes and their condensation products have also been disclosed for use as masonary additives, e.g., as in WO 81/01703 entitled "Process for the Preparation of a Mortar and the Product Thereby Obtained." However, this patent application does not disclose the use of silanes as a grinding aid for cement clinker, slag, or clinker/slag blends. It would be desirable to be able to form a hydraulic cement powder product having enhanced properties, such as strength and stability, by grinding in the presence of a grinding aid capable of causing an improved product. SUMMARY OF THE INVENTION The present invention is directed to a novel grinding aid for slag and slag/clinker raw material blends. The grinding aid is any silicon containing fluid or blends thereof. The compositions improve grinding efficiency of the slag or slag/clinker blends by reducing energy consumption during the grinding process. DETAILED DESCRIPTION OF THE INVENTION The grinding aid of the present invention is added to the slag or slag/clinker blend to reduce the energy consumed during grinding and/or to improve the properties of the hydraulic cement product. The grinding aid can be a siloxane fluid, a cyclic siloxane, silane, siliconate, polydiorganosiloxanolate, or mixtures thereof. Each of these components will be described herein in detail. The polydiorganosiloxanes useful in the invention are preferably linear polydiorganosiloxanes, but branched polydiorganosiloxanes would work as well. The polyorganosiloxanes could be functional or non-functional. By functional siloxane, it is meant a polydiorganosiloxane having at least one pendant or terminal functional group, such as hydroxyl, alkoxy, vinyl, amine, etc. The functional polydiorganosiloxane could also be terminated with hydrogen atoms. Non-functional siloxane fluids are typically endblocked with methyl or ethyl groups. The organic groups along the backbone of the siloxane can be methyl, ethyl or phenyl, with methyl being most preferred. The polymers are preferably ' short chain molecules having from 1 to 50 repeating silicon units and are well known in the art. The functional polydiorganosiloxanes preferably have an average of at least two functional groups per molecule and the most preferred functional groups are hydroxyl groups situated at the terminal positions of the polydiorganosiloxane. The non-functional siloxanes are preferably endblocked with methyl groups. Preferably the trimethyl end blocked polydiorganosiloxanes have a viscosity in the range of 0.65 cst to 20 (mm)2/s. Particularly preferred are hydroxyl terminated polydiorganosiloxanes represented by the general formula Y[ Rl 2 SiO] x H in which Y is a methyl or hydroxyl, Rl is alkyl or aromatic group having 1 to 8 carbon atoms, and the chain length, x, has an average value which ranges from 2 to 1,000. Hydroxyl terminated polydiorganosiloxanes are well known in the art and can be prepared by conventional methods. The chain length of the siloxane polymer preferably has an average number of siloxane units per polymer molecule of at least 2. Thus, for example, the hydroxylated siloxane can vary from thin fluids to non-flowable gums. Preferred R! groups are methyl, ethyl or phenyl, with methyl being most preferred. Accordingly, it is often preferred to employ a mixture of lower and higher molecular weight siloxanes in the compositions used in this invention. The polydiorganosiloxane can be completely hydroxyl terminated or a portion of the polymer chains can be terminated on one end by a methyl radical. It is preferred that siloxane is hydroxyl terminated and that all Y groups in the general formula are hydroxyl radicals. The cyclic siloxanes used as grinding aids can be used alone or blended with the other components described herein. Cyclic siloxanes are well known in the art, and may have functional groups such as vinyl, hydroxy, alkoxy or SiH disposed thereon or may be non- functional, such as those cyclic siloxanes defined by the formula: [(CH 3 ) 2 SiO] m - where m has a value of 3 to 8 inclusive. Specific cyclic siloxanes are respectively hexamethylcyclotrisiloxane, octaniethylcyclotetrasiloxane, decamethylcyclopentasiloxane and dodecamethylcyclohexasiloxane. The cyclic siloxanes employed according to this invention ' are relatively volatile materials having boiling points below about 250°C at 760 mm Hg. The cyclic siloxanes may be employed as the individual compounds or as mixtures of two or more different cyclic siloxanes. In addition other types of silicon containing additives may be used as the grinding aid, such as alkoxy silanes, trimethyl end blocked polydiorganosiloxane, siliconates, or polydiorganosiloxanolates. Both of the latter two types of compounds by definition contain an ionic silanolate group, ^SiO Siliconates are defined as a salt of a silanol of the following structure: HOSiR(OZ) 2 . The cation, M , of this salt may be either an alkaline metal cation or a quaternary ammonium or phosphonium cation. Thus, siliconates contain the following structure: M + " OSiR(OZ) 2 where R is any organic group and OZ designates either an additional salt group (OZ = O " M), a non-reacted silanol, or an alkoxy group. If some self-condensation has occurred, then the SiOZ structure may be a disiloxane or a higher oligomer. If cross- condensation with a polydiorganosiloxane has occured, then the SiOZ structure links the siliconate salt to a polydiorganosiloxane. Preferred siliconates include potassium alkylsiliconates and sodium alkylsiliconates, most preferred being potassium methylsiliconate and sodium methylsiliconate. The polydiorganosiloxanolates (abbreviated as siloxanolates) are defined as salts of the terminal silanol or silanols of a polydiorganosiloxane, and include the same range of cations as do the siliconates. Preferred siloxanolates include dipotassium and disodium polydialkylsiloxanolates, the most preferred being dipotassium or disodium polydimethylsiloxanolate, K or NaO(Me 2 SiO) x K or Na. The silanes useful for this invention are represented by the general formula (RO) n SiR2 4 . n wherein R is a methyl, ethyl, propyl or methoxyethyl radical, R^ is a monovalent hydrocarbon or halogen substituted hydrocarbon radical having from 1 to 4 carbon atoms, and ■ n has a value of 3 or 4. Thus specific examples include N-(2-aminoethyl)-3- aminopropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3 [2(vinylbenzylamino) ethylamino]propyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, triacetoxyvinylsilane, tris-(2-methoxyethoxy)vinylsilane, 3-chloropropyltrimethoxysilane, 1 -trimethoxysilyl-2- (p,m-chlorornethyl)phenyl-ethane, 3-chloropropyltriethoxysilane, N-(aminoethylaminomethyl)phenyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyl tris(2- ethylhexoxy)silane, 3 -aminopropyltrimethoxy silane, trimethoxysilylpropyl diethylenetriamine, beta (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyl dimethoxysilane, bis(2-hydroxyethyl)-3- aminopropyltrimethoxysilane, 1 ,3 divinyltetramethyldisilazane, vinyltrimethoxysilane, 2- (diphenylphosphino)ethyltriethoxysilane, 2-methacryloxyethyldimethyl [3 - trimethoxysilylpropyl] ammonium chloride, 3-isocyanatopropyldimethylethoxysilane, N-(3- acryloxy-2-hydroxypropyl)-3 -aminopropyltriethoxysilane, vinyl tris(t-butylperoxy)silane, 4-aminobutyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, phenyltrimethoxysilane, and phenyltriacetoxysilane. Other silane compounds which are considered alkoxy silanes for the purpose of the present application include methyltrimethoxysilane, phenyltrimethoxysilane, ethylorthosilicate, phenyltriethoxysilane and n-propylorthosilicate. In addition to the monomeric alkoxysilanes, oligomeric products from partial hydrolysis and condensation of the alkoxy silanes can also be used in the compositions of this invention. It will be apparent to the skilled artisan that mixtures and combinations of the materials can also be employed to achieve the results of the invention, such as mixtures of different cyclic siloxanes or different hydroxyl terminated polydiorganosiloxanes, etc., or combinations of a particular cyclic siloxanes and hydroxyl terminated polydiorganosiloxanes, or siliconates, etc. The grinding aids of the present invention may be added to the slag or slag/clinker mixture at any time during the grinding process but is preferably added just prior to the commencement of the grinding. The grinding aid will be added in the amount of 10 to 20,000 grams per metric ton of slag or slag/clinker mixture. ' The silicon containing grinding aid may be dispersed in appropriate solvents such as hydrocarbons derived products like xylene, toluene, mineral spirits, mineral oils, naphtha, isoparaffin and others that can dilute siloxane based products. In addition, the grinding aids may be emulsified and thereafter added to the clinker. As shown in the below examples, the compositions of the present invention improve grinding efficiency of the slag during grinding, thus reducing the amount of energy consumed during the grinding process. In addition, concrete made from the slag/clinker containing the additive shows better short and long term compression strength over concrete made having no such grinding aid. It is also expected that the present compositions will produce cement having a reduced tendency for gravelling. Given that the invention unexpectedly provides increased grinding efficiency and anti-graveling, other anticipated benefits include greater production throughput during and after grinding while handling powdered clinker or cement, and improved resistance to water damage of cured cement or concrete. EXAMPLES In the examples below, the grinding aides were tested to show how they improved both the efficiency of grinding slag and the grinding of slag/clinker mixtures. Cements were made using the slag/clinker mixtures and their compression strength was tested. The grinding aides showed improved efficiency in grinding, as well as improved compression strength in the resulting concrets. The grinding aides used in the experiments are described below: DCC1 is 100% trimethyl silyl endblocked dimethyl siloxane, having a viscosity of 10 (mm)2/s. DCC 2 is a commercial grade of methyl trimethoxy silane. DCC 3 is a commercial grade of phenyl trimethoxy silane. DCC 4 is a commercially available solution of 32% by weight of a sodium methyl siliconate in 68% water. DCC 5 is a commercially available solution of 42% by weight of a potassium methyl siliconate in 58% water. DCC 6 is a commercially available mixture of cyclic siloxanes comprising 4% decamethyl cyclopentasiloxane and 96% octamethylcyclotetrasiloxane. DCC 7 is a commercially available mixture of cyclic and linear siloxanes comprising 45% dimethycyclosiloxanes and 55% hydroxyl terminated dimethyl siloxane. DCC 8 is a commercially available hydroxyl terminated polydimethylsiloxane having a viscosity of 55 to 90 (mm)2/s at 25°C and having a hydroxyl content of 1.0 to 2.5 wt%. DCC 9 is made from two components. The first component is used in an amount of 80% and has a viscosity of 2.2 to 3 (mm)2/s. It is a mixture of cyclic siloxanes, comprising about 22% by weight decamethylcyclopentasiloxane and 77% by weight octamethylcyclotetrasiloxane and trace amounts of other dimethylcyclosiloxanes. The second component is used in an amount of 20% and is 32% by weight of sodium methyl siliconate in water. The two immiscible liquids are mixed in a high shear mixer for 30 minutes, and allowed to separate overnight. The clear supernatent is recovered by decantation and the underlying aqueous layer is discarded. The supernatent is primarily a mixture of the cyclic siloxanes but is also thought to contain some sodium polydimethylsiloxanolate formed by the attack of sodium methylsiliconate to cleave some of the cyclics. Slags The slag fed into the laboratory mill was previously separated from the same lot to avoid test variations. The slag was obtained from Belgo Mineira, and the slag had a composition of : SiO 2 , 36.04%; Al 2 O 3 , 13.28%; Fe 2 O 3 , 2.30%; CaO, 39.89%; MgO, 6.78%; CO 2 , 0.79%; SO 3 , 0.03%; Fire loss: 0.00. The grinding aids were added to the slag in an amount of 200 grams/metric ton of slag. Chrome alloy balls of the following sizes were used in the single chamber mill: 29.8 % were 20 mm in diameter, and the remainder were equally divided between diameters of 40, 50, 60 and 70 mm. The slag was then ground for 120 minutes in the ball mill with an average ball mill surface area of about 20 m 2 /ton and filling about 42% of the total void space of ball mill. The rotational speed of the ball mill was around 65% of its critical rotational speed. A sample of the milled product was analyzed. The specific surface area of milled slag, designated as the Blaine in m2/Kg, was measured using NBR 7224. The average value of 3 different samples was taken and values with more than 5% variation from the average were discarded, following standards defined by Brazilian Portland Cement Association ABCP and also accepted by cement producers. Blaine is correlated directly with the strength of the resulting cement. The percent of retained material was measured for screen 200 mesh by using standard NBR 11579 and for screen 325 mesh by using standard NBR 9202. The average value of 3 different samples was taken and the values with more than 5% variation from the average were discarded, following standards defined by Brazilian Portland Cement Association ABCP. Larger mesh numbers correspond to finer mesh openings through which particles can pass. The primary purpose of grinding is to reduce the size of the particles being ground. Smaller particles have higher specific surface area and also pass more readily through finer mesh screens. The progress of grinding can be followed by periodically measuring the specific surface area or by measuring the percent of particles that pass through mesh screens. We quantitate the percent improvement in grinding efficiency by the following: With respect to Blaine: (SURFACE AREA WITH GRINDING AHJ)X100% - 100% (SURFACE AREA WITHOUT GRINDING AID) With respect to passing through a screen (often called "Grinding Efficiency"): 100% - (%RETENTION WITH GRINDING AID) XI 00%. (%RETENTION WITHOUT GRINDING AID) Measurement of improvement in Blaine or in passage through a mesh screen depends on grinding time. Of course, the measurement based on screen passage also depends on the screen size. The results of the grinding tests for 100% slag are shown in Table 1 below: Table 1 The results in Table 1 show that all the silicon containing grinding aides improve the Blaine up to 19% and improve the efficiency up to 34% when compared to the values obtained without the silicon containing grinding aides. Slag/Clinker The grinding aides of the present invention also improve the grinding efficiency of slag/clinker mixtures. The clinker commonly is produced with a mixture of 3 - 5 parts of limestone and 1 part of clay. This mixture is burned with iron ore and sand in a cement kiln with temperature around 1500 deg. Celsius generating the material named clinker. The clinker used in this work was produced by a Brazilian cement producer named Soeicom S.A. located at Vespasiano in Minas Gerais state. The same procedures as those above were followed except that the slag mixture was 30% slag, 66% clinker and 4% gypsum. The results are shown in Table 2 below. Table 2 As in the 100% slag examples, the addition of the additives to slag/clinker mixtures resulted in improvements of up to 20% in Blaine and up to 42% in efficiency over the examples having no grinding aide. Compression strength of Concrete from slag/clinker mixtures Cements were made from the slag/clinker blends. The cements for the examples were prepared by milling 5.0 kg of sample in a laboratory ball mill, having different chemical ■ compositions that meet Brazilian Portland Cement Specifications, type CP II-E 32. CP II-E 32 is a Compound Portland Cement defined by standard EB-2138/NBR 11578 created by Brazilian Technical Standards Association (ABNT). According to this standard cement type CP II-E 32 has from 56 to 94 % of clinker plus gypsum (normally in the range from 3.0 % to 5.0 %) and from 6 % to 34 % of Slags on its formulation. It is also allowed to add from 0 % to 10 % of Limestone powder to cement type CP II-E 32 as a filler. This cement belongs to a compressive strength class of 32 MPa after 28 days of age, having a lower control limit of 32 MPa and an upper control limit of 49 MPa. * Note: 1.0 Mega-Pascal (MPa) = 10 kgf/cm 2 . Compressive strength was measured using methods defined by ABNT (standard NBR 7215) for ages of 1 and 3 days and the same results are showed below in Table 3. The standard NBR 7215 is related to the measurement of compressive strength of cylindrical samples having diameter of 50 mm and height of 100 mm. These samples are prepared with a rendering mortar having the following composition (by weight): one part of cement, three parts of standard sand (defined by ABNT standard NBR 7214: 1982) and with a water/cement ratio of 0.48. This rendering mortar is blended with a mechanical mixer and is manually compacted inside a mold using a standard procedure. The molds with the samples are kept in a wet environment for the initial cure and after some time the samples are released from the molds and cured in hydrated lime saturated water until the date of the test. The compressive strength method and specification of the machine used to perform this test is defined by ABNT standard NBR 6156:1983 and the specification for the wet chambers and tanks for the cure of rendering mortar and concrete samples is defined by ABNT standard NBR 9479:1994. Table 3 The additives of the present invention also improve the compression strength of the resulting cement made by grinding the slag/clinker mixtures. The improvement when compared to the values obtained with no grinding aid is up to 69% and 41% after 1 and 3 days of curing, respectively.

Claims: • What is claimed: 1. A composition comprising: slag treated with a silicon containing grinding aid. 2. The composition of claim 1, wherein the silicon containing grinding aid is present in an amount from 10 grams to 20,000 grams per metric ton of slag. 3. The composition of claim 1, wherein the silicon containing grinding aid comprises a trimethyl endblocked polydiorganosiloxane. 4. The composition of claim 1, wherein the silicon containing grinding aid comprises a siliconate, silanolate or siloxanolate. 5. The composition of claim 1, wherein the silicon containing grinding aid comprises an alkoxy silane. 6. The composition of claim 1 , wherein the silicon containing grinding aid comprises a cyclic siloxane. 7. The composition of claim 1, wherein the silicon containing grinding aid comprises a hydroxyl terminated polydiorganosiloxane. 8. The composition of claim 1, wherein the silicon containing grinding aid comprises a mixture of a cyclic siloxane and hydroxyl terminated polydiorganosiloxane. 9. The composition of claim 1 , further comprising clinker in an amount of 0-90% by weight of the composition. 10. The composition of claim 1, wherein the silicon containing grinding aid has been emulsified or is in a solvent. - 11. The composition of claim 9, wherein the clinker has been ground prior to mixing with the slag. 12. The composition of claim 9, wherein the clinker was made by sintering a mixture that contains from 0 - 80% slag. 13. A method for improving the efficiency of slag grinding, comprising the steps of: treating slag with a silicon containing grinding aid; and grinding the slag. 14. The method of claim 13, wherein the silicon containing grinding aid is present in an amount from 10 grams to 20,000 grams per metric ton of the total composition. 15. The method of claim 13, wherein the silicon containing grinding aid comprises a trimethyl endblocked polydiorganosiloxane. 16. The composition of claim 13, wherein the silicon containing grinding aid comprises an alkoxy silane. 17. The method of claim 13, wherein the silicon containing grinding aid comprises a siliconate, silanolate or siloxanolate. 18. The method of claim 13, wherein the silicon containing grinding aid comprises a cyclic siloxane. 19. The method of claim 13, wherein the silicon containing grinding aid comprises a hydroxyl terminated polydiorganosiloxane. 20. The method of claim 13, wherein the silicon containing grinding aid comprises a mixture of a cyclic siloxane and hydroxyl terminated polydiorganosiloxane. - 21. The method of claim 13, wherein comprising the additional step of adding, before or after grinding, clinker in an amount of from 0 - 90% by weight of the composition. 22. The method of claim 21 , wherein the clinker has been ground. 23. The method of claim 21 , wherein the clinker was made by sintering a mixture that contains from 0 - 80% slag. 24. The composition of claim 13, wherein the grinding aid has been emulsified or is in a solvent. 25. A cement made with the slag of claim 1. 26. A cement made with the ground slag of claim 13. 27. A cement made with the composition of claim 21.

Inventors: LOPES DA CUNHA SEBASTIAO WALTE, LOPES DA CUNHA, SEBASTIAO, WALTER, JR.
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1999
Main classification: C04B24
IPC codes: B02C19, B02C23, C04B5, C04B7, C04B24