Phase-selective determination of c3a and c3s surface in clinker

Abstract

The present invention relates to a method for determining the relative fineness of the C3A phase and the C3S phase in clinker, in which method: the clinker is mixed with an activator liquid and is examined in a heat flow calorimeter; the initial peak from the start of measurement up to one hour is used as a value for the reactivity and thus for the fineness of the C3A; and the main peak between 2 hours and 25 hours after the start of measurement is used as a value for the reactivity and thus for the fineness of the C3S.

Description

[0001] Phase-selective determination of the surface area of ​​C3A and C3S in clinker

[0002] The invention relates to a method for phase-selective particle size determination in a Portland cement clinker for targeted prediction of the setting behavior.

[0003] In systems of substances consisting of two or more solid reactive components, the solution or reaction kinetics are determined by the specific surface area of ​​the individual components and the reaction kinetics of the components of the substance. In practice, however, reactivity is only used descriptively, since the reaction rate is influenced by the concentration of reactants, their surface area, the temperature, and other minor constituents.

[0004] Reactive components are metastable in thermodynamic disequilibrium with their surroundings and can react spontaneously or upon excitation, for example, by the addition of a liquid. Generally, the greater the energy content and the larger the surface area provided, the more intense and rapid the reaction, potentially leading to spontaneous conversion without additional excitation.

[0005] Examples of such systems include insulating materials made from a polymer and a pore-forming agent that react together to form foam, or binders based on calcium sulfate aluminate or calcium sulfate that react upon addition of water, or the pore formation in the production of calcium silicate bricks through pore-forming agents made from aluminum powder and the interaction with the alkaline solution.

[0006] Cements serve as an example of materials in which a reaction involving phase changes is triggered by excitation. After the sintering process during clinker production, the mineral phases of a cement clinker are kept metastable by cooling. They are stimulated to hydrate by the addition of water and react with the water over an extended period to form strength-imparting hydrate phases. The rate of this reaction can be influenced, for example, by varying the fineness of the clinker sample, even if the sample is otherwise identical. In practice, the cement industry verifies the strength development required by the applicable standards on the shipping samples.For process control, these strength data are only of limited use or not at all usable, since the results of this investigation are only available with a distance from production and an assignment of the strength values ​​to higher-frequency values ​​used for control from the process control is only inadequately possible.

[0007] For this reason, in production control during cement milling, fineness measurements from sieving, Blaine testing, or a laser-based measuring device (laser granulometer) are frequently used to indirectly estimate the intensity of the subsequent cement reaction based solely on the particle size distribution, assuming a constant sample. Other measuring devices, primarily used in research and development, are employed to determine the BET surface area or zeta potentials. However, fineness measurements generally cannot distinguish between different phases. This becomes particularly evident with cement, whose components each exhibit a specific grinding resistance. When these components are milled together, this leads to multimodal distribution curves, composed of two or more distribution curves of the individual components. Therefore, the analyzers cannot resolve a specific particle size distribution for the individual components.In addition, each phase involved in the reaction has a specific solution behavior and therefore, via the surface involved in the reaction and the solution kinetics, initially determines the hydration of this phase and subsequently, indirectly via the saturation status of the pore solution achieved, also the formation of further strength-giving hydrate phases.

[0008] Clinker, or cement, is a very complex material consisting of a large number of phases, each contributing differently to the reactivity during concrete production. The main component of cement, particularly clinker, consists primarily of four mineral phases. These are essentially the calcium silicates C3S (CasSiOs), C2S (Ca2SiO4), aluminate (C3A = CasA^Oe), and calcium aluminate femt (C4AF = Ca4Al2Fe2O). Clinker also contains small amounts of free lime (CaO), alkali sulfate (K2SO4, Na2SO4), and periclase, as well as other complex salts. The mixing ratio of these phases directly influences the setting behavior. The phase composition of this mixture can be determined relatively well and reliably, for example, using X-ray diffraction. Similarly, the particle size distribution of the material can also be reliably determined before and after grinding, as previously described.

[0009] In addition, a complex interaction occurs between the phases and the respective fineness of the material. The challenge here is that the different phases undergo changes both during grinding, due to specific grinding resistance, and during firing, due to differing diffusion characteristics and temperature ranges for phase formation during the sintering process. These changes are influenced differently by the processes themselves and by the starting materials. However, since the crystalline domains of these phases are comparatively large, the crystal size of an individual phase cannot be determined by X-ray diffraction. Similarly, particle size measurement does not allow for differentiation of the content of the individual phases according to grain size.

[0010] Microscopic methods that allow for such particle size measurement and are used in academia often require a trained operator. Due to the considerable time investment, sufficiently high repetition rates are not achievable to utilize the data for process control. Furthermore, the analytical results are subjectively influenced by the operator, which reduces reproducibility between different operators. At the same time, the sample that can be evaluated through visual differentiation and size determination is extremely small, so that, for example, inhomogeneity can significantly affect the quantification. Microscopic methods allow for the simultaneous determination of particle size and chemical / mineralogical composition.Polarized transmitted light microscopy (polarization microscopy) or reflected light microscopy after etching can be used to determine both grain size and crystal type, provided the observer is appropriately trained. However, both light microscopy methods are susceptible to color shifts caused by factors such as sample thickness or insufficiently reproducible etching processes. For this reason, experienced preparators continuously monitor the preparation progress. Automating sample preparation is difficult. Furthermore, due to the wavelength limitations of visible light, the method reaches its resolution limit for small particles. Scanning electron microscopy, in conjunction with energy-dispersive microanalysis, also allows for mineral-phase-specific grain size analysis.The resolution of this method is limited by electron scattering in the sample and reaches a resolution limit for small particles. Automated sample preparation is complex, and in practice, samples are often prepared manually. Finally, scanning transmission electron microscopy analyses in so-called dark-field imaging can be used simultaneously to determine the phase composition and grain size. This method requires specialized equipment and considerable expertise from the observer. The validity of the method is limited by the small sample sizes and is not currently used in automated applications.

[0011] The challenge therefore arises that while the different particle sizes of the different phases have an influence on the setting behavior, they cannot be determined using conventional analysis methods, meaning that the clinker process cannot be specifically controlled.

[0012] From DE 10 2016 105 319 A1 a calorimetric method and a device for determining the specific grinding resistance are known.

[0013] From the SANDBERG PAUL ET AL: "When dreams come true", WORLD CEMENT, November 2020 (2020-11 ), pages 59-63, XP093282834, the Enders Michael ET AL: "Impact of particle size, clinker mineralogy and sulfate availability on early cement hydration: Observations from isothermal heat-flow calorimetry", Cement and Concrete Research, Vol. 185, August 2, 2024 (2024-08-02), page 107613, XP093199527, ISSN: 0008-8846, DOI: 10.1016 / j.cemconres.2024.107613, the Von Mentzer Kristina: "Study on Early Hydration Reactions of Cement Clinker using Isothermal Calorimetry - Influence of C3A content, SO3 content, Blaine Number and Mixing Type", July 2, 2024 (2024-07-02), pages 1-70, XP093251775, URL: http: / / lup.lub.lu.se / student-papers / record / 9169683 and NEUMANN THOMAS ET AL: "From process control to quality prediction: Artificial intelligence in clinkering process control", ZKG, 2021, XP093282828 are known scientific contributions to developments in the cement industry.

[0014] The object of the invention is to provide an analytical method that determines the parameters relevant for a clinker and thus enables more targeted process control, which can relate to the firing process only, to a grinding process only or to a combination of the two.

[0015] This problem is solved by the method with the features specified in claim 1. Advantageous further developments are described in the dependent claims, the following description, and the drawings.

[0016] The method according to the invention serves to determine the change in fineness of the C3A phase and the change in fineness of the C3S phase in clinker. Besides the pure proportion of C3A and C3S, their respective fineness is also important for the setting behavior of the cement, since a higher fineness also allows for better accessibility to water and thus a faster reaction. Faster is not necessarily better or worse; this depends on the intended application and thus the goal of the production process, as different applications require different setting behaviors. Therefore, targeted adjustability is desirable. The aim is thus not the direct absolute determination of the fineness, but rather the relative change in fineness over two or more successive measurements.

[0017] The clinker, usually a small sample, is mixed with an excitation liquid. Suitable excitation liquids include water and aqueous alkalis, especially dilute sodium or potassium hydroxide solutions. The clinker-excitation liquid mixture is analyzed in a heat flow calorimeter. To begin the measurement as quickly as possible after the addition of water, the water can be added directly in the calorimeter, particularly using an excitation liquid pre-heated to the calorimeter temperature. The initial peak from the start of the measurement up to one hour is used as a measure of the reactivity and thus the fineness of the C3A. The main peak, occurring between two and 25 hours after the start of the measurement, is used as a measure of the reactivity and thus the fineness of the C3S.If one initially assumes a constant C3A to C3S ratio between measurements, or determines this ratio in parallel, then changes in the initial and main peaks can directly indicate changes in fineness. The particle size of the C3A and C3S phases is therefore not determined directly or absolutely; only a relative change is observed, and this is done in a way that allows direct feedback for process control, even if the duration of the main peak is around a day on a timescale, which is still a significant improvement over current systems. Thus, calorimetry is used, an analytical method that would not be considered for particle size determination, as it does not provide particle size as an analytical result and therefore would not be used for this purpose.But especially in the context of the complex clinker composition, this method has proven to be surprisingly effective.

[0018] According to the invention, the increase in the initial peak between two measurements is used as a measure of the reduction in the particle size of C3A, and the increase in the main peak between two measurements is used as a measure of the reduction in the particle size of C3S. Mathematically, a negative increase (reduction) corresponds to a negative decrease (and thus increase) in the particle size. The finer the material, the better the excitation fluid can come into contact with it, and the stronger the reaction, resulting in more heat being released, which is detected by the calorimeter. Thus, if, for example, variations in the combustion process, such as fluctuations in the fuel and therefore in the temperature profile during combustion, affect the crystallite size of C3A and C3S differently, this can be quantitatively determined.It is therefore possible to adjust the firing processes accordingly to obtain a clinker that meets the desired specifications. The aim is not the absolute measurement of the fineness of the two phases, but rather continuous monitoring to detect relative changes in the process in a timely manner, for example, whether one phase becomes larger or smaller in particle size. In a further embodiment of the invention, the phase ratio between C3A and C3S is additionally determined using X-ray diffraction. By determining the absolute phase proportions, this influence on the increased or decreased activity can be factored out, thus isolating the influence of particle size.Even though the assumption of a constant phase ratio is sufficient as a first approximation, since this involves monitoring production and therefore only effects occurring on a short timescale are important and not comparability with other systems or on large timescales, the accuracy can be further increased in this way.

[0019] In a further embodiment of the invention, the fineness ratio of C3A to C3S is used to control a clinker production plant for the production of clinker containing C3A and C3S. In particular, the fineness ratio is used to regulate the rotational speed of a rotary kiln, to regulate the fuel supply to a rotary kiln and / or a calciner, and / or to regulate a mill. The necessary relationships are known to those skilled in the art, for example, from Chuck Buchanan: Silicate Crystal Size versus Kiln Speed ​​in Portland Cement Clinker, MICROSCOPY AND ANALYSIS • MARCH 2003, page 23ff, and Arthur Harrison: Aligned Size; CEMENT CHEMISTRY, ICR July 2014, page 54ff.

[0020] In a further embodiment of the invention, a secondary peak, superimposed on the main peak between 2 and 25 hours, is determined between 12 and 17 hours. This secondary peak is attributed to sulfate consumption and thus subtracted from the main peak, since the latter is not attributable to C3S. This secondary peak can, however, be readily separated from the main peak. Sulfates are mixed with clinker during cement production to modify the setting behavior. This is therefore particularly advantageous when the process to be controlled involves the grinding of the cement, i.e., a mixture of clinker and sulfate carriers, among other things, since this secondary peak can be relevant in the finished cement. The method according to the invention is explained in more detail below with reference to an embodiment illustrated in the drawings.

[0021] Fig. 1 Example measurement

[0022] Fig. 2 two example measurements

[0023] Figure 1 shows a highly schematic representation of a first example measurement. The measurement is divided into two parts of the diagram, with the time axis on the left ranging from 0 to 1 hour and on the right from 2 to 25 hours. Because the time scales are so different, a separate representation makes sense, as otherwise one of the two peaks would be practically invisible. The division into two areas thus serves only to improve visibility. The initial peak, which is due to the reaction of C3A, can be seen in the left area. The main peak, which is due to the reaction of C3S, can be seen in the right area. The heat output P is plotted on the ordinate.

[0024] Fig. 2 shows, in addition to the first example measurement shown in Fig. 1, a second example measurement (shown with dashed lines). It is evident that the initial peak is smaller and the main peak is larger. This means that, assuming the ratio of the C3A phase to the C3S phase remains unchanged, the C3A phase has become coarser and the C3S phase finer. Therefore, a relative statement can be made regarding the particle size of the phases.

[0025] As previously explained, different cements are produced for different setting properties and are in demand by the market. Therefore, it's not a question of better or worse, but rather about being able to produce the right product based on demand.

Claims

Patent claims 1. A method for determining the change in the fineness of the C3A phase and the change in the fineness of the C3S phase in clinker, wherein the clinker is mixed with an excitation liquid and examined in a heat flow calorimeter, wherein the initial peak from the start of the measurement up to one hour is used as a value for the reactivity and thus for the fineness of the C3A, and wherein the main peak between 2 hours and 25 hours after the start of the measurement is used as a value for the reactivity and thus for the fineness of the C3S, characterized in that the increase in the initial peak between two measurements is used as a measure for the reduction in the particle size of the C3A, and the increase in the main peak between two measurements is used as a measure for the reduction in the particle size of the C3S.

2. Method according to claim 1, characterized in that the phase ratio between C3A and C3S is additionally determined by means of X-ray diffraction.

3. Method according to one of the preceding claims, characterized in that the fineness ratio of C3A to C3S is used to control a clinker production plant for the production of the clinker containing C3A and C3S.

4. Method according to claim 3, characterized in that the fineness ratio is used to control the rotational speed of a rotary kiln, to control the fuel supply to a rotary kiln and / or a calcinator and / or to control a mill.

5. Method according to one of the preceding claims, characterized in that a secondary peak superimposed on the main peak between 2 hours and 25 hours is determined between 12 and 17 hours, wherein the secondary peak is assigned to the sulfate consumption.

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