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  • 1
    Language: English
    In: Chemical Engineering Science, 2011, Vol.66(21), pp.4943-4952
    Description: In many cases nanosized particles are produced not as single primary particles but rather as particle collectives consisting of several primary particles. For many applications the particles must be available in liquid as separately dispersed primary particles or in a certain aggregate size. Especially the micromechanical properties of nanostructured aggregates, for example the breakage energy, have a strong impact on their breaking behaviour and, thus, on the dispersion process. For the determination of the micromechanical properties of nanostructured silica aggregates different measurements with a nanoindenter have been carried out. Comparing the measured micromechanical properties with dispersion results in a stirred media mill, conclusions concerning the influence of particle interactions and solid bridges between the primary particles and the strength of aggregates and their dispersibility can be drawn. The strength of the aggregates can be changed using different primary particle sizes. Generally, the maximum achievable product fineness and the efficiency of the dispersion process increases with decrease in aggregate strength and, thus, increasing primary particle size. With the help of the calculated stress energy distribution in the stirred media mill using the discrete element method and the measured fracture distribution of the aggregates measured via nanoindentation an effective dispersion fraction can be calculated. Comparing the effective dispersion fraction with the dispersion progress in the stirred media mill a linear correlation can be obtained. ► The breakage energy of nanostructured aggregates can be characterised via nanoindentation. ► The breakage energy can be compared with dispersion results in a stirred media mill. ► Strength and structure of the aggregates can be changed by using different primary particle sizes. ► The stress energy in the mill can be calculated and compared to dispersion and indentation results.
    Keywords: Nanostructure ; Dispersion ; Simulation ; Product Processing ; Nanoindentation ; Stirred Media Mill ; Engineering
    ISSN: 0009-2509
    E-ISSN: 1873-4405
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  • 2
    Language: English
    In: Chemical Engineering Science, May 3, 2013, Vol.94, p.127(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ces.2013.02.042 Byline: Carsten Schilde, Christian Hanisch, Dennis Naumann, Theresa Beierle, Arno Kwade Keywords: Particle formation; Particle processing; Precipitation; Stirred media milling; Dispersion; Nanoparticle Abstract: Certain characteristics of the product quality particularly the aggregate structure of precipitated nano- und micro-particles are relevant depending on the application of precipitated solids. This structure depends on the physicochemical properties of the material as well as on the operating and formulation parameters of the precipitation process and the following process steps. In most of the cases large aggregates are produced by precipitation processes. These aggregates have to be redispersed in a subsequent dispersion step to produce colloidal systems with the desired product properties. In this study the effect of grinding media on the formation of aggregates in a precipitation process was investigated by implementing a basket mill in the precipitation reactor instead of a stirrer. This enables simultaneous precipitation and stirred media milling. The aggregate size range by this method was considerably smaller compared to the one obtained by standard precipitation and dispersion processes. During the following drying step, these aggregates aggregate further forming larger tertiary structures consisting of secondary aggregates. Therefore, compared to the secondary particles obtained from the precipitation process at standard conditions, a new product with a novel tertiary aggregate structure and different micromechanical properties, which can be characterized qualitatively via nanoindentation, was developed. A correlation between the maximum product fineness at the end of the precipitation process and the number of stress events according to the stress model for grinding and dispersing with stirred media mills has been observed. Author Affiliation: Institute for Particle Technology, TU Braunschweig, Volkmaroder Strasse 5, 38104 Braunschweig, Germany Article History: Received 12 July 2012; Revised 12 February 2013; Accepted 15 February 2013
    Keywords: Calcium Carbonate -- Methods ; Calcium Carbonate -- Analysis ; Rain -- Methods ; Rain -- Analysis ; Silicon Dioxide -- Methods ; Silicon Dioxide -- Analysis
    ISSN: 0009-2509
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Journal of Colloid And Interface Science, April 15, 2014, Vol.420, p.80(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jcis.2014.01.005 Byline: Nina Barth, Carsten Schilde, Arno Kwade Abstract: Display Omitted Article History: Received 11 December 2013; Accepted 5 January 2014
    Keywords: Coatings Industry -- Analysis ; Coatings -- Analysis
    ISSN: 0021-9797
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Journal of Nanoparticle Research, 2012, Vol.14(3), pp.1-11
    Description: Depending on the application of nanoparticles, certain characteristics of the product quality such as size, morphology, abrasion resistance, specific surface, dispersibility and tendency to agglomeration are important. These characteristics are a function of the physicochemical properties, i.e. the micromechanical properties of the nanostructured material. The micromechanical properties of these nanostructured agglomerates such as the maximum indentation force, the plastic and elastic deformation energy and the strength give information on the product properties, e.g. the efficiency of a dispersion process of the agglomerates, and can be measured by nanoindentation. In this study a Berkovich indenter tip was used for the characterisation of model aggregates out of sol–gel produced silica and precipitated alumina agglomerates with different primary particle morphologies (dimension of 15–40 nm). In general, the effect of the primary particle morphology and the presence or absence of solid bonds can be characterised by the measurement of the micromechanical properties via nanoindentation. The micromechanical behaviour of aggregates containing solid bonds is strongly affected by the elastic–plastic deformation behaviour of the solid bonds and the breakage of solid bonds. Moreover, varying the primary particle morphology for similar particle material and approximately isotropic agglomerate behaviour the particle–particle interactions within the agglomerates can be described by the elementar breaking stress according to the formula of Rumpf.
    Keywords: Nanoparticles ; Agglomerates ; Nanoindentation ; Micromechanical properties ; Particle morphology
    ISSN: 1388-0764
    E-ISSN: 1572-896X
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  • 5
    Language: English
    In: Journal of Colloid And Interface Science, 15 April 2014, Vol.420, pp.80-87
    Description: Particulate coatings are used in a wide range of technical applications. The application affecting properties of these coatings depend strongly on the structure formation along the production process. Thus, primary and secondary particle size, size distribution, particle morphology as well as the particle–particle and particle–fluid interactions of the used formulation affect the resulting coating properties. In this investigation titanium dioxide particles were dispersed in ethanol with a stirred media mill and stabilised electrostatically. Subsequently, the suspension was destabilised to reach specific pH values and processed into coatings by dip coating. The influence of the pH value of the suspension on the suspension’s properties such as viscosity, agglomerate size and zeta potential and on its application properties such as coating thickness, micro-mechanical properties, abrasion resistance, gloss, roughness and adhesion was examined. The electrostatic particle interactions show a significant influence on the structure formation as well as on the properties of nanoparticulate coatings. The coating properties are affected by the coating structures on micro-, meso- or macroscopic scale. Selective coating properties were related to the coating structure using the theoretical model of Rumpf. Besides other important process and formulation parameters, for the production of homogeneous, functional coatings with the desired properties a precise adjustment of the particle interactions is necessary.
    Keywords: Process Chain ; Nanoparticle ; Dispersing ; Stirred Media Mill ; Interaction Potential ; Dip Coating ; Micromechanical Property ; Coating Thickness ; Porosity ; Process–Structure–Property-Relation ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 6
    Language: English
    In: Chemical Engineering Science, 2010, Vol.65(11), pp.3518-3527
    Description: For many applications nanoparticles have to be suspended in a fluid phase and dispersed into primary particles or to a definite agglomerate size. Thereby, the prediction of the dispersion kinetic is important among others for comparing the energy efficiency of different dispersion machines. The kinetic models existing today are not able to describe the kinetics over the entire process time correctly. Moreover, a prediction of the dispersion kinetics for new process parameters is not possible. For characterizing the dispersing process and deriving an enhanced model for the dispersion kinetic the stress intensity and the number of stress events in different dispersing machines were investigated. The dispersion kinetic was investigated by dispersing Alumina Alu C (Aeroxide Alu C, evonik) in distilled water and glycerol using a dissolver, kneader, 3-roller-mill and stirred media mill. Based on these investigations a new model was developed which is able to describe the dispersion process for different dispersing machines and operating parameters with high accuracy. The new model allows the prediction of the minimum reachable end-particle-size in the studied dispersion process and at varying process parameter based on only a few data points. Within the new model the dispersion kinetics depends on two fit parameters, which are only a function of stress intensity and stress frequency alone. Moreover, using the characteristic parameters stress intensity and stress number the dispersion kinetics for new process parameters can be predicted.
    Keywords: Nanostructure ; Dispersion ; Kinetics ; Suspension ; Product Processing ; Product Design ; Engineering
    ISSN: 0009-2509
    E-ISSN: 1873-4405
    Source: ScienceDirect Journals (Elsevier)
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  • 7
    Language: English
    In: Powder Technology, Feb, 2013, Vol.235, p.1008(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.powtec.2012.11.037 Byline: Carsten Schilde, Sandra Breitung-Faes, Ingo Kampen, Arno Kwade Keywords: Nanostructure; Comminution; Kinetics; Suspension; Product processing; Stirred media mill Abstract: Besides the direct syntheses of nanoparticles via pyrolysis, sol gel or precipitation processes, wet grinding in stirred media mills is suitable for producing nanoparticles. Important requirements for nanomilling processes are low grinding media wear on the one hand and an against reagglomeration stabilized suspension on the other hand. For process design and optimization the prediction of grinding kinetics enables the comparison of the energy efficiency of grinding processes at different operating parameters and for different stabilizing additives. In this study the grinding kinetics of fused corundum in a stirred media mill was investigated using different acids as electrostatic stabilizing additives in distilled water. Based on the results a kinetic model, which was developed for dispersion processes and is based on the stress intensity and the stress frequency acting in the stirred media was enhanced regarding the product stability. The results of the grinding experiments using different stabilizing acids are transferable to the parameters of the enhanced grinding kinetics and the calculated particle-particle interaction potential. Article History: Received 6 July 2012; Revised 23 November 2012; Accepted 24 November 2012
    Keywords: Pyrolysis -- Analysis
    ISSN: 0032-5910
    Source: Cengage Learning, Inc.
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  • 8
    Language: English
    In: Journal of Colloid And Interface Science, 15 February 2016, Vol.464, pp.183-190
    Description: Spray drying processes were utilized for the production of hierarchical materials with defined structures. The structure formation during the spray drying process and the micromechanical properties of the obtained aggregates depend on the particle–particle interactions, the primary particle size and morphology as well as the process parameters of the spray drying process. Hence, the effect of different primary particle systems prepared as stable dispersions with various surface modifications were investigated on the colloidal structure formation and the micromechanical properties of silica particles as model aggregates and compared to theoretical considerations. The obtained results show that the structure formation of aggregates during the spray drying process for stable suspensions is almost independent on the functional groups present at the particle surface. Further, the mechanical properties of these aggregates differ considerably with the content of the bound ligand. This allows the defined adjustment of the aggregate properties, such as the strength and surface properties, as well as the formation of defined hierarchical aggregate structures.
    Keywords: Nanoindentation ; Silica ; Surface Modification ; Micromechanical Properties ; Spray Drying ; Aggregates ; Structure Formation ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 9
    Language: English
    In: Chemical engineering science, 2013, Vol.94, pp.127-137
    Description: Certain characteristics of the product quality particularly the aggregate structure of precipitated nano- und micro-particles are relevant depending on the application of precipitated solids. This structure depends on the physicochemical properties of the material as well as on the operating and formulation parameters of the precipitation process and the following process steps. In most of the cases large aggregates are produced by precipitation processes. These aggregates have to be redispersed in a subsequent dispersion step to produce colloidal systems with the desired product properties. In this study the effect of grinding media on the formation of aggregates in a precipitation process was investigated by implementing a basket mill in the precipitation reactor instead of a stirrer. This enables simultaneous precipitation and stirred media milling. The aggregate size range by this method was considerably smaller compared to the one obtained by standard precipitation and dispersion processes. During the following drying step, these aggregates aggregate further forming larger tertiary structures consisting of secondary aggregates. Therefore, compared to the secondary particles obtained from the precipitation process at standard conditions, a new product with a novel tertiary aggregate structure and different micromechanical properties, which can be characterized qualitatively via nanoindentation, was developed. A correlation between the maximum product fineness at the end of the precipitation process and the number of stress events according to the stress model for grinding and dispersing with stirred media mills has been observed. ; p. 127-137.
    Keywords: Models ; Product Quality ; Chemical Engineering ; Silica ; Drying ; Physicochemical Properties ; Milling ; Mechanical Properties ; Calcium Carbonate ; Grinding ; Fineness
    ISSN: 0009-2509
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 10
    Language: English
    In: Chemical Engineering Science, 03 May 2013, Vol.94, pp.127-137
    Description: Certain characteristics of the product quality particularly the aggregate structure of precipitated nano- und micro-particles are relevant depending on the application of precipitated solids. This structure depends on the physicochemical properties of the material as well as on the operating and formulation parameters of the precipitation process and the following process steps. In most of the cases large aggregates are produced by precipitation processes. These aggregates have to be redispersed in a subsequent dispersion step to produce colloidal systems with the desired product properties. In this study the effect of grinding media on the formation of aggregates in a precipitation process was investigated by implementing a basket mill in the precipitation reactor instead of a stirrer. This enables simultaneous precipitation and stirred media milling. The aggregate size range by this method was considerably smaller compared to the one obtained by standard precipitation and dispersion processes. During the following drying step, these aggregates aggregate further forming larger tertiary structures consisting of secondary aggregates. Therefore, compared to the secondary particles obtained from the precipitation process at standard conditions, a new product with a novel tertiary aggregate structure and different micromechanical properties, which can be characterized qualitatively via nanoindentation, was developed. A correlation between the maximum product fineness at the end of the precipitation process and the number of stress events according to the stress model for grinding and dispersing with stirred media mills has been observed. ► Aggregate structure depends on operating and formulation parameters of the particle synthesis. ► Effect of stirred media milling during the precipitation process was investigated. ► In contrast to the standard precipitation process we obtained a novel aggregate structure.► The novel aggregate structure shows different micromechanical aggregate properties. ► The product fineness can be correlated with the stress model of stirred media milling.
    Keywords: Particle Formation ; Particle Processing ; Precipitation ; Stirred Media Milling ; Dispersion ; Nanoparticle ; Engineering
    ISSN: 0009-2509
    E-ISSN: 1873-4405
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