Effect of Important Precipitation Process Parameters on the Redispersion Process and the Micromechanical Properties of Precipitated Silica

Abstract

In the past, the importance of the industrial mass production of high-quality products and specialty chemicals by precipitation increased rapidly. In the industry, usually larger aggregates are produced and in order to produce colloidal systems with the desired properties, a more or less intense dispersion of the precipitated particles is necessary. The micromechanical properties such as the maximum indentation force, the plastic and elastic deformation energy, and the strength can give information on the product and the efficiency of the dispersion process. Generally, the temperature, as one of the most important parameters of the semibatch precipitation process of silica, was varied in order to change the structure, the primary particle size, the aggregate size, and the primary particle interactions in the aggregates. Dispersion of the precipitated silica in a stirred media mill and a dissolver show that the higher the precipitation temperature, the higher is the product fineness and, thus, the smaller is the strength of the aggregates. The reason for this effect is the increase of the primary particle size and the decrease of the solid bonds with increasing precipitation temperature. Because of higher stress intensities, the product fineness in a stirred media mill is considerably higher than in the dissolver. In principal, the maximum achievable product fineness and the energy efficiency of the dispersion process increase with decreasing particle strength and maximum indentation force. Besides the maximum indentation force, the maximum achievable product fineness and the energy efficiency of the dispersion process increase with increasing quotient of plastic and elastic deformation energy.

Effect of Microchannel Geometry on High‐Pressure Dispersion and Emulsification

“…Inorganic nanoparticles are mainly synthesized by flame pyrolysis [1] or by precipitation [2,3] which lead to process-related agglomeration and aggregation of primary particles. The fabricated powders typically consist of primary particles of a few nanometers which are agglomerated physically by van der Waals forces or aggregated to clusters of a few hundred or thousand nanometers by sinter bridges or chemical bonds.…”

Synthesis, Structure and Mechanics of Nano-Particulate Aggregates

“…ion concentration, supersaturation, additives, and process parameters, e.g. precipitation temperature, pH-value, precipitation time, stirrer tip speed, supply of mechanical energy for fragmentation, and flow rate was investigated [30,36,37]. Figure 3 illustrates an example of the effect of mechanical energy input by different process units on the precipitated product.…”

“…2 Primary and secondary processes during silica precipitation process according to Schlomach and Kind [43,44] (condensation, phase separation, growth and aggregation, gelation, fragmentation and reorganization) the resultant processing and application properties of the finished product, e.g. the depressibility in further processing, are related to the various formulation and process parameters in a complex way [36]. An extensive investigation of process and formulation parameters of the specific set-up used in this work is given by Schlomach, Kind and Quarch [24,43,44].…”

“…Further specifications as well as a detailed description on the working principle of the nanoindentation device and the sample preparation (precise calibration regarding parallelism between sample and indenter tip and sample preparation via the dry dispersing device RODOS, company Sympatec) are summarized by Schilde [30] and Arfsten [3]. Since the model of Oliver and Pharr (calculation of Young's modulus or hardness) is not applicable for materials with high viscoplastic deformation behavior, the maximum indentation force as well as plastic and elastic deformation energies were determined as characteristics for the micromechanical aggregate properties [36,39,42]. Typically, the measurement of these micromechanical properties approached a constant median value as well as a constant standard deviation of approximately 40 single measurements [42].…”

Simultaneous Emulsification and Mixing

“…Mahlen ist heute der Stand der Technik, um feste, spröde Materialien bis in den Nanometerbereich zu zerkleinern [Mende et al, 2002;Schilde et al, 2009] [Abend et al, 1998]. …”