Calcium carbonate particle size

A combination of graded calcium carbonate particle sizes, a nonionic polysaccharide of the scleroglucan type, and a modified starch, has been claimed for use as a fluid loss formulations [915]. It is important that the calcium carbonate particles are distributed across a wide size range to prevent filtration... 

Ageing is better for the coarser PCC grade. The observation that the finer the calcium carbonate particle size, the higher the tendency to gel is likely due to fine particles having greater surface area, thus having inadequate dispersant to cover the surface and provide particle stability. 

With the paper industry requiring more and more sophisticated products from mineral producers and particularly finer and finer calcium carbonate particle size slurries, the need to improve dispersants is becoming a reality. The work described in this paper is the beginning of research on improved dispersants for preparation of PCC and GCC slurries and also other minerals. 

Tensile properties of PVC filled with precipitated calcium carbonate particles having two different mean sizes were studied. The particles were porous agglomerates of spherical primary particles. 10-50 parts of the particles were mixed with 100 parts PVC and 3 parts lead stearate using a mixing roll. Tensile tests were carried out using dumbbell test specimens. 20 refs. 

The final examples, taken from a range of possibilities, illustrate first the use of nanoparticles (in Fig. 29, dendrimers of two generations) on the morphology of calcium carbonate particles prepared in their presence. The larger dendrimer has a greater effect on the product whose particles size is much smaller than that prepared with the lower generation dendrimer. 

This example (supplemented by the additional results of Anderson et al., 1998a,b) shows that a microphase can greatly influence the nucleation and growth rates of crystals, which in turn can drastically alter the crystal size distribution of the precipitate. In other words, the average precipitate size can be controlled to enhance the precipitation and therefore the reaction rate. A parallel example is the use of microemulsion media to obtain monodispersed calcium carbonate particles via carbonation of calcium phenate (Marsh, 1987). 

Zhou and co-workers [27] studied the effects of surface treatment on the mechanical and thermal properties of composites comprising calcium carbonate particles with varying proportions of PEEK. Tensile impact and flexural testing were carried out and the effect of particle size, loading and surface treatment on deformation and crystallinity was investigated. 

At a lower temperature of 5 °C, a large number of leaflike structures was observed. Again these objects consisted of smaller particles that typically had diameters between 50 and lOOnm. Similar stmctures were observed at very low subphase concentrations (see Fig. 2). The structures on the lower side of the lower leaf shown in Fig. 2 resemble small vaterite florets in an early growth state. So it may be assumed that these objects are metastable intermediates or precursor-aggregates that are trapped in this state because of the removal of water. The size of the particles from which these stmctures were formed was about 50-l(X)nnL From these observations it can also be concluded that the primary calcium carbonate particles are more stable at lower temperatures or very low subphase concentrations. 

Figure 2.10 Influence of calcium carbonate particles on polymer melt viscosity (a) particle loading [26], (b) particle size at 30 vol% loading [9]...

Ma C G, Rong M Z and Zhang M Q, Irradiation initiated grafting of poly(hutyl acrylate) onto nano-sized calcium carbonate particles . Chin Chem Lett 2005 16(3) 409-12. 

It is also made by precipitation from dissolved calcium hydroxide and carbon dioxide. The natural ground calcium carbonate and the precipitated material compete industrially based primarily on particle size and the characteristics imparted to a product. 

Precipitated Calcium Carbonate. Precipitated calcium carbonate can be produced by several methods but only the carbonation process is commercially used in the United States. Limestone is calcined in a kiln to obtain carbon dioxide and quicklime. The quicklime is mixed with water to produce a milk-of-lime. Dry hydrated lime can also be used as a feedstock. Carbon dioxide gas is bubbled through the milk-of-lime in a reactor known as a carbonator. Gassing continues until the calcium hydroxide has been converted to the carbonate. The end point can be monitored chemically or by pH measurements. Reaction conditions determine the type of crystal, the size of particles, and the size distribution produced. 

Following carbonation, the product can be further purified by screening. This screening, also used to control the maximum size of the product, is followed by dewatering (qv). Rotary vacuum filters, pressure filters, or centrifuges are used in the mechanical removal of water. Final drying is accompHshed as with natural calcium carbonate in either a rotary, spray, or flash dryer. Products having mean particle sizes from submicrometers (- O-OS fiTo) to several micrometers are available. 

The most comprehensive set of test methods for calcium carbonate has been assembled by the Pulverized Limestone Division of the National Stone Association. Methods for particle size, brightness, +325 mesh (44 -lm), and percentage of calcium carbonate have been pubflshed standards are available and have been well characterized (5). The Technical Association of the Pulp and Paper Industry (TAPPl) has pubflshed methods for calcium carbonate used in the paper industry (6). 

Calcium carbonate is one of the most common filler/extenders used in the paint and coatings industry. Consumer and contractor paint formulas can include products from submicrometer size to coarse mesh sizes. The main function of calcium carbonate in paint is as a low cost extender. It is also used to improve brightness, appHcation properties, stabiHty, and exposure resistance. Coarse products help to lower gloss and sheen or even provide textured finishes. The selection of product type and particle size is deterrnined by the desired performance and cost of the coating. 

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