Lamellar particle

Let us consider a nanostructured thin film built from lamellar particles [84], If the principal axis of layer stacks is oriented normal to the film surface, the scattered intensity measured in symmetrical-reflection geometry (SRSAXS) is... 

The synthesis procedure led to a highly crystalline MCM-22 zeolite, as indicated by XRD data (Fig. 1A, a). The introduction of platinum by ion exchange procedure does not modify the crystallinity of the zeolite (Fig. 1A, b). SEM micrographs show that the sample obtained in static hydrothermal conditions is characterized by the presence of homogeneous round-shaped particles of ca. 10 pm in diameter formed by aggregation of lamellar particles [7,8], The morphology of the zeolite is not modified after platinum introduction (Fig. IB). 

More important than the particle size are the purity and the particle shape. The effect of bad milling on a large lamellar particle is a particle having far smaller "shape factor" or aspect ratio than the original material. Since it is the basal plane surface which provides low friction and the edges which cause abrasion, it is therefore important in milling to maintain the highest possible aspect ratio consistent with the required particle size. 

The barrier effect can be achieved, for example, by using pigments with a platelet-like or lamellar particle shape. This allows them to form a wall of flat particles within a paint film and therefore water and electrolytes have to take an extended/less direct route through the paint film to the substrate. 

Synthetic MIO-pigments are also available, but these have not achieved the economic importance of the processed natural pigments (see Section 3.1.1). The currently available MIO-pigments on the market consist mostly of more lamellar particles. Other barrier pigments of a certain economical importance are aluminum flakes, steel flakes, phlogopite and muscovite mica. 

Zinc as a pigment for application in protective coatings is also available in the form of zinc flakes with a lamellar particle shape. Zinc flakes are mainly used in so-called... 

At the same time, elasticity may also have completely different, i.e. entropic, nature. For instance, the applied stress causes segments of macromolecules in polymers, or lamellar particles present in clay suspensions to co-orient in a way that leads to a decrease in entropy. In this case the tendency of an object to restore its original configuration is related to thermal motion, which distorts the acquired co-orientation. Under these conditions elasticity modulus (the entropic elasticity modulus) is small and to a significant extent depends on temperature. 

Many raw materials for ceramic parts contain days. During densification, the lamellar shape of clay minerals results in a more-or-less defined texture because the foliated silicates tend to orient themselves vertically to the direction of force. Since lamellar particles shrink non-isotropically, such textures may result in high stresses in the sintered part, causing cracking during cooling. The orientation effect also plays a role in... 

In fact, if the width and thickness of a lamellar particle are defined as a fraction of its longest and main dimension, Ir, it is easy to define the surface/volume ratio (5A0 for each particle as follows ... 

The corresponding D r) functions for the cross-section and thickness of rod-like and lamellar particles are given in that order by ... 

It is appropriate to first of all look into optimisation of the plastic body in regard to minimising laminations. Certain materials are particularly unfavourable and tend to the formation of extrusion laminations. These are those body compositions which contain a high percentage of extremely fine and anisomorphic particles, mainly clays and kaolines with a proportion of clay minerals, whereby the lamination problems have a tendency to increase as the specific surface is enlarged. But also other materials like talcum or micaceous natural raw materials with lamellar particles are prone to the formation of extrusion laminations. 

Ferrage, E. Martin, F. Boudet, A. Petit, S. Fourty, G. Jouffret, F. Micoud, P. De Parseval, P. Salvi, S. Bourgerette, C. Ferret, J. Saint-Gerard, Y. Buratto, S. Fortune, J. (2002) Talc as Nucleating Agent of Polypropylene Morphology Induced by Lamellar Particles Addition and Interface Mineral-matrix Modelization. /. Mater. Sci. Vol.37, No.8, pp.1561-1573... 

Interactions among lamellar particles and surfaces are important in many contexts. Most surfaces have a contaminant or oxide layer, while particles can be built up from a primary nucleus which subsequently undergoes a variety of thermodynamic conditions. In this fashion, one or more layers of potentially different composition from the nucleus can be added to form a lamellar particle. Interactions of multilayer systems of any geometry resemble the interactions between half-spaces for very small separations. DZYALOSHINSKII et al. [5.581 gave the expression for the nonretarded, zero temperature interaction force between two half-spaces of frequency-dependent dielectric susceptibilities e (x) and e2(x) which were separated by a slab of susceptibility e ix) and thickness l as... 

Here clay is proved to be high-modulus lamellar particles that strongly adhere to the rubber latex leading to excellent reinforcement. A lot of scope exists... 

Examples of inert or extender fillers include china clay (kaolin), talc, and calcium carbonate. Calcinm carbonate is an important filler, with a particle size of about 1 pm. It is a natural product from sedimentary rocks and is separated into chalk, limestone, and marble. In some cases, the calcium carbonate may be treated to improve interaction with the thermoplastic. Glass spheres are also used as thermoplastic fillers. They may be either solid or hollow, depending on the particular application. Talc is a filler with a lamellar particle shape. It is a namral, hydrated magnesium silicate with good slip properties. Kaolin and mica are also natural materials with lamellar structures. Other fillers include woUastonite, silica, barium sulfate, and metal powders. Carbon black is used as a filler primarily in the rnbber industry, but it also finds application in thermoplastics for conductivity, for UV protection, and as a pigment. Fillers in fiber form are often used in thermoplastics. Types of fibers inclnde cotton, wood flour, fiberglass, and carbon. Table 1.3 shows the fillers and their forms. An overview of some typical fillers and their effect on properties is shown in Table 1.4. Considerable research interest exists for the incorporation of nanoscale fillers into polymers. This aspect will be discussed in later chapters. 

Calcium carbonate is an important filler with a particle size of about 1 p,m. It is a natural product from sedimentary rocks and is separated into chalk, limestone, and marble. In some cases the calcium carbonate may be treated to improve the bonding with the thermoplastic. Glass spheres are also used as thermoplastic fillers. They may be either solid or hollow, depending on the particular application. Talc is an important filler with a lamellar particle shape. It is a natural hydrated magnesium silicate with good slip properties. Kaolin and mica are also natural materials with lamellar stracture. Carbon black is used as a filler primarily in the rubber industry. 

A. Kalendova, P. Tamchynova, V. Stengl, J. Subrt, Behaviour of surface-treated mica and other pigments with lamellar particles in anticorrosive coatings. Macro-mol. Symp. 2002, 187, 367-376. 

In the absence of orientation and with the scattering vector normal to the lamellar particle surface, then ... 

Kaolin was produced 150 million years ago. Its main content is kaolinite, occurring with other silicates such as mica, feldspar, and quartz or metallic oxides such as hematite and rutile. In form it consists of thin pseudo-hexagonal lamellar particles. When heated to above 500°C, kaolinite loses its water of crystallization and changes to metakaolinite, which is stable up to 960°C. 

The significant increase in thixotropy and yield values and also the formation of viscoelastic gels only below pH 6.5 verify that attractive interaction exists between oppositely charged parts of lamellar particles. 

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