Pigments spherical shape

The stable form of arsenic is the gray or metallic form, although other forms are known. Cooling the vapor rapidly produces yellow arsenic, and an orthorhombic form is obtained if the vapor is condensed in the presence of mercury. Arsenic compounds are used in insecticides, herbicides, medicines, and pigments, and arsenic is used in alloys with copper and lead. A small amount of arsenic increases the surface tension of lead, which allows droplets of molten lead to assume a spherical shape, and this fact is utilized in the production of lead shot. 

Conductive Nickel Flake Powder HCA-1 - product developed for conductive paints and adhesives which provides EMI shielding when used in surface coatings, inks, and adhesives. The flakes are treated in a controlled atmosphere to give cleaner surface which enhances conductivity Conductive Nickel Pigment 525 - dendritic filamentary shape similar to INCO products CNS - spherical shape and uniforms size for thick film inks... 

Nano-sized and homogeneous hematite particles were obtained into sintered cristobalite-zircon matrix after heat treatment at 1000°C/3h and 1100°C/3h. Occluded hematite particles have been spherical shapes with 5-10 nm diameters. Changes of sintering temperatures did not show any effect on hematite morphology but it was important about red shade, inclusion efficiency and thermal-chemical stability of the pigments. 

It turns out that nature has two ways of making color—one of them is to build a molecule, often referred to as a pigment. Pigments are made in nature s chemical factory, one bond at a time. The other method is to build a structure out of an otherwise colorless material. Rainbows have color due to the refraction of light in small, colorless water droplets. The spherical shape of a water droplet, and the angle between it and the sun, determines the colors you see. The rainbow of colors you see when you look at the surface of a DVD or a CD also comes from a structure— in this case, the fine, parallel grooves in the clear plastic disk. We call this structural color. 

Huber shows another morphological features of its structured pigment product which is in the form of porous aggregates with high brightness (Figure 2.37). Particles are composed of stacks which form aggregates closer in shape to spherical particles. 

These red-pored mushrooms are recognized by large size and club-shaped stem with coarse, reddish scales. Caps range from 3" to 7" wide and are broadly convex, almost spherical. The surface is dry, uneven or pitted, color ranging from dull-brown to cream-brown, the pigments often mottled, frequently tinged reddish towards the edge. 

If you ever had the opportunity to use almninum pigments in plastics, you are familiar with the fact that you are not dealing with spherical pigments, but with flakes. Because of their shape, metallic pigments appear to behave in regard to their optical properties in almost every way opposite to non-metallic pigments. Here are some examples ... 

Particles may be nearly spherical, cubic, nodular (a rounded irregular shape), acicular (needle- or rod-like) or lamellar (plate-like). Since particle shape affects pigment packing, it therefore affects hiding power. Rod-shaped particles can reinforce paint films, like iron bars in concrete, or they may tend to poke through the surface reducing gloss. 

Usually, we assume particles to be spherical for particle size analysis because a sphere is the only shape that can be described by one number, its diameter d. The precise shape of particles relevant for chemical and mechanical engineering (coal, catalysts, ores, cement, paint pigments etc.) differs, but we can easily convert the volume (Vp) or the mass of a particle (mp) into the diameter of an equivalent sphere (equivalent sphere theory) ... 

Fine particles of malleable metals in elemental form are also used as pigments in coatings for aesthetic as well as protective purposes. They are generally platelet-shaped particles, but some are spherical. 

The primary shape of pigmented particles is determined by their chemical nature, their crystalline structure (or lack of it) and the way the pigment is created in nature or made synthetically. Pigments as primary particles may be spherical, nodular, needle or rod-like, or plate-like (lamellar). This is illustrated in Fig. 4.1. 

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