Pigments, nacreous

Pearlescence comes about by multiple partial reflection of every incident ray of light on several platelet-shaped particles at different depths in the coating. 

Manufacture of synthetic nacreous luster pigments by precipitating Ti02 on mica platelets 

---

Nacreous Pigments. Mica is used as a substrate for coatings (qv) of various metal oxides to obtain a peadescent effect. Mica coated in this fashion is used as filler and as a coloring agent in certain types of plastics. 

Eyeliners are available in two popular forms. One of these is a deeply pigmented emulsion that is appHed with a fine bmsh. The emulsion must be viscous to avoid miming and should dry to a waterproof film. The emulsion can be patterned after the emulsions used in mascaras. Glossy eyeliners require the use of nacreous pigments suspended in polymeric film formers, for example, acryUc acid copoljmiers. 

N1 -acylsulfanilamides, 23 508 A21-heterocyclic derivatives, 23 508 Ar -heterocyclic-Ar -acylsulfanilamides, 23 508 A21-heterocyclic sulfanilamides, 23 507—508 2V-(2-aminoethyl)-l,3-propylenediamine physical properties, 5 486t 2V-(2-aminoethyl)-piperazine (AEP), 5 485 N2 oxidation, Birkeland-Eyde process of, 27 291-292, 316. See also Dinitrogen entries Nitrogen entries N3 -P5 phosphoramidates, 27 630-631 Na+, detection in blood, 24 54. See also Sodium entries Nabarro-Herring creep, 5 626 Nacol 18, chain length and linearity, 2 10t Nacreous pigments, 7 836-837 19 412 Nacrite, 6 659... 

Thermal decomposition of iron pentacarbonyl. Very finely divided red iron oxide is obtained by atomizing iron pentacarbonyl, Fe(CO)5, and burning it in excess of air. The size of the particles depends on the temperature (580-800 °C) and the residence time in the reactor. The smallest particles are transparent and consist of 2-line ferri-hydrite, whereas the larger, semi-transparent particles consist of hematite (see Chap. 19). The only byproduct of the reaction is carbon dioxide, hence, the process has no undesirable environmental side effects. Magnetite can be produced by the same process if it is carried out at 100-400 °C. Thermal decomposition of iron pentacarbonyl is also used to coat aluminium powder (in a fluidized bed) and also mica platelets with iron oxides to produce interference or nacreous pigments. 

As shown in Figure 71 A, conventional pigments interact with light by absorption and/or diffuse scattering (see Section 1.3). Luster pigments comprise nacreous pigments (Section 5.3.1) and metal effect pigments (Section 5.3.2). 

Figure 71. Optical principles of conventional and luster pigments A) Conventional pigment that absorbs and scatters light B) Metal effect pigment with complete regular reflection C) Natural pearl composed of alternating layers of protein and CaC03 D) Nacreous pigment the pearl is simulated by parallel orientation of the pigment platelets...

Important nacreous pigments and producers are listed below ... 

With the given n1 and n2 values, the maximum and minimum intensities of the reflected light - seen as interference colors - can be calculated and agree well with experimental results [5.206]. Refractive indices of materials commonly used in nacreous pigments follow ... 

In practice, platelet crystals are synthesized with a layer thickness d calculated to produce the desired interference colors (iridescence) [5.206], [5.207], Most nacreous pigments now consist of at least three layers of two materials with different refractive indices (Fig. 73). Thin flakes (thickness ca. 500 nm) of a material with a low refractive index (mica) are coated with a highly refractive metal oxide (e.g., Ti02, layer thickness ca. 50-150 nm). This results in particles with four interfaces that constitute a more complicated but still predictable thin film system. The behavior of more... 

The first commercially successfull synthetic nacreous pigments were hexagonal platelet crystals of lead salts Thiosulfate, hydrogen phosphate, hydrogen arsenate and most important nowadays, basic carbonate. Basic lead carbonate [1319-46-6] Pb(OH2) 2PbC03, Mr 775.7, is precipitated from aqueous lead acetate or lead propionate solutions with carbon dioxide ... 

Powders containing bismuth compounds have long been used for decorative purposes to generate a shiny luster or lustrous colors (e.g., facial cosmetic powder in ancient Egypt, imitation pearls made by coating glass and ceramic beads). Bismuth oxychloride [7787-59-9], BiOCl, Mr 260.4, was the first synthetic nontoxic nacreous pigment. It is produced by hydrolysis of acidic bismuth solutions in the presence of chloride ions. Precipitation conditions may be varied (concentration, temperature,... 

The dominant class of nacreous pigments is based on platelets of natural mica coated with thin films of transparent metal oxides (see Fig. 73). Mica minerals are sheet silicates (laminar). Nacreous pigments are usually based on transparent muscovite [9941-63-5] but some are based on natural or synthetic phlogopite [110710-26-4]. Although muscovite occurs worldwide, few deposits are suitable for pigments it is biologically inert and approved for use as a filler and colorant [5.220], [5.221],... 

Nacreous pigments require transparent or at least translucent binders or other carriers. Formulations with other pigments have to take their transparency and color mixing rules into account. Producers specify certain product lines for specific applications on the basis of national regulations and technical considerations. They also provide handling guidelines and starting formulas. 

Color systems with nacreous pigments can be formulated in four ways [5.211] ... 

Blending nacreous pigments with other pigments in a single color formulation... 

Using a two-layer coating system in which an upper coat contains the nacreous pigment and the lower coat contains the hiding absorption or metal effect pigments... 

Using a two-layer system with a transparent absorption color formulation applied on top of a layer containing the nacreous pigment... 

Using a multilayer nacreous pigment consisting of an absorbing and/or iridescent coating applied in single coat to the substrate in the form of platelets (see Section 5.3.1.5)... 

MW 0/1mud Mica. Wei ground mica is used because of its unique properties, i.e.. luster, slip and sheen, and high aspect ratio. It is used in wallpaper and coated paper, nacreous pigments, as a coating for rubber, in ouidoor house paint, and in aluminum paints. Mica is used in all types of scalers for porous surfaces, such as vvallboard masonry, and concrete blocks, to reduce penetration and improve holdout and as a filler in plasties to improve its electrical and thermal resistance and its insulating qualities. See also Sealants. 

Nacreous Pigments Nacreous, i.e.. pearlescent pigments are used for creating special decorative effects typical of natural pearls. Nacreous pigments are fine, thin, plate-like transparent particles having a high refractive index. Because of these physical characteristics, when dispersed in a transparent film, they produce a silky appearance. 

---