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  Organic, Inorganic and Metallic Pigmentsigments, Chemistry tutorial

Introduction

There are a number of pigments available today. In fact, after the advent of synthetic pigments there has evolved diverse kinds of pigments that are suited to particular needs and kinds of industries.

Definition of types of Pigments

Inorganic Pigments: Pigments that are made up of mineral compounds are recognized as Inorganic Pigments. Organic Pigments: Organic Pigments aren't generally found in nature. That is the reason why a majority of such pigments are chemically synthesized. They enclose carbon and come through comparatively low levels of toxicity, not providing any major environmental challenge.

Industrial Pigments: Such are depend on their industrial application.

Organic pigments

Raw materials comprise coal tar and petroleum distillates that are converted into insoluble precipitates. Conventionally organic pigments are utilized as mass colourants. They are fashionable in plastics, artificial fibres and as surface coatings-paints and inks. In recent years the organic pigments are utilized for hi-tech applications that include photo- reprographics, opto-electronic displays and optical data storage.

Categories of Organic Pigments

a. Monoazo Pigments

b. Diazo Pigments

c. Acid and base dye Pigments

d. Phthalocyanine Pigments: Several of the striking features which make it a extremely helpful for a variety of applications are the following: Light fastness, tinting strength, covering power, resistance to the effects of alkalies and acids and good stability

e. Quinacridone Pigments: The subsequent are significant features of such pigments;  outstanding light fastness, excellent bleed and heat resistance, bright and vibrant tones, extremely good tinting value along through working properties and high transparencies

f. Other polycyclic Pigments

Key Features of Organic Pigments

a. Very good stability to solvents, light, heat, and weathering

b. Good tinctorial strength

c. Cost effectiveness

d. Consistency and unique shades

e. Completely non-toxic

f. Very bright, pure, rich colors

g. Organic pigments shows good color strength

Inorganic pigments

Inorganic pigments might be attained from vivid naturally occurring mineral sources or minerals that have been attained synthetically. They are of the kind mineral-earth but usually are metallic oxides or synthetics. Pigments that are of the kind Mineral-earth are extremely easy and naturally occurring coloured materials. The preparation procedure is as well simple and consists of the steps of washing, drying, pulverizing and mixing into a formulation. Inorganic pigments are available in the market in different forms. Such different forms are powder, pastes, slurries and suspensions. The Inorganic Pigments are another time separated into 2 sub kinds.

Natural inorganic pigments

Natural inorganic pigments are the earth colours in natural form as ochers, umbers and so on. Such colour pigments are extracted from the earth bed, Iron oxide and hydroxide that are present in the soil. Such 2 compounds are responsible for the colouration of such colour pigments. Clay, chalk and silica are as well present in such pigments in fluctuating quantity.

The kinds of Natural Inorganic Pigments are:

(i) Azurite-Actually such kind of natural inorganic pigments are copper carbonates having greenish blue shading. Over an extremely long period, azurite has been utilized as a pigment. But, often such pigments have been replaced through synthetic pigments or utilized to paint the expensive ultramarine as under paintings.

(ii) Red earths- Such pigments are the most diverse kind of natural inorganic pigments. Such are made from clay and they have a huge amount of iron oxide. The colour varies from dull yellow to dull deep yellow or from dull orange to dull red or from dull dark brown to dark brown.

(iii) Yellow earths- Such are natural earth containing silica and clay. Such pigments are present in hydrous form of iron oxide. These pigments as well enclose gypsum or manganese carbonate.  All over the world, such pigments are available and have been utilized from the prehistoric period.

Synthetic inorganic pigments

Synthetic inorganic pigments are created in the laboratory. Such pigments consist of metallic compounds as manganese violet; cobalt blue and so on. Synthetic inorganic pigments can as well be produced via the replication of the natural earth colours as mars, red or yellow. As such pigments are manufactured in the laboratory, so they are found in pure form having fine particles.

Table: Refractive Index of some of the very Popular Class of

Pigment

Refractive

Index

TiO2  (rutile)

2.71

TiO2  (Anatase)

2.55

Antimony Oxide

2.20

Zinc Oxide

2.01

Calcium

Carbonate

1.65

Fumed Silica

1.45

Synthetic organic pigments are mainly derived from several selective elements atoms. Such are as follows:

Chromophore is a pair or collection of atoms that produces a complex and dynamic clouding of the electrons within the individual electron shells in single atom or more than one atom. Such chromophores are dependable for the colour creation phenomena of the pigment's molecules.

Shortcomings of Inorganic Pigments

Colour that comes from inorganic pigments is reasonably less bright. Such pigments as well seemed to be less rich and pure than the organic pigments. As such pigments have low tinting strength so a huge number of pigments are needed to produce the desired effects.

Differences between Organic and Inorganic Pigments

The differences between organic and inorganic pigments are depends upon 3 principal aspects.

i. Molecular formation of the pigments Carbon chains or carbon circles are always present in the molecules of the Organic Pigments. As carbon element is connected through nitrogen and sulphur elements of the similar class of the atomic table, so, sometimes in the  molecules  of  the  organic  pigments,  the  atoms  of  nitrogen  and sulphur are as well found along by the carbon atoms.

Instances: Azo, Phthalocyanine, Diazo and Anthraquinone pigments. Though, in the molecules of the Inorganic Pigments, the cations of metal are originate in an array form by the non-metallic anions. This arrangement doesn't permit such pigments to dissolve in the solvent and plastic. Instances: Iron oxide, yellow, black, red and tan pigments.

ii. Sources

The major sources of organic pigments are plants and plant products.

iii. Exposure

Inorganic pigments are considered better over their organic counterparts. These inorganic pigments can withstand the impact of sunlight and chemical much better. .They has also good opacity and thus can protect other objects by preventing light. These pigments as well raise rash inhibition, abrasion resistance and stiffness to the molecules. These pigments are available at low price in respect to the organic pigments.

They are as well durable.

Table: The Differences between Organic and Inorganic Pigments

Particulars

Inorganic  Pigments

Organic Pigments

Source

Minerals

Chemically refined oil

Color

Often dull

Bright

Dyeing/Coloring Strength

Low

High

Opacity

Opaque

Transparent

Light fastness

Very good

Vary from poor to good

Solubility

Insoluble  in  solvents

Have little degree  of

solubility

Degree of safety

May be unsafe

Usually safe

Chemical Stability

Often sensitive

Usually good

Cost

Moderate

Mostly too expensive

Metallic pigments

Nowadays, metallic pigments are an extremely popular category of pigments, as a further classification. Metallic pigments can be of 2 kinds:  

(i) Aluminium Pigments: Aluminium pigments are additional separated into 2 categories namely leafing grade and non-leafing grade. The aluminum pigments are generated from aluminium that has purity in the range of 99.3-99.97%. The particle has lamellar shape with 0.1-2 µm in thickness and diameter of 0.5-200 µm. Such pigments found utilize in automotive topocoats. Several of the preferred applications of Aluminium pigments are the following:

i. Corrosion protection coats

ii. Reflective paints

iii. In Marine paints (covering coats)

iv. Roof coatings

v. In Heat-proof and highly heat-resistance paints

vi. Chrome effect paints

vii. Aerosols

(ii) Zinc Pigments: Zinc Pigments come in 2 forms of powder and dust. Generally the zinc dust is finer as evaluated to powder and is spherical in shape. The dust as well has a light coating of zinc oxide.

Table: Zinc Pigments along with their Applications

Zinc Pigments

Application

Zinc dust

Chemical applications Metallurgical applications

Zinc phosphate

Active ingredient in domestic cleaning products

Zinc oxide

Agricultural applications

Rubber industry

Brick kilns

Ceramics

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