Nabanita Sadhukhan
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Color pigment
• Absorption and Scattering coefficient
Particle size
Particle shape
Distribution ☛ Color and Hiding power
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Inorganic Color Pigment
Transition metal
Metal oxides and hydroxides
1. Optical Properties
2. Low price
3. Ready availability
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Prehistoric times painting
• Altamira cave painting : Great hall of polychrome Roucadour Cave Art
• limonite,
• hematite,
• red ochre,
• yellow ochre and umber
• charcoal from fire,
• carbon black, and burnt bones
• White from grounded calcite – lime white.
*Modern interpretation of bison 5
Iron based color and economic importance
• Hematite (Fe2O3) Red Pigment
• Geothite (-FeOOH) Yellow
• Umbers and Sienna Brown Pigment
• Magnetite (Fe3O4) Black pigment
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Iron oxide & hydroxides Yellow orange red brown black
• Less toxic
• Chemical stability
• Wide variety of colors Fe2O3+FeOOH
Fe (III )O Mixed Iron Oxide Fe (II, III )O
• Good performance / price ratio
Fe2O3
Composed of single component / mixed phases
Speciality pigment like magnetic pigment, transparent pigment based on iron oxide will be discussed later.
Natural and synthetic iron oxide pigments consist of well defined compounds with know crystal structures.
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Iron oxide used a pigments
Formula Ore Structure Properties
-FeOOH Goethite Diaspore Color changes with increasing
particle size from green yellow
to brown yellow
-FeOOH lepidocrocite Boehmite Color changes with increasing
particle size from Yellow to
Orange
-Fe2O3 Hematite Corundum Color changes with increasing
particle size from light red to
dark violet
Fe2O3 Maghnemite spinel Ferrimagnetic, brown
Fe3O4 Magnetite spinel Ferrimagnetic, Black
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Natural Hematite
Spanish red Parsian red
Micaceous iron oxide
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Ore Powder Powder under microscope
Goethite : Natural Yellow Ocher
• Iron oxide hydroxide FeO(OH)
• This is stable at the pressure and temperature conditions of the Earth's
surface
• It also possess crystal structure that is stable at high pressure and high
temperature
Hardness – 5.0 – 5.5 Mohs scale
Minerals structure – needle like crystals
• South Africa (55%)
• France (20%)
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Formation of goethite
• Yellow rock in Utah Pierce County “crosses” – Goethite replacing marcasite
clusters, quarry near Maiden Rock , Pierce County
• Weathering product of other iron rich minerals
• Iron oxidation state changes to Fe(II) to Fe(III)
• It remain on the earth surface
Goethites after pyrite, goethite, siderite, and marcasite
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Umbers
• Fe2O3 (45 -70%) contain 5-20% of Manganese dioxide
• Raw state : deep brown to greenish brown
• Calcined : dark brown (burnt umbers), used in oil and water color
paint
to create the darkness for the shadows on the whitewashed to create his rich and complex brown
walls, since they were warmer than
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those made with black
Siennas : Lighter in shade than a raw umber
Limonite
Found in Tuscany
Fe2O3 content of 50% and <1% Manganese dioxide
It is yellow-brown and is called raw sienna
When heated, it becomes a reddish brown and is called burnt sienna
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Toxicology and Environmental Aspects
Iron oxide pigments produced from pure starting materials may
be used as colorants for food and pharmaceutical products
Pure synthetic iron oxides do not contain crystalline silica or
other element. Therefore are not considered to be toxic.
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Production Three basic methods to produce Iron pigments are :
Raw materials : by 1) Solid state reactions (Red, Black, Brown): Thermal
products of other industries decomposition of Iron salts and compounds
Steel scrap obtained from 2) Precipitation and hydrolysis of solutions of iron salts
deep drawing, grindings (Yellow, Red, Orange, Black), accompanied by oxidation
from cast iron 3) Laux process involving reduction of nitrobenzene/organic
FeSO4 7H2O from TiO2 compounds (Black, Yellow, Red) by Iron
production
FeSO4 and FeCl2 from steel
pickling
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Aniline
Laux Process
Steam distillation
Nitro benzene 100 oC Mixture Brown
FeOOH Yellow
Cast Iron
Reaction
Fe3O4black Oxidation Red Fe2O3
2Fe +C6H5NO2 + 2H2O 2-FeO(OH) + C6H5NH2
9Fe + 4C6H5NO2 + 4 H2O 3Fe3O4 (Black) + 4 C6H5NH2
3Fe3O4 + 0.5 O2 3 Fe2O3 19
Laux process
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Many types of pigments can be obtained by varying the reaction
conditions……
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• The range extends from yellow to brown (mixtures of
-FeOOH and/or -Fe2O3 and/or Fe3O4) and from red
to black.
a) Iron(II) chloride is added, a black pigment with very
high tinting strength is produced.
b) The nitro compounds are reduced in the presence
of aluminum chloride, high-quality yellow
pigments are obtained.
c) Addition of phosphoric acid leads to the formation
of light to dark brown pigments with good tinting
strength.
d) Calcination of these products (e.g., in rotary kilns)
gives light red to dark violet pigments.
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Quality of pigment:
Reaction rate is depend on
• Nature of additives Grades of iron used
Particle side if iron
• Concentration of additives Rates of addition of the iron
Rates of nitro benzene
• Reaction rate The pH value
Amount of acid
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Pigment Properties obtained from Leux Process
• Light-fastness
• Temperature stability
• Miling stability
• Viscosity
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Pigment Properties
• RED : Due to the scaterring power of iron oxides, the particle size influences on
the shade. Particle size spans ~ 0.09 m to 0.7 m
• Red : Smaller the particles, more pronounces the yellow undertone
Larger the particles, produce blue undertone.
Size of the particle influences the color
• Small particle shows yellow tinge and larger particle
show violet hues
• Scanning electron microscopic picture of Iron oxide Red
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Black
• Black: The shade and tinting strength are directly influenced by
particle size.
Increasing
Particle size
Tinting strength Decreasing
Shade Brownish Bluish
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Optical properties of the yellow : Needle shape
• Length to width ratio Example : Length = 0.3-0.8 m, and Diameter = 0.05 - 0.2 m
Length : diameter ratio = ~ 1.5 – 8 m
• In application, needle shape particles are unsuitable.
• Spheroidal pigments are available
Needle like pigments Spheroidal pigments
SEM pictures of -FeOOH pigments
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Precipitation process
Red 2FeSO4 + ½ O2 + 4 NaOH Fe2O3 + 2 Na2SO4 + 2 H2O
Yellow 2 FeSO4 + 4 NaOH + ½ O2 2 -FeOOH + 2 H2SO4
Orange 2 FeSO4 + 4 NaOH + ½ O2 2 -FeOOH + 2 Na2SO4 + H2O
Black 3 FeSO4 + 6 NaOH + ½ O2 Fe3O4 + 2 Na2SO4 + 3 H2O
2 FeOOH + FeSO4 + 2NaOH Fe3O4 + Na2SO4 + 2 H2O
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Precipitation process The manufacture of -FeOOH yellow is described as an example
Orange – Neutral, lepidocrocite
Yellow – Acidic
FeSO4 Black – pH7, Fe(OH)2 at 90 C, magnetite
Red – excess NaOH and oxidation with air at 80 C
NaOH
Air, Stream Filtration Unit
Precipitation pigment reactor
Air, Stream
Oxidation Yellow FeOOH
Seeding tank
pH – Acidic Dryer Mill
Temp – 10-90 oC
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Penniman process
2 Fe + 2 H2SO4 → 2 FeSO4 + 2 H2
2 FeSO4+0.5 O2 + 3 H2O → 2 -FeOOH + 2 H2SO4
FeSO4
NaOH
Air, Stream Filtration Unit
Precipitation pigment reactor
Scrap iron
Air, Stream
Oxidation
Seeding tank
pH – Acidic
Temp – 20-50 oC
Dryer Mill Yellow FeOOH
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Use of Natural Iron oxide Pigments
• Inexpensive marine coatings
• Coating with a glue, oil, lime base
• Employed to color cement, artificial stone and wallpaper
• Crayons, drawing pastels and chalks
1. Housing materials (Roof tile, Coloring mortars, paving blocks, Chequesred tiles,
Designer Tiles, Stamped concrete etc),
2. Paint and inks
3. Automotive
4. Construction (Architectural coating)
5. Ceramic, rubber, plastics
6. Cosmetics
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Wood colorants
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Synthetic Iron oxide pigments Properties
• Pure hue
• Lightfast
• Good Tinting strength
• Excellent Hiding Power
• Resistant to alkalis
Main areas of use for natural and synthetic iron oxide pigments
Use Europe US Worlds
Coloring construction materials 64 50 50
Paint and coating 30 31 28
Plastic and rubber 4 18 6
Miscellaneous 2 1 16 34
Synthetic Iron oxide pigments
• Pure hue
• Consistent Properties
• Tinting strength
Single component are Red, Yellow, Orange, Black
Composition : Hematite, Geothite, Lepidocrocite, Magnetite
Brown : (Fe, Mn)2O3, and Fe2O3
Particle size, Particle size distribution, Particle shape
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Pigments quality
• Quantity and nature of the water soluble salts
• Particle size distribution (Hue and tinting strength are affected)
• The average particle size of the ground product
(red iron oxide 0.1 m yellow tinge and 1.0 m violet hues)
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Applications : Flooring colors
• Use of coloured flooring and mosaic flooring is prevalent in several
parts of India. In fact mosaic flooring is coming back in fashion these
days and skilled masons for the job are hard to find.
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Applications : Ceramic colors
Iznik tiles made of ceramic found in the city of Istanbul
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Applications : Plastic masterbaches
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Applications : Architectural Products
• Plasters
• Concrete blocks
• Surface textures
used to restore heritage building
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Leather colourants
Varied shades
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Applications : Paints and primer • High strength,
• Excellent dispersibility
Varied shades • Excellent colour stability
Extreme weather and atmospheric conditions
Primer Iron paint Interior wall
Brick painting
Exterior wall paint
Toys pigment
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Applications : Roof tiles
Long-lasting colour intensity
Resistance to UV rays
Weathering resistance
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Applications
• Colouring construction materials
Roof tiles Does not affect the setting time
paving bricks Compression strength
Tensile strength
fibrous cement
bitumen
• Natural rubber can only be coloured with iron oxides that contain very low level of
Cu (<0.005%) and Mn(<0.02%)
• Paint and coating industries Can be incorporated in many types of binders
Pure Hue
Good hiding power
Good abrasion resistance
Low settling tendency
• Enamels and ceramics High temperature resistance
• Plastics articles for food and commodities Low tendency of migration and bleeding
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Iron Blue Pigments
Iron blue pigment: Insoluble
pigment based on
microcrystalline Fe(II)Fe(III)
cyano complex
Soluble blue is C.I. Pigment
Blue 27:77520 was discovered
in 1704 by Diesbach in Berlin
by precipitation reaction
Milori was the first to produce
it as a pigment on an industrial
scale in the early nineteenth
century.
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Application of Prussian blue
The great wave of Kanagawa by Hokusai :
Kinryuzan Temple in Asakusa from the
series Famous Places in the Eastern
Capital by Hiroshige II
White Falcon in a pine tree
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Iron blue Pigment
• Paris blue Mirocrystaline Fe(II)Fe(III) cyano complexes.
• Prussian blue
• Berlin blue
• Milori blue
• Turnbull’s Blue
• Tonic Blue
Tonic blue
• Nonbronze Blue
Milori Blue
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Prussian Blue
• Prussian blue has a reddish tint and is used almost exclusively in
paints, enamels, and lacquers
• Chinese blue is very dark, with a greenish tint, and is favoured for
use in printing inks;
• Milori blue has a reddish tint;
• Toning blue is dull, with a strong red tone.
All these pigments are chemically similar, differences in shade
arising from variations in particle size and details of the
manufacturing process.
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History
• Synthesized for the first time by the paint maker Diesbach in Berlin
around 1706
• Diesbach was attempting to create a red lake pigment from cochineal
• The original dye required potash, ferric sulfate, and dried cochineal
which results in a red pigment
• He borrowed the potash from Dippel, who had used it to produce his
"animal oil“
• He got blood contaminated potash.
• He obtained blue instead red.
Thus, the pigment is believed to have been accidentally created.
• Thus blood, potash, and iron sulphate reacted to create a compound
known as iron ferrocyanide which, has a very distinct blue hue. It was
named Preußisch blau and Berlinisch Blau in 1709 by its first trader.
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Production
• Ferrous salt + potassium ferrocyanide Insoluble berlin white
• FeCl2 + K4[FeII(CN)6] K2 Fe[FeII(CN)6] white solid Burlin White
K2Fe[Fe(CN)6] where M+ = Na+ or K+ .
Ferrous ferrocyanide
H2O2 / Sodium Chlorate (White solid)
K[FeIIIFeII(CN)6]
Soluble colloidal, Prussian blue Potassium ferric ferrocyanide
"Insoluble" Prussian blue is produced if, in the reactions above, an
excess of Fe3+ is added:
4Fe3+ + 3[FeII(CN)6]4− → FeIII[FeIIIFeII(CN)6]
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Industrial method
K4[FeCN)6
FeII
1. Aging
Concentration 2. Oxidation
• Temperature
• Excess of iron H2O2 / KClO4
Size and shape
K2 Fe[FeII(CN)6]
white solid Burlin White
Prussian Blue
K[FeIIIFeII(CN)6]
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Turnbull’s Blue
• In former times, the addition of iron(II) salts to a solution of
ferricyanide was thought to afford a material different from
Prussian blue. The product was traditionally named Turnbull's
blue (TB). X-ray diffraction and electron diffraction methods
have shown, though, that the structures of PB and TB are
identical.[19][20] The differences in the colors for TB and PB
reflect subtle differences in the methods of precipitation, which
strongly affect particle size and impurity content.
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Properties
• Prussian blue is a microcrystalline blue powder.
• It is insoluble, but the crystallites tend to form a colloid. Such colloids
can pass through fine filters.
The composition of Prussian blue remained uncertain for many years.
Its precise identification was complicated by three factors:
• Prussian blue is extremely insoluble, but also tends to form colloids
• Traditional syntheses tend to afford impure compositions
• Even pure Prussian blue is structurally complex, defying routine
crystallographic analysis
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Properties 1. It is used in pure form for printing inks
2. Micronized particle with ~ 5m gives better
• Hue
tinting strength
• Tinting strength
3. Iron blue is stable for short period of time up
• Dispersibility to at 180 0C.
• Rheological behaviour 4. The powder pigment is combustible in powder
form. Ignition in air being possible at above
140 oC.
5. It has excellent light and weather fastness.
6. Pigments are resistant to diluted mineral acids
and oxidizing agents.
7. Do not bleed
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Crystal structure of Prussian blue :
Empirical formula = Fe7(CN)18
Name : iron(III) hexacyanoferrate(II)
Composition : Fe4[Fe(CN)6]3
Ferricyanides 55
Crystal structure of Prussian blue : empirical formula = Fe7(CN)18
iron(III) hexacyanoferrate(II)
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Fe7(CN)18
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Uses
Uses for Prussian Blue
Paints, inks, and enamels
Textiles, rubber, and plastics
Antidote for heavy-metal poisoning
Histopathology stain for detecting iron
Typewriter ribbons and carbon paper (now obsolete of course!)
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• Pigment
• Stain for iron
• By machinists and toolmakers
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Prussian blue use
• Printing Ink Industry
• deep hue, good hiding power and economic cost/performance-basis.
• Iron blue is often mixed with phthalocyanine pigments for multicolour
printing.
• Another important use is in controlling the shade of black printing
inks.
• Iron blue pigments are used in the manufacture of single- and
multiple-use carbon papers and blue copying papers
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Agriculture
• Blue inorganic fungicides based on copper and mostly used for treating
vines, olives or citrus fruits.
• Micronized iron blue pigments are used to color these fungicides
(normally at a concentration of 3–6 wt.%), so that even small amounts
become visible due to the high color intensity, and precise control is
possible. The fungicide is usually milled or mixed with a micronized iron
blue pigment
• A good side effect of treating fungi with iron blue is the fertilizing of
vines in soils that give rise to chlorosis. Leaf color is intensified, ageing
of the leaves is retarded, and wood quality (“ripeness”) is also
improved.
• Iron is necessary for chlorophyll synthesis, which improves grape
quality and yield. Other iron salts do not have this effect.
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Paint and coating
• Iron blue pigments are used in the paint industry, e.g. for full, dark
blue colors for automotive finishes. A full shade with good hiding
power is produced by 4–8% iron blue pigments
Paper
Adding “water-soluble” iron blue pigment directly to the aqueous phase
can produce blue paper.
Alternatively, a suitable iron blue pigment can be ground together with a
water-soluble binder, applied to the paper, dried, and glazed
Pigment Industry
The importance of iron blue in the production of chrome green and zinc
green pigments has greatly increased worldwide
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Toxicology
• In human volunteers who received 1.5 or 3.0 g ferric hexacyanoferrate(II) for up to 22 days
apart from a slight obstipation no effects were reported
• Prussian blue Fe4[Fe(CN)6]3 can bind cesium; therefore it is used in clinical practice as an
antidote for the treatment of humans contaminated with radioactive cesium. Clinical use of
ferric ferrocyanide in doses up to 20 g d−1 for decontaminations of persons exposed to
radiocesium has not been associated with any reported toxicity.
• There are no harmful effects on fish, but the toxic effects on bacteria constitute a slight
hazard when iron blue is present in water.
• Prussian blue is also used as an effective antidote for thallium intoxication. Ferric ferrocyanide
interferes with the enterosystemic circulation of thallium ions and enhances their fecal
excretion.
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