An opacifier is a substance added to a material in order to make the ensuing system opaque. An example of a chemical opacifier is

titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insoluble ...

(TiO₂), which is used as an opacifier in paints, in paper, and in plastics. It has very high refraction index (rutile modification 2.7 and anatase modification 2.55) and optimum refraction is obtained with crystals about 225 nanometers. Impurities in the crystal alter the optical properties. It is also used to opacify

ceramic glaze Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a pottery body through firing. Glaze can serve to color, decorate or waterproof an item. Glazing renders earthenware vessels suitable for holdi ...

s and milk glass; bone ash is also used. Opacifiers must have a

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, o ...

(RI) substantially different from the system. Conversely, clarity may be achieved in a system by choosing components with very similar refractive indices.

Glasses

Ancient milk glasses used crystals of calcium antimonate, formed in the melt from calcium present in the glass and an antimony additive. Opaque yellow glasses contained crystals of

lead antimonate Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...

;

bindheimite __TOC__ B Ba # Babánekite (vivianite: IMA2012-007) 8.CE o o(IUPAC: tricopper diarsenate octahydrate) #Babefphite (IMA1966-003) 8.BA.1

mineral may have been used as the additive. Under oxidizing condition, lead also forms incompletely dissolved

lead pyroantimonate Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...

(Pb₂Sb₂O₇). From 2nd century BC tin oxide appears in use as opacifier, likely in the form of cassiterite mineral. Opaque yellow can be produced as

lead stannate Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, le ...

; the color is paler than the lead antimonate one. Later calcium and sodium phosphates became used; bone ash contains calcium phosphate in a high proportion. Calcium fluoride was also used, especially in China. For dental ceramics, several approaches are in use. Spodumene or

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

crystals can be precipitated. Fluorides of aluminium, calcium, barium, and magnesium can be used with suitable heat treatment. Tin oxide can be used, but zirconia and titania give better results; for titania, the appropriate resulting particle size is between submicron to 20 μm. Another desirable opacifier is

zinc oxide Zinc oxide is an inorganic compound with the Chemical formula, formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceram ...

. Opacifiers must also form small particles in the system. Opacifiers are generally

inert Inert may refer to: * Chemically inert, not chemically reactive ** Inert gas ** Noble gas, historically called inert gas * Inert knowledge, information which one can express but not use * Inert waste, waste which is neither chemically nor biol ...

X-ray opacifiers

In context of x-rays, opacifiers are additives with high absorption of x-rays; typically these are particles or compounds of lead, barium (often barium sulfate), tungsten, or other high atomic weight elements. Sometimes opacifiers are added to medical implants to make them visible under

X-ray X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

imaging. This is especially true in the case of most

polymer A polymer (; Greek ''poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...

s which are often unrecognizable in the body when viewed using X-rays.

Rocket propellants

In solid rocket propellants and some translucent

smokeless powder Finnish smokeless powderSmokeless powder is a type of propellant used in firearms and artillery that produces less smoke and less fouling when fired compared to gunpowder ("black powder"). The combustion products are mainly gaseous, compared to ...

s, the primary method of heat transfer into the propellant grain from the combustion process is by radiation, and opacifiers such as " lamp black" may be added to the propellant mixture to ensure the heat does not penetrate far below the surface of the grain, which could cause detonation. The opacifiers also prevent sub-surface overheating and localized premature ignition in the grains where imperfections absorbing the thermal radiation are present.

Carbon black Carbon black (subtypes are acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion of coal and coal tar, vegetable matter, or petroleum products, including fuel oil, fluid ...

is commonly used for this purpose; other possible additives are

nigrosin In staining dyes, nigrosin (CI 50415, Solvent black 5) is a mixture of black synthetic dyes made by heating a mixture of nitrobenzene, aniline, and hydrochloric acid in the presence of copper or iron. Related to induline, it is a mixture of ...

Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe Cyanide.html" ;"title="e(Cyanide">CN ...

methylene blue Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. Methylene blue is a thiazine dye. As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglob ...

, etc. in amounts ranging commonly between 0.1 and 0.5%.US Army. ''Encyclopedia of Explosives and Related Items'', vol.8

References

{{reflist Physical chemistry Materials science