How to coloring ceramic ?

Oct. 9,2021

Ceramic coloring mechanism

Color is another optical property that enables ceramics to have many applications. When certain ions in the ceramic material contain electrons that are easy to excite, the light in the visible light range may be absorbed. At this time, the ceramic shows a color. This situation mainly occurs in transition elements with single-filled d-layers (such as v.Cr, Mn.Fe.Ni.Cu. or f-layers (rare earth elements)), which are relatively unstable. They have higher energy and require more It can be excited with less energy, so it can selectively absorb visible light, such as C+ ions, and slightly collect orange, yellow and part of the green light, showing a purple blue; Ni2+ absorbs other light through purple and red light to form purple gray; Cu+ Ions absorb red, orange, yellow and violet light, allowing blue and green to pass through: rare earth elements such as Ce have a plume absorption at the blue-violet place, appearing yellow; Nd3+ (neodymium) absorbs orange and yellow, appearing reddish purple.

1.Coloring of Alumina 

Al2O3 often need to be colored in practical applications, and they can show different colors by introducing colored ionic compounds. For example, in semiconductor integrated circuits, the alumina used as the package shell should have light-shielding properties. Therefore, the Al2O3 of the digital tube backing plate is also required to be black to ensure clear digital display. For this reason, Fe2O3, CoO.Cr2O3, TiO2, MnO and other colored oxides can be introduced into Al2O3. The black color of Al2O3 ceramics is due to the fact that Ti+ in the ceramic is partially reduced to Ti4+ under the action of reducing atmosphere (H2) and high temperature. Ti3+ can actually be regarded as T1+ that binds electrons, that is, Ti4+e-. This bound electron is Weakly bound electrons can be regarded as the "color center" in TiO2, so this type of ceramic appears black.Another commonly used red-purple Al2O3 is the introduction of Cr2O3 and MnO into Al2O3 ceramics. Containing about 1% Cr2O3, Al2O3, ceramics often appear red, because the Cr3+ ion in the solid solution α-Al2O3 lattice has a strong selective absorption of the blue-green band of visible light, so that the body presents a blue-green complementary color , Which is pink.

2. Coloring of Zirconia 

 The colorful colors greatly broaden the application fields of polycrystalline zirconia toughened ceramic materials. At present, zirconia have black, blue pink, green, cyan, gold and other colors. Its products involve watch cases and bracelets in the watchmaking industry, high-end mobile phone shells and buttons, ceramic knives used in the kitchen, and imitation gems. Kind of zirconia  rings and necklaces, etc. Traditional watch cases and bracelets are made of metal and electroplating. This kind of watch cases and bracelets are prone to plating peeling off and rusting. After a long period of use, the phenomenon of wear is particularly prominent. The case and bracelet made of colored zirconia have many excellent properties: for example, excellent wear resistance, the weight reduction of the watch, the hardness is about 10 times that of stainless steel, and the resistance to rust and chemical erosion, the watch wears time The longer it is, the brighter it is. Therefore, some well-known international watch manufacturers have launched multiple series of ceramic watches, as shown in Figure 28. For example, Ruitu's Rado (radar) watch and Japan's Seiko Co., Ltd. (Rado, 2003)

At present, the coloring of zirconia ceramics mainly includes the following methods.

(1)Solid form mixing method

Solid form mixing method is a method of synthesizing colored zirconia based on solid ignorance. That is, oxide particles such as colorants and mineralizers are mixed into stabilized zirconia powder according to a certain chemical ratio for mixing and ball milling. In this process, the solid particles are refined and the crystal lattice is distorted. The surface energy is increased. The reaction ability is enhanced, thereby increasing the chemical coloring reaction during the sintering process.Etho et al. (2004) used Y-TZI solid phase mixing and adding Co3O4, Cr2O3, TiO2, Al2O3, etc. to successfully prepare black oxide-bonded ceramic materials. However, the color stability is poor, the sintering temperature cannot be too high, and the colorant volatilizes. serious. If you add CoFe2O4 directly, you can also prepare black oxygen-junction ceramics, thus avoiding the use of heavy metal Cr (Briod, 1995). Using micron-grade ZrO2 as the raw material, the praseodymium zirconium yellow material as the coloring agent and a small amount of sintering aids, bright light yellow zirconia ceramics (Zhang Canying 2007) can be prepared, and ammonium metavanadate is used instead of the praseodymium zirconium yellow material as the coloring agent. 

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