Ceramic coloring methods

There are a number of ways to obtain color in a ceramic material (1). First, certain transition-metal ions can be melted into a glass or dispersed in a ceramic body when it is made. Although suitable for bulk ceramics, this method is rarely used in coatings because adequate tinting strength and purity of color caimot be obtained this way. 

Filtered-Particle Inspection. Solids containing extensive inteiconnected porosity, eg, sintered metallic or fired ceramic bodies formed of particles that ate typically of 0.15-mm (100-mesh) screen size, are not inspectable by normal Hquid penetrant methods. The preferred test medium consists of a suspension of dyed soHd particles, which may be contained in a Hquid vehicle dyed with a different color. Test indications can form wherever suspensions can enter cracks and other discontinuities open to the surface and be absorbed in porous material along interior crack walls. The soHd particles that form test indications ate removed by filtration along the line of the crack at the surface where they form color or fluorescent indications visible under near-ultraviolet light (1,3). 

X-ray photoelectron spectrometry (XPS) is used to determine major and minor element compositions of metallic and ceramic surfaces. It can also be used to determine the oxidation states of ions on the surface of a sample. However, it has a limited depth penetration of 2-20 atomic layers and so the measurements taken will be greatly influenced by the method of sample preparation. The ability to characterize elements with atomic numbers less than 10, coupled with the ability to analyze samples smaller than 1.5 cm, make this technique particularly useful for the colorants and clarifying agents used in glasses and ceramics. For example, it has been used to... 

Fig. 7.9 Microstructure of the four Y-TZP ceramics (20,000x). The average grain size according to the Linear interceptive count method was as follows Zeno (ZW) (383 47 nm) Everest (KV) (383 47 nm) Lava (LV) 537 nm ( 47) Lava colored (LVB) 643 nm ( 61) [26], With kind permission of Elsevier...

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