Thread Content
This post was last edited by sunjl1981 on 2016-3-5 10:12. Titanium dioxide has good chemical stability; it is non-toxic and insoluble in water, dilute acids, organic solvents, and weak inorganic acids. It is slightly soluble in alkalis and hot mineral acids, and can only be dissolved in concentrated sulfuric acid and hydrofluoric acid after prolonged boiling. Titanium dioxide can strongly absorb ultraviolet rays, generating activated substances. This activating substance can promote the degradation of organic compounds in the application systems (such as coatings, plastics, etc.), affecting their performance. To eliminate this photochemical activity, modern titanium dioxide pigments must undergo surface modification. There are two methods for determining color fading power. (1) The relative colorimetric method generally involves mixing the sample (titanium dioxide) with another sample used as a standard (also titanium dioxide) with a coloring agent (ultramarine or carbon black), grinding the mixture with linseed oil, and then comparing the intensity of color between the sample and the standard to determine the percentage by which the sample matches the standard. (2) In foreign commerce, the Reynolds number is sometimes* conventionally used to indicate coloring power. The Renault value is determined by adding equal amounts of carbon black ultramarine and oil to both a standard sample and a test sample until their lightness levels are the same; then, based on the amount of coloring agent added to the test sample, the corresponding value is read from a pre-established index table. When coloring with titanium dioxide and colored pigments, less titanium dioxide with high tinting power (light-eliminating power) is required. Chromatic strength is the result of a pigment’s absorption and scattering of light. Titanium dioxide is a white pigment that absorbs very little light; unlike colored pigments, where light absorption plays an important role, its coloring power (light-extinguishing power) depends mainly on its ability to scatter visible light. The greater the scattering ability, the higher the coloring power (light-extinguishing power). Therefore, it is different from whiteness; whiteness is a function of both the absorption coefficient K and the scattering coefficient S, whereas the coloring power (lightening power) is merely a function of the scattering coefficient S. As can be seen from the table below, titanium dioxide has the highest refractive index among white pigments; therefore, its coloring power (light-absorbing capacity) is also higher than that of other white pigments. For the two crystal forms of titanium dioxide, the rutile form has a higher refractive index than the anatase form, which means its coloring power (light-absorbing capacity) is also greater than that of anatase titanium dioxide. The refractive index and coloring power of various commonly used white pigments are important characteristics of titanium dioxide; they indicate the ability of titanium dioxide, when mixed with another pigment, to enable the mixture to exhibit the coloring properties of that pigment. Sometimes, to distinguish between white pigments and colored pigments, the coloring ability of colored pigments is referred to as coloring power, while the coloring ability of white pigments is called lightening power. In other words, for white pigments, the lighter the color of the mixture formed when they are mixed with dark pigments, the greater their lightening power