Photo‐chemistry of pigments. Studies on the mechanism of chalking

Abstract

Studies are presented which demonstrate that: (1) irradiation of titanium and zinc oxide pigments produces singlet oxygen; (2) irradiation of titanium dioxide pigments in water yields, hydrogen peroxide; and (3) the formation of singlet oxygen and hydrogen peroxide correlates with chalking tendencies of the pigments. These findings, together with the results of quenching studies, are interpreted in terms of a working hypothesis, for the generation of reactive oxidants, which ties together previous work into a unified scheme. The relative chalking rates of anatase and rutile titanium dioxide as well as the improvement of chalk resistance by surface treatment, are discussed within the framework of this scheme. The role of singlet oxygen in the chalking process, the importance of its presence with regard to the control of chalking, and possible mechanisms for its formation are also discussed.

On the Lifecycle of Nanocomposites: Comparing Released Fragments and their In‐Vivo Hazards from Three Release Mechanisms and Four Nanocomposites

“…Polymeric materials are susceptible to damage by UV radiation; especially ‘chalking’, i.e., the release of pigments (such as chalk) is a standard problem for paints and coatings, causing a whitish and matte appearance 21, 24. Hence also release of nanofillers may occur 11, 15.…”

“…Concerning ecological safety after service life, incineration of nanocomposite materials with energy recovery is preferable and recommended over landfilling due to the slow but undeniable ‘chalking’ under UV irradiation 15, 21, 23. Depending on the nanocomposite material, recycling also provides options to separate and reuse nanofillers, possibly including feedstock recycling by gasification and blast furnace.…”

Determination of early warning signs for photocatalytic degradation of titanium white oil paints by means of surface analysis

“…The current paper focuses on the latter process, more specifically on the degradation of the oil binder (Scheme 1, process 3). This degradation process causes roughening of the surface and eventually leads to chalking: the top layer of the paint has degraded and the pigment is now located freely on the surface [18,[25][26][27]. Chalking of titanium white alkyd paints was first demonstrated by Voltz et al in 1981 [18].…”

Structure Se nsitivity of Photochemical Oxidation and Reduction Reactions on SrTiO3 Surfaces

“…When these reactions occur on the surface of an oxide pigment particle embedded in a composite, the stability of the system is usually compromised. 1,2 Therefore, pigment particles are modified to minimize photochemical reaction rates. 3 However, there are also a number of applications for photochemically active ceramics where it is desirable to maximize the efficiency of photon stimulated reactions.…”