Pigments chemical reactions

So far we have exclusively discussed time-resolved absorption spectroscopy with visible femtosecond pulses. It has become recently feasible to perfomi time-resolved spectroscopy with femtosecond IR pulses. Flochstrasser and co-workers [M, 150. 151. 152. 153. 154. 155. 156 and 157] have worked out methods to employ IR pulses to monitor chemical reactions following electronic excitation by visible pump pulses these methods were applied in work on the light-initiated charge-transfer reactions that occur in the photosynthetic reaction centre [156. 157] and on the excited-state isomerization of tlie retinal pigment in bacteriorhodopsin [155]. Walker and co-workers [158] have recently used femtosecond IR spectroscopy to study vibrational dynamics associated with intramolecular charge transfer these studies are complementary to those perfomied by Barbara and co-workers [159. 160], in which ground-state RISRS wavepackets were monitored using a dynamic-absorption technique with visible pulses. 

The pigment was first described in 1866 (47). Based on degradative studies and chemical reactions, it was proposed that lapacol was the alkenyUiydroxynaphthoquinone (7) (48), but it was later deterrnined that its stmcture is actually (8) (49). 

Azoic dyeing of cellulosic fibres is a process that is used only to a small extent today. In this process, an azo pigment is formed by chemical reaction within the fibre. The cotton fibres are first impregnated with an appropriate coupling component such as the anilide of 3-hydroxy-2-naphthoic acid, 156, under aqueous alkaline conditions. The fibre is then treated with a solution of a stabilised diazonium salt, in which the... 

The most important use of selenium is as a pigment which gives a red colour to glasses and enamels. However, selenium is a catalyst in many chemical reactions and is widely used in various industrial and laboratory syntheses. 

OSL Acronym for optically stimulated luminescence. oven A furnace used at relatively low temperatures, overglaze Pigment applied to the surface of pottery after glazing. oxidation A type of chemical reactions in which an atom or atomic group combines with oxygen or one or more electrons are removed from it. oxide A substance composed by the chemical combination of oxygen with another element. 

Abstract. The photocatalytic oxidation cycle (POC) is that process in chalking in which the pigment participates. This paper has shown the chemical reaction scheme for the course of this process as well as the experimental results confirming this scheme. 

Two different categories of pigments may be involved in lesion discoloration pigments resulting from chemical reactions of the organic contents of the lesion, and exogenous pigments from bacteria or food, which penetrate the lesion and bind to lesion constituents. 

Iron oxides have served man for centuries. Since the red and yellow ochres were first used to help produce prehistoric paintings in caves such as those at Lascaux, the role of iron oxides has expanded enormously. Their application as pigments and their ability to catalyse various chemical reactions, their role as the precursors of iron and steel and their activity as adsorbants in the ecosphere are just a few examples of the contribution of these compounds to the well-being of man. 

These thermoplastic resoles and novolacs are mixed with lubricants, pigments and additives, such as wood flour. The molding compound is converted to an infusible resin by heating it under pressure in a mold. A typical sequence of chemical reactions associated with the formation of this complex, three-dimensional polymer is shown in Figure 15.4. Typical properties of phenolic plastics are shown in Table 15.4. 

The anticorrosive action of the chromate pigments is based both on chemical and electrochemical reactions [5.66], [5.108]—[5.113]. Electrochemical passivation and chemical reaction are illustrated in Figure 70 [5.114], [5.115], Passivation is based on electrochemical processes in the cathodic region. In addition, a protective film is also... 

---