ELECTRONIC TRANSITIONS IN α-FE2O3: THEORETICAL MODELS AND LIMITATIONS. Addressing electronic transitions of hematite (α-Fe2O3) is still considered a topic in active debate, even though it is one of the most widely used compounds from ancient times to the present and also one of the most extensively investigated iron oxides. In this review, a general analysis of the approaches and theoretical models which had been used to explain the electronic absorption spectrum of α-Fe2O3, from the frst proposal presented by Tandon and Gupta (1970) to the more recent results obtained by quantum mechanical calculations, is presented. The analysis of the already published studies is made pointing out the main factors that must be considered to allow a more reliable understanding of the UV-Vis-NIR spectra of α-Fe2O3. Furthermore, controversies in the calculated results are discussed, analysing the suitability of each of the approaches used. Reasons for differences observed in the experimental data reported in the literature are also discussed.

The introduction of Raman spectroscopy in South America and the development of techniques which allowed the use of radiation in the red and near infrared are discussed in this work, highlighting not only the technical aspects but also the European political and social contexts in the 1930s. When the Nazis came to power in 1933, thousands of jewish scientists, journalists and artists fled Germany, escaping from oppression, persecution and death; many of them played a pivotal role in the development of science in America. This is the case of Hans Stammreich.

The preservation of Cultural Heritage is undoubtedly important for the society, and Conservation Science must dedicate itself to attempts to minimize the inherent processes of degradation to which cultural assets are susceptible. In this context, the evaluation of the chemical aspects of the composition of the objects and their relation with the environment where they are located are essential for the understanding of the decay signs observed, supporting the establishment of effective conservation strategies. These characteristics are demonstrated here by vibrational spectroscopy, scanning electron microscopy and microbiological analysis of efflorescences observed in two types of paintings: a tempera on canvas painting ("Barco com bandeirinhas e pássaros", Alfredo Volpi, 1955) and an oil mural painting of the Throne Room of the National Palace of Mafra (18th-19th century, Mafra, Portugal). The challenges involved in the investigation of the efflorescences are demonstrated in both cases, suggesting the occurrence of degradation processes of different origins: in Alfredo Volpi's tempera on canvas painting, the migration of substances from the preparation layer to the surface of the pictorial layer and microbiological colonization; and in the mural painting the migration of calcium salts from the constituent materials of plaster and of neoformation, besides associated microbiological colonization.

The understanding of chemical and physical behavior of materials, especially metals and their alloys, is of utmost importance for industrial and technological applications, development of new materials and preservation of cultural heritage. The use of complementary analytical techniques has allowed a better understanding of corrosion mechanisms, and results obtained by Raman micro-spectroscopy, for example, have been complemented by FTIR and XRD. When focusing on the development of new materials and proposition of preservation strategies, the understanding of corrosion processes and of their very initial steps (nanometric scale) is fundamental. SERS reaches such lateral resolution if TERS is used, however, it cannot be universally applied and needs to be complemented by other techniques. In this work it is presented the potentials of a recent installed technique at the Brazilian Synchrotron Light Laboratory (LNLS), which can be used for nano-speciation of corrosion products, complementing investigation carried out by, for example, Raman micro-spectroscopy and TERS. It is Synchrotron Infrared Nano-Spectroscopy (SINS), which allows the investigation of both chemical nature and physical distribution of corrosion products. The infrastructure presented at LNLS is one of the few available in the world. As a model system, thin films of Pb exposed to formic acid were used.

A few years ago, during a storage room clean out at the University of São Paulo (Biblioteca do Conjunto das Químicas), several items were discarded, including apparently modern worthless large-scale reproductions of paintings by famous painters. A member of staff retrieved these reproductions from the litter bin, one of which was carefully inspected and non-destructively analyzed by spectroscopic techniques (Raman and XRF). The results showed that instead of being a modern reproduction of the gouache "Clinique de Sannois" (Maurice Utrillo, 1923), it was hand-painted probably between the late 1940s and early 1950s using the Jacomet process. This technique was developed by the French printer Daniel Jacomet in the 1920s, who made authorized reproductions of works of art by some of the most celebrated painters of the time.

The viability of small-scale heavy-metal waste immobilization into iron phosphate glasses was investigated. Several waste forms containing different amounts of heavy-ion wastes were evaluated (5%, 10%, 15%, 20%, 26%, 33%, 40% and 50% by mass) and their X-ray diffraction patterns revealed that no crystallization occurred in glasses with waste concentrations up to 26%. The dissolution rates for all of the reported glass compositions (ca. 10-8 g cm-2 min-1) are similar to those reported for the materials most commonly used for waste vitrification. Iron phosphate glasses thus proved to be very useful for the immobilization of heavy-metal wastes, exhibiting good contention and chemical durability comparable to that of borosilicate glasses.

Esculturas policromadas de Pb do Museu do Oratório em Ouro Preto (Minas Gerais, Brasil), expostas em um mostruário de vidro foram severamente degradadas. Os produtos de corrosão foram analisados por difratometria de raios X (XRD), espectroscopia no infravermelho com transformada de Fourier (FTIR), microscopia eletrônica de varredura (SEM), fluorescência de raios X por dispersão de energia (EDX) e microscopia Raman, e constatou-se a formação majoritária de carbonatos e formiatos de Pb. Embora carbonatos sejam comuns na corrosão atmosférica de Pb, formiatos podem ser formados tanto pela ação de ácido fórmico quanto de formaldeído, sendo sua origem um ponto importante a ser investigado. Simulações ambientais com tiras de Pb expostas a possíveis fontes desses compostos orgânicos voláteis possibilitaram concluir que o processo de degradação foi causado principalmente pelo processo de cura da tinta utilizada na base do mostruário. Contudo, produtos de limpeza, que podem conter formaldeído como conservante, mostraram-se potencialmente capazes de causar danos a objetos de chumbo, acelerando sua corrosão.

Polychrome lead sculptures from Oratory Museum in Ouro Preto (Minas Gerais, Brazil) kept inside a glass showcase were severely degraded. The formed corrosion products were analyzed by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDX) and Raman microscopy and proved to be mostly Pb carbonates and formates. Although carbonate is a very common finding in Pb atmospheric corrosion, Pb formates can be formed by the action of formic acid or formaldehyde, being their origin a key point to be investigated. Environmental simulations with Pb coupons exposed to possible sources of these volatile organic compounds led to the conclusion that the degradation process was caused mainly by the curing process of the painted showcase baseplate. However, cleaning products, which can also contain formaldehyde as preservative, proved to be potentially harmful to Pb, accelerating its corrosion.

The Surface Enhanced Raman Scattering (SERS) effect was observed for the first time in 1974, but it was only considered a new effect three years later, hence, nearly twenty years ago. Since its discovery, a significant amount of investigations have been performed aiming at to clarify the nature of the observed enhancement, to improve the surface stability and to establish applications which nowadays range from the study of biomolecules to catalysis. Some of the more relevant aspects of this effect which have been examined across the last two decades are summarized in this paper which presents the introductory aspects of SERS alongside with several of its applications.