Synthesis and Characterization of Single Crystal Zircon-Hafnon Zr(1-x)Hf(x)SiO4 Solid Solutions and the Comparison with the Reaction Products of a TEOS-Based Hydrothermal Route.

Two synthesis routes of the zircon-hafnon solid solution series were carried out. The high-temperature route uses the growth of single crystals via a flux mixture that has been cooled down slowly from 1400 °C over 4 weeks. The reaction products were colorless and idiomorphic without byproducts. The hydrothermal tetraethoxysilane (TEOS)-based route represents the low-temperature method at 200 °C for approximately 7 days. The hydrothermal route yielded a white powder and scanning electron microscopy analysis thereof did not reveal any specific idiomorphic properties. However, the synthesis also featured some byproducts besides the zircon-hafnon solid solutions. Thermogravimetric analysis coupled with differential scanning calorimetry, and mass spectroscopy indicated, that hydrothermal reaction products feature the presence of organic residues originating from the starting materials. However, a specific dependency on the hafnium content could not be observed due to the data scatter. Infrared (IR) analysis revealed the presence of Zr/Hf-oxides. The structural characterization demonstrated that properties change constantly with the hafnium amount, however, gradual variations of some properties related to the composition of the solid solution series depend in part on the synthesis route, considering the c/a ratio and IR modes. Furthermore, analyses of the single crystals by Raman spectroscopy and µXRF suggested a nonequilibrated crystal growth based on the starting composition.

Locally preserved α → ß phase transition in natural radiation-damaged titanite (CaTiSiO5): evidence from laser-induced photoluminescence and dielectric measurements.

In situ temperature-dependent laser-induced photoluminescence and dielectric measurements provide new evidence for the local occurrence of the α → ß phase transition near 500 K in the preserved crystalline parts of natural radiation-damaged titanite (sample E2335 with ~24% amorphous fraction, containing Fe and Al impurities). Photoluminescence spectroscopic measurements show an anomaly in the vicinity of 500 K. The temperature-dependent evolution of the real part of the electrical conductivity (σ) and the real (ε') and the imaginary (ε″) part of the complex dielectric permittivity (ε *) of titanite have been measured at various AC frequencies (~1.2-96.8 kHz). Despite the masking and smearing effect of impurities and defects, the temperature-dependent behaviour of ε' and ε″ around the transition temperature of the investigated natural titanite E2335 shows a remarkable similarity to that of the synthetic end-member material (see Zhang et al (1995 Phys. Chem. Miner. 22 41-9)). This study indicates the suitability of photoluminescence and impedance spectroscopy for the detection of phase transitions, even in heavily disordered systems.

Crystal structures of calcium hemicarboaluminate and carbonated calcium hemicarboaluminate from synchrotron powder diffraction data.

One of the main phases formed at the beginning of the carbonation reaction of cementitious building materials is the calcium hemicarboaluminate (abbreviated as Hc). This AFm (shorthand for hydrated calcium aluminate phases structurally related to hydrocalumite) phase was synthesized, crystallized and then studied by synchrotron X-ray powder diffraction and micro-Raman spectroscopy. At room temperature and standard experimental conditions two major cementitious phases were detected, the Hc phase (as a major phase) and carbonated calcium hemicarboaluminate (abbreviated as cHc). By increasing the temperature the Hc form transforms into cHc. The crystal structures of these important AFm phases were successfully solved and refined in the R3c space group of the trigonal crystal system. Hc has the unit-cell parameters a = 5.7757 (1) and c = 48.812 (2) Å, and cHc the unit-cell parameters a = 5.7534 (1) and c = 46.389 (1) Å. The two crystal structures are composed of positively charged main layers, [Ca(4)Al(2)(OH)(12)](2+), and negatively charged interlayers, [OH(2n)(CO(3))(1 - n)·4H(2)O](2-). The structure of the main layers is typical of the AFm family. Conversely, the interlayer region has a characteristic structure built up from water molecules and statistically distributed anions. In the interlayer, the Hc carbonate and hydroxyl anions are distributed in a 0.25:0.5 ratio, whereas the ratio of the anions in the cHc interlayers is 0.4:0.2.

Active iron-rich belite sulfoaluminate cements: clinkering and hydration.

Ordinary Portland cement (OPC) is an environmentally contentious material, as for every ton of OPC produced, on average, 0.97 tons of CO2 are released. Conversely, belite sulfoaluminate (BSA) cements are promising eco-friendly building materials, as their production may deplete CO2 emissions up to 35% (compared to OPC). However, the hydration rate of belite is slow. Here, we report the clinkering of iron-rich BSA materials, their activation with B2O3, and establishing a methodology to measure their improved reactivities. Nonactivated BSA clinker contained only beta belite phase, 52 wt %. Meanwhile, BSA clinkers activated with 1 and 2 wt % of B2O3 contained 28 wt % of beta and 25 wt % of alpha'H; and 54 wt % of alpha'H phase, respectively. Therefore, activation of BSA has been proved as alpha'H-belite is stabilized. The hydration of the cements has been studied by laboratory and synchrotron X-ray powder diffraction (using Rietveld method and chemical constraints), calorimetry, and environmental scanning electron microscopy. Cement pastes have different hydration rates. For nonactivated BSA cement, 20 and 48% of the belite reacted after one and three months, respectively. Conversely, 37-49% after one month and 52-62% after three months of overall belite reactivities have been measured for BSA cements activated with B2O3.

Muyrakyta ou muiraquita: um talismã arqueológico em jade procedente da amazônia: aspectos físicos, mineralogia, composição química e sua importância etnogeológica

Muiraquitãs arc frogshape stone artifacts made mainly in greenstones like jade, used by peoples of Tapajó/Santarém and Conduri tradition/culture from Lower Amazon region, which were extinguished by european colonizators. They used as amulets, symbol of power and as trade materials. The majority of studiers believe that the greenstone jade come from Asia and reinforce the peopling of South America from Asia through North America. Mineralogical and chemical analyses over ten pieces of muiraquitãs from Museu Paraense Emílio Goeldi (MPEG), Museu de Arqueologia e Etnografia from Universidade de São Paulo and from prof. Amarilis Tupiassu show that they are made of tremolite for MPEG and prof. Amarilis and acti-nolite, talc and pyrphyllite for MAE. Tremolite and actinolite are the most common minerals of the nephritic jade, which is not too rare. The microchemical analysis aggree with the mincralogical determinations and show that the jade from MAE contain sulphate and ferrous iron and differ from the jade of muiraquitã of MPEG. Both jade can not be correlated with the jade of Baytinga (Amargosa-BA). Tremolite and actinolite are common minerals in proterozoic formations of Amazon region and dismitified the asking for an asian provenience of raw material of muiraquitãs as well as the interpretation of a peopling move from Asia to South America trough North America.

Os muiraquitãs são artefatos líticos com formas batraquianas confeccionados principalmente em pedra verde, tipo jade, utilizados pelos povos Tapajó/Santarém e Conduri do Baixo Amazonas, dizimados pelos colonizadores europeus. Eram utilizados como amuletos e como símbolo de poder e ainda como objeto de troca. Supunha-se que o jade viera da Ásia. Estudos mineralógicos e químicos em dez peças do Museu Paraense Emílio Goeldi (MPEG), do Museu de Arqueologia e Etnografia (MAE) da Universidade de São Paulo e profa. Amarilis Tupiassu mostram que os muiraquitãs do MPEG e da profa. Amarilis são confeccionados em tremolita e os do MAE em actinolita, talco e pirofdita. Tremolita e actinolita são os minerais mais comuns de jade nefrítico, que não é assim tão raro. As microanálises químicas confirmam as determinações mineralógicas e ainda mostram que o jade do MAE contém sulfato e ferro ferroso. Tanto o jade do MPEG como do MAE diverge daquele de Baytinga (Amargosa-BA). Rochas ricas cm tremolita e actinolita são muito comuns no Proterozóico da Amazônia, encontrados tanto ao norte como ao sul da bacia, próximo na região do Baixo Amazonas, sendo desnecessário invocar uma fonte asiática para o jade dos muiraquitãs. Portanto se tornam vulneráveis às interpretações etnográficas e antropológicas com base em área asiática como fonte para a matéria-prima destes artefatos.