Thermal behaviour of organic radicals and paramagnetic centres in chert: A case study of Bergeracois brown chert, Dordogne, France

In order to successfully understand the complex evolution of prehistoric societies, archaeologists require absolute dating tools, which are not only accurate but also widely applicable. Thermoluminescence (TL) dating is one such approach that has been successfully used to establish a general chronological framework for prehistoric sites and is particularly suited for use on heated lithic artefacts. Experiments conducted in this study have clearly shown the applicability of Electron Spin Resonance (ESR) isothermal modelling in combination with TL dating to constrain firing temperature. This expands the potential application for TL dating to include artefacts treated at low firing temperatures. The present study shows potential in terms of precision and accuracy for framing the “equivalent firing temperature”. At the same time, the comparison of the TL signal with the lattice-defects and aluminium centres invigorate the use of ESR dating on heated flint, especially with samples that have received low thermal treatment. The presence of organic matter in large quantity raises concern on the pyrolysis effect on the luminescence signal; however, the use of ESR isothermal and isochronal modelling could potentially lead to the ability to overcome current interferences of the organic radicals within the dating signal of TL.

Design of Magnesia–Spinel Bricks for Improved Coating Adherence in Cement Rotary Kilns

It is well known that doloma bricks present better coating adherence than magnesia–spinel bricks when applied in cement rotary kilns, which is related to the different coating formation mechanism. The coating has an essential role in prolonged operation by protecting the refractory lining; thus, it is important to improve its adherence on magnesia–spinel refractories. The objective of this investigation is to study different compositions of magnesia–spinel bricks, achieved by varying additives used (calcined alumina, limestone, hematite and zirconia) and firing temperature (1500 °C and 1700 °C), to enhance the coating adherence measured by the sandwich test. The results have pointed out that the use of higher firing temperature contributes positively to physical adherence due to well-sintered refractory structure and elevated permeability, attaining coating strength superior to 2 MPa. For the chemical adherence, the addition of 2 wt.% of limestone increased the coating strength to 3 MPa, but resulted in a drop in hot properties. In this context, the most suitable approach to improve adherence of clinker coating and maintain hot properties in suitable levels is to increase the firing temperature.

Microstructure Study of Phase Transformation of Quartz in Potassium Silicate Glass at 900 °C and 1000 °C

Interfacial reaction between quartz and potassium silicate glass was studied at both 900 °C and 1000 °C. The results showed that no phase transformation was observed for the pure quartz at 900 °C or 1000 °C. Instead, for quartz particles in K2O-SiO2 glass, the transformation from quartz to cristobalite occurred at the quartz/glass interface at first, and then the cristobalite crystals transformed into tridymite. The tridymite formed at the interface between particles and glass became the site of heterogeneous nucleation, which induces plenty of tridymite precipitation in potassium silicate glass. The influential mechanism of firing temperature and size of quartz particles on transformation rate was discussed.

Cementless refractory castable. Part 9. HCBS and ceramic concretes in the Al2O3‒SiO2‒SiC system

The priority-chronological aspect of research and technological development in the field of SiC-containing HCBS and ceramic castables in the systems Al2O3‒SiO2‒SiC and Al2O3‒SiO2‒SiC‒C is characterized. The results of studies on the effect of the firing temperature and prolonged (up to 100 h) high-temperature heat treatment on the oxidation kinetics of SiC of different dispersion and content are considered. A noticeable oxidation, accompanied by an increase in the mass and growth of samples, is noted after 1200 °C and significant at 1300‒1400 °C. The effect of the firing temperature in the range of 1000‒1400 °C and long holding in a tunnel furnace (60 h at 1300‒1400 °C) on the dynamics of phase transformations and the structure of samples of the matrix system based on HCBS of composite composition (bauxite + 11 % VFQG), as well as with an additional content of 15% SiC. In contrast to firing in air, during the service of monolithic gutter masses in the Al2O3‒SiO2‒SiC‒C system, the working surface of concrete is largely isolated from the air due to cast iron and slag. This drastically reduces the rate of both SiC oxidation and carbon burnout. The zonal structure of the lining is characterized. The data on the effect of heating and cooling on the modulus of elasticity of ceramic castable are presented.

Research of the kinetics of synthesis and peculiarities of solid-phase formation of mullite

The article presents the production of ash silica during heat treatment and the schemes of modification transformation at different temperatures. On the basis of ash silica and aluminum oxide in the alumina‒silica system, mullite 3Al2O3·2SiO2 was synthesized for the first time at a relatively low firing temperature.

Effect of Firing Temperature on some Mechanical Properties of Osun State Ceramic Tiles

The work evaluates the effect of firing temperature on the mechanical properties of ceramic tiles. This was with the view to determine the optimum processing condition for Osun State ceramic tiles. Ceramic raw materials collected from Osun State were batched using clay-feldspar-silica sand blending ratio of 5:4:1, 5:3:2, 5:2:3, 5:1:4, 6:3:1, 6:2:2, 6:1:3, 7:2:1, 7:1:2 and 8:1:1 by weight; and homogeneously mixed. Three replica samples were moulded by the method of dry forming, fired at 1200, 1300 and 1400 oC and subjected to breaking and flexural strength tests using the Universal Testing Machine while the hardness test was carried out on a Moh’s scale. The results showed that breaking strength, flexural strength and Moh’s hardness fell within the range 199.43 to 325 N, 11.97 to 19.50 N/mm2 and 2.5 to 4 MH respectively, while Figures revealed that samples with 60% clay, 10% feldspar and 30% silica sand fired at 1320 oC will process the best mechanical properties. In conclusion, ceramic raw materials collected from Osun State are viable for ceramic tile production.

Scientific Analysis of Firing Characteristics for Walls and Rooftiles Excavated from Jeseoksa Dump-site, Iksan

In this study, the physicochemical properties of 21 wall fragments and rooftile pieces excavated from Jeseoksa Dump-site were analyzed, and the possibility of heat exposure, such as the fire reported in the literature, was investigated by estimating the firing temperature. From the results, it was estimated that the rooftiles were composed of refined materials, and the walls were composed of materials having different particle sizes depending on the layer. Unlike ordinary rooftiles and walls, they exhibited an uneven surface with traces of bloating phenomenon in the cross section. It was estimated from the blackening of some portions that firing was not performed in a controlled state in a constant firing environment. In addition, the estimated firing temperature showed that the non-overfired rooftiles had endured a firing temperature of 900°C or less, but the over-fired samples were subjected to a temperature of 1,000°C or higher and were fired at a temperature higher than the manufacturing temperature at that time. Additionally, the rooftiles probably became defective during firing or molding at the time of production, but the non-overfired rooftiles exhibited an intact shape and showed the possibility of heat exposure due to fire. Therefore, the analytical results of this study confirm that the defective architectural components damaged by the fire, as reported in the literature, were discarded in the Jeseoksa dump-site.

An Analysis of Material Property on Eartherwares Excavated at Auraji site in Jeongseon

In this study, we aimed to elucidate the materialistic characteristics of 11 pieces of earthenware belonging to the Neolithic and Bronze Age excavated from Jeongseon Auraji, South Korea. As a result, the chemical composition of earthenwares belonging to the early Bronze Age was distributed in the intermediate area between the Neolithic and Bronze Age earthenwares, but no significant difference was confirmed based on their manufacturing period. Upon comparison, the earthenwares excavated from Jeongseon Auraji site were found to comprise less acidic components than those excavated from Yeongdong, and are characterized by the alkaline components depending on the excavated site. In the rare earth elements distribution pattern, all the analyzed earthenwares exhibited similar pattern, confirming that the raw materials present in the clay were the same. As a result of microstructure analysis, the clay particles and voids were found to be irregularly distributed in the analyzed earthenwares. Neolithic earthenwares exhibited many irregular voids, and an arrangement of aluminosilicate, including feldspar, was observed along with the clay substrate. Furthermore, we confirmed that the empty space in early Bronze Age earthenwares was filled with fine particles and cube crystals. Moreover, the main mineral phase of earthenwares excavated from Jeongseon Auraji exhibited similar composition, and therefore, there was no significant difference in the firing temperature of these earthenwares. The firing temperature of the earthenwares ranged from 750 to 850°C.