1. Investigación

The production of porcelain stoneware has experienced a considerable increase. Therefore, it was necessary to undertake an investigation that would allow knowing the mineralogical evolution that porcelain stoneware undergoes during the firing process, as well as establishing the influence of the formation of mullite and other mineral or vitreous phases and their quantification. The firing transformations of mine spoils associated with mined coal in the Utrillas-Escucha-Estercuel and Ariño-Andorra areas are studied in this paper. The mineralogical composition of the bulk mine spoils is kaolinite, illite, chlorite, and smectites (in traces), with quartz and feldspar, and minor hematite, calcite, and dolomite. The main objective is to understand the generation of high-temperature mineral phases after firing, and their quantification. The formation of mullite and other high-temperature phases are studied from samples that include variable proportions of illite. Samples with a high content of illite generate mullite at 995 C. Cristobalite was not detected as a high-temperature phase. Mullite is the most abundant mineral. The hercynite content is higher at low temperatures (995 C), and hematite content is higher at 1150 C. The vitreous phase represents about 50% of fired bodies. Despite observing a porous microstructure, the non-porous areas are well sintered.

A method for quantitative mineralogical analysis by ATR-FTIR [1] has been used first timefor analysis of historical mortars. Mixtures of different minerals and gypsum were used in orderto measure the minimum band intensity that must be considered for calculations and the detectionlimit. In this way, the molar absorptivity coefficient in the Lambert–Beer law and the components ofa mixture in mol percentage can be calculated. The GAMS equation modeling environment and theNLP solver CONOPT (©ARKI Consulting and Development) were used to correlate the experimentaldata in the samples considered. The characterization of the vernacular mortars by FTIR analysisidentifies the predominant minerals of the samples, and in conjunction with XRF and XRD, showsthe exact composition of historical mortars, which will optimize the restoration and conservation ofmonuments, preserving our heritage.