Celda de alta presión y temperatura para el estudio de la hidratación de cementos "in situ" mediante radiación sincrotrón

Resumo

Powder diffraction is a scientific technique that consists on the diffraction of X-rays, neutrons or electrons to characterize the internal structure of microcrystals of a material in powder form. The purpose of using powder is to achieve an equitable orientation of the microcrystals in all directions of space; this allows that the three-dimensional reciprocal space of the diffraction given by a single crystal can be projected into a single dimension. If the material to be studied contains more than one phase, this condition must be fulfilled for each and every one of the phases, which allows doing quantitative analysis free of errors. For this purpose, the sample can also be rotated so that the average of equitable oriented crystals is improved. Specifically, the X-ray diffraction offered in modern synchrotron radiation sources offers high intensity beams compared to conventional, narrow and highly collimated x-ray tubes and high-energy photons that allow penetration into complex sample environments. Cements are a typical case of crystalline powder, of special scientific interest are the cements used in the oil industry, Portland cements are used to support the metal pipes in the wells and as a means of sealing the wells in which these pipes are used. These wells can be very deep, and the cements are subjected to high pressures and temperatures, this causes the hydration mechanism to change substantially compared to what happens at the pressures and temperatures that can be found on the surface. The effect on the hydration process of cements with temperature and pressure has been studied using several methods, including the powder diffraction method. But due to the pressure these cements might be subject to, of around 1 Kilobar there are relatively few works that examine how the effects of pressure and temperature changes affect the hydration process. Although it has been seen that pressures lower than 200 bar can already significantly affect the hydration process of the tricalcium silicate, Ca3SiO5, the most important phase in Portland cement. The lack of information on the role played by the pressure is due in part to the lack of tools for the in situ study of cement hydration. The goal of this Thesis is to design and build a cell that can reproduce these pressure and temperature conditions (at least 200 bar and 200 °C). That allows a rapid injection of the sample in order to be able to measure the first stages of hydration. That allows spinning in order to improve the quality of the powder diffraction data. That allows performing powder diffraction experiments with synchrotron radiation, which implies that the area where the sample carrier is almost transparent to X-rays and the material is stiff enough to withstand the high pressure, typical materials that meet these conditions they are fused silica (amorphous siliceous glass produced by melting quartz at high temperatures) or Sapphire. And of course, it could be used not only for the case of study of a cement but of any sample in the form of crystalline powder in which one wants to know its structure by means of the method of powder diffraction in the aforementioned conditions.