Study On Cement Quality Analysis Based On Laser-induced Breakdown Spectroscopy

The quality of the cement is closely related to the safety of construction projects and the use of qualified cement is the necessary condition to guarantee the construction safety. So, quality test in the cement production process is of significant importance. In the test process, the traditional analysis method is time-consuming, hulking or radioactive, so it is necessary to develop a new kind of technique and the associated apparatus for the cement quality test.In this thesis, laser-induced breakdown spectroscopy (LIBS) was introduced as an efficient method for the cement quality test, and the new method was both theoretically and experimentally studied in detail. The results show good feasibility of the LIBS-based method, and an industrialized apparatus for cement quality test was designed.Firstly, the mechanism of laser induced was introduced. The quantitative analysis principle based on LIBS, and plasma parameters measurements were elaborated in detail.Then, in order to expend the application range of the LIBS in element and improve the accuracy of Boltzmann plot method and double-line method, the combination of Boltzmann-Maxwell distribution with the Saha-Eggert formula was proposed to improve the measurement accuracy of the plasma temperature. To simplify the cockamamie measurement of spectral line-width in the process of calculating electron density, we established an simple algorithm by use of Guass formula; and a local thermal equilibrium (LTE) condition of the plasma was established based on the McWhirter criterion, which can provide effective spectral data for quantitative analysis.A industrialized cement quality analysis apparatus based on LIBS was elaborated, and then introduce the design principles of the structure, optical module and analysis chamber respectively. The apparatus was applied to analysis the compositions (SiO2, Al2O3, CaO, and Fe2O3) of the cement and the three ratio values (KH, SM, and IM) was also measured. When determining the calibration model, different kinds of calibration samples were assessed for improving the measurement accuracy, and found that the calibration models for raw materials and clinker should be created separately. In order to minimize the measurement error caused by the laser energy drift during the long term running of the apparatus, a linear correction method was proposed to increase the calibration cycle. According to the obtained results, the absolute measurement errors presented here for oxides analysis were within 0.5%, while those of ratio values were in the range of 0.02 to 0.05, meet the GB/T 176-2008 requirements.Finally, general summary and conclusion of the thesis as well as further development direction about research of LIBS in cement are presented, and the outlook of ongoing work is determined.The innovation points of this thesis are:1. Combining the Boltzmann-Maxwell distribution with the Saha-Eggert formula, a new method was proposed to improve the measurement accuracy of the plasma temperature.2. The plasma local thermal equilibrium (LTE) condition based on the McWhirter criterion was established to provide effective spectral data for quantitative analysis.3. A convenient linear correction method was proposed to simplify the calibration process of the apparatus and extend the calibration cycle.