Model Analysis And Comparison Of Quasi-elastic Neutron Scattering Spectrum (QENS)

Cement is a widely used building material in the world.In the long-term hydration process of cement,there are two kinds of water in the nanopogel pores of its hydration products.One is bound water,which becomes a part of the pore structure itself through chemical combination of water molecules an d cannot move freely.The other type is confined water,which is located in the micro nanopore and is in a restricted or strongly restricted state and can move freely.The proportion of bound water and the restricted water dynamics affect the macroscopic mechanical properties such as cement strength and durability.Therefore,it is of great significance to study the microstructure of cement hydration process and the water content and water dynami cs restricted by micro and nanopores for understanding and improving cement performance.The Quasi-Elastic Neutron Scattering(QENS)experiment is a novel method to study confined water dynamics by measuring the neutron energy transfer(E)and scattering vector(Q)after the neutron interacts with the sample target.By adopting a suitable theoretical model and performing nonlinear least-squares fitting analysis on the Quasi-Elastic Neutron scattering spectra,the relevant physical parameters describing the water dynamics can be obtained,and then the constrained water dynamics in the sample can be detected.There are many types of Quasi-Elastic Neutron Scattering spectra fitting analysis models,and the fitting effects of different models and the relevant physical parameters obtained to characterize water dynamic information are not the same.This paper uses the Jump-diffusion and Rotating-diffusion Model(JRM)and the revised Jump-diffusion and Rotating-diffusion Model(rJRM)to fit the QENS spectra of pure magnesium silicate(M-S-H)and pure calcium silicate(C-S-H)samples,respectively.The measurement temperatures of QENS spectra from M-S-H and C-S-H samples are210 K up to 280 K and 230 K up to 280 K,respectively,the E ranges from-120 to 120 and the Q value 0.3 ?1.9.Different physical parameters describing the dynamic information of confined water can be obtained by using the two models for QENS spectra fitting analysis.Compared with the JRM model,the physical parameters obtained by using the rJRM model are more comprehensive,and it is suitable for all neutron energy transfer and scattering vector measurements.From the qualitative point of view,the QENS spectra fitting curve of rJRM model is more consistent with the original data points.From the quantitative point of view,the chi-square value fitted by the rJRM model is more consistent with the mathematical statistics law than the JRM model,and the time required for nonlinear fitting is shorter.