Franco D'Orazio

Application of nuclear magnetic resonance pore structure analysis to porous silica glass

The internal pore structure of a series of porous silica glasses has been investigated using nuclear magnetic resonance (NMR). Longitudinal and transverse relaxation of protons in deionized water confined to the pores of the samples has been measured and interpreted to provide pore size distributions. Two sets of leached, phase‐separated porous glasses were used: the first nominally bimodal, the second with a more uniform pore space with pore sizes varying from 32 to 1350 A. Our results provide a stringent test of NMR relaxation as a method for pore size analysis. NMR relaxation experiments were performed on one sample as a function of the amount of water imbibed confirming the validity of the theoretical model used to interpret the magnetic resonance data.

Microstructure determination of cement pastes by NMR and conventional techniques

Applicability of NMR relaxation analysis to the characterization of pore structure in hydrating white cement pastes has been investigated. Measurements of transverse magnetization relaxation were made in specimens saturated and partially filled with water for periods of hydration between 1 and 28 days. The fast diffusion model successfully accounts for all relaxation measurements. The transverse surface relaxation rate was determined. A two-component pore volume size distribution was found. Comparison was made with mercury porosimetry and nitrogen sorption experiments and the results were correlated with compressive strength.

Relaxation and dynamical properties of water in partially filled porous materials using NMR techniques

Abstract The study of relaxation times of NMR active nuclei in liquids confined to pore structures allows characterization of the geometry of the open volume providing information regarding its homogeneity, spatial distribution, and tortuosity. Experiments performed on samples containing different amounts of fluid can probe the degree of homogeneity at smaller and smaller length scales, permitting a determination of the intrinsic nature of the liquid-solid interaction responsible for the observed enhancement of the relaxation rates. The results of longitudinal and transverse relaxation experiments on water filling a microporous leached borosilicate glass are discussed. Particular emphasis is devoted to relaxation and dynamical properties at sub-monolayer coverage. This is discussed in the context of the molecular interaction at the liquid-solid interface. The results are interpreted in terms of anisotropic rotation of the adsorbed molecules and the characteristic times of such motion are extracted. This is compared with the molecular translation degree of freedom derived from NMR pulsed field gradient techniques suggesting that the two types of motion are closely related.

Microwave absorption of aligned crystalline grains of YBa2Cu3O7−x

We investigate here the anisotropic magnetic and electric properties of aligned crystalline grains of YBa2Cu3O7−x. The microwave absorption is indeed consistent with the expected temperature behaviors of the resistivity in the normal state along the c axis and in the a‐b plane. In the superconducting state, both the absorptions in pure rf electric and magnetic fields are high compared to the conventional superconductors; for the magnetic case activation energies are deduced and the dispersion is related to the diamagnetic susceptibility. These results are discussed qualitatively in relation to similar data obtained on single crystals and ceramic samples.