NMR characterization of silicon nitride: slurry homogeneity by T2-weighted proton imaging

The Si3N4/water slurries were studied by proton nuclear magnetic resonance (1HNMR) imaging for homogeneity. 1H nuclear spin echo signals from Si3N4/water slurries were observed by a (π/2)-τ-π-τ-echo pulse sequence. Bloch’s equations were used to calculate the spin-spin relaxation times (T2) from these echo intensities. The T2 for the protons in these slurries was measured to be 53.7±0.1 ms. The T2-weighted imaging technique utilizing (π/2)-τ-π-τ multiple pulse sequence was mixed with a “shape pulse” for radio frequency (RF)-excitation to detect nuclear spin echo signals for image construction. Sinc shape pulses were used to mix with both the (π/2) and the π pulses as a frequency carrier because of the mobility of water molecules in the slurry. The nuclear spin echo intensities were transformed into three-dimensional pictures by magnetic field gradients generated by coils along x, y and z-co-ordinates. Axial-section slices were taken to map the water distribution of the slurry in an NMR tube. A stable and well-dispersed Si3N4/H2O slurry, with ammonium polymethacrylate as dispersant, was observed for several hours. Agglomerization of this slurry was detected after 15 h of standing and NMR imaging shown in contour plots depicted clearly the location and the degree of agglomerization. The water distribution can also be presented in three dimensions by stack plotting of the water intensity profiles. This revised version was published online in November 2006 with corrections to the Cover Date.