NMR CHARACTERIZATION OF INJECTION-MOLDED ALUMINA GREEN COMPACTS .1. NUCLEAR SPIN-SPIN RELAXATION

Development of proton nuclear magnetic resonance (H-1 NMR) analysis at 400 MHz has been initiated to evaluate the binder in green injection- moulded alumina compacts. The nuclear spin-spin relaxation times, T-2, of protons in the binder components (paraffin wax, polypropylene, and stearic acid) were measured to allow comparison with those in the inj ection-moulded green compacts. H-1 nuclear spin echo signals were obse rved by a (pi/2)-tau-pi-tau-echo pulse sequence. Bloch's equations wer e used to calculate the spin-spin relaxation times from these echo int ensities. The T-2 for paraffin wax and polypropylene we re in the 30-3 3 mu s range and their intensity decay behaviours were very similar. H owever, the T-2 value for stearic acid was found to be only 17 mu s an d its echo signal intensity decayed more rapidly than those for paraff in wax and polypropylene. Binder content variations in three green com pacts moulded from the same nominal blend composition were detected. A nalysis of the moulded compacts also showed the presence of a species with a T-2 value near 300 mu s This unexpected species may be the resu lt of reaction during processing or the presence of moisture. The widt h of r.f. pulses used to measure echoes did not have a significant eff ect on relaxation times but should be considered in calculation of ech o intensities at equilibrium and, hence, binder composition. This tech nique development is expected to allow analysis of both binder content and distribution in moulded components with application in process mo dels.