Info

Improper extraction of binder/plasticizer

X-ray CT/image gray scale as a function of volume percent organic binder

X-ray CT/image gray scale as a function of volume percent organic binder

Vol % Binder

FIGURE 13.2 Determination of organic binder content in green-state ceramics by X-ray computed topographic imaging.

Vol % Binder

FIGURE 13.2 Determination of organic binder content in green-state ceramics by X-ray computed topographic imaging.

FIGURE 13.3 NMR image of cross section of 25-mm-diameter green-state (15 wt% binder) cold-pressed Si3N4 sample with intentional holes. Two holes at 1.1 mm, one at 2.2 mm, one at 3.2 mm, and one at 4.8 mm. Data acquisition time was 29 min.

Figure 13.3 shows a transaxial NMR image of a green, Si3N4 compact disk with 15 wt % organic material. In this sample, several holes were drilled, with diameters from 1.1 to 4.8 mm. Spatial resolution in the image is approximately 640 ^m in either direction and the time to acquire the imaging data was 29.3 min.

It is possible to achieve images with higher spatial resolution and to observe lower concentrations of NMR-sensitive nuclei but with a significant increase in imaging time.

In the slip-casting process, the location of the cast surface/slip interface and the efficacy of molds depend on the amount of solids that fill the open pores as well as other parameters [26]. These features can be measured using magnetic resonance imaging (MRI) NDE methods because most slips are water based (hence an abundance of 1H protons).

Hayashi and Kawashima [27] examined an Al2O3 slip in a plaster of paris cylindrical mold [20 mm outer diameter (OD) and 10 mm inner diameter (ID)]. The water content of the slip was 30 wt % and the experiment consisted of observing the cross section of the mold at different time intervals.

Figure 13.4 is a sequence of cross-sectional 1H NMR images obtained as a function of time after the slip was poured into the mold. In each image, three

FIGURE 13.4 Sequence of time-dependent NMR images of slip-casting process of Al2O3 [27].

Time After Pouring Slip into Mold (min)

FIGURE 13.5 Rate of deposit buildup from AI2O3 slip in mold using NMR image data [27].

Time After Pouring Slip into Mold (min)

FIGURE 13.5 Rate of deposit buildup from AI2O3 slip in mold using NMR image data [27].

distinct rings of different "brightness" are apparent. The bright region in the center represents the slip, the next ring is the solids buildup, and the last ring is the mold itself. The mold is observable because water is migrating through it.

By measuring the thickness of the solids buildup as a function of time, one can obtain the rate of solids buildup. A typical result is illustrated in Fig. 13.5.

0 0

Post a comment