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Solid-state characterization of MgSt hydrates. Isolation of the dihydrate and monohydrate forms by using the vegetable source of MgSt was successfully conducted by the
Mallinckrodt team (10). The results of the solid-state characterization showed that on the basis of particle and molecular
characterization, substantive evidence exists to support differences in the nature and behavior of the two hydrates (11).
Lubrication efficacy of MgSt, vegetable or animal source, has been widely associated with its physicochemical properties such
as crystalline state, crystal shape, particle size, particle-size distribution, and particle morphology with a given fatty
acid composition consisting of stearic and palmitic acids and fatty acid ratio (9).
Table III: MgSt pseudopolymorph particle size and percent water.
Powder X-ray diffraction. Figure 1 shows the results of the powder X-ray diffraction conducted on the MgSt hydrates.
Figure 3
Scanning electron microscope. Figure 2 shows the results of the characterization conducted on the MgSt hydrates using scanning electron microscopy at a
magnification of 2500×.
Figure 4
Particle size, percent water, and concentration of neat MgSt-M and MgSt-D. Results of particle size and free and bound-moisture analysis for the MgSt hydrates are shown in Table III. The neat dihydrate
had a concentration of 95.4%, and the neat monohydrate had a concentration of 92.0%. The results also indicate that the nominal
mean particle size of the monohydrate is 10.6 μm, and the dihydrate has a nominal mean particle size of 14.3 μm. In addition,
percent bound moisture was 2.8% for MgSt-M and 5.6% for MgSt-D. Although the percent of free water was generally low, MgSt-M
had 0.6%, and little or no free water was found in MgSt-D.
Figure 5
Differential scanning calorimetry, thermogravimetry, and NIR spectroscopy. The profiles depicted in Figures 3a–c show the results of the DSC, thermogravimetry, and NIR reflectance for the MgSt hydrates.
These profiles depict the differences between the hydrates of MgSt. The NIR spectra were provided by Kaufman (11).
