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Biomedical subjects

M J Buerger

Publications and source records attributed to M J Buerger.

At least 19 recordsLinked to original sources
PubMed1974

Serendibite, a complicated, new, inorganic crystal structure.

Serendibite with very similar analyses is known from Ceylon and New York. The triclinic cell of symmetry P[unk] and volume 670.9 A(3) contains 2Ca(1.64)Mg(2.64)Fe(0.27) (II)Al(4.64)B(1.66)Si(3)O(20), with 14 metal atoms and 20 oxygen atoms in the asymmetric unit. It was solved by the "direct" method of transforming the ordinary three-dimensional Patterson function into an approximation of the electron density by using conjugate peaks and minimum functions, followed by successive Fourier syntheses and least-squares refinement to R = 7.1%. This new structure is composed of interrupted brucite-type layers which form an octahedral framework, and winged single chains of tetrahedra. The structure has units of similar, but not identical, geometry to those of the minerals sapphirine and aenigmatite, and these similar units are assembled in a different way.

Journal Article↗
PubMed1972

Thermal effect in opal below room temperature.

Opal, once believed to be amorphous silica, was shown by Levin and Ott (1932, J. Amer. Chem. Soc. 54, 828-829) to give an x-ray powder pattern of the high-temperature form of cristobalite. The early explanation of this anomalous existence of a phase below its high-low transition temperature is now known to be untenable. One of us suggested that the tiny sizes of the component cristobalite crystals might explain the anomaly; if so, the transition might be expected below ambient temperatures. The record of a du Pont 900 Thermoanalyzer indeed revealed heat effects in opal below ambient temperatures, with an exotherm having a maximum at about -40 degrees on cooling and an endotherm that began about -50 degrees on heating. This was not a latent-heat effect due to the high-low transition of cristobalite, however, for the low-cristobalite pattern persisted to below -50 degrees . Opal normally contains 4-9% water, which is tenaciously held; water loss is nearly linear with temperatures up to about 422 degrees , when water loss is abruptly complete. Water-free opal does not display the thermal effect, but the same opal rehydrated does display it. Water is housed in minute voids, judged to be a few hundred Angströms across, between minute particles of cristobalite. This water behaves differently from water in bulk, for its begins to melt at about -50 degrees .

Journal Article↗