Fibrous nanoinclusions in massive rose quartz: HRTEM and AEM investigations
Abstract Pink fibrous crystals within massive rose quartz from localities in California, South Dakota, Brazil, Madagascar, and Namibia were examined with high-resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM). This study reveals that the nanofibers in all samples are related to dumortierite. Selected-area electron diffraction (SAED) patterns and HRTEM images indicate that the dumortierite-related fibers have a superstructure with a doubled periodicity along the a and b axes of dumortierite, giving cell parameters a = 2adum = 2.36 nm, b = 2bdum = 4.05 nm, c = cdum = 0.47 nm. Computer simulations suggest that periodic arrangements of two different M1 site occupancies in the octahedral face-sharing chains give rise to the superstructure. One type of M1 site is occupied mainly by Al, whereas the other type is dominated by Ti and Fe. Simulated HRTEM images based on our proposed model match the experimental images. Most of the fibers, elongated along the c axis, are free of defects. AEM analysis shows that the dumortierite-related fibers have a composition similar to well-characterized dumortierite, but that they contain a greater amount of Fe substituting for Al in the M1 sites. Boron was detected in all fibers examined by electron energy loss spectroscopy as well as in sillimanite crystals found as a minor component in one rose quartz from Brazil.
Crystal chemistry of some Fe- and Ti-poor dumortierites
Of twelve specimens of dumortierite from various localities, we have analyzed all by electron microprobe, determined lattice parameters for all, measured optical properties for six, performed X-ray crystal-structure refinements on four, and obtained infrared absorption spectra for three. Aside from major Si and Al, the only cations detected above the -0.O2wo/o concentration level were minor Ti, Fe, Mg, and Ca. Infrared spectra confirmed the presence of similar amounts of (OH) in the three specimens checked, and we assume that (OH) is present in all twelve. From rough charge-balance considerations, based on the numbers of vacancies at the partially occupied Al(l) site, it appears that there are -0.4 (OH) per formula unit. X-ray site refinements showed the B site to be fully occupied in all four refined structures, and there are no crystallochemically reasonable substituents for three-coordinated B. All but one specimen showed a deficiency of Si, which is supplemented by substituent Al, yielding the observed full occupancy of the Si(l) and Si(2) sites. For the twelve specimens investigated, an approximate average forrnula is
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.