Effect of airborne-particle abrasion and polishing on novel translucent zirconias: Surface morphology, phase transformation and insights into bonding.

PURPOSE: The purpose this study was to investigate the effect of Kern´s air-borne particle abrasion protocol (KAPA) and polishing on two translucent zirconias (4Y, 5Y-zirconias) compared to a traditional zirconia (3Y-zirconia). METHODS: Two different surface treatments were analysed by X-ray diffraction (XRD) and interferometry 1) KAPA (0.1 MPa, 50 µm alumina, 10-12 mm distance, 15 sec and 30 sec and cleaning in ultrasound using isopropyl alcohol 99%) and 2) Clinical-delivery polishing paste (Zircon Brite, Dental Ventures, USA). Shear-bond strength tests (SBS's) were performed with a highly polished and virtually flat surface in combination with a 10-MDP based cement and a surface modified by KAPA in combination with zinc phosphate cement. The SBS was expressed in terms of MPa. RESULTS: The mean values for monoclinic content were 13 wt%, 7 wt% and 2 wt% for 3Y-, 4Y- and 5Y-zirconias respectively, no differences were found between 15 and 30 seconds. Polishing did not result in phase transformation to monoclinic phase in any of the zirconias. The rhombohedral phase was identified in all types of zirconias regardless of surface treatment. Shear-bond strength tests showed 5 MPa for polished/10-MDP based cement and 3 MPa for KAPA/ Zinc phosphate. Statistically significant differences were found between the two different surface treatments but not between the types of zirconias. CONCLUSIONS: KAPA for 15 sec seems to be equal to 30 sec regarding morphology and phase transformation. Sole micro-retention appears not to be fully responsible for the bonding phenomena of 10-MDP and zirconia that underwent KAPA.

Selective Adsorption of CO2 on Zeolites NaK-ZK-4 with Si/Al of 1.8-2.8.

Zeolites with appropriately narrow pore apertures can kinetically enhance the selective adsorption of CO2 over N2. Here, we showed that the exchangeable cations (e.g., Na+ or K+) on zeolite ZK-4 play an important role in the CO2 selectivity. Zeolites NaK ZK-4 with Si/Al = 1.8-2.8 had very high CO2 selectivity when an intermediate number of the exchangeable cations were K+ (the rest being Na+). Zeolites NaK ZK-4 with Si/Al = 1.8 had high CO2 uptake capacity and very high CO2-over-N2 selectivity (1190). Zeolite NaK ZK-4 with Si/Al = 2.3 and 2.8 also had enhanced CO2 selectivity with an intermediate number of K+ cations. The high CO2 selectivity was related to the K+ cation in the 8-rings of the α-cage, together with Na+ cations in the 6-ring, obstructing the diffusion of N2 throughout the zeolite. The positions of the K+ cation in the 8-ring moved slightly (max 0.2 Å) toward the center of the α-cage upon the adsorption of CO2, as revealed by in situ X-ray diffraction. The CO2-over-N2 selectivity was somewhat reduced when the number of K+ cations approached 100%. This was possibly due to the shift in the K+ cation positions in the 8-ring when the number of Na+ was going toward 0%, allowing N2 diffusion through the 8-ring. According to in situ infrared spectroscopy, the amount of chemisorbed CO2 was reduced on zeolite ZK-4s with increasing Si/Al ratio. In the context of potential applications, a kinetically enhanced selection of CO2 could be relevant for applications in carbon capture and bio- and natural gas upgrading.

Highly selective uptake of carbon dioxide on the zeolite |Na10.2KCs0.8|-LTA- a possible sorbent for biogas upgrading.

The|Na10.2KCs0.8|8[Al12Si12O48]8(Fm3[combining macron]c)-LTA zeolite adsorbs CO2-over-CH4 with a high selectivity (over 1500). The uptake of carbon dioxide is also high (3.31 mmol g(-1), 293 K, 101 kPa). This form of zeolite A is a very promising adsorbent for applications such as biogas upgrading, where keeping the adsorption of methane to a minimum is crucial.

Structure Characterization and Properties of K-Containing Copper Hexacyanoferrate.

Copper hexacyanoferrate, Cu(II)[Fe(III)(CN)6]2/3·nH2O, was synthesized, and varied amounts of K(+) ions were inserted via reduction by K2S2O3 (aq). Ideally, the reaction can be written as Cu(II)[Fe(III)(CN)6]2/3·nH2O + 2x/3K(+) + 2x/3e(-) ↔ K2x/3Cu(II)[Fe(II)xFe(III)1-x(CN)6]2/3·nH2O. Infrared, Raman, and Mössbauer spectroscopy studies show that Fe(III) is continuously reduced to Fe(II) with increasing x, accompanied by a decrease of the a-axis of the cubic Fm3̅m unit cell. Elemental analysis of K by inductively coupled plasma shows that the insertion only begins when a significant fraction, ∼20% of the Fe(III), has already been reduced. Thermogravimetric analysis shows a fast exchange of water with ambient atmosphere and a total weight loss of ∼26 wt % upon heating to 180 °C, above which the structure starts to decompose. The crystal structures of Cu(II)[Fe(III)(CN)6]2/3·nH2O and K2/3Cu[Fe(CN)6]2/3·nH2O were refined using synchrotron X-ray powder diffraction data. In both, one-third of the Fe(CN)6 groups are vacant, and the octahedron around Cu(II) is completed by water molecules. In the two structures, difference Fourier maps reveal three additional zeolitic water sites (8c, 32f, and 48g) in the center of the cavities formed by the -Cu-N-C-Fe- framework. The K-containing compound shows an increased electron density at two of these sites (32f and 48g), indicating them to be the preferred positions for the K(+) ions.

Crystal and magnetic structure in co-substituted BiFeO3.

Ultra-high-resolution neutron diffraction studies of BiFe(0.8)Co(0.2)O3 show a transition from a cycloidal space modulated spin structure at T = 10 K to a collinear G-type antiferromagnetic structure at T = 120 K. The model of antiparallel directions of Fe(3+) and Co(3+) magnetic moments at the shared Wyckoff position describes well the observed neutron diffraction intensities. On heating above RT, the crystal structure of BiFe(0.8)Co(0.2)O3 changes from a rhombohedral R3c to a monoclinic Cm. At 573 K only the Cm phase is present. The collinear C-type antiferromagnetic structure is present in the Cm phase of BiFe(0.8)Co(0.2)O3 at RT after annealing.