1,643 research outputs found
Effect of Additives on Mineral Trioxide Aggregate Setting Reaction Product Formation
Introduction Mineral trioxide aggregate (MTA) sets via hydration of calcium silicates to yield calcium silicate hydrates and calcium hydroxide (Ca[OH]2). However, a drawback of MTA is its long setting time. Therefore, many additives have been suggested to reduce the setting time. The effect those additives have on setting reaction product formation has been ignored. The objective was to examine the effect additives have on MTA\u27s setting time and setting reaction using differential scanning calorimetry (DSC). Methods MTA powder was prepared with distilled water (control), phosphate buffered saline, 5% calcium chloride (CaCl2), 3% sodium hypochlorite (NaOCl), or lidocaine in a 3:1 mixture and placed in crucibles for DSC evaluation. The setting exothermic reactions were evaluated at 37°C for 8 hours to determine the setting time. Separate samples were stored and evaluated using dynamic DSC scans (37°C→640°C at10°C/min) at 1 day, 1 week, 1 month, and 3 months (n = 9/group/time). Dynamic DSC quantifies the reaction product formed from the amount of heat required to decompose it. Thermographic peaks were integrated to determine enthalpy, which was analyzed with analysis of variance/Tukey test (α = 0.05). Results Isothermal DSC identified 2 main exothermal peaks occurring at 44 ± 12 and 343 ± 57 minutes for the control. Only the CaCl2 additive was an accelerant, which was observed by a greater exothermic peak at 101 ± 11 minutes, indicating a decreased setting time. The dynamic DSC scans produced an endothermic peak around 450°C–550°C attributed to Ca(OH)2 decomposition. The use of a few additives (NaOCl and lidocaine) resulted in significantly less Ca(OH)2 product formation. Conclusions DSC was used to discriminate calcium hydroxide formation in MTA mixed with various additives and showed NaOCl and lidocaine are detrimental to MTA reaction product formation, whereas CaCl2 accelerated the reaction
Magnetically-induced electric polarization in an organo-metallic magnet
The coupling between magnetic order and ferroelectricity has been under
intense investigation in a wide range of transition-metal oxides. The strongest
coupling is obtained in so-called magnetically-induced multiferroics where
ferroelectricity arises directly from magnetic order that breaks inversion
symmetry. However, it has been difficult to find non-oxide based materials in
which these effects occur. Here we present a study of copper dimethyl sulfoxide
dichloride (CDC), an organo-metallic quantum magnet containing Cu
spins, in which electric polarization arises from non-collinear magnetic order.
We show that the electric polarization can be switched in a stunning hysteretic
fashion. Because the magnetic order in CDC is mediated by large organic
molecules, our study shows that magnetoelectric interactions can exist in this
important class of materials, opening the road to designing magnetoelectrics
and multiferroics using large molecules as building blocks. Further, we
demonstrate that CDC undergoes a magnetoelectric quantum phase transition where
both ferroelectric and magnetic order emerge simultaneously as a function of
magnetic field at very low temperatures
Anisotropic Hc2 of K0.8Fe1.76Se2 determined up to 60 T
The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are
determined over a wide range of temperatures down to 1.5 K and magnetic fields
up to 60 T. Anisotropic initial slopes of Hc2 ~ -1.4 T/K and -4.6 T/K for
magnetic field applied along c-axis and ab-plane, respectively, were observed.
Whereas the c-axis Hc2|c(T) increases quasi-linearly with decreasing
temperature, the ab-plane Hc2|ab(T) shows a flattening, starting near 25 K
above 30 T. This leads to a non-monotonic temperature dependence of the
anisotropy parameter \gamma= Hc2|ab/Hc2|c. The anisotropy parameter is ~ 2 near
Tc ~ 32 K and rises to a maximum \gamma ~ 3.6 around 27 K. For lower
temperatures, \gamma decreases with T in a linear fashion, dropping to \gamma ~
2.5 by T ~ 18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and
(Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state
and proximity to an insulating state, the Hc2(T) curves are remarkably similar.Comment: slightly modified version, accepted to PRB, Rapid Communication
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