Styrylquinolinium borates as donor–acceptor initiators for sensitized photopolymerization of TMPTA

Several photoredox pairs containing mono- and bicationic hemicyanine dyes have been evaluated as photoinitiators for free radical polymerization induced with an argon-ion laser irradiation. The tested photoredox couples are the pairs composed of the hemicyanine dye cations acting as electron acceptors and n-butyltriphenyl borate anions being the electron donors. The photoinitiating abilities of the series of monochromophoric stilbazolium borates, 4-(p-N,N-dialkylaminostyryl)quinolinium n-butyltriphenylborate, were compared to the photochemistry of structurally related, bicationic styrylquinolinium borates. The obtained results clearly documented that the dicationic photoinitiators exhibit a marked increase in the photoinitiation ability compared to the initiators consisting of a single charged hemicyanine dye.Our studies revealed also that the rate of photopolymerization depends on ΔG_el of electron transfer between borate anion and styrylquinolinium cation. The relationship between the rate of polymerization and the free energy of activation shows the dependence predicted by the classical theory of electron transfer.     

A novel thermal treatment on a Mg–4.2Y–2.3Nd–0.6Zr (WE43) alloy

A double-stage thermal treatment has been adopted on a Mg–Y–Nd–Zr (WE43) alloy, following suggestions of a previous calorimetric investigation. A secondary precipitation is claimed to occur at a temperature as low as 150 °C after a preliminary precipitation at 210 °C, with the effect of enhancing the hardness increase and reducing the annealing times.     

Extraordinary role of Ce–Ni elements on the electrical and magnetic properties of Sr–Ba M-type hexaferrites

The structural, electrical and magnetic behavior of Sr_0.5Ba_0.5−xCe_xFe_12−yNi_yO₁₉ (where x = 0.00–0.10; y = 0.00–1.00) hexaferrite nanomaterials are reported in this paper. The structural analysis indicates that the Ce–Ni doped Sr–Ba M-type hexaferrite samples synthesized by the co-precipitation method are stoichiometric, single magnetoplumbite phase with crystallite sizes in the range of 35–48 nm. The dc-electrical resistivity of the pure Sr–Ba hexaferrite is enhanced to almost 10² times by doping with Ce–Ni contents of x = 0.06; y = 0.60. The dielectric constant and dielectric loss tangent decrease to values 14 and <0.2, respectively, by increasing the frequency up to 1 MHz. Small relaxation peaks at frequencies >10⁵ Hz are observed for the samples with Ce content of x > 0.06. The values of saturation magnetization increase from 66.32 to 84.33 emu/g and remanance magnetization from 42.64 to 56.01 emu/g but coercivity decreases from 2.85 to 1.59 kOe by substitution of Ce–Ni. Sharp ferri-paramagnetic transition is observed in the samples, which is confirmed by DSC results. Ce–Ni substitution acts to reduce the electron-hopping between Fe²⁺/Fe³⁺ ions and also improves the magnetic properties. These characteristics are desirable for their possible use in microwave and chip devices.