Oxygen Inhibition and Coating Thickness Effects on Uv Radiation Curing of Weatherfast Clearcoats Studied by Photo-DSC

Radiation curing is an environmentally-friendly technology. Furthermore, radiation curing is a faster, energy saving and more efficient industrial process than the heat-curable process. One of the most important requirements for the widespread application of UV curable coatings in the coating industry is that they are stable vs. atmospheric degradation. Today's state of the art in oxidative drying and thermosetting coatings is the use of light stabilizers to protect polymers vs. the damage of outdoor exposure. Oxygen has a detrimental effect on the cure response of free radical systems, especially in thin-film coatings. Differential photocalorimetry (photo-DSC) was used to investigate the oxygen effect and the use of light stabilizers on UV curing of photocurable formulations based on acrylate materials. Coating thickness influence was also considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

Differential scanning calorimetry of sodium and potassium nitrates and nitrites

Differential scanning calorimetry (DSC) experiments were performed with NaNO₃, KNO₃, (Na,K)NO₃, NaNO₂ and KNO₂ over the temperature range 350–990 K. Endothermic peaks, indicative of decomposition reactions, were observed to occur in the single salts above their melting points. The equimolar mixture of sodium and potassium nitrate did not decompose in the temperature range specified. The nitrites began to decompose at 800±10 K. Sodium nitrate began to decompose at 840±10 K and potassium nitrate began to decompose at 820±20 K. These results were compared with previously reported differential thermal analysis investigations of NaNO₃ and KNO₃.     

Cure Degree Estimation of Photocurable Coatings by DSC and Differential Photocalorimetry

Radiation-curable coatings have acquired importance, because they are environmentally-friendly (no solvent emission)and require low energy for curing, when compared to other conventional heat-curable products. UV-curable coatings performance depends on the cure quality. Suitable methods were evaluated to estimate the degree of cure applying quantitative techniques, such as differential scanning calorimetry (DSC) and differential photocalorimetry (DPC), in order to determine the residual heat of curing in UV-cured films. The results of the DPC technique showed better sensibility than DSC technique, although the use of suitable pans for the case of clear coats must be considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of acidity on chelate ring closure occurring by chloro,nitro or azido group displacement in rhodium(III) complexes

The effect of CH₃COOH, ClCH₂COOH, Cl₂CHCOOH, Cl₃CCOOH and of ClCH₂COOH-ClCH₂COO^? buffers on the rates of the conversion of mer-[Rh(L)(L′)Cl₂X] into trans-[Rh(L)₂Cl₂]⁺ + X^? has been investigated in methanol [L and L′ = (o-dimethylaminophenyl)dimethylarsine-NAs and -As, respectively; X^? = Cl^?, NO₂^?, N₃^?. The rates have been found to depend only on the hydrogen ion concentration and not on the particular concentration or strength of the acid used. The observed rate constant of mer-[Rh(L)(L′)Cl₃] is decreased by increasing the hydrogen ion concentration. Conversely, k_obs for mer-[Rh(L)(L′)Cl₂N₃] increases smoothly up to a maximum limiting value by increasing the hydrogen ion concentration. A similar behaviour is shown by mer-[Rh(L)(L′)Cl₂NO₂], but in this case the rate constant achieves a maximum value and then it decreases towards a limiting value as the hydrogen ion concentration is increased further. The dependence of k_obs on [H⁺] for the acid-dependent reaction path of the mer → trans conversion of mer-[Rh(L)(L′)Cl₃] and mer-[Rh(L)(L′)Cl₂N₃] is explained in terms of protonation at the - NMe₂ free end of L′, whereas also diprotonation of the complex is tentatively invoked to explain the kinetic effect of acidity on the reactions of mer-[Rh(L)(L′)Cl₂NO₂].     

Rhodium(III) halide complexes with sulphur donors. The crystal structure ofmer-tris(o-ethylthiocarbamate)-trichlororhodium(III)acetone(1/1)

Summary The complexes [Rh(TC)₃Cl₃] · Me₂CO and [Rh(TC)₃X₃] · 0.5 Me₂CO (TC=O-ethylthiocarbamate; X=Br or I) have been prepared and characterized by i.r. and¹H n.m.r. spectroscopy.The crystal structure of [Rh(TC)₃Cl₃] · Me₂CO has been determined by x-ray diffractometer data and refined to R=0.040. Crystals are monoclinic, space group P2₁, with a=9.101(5), b=15.785(8), c=8.776(5) Å, and =103.00(3)°; Dx=1.57 gcn^–3 for Z=2. The complex is monomeric with octahedral Rh. Relevant distances are Rh-Cl (trans to one another) 2.354(2) and 2.353(2) Å, Rh-Cl (trans to S) 2.388(2) Å; Rh-S (trans to one another) 2.376(3) and 2.369(3) Å, Rh-S (trans to Cl) 2.332(3) Å. There is intramolecular, and possibly intermolecular, hydrogen bonding in the structure.     

Simultaneous dynamic thermogravimetry and mass spectrometry of the evaporation of alkali metal nitrates and nitrites

Six alkali metal nitrates and nitrites were evaporated in vacuum at a constant heating rate in a combined mass spectrometric and thermogravimetric apparatus. Time resolved profiles of decomposition gases and kinetics were obtained for LiNO₃, NaNO₃, KNO₃, Na/KNO₃, NaNO₂ and KNO₂. Activation energies for the evaporation of these salts were calculated and compared to previous results of isothermal experiments. In the temperature range 650–850 K, the decomposing nitrates released NO, N₂ and O₂ while the nitrites released only NO and N₂.

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Zusammenfassung Sechs Alkalimetallnitrate und -nitrite wurden in Vakuum, bei konstanter Erwärmungsgeschwindigkeit in einer kombinierten massenspektroskopischen und thermogravimetrischen Vorrichtung verdampft. Für LiNO₃, NaNO₃, KNO₃, Na/KNO₃, NaNO₂ und KNO₂ wurden die zeitzerlegten Profile der Zersetzungsgase, sowie die Kinetik erhalten. Für die Verdampfung dieser Salze wurden die Aktivationsenergien berechnet, und mit früheren Ergebnissen der isothermischen Versuche verglichen. In dem Temperaturbereich 650 bis 850 K wird von den zerfallenden Nitraten NO, N₂ und O₂ befreit, die Nitrite entwickeln dagegen nur NO und N₂.

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- . - LiNO₃, NaNO₃, KNO₃, Na/KNO₃, NaNO₂ KNO₂. . 650–850 , , — .

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This work is based in part on a thesis submitted by C. M. Kramer in partial fulfillment of the requirements for the degree of Doctor of Philosophy to the Division of Materials Science and Engineering, College of Engineering, University of California at Davis. The work was performed at the Sandia National Laboratories, Livermore, CA.