Influence of some lime-containing additives on the thermal behavior of urea

Urea is one of the main nitrogen fertilizers used in agriculture. But being well soluble in water, hardly 50% of its nitrogen is assimilated by plants. One possibility to eliminate this disadvantage is to use coating agents for modification of urea to obtain a controlled-realized fertilizer. The aim of this research was to study the influence of different lime-containing additives on the thermal behavior and decomposition kinetics of urea in oxidizing atmosphere. Commercial fertilizer-grade urea (46.4% N) and analytical-grade CaO, MgO, CaCO₃, MgCO₃ were used in the experiments. In addition, one Estonian limestone and one dolomite sample were used as additive or coating material. The experiments with a Setaram Setsys 1750 thermoanalyzer coupled to a Nicolet 380 FTIR Spectrometer by a heated transfer line were carried out under non-isothermal conditions up to 900 °C at the heating rate of 5 °C min^?1 and to calculate kinetic parameters, additionally, at 1, 2, and 10 °C min^?1 in the atmosphere containing 80% of Ar and 20% of O₂. The differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results obtained indicate that thermooxidative decomposition of urea as well as the blends of urea with lime-containing materials and urea prills coated with limestone or dolomite powder follows a complex reaction mechanism.     

TG-FTIR/MS analysis of thermal and kinetic characteristics of some coal samples

Thermooxidative decomposition (TOD) of seven coal samples from different deposits (Bulgaria, Russia, Ukraine) was studied with the aim to determine characteristics of the process and the differences related to the origin of the coal samples studied. The experiments with a Setaram Setsys 1750 or Labsys Evo 1600 thermoanalyzers coupled to a Nicolet 380 FTIR spectrometer or Pfeiffer mass spectrometer, respectively, were carried out under non-isothermal heating conditions up to 1,000 °C at the heating rates of 1, 2, 5, 10, and 20 °C min^?1 in an oxidizing atmosphere. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman was used to calculate the kinetic parameters. The combined TG-FTIR and TG-MS study of TOD of the coal samples made it possible to identify a number of gaseous species formed and evolved at that as well as to determine the differences in the thermal behavior of the coal samples and in the emission profiles of these species depending on their origin. The value of activation energy E along the reaction progress α varied more for the samples with higher content of organic matter and, especially, for the samples having at that also quite high content of mineral matter, indicating to the close association of mineral matter with organic matter and fixed carbon.     

Vaccum-ultraviolet low-tenperature spectroscopic study of free excitons in alkali iialide crystals under hydrostatic pressure

Abstract

Effect of pressure up to 14 kbar on free exciton reflection bands of alkali bromide crystals in VUV spectral region at 77 K was studied for the first time, In CsBr a strong resonance coupling of three exciton levels (an exciton analog of pressure-scanned Fermi resonance) was observed and computer-calculated. In NaBr, KBr and RbBr the increase of the spin-orbit splitting of the valence band was found, Besides, the exciton binding energy was estimated to decrease with pressure in NaI, KI and RbI.     

Influence of the post-granulation treatment on the thermal behaviour and leachability characteristics of Estonian oil shale ashes

The power and heat production in Estonia is based over 90% on the combustion of a local solid fossil fuel—Estonian oil shale (OS), and at that 7–8 million tons of OS ash are formed annually. One promising possibility for large-scale utilization of cheap alkali ashes is the liming of acidic soils. In Estonia, there is 350,000 ha of agricultural land that needs permanent liming. To eliminate possible environmental contamination at liming of soils the oil shale ashes should be granulated. Thermal analysis was used for determination of the relationships between physico-mechanical and physico-chemical characteristics of granulated products and the post-granulation treatment conditions. For determination of leachability of ash components, the granulated products as well as the origin ashes were tested using laboratory lysimetries. Depending on OS ash and different post-granulation treatment used, it was possible to obtain granulated product with compressive strength between 5 and 15 N per granule. The leaching of Ca²⁺ decreased up to 26 and 34%, SO₄ ^2? 70 and 53%, Mg²⁺ and K⁺ up to 7–12% for granulated CA and ESPA, respectively, comparing with original ashes. The results of soil analysis indicate that the use of OS ashes improved the pH level of soil significantly. pH increased equally with initial and granulated ash: from 4.7 up to 6.4 and 5.8, respectively, using for that CA and ESPA. Prolonged effect of soil neutralizing ability by granulated product (if compare with fine ashes) was proven by decrease in the content of leached ions in filtrate solutions as well as not mobile ions in soil.     

Reaction pathway to Cu2ZnSnSe4 formation in CdI2

Journal of Thermal Analysis and Calorimetry - We investigated various possible chemical interactions between individual precursor compounds (ZnSe, SnSe, and CuSe) and CdI2 as a flux material used...     

Separation of isotropic chemical and second-order quadrupolar shifts by multiple-quantum double rotation NMR

Using a two-dimensional multiple-quantum (MQ) double rotation (DOR) experiment the contributions of the chemical shift and quadrupolar interaction to isotropic resonance shifts can be completely separated. Spectra were acquired using a three-pulse triple-quantum z-filtered pulse sequence and subsequently sheared along both the ν₁ and ν₂ dimensions. The application of this method is demonstrated for both crystalline (RbNO₃) and amorphous samples (vitreous B₂O₃). The existence of the two rubidium isotopes (⁸⁵Rb and ⁸⁷Rb) allows comparison of results for two nuclei with different spins (I = 3/2 and 5/2), as well as different dipole and quadrupole moments in a single chemical compound. Being only limited by homogeneous line broadening and sample crystallinity, linewidths of approximately 0.1 and 0.2 ppm can be measured for ⁸⁷Rb in the quadrupolar and chemical shift dimensions, enabling highly accurate determination of the isotropic chemical shift and the quadrupolar product, P_Q. For vitreous B₂O₃, the use of MQDOR allows the chemical shift and electric field gradient distributions to be directly determined—information that is difficult to obtain otherwise due to the presence of second-order quadrupolar broadening.