Berislav Marković

Crystal Growth of Lead Fluoride Phases Using the Constant Composition Method. III. Effect of pH and Ionic Strength

Abstract The kinetics of crystal growth of the lead fluoride phases was studied at 25°C using the so-called constant composition method (pF-stat method). A linear growth law was obeyed for αPbF 2 growth from equivalent lead nitrate and potassium fluoride solutions with low supersaturation and pH between 5.2 and 5.6 in pure water and in 0.1 mol dm −3 KNO 3 solution. The rate is about 5 times greater at high ionic strength. It decreases linearly with changing pH of the supersaturated solution both to higher and to lower values than mentioned (addition of KOH and HNO 3 , respectively), i.e. reaching the pHs at which two other lead fluoride phases grow: (a) with large excess of Pb(NO 3 ) 2 over KF and KOH to pH = 5.2 phase(s) of so far unresolved structure, which undergoes the recrystallization in water to pure αPbF 2 , and after annealing to 450°C decomposes into β-PbF 2 , and an unidentified phase (probably α(K N Pb N−1 )F 2−N phase with N varied); (b) with large excess of KF over Pb(NO 3 ) 2 and HNO 3 to pH = 4.3, the βPbF 2 phase was identified. The characterization of the grown phases was done on the basis of polarizing microscopy, Fourier transform infrared (FTIR) spectra and X-ray powder diffraction analysis.

Temporal Variations in Concentrations of Ozone, Nitrogen Dioxide, and Carbon Monoxide at Osijek, Croatia

The purpose of this study was to investigate the ozone, carbon monoxide, and nitrogen dioxide variations and their correlation with meteorological parameters in Osijek (Eastern Croatia) during the summer seasons of 2002, 2007, and 2012. The measured data are discussed in relation to the EU guidelines (Directive 2002/3/EC, Directive 2008/50/EC). In order to characterize ambient air with respect to ozone photochemical pollution we calculated three photochemical pollution indicators. These indicators may also be a valid measure for harmful effects on living organisms. The influence of local meteorological parameters on the measured concentrations of ozone, carbon monoxide, and nitrogen dioxide was also investigated. We have attempted to establish correlations between measured pollutant concentrations and meteorological parameters using the technique of multivariate principal component analysis (PCA).

Triclinic polymorph of 4-[4-(4-formyl­phen­oxy)but­oxy]benzaldehyde

The title compound, C18H18O4, is a triclinic polymorph of the previously reported monoclinic polymorph [Han & Zhen (2005 ▶). Acta Cryst. E61, o4358–o4359]. In the crystal of the triclinic polymorph, molecules are linked by two pairs of C—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (102), and enclosing loops with graph set motifs of R 2 2(8) and R 2 2(6).

4-[5-(4-Formyl­phen­oxy)pent­oxy]benzaldehyde

In the title compound, C20H19O4, the benzene rings, linked via five methylene C atoms, form a dihedral angle of 77.28 (6)°. In the crystal, molecules are linked via pairs of weak C—H⋯O interactions [graph set R 2 2(6)] into dimers that are further connected by additional weak C—H⋯O interactions [graph sets R 2 2(14), R 2 2(26) and R 2 2(6)].

Freeze-thaw resistance assessment of cement-bound steel slag aggregate for pavement structures

Abstract This paper investigates the durability of cement-bound layers with steel slag as a partial aggregate replacement. Mixtures with various amounts of slag and cement are investigated for their durability after freeze–thaw cycles and exposure to de-icing agent. Optical microscopy analysis is conducted as a method for assessing the behaviour of low-strength material in order to determine why the application of slag resulted in greater compressive strength and durability properties. It was shown that this method is suitable for providing more details and insights into the material’s internal structure. All the mixtures show a loss in compressive strength after exposure to freeze–thaw cycles and de-icers, but this loss is more pronounced in mixtures with gravel-only aggregates. A strong linear correlation is obtained between 28-day compressive strength and retained compressive strength after 10 freeze–thaw cycles. The main conclusion of the research presented here is that steel slag aggregate presents good potential for use in adverse climates, and it is possible to predict the freeze–thaw resistance of cement-bound aggregate on the basis of compressive strength.

IMPACTO DE FATORES METEOROLÓGICOS SOBRE AS CONCENTRAÇÕES DE OZÔNIO MODELADOS POR ANÁLISE DE SÉRIES TEMPORAIS E MÉTODOS ESTATÍSTICOS MULTIVARIADOS

O objetivo desta pesquisa foi de desenvolver um modelo para prever as concentracoes de ozonio em funcao das variaveis climaticas. As medidas de concentracao do ozonio foram realizadas na Universidade Federal de Mato Grosso do Sul, utilizando dados do periodo de janeiro a dezembro de 2014. As variaveis preditoras referentes ao clima (umidade relativa, velocidade do vento, chuva, aeerossois, indice de claridade, radiacao solar global e temperatura) foram cedidas pela CEMTEC-Campo Grande-MS. Foram realizadas analise de componentes principais (PCA) e analise de regressao linear multipla (MLR) aplicadas a estas series temporais. As principais relacoes observadas nestas analises foram entao usadas para obter uma equacao de regressao que liga as concentracoes de ozonio diurnas com parâmetros climaticos. O modelo desenvolvido e capaz de explicar 99% da variabilidade nas concentracoes de ozonio de superficie com um erro de 0,2%