Conformation-aggregation interplay in the simplest aliphatic ethers probed under high pressure.

The structures of the simplest symmetric primary ethers [(CnH2n+1)2O, n = 1-3] determined under high pressure revealed their conformational preferences and intermolecular interactions. In three new polymorphs of diethyl ether (C2H5)2O, high pressure promotes intermolecular CH...O contacts and enforces a conversion from the trans-trans conformer present in the α, ß and γ phases to the trans-gauche conformer, which is higher in energy by 6.4 kJ mol-1, in the δ phase. Two new polymorphs of dimethyl ether (CH3)2O display analogous transformations of the CH...O bonds. The crystal structure of di-n-propyl ether (C3H7)2O, determined for the first time, is remarkably stable over the whole pressure range investigated from 1.70 up to 5.30 GPa.

Effects of the Mixing Process on the Rheological Properties of Waste PET-Modified Bitumen.

This paper analyses the key findings of a study devoted to PET-modified bitumen. The research program was run according to the D-optimal experimental plan based on a factorial design. Five factors, i.e., the type of polymer (source), the type of bitumen (qualitative factors), PET amount, mixing rate, and mixing temperature (quantitative factors), controlled the bitumen-polymer mixing process. The experiment included a series of determinations of bitumen's rheological characteristics obtained by MSCR (Jnr, R) and G*/sin(δ) at 50 °C, 60 °C, and 70 °C. The low-temperature properties of the composite (critical temperature) were evaluated using a BBR test. The findings showed that bitumen modification with PET primarily reduced the creep susceptibility of the bituminous-polymer mixture. The low-temperature characteristics of the modified bitumen played a secondary but essential role. The amount of polymer and the mixing rate interacted with the temperature, significantly reducing the stiffness of the composite, while the type and amount of bitumen had a substantial effect on the results obtained in the BBR test. It is worth noting that when combining bitumen and plastomer, special attention should be paid to ensuring a high level of homogeneity of the mixture by controlling the parameters of the mixing process accordingly. The tests and analyses provided crucial models (GLM), which allowed for the prediction of the plastomer-modified bitumen's low- and high-temperature properties. The resulting relationships between factors and the identification of their impact on the bitumen properties enable a better understanding of the process of bitumen modification with PET. The conclusions presented here serve as a basis for future optimisation of the modified bitumen composition. The performed studies indicate that the use of >3% plastomer in bitumen 70/100 allows for a reduction in its susceptibility (MSCR) to below 0.5 kPa-1, making it suitable for bituminous mixtures for high-traffic roads. No significant increase in critical temperature (BBR) was observed.

Effect of Zirconium Diboride and Titanium Diboride on the Structure and Properties of 316L Steel-Based Composites.

The effect of zirconium diboride (ZrB2) and titanium diboride (TiB2) on the microstructure as well as the physical, mechanical, and tribological properties of composites based on 316 L steel is presented. Each reinforcing phase was added to the base alloy in the amount of 5 wt% and 10 wt%. The composites were fabricated by the SPS process (Spark Plasma Sintering). The results show that the weight fraction of the reinforcing phase affects the physical, mechanical, and tribological properties of the sintered composites. The sintered materials were characterized by a very high level of density. The addition of TiB2 has proved to be effective in increasing the hardness and compressive strength of the composites. The hardness of the composites with the addition of 10% TiB2 increased by 100% compared to the hardness of sintered 316L steel. It was found that introducing ZrB2 to the steel matrix significantly improved the wear resistance of the composites. The results showed that compared to 316L steel with the wear rate of 519 × 10-6 mm3/Nm, the wear rate of the composites containing 10% ZrB2 decreased more than twice, i.e., to 243 × 10-6 mm3/Nm.

Stochastic hydration of a high-nitro-gen-content molecular compound recrystallized under pressure.

Partial hydration of organic compounds can be achieved by high-pressure crystallization. This has been demonstrated for the high-nitro-gen-content compound 6-chloro-1,2,3,4-tetrazolo[1,5-b]pyridazine (C4H2N5Cl), which becomes partly hydrated by isochoric crystallizations below 0.15 GPa. This hydrate, C4H2N5Cl·xH2O, is isostructural with the ambient-pressure phase α of C4H2N5Cl, but the crystal volume is somewhat larger than that of the anhydrate. At 0.20 GPa, the α-C4H2N5Cl anhydrate phase transforms abruptly into a new higher-symmetry phase, α'; the transformation is clearly visible due to a strong contraction of the crystals. The hydrate α-C4H2N5Cl·xH2O can also be isothermally compressed up to 0.30 GPa before transforming to the α'-C4H2N5Cl·xH2O phase. The isochoric recrystallization of C4H2N5Cl above 0.18 GPa yields a new anhydrous phase ß, which, on releasing pressure, transforms back to the α phase below 0.15 GPa. The structural transition from the α to the ß phase is destructive for the single crystal and involves a large volume drop and significant elongation of all the shortest intermolecular distances which are the CH⋯N and CH⋯Cl hydrogen bonds, as well as the N⋯N contacts. The α-to-α' phase transition increases the crystal symmetry in the subgroup relation; however, there are no structural nor symmetry relations between phases α and ß.

Thermal Analysis-Based Field Validation of the Deformation of a Recycled Base Course Made with Innovative Road Binder.

The deformation of the cold recycled mixture with foamed bitumen in a recycled base with an innovative three-component road binder and foamed bitumen is analysed. Numerical simulation results for the pavement constructed, based on laboratory test results, were verified against the data from the monitoring system installed on the road trial section. In addition, environmental effects, such as air temperature and humidity levels in the pavement structure layers, were considered. Thermal analyses were conducted to identify the thermal properties of the pavement materials under steady heat transfer rate. Determining temperature distribution in the road cross-section in combination with relaxation functions determined for individual pavement layers contributed to the high effectiveness of the numerical simulation of deformation and displacement in the recycled base and the entire pavement. The experimental method of identifying thermal properties allows a fast and satisfactory prediction of temperature distribution in the pavement cross-section.

The Pressure Compaction of Zr-Nb Powder Mixtures and Selected Properties of Sintered and KOBO-Extruded Zr-xNb Materials.

Materials were obtained from commercial zirconium powders. 1 mass%, 2.5 mass% and 16 mass% of niobium powders were used as the reinforcing phase. The SPS method and the extrusion method classified as the SPD method were used. Relative density materials of up to 98% were obtained. The microstructure of the sintered Zr-xNb materials differs from that of the extruded materials. Due to the flammability of zirconium powders, no mechanical alloying was used; only mixing of zirconium and niobium powders in water and isopropyl alcohol. Niobium was grouped in clusters with an average niobium particle size of about 10 µm up to 20 µm. According to the Zr-Nb phase equilibrium system, the stable phase at RT was the hexagonal α-phase. The tests were carried out for materials without the additional annealing process. The effect of niobium as a ß-Zr phase stabilizer is confirmed by XRD. Materials differed in their phase composition, and for both methods the ß-Zr phase was present in obtained materials. A very favorable effect of niobium on the increase in corrosion resistance was observed, compared to the material obtained from the powder without the addition of niobium.

Microstructure and Properties of TiB2 Composites Produced by Spark Plasma Sintering with the Addition of Ti5Si3.

Titanium diboride (TiB2) is a hard, refractory material, attractive for a number of applications, including wear-resistant machine parts and tools, but it is difficult to densify. The spark plasma sintering (SPS) method allows producing TiB2-based composites of high density with different sintering aids, among them titanium silicides. In this paper, Ti5Si3 is used as a sintering aid for the sintering of TiB2/10 wt % Ti5Si3 and TiB2/20 wt % Ti5Si3 composites at 1600 °C and 1700 °C for 10 min. The phase composition of the initial powders and produced composites was analyzed by the X-ray diffraction method using CuKα radiation. The microstructure was examined using scanning electron microscopy, accompanied by energy-dispersive spectroscopy (EDS). The hardness was determined using a diamond indenter of Vickers geometry loaded at 9.81 N. Friction-wear properties were tested in the dry sliding test in a ball-on-disc configuration, using WC as a counterpart material. The major phases present in the TiB2/Ti5Si3 composites were TiB2 and Ti5Si3. Traces of TiC were also identified. The hardness of the TiB2/Ti5Si3 composites was in the range of 1860-2056 HV1 and decreased with Ti5Si3 content, as well as the specific wear rate Wv. The coefficient of friction for the composites was in the range of 0.5-0.54, almost the same as for TiB2 sinters. The main mechanism of wear was abrasive.

Fabrication of the Zirconium Diboride-Reinforced Composites by a Combination of Planetary Ball Milling, Turbula Mixing and Spark Plasma Sintering.

The aim of this study was to carry out the consolidation of zirconium diboride-reinforced composites using the SPS technique. The effect of the adopted method of powder mixture preparation (mixing in Turbula or milling in a planetary mill) and of the reinforcing phase content and sintering temperature on the microstructure, physical properties, strength and tribological properties of sintered composites was investigated. Experimental data showed that the maximum relative density of 94%-98% was obtained for the composites sintered at 1100 °C. Milling in a planetary mill was found to contribute to the homogeneous dispersion and reduced clustering of ZrB2 particles in the steel matrix, improving in this way the properties of sintered steel + ZrB2 composites. Morphological and microstructural changes caused by the milling process in a planetary mill increase the value of Young's modulus and improve the hardness, strength and wear resistance of steel + ZrB2 composites. Higher content of ZrB2 in the steel matrix is also responsible for the improvement in Young's modulus, hardness and abrasive wear resistance.

The Extrusion and SPS of Zirconium-Copper Powders and Studies of Selected Mechanical Properties.

Zr-2.5Cu and Zr-10Cu powder mixtures were consolidated in the extrusion process and using the spark plasma sintering technique. In these studies, material tests were carried out in the fields of phase composition, microstructure, hardness and tensile strength for Zr-Cu materials at room temperature (RT) and 400 °C. Fractography analysis of materials at room temperature and 400 °C was carried out. The research took into account the anisotropy of the materials obtained in the extrusion process. For the nonequilibrium SPS process, ZrCu2 and Cu10Zr7 intermetallic compounds formed in the material at sintering temperature. Extruded materials were composed mainly of α-Zr and ZrCu2. The presence of intermetallic compounds affected the reduction in the strength properties of the tested materials. The highest strength value of 205 MPa was obtained for the extruded Zr-2.5Cu, for which the samples were cut in the direction of extrusion. For materials with 10 wt.% copper, more participation of the intermetallic phase was formed, which lowered the mechanical properties of the obtained materials. In addition to brittle intermetallic phases, the materials were characterized by residual porosity, which also reduced the strength properties.

A Novel Approach by Spark Plasma Sintering to the Improvement of Mechanical Properties of Titanium Carbonitride-Reinforced Alumina Ceramics.

Ti(C,N)-reinforced alumina-zirconia composites with different ratios of C to N in titanium carbonitride solid solutions, such as Ti(C0.3,N0.7) (C:N = 30:70) and Ti(C0.5,N0.5) (C:N = 50:50), were tested to improve their mechanical properties. Spark plasma sintering (SPS) with temperatures ranging from 1600 °C to 1675 °C and pressureless sintering (PS) with a higher temperature of 1720 °C were used to compare results. The following mechanical and physical properties were determined: Vickers hardness, Young's modulus, apparent density, wear resistance, and fracture toughness. A composite with the addition of Ti(C0.5,N0.5)n nanopowder exhibited the highest Vickers hardness of over 19.0 GPa, and its fracture toughness was at 5.0 Mpa·m1/2. A composite with the Ti(C0.3,N0.7) phase was found to have lower values of Vickers hardness (by about 10%), friction coefficient, and specific wear rate of disc (Wsd) compared to the composite with the addition of Ti(C0.5,N0.5). The Vickers hardness values slightly decreased (from 5% to 10%) with increasing sintering temperature. The mechanical properties of the samples sintered using PS were lower than those of the samples that were spark plasma sintered. This research on alumina-zirconia composites with different ratios of C to N in titanium carbonitride solid solution Ti(C,N), sintered using an unconventional SPS method, reveals the effect of C/N ratios on improving mechanical properties of tested composites. X-ray analysis of the phase composition and an observation of the microstructure was carried out.

Crystal design by CH...N and N...N interactions: high-pressure structures of high-nitrogen-content azido-triazolopyridazines compounds.

High-nitrogen-content compounds 6-azido-1,2,4-triazolo[4,3-b]pyridazine (C5H3N7) and its 3-methyl derivative (C6H5N7) have been in situ crystallized in a diamond-anvil cell and their structures determined by single-crystal X-ray diffraction. Under ambient and high-pressure conditions the crystallizations yield the same phases: the C5H3N7 anhydrate and C6H5N7 hydrated clathrate. In both the structures there are clearly distinguished regions of short CH...N and N...N intermolecular contacts, the latter involving exclusively the azide groups. High pressure initially increases the contents of water in the channel pores of the clathrate.

Vitrification and New Phases in the Water:Pyrimidine Binary Eutectic System.

The binary diagram for pyrimidine:water mixtures has been determined by differential scanning calorimetry, in situ single-crystal, and powder X-ray diffraction experiments. The eutectic point has been located near the 1:4 n/n ratio at 234.5 K. The eutectic and nearly eutectic mixtures easily vitrify, and the vitrification could be kinetically induced for 1:3 n/n mixtures, too. Depending on the cooling rate, the 1:4 mixture freezes in the glass state, as a conglomerate of the glass and crystalline phases, or as the eutectic mixture of pyrimidine phase I and hexagonal ice Ih. When heated above 160 K, the glass phase transforms to a novel crystalline phase, tentatively identified as a pyrimidine hydrate, which in turn at ca. 200-210 K transforms into a eutectic mixture of pyrimidine phase I and hexagonal ice Ih. The pyrimidine-water binary diagram and novel crystalline and amorphous phases are relevant to the thermodynamic behavior of hydrophilic pyrimidine and its natural and synthetic derivatives in humid environments. The presently determined binary diagram can be straightforwardly applied for assessing the contents of water in highly hygroscopic pyrimidine samples.

Pressure-induced collapse of guanidinium nitrate N-H···O bonded honeycomb layers into a 3-D pattern with varied H-acceptor capacity.

Highly favoured N-H···O bonded honeycomb layers in guanidinium nitrate, C(NH(2))(3)(+)NO(3)(-), have been destabilized by a pressure of 0.6 GPa, and the novel motif of 3-dimensional N-H···O bonded aggregation in high-pressure phase IV determined for in situ grown single-crystal by X-ray diffraction. The mechanism of the transition involves the collapse of voids present in phases I, II and III. In the P/T phase diagram a large hysteresis of the phase IV boundaries is caused by the strongly reconstructive character of the transition and pressure dependent H-accepting capacity of oxygen atoms.

Molecular symmetry and isostructural relations in crystal phases of trihalomethanes CHCl3, CHBrCl2, CHBr2Cl, and CHBr3.

Bromodichloromethane (CHBrCl(2)), dibromochloromethane (CHBr(2)Cl), and their parent trihalomethanes, chloroform (CHCl(3)) and bromoform (CHBr(3)), form an intriguing series of isostructural crystal phases, the sequence of which depends on the Br/Cl substitution and thermodynamic conditions. The phase behavior of these compounds has been studied by isobaric calorimetry and isothermal compression, and the crystal structure of CHBrCl(2) has been determined at 0.10 MPa/200 K, 0.73, 1.26, 2.53 GPa (all at 295 K), and that of CHBr(2)Cl at 0.43, 1.24 GPa (all at 295 K). CHBrCl(2) frozen by isobaric cooling at 0.10 MPa crystallizes in space group P1 with Z = 2, while its high-pressure polymorph in space group Pnma (Z = 4) is stable at 295 K from its freezing pressure at 0.48 to at least 2.53 GPa. At the freezing pressure of 0.29 GPa, CHBr(2)Cl crystallizes in space group P6(3), with Z = 2, and at 1.27 GPa, it transforms to the orthorhombic structure, space group Pnma (Z = 4); CHCl(3) has the identical symmetries, but their reverse sequence was observed. A subtle isostructural phase transition has been observed at 0.10 MPa and 214.9 K in CHBr(2)Cl. The relations between isostructural phases, their symmetry, and site occupation factors of halogen atoms observed in the low-temperature and high-pressure phases of trihalomethanes (CHCl(3), CHBrCl(2), CHBr(2)Cl, and CHBr(3)) have been explained by the directional character of electrostatic interactions between the molecules. A gradual ordering of the disordered Br and Cl atoms has been achieved in the compressed crystals, where the narrower volume of the atomic sites correlates with the increased occupancy of the smaller atom (chlorine). The molecular symmetry has been shown to control the molecular aggregation in the crystalline state, consistent with the crystal site-symmetry and the balance of electrostatic matching and dispersion forces between molecules.

Energetics of conformational conversion between 1,1,2-trichloroethane polymorphs.

Pressure-induced transformations between gauche-, gauche+ and transoid conformations have been evidenced by X-ray single-crystal diffraction for 1,1,2-trichloroethane, and the energies of intermolecular interactions, conformational conversion, and the latent heat have been determined.

Competing patterns of weak directional forces in pressure-frozen CH2ClI and CH2I2.

Isostructural relations and phase transitions of dihalomethanes have been rationalized by the competing patterns of CH...halogen hydrogen bonds and halogen...halogen interactions, the common weak directional interactions in soft organic matter. Pressure-frozen chloroiodomethane, CH(2)ClI, at 295 K and 0.72 GPa forms centrosymmetric phase III, which at ca. 400 K and 1.6 GPa disproportionates into CH(2)Cl(2) and CH(2)I(2). The directional character of intermolecular contacts between halogen atoms results from the characteristic anisotropic charge distribution on molecular surface.

1,1-Dichloroethane: a molecular crystal structure without van der Waals contacts?

Isochoric and isobaric freezing of 1,1-dichloroethane, CH3CHCl2, mp=176.19 K, yielded the orthorhombic structure, space group Pnma, with the fully ordered molecules, in the staggered conformation, located on mirror planes. The CH3CHCl2 ambient-pressure (0.1 MPa) structures were determined at 160 and 100 K, whereas the 295 K high-pressure structures were determined at 0.59 and 1.51 GPa. At 0.1 MPa, all intermolecular distances are considerably longer than the sums of the van der Waals radii, and only a pressure of about 1.5 GPa squeezed the Cl...Cl and Cl...H contacts to distances commensurate with these sums. The exceptionally large difference between the melting points of isomeric 1,1- and 1,2-dichloroethane can be rationalized in terms of their molecular-packing efficiency. It has been shown that the location of atoms in molecules affects their intermolecular interactions, and hence their van der Waals radii are the function of molecular structures.

Isobaric and isochoric freezing of CH2BrCl and isostructural relations between CH2Cl2, CH2Br2 and CH2BrCl.

Bromochloromethane, CH(2)BrCl, has been temperature-frozen and in situ pressure-frozen and the structure determined by X-ray diffraction at low temperatures of 170 and 100 K at ambient pressure (0.10 MPa), and at high pressures of 1.04 and 1.72 GPa at room temperature (295 K). CH(2)BrCl exhibits a remarkable polymorphism: at low temperature it crystallizes in the monoclinic space group C2/c (phase I), isostructural to the crystals of CH(2)Br(2). The pressure-frozen crystal of CH(2)BrCl is orthorhombic, space group Pbcn, and is isostructural to the crystal of CH(2)Cl(2). In both phases I and II the Br and Cl atoms are substitutionally disordered. The freezing temperatures and pressures of simple dihalomethanes have been correlated to their molecular weight and halogen... halogen distances. Calculated electrostatic potential surfaces have been related to the different crystal packing of dihalomethanes investigated.