Interface phenomena in (super)hard nitride nanocomposites: from coatings to bulk materials

Mechanical properties of nanocomposites usually surpass the mechanical properties of their micro-structured and single-crystalline counterparts. This is mainly due to an extremely high density of internal interfaces in nanocomposites like grain, crystallite and phase boundaries. When compared to diamond, carbides and borides, nitrides are of interest because of their high temperature oxidation resistance and compatibility with iron containing alloys. This tutorial review classifies the contributions of various internal interfaces to the hardness of the nanocomposites, and appreciates the outstanding role of partially coherent phase boundaries in the hardness enhancement. With selected examples of transition metal nitrides containing aluminium and silicon as well as of boron nitrides, it is explained how the nanocomposites with partially coherent phase boundaries and thus with enhanced hardness can be synthesised. As the possible ways of the formation of coherent phase boundaries, the local epitaxial growth of phases with limited mutual solubility, the production of supersaturated solid solutions followed by the segregation of elements during the spinodal decomposition and the incomplete phase transformation are discussed. The most important techniques, used for synthesis of nitride nanocomposites, like CVD, PVD, precursor-based methods, mechanical alloying and high-pressure-high-temperature synthesis are briefly reviewed. Besides, a short overview on hardness definitions and hardness measurements is included.     

Urotropine as a ligand for the efficient synthesis of metal-organic frameworks

Russian Chemical Bulletin - Urotropine is a cheap and promising ligand for the synthesis of metal-organic frameworks containing uncoordinated nitrogen atoms. The reactions between urotropine,...     

Penetration isotherms of binary mobile phases for liquid chromatography

Penetration isotherms ψ of eight binary solvent systems used as mobile phases in liquid chromatography are calculated. Dependences of penetrability coefficients of binary mixtures on the volume fraction of the more active solvent are described using modified polynomial functions, in which some empirical coefficients are changed for penetrability coefficients of pure solvents.     

Asymptotically Optimal in Reliability Circuits in Two Bases Under Failures of 0 (<Emphasis Type="Italic">k</Emphasis> − 1) Type at the Outputs of Elements

We consider a problem of the realization of k-valued logics functions (k ≥ 3) by circuits in two bases: in the Rosser–Turkett basis and in its dual basis. We assume that the basis gates are exposed to faults at outputs: only of type 0 or only of type k ? 1, and they pass into faulty states independently of each other. We describe a constructive method for the synthesis of an asymptotically optimal reliable circuit for almost any function of k-valued logic, we found the upper and lower bounds of circuits unreliability and the class of functions for which the lower bounds are true.     

Limits for the central production of Theta+ and Xi(--)pentaquarks in 920-GeV pA collisions

We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).     

Synthesis of hydrazones containing sterically hindered phenol groups and tetrathiacalix[4]arene fragment

1,3-Alternate and cone stereoisomers of tetrathiacalix[4]arene and 4-tert-butyltetrathiacalix[4]arene functionalized by carbohydrazide groups reacted with 3,5-di-tert-butyl-4-hydroxybenzaldehyde to give the corresponding hydrazones having sterically hindered phenol fragments.     

Growth of ZnSe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solution crystals from vapor phase

Partially faceted ZnSe_{1 − x} S _x solid solution crystals have been grown from a vapor phase in a closed stationary horizontal system. The growth has been performed in cylindrical quartz ampoules—∼10 mm in diameter and evacuated to a residual pressure of less than ∼10⁻³ Pa-at a temperature of 1050°C and a temperature drop between the source and growth zones of 10–16°C. The crystal structure, optical absorption, and composition inhomogeneity along the ingot length have been investigated by X-ray diffractometry and optical spectroscopy in the wavelength range of 300–3000 nm. The solid-solution composition range corresponding to cubic polymorphs is determined. The concentration dependences of the lattice parameter and band gap are presented.     

Structure-forming role of heterocyclic compounds in the synthesis of metal-organic frameworks based on cadmium(<Emphasis Type="SmallCaps">II</Emphasis>)

The influence of heterocyclic compounds on the formation of coordination polymers in the system of cadmium(II) nitrate tetrahydrate and biphenyl-4,4′-dicarboxylic acid is demonstrated. Two new coordination polymers [Cd(H₂O)(bpdc)(im)₂] (1, bpdc^2– is biphenyl-4,4′-dicarboxylate, im is imidazole) and [(CH₃)₂NH₂]₄[Cd₆(dmf)(bpdc)₈]·10DMF (2) were obtained under solvothermal conditions in the presence of imidazole or benzimidazole, respectively. Product 1 has a chain structure, while compound 2 possesses a three-dimensional structure with the hex topology. The obtained compounds were characterized by IR spectroscopy, thermogravimetry, elemental analysis, and powder X-ray diffraction.     

Mercury(II) and silver(I) receptors based on tetrathiacalix[4]arene hydrazones

The extraction ability of phenyl hydrazone derivatives of cone- and 1,3-alternate tetrathiacalix[4]arenes towards to some alkali, alkaline earth, transition and heavy metal ions has been investigated by picrate extraction method. The synthesized cone-tetrathiacalix[4]arene hydrazones show a high efficiency coupled with an excellent selectivity towards for Ag⁺ and Hg²⁺ ions. The stoichiometry of complexes and the extraction constants have been determined. The influence of calix[4]arene platform’s structure and the electron donor substituents in phenyl fragments on the extraction efficiency has been discussed.