High-temperature nitridization of zirconium, production of ceramic and metal-ceramic refractory structures

Based on the results of the work performed, the nature of the phase distribution in the resulting material, structural and morphological differences between the layered metal-ceramic and ceramic structures were established. The temperature range of zirconium nitride synthesis from 1500 to 2400° C is investigated, and the possibility of successful synthesis of nitride ceramics by the indicated method at temperatures significantly exceeding the melting point of the metal is shown.

The study of thermal stresses and parameters of refractory structures for the formation of the temperature field when changing the heating rate of the working surface of products

An experimental setup for micro- and macro-studies of specific heat fluxes and thermomechanical properties of refractories has been developed. The influence on the heat resistance of refractory structures of thermal stresses, temperature field, shape and size of products under various heating conditions of their working surface is studied. It is shown that reducing the width of the side of the working surface of the refractory allows you to increase the speed and specific heat flux without violating the integrity of the structure of the refractory material. The distribution of the temperature fields of the refractory with a change in the heating rate of its working surface, as well as its shape, is studied. Ill. 5. Ref. 11.

Human mitochondrial ribosomes can switch their structural RNA composition

The recent developments in cryo-EM have revolutionized our access to previously refractory structures. In particular, such studies of mammalian mitoribosomes have confirmed the absence of any 5S rRNA species and revealed the unexpected presence of a mitochondrially encoded tRNA (mt-tRNA) that usurps this position. Although the cryo-EM structures resolved the conundrum of whether mammalian mitoribosomes contain a 5S rRNA, they introduced a new dilemma: Why do human and porcine mitoribosomes integrate contrasting mt-tRNAs? Human mitoribosomes have been shown to integrate mt-tRNAVal compared with the porcine use of mt-tRNAPhe. We have explored this observation further. Our studies examine whether a range of mt-tRNAs are used by different mammals, or whether the mt-tRNA selection is strictly limited to only these two species of the 22 tRNAs encoded by the mitochondrial genome (mtDNA); whether there is tissue-specific variation within a single organism; and what happens to the human mitoribosome when levels of the mt-tRNAVal are depleted. Our data demonstrate that only mt-tRNAVal or mt-tRNAPhe are found in the mitoribosomes of five different mammals, each mammal favors the same mt-tRNA in all tissue types, and strikingly, when steady-state levels of mt-tRNAVal are reduced, human mitoribosome biogenesis displays an adaptive response by switching to the incorporation of mt-tRNAPhe to generate translationally competent machinery.

Sizing of Refractory Castable Gas-Burner Using Thermomechanical Simulations

Damage is a crucial characteristic of refractory castables and has to be considered to simulate correctly the behaviour of refractory structures. But, damage modelling by finite element simulations remains difficult. Indeed, the use of a continuum damage model with softening leads to strain localization phenomena. Numerical results depend on the mesh. Several numerical methods allow solving this meshing dependence by introducing an internal length in the material constitutive laws. In this paper, a regularization method has been applied with the damage plasticity model, considering a scalar value for damage. This model enables to take into account permanent strains due to plasticity and damage before and after the peak stress in tension and compression. Thermomechanical simulations are performed with this model to predict damage in a gas-burner. The damage level is evaluated after a thermal simulation generating high temperature gradients. Interests to take into account damage in the refractory structures are discussed. Sensitivity of results to material properties is studied. This work gives an example of using thermomechanical simulations to improve the design of refractory castable structures and to help in the material choice.

Thermal Schock Criteria of Refractory Ceramics: Limitations of Conventional Analyses and Some Numerical Approaches to Improve the Prediction of the Resistance to Thermal Schock

Significant advances in the mechanical design of ceramic parts were realized since the pioneer works of Kingery and Hasselman to define thermal shock resistance. But for high heterogeneous refractories and contrasted local phase properties the use of these criteria is not always convincing because the assumptions made are too simplicist. First, we underline how thermal shock resistance parameters helped to improve the global performance of ceramics and make some comments on their limitations for refractory materials. Then we show how numerical tools are useful for the design of refractory structures at high temperatures through several approaches we have developed for refractory structures: prediction of macroscopic thermal shock resistance of heterogeneous refractories using multi-scale analysis, finite element methods applied to a specific structure considering either a two-scale approach to describe the thermo-elastic quasi brittle behavior of heterogeneous materials, at the macroscopic scale approach considering homogeneous microstructure.