Revealing specific features of structure formation in composites based on nanopowders of synthesized zirconium dioxide

Abstract

Peculiarities of formation of microstructure in composites based on chemically synthesized zirconium nanopowders obtained by the method of decomposition from fluoride salts were considered. Hydrofluoric acid, concentrated nitric acid, aqueous ammonia solution, metallic zirconium, and polyvinyl alcohol were used. It was established that the reduction of porosity in nanopowders in the sintering process is the main problem in the formation of high-density materials. Analysis of various initial nanopowders, their morphology, and features of sintering by the method of hot pressing with direct transmission of electric current was made. Peculiarities of obtaining the composites based on them with the addition of Al2O3 nanopowders applying the electric sintering method were considered. It was shown that the increase in the content of alumina nano additives leads to an increase in strength and crack resistance of the samples due to simultaneous inhibition of abnormal grain growth and formation of a finer structure with a high content of tetragonal phase. The influence of sintering modes on the formation of the microstructure of zirconium nanopowders has been studied for different contents of alumina additives. Electric current promotes the surface activity of nanopowders and its variable value promotes partial fragmentation of agglomerated grains thus affecting the composite structure. Physical-mechanical properties of the obtained samples, optimal compositions of mixtures, and possibilities of improving some parameters were determined. It was found that nanopowders of zirconium dioxide obtained by the method of decomposition from fluoride salts are quite suitable for the production of composite materials with high physical and mechanical properties. They can compete with imported analogs and enable obtaining of crack resistance of 7.8 MPa·m1/2 and strength of 820 MPa.

Determining patterns of vertical load on the prototype of a removable module for long-size cargoes

“…In addition, one of the further areas of the current study is the introduction of promising materials in the design of the removable module [42][43][44]. The issue related to experimental determination of the strength of the removable module requires attention.…”

Peculiarities of the Phase Formation during Electroconsolidation of Al2O3–SiO2–ZrO2 Powders Mixtures

“…The indenter was in form of a Vickers pyramid with an angle of α = 136°. The microhardness HV was calculated from the following equation [ 23 ]: where P —load on the indenter, in our study P = 10 N, 2· a —an average length of the indentation diagonal [μm], k —is the factor taken for a Vickers pyramid k = 1.854.…”

Activated Sintering of Cr2O3-Based Composites by Hot Pressing

“…The fracture toughness K IC was determined from the indentation with Vickers’ pyramid on the polished surfaces according to the following formula [ 25 , 26 ]: where F is the constraint factor, F = 3; H is the hardness; a is the half-diagonal of the Vickers indent; E is the Young’s modulus; and l is the length of the surface crack. The dimensions of samples made for that purpose were 13 mm × 13 mm × 5 mm.…”