M. A. Gol’dberg

Hydroxyapatite-Calcium Carbonate Ceramic Composite Materials

Hydroxyapatite/calcium carbonate (CC) composite powders containing up to 50 wt % CO32−, have been prepared via precipitation from aqueous solutions. According to chemical analysis data, the CO32− content of the powders coincides with the intended one over the entire composition range studied. With increasing CO32− content, the specific surface area of the powders decreases because of the formation and growth of large needlelike CC crystals up to 1.5 μm in size. The addition of low-melting-point alkali carbonates to the starting powder mixture reduces the sintering temperature of the powders to below 720°C, thereby preventing the thermal decomposition of CC. The highest bending strength, up to 76 MPa, is offered by the materials with the lowest CC content, about 20 wt %, and an average crystal size of 100 nm. The solubility of the composites gradually increases with CC content. In vitro experiments with a human fibroblast model (MTT test) demonstrate that the composites have zero cytotoxicity.

Influence of ripening time on the properties of hydroxyapatite-calcium carbonate powders

Abstract80 wt % hydroxyapatite + 20 wt % calcium carbonate composite powders have been synthesized through precipitation from aqueous solutions. Increasing the ripening time of the precipitate in the mother liquor leads to partial calcium carbonate dissolution and the formation of carbonate-substituted hydroxyapatite and improves its crystallinity. In addition, the specific surface area of the powders increases from 83.2 to 238.7 m2/g. The powders ripened for 14 and 21 days show the best sinterability.

Effect of ripening time on the sintering of CaCO3 powders and the properties of the resultant ceramics

We have studied the effect of the ripening time in the synthesis of calcium carbonate powders through mechanochemical activation on the characteristics and sintering behavior of the powders. The results demonstrate that increasing the ripening time leads to recrystallization of the precipitate and formation of larger, more perfect crystals. This impairs the sinterability of the powder and, as a consequence, leads to an increase in the porosity of the ceramics and a reduction in their strength. We have obtained calcium carbonate ceramics with a grain size of 1–3 μm and bending strength of up to 73 MPa, potentially attractive for bone tissue regeneration.

Long-term corrosion tests of nanostructural nitinol of (55.91 wt % Ni, 44.03 wt % Ti) composition under static conditions: Ion release

The corrosion resistance of nanostructural nitinol in solutions with pH from 1.68 to 9.18 for a long time is investigated. The metal concentration in solution was determined using atomic emission spectrometry with inductively coupled plasma. The ion yield is inhibited in NaCl and hardly so in acidic media, and corrosion is not observed in alkaline medium. The corrosion resistance increases by polishing and deteriorates with annealing. The nanostructure promotes a lower yield of nickel ions.

Long-term corrosion tests of nanostructural nitinol of (55.91 wt % Ni, 44.03 wt % Ti) composition under static conditions: Composition and structure before and after corrosion

Nanostructural nitinol is investigated before and after storage for a long time in solutions simulating pH of physiological liquids. The structure and composition are determined by SEM, TEM, and Auger spectroscopy. The material base is the B2 phase in the form of fibers 30–70 nm in diameter. Polishing promotes the formation of a thin homogeneous surface layer of titanium oxide, which thickens after solution storage; and annealing, the layer unchanging, thick, and heterogeneous.

Preparation of a nanostructured shape-memory composite material for biomedical applications

We have obtained nanoscale and microscopic surface tantalum layers on NiTi flat substrates and wires. The structure and composition of the samples were determined by scanning electron microscopy, Auger electron spectroscopy, and X-ray diffraction. With increasing sputtering time, the thickness of the surface layer increases nonlinearly. The transition layer ensures strong adhesion of the surface layer to the substrate.

Agglomeration and Properties of Ceramics Based on Partially Stabilized Zirconium Dioxide Containing Oxides of Aluminum and Iron

Agglomeration of ceramics of partially stabilized zirconium dioxide containing 5 wt % of aluminum oxide depending on the amount of additive (iron oxide) was studied. It was shown that introduction of an additive promotes a decrease in agglomeration temperature to 1400–1450°С and formation of a dense structure, as well as acquisition of high strength up to 450 MPa (after agglomeration at 1400°С).

Influence of the tensile strain rate on the mechanical properties and phase composition of VNS 9-Sh TRIP steel

The influence of the strain rate on the mechanical properties and the phase composition of a sheet VNS 9-Sh (23Kh15N5AM3-Sh) TRIP steel is studied during static tension. The strain rate is changed in the range from 8.3 × 10–5 to 25 × 10–3 s–1. The dependence of the mechanical properties on the strain rate is found to be nonlinear. The TRIP effect is most pronounced at a strain rate of (8.3–17) × 10–5 s–1. In this strain rate, the deformation martensite content increases significantly, from 50 to 87%, as is detected by X-ray diffraction.

Reaction of Bauxite with Hydrochloric Acid Under Autoclave Conditions

Studies are made of the use of hydrochloric acid for the autoclave decomposition of boehmite-kaolinite bauxites from the North Onezhky Deposit. The spatial location and structure of the bauxites are investigated, and the solid residue left after autoclave decomposition is examined by x-ray phase analysis and electron microscopy to study the mechanism of the bauxites’ dissolution. The data that is obtained confirms the presence of hard films of amorphous silica. These films prevent complete dissolution of the aluminum-bearing minerals: boehmite and kaolinite.

Low-cycle fatigue of a VZh175 high-temperature alloy under elastoplastic deformation conditions

The low-cycle fatigue of a VZh175 nickel superalloy is studied under conditions of complete deformation per loading cycle at an initial cycle asymmetry R = 0, a deformation amplitude ɛa = 0.4–0.6%, and a temperature of 20 and 650°C. The specific features of cyclic hardening/softening of the alloy under these conditions are detected. The mechanisms of fatigue crack nucleation and growth are analyzed as functions of the deformation amplitude and the test temperature.