Structure and Properties of Nanocomposites Formed by the Occlusion of Block Copolymer Worms and Vesicles Within Calcite Crystals

This article describes an experimentally versatile strategy for producing inorganic/organic nanocomposites, with control over the microstructure at the nano‐ and mesoscales. Taking inspiration from biominerals, CaCO₃ is coprecipitated with anionic diblock copolymer worms or vesicles to produce single crystals of calcite occluding a high density of the organic component. This approach can also be extended to generate complex structures in which the crystals are internally patterned with nano‐objects of differing morphologies. Extensive characterization of the nanocomposite crystals using high resolution synchrotron powder X‐ray diffraction and vibrational spectroscopy demonstrates how the occlusions affect the short and long‐range order of the crystal lattice. By comparison with nanocomposite crystals containing latex particles and copolymer micelles, it is shown that the effect of these occlusions on the crystal lattice is dominated by the interface between the inorganic crystal and the organic nano‐objects, rather than the occlusion size. This is supported by in situ atomic force microscopy studies of worm occlusion in calcite, which reveal flattening of the copolymer worms on the crystal surface, followed by burial and void formation. Finally, the mechanical properties of the nanocomposite crystals are determined using nanoindentation techniques, which reveal that they have hardnesses approaching those of biogenic calcites.     

Elucidating Mechanisms of Diffusion‐Based Calcium Carbonate Synthesis Leads to Controlled Mesocrystal Formation

Aggregation‐based crystal growth often gives rise to crystals with complex morphologies which cannot be generated via classical growth processes. Despite this, understanding of the mechanism is rather poor, particularly when organic additives or amorphous precursor phases are present. In this work, advantage is taken of the observation that aggregation‐based growth of calcium carbonate, and indeed many other minerals, is most often observed using diffusion‐based synthetic methods. By fully characterizing the widely used ammonia diffusion method (ADM)–which is currently used as a “black box”–the solution and supersaturation conditions which accompany CaCO₃ precipitation using this method are identified and insight is gained into the nucleation and growth processes which generate calcite mesocrystals. This reveals that the distinguishing feature of the ADM is that the initial nucleation burst consumes only a small quantity of the available ions, and the supersaturation then remains relatively constant, and well above the solubility of amorphous calcium carbonate (ACC), until the reaction is almost complete. New material is thus generated over the entire course of the precipitation, a feature which appears to be fundamental to the formation of complex, aggregation‐based morphologies. Finally, the importance of this understanding is demonstrated using the identified carbonate and supersaturation profiles to perfectly replicate CaCO₃ mesocrystals through slow addition of reagents to a bulk solution. This approach overcomes many of the inherent problems of the ADM by offering excellent reproducibility, enabling the synthesis of such CaCO₃ structures in large‐scale and continuous‐flow systems, and ultimately facilitating in situ studies of assembly‐based crystallization mechanisms.     

Nanocomposite biomaterials based on hydroxyapatite xerogel

A hydroxyapatite xerogel with high adsorption-structural characteristics and nanometer-sized crystals has been synthesized using dehydration of a hydroxyapatite gel in air at temperatures of 20–40°C with dehydrating agents, cryogenic treatment (−18 and −196°C), lyophilic drying, and vacuum conductive-sorption drying. The following nanocomposite biomaterials based on the hydroxyapatite xerogel have been prepared and investigated: hardening hydroxyapatite cements, elastic “hydroxyapatite-fiber carrier (cellulose, carbon)” composites, and hydroxyapatite coatings on titanium substrates. It has been established that the hardening calcium phosphate cements based on a 4- to 17-wt % hydroxyapatite gel and a hydroxyapatite powder are characterized by a hardening time in the interval from 1 min to 1 h and by a static strength up to 2.7 MPa. The hydroxyapatite content in the elastic composites varies from 4 to 540 mg/g depending on the type of fiber carriers and on the preparation conditions. In vitro and in vivo preclinical tests performed on rats have demonstrated that titanium implants with a biocoating based on the hydroxyapatite cement possess a high biocompatibility and a toxicological safety.     

Production of Granulated Relite by High-Speed Electron-Beam Evaporation

Powder Metallurgy and Metal Ceramics - The conditions of high-speed vacuum evaporation–condensation for producing granulated relite (a eutectic alloy of tungsten monocarbide and semicarbide)...     

Plastic compaction of porcelain products in porous dies

Translated from Steklo i Keramika, No. 8, pp. 18–19, August, 1990.     

Structure and mechanical properties of the Ti-Ga-Si alloys in the Ti-rich corner

The structure and mechanical properties (bending strength and bending deflection) of three alloys with high content of eutectic constituents were investigated. The formation of the structure is considered according to the Ti-Ga-Si phase diagram presented by the sections through the points of compositions of the alloys investigated. The mechanical properties have been determined by means of bending test of the samples by a scheme of the three-point bend in the air in the temperature interval of 20–800°C. The correlation between the structure and mechanical properties is considered.     

A photorefractive effect accompanying the acoustooptical interaction in gyrotropic cubic crystals in the presence of an alternating electric field

A photorefractive effect in gyrotropic cubic crystals is considered. The effect accompanies the Bragg diffraction of light by an ultrasound in the presence of an alternating electric field. The possibility of recording holographic gratings with the help of the light waves diffracted by traveling ultrasonic waves is demonstrated. The amplitude of the index phase grating is studied as a function of the intensity of the recording ultrasound, the length of the region of acoustooptical interaction, and the specific rotation of the crystal.     

Microplasma electrochemical deposition of aluminum oxide-polyethylene composite coatings on iron surface

Composite coatings containing aluminum oxide and polyethylene are deposited using microplasma electrochemical anodic treatment of the iron surface in an aluminate bath at a voltage of 260–360 V. Using scanning electron microscopy, microprobe analysis, Fourier transform infrared spectroscopy, and electrochemical polarization measurements, the composition, structure, and corrosion characteristics of the coatings are determined. Adding 0.5–1.0 wt % polyethylene dispersion to the electrolyte is shown to substantially facilitate the origination of microplasma conditions, prevent the strong warming of electrolyte during anodizing, and obtain coatings with substantially higher corrosion resistance compared to those produced in an aluminate bath containing no polymer dispersion.