Oxygen-containing Atmosphere Research Articles

High-Temperature Chlorination of Rhodium Using Alkali-Metal and Alkaline-Earth-Metal Chlorides

This study was aimed at investigating an effective chlorination method for Rh and its oxide to develop an efficient Rh extraction process. The feasibility of using alkali-metal and alkaline-earth-metal chlorides (NaCl, KCl, MgCl2, and CaCl2) as chlorinating agents was evaluated from the perspective of thermodynamics; the prediction results revealed MgCl2 as a suitable agent for chlorinating metallic Rh and Rh2O3 in an oxygen-containing atmosphere. The thermodynamic analysis results were then experimentally validated. Metallic Rh converted to RhCl3 when mixed with MgCl2 and heated at 973 K (700 °C) in an O2 atmosphere. The Rh2O3 powder was efficiently chlorinated when reacted with liquid MgCl2 at 1073 K (800 °C) in an Ar–1 pct O2 atmosphere. Therefore, the chlorination of Rh using MgCl2 is feasible; its use has potential to make the extraction and recovery of Rh from various raw materials more efficient.Graphical

High crystalline quality homoepitaxial Si-doped β-Ga2O3(010) layers with reduced structural anisotropy grown by hot-wall MOCVD

A new growth approach, based on the hot-wall metalorganic chemical vapor deposition concept, is developed for high-quality homoepitaxial growth of Si-doped single-crystalline β-Ga2O3 layers on (010)-oriented native substrates. Substrate annealing in argon atmosphere for 1 min at temperatures below 600 °C is proposed for the formation of epi-ready surfaces as a cost-effective alternative to the traditionally employed annealing process in oxygen-containing atmosphere with a time duration of 1 h at about 1000 °C. It is shown that the on-axis rocking curve widths exhibit anisotropic dependence on the azimuth angle with minima for in-plane direction parallel to the [001] and maximum for the [100] for both substrate and layer. The homoepitaxial layers are demonstrated to have excellent structural properties with a β-Ga2O3(020) rocking curve full-widths at half-maximum as low as 11 arc sec, which is lower than the corresponding one for the substrates (19 arc sec), even for highly Si-doped (low 1019 cm−3 range) layers. Furthermore, the structural anisotropy in the layer is substantially reduced with respect to the substrate. Very smooth surface morphology of the epilayers with a root mean square roughness value of 0.6 nm over a 5 × 5 μm2 area is achieved along with a high electron mobility of 69 cm2 V−1 s−1 at a free carrier concentration n=1.9×1019 cm−3. These values compare well with state-of-the-art parameters reported in the literature for β-Ga2O3(010) homoepitaxial layers with respective Si doping levels. Thermal conductivity of 17.4 Wm−1K−1 is determined along the [010] direction for the homoepitaxial layers at 300 K, which approaches the respective value of bulk crystal (20.6 Wm−1K−1). This result is explained by a weak boundary effect and a low dislocation density in the homoepitaxial layers.

Enhanced Biocidal Activity of Heterophase Zinc Oxide/Silver Nanoparticles Contained within Painted Surfaces

Today, one of the biggest challenges is infections in the painted walls of hospitals. Acrylic-based paints are a target of antibiotic-resistant microorganisms since they contain cellulosic compounds as thickeners. The aim of this study was to synthesize and investigate the biocidal activity and toxicity of heterophase ZnO-Ag nanoparticles fixed in water-based acrylic paint layers in reference to a nontreated water-based paint. The ZnO-Ag nanoparticles with average particle sizes of about 80 nm were simply obtained by electrical explosion of two twisted wires in an oxygen-containing atmosphere. The nanoparticles and modified paint were characterized using SEM, TEM, XPS, and XRD techniques. The antimicrobial activity of the nanoparticles and modified paint layers was tested against P. aeruginosa, S. aureus, MRSA, E. coli bacteria, and C. albicans using ISO 22196. The antiviral activity against smallpox virus was tested according to ISO 21702. Flow cytometry tests were used to investigate the toxicity of the modified paint coating. As-synthesized nanoparticles had “Janus-like” morphology, with a clear interface inside the nanoparticle. Nanoparticles had enhanced antibacterial activity, which is based on the nanoparticle photocatalytic activity in water decomposition and reactive oxygen species generation. The paint coating with a ZnO-Ag nanoparticle mass ratio of 1.0 wt.% displayed significant antibacterial activity (more than a 99% reduction) and 100% antifungal activity. In addition, this coating inactivates >99% of the virus after 2 h of contact relative to a nontreated control paint. The paint coating showed low toxicity against the sensitive 3T3 fibroblast cell line. More than 90% cell viability was observed after 24 h of incubation with the sample extract. Therefore, heterophase ZnO-Ag nanoparticles have high biocidal activity and low toxicity use and can be applied to other commercial water-based paints to improve their performance against pathogens.

Layered carbon nitride films deposited under an oxygen-containing atmosphere and their electronic properties

Layered carbon nitride (g-C3N4) is a novel semiconducting and functional material for optoelectronic applications. The physical and chemical properties of g-C3N4 films differ depending on the preparation atmosphere. Herein, we deposited g-C3N4 films under a mixed oxygen (O2)-nitrogen (N2) gas atmosphere and studied their effects on the carrier transport properties. Although no significant change in the film orientation was observed, the deposition rate decreased as the O2 gas ratio in the mixed N2/O2 atmosphere increased. Despite their thinness, the luminescence intensity of g-C3N4 films deposited under an O2-containing atmosphere increased by 3.5–5.0 times compared to that deposited under an N2 atmosphere. With respect to voltage application, carrier transport owing to the thermionic emission and/or direct tunneling initially followed ohmic conduction, followed by insufficient trap-filled conduction. As the applied voltage increased further, fully trap-filled conduction was confirmed owing to Fowler–Nordheim tunneling. Moreover, the conductivity type could be changed to p-type and n-type using N2 gas and mixed N2/O2 gas atmospheres, respectively, during film deposition. In addition to the intrinsic transport properties, the intentionally formed Schottky barrier also affected the carrier transport; therefore, the diode-like rectifying behavior of the current density was achieved.

Ultra-fast synthesis of hierarchical SAPO-11 molecular sieves with the assistance of hydroxyl radicals.

Considering the traditional time-consuming synthesis route and diffusion-limited micropore system of SAPO-11 (i.e., SAPO-11W), a hydroxyl radical assisted method has been developed to prepare hierarchical SAPO-11 within 5 min (i.e., SAPO-11M). Compared to previous reports, the unique contribution is to induce hydroxyl radicals by exposing carbon materials to microwave irradiation in an oxygen-containing atmosphere. Carbon materials play a dual role as mesopore filler and hydroxyl radical initiator. When employed to prepare deoxygenation catalysts for stearic acids, a higher selectivity for C15-C18 and isomers is observed due to the mild acidity of SAPO-11M. The Lewis-rich acidity of SAPO-11M exhibits an electron deficiency to interact with the hydroxyl oxygen atoms and promotes the hydrodeoxygenation of stearic acids with excellent atom economy. These results are important for opening up a new prospect of synthesizing SAPO molecular sieves (e.g., SAPO-11 and SAPO-5) by an efficient and facile route.

Oxidation of fine aluminum particles: thermally induced transformations in particle shells and kinetics of oxide nucleation.

This paper investigates the process of oxidation of fine aluminum powder, consisting of spherical Al particles of 'metal core/oxide shell' type, when heated in air at temperatures below 550 °C. The highly dispersed aluminum powder 'Alex' used in this work (particle size: 0.05-1.5 μm and number average particle diameter (DN): 0.11 μm) was produced by electric explosion of a thin Al wire in argon with subsequent passivation in an oxygen-containing atmosphere. For the first time, the influence of the particle size on the oxidation process has been identified. During the reaction, individual γ-Al2O3 oxide nuclei grow at the surface of Al particles with diameters less than 300 nm without laterally overlapping to form a protective passivating layer, as typically occurs during the oxidation of micron-sized particles or bulk metal. The localization of γ-Al2O3 nuclei is determined by the regions where peeling of the primary amorphous oxide film from the surface of the metal core of an Al particle occurs due to the thermal decomposition of aluminum hydroxides (T ≈ 350 °C) present within the particle shells. A significant increase in the contributions of the following factors leads to a high oxidation rate: the diffusion within the disordered structure of a particle core and the surface diffusion of cations (Ea = 80.6 ± 5.3 kJ mol-1, 400-450 °C), the surface and grain boundary diffusion of oxygen during the growth of γ-Al2O3 crystallites (Ea = 108.3 ± 11.2 kJ mol-1, 470-500 °C) and the surface and grain boundary transport of anions through an amorphous and underlying nanocrystalline oxide layer with a constant thickness (Ea = 205.1 ± 8.6 kJ mol-1, 520-550 °C). The results obtained make it possible to expand the theoretical understanding of the manifestations of the size effect in solid-phase reactions and take into account its influence in practice.

A New Method for Tungsten Oxide Nanopowder Deposition on Carbon-Fiber-Reinforced Polymer Composites for X-ray Attenuation

A new method for the synthesis and deposition of tungsten oxide nanopowders directly on the surface of a carbon-fiber-reinforced polymer composite (CFRP) is presented. The CFRP was chosen because this material has very good thermal and mechanical properties and chemical resistance. Also, CFRPs have low melting points and are transparent under ionized radiation. The synthesis is based on the direct interaction between high-power-density microwaves and metallic wires to generate a high-temperature plasma in an oxygen-containing atmosphere, which afterward condenses as metallic oxide nanoparticles on the CFRP. During microwave discharge, the value of the electronic temperature of the plasma, estimated from Boltzmann plots, reached up to 4 eV, and tungsten oxide crystals with a size between 5 nm and 100 nm were obtained. Transmission electron microscopy (TEM) analysis of the tungsten oxide nanoparticles showed they were single crystals without any extended defects. Scanning electron microscopy (SEM) analysis showed that the surface of the CFRP sample does not degrade during microwave plasma deposition. The X-ray attenuation of CFRP samples covered with tungsten oxide nanopowder layers of 2 µm and 21 µm thickness was measured. The X-ray attenuation analysis indicated that the thin film with 2 µm thickness attenuated 10% of the photon flux with 20 to 29 KeV of energy, while the sample with 21 µm thickness attenuated 60% of the photon flux.

High transparent conductive Ga-doped ZnO-based multilayer thin films with embedded ultrathin TiN layer deposited in oxygen-containing atmosphere.

To avoid metal layer oxidation during the deposition of transparent conductive oxide (TCO)/metal/TCO multilayer films in an oxygen-containing atmosphere, the ultra-thin (<10 nm) titanium nitride (TiN) layer has been proposed to replace metal embedding in gallium-doped zinc oxide (GZO) film for the development of indium-free transparent electrodes. The effects of TiN thickness on the structure, morphology, electrical, and optical properties of GZO/TiN/GZO multilayer thin films deposited in argon-oxygen mixtures on glass substrates by magnetron sputtering are investigated. The experimental results reveal that multilayers with the 8 nm-thick TiN layer have the optimal performance (figure of merit of 2.75 × 10-1 Ω-1): resistivity of 4.68 × 10-5 Ω cm, and optical transmittance of above 91% in the visible region, which is superior to the sandwich film with the metal embedded layer.

Superior oxygen-resistance and intrinsic mechanisms of coherent Pd/Pd3Zr@ZrCo structure with excellent cycling durability

As a promising candidate for hydrogen isotopes storage, ZrCo alloy suffers tremendously from the poisoning of impurity gases, especially in oxygen-containing atmospheres, but related effective modification method for long cycling durability is still lacking. In this work, the anti-oxygen-poisoning behaviors and mechanisms of virginal ZrCo and palladium-coated ZrCo with different heating evacuation methods were detailly investigated. Notably, the phase transition occurs during traditional heating evacuation (550 °C for 60 min) with the gradual generation of Pd3Zr from original Pd coating and ZrCo substrate. According to absorption behaviors and degeneration state of O πp-orbital peak from theoretical calculations, O2 undergoes spontaneous dissociation and strong hybridization at the surface of ZrCo and Pd3Zr, especially for ZrCo, while much weak surface absorption is recognized on Pd. Considering the superior anti-poisoning properties but weak substrate anchoring strength of Pd, it’s valuable to reconstruct the Pd/ZrCo interface to generate transition Pd3Zr layer that is less susceptible to hydrogen embrittlement. Accordingly, a coherent structure of Pd/Pd3Zr@ZrCo was successfully obtained by high temperature short time pretreatment (550 °C for 10 min), and its cycling capacity retention in O2-containg hydrogen atmosphere is significantly enhanced from initial 74.87 % after 5 cycles to 90.83 % after 10 cycles, which is superior to Pd-plating hydrogen storage alloys ever reported. The interface reconstruction of coherent structure proposed here can function as a promising strategy for construction of protective layer for all related surface engineering.

Effect of doping on the optical properties of lanthanum-gallium tantalate

Nominally pure lanthanum-gallium tantalate La3Ga5.5Ta0.5O14 crystals doped with aluminum, silicon and gallium oxide to above stoichiometric content have been grown by the Czochralski technique in iridium crucibles in argon and in agron with addition of oxygen atmospheres. The transmittance spectra of the crystals have been measured on a Cary-5000 UV-Vis-NIR spectrophotometer in the 200–800 nm range. Absorption spectra α(λ) have been plotted on the basis of the experimental data. The absorption spectra of the undoped crystals grown in an oxygen-free atmosphere have one weak absorption band at λ ~ 290 nm. The absorption spectra of the crystals grown in an agron with addition of oxygen have absorption bands at λ ~ 290, 360 and 480 nm. We show that for the crystals grown in an oxygen-free atmosphere, gallium doping to above stoichiometric content reduces the intensity of its only λ ~ 290 nm absorption band. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-free atmosphere significantly reduces the intensity of the λ ~ 290 nm absorption band and increases the intensity of the λ ~ 360 and 480 nm bands. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-containing atmosphere reduces the intensity of the λ ~ 360 and 480 nm bands and increases the intensity of the λ ~ 290 nm absorption band. Silicon doping of these crystals significantly reduces the intensity of the λ ~ 480 nm band and also reduces the intensity of the λ ~ 290 and 360 nm bands.

Effect of carbon dioxide concentration on the combustion characteristics of boron agglomerates in oxygen-containing atmospheres

Effect of carbon dioxide concentration on the combustion characteristics of boron agglomerates in oxygen-containing atmospheres

New PMMA-Based Hydroxyapatite/ZnFe2O4/ZnO Composite with Antibacterial Performance and Low Toxicity.

Polymethylmethacrylate (PMMA) is the most commonly used bone void filler in orthopedic surgery. However, the biocompatibility and radiopacity of PMMA are insufficient for such applications. In addition to insufficient biocompatibility, the microbial infection of medical implants is one of the frequent causes of failure in bone reconstruction. In the present work, the preparation of a novel PMMA-based hydroxyapatite/ZnFe2O4/ZnO composite with heterophase ZnFe2O4/ZnO NPs as an antimicrobial agent was described. ZnFe2O4/ZnO nanoparticles were produced using the electrical explosion of zinc and iron twisted wires in an oxygen-containing atmosphere. This simple, highly productive, and inexpensive nanoparticle fabrication approach could be readily adapted to different applications. From the findings, the presented composite material showed significant antibacterial activity (more than 99% reduction) against P. aeruginosa, S. aureus, and MRSA, and 100% antifungal activity against C. albicans, as a result of the combined use of both ZnO and ZnFe2O4. The composite showed excellent biocompatibility against the sensitive fibroblast cell line 3T3. The more-than-70% cell viability was observed after 1-3 days incubation of the sample. The developed composite material could be a potential material for the fabrication of 3D-printed implants.

Complex Plastids and the Evolution of the Marine Phytoplankton

Photosynthesis allows for the formation of biomass from inorganic carbon and therefore greatly enhances the amount of organic material on planet Earth. Especially, oxygenic photosynthesis removed a major bottleneck in the formation of biomass by utilising ubiquitous water (H2O) and CO2 molecules as raw materials for organic molecules. This, over billions of years, shaped the world into the form we know today, with an oxygen-containing atmosphere, largely oxygenated water bodies and landmasses consisting of sediment rocks. Oxygenic photosynthesis furthermore enabled the evolution of aerobic energy metabolism, and it would be very difficult to imagine animal (including human) life in the absence of molecular oxygen as an electron acceptor. Oxygenic photosynthesis first, and exclusively, evolved in cyanobacteria. However, eukaryotes also learned to photosynthesise, albeit with a trick, which is the integration of formerly free-living cyanobacteria into the eukaryotic cell. There, the former bacteria became endosymbionts, and from these endosymbionts, the photosynthetic organelles (termed plastids) evolved. In almost all major groups of eukaryotes, plastid-containing members are found. At the same time, plastid-related features also indicate that these plastids form a monophyletic group. This can be explained by the transfer of plastids between the eukaryotic super-groups, leading to plastids being found in groups that are otherwise non-photosynthetic. In this chapter, we discuss the evolutionary origin of plastids, with a special emphasis on the evolution of plankton algae, such as diatoms or dinoflagellates, who acquired their plastids from other photosynthetic eukaryotes.

Effect of doping on the optical properties of lanthanum-gallium tantalate

Nominally pure lanthanum-gallium tantalate La3Ga5.5Ta0.5O14 crystals doped with aluminum, silicon and gallium oxide to above stoichiometric content have been grown by the Czochralski technique in iridium crucibles in argon and in agron with addition of oxygen atmospheres. The transmittance spectra of the crystals have been measured on a Cary-5000 UV-Vis-NIR spectrophotometer in the 200–800 nm range. Absorption spectra α(λ) have been plotted on the basis of the experimental data. The absorption spectra of the undoped crystals grown in an oxygen-free atmosphere have one weak absorption band at λ ~ 290 nm. The absorption spectra of the crystals grown in an agron with addition of oxygen have absorption bands at λ ~ 290, 360 and 480 nm. We show that for the crystals grown in an oxygen-free atmosphere, gallium doping to above stoichiometric content reduces the intensity of its only λ ~ 290 nm absorption band. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-free atmosphere significantly reduces the intensity of the λ ~ 290 nm absorption band and increases the intensity of the λ ~ 360 and 480 nm bands. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-containing atmosphere reduces the intensity of the λ ~ 360 and 480 nm bands and increases the intensity of the λ ~ 290 nm absorption band. Silicon doping of these crystals significantly reduces the intensity of the λ ~ 480 nm band and also reduces the intensity of the λ ~ 290 and 360 nm bands.

Kinetic Study on the Dehydration Behavior of Titanium Dioxide as a Denitration Catalyst Carrier

The dehydration of titanium dioxide, which is the carrier for denitration catalysts, is a crucial control step in the preparation of functional materials and has an impact on the performance of the product. In this study, the kinetics of the dehydration behavior and reaction mechanism of titanium dioxide were investigated under different atmospheres by measuring the thermal analysis curve of titanium dioxide at different heating rates. The results indicate that the dehydration behavior of the catalyst carrier titanium dioxide is closely related to the calcination atmosphere. The dehydration rate differed for oxygen and no-oxygen atmospheres. Dehydration began quickly in an oxygenated atmosphere and then slowed down towards the end of the reaction, completing slowly in an oxygen-free atmosphere. Kinetic calculations were carried out using modeless and mode function methods. The results show that dehydration of titanium dioxide is consistent with the Avrami–Erofeev equation in an oxygen-containing atmosphere and with the power function rule in an oxygen-free atmosphere, with the process of dehydration being influenced by the formation and growth of crystal nuclei.

Effect of annealing ambient on SiGe layer formation using Al–Ge paste for III–V solar cell application

A mixed paste of aluminum (Al) and germanium (Ge) (7:3) was prepared and screen-printed on silicon (Si) substrates, followed by annealing at a peak temperature of 1000 °C in an IR rapid thermal annealing furnace to investigate the liquid-phase growth of silicon–germanium (SiGe) epitaxial layers. The gas ambient during annealing was changed to investigate the effect on SiGe layer quality and physical properties. The SiGe formed samples were observed by scanning electron microscopy and energy dispersive X-ray spectroscopy. Oxygen-containing atmosphere suppressed the SiGe layer formation by oxidizing the Al particle surface, limiting the reaction of the particle to the Si surface. On the other hand, annealing in an argon atmosphere without oxygen resulted in the formation of SiGe layers with a thickness of over 30 μm.

Performance of Mn-Ce-Fe/FA Catalysts on Selective Catalytic Reduction of NOX with CO under Different Atmospheres

Gas turbines produce a large amount of NOx and CO due to high temperatures and insufficient combustion. Through the selective catalytic reduction of NO with CO (CO-SCR) in a gas turbine, the activities of the Mn-Fe-Ce/FA catalyst using fly ash (FA) as a carrier under different atmospheres were studied. The catalysts prepared by calcining different active materials under different atmospheres were used to analyze their denitrification abilities and resistance to water vapor. The denitrification performance of the catalyst prepared under reducing atmosphere is about 30 percent higher than that of the catalyst prepared under air atmosphere, and the decarburization performance is about 40 percent higher. In the presence of oxygen, the denitrification rate and decarburization rate of the 1:1 ratio of the Mn-Ce catalyst reach 67.16% and 59.57%, respectively. In an oxygen-containing atmosphere, the catalyst prepared by replacing Ce with Fe shows better denitrification and decarburization performances, which are 78.56% and 78.39%, respectively. When the flue gas space velocity is 4000 h−1 and the carbon-nitrogen ratio is 1.6, the catalyst shows better performance. After the water vapor is introduced, the denitrification and decarbonization rates of the catalyst decrease by about 10% and 9%, respectively. After ceasing water vapor, it rebounds by about 8%, and the activity could not be fully restored. However, the catalyst still shows strong water resistance in general.

Structure and Oxidation Behavior of Multicomponent (Hf,Zr,Ti,Nb,Mo)C Carbide Ceramics.

Multicomponent ceramics based on transition metals carbides are widely known for their excellent physicomechanical properties and thermal stability. The variation of the elemental composition of multicomponent ceramics provides the required properties. The present study examined the structure and oxidation behavior of (Hf,Zr,Ti,Nb,Mo)C ceramics. Single-phase ceramic solid solution (Hf,Zr,Ti,Nb,Mo)C with FCC structure was obtained by sintering under pressure. It is shown that during the mechanical processing of an equimolar powder mixture of TiC-ZrC-NbC-HfC-Mo2C carbides, the formation of double and triple solid solutions occurs. The hardness of (Hf,Zr,Ti,Nb,Mo)C ceramic was found at 15 ± 0.8 GPa, compressive ultimate strength-at 1.6 ± 0.1 GPa and fracture toughness-at 4.4 ± 0.1 MPa∙m1/2. The oxidation behavior of the produced ceramics in an oxygen-containing atmosphere was studied in the range of 25 to 1200 °C by means of high-temperature in situ diffraction. It was demonstrated that (Hf,Zr,Ti,Nb,Mo)C ceramics oxidation is a two-stage process accompanied by the change of oxide layer phase composition. As a possible mechanism of oxidation, diffusion of oxygen into the ceramic bulk results in the formation of a complex oxide layer made of c-(Zr,Hf,Ti,Nb)O2, m-(Zr,Hf)O2, Nb2Zr6O17 and (Ti,Nb)O2 was proposed.

Effect of postgrowth annealing in an oxygen-containing atmosphere on the microhardness of single-crystal calcium molybdate CaMoO4

Effect of postgrowth annealing in an oxygen-containing atmosphere on the microhardness of single-crystal calcium molybdate CaMoO4

Effect of post-growth anneals in oxygen-containing atmosphere on the microhardness of single crystal calcium molybdate CaMoO4

Single crystal calcium molybdate CaMoO4 is a well-known material. However the interest to CaMoO4 has recently grown due to a number of its important applications including as a working material in cryogenic scintillation bolometers. CaMoO4 single crystals acquire blue color during growth due to the presence of color-center type defect centers which are unacceptable for optical applications. Color can be eliminated through annealing in an oxygen containing atmosphere, following which required optical components can be produced from the single crystals by mechanical treatment (cutting, polishing etc.). Therefore assessment of the mechanical properties of these single crystal materials is an important task for the optimal solution of issues occurring in the fabrication of optical components and their further practical application. There are but scarce data on the mechanical properties of CaMoO4, and the available ones have been reported without allowance for anisotropy. There is a significant scatter of data on the Mohs hardness of the single crystals, ranging from 3.3 to 6 in different publications. In this work we present data on calcium molybdate single crystals in the initial state and after high-temperature anneals of different durations in an oxygen containing atmosphere. We show that long-term annealing leads to decolorization of the crystals. Calcium molybdate single crystals prove to be quite brittle: the brittleness index Zp of the crystals in the initial state is the highest and equals 5, while annealing reduces the brittleness index to 4. The Palmqvist toughness factors S have been calculated The limit indentation destruction loads Flim have been determined and annealing in an oxygen containing atmosphere has been shown to increase Flim by 2.5 times for the Z cut and by 10 times for the X cut. The microhardness of the crystals has been shown to exhibit a II type anisotropy: the microhardness of all the specimens was higher for the Z cut than for the X cut. The microhardness anisotropy coefficients KH of the specimens have been evaluated. The bond ionicity degree I has been calculated on the basis of the experimentally measured microhardness.