Applying CO2 and ytterbium fiber lasers to high-performance production of refractory oxide nanopowders

The main features of obtaining refractory oxide nanopowders using a repetitively-pulsed CO2-laser (10,6 µm) with an average radiation power of 500 W or a CW ytterbium fiber laser (1,07 µm) with a radiation power of up to 700 W are considered. In particular, the influence of pressure, buffer gas composition and average radiation power on the size of nanoparticles and the productivity of their obtaining were studied. Depending on the thermophysical properties of the material, in atmospheric pressure air the productivity of nanopowder synthesis varies from 15 – 23 g/h (YSZ) to 350 g/h (WO3). The mass yield of nanopowder obtained upon evaporation of one target is usually is 30 wt. % of the weight of the initial target. The obtained nanopowders contain weakly agglomerated nanoparticles of spherical shape. The average size of nanoparticles 11 – 20 nm weakly depends on their material. The most important features of using a CW ytterbium laser to obtain nanopowders of refractory oxides are their high transparency for radiation of 1,07 μm, as well as the spraying of many melt droplets. These features led to a reduction in the productivity of nanopowder production and its mass yield. On the other hand, the scattering of laser radiation in porous of the initial target and its concentration in some regions makes it possible to efficiently evaporate oxide targets from materials with a refractive index of more than 1.7 – 1.75. The transition to a repetitively-pulsed mode of radiation (pulse duration 120 μs, square waveform, and peak power 600 W), an increase in the spot diameter and the speed of beam movement over the target surface made it possible to significantly reduce droplet spattering and increase the yield of Nd: Y2O3 nanopowder from 9,7 to 30 wt.% of the weight of the initial target. However, a twofold decrease in the average radiation power led to the fact that the productivity of obtaining the nanopowder was only 15 g/h. Thus, to obtain nanopowders of refractory oxides, it is desirable to use a quasi-CW fiber ytterbium laser, which is specially designed for operation in a repetitively pulsed mode. The obtained nanopowders YSZ, Nd: Y2O3, Al2O3, etc. are used for the manufacture of ceramic solid electrolytes of the YSZ type and highly transparent laser ceramics.

Did a Complex Carbon Cycle Operate in the Inner Solar System?

Solids in the interstellar medium consist of an intimate mixture of silicate and carbonaceous grains. Because 99% of silicates in meteorites were reprocessed at high temperatures in the inner regions of the Solar Nebula, we propose that similar levels of heating of carbonaceous materials in the oxygen-rich Solar Nebula would have converted nearly all carbon in dust and grain coatings to CO. We discuss catalytic experiments on a variety of grain surfaces that not only produce gas phase species such as CH4, C2H6, C6H6, C6H5OH, or CH3CN, but also produce carbonaceous solids and fibers that would be much more readily incorporated into growing planetesimals. CH4 and other more volatile products of these surface-mediated reactions were likely transported outwards along with chondrule fragments and small Calcium Aluminum-rich Inclusions (CAIs) to enhance the organic content in the outer regions of the nebula where comets formed. Carbonaceous fibers formed on the surfaces of refractory oxides may have significantly improved the aggregation efficiency of chondrules and CAIs. Carbonaceous fibers incorporated into chondritic parent bodies might have served as the carbon source for the generation of more complex organic species during thermal or hydrous metamorphic processes on the evolving asteroid.

Did a Complex Carbon Cycle Operate in the Inner Solar System?

Solids in the interstellar medium consist of an intimate mixture of silicate and carbonaceous grains. Because 99% of silicates in meteorites were reprocessed at high temperatures in the inner regions of the Solar Nebula, we propose that similar levels of heating of carbonaceous materials in the oxygen-rich Solar Nebula would have converted nearly all carbon in dust and grain coatings to CO. We discuss catalytic experiments on a variety of grain surfaces that not only produce gas-phase species such as CH4, C2H6, C6H6, C6H5OH or CH3CN, but also produce carbonaceous solids and fibers that would be much more readily incorporated into growing planetesimals. CO and other more volatile products of these surface mediated reactions were likely transported outwards along with chondrule fragments and small Calcium Aluminum Inclusions (CAIs) to enhance the organic content in the outer regions of the nebula where comets formed. Carbonaceous fibers formed on the surfaces of refractory oxides may have significantly improved the aggregation efficiency of chondrules and CAIs. Carbonaceous fibers incorporated into chondritic parent bodies might have served as the carbon source for the generation of more complex organic species during thermal or hydrous metamorphic processes on the evolving asteroid.

Experimental Study of Surface Etching in Synthetic Diamond Microcrystals due to Presence of Cu and Fe at High Pressure

In the present work, microcrystals of synthetic diamond extracted from a metal-diamond composite were investigated. A composite based on Cu and Fe was obtained by sintering at a pressure of 4 GPa and a temperature of1300 °C. The experiments were carried out using a split-sphere high-pressure apparatus BARS. The high-pressure cell was made of refractory oxides ZrO2, CaO, and MgO using a tubular graphite heater. In the composite, diamond grains were in close contact with neighboring diamonds, and the metal phase filled the interstices. The study of the diamond crystals demonstrated the appearance of newly formed micromorphological structures on the surfaces in the form of numerous cavities of irregular shape on the faces of octahedron, as well as pyramids on the faces of cube, the morphological elements of which follow the contours of the cube face of the diamond. Thus, the results of the work evidence for the processes of etching of the diamond crystals during the experiments, which is associated with the presence of metallic iron in the composite. This type of etching forms a roughly cavernous surface on the diamond crystals, which can be considered as an additional factor for improving the metal-diamond bond in copper-based composites.

Contemporary Apparatus for Single Crystals Growth of Oxide Compounds and Metals by Optical Floating Zone (FZ)

A contemporary apparatus with radiation (light) heating for growth of single crystals of refractory oxides and metals is described. To reduce the dissociation or evaporation of the melt or crystal components, the growth process was carried out in oxygen or an alternative gas at pressures up to 100 bar. The annealing system applied directly in the growth process at 1650 °C under O2 pressure and at temperatures up to 2500 °C under protective gas flow, allows the obtaining of large and perfect single crystals. Many single crystals of oxide materials, including incongruently melting substances, such as Y3Fe5O12, Gd3Fe5O12, BaFe12O19, SrFe12O19, BaFe12-x AlxO19, and many others have been grown, and much more could be grown.

About the effect of additives on the physicomechanical characteristics of high-strength AS-materials

The results of studies of the effects of high temperatures on high-refractory unshaped materials based on refractory oxides and silicides are given. The effect of mineral additives on their characteristics and physicomechanical characteristics is also shown. It has been established that unshaped aluminosilicate materials based on electrofusion or tabular material are able to work without loss of their properties at operating temperatures not lower than 1600 ºC. The introduction of carbon or basalt microfiber into the material makes it possible to reduce the volume and diameter of coronal refractories, but at the same time increases their linear average when exposed to high temperatures. Ill. 3. Ref. 2. Tab. 4.

High Temperature Coatings for Oxidation and Erosion Protection of Heat-Resistant Carbonaceous Materials in High-Speed Flows

Modern approaches to the creation of single-layer and multi-layer high-temperature coatings for the protection of heat-resistant carbon-containing composite materials from oxidation and erosion in the high-speed fluxes of oxygen-containing gases are analyzed. Particularly have been outlined the heat-resistant coatings, the main components of which are either super refractory transition metal borides (ZrB2, HfB2, TiB2) with the addition of carbides (SiC, ZrC, HfC, TiC, TaC), silicides (MoSi2, TiSi2, ZrSi2, TaSi2, WSi2) and nitrides (HfN, ZrN, TiN), or refractory oxides (HfO2, ZrO2), or more complex synthetic compositions based on oxide ceramics. The results of fire gas-dynamic tests of coatings of perspective compositions are presented. The potential architecture of ultra-high-temperature coatings with high efficiency of protective action is justified.

Influence of material melt kinematic viscosity upon treatment quality at fine-jet plasma cutting of bimetallic compositions

The paper reports the peculiarities in the formation of a cut slot of bimetallic “steel 3 + aluminum 5 M” composition and “steel 3 + copper M1” composition at fine-jet plasma cutting. A different character of a cut channel formation of compositions at a package cut on different sides is revealed. When processing “steel + aluminum” composition on the side of steel a cut surface on the aluminum area has course roughness. A burr formation on the lower edge of a cut is also observed. It is explained by considerable difference in melting temperatures and thermal conduction of steel and aluminum. At the changed of a front side of a cut from steel to aluminum occurs sedimentation of aluminum melt on the steel area which is explained by a high kinematic viscosity of aluminum melt. The formation of refractory oxides in aluminum melt is defined that contributes to the increase of its viscosity and difficulty in the complete elimination from a cut channel. At the cutting of bimetallic “steel 3 + copper M1” composition of a copper side a cut surface on both areas is formed without visible traces of sedimentation of steel and copper melt caused by a low kinematic viscosity of copper and steel melts.