Diamond synthesis from methane-hydrogen-water mixed gas using a microwave plasma

Fine particles of diamond or diamond-like carbon were synthesized from methane-hydrogen-water mixed gas using a microwave plasma. The growth rate was several times as fast as that of methane-hydrogen mixed gas, which is the conventional method to prepare diamond from the gas phase. Promotion of the methane decomposition reaction and the removal reaction of byproduct graphite by OH radicals produced in the plasma were credited with enhancing the rate.     

Synthesis and characterization of silicon oxide nanoparticles using an atmospheric DC plasma torch

An atmospheric pressure DC plasma torch reactor was employed using Hexamethyldisiloxane (HMDSO) and oxygen reactants in nitrogen carrier gas to produce silicon oxide nanoparticles and nanoparticle agglomerates with the diameters in the ranges of 8–14?nm and 130–260?nm, respectively. The mean sizes of primary nanoparticles and nanoparticle agglomerates as well as their surface properties are studied by varying the process conditions. In general the mean sizes of primary nanoparticles and nanoparticle agglomerates decrease with the increase of the plasma torch power, the increase of the oxygen concentration, and the decrease of the HMDSO concentration. Under those conditions, the more completely-oxidized silicon oxide clusters are formed and aggregate into the compact, densely-packed, and small-size primary silicon oxide nanoparticles, which further agglomerate into the densely-packed, small nanoparticle agglomerates. The hydrophilic and white nanoparticle powder with a low BET surface area can be thus obtained. Under the opposite processing conditions, the loosely-packed, low density and large-size carbon-containing silicon oxide nanoparticles and nanoparticle agglomerates can be obtained with hydrophobic surface, high BET surface areas, and gray color.     

Plasmachemical synthesis of maghemite nanoparticles in atmospheric pressure microwave torch

The powder of γ − Fe₂O₃ nanoparticles was synthesized in microwave torch at atmospheric pressure from 0.05 sccm of Fe(CO)₅ vapors in 670 sccm of argon. The optimization of the torch reactor design and deposition conditions allowed continual synthesis of γ − Fe₂O₃ nanoparticles at low power consumption. The synthesized powder was collected at the reactor walls and analyzed by TEM, X-ray diffraction and Raman spectroscopy without any further purification or treatment. The mean diameter of NPs, as observed by TEM, was 12 nm with a 90% confidence interval 5.5-22 nm.     

Carbon nanotubes synthesis in microwave plasma torch at atmospheric pressure

Well aligned multi-walled carbon nanotubes were synthesized at atmospheric pressure using a microwave plasma torch on silicon substrates with silicon oxide buffer layer and catalyst overlayer in the mixture of argon, hydrogen and methane. Iron or nickel was used as catalysts. The optimum substrate temperature for the deposition on Si/SiO₂/Fe substrates was about 970 K. In this case SEM micrographs of the deposits revealed a presence of vertically aligned nanotubes with the diameters around 15 nm. TEM micrographs showed a presence of amorphous carbon particles in the samples and some defects in the wall structure of the produced nanotubes. In Raman spectra two peaks at 1332 and 1584 cm⁻¹ were observed. The CNTs were also synthesized on the substrates without SiO₂ buffer layer but their quality was lower. The synthesis with Ni instead of Fe catalyst required lower temperature and the alignment of the nanotubes was worse. The deposition process was monitored by optical emission spectroscopy. Atomic lines of hydrogen and argon, an emission of CN due to a presence of nitrogen impurities from atmosphere, a weak molecular band of CH and strong C₂ emission were detected in the spectra.     

Diamond synthesis by weak shock loading

A hexagonal polymorph of diamond has been synthesized by relatively weak shock loading (in a range of projectile velocity 0.655 to 1.88 km sec^–1) with a recovery technique. Four mixtures of copper with spectroscopic graphite, amorphous carbon, glassy carbon and graphite fluoride, with densities of 4.8 to 7.8 g cm^–3, were used to control the shock temperature rise and to quench efficiently. Spectroscopic graphite gave the maximum yield of diamond (8%). Chaoite was also observed in the shocked amorphous carbon and glassy carbon. A local temperature rise during shock was inferred from the temperature of some spherical particles, indicative of superheating of the particles to near or above the melting point.     

Mixed oxides prepared with an induction plasma torch

Pure and mixed titania and chromia have been prepared and characterised by methods described in the previous paper [1]. The titania and chromia/titania contained mostly spherical particles in the size range 0.01 to 0.15m. The pure titania was mainly the metastable phase, anatase, but the proportions of rutile and of stacking faults in the rutile structure increased with increasing chromium concentration.A high degree of solid solution was achieved for the mixed oxides, a result which accords with the proximity of the temperature ranges for condensation, predictable from thermodynamic data. This is the chief factor which distinguishes the behaviour of the chromia/titania from that of the chromia/alumina system. It is concluded that reference to such data should enable processes in the gas phase to be predicted and controlled. Processes in the condensed phase are governed as much by kinetic as equilibrium factors.     

Diamond film synthesis in high-alternating-current glow discharge

Results of experiments with the deposition of polycrystalline diamond films onto silicon, titanium, and molybdenum substrates in a specially designed ac glow discharge system are presented. The phase composition and morphology of deposited films have been studied using the atomic force microscopy and X-ray diffraction techniques. It is established that the obtained diamond films possess high purity and degree of crystallinity. Inclusions of non-diamond carbon phases are absent. The rate of diamond film growth in the proposed system is 6–7 μm/h.     

Diamond synthesis from CO-H2 mixed gas plasma

Particulate or film-like diamond was prepared on silicon substrates from CO-H₂ mixed gas using a microwave plasma technique. The growth rate of diamond without graphite and amorphous carbon, as measured by Raman spectroscopy, was 9m h^–1 for particles and 4mh^–1 for flims. These values were larger than those in other source gas systems, such as CH₄-H₂, CH₄-H₂-H₂O and CH₃OH-H₂. The good formation rate and high quality of diamond in the CO-H₂ system was attributed to acceleration of methyl radical formation by the reaction of excited CO and H₂ molecules and removal of by-product graphite by OH radicals in the plasma.     

Processing of bovine hydroxyapatite (HA) powders and synthesis of calcium phosphate silicate glass ceramics using DC thermal plasma torch

In the present work, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) was prepared from bovine bones with calcination method (up to 850 °C).The calcinated hydroxyapatite was powdered (30-40 μm) using a mechanical grinder; the particles were highly irregular in shape with sharp edges, angular, rounded, circular, dentric, porous and fragmented morphologies. The irregular shaped calcinated hydroxyapatite was plasma processed to produce spherical powders for thermal spray coating applications. More over; calcium phosphate silicate glass ceramics was produced by plasma melting of ball milled hydroxyapatite-borosilicate glass (50 wt.%) mixture. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD) and energy dispersive X-ray analysis (EDX). The morphology was determined using scanning electron (SEM) and optical microscopy (OM). The microhardness, density and porosity measurements for the synthesized samples were made.     

Pyrolysis of waste using a hybrid argon–water stabilized torch

An experimental plasmachemical reactor equipped with the novel IPP-ASCR hybrid gas–water stabilized DC torch (160 kW) has recently been started at IPP Prague for the innovative and environmentally friendly plasma treatment of waste streams with a view to their sustainable energetic and chemical valorization and to a reduction of the emission of greenhouse gases. Since the process energy is provided by direct heat transfer from plasma, gases of widely varying chemical composition may be used. The use of electrical energy also reduces the gas flows and requirements for exhaust-gas treatment, and offers control over the chemistry. Pyrolysis of biomass was experimentally studied using wood chips as a model substance. Syngas with a high content of hydrogen and CO was produced. The influence of adding CO₂ for increase of oxygen content in the reactor was investigated.     

Diamond synthesis from C<Subscript>60</Subscript> fullerite using boron and titanium diboride

Boron-doped diamond has been synthesized from C₆₀ fullerite at 7 GPa and 2000–2050 K using unconventional solvents for carbon: boron and titanium diboride.     

Effect of stepover and torch tilting angle on a repair process using WAAM

To sustain the transition to a greener economy and greener manufacturing, it is necessary to develop new approaches and technologies to repair metal components; this will result in a drastic reduction in energy and material usage. In this study, wire arc additive manufacturing (WAAM) was used to deposit a layer of new material on an existing surface, with the objective of finding the optimal configuration that maximized the layer quality and material efficiency. The parameters considered are the stepover among the deposited beads and the inclination of the torch with respect to the repaired surfaces. The inclination angle is crucial when repairing complex surfaces, like those of a mold, owing to accessibility issues, the torch cannot be maintained orthogonal to the surfaces along the entire toolpath. Different configurations were tested in order to assess the quality of the materials in terms of the presence of material voids, depth of penetration, and the heat affected zone (HAZ) and to understand the effects of these variables on the material efficiency and thickness of the repairing layer. It should be noted that by adopting deposition parameters set to have a low heat input, the use of a tilting angle has beneficial effects on the quality of the deposited layer and the process efficiency. Metallurgical and geometrical measurements were carried out to assess the effect of these two variables depositing a layer of plain carbon steel.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00393-2     

SiOx plasma thin film deposition using a low-temperature cascade arc torch

Plasma thin films were deposited from gas mixtures of hexamethyldisiloxane (HMDSO) and oxygen (O₂) using a low-temperature cascade arc torch (LTCAT). Various properties of the deposited HMDSO plasma coatings, including refractive index (RI), surface contact angle, and hardness were evaluated. The characterization results using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ellipsometry, and water contact angle measurements indicated that, with increased O₂ addition, the deposited HMDSO plasma thin films were of inorganic SiO_x nature. It was also found that, in the LTCAT plasma system, O₂ addition significantly improves the hardness of the resulting HMDSO plasma coatings. The film hardness of the deposited HMDSO plasma coatings measured by a standard pencil test (ASTM D3363-05) reached 6H with increased O₂ addition in the HMDSO/O₂ gas mixture. Such hard plasma coatings could be potentially used for many important industrial applications, such as anti-scratch coatings on plastic glasses and various plastic lens materials.     

Diamond as an Optical Material for Space Optics

A diamond window was used in the Pioneer Venus I.R. radiometer. The paper suggests that diamond should be considered more widely as a possible optical component for windows and small lenses in space-optics and other optical applications. The cost is not high in relation to other costs involved in space research or for some land-based instruments. The optical properties of type II diamond are (i) transparency from 230 nm to far infra-red (with only weak absorption in the near infra-red), and (ii) high refractive index (2·43). Mechanically, diamond is the strongest of all solids and strong vacuum-tight joints to metal can be made. The thermal conductivity is better than copper. The main difficulty and cost is in working surfaces (other than flats) to optical tolerances.     

Diamond synthesis in graphite/nickel composite powders subjected to shock compression

Characterization of graphite/nickel composite powders subjected to high-pressure shock-wave compression was performed using optical and transmission electron microscopy. Unique spherulites of graphite were observed in the nickel matrix of those specimens in which the nickel apparently melted under the shock-wave loading. The morphology of these spherulites resembles that of nodular graphite found in cast iron. Evidence of diamond formation was found both at the centre of spherulites (polycrystalline) as well as in the remaining graphite flakes (single crystal).     

Economical synthesis of nano alumina powder using an aqueous sol-gel method

Nano alumina powder can be widely used in the fields of electronics, catalyst supports and high temperature applications. In the present article, a nano Al₂O₃ powder was synthesized by a simple aqueous sol-gel method using inexpensive AlCl₃·6H₂O and Al powder as raw materials. It was shown that the gel calcined at 1100 °C resulted in the formation of a crystalline α-Al₂O₃ nano powder. It had a particle size distribution ranging from 32 to 100 nm after heat treatment at 1200 °C.     

Automated synthesis of modular fixture designs using an evolutionary search algorithm

Fixture design is a complex problem that requires a designer to ensure that a workpiece is located deterministically, totally restrained and sufficiently supported during a manufacturing process. The use of modular fixtures, while presenting an opportunity to improve the responsiveness of a manufacturing system, adds to the complexity of the fixture design problem. The complexity is a result of the large number of fixture elements in a modular fixture system and the constraints of specified locations in which fixture elements can be placed in a grid-based modular system. This paper presents an evolutionary search algorithm that aids a fixture designer by exploring the large number of possible fixture designs and suggesting an appropriate one. The algorithm can explore the large solution space using a flexible and generic representation and it considers fixture layout and fixture configuration constraints concurrently in arriving at appropriate solutions. The initial results of the algorithm are promising.     

Erosion laser torch in the light of the gating radiation from an auxiliary laser

A gating laser illumination pulse has been used to visualize different stages of the formation of the liquid-drop phase formed by the hydrodynamic mechanism in the erosion laser torch of a metal. Analysis of the sequence of photographs obtained under different irradiation conditions has been performed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 211–215, March–April, 2008.