A new experimental approach to the analysis of thermodynamic properties of amorphous carbon nanoparticles synthesized via hydrocarbon pyrolysis behind shock waves is discussed. The proposed approach ...is based on the analysis of thermal radiation of nanoparticles heated by a laser pulse. The sublimation temperature of the carbon nanoparticles might be determined by the two-colour pyrometry; their sizes, by laserinduced incandescence; and the volume fraction of the sublimated substance, by the laser extinction method. The sublimation temperature depends on both the particle size and the temperature conditions of their formation. The value of surface energy for amorphous carbon nanoparticles was estimated.
The decomposition of methane on molybdenum nanoparticles was studied experimentally at room temperature. The molybdenum nanoparticles were synthesized in the gas phase using UV laser photolysis of ...Mo(CO)
6
vapor in a flow reactor. The working part of the flow reactor was equipped with quartz windows for introducing the radiation from a pulsed Nd:YaG laser operating at the fourth harmonic (266 nm) at a frequency of 10 Hz. Methane was used as a carrier gas. As a result of irradiation of a mixture of methane with Mo(CO)
6
vapors in the gas phase at room temperature, nanoparticles with sizes of 2–50 nm were synthesized. The phase composition of the nanoparticles included pure molybdenum, molybdenum carbide Mo
2
C, and molybdenum oxide MoO
3
. During the reaction, the hydrogen yield was measured with a VG-7 highly sensitive hydrogen analyzer based on a semiconductor metal–dielectric sensor. The measured H
2
concentration varied from 5 to 25 ppm depending on the concentration of Mo(CO)
6
. The possibility of methane decomposition on molybdenum nanoparticles at room temperature was discussed based on the obtained data.
The experimental investigation of iron-carbon nanoparticles synthesis by joint laser photolysis of iron pentacarbonyl in the mixture with methane or acetylene has been carried out. The radiation ...source used for photo-dissociation of precursors was a pulsed Nd:Yag laser operated at a wavelength of 266 nm. Under uv radiation the molecules of Fe(CO)5 decomposed, forming atomic iron vapor and unsaturated carbonyls at well-known and readily controllable parameters. The subsequent condensation of supersaturated metal vapor resulted in small iron clusters and nanoparticles formation. It was assumed that the active catalytic surface of metal nanoparticles could activate the hydrocarbon molecules up to carbon layer formation on their surface. The growth process of the nanoparticles was observed by a method of laser light extinction. Additionally nanoparticle samples were investigated by a transmission electron microscope. The particle sizes were measured by microphotographs treatment. The sizes of synthesized particles from methane-iron-pentacarbonyl mixture were found to be in a range of 4-16 nm with a count median diameter of 8.9 nm and standard deviation of 1.13. These particles consisted of iron oxide without any carbon content. The particles formed in photolysis of acetylene-iron-pentacarbonyl mixture had the sizes of 3-7 nm with count median diameter of 4 nm and standard deviation of 1.28 and contained the essential amount of carbon. The iron cores were surrounded with a carbon shell.
The influence of laser heated iron and carbon nanoparticles on ignition of 20 vol% stoichiometric methane-oxygen mixture in argon was studied experimentally in shock tube reactor. The concentration ...of nanoparticles 0.3-2.0 ppm was measured by laser light extinction. The particles were heated by Nd:Yag laser pulse operated at wavelength 1064 nm. The ignition delay times were registered by increase of OH chemiluminescence and pressure rise. The temperatures of laser heated particles and their sizes were measured by laser induced incandescence technique. The significant decrease of ignition delay times were found at addition of iron particles heated by laser pulse to the combustible mixture at the temperatures less than 1400 K. Analysis performed has shown that the effect supposedly involves catalytic reactions of methane decomposition on the surface of heated particles and allowed estimating their effective activation energy.
The
Gerda
collaboration is performing a search for neutrinoless double beta decay of
76
Ge with the eponymous detector. The experiment has been installed and commissioned at the Laboratori Nazionali ...del Gran Sasso and has started operation in November 2011. The design, construction and first operational results are described, along with detailed information from the R&D phase.
Upgrade for Phase II of the Gerda experiment Agostini, M.; Bakalyarov, A. M.; Balata, M. ...
The European physical journal. C, Particles and fields,
05/2018, Letnik:
78, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The
Gerda
collaboration is performing a sensitive search for neutrinoless double beta decay of
76
Ge
at the INFN Laboratori Nazionali del Gran Sasso, Italy. The upgrade of the
Gerda
experiment from ...Phase I to Phase II has been concluded in December 2015. The first Phase II data release shows that the goal to suppress the background by one order of magnitude compared to Phase I has been achieved.
Gerda
is thus the first experiment that will remain “background-free” up to its design exposure (
100 kg
year
). It will reach thereby a half-life sensitivity of more than
10
26
year within 3 years of data collection. This paper describes in detail the modifications and improvements of the experimental setup for Phase II and discusses the performance of individual detector components.
In this study the laser photolysis of the mixtures containing vapors of various hydrocarbons and iron pentacarbonyl was implemented to nanoparticle formation. The radiation source used for ...photo-dissociation of precursors was a pulsed Nd:Yag laser operated at a wavelength of 266 nm. Under UV radiation the molecules of Fe(CO)5 decomposed, forming atomic iron vapor and unsaturated carbonyls at well-known and readily controllable parameters. The subsequent condensation of supersaturated metal vapor resulted in small iron clusters and nanoparticles formation. The growth process of the nanoparticles was observed by a method of laser light extinction. Laser induced incandescence technique was applied for particle sizing during the process of their formation. Additionally nanoparticle samples were investigated by a transmission electron microscope. The particle size distribution was measured by statistical treatment of microphotographs. The elemental analysis by energy-dispersive x-ray spectroscopy and electron diffraction pattern gave the composition and structure of nanoparticles. The core-shell iron−carbon nanoparticles were synthesized by joint laser photolysis of iron pentacarbonyl with benzene and acetylene. The photolysis of the mixtures of toluene, butanol and methane with iron pentacarbonyl revealed in a pure iron particles formation which fast oxidized in air when were extracted out of the reactor.
Atomic resonance absorption spectroscopy has been used to study the yield of molybdenum atoms in the process of ultraviolet laser pulse photo-dissociation of Mo(CO)6 vapor. Molybdenum atoms in a ...ground state were formed by the quenching of the electronically excited Mo atoms generated during photolysis and were detected using the resonance absorption at a wavelength of 386.41 nm. The effective quenching rates were measured in the presence of various bath gases.
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