Study of the radiation resistance of a carbon fiber based on viscose in carbon-carbon and carbon-ceramic composites

The results of the experimental study of the crystalline structure and morphology of carbon fibers based on viscose in a FEBUS carbon-ceramic composite and its preform as functions of temperature ranging from room values to ～400°C under irradiation with Ar⁺ ions with an energy of 10–30 keV are obtained. The average level of radiation damage corresponding to the initial fiber graphitization (〈ν_gr> ～ 80 dpa) is determined based on an analysis of the energy dependences of the ion-electron emission coefficient at different irradiation temperatures. It is shown that carbon fibers based on viscose are immune (in contrast to polyacrylonitrile fibers) to ion-induced destruction in the form of crimping. This is indicative of their enhanced radiation resistance.     

Antistatic behavior of PAN-based low-temperature carbonaceous fibers

A kind of antistatic coatings which were applied to nonconductive surfaces were prepared with polytetrafluoroethylene (PTFE) paint as matrix, polyacrylonitrile (PAN)-based low-temperature carbonaceous fibers as conductive filler. The influences of carbonaceous fiber content, carbonization temperature, size and testing voltage on the surface resistivity of the coating were investigated. The surface resistivity could be well controlled in the static dissipative range (10⁶–10⁹ Ω) by changing the content, size and carbonization temperature of carbonaceous fibers. The present study could be useful for the application of chopped carbonaceous fibers in antistatic materials.     

Novel electrospun PAN�CPVC composite fibrous membranes as polymer electrolytes for polymer lithium-ion batteries

Composite fibrous membranes based on poly(acrylonitrile)(PAN)-poly(vinyl chloride)(PVC) have been prepared by electrospinning. The fibrous membranes are made up of fibers of 850- to 1,300-nm diameters. These fibers are stacked in layers to produce a fully interconnected pore structure. Polymer electrolytes were prepared by immersing the fibrous membranes in 1 M LiClO₄-PC solution for 60 min. The condition of pure PAN polymer electrolytes is jelly, which has poor mechanical performance and cannot be used. But when PVC with a good mechanical stiffener was added to PAN, the condition of composite PAN?CPVC polymer electrolytes becomes free-standing. In addition, the optimum electrochemical properties have been observed for the polymer electrolyte based on PAN?CPVC (8:2, w/w) to show ionic conductivity of 1.05?×?10^?3 S cm^?1 at 25 °C, anodic stability up to 4.9 V versus Li/Li⁺, and a good compatibility with lithium metal resulting in low interfacial resistance. The promising results showed that fibrous PEs based on PAN?CPVC (8:2, w/w) have good mechanical stability and electrochemical properties. This shows a great potential application in polymer lithium-ion batteries.     

Heavy-ion irradiations of Fe and Fe–Cr model alloys Part 1: Damage evolution in thin-foils at lower doses

The evolution of radiation damage in Fe and Fe–Cr alloys under heavy-ion irradiation was investigated using transmission electron microscopy. Thin foils were irradiated with 100 or 150 keV Fe⁺ and Xe⁺ ions at room temperature (RT) and 300°C. Dynamic observations followed the evolution of damage and the early stages in damage development are reported. Small (2–5 nm) dislocation loops first appeared at doses between 10¹⁶ and 10¹⁷ ions m^?2 in all materials. Loop number densities depended strongly on the foil orientation in pure Fe but not in Fe–Cr alloys. Number densities did not depend strongly on Cr content. For a given material, defect yields were higher for Xe⁺ ions than for Fe⁺ ions, and were higher at RT than at 300°C. Loops with both ?100? and ½?111? Burgers vectors were identified. The proportion of ?100? loops was larger, especially in pure Fe. Dynamic observations showed that: the contrast of some new loops developed over intervals as long as 0.2 s; hopping of ½?111? loops was induced by the ion and electron beams and was pronounced in ultra-pure iron; and many loops were lost during and after ion irradiation by glide to the foil surface. The number of loops retained was strongly dependent on the foil orientation in Fe, but less so in Fe–Cr alloys. This is due to lower loop mobility in Fe–Cr alloys, probably due to pinning by Cr atoms. Reduced loop loss probably explains the higher loop number densities in Fe–Cr alloys compared with pure Fe.     

Stored energy release behaviour of disordered carbon

The use of graphite as a moderator in a low temperature thermal nuclear reactor is restricted due to accumulation of energy caused by displacement of atoms by neutrons and high energetic particles. Thermal transients may lead to a release of stored energy that may raise the temperature of the fuel clad above the design limit. Disordered carbon is thought to be an alternative choice for this purpose. Two types of disordered carbon composites, namely, CB (made up of 15 wt. % carbon black dispersed in carbonized phenolic resin) and PAN (made up of 20 vol. % chopped polyacrylonitrile carbon fibre dispersed in carbonized phenolic resin matrix) have been irradiated with 145 MeV Ne⁶⁺ ions at three fluence levels of 1.0×10¹³, 5.0×10¹³ and 1.5×10¹⁴ Ne⁶⁺/cm², respectively. The XRD patterns revealed that both the samples remained disordered even after irradiation. The maximum release of stored energy for CB was 212 J/g and that of PAN was 906 J/g. For CB, the release of stored energy was a first order reaction with activation energy of 2.79 eV and a frequency factor of 3.72×10²⁸ per second. 13% of the defects got annealed by heating up to 700 °C. PAN showed a third-order release rate with activation energy of 1.69 eV and a frequency factor of 1.77×10¹⁴ per second. 56% of the total defects got annealed by heating it up to 700 °C. CB seems to be the better choice than PAN as it showed less energy release with a slower rate. PACS 61.80.Jh; 61.80.-x; 61.43Er; 61.43.-j; 68.43.Vx     

Protective films of diamond for high Tc superconducting detectors

Deposition of diamond like carbon (DLC) films on YBCO superconducting detectors is reported. The method is to make a DLC film by C⁺ implantation and XeCl excimer laser irradiation. The implantation energy is 20–35 keV and C⁺ implantation dosages D=1×10¹⁴–5×10¹⁸ ions/cm². The parameters of XeCl excimer laser ablation are: wavelength, 308 nm; energy density, 20–50 mJ/cm²; and width of pulse, 45 ns. The superconductivity of C⁺-implanted YBCO is also investigated, while the damage behavior of C⁺ implantation and the mechanism of coating DLC are analyzed.     

A comparative study of lithium and sodium salts in PAN-based ion conducting polymer electrolytes

The conducting polymer electrolyte films consisting of polyacrylonitrile (PAN) as the host polymer, lithium triflate (LiCF₃SO₃) and sodium triflate (NaCF₃SO₃) as inorganic salts were prepared by the solution-cast technique. The pure PAN film was prepared as a reference. The ionic conductivity for the films is characterized using impedance spectroscopy. The room temperature conductivity for the PAN + 26 wt.% LiCF₃SO₃ film and the PAN + 24 wt.% NaCF₃SO₃ film is 3.04 × 10⁻⁴ S cm⁻¹ and 7.13 × 10⁻⁴ S cm⁻¹, respectively. XRD studies show that the complexation that has occurred in the PAN containing salt films and complexes formed are amorphous. The FTIR spectra results confirmed the complexation has taken place between the salt and the polymer. These results correspond with surface morphology images obtained from SEM analysis. The conductivity–temperature dependence of the highest conducting film from PAN + LiCF₃SO₃ and PAN + NaCF₃SO₃ systems follows Arrhenius equation in the temperature range of 303 to 353 K. The PAN containing 24 wt.% LiCF₃SO₃ film has a higher ionic conductivity and lower activation energy compared to the PAN containing 26 wt.%LiCF₃SO₃ film. These results can be explained based on the Lewis acidity of the alkali ions, i.e., the interaction between Li⁺ ion and the nitrogen atom of PAN is stronger than that of Na⁺ ion.     

Interference method of measuring the extinction coefficient of birefringent optical fibers

The extinction coefficient of a birefringent optical fiber (the ratio between the radiation power output of the polarization mode and the radiation power transferred from this mode to another one) characterizes the capability of a birefringent fiber to retain the polarization state of the radiation. In relatively short birefringent fibers (1–100 m), the extinction coefficient may reach 10⁴–10⁶. Such high values of the extinction coefficient are difficult to measure by standard techniques (excitation of one polarization mode by an incoherent source with subsequent recording of the light intensity at the output of the analyzer). An interference method of measuring the extinction coefficient of birefringent fibers is suggested. It is based on using a coherent source and measuring interference oscillations caused by an additional phase modulation at the input of the fiber. This method does not require precise polarization matching between the laser source and fiber and considerably loosens requirements for the polarizer-analyzer extinction and resolution of the photodetector. As a result, using simple standard components (semiconductor laser, film polarizer, and photodetector), one can measure extinction coefficient as high as 10⁶. The suggested interference method of measuring the extinction coefficient of birefringent fibers receives a theoretical analysis, and experimental data obtained for 2- to 1000-m-long fibers are presented.     

Structural and Morphological Changes of Carbon Fiber Surfaces,Produced via Sputtering by Noble Gas Ions

SEM, laser goniophotometry, and Raman spectroscopy are used to analyze a modification of the carbon PAN fiber shell of KUP-VM composite upon irradiation with 30 keV Ne⁺ and Ar⁺ ions at normal incidence and temperatures of RT to 600°C. It is found that the formation of corrugated submicron structures in the composite upon irradiation at elevated temperatures (≥125°C for neon and ≥250°C for argon) displays certain features at temperatures of 400–500°C. The corrugated faces’ angles of inclination and the fraction of the corrugated structure on the fiber surface at these temperatures are minimal. Together with regularities established earlier, the observed patterns allow us to relate ion-induced corrugation to anisotropic radiation- induced plastic processes of dimensional changes in carbon materials affected by ion sputtering of their surfaces.     

Study of carbon material surface layers modified by nitrogen and argon ion irradiation

We present the results of the study of the elemental composition and defects of the electronic structure of the surface layer modified by high-dose irradiation (10¹⁸–10¹⁹ ion/cm²) of highly oriented pyrolytic graphite (UPV-1T) by 30-keV N ₂ ⁺ and Ar⁺ ions in the temperature range from 180 to 400°C. The EPR spectra observed during irradiation with argon ions at high temperatures and with nitrogen ions at temperatures near the liquid-nitrogen temperature T = 77 K exhibit anomalously narrow lines which probably result from the exchange interaction inside paramagnetic clusters of displaced carbon atoms. During nitrogen ion irradiation at room and higher temperatures, paramagnetic defects typical of many carbon materials (single EPR lines with g = 2.0027–2.0029) and belonging to carbon atoms bound to one or three nitrogen atoms were detected.     

Radiation damage and annealing studies of ion bombarded cobalt

The effects of implantation-induced radiation damage on the thermal oxidation of cobalt have been studied. Bombardment by both Co⁺ self-ions and by Xe⁺ has been studied as a function of ion dose, energy and annealing temperature. A major increase in oxidation was observed for doses of >10¹⁶ Co⁺ cm^–2 in agreement with previous studies on Al. The oxidation behaviour as a function of annealing temperature was markedly different for Co⁺ and Xe⁺ bombarded samples. For Co⁺ bombarded samples, damage anneals rapidly in the temperature range 20–300°C due to thermally assisted repair of point defects and vacancy clusters. However, for Xe⁺ bombardment, it is proposed that the higher annealing temperatures required for damage repair arise due to the stabilisation of three-dimensional vacancy clusters by the oversized Xe atoms. The increase in oxidation after annealing in the temperature range 300–500°C is thought to be due to vacancy release mechanisms which may affect oxide nucleation.     

In situ phase changes in a Fe-40 at.% Al ordered alloy during ion implantation: T.E.M. study

The radiation damage and disordering phenomena produced at room temperature during Fe⁺, Bi⁺⁺ and Xe⁺ ion implantations in a Fe-40 at.% A1 ordered alloy were studied by in situ transmission electron microscopy. Progressive, but not total disordering was achieved in the thinnest areas of the specimens during high fluence implantations (> 10¹⁵ ions/cm²). Simultaneously, the athermal formation of a new phase occurs in the case of Fe⁺ and Bi⁺⁺ implantations. The diffusion-less mechanism suggests a martensitic like transformation.

During post-implantation annealing, reordering and long-range order domain growth occurred in the temperature range up to 570 K. Above 670 K another phase appeared, which was stable up to 1070 K. The results are discussed and compared with those obtained on melt-quenched or neutron irradiated specimens of the same alloy.     

Nitrogen centers in GaP produced by hot implantation

Backscattering yields of 1.5 MeV?He⁺ ions and low temperature photoluminescence (PL) spectra were measured in GaP crystals implanted with 200 keV?N⁺ ions as functions of ion-dose, temperature during implantation and annealing temperature after implantation. Backscattering results indicate that hot implantation at 500°C greatly reduces radiation damage. The PL intensities of NN lines become maximum in the sample implanted with N⁺ ions of 3 × 10¹⁴cm^?2 at 500°C, and annealed at 1000°C for 1 hr with aluminum glass. The PL intensity is comparable to that of the nitrogen-doped sample during liquid phase epitaxy which is widely accepted as the best method of introducing nitrogen into GaP crystals. In the case of 500°C—hot implantation, the radiation damage produced during implantation is annealed out at 700 ~ 800°C and the implanted nitrogen substitutes for the phosphorous sites after annealing at 900 ~ 1000°C. Some kinds of defects or strains remain around the NN centers even in implanted samples with a maximum PL efficiency. These defects or strains don't seem to reduce the PL efficiency. In the case of room temperature implantation, PL efficiency decreases to one-hundredth or one-thousandth due to the formation of the non-crystalline state compared with hot implantation.     

Analysis of a tungsten surface irradiated by fast ions and deuterium plasma

The effects occurring on the surface of tungsten under irradiation with fast ions with an energy in the megaelectrolvolt range and with high fluxes of hydrogen (deuterium) plasma are considered. These effects are radiation damage of the surface layer of the material, its erosion and deuterium retention in it. Irradiation with helium ⁴He²⁺ (3.2–4.0 MeV) and carbon ¹²C³⁺ (10 MeV) ions is performed using a cyclotron at the National Research Center Kurchatov Institute. The thickness of the damaged layer is 3.5–6 μm. The irradiated samples are exposed to steady-state deuterium plasma using a LENTA linear plasma facility to reach a plasma ion fluence of 10²¹–10²² cm^?2. Tungsten erosion and modification of the structure of the damaged layer are analyzed at a plasma-ion energy of 250 eV. Deuterium retention in the damaged layer is studied by elastic recoil detection analysis. The deuterium concentration and its penetration depth into the material are measured. The data obtained for different kinds of fast ions used in the work are compared.     

The atkermal stress component in neutron irradiated mild steel

Abstract

The temperature dependence of the tensile lower yield stress of an annealed aluminium grain size controlled mild steel has been investigated in the range 23–250 °C and at a strain rate of 1.67 × 10^?4 sec^?l before and after neutron irradiation to 2.3 × 10¹⁸ n/cm² (fission). The yield stress of the irradiated steel decreases with increasing temperature due to thermal activation of the radiation damage and is predicted to reach asymptotically that of the unirradiated steel at ～285 °C; the maximum test temperature was below that at which thermal annealing of the damage occurs. This implies that the athermal stress component due to irradiation is zero and hence there is negligible long range interaction between dislocations and radiation-induced defects.     

The effect of radiation damage on microstructure and ion electron emission of pyrolytic graphites

The influence of radiation damage on the microstructure of pyrolytic graphites was analyzed. The correlation between the temperature dependences of ion-induced electron emission and structural modification of UPV-1 pyrolytic graphite and highly oriented UPV-1T pyrolytic graphite under neutron and high-fluence (10¹⁷–10¹⁹ cm⁻²) (30 keV) Ar⁺ irradiation was experimentally studied and discussed.     

Bestimmung von Temperatur und Dichte eines Gleitfunkens aus der Bremsstrahlung im Infrarot

The absolute intensity of a vacuum sliding spark (length 2–10 cm, half cycle 0,8 μsec) has been measured in the spectral region between 0,4 and 3μ. From the long wavelength radiation emitted from an optically thick layer, one gets the temperature, from the short wavelength radiation emitted from an optically thin layer, one obtains the density. Using polyethylene as an insulator we reached a temperature of 4·10⁵ °K at electron densities of 8·10¹⁸ cm^?3 and current densities of 1.2·10⁶ A/cm². The temporal development of temperature and density has been determined. The maximum intensity at λ=0.43 μ was found to be 5·10⁴ (7·10¹⁰ W/cm³ ster) as large as that of the positive crater of a properly driven carbon arc. At λ=3 μ this same parameter turned out to be 300 times as large (5·10⁷ W/cm³ ster).     

199Hg+光频标的黑体辐射频移

光学频率标准会受到环境温度的黑体辐射影响发生频移,进而影响其准确度. 本文估算了¹⁹⁹Hg⁺的超精细能级5d¹⁰6s²S_1/2 (F=0)和5d⁹6s^{2 2}D_5/2 (F=2)的极化率,得到了室温(300 K)下黑体辐射引起的相对频移为-5.4×10^-17, 最后讨论了低温环境下黑体辐射对¹⁹⁹Hg⁺光频标的影响.     

Doping and radiation damage profiles of P+ ions implanted in silicon along the [110] axis

Several doses of 200 KeV phosphorus ions have been implanted under channeling conditions along the [110] direction in silicon.

Range distribution has been determined for the three implant doses 10¹³, 10¹⁴, 10¹⁵ P⁺/cm² both with the electrical measurements and the neutron activation techniques.

The radiation damage distribution has been determined both with 290 KeV proton back-scattering analysis and with transmission electron microscopy (TEM) observations.

Good agreement has been found between electrical and neutron activation profiles in the samples where 100% of the implanted dose had been electrically activated by means of annealing.

Carrier concentration profiles, from samples implanted with 10¹⁵ P⁺/cm², determined after two different annealing temperatures (500°C and 700°C) have bcen compared with the radiation damage distribution and a correlation between damage and phosphorus electrical activation process seems to be possible.

Maximum damage peak, as determined by back-scattering analysis, shifts from ～0.4 μ depth in the lower dose(5 × 10¹⁴ P⁺/cm²), to ～0.22 pm depth in the higher implanted dose (4 × 10¹⁵ P⁺/cm²). Damage distribution of phosphorus ions random implanted in the same experimental conditions shows 3 peak at ～0.2 μn depth.

In accordance with the back-scattering analysis, T.E.M. observations on 10¹⁵P⁺/cm² implanted samples show the presence of amorphous regions at depth between 0.25 and 0.5 μm from the surface. In the most damaged layer ～0.3μm in depth, a surface density of ～10¹²/cm² amorphous regions 25-50 A diameter was observed.     

AES-LEED-ellipsometry study of the kinetics of the interaction of methane with Ni(110)

The interaction of methane with Ni(110) was studied with AES, LEED and ellipsometry. Sticking coefficients were determined in the temperature range 298–600 K at methane pressures of 10^?4–10^?2 Torr. The carbon coverages were derived from Auger spectra by calibration with ellipsometry. At room temperature no detectable adsorption was observed without use of electron sources. In the temperature range 473–579 K the coverage versus exposure curves show an induction effect at low coverage followed by an almost linear increase up to a saturation coverage of about $\text{1}\text{3}$ monolayer of carbon. At these temperatures a Ni(110)-(2 × 3)-C structure was observed with streaks in the direction of constant h. The observed behaviour is explained with a nucleation and growth model in which mobile carbon species are captured at the edges of surface nickel carbide islands. At temperatures above 600 K carbon diffuses into the bulk and the Ni(110)-(4 × 5)-C superstructure is observed.