Desorption of water vapour by gamma irradiation

The desorption of water vapour from an unbaked stainless steel 304 vacuum vessel, wall thickness 0.5 mm, by means of gamma irradiation was measured. Small Co⁶⁰ sources (gamma energy 1.3328 MeV, 1.1733 MeV) were attached to the outer side of the vessel and the desorption of water determined with a magnetic gas analyzer. The outgassing effect was of the order of 10⁻¹³ torr l./cm² sec, per μCi of Co⁶⁰.     

An on-line tritium-in-water monitor

The paper describes the development and operation of a continuous on-line tritium-in-water monitor for the detection of heavy water leaks into the secondary coolant light water of a heavy water power reactor. The heart of the instrument is its plastic scintillator sponge detector, made from 5 μm thick plastic scintillator films. The sponge weighs only about 1 g and is in the form of disc of 48 mm diameter and 8 mm thickness. The total surface area of the films is about 3000 cm². In the coincidence mode of counting, the detector gives 1000 cps for the passage of 3.7 × 10⁴ Bq/cm³ (1 μCi/cm³) of tritiated water. The background in 6 cm thick lead shielding in the laboratory is 0.2 cps, and inside the reactor building it is below 1 cps. The monitor presently scans 18 sample lines in sequence for 5 min each and gives a printout for the activity in each line.     

Pumpkin seed oil cake/polyethylene film as new food packaging material,with perspective for packing under modified atmosphere

Biopolymer packaging materials show increasing perspective in food packaging. Main limitation remains their high water sensitivity and poor water vapour barrier properties, compared to non polar materials of synthetic origin like polyethylene. In this paper, biopolymer layer obtained from by‐product of oil industry (pumpkin seed oil cake) was laminated on polyethylene in order to obtain new packaging material that would preferably combine water barrier properties of polyethylene and oxygen barrier properties of biopolymer composite material and perform satisfactory mechanical properties. Obtained two‐layer material showed good barrier properties for water vapour (7–8 g/m² 24h), as well as oxygen (12–45 cm³/m² 24h) and light. In addition, mechanical and water sensitivity tests were performed and results showed that new material inherited biopolymer film water sensitivity and mechanical properties with slight improvement. Measured tensile strength and elongation at break was 2–4 MPa and 150–250% in transversal direction and 6–8 MPa and 100–150% in longitudinal direction. Packing in modified atmosphere assay showed that new material can be used for this purpose with good control of oxygen concentration, while packing under increased concentration of CO₂ could be performed for shorter storage period. New two layer material shows promising properties for sensitive food packing under modified atmosphere conditions with reduced use of synthetic, oil‐based materials.     

Anorganische Fasern. Herstellung,Eigenschaften und Verwendung

Inorganic Fibres – Fabrication, Properties and Application Glass- and carbon fibres are preferred reinforcement materials for composites with polymer matrix. Basing on an analysis of their properties it is shown that other inorganic fibres can combine the advantages of both, and avoid their disadvantages. Boron-, siliconcarbide- and alumina-fibres are discussed in detail. The boron fibre has a YOUNG's modulus up to 45 MN/m² and a strength of 3000–4000 MN/m² as well as high compressive and shear strength. Therefore the boron fibres are superior to the carbon fibres as high modulus reinforcement material. The disadvantages of the boron fibres are their complicated fabrication process (chemical vapour deposition on a tungsten monofilament), and their only availability in form of monofilaments with diameters of at least 60 μm. The boron fibre recristallizes at 6000 °C and reacts also with the tungsten substrat. Thus, its application at elevated temperatures is limited. The SiC-fibre shows the same mechanical properties as the boron fibre but it can be fabricated by chemical vapour deposition also on a carbon monofilament. The advantages are the chemical compatibility with carbon substrat and the resistance against oxidation. The disadvantage is the higher density compared with that of boron (3,5 against 2,6 · 10³ kg/m³) Carbon yarns (with 10 000 monofilaments of 10 μm diameter) with SiC coatings of 0,5 μm can be seen as an alternative to the relatively thick SiC-monofilaments with 60 μm diameter. The advantage of such coated carbon yarn is a better applicability in fibre reinforced composite materials. There exists a further alternative preparation process for SiC-yarn, namely the spinning of polycarbosilanes with subsequent formation of SiC by pyrolysis treatment. Al₂O₃-fibres are chemically inert against most oxidic and metallic matrix materials, and promises to be candidate reinforcement materials for aluminium. They can be prepared by melt-spinning process as well as by a hydrolysis-process starting from aluminium organic compounds with subsequent heat treatment for thermal decomposition. The properties of all these fibre materials are compared with those of glass-, polyamid- and carbon-fibres as well as with metal wires.     

ROOM-TYPE AIR CLEANER DESIGN CRITERIA AND PROTOTYPE PERFORMANCE

ABSTRACT

Two rules-of-thumb for minimum performance of a room-type air cleaner have been developed from consideration of a first order model for room air quality. By adopting a criterion that the use of an air cleaner should cause the particle concentration to be at least cut in half, the rule-of-thumb for a room with no smokers is that the product of filter efficiency and flow rate should be ≥.8 m³/min (≥30 cfm). If the particle concentration is dominated by smokers or other sources, the product of filter efficiency and filter flow rate should be = m³ /min (= 100 cfm)

Tests were conducted to determine the efficiencies of candidate filter media. The selected media, Filtrete G-0115, has a fractional efficiency for 1 μm particles of 97 percent when clean, and an efficiency of 78 percent when fully loaded. This drop in efficiency is due to the masking of the electrets on the surfaces of the filter fibers.

A fibrous filter room-type air cleaner was designed to perform in accordance with the rules-of-thumb. When operated with a clean filter, the maximum flow rate is 3.2 m³/min and, when operated with a fully loaded filter, the maximum flow rate is 1.8 m³/min. The system has a multispeed fan which will provide lower flow rates.     

High temperature oxidation of hot-pressed aluminium nitride by water vapour

Hot pressed AIN without additives was oxidized et 1100 to 1400°C in dry air, wet air and wet nitrogen gas atmospheres with 1.5 to 20 kPa of water vapour pressure. AIN was oxidized by both air and water vapour, and formed -Al₂O₃ film on the surface above 1150°C. The oxidation kinetics in air were parabolic end were promoted by water vapour. On the other hand, the oxidation kinetics in wet nitrogen were linear below 1250°C and parabolic above 1350°C. The oxidation rate in wet nitrogen was much greater than that in wet air. The rate of oxidation increased with increasing temperature until 1350°C, and then decreased. The parabolic rate constant decreased with increasing temperature and increased linearly with increasing water vapour pressure. The linear rate constant at 1150 to 1250° C increased with increasing the temperature with the apparent activation energy of 250 kJ mol^–1. The relation between the linear rate constant and water vapour pressure was of the Langmuir type.     

Determination of oxygen in W-C-Co nanopowders

The oxygen content of W-C-Co nanopowders produced by plasma reduction of WO₃, followed by low-temperature carburization in hydrogen has been determined by carrier gas hot extraction. The oxygen in adsorbed water, carbon-oxygen complexes weakly bound to the surface, and surface oxides (WO _x and CoO _x ) has been determined separately. Freshly prepared, passivated WC and WC + 8% Co powders with a specific surface area of 6–11 m²/g were found to contain 0.03–0.07 μg/cm² of oxygen, not counting adsorbed water. Strongly bound oxygen in the form of surface oxides accounts for at least 80% of the total oxygen. These oxygen contents are equivalent to surface coverages from 1.2 to 2.5 oxygen monolayers (monolayer density of 10¹⁵ at/cm²). The water content varies from 0.15 to 0.3%, which corresponds to a water film no thicker than a monolayer. All of the water is physisorbed. The products of the plasma reduction of WO₃ have a complex phase composition (W₂C, WC_{1 ? x} , W, α-WC) and a specific surface area from 21 to 24 m²/g. In spite of the high content of the readily oxidizable phases W and W₂C, the plasma-synthesized mixtures have submonolayer surface coverages with oxygen. They are protected from air oxidation by thin (one to three monolayers) pyrolytic carbon films, while the small amount of oxygen present originates from unreacted particles. In dry air, the powders oxidize insignificantly. At 100% humidity, stoichiometric WC powders are the most stable, while WC + 8% Co shows the lowest stability. The oxidation rate of W-C powders is proportional to the overall content of W and W₂C.     

A transient method of measuring the water vapour permeability of packaging films I. Dynamic performance of a sorptive sensor

Principles of an analysis of the inertia of a sorptive sensor used for transient measurements of water vapour permeability through packaging films have been developed. The construction of the measuring cell and the method of measurement of water vapour permeation through packaging films have been readjusted to the developed principles. It is shown that the inertia of a sorptive sensor, defined as a difference Δ between measured signal value RH* and an estimated value of air relative humidity RH₁ close to the film surface in an input chamber can be described as a difference of exponential functions Δ = RH₀·[exp(−Aτ) − exp(−Bτ)]. The characteristic parameter determining the sensor inertia is the maximum delay time τ_m; the roots of the function Δ(τ) derivative. The theory and procedure for using τ_m for the iterative determination of water vapour permeability through packaging films based on analysis of the sorptive sensor inertia is presented.     

COMPARISON OF PLASTIC WORK OF FATIGUE CRACK PROPAGATION IN LOW CARBON STEEL MEASURED BY STRAIN-GAGES AND ELECTRON CHANNELING

Abstract— The plastic work to propagate a fatigue crack by a unit area, U, measured by the foil strain gage technique requires an extrapolation to estimate the contribution closer than 100 μm to the crack tip. This is due to the size of the strain-gages used, 200 × 210 μm. Conversely, the electron channeling technique for determining U is useful mainly close to the crack tip where subgrains form. In the present work U was measured by both techniques in the same low carbon steel at ΔK= 8 MN/m^3/2. The contribution to U from closer than 100 μm of the crack tip was determined to be 1·7 × 10⁶ J/m² using electron channeling and 2·0 × 10⁶ J/m² by extrapolation. The measured contribution to U from further than 100 μm from the crack tip was 3·6 × 10⁶ J/m² giving 5·3 × 10⁶ J/m² for U. Thus, a large amount of energy is absorbed outside the region where sub-grains form. The non-hysteretic plastic work was found to be about four orders of magnitude smaller than the hysteretic plastic work, and may be neglected. A map of the plastic zone results from the strain-gage measurement. Rice's theory predicts the measured plastic zone sizeif the proper material's strength is employed in the formula.     

Chemical thinning of III–V compound semiconductors for transmission electron microscopy

A vapour jet etching method and suitable equipment are tested in order to thin monocrystalline and polycrystalline material of GaAs, InP and InAs for transmission electron microscopy. The reactive vapour jet consists of air, bromine and methanol. The thinning procedure is monitored by an optical microscope. Large thin areas could be obtained using a bubbler temperature of 60° C, 20% bromine in methanol, a distance between nozzle and sample surface of 1.5 mm and a nozzle mouth diameter of 0.7 mm. During pre-etching the vapour flow rate was 0.71 min^–1, and 0.31 min^–1 was realized during final etching up to perforation. The etching times ranged between 1 to 2 min with an initial sample thickness of 350 to 365 m. Large thin areas have only been obtained using an excentric position of the nozzle with respect to the sample centre in combination with a manual rotation of the specimen holder.     

The growth and electrical properties of single crystal Cd3As2 platelets

Single crystal platelets of Cd₃As₂ having carrier concentrations less than 10²⁴ m⁻³ have been grown from the vapour in the presence of argon gas and excess cadmium vapour. It is shown that the resistivity and Hall data is consistent with a band model in which there is a direct band-gap atk=0 of approximately 0.38 eV and an indirect zero band-gap. It is suggested that the large electron carrier concentrations usually present in Cd₃As₂ result from anti-structure disorder.     

Application of digital tomography in two-phase flow studies

Computer-aided-tomography (CAT) is being widely used in the medical area for the diagnosis of cancerous tissues. A review of the existing literature indicates that this concept of reconstruction tomography has been successfully adapted for measuring densities in two-phase air-water flows. The present study is aimed at improving the reconstruction process and developing a more efficient algorithm appropriate for two-phase flow measurement studies. Various sensitivity tests have been performed on different parameters including filter functions. A comparative study of the results reveals a significant improvement in the prediction of densities if the “generalized filter” is used. The reconstructed density values are −0.001 for air (density, zero g/cm³) and 0.99 for water (density, 1.0 g/cm³). The air-water system densities are predicted with a maximum dispersion of ±0.02 g/cm³ and a maximum absolute error of ± 0.01 g/cm³ for densities between 0.6 and 1.0 g/cm³.     

Wasserpermeation durch Polymere und keramische Substrate

Water permeation through polymers and oxide layers For the measurement of water permeation through solid materials plates (TorrSeal (epoxy resin) and FIMO (composite of PVC and calk)) and Polycarbonate foils – at different ambient temperatures – a device consisting of three parts, one filled with water, the second holds the material to be measured and the last contains a capacity humidity sensor, was used. Permeation of liquid water and water vapour was tested with no difference in results. The sensitivity for the measurement of the water permeation and the diffusion coefficient was 7,98 · 10^?13 m²/s. For polycarbonate foils the diffusion coefficient, its temperature dependence and its activation energy were found to be in reasonable agreement with data from literature. In later experiments the materials will be coated with different barrier layers to further decrease permeation.     

An Interfacial Solar‐Driven Atmospheric Water Generator Based on a Liquid Sorbent with Simultaneous Adsorption–Desorption

Water scarcity is one of the greatest challenges facing human society. Because of the abundant amount of water present in the atmosphere, there are significant efforts to harvest water from air. Particularly, solar‐driven atmospheric water generators based on sequential adsorption–desorption processes are attracting much attention. However, incomplete daytime desorption is the limiting factor for final water production, as the rate of water desorption typically decreases very quickly with decreased water content in the sorbents. Hereby combining tailored interfacial solar absorbers with an ionic‐liquid‐based sorbent, an atmospheric water generator with a simultaneous adsorption–desorption process is generated. With enhanced desorption capability and stabilized water content in the sorbent, this interfacial solar‐driven atmospheric water generator enables a high rate of water production (≈0.5 L m^?2 h^?1) and 2.8 L m^?2 d^?1 for the outdoor environment. It is expected that this interfacial solar‐driven atmospheric water generator, based on the liquid sorbent with a simultaneous adsorption–desorption process opens up a promising pathway to effectively harvest water from air.     

High-temperature oxidation of silicon nitride-based ceramics by water vapour

Hot-pressed Si₃N₄, sintered Si₃N₄ and three kinds of sialon with different compositions were oxidized in dry air and wet nitrogen gas atmospheres at 1100 to 1350° C and 1.5 to 20 kPa water vapour pressure. All samples were oxidized by both dry air and water vapour at high temperature, and formed oxide films consisting of SiO₂, Y₂Si₂O₇ and Y4A1209. The oxidation rate was in the order sialon > sintered Si₃N₄ > hot-pressed Si3N4. The oxidation rate of sialon increased with increasing Y₂O₃ content, and oxidation kinetics obeyed the usual parabolic law. The oxidation rates in dry air and wet nitrogen were almost the same: the rate in wet nitrogen was unaffected by water vapour pressure above 1.5 kPa. The activation energy was about 800 kJ mol^–1.     

Thermal decomposition of ferrous oxalate dihydrate studied by direct current electrical conductivity measurements

The feasibility of the use of direct current electrical conductivity,, measurements in the study of solid-state reactions involved in the synthesis of-Fe₂O₃ from ferrous oxalate dihydrate has been reported. The study has been carried out in static air, dynamic air, dry nitrogen and dynamic air + water vapour environments. The conductivity data determined in static air are quite complex; nevertheless, the formation of Fe₃O₄ and-Fe₂O₃ with the probable intermediate formation of-Fe₂O₃ has been indicated. In dry nitrogen the step corresponding to dehydration is well resolved in the temperature region 145–220° C; the formation of FeO and Fe₃O₄ is also well characterized. In dry dynamic air the reaction further proceeds to the formation of-Fe₂O₃. In dynamic air containing water vapour there are definite indications of the formation of-Fe₂O₃ prior to the formation of-Fe₂O₃. Definite experimental conditions have been determined for the formation of-Fe₂O₃ in dynamic air containing water vapour. The conductivity measurements have been supplemented with infra-red spectroscopy and X-ray diffraction pattern measurements. The electrical conductivity measurements were found to give additional information on the solid-state reaction to that obtained from conventional thermal analytical techniques (such as differential thermal, thermogravimetric and differential thermogravimetric analyses).Fe₂O₃, obtained from the decomposition of FeC₂O₄ · 2H₂O in dynamic air + water was found to have a coercive force of 3.142 A m^–1, a saturation magnetization value of 7.1 T kg^–1 and a ratio of remanence to saturation magnetization of 0.64.     

Characteristics of subcooled water boiling on structured surfaces

Characteristics of the process and heat transfer of subcooled water boiling on mesostructured surfaces obtained by microarc oxidation of titanium foil with formation of a TiO₂ layer and deposition of Al₂O₃ particles from boiling nanofluid have been experimentally investigated. The experiments have been carried out in the forced flow of deaerated water in a vertical rectangular channel, 21 × 5 mm in size. The ranges of regime parameters are as follows: water mass velocity is up to 650 kg/(m2 s), subcooling is 30–75°C, pressure is ~10⁵ Pa, and heat flux rate is 0.7–5.0 MW/m². It is established that the number of active nucleation sites is (70–80) × 105 1/(m² s) at the heat flux of 1.5–2.0 MW/m². Significant subcooling of the liquid and good wettability of the structured surface provide intense deactivation and lead to random spatial distribution of the nucleation sites. The characteristic size of vapor bubbles is about 200–250 μm and the bubble lifetime is 200–500 μs. Application of the coating prepared by microarc oxidation enhances heat transfer by 20–30%. At high subcoolings of liquid, the characteristics of boiling on smooth surfaces and surfaces with the coating were fairly close.     

An International Marine-Atmospheric 222Rn Measurement Intercomparison in Bermuda Part II: Results for the Participating Laboratories

As part of an international measurement intercomparison of instruments used to measure atmospheric ²²²Rn, four participating laboratories made nearly simultaneous measurements of ²²²Rn activity concentration in commonly sampled, ambient air over approximately a 2 week period, and three of these four laboratories participated in the measurement comparison of 14 introduced samples with known, but undisclosed (“blind”) ²²²Rn activity concentration. The exercise was conducted in Bermuda in October 1991. The ²²²Rn activity concentrations in ambient Bermudian air over the course of the intercomparison ranged from a few hundredths of a Bq · m⁻³ to about 2 Bq · m⁻³, while the standardized sample additions covered a range from approximately 2.5 Bq · m⁻³ to 35 Bq · m⁻³. The overall uncertainty in the latter concentrations was in the general range of 10 %, approximating a 3 standard deviation uncertainty interval. The results of the intercomparison indicated that two of the laboratories were within very good agreement with the standard additions, and almost within expected statistical variations. These same two laboratories, however, at lower ambient concentrations, exhibited a systematic difference with an averaged offset of roughly 0.3 Bq · m⁻³. The third laboratory participating in the measurement of standardized sample additions was systematically low by about 65 % to 70 %, with respect to the standard addition which was also confirmed in their ambient air concentration measurements. The fourth laboratory, participating in only the ambient measurement part of the intercomparison, was also systematically low by at least 40 % with respect to the first two laboratories.     

Describing non-Fickian water-vapour sorption in wood

Moisture transport and sorption in wood may not be accurately described by Fick's law of diffusion. The problem of making a model of non-Fickian behaviour (NFB) for wood is discussed. Some measurements in which NFB in wood is clearly seen are also reviewed. Four criteria, which must be satisfied by a model describing sorption in wood cell walls, are presented: (1) the model should not only describe the response to step changes in vapour pressure; (2) it should be able to predict sorption with more than one time scale; (3) the sorption rate should not depend on the thickness of the cell wall; (4) small rapid changes in vapour pressure should give slower fractional weight change than large rapid changes. A review of models of NFB in synthetic polymers indicates that there is presently no model of NFB which fulfills the above criteria. More measurements of the sorption behaviour of the cell wall are needed to construct such a model for wood. This model can then probably be used, together with a Fickian diffusion model, to model the sorption behaviour of whole wood.Nomenclature c concentration in a material kg m^–3 - D _c diffusivity with c as potential m² s^–1 - D _p diffusivity with p as potential kg/(m s Pa) - F flux kgm^–2–1 - p partial vapour pressure Pa - t time s - x distance m