Vacuum Value Research Articles

Aspect ratio optimization of piezoelectric extensional mode resonators for quality factor and phase noise performance enhancement

Abstract This study focuses on optimizing the resonator geometry via the aspect ratio design of a width-extensional mode resonator to improve its quality factor (Q), which is one of the critical performance parameters for resonators in either sensing (Allan deviation) or frequency reference (phase noise) applications. The proposed approach uses finite element analysis to reduce the strain energy at anchor supports by altering the resonator geometric structure, thereby reducing energy loss through anchors. Moreover, process limitations on feature sizes are used as constraints to find aspect ratios that can not only increase the Q but also reduce spurious modes near the targeted frequency. The devices were fabricated using AlN thin film piezoelectric on a substrate (TPoS) process. The simulated energy dissipation trends for specific length-to-width (L/W) ratios closely match the measured changes in the resonator Q values in vacuum. In vacuum, the highest Q-factor achieved by the device is close to 8816, with a motional resistance of a few tens of ohms. Additionally, a board-level oscillator realized using a commercial low-noise amplifier exhibits phase noise performance of −141.21 dBc Hz−1 and −164.25 dBc Hz−1 at 1 kHz and 1 MHz frequency offsets, respectively. The calculated figures of merit for these offsets are 204 and 168, respectively.

Gas‐Phase Anion Photoelectron Spectroscopy of Alkanethiolate‐Protected PtAu12 Superatoms: Charging Energy in Vacuum vs Solution

AbstractThe charging behavior of molecular Au clusters protected by alkanethiolate (SCnH2n+1=SCn) is, under electrochemical conditions, significantly affected by the penetration of solvents and electrolytes into the SCn layer. In this study, we estimated the charging energy EC(n) associated with [PtAu24(SCn)18]−+e−→[PtAu24(SCn)18]2− (n=4, 8, 12, and 16) in vacuum using mass‐selected gas‐phase anion photoelectron spectroscopy of [PtAu24(SCn)18]z (z=−1 and −2). The EC(n) values of PtAu24(SCn)18 in vacuum are significantly larger than those in solution and decrease with n in contrast to the behavior reported for Au25(SCn)18 in solution. The effective relative permittivity (ϵm*) of the SCn layer in vacuum is estimated to be 2.3–2.0 based on the double‐concentric‐capacitor model. Much smaller ϵm* values in vacuum than those in solution are explained by the absence of solvent/electrolyte penetration into the monolayer. The gradual decrease of ϵm* with n is ascribed to the appearance of an exposed surface region due to the bundle formation of long alkyl chains.

Gas-Phase Anion Photoelectron Spectroscopy of Alkanethiolate-Protected PtAu12 Superatoms: Charging Energy in Vacuum vs Solution.

The charging behavior of molecular Au clusters protected by alkanethiolate (SCnH2n+1=SCn) is, under electrochemical conditions, significantly affected by the penetration of solvents and electrolytes into the SCn layer. In this study, we estimated the charging energy EC(n) associated with [PtAu24(SCn)18]-+e-→[PtAu24(SCn)18]2- (n=4, 8, 12, and 16) in vacuum using mass-selected gas-phase anion photoelectron spectroscopy of [PtAu24(SCn)18]z (z=-1 and -2). The EC(n) values of PtAu24(SCn)18 in vacuum are significantly larger than those in solution and decrease with n in contrast to the behavior reported for Au25(SCn)18 in solution. The effective relative permittivity (ϵm*) of the SCn layer in vacuum is estimated to be 2.3-2.0 based on the double-concentric-capacitor model. Much smaller ϵm* values in vacuum than those in solution are explained by the absence of solvent/electrolyte penetration into the monolayer. The gradual decrease of ϵm* with n is ascribed to the appearance of an exposed surface region due to the bundle formation of long alkyl chains.

Analysis of Maintenance Methods and Process Improvement of Vacuum Laser Collimation System for Dams

The method and process of vacuum laser collimation system maintenance is one of the key technologies directly related to the accuracy of dam vacuum laser collimation system measurement value. Taking the maintenance methods and processes of vacuum laser collimation system in Lianlu and Xiacheng as the background, a new set of dam vacuum laser collimation system maintenance methods and processes are proposed, aiming to make up for the gaps in the maintenance of vacuum laser collimation system. It was found that the vacuum pipeline operates at vacuum values between 400 Pa and 900 Pa. The influence of light on the vacuum laser is avoided by correcting the system and shading the transmitting end as well as the connecting part of the receiving end and the vacuum pipeline with a rubber sheet. This new maintenance method and process also provides a useful reference for the safety monitoring of similar projects.

Exploring CP violation beyond the Standard Model and the PQ quality with electric dipole moments

In some models of physics beyond the Standard Model (SM), one of the leading low energy consequences of the model appears in the form of the chromo-electric dipole moments (CEDMs) of the gluons and light quarks. We examine if these CEDMs can be distinguished from the QCD θ-term through the experimentally measurable nuclear and atomic electric dipole moments (EDMs) in both cases with and without the Peccei-Quinn (PQ) mechanism solving the strong CP problem. We find that the nucleon EDMs show a distinctive pattern when the EDMs are dominantly induced by the light quark CEDMs without the PQ mechanism. In the presence of the PQ mechanism, the QCD θ-parameter corresponds to the vacuum value of the axion field, which might be induced either by CEDMs or by UV-originated PQ breaking other than the QCD anomaly, for instance the PQ breaking by quantum gravity effects. We find that in case with the PQ mechanism the nucleon EDMs have a similar pattern regardless of what is the dominant source of EDMs among the CEDMs and θ-term, unless there is a significant cancellation between the contributions from different sources. In contrast, some nuclei or atomic EDMs can have characteristic patterns significantly depending on the dominant source of EDMs, which may allow identifying the dominant source among the CEDMs and θ-term. Yet, discriminating the gluon CEDM from the QCD θ-parameter necessitates additional knowledge of low energy parameters induced by the gluon CEDM, which is not available at the moment. Our results imply that EDMs can reveal unambiguous sign of CEDMs while identifying the origin of the axion vacuum value, however it requires further knowledge of low energy parameters induced by the gluon CEDM.

The spatiotemporal distribution characteristics analysis and suppression of the axial tip clearance leakage flow for the liquid-ring vacuum pump

The clearance leakage flow of liquid-ring pump has complex spatiotemporal distribution characteristics, and it has severe negative impact on its performance. In order to suppress the axial blade tip leakage flow of liquid-ring pump, the spatiotemporal distribution characteristics of leakage flow was analyzed in detail by numerical simulation method. The composite tip of winglet and squealer was introduced to the liquid-ring pump, and its suppression mechanism was analyzed. The RNG k-ε turbulence model and VOF multiphase flow model were selected to simulate transient flow in liquid-ring pump. The results show that the leakage flow in the suction zone gradually decreases from hub to rim, and the leakage flow intensity gradually increases along the rotation direction of the impeller. The gas leakage velocity of compression zone is the highest, and the leakage flow intensity gradually increases along the rotation direction of the impeller. In the exhaust zone, the reverse leakage flow forms near the hub, which flows from the clearance suction side to the pressure side, and the leakage flow intensity gradually decreases from the hub to the rim. Near the rim, the leakage flow direction changes, flowing from pressure side to suction side. In the transition zone, as the impeller flow passage approaching suction zone gradually, the pressure decreases continuously. The pressure on the clearance suction side is greater than that of the pressure side, and the reverse leakage flow forms near the hub. The composite tip blade of winglet and squealer not only lengthens the clearance channel but also blocks the clearance by the pressure side squealer corner vortex and the squealer vortex, thus the leakage flow was effectively suppressed. To some extend the composite tip can suppress the leakage flow, the vacuum values are improved by 3.5%, 3.9%, and 5.3% under different conditions respectively.

Modelling Annihilation Properties of Positronium Confined in Nanoporous Materials: A Review.

Positronium (Ps) is a valuable probe to investigate nanometric or sub-nanometric cavities in non-metallic materials, where Ps can be confined. Accessible experimental measurements concern the lifetime of trapped Ps, which is largely influenced by pick-off processes, depending on the size of the cavity as well as on the density of the electrons belonging to the surface of the host trap. Another relevant physical quantity is the contact density, that is the electron density at the positron position, which is usually found to be well below the vacuum value. Here, we review the principal models that have been formulated to account and explain for these physical properties of confined Ps. Starting with models, treating Ps as a single particle formulated essentially to study pick-off, we go on to describe more refined two-particle models because a two-body model is the simplest approach able to describe any change in the contact density, observed in many materials. Finally, we consider a theory of Ps annihilation in nanometric voids in which the exchange correlations between the electron of Ps and the outer electrons play a fundamental role. This theory is not usually taken into account in the literature, but it has to be considered for a correct theory of pick-off annihilation processes.

Productivity, selectivity, and energy consumption of pilot-scale vacuum assisted air-gap membrane distillation for the desalination of high-salinity streams

The implementation of air gap membrane distillation systems is limited by a lack of overall performance predictions which rely on few available pilot-scale studies. This study evaluates the productivity, energy consumption, and selectivity of a pilot-scale air gap membrane distillation system by combining experiments and modeling activities. The effect of operating conditions, i.e., applied vacuum, feed flow rate, and feed stream salinity, was investigated to identify regulating factors and quantify dependencies. Response surface methodology was applied to model the phenomena and provide statistical analysis. Increasing flow rates produced a near linear increase of productivity within the investigated range. Operating at higher applied vacuum also translated into enhanced productivity, though the distillate flux increased by a maximum of 10 % when vacuum increased from −100 mbar to −500 mbar. Flow rate and vacuum also governed the observed salt flux by a similar magnitude because salt flux resulted mainly from liquid pore flow phenomena. The trans-membrane pressure regulated the membrane rejection: increasing the pressure difference led to a lower rejection. Moreover, high feed stream salinity lowered both the productivity and the distillate quality. The productivity gains were typically achieved at the expense of an increase in specific thermal energy consumption; however, an interesting relation was observed with feed stream salinity, with a minimum of specific thermal energy consumption of roughly 300kWhth⋅m−3 identified in the treatment of a stream with a salinity of 150g/L.

Investigation of Light Baryons in Hot QCD

We investigate the behavior of light baryons in hot QCD. To this aim, we evaluate the light baryons mass and residue in hot medium using the thermal correlation function with two-point by means of the thermal QCD sum rule. In sum rule calculations, we consider the additional thermal condensates appearing in Wilson expansion at T≠0. We determine the thermal continuum threshold using obtained sum rules expressions to analyze numerically. We observe that the masses and residues of light baryons stay approximately the same until the temperature reaches a certain value and then they fall with the temperature increase. We see that vacuum values of parameters in our calculations are in good consistency with other studies in the literature. Also, we define the fit functions that show how the spectroscopic parameters for light baryons behave at T≠0.

(First Best Paper Award) Vacuum Quality Impact on Covalent Bonding

As already described in the literature [1, 2, 3, 4], covalent bonding is based on direct bonding process. The first step of this process consists in creating dangling bonds at the wafer surface using an Ar+ ion bombardment. Then, the two activated surfaces are brought in contact, resulting in covalent bonds between them. Using silicon surfaces, no further annealing is required to enhance the bonding strength, as opposed to direct hydrophilic bonding. The adherence energy (Gc=2γc) of such Si/Si bond pairs reaches the silicon fracture energy (5J/m²). Indeed, all bonded samples break during double cantilever beam (DCB) measurements of it.Dangling bonds are highly reactive. Queue time between activation and bonding is crucial, as dangling bonds must be preserved. One way, commonly used, is to process activated materials while always staying under Ultra High Vacuum (UHV). Indeed, reactive dangling bonds should not get in contact with others reactive molecules, like H2O, O2 or N2, for instance. However, some molecules always remain, for any given vacuum value. Depending on their nature, the UHV quality for bonding purpose is affected. This paper aims at studying the impact of the UHV quality on the dangling bonds stability and bonding quality.In order to study the UHV quality, a mass spectrometer has been installed inside the bonding chamber. It has been shown that among all the reactive potential molecules, water is the most harmful one. Indeed, its removal enhances the vacuum quality. Baking vacuum systems is a well-known technic to remove adsorbed water molecules from metallic surfaces [5]. Although background water concentration in UHV is hardly detectable at room temperature, tracking its partial pressure during bakeout cycles enables to define a water threshold. Indeed, during a bakeout cycle, a water concentration peak is clearly seen by the mass spectrometer, as shown in figure 1. The impact of several system bakeouts at 100°C was also evaluated. After each bakeout, a Si/Si bonding energy was measured. After the first bakeout, the adherence energy was only around 2.5J/m². However, after the second bakeout, it reached the silicon fracture energy of 5J/m². More bakeout cycles were also tested. Adherence energy results will be discussed as well as partial pressures of other reactive molecules.The impact of queue times between wafer surfaces activations and bonding was also studied. For a standard process, this waiting time represents the handling time to activate both substrates (in a system having only one activation chamber), and to move them from the activation chamber to the bond chamber. We showed that the impact of queue time depended on the number of bakeout cycles and that the adherence energy decreasing rate was strongly affected by the UHV quality. With our best tool conditioning, an adherence energy higher than 3,4J/m² can be maintained up to 5mn added to the minimum queue time.Thanks to our EVG®Combond® system, covalent bonding in temperature can be performed using heated electrostatic chucks (ESC)[6]. However, even after two or more system bakeouts, 200°C covalent bonding failed to exhibit high adherence energy and it was not possible to reach the silicon fracture energy. Tracking the pressure level inside the bonding chamber during a high temperature bakeout of the ESC (>300°C) showed that water still desorbed during this process. Optimized tool preconditioning thus have to be implemented for such specific hot bonding, with a need for global baking (even of internal chamber pieces).In conclusion, we will describe the experimental setup and the impact of tool preconditioning (i.e. bakeout sequences) on manufacturing. Mass spectrometers and bond strength measurements will be presented, as well as curves of bond strength against the waiting time between the activation and the bonding, for bond pairs processed at room temperature or higher (200°C). Suga T, Takahashi Y. STRUCTURE OF A1-A1 A N D A1-Si3N4 INTERFACES BONDED AT ROOM TEMPERATURE BY MEANS OF THE SURFACE ACTIVATION METHOD. :5.Takagi H, Kikuchi K, Maeda R, Chung TR, Suga T. Surface activated bonding of silicon wafers at room temperature. Appl Phys Lett. 15 avr 1996;68(16):2222-4.Taniyama S, Wang YH, Fujino M, Suga T. Room temperature wafer bonding using surface activated bonding method. In: 2008 IEEE 9th VLSI Packaging Workshop of Japan. 2008. p. 141-4.Flötgen C, Razek N, Dragoi V, Wimplinger M. Novel Surface Preparation Methods for Covalent and Conductive Bonded Interfaces Fabrication. ECS Trans. 14 août 2014;64(5):103.Berman A. Water vapor in vacuum systems. Vacuum. avr 1996;47(4):327-32.Lomonaco Q, et al. Stress Engineering in Germanium-Silicon Heterostructure Using Surface Activated Hot Bonding. ECS Trans. 30 sept 2022;109(4):277-87. Figure 1

Mass Generation via the Phase Transition of the Higgs Field

The commonly quoted bistable Higgs potential is not a proper description of the Higgs field because, among other technical reasons, one of its stable states acquires a negative expectation value in vacuum. We rely on formal catastrophe theory to derive the form of the Higgs potential that admits only one positive mean value in vacuum. No symmetry is broken during the ensuing phase transition that assigns mass to the Higgs field; only gauge redundancy is “broken” by the appearance of phase in the massive state, but this redundancy is not a true symmetry of the massless field. Furthermore, a secondary, certainly amusing conclusion, is that, in its high-energy state, the field oscillates about its potential minimum between positive and negative masses, but it is doubtful that such evanescent states can survive below the critical temperature of 159.5 GeV, where the known particles were actually created.

Experimental study on internal explosion of thermobaric explosives containing metastable intermolecular composite (MIC) materials

In order to study the influence of metastable intermolecular composite (MIC) materials on the internal implosion properties of thermobaric explosive, the calorimetric bomb and closed chamber were used to measure the detonation heat, quasi-static pressure and energy impulse of five explosive formulations containing different MIC materials. Compared with the traditional aluminized warm compressed explosives, the energy release characteristics and output characteristics were analyzed. The results show that the explosive formula containing MIC material has lower detonation heat value in air and vacuum than that containing traditional Al powder; The quasi-static pressure and energy impulse of the former are higher than those of the latter, indicating that MIC materials can improve the output energy of thermobaric explosives. The results can be used to guide the formulation design of thermobaric explosives.

Chiral symmetry restoration at high matter density observed in pionic atoms

According to quantum chromodynamics, vacuum is not an empty space, because it is filled with quark–antiquark pairs. The pair has the same quantum numbers as the vacuum and forms a condensate because the strong interaction of the quantum chromodynamics is too strong to leave the vacuum empty. This quark–antiquark condensation, the chiral condensate, breaks the chiral symmetry of the vacuum. The expectation value of the chiral condensate is an order parameter of the chiral symmetry, which is expected to decrease at high temperatures or high matter densities where the chiral symmetry is partially restored. Head-on collisions of nuclei at ultra-relativistic energies have explored the high-temperature regime, but experiments at high densities are rare. Here we measure the spectrum of pionic 121Sn atoms and study the interaction between the pion and the nucleus. We find that the expectation value of the chiral condensate is reduced at finite density compared to the value in vacuum. The reduction is linearly extrapolated to the nuclear saturation density and indicates that the chiral symmetry is partially restored due to the extremely high density of the nucleus. In quantum chromodynamics, the condensation of quark–antiquark pairs breaks the chiral symmetry of vacuum. Experiments with pionic tin atoms demonstrate that the symmetry is partially restored at high densities.

Parametric resonance in neutrino oscillations induced by ultra-light dark matter and implications for KamLAND and JUNO

If Ultra-light dark matter (ULDM) exists and couples to neutrinos, the neutrino oscillation probability might be significantly altered by a parametric resonance. This resonance can occur if the typical frequency of neutrino flavor-oscillations ∆m2/(2E), where ∆m2 is the mass-squared difference of the neutrinos and E is the neutrino energy, matches the oscillation frequency of the ULDM field, determined by its mass, mϕ. The resonance could lead to observable effects even if the ULDM coupling is very small, and even if its typical oscillation period, given by τϕ = 2π/mϕ, is much shorter than the experimental temporal resolution. Defining a small parameter ϵϕ to be the ratio between the contribution of the ULDM field to the neutrino mass and the vacuum value of the neutrino mass, the impact of the resonance is particularly significant if ϵϕmϕL ≳ 4, where L is the distance between the neutrino source and the detector. An outlier in the data collected by the KamLAND experiment which, until now, has been assumed to constitute a statistical fluctuation, or associated with the binning, can actually be explained by such narrow parametric resonance, without affecting the measurements of other current neutrino oscillation experiments. This scenario will be tested by the JUNO experiment.

ВАКУУМНЫЕ ТЕХНОЛОГИИ ПРОИЗВОДСТВА ПОРОШКОВ И ЭКСТРАКТОВ ИЗ ОВОЩЕЙ, ПЛОДОВ И ЯГОД ДЛЯ ФУНКЦИОНАЛЬНЫХ ПРОДУКТОВ ПИТАНИЯ

The development of technologies and equipment for obtaining food products with the addition of functional biologically active substances from vegetables, fruits, berries in the form of powders and extracts is promising. The technologies of vegetable processing of raw materials: cleaning, cutting, drying, grinding, extraction are analyzed. The scheme of the technological processing line for the production of plant powders and extracts is given, which provides for the use of production waste as animal feed. It was revealed that the finished product in the form of dried material (chips) can be obtained at the drying stage, and the remaining distillate is collected after extraction. As an example of the results obtained empirically, the drying curve of the cauliflower "Françoise" and the curves of the extraction of strawberries "Moroshko" are considered. Experimental studies of the drying process were carried out on the developed two-stage convective vacuum impulse drying plant, consisting of a convective fluidized bed dryer and a vacuum cabinet. The universal vacuum-pulse extraction-evaporator is designed for the study of extraction. A comparison of different extraction options was carried out: infusion, heating, heating with stirring and extraction using vacuum. It has been established that vacuum extraction gives the highest yield of dry soluble substances. The main element of the described installations is a liquid ring vacuum pump. Depending on the required vacuum value, it can be singlestage or two-stage. Its use provides sparing temperature conditions, excluding the loss of biologically active substances, and also helps to reduce the time spent on processes.

Determination of heat transfer mechanisms during vacuum drying of solid-moist and liquid-viscous materials

Most drying methods combine convective, conductive and radiation heat transfer processes. The share of each type of heat transfer may vary depending on the type and mode of drying, type of product, etc. In this study, the problem of determining the heat transfer mechanism of vacuum drying of solid-moist and liquid-viscous materials is solved. The objects of the study are Jerusalem artichoke tubers, camel and mare milk. The numerical values of the heat transfer components are found experimentally and their shares in the total heat flux are determined. During vacuum drying of Jerusalem artichoke at a medium pressure of 4 kPa and a temperature of 55 °C (with a layer height of 0.01 and 0.02 m), the convective component predominates (58.55 and 67.65 %). The share of thermal conduction (18.96 and 29.39 %) and radiation (13.39 and 12.05 %) is much lower. The mechanism of thermal conduction begins to prevail with an increase in the height of the material layer (0.03 and 0.04 m). The convective component is also dominant for vacuum drying of milk: at medium pressures of 6÷10 kPa and a temperature of 40 °C, its value for mare milk reaches 78.21 %, for camel milk – 73.33 %. The second most important is the share of radiation (19.45 and 22.58 %). Conductive heat transfer has the minimum indicators (5.66 and 6.17 %). The large values of the share of thermal conduction during drying of Jerusalem artichoke compared to milk are explained by the fact that heat transfer occurs inside the tubers due to conduction, and inside milk – due to convection. Insignificant shares of radiation are explained by low and medium vacuum values in the chamber. In the studied range, heat and mass transfer occurs due to molecular diffusion and convection. The results obtained can be used to formulate criterion heat transfer equations, in engineering calculations, and optimization of the vacuum dryer operation.

Development of Vacuum Tube Well Dewatering Test Device and Study on Vacuum Degree Transfer Law

Vacuum tube well dewatering technology has gradually become an effective means to deal with low-permeability soil groundwater. The vacuum degree transfer law is an important element in the study of the mechanism of deep foundation pit vacuum tube well dewatering. To further study the transfer law of vacuum degree in vacuum tube well dewatering, a laboratory test setup for vacuum tube well dewatering was developed, and vacuum tube well dewatering tests were conducted under various in-well vacuum values, tube diameter, depth of tube well, and other factors. The variation law of vacuum degree under various working condition coupling was thoroughly analyzed in this research. The results show that with the increase of vacuum value in the well, the radial vacuum degree and vertical vacuum degree have about 14.9~47.7% and 14.9~32.4% increase, respectively, and transmission attenuation of radial vacuum degree, transmission attenuation of vertical vacuum degree, and the range of the vacuum field all increase to some extent. With the outward transmission of the vacuum degree, the transmission attenuation of the radial vacuum degree decreases rapidly and then tends to be stable, and the transmission attenuation of the vertical vacuum degree decreases gradually. The radial vacuum degree, the transmission attenuation of the radial vacuum degree, and the range of the radial vacuum field are not affected by the buried depth of the tube well. The study’s conclusions can serve as a foundation and point of reference for projects involving the design and implementation of deep foundation pit vacuum tube well dewatering.

Triangle singularities waning in Heavy Ion Collisions: the case of [formula omitted

We have recently observed that hadron triangle singularities, that can mock new exotic hadrons, can be significanttly suppressed in relativistic heavy ion collisions, provided two conditions are met: these are, first, that the fireball lives long enough so that the triangle process has enough time to complete in the Norton-Coleman classical sense, and second, that the mass and/or width of the particles in the triangle diagram are sufficiently modified from their vacuum values. Here we add a very interesting example to the canon, which is Y(4260)→D1D→πD⁎D→π+J/ψπ. This reaction has been proposed as a mechanism to explain the appearance of Zc(3900) in the J/ψπ spectrum. If the two muons and two pions reconstructing the initial-state Y can be isolated from the combinatorial background, then the mechanism can provide a spectroscopy test: presence of Y(4260) but absence of Zc(3900) would be more indicative of such triangle mechanism, while presence of both would rather point out to Zc being an exotic hadron.

Effect of Expanded Perlite in the Brick Mixture on the Physicochemical and Thermal Properties of the Final Products

Thermal insulation is an efficient solution to reduce energy consumption. A great way to reduce the energy consumption of a building is the use of thermal insulation bricks which provide fire resistance and a remarkable thermal capacity, which make them a unique building material for energy efficient buildings. In this study, a fine grain size of expanded perlite was used as additive in a ceramic mass. Brick solid samples were produced from three different mixtures with different ratios of expanded perlite in the mass. From every mixture, three different vacuum values were used. The constructed brick samples were dried and fired in the same conditions and their properties such as bending strength, density and thermal insulation were gathered for six different peak temperatures. The thermal insulation coefficient of every constructed mixture was calculated according to EN1745. It was found that the addition of perlite when keeping the other parameters constant led to decreases in products’ density by 2.9% up to 7.1% and in the thermal conductivity coefficient by 5.4% up to 9.5%, confirming that expanded perlite is a very good porogen material. The bending strength also decreased by 18% up to 28%, but in all cases, it remained well above the minimum accepted value of 100 kp/cm2. The vacuum employed during extrusion proved an important parameter affecting the results; however, its effect proved less significant as the perlite percentage in the mixture increased.

Adhesion of lunar simulant dust to materials under simulated lunar environment conditions

A test stand was designed to semi quantitively measure the adhesion of JSC-1/1A lunar simulant dust to materials proposed for use in the lunar surface environment. Sieved simulant <45 μm in diameter was uniformly deposited on sample surfaces. Dust adhesion was indicated as the centrifugal force created from rotation of the test stand to shed dust under high vacuum and UV exposure conditions The device generated a maximum centripetal force greater than 400 g's. Dust adhesion on aluminum, anodized aluminum, Ortho fabric and Z93P painted aluminum was observed and analyzed over a 12 step, increasing acceleration profile. At each rotation cycle, dust coverage was recorded using a camera and changes in the coverage were analyzed in post-processing to provide an indication of the adhesive force dust particles would have to overcome to be removed from the surface. Results showed that all material coverage amounts exhibited a similar shedding profile with individual plateaus occurring below 30 μm depending on material. Bare and anodized aluminum had higher adhesion values in vacuum than did the samples exposed to UV at high centripetal acceleration levels. The Z93P painted aluminum and Ortho fabric indicated the opposite, whereby UV exposed samples retained more dust at higher acceleration levels and thereby larger dust particles likely adhered to the surfaces. Ultimately, this testing indicates that the apparatus provides acceptable control and conditions to assess dust adhesion of lunar simulants. Increased precision can be attained by changes in lighting, camera orientation and clarity, and sample dust application.