Thermal Vacuum Research Articles

Temperature transition optimization in cryogenic systems: Application to liquid nitrogen expenditure reduction in a thermal vacuum chamber case study

This paper presents outcomes regarding liquid nitrogen consumption reduction in a thermal vacuum chamber, with the motivation of lessening operational costs during space equipment testing. The article briefly outlines the optimal control application to thermal and cryogenic-related control systems based on a gas cycle, and assesses liquid nitrogen savings opportunities for a chamber including six shrouds with independent temperature requirements. In this case study, optimization of temperature transition profiles and a proposed modification in the control setup yielded potential savings from 14.1% to 20.4% in the examined experimental transitions.

Optical Properties of CuCdS Thin Film Prepared by Vacuum Thermal Evaporation Technique

This study reports on the synthesis and characterizations of copper cadmium sulfide (CuCdS) thin films prepared using the vacuum thermal evaporation technique with copper sulfide and CdS as precursors in a 1:1 molar ratio. The structural properties of the thin films were analyzed using X-ray diffraction (XRD) which revealed that the main composition of the thin film was CdS with the preferred orientation of the (101) plane. The optical properties were examined using UV–Vis spectrophotometry. The photosensitivity of the films was determined using I–V measurements performed with a two-probe technique. The prepared CuCdS thin films have high optical transmittance of 92%.

Freeze Frame Reflow to Enhance Yields for Advanced Low-Profile Bottom Terminated Packages

Today, designers are demanding an overall form-factor reduction to save board space, increase functionality, and allocate more circuit board real estate toward end-user applications – all with less space allocated to power management where not just the X-Y shrink but the 3D volumetric shrink is required. Unlike most gull wing style leaded packages, QFNs (Quad Flat Pack No lead packages) also known as BTCs (Bottom Terminated Components) have coplanar terminals below the package body to answer this ever-decreasing form-factor requirement. The final standoff in these QFN style packages are dictated by the solder joint geometry formed. Within this advanced package family also finding a similar trend are power WCSPs (Wafer Chip Scale Packages) where traditional solder spheres are being replaced with low profile interconnects in expanded and asymmetrical geometries. This paper presents factors that influence advanced low standoff package solderability performance with the use of video microscopy and live in situ X-ray reflow. To reflect the QFN board assemblies that are typically designed a series of layouts were implemented across different coupon test boards. Assembled coupon test board were designed by varying 1) through hole via design, 2) solder mask tenting techniques, 3) periphery and center thermal pad printed solder joint volumes, 4) no-clean and water-soluble solder paste flux chemistry all using SAC 305 alloy and type 4.5 powder size. One case study using live in-situ X-ray system will explain the effects of a QFN land pattern layout incorporating vias in the center thermal pad with solder mask tenting over the via openings located on the back of the PCB. In another configuration vias were removed from the center thermal pad and vacuum reflow performed during the liquidus phase of the solder with an explanation of why some of the voids remained. The first and second order results presented within this paper have practical implications and from their observations a novel process evaluation technique coined as Freeze Frame Reflow (FFR) was developed. In the last case study presented, an advanced mrQFN (multi-row QFN) package is investigated for factors affecting yields. FFR is then implemented resulting in an increase in yield further demonstrating the benefits this new & novel technique can offer.

Automated control of thermal vacuum impregnation and swelling of oil- and gasoline-resistant elastomers

Polymeric materials used in the rolling stock are currently subject to increased requirements for durability. We present a method for accelerated and automated rapid analysis of the impregnation of polymeric materials used in various aggressive environments to determine their service life as sealing products. The results of studying changes in the physical and mechanical properties of samples are given on the example of elastomeric materials used as separating and sealing materials made of oil- and petrol resistant rubber MBS-S. Hydrocarbons based on mineral oil products with different viscosity coefficients were used as working media. It is shown that the time of impregnation of the MBS-S polymer, spent on testing according to the standard method, exceeds more than 10 times the standard terms rated for repair and maintenance. Tests using the developed express filling unit showed a reduction of the impregnation time to a level acceptable in production. The derived mathematical dependences for the process of filling MBS-S oil and petrol resistant rubber with a standard working fluid and automation of filling control make it possible to predict changes in the resistance of polymeric materials. The results obtained can be used in developing database of the swelling dynamics for various materials and predicting the service life of polymers in an aggressive environment of various etiology.

Analysis of the thermal design of a COTS-based modular battery system for satellites by thermal vacuum testing

The qualification of components for satellite applications is a costly process due to the extreme conditions that must be endured in space. Therefore, space market access of battery technology innovations is often inhibited. However, modern battery technologies offer great advantages for satellite applications. In this work, a commercial off-the-shelf (COTS) based and modular lithium-ion battery system for satellites in Low Earth Orbit (LEO) is presented. A comparative analysis to evaluate system parameters and functionality of the proposed battery system and literature data is performed. A thermal vacuum test campaign is carried out to investigate the behaviour under LEO relevant conditions and to achieve qualification of the system performance according to the ECSS (European Cooperation for Space Standardization) standard. The tested system consists of two modules with 28 V nominal voltage and eight battery cells each. Experiments were conducted inside a vacuum chamber. The battery system was charged and discharged in temperatures from 0 °C to 45 °C in a high-vacuum for three weeks. The influence of the battery management electronics, the behaviour of the cells and the heating were analyzed. The cell temperatures stayed in the operating limit during 3.5 A and 10 A cycling. The battery system, however, exceeded the cell’s upper operating limit with a 40 °C baseplate and 3.5 A charging. Despite the dense system architecture with electronics between the cells the battery system can safely deliver power in a broad temperature range. Further investigations regarding safety and failure modes are necessary, along with advancements on software and state estimation algorithms.

Photoluminescence of Cesium-Doped Sodium Iodide Films Irradiated by UV LED.

Alkali metal halides have long been used as scintillators for applications as sensors and detectors. Usually, a small amount of impurities are added to these inorganic materials to improve their luminescence efficiencies. We investigate the structures and luminescent properties of un-doped sodium iodide (NaI) and cesium-doped NaI (NaI:Cs) films deposited by thermal vacuum evaporation. Instead of using the toxic element thallium (Tl), we introduced cesium dopant into NaI. This is the first study for the NaI:Cs film excited by UV LED's ultraviolet C (273 nm, 4.54 eV). The luminescence spectra show two main peaks at 3.05 and 4.32/3.955 eV (for fused silica/B270 substrate), originating from the intrinsic defects and/or activator excited states and the intrinsic self-trapped excitons (STEs), respectively. In general, both Cs-doping and post-annealing processes enhance the luminescence performance of NaI films.

Efficiency amplified: Enhancing energy performance in biodiesel vacuum thermal water removal system

Thermal vacuum is a common method for removing water from biodiesel, where water content is one of the biggest challenges in the implementation of biodiesel as a fuel. This process has been confirmed through performance testing in this study and has successfully reduced the water content of biodiesel by 65.8 %. There is potential to improve the energy performance of this process by using heat exchangers. Accordingly, this study presents both experimental and economic evaluations to find the efficacy of shell-tube heat exchangers and plate heat exchangers in biodiesel vacuum thermal water removal system. The heat exchangers were designed with a capacity of 300 L/hour to facilitate the heat transfer between a 35 °C and a 105 °C fluids. This experiment included performance tests analyzed by the effectiveness-Number of Transfer Units (Ɛ-NTU) method and economic analysis. The shell-tube heat exchangers employed 189 tubes and three shells with a total heat transfer area of 18.5 m2, whereas the plate heat exchangers consisted of two U-type units with a total heat transfer area of 4.41 m2. The effectiveness and NTU provided by plate heat exchangers are 86.33 % and 6.02, while by shell-tube heat exchangers are 70.64 % and 2,81 respectively. From the economic analysis, plate heat exchangers and shell-tube heat exchangers were able to reduce annual process costs by IDR 76,818,565 and IDR 76,818,565 respectively. These findings indicate that implementing plate heat exchangers in the biodiesel vacuum thermal water removal system is more advantageous than utilizing shell-tube heat exchangers.

Standard diesel production from mixed waste plastics through thermal pyrolysis and vacuum distillation

Plastic pyrolysis oil (PPO) was produced in a pilot-scale batch pyrolysis reactor at 540 °C from mixed waste plastic (MWP) (high-density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS)). The produced PPO was then distilled in a vacuum distillation unit and diesel was obtained at temperatures between 170 and 380 °C along with light petrol (<170 °C) and heavy residue (>380 °C). This study found that MWP can produce over 80% liquid oils without operational problems or wax formation. Distilled PPO produces 49.5–53% diesel, 39 – 46.5% petrol and residue 1.5 – 8% by weight. Although PPO has calorific value ranging from 43.85 to 45.26 MJ/kg like commercial diesel however, PPO is not suitable for direct use in diesel engine for low kinematic viscosity (KV) and density values at 1.1–1.26 mm2/s and 0.78 – 0.83 gm/cm3 respectively. For the distilled diesel cut (DC), KV, density, higher heating value (HHV), cetane index (CI), aromatic hydrocarbon (AH) and poli-aromatic hydrocarbon (PAH) were found 1.95–2.15 mm2/s, 0.81 – 0.85 gm/cm3, 44.92–46.36 MJ/kg, 46 – 58, 18.81 – 35.1% and 4.81 – 11.9% respectively indicating better option for direct use as automobile diesel with significant effect of HDPE amount present in feedstock.

Thermal vacuum evaporation peculiarities of perovskite-type barium-strontium hafnate

Experimental results are presented on the thermal vacuum evaporation of barium hafnate BaHfO3 and double barium-strontium hafnate Ba0.5Sr0.5HfO3, which are included together with finely dispersed tungsten as components in sintered composites. It is found that at T = 1900 K only barium and barium oxide are the products of BaHfO3 evaporation, i.e., congruent evaporation of BaHfO3 does not occur. Investigations of Ba0.5Sr0.5HfO3 evaporation at T = 1600 K showed that it also does not evaporate congruently. At the same time, the nucleation of a new phase of BaO·SrO in the form of structures with D6 symmetry was detected. Using a high-current vacuum arc discharge, congruent evaporation of Ba0.5Sr0.5HfO3 takes place, forming various crystalline formations of double barium-strontium hafnate on the substrate.

In-situ oxygen extraction from TiO2 using laser thermal vacuum metallurgy

One of the greatest challenges for long-term human activities on the Moon is the development of in-situ resource utilization (ISRU) technologies, including in-situ oxygen extraction. In this study, a novel method called laser thermal vacuum metallurgy (LTVM) was proposed for oxygen extraction from lunar regolith, specifically using TiO2 as raw material. Firstly, the theoretical feasibility of oxygen production from TiO2 was elucidated through thermodynamic calculations. Subsequently, the impact of laser power density on the decomposition behavior of TiO2 was investigated. The results demonstrate that through the augmentation of laser power density to elevate temperatures, there is a substantial enhancement observed in both the pyrolysis and vaporization processes of TiO2. Under the conditions of a laser power density of 2.48 kW/cm2, the surface temperature of TiO2 can be maintained at approximately 2175 °C. The resulting pyrolysis products consist of Ti6O11 (8.2 ± 0.5 wt %), Ti5O9 (23.7 ± 0.6 wt %), Ti4O7 (10.9 ± 0.4 wt %), and Ti3O5 (57.2 ± 0.8 wt %). Further combining with the result of gas collection, the estimated oxygen extraction rate is approximately 43.3 L per kilogram of TiO2. Therefore, LTVM holds the potential to provide a new approach for in-situ oxygen extraction from titanium-containing lunar regolith on the Moon.

Selective Surface Treatment Using Atmospheric Ar Plasma Jet for Aluminum‐doped Zinc Oxide Based Transparent and Flexible Electronics

AbstractTransparent and flexible electronics are emerging technologies with the potential to enable new applications. However, to ensure high‐performance transparent electronics, post‐processing such as thermal annealing and vacuum plasma treatment is necessary, which are difficult to apply to polymer‐based flexible substrates. This study analyzed the feasibility of applying selective Ar plasma jet treatment at atmospheric pressure to transparent flexible electronics. When atmospheric Ar plasma treatment is applied to transparent flexible aluminum‐doped zinc oxide (AZO), it showed a maximum 83.1% improvement in sheet resistance while maintaining a high transmittance performance, of over 70%. To verify the mechanism behind the surface treatment effect using atmospheric Ar plasma, comprehensive analyses are performed using atomic force microscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy, which confirmed that the effect is due to oxygen vacancy formation caused by ion bombardment and thermal diffusion. The application of atmospheric plasma treatment to a patterned transparent flexible AZO device resulted in a reduction in contact resistance, and it is confirmed that the performance improvement effects can be retained for &gt;500 h by applying additional passivation.

Multifidelity Framework for Small Satellite Thermal Analysis

Anomalies, unexpected events, and model inaccuracies have detrimental effects on satellite operations. High-fidelity models are required, but these models quickly become large and expensive. Cheap or low-fidelity models speed up computation but lack accuracy. To compromise these requirements, this study proposes a multifidelity framework based on cokriging. The proposed multifidelity framework is compared against three other standard methods often used in satellite simulations: a standalone gated recurrent unit, Gaussian process regression, and the autoregressive integrated moving average with explanatory variables model. The robustness of high-fidelity data point placement is also examined. Moreover, the real-time aspect of the simulation is considered by applying the sliding window technique. This multifidelity framework is demonstrated using temperature data obtained from thermal vacuum testing of Small Demonstration Satellite 4: a 50-kg-class satellite. The multifidelity framework provided higher accuracy and robustness than the other methods, however, having a higher computational cost as compared to a purely low-fidelity model. Up to 92% reduction of the error was achieved by the proposed framework.

High Vacuum Capable Fused Filament Fabrication 3D Printer, Part I: Low-Temperature Polymers and Early Lessons Learned

On-orbit manufacturing and assembly have become major research and development topics for government and commercial entities seeking the capability to build very large structures in space. Additive manufacturing is well suited to this paradigm since the process is highly automated, produces little material waste, and allows for a large degree of geometric freedom. This paper presents a design for a 3D printer that operates in high vacuum. The vacuum 3D printer has completed multiple thermal vacuum test campaigns, with dozens of parts printed to date using low-temperature thermoplastics. Testing of material coupons shows that samples printed in vacuum have strength properties generally within a standard deviation of samples printed at ambient pressure. The overall results from multiple successful tests of the vacuum 3D printer promote the feasibility of on-orbit additive manufacturing while exposed to the space environment. This paper is part one of a two-part series. Part I presents the results using a low-temperature hotend capable of printing hobby-grade materials and documents some initial findings and lessons learned for applying FFF in vacuum. Part II presents the results for a high-temperature hotend capable of printing engineering grade plastics that are suitable for on-orbit manufacturing. The combined results of the two papers in this series can be used to inform future on-orbit additive manufacturing applications as well as potential uses on future moon missions.

Temperature Dependence of 3С-SiC Growth During Rapid Vacuum Thermal Silicon Treatment

The paper presents the results of a study of the structure, phase composition, and growth kinetics of silicon carbide epitaxial layers on silicon substrates during their rapid vacuum thermal treatment. Transmission electron microscopy revealed the formation of layers of the cubic polytype SiC (3C-SiC) on silicon during carbidization in the temperature range of 1000–1300 °C. It was found that the formation of SiC layers proceeds in two stages, characterized by different activation energies. In the lower temperature range from 1000 to 1150 °C, the activation energy of the SiC growth process is Ea = 0.67 eV, while in the temperature range from 1150 to 1300 °C, the activation energy increases by almost an order of magnitude (Ea = 6.3 eV), which indicates a change in the limiting physical process. It has been established that the type of conductivity and the orientation of the substrate affect the thickness of the formed SiC layers. In this case, the greatest thickness of silicon carbide layers is achieved on silicon substrates with (111) orientation of p-type conductivity.

A system of automated control of thermal vacuum impregnation and swelling of sealing elastomers

When determining the swelling of polymeric materials in aggressive environments by standard test methods, significant measurement errors occur which entails the necessity of improving laboratory methods and diagnostic tools to solve research problems by automation of existing testing processes and minimization or complete elimination of the subjective components of measurement errors. We present an automated control system (ACS) for the process of swelling of sealing elastomers used in the construction of containers, tanks and units for storage, transportation, operation and pumping of liquids of various origins and properties. Methods of hardware and algorithmic implementation of the developed automated system for studying and testing impregnation and swelling of sealing polymers are shown on the example of filling MBS elastomer samples with a standard working fluid. The results obtained can be used to reduce the time of impregnation and swelling of sealing elastomers due to the proposed filling method and the developed integrated automatic control system for the filling process.

Investigation and Characterization of Graphene/Al, ZnO/Al and Al/Graphene/ZnO Contacts

In this paper, investigation has been made on the electrical properties of graphene/Al contact, ZnO/Al contact and Al/graphene/ZnO contacts in detail. Al metallization is considered, and it is performed via thermal vacuum coating technique under strict monitoring of the rate of thickness of the metal. Spin coating method and shadow masking are done for depositing fabricated graphene and ZnO on the thin film. Comparative analysis has been made on the parameters like saturation current, Barrier height and ideality factors which are calculated using Schottky barrier height (SBH) method. I–V characteristics are analyzed using the key‐sight B2029A semiconductor parameter analyzer. It is seen that the ZnO/Al contact has more ideality factor nearly 0.059 and exhibits Schottky behavior. Meanwhile, maximum saturation current is obtained for Graphene/Al contact whereas maximum barrier height is for ZnO/Al contact. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Effect of copper and silver as a middle layer on the structural, electrical, photocatalytic, and optical properties of ZnS/metal/ZnS films for optoelectronics applications

In this work, we utilized the thermal vacuum evaporation technique to fabricate ZnS single-layer thin films, ZnS/Cu/ZnS (ZCZ), and ZnS/Ag/ZnS (ZAZ) multilayer thin films. The influence of the middle layer of metals like copper and silver on the physical properties of ZnS/metal/ZnS multilayers is investigated. The results of the X-ray investigation demonstrate that the samples are polycrystalline, with a cubic ZnS structure and texture (111) at 2 = 29.1°. The optical investigation using Tauc’s approach yields energy gap values of 3.76 eV, 3.68 eV, and 3.6 eV for ZnS, ZCZ, and ZAZ films, respectively. CO2 gas sensing efficiency of ZnS, ZCZ, and ZAZ films were found to be at different operating temperatures. The optimal temperatures for ZnS, ZCZ, and ZAZ thin films were determined to be 483 K, 693 K, and 693 K, respectively. Under ultraviolet (UV) irradiation, the photocatalytic activity of ZnS, ZCZ, and ZAZ films for the degradation of methylene blue were studied. The results suggest that the metal intermediate layer is significant in improving the photocatalytic capabilities of ZnS films. When compared to ZnS single layer film (degradation efficiency of 15% after 180 min of UV irradiation), ZAZ multilayer film demonstrates the highest photocatalytic activity (degradation efficiency of 50% after 180 min of UV irradiation). The mechanism of the metal middle layer’s improved UV photoactivity is briefly discussed.

Non-flammable solvent-free liquid polymer electrolyte for lithium metal batteries

As a replacement for highly flammable and volatile organic liquid electrolyte, solid polymer electrolyte shows attractive practical prospect in high-energy lithium metal batteries. However, unsatisfied interface performance and ionic conductivities are two critical challenges. A common strategy involves introducing organic solvents or plasticizers, but this violates the original intention of security design. Here, an electrolyte concept called liquid polymer electrolyte without any small molecular solvents is proposed for safe and high-performance batteries, based on the design of a room-temperature liquid-state brush-like polymer as the sole solvent of lithium salts. This liquid polymer electrolyte is non-flammable and exhibits high ionic conductivity (1.09 times 10−4 S cm−1 at 25 °C), significant lithium dendrite suppression, and stable long-term cycling over a wide operating temperature range ( ≥ 1000 cycles at 60 °C and 90 °C). Moreover, the pouch cell can resist thermal abuse, vacuum environment, and mechanical abuse. This electrolyte and design strategy are expected to provide enlightening ideas for the development of safe and high-performance polymer electrolytes.

Study on combined stress failure envelope of CMG based on PSO-BP neural network

The investigation of the failure envelope of control moment gyroscopes (CMGs) under simulated dynamic and thermal vacuum conditions on the ground is crucial for ensuring the reliability of CMGs. In this study, a test rig is employed to simulate the combined stresses in a vacuum environment, including the temperature, CMG gimbal rotating speed, and satellite rotating speed. The objective is to obtain high-fidelity running status data of the CMG. The particle swarm optimization and BP neural network (PSO-BP) model is utilized to learn from these test data and subsequently predict the running status for other stress combinations, ultimately enabling the determination of the failure envelope surface of the CMG. The results demonstrate that this method significantly reduces the cost of testing to detect the CMG failure envelope while achieving high prediction accuracy and adaptability under combined stress situations. By employing the k-fold cross-validation method, the PSO-BP model demonstrates superior generalization performance to the BP model in predicting the running status of CMGs. The optimized hidden layer size and learning rate of the PSO-BP model are also discussed. Furthermore, the method presented in this paper can effectively incorporate the hidden experience data from the test. Finally, the PSO-BP method, in comparison to the BP method, yields a smooth and stable initial predicted value, effectively preventing the prediction result from falling into local optimization.

Characterization and performance evaluation of fully biocompatible gelatin-based humidity sensor for health and environmental monitoring

Biomaterials will have far reaching effects on solving the ever-rising environmental problems caused by the presently used toxic materials. Disposal of hazardous materials based electronic devices is causing a huge environmental problem in the form of electronic wastes (E-wastes). This study is an effort to contribute in the reduction of E-wastes by presenting the design, fabrication, and performance evaluation of a fully biocompatible humidity sensor with gelatin as the active layer. Gelatin is an excellent choice for humidity sensing because it is a hygroscopic material with the natural ability to attract and absorb water molecules, allowing for an effective detection and measurement of humidity levels in its surrounding environment. We patterned highly conductive (2.05 μΩ-cm) gold (Au) interdigitated electrode (IDE) (50 nm thickness) structure on a glass substrate by using thermal vacuum evaporation followed by the deposition of gelatin thin film by using cost effective technique of spin coating (at 1,500 rpm for 15 s). The device size was 25 mm × 22 mm with a line spacing of 1.50 mm between IDEs. Electrical characterisation was carried out to determine necessary performance parameters of the fully biocompatible humidity sensor and the obtained results exhibited a fast response/recovery time (4/6.30 s), wide operating range (15 %RH to 86 %RH), highly repeatable behaviour of 3 different samples and long lifetime (1 month). Wide variation in the resistance of sensor was observed at extreme humidity sensors ranging from 2.45 MΩ (15 %RH) to 0.12 MΩ (86 %RH). The fabricated sensor was used for the practical applications of health monitoring, touch less sensing, and environment monitoring. Moisture content of multiple commercially available moisturizers was determined by using gelatin based fully biocompatible humidity sensor and the obtained results showed that moisturizing cream had highest moisture content of 87 %RH (0.1 MΩ), followed by 80 %RH (0.30 MΩ) of rose water, and 72 %RH (0.67 MΩ) of baby oil.