Working Temperature Research Articles

Ultra-thin V2O5 nanowires: synthesis and gas sensing characteristics

This study presents the synthesis of vanadium oxide nanowires via a simple hydrothermal method and explores their potential as high-performance sensors for monitoring harmful gases, with a particular focus on NO2. The microstructure and morphology of the nanowires were characterized using scanning electron microscopy, powder x-ray diffraction, and Raman spectroscopy. The vanadium oxide nanowire material demonstrates outstanding NO2 gas sensing capabilities, detecting 5 ppm with a rapid response and high sensitivity at an optimal working temperature of 150 °C. It exhibits a relative resistance change of 70%, showcasing a sub-ppm detection limit. The V2O5 nanowires exhibited good stability and high gas selectivity for NO2 over other interfering gases (H2S, NH3, C2H4, and CO). The ultrathin structure of the nanowires holds promise for practical applications in developing NO2 gas sensors. The study sheds light on the superior sensitivity of the V2O5 gas sensor toward NO2 at low temperatures, emphasizing the influence of the 1D structure on the sensing mechanism.

Highly sensitive and low-temperature triethylamine sensor based on in situ growth of hierarchical α-MoO3 flowers

To challenge high working temperature of present triethylamine (TEA) sensor, well-defined hierarchical α-MoO3 flowers were in situ grown on Al2O3 tubes through a simple solvothermal method. The α-MoO3 flowers were about 3 μm in diameter consisted of overlapping nanosheets with average thickness of ∼30 nm, growing radially from the center of the flowers. The α-MoO3 flowers in situ grew on Al2O3 tubes to constitute the thin film sensors, which exhibited improved gas-sensing performance to TEA compared to the thick film sensors painted with the powder of α-MoO3 produced in the same reaction system. The average response value of the α-MoO3 thin film sensors to 10 ppm TEA was 243.5 at relatively low operating temperature of 133 °C, which was 4.5 times as high as that of the thick film sensors (54.2). And the detection limit of the thin film sensors to TEA is further decreased to 0.001 ppm compared to the α-MoO3 thick film ones. The superior TEA-sensing capability should be attributed to the hierarchical nanostructure grown in situ that supplies more active sites for gas molecule adsorption and electron transfer. The synthesized α-MoO3 flowers with hierarchical nanostructure are promising material for trace TEA detection in practical application.

Forming limit analysis of magnesium alloy sheet metal forming process at elevated temperatures

Abstract Magnesium alloys are valued by industry for their lightweight structures. Magnesium alloy are mainly produced by warm forming because the sheet formability is poor at room temperature. The mechanical properties of magnesium alloy AZ31, such as stress-strain curves and damage values at different elevated temperatures, were obtained by this study using a computerized screw universal testing machine. Freudenthal fracture criteria were used to obtain the forming limit at distinct temperatures. The forming limit analysis proceeded during the sheet metal forming process at various elevated temperature. The fracture’s forming load, stroke, and position were determined for different working temperatures of the sheet metal forming process for AZ31, using a finite element simulation combined with the ductile fracture criteria. Finally, the predicted values were compared with the experimental results during the sheet metal forming process. The simulation results agreed with the experimental values for the fracture forming load, stroke, and position of the sheet metal forming process. The feasibility of the present method was confirmed to predict forming limit during the sheet metal forming process for different elevated temperatures. A finite element analysis for forming limit prediction would be beneficial to the design of sheet metal processes for AZ31 magnesium alloys.

A High-Power, Flexible, and Magnetically Attachable Radiative Cooling Film

Radiative cooling is an environmentally friendly, passive cooling technology that operates without energy consumption. Current research primarily focuses on optimizing the optical properties of radiative cooling films to enhance their cooling performance. In practical applications, thermal contact between the radiative cooling film and the object significantly influences the ultimate cooling performance. However, achieving optimal thermal contact has received limited attention. In this study, we propose and experimentally demonstrate a high-power, flexible, and magnetically attachable and detachable radiative cooling film. This film consists of polymer metasurface structures on a flexible magnetic layer. The monolithic design allows for convenient attachment to and detachment from steel or iron surfaces, ensuring optimal thermal contact with minimal thermal resistance and uniform temperature distribution. Our magnetic radiative cooling film exhibits superior cooling performance compared to non-magnetic alternatives. It can reduce the temperature of stainless-steel plates under sunlight by 15.2 °C, which is 3.6 °C more than that achieved by non-magnetic radiative cooling films. The radiative cooling power can reach 259 W∙m−2 at a working temperature of 70 °C. Unlike other commonly used attachment methods, such as thermal grease or one-off tape, our approach allows for detachment and reusability of the cooling film according to practical needs. This method offers great simplicity, flexibility, and cost-effectiveness, making it promising for broad applications, particularly on non-horizontal irregular surfaces previously considered challenging.

Magnetostructural transformation and magnetocaloric response in Mn(Fe)NiSi(Al) alloys

An efficient magnetocaloric refrigerant must have certain characteristics such as a sharp transition near the desired working temperature, a large cyclic magnetocaloric response, and the use of raw materials with reduced costs and low environmental consequences. In this sense, this work focuses on a series of rare-earth- and Co-free Mn0.5Fe0.5NiSi1-xAlx alloys (x = 0.0525, 0.060, 0.0685) with promising magnetocaloric properties. The alloys were synthesized using combined arc melting and induction melting techniques, as this synthesis route provides improved control on the sample composition and homogeneity. We investigated how the heat treatment temperature and Al content affect the magnetostructural and magnetocaloric properties of the alloys. On the one hand, it is found that annealing at 1173 K for 7 days leads to a sharp magnetostructural transformation with no traces of impurities for the alloy with x = 0.0525. Under these conditions, a large isothermal entropy change of –11.5 J kg−1 K−1 for 1 T is obtained near room temperature, significantly improving the value of the as-cast sample. On the other hand, following this optimal heat treatment, the influence of Al content is studied: upon increasing the Al concentration the magnetostructural transformation shifts to lower temperatures, ranging from 320 K for x = 0.0525 to 220 K for x = 0.0685 (measured upon heating).

Work and the Veins. A Retrospective Analysis of Work Activities in Patients with Chronic Venous Disease

This study aimed to investigate the relationship between work activities and chronic venous disease of the lower limbs. Patients referred to our clinical units of Interuniversity Center of Phlebolymphology for chronic venous disease (CVD) assessment between January 2019 and December 2023 were retrospectively enrolled in the study. Inclusion criteria were (a) CVD status confirmed by office visit and Duplex ultrasound, (b) not having any other vascular disease of the lower limbs (such as arterial or lymphatic problems), (c) work activities of at least 1-year duration, in the medical records. A total of 948 patients (642 females and 306 males) were retrospectively enrolled. Of these, 613 patients (431 females and 182 males) were affected by CVD and 335 patients (211 females and 124 males) were not affected by CVD and served as controls. Sedentary jobs and jobs where the ambient work temperature ambient is hot have been associated with CVD. Other types of work with no sedentary activities or with a cool ambient work temperature were not associated with CVD. Work activity and the occupational environment may be tightly related to the onset and progression of CVD. Forced postures, excessive standing or sitting, and high ambient temperatures can reduce lower limb venous function at work and cause CVD.

Design of a Novel Hybrid Concentrated Photovoltaic–Thermal System Equipped with Energy Storages, Optimized for Use in Residential Contexts

Concentrated photovoltaic (CPV) technology is based on the principle of concentrating direct sunlight onto small but very efficient photovoltaic (PV) cells. This approach allows the realization of PV modules with conversion efficiencies exceeding 30%, which is significantly higher than that of the flat panels. However, to achieve optimal performance, these modules must always be perpendicular to solar radiation; hence, they are mounted on high-precision solar trackers. This requirement has led to the predominant use of CPV technology in the construction of solar power plants in open and large fields for utility scale applications. In this paper, the authors present a novel approach allowing the use of this technology for residential installations, mounting the system both on flat and sloped roofs. Therefore, the main components of cell and primary lens have been chosen to contain the dimensions and, in particular, the thickness of the module. This paper describes the main design steps: thermal analysis allowed the housing construction material to be defined to contain cell working temperature, while with deep optical studies, experimentally validated main geometrical and functional characteristics of the CPV have been identified. The design of a whole CPV system includes thermal storage for domestic hot water and a 1 kWh electrical battery. The main design results indicate an estimated electrical conversion efficiency of 30%, based on a cell efficiency of approximately 42% under operational conditions and a measured optical efficiency of 74%. The CPV system has a nominal electric output of 550 Wp and can simultaneously generate 630 W of thermal power, resulting in an overall system efficiency of 65.5%. The system also boasts high optical acceptance angles (±0.6°) and broad assembly tolerances (±1 mm). Cost analysis reveals higher unit costs compared to conventional PV and CPV systems, but these become competitive when considering the benefit of excess thermal energy recovery and use by the end user.

Enhancing interfacial polarization and electrorheological effect of crosslinked poly(ionic liquid)s by doping aniline oligomer

Poly(ionic liquid)s (PILs) are providing potential platforms to develop next generation water-free polyelectrolyte-based electrorheological (ER) fluids because they well overcome water sensitivity problem of classic polyelectrolyte-based ER fluids by incorporating with large size fluoric counterions. Especially, crosslinked PILs (CPILs) can further broaden the working temperature range of ER effect compared to linear PILs. However, the crosslinking network easily restricts the ion dissociation due to decreased dielectric constant and thus weakens ion movement-induced interfacial polarization and ER effect. In this paper, we propose a way to improve ion dissociation and ion movement-induced interfacial polarization of CPILs by doping polar aniline oligomer to improve the dielectric constant of CPILs. Several kinds of CPILs are synthesized and then aniline oligomer is doped into CPILs by swelling method. The structure of doped CPILs is characterized by different techniques, the dielectric property of ER fluids of doped CPIL particles in silicone oil is analyzed by dielectric spectroscopy, and the ER effect of ER fluids of doped CPIL particles is measured by rheometer under electric fields. It shows that doping aniline oligomer can increase the dielectric intensity and decrease the relaxation time and corresponding activation energy of interfacial polarization and improve the ER effect of CPILs with a relatively loose crosslinking network, while doping aniline oligomer has no contribution to the interfacial polarization and ER effect of CPILs with a relatively tight crosslinking network.

High-Temperature Mechanical–Conductive Behaviors of Proton-Conducting Ceramic Electrolytes in Solid Oxide Fuel Cells

Proton-conducting solid oxide fuel cells (P-SOFCs) are widely studied for their lower working temperatures than oxygen-ion-conducting SOFCs (O-SOFCs). Due to the elevated preparation and operation temperatures varying from 500 °C to 1500 °C, high mechanical stresses can be developed in the electrolytes of SOFCs. The stresses will in turn impact the electrical conductivities, which is often omitted in current studies. In this work, the mechanical–conductive behaviors of Y-doped BaZrO3 (BZY) electrolytes for P-SOFCs under high temperatures are studied through molecular dynamics modeling. The Young’s moduli of BZY in fully hydrated and non-hydrated states are calculated with different Y-doping concentrations and at different temperatures. It is shown that Y doping, oxygen vacancies, and protonic point defects all lead to a decrease in the Young’s moduli of BZY at 773 K. The variations in the conductivities of BZY are then investigated by calculating the diffusion rates of protons in BZY at different triaxial, biaxial, and uniaxial strains from 673 K to 873 K. In all cases, the diffusion rate present a trend of first increasing and then decreasing from compression state to tension state. The variations in elementary affecting factors of proton diffusion, including hydroxide rotation, proton transfer, proton trapping, and proton distribution, are then analyzed in detail under different strains. It is concluded that the influences of strains on these factors collectively determine the changes in proton conductivity.

Driving net zero: Comprehensive evaluation of whole life carbon in domestic hot water systems

Low-temperature domestic hot water (DHW) systems provide significant carbon reduction benefits, supporting the UK’s 2050 net-zero target. Typically, low water volume applications do not need recirculation and storage when instantaneous heaters are employed, such applications can be more flexible in terms of temperature range and safety requirements. However, commercial applications may have high volumes of hot water and hence, will require high working temperatures to satisfy the recirculation requirements. This study developed a comprehensive toolkit to benchmark the embodied and operational carbon in terms of kgCO2e/m2 for various DHW systems, including equipment, refrigerants, and operational emissions. Analysis of seven DHW designs for an office building revealed that low-temperature systems consistently demonstrate the lowest whole-life carbon (WLC), underscoring the impact of grid decarbonisation and low-GWP refrigerants. The WLC results are normalised per square metre of floor area. Low-temperature systems showed the lowest WLC even with the inclusion of water treatment and chemical dosing systems.

Performance analysis and optimization of SnSe thin-film solar cell with Cu2O HTL through a combination of SCAPS-1D and machine learning approaches

Tin selenide (SnSe) is an auspicious light-harvesting material in photovoltaic (PV) technology due to its larger absorption coefficients and earth-abundance nature. However, because of the potential difficulty of defect-free fabrication, and non-optimized electron transport layer (ETL) and hole transport layer (HTL) alignment, it could no longer achieve its realistic objectives. Therefore, designing a suitable SnSe-based PV device with an appropriate ETL and HTL is crucial to achieving optimum performance. In this research, we proposed a novel heterojunction thin-film solar cell (TFSC) configuration of Ni/Cu2O/SnSe/WS2/FTO/Al and simulated its PV performance metrics using SCAPS-1D solar cell simulation software. This research additionally provided a comparative performance analysis of the SnSe TFSC with numerous ETLs and HTLs. It is evident that the suggested TFSC with WS2 ETL and Cu2O HTL creates appropriate band alignment with the SnSe light harvesting layer, which reduces charge recombination at both the ETL/absorber and absorber/HTL interfaces. Here, the impact of absorber layer thickness, doping concentration, bulk defect density, and defect density at the ETL/absorber and absorber/HTL interfaces is investigated. Besides, the impact of radiative recombination, back contact metal work function, and working temperature are carefully examined. After optimization of all the material properties, a maximum efficiency of 29.31 % with open circuit voltage (Voc) of 0.89 V, short circuit current density (Jsc) of 38.23 mA/cm2, and fill-factor (FF) of 86.30 % were attained for the SnSe-based proposed structure. Furthermore, a supervised linear regression machine learning algorithm is employed to investigate how the behavior of the material attributes affects the solar cell's designed PV performance. Overall, our findings can be helpful to experimentalists to fabricate inexpensive, highly efficient, and Cd-free SnSe-based heterostructure solar cells in the near future.

Hydrothermal fabrication of composite chitosan grafted salicylaldehyde/coal fly ash/algae for malachite green dye removal: A statistical optimization

In this study, chitosan grafted salicylaldehyde/coal fly ash/algae (Chi-SL/CFA/Alg) was synthesized by assistance of hydrothermal process to be an effective adsorbent to remove cationic dye (malachite green: MG) from water. The physicochemical properties of the Chi-SL/CFA/Alg biomaterial were examined using SEM-EDX, pHpzc, specific surface area (BET), and FTIR analyses. The optimization process of the adsorption operation parameters for MG removal by Chi-SL/CFA/Alg were optimized using a Box-Behnken design (BBD). The selected adsorption operation parameters Chi-SL/CFA/Alg dosage (A: 0.02–0.1 g/100 mL), solution pH (B: 4–8), and contact time (C: 20–360 min). Analysis of variance (ANOVA) test was applied to determine the significant interaction between the adsorption operation parameters and to validate BBD output. The adsorption kinetics and isotherms of MG dye by Chi-SL/CFA/Alg were well described by pseudo-second order (PSO) kinetic and Freundlich isotherm model respectively. Thus, the maximum adsorption capacity (qmax) of MG dye by Chi-SL/CFA/Alg was found to be 493.7 mg/g at basic pH environment (pH = 8) and working temperature 25 °C. The adsorption mechanism can be ascribed to various interactions, including hydrogen bonding, π-π interactions, electrostatic attraction, and n-π interactions. Thus, Chi-SL/CFA/Alg can be considered as preferable and potential adsorbent for removing cationic dye from aqueous environment.

Polymer Boron-Containing Composite for Protecting Astronauts of Manned Orbital Stations from Secondary Neutron Radiation

This article considers the prospects of using heat-resistant polyimide boron-containing composites to protect astronauts of manned orbital stations from secondary neutron radiation. Variant calculations are performed regarding neutron and gamma-quanta flux distributions in a polyimide composite material with different boron content used to reduce capture radiation. The dependences of spatial distributions of thermal neutron flux density and the gamma-quanta dose rate in a polyimide composite layer with a boron content of 0 to 5% are obtained. An experimental assessment of the energy distribution of neutron and gamma radiation behind the protective polyimide composite is carried out. The introduction of boron atoms in an amount of 3.0 wt.% shows the absence of bursts of secondary gamma radiation energy in the composite, which is due to the high cross-section of thermal neutron absorption by boron atoms. As a result, with a material layer thickness of 3–10 cm, the gamma-quanta dose rate decreases by 2–3 times. The differential thermal analysis method showed that the upper limit of the working temperature of the polyimide composite is 500 °C. The polyimide matrix filled with boron atoms can find effective application in the development of new radiation-protective polymer materials used in manned orbital stations.

Fabrication of BiScO3–PbTiO3/epoxy 1–3 piezoelectric composites for high‐temperature transducer applications

Abstract1–3 piezoelectric composites are widely used in piezoelectric ultrasonic transducers due to their high thickness electromechanical coupling factor. However, the applications of the composites in high‐temperature fields are limited by the low heat resistance of both the piezoelectric and polymer phases. To tackle this, we designed and fabricated the BiScO3–PbTiO3/epoxy high‐temperature 1–3 piezoelectric composites. These composites exhibit a high thickness electromechanical coupling factor kt of 63%, a large piezoelectric coefficient d33 of 470 pC/N, and a pure thickness vibration mode. Furthermore, we fabricated a high‐temperature transducer based on the BiScO3–PbTiO3/epoxy 1–3 composites. The bandwidths of the composites measured in water and silicone oil (30% and 23%, respectively) are approximately 1.65 times greater than those of monolithic piezoelectric ceramics (18% and 14%, respectively). The bandwidth of the transducer can be increased to 78% by adding a porous alumina backing layer, with the working temperature reaching up to 300°C. The results indicate that the BS–PT/epoxy 1–3 composite is a potential candidate for high‐temperature transducer applications.

Chemiresistive detection of xylene vapor using MOF-derived porous Co3O4 microrods activated by Mo6+ cations

Incorporation of high-valence cation into catalytic oxide (eg. Co3O4) is favorable for regulating the carrier concentration and creating more active centers for surface reaction process, thus promoting the sensing capability towards low reactive gas (eg. xylene). Herein, the metal-organic framework (MOF)-derived Mo-doped porous Co3O4 microrods are achieved through a simple solution method combing with a thermal method. The introduction of Mo6+ into Co3O4 matrix enhances the concentration of oxygen defects and Co3+, coupled with the specific surface area. As a result, the 5 at% Mo/Co3O4-based gas sensor sample exhibits a nice selectivity, clear response value (Rg/Ra=29.8 – 100 ppm), low concentration limit (0.5 ppm), and reliable stability to xylene vapor under a low working temperature (140 °C). Moreover, the possible reaction pathway (benzyl-benzaldehyde-benzoate-aromatic ester/anhydride) of xylene oxidation over this 5 at% Mo-doped Co3O4 microrod is proved by an in-situ DRIFTS analysis. Importantly, this optimized xylene-sensing capability is further discussed from the viewpoint of Mo-introducing effect into the porous Co3O4 microrods. This work further demonstrates a reliable approach of high valence cation-doped catalytic oxides to detect low reactive vapor.

Reversible Giant Barocaloric Effect with Broad Working Temperature Range in an Amorphous Ethylene Propylene Diene Monomer.

The barocaloric effect of a solid material is an intense research topic due to its potential application in solid-state refrigeration. Among the proposed candidates, elastic polymers are distinctive because their barocaloric responses are independent from a pressure-induced phase transition which makes it possible to realize a broad working temperature range in principle. However, the barocaloric performance of most elastic polymers diminishes significantly as temperature decreases. In this work, giant and reversible barocaloric effects were observed in a broad working temperature range from 252 to 345 K in an amorphous polymer of ethylene propylene diene monomer, which are much higher than the investigated crystalline and partially crystallized ones. It is demonstrated that the degree of crystallinity can be a key factor responsible for the mobility of polymer chains and the corresponding barocaloric performance at low temperatures. The reversible giant barocaloric effects, broad working temperature regions, low cost, and absence of pressure-transmitting fluid make the ethylene propylene diene monomer attractive for solid-state barocaloric refrigeration.

Ir doping improved oxygen activation of WO3 for boosting acetone sensing performance at low working temperature

Thermally excited oxygen activation is the key to realize gas sensing by semiconductor. However, the relevant strategies and mechanisms are rarely studied. Herewith, the model material of highly oxygen catalytic active Ir doped WO3 (Ir-WO3) is prepared to elucidate the impact of enhanced oxygen activation on sensing performance. Interestingly, the 0.5 wt% Ir doped WO3 successfully reduced the working temperature of WO3 from 370 to 260 ℃ and significantly enhanced the response from 25.1 to 127.9 (at 50 ppm) for acetone. Meanwhile, the sensor also has fast response/recovery times (∼8.3/3.8 s), long-term stability, low detection limit (19 ppb) and high selectivity. Gas sensitive performance tests, in situ-DRIFTS and DFT calculations reveal that the Ir doping facilitates the oxygen adsorption and activation, which can significantly weaken the activation energy of acetone at low temperatures and contribute to enhance sensing performance. Our work paves a new pathway to improving metal oxide-based gas sensors at lower operating temperatures.

Synthesis and enhanced H2S gas sensing performances of Co-doped NiO@g-C3N4 heterocomposites

Metal doping is an efficient approach to improve H2S gas sensing performances, but the metal-doped NiO is still faced poor recovery capability at low working temperature. Herein, Co-doped NiO@g-C3N4 heterocomposites were constructed firstly via a simple solid phase reaction. Texture characterizations indicate that Co-doped NiO@g-C3N4 heterocomposites with the architecture of hierarchical microspheres show high specific surface areas and rich surface oxygen vacancies. The gas-sensitive measurements exhibit that the response value of the heterocomposites with g-C3N4 content of 30 wt% (Co-NiO@g-C3N4-3) increases to 45 toward 20 ppm H2S gas at 172 °C, which is about 1.8 times of Co-NiO (23), as well as response/recovery times decreased to ca. 100/130 s. Besides, excellent repeatability, stability and selectivity of Co-NiO@g-C3N4-3 sensors are obtained. The improved H2S gas sensing performances of Co-NiO@g-C3N4 heterocomposites is mainly contributed to the formation of nano-heterojunctions, which promotes electron accumulation at nano-heterojunctions near Co-NiO, facilitates O2 molecules adsorption on the material surface and accelerates the resistance change of the sensors, resulting the enhanced gas sensing performances.

Colossal Barocaloric Effect in Encapsulated Solid‐Liquid Phase Change Materials

AbstractBarocaloric cooling as an emerging cooling technology offers an eco‐friendly alternative to traditional vapor compression refrigeration. Research on barocaloric materials primarily concentrates on solid–solid phase change materials (PCMs), among which plastic crystals exhibit colossal barocaloric effect. Solid‐liquid PCMs such as paraffin also exhibit giant barocaloric effect, however, their potential is often overshadowed by leakage issues. In this work, a strategy is demonstrated by encapsulating solid‐liquid PCMs into porous carbon matrixes to generate a large family of colossal barocaloric materials. In practice, by orthogonally combining paraffins with encapsulation matrixes like graphene foam, carbon nanotube foam, and carbon foam, it can be obtained composites that work without leakage issues. The significant advantage is their colossal barocaloric effect with the highest entropy value up to 570 J K−1 kg−1 in paraffin‐20@graphene foam. Moreover, the composites possess thermal conductivity up to 89.9 W m−1 K−1 in paraffin‐20@carbon foam, and tunable working temperature in the range of 270—330 K. Most importantly, this strategy, demonstrated with 5 solid‐liquid PCMs and 3 encapsulation matrixes in this work, is just the beginning. Further exploration with more materials can develop a huge family of encapsulated solid‐liquid PCMs with colossal barocaloric performance for modern cooling technology.

Study of the instability of the fixed points cells temperature of working standards: establish the optimal time intervals between the comparisons

The cells of fixed freezing points of metals are an important component of the working standards of temperature of the 0th category. These standards are intended to reproduce the unit of temperature kelvin in accordance with ITS-90, which is currently the main method in the temperature range from –189 to 1084 °C. The transfer of the temperature unit is carried out by comparing the cells of the working standards of temperature with the cells of the state secondary standard of temperature. In order to develop recommendations for increasing the interval between comparisons and changing the requirements of the State Verification Scheme, one of the most important characteristics of the cells of the working standards of temperature was studied – the instability of the cell temperature in the interval between comparisons. The paper summarizes the results of the study of 26 cells of fixed points of tin, zinc and aluminum, the service life of which was from 2 to 10 years, and the interval between comparisons was from 2 to 5 years. Possible causes of instability of the reproducible temperature are described and the uncertainty of comparisons of working standard cells with secondary standard cells is calculated. The analysis of the results showed that the instability values over a long period of time do not exceed 1.02 mK for tin cells, 1.75 mK for zinc cells and 6.47 mK for aluminum cells. The most probable cause of deviation of the temperature of working standard cells from secondary standard cells is the different purity of the metals used. It is noted that the destruction of the quartz shell of the cell without mechanical action is unlikely, and the effect of pressure on the temperature of the reference point is absent. Based on the results of the comparative analysis, it was concluded that it is possible to increase the interval between comparisons for ampoules of tin and zinc to five years. Such an increase in the interval has a positive economic effect by reducing the cost of operating the state secondary temperature standard and transporting ampoules to the comparison site. For aluminum cells, an individual approach to setting the interval between comparisons is recommended based on the analysis of the results of previous comparisons. The materials published in this paper may be useful to specialists of metrological centers working with working temperature standards, as well as to all scientists studying the processes occurring in cells for measuring the solidification temperature of metals.