Low-temperature Preparation Research Articles

Synthesis, Structure, and Characterizations of a Volatile/Soluble Heterometallic Hexanuclear Precursor [NaMn2(thd)4(OAc)

The paper describes a heterobimetallic mixed-ligand hexanuclear precursor [NaMn2(thd)4(OAc)]2 (1) (thd = 2,2,6,6-tetramethyl-3,5-heptadionate; OAc = acetate) that was designed based on its lithium homoleptic analogue, [LiMn2(thd)5], by replacing one of the thd ligands with an acetate group in order to accommodate 5-coordinated sodium instead of tetrahedral lithium ion. The complex, which is highly volatile and soluble in a variety of common solvents, has been synthesized by both the solid-state and solution methods. The unique “dimer-of-trimers” heterometallic structure consists of two trinuclear [NaMnII2(thd)4]+ units firmly bridged by two acetate ligands. X-ray diffraction techniques, DART mass spectrometry, ICP-OES analysis, and IR spectroscopy have been employed to confirm the structure and composition of the hexanuclear complex. Similar to the Li counterpart forming LiMn2O4 spinel material upon thermal decomposition, the title Na:Mn = 1:2 compound was utilized as the first single-source precursor for the low-temperature preparation of Na4Mn9O18 tunnel oxide. Importantly, four Mn sites in the hexanuclear molecule can be potentially partially substituted by other transition metals, leading to heterotri- and tetrametallic precursors for the advanced quaternary and quinary Na-ion oxide cathode materials.

Rapid preparation of traditional and high-entropy garnet ceramics by SPS at low temperature with ultrafast densification

Spark plasma sintering (SPS) is a fast and efficient method for preparing functional ceramics. This article investigates the phase evolution, thermal expansion and chemical stability of traditional (Y1.2Nd1.8Fe5O12) and high-entropy ((Y, Gd, Sm, Eu, Dy)3Fe5O12) garnet ceramics. Prepared under conventional SPS (50 MPa) conditions at 900–1100 °C. The results indicate that using SPS sintering method can significantly reduce the sintering temperature (1100 °C) and time (3 min) of garnet ceramics. (Y, Gd, Sm, Eu, Dy)3Fe5O12 (1.6 × 10−6 K−1) exhibits superior thermal expansion stability compared to Y1.2Nd1.8Fe5O12 (5.4 × 10−6 K−1). The strong REE-O bond energy and severe lattice distortion of high entropy garnet ceramics hinder the migration and diffusion of cations, resulting in higher leaching resistance of high-entropy garnet ceramics (∼10−7 g m−2 d−1-10−8 g m−2 d−1) compared to traditional garnet ceramics (∼10−5 g m−2 d−1-10−6 g m−2 d−1). Therefore, SPS has broad application prospects in the low-temperature preparation of high-entropy garnet ceramics for immobilization of actinide elements.

Promoting effect of oxygen vacancies in Co/CoAl2O4 catalyst steered with a straightforward method on hydrogenation of furfural to 2-methylfuran

The exploitation of base metal catalysts to upgrade biomass chemicals remains a daunting challenge and a sustainable strategy. Here, a series of Co-Al spinel catalysts are rapidly prepared by low-temperature solution combustion synthesis for hydrogenation of furfural (FF) to 2-methylfuran (2-MF), in which oxygen vacancies are easily manipulated by regulating the proportion of glycine in the ingredients. The screened Co/CoAl2O4 incorporating adequate oxygen vacancies yields 2-MF over 97 % at 150 ℃ for 5 h, rivalling the state-of-the-art catalysts to date. Characterizations and DFT calculations attribute the success to oxygen vacancies, which not only enhance the adsorption of FF by changing the adsorption geometry, but also facilitate the hydrogen spillover from Co to substrate by moving down the d-band center of CoAl2O4. This study provides a versatile methodology for the efficient and low-temperature preparation of spinel and the construction of defect engineering on catalysts, enlightening the design of phenomenal catalysts.

Rapid and low-temperature preparation of zircon ceramic by hydrothermal-assisted sol-gel process and microwave sintering

During the traditional preparation of zircon, higher sintering temperatures and longer holding times are inevitable. A novel hydrothermal-assisted sol-gel process and microwave sintering (HM, microwave sintering precursors derived from hydrothermal-assisted sol-gel process) were provided to prepare zircon ceramics hereof. The influences of sintering temperature and holding time on the phase composition, microstructure, and compactness of ceramics were investigated. Data display that the properties of the obtained ceramics were highly dependent on the temperature and time, and the ZrSiO4 formation efficiency can be improved by increasing these two factors. The sample prepared by the HM process has the formation efficiency of ZrSiO4 up to 91.74 wt% (HM-1350-300), which far exceeds that of conventional microwave sintering (M-1350-300, 45.02 wt%). The results demonstrate that the HM process can be employed to obtain ZrSiO4 ceramics rapidly at low temperatures.

A new low-temperature preparation technology of heat-resistant diamond/Cu joint using composite braze: microstructure evolution and mechanical properties strengthening

A low-temperature brazing method of diamond and Cu was proposed by using composite filler of Au-Si eutectic + NiTi particle. Prior to joining, diamond surface was modified by an active alloy of AgCu28 +TiH2, the resulting Ag-Cu coating could ensure the good wettability of Au-Si filler during brazing and formed TiC layer could ensure a tight interfacial bonding. In the brazing process, it was found that melting point depressant element of Si in Au-Si filler could be completely consumed by (i) reacted with NiTi alloy and formed NiTiSi whiskers and (ii) precipitation in form of Ti5Si3C and TiCuSi in modified layer, while the interdiffusion between Au and Cu substrate lead to a ductile seam matrix of heat-resistant (Au, Cu)ss. Attributed to the excellent plasticity and high melting temperature of (Au, Cu)ss and the strengthening effect of NiTiSi whiskers, the joint brazed at 600 ℃ not only have a high shear strength of 108 MPa at room temperature, but also exhibited a excellent heat-resistance, the joint showed a shear strength of 89 MPa and 28 MPa at 300 ℃ and 500 ℃, respectively.

Strain Effects on Flexible Perovskite Solar Cells.

Flexible perovskite solar cells (f-PSCs) as a promising power source have grabbed surging attention from academia and industry specialists by integrating with different wearable and portable electronics. With the development of low-temperature solution preparation technology and the application of different engineering strategies, the power conversion efficiency of f-PSCs has approached 24%. Due to the inherent properties and application scenarios of f-PSCs, the study of strain in these devices is recognized as one of the key factors in obtaining ideal devices and promoting commercialization. The strains mainly from the change of bond and lattice volume can promote phase transformation, induce decomposition of perovskite film, decrease mechanical stability, etc. However, the effect of strain on the performance of f-PSCs has not been systematically summarized yet. Herein, the sources of strain, evaluation methods, impacts on f-PSCs, and the engineering strategies to modulate strain are summarized. Furthermore,the problems and future challenges in this regard are raised, and solutions and outlooks are offered. This review is dedicated to summarizing and enhancing the research into the strain of f-PSCs to provide some new insights that can further improve the optoelectronic performance and stability of flexible devices.

Rapid and low-temperature preparation of tungsten oxide electrochromic thin films by oxygen plasma treatment

Electrochromic materials have attracted considerable attention due to their ability to change color reversibly and rapidly under an external electrical stimulus, making them highly promising for use in various applications such as smart windows, displays, and optical memory devices. In particular, tungsten trioxide (WO3) thin films have shown excellent electrochromic properties, leading to their wide application in electrochromic devices. In this study, oxygen plasma treatment was used to convert WCl6 thin film to WO3 electrochromic thin film on ITO glass substrate. Surface morphology, element composition, phase, optical property, and electrochromic characteristics of WO3 film are analyzed. It has been proved that the conversion of precursor films is rapid and efficient, the mean roughness and root mean square of amorphous WO3 thin film are lower than 1.8 nm and 2.2 nm respectively, and the film exhibits good electrochromic performance parameters. The optical modulation range and coloration efficiency of the film can reach 58.5% and 80.2 cm2/C before cycle and 56.3% and 84.0 cm2/C after 100 cycles, coloration time and bleaching time are within 10 s. The method of plasma treatment avoids annealing and prepare WO3 film with good and stable performance. This method has the potential to expand to other electrochromic materials, and provides a new solution for the large area preparation and flexible application of electrochromic materials.

Low temperature preparation of diopside nanoparticles: in-vitro bioactivity and drug loading evaluation

Bioactive diopside (CaMgSi2O6) nanoparticles have recently gained potential usefulness as bone replacement materials and nano vehicles for delivering therapeutics. The structural characteristics of this ceramic have found to be a key factor in bone bonding ability. To attain the desired product for 100% clinical success, it is important to realize the relationship between structure and biological activity. Synthesis of these nanoparticles via the solid-state method has been regarded as a low-cost and easy process in large-scale, but time consuming reactions and high temperature (≈ 1400 °C) are required. On the other side, the wet chemistry can overcome these drawbacks, whereas the presence of byproducts in the final powder has limited this method in large-scale production. The present document has represented a simple, fast and one-pot sol–gel approach for the synthesis of highly pure diopside nano-powders (< 20 nm) by using not-expensive precursors. Calcination of the obtained powder has been conducted at various temperatures (700, 1000 and 1200 °C). The physicochemical and microstructural properties of the products have been characterized by XRD, FTIR, FESEM and TEM. Moreover, the impact of the crystallinity on the bioactivity, drug loading capacity and drug release behavior of the synthesized nanoparticles have been investigated here for the first time. The in-vitro bioactivity results of the prepared diopside samples in a simulated body fluid (SBF) at 37 °C revealed the higher capability of the sintered sample to deposit calcium phosphate, compared with the amorphous one. High quantity of gentamicin (around 10 µg) could attach to the surface of 1 miligram of the sintered diopside during the early stages of contact (3 h), suggesting the potential use of diopside as a new class of nano-vehicles for antibiotics. The release behavior indicated a sustained release of gentamicin (80%) after 24 h. In conclusion, diopside nanoparticles can be a promising candidate as a drug-vehicle for bone filling, implant coating or bone cement applications.

Phase composition, densification behavior and high-temperature strength of carbon-doped ZrB2–ZrSi2 ceramics

Sintering additive of ZrSi2 is beneficial to low-temperature densification of ZrB2-based ultra-high temperature ceramics (UHTCs), nevertheless, residual ZrSi2 would severely reduce the high-temperature strength of UHTCs. In the current work, to achieve low-temperature preparation of ZrB2-based UHTCs with good high-temperature strength, active carbon (C) was added into ZrB2–ZrSi2 ceramics to convert the sintering additive into refractory phases of SiC/ZrC. C-doped ZrB2–ZrSi2 powders were hot-pressed at different temperatures to investigate the phase composition, microstructure and densification behavior. TG-DSC, XRD and SEM results indicated that ZrSi2 was almost entirely converted into SiC and ZrC at 1600 °C for 2h, meanwhile, a fully-dense C-doped ZrB2–ZrSi2 ceramic was obtained at such sintering conditions. In addition, the high-temperature (1800 °C) strength of C-doped ZrB2–ZrSi2 ceramic was 390 ± 21 MPa, which was much higher than that of the C-undoped one. The excellent high-temperature mechanical properties could be attributed to the transformation of low-melting-point phases into refractory phases.

An effective oxygen vacancy restrain method for flexible perovskite solar cells with enhanced performance and bending resistance

Flexible perovskite solar cells (F-PSCs) are currently a research hotspot due to their lightweight, solution processability, and low cost. However, oxygen vacancies in SnO2 would deteriorate the crystallization of perovskite, especially in F-PSCs due to the low temperature of SnO2 preparation with flexible substrates, thus inducing poor performance and decreased bending resistance. Here, trichlorobenzene sulfonic acid potassium salt (TSAPS) is used as an effective oxygen vacancy restrain additive on the SnO2 surface for F-PSCs. The oxygen vacancies are reduced from 68.40% to 45.26% after TSAPS modification. Meanwhile, the interfacial defects are suppressed by the synergistic passivation of individual ions in TSAPS, thus the carrier extraction and transportation are effectively improved. As a result, the PCE of the F-PSCs greatly increased from 15.22% to 18.63%. In addition, the unencapsulated SnO2/TSAPS-based flexible device can maintain 84% of its initial efficiency after 3000 bending cycles, exhibiting superior mechanical stability, while the control one decreased to only 9%. This work demonstrates a dependable method for improving the quality of the interface between the ETL and perovskite layer, resulting in enhanced bending resistance and performance for flexible PSCs.

Low temperature preparation of YSZ-based thin-film limiting current type oxygen sensor

Oxygen sensors based on YSZ solid electrolyte thin films have great application prospects due to their advantages in miniaturization and integration. Here, we report the gas sensing performance of Pt/YSZ/Pt oxygen gas sensors with low preparing temperatures. YSZ thin films with (200) preferred orientation have been prepared by room temperature RF magnetron sputtering combined with annealing at a temperature of 650 °C. The 700 nm-thick YSZ films exhibit an obvious limiting current platform, and the limiting current IL shows a linear dependence on oxygen concentration X(O2) (in the range of 6%–21%). Moreover, the devices with 700 nm-thick YSZ films worked well at the temperature range from 500 to 650 °C, and a linear relationship between logIL and 1000/T has been observed. These results demonstrate that YSZ thin films prepared by low temperature magnetron sputtering combined with the annealing process can reduce the working temperature.

Facile transformation of graphene oxide nanospheres based on AAO template

In this paper, a facile one-step drop method is developed to convert reduced graphene oxide into graphene oxide nanoparticles. An aqueous solution of reduced graphene oxide is poured through the pores of anodic aluminum oxide templates to form graphene oxide nanospheres at low temperature (120 ​°C) and low pressure (0.8 ​bar) preparation conditions. Electrochemical exfoliation of graphite and reduced graphene oxide nanospheres (not hollow) were adopted to fabricate reduced graphene oxide within the pores of an anodic aluminum oxide template. The prepared reduced graphene oxide nanospheres show uniform diameters (∼42.5 ​nm) and a low O/C ratio (8%). Graphene nanospheres achieve higher sensitivity to CO2 gas in air (at room temperature) compared to graphene oxide nanosheets (i.e., in contrast to carbon dioxide gas sensors in graphene sheets). Its sensitivity increased to 35% by shaping the nanosheets to nanospheres of reduced graphene oxide which is attributed to a surface area expansion of 7.4 ​× ​105 times. Moreover, graphene oxide, reduced graphene oxide, and reduced graphene oxide nanospheres show a fast response time of 0.19 ​s, 0.24 ​s, and 0.31 ​s, and short recovery times of 1.14 ​s, 1.17 ​s, and 1.22 ​s, respectively, with higher sensitivity of reduced graphene oxide nanospheres.

Low temperature preparation of high-performance citric acid crosslinked starch gels with adjustable properties based on cationic esterification synergistic crosslinking

Citric acid (CA) is a commonly used crosslinking agent for good-grade starch gels, but its high crosslinking temperature limits its application. Recent attempts to prepare CA-crosslinked modified starch gels (SC) at low temperatures have resulted in low crosslinking degrees that do not meet application requirements. This study presents a new method for stable preparation of high-strength Fe3+-CA synergistic crosslinked starch gels at low temperatures (90 °C), carried out in a stable and controlled multi-physical field high-shear reaction environment. The enhancement effect of synergistic crosslinking reaction on starch gel properties was quantitatively characterized by linear and nonlinear rheological properties. The results showed that the elastic modulus of synergistically crosslinked modified SC-0.6Fe3+ (G' = 1082.71 ± 21.50) at 0.1% strain was significantly increased by 491.57% compared to the elastic modulus of SC (G' = 183.04 ± 13.32) without synergistic crosslinking modification. SC-0.6Fe3+ demonstrated the largest elastic Lissajous ring area, indicating stronger resistance to deformation in the synergistic crosslinked gel system. Additionally, adjusting the cation concentration allowed for flexible modulation of the rheological properties of starch gels. SEM and N2 adsorption data revealed that SC-0.6Fe3+ had a denser honeycomb porous structure and a smaller pore size distribution. FTIR, XRD, DSC, and TGA results suggested that the synergistic crosslinking enhancement effect might be achieved through electrostatic attraction, hydrogen bonding, ionic dipole interactions, and ester bonding. Our work provides an effective strategy for batch preparation of adjustable high-performance food-grade crosslinked starch gels in low-temperature environments.

Metal oxide thin film transistor and its active layer materials

Metal oxide thin-film transistors (MOTFTs) have the characteristics of high electron mobility, large-area production, and relatively low fabrication temperature and have received extensive attention as a research hotspot in recent years. Based on a large number of literatures, this paper introduces the typical single-component representative of MOTFT, multi-component compound oxide semiconductor active layer materials such as IZO, IGO, IGZO, etc. At the same time, due to the unique advantages of nanomaterials, material modification is carried out in different dimensions, and six physical and chemical preparation methods of its active layer are described, including a relatively unique Low-temperature preparation method based on improved gel precursor components and UV photocatalysis. Multi-component oxides and composite structures based on nanomaterials are currently the most studied fields, and on this basis, more excellent performance can be studied and prepared. It mainly summarizes its application in large-scale display and flexible electronics and looks at its development direction.

Effects of the original state of sodium-based additives on microstructure, surface characteristics and filtration performance of SiC membranes

Sodium-contained compounds are promising sintering additives for the low-temperature preparation of reaction bonded SiC membranes. Although sodium-based sintering additives in various original states were attempted, their effects on microstructure and surface properties have rarely been studied. In this work, three types of sodium-based additives, including solid-state NaA zeolite residue (NaA) and liquid-state dodecylbenzene sulfonate (SDBS) and water glass (WG), were separately adopted to prepare SiC membranes, and the microstructure, surface characteristics and filtration performance of these SiC membranes were comparatively studied. Results showed that the SiC membranes prepared with liquid-state SDBS and WG (S-SDBS and S-WG) showed lower open porosity yet higher bending strength compared to those prepared with solid-state NaA (S-NaA). The observed differences in bending strength were further interpreted by analyzing the reaction process of each sintering additive and the composition of the bonding phase in the reaction bonded SiC membranes. Meanwhile, the microstructural differentiation was correlated to the original state of the additives. In addition, their surface characteristics and filtration performance for oil-in-water emulsion were examined and correlated to the membrane microstructure. The S-NaA samples showed higher hydrophilicity, lower surface roughness (1.80 μm) and higher rejection ratio (99.99%) in O/W emulsion separation than those of S-WG and S-SDBS. This can be attributed to the smaller mean pore size and higher open porosity, resulting from the originally solid-state NaA additives. Therefore, this work revealed the comprehensive effects of original state of sintering additives on the prepared SiC membranes, which could be helpful for the application-oriented fabrication by choosing additives in suitable state.

Synthesis, Structure, and Characterizations of a Heterobimetallic Heptanuclear Complex [Pb2Co5(acac)14

An unusual heterobimetallic volatile compound [Pb2Co5(acac)14] was synthesized by the gas phase/solid-state technique. The preparation can be readily scaled up using the solution approach. X-ray powder diffraction, ICP-OES analysis, and DART mass spectrometry were engaged to confirm the composition and purity of heterobimetallic complex. The composition is unique among the large family of lead(tin): transition metal = 2:1, 1:1, and 1:2 β-diketonates compounds that are mostly represented by coordination polymers. The molecular structure of the complex was elucidated by synchrotron single crystal X-ray diffraction to reveal the unique heptanuclear moiety {Co(acac)2[Pb(acac)2-Co(acac)2-Co(acac)2]2} built upon bridging interactions of acetylacetonate oxygens to neighboring metal centers that bring their coordination numbers to six. The appearance of unique heptanuclear assembly can be attributed to the fact that the [Co(acac)2] units feature both cis- and trans-bis-bridging modes, making the polynuclear moiety rather flexible. This type of octahedral coordination is relatively unique among known lead(tin)-3d transition metal β-diketonates. Due to the high-volatility, [Pb2Co5(acac)14] can be potentially applied as a MOCVD precursor for the low-temperature preparation of lead-containing functional materials.

The electromagnetic wave absorption composite of flower-like structure NiCo2O4 and Fe3O4 derived from low-temperature preparation method

The NiCo2O4@Fe3O4 composites with excellent electromagnetic wave absorption performance was prepared by the low-temperature (50 °C) co-precipitation method, avoiding the traditional high-temperature hydrothermal synthesis method. The specific surface area of the composite material was increased due to the combination of NiCo2O4 with 3D hierarchical flower-like structure and Fe3O4 with spherical structure, which is conducive to the full reflection and scattering of electromagnetic waves. The combination of typical magnetic material and excellent dielectric material could adjust the impedance matching value of the material and thus the absorption loss performance of electromagnetic wave was improved. The ε value of the dielectric material was larger than those of magnetic materials and the maximum reflection loss value appeared at the high frequency (the thickness is small), while the μ value of magnetic materials was larger than those of dielectric materials and the maximum reflection loss value generally appeared at low frequency (the thickness is large).The results showed that the maximum RL value reached −53.35 dB at about 13 GHz with the thickness of 2.0 mm and the effective absorption bandwidth was 4.4 GHz when the weight ratio (NiCo2O4:Fe3O4) of composite samples was 6:1. The excellent EMW absorption property was mainly due to the combination of NiCo2O4 and Fe3O4, which could achieve impedance matching to loss EMW by dielectric loss and magnetic loss.

Low-temperature and short-time preparation of short rod-like Zn2GeO4:Mn2+ luminescent nanoparticles

Low-temperature and short-time preparation of short rod-like Zn2GeO4:Mn2+ luminescent nanoparticles

LTCC glass-ceramics based on diopside/cordierite/Al2O3 for ultra-high frequency applications

In this work, three glass-ceramic composites based on a commercial SiO2-B2O3-Al2O3-CaO-MgO glass and cordierite, diopside or Al2O3 were used for preparation of green tapes and low temperature cofired ceramics (LTCC) substrates. The thermal behavior, phase composition, microstructure and dielectric properties of the fabricated glass-ceramics were characterized using a heating microscope, thermal analysis, X-ray diffraction, scanning electron microscopy and time domain spectroscopy. The applicability of the developed materials for LTCC technology was demonstrated by the preparation of test multilayer substrates. The glass-ceramic substrates exhibit advantageous properties for ultra-high frequency LTCC applications, including low sintering temperatures of 900-980°C, good compatibility with commercial Ag and AgPd conductive pastes and a low dielectric permittivity of 3.5-7 at 1 THz.

Low-temperature and efficient preparation of starfish-like Mo2C/C composites from waste biomass

In this study, starfish-like Mo2C/C biomass ceramic composites were successfully prepared using waste pine as a C template precursor through rapid heat and mass transfer in a molten salt environment. The effects of the reaction temperature and molten salt on the formation of the Mo2C/C ceramic composites were investigated. The mechanism involved in the preparation of Mo2C/C ceramic composites in a molten salt liquid environment was determined. The results showed that the mixed molten salt environment comprising KF/KCl with a low KF content could promote the formation of Mo2C. The mixed molten salt environment was beneficial for the formation of regular Mo2C flakes, which interwove together to form a “starfish-like” shape as the reaction temperature increased to significantly increase the proportion of micropores and specific surface area of the composites. In addition, the formation of Mo2C in the C template occurred in two steps, where Mo first reacted with C to form MoC and the liquid Mo then reacted with MoC to form Mo2C.