Super-hydrophobic hexamethyl-disilazane modified ZrO2–SiO2 aerogels with excellent thermal stability

2016 ◽  
Vol 4 (15) ◽  
pp. 5632-5638 ◽  
Author(s):  
Jian He ◽  
Xiaolei Li ◽  
Dong Su ◽  
Huiming Ji ◽  
Xing Zhang ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Contact Angle ◽  
Elevated Temperatures ◽  
Hydroxyl Groups ◽  
Surface Groups ◽  
Hydrophobic Properties ◽  
Excellent Thermal Stability

Hexamethyl-disilazane (HMDS) is introduced to replace the hydroxyl groups of ZrO2–SiO2 aerogels (ZSAs) to form inert methyl siloxy surface groups and produce SiO2 particles as the “pinning” particles in air at elevated temperatures. Thus, HMDS/ZSAs exhibit an excellent thermal stability and super-hydrophobic properties with a contact angle of 154°.

A high-temperature dielectric polymer poly(acrylonitrile butadiene styrene) with enhanced energy density and efficiency due to a cyano group

2020 ◽  
Vol 8 (30) ◽  
pp. 15122-15129
Author(s):  
Fei Wen ◽  
Lin Zhang ◽  
Ping Wang ◽  
Lili Li ◽  
Jianguo Chen ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Energy Density ◽  
Elevated Temperatures ◽  
Cyano Group ◽  
Acrylonitrile Butadiene Styrene ◽  
Promising Candidate ◽  
Excellent Thermal Stability ◽  
Poly Acrylonitrile ◽  
Dielectric Polymer ◽  
Butadiene Styrene

An ABS film, which exhibits a high gravimetric energy density of 6.3 J g−1 with satisfactory efficiency, excellent thermal stability, and cycling reliability at elevated temperatures, is a promising candidate for high power energy storage capacitors.

scholarly journals Thermal stability of polyurethane coating prepared by using diphenylolpropane

2020 ◽  
Vol 62 (4) ◽  
pp. 81-87
Author(s):  
Indira N. Bakirova ◽  
Keyword(s):  
Thermal Stability ◽  
Thermal Decomposition ◽  
Weight Loss ◽  
Elevated Temperatures ◽  
Onset Temperature ◽  
Phenolic Hydroxyl ◽  
Hydroxyl Groups ◽  
Polyurethane Coating ◽  
Urethane Group ◽  
Thermal Stability Of

Thermal stability of polyurethane varnish coating prepared by using diphenylolpropane, polyetherpolyol and polyisocyanate with an equimolar ratio of isocyanate and hydroxyl groups was assessed in the air. The polyurethane weight loss thermogram shows three temperature regions: I – (217-275)°С, II – (275-380)°С, and III – above 380°С. For interpreting thermogram of the polyurethane under study the model substances simulating the urethane groups of a polymer were synthesized. The substance containing the urethane group formed by phenolic hydroxyl of diphenylolpropane was shown to demonstrate relatively low thermal stability and gets broken down into isocyanate and bisphenol. Decomposition of the substance containing the urethane group formed by alcoholic hydroxyl occurs at the higher temperature. The data obtained allow interpreting the occurrence of thermal decomposition step I in TGA curve by structural changes in the blocks formed by diphenylolpropane and polyisocyanate being the least stable when exposed to elevated temperatures. The next step can be attributed to decomposition of more thermostable urethane groups formed by functional groups of oligooxypropylenetriol and polyisocyanate. Transition to the step III accompanied by severe sample weight loss due to decomposition of urethane groups is explained by thermal oxidation of oligoether units of polymer. Based on the data obtained the conclusion was made that the presence of urethane groups formed by phenolic hydroxyl of diphenylolpropane in polymer structure results in the decreased thermooxidative decomposition onset temperature of polymer. At the same time, a deceleration of thermooxidative processes due to the stabilizing effect of diphenylolpropane released at the beginning of thermal decomposition of polyurethane is observed in a high-temperature region. The proposed polyurethane coating is inferior to commercial counterparts in thermal decomposition onset temperature but superior to them in the temperature corresponding to a 50% polymer weight loss.

The Reactions of Isocyanates and Isocyanate Derivatives at Elevated Temperatures

1959 ◽  
Vol 32 (2) ◽  
pp. 337-345 ◽  
Author(s):  
J. H. Saunders
Keyword(s):  
Elevated Temperatures ◽  
Temperature Stability ◽  
Hydroxyl Groups ◽  
Final State ◽  
Excellent Thermal Stability ◽  
Decomposition Reactions ◽  
Quantitative Studies ◽  
Polymer Stability ◽  
Reactive Groups ◽  
Selection Of

Abstract Qualitative and quantitative studies with model compounds have shown that a variety of reactions may occur at 100–300° in molecules containing isocyanate, urea and urethane groups. All or most of these reactions are subject to catalysis so that they may be induced to proceed at lower temperatures. These reactions are quite important as they may affect the production and practical use of polyurethanes and polyureas. By the proper selection of reaction components one may design a polyurethane or polyurea molecule which will give both a reasonable rate of cure to the final state and a degree of temperature stability suitable for many rigorous applications. The choice of reactive groups providing approximately the desired rates of reaction and of suitable catalysts may be used to achieve the necessary curing rate. The initial choice of a catalyst which will have a minimum effect on decomposition reactions, or the removal of the catalyst from the cured polymer will favor polymer stability. A selection of reactants which will minimize those decomposition reactions leading to chain rupture, and which will compensate for what rupture may occur, will promote polymer stability. Simple illustrations of such choices would include eliminating tertiary aliphatic hydroxyl groups from the hydroxyl-bearing component and including some degree of branching commensurate with the degree of elasticity or rigidity desired. Branching should be achieved through the more stable groups, e.g., urethane, urea or trimer, rather than through the less stable allophanate and biuret groups. Many thoroughly tested applications of polyurethanes and mixed polyureaurethanes show that it is readily possible to produce such polymers with excellent thermal stability.

scholarly journals Effect of Lignin Modification on Properties of Kenaf Core Fiber Reinforced Poly(Butylene Succinate) Biocomposites

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4043 ◽  
Author(s):  
Harmaen Ahmad Saffian ◽  
Kim Hyun-Joong ◽  
Paridah Md Tahir ◽  
Nor Azowa Ibrahim ◽  
Seng Hua Lee ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Maleic Anhydride ◽  
Elevated Temperatures ◽  
Kraft Lignin ◽  
Hydroxyl Groups ◽  
Fiber Reinforced ◽  
Butylene Succinate ◽  
Kenaf Core ◽  
Lignin Modification ◽  
Core Fiber

In this study, the effects of lignin modification on the properties of kenaf core fiber reinforced poly(butylene succinate) biocomposites were examined. A weight percent gain (WPG) value of 30.21% was recorded after the lignin were modified with maleic anhydride. Lower mechanical properties were observed for lignin composites because of incompatible bonding between the hydrophobic matrix and the hydrophilic lignin. Modified lignin (ML) was found to have a better interfacial bonding, since maleic anhydrides remove most of the hydrophilic hydrogen bonding (this was proven by a Fourier-transform infrared (FTIR) spectrometer—a reduction of broadband near 3400 cm−1, corresponding to the –OH stretching vibration of hydroxyl groups for the ML samples). On the other hand, ML was found to have a slightly lower glass transition temperature, Tg, since reactions with maleic anhydride destroy most of the intra- and inter-molecular hydrogen bonds, resulting in a softer structure at elevated temperatures. The addition of kraft lignin was found to increase the thermal stability of the PBS polymer composites, while modified kraft lignin showed higher thermal stability than pure kraft lignin and possessed delayed onset thermal degradation temperature.

Improvement of Thermal Stability of ZrO2-SiO2 Aerogel Modified by Ca(II) Cations

2018 ◽  
Vol 281 ◽  
pp. 105-110 ◽  
Author(s):  
Hang Yuan Zhao ◽  
Xiao Lei Li ◽  
Jian He ◽  
Zhi Peng Hu ◽  
Hui Jun Yu
Keyword(s):  
Thermal Stability ◽  
High Temperature ◽  
Calcium Nitrate ◽  
Temperature Stability ◽  
Secondary Phase ◽  
Ethanol Solution ◽  
Hydroxyl Groups ◽  
High Temperature Stability ◽  
Excellent Thermal Stability ◽  
Surface Hydroxyl

Ca (II) modified ZrO2-SiO2 aerogel (CaZSA) with excellent thermal stability at 1000 °C was prepared by aging the ZrO2-SiO2 wet gel in calcium nitrate (Ca (NO3)2) ethanol solution followed with alcohol supercritical fluid drying method. The reaction between surface hydroxyl groups on the aerogel and Ca (II) ions played an important role in reducing the high temperature activity and inhibiting the particle growth caused by the condensation of hydroxyl groups of aerogel. Moreover, tiny secondary-phase particles, Ca (II) ions, introduced along grain boundaries serve as the pinning particles to inhibit the crystallization of ZrO2-SiO2 aerogel (ZSA). Thus the high-temperature stability of ZSA was significantly improved by surface modification with Ca (II). The specific surface area of CaZSA still maintained 223 m2·g-1 after 1000 °C calcination, which was 52.7% higher than that of ZSA at the same treatment condition.

scholarly journals Hydrophobic Properties of CuO Thin Films Obtained by Sol-Gel Spin Coating Technique-Annealing Temperature Effect

2021 ◽  
Vol 45 (6) ◽  
pp. 439-445
Author(s):  
Ali Bougharouat ◽  
Nassim Touka ◽  
Dalila Talbi ◽  
Kamel Baddari
Keyword(s):  
Contact Angle ◽  
Copper Oxide ◽  
Annealing Temperature ◽  
Sol Gel ◽  
Sem Analysis ◽  
Hydroxyl Groups ◽  
Adhesive Properties ◽  
Hydrophobic Properties ◽  
Angle Measurements ◽  
Angle Data

The adhesive characteristics of sol-gel copper oxide (CuO) film surfaces at annealing temperatures ranging from 350 to 550°C were examined in this work. Hydrophobic properties of these oxide film surfaces were studied by contact angle measurements. The surface energy was calculated from contact angle data using harmonic mean method. The structural, morphological and chemical analysis of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR). The increase in annealing temperature induces a reduction in the hydrophilic properties of the films (adhesive properties). The rise in the hydrophobicity of the CuO surface has been claimed to be explained by a change in interfacial tension. The FTIR spectroscopy analysis revealed that the increase in the annealing temperature eliminates activated neutral species (hydroxyl groups) reacting with the surface of the sample responsible for the wettability. SEM analysis showed that the morphology of the samples is nanostructured containing agglomerates of various forms, a few hundred nanometers in size, randomly dispersed across the surface. The enhanced roughness of the produced film is primarily responsible for the increased hydrophobicity of the films. The XRD data reveal that the films are highly textured and that increasing the annealing temperature induces better layer crystallization and confirms the development of copper oxide CuO.

Microstructure studies of tungsten silicide schottky contacts on Gaas

1987 ◽  
Vol 45 ◽  
pp. 328-329
Author(s):  
Yih-Cheng Shih ◽  
E. L. Wilkie
Keyword(s):  
Thermal Stability ◽  
Field Effect Transistors ◽  
Schottky Contact ◽  
Schottky Contacts ◽  
Excellent Thermal Stability ◽  
Barrier Heights ◽  
Gaas Substrates ◽  
Film Adhesion ◽  
Threshold Voltages ◽  
Thermal Stability Of

Tungsten silicides (WSix) have been successfully used as the gate materials in self-aligned GaAs metal-semiconductor-field- effect transistors (MESFET). Thermal stability of the WSix/GaAs Schottky contact is of major concern since the n+ implanted source/drain regions must be annealed at high temperatures (∼ 800°C). WSi0.6 was considered the best composition to achieve good device performance due to its low stress and excellent thermal stability of the WSix/GaAs interface. The film adhesion and the uniformity in barrier heights and ideality factors of the WSi0.6 films have been improved by depositing a thin layer of pure W as the first layer on GaAs prior to WSi0.6 deposition. Recently WSi0.1 has been used successfully as the gate material in 1x10 μm GaAs FET's on the GaAs substrates which were sputter-cleaned prior to deposition. These GaAs FET's exhibited uniform threshold voltages across a 51 mm wafer with good film adhesion after annealing at 800°C for 10 min.

scholarly journals Boosted piezoelectricity with excellent thermal stability in tetragonal NaNbO3-based ceramics

2020 ◽  
Author(s):  
Lu Wang ◽  
Shengdong Sun ◽  
Huajie Luo ◽  
Yang Ren ◽  
Hui Liu ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Temperature Stability ◽  
Lead Free ◽  
Excellent Thermal Stability ◽  
Lead Free Ceramics ◽  
Piezoelectric Performance

The realization of high piezoelectric performance and excellent temperature stability simultaneously in lead-free ceramics is the key for replacing Pb-containing perovskites in industry. In this study, large piezoelectric performance (d33...

scholarly journals Anion Coordination Improves High-Temperature Performance and Stability of NaPF6-Based Electrolytes for Supercapacitors

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4409
Author(s):  
J. Landon Tyler ◽  
Robert L. Sacci ◽  
Jagjit Nanda
Keyword(s):  
Thermal Stability ◽  
Electrolyte Solution ◽  
Elevated Temperatures ◽  
Electrochemical Impedance ◽  
Cycle Life ◽  
Stable Complex ◽  
Complexing Agents ◽  
Anion Coordination ◽  
Decomposition Processes ◽  
Hexamethyl Phosphoramide

Electrolyte stability can be improved by incorporating complexing agents that bind key decomposition intermediates and slow down decomposition. We show that hexamethyl-phosphoramide (HMPA) extends both the thermal stability threshold of sodium hexafluorophosphate (NaPF6) in dimethoxyethane (DME) electrolyte and the cycle life of double-layer capacitors. HMPA forms a stable complex with PF5, an intermediate in PF6 anion thermal degradation. Unbound, this intermediate leads to autocatalytic degradation of the electrolyte solution. The results of electrochemical impedance spectroscopy (EIS) and galvanostatic cycling measurements show large changes in the cell without the presence of HMPA at higher temperatures (≥60 °C). Fourier transform infrared spectroscopy (FTIR) on the liquid and gas phase of the electrolyte shows without HMPA the formation of measurable amounts of PF5 and HF. The complimentary results of these measurements proved the usefulness of using Lewis bases such as HMPA to inhibit the degradation of the electrolyte solution at elevated temperatures and potentially lead to improve cycle life of a nonaqueous capacitor. The results showed a large increase in capacitance retention during cycling (72% retention after 750,000 cycles). The results also provide evidence of major decomposition processes (0% capacitance retention after 100,000 cycles) that take place at higher temperatures without the additive of a thermal stability additive such as HMPA.

Sign in / Sign up

Export Citation Format

Share Document