In situ filling of SiO2 nanospheres into PTFE by sol–gel as a highly wear-resistant nanocomposite

In situ filling of nanomaterials into polymers facilitates the dispersion of the nanofillers and their interface combination with the matrices, and reduces the agglomeration encountered in the nanocomposites prepared by a mechanical mixing method. Polytetrafluoroethylene (PTFE) nanocomposites filled with SiO₂ nanospheres (SNS) were fabricated by an in situ sol–gel method in this paper. The SNS in situ filled was highly dispersed in PTFE and showed an excellent combination with the matrix, and the fabricated SNS/PTFE nanocomposites were found a pronounced improvement in stiffness, hardness, glass transition temperature, and hydrophobicity in comparison with the pristine PTFE and the ones prepared by mechanical mixing with the same content. Furthermore, significantly reduced coefficients of friction and volume wear rates were observed on the SNS/PTFE nanocomposites prepared by in situ sol–gel. An operating temperature high up to 200°C and very low volume wear rate were accessible on the optimized SNS/PTFE nanocomposite by in situ filling. The methodology, in situ filling of nanofillers into matrices, might pave a way to prepare nanocomposites with excellent mechanical, thermal, and tribological properties.     

In situ Raman spectroscopic–electrochemical studies of lithium-ion battery materials: a historical overview

In this review, the recent advances in the development of in situ Raman spectroscopy and electrochemical techniques and their application for the study of lithium-ion batteries are revisited. It is demonstrated that, during a relatively short period of time (1995–2013), the spectroelectrochemical techniques used for the investigation of battery components, benefited directly from the tremendous advances of Raman technology. The most important step was the implementation of confocal Raman microscopy in the battery research, which opened the way to new and more sophisticated applications. This review shows how the discovery of new Raman techniques such as surface-enhanced Raman scattering, tip-enhanced Raman spectroscopy, spatially offset Raman spectroscopy as well as the integration of Raman spectrometers into non-optical microscopes, for example AFM and SEM, allowed to perform two or more analytical techniques on the same sample region, with an exceptionally high resolution. All these progresses led to new insights into battery materials and components such as electrodes and electrolytes, and helped to understand the electrode/electrolyte interface phenomena. This enhanced understanding allowed a deeper insight into important phenomena, as e.g., battery aging and the dynamic nature of the solid electrolyte interfaces in lithium batteries. The high relevance of the information provided by these techniques in the progress of battery modeling is another positive contribution. Another area of high practical significance for the battery field is the screening of electrode materials, which is facilitated by the availability of the data provided by spectroscopic methods.     

In situ synthesis of vanadium carbide–copper nanocomposite by a modified mechanochemical combustion method

Synthesis of vanadium carbide–copper nanocomposite was achieved via mechanochemical combustion method from reactant mixture of V₂O₅, CuO, C and Mg powders. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). X-ray diffraction investigations indicated that the combustion products were V₄C₃, V₂C and Cu phases. Microstructural studies showed that a nanostructured powder with a mean particle size of about 100 nm was procured in the samples milled for 90 min.     

In situ EXAFS study of the bimetallic interaction in a rhenium-promoted alumina-supported cobalt Fischer–Tropsch catalyst

The local environments about the rhenium atoms in a Co–Re/-Al₂O₃ catalyst after different reduction periods have been studied by X-ray absorption spectroscopy (EXAFS). The bimetallic catalyst containing 4.6 wt% cobalt and 2 wt% rhenium has been compared with a corresponding monometallic sample with 2 wt% rhenium on the same support. The rhenium L_III EXAFS analysis shows that bimetallic particles are formed after reduction at 450C with the average particle size being less than 15 Å. More than 6 h reduction at 450C is required for complete reduction of accessible rhenium.     

In situ synthesis of ZrB2–ZrC–SiC ultra-high-temperature nanocomposites by a sol–gel process

ABSTRACT

ZrB₂–ZrC–SiC is one of the ultra-high-temperature ceramic composites with excellent properties. In this research, high-purity ZrB₂–ZrC–SiC nanopowders were synthesised using a carbothermal reduction reaction at a relatively low temperature (1370°C) from cost-effective zirconium(IV) chloride by a sol–gel method. The effect of heat treatment temperature on the synthesis of ZrB₂–ZrC–SiC composite powder was studied. X-ray diffractometry results showed that the phases ZrB₂, β-SiC and ZrC were synthesised at 1370°C. The mean crystallite sizes for each of the phases were calculated using the Scherrer method. The specific surface area for the sample calcined at 1370°C was 81.479?m²?g^?1. SEM observation revealed that the particles had a size lower than 250?nm. Backscattered electron image and map analysis with scanning electron microscopy showed that a suitable phase homogeneity was achieved, as confirmed by energy-dispersive X-ray spectroscopy.     

In situ incorporation and loading of copper nanoparticles into a palmitic–lauric phase-change material on polyester fibers

This article introduces a facile approach for applying a eutectic mixture of fatty acid phase-change materials (PCMs) on polyester fibers for thermal conductivity improvement via the in situ incorporation of copper nanoparticles. For this purpose, a eutectic mixture of palmitic acid and lauric acid was applied as PCMs and ascorbic acid was applied for the synthesis of copper nanoparticles. The thermal properties and stability of the treated samples were also determined by differential scanning calorimetry and thermogravimetry analysis. The treated samples indicated appropriate phase-transition temperatures between 29.1 and 36.8 °C, with relevant latent heats of 49.4 and 49.9 J/g, respectively. The in situ formation of copper nanoparticles into eutectic fatty acid applied on the polyester fibers resulted in the promotion of the thermal conductivity of the composite by about 100.1% with the maximum amount of nanoparticles. In addition, the treated samples maintained good thermal durability and stability after 100 melting and freezing cycles. In addition, the tensile strength of the treated samples was improved. Overall, this treatment could be used to produce promising form-stabilized composite PCMs and thermoregulated polymers and textiles with appropriate phase-transition ranges and thermal conductivity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46951.     

In situ catalyst activity control in a novel membrane reactor—Reaction driven wireless electrochemical promotion of catalysis

A dual chamber membrane reactor was used in order to study the effect of macroscopically applied oxygen chemical potential differences to a platinum catalyst supported on a mixed oxygen ion and electronic conducting membrane. It is believed that the oxygen chemical potential difference imposed by the use of an oxygen sweep in one of the reactor chambers causes the back-spillover of oxygen species from the support onto the catalyst surface, resulting in the modification of the catalytic activity. The use of different sweep gases, such as ethylene and hydrogen was investigated as the means to reverse the rate modification by removing the spilt over species from the catalyst surface and returning the system to its initial state.Oxygen sweep in general had a positive effect on the reaction rate with rate increases up to 20% measured. Experimental results showed that hydrogen is a more potent sweep gas than ethylene in terms of the ability to reverse rate modification. A 10% rate loss was observed when using an ethylene sweep as compared with an almost 60% rate decrease when hydrogen was used as the sweep gas.     

In situ compatibilization of a polyethylene,polypropylene, and polystyrene ternary blend through Friedel–Crafts alkylation

The Friedel–Crafts alkylation reaction has been applied to reactively compatibilize a ternary blend of high-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS). The reactions were carried out in an internal mixer using varying catalyst concentrations. The resulting compatibilizer was quantified after Soxhlet extraction. In addition, p-substitution due to the grafting of alkyl groups onto the PS benzene ring was identified via nuclear magnetic resonance spectroscopy. The size of the PS domain in the reactive compositions is decreased by 80%. Moreover, the phase in which PS droplets were dispersed varied, that is, in the nonreactive blends they were found in the PP phase and in the reactive blends they shifted toward the HDPE phase. The effect of the compatibilizing agent was to improve the mechanical properties of the blend. Even with the lowest catalyst content, the properties of elongation-at-break, tensile strength, toughness, and elastic modulus showed improvements. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48295.     

Synthesis of a Re-usable Cellobiase Enzyme Catalyst through In situ Encapsulation in Nonsurfactant Templated Sol–Gel Mesoporous Silica

We present a re-usable enzyme catalyst system via direct encapsulation of cellobiase in nonsurfactant templated sol?Cgel mesoporous silica host material with d-fructose as the template. The pore diameter and porosity of the silica host material, controlled by the fructose content, controlled the diffusion of substrate to the enzyme. This in situ immobilized cellobiase showed little or no leakage while could be repeatedly used as biocatalyst with little or no loss of activity after at least 9 cycles.     

In situ analysis of metal-oxide systems used for selective oxidation catalysis: how essential is chemical complexity?

The mode of operation of selective oxidation reactions is described by a series of chemical rules defining the catalyst and some reaction intermediates. In contrast to catalytic processes over metallic elements, little is known, however, about the atomistic details of selective oxidation. In particular, the participation of the subsurface region of the catalyst in the kinetically relevant elementary steps (Mars–van Krevelen mechanism) is not positively verified. Using in situ X-ray absorption techniques to study binary and ternary molybdenum oxides the present contribution shows that it is possible to tackle some of the problems in selective oxidation by direct experimental observation. The modification of the Mo–O local bonding interaction upon thermal reduction of MoO₃to MoO_3-x is illustrated. This was also found for mixed Mo–V oxides in which the chemical state of the vanadium seemed unaffected by the reaction but the surface Mo:V ratio varied substantially with the gas phase composition. It is further shown that the solid-state phase transformation between reduced and oxidised forms of molybdenum oxides occur so rapidly, that possibly relevant suboxide cannot be identified by ex situ phase analysis. Observation of the time-law of redox transformations showed that lattice oxygen is only available for selective oxidation if the associated solid-state transformation occurs in the kinetic regime of reaction control and not in that of diffusion control.     

In situ Mössbauer spectroscopy in catalysis

As one of a handful of tools capable of giving chemical and structural information on working catalysts at reaction conditions, Mössbauer spectroscopy is in an elite group of in situ characterization methods. This focus on ⁵⁷Fe applications reviews the method and discusses phase identification and transformation kinetics, particle size measurements, and the self assembly of bimetallic systems to catalyze methanol synthesis.     

In situ Reaction Synthesis and Mechanical Properties of TaC–TaSi2 Composites

TaC–TaSi₂ composites were fabricated at 1700°C by an in situ reaction/hot pressing method using Ta, Si, and graphite as initial materials. TaSi₂ content was 0–100 vol%. The microstructure and mechanical properties of the composites were investigated. It was found that the relative densities of composites were above 97.5% when the volume content of TaSi₂ was above 10%. The TaC/10 vol% TaSi₂ composite presented the highest flexural strength of 376 MPa. When the TaSi₂ content was 30–50 vol%, the composites showed the highest fracture toughness of about 4.3 MP·am^1/2. In addition, the composites could retain high Young's modulus up to at least 1525°C.     

In situ miniemulsion polymerization of water-borne polyurethanes（Ⅰ）Competition of polyaddition with hydrolysis of isocyanate

采用异佛尔酮二异氰酸酯(IPDI)与憎水性二醇进行原位细乳液聚合制备水性聚氨酯,根据已建立的FTIR定量分析方法来表征聚合产物结构,通过产物中氨酯键/脲键的浓度比来研究主反应（加聚）与副反应（水解）的竞争。考察了憎水性二醇、乙烯基单体、反应温度、催化剂和乳化剂等因素对主副反应竞争情况的影响,并建立细乳液中加聚与水解反应竞争的物理模型。研究发现,二醇的反应活性越高越有利于加聚反应;乙烯基单体的引入能够抑制水解反应,促进加聚反应,而且其水溶性越小,加聚反应更容易在竞争中占优势;降低反应温度和增加催化剂浓度可促进加聚反应,抑制水解反应。     

In situ formation of SiC in Al–40Si alloy during high-pressure solidification

The in situ formation of SiC in Al–40Si alloys during the fabrication of SiC/Al–Si composites by high-pressure solidification were investigated. The results demonstrate that the in situ formation of SiC occurs by a gradual conversion of Al₄C₃ and Al₄SiC₄ to SiC. In situ SiC can be formed in an Al–40Si alloy solidified under a pressure of 3 GPa at a temperature of 1373 K. The SiC particles (SiC_p) formed in situ was compatible with the α-Al matrix and the Si phases. The relative density of the SiC/Al-38.6Si composite was 99.9%. The bending strengths of the Al–40Si alloy and the SiC/Al-38.6Si composite obtained by solidification under a pressure of 3 GPa were 200.8 MPa and 322 MPa, respectively, which represents an enhancement of 60.3% as a result of reinforcement by the in situ-formed SiC.     

In situ X-ray diffraction study of the growth of nitrogen-doped carbon nanofibers by the decomposition of ethylene–ammonia mixtures on a Ni–Cu catalyst

The growth of nitrogen-doped carbon nanofibers (N-CNFs) by the decomposition of ethylene–ammonia mixtures on a Ni–Cu catalyst was studied using in situ X-ray diffraction analysis. The catalyst consists of the Ni-enriched (Ni_0.85Cu_0.15) and Cu-enriched (Cu_0.95Ni_0.05) alloys. It was found that the growth of N-CNFs, similar to the growth of carbon nanofibers, proceeds on the Ni-enriched alloy, whereas the Cu-enriched alloy remains inactive. During the N-CNF growth, carbon dissolves in the Ni_0.85Cu_0.15 alloy with the formation of a oversaturated solid solution, but without formation of bulk nickel carbide. It was supposed that nitrogen also dissolves in this alloy, but the driving force is the primary dissolution of carbon.     

In situ studies of oxidation of ZrB2 and ZrB2–SiC composites at high temperatures

High temperature oxidation of ZrB₂ and the effect of SiC on controlling the oxidation of ZrB₂ in ZrB₂–SiC composites were studied in situ, in air, using X-ray diffraction. Oxidation was studied by quantitatively analyzing the crystalline phase changes in the samples, both non-isothermally, as a function of temperature, up to ～1650 °C, as well as isothermally, as a function of time, at ～1300 °C. During the non-isothermal studies, the formation and transformation of intermediate crystalline phases of ZrO₂ were also observed. The change in SiC content, during isothermal oxidation studies of ZrB₂–SiC composites, was similar in the examined temperature range, regardless of sample microstructure and composition. Higher SiC content, however, markedly retarded the oxidation rate of the ZrB₂ phase in the composites. A novel approach to quantify the extent of oxidation by estimating the thickness of the oxidation layer formed during oxidation of ZrB₂ and ZrB₂–SiC composites, based on fractional conversion of ZrB₂ to ZrO₂ in situ, is presented.     

In situ measurement of combustion wave propagation during combustion synthesis of α-Si3N4 powder

α-Si₃N₄ powder was prepared by combustion synthesis method. The propagation characteristics of combustion wave were investigated by thermocouple temperature measurement and “resistance—combustion wave displacement response device.” The results show that the combustion reaction takes place in a narrow area, and there is a maximum temperature gradient of 180°C/mm in the combustion front. The “resistance—combustion wave displacement response device” was innovatively used to realize the in situ measurement of combustion wave propagation process. The test results showed the pulse combustion mode in which the combustion front took 10 s as a cycle, and the quantitative data of Si–N₂ discrete combustion characteristics were obtained for the first time.