Synthesis of Al2O3–SiC from kyanite precursor

2001 ◽  
Vol 16 (6) ◽  
pp. 1609-1613 ◽  
Author(s):  
A. Amroune ◽  
G. Fantozzi

Carbothermal reduction of kyanite, a natural aluminosilicate with high alumina content (Al2O3 · SiO2), was used as a way to synthesize SiC–Al2O3 powder. Carbon black was mixed with the mineral precursor in a molar ratio of (C/SiO2) = 5.5. The Carbothermal reaction sequence was studied in the temperature range 1260–1550 °C. Completion of the reaction at 1550 °C gave β–SiC-whiskers and α–Al2O3 particles as final products. From observations, the impurities contained in the mineral precursor behave as catalysts for the vapor–liquid–solid whisker growth mechanism. When the specific surface area of the starting carbon was increased from 330 to 996 m2/g, the carbothermal reaction rate increased but the morphology of the SiC-whiskers became very irregular. This study aimed to identify the main reaction conditions for obtaining a favorable morphology of the synthesized powder for elaborating Al2O3–SiC-whisker composite materials by using low cost starting materials and a relatively simple in situ synthesis route in comparison to the conventional way of separately preparing the phases SiC (whiskers) and Al2O3 before elaborating composites.

2013 ◽  
Vol 9 ◽  
pp. 974-982 ◽  
Author(s):  
Tamashree Ghosh ◽  
Abhishek Santra ◽  
Anup Kumar Misra

A series of glycosyl hemiacetal derivatives have been transformed into thioglycosides and glycosyl thiols in a one-pot two-step reaction sequence mediated by Appel reagent (carbon tetrabromide and triphenylphosphine). 1,2-trans-Thioglycosides and β-glycosyl thiol derivatives were stereoselectively formed by the reaction of the in situ generated glycosyl bromides with thiols and sodium carbonotrithioate. The reaction conditions are reasonably simple and yields were very good.


2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Chanbasha Basheer

We applied a simple, low-cost design of glass capillary microreactor for the catalytic oxidation of benzene to phenol at ambient conditions. Polyvinylchloride-nanofiber-membrane-supported titania nanoparticle (TiO2-PVC) as catalyst and in situ production of hydroxyl radicals as oxidant. The reaction was monitored by gas chromatography-mass spectrometry (GC-MS). The reaction conditions were optimized and the performance of the microreactor was then compared with the conventional laboratory scale reaction which used hydrogen peroxide as oxidant. The microreactor gave a better yield of 14% for phenol compared to 0.14% in the conventional laboratory scale reaction. Reaction conditions such as reaction time, reaction pH, and applied potential were optimized. With optimized reaction conditions selectivity of >37% and >88% conversion of benzene were obtained.


Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3502 ◽  
Author(s):  
Xiaoqing Lian ◽  
Xiaohu Hua ◽  
Xiaogang Wang ◽  
Lirong Deng

Aiming to provide key materials in order to improve the fracture toughness of ZrB2 ceramics, ZrB2-SiC composite powders with in situ grown SiC whiskers were successfully synthesized via a simple molten-salt-assisted ferrous-catalyzed carbothermal reduction method. Thermodynamic calculations on the ZrO2-SiO2-B2O3-C-Fe system were carried out. The effects of heating temperature and ferrous catalyst amount on the growth behavior of SiC whiskers in ZrB2-SiC composite powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The results showed that the aspect ratio of SiC whiskers and the relative content of ZrB2 particles increased with increasing heating temperature (1523–1723 K) and a molar ratio of Fe to ZrSiO4 from 0:1 to 0.2:1. Phase-pure ZrB2-SiC composite powders were obtained at 1723 K when the molar ratio of raw materials was 0.2:0.5:1:1.5:8.4 (Fe:NaCl:ZrSiO4:B2O3:C). Single crystalline β-SiC whiskers with a mean diameter of 0.15 μm and an aspect ratio of 70–120 were homogeneously distributed in the final composite powders. A molten-salt-assisted iron-catalyzed vapor–solid mechanism was promoted for the growth mechanism of in situ grown SiC whiskers.


2013 ◽  
Vol 685 ◽  
pp. 357-361 ◽  
Author(s):  
Min Sha ◽  
Ren Ming Pan ◽  
Biao Jiang

Perfluoro epoxy compounds are important intermediates in organic chemistry, however, the methods for preparing them are scanty. We found that in situ generated tri-n-butylamine N-oxide and N,N-Dimethylcyclohexylamine N-oxide were found to be good reagents for the epoxidation of tri-substituted Perfluoro-2-methyl-2-pentene in good to excellent yields. Catalytic epoxidation methods were developed by coupling this reaction with the N-oxidation of tertiary amine by hydrogen peroxide or MCPBA. The advantages of these methods are easy work-up, mild reaction conditions, environmentally friendly and low cost. The reaction using MCPBA as a oxidant is better than hydrogen peroxide for it is fast and high yielding.


Catalysts ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 769
Author(s):  
Li Zhang ◽  
Sébastien Paul ◽  
Franck Dumeignil ◽  
Benjamin Katryniok

Selective oxidation of isobutane to methacrolein (MAC) and methacrylic acid (MAA) has received great interest both in the chemical industry and in academic research. The advantages of this reaction originate not only from the low cost of the starting material and reduced process complexity, but also from limiting the use of toxic reactants and the production of wastes. Successive studies and reports have shown that heteropolycompounds (HPCs) with Keggin structure (under the form of partially neutralized acids with increased stability) can selectively convert isobutane to MAA and MAC due to their strong and tunable acidity and redox properties. This review hence aims to discuss the Keggin-type HPCs that have been used in recent years to catalyze the oxidation of isobutane to MAA and MAC, and to review alternative metal oxides with proper redox properties for the same reaction. In addition, the influence of the main reaction conditions will be discussed.


Author(s):  
Jian-Shing Luo ◽  
Hsiu Ting Lee

Abstract Several methods are used to invert samples 180 deg in a dual beam focused ion beam (FIB) system for backside milling by a specific in-situ lift out system or stages. However, most of those methods occupied too much time on FIB systems or requires a specific in-situ lift out system. This paper provides a novel transmission electron microscopy (TEM) sample preparation method to eliminate the curtain effect completely by a combination of backside milling and sample dicing with low cost and less FIB time. The procedures of the TEM pre-thinned sample preparation method using a combination of sample dicing and backside milling are described step by step. From the analysis results, the method has applied successfully to eliminate the curtain effect of dual beam FIB TEM samples for both random and site specific addresses.


2019 ◽  
Author(s):  
Nikki Theofanopoulou ◽  
Katherine Isbister ◽  
Julian Edbrooke-Childs ◽  
Petr Slovák

BACKGROUND A common challenge within psychiatry and prevention science more broadly is the lack of effective, engaging, and scale-able mechanisms to deliver psycho-social interventions for children, especially beyond in-person therapeutic or school-based contexts. Although digital technology has the potential to address these issues, existing research on technology-enabled interventions for families remains limited. OBJECTIVE The aim of this pilot study was to examine the feasibility of in-situ deployments of a low-cost, bespoke prototype, which has been designed to support children’s in-the-moment emotion regulation efforts. This prototype instantiates a novel intervention model that aims to address the existing limitations by delivering the intervention through an interactive object (a ‘smart toy’) sent home with the child, without any prior training necessary for either the child or their carer. This pilot study examined (i) engagement and acceptability of the device in the homes during 1 week deployments; and (ii) qualitative indicators of emotion regulation effects, as reported by parents and children. METHODS In this qualitative study, ten families (altogether 11 children aged 6-10 years) were recruited from three under-privileged communities in the UK. The RA visited participants in their homes to give children the ‘smart toy’ and conduct a semi-structured interview with at least one parent from each family. Children were given the prototype, a discovery book, and a simple digital camera to keep at home for 7-8 days, after which we interviewed each child and their parent about their experience. Thematic analysis guided the identification and organisation of common themes and patterns across the dataset. In addition, the prototypes automatically logged every interaction with the toy throughout the week-long deployments. RESULTS Across all 10 families, parents and children reported that the ‘smart toy’ was incorporated into children’s emotion regulation practices and engaged with naturally in moments children wanted to relax or calm down. Data suggests that children interacted with the toy throughout the duration of the deployment, found the experience enjoyable, and all requested to keep the toy longer. Child emotional connection to the toy—caring for its ‘well-being’—appears to have driven this strong engagement. Parents reported satisfaction with and acceptability of the toy. CONCLUSIONS This is the first known study investigation of the use of object-enabled intervention delivery to support emotion regulation in-situ. The strong engagement and qualitative indications of effects are promising – children were able to use the prototype without any training and incorporated it into their emotion regulation practices during daily challenges. Future work is needed to extend this indicative data with efficacy studies examining the psychological efficacy of the proposed intervention. More broadly, our findings suggest the potential of a technology-enabled shift in how prevention interventions are designed and delivered: empowering children and parents through ‘child-led, situated interventions’, where participants learn through actionable support directly within family life, as opposed to didactic in-person workshops and a subsequent skills application.


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yongmeng Wu ◽  
Cuibo Liu ◽  
Changhong Wang ◽  
Yifu Yu ◽  
Yanmei Shi ◽  
...  

AbstractElectrocatalytic alkyne semi-hydrogenation to alkenes with water as the hydrogen source using a low-cost noble-metal-free catalyst is highly desirable but challenging because of their over-hydrogenation to undesired alkanes. Here, we propose that an ideal catalyst should have the appropriate binding energy with active atomic hydrogen (H*) from water electrolysis and a weaker adsorption with an alkene, thus promoting alkyne semi-hydrogenation and avoiding over-hydrogenation. So, surface sulfur-doped and -adsorbed low-coordinated copper nanowire sponges are designedly synthesized via in situ electroreduction of copper sulfide and enable electrocatalytic alkyne semi-hydrogenation with over 99% selectivity using water as the hydrogen source, outperforming a copper counterpart without surface sulfur. Sulfur anion-hydrated cation (S2−-K+(H2O)n) networks between the surface adsorbed S2− and K+ in the KOH electrolyte boost the production of active H* from water electrolysis. And the trace doping of sulfur weakens the alkene adsorption, avoiding over-hydrogenation. Our catalyst also shows wide substrate scopes, up to 99% alkenes selectivity, good reducible groups compatibility, and easily synthesized deuterated alkenes, highlighting the promising potential of this method.


Author(s):  
Zhikai Shi ◽  
Zebin Yu ◽  
Ronghua Jiang ◽  
Jun Huang ◽  
Yanping Hou ◽  
...  

The oxygen evolution reaction (OER) is an important half-reaction in the field of energy production. However, how effectively, simply, and greenly to prepare low-cost OER electrocatalysts remains a problem. Herein,...


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