Effect of Calcination Temperature on Mechanical Properties of Magnesium Oxychloride Cement

In order to make full use of magnesium chloride resources, the development and utilisation of magnesium oxychloride cement have become an ecological and economic goal. Thus far, however, investigations into the effects on these cements of high temperatures are lacking. Herein, magnesium oxychloride cement was calcinated at various temperatures and the effects of calcination temperature on microstructure, phase composition, flexural strength, and compressive strength were studied by scanning electron microscopy, X-ray diffraction, and compression testing. The mechanical properties varied strongly with calcination temperature. Before calcination, magnesium oxychloride cement has a needle-like micromorphology and includes Mg(OH)2 gel and a trace amount of gel water as well as 5 Mg(OH)2·MgCl2·8H2O, which together provide its mechanical properties (flexural strength, 18.4 MPa; compressive strength, and 113.3 MPa). After calcination at 100 °C, the gel water is volatilised and the flexural strength is decreased by 57.07% but there is no significant change in the compressive strength. Calcination at 400 °C results in the magnesium oxychloride cement becoming fibrous and mainly consisting of Mg(OH)2 gel, which helps to maintain its high compressive strength (65.7 MPa). When the calcination temperature is 450 °C, the microstructure becomes powdery, the cement is mainly composed of MgO, and the flexural and compressive strengths are completely lost.

Interactions between atomically dispersed copper and phosphorous species are key for the hydrochlorination of acetylene

Vinyl chloride, the monomer of polyvinyl chloride (PVC), is industrially synthesized via acetylene hydrochlorination. Thereby, easy to sublimate but toxic mercury chloride catalysts are widely used. It is imperative to find environmentally friendly non-mercury catalysts to promote the green production of PVC. Low-cost copper-based catalysts are promising candidates. In this study, phosphorus-doped Cu-based catalysts are prepared. It is shown that the type of phosphorus configuration and the distribution on the surface of the carrier can be adjusted by changing the calcination temperature. Among the different phosphorus species, the formed P-C bond plays a key role. The coordination structure formed by the interaction between P-C bonds and atomically dispersed Cu2+ species results in effective and stable active sites. Insights on how P-C bonds activate the substrate may provide ideas for the design and optimization of phosphorus-doped catalysts for acetylene hydrochlorination.

LaNiO3 Perovskite Synthesis through the EDTA–Citrate Complexing Method and Its Application to CO Oxidation

A series of LaNiO3 materials were synthesized by the EDTA–citrate complexing method, modifying different physicochemical conditions. The LaNiO3 samples were calcined between 600 and 800 °C and characterized by XRD, SEM, XPS, CO-TPD, TG, DT, and N2 adsorption. The results evidence that although all the samples presented the same crystal phase, LaNiO3 as expected, some microstructural and superficial features varied as a function of the calcination temperature. Then, LaNiO3 samples were tested as catalysts of the CO oxidation process, a reaction never thoroughly analyzed employing this material. The catalytic results showed that LaNiO3 samples calcined at temperatures of 600 and 700 °C reached complete CO conversions at ~240 °C, while the sample thermally treated at 800 °C only achieved a 100% of CO conversion at temperatures higher than 300 °C. DRIFTS and XRD were used for studying the reaction mechanism and the catalysts’ structural stability, respectively. Finally, the obtained results were compared with different Ni-containing materials used in the same catalytic process, establishing that LaNiO3 has adequate properties for the CO oxidation process.

Study on Formation Kinetics and Mechanism of Barium-Calcium Phosphoaluminate Mineral

Barium-calcium phosphoaluminate ((C,B)8A6P) mineral was synthesized by introducing Ba2+ into the lattice of calcium phosphoaluminate (C8A6P) mineral and it owned the better hydration activity than C8A6P. In this study, the formation kinetics and mechanism of (C,B)8A6P mineral was firstly systematically explored. The experimental results indicated that calcination temperature had a significant effect on the formation of (C,B)8A6P mineral. The conversion rate of (C,B)8A6P mineral was less than 0.5 and reaction rate was less than 9.4 × 10-7 with the holding time of 8 h at 1500-1530 °C. Nevertheless, the conversion rate and reaction rate reached 0.8 and 9.4 × 10-7, respectively, with the holding time of only 2 h when the calcination temperature ranged from 1540 °C to 1560 °C. In addition, the Jander equation was feasible for the formation of (C,B)8A6P with activation energy of 1310 kJ ∙ mol-1 at 1500-1530 °C, while the Ginstling equation was feasible for use with activation energy of 324 kJ ∙ mol-1 when the calcination temperature ranged from 1540 to 1560 °C.

Effect of calcination temperature on the morphology and catalytic properties of ZnO nanostructures fabricated from a chiral precursor for photodegradation of both cationic and anionic dyes

Diverse ZnO nanostructures (ZnO_1 to ZnO_3) were synthesized by direct calcination of a chiral MOF precursor {[Zn4(µ3-OH)2(D-2,4-cbs)2(H2O)4].5H2O}n (Zn-CBS) at three different temperatures 600, 700 and 800 oC, respectively. On the...

Effect of calcination temperature and Ti substitution on optical properties of (Fe,Cr)2O3 cool black pigment prepared by spray pyrolysis

Ti-Dispersed (Fe,Cr)2O3 cool black pigment particles synthesized by a spray pyrolysis process showed improvement in NIR reflectance by about 10.0% and heat-shielding performance.

Adsorption performances and electrochemical characteristics of methyl blue onto magnesium-zinc ferrites

A novel and facile rapid combustion approach was developed for the controllable preparation of small size and easy recovery magnesium-zinc ferrites for methyl blue (MB) removal in dye solution. The effects of prepared criteria of x value, calcination temperature, and the amount of ethanol on the average grain sizes and magnetic property were reviewed. The characterization results displayed that Mg0.5Zn0.5Fe2O4 nanoparticles met the expectations of the experiment at the calcination temperature of 400℃ with absolute ethanol volume of 20 mL, and they were selected to remove MB. The adsorption process belonged to chemical adsorption on the basis of the pseudo-second-order model. The electrochemical characteristics of MB onto the prepared nanoparticles were analyzed by cyclic voltammetry (CV). The influences of pH and cycle times on the removal efficiency were investigated. When the pH went beyond 3, the removal efficiency of MB onto the magnetic Mg0.5Zn0.5Fe2O4 nanoparticles maintained above 99%，the maximum adsorption capacity was 318.18 mg/g. After seven cycles, the relative removal rate of MB remained 96% of the first one.

Synthesis of Mesoporous Cu-Ni/Al2O4 Catalyst for Hydrogen Production via Hydrothermal Reconstruction Route

Mesoporous Cu-Ni/Al2O4 catalyst of high surface area (176 m2g−1) is synthesized through a simple hydrothermal reconstruction process by using low-cost activated alumina as the aluminate source without organic templates. The desired mesoporous structure of the catalyst is formed by the addition of Cu2+ and Ni2+ metal ions in the gel solution of the activated alumina followed by hydrothermal treatment at 70 °C and calcination at temperatures in the range of 600 to 800 °C. To consider the environmental concern, we found the concentration of the Cu2+ and Ni2+ ion in the residual filtrate is less than 0.1 ppm which satisfies the effluent standard in Taiwan (<1.0 ppm). The effects of the pH value, hydrothermal treatment time, and calcination temperature on the structure, morphology and surface area of the synthesized Cu-Ni/Al2O4 composites are investigated as well. In addition, the Cu-Ni/Al2O4 catalyst synthesized at pH 9.0 with a hydrothermal treatment time of 24 h and a calcination temperature of 600 °C is used for hydrogen production via the partial oxidation of methanol. The conversion efficiency is found to be >99% at a reaction temperature of around 315 °C, while the H2 yield is 1.99 mol H2/mol MeOH. The catalyst retains its original structure and surface area following the reaction process, and is thus inferred to have a good stability. Overall, the hydrothermal reconstruction route described herein is facile and easily extendable to the preparation of other mesoporous metal-alumina materials for catalyst applications.

Impurity Defect Induced Ferromagnetism Investigation of SiO2-Supported NiO Particles

This study examines amorphous SiO2-supported NiO particles by nickel concentration and calcination temperature arrangement to determine photoluminescence emission peaks and magnetic properties. Conventional co-precipitation with thermal calcination was used to produce NiO nanoparticles. Cubic NiO crystallization with single phase was improved by doubling the nickel concentration by calcination at 500 ºC and 600 ºC. Average crystalline size of 72 nm was obtained in the samples where double nickel concentration with calcination temperature at 600 ºC. Granular forms have been observed in all samples, and nickel clusters were shown in the samples where the nickel concentration is twice as high. Green band emission intensity increases with improved NiO crystallinity due to surface oxygen vacancies at 505 nm. It is interesting to observe ferrimagnetism for SiO2-supported NiO particles calcined at 500 ºC. From these results, optimal synthesis procedure and reduction in nucleation growth of NiO nanoparticles was achieved by double nickel concentration with calcination temperature at 600 ºC. Resumen. Este estudio examina partículas de NiO soportadas en SiO2. El estudio comprende la variación de la concentración de níquel y la temperatura de calcinación para determinar los picos de emisión de fotoluminiscencia y las propiedades magnéticas. Se utilizó la coprecipitación convencional con calcinación para producir nanopartículas de NiO. Se mejoró la cristalización cúbica de NiO con fase única al duplicar la concentración de níquel y calcinación a 500 ºC y 600 ºC. Se obtuvo un tamaño cristalino promedio de 72 nm en las muestras donde se duplicó la concentración de níquel con temperatura de calcinación a 600 ºC. Se observaron formas granulares en todas las muestras, y se encontraron agregados de níquel en las muestras donde la concentración de níquel fue el doble. La intensidad de la banda de emisión aumenta con la cristalinidad de NiO debido a las vacantes de oxígeno en la superficie. Es interesante observar el ferrimagnetismo de las partículas de NiO soportadas en SiO2 calcinadas a 500 ºC. A partir de estos resultados, se logró un procedimiento de síntesis óptimo y la reducción del crecimiento de nucleación de nanopartículas de NiO mediante una concentración doble de níquel con una temperatura de calcinación de 600 ºC.