Composition Of Reaction Products Research Articles

Characterizing the effects of Al(OH)3 and Mg(OH)2 on reaction products and drying shrinkage characteristics of alkali-activated slag

This study is undertaken to explore the relationship between the reaction products and the drying shrinkage of alkali-activated slag (AAS) with the varying hydroxide dosage. AAS pastes were firstly produced with either Al(OH)3 or Mg(OH)2 to investigate the effects of hydroxide on the composition of reaction products and the drying shrinkage of AAS. Secondly, the main reaction products formed in AAS pastes, viz. C4AH13, M4AH10, C-S-H, C-A-S-H and C-M-S-H, were synthesized individually. Synthetic products were then taken to cast the respective paste sample to examine the performance against the drying exposure. The results show that adding Mg(OH)2 indeed improved the shrinkage resistance of AAS. This is primarily connected to the increased crystalline phases, namely the hydrotalcite-like phases and the unreacted Mg(OH)2. Whereas adding Al(OH)3 did not relieve the drying shrinkage of AAS as the interlayer spacing of C-A-S-H was enlarged, which in turn allowed for more shrinkage. Further, the investigation of individual synthetic products illustrates that their drying shrinkage scales satisfied the following order: C4AH13 < M4AH10 < C-M-S-H < C-S-H < C-A-S-H. Moreover, the shrinkage scale of C-S-H was found to evolve as the Ca/Si ratio decreased.

Reusing waste red brick powder as partial mineral precursor in eco-friendly binders: Reaction kinetics, microstructure and life-cycle assessment

A large number of solid wastes are produced in the process of demolishing old buildings, and waste red brick is one of such wastes. To discuss the reutilization of waste red brick powder (WRBP) in alkali-activated material, a novel ternary eco-friendly binder was prepared by using slag, fly ash and WRBP as precursor. The impact of WRBP on the reaction kinetics, microstructure and life-cycle assessment of alkali-activated cement paste were evaluated. The Johnson-Mehl-Avrami-Kolmogrov model was established based on the heat release results. With the incorporation of WRBP, the degree of reaction was deepened, supporting the enhancement of matrix strength. X-ray diffraction and thermogravimetric analysis results show the consistent mineralogical composition of reaction products and increase of gel quantity. Pore characteristics determined by mercury intrusion porosimetry method exhibit that large capillary pores were refined by enrichment of gels and filling effect of WRBP. From the economic and environmental aspects, the reuse of WRBP significantly saved the energy consumption and reduced the carbon dioxide (CO2) emission. On the basis of the optimal compressive strength, the energy consumption efficiency index and CO2 intensity index were 27.3 MJ/MPa and 1.7 kg/MPa, which can provide 38.55% energy consumption and 44.90% carbon footprint savings. Such work may shed valuable insights to the recycling of various types of solid waste and low-carbonation of building field.

Influences of different bischofite on the properties of magnesium oxychloride cement

In recent years, magnesium oxychloride cement (MOC) has been widely used in the field of building materials. As the main raw material in MOC, bischofite plays an important role in the composition, performance, and cost of MOC. This work systematically investigated the influence of salt lake/marine bischofite on the properties of MOC pastes, and a series of tests on the compressive strength, water resistance, reaction product composition, thermal stability, and microstructure of the MOC pastes was carried out. The results indicated that salt lake bischofite had lower content of impurity ions than marine bischofite, which endowed salt lake bischofite-based MOC with better mechanical strength, thermal stability, and microstructure than marine bischofite-based MOC. In addition, the anions in bischofite were the leading factor in the phase composition difference of MOC, and the dissolution rate of the cations was related to the Coulombic forces of the ions.

Pyrolysis of Polyamide-Containing Materials. Process Features and Composition of Reaction Products

Pyrolysis of Polyamide-Containing Materials. Process Features and Composition of Reaction Products

In situ study of solid-state synthesis of Li4Ti5O12–Li2TiO3 and Li4Ti5O12–TiO2 composites

Lithium titanate Li4Ti5O12 (LTO) with a spinel structure has been actively studied as a potential candidate for the negative electrode material in lithium ion batteries. In this work, LTO-Li2TiO3 (LTC) and LTO-TiO2 (LTT) composites were investigated. The use of powder X-ray diffraction (PXRD) with synchrotron radiation (SR) made it possible to trace the process of formation of the composites in situ and obtain information on changes in the phase composition of reaction products depending on the temperature and the ratio of the initial reagents, Li2CO3 and TiO2. It was found that irrespective of the initial ratio of reagents (lack of Li2CO3, stoichiometric ratio or excess of Li2CO3 for LTC, LTO and LTT samples, respectively), the synthesis proceeds in three stages, including formation of nanocrystalline Li2TiO3 as intermediate phase. LTC composites consist of microparticles of Li4Ti5O12phase covered by a layer of Li2TiO3phase, whereas in LTT composites large particles of TiO2 phase are surrounded by microparticles of LTO phase. Electrochemical studies showed that LTT composites have relatively low capacity as expected assuming that TiO2 is electrochemically inactive phase in the composites. In contrast, LTC composites have a specific capacity of 187 mAh/g that exceeds the theoretically expected capacity values. According to high-resolution electron microscopy data (HREM), LTC composites have a large number of Li4Ti5O12/Li2TiO3 interfaces, which are diffuse and seem to be coherent due to similarity of crystal structures LTO and Li2TiO3.

UV‐Induced C−H Functionalization of Alkanes with NO2 in Supercritical Carbon Dioxide

AbstractA novel catalyst‐free method for functionalization of unbranched alkanes via radical nitration with UV‐activated nitrogen oxide (IV) in supercritical carbon dioxide medium has been developed. The method allows to transform these inactive substrates into corresponding nitrates and nitro compounds with outstanding yields (up to 65 %), using available reagents (NO2, O2) under mild reaction conditions (35–50 °C), and exhibits lower hazards compared to conventional analogues. An improved selectivity towards the nitrates has been achieved by adding pure oxygen to the reaction. Based on changes in reaction rate and product composition, the plausible reaction mechanism for the UV‐induced C−H functionalization of alkanes with nitrogen oxide (IV) and pure oxygen has been proposed.

Chloride binding behavior of synthesized reaction products in alkali-activated slag

The chemical composition and surface properties of reaction products in alkali activated slag (AAS) are different from ordinary Portland cement, thus significantly affect their chloride binding behavior. The objective of this study is to investigate the relationship between physical/chemical characteristics and chloride binding capacity of the reaction products in AAS, i.e. C-S-H gel, C-A-S-H gel and LDHs. In this study, typical reaction products with different chemical compositions in AAS were chemically synthesized and characterized by XRD, NMR, BET and zeta potential. The chloride binding capacity of synthesized reaction products was evaluated in neutral and alkaline NaCl solution. The results indicate that C-S-H and C-A-S-H gels bind chlorides more physically. The increase of Ca/Si ratio and Al/Si ratio results in more positive zeta potential, which is beneficial for chloride binding of C-(A)-S-H gels. Further, the chloride binding capacity of C-A-S-H gels is higher than C-S-H gel, due to more positive zeta potential and larger layer spacing in the presence of Al. LDHs possess higher chloride binding capacity than C-(A)-S-H gels, due to its higher specific surface area (120.3–125.5 m2/g) and positive zeta potential (22.5–28.5 mV); the increase of Mg/Al ratio results in increased layer spacing and subsequently higher chloride binding capacity. The physical binding contributed most chloride binding of LDHs; due to the difficulty of exchange between Cl− and intercalated CO32− in Mg-Al LDH, its chemical binding is weak, which is resulted from the entering of chlorides into the interlayer from the edge of LDHs.

Introduction of tungsten carbide into 08Kh18N10T corrosion-resistant steel and its effect on mechanical properties

Interfacial phenomena and reactions between tungsten semicarbide (W2C) and corrosion-resistant steel melt have been studied using wetting experiments. This process was followed by the method of high­temperature contact heating of W2C substrate and a metal sample made of 08Kh18N10T steel. It was established that wolfram carbide has good indicators of wettability by corrosion-resistant steel, wetting angle is 135 – 145°. Composition of the substrate surface has been studied by electron scanning microscopy to determine composition of reaction products. Analysis of the obtained results allows us to state that content of chemical elements varies over the entire contact area, but pattern of their distribution there is uniform. Due to the obtained data we can make an assumption about the applicability of combination of these components to create dispersed-hardened materials. To this end, experiments have been carried out to produce dispersedly hardened centrifugal cast blanks with various types of casting – horizontal and vertical. To obtain experimental materials, the horizontal and vertical type centrifugal casting was introduced into tungsten semicarbide ingots in an amount of 1 % wt. After producing experimental materials, a number of mechanical properties were studied, such as tensile strength, yield strength and hardness. The experimental results allow us to conclude that the use of dispersed hardening in process of centrifugal casting makes it possible to obtain metal materials with increased mechanical properties. Indicators of ultimate strength increase (for all samples on average) by 2.49 %, yield strength – by 2.27 %, hardness – by 5.02 %, which correlates with the provisions on metals physico-chemical properties when using dispersed hardening technologies.

Pyrolysis of Polyurethanes. Process Features and Composition of Reaction Products

Pyrolysis of Polyurethanes. Process Features and Composition of Reaction Products

Enhanced Hydrogen Generation Performance of Al-Rich Alloys by a Melting-Mechanical Crushing-Ball Milling Method.

The main problem for the application of hydrogen generated via hydrolysis of metal alloys is the low hydrogen generation rate (HGR). In this paper, active Al alloys were prepared using a new coupled method-melting-mechanical crushing-mechanical ball milling method to enhance the HGR at room temperature. This method contains three steps, including the melting of Al, Ga, In, and Sn ingots with low melting alloy blocks and casting into plates, then crushing alloy plate into powders and ball milling with chloride salts such as NiCl2 and CoCl2 were added during the ball milling process. The microstructure and phase compositions of Al alloys and reaction products were investigated via X-ray diffraction and scanning electron microscopy with energy dispersed X-ray spectroscopy. The low-melting-point Ga-In -Sn (GIS) phases contain a large amount of Al can act as a transmission medium for Al, which improves the diffusion of Al to Al/H2O reaction sites. Finer GIS phases after ball milling can further enhance the diffusion of Al and thus enhance the activity of Al alloy. The hydrogen generation performance through hydrolysis of water with Al at room temperature was investigated. The results show that the H2 generation performance of the Al-low-melting point alloy composite powder is significantly higher than the results reported to date. The highest H2 generation rate and H2 conversion efficiency can reach 5337 mL·min−1·g−1 for the hydrolysis of water with 1 g active alloy.

Theoretical Simulation and Experimental Optimization of Reaction Conditions and Product Composition of Ferrocene Acylation

Theoretical Simulation and Experimental Optimization of Reaction Conditions and Product Composition of Ferrocene Acylation

Direct Cobalt‐Catalyzed Phosphorylation of Porphyrins

AbstractA new approach has been proposed for synthesizing porphyrins with phosphoryl substituents by Co‐and Mn‐catalyzed C−H‐functionalization. The paper shows the effect of the solvent, oxidizer, and catalyst, porphyrin, and phosphite nature on the yield and composition of reaction products. It is shown that cobalt porphyrins can interact with phosphites in the absence of a catalyst, forming the products of axial binding to the metal cation. The reaction mechanism has been proposed.

Relationships between reaction products and carbonation performance of alkali-activated slag with similar pore structure

The composition of reaction products is one of the most significant factors affecting the carbonation performance of alkali-activated slag (AAS). However, the relationships between the reaction products and the carbonation performance of AAS have not been established. To address this gap, AAS pastes with different composition and similar pore structure were prepared by adding Al(OH)3 or Mg(OH)2 to evaluate the effect of the composition on the carbonation performance of AAS. Further, in order to gain insight into the influential mechanism of the composition, the principal reaction products in AAS were also synthesized. All produced specimens were tested for carbonation performance, alongside morphological, thermal and chemical characterizations. The results show that among the examined reaction products, the hydrotalcite-like phase (MAH) displayed the strongest carbonation resistance, which was almost immune to the attack of aggressive CO2. By contrast, the calcium aluminate hydrate (CAH) and calcium (alumino) silicate hydrate (C-(A)-S-H) were much more susceptible to the CO2-rich environment. Further, adding Mg(OH)2 to AAS could promote the formation of MAH and in turn, alleviated the carbonation depth of AAS. Whereas, the content of CAH and the A/S (Al2O3/SiO2) ratio of C-(A)-S-H were raised with the increase of Al(OH)3, resulting in a poor carbonation resistance of AAS. Moreover, a multi-factor model with R2 of 0.95 was established to associate the carbonation depth of AAS with the A/S ratio of C-(A)-S-H, the proportion of MAH, and the proportion of CAH. According to the proposed model, the carbonation depth of AAS is believed the most sensitive to the A/S ratio of C-(A)-S-H.

Time-Resolved ATR-FTIR Spectroscopy and Macro ATR-FTIR Spectroscopic Imaging of Inorganic Treatments for Stone Conservation.

In this study, the novel application of ATR–FTIR spectroscopy and macro ATR–FTIR spectroscopic imaging overcame an analytical challenge in conservation science: the time-resolved, chemical, and spatial investigation of the reaction of inorganic treatments for stone conservation (ammonium oxalate, AmOx; ammonium phosphate, DAP) occurring in water-based solutions. The aim was to (1) assess the composition and localization of reaction products and their phase variation during the reaction in real time and directly in an aqueous environment and (2) investigate the reaction of AmOx and DAP with calcite and the transformations induced to the substrate with a time-resolved approach. The new analytical results showed that for both treatments, the formation of new crystalline phases initiated at the early stages of the reaction. Their composition changed during the treatment and led to more stable phases. The reactivity of the stone substrate to the treatments varied as a function of the stone material features, such as the specific surface area. A clear influence of post-treatment rinsing on the final composition of reaction phases was observed. Above all, our research demonstrates the actual feasibility, practicality, and high potential of an advanced ATR–FTIR spectroscopic approach to investigate the behavior of conservation treatments and provided new analytical tools to address the choices of conservation in pilot worksites. Lastly, this study opens novel analytical perspectives based on the new possible applications of ATR–FTIR spectroscopic imaging in the field of conservation science, materials science, and analytical chemistry.

Tire Pyrolysis. Process Features and Composition of Reaction Products

Tire Pyrolysis. Process Features and Composition of Reaction Products

Preparation of high active Al-Ga-In-Sn alloy by alloying & ball milling method and its hydrogen production via water splitting

The Al-water reaction has attracted the attention for it’s a convenient method for producing hydrogen for fuel cell. In this study, High active Al alloy was prepared using a melting-mechanical crushing-mechanical ball milling method. The microstructure and phase compositions of Al alloy and reaction products were investigated via X-ray diffraction and scanning electron microscopy with energy dispersed X-ray. The different low-melting-point phases at the Al grain boundaries are related to the activation of the Al alloy. This work The H2 generation performance of the alloy prepared by this method can be significantly improved. The highest H2 generation rate and H2 conversion efficiency can reach 613mL.min-1 and 76.27% at room temperature.

Phase formation behavior of alkali-activated calcined clays: effects of the reactive phase and NaOH concentration

ABSTRACT The relevance of calcined clays as sources with a great potential for non-clinker alkali-activated materials has significantly increased in recent decades. This article reports on a study to investigate how NaOH with concentrations in the 5–14 M range affects the mechanical properties, amorphous-crystalline phase transformations, and reaction product composition of alkali-activated calcined kaolinite/montmorillonite cements with reactive phases of 60% and 33%, and with the SiO2/Al2O3 ratios of 1.54 and 1.74. The hardened pastes based on both calcined clays exhibited the highest compressive strength up to 9.1 MPa following their activation with 8 M NaOH. The higher amorphous fraction in the calcined clay provided gradual zeolitisation/crystallisation at Na2O/SiO2 and Na2O/Al2O3 molar ratios in the 0.36–0.63 and 0.56–0.98 ranges, respectively, accompanied by the deterioration of the mechanical characteristics of the samples. The zeolite content in the alkali-activated calcined clay cements with an amorphous fraction of 33% peaked for NaOH at 11 M, and the corresponding molar ratios of Na2O/SiO2 and Na2O/Al2O3 were 0.85 and 1.46, respectively. The main reaction products in the studied systems determined by XRD, TG/DSC, and FTIR spectroscopy analyses were N-A-S-H and zeolite A. The properties and reaction products obtained favor the use of proposed alkali-activated cements for controlled low-strength materials.

Design and thermal characterization of an induction-heated reactor for pyrolysis of solid waste

A small-scale induction heated reactor (IHR) was specifically developed to study fast pyrolysis, here investigated as the first step of gasification process, representing some of the reaction conditions encountered in a fluidized bed reactor. First, the thermal response of the system was characterized at transient and steady state, and CFD calculations were performed to have a complete description of the temperature profiles inside the reactor. The novel device can handle a few grams of solid at temperatures up to 900 °C, allowing high heating rates (near 80 °C/s) and a uniform distribution of temperature in the sample. Secondly, the pyrolysis of a solid recovered fuel (SRF) sample was carried out at 800 °C, and the distribution and composition of reaction products were analyzed and compared with tests performed in a pilot scale fluidized bed reactor (FBR). The results obtained in the IHR showed a good reproducibility. The same main gas and tar species were measured in the IHR and FBR, with some differences in gas and tar composition that were attributed to the extent of secondary reactions, enhanced by higher heat transfer rates and the presence of bed material in the FBR.

Investigation on the roles of solution-based alkali and silica in activated low-calcium fly ash and slag blends

An evaluation of strength-gain in binders with equal mass proportions of low-calcium fly ash and slag activated with alkaline solutions containing dissolved silica is conducted. The roles of Si and Na in the activating solution on compressive strength, reaction kinetics, and content and phase composition of reaction products are evaluated. The early reactions within the activated binder are due to the dissolution and hydration of slag. In the presence of silica, there is early precipitation of calcium silicate hydrate (CSH) before the hydration of slag. Silica in the activating solution delays the primary hydration of slag. The reactivity of silica depends on the SiO2/Na2O ratio in the activating solution. A less polymerized form of silica with higher reactivity is produced at a higher Na content in the activating solution. More reactive silica form produces a more rapid early precipitation of CSH following the initial dissolution of slag. Fly ash in the binder provides additional Si and Al to the calcium aluminosilicate hydrate (CASH) formed from the slag reaction. The Na identified in the reaction products is in a water-soluble form and not chemically bound to the CASH. The Na does not contribute directly to the compressive strength. In the long-term, the content and the silica incorporation in the CASH scales with the silica content in the activating solution and it does not depend on the form of silica. Increasing the activating solution silica content results in its larger incorporation in CASH and produces compressive strength enhancement. The form of silica has a negligible effect on the dissolution of fly ash in the binder and ultimate strength achieved.

Utilization of ZSM-5 waste for the preparation of autoclaved aerated concrete (AAC): Mechanical properties and reaction products

Used ZSM-5 (Zeolite Socony Mobil-5) were directly dumped into ponds after high-temperature incineration in the past, which causes environmental pollution and brings economic burden. In this paper, ZSM-5 waste was used as a siliceous raw material in the preparation of AAC. The compositions of ZSM-5 waste and reaction products of AAC were analyzed by X-ray diffraction (XRD), Thermal gravimetric (TG), Fourier transform infrared spectroscopy (FTIR), and Scanning electron microscope (SEM). The bulk density and compressive strength of AAC are approximately 500 kg/m3 and 4.2 MPa, respectively. NaOH was employed during the preparation, and the influence of NaOH content on the gas-foaming effect and mechanical property was investigated. The results show that the optimum quantity of NaOH is 0.6% and the resultant bulk density and compressive strength of AAC are 414 kg/m3 and 2.9 MPa, respectively.