Influence Of CaO Research Articles

Investigation on the influences of CaO on tar of biomass model compounds by Boltzmann-Monte Carlo-Percolation (BMCP) model

CaO have been widely used in biomass thermal conversion processes to deal with tar of biomass. The influences of the CaO on the function groups or intermediates of the bio tars are crucial because strategies on refining bio tars can be determined. The pyrolysis experiments of three typical model compounds, lignin, cellulose, hemicellulose, are carried out in a multi-stage tube followed by a cold trap. The influence of CaO can be analyzing the products distribution and components obtained from Nuclear Magnetic Resonance and Gas Chromatography-Mass Spectrometry technologies with and without CaO-loaded honeycombs. As the adsorbed matters on CaO-loaded honeycombs are hardly to be analyzed, the Boltzmann-Monte Carlo-Percolation model is introduced to make further investigations on the possible influence of CaO. The experimental results suggest that generations of unsaturated structures are inhibited by CaO, and the comparison of simulation and experimental results suggest that aliphatic carbon-centered radicals rather than oxygen-centered radicals are adsorbed and stabilized by CaO.

Effect of alkaline oxides (CaO and MgO) on the mechanical properties of SiC-based foam ceramics

Fly ash is potentially useful as a sintering additive in the synthesis of SiC-based foam ceramics (SFC). However, the influence of CaO and MgO, the main alkaline oxides in fly ash, on the performance of SFC is not well understood. This study synthesized SFC using SiC and fly ash as the primary raw materials (mass ratio of 7:3), and systematically investigating the effects of CaO and MgO on the properties of SFC, including porosity, density, strength, apparent morphology, and phase composition. The results indicated that addition of CaO and MgO promoted oxidation of SiC at relatively low temperatures. With a CaO content of 1.5 wt% or an MgO content of 2 wt%, SFC with uniformly distributed porous structures and exceptional properties was achieved at sintering temperatures as low as 1150 °C. Additionally, CaO and MgO facilitated formation of crystalline phases such as wollastonite, calcium feldspar, and cordierite, enhancing the thermophysical properties of SFC. However, excessive CaO or MgO led to over-sintering of the SFC samples. With a CaO content of 1.5 wt% and a sintering temperature of 1175 °C, SFC was completely deformed. This was also observed with an MgO content of 3 wt% and a sintering temperature of 1250 °C, indicating that CaO promotes SiC oxidation more effectively than MgO. It is suggested that addition of appropriate amounts of CaO and MgO is conducive to production of high-quality SFC at low sintering temperatures, significantly enhancing their commercial viability.

Study on the Influence of CaO on the Electrochemical Reduction of Fe2O3 in NaCl-CaCl2 Molten Salt.

The presence of calcium-containing molten salts in the electrolysis of oxides for metal production can lead to the formation of CaO and, subsequently, the generation of intermediate products, affecting the reduction of metals. To investigate the impact of CaO on the reduction process, experiments were conducted using a Fe2O3-CaO cathode and a graphite anode in a NaCl-CaCl2 molten salt electrolyte at 800 °C. The electrochemical reduction kinetics of the intermediate product Ca2Fe2O5 were studied using cyclic voltammetry and I-t curve analysis. The phase composition and morphology of the electrolysis products were analyzed using XRD, SEM-EDS, and XPS. The experimental results demonstrate that upon addition of CaO to the Fe2O3 cathode, Ca2Fe2O5 is formed instantly in the molten salt upon the application of an electrical current. Research conducted at different voltages, combined with electrochemical analysis, indicates that the reduction steps of Ca2Fe2O5 in the NaCl-CaCl2 molten salt are as follows: Ca2Fe2O5 ⟶ Fe3O4 ⟶ FeO ⟶ Fe. The presence of CaO accelerates the electrochemical reduction rate, promoting the formation of Fe. At 0.6 V and after 600 min of electrolysis, all of the Ca2Fe2O5 is converted into Fe, coexisting with CaCO3. With an increase in the electrolysis voltage, the electrolysis product Fe particles visibly grow larger, exhibiting pronounced agglomeration effects. Under the conditions of a 1 V voltage, a study was conducted to investigate the influence of time on the reduction process of Ca2Fe2O5. Gradually, it resulted in the formation of CaFe3O5, CaFe5O7, FeO, and metallic Fe. With an increased driving force, one gram of Fe2O3-CaO mixed oxide can completely turn into metal Fe by electrolysis for 300 min.

Regulatory effect of CaO on glutamate pyrolysis and NOx precursors formation

Pyrolysis is an effective method for safely disposing of sewage sludge via conversion into a usable energy source. However, municipal sludge has a high protein content, which is a major source of NOx precursors. This study investigated the effect of CaO on NOx precursor formation during glutamate pyrolysis and demonstrated that CaO occupies the carboxyl site of glutamic acid at 320 °C, which delays its decomposition and promotes the conversion of glutamic acid from a five- to a six-membered ring. At 400 °C, heterocyclic nitrogen in the tar peaked from 4.87 to 53.87% after adding CaO. As the temperature increases to 480 °C, CaO might promote the conversion of heterocyclic nitrogen into tricyclic piperazine dione in the tar, which subsequently decomposed to produce HCN in large quantities. At 480 °C, CaO contributed to the decrease in pyrrole, pyridine, and quaternary nitrogen in the semi-coke from 24.81%, 12.93%, and 7.43% to 1.91%, 5.97%, and 1.43%, respectively and promoted HCN hydrolysis to form NH3. At 480–680 °C, CaO interacted with NH3 to form CaCN2. The product of CaCxNy decomposition—CaCx—captured NH3. At high temperatures, CaO inhibited HCN release, which might be related to the reaction between CaO and HCN to form CaCxNy, subsequently reconverted into CaO at temperatures above 680 °C. These findings provide novel insights into the influence of CaO on amino acid pyrolysis to produce NOx precursors and the regulation of NOx precursor production.

Pyrolytic mechanisms of typical organic components of sewage sludge in the presence of CaO: Polysaccharides, proteins, and lipids

The addition of CaO could facilitate the conversion of sewage sludge (SS) from waste to high-purity syngas. The pyrolytic characteristics of SS are a comprehensive manifestation of polysaccharides, proteins, and lipids, while the influence of CaO on their pyrolytic characteristics is rarely reported. This study conducted a thorough investigation into the pyrolytic mechanism of starch, protein, and lipid in the presence of CaO by analysing their thermal behavior, gaseous products, liquid tar, and residual char. The findings from TGA, GC, GC–MS, and FT-IR analysis indicate that the addition of CaO catalytically lowers the pyrolysis temperature of starch, protein, and lipid components and promotes their conversion into small molecules, resulting in increased syngas production. Moreover, the combination of char with the carbonation and calcination cycle of CaO leads to a significant boost in syngas (H2 and CO) yield, with up to 3 and 10 times increase from starch and protein, respectively, and a higher syngas selectivity of up to 65 %. The study also identifies those polysaccharides and proteins are the primary sources of syngas. This study can provide further insight into SS pyrolysis for syngas production in the presence of CaO and the necessary parameters to predict the pyrolysis behavior of SS in industrial applications.

Influence of CaO and Fe2O on the surface tension and structure of SiO2-Al2O3-CaO-Fe2O3-MgO synthetic slags

The surface tension of coal slags influences the adhesion between the slag and furnace walls in slagging gasifiers, which further influences the efficiency, maintenance cost and reliability of the gasifier. The influence of CaO and Fe2O3 on the surface tension and structure of synthetic slags were investigated. The results indicate that the surface tension linearly increases with the increase of CaO content in the synthetic slag. When Fe2O3 exceeds 3.8 mole%, the surface tension of synthetic slag increases slowly with the increase of Fe2O3, which is related to Fe2O3 acting as an intermediate oxide. The degree of polymerization and the electrostatic potential of ions are related to a variation in surface tension, and the number of unsatisfied bonds increases because the Si-O-Si network structure was depolymerized. Here, NBO/T cannot reflect the degree of depolymerization of slag due to the variation in intermediate Fe2O3 contents.

Influence of CaO on Physical and Environmental Properties of Granulated Copper Slag: Melting Behavior, Grindability and Leaching Behavior.

Due to its potential pozzolanic activity, granulated copper slag (GCS) has been proven to act as a supplementary cementitious material (SCM) after thermochemical modification with CaO. This modification method reduces cement consumption and CO2 emissions; however, the additional energy consumption and environmental properties are also not negligible. This paper aims to evaluate the economics and environmental properties of thermochemically modified GCS with CaO through the melting temperature, grindability, and heavy metal leaching characteristics. The X-ray fluorescence spectroscopy (XRF) results indicated that the composition of the modified GCS shifted to the field close to that of class C fly ash (FA-C) in the CaO-SiO2-Al2O3 ternary phase diagram, demonstrating higher pozzolanic activity. The test results on melting behavior and grindability revealed that adding CaO in amounts ranging from 5 wt% to 20 wt% decreased the melting temperature while increasing the BET surface area, thus significantly improving the thermochemical modification’s economics. The unconfined compressive strength (UCS) of the cement paste blended with 20 wt% CaO added to the modified GCS after curing reached 17.3, 33.6, and 42.9 MPa after curing for 7, 28, and 90 d, respectively. It even exceeded that of Portland cement paste at 28 d and 90 d curings. The leaching results of blended cement proved that the heavy metal elements showed different trends with increased CaO content in modified GCS, but none exceeded the limit values. This paper provides a valuable reference for evaluating thermochemically modified GCS’s economics and environmental properties for use as SCM.

The Influence of CaO and MgO on the Mechanical Properties of Alkali-Activated Blast Furnace Slag Powder.

CaO and MgO are both reported as effective activators for blast furnace slag. However, the synergistic effect of these two components on the mechanical properties of alkali-activated blast furnace slag remains unclear. In this study, the flexural and compressive strengths of alkali-activated blast furnace slag powder with MgO and CaO range from 0% to 30% by the mass ratio of alkali-activated blast furnace slag powder are investigated. Moreover, the dry shrinkage rate of alkali-activated blast furnace slag powder is measured. One percent refractory fibers by volume of binder materials are added in the alkali-activated blast furnace slag. Some refractory fibers are treated with water flushing, meanwhile, some refractory fibers are directly used without any treatment. Finally, the scanning electron microscope, the thermogravimetric analysis curves and the XRD diffraction spectrums are obtained to reflect the inner mechanism of the alkali-activated blast furnace slag powder’s mechanical properties. The water-binder ratios of the alkali-activated blast furnace slag powder are 0.35 and 0.42. The curing ages are 3 d, 7 d and 28 d. The measuring temperature for the specimens ranges from 20 °C to 800 °C. Results show that the flexural and compressive strengths increase with the increased curing age, the decreased water-binder ratio and the addition of refractory fibers. The water-treated refractory fibers can improve the mechanical strengths. The mechanical strengths increase in the form of a quadratic function with the mass ratio of MgO and CaO, when the curing age is 3 d, the increasing effect is the most obvious. A higher water-binder ratio leads to an increasing the drying shrinkage rate. The activated blast furnace slag powder with CaO shows a higher drying shrinkage rate. The mechanical strengths decrease with the increasing testing temperature.

Influence of CaO and Dy2O3 on the structural, chemical and optical properties of thermally stable luminescent silicate nanoglass-ceramics

In this work, nano-glass ceramics constituted by SiO2–Na2O–CaO–Dy2O3 are synthesized with different contents of CaO (0–30 mol%) and Dy2O3 (0.1–4 mol%) through the melt-quenching technique at 1500 °C. The precipitation of nanocrystals occurs during the cooling stage of molten glass precursors. Depending on CaO content, nanocrystals of cristobalite (0 mol%) or combeite (30 mol%) are grown inside the amorphous silicate phase. FTIR and XPS studies indicate that non-bridging oxygens increase with CaO due to [SiO]4 tetrahedral rupture. However, if CaO is higher than 20 mol%, the non-bridging oxygens slightly decrease due to the prevalence of combeite nanocrystals. Moreover, the addition of CaO decreases the optical bandgap (4.18–3.91 eV) and increases the Urbach energy (0.54–0.75 eV). Although PL spectra acquired at λex of 348 and 386 nm show four peaks whose intensities augment with CaO, the most prominent peaks appear at 490 (4F9/2 → 6H15/2, blue) and 577 nm (4F9/2 → 6H13/2, yellow). The decrease in the yellow to blue ratio, with an increment in CaO content, is attributed to the devitrification of glass phase. The most intense PL intensity is obtained in the nano-glass ceramic constituted of 30 mol% CaO and 1 mol% Dy2O3. This sample demonstrates excellent thermal PL stability up to 400 °C, retaining 95.2% of the initial PL value. The results indicate that these nano-glass ceramics are good candidates for their use as yellow phosphors in high-power consuming and high-temperature applications, such as LED chips and luminescent solar concentrators.

Influence of CaO on the thermodynamic and transport properties of cobaltous oxide

The electrical conductivity of Ca-doped Co 1-xO single crystals was measured as a function of oxygen partial pressure, over the temperature range 1273–1673 K. The results were analyzed using Seebeck coefficient measurements, microstructural characterizations, EELS and X-ray diffraction experiments. From this set of results, we have shown that the influence of calcium on the thermodynamic and transport properties of cobaltous oxide is due to the reducing behavior of these solute cations, leading to both the shift of the Co/CoO phase boundary to higher PO2 and the formation of singly ionized cobalt cations (Co+) in the stability range of CoO.

Influence of CaO on in-situ tar formation during the co-pyrolysis of coal and cow dung in a Py-GCMS

Co-pyrolysis is one of the most important way to achieve the efficient and clean co-conversion of animal waste and coal. CaO has been verified as an efficient additive to enhance the synergy between them but the catalytic mechanism of CaO on co-pyrolysis process is still unclear. In this paper, the influence of CaO on tar composition during the co-pyrolysis of cow dung (CD) and Meihuajing (MHJ) coal and their interaction are in-situ investigated by using a Py-GCMS analyser. The results indicate that the influence of CaO on interaction between CD and MHJ is different at each temperature range, and affected by the additional amount of CaO. Positive synergistic effect between coal and cow dung presents on the hydrocarbons production in 350-450 °C and the formation of oxygen-containing compounds in 450-550 °C after CaO is added. The area content of aliphatic hydrocarbons containing olefins in tar increases with the addition amount of CaO in 50-450 °C, but excessive CaO hinders the formation of these compounds in 550-850 °C. Additionally, the influence of CD-MHJ interaction during co-pyrolysis on different tar compositions varies with the temperature range and the addition of CaO.

Study on the effect of calcium and sulfur content on the properties of fly ash based geopolymer

Fly ash based geopolymer is a green cementitious material with the potential to replace portland cement. Due to the changes of raw coal and coal combustion technology in recent years, the fly ash often has high CaO and SO3 contents. The action mechanism of CaO and SO3 on the mechanical properties and dimensional stability of fly ash-based geopolymers is not clear, which restricts its application. The influence of CaO and SO3 content on the flexural strength, compressive strength, water immersion expansion rate and drying shrinkage rate of fly ash based geopolymer were studied, and X-ray diffractography (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and 29Si nuclear magnetic resonance (NMR) were used to study the influence mechanism of calcium and sulfur on the geopolymer. The results show that the mechanical properties of fly ash based geopolymers increase initially and then decrease with the increase of CaO and SO3 content. When the contents of CaO and SO3 are 11% and 4% respectively, the properties of geopolymer prepared at ordinary temperature (20 ℃) are the optimum. The 28d flexural strength and compressive strength can be increased by 17.91% and 15.56% respectively, and compared with the unmodified fly ash based geopolymer, the drying shrinkage is reduced by 60.65%. Microscopic test results show that the addition of CaO and SO3 promoted the geopolymer reaction, increased the gel products and generated ettringite, which enhanced the strength of the matrix and compensated the shrinkage of geopolymer.

Effects of CaO added to raw basalt on producing continuous basalt fibers and their mechanical properties

The influence of CaO on spinnability (the capability of being spun) of continuous basalt fibers (CBF) and strength property were investigated. The addition of CaO in raw basalts was found to eliminate spinel crystals (magnesioferrite), and to reduce frequency of fiber breaks during the fiber-drawing. The tensile strength of CBF was enhanced by 13% after addition 3% wt. of CaO to the starting materials. Excessive addition of CaO (>5.0%) would result in less spinnability and inferior mechanical strength. The structure of basaltic glass fibers with varying CaO contents was studied by various characterizations. Doping of CaO reduced the degree of fiber polymerization and increased the amount of non-bridging oxygen. Results showed that increase of CaO changes the crystallization behavior of fibers, inhibits the crystallization of spinel, and promotes the crystallization of pyroxene and plagioclase.

A New Artificial Neural Network Model for the Prediction of the Effect of Molar Ratios on Compressive Strength of Fly Ash‐Slag Geopolymer Mortar

Geopolymers are inorganic polymers produced by the alkali activation of alumina‐silicate minerals. Geopolymer is an alternative cementitious binder to traditional Ordinary Portland Cement (OPC) leading to economical and sustainable construction technique by the utilisation of alumina‐silicate waste materials. The strength development in fly ash‐slag geopolymer mortar is dependent on the chemical composition of the raw materials. An effective way to study the effect of chemical components in geopolymer is through the evaluation of molar ratios. In this study, an Artificial Neural Network (ANN) model has been applied to predict the effect of molar ratios on the 28‐day compressive strength of fly ash‐slag geopolymer mortar. For this purpose, geopolymer mortar samples were prepared with different fly ash‐slag composition, activator concentration, and alkaline solution ratios. The molar ratios of the geopolymer mortar samples were evaluated and given as input to ANN, and the compressive strength was obtained as the output. The accuracy of the assessed model was investigated by statistical parameters; the mean, median, and mode values of the ratio between actual and predicted strength are equal to 0.991, 0.973, and 0.991, respectively, with a 14% coefficient of variation and a correlation coefficient of 89%. Based on the mentioned findings, the proposed novel model seems reliable enough and could be used for the prediction of compressive strength of fly ash‐slag geopolymer. In addition, the influence of molar compositions on the compressive strength was further investigated through parametric studies utilizing the proposed model. The percentages of Na2O and SiO2 of the source materials were observed as the dominant chemical compounds in the mix affecting the compressive strength. The influence of CaO was significant when combined with a high amount of SiO2 in alkaline solution.

Influence of CaO and SiO2 additives on the sintering behavior of Cr,Ca:YAG ceramics prepared by solid-state reaction sintering

Yttrium aluminum garnet optical ceramics (Y3−xCaxAl4.95Cr0.05O12) doped with 0.1 at.% of chromium ions and 0.5, 0.8 and 1.2 at.% of calcium ions were prepared by reactive sintering in vacuum at 1750°C. The influence of SiO2 and CaO sintering aids on optical properties and microstructure of Cr,Ca:YAG ceramics was investigated. A decrease in CaO concentration led to a reduction of the Cr,Ca:YAG ceramics transparency from 81 to 0% at 1064 nm, moreover, samples with a lower concentration of CaO had abnormal grains and high-level porosity. The obtained features were attributed to the interactions between silica and calcium oxide during vacuum sintering of Cr,Ca:YAG ceramics. We propose and discuss two possible ways in which CaO and SiO2 influence the formation of Ca,Cr:YAG ceramics. The first one involves the appearance of a liquid phase thanks to the CaO–SiO2 interaction during the heating stage of ceramics sintering which results in abnormal growth of ceramics grains. The second mechanism consists on the mutual consumption of Si4+ and Ca2+ ions during the isothermal stage of ceramic sintering, which leads to a decrease in Cr4+ concentration. Both mechanisms have a negative effect on the optical and laser properties of the ceramics.

Influence of CaO on structural features of polyphosphate P2O5-Fe2O3-FeO glasses by molecular dynamics simulations

Phosphate glasses can be used in many applications fields like medicine, optoelectronics, environmental protection, etc. Their properties are strongly dependent on the glass network structure. The paper presents classical molecular dynamics simulations studies of the influence of the gradual addition of CaO on structural features of 55P2O5-30Fe2O3-15FeO glass. The base glass is built of different lengths chains and rings which are being shortened due to CaO addition. Thus, the glass network depolymerization takes place. The phosphate network is joined by iron-oxygen polyhedrons which increase polymerization of the network. The increase of non-network oxygen ions is observed what can be related to the rising of Ca and Fe ions aggregation. The aggregation of calcium is the most dominant at the low concentration of this oxide. The effect leads to the observation of the glass network non-homogeneity. The increase of the CaO concentration causes expansion of the Ca-rich regions which finally extend over the entire glass network for the CaO content above 45%. Above this point, the phosphate network is mostly composed of isolated Q0 structural units. The P-O-P bridges are broken more easily than P-O-Fe due to an increase in the modifier content.

The influence of CaO on alumina grain boundary mobility

The influence of CaO on the evolving microstructure of alumina has been studied in a range of concentrations below the solubility limit. The amount of Ca in the alumina was determined by conducting fully standardized wavelength dispersive spectroscopy, and the change in grain boundary mobility as a function of the amount of dopant was characterized using scanning electron microscopy. Unlike segregating dopants which reduce grain boundary mobility by solute-drag, CaO increases the rate of grain growth, and a trend of increased mobility with increasing dopant level was shown. The increased mobility with Ca segregation is believed to be due to an increase in vacancy concentration in the vicinity of the grain boundaries, thus facilitating faster grain boundary motion.

Evaluation of Ca-doped BaZrO3 as the crucible refractory for melting TiAl alloys

In this study, a new Ca-doped BaZrO3 refractory was designed by using thermodynamics approaches and tested for its applicability for vacuum induction melting (VIM) of TiAl alloys. The influence of CaO on the BaZrO3 phase constitution and microstructure, as well as the key features of the TiAl melt interaction with the Ca-doped BaZrO3 crucibles were investigated by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). Results revealed that the Ca-doped BaZrO3 refractory consisted of Ba1-xCaxZrO3 and CaO phases. An obvious interaction occurred during the melting of the TiAl alloy in the Ca-doped BaZrO3 crucible along with the generation of BaAl2O4 as a reaction product, with formation of a reaction layer up to 5 µm thick. Dissolution of Ca-doped BaZrO3 refractory in the TiAl melt was the main reason for the alloy-crucible reaction. Moreover, the Ca-doped BaZrO3 crucible was found to substantially reduce the contamination of the TiAl alloy, with lower oxygen concentration as compared with other conventional oxide crucibles. Overall results confirmed that vacuum induction melting using the Ca-doped BaZrO3 refractory can be considered as an appropriate method for the fabrication of TiAl alloys.

Experimental study of influence characteristics of flue gas fly ash on acid dew point

The long-term operation experience of a large number of utility boilers shows that the measured value of acid dew point is generally lower than estimated value. This is because the influence of CaO and MgO on acid dew point in flue gas fly ash is not considered in the estimation formula of acid dew point. On the basis of previous studies, the experimental device for acid dew point measurement was designed and constructed, and the acid dew point under different smoke conditions was measured. The results show that the CaO and MgO in the flue gas fly ash have an obvious influence on the acid dew point, and the content of the fly ash is negatively correlated with the temperature of acid dew point At the same time, the concentration of H2SO4 in flue gas is different, and the acid dew point of flue gas is different, and positively correlated with the acid dew point.

Influence of CaO on urea pyrolysis in the selective non-catalytic reduction deNOx process

CaO affects urea pyrolysis when coalescing with melting urea, which decreased the performance of urea-SNCR deNOx process. The influence of CaO on urea pyrolysis was studied with a thermogravimetric analyzer, a fixed bed reactor, and DRIFTS. The mechanism of CaO was also analyzed. Experimental results showed that CaO decreased the pyrolysis rate of urea, especially in the presence of O2. NH3 production in urea pyrolysis was not influenced by CaO, whereas HNCO in the gaseous products disappeared and CO2 production was increased remarkably. NO, N2O, and CO were also produced in the presence of O2. DRIFTS experiments showed that Ca(NCO)2 and CaCN2 were produced and the composition of the solid products varied with the atmosphere. Mechanism analysis showed that CaO initially reacted with melting urea and biuret to produce Ca(NCO)2 and release NH3 and H2O. Ca(NCO)2 decomposed to CaCN2 and CO2 with increasing temperature, and CaCN2 can exist stably in the absence of O2 because of its high thermostability. In the presence of O2, Ca(NCO)2 can be oxidized to N2O, CO2, and N2, whereas CaCN2 can be oxidized to NO, CO, and N2.