Effect of titanium chelating compound on hydration resistance of CaO material

The hydration resistance of CaO materials prepared by Ca(OH)₂ calcination with titanium chelating compounds is investigated in this paper. The crystalline phases and microstructure characteristics of sintered specimens were studied by X-ray diffraction (XRD), define FTIR spectroscopy, scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The results showed that the hydration resistance of CaO samples was improved significantly, especially for samples with 9 wt% Ti chelating compound. The specimens with Ti chelating compound showed an increase in bulk density and a decrease in apparent porosity after heating when compared to the specimens without additive. The grain surface of CaO grain and the gaps between the CaO grain boundaries were covered with calcium phosphate glass phase, calcium phosphate showed two different shapes: irregular shape and rod shape. The formation and distribution of these two forms were the key factors that affecting the hydration resistance of CaO samples.     

Densification and Properties of Fe2O3 Nanoparticles added CaO Refractories

Up to 8 wt. % of Nano-iron oxide was added to CaO refractory matrix. The crystalline phases and microstructure characteristics of specimens sintered at 1650 °C for 5 h in an electric furnace were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The physical properties are reported in terms of bulk density, apparent porosity and hydration resistance. The mechanical behavior was studied by a cold crushing strength (CCS) and flexural strength at 1200 °C test. As a result, it was found that the presence of Nano-iron oxide in the CaO refractory matrix induced 2CaO.Fe₂O₃ (C₂F), CaO.Fe₂O₃ (CF) and 3CaO.Al₂O₃ (C₃A) phase’s formation, which improved the sintering process. Nano-iron oxide also influenced the bonding structure through a direct bonding enhancement. On the Other hand, the presence of Nano-iron oxide resulting in improvement properties of CaO refractory matrix refractories such as bulk density, hydration resistance and cold crushing strength. The maximum flexural strength at 1200 °C is achieved by the samples containing 4 wt. % nano-Fe₂O₃.     

Role of ZrO2 in sintering and mechanical properties of CaO containing magnesia from cryptocrystalline magnesite

As main components of magnesia-based refractories, magnesia exhibits excellent properties such as high refractoriness and good basic slag corrosion resistance. However, magnesia produced from CaO containing cryptocrystalline magnesite has limited application owing to the low hydration resistance and poor thermal shock resistance (TSR). This work aimed to investigate the reinforcing effects of microscale monoclinic ZrO₂ on free CaO containing magnesia for optimizing mechanical properties, TSR and hydration resistance. The results showed that adding ZrO₂ could promote the removal of the open pores, strengthen the interface bonding between various grains and produce crack deflection, which improved flexural strength and fracture toughness. As a result, the TSR of the specimens was enhanced effectively due to increased strength and toughness and reduction in the thermal expansion coefficient. Besides, as the ZrO₂ was introduced, hydration resistance of the specimens improved significantly, mainly attributing to the decrease in apparent porosity and elimination of the free CaO by forming CaZrO₃ and cubic ZrO₂ phases.     

Influence of tricalcium aluminate on the microstructure evolution of CaO specimen during hydration

C₃A-containing CaO specimen was prepared and the evolution of its microstructure during hydration process was investigated to clarify the protective mechanism of tricalcium aluminate (C₃A) on hydration resistance of CaO specimen. The slit-shaped micropores were formed on the grain boundary of CaO due to the stacking of lamellar C₄AH₁₃ formed by the hydration of C₃A. The contact area of residual C₃A with the moisture was reduced by the porous C₄AH₁₃ layer at the original site, which resulted in a slower dissolution rate of C₃A grain through the porous layer. In addition, the crack propagation and the formation of macropores were inhibited by the pinning effect of C₄AH₁₃, which was beneficial to the improvement of hydration resistance.     

Effect of porosity on carbonation and hydration resistance of CaO materials

CaO pellets with different porosity were carbonated at 700 °C in CO₂ atmosphere. The carbonation rate was controlled by the diffusion of CO₂, regardless of the difference in porosities. For the low-porosity pellet, carbonation reaction only occurred on the surface, with a dense CaCO₃ film thus formed, which combined well with the substrate material; while for the pellet of high-porosity, the carbonation reaction occurred simultaneously both on surface and inside pores, and each CaO grain was surrounded by CaCO₃ film that contained microfissures. Hydration test results showed that carbonation treatment could effectively improve the hydration resistance of CaO materials regardless of porosity, but the carbonated high-porosity pellet was prone to breakage due to poor combination between the carbonated CaO grains. Therefore, for the purpose to improve the hydration resistance by carbonation treatment, it is recommended that the CaO materials should be either with less appreciable apparent porosity or with a limited carbonation ratio for the high-porosity CaO material.     

铝-锆有机金属络合物偶联剂的合成及应用

用１,２ 丙二醇及不同的有机羧酸桥联配位基合成了ＣＭ、ＣＳＬ、ＣＭＳ等铝－锆有机金属络合物偶联剂,并对乙醇、水、碳酸钙和高岭土等不同溶剂－填料体系的降粘及纤维抗水性进行了应用试验。在ｗ（ＣａＣＯ３）＝５０％的乙醇浆料体系中,添加填料质量０．４％的该类ＣＭＳ偶联剂,可使其粘度值由１３．２Ｐａ·ｓ下降至０．２０Ｐａ·ｓ。     

Microstructure of tricalcium silicate and Portland cement systems at middle periods of hydration-development of Hadley grains

The development of the microstructure of C₃S paste and a Portland cement paste was studied between 7 and 24 h by means of backscattered electrons in a field-emission SEM. The course of hydration was measured by isothermal calorimetry. While the abundant occurrence of Hadley grains (hollow-shells) in Portland cement systems is well documented from a number of SEM and other microscopy studies, some earlier reports have noted that Hadley grains do not form in C₃S or alite paste alone. This report shows evidence of Hadley grains in C₃S paste, and follows their development from middle to late hydration stages. At around 10 h the microstructure with respect to Hadley grains were seen to develop in a very similar manner in C₃S and cement. In both systems, a narrow gap often developed between the receding anhydrous cores and layer of reaction product enveloping the cores. By 1 day, Hadley grains had continued to develop only in the cement paste, where they became a prominent feature. Only small ‘hollowed-out’ hydration shells were observed in the C₃S paste by 1 day. These were presumably reminiscences of the small gapped Hadley grains seen at the earlier hydration stages.     

3D printing of CaO-based ceramic core using nanozirconia suspension as a binder

The 3D printing of a ceramic core with nanoceramic suspension as a binder was performed to investigate a novel method for the fabrication of a complex-shaped ceramic core. Green bodies were printed using CaO powder as a precursor material and nanozirconia-absolute ethyl alcohol solution suspension as a binder. The green bodies were sintered at 1300–1500 °C for 2 h. The effects of binder saturation level on the properties of the sintered bodies were investigated. Increasing the binder saturation level caused decreases in the linear shrinkage of the sintered bodies, but increases in hydration resistance and bending strength. The nanozirconia particles were deposited on the surfaces of the CaO particles and filled the pores of green bodies, and then formed a high melting temperature CaZrO₃ layer with the CaO at the surfaces of the CaO grains, which improved the hydration resistance of the CaO-based ceramic core parts.     

Densification and properties of ZrO2 nanoparticles added magnesia–doloma refractories

In this work the effect of nano- and microZrO₂ addition on the densification and hydration resistance of MgO–CaO refractories was investigated. 0, 2, 4, 6 and 8 wt% ZrO₂ was added to MgO–CaO refractories that contain 35 wt% CaO. The crystalline phases and microstructure characteristics of specimens sintered at 1650 °C for 5 h in an electric furnace were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The physical properties are reported in terms of bulk density, apparent porosity and hydration resistance. Results show that with addition of ZrO₂ the bulk density and hydration resistance of the samples increased while apparent porosity decreased. Also the hydration resistance of the samples was appreciably improved by the addition of ZrO₂ due to its effect on decreasing the amount of free CaO in the refractories, promotion of densification as well as modification of the microstructure. Also it revealed that the nanoZrO₂ addition was more effective than microZrO₂ due to its higher activity.     

Effect of MgAl2O4 nanoparticles addition on the densification and properties of MgO-CaO refractories

MgAl₂O₄nanoparticles were added to MgO–CaO refractory ceramic composites in the range of 0–8 wt%. Refractory specimens were obtained by sintering at 1650 °C for 3 h in an electric furnace. Refractory specimens were characterized by measurements of bulk density, apparent porosity, hydration resistance, cold crushing strength, crystalline phase formation, and microstructural analysis. Results show that with additions of MgAl₂O₄ nanoparticles the bulk density of the samples increased. But the apparent porosity and cold crushing strength decreased and increased, respectively with addition MgAl₂O₄ nanoparticles up to 6 wt% and for further MgAl₂O₄ nanoparticles, due to the thermal expansion mismatch, the results is reversed. Also, the hydration resistance of the samples was appreciably improved by the addition of MgAl₂O₄ nanoparticles due to its effect on decreasing the amount of free CaO in the refractory composite and promotion of densification by creating a dense microstructure.     

Improving hydration resistance of MgO–CaO ceramics by in situ synthesized CaZrO3 coatings prepared using a non-hydrolytic sol

As refractories, MgO–CaO materials exhibit excellent properties such as high refractoriness and good thermal shock resistance; however, their poor hydration resistance limits their practical applications. In this study, calcium zirconate (CaZrO₃) coatings were deposited on CaO and MgO–CaO ceramics by dipping the ceramics in a non-hydrolytic sol. The optimised coating on the MgO–CaO ceramics was prepared by dipping the ceramics once in a 0.6 mol/L zirconia sol. The CaZrO₃ coating was in situ synthesized after calcination. The multiphase ceramics with different CaO contents were characterised using scanning electron microscopy to determine the grain sizes of MgO and CaO and to analyse the distribution of CaO in the MgO matrix and the surface porosity of the samples. The microstructure and phase analysis results showed that most of the CaO on the surface transformed into CaZrO₃ and was located at the grain boundaries. The MgO–CaO ceramics with the CaZrO₃ coatings, especially the ceramics with 20 wt% CaO, showed significantly improved hydration resistance as compared to the untreated ceramics.     

Influence of raw material type and of the overall chemical composition on phase formation and sintered microstructure of mullite aggregates

Dense mullite aggregates with varied (47–70%) alumina contents have been prepared by a conventional dry-powder pressing technique followed by heat treatments at temperatures in the range of 1450–1725 °C. Different types of clays, beach sand sillimanite (BSS) and a high purity aluminium hydroxide were used as starting materials. Mullites derived from BSS consisted of equi-axed grains whereas those obtained from clay containing precursor mixtures exhibited elongated grains. The bulk density (BD), apparent porosity (AP) and water absorption (WA) capacity of sintered mullites were found to be strongly influenced by the pre-mullitization step of the precursors and in a less extent by the type of raw material, its hydration degree and the impurity contents of Fe₂O₃, CaO and Na₂O. Mullite aggregates obtained from the three different types of aluminosilicate raw materials (i.e., ball clay, china clay and beach sand sillimanite) through a double-stage heat treatment process exhibited better sintered properties in terms of bulk density, apparent porosity, water absorption capacity and higher mullite contents in comparison to those obtained following a single-stage firing process.     

Improvement in hydration resistance of CaO granules by addition of Zr(OH)4 and Al(OH)3

Improving the hydration resistance of CaO aggregates is the key to successful application of lime-based refractories in metallurgical industry. Additive Zr(OH)₄ and Al(OH)₃ were introduced in the preparation of CaO granules using granulation equipment and calcination method in this study. The results showed that the hydration resistance of CaO granules was improved significantly, especially for granules with 0.6 wt.% Zr(OH)₄ and 0.9 wt.% Al(OH)₃, respectively. The shell of CaO granules was relatively dense after calcination and the volume of open pores of CaO granules decreased from 3.56 × 10⁻² to 1.80 × 10⁻² cm³/g when additive was introduced. Zr(OH)₄ and Al(OH)₃ have the opposite effect on the closed porosity of CaO granules, the closed porosity of CaO granules was decreased with Zr(OH)₄ addition, but increased with Al(OH)₃ addition.     

Preparation of CaO granules using the granulation method

ABSTRACT

Improving the hydration resistance of CaO particle in manufacturing and application of free CaO-containing materials has practical significance. In this study, CaO granules was made from Ca(OH)₂ particles, which were fabricated by the granulation method. The results showed that the hydration resistance of the CaO granules which was prepared under 1700?r?min^?1 was the best, the CaO granules was sintered well in calcination process, the shell of CaO granules was relatively dense, which improves the hydration resistance of CaO granules, and the rate of hydration weight increment was 0.58% after placed in the air for 20 days under a temperature of 10–14°C and a relative humidity of 57–81%.     

Electrochemical properties and microstructures of LiMn2O4 cathodes coated with aluminum zirconium coupling agents

In this study, we developed a novel and facile modification method to improve the performance of LiMn₂O₄ (LMO) electrodes for lithium ion batteries. We used an aluminum-zirconium coupling agent (AZCA) to treat LMO cathodes via a simple pyrolysis method at 450 °C. The microstructures and properties of the cathodes were examined by carrying out X-ray diffraction, scanning electron microscopy, X-ray photoelectron microscopy, transmission electron microscopy, and electrochemical analyses. The results showed that an amorphous Al₂O₃/ZrO₂ composite layer was uniformly coated on the surface of the positive material, and the thickness of the coating was about 6 nm. The coating did not affect the particle morphology and crystal structure of the samples. However, it could enhance the surface stability and result in reducing the polarization, improving the rate properties and cycle reversibility of LMO especially at high temperatures. The optimum AZCA amount for the deposition of the composite coating was found to be 3 wt%. After coating, the discharge capacity of LMO at 3C increased by 14.37% and 74.95% at 25 and 55 °C, respectively. Noteworthy, after 100 cycles at 55 °C and 1C rate, the capacity retention of LMO increased from 61.3% to 88.1%. The improvement in the properties of the AZCA-treated LMO cathodes can be attributed to the synergy between Al₂O₃ and ZrO₂, which improved the chemical stability of the cathode surface, suppressed the side reaction between the cathode and the electrolyte and enhanced the reversible deinsertion/insertion ability of Li⁺. In addition, the composite coating can greatly stabilize the crystal structure of LMO during charging-discharging cycling.     

Influence of triethanolamine on the hydration characteristics of tricalcium silicate

The hydration characteristics of 3CaO.SiO₂ or β2CaO.SiO₂ are studied by an addition of 0.0, 0.1, 0.5 or 1.0% triethanolamine. The amount of Ca(OH)₂ found at 1, 3, 7 or 28 days was in the order C₃S + 0% TEA > C₃S +0.1% TEA > C₃S + 0.5% TEA > C₃S+1.0% TEA, irrespective of whether lime was estimated by X-ray, DTA, TGA or chemical analysis. The rate of hydration, in terms of the disappearance of 3CaO.SiO₂, showed that hydration proceeded faster in the presence of TEA after 1 day. Additions of TEA increase the induction period, promote the formation of a C-S-H with higher CaO/SiO₂ ratio, increase the formation of non-crystalline Ca(OH)₂ and enhance the surface area of the hydrated silicate product.     

铝锆有机金属偶联剂对超微二氧化钛表面的改性

利用铝锆有机金属偶联剂对超微二氧化钛粉体进行表面改性。讨论了改性前后超微二氧化钛的润湿性、沉降体积等表面性质的变化。结果表明：改性的超微二氧化钛与水的接触角增大，在有机介质中分散性提高。红外光谱和能谱分析表明，在超微二氧化钛粉体表面接枝上了铝锆有机基团；通过扫描电镜可看出经过改性后的超微二氧化钛分散性得到改善。     

低压缩永久变形氟橡胶与铝合金粘合的研究

研究ＫＨ５５０、ＫＨ５６０、Ａ－１５１三种硅烷偶联剂以及ＴＡＩＣ和２，５－二甲基－２，５－二叔丁基过氧己烷硫化助剂对低压缩永久变形氟橡胶胶料硫化的影响，分析了上述五种材料有机官能团参与交联反应的活性。采用以ＫＨ５６０为主配制的胶粘剂可良好地将铝合金与低压缩永久变形氟橡胶粘接，同时对铝合金表面的处理作了一定的研究，解决了目前快速硫化的低压缩永久变形氟橡胶与铝合金粘接的难点。     

Influences of solid content of slurry on the microstructure of CaO crucible prepared by slip casting

CaO crucible was prepared from Ca(OH)₂ slurry via a slip-casting method in order to avoid hydration problem caused by free CaO during preparation process. The effect of solid content of Ca(OH)₂ slurry on microstructure of CaO crucible was investigated. It was found that the rheological property of the slurry was significantly improved when the solid content of the slurry within a certain range. The change of solid content of slurry affects the microstructure of the final products. When the solid content of the slurry was 71 wt%, the manufactured CaO crucible was of smallest mean pore size (2.58 μm) after 1600°C heating treatment. The heated CaO sample was of lower apparent porosity (4.1%) and higher bulk density (2.93 g/cm³). And the size distributions of most CaO grains are between 10 and 40 μm.     

The optimization of the microstructure and phase assemblage of high chromia refractories

The effect of Al₂O₃ and ZrO₂ addition in chromia-based refractories was investigated. The strength of ZrO₂-bearing chromia refractories was greatly enhanced by 4–8 wt% Al₂O₃ additive. In the range of 0–12 wt% ZrO₂ addition, 6 wt% ZrO₂ was most beneficial to the improvement in thermal shock resistance. Corrosion resistance was compared by exposing to three kinds of coal slag with various CaO contents. As the substitution of ZrO₂ for Cr₂O₃ increased, slag penetration increased, particularly in the case of the slag containing ∼16 wt% CaO. Considering the trade-offs between corrosion resistance, thermal shock resistance and mechanical properties, the optimum phase assemblage of high chromia refractories consists of the large granular Cr₂O₃ grains bonded by annular (Cr, Al)₂O₃ grains and well-distributed fine ZrO₂ grains.