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%.     

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.     

真空冶炼用MgO-CaO坩埚的研制

为了降低真空冶炼用MgO坩埚因MgO的高温不稳定性对冶炼合金造成的影响,同时发挥CaO的脱硫作用,以w(MgO CaO)>97%的MgO-CaO熟料为原料,在对MgO-CaO熟料进行水化试验和烧结试验研究的基础上,研制了MgO-CaO坩埚,并且与CaO坩埚一起对一种纯金属和同材质的高温合金进行了对比冶炼试验。结果表明:MgO-CaO熟料的抗水化性远高于石灰熟料的;在添加适当种类和数量的烧结助剂后,MgO-CaO熟料的可烧结性明显改善;MgO-CaO坩埚的冶炼效果达到甚至超过了CaO坩埚。     

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.     

外加剂对白云石烧结及抗水化性的影响

研究了钢渣、Al2 O3、Fe2 O3 及复合稀土氧化物对白云石烧结及抗水化性的影响。发现它们都在一定程度上促进了白云石的烧结 ,并提高了其抗水化性。其中以添加复合稀土氧化物的效果最好 ,而其他几种添加剂的作用基本相同。考虑成本及环境因素 ,选择钢渣还是可取的。添加剂中的Fe2 O3、Al2 O3等与CaO反应生成C2 S、C4 AF、C2 A、C3A等物质 ,但仍有游离CaO存在 ,可对钢水起净化作用     

Microstructural and hydration resistance study of CaO with powder surface modification by Al coupling agents: Alkoxy type and phosphate type

The surface of Ca(OH)₂ powders were pre-treated with alkoxy type aluminium coupling agent (ALC) and phosphate type aluminium phosphorus coupling agent (ALPC), respectively in this work. The shaped specimens were calcinated at 1600 °C for 3 h and then the phase compositions and microstructures of CaO specimens were investigated. The results revealed that both ALC and ALPC could conspicuously enhance the hydration resistance of CaO specimens by modifying surface microstructures in different ways. The boundaries of CaO grains in the specimens were covered with C₃A glass phase after introducing of ALC, which was replaced by calcium phosphate when the ALC was replaced by ALPC. The hexagonal barrier layer, which was the hydration product of C₃A, played a protective role in CaO grains. The obtained results in our work indicated that ALC was more effective in improving hydration resistance of CaO materials.     

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.     

Effect of Additives on the Hydration Resistance of Materials Synthesized from the Magnesia–Calcia System

The effect of a variety of doping additives on the hydration resistance of calcined materials in the MgO–CaO system was investigated. Samples were prepared from lightly calcined flotation magnesite that was mixed with dolomite, as well as from analytically pure CaO and MgO; then, the samples were doped with additives that contained cations with various valences (monvalent to tetravalent). Both the hydration rate and the powdering rate were measured. The important role of the higher-valence cations in improving the hydration resistance of the MgO–CaO materials was revealed. This behavior is believed to be due to the formation of vacancies in solid solutions of CaO or MgO with higher-valence cations. The Ti⁴⁺ cation forms a solid solution with CaO, which reduces the Ca²⁺ concentration and leads to the improved hydration resistance of calcined materials from the MgO–CaO system.     

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.     

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.     

Thermal stability of Pt particles of Pt/Al2O3 catalysts prepared using microemulsion and catalytic activity in NO–CO reaction

Sintering behaviors of the Pt particles of Pt/Al₂O₃ catalyst prepared using different preparation methods (microemulsion, sol–gel, and impregnation methods) were investigated. It was found that the catalyst prepared by microemulsion had a higher resistance to sintering than did the sol–gel and impregnation catalysts. To limit the sintering even more, the catalysts were pressed. The resistance to sintering in all the catalysts was improved by pressing. The pressed microemulsion catalyst was little deactivated in the NO–CO reaction by thermal treatment at 700 °C for 12 h, and had a high activity relative to that of the sol–gel and impregnation catalysts.     

Synthesis of a Porous Nano‐CaO/MgO‐Based CO2 Adsorbent

A porous nano‐CaO/MgO‐based adsorbent was prepared using MgO as a support in order to increase the sorption capacity and durability. The magnesium sol prepared by reacting MgO slurry with citric acid was added to nano‐CaCO₃ slurry and the mixture was calcinated to obtain the nano‐CaO/MgO‐based adsorbent. The influence of MgO content on the structure and sorption performance of the resulting adsorbent was studied in detail. The pore radius and specific surface area of the adsorbent increased with higher MgO content. The adsorbent exhibited superior sorption performance during calcium looping and maintained a good durability at the calcination temperature, thus being an interesting candidate for future work.     

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.     

Improved Hydration Resistance of Synthesized Magnesia–Calcia Clinker by Surface Modification

Hydration resistance of synthesized MgO–CaO clinker was improved by surface modification using oleic acid, stearic acid, or complex acids as modifiers, with phosphoric acid as a reference. Unmodified and modified samples were evaluated using a powdering resistance test, weight change test, and flowability test. The remarkable effects of the modifiers on the hydration resistance and flowability of the clinker were manifested, and the complex modifier caused the most significant effect. The mechanism involved the formation of calcium-containing films on the surfaces of the clinker particles, which protected them from hydration. The flowability of the clinker also increased with improved hydration resistance because of the decreased bonded-moisture content. Comparison of infrared spectra between unmodified and modified samples confirmed the formation of surface films.     

纳米氮化铝填充聚四氟乙烯复合材料的性能研究

采用高速混合、冷压烧结成型的方法制备了聚四氟乙烯/纳米氮化铝（PTFE/nano AlN）复合材料,考察了nano AlN含量对复合材料结晶性能、力学性能与摩擦性能的影响,并采用扫描电子显微镜对样品磨损表面进行分析。结果表明：随着nano AlN含量的增加,复合材料的结晶度呈现先增大后降低的趋势;nano AlN可显著提高复合材料的力学性能与耐磨损性能,当其含量为4 %时,耐磨损性能与纯PTFE相比提高了2个数量级。     

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.     

Enhancement of electrical properties of anisotropically conductive adhesive joints via low temperature sintering

The electrical properties of anisotropically conductive adhesives (ACAs) joints through low temperature sintering of nano silver (Ag) particles were investigated and compared with that of the submicron‐sized Ag‐filled ACA and lead‐free solder joints. The nano Ag particles used exhibited sintering behavior at significantly lower temperatures (<200°C) than at the bulk Ag melting temperature (960°C). The sintered nano Ag particles significantly reduced the joint resistance and enhanced the current carrying capability of ACA joints. The improved electrical performance of ACA was attributed to the reduced interfaces between the Ag particles and the increased interfacial contact area between nano Ag particles and bond pads by the particle sintering. The reduced joint resistance was comparable to that of the lead‐free (tin/3.5 silver/0.5 copper) metal solder joints. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1665–1673, 2006     

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.     

纳米SiO2颗粒对PU树脂热稳定性能的影响

采用溶胶-凝胶法制备纳米SiO2颗粒，并以此制备了SiO2／PU复合材料，用扫描电子显微镜、红外光谱仪、量热示差扫描仪和热重法分别表征了纳米复合树脂材料的结构和形态及热稳定性。结果表明，纳米SiO2能够均匀地以纳米尺寸分散于Pu树脂中，并与PU中的基团发生了化学反应，形成了键合。SiO2对PU树脂的耐低温性能影响不大，却提高了树脂的热稳定性能，使树脂的使用温度范围变宽。     

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.