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%.     

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.     

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.     

On the Modification of Hydration Resistance of CaO with ZrO2 Additive

Various ZrO₂/CaO samples were fabricated by cold isostatic pressing and sintered at 1750°C for 4 h. It was observed that the sample with 12% ZrO₂ additive possessed the good hydration resistance and had the lowest apparent porosity of about 0.75%; its weight additive stored after 56 days was less than 0.6 wt%, and it contributed to the occurrence of CaZrO₃ on the surface of CaO. The CaO crucible with 12 mol% ZrO₂ additive did not react with titanium melt during melting TiNi alloy. This provides a support for searching a new refractory with the good hydration resistance for induction melting titanium alloys.     

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.     

Enhanced oxidation resistance of SiC/SiC minicomposites via slurry infiltration of oxide layers

SiC based composite materials commonly have protective silica surface in air. Under humid environments at high temperatures, like occur in jet engines, the silica surface layer reacts with water molecules to form volatile silicon hydroxide (Si(OH)₄) and the protection is reduced which cause jet engine degradation. An alternative approach to protect SiC based composites would be to infiltrate the SiC matrix via slurry with an oxide material that is resistant to the high-temperature and humid environment. As proof of concept, aqueous based mullite particle slurries were infiltrated by pressurized flow and by capillarity of the wetting slurry on the external surface of the porous SiC matrix of single-fiber-tow SiC/SiC minicomposites. Minicomposites were precracked at room temperature during tensile tests then tested in tensile creep in air at 1200 °C to study the degree of protection that the infiltrated mullite provided at high temperatures. Next, fracture surfaces were examined using SEM.     

浸蜡工艺对高钙镁钙质耐火材料抗水化性的影响

为了提高高钙镁钙质耐火材料的抗水化性能,以高纯烧结白云石砂和高纯镁砂为主要原料,制成φ36mm×36 mm的高钙镁钙质耐火材料试样,于1 600℃保温3 h煅烧后,采用不同的浸蜡工艺进行浸蜡处理,并采用自然存放法检测浸蜡试样的抗水化性能,以研究试样预热温度(分别为75、100、125、150、175和200℃)、预热时间(分别为0.5、1、2和3 h)、蜡液温度(分别为75、100、125、150、175和200℃)、浸蜡时间(分别为5 s、30 s、1 min、5 min、10 min、15 min)对试样抗水化性能的影响。结果表明:1)最佳浸蜡工艺是试样先在150℃预热1 h,然后在150℃蜡液中浸渍5 min;2)按最佳浸蜡工艺处理的试样,在自然环境中可保存半年以上。     

CaO耐火材料的抗水化研究进展

分析了CaO耐火材料的水化机理,指出评价CaO耐火材料抗水化性的方法主要有蒸压法、煮沸法、常压长期保存法和实际使用状况评价法,总结了提高CaO材料抗水化性能的方法主要有两种:引入添加剂法和表面处理法。比较了国内外各研究者在CaO耐火材料抗水化方法上的研究进展,展望了解决CaO耐火材料水化问题的方法和前景。     

添加Y2O3对CaF2陶瓷烧结和抗水化性的影响

为了制备致密且抗水化的CaF_2陶瓷,以w(CaF_2)=99.9%的氟化钙为原料,分别添加质量分数为0、0.5%、1%、2%、4%和6%的高纯Y_2O_3粉作为添加剂,经180 MPa等静压成型后,在空气气氛中于1 300℃保温2 h烧结制成CaF_2陶瓷,研究添加Y_2O_3对CaF_2陶瓷烧结及抗水化性能的影响。结果表明:在氟化钙原料粉中添加适量的Y_2O_3制备的CaF_2陶瓷,其烧结致密度和抗水化性能显著提高。这是因为Y_2O_3与CaF_2陶瓷在烧结过程中产生的Ca O杂质反应生成了Ca3Y2O6液相,覆盖在氟化钙陶瓷表面,从而阻止了氟化钙陶瓷和水蒸气的进一步接触。在本研究中,Y_2O_3的适宜添加量在1%(w)左右。     

铁红对白云石熟料烧结性和抗水化性的影响

以河南卫辉白云石为主要原料,采用二步煅烧法,在实验室研究了不同温度条件下铁红(Fe2O3)对白云石熟料烧结与抗水化性能的影响,并采用扫描电子显微镜对试样的显微结构进行了分析。结果表明:当煅烧温度为1 400~1 500℃和1 500~1 600℃时,分别添加质量分数为0.5%和0.25%的铁红能显著提高白云石熟料的烧结和抗水化性能。白云石烧结过程中形成的C2F分布于颗粒间隙处,形成防水保护膜包裹在方钙石和方镁石颗粒表面,提高了白云石的抗水化性能。     

电泳沉积氧化铝陶瓷涂层的制备及耐腐蚀性能

以氧化铝溶胶为前驱体,采用电泳沉积和低温煅烧法在低碳钢基体上制备了氧化铝陶瓷涂层,并对其成分、表面形貌及耐蚀性进行了研究。结果表明,将低碳钢片置于以乙醇作为分散介质的0.45mol/L氧化铝溶胶中,在60V恒电位下沉积180s后,再于马弗炉中700°C下煅烧5min,所制得的氧化铝陶瓷涂层在2mol/L盐酸溶液中具有良好的耐蚀性。     

Surface functionalization of aramid fibers via constructing different zinc oxide nanostructures for improved UV resistance

Aramid fibers (AFs) with high strength and modulus have a vital application in harsh outdoor bulletproof protection and ship ropes; however, solar radiation, especially ultraviolet (UV) radiation, is one of the main factors for affecting their service life. Herein, different zinc oxide (ZnO) nanostructures were constructed on the surface of AFs by the growth of ZnO nanowires (AF-ZnO NW) and coating of waterborne polyurethane/ZnO nanoparticles composite emulsion (AF/ZnO), respectively. The surface functionalized AFs exhibited enhanced mechanical properties retention after UV radiation. Nevertheless, the tensile strength of AF-ZnO NW before UV aging was already lower than the tensile strength of original AFs due to the surface structure damage from chemical grafting modification. The tensile strength and elongation retention rates of AF/ZnO-5% reached 74.4% and 84.4% after UV exposure for 168 h, respectively, which were much higher than the value of 48.3% and 60.5% of the neat AFs. These results provide an effective and low-cost strategy for improving the UV-resistance of advanced high-performance fibers.     

Improved flashover performance and tracking resistance of silicone rubber by direct fluorination

Silicone rubber (SIR) samples are fluorinated using a F₂/N₂ mixture at different temperatures. Physicochemical characteristics are analyzed by attenuated total reflection infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Basic properties of the fluorinated surface layers are investigated, and the intrinsic alternating current (AC) flashover performance and tracking resistance of the surface fluorinated samples are evaluated. The flashover test results indicate that the fluorination leads to an improvement in AC flashover performance of the SIR material, as a result of the competition between the favorable effect of the increase in surface conduction and the adverse effect of a likely increase in surface layer permittivity. The increase in AC flashover voltage is associated with the voltage-increasing mode of the flashover test. The flashover test results also show an improved tracking resistance of the SIR material by the fluorination, and the improvement is especially significant for the fluorinated surface layer that has less cleavage of Si C bonds or a good compactness as well as a large thickness. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48556.     

Surface sedimentation and adherence of Nano‐SiO2 to improve thermal stability and flame resistance of melamine‐formaldehyde foam via sol‐gel method

Melamine‐formaldehyde foam possesses intrinsic flame retardance; however, relative poor thermal stability and a certain amount of heat release rate restrict its applications in heated environment to a degree. In the present research, sol‐gel method has been adopted to precipitate nano‐SiO₂ particles on the surface of the melamine‐formaldehyde foam's fibers to construct a protective inorganic gel layer. Taking advantages of the shielding effects of the gel layer, the thermal‐oxygen degradation of the foam can be greatly retarded during heating; hence, the thermal stability is remarkably improved, and the flame retardance is further enhanced. In addition, introducing a small amount of membrane‐forming agent in the sol‐gel system can make the depositional nano‐SiO₂ particles well adhered to avoid dusting.     

45钢与QT450-10的表面耐腐蚀处理工艺及性能研究

针对注塑机零件中常用的材料45钢和QT450-10,采用未经热处理的模拟试样,分别进行两组不同工艺参数的软氮化及磷化（发黑）和浸涂防锈油等处理方式。最后使用中性盐雾腐蚀试验评估各试样获得的耐腐蚀性能。研究表面：采用相同的表面处理工艺,45钢的耐腐蚀性能优于QT450-10;QT450-10未经磷化（发黑）处理,无论是否浸涂防锈油,表面耐腐蚀性均很差。