发泡法制备轻质莫来石结合氧化铝空心球制品的性能研究

为了改善莫来石结合氧化铝空心球制品的隔热性能,以氧化铝微粉、二氧化硅微粉和≤3 mm的氧化铝空心球为主要原料,采用发泡法结合凝胶注模工艺制备了轻质莫来石结合氧化铝空心球制品,并研究了发泡时间(5、10、15和20 min)对试样的体积密度、气孔率、耐压强度、显微结构和热导率的影响。结果表明:合成试样的基质部分为气孔孔径50~100μm的多孔结构,与氧化铝空心球结合紧密;随着发泡时间增加,试样的气孔率增加,而体积密度、耐压强度和热导率降低;当发泡时间为20 min时,试样体积密度为0. 71 g·cm-3,气孔率为80. 2%,常温耐压强度为1. 81 MPa,600℃热导率为0. 467 W·m^(-1)·K^(-1)。

镧系钙钛矿型红外辐射陶瓷材料的研究进展

高温加热装置的高辐射涂层材料在节能应用方面的研究开发目前受到了广泛关注,因此介绍了红外辐射的理论研究进展,综述了近年来备受关注的镧系钙钛矿化合物(LaMnO3、LaCrO3、LaFeO3和LaAlO3)红外辐射陶瓷材料的研究现状以及掺杂对红外辐射率的影响,提出了现阶段材料研究中所存在的问题,并展望了镧系钙钛矿型(ABO3)化合物作为红外辐射材料的工业应用前景及未来的研究趋势。

氮化温度对直接氮化法制备氮化硅纤维材料显微结构的影响

用工业硅粉为原料,首先通过发泡法结合凝胶注模制备硅的多孔坯体,然后高温氮化制备氮化硅纤维材料,借助XRD和SEM研究氮化温度对该材料显微结构的影响。结果表明:在1400℃氮化5 h,已经基本完全氮化,并且坯体在1375℃发生了剧烈的反应。氮化硅纤维主要在气孔中生长,生成的氮化硅纤维均为纳米纤维,其直径在50~250 nm,长度约10μm。随着氮化温度的升高,氮化硅纤维逐渐增多,泡沫孔壁趋于消失,孔壁的消失是由于SiO的生成。氮化硅纤维生长遵循VS和VLS机制。

Si3N4粉加入量对直接氮化制备氮化硅纤维材料显微结构和性能的影响

为进一步提高氮化硅纤维材料的强度,在Si基浆料中加入Si3N4粉体,发泡法制备Si基多孔坯体,经1420℃保温10 h高温氮化制备氮化硅纤维材料试样。重点研究了Si3N4粉体加入量(质量分数分别为10%、20%、30%、40%、50%)对试样显微结构和性能的影响。结果表明:1)引入Si 3N 4粉体,试样的骨架结构得到强化,氮化后试样的抗折强度和耐压强度显著提高。2)随Si 3N 4粉体添加量的增加,试样孔壁结构中纤维由纤维状逐步转变为针状、粒状,孔壁结构由纤维结合逐步转变为纤维和烧结共同结合,材料强度提高。但引入过多的Si 3N 4粉体不利于Si 3N 4纤维的生长,适宜加入量为20%~40%(w)。

发泡对直接氮化制备氮化硅纤维材料显微结构和性能的影响

借助发泡法将气孔引入Si多孔坯体,使坯体的体积分别增加0、1、2、3倍,通过原位氮化工艺制备了氮化硅纤维材料,重点研究了发泡体积倍数对氮化硅纤维材料显微结构和性能的影响。结果表明:(1)发泡法引入气孔后,坯体中存在发泡孔、孔壁窗口、孔壁微孔三种孔结构。提高发泡倍数,试样中气孔率升高,孔壁窗口数量增多,N 2易流通,有利于氮化反应的进行。(2)氮化硅纤维只能生长在材料的孔缝部位,引入的气孔为氮化硅纤维提供了足够大的生长空间,反应后试样孔中长满了絮状的氮化硅纤维。随发泡体积倍数增加,试样孔壁中生成的氮化硅由粒状转变为纤维状,形成了氮化硅纤维交织孔壁结构。(3)发泡法引入气孔后,材料的强度由孔壁提供。随发泡倍数增加,试样的气孔率升高,单位面积内孔壁的有效截面减小,导致材料的强度降低。

添加Si粉-埋碳热处理对刚玉浇注料性能的影响

为了进一步提高刚玉浇注料的高温使用性能,在超低水泥刚玉浇注料中加入不同质量分数(分别为0、4%、6%、8%、10%)的Si粉,经振动浇注成型、养护、烘干后,在埋碳条件下于1400℃热处理6 h,测定试样的加热永久线变化率及烧后试样的显气孔率、体积密度、常温抗折强度、常温耐压强度以及1200和1400℃的热态抗折强度,并对部分热处理后试样进行了XRD和SEM分析。结果表明:1、在刚玉浇注料中引入Si粉,并在埋碳条件下热处理可显著提高浇注料的热态强度。2、埋碳热处理后,试样中不仅形成了非氧化物SiAlON和SiC,而且生成了莫来石,可有效提高浇注料在1400℃的热态强度。

采用Si粉发泡氮化制备Si3N4纤维材料的抗氧化性研究

采用发泡法将气孔引入Si坯体,使体积分别增加0、1、2、3倍,经原位氮化制备出显气孔率分别为49%、74%、81%和87%的Si3N4纤维材料,研究了氧化温度(1 150、1 350和1 550℃)和显气孔率对Si3N4纤维材料抗氧化性的影响。结果表明:1)温度是影响Si3N4纤维材料抗氧化性的关键因素,随温度升高试样氧化后生成SiO2的量逐渐增多。孔中Si3N4纤维因具有较大的比表面积,1 550℃氧化后全部转化为串珠状SiO2结构,Si3N4纤维材料理想的使用温度应低于1 150℃;2)试样显气孔率由49%提高至87%,氧化后生成SiO2的量变化不大;3)发泡法引入的气孔可部分吸收孔壁上Si3N4氧化产生的体积效应,避免孔壁在氧化中产生裂纹。同时,Si3N4氧化产生的体积膨胀可使孔壁结构致密化,有利于提高材料强度。

不同氮化条件对聚氨酯泡沫浸渍氮化制备Si3N4纤维材料的影响

为了探究不同氮化条件对聚氨酯泡沫浸渍氮化制备Si3N4纤维材料的影响,明确影响Si3N4纤维材料制备的关键因素,以不同孔径(200、1000、5000μm)聚氨酯泡沫为模板,通过浸渍工艺制备Si多孔坯体,采取直接氮化和放置在坩埚中的两种氮化方式制备了Si3N4纤维材料,重点研究了两种氮化条件对Si3N4纤维材料显微结构的影响。结果表明:1)Si3N4纤维的生成反应为SiO和N 2双气相控制反应,氮化过程中SiO与N 2发生反应生成Si3N4纤维,Si3N4纤维优先在Si3N4基材料上附着生长;2)SiO分压是影响Si3N4纤维材料制备的关键因素,将试样放置在坩埚中氮化可确保在坩埚内形成较高的SiO分压,有利于Si3N4纤维的制备;3)200μm孔径的聚氨酯泡沫因孔径较小,浸渍挂浆后易形成闭孔结构,可以抑制SiO从贯通孔中逸出,易在材料内部形成较高的SiO分压,有利于Si3N4纤维的生长。两种氮化条件对采用200μm孔径的聚氨酯泡沫浸渍氮化后生成Si3N4的量影响不大。

Preparation and Properties of Calcium Hexaaluminate Porous Ceramics

In this paper,calcium hexaaluminate(CA6)porous ceramics were prepared by a foaming method combined with cement solidification molding.The effects of the foaming agent addition on the microstructure and the properties of the ceramics were studied.The results show that the microstructure and the porosity of the ceramics can be controlled by adjusting the addition of the foaming agent.As the addition of the foaming agent increased,the bulk density reduced from 1 g·cm^-3 to 0.35 g·cm^-3,the porosity increased from 70.4%to 89.6%,the compressive strength reduced from 18.46 MPa to 1.66 MPa,and the thermal conductivity at 1000°C decreased from 0.382 W·m^-1·K^-1 to 0.144 W·m^-1·K^-1.It is indicated that calcium hexaaluminate porous ceramics with low density,high strength and low thermal conductivity can be obtained by the foaming method.As the lining material of high temperature electric furnaces,the ceramic has excellent energy saving effect.

Preparation and Properties of Alumina Heat Insulation Materials with High Purity

With the wide using of transparent alumina ceramics and synthetic sapphire, the demand of the furnace for them is promoted steadily, and the furnace lining materials are upgrading. Having low thermal conductivity and the same composition with transparent alumina ceramics and sapphire, porous alumina ceramics with. high purity are expected to lower the high energy consumption without contamination, in this paper, porous alumina ceramics with porosity of 75.3% -81.9% and impurity less than 0. 1% were prepared by a foaming method combined with gelcasting, using high purity alumina powders as raw materials. By changing the amount of foaming agent and the solid content, the microstructure and properties of porous ceramics were tailored. The compressive strength of the porous ceramics ranged .front （ 22.4 ±2.5） MPa to （48. 1± 3. 1 ） MPa, the thermal conductivity of porous ceramics at 1 000℃ ranged between 0. 41 -0. 65 W · （ m · K）^-1.

Effect of Nitriding Process on Phase and Microstructure of Silicon Nitride Fibers Prepared by Direct Nitriding Method

In this paper,Si3N4 fiber materials were fabricated by nitridation of porous Si green bodies,which were prepared by the foaming method combined with gel-casting.The effect of the nitriding process(the heating rate and the nitrogen flow rate)on the phase and the microstructure was studied.The results show that decreasing the heating rate and the nitrogen flow rate is both beneficial to the growth of Si3N4 nanofibers and promoting the disintegration of the pore wall structure of the porous green bodies.The optimized nitrogen flow rate and the heating rate for the growth of silicon nitride fibers are 150 mL/min and 0.5℃/min,respectively.

Thermal Insulation Materials of Alumina Based Porous Ceramics

Significant energy saving effects can be made through the improvement of furnace refractories,especially the thermal insulation refractories. In this study,the preparation and the application of different alumina based porous ceramics were briefly introduced. Alumina based porous ceramics were prepared combined foaming method with gelcasting,sol- gel process or cement curing process. The influences of different preparation methods on the sintering shrinkage, porosity, phase composition, microstructure, compressive strength and thermal conductivity were discussed. Alumina based porous ceramics with relatively high strength and low thermal conductivity could be obtained through the above mentioned methods. Compared with the traditional lining materials,about 40% energy could be saved when they were used as the furnace wall.

Ca^2+–Cr^3+共掺杂LaAlO3陶瓷的制备及性能

采用高温固相反应法,在空气气氛中制备了纯LaAlO3和Ca^2+–Cr^3+共掺杂LaAlO3陶瓷材料,对其在近红外的发射率以及热导率进行了研究比较。结果表明:20%Ca^2+(摩尔分数)和20%Cr^3+掺杂后的La0.8Ca0.2Al0.8Cr0.2O3在0.76~2.50μm的红外发射率达0.92,比纯LaAlO3提高了300%;Ca^2+和Cr^3+的掺杂降低了陶瓷材料的热导率,在1200℃时LaAlO3和La0.8Ca0.2Al0.8Cr0.2O3的热导率最低,La0.8Ca0.2Al0.8Cr0.2O3的热导率最低值为2.602 W·m^–1·K^–1,较纯LaAlO3降低了38%。