保温时间对β-Sialon结合镁铝尖晶石-碳材料的影响及其氧化动力学

doi:10.15541/jim20160419

摘要/Abstract

摘要：

以电熔尖晶石、Si粉和鳞片石墨为主要原料, 木质磺酸钙溶液(1.25 g/mL)为成型结合剂, 在氮气气氛下1450℃分别保温1、2、3和4 h原位生成β-Sialon结合MgAl₂O₄-C材料, 研究了保温时间对材料的物相组成、β-Sialon的显微结构及常规物理性能的影响, 并对该复合材料进行氧化动力学研究。结果表明: 当保温时间从1 h增加到4 h, 试样的物相变化规律基本相同, Si单质相消失, 完全转化为SiC、Si₃N₄和β-Sialon(Si₃Al₃O₃N₅)。当保温时间为3 h时, 生成的β-Sialon(Si₃Al₃O₃N₅)为完整圆柱状晶粒, 尺寸分布均匀, 交错成网络结构。随着保温时间的增加, 试样内部产生较多的SiO气体, 导致试样的显气孔率增加, 体积密度下降, 耐压强度和抗折强度先增加后下降, 当保温时间为3 h时, 耐压强度和抗折强度达到最大。氧化动力学研究表明, 氧化过程随着时间的推移分为化学反应控制阶段、化学反应和扩散共同控制阶段及扩散控制三个阶段。

关键词: β-Sialon结合MgAl2O4-C复合材料, 原位生成, 保温时间, 氧化动力学

Abstract:

A β-Sialon bonded MgAl₂O₄-C refractory was prepared in-situ by fused spinel, silicon powder, flake graphite as raw materials, and calcium lignosulfonate with the concentration of 1.25 g/mL as the binder. The samples were sintered under N₂ atmosphere at 1450℃ for 1, 2 3 and 4 h, respectively. The effects of holding time on the conventional physical properties, phase compositions and microstructure of MgAl₂O₄-C refractory were investigated. The phase composition and microstructure of the sintered samples were investigated by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM), respectively. XRD patterns showed that there were no evident differences on the phase compositions and the silicon phase had completely disappeared to form SiC, Si₃N₄ or β-Sialon (Si₃Al₃O₃N₅). The β-Sialon crystals had columned microstructure stagger on each other when holding time was 3 h. With the holding time increasing from 1 h to 4 h, the increased SiO gas lead to an increase of apparent porosity and a decrease of bulk density. In addition, the cold crushing strength and flexural strength of the samples sintered at 1450℃ for 3 h reach the highest. Research on oxidation kinetics of composite material indicates that oxidation process can be divided into three stages: chemical reaction rate controlling stage, diffusion rate controlling stage, and co-effect controlling of chemical reaction and diffusion rate stage.

Key words: β-Sialon bonded MgAl2O4-C refractory, in-situ, holding time, oxidation kinetics

宋云飞, 王少华, 邓承继, 祝洪喜, 刘建鹏, 丁军, 余超. 保温时间对β-Sialon结合镁铝尖晶石-碳材料的影响及其氧化动力学[J]. 无机材料学报, 2017, 32(5): 495-501.

SONG Yun-Fei, WANG Shao-Hua, DENG Cheng-Ji, ZHU Hong-Xi, LIU Jian-Peng, DING Jun, YU Chao. Effects and Oxidation Kinetics of Holding Time on the β-Sialon Bonded MgAl₂O₄-C Composites[J]. Journal of Inorganic Materials, 2017, 32(5): 495-501.

图/表 9

表1 MgAl2O4-C材料的实验配方

Table 1 Experimental formula of MgAl2O4-C materials

Materials	Size/mm	wt/%
Fused spinel	1-3	40
	≤1	30
	≤0.088	10
Flake graphite	≤0.088	10
Silicon powder	≤0.074	10
Calcium lignosulfonate	1.25 g/mL	4

图1 1450℃分别保温1、2、3和4 h氮化试样的XRD图谱

Fig. 1 XRD patterns of samples nitride at 1450℃ for 1 h (a), 2 h (b), 3 h (c) and 4 h (d)

表2 理论计算与实验结果的Z值和d值的关系

Table 2 Relationship between Z and d values from the theoretical and experimental results

Crystal face symbols	d/nm
	XRD results	Theoretical results
		Z=2	Z=3	Z=4
(2 0 0)	0.332011	0.331674	0.33284	0.33401
(1 0 1)	0.270064	0.270081	0.272096	0.27411
(2 1 0)	0.251264	0.250722	0.251604	0.25249

图2 1450℃保温不同时间氮化试样中β-Sialon晶粒的SEM照片

Fig. 2 Morphologies of β-Sialon crystals in sintered specimens at 1450℃ with different holding time

图3 1450℃下保温氮化1 h试样中β-Sialon的TEM照片

Fig. 3 TEM images of β-Sialon nitridized at 1450℃ for 1 h

图4 保温时间对试样的显气孔率、体积密度、耐压强度和抗折强度的影响

Fig. 4 Effects of holding time on the apparent porosity, bulk density, cold crushing strength and flexural strength of the sample

图5 试样1200℃下氧化4 h后的SEM照片

Fig. 5 SEM image of specimen oxidized at 1200℃ for 4 h

图6 复合材料的(a)恒温氧化动力学曲线, (b)化学反应速率控制的氧化动力学曲线, (c)界面化学反应速率和扩散速度混合控制的氧化动力学曲线和(d)扩散速率控制的氧化动力学曲线

Fig. 6 (a) Oxidation kinetics of curves at constant temperatures, (b) oxidizing kinetic curves controlled by chemical reaction rate, (c) oxidizing kinetic curves controlled by interfacial chemical reaction and diffusion rate and (d) oxidizing kinetic curves controlled by diffusion rate of specimens SMAC

图7 等温氧化温度对SMAC复合材料的氧化反应速率常数的影响

Fig. 7 Effect of constant oxidation temperatures on the oxidationrate constant of SMAC specimens

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