焙烧炭砖孔结构和热导率与硅粉加入量的关系

Effect of silicon addition on pore structure and thermal conductivity of fired carbon specimens

以电煅无烟煤(5～3、3～1、≤1及≤0.088 mm,w(固定碳)=95.17%,w(挥发分)=0.37%,w(灰分)=4.14%)、鳞片石墨(≤0.147和≤0.074 mm,w(固定碳)=96.5%)、棕刚玉粉(≤0.074 mm,w(A l2O3)=93.5%,w(TiO2)=2.3%)和硅粉(≤0.043 mm,w(Si)=96.37%)为原料,固定骨料与细粉的质量比为60∶40,细粉中硅粉和电煅无烟煤细粉总量固定为14%(质量分数),改变硅粉加入量(质量分数)分别为3%、5%、8%、10%、14%,以液态热塑性酚醛树脂为结合剂,乌洛托品作固化剂制成炭砖,于1 400℃3 h埋炭焙烧,借助于X射线衍射仪、压汞仪、激光导热仪、扫描电子显微镜和能谱分析仪等测试手段,研究了不同硅粉加入量的焙烧炭砖的孔结构及热导率。结果表明:因炭砖焙烧过程单质硅原位反应形成β-SiC、Si2N2O和石英等陶瓷相,填充、阻隔或封闭了气孔,故硅粉加入量控制着试样内部的气孔分布、平均孔径和孔径<1μm气孔的孔容积率;受材料组成和孔结构变化影响,炭砖的热导率也发生相应变化;随硅粉加入量增加,试样中孔径分布范围由宽变窄,平均孔径逐渐减小,<1μm孔的容积率增加,气孔呈微孔化趋势;当试样中硅粉加入量超过8%时,气孔的平均孔径<0.3μm,<1μm孔容积率超过70%,试样的热导率急剧下降。

The anthracite based carbon bricks were prepared using calcined anthracite （particle sizes were 5-3, 3-1,≤1 and ≤0.088 mm, respectively, ω（ fixed carbon ）=95.17%, ω（ volatilizing component）=0.37%, ω（ash） =4.14% ） ,flake graphite（ particle sizes were ≤0.147 and ≤0.074 mm, w（ fixed carbon） =96.5% ）, brown corundum powder（particle size was ≤0.074 mm, w（Al2O3）=93.5%, w（TiO2） =2.3%） and silicon powder（ particle size was ≤0.043 mm, w（Si） =96.37% ） as starting materials,liquid thermoplastics phenol formaldehyde resin as binder, hexamine methenamine urotropin as curing agent, then carbon embedded fired at 1400℃ for 3h. The mass ratio of fixed aggregate and powder was 60：40,and the total amount of silicon powder and calcined anthracite powder was 14% （mass ratio）. Effect of silicon addition （3wt%, 5wt%,8 wt% ,10wt% and 14 wt% ,respectively） on the pore size distribution and thermal conductivity of the carbon bricks was investigated by using XRD, mercury porosimeter, laser thermal conductivity instru- ment,SEM and EDS,etc. The results indicated that the pore size distribution, mean pore size and 〈1μm pore volume were controlled by silicon powder addition, and the thermal conductivity of the bricks was affected by the composition and pore structure. The pore size distribution became narrow, mean pore size reduced, 〈1μm pore volume gradually increased with silicon powder addition increasing owing to the formation of ceramics phases such as Si2N2O and β-SIC whisker,etc, in matrix of carbon brick. When the silicon powder addition exceeded 8wt% ,the mean pore size was 〈0.3μm,percentage of 〈1μm pore volume exceeded 70% ,and the thermal conductivity dropped remarkably.