Steam Oxidation Resistance of Silicon Carbide Castables at Elevated Temperatures

Silicon carbide castables of different SiC contents(86%and 71%,by mass)were prepared using white fused corundum,silicon carbide particles and fines,activated alumina powder,silica fume and pure calcium aluminate cement as main starting materials,heat treating at 1000℃ for 3 h,and oxidizing in steam atmosphere at 1000℃ for different durations(100,200,300,400 and 500 h).The mass and volume before and after oxidation,the bulk density,the apparent porosity and the cold compressive strength were tested.The phase composition and the microstructure before and after oxidation were analyzed by XRD and SEM.The results indicate that:(1)within 300 h of oxidation duration,silicon carbide shows an increasing oxidation rate;however,the oxidation rate is low during 300-500 h of oxidation duration;2)the oxidation rate of the specimen with 71%SiC is slightly higher than the one with 86%SiC;3)with the increasing oxidation degree of silicon carbide,the apparent porosity of the specimens tends to increase,followed by the declining bulk density and cold compressive strength.

Effects of a Combined Silica-containing Additive on Structural and Rheological Properties of a Low-cement Silicon Carbide Castable

The use of a combined additive consisting of silica-containing additives“F”(thinning)and“S”(accelerating castable hardening)instead of the previously used silica-containing additive“A”and a mixture of dispersing additives based on polyethylene glycol in low-cement silicon carbide castable allows to improve the castable workability by increasing(in 5.4 times)the flowability of a freshly prepared castable,and increase by 1.2 and 1.1 times the cold crushing strength of heat-treated at temperatures of 110 and 1580°C,respectively,castable samples from low-cement silicon carbide castable with practically equal values of open porosity(15.8%and 16.0%).The petrographic studies of the castable sample microstructure after firing at a temperature of 1580°C showed that the investigated silica-containing additives“F”and“S”contribute to the denser and more uniform structure formation.As a result of the carried out research,the manufacturing technology of a low-cement silicon carbide castable was improved,of which the production was mastered at JSC“URIR named after A.S.Berezhnoy”.

Rheological Behavior of Bauxite-Based SiC-Containing Castables

Low cement (LC) and ultra low cement (ULC) bauxite SiC castables are important and high performance monolithic refractories and they have been widely used in iron making and incinerator linings. In this work, rheological behavior of LC and ULC bauxite based SiC containing castables has been studied, including the effects of SiC content and cement content on rheological properties of the castables. The results show that with an increase of SiC and cement content, rheological properties of the castables deteriorate. On the other hand, moderate amounts of SiC (4%～8%) and of calcium aluminate cement (2%～4%) have very slight influence on rheological properties, (i.e. when the castables are sheared their torque and yield torque only slightly increase with the shearing speed). The rheological characteristics of the castables follow Bingham fluid and always show shear thinning behavior.

Effects of B_4C Addition on Properties of Al_2O_3-SiC-Si_3N_4 Castables for Iron Trough

Effects of B4C additions （0,0.2%,0.4%,and 0.6%） on cold physical properties and hot modulus of rupture of Al2O3-SiC-Si3N4 castables for iron trough were investigated. The phase composition and microstructure were analyzed by XRD and SEM. The results show that bulk density,cold strength,and hot modulus of rupture of the castables first increase and then decrease while apparent porosity first drops and then increases with B4C addition increasing. The optimum addition of B4C is 0.4%. B4C mainly contributes to sintering and antioxidation. Compared with the specimens without B4C,the specimens with B4C have more fibrous O＇-SiAlON with larger length-diameter ratio. The growth mechanism of O＇-SiAlON crystals is deduced to gas-solid mechanism.

Erosion Mechanism of Al_(2)O_(3)-SiC Castables for Lining Maintenance in Blast Furnace Hearths

Al_(2)O_(3)-SiC castables,for the relining of BF hearths in mid-campaign repair,were sampled and investigated after two years’service.The chemical and mineralogical characteristics of the residual castables were analyzed by X-ray diffraction,scanning electron microscopy,and energy dispersive X-ray spectrometry to study the erosion mechanism.The results show that as gaseous K diffuses in the castables,leucite(KAlSi_(2)O_(8))and multiple cracks are formed.Molten iron and slag penetrate through the cracks to form anorthite([Ca,Na][Al,Si]_(4)O_(8))and iron,which will not form an embrittlement layer similar to carbon bricks.The entire repair of the hearth with Al_(2)O_(3)-SiC castables combined with the design of thin-wall lining hearth eliminates“elephant foot shaped”erosion,greatly prolonging the service life of the hearth lining.

Effect of Andalusite Aggregate Pre-fired at Different Temperatures on Properties of Al2O3-SiC-C Castables

This work investigates the effect of the pre-firing temperature of andalusite aggregate(5-3 mm)on the conversion of andalusite,the volume stability,the thermal shock resistance and the slag resistance of Al2O3-SiC-C castables.The results show that the volume stability and the thermal shock resistance of the castables could be adjusted at different pre-firing temperatures of andalusite aggregates.There was no noticeable difference in the slag resistance between the specimens without andalusite and those with andalusite aggregate pre-fired at different temperatures.

Steel Fiber Toughening Mullite-SiC Castables for Coke Dry Quenching Furnace Corbel Pillar

The mullite-SiC castables for coke dry quenching（CDQ）furnace corbel pillar were prepared by taking mullite and silicon carbide as aggregates,silicon carbide powder,fused silica powder,α-Al2O3powder and silica fume as matrix,calcium aluminate cement as binding system,and extra-adding steel fibers to extend the CDQ furnace refractory life.The effects of steel fiber types（melt pumping meniscus,cut straight,wavy indentation,cold-drawn hook）and steel fiber extra-additions（0,1%,2%,3%by volume）on the properties of mullite-SiC castables were investigated.Then the toughening mechanism of steel fiber in the castables was analyzed according to the load-displacement curves.The results show that：（1）the toughening effects of the melt pumping meniscus steel fiber with rough surface and colddrawn hook steel fiber with strong anchoring effect with the matrix are better than those of cut straight steel fiber and wavy indentation steel fiber;（2）the suitable amount of steel fiber（less than 2%）in mullite-SiC castables not only significantly improves the mechanical properties,thermal shock resistance and wearing resistance,but also improves the fracture energy by 49.0%and slows the crack growth;（3）the bond strength and mechanical anchoring force between steel fiber and castable interface are key elements of steel fiber reinforced castables.

Effect of Treated Graphite on Properties of Al_2O_3-SiC-C Castables

Al2O3 - SiC - C castables with 2% pitch or 2%, 4% and 6% treated graphite, respectively, were prepared based on the basic formulation of traditional Al2O3 - SiC - C castables. The flowability of castables, and bulk density, volume stability, strength, oxidation resistance and slag resistance of specimens fired at 110 ℃, 1 100 ℃, and 1 500 9Z respectively were comparatively studied. The results showed that： （1） With carbon source changing from pitch to treated graphite and the increase of treated graphite addition, water addition of castables increased, bulk density of specimens fired at different temperatures increased firstly and then decreased, strength after drying decreased obviously, strength after firing and oxidation resistance changed slightly, hot modulus of rupture increased obviously; （2） Slag resistance of specimen with treated graphite was worse than that of specimen with the same amount of pitch, but the former was obviously improved with the increase of treated graphite addition.

Application Research of Dense Sintered Alumina in Iron Runner Castables

Three different kinds of corundum aggregates-tabular sintered alumina, dense sintered alumina, and fused dense corundum-were introduced into the silica fume .free or silica fume containing Al2O3 -SiC - C iron runner castables to investigate their influences on the flow ability, linear change on heating, bulk density, apparent porosity, cold strength, hot modulus of rupture, therm, al shock resistance, slag resistance, oxidation resistance as well as wear resistance of Al2O3 - SiC - C iron runner castables. The results show that （ 1 ） compared with the specimens with fused dense corundum, the specimens with dense sintered alumina have equivalent installation property, slag resistance and oxidation resistance, equivalent or even higher cold modulus of rupture, cold crushing strength and hot modulus of rupture, exhibiting better thermal shock resistance and cold wear resistance ; （2） adopting bimodal alumina micropowder LISAL22RABL as well as water reducers ZX2 and ZD2 can well reduce the water requirement of silica fume free castables, solving the problem of deteriorated flow ability resulted from the lack of silica fume; since the lack of silica fume avoids the formation of low melting point liquid, the hot modulus of rupture and the thermal shock resistance of the silica fume free castables are both better than those of the silica fume containing castables ; （3） the density of the castable specimens with dense sintered alumina is 4% -6% lower than that of the castable specimens with Jhsed dense corundum so the refractories consumption of one iron runner reduces by 5% by using the tastable with dense sintered alumina, which obviously reduces the cost of refractories.

Effect of Pelletized Graphite Addition on Properties of Al_2O_3-SiC-C Castables

Al2O3 - SiC - C castables with pelletized graphite addition of 0. 2%, 4% or 6% （by mass, the same hereinafter ） were prepared using brown fused corundum （8 - 5, 5 - 3 and 3 - 1 mm ） , dense fused corundum （ ≤1 and 0. 045 mm） and SiC （ ≤1 and ≤0. 064 mm） its main starting materials with mass ratio of aggregate： matrix = 71： 29, 2% silicon powder and 0. 4% B4C as antioxidants, and pelletized graphite as carbon source, Effect of pelletized graphite addition on physical properties, oxidation resistance, slag resistance arid thermal shock resistance of Al2O3 -SiC- C eastables was researched. The results show that： with the in.crease of pelletized graphite addition, the required water amount of castables increases, the bulk density and strength reduce; with 4% pelletized graphite, the eastable performs the best oxidation resistance; the increase of graphite is beneficial to the improvement of slag penetration resistance and corrosion resistance; with 6% pelletized graphite, the thermal shock resistance is the best.

氧化硼对Al_(2)O_(3)-SiC-C质浇注料力学性能的影响

为了利用氧化硼“间接烧结”特性,进一步提升Al_(2)O_(3)-SiC-C质浇注料的力学性能,以氧化硼(≤0.075 mm)为助烧剂,制备了以FM60莫来石颗粒、致密刚玉、碳化硅、α-Al_(2)O_(3)微粉等为主要原料的浇注料,探究了氧化硼细粉加入量(加入质量分数分别为0、0.2%、0.4%和0.6%)对Al_(2)O_(3)-SiC-C质浇注料结构与性能的影响。结果表明,添加氧化硼细粉会显著提升浇注料的加水量,但其有利于晶须状莫来石的生成,从而加强骨料和基质间的结合强度,试样的力学性能得到明显提升。但当氧化硼细粉加入量提高至0.6%(w)时,试样中莫来石晶须长径比减小,试样的强度降低。综合以上结果,氧化硼最佳加入量为0.4%(w)。

用后铁沟料加入量对Al_(2)O_(3)-SiC-C质浇注料性能的影响

为提高用后耐火材料的再利用率,以棕刚玉、用后铁沟料、白刚玉、碳化硅、α-Al_(2)O_(3)微粉、SiO_(2)微粉等为主要原料,制备了Al_(2)O_(3)-SiC-C质浇注料。探究了用后铁沟料加入量(加入质量分数分别为0、14%、28%、42%和56%)对浇注料性能的影响。结果表明,随用后铁沟料加入量的增加,浇注料的加水量显著增加,试样经1450℃保温3 h热处理后由膨胀转变为收缩,试样经110℃保温24 h及1450℃保温3 h热处理后的体积密度、常温抗折强度、抗侵蚀性能均呈现下降趋势,但当用后铁沟料加入量不超过28%(w)时,性能下降幅度较小。将用后铁沟料加入量为28%(w)的浇注料用于1080和1350 m3高炉铁沟支沟与渣沟,取得了良好服役效果,主体结构服役周期大于70 d。

Application of Sol Self-Clean Bonded Al_2O_3-SiC-C Castable for Iron Runner

The properties and microstructure of sol self-clean bonded Al2O3-SiC-C castable in iron runner were studied, and the relation between the amount of sol self- clean binder and the properties of castable were discussed. It is believed that the addition of sol self-clean binder can improve the compressive strength, but has little effect on the bulk density and the apparent porosity, which enable the castable to be applicable in different conditions.

钛铁渣加入量对Al_(2)O_(3)-SiC-C铁沟浇注料性能的影响

为合理利用钛铁渣进而缓解资源紧张,以矾土熟料、致密刚玉、SiC、α-Al_(2)O_(3)微粉、SiO_(2)微粉、Si粉为主要原料,添加质量分数分别为0、11.2%、22.4%、33.6%、44.8%和56.0%的钛铁渣等量替代矾土熟料,于1450℃保温3 h热处理后制备了Al_(2)O_(3)-SiC-C浇注料,研究钛铁渣的加入量对浇注料性能的影响。结果表明:1)随着钛铁渣加入量的增多,浇注料的体积密度降低,显气孔率增加,常温强度总体呈下降趋势,但同时会在一定程度上提高浇注料的高温抗折强度和抗热震性;2)钛铁渣的引入带来过多的气孔为氧气的扩散提供了更多通道,且经氧化处理后由钛铁渣引入的杂质会生成较多液相,使得浇注料结构疏松,显著降低抗氧化性能;3)钛铁渣与熔渣反应会生成镁铝尖晶石,能够阻止熔渣的进一步侵蚀,提高其抗渣侵蚀性。综合考虑,钛铁渣的最佳加入量为56.0%(w)。

锂辉石粒度对Al_(2)O_(3)-SiC-C浇注料性能的影响

为了进一步改善高炉出铁沟用Al_(2)O_(3)-SiC-C浇注料的性能,以棕刚玉、致密刚玉、碳化硅、铝酸钙水泥、球沥青、α-Al_(2)O_(3)微粉、SiO_(2)微粉等为主要原料,在传统抗氧化剂(Al粉和Si粉)的基础上,分别加入2%(w)不同粒度(粒度分别为≤0.076、≤0.048和≤0.038 mm)的锂辉石粉为抗氧化剂,经1450℃热处理制备了Al_(2)O_(3)-SiC-C浇注料,研究了锂辉石粒度对其性能的影响。结果表明:随着锂辉石的添加及粒度的减小,热处理后试样残留碳化硅的量减小,显气孔率显著降低,高温性能和抗氧化性能显著提高;但当加入粒度较小的锂辉石时,试样中的SiC晶须生成量较多,并且具有更大的长径比,这明显改善了试样的力学性能。在Al_(2)O_(3)-SiC-C浇注料中加入≤0.038 mm的锂辉石,可以显著改善试样的抗氧化性和综合性能。

铁沟长寿命撇渣器用超低水泥浇注料的研究

选用复合硅微粉、超细硅微粉,加入到棕刚玉、97碳化硅、活性氧化铝微粉、纯铝酸钙水泥为主要原料的撇渣器浇注料中,就改善撇渣器浇注料承受流动高温铁水的剧烈冲击、侵蚀进行研究。讨论分析复合硅微粉、超细硅微粉的组合对撇渣器浇注料性能以及110℃×24h、1450℃×3h热处理后常温性能以及1450℃×1h高温抗折强度性能的影响。研究表明:材料中加入2.0%~2.5%的超细硅微粉原料时,材料的常温耐压强度、高温抗折强度有显著提高。

缓凝剂对低水泥高铝碳化硅浇注料性能的影响

以83回转窑矾土、90碳化硅,α-氧化铝微粉和硅灰为主要原料,纯铝酸钙水泥为结合剂制备低水泥高铝碳化硅浇注料。研究了在夏季施工时,添加的柠檬酸、硼酸和氟硅酸钠三种缓凝剂对低水泥高铝碳化硅浇注料可施工时间、抗折强度和耐压强度的影响。结果表明:氟硅酸钠的缓凝效果最好;110℃烘干24 h后常温抗折强度和耐压强度均有所降低,而1 100℃和1 400℃热处理3 h后抗折强度和耐压强度增减不明显,故在夏季施工时可优先选用硼酸或氟硅酸钠作为缓凝剂。

B_4C加入量对Al_2O_3-SiC-C铁沟浇注料力学性能的影响

以电熔棕刚玉为骨料,碳化硅、白刚玉、硅粉、球沥青、硅微粉、氧化铝微粉及高铝水泥为细粉,按大颗粒、中颗粒、细粉的质量比为55∶15∶30配料,分别外加0、0.2%、0.4%、0.6%的碳化硼细粉,加水和少量减水剂共混后,振动成型为160 mm×40 mm×40 mm的试样。自然干燥24 h脱模后,再自然干燥24 h,在空气气氛中分别于800、1 000、1 200、1 550℃下热处理3 h。检测各温度热处理后试样的线变化率、显气孔率、体积密度、耐压强度、抗折强度以及抗氧化性,高温抗折强度是在空气气氛中于1 400℃0.5 h进行检测,并利用XRD分析部分试样经高温抗折试验后的物相组成。结果表明:由于B4C在较低温度下氧化产生少量液相,一方面促进了材料的烧结,增大了中温强度;另一方面在材料表面形成防氧化膜,阻碍了炭素材料的氧化,利于次生β-SiC的形成,因而增大了浇注料的高温抗折强度。在本试验条件下,B4C加入量为0.4%时,浇注料的力学性能最好。

蓝晶石对硅溶胶结合Al_2O_3-SiC-C浇注料性能的影响

为了提高Al2O3-Si C-C浇注料在高温使用过程中的体积稳定性,用蓝晶石粉部分替代Al2O3-Si C-C浇注料中的白刚玉粉,研究了蓝晶石加入量(质量分数分别为0、1%、2%、3%、4%、5%和6%)对浇注料经烘干和1 400℃保温3 h热处理后物理性能的影响。结果表明:随着蓝晶石加入量的增加,试样经1 400℃保温3 h热处理后由微收缩逐渐变为微膨胀,体积稳定性以蓝晶石加入量为5%(w)时为最好。经110℃烘24 h后试样的显气孔率、常温耐压强度和常温抗折强度变化都很小,体积密度基本上呈降低趋势;经1 400℃保温3 h热处理后试样的显气孔率基本上呈先升高后降低的变化趋势,体积密度则呈相反的变化趋势,并且均以蓝晶石加入量3%(w)为拐点;常温耐压强度和常温抗折强度略有降低,但降低幅度很小。同一配比的试样,1 400℃保温3 h热处理后的体积密度、显气孔率、常温耐压强度、常温抗折强度均比经110℃烘24 h后的高。XRD、SEM和EDS分析表明,蓝晶石发生了一次莫来石化反应而产生体积膨胀,有效缓解了试样的烧结收缩,使试样具有较好的体积稳定性。

改性石墨对Al_2O_3-SiC-C质铁沟浇注料性能的影响

为了解决鳞片石墨因密度小、润湿性差和分散困难而难以在浇注料中使用的问题,首先采用硅烷偶联剂KH-560对≤0.178和≤0.074 mm的鳞片石墨分别进行改性处理,得到两种粒度的改性石墨;然后在传统Al2O3-SiC-C质铁沟浇注料配方(w):电熔致密刚玉62%、SiC粉24%、α-Al2O3微粉5%、纯铝酸钙水泥4%、SiO2微粉3%、球状沥青(≤1 mm)2%的基础上,分别用0.5%(w)的改性前后的石墨等量取代球状沥青,以研究KH-560硅烷偶联剂改性鳞片石墨对Al2O3-SiC-C铁沟浇注料性能的影响。结果表明:与原石墨相比,改性后石墨的分散性明显改善,浇注料的需水量大幅降低,且加入≤0.178 mm改性石墨的试样分散效果较好;含石墨试样的常温物理性能均有所下降,但加入≤0.178 mm改性石墨的试样强度和体积密度都明显高于加入其他石墨的,仅略低于无石墨的;加入石墨的试样抗渣性能明显得到提高,且加入≤0.178 mm改性石墨试样的抗渣性能最佳。综合考虑浇注料的各项性能,认为经硅烷偶联剂改性的鳞片石墨可部分取代球状沥青,且最佳粒度为≤0.178 mm。