Silicon Nitride Bonded Silicon Carbide Bricks YB/T 4035-2007

1 Scope This standard specifies the definition, classifica- tion, technical requirements, test methods, quality appraisal procedures, packing, marking, transportation, storage, and quality certificate of silicon nitride bonded silicon carbide bricks.

采用煤矸石和用后Al_2O_3-SiC-C铁沟料合成β-SiAlON

在热力学分析的基础上,以用后Al2O3-SiC-C铁沟料、煤矸石和活性炭为主要原料,采用碳热还原氮化法合成了β-SiAlON。详细讨论了合成温度(1 723和1 823 K)、活性炭加入量(理论需碳量、过量15%、过量30%和过量45%)、Si与Al元素摩尔比(分别为3:3,3.5:2.5和4:2)和煤矸石种类(低碳煤矸石和高碳煤矸石)对合成β-SiAlON的影响,并采用XRD、SEM和EDS等对合成产物进行分析。结果表明:(1)当合成温度由1 723 K增加到1 823 K时,合成后试样中β-SiAlON相含量增加,O’-SiAlON和α-Al2O3的含量降低;(2)加入过量的活性炭有利于合成后试样中β-SiAlON相含量的增加;(3)随着Si、Al元素摩尔比的增大,合成后试样中β-SiAlON相含量增多;(4)采用低碳煤矸石的试样中β-SiAlON相含量高于采用高碳煤矸石的,其原因是配料时前者中配入的活性炭更多,而活性炭的活性较高,更有利于促进碳热还原氮化反应的进行。

B_4C外加量对Al_2O_3-SiC-Si_3N_4铁沟浇注料性能的影响

研究了B4C外加量（外加质量分数为0~0.6%）对Al2O3-SiC-Si3N4铁沟浇注料常温物理性能和高温抗折强度的影响。用X射线衍射仪、扫描电镜和能谱仪测定了试样的物相组成和显微结构。结果表明：随着B4C加入量的增大,浇注料体积密度和常温强度先增大后减小,显气孔率先减小后增大,高温抗折强度先增大后减小;B4C外加质量分数为0.4%时,浇注料综合性能达到最佳。B4C在材料中的作用主要是促进烧结和防氧化。与未添加B4C试样相比,添加B4C的试样中生成了更多纤维状的O’-SiAlON,且长径比更大。O’-SiAlON的生长机制推断为气-固机制。

Thermo-mechanical Properties of In-situ Formed Al_2O_3-SiC-SiAION Composites

Al2 O3 - SiC - SiAION composite specimens have been prepared using fused alumina, ultra fine α-Al2O3, Si and Al powders as starting materials and liquid phenol formaldehyde resin as binder and firing at 1 500 ℃ for 3 h in carbon embedded condition. Thermo-mechanical properties of Al2 O3 - SiC - SiAlON composites have been studied. The results show ： （ 1 ） Al2 O3 - SiC - SiAION composites can be prepared and sintered at 1 500 ℃ under carbon embedded condition. When Si/Al ratio is 8/0 and 7/1, the prepared composite is Al2O3 - SiC - O＇ -SiAlON; when Si/Al ratio is 5/3 and 3/5, the pre- pared composite is Al2 O3 - SiC - β-SiAION. （ 2 ） The composites possess high temperature strength properties. Hot modulus of rupture at 1 400 ℃ is 10 - 30 MPa. They are in elastic range up to 1 000 ℃, after which plastic deformation is observed; even at 1 400 ℃, amount of deformation is relatively low. （3） The com- posites possess good thermal shock resistance, their resid- ual strength ratio （AT = 1 100 ℃ ） is 65% - 80%. （4） The marked improvement in thermo-mechanical properties of Al2O3 - SiC - SiAlON composites may be at- tributed to the in-situ formation of SiC, SiAlON and AIN, the fibrous SiC, columnar SiAlON and tabular-like AlN fill in the corundum skeleton structure creating strengthening and toughening effects.

煅烧温度对Al_2O_3-SiC-Si材料相组成、结构与性能的影响

以82%(质量分数,下同)的电熔白刚玉、5%的α-Al2O3微粉、5%的SiC细粉和8%的Si粉为原料,以纸浆废液为结合剂,在埋炭条件下分别于1100、1200、1300、1400和1500℃煅烧制备了Al2O3-SiC-Si材料,并研究了煅烧温度对此材料常温物理性能、热态抗折强度、抗热震性、抗氧化性的影响,以及材料在煅烧过程中的相组成和显微结构变化。结果表明:1)1100℃烧后,有少量SiC纤维生成;1200℃烧后,大量原位生成的SiC纤维穿插在刚玉骨架结构中,SiC纤维随煅烧温度的升高而长大,且其生成量也增加;在1300℃时,开始生成SiAlON;1400℃时,单质硅完全反应。2)随煅烧温度的提高,Al2O3-SiC-Si材料的常温性能和高温强度都有所提高;1200℃烧后,材料已具有优异的抗热震性和抗氧化性,随煅烧温度的升高,材料保持良好的抗热震性和抗氧化性。

Influences of ZrO_2-SiC Composite Powder and Commercial SiC on Properties of Al_2O_3-C Refractories

In order to improve oxidation resistance and ther- mal shock resistance of Al2O3-C refractories, two groups of specimens were prepared with phenolic resin as binder, adding 0, 2 wt% , 4 wt% and 6 wt% commercial SiC or ZrO2-SiC composite powder synthesized from zircon respectively to Al2O3- C refractories, pressing at 200 MPa, drying fully at 250℃, and then carbon embedded firing at 1400℃ for 2 h. Oxidation resistance and thermal shock resistance were researched, phase composition was analyzed by XRD. The results showed that the oxidation of SiC in additives could protect carbon in specimens effectively and thus decreased the mass loss ratio and oxidation area, and improved the oxidation resistance of the specimen. Thermal shock resistance was improved owing to the micro crack toughening of ZrO2 and grain toughening of SiC. In this experiment, the specimens with 6 wt% ZrO2 -SiC composite powder or 6 wt% SiC powder had the best oxidation resistance and thermal shock resistance.

Properties and Microstructure Evolution of Al_2O_3-Si Material Fired in Different Atmospheres

A1203-Si composite specimens were prepared using fused corundum, ultra-fine α-A1203 and Si powder as starting materials and resin as binder. Effects of sintering atmospheres on properties, phase composition and microstructure of specimens after firing at 1 500 ℃ were investigated. The results show that： （ 1 ） after .firing in oxidizing or weak oxidizing atmosphere, there is some Si in the specimens and some glass phases containing mullite form on specimen surface, the density and strength at room temperature are relatively high, but hot modulus of rupture and thermal shock resistance are relatively poor; （2） after firing in, weak reducing or reducing atmosphere, Si reacts completely with CO or N2forming whisk-phere, Si reacts completely with CO or N2forming whisk-er-like SiC, granular Si2N20 or 0＇-SiAION, and the er-like SiC, granular Si2N20 or O＇-SiMON, and the thermo-mechanical properties of specimens are enhanced;（3） after firing in nitrogen atmosphere, Si reacts completely with N2, CO or G forming wbisker-like SiC and columnar β-SiA10N crystals, the hot modulus of rupture and thermal shock resistance of specimens are enhanced noticeably.

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.

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.

Effect of Pyrophyllite Particle Size on Properties of AI_2O_3-SiC-C Bricks for Iron Ladles

The Al2O3 -SiC-C bricks for iron ladles were pre-pared asing bauxite, fused corundum,pyrophyllite, SiC powder and flake graphite as main starting materials, and phenolic resin as binder. The effect of pyroph,yllite particle size on permanent change in dimensions, cold crushing strength, oxidation resistance, and corrosion resistance of Al2O3 - SiC - C bricks was investigated. The results show that with the decrease of the pyrophyllite particle size, the permanent change in dimensions of Al2O3 - SiC - C bricks decreases, cold crushing strength increases, the oxidation resistance at 1400 ℃ increases, and the corrosion resistance at 1500℃ decreases.

Flexibility of Burned Al_2O_3-C Due to Bending Tests at Room Temperature

Simple three-point bending test at ambient tempera- ture characterized the mechanical behavior of burned Al2O3 -C refractories before and after thermal shock in association with the processing parameters （graphite content and coking temperature, etc. ）. The results showed that non-linear plastic-elastic behavior under load lower than cold modulus of rupture （CMOR） was registered in all specimens and real linear elastic behavior could be identified after the first load, The total deformation could be divided into two parts, plastic and elastic areas. The graphite content and joint bonding system of carbon and ceramic phases were responsible for mechanical behavior of Al2O3 - C refractories.

Impact of Bauxite on Performance and Structure of SiC-mullite Brick

SiC- mullite brick is widely used in the upper and lower transitional zones of cement rotary kilns, due to excellent thermal shock resistance, and abrasion resist- ance. The investigation of different bauxites was made on the performance and micro-structure of SiC - mullite brick, especially thermal shock resistance. In two batches of bricks （ G1 and G2 ） , and two grades of bauxites （ L1 and I_2 ）, samples＇ physical and chemical properties were tested, and microstructure and phase composition were studied by SEM and XRD. The results show that raw material I2, containing large numbers of micro- pores smaller than 4 μm, has well developed mullite phase. While using L2 as aggregates and flues, SiC- mullite brick G2 has excellent thermal shock resistance. Therefore, for manufacture of SiC - mullite brick, not only chemical composition, bulk density and open porosi- ty of bauxite are important, but also its microstructure has to be considered, such as phase composition, crystal size and pore size distribution.

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.

Development and Application of Al_2O_3-Si_3N_4 Refractories Used in Blast Furnace

Newly developed Al2O3-Si3N4 composite refractories used for blast furnace is introduced in this work. Al2O3-Si3N4 composite refractories attacked by alkali vapor and blast furnace slag was investigated. High performance Al2O3-Si3N4 composite refractories was produced and used at both 2560m^3 blast furnaces of Tan-gsteel and No. 5 blast furnace of Shaosteel.

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.

Thermal plasma synthesis of SiC

Synthesis of silicon carbide has been carried out using thermal plasma processing technique using SiO2 as the solid feed and CH4 as the gaseous reducing agent. Thermochemical calculations have been performed varying the molar ratio of silicon dioxide and methane to determine the feasibility of the reaction. Experiments using a molar ratio of SiO2：CH4 equal to 1：2 produced maximum yield of SiC of about 65 mol % at a solid feed rate of 5 g/min. Mostly spherical morphology with some nanorods has been observed. The presence of Si had been observed and was quantified using XRD, HRTEM, Raman spectroscopy and X-ray photoelectron microscopy （XPS）. Si acts as a nucleating agent for SiC nanorods to grow.