钾掺杂对纤锌矿型氧化锌电子结构和光学性质的影响

针对纯纤锌矿型ZnO禁带宽度较高,不能吸收大部分可见光的问题,采用基于密度泛函理论的第一性原理,构建了钾掺杂ZnO的4种超胞模型,并对4种模型进行几何优化,计算了KXZn1-XO的能带结构、态密度和光吸收性能。结果表明:采用广义梯度近似法(GGA)+U方法计算得到纯氧化锌带隙为3.373 eV,与实验值一致;随着钾掺杂量X的增大,ZnO的禁带宽度Eg出现先增大后减小再增加的现象,KXZn1-XO吸收带发生先蓝移后红移的现象。

2Si-B-3C-N陶瓷的热压烧结工艺

采用热压烧结工艺对机械合金化的2Si-B-3C-N陶瓷进行烧结成型。采用XRD、SEM、TEM等方法研究了工艺参数改变对陶瓷组织性能的影响规律。结果表明,温度和压力对陶瓷组织性能的影响较大,而保温时间与气氛压力的影响较小。当温度和压力分别为1900℃和80MPa时,陶瓷具有较高的力学性能,其致密度、抗弯强度、弹性模量、断裂韧度、维氏硬度分别为88.7%、331.1MPa、139.4GPa、2.8MPa·m^1/2和5.7GPa。当温度降至1800℃或压力减为50MPa时,陶瓷的致密度和力学性能都明显降低。这说明高温高压有利于原子扩散与颗粒滑动重排,从而促进陶瓷的烧结致密化与力学性能的提高。

结合系统对刚玉基浇注料常温断裂行为的影响

为揭示结合系统对刚玉基浇注料常温断裂行为的影响,以板状刚玉颗粒、板状刚玉细粉、α-Al2O3微粉、Si O2微粉、纯铝酸钙水泥和水合氧化铝为主要原料,通过改变基质中纯铝酸钙水泥的加入量(加入质量分数分别为0、1%、3%和5%),制备了低水泥、超低水泥和无水泥刚玉基浇注料,采用楔入劈拉法研究了刚玉基浇注料的断裂行为。结果表明:结合体系的不同显著改变了浇注料的断裂行为。低水泥和超低水泥刚玉基浇注料的载荷-位移曲线呈线性,属典型的脆性断裂,表明浇注料的韧性差。无水泥刚玉基浇注料的载荷-位移曲线呈非线性,属准稳态断裂,说明浇注料的韧性高。含水泥浇注料中结合相为玻璃相或钙长石,玻璃相多且连续分布导致浇注料呈脆性。而在无水泥浇注料中,结合相为针柱状莫来石,玻璃相少且孤立分布于莫来石形成的网络中,有利于韧性的提高。

不同粒度莫来石球形骨料对Al_2O_3-SiO_2浇注料性能的影响

由于球形骨料的流动性高,有利于致密堆积,可制备高性能耐火材料,因此,在以传统不规则形状莫来石骨料(以下称"传统骨料")、矾土均化料细粉、SiO_2微粉、纯铝酸钙水泥等为原料制备的低水泥Al_2O_3-SiO_2浇注料基础上,研究分别用粒度为8~5、5~3、3~1和≤1 mm的球形莫来石骨料(以下称"球形骨料")逐级取代同粒度的传统骨料对浇注料施工性能以及热处理后强度的影响,并借助SEM分析了试样的显微结构。结果表明:1)不同粒度球形骨料的引入均有效地改善了浇注料的流动性,降低了加水量,其中以引入3~1和5~3 mm的改善效果较好,使浇注料的加水量从采用传统骨料的5.8%(w)减少至5.2%(w);2)与传统骨料相比,除≤1 mm的球形骨料外,均可提高浇注料的可泵送性;3)球形骨料的引入提高了浇注料的致密度和常温耐压强度,但对浇注料的常温抗折强度影响不大,其中3~1 mm的球形骨料对浇注料强度的提升较大;4)热处理后浇注料的显微结构分析表明,球形骨料与基质边界结合紧密,与传统骨料的相当。

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。

Effects of Spherical Aggregates Addition on Properties of Al2O3-SiO2 System Castables

Compared with traditional aggregates,spherical aggregates with high flowability,easy control of particle size distribution and favor of dense packing and so on,are expected to replace traditional aggregates as important raw materials for future high performance refractories. Therefore,investigation of effects of spherical aggregates addition on properties of refractories becomes very meaningful. Using A70 mullite traditional aggregates and A70 mullite spherical aggregates, bauxite homogenization powder,microsilica,and calcium aluminate cement as raw materials,different AlO-SiOsystem low cement castables were prepared by replacing conventional aggregates with spherical aggregates. The effect of spherical aggregates addition on workability and mechanical properties of castables after heated at different temperatures was researched,and microstructure of the specimen was analyzed by SEM. Compared with traditional irregularly shaped aggregates,spherical aggregates endow castables with better flowability and easy pump ability. By introduction of spherical aggregates into the castables,flowability and pumpability are significantly improved,and water addition and ball completely sunk time are reduced. The introduction of spherical aggregates is favorable to density and cold crushing strength of castables,but unfavorable to CMOR. The effect of spherical aggregates addition on HMOR at1 400 ℃ can be negligible. Microstructure analysis showsthat the boundary bonding between spherical aggregates and matrix is strong,similar to the traditional aggregates.

Thermodynamic Analysis for Carbothermal Reduction and Nitridation of TiO_2

The diagrams of stability relations（namely,Predominance area phase diagram,PAPD）of nitride,carbide and oxides in Ti-C-N-O system were plotted by thermodynamic calculation.The optimum conditions and main influence factors for the synthesis of titanium nitride and titanium carbide by carbothermal reduction in nitrogen atmosphere were discussed.

Effect of Zircon Addition on Properties of Low Carbon AL_2O_3-C Refractories

Using tabular alumina as aggregate,tabular alumina fines,reactive alumina ultra-fines,aluminum powders,silicon powders,carbon black,flake graphite,B4 C and zircon fines as matrix,low carbon Al2O3-C refractories were prepared.Influences of zircon powders additions （0,3%,5% and 7%,in mass,the same hereinafter） on properties,phase composition and microstructure were investigated.The results show that the ZrO2-nitride can be in-situ formed through carbothermal reduction and nitridation in Al2O3-C refractories.With the increase of zircon powder,the oxidation resistance of the Al2O3-C refractories improves obviously,the oxidized layer thickness decreases from 7.94 mm without zircon to 2.71 mm with 5% zircon.HMOR at 1 400 ℃ of the Al2O3-C refractories reaches the maximum 14.9 MPa when zircon addition is 5%.With the increase of zircon powder,the apparent porosity and bulk density change a little,CMOR and CCS increase.

Role of in-situ Formed Nonoxides Bonded Phases in Property Improvement of Alumina ULC Castables

In order to enhance performance of pre-cast shapes of alumina based castables, the present work explored the approach of forming in-situ bonding phases by incorporating Si powders and then heating in carbon, embedded atmosphere. Using tabular alumina as aggregates, tabular alumina, SiC powders, Si powders, calcium aluminate cenwnt, microsilica and ultrafine α-A12 03 powders as matrix, alumina based ultra low cement （ULC） castables were prepared. Influences of Si powder addition at O, 4% , 6% , 8% alul 10% （in nutss ） on regular properties, cold modulus of rupture （CMOR）, hot modulus of rupture （HMOR）, thermal shock resistance （TSR） and microstructure of the castables after carbonization were investigated. After incorporation of Si powders and carbon embedded heating, the in-situ mullite and nonoxide phases such as SiAION and SiC can be fornwd by oxidation, nitridation or carbomlzation reaction. HMOR and TSR of the castables with in-situ nonoxides bonding are obviously improted. After carbon embedded heating, the HMOR at 1 400 ℃ increases from 1.6 MPa to 8. 3 MPa, and the residual CMOR ratio after thermal shock increases from 64. 9% to 137. 9% when Si addition increases from 0 to 10%.

Effect of Ultrafine Spinel Sources on Slag Resistance and Microstructure of Alumina-spinel Castables

In order to clarify the effect of ultrafine spinel sources on slag resistance and microstructure of alumina -spinel castables,using tabular alumina and spinel as coarse aggregates,tabular alumina powders,spinel powders,calcium aluminate cement,spinel containing cement,spinel micro-powder and reactive alumina ultrafines as matrix,alumina-spinel castables used for RH snorkels were prepared by changing the particle size and sources of preformed spinel.The effects of different ultrafine spinel sources (CMA72,spinel micro-powder) on the properties of alumina-spinel castables were investigated.Thermal shock resistance and slag resistance of specimens were compared by the residual strength rate (1 100 ℃,air cooling 1 cycle) and static crucible method.The microstructure and the slag corrosion resistance mechanism of the specimens were analyzed by SEM and EDS.The result shows that slag resistance of alumina-spinel castables can be improved by adding ultrafine preformed spinel,such as CMA72,and spinel micro-powder.The introduction of ultra-fine preformed spinel has little effect on HMOR of alumina-spinel castables,but has negative effect on TSR.ultra-fine and dispersive preformed spinel in the matrix and fine microstructure are the main reasons for the improvement of slag resistance of castables.

Effects of Spherical Light-weight Aggregates Additions on Workability and Mechanical Properties of Al_2O_3-SiO_2 System Castables

In order to clarify the effect of spherical light-weight aggregates addition on properties of A12 07 - Si02 system castables, adopting ATO mullite traditional light-weight aggregates and ATO mullite spherical light-weight aggre- gates, bauxite homogenization powder, microsilica , cal- cium aluminate cement as main raw materials, light- weight Al2 03 - SiO2 system castables were prepared by replacing conventional light-weight aggregate with spherical light-weight aggregates. The effects of spheri- cal light-weight aggregates addition on workability, me- chanical properties of castables after heated at different temperatures were researched; the microstructure of the aggregates was analyzed by SEM. The result shows that the introduction of spherical light-weight aggregates can significantly improve the flowability and reduce the water addition of the castables. Water demand of the castable is reduced from 18% with the conventional light-weight aggregates to 14% with spherical light-weight aggre- gates. In addition, light-weight castables prepared by spherical aggregates can keep the same workability with- in a wider range of water addition. Therefore, spherical aggregates are user-friendly. The introduction of spheri- cal light-weight aggregates is favorable to packing densi- ty and mechanical properties of castables, such as cold crushing strength, cold modulus of rupture, hot modulus of rupture at 1 200℃.

Characteristics of Hercynite and Its Application in Refractories

The characteristics of hercynite including corystal structure, chemical compositions and physical properties, R ＆ D background of hercynite, synthesis problems of heronite, amt roles of hercynite in refractories were re-riewed. The application of hercynite in refractories was introduced with emphasis. The practical applications in cement rotary kiln showed the prepared magnesia her-cynite brick had better performance than the original magnesia chrome brick obviously.

Influences of Technological Parameters on Carbothermal Reduction and Nitridation of Titanium Dioxide

The particle size of starting materials, the homogeneity of the carbon/oxide mixtures, and the carbon content are important parameters for a rapid reaction. The influences of technological parameters（carbon particle size, oxide particle size, mixing method, carbon content） on the reaction rate of carbothermal reduction and nitridation of titanium dioxide （TiO2 ） were investigated by a continuous thermo-gravimetric analyzer for large size specimen. The carbon particle size is the most impor tant parameter for a rapid reaction, but carbon particle may have no influence on the morphology of titanium nitride （TiN） powder. Oxide particles are the precursors of TiN powder, but the TiO2 particles size has very little influence on the reaction rate. The carbon content not only influences the reaction rate to some degree, but also influences the purity of TiN powder. The mixing method of the specimen has very little influence on the reaction rate. These results are suitable for other nitrides and carbides prepared by carbothermal reduction method.

Chemical Corrosion Mechanisms of Magnesite-chrome Bricks by Converter Slag

The corrosion resistance of four kinds magnesitechrome bricks against converter salg was investigated by static crucible slag tests. The microstructures of the asdelivered and tested refractories were analyzed by means of SEM and EDS. The results showed that： Different magnesite-chrome bricks have different slag resistances. Generally, the slag resiantance sequence is as follows： rebounded fused magnesite-chrome brick 〉 semi-reboun- ded magnesite-chrome brick 〉 direct-bonded magnesitechrome brick 〉 silicate bonded magnesite-chrome brick. Slag reacts with the periclase of magnesite-chrome refractories, which results in the dissoving of periclase in fayalite slag. However, the complex spinels have superior slag resistance.