添加物对镁铬砖性能的影响

在电熔镁铬砂的质量分数分别为50%(3~1mm)、13%(≤1mm)和37%(≤0.088mm)的镁铬砖基础配方中,分别外加2%的纯氧化铬、α-Al2O3、氧化锆、锐钛矿、α-Al2O3(1%) 锐钛矿(1%),以3%亚硫酸纸浆废液(外加)为结合剂,混匀后在200MPa压力下成型为50mm×50mm的圆柱试样和中心有20mm×20mm孔洞的坩埚试样,110℃干燥箱中烘6h后,在高温隧道窑中于1800℃保温3h烧成。检测烧后试样的显气孔率,并用XRD分析试样的物相组成,用光学显微镜分析1640℃保温4h静态渣侵试验后试样的显微结构。结果表明:各种添加物的加入使镁铬砖的抗渣性和抗热震性都有所提高。添加物提高镁铬砖抗渣性的顺序为:α-Al2O3 锐钛矿>α-Al2O3>氧化铬>锐钛矿>氧化锆;添加物在提高镁铬砖抗热震性上的顺序为:α-Al2O3 锐钛矿>α-Al2O3>氧化锆>锐钛矿>氧化铬,其中α-Al2O3 锐钛矿复合添加物不但使镁铬砖具有较强的抗渣性,而且抗热震性也同步提高,是提高镁铬砖性能的理想添加物。     

TiO2对水泥窑用镁尖晶石砖性能的影响

镁铬砖因高温性能良好而广泛用于水泥回转窑的烧成带。但是废镁铬砖存在环境污染的问题,替代镁铬砖的无铬砖产品逐渐增加,如向镁砖中加入MgA l2O4或Al2O3。由于尖晶石和镁砂间的热膨胀系数存在差异,会使砖中产生微裂纹,使其弹性增大,因此,制备镁尖晶石砖的途径是向镁砖中添加Al2O3和TiO 2在烧制过程中通过原位反应生成尖晶石。伊朗的研究人员研究了TiO 2对水泥窑用镁尖晶石砖性能的影响。     

TiO_2对镁铬砖抗渣蚀性的影响

利用XRD分析和光学显微镜等测试手段 ,研究了添加TiO2 对镁铬砖抗渣蚀性的影响。结果表明 :炉渣中的CaO能分解镁铬砖中的二次尖晶石而使镁铬砖损毁 ,但加入TiO2 后 ,TiO2 能优先于尖晶石中的Cr2 O3与渣中CaO反应 ,生成高熔点的CaTiO3,从而抑制CaO对砖中镁铬尖晶石的分解 ,提高了镁铬砖的抗高钙渣渣蚀能力     

TiO2对镁铬砖抗渣蚀性的影响

利用xRD分析和光学显微镜等测试手段,研究了添加TiO2对镁铬砖抗渣蚀性的影响.结果表明炉渣中的CaO能分解镁铬砖中的二次尖晶石而使镁铬砖损毁,但加入TiO2后,TiO2能优先于尖晶石中的Cr2O3与渣中CaO反应,生成高熔点的CaTiO3,从而抑制CaO对砖中镁铬尖晶石的分解,提高了镁铬砖的抗高钙渣渣蚀能力.     

复合添加剂对RH炉浸渍管用MgO-MgO·Al2O3砖性能的影响

为了提高RH炉浸渍管用MgO-MgO·Al2O3砖性能,以电熔镁砂、烧结镁铝尖晶石、板状刚玉为基础原料,添加不同含量的TiO2和ZrO2复合添加剂来制备MgO-MgO·Al2O3材料.研究了添加剂对材料体积密度、显气孔率、抗热震性、高温抗折强度和抗RH精炼渣侵蚀和渗透性的影响.结果表明:引入复合添加剂能促进MgO-MgO·Al2O3材料的烧结,提高材料的体积密度、高温抗折强度、抗热震性、抗渣侵蚀和渗透性,加入2％的TiO2和1％ ZrO2时烧结性能最好,加入1％的TiO2和2％ ZrO2时抗热震性最佳,加入2％的TiO2和2％ZrO2时高温抗折强度最大,抗渣侵蚀性和渗透性最好.     

AION加入物对碱性浇注料抗渣性的影响

氧化镁—氧化铝碱性浇注料一个弱点为抗渗透性差，为改善钢包浇注料抗渣性能，提高其使用效果和寿命，运用静态坩埚法研究含AION的MgO—Al2O3浇注料抗渣性。实验温度为1600℃，渣侵蚀时间为3h。研究结果表明：在还原气氛下，AION取代浇注料基质中Al2O3能显著提高试样的抗渣侵蚀和抗渗透性。在氧化气氛下，AION对基质中Al2O3取代质量比不超过50％时，抗氧化剂的加入有助于保持AION优良的抗渣性，产生这种结果的原因可归结于形成在高温下与氧化物渣难以润湿的含N尖晶石MgAION，从而延缓渣对浇注料的侵蚀和渗透。     

热压烧结Al2O3-ZrB2-SiC复相陶瓷的高温力学性能研究

为提高Al2O3陶瓷的高温力学性能,采用热压烧结工艺(烧结温度1 800℃,烧结压力20 MPa,保温1 h)制备了Al2O3-ZrB2-SiC复相陶瓷(简称AZS),并研究了ZrB2含量对Al2O3基陶瓷高温抗折强度和抗热震性的影响。结果表明:1)在Al2O3基陶瓷中加入第二相ZrB2能有效改善材料的高温抗折强度和高温强度保持率,在1 000和1 200℃时,加入20%体积分数ZrB2的AZS陶瓷试样具有最高的高温抗折强度,而加入24%体积分数ZrB2的AZS陶瓷试样具有最高的高温强度保持率。2)AZS陶瓷的抗热震性能优于纯Al2O3陶瓷。经100℃温差急冷后,加入20%体积分数ZrB2的AZS陶瓷具有最高的残余强度,比纯Al2O3陶瓷提高了17.2%;经300和500℃温差急冷后,加入24%体积分数ZrB2的AZS陶瓷都具有最高的残余强度,比Al2O3陶瓷分别提高了35.3%和20.9%。     

不同基质组成的刚玉-尖晶石浇注料性能研究

以板状刚玉、电熔尖晶石和铝酸钙水泥为原料,设计了尖晶石细粉质量分数分别为0、7.5%、15%和22.5%的4组浇注料,每组浇注料又依水泥量的不同设计了m(CaO)/m(Al2O3)分别为0.03、0.06、0.09、0.15、0.18的5个配方,制备了不同基质组成的刚玉-尖晶石浇注料试样,系统研究了试样经1 600℃3 h处理后的性能(尤其是高温抗折强度和抗热震性)及基质显微结构。结果表明:1)高温下尖晶石与基质中的Al2O3发生固溶而影响浇注料的高温强度,加入7.5%~15%质量分数的尖晶石细粉时,基质中的Al2O3与尖晶石固溶程度较大,基质的结合强度较强,高温强度明显较高;而加入尖晶石较多时,Al2O3量相对降低,减弱了固溶产生的结合,形成了"松散"的基质结构,可有效提高浇注料的抗热震性,因此加入22.5%质量分数尖晶石细粉的浇注料抗热震性最优。2)随着铝酸钙水泥的增加,浇注料的体积密度逐渐减小,常温抗折强度和弹性模量逐渐降低;当基质中m(CaO)/m(Al2O3)=0.09时,基质中刚玉细粉和Al2O3微粉与水泥在高温下全部反应,生成了大量交错分布的板状六铝酸钙,浇注料的高温抗折强度最高,抗热震性最好。     

AlON加入物对碱性浇注料抗渣性的影响

氧化镁氧化铝碱性浇注料一个弱点为抗渗透性差, 为改善钢包浇注料抗渣性能, 提高其使用效果和寿命, 运用静态坩埚法研究含AlON的MgO-Al2O3浇注料抗渣性.实验温度为1 600 ℃, 渣侵蚀时间为3 h.研究结果表明: 在还原气氛下, AlON取代浇注料基质中Al2O3能显著提高试样的抗渣侵蚀和抗渗透性. 在氧化气氛下, AlON对基质中Al2O3取代质量比不超过50%时, 抗氧化剂的加入有助于保持AlON优良的抗渣性, 产生这种结果的原因可归结于形成在高温下与氧化物渣难以润湿的含N尖晶石MgAlON, 从而延缓渣对浇注料的侵蚀和渗透.     

镁锆砖和镁铬砖的抗RH炉渣侵蚀性对比

为取代RH炉用镁铬材料,以电熔镁砂为主原料,分别加入单斜锆、脱硅锆、单斜锆与脱硅锆的混合粉、锆英石制备了ZrO2质量分数分别为15%和20%的镁锆砖,并利用静态坩埚法对比研究了镁锆砖和镁铬砖的抗RH炉渣侵蚀性。结果表明:对于Al2O3含量高且碱度(CaO/SiO2比)大的RH炉渣,镁锆砖抗侵蚀性能优于镁铬砖的;镁锆砖的侵蚀机理是砖中的ZrO2与渣中的CaO迅速反应,形成高熔点物相CaZrO3,能堵塞砖中的孔隙而形成致密保护层,从而阻止钢渣对镁锆砖的进一步侵蚀;而镁铬砖的侵蚀机理是渣中的Al2O3、Fe2O3等R3 和镁铬尖晶石中Cr3 交换,渣与砖反应生成的镁铝尖晶石和镁铁尖晶石使得材料变性,同时由于体积效应使镁铬材料鼓胀开裂,从而导致镁铬砖的严重侵蚀。     

Enhanced piezoelectric response and high-temperature sensitivity by site-selected doping of BiFeO3-BaTiO3 ceramics

Effect of Zn site-selected doping on electrical properties, high-temperature stability and sensitivity of piezoelectric response for BiFeO₃-BaTiO₃ ceramics was investigated. The results revealed that the addition of Zn leaded to an evident modification of the microstructure. The B-site selected doping was a more effective approach in improving piezoelectric properties as well as their thermal stability than those of A-site selected doping. Moreover, the enhanced piezoelectric properties accompanying by excellent high-temperature stability and sensitivity in B-site selected doping ceramics were obtained. The microstructure, domain switching behavior and temperature-dependent piezoelectric response in Zn site-selected doping ceramics were investigated, and their relationships with improving piezoelectric properties and high-temperature stability were explored. These results showed that the B-site selected doping ceramics had excellent piezoelectric properties (d₃₃ = 192pC/N) along with a high-temperature stability (T_d = 450 °C).     

Effect of SiC interphase on the mechanical,high-temperature dielectric and high-temperature microwave absorption properties of the SiCf/SiC/Mu composites

In this study, SiC interphase was prepared via a precursor infiltration-pyrolysis process, and effects of dipping concentrations on the mechanical, high-temperature dielectric and microwave absorption properties of the SiC_f/SiC/Mu composites had been investigated. Results indicated that different dipping concentrations influenced ultimate interfacial morphology. The SiC interphase prepared with 5 wt% PCS/xylene solution was smooth and homogeneous, and no bridging between the fiber monofilament could be observed. At the same time, SiC interphase prepared with 5 wt% PCS/xylene solution had significantly improved mechanical properties of the composite. In particular, the flexural strength of the composite prepared with 5 wt% PCS/xylene solution reached 281 MPa. Both ε′ and ε′′ of the SiC_f/SiC/Mu composites were enhanced after preparing SiC interphase at room temperature. The SiC_f/SiC/Mu composite prepared with 5 wt% PCS/xylene solution showed the maximum dielectric loss value of 0.38 at 10 GHz. Under the dual action of polarization mechanism and conductance loss, both ε′ and ε′′ of the SiC_f/SiC/Mu composites enhanced as the temperature increased. At 700 °C, the corresponding bandwidth (RL ≤ ?5 dB) of SiC_f/SiC/Mu composites prepared with 5 wt% PCS/xylene solution can reach 3.3 GHz at 2.6 mm. The SiC_f/SiC/Mu composite with SiC interphase prepared with 5 wt% PCS/xylene solution is expected to be an excellent structural-functional material.     

Modeling for high-temperature dielectric behavior of multilayer Cf/Si3N4 composites in X-band

The high-temperature dielectric behavior of multilayer C_f/Si₃N₄ composites fabricated by gelcasting and pressuureless sintering was intensively investigated at temperatures coverage up to 800 °C in X-band (8.2–12.4 GHz). Experimental results have shown the permittivity of Si₃N₄ matrix exhibits excellent thermo-stability with temperature coefficient lower than 10⁻³ °C⁻¹. Besides, both the real and imaginary parts of permittivity of multilayer C_f/Si₃N₄ composites exhibit positive temperature coefficient characteristic which attributed to the enhancement of space charge polarization. Furthermore, temperature-dependent permittivity of C_f/Si₃N₄ composites is demonstrated to be well distributed on circular arcs with centers actually keep around the real ($\epsilon \text{'}$) axis in Cole-Cole plane. Finally, the relaxation time for multilayer C_f/Si₃N₄ composites gradually increases from 216.1 ps to 250.2 ps when heated from room temperature to 800 °C, and is almost twice as much as a single cycle for electromagnetic wave in X-band which leads to continuous decrease in permittivity with frequency.     

Non-additive sintering of Si2N2O ceramic with enhanced high-temperature strength,oxidation resistance,and dielectric properties

The high-temperature mechanical and dielectric properties of Si₂N₂O ceramics are often limited by the introduction of a sintering aid. Herein, dense Si₂N₂O was prepared at 1700 °C by hot-pressing oxidized amorphous Si₃N₄ powder without sintering additives. A homogeneous network with short-range order and a SiN₃O structure was formed in the oxidized amorphous Si₃N₄ powder during the hot-pressing process. Si₂N₂O crystals preferentially nucleated at positions within the SiN₃O structure and grew into rod-like and plate-like grains. Fully dense ceramics with mainly crystalline Si₂N₂O and some residual amorphous phases were obtained. The as-prepared Si₂N₂O possessed a good flexural strength of 311 ± 14.9 MPa at 1400 °C, oxidation resistance at 1500 °C, and a low dielectric loss tangent of less than 5 × 10⁻³ at 1000 °C.     

Preparation of dense SiHf(B)CN-based ceramic nanocomposites via rapid spark plasma sintering

Dense SiHf(B)CN-based ceramic nanocomposites were prepared by spark plasma sintering (SPS) using high heating rates (∼450 ^°C/min.) and high pressures (≥100 MPa). The obtained nanocomposites were investigated by X-ray diffraction, Raman spectroscopy and electron microscopy concerning their phase evolution and microstructure.The hardness and the elastic modulus of dense SiHfCN were found to be 26.8 and 367 GPa, respectively. Whereas the SiHfBCN samples exhibited a hardness of 24.6 GPa and an elastic modulus of 284 GPa. The investigation of the oxidation of the prepared dense ceramic nanocomposites at high temperature revealed that the parabolic oxidation rates of SiHfCN were comparable to those of ultra-high temperature ceramics (UHTCs, e.g. HfC-20 vol% SiC); whereas the parabolic oxidation rates of SiHfBCN were several orders of magnitude lower than those. The results obtained within this study indicate the feasibility of SPS for rapid preparation of dense though nano-scaled Hf-containing ceramic nanocomposites that are promising candidates for high-temperature applications in harsh environments.     

Preparation and characterization of corundum ceramics doped with Fe2O3 and TiO2 for high temperature thermal storage

High-temperature thermal storage materials have received urgent attention for efficient thermal transfer in solar thermal power generation. Corundum ceramics doped with Fe₂O₃ and TiO₂ were prepared via a pressureless sintering. A Fe₂O₃–TiO₂ system with different Fe₂O₃/TiO₂ ratios was applied to corundum ceramics. Phase composition, microstructural evolution, sintering properties, high temperature resistance and thermophysical properties were evaluated. The results indicated that Fe₂O₃ and TiO₂ rendered the grains highly active and enhanced the bonding between grains due to existing stably in the lattice of corundum. In addition, decrease in the Fe₂O₃/TiO₂ ratio led to a new phase of FeAlTiO₅, which refined the grains. These effects gave the samples good sintering properties and thermal shock resistance, but the thermal expansion coefficient mismatch between FeAlTiO₅ and corundum deteriorated the high-temperature (1300 °C) stability. Formula C1 (Fe₂O₃/TiO₂ ratio of 9:1) sintered at 1600 °C had the optimum comprehensive properties, possessing a bending strength loss rate of 1.54% after 30 cycles of thermal shock (1100 °C-room temperature, air cooling) and a constant strength retention rate of approximately 71.34% after 90 h high-temperature cycle. The corresponding thermal conductivity and specific heat capacity were 18.81 W/(m·K) and 1.02 J/(g·K) at 25 °C, which was suitable as a high-temperature thermal storage material.     

自蔓延高温合成法制备金属—陶瓷复合材料

本文就自蔓延高温合成技术（ＳＨＳ）在制备金属－陶瓷复合材料方面的进展进行了回顾，对ＳＨＳ技术用于制备金属－陶瓷块体复合材料，梯度功能材料（ＦａＭ），金属－陶瓷复合管，金属－陶瓷的焊接工艺原理以及金属材料的陶瓷涂层进行了探讨。     

Effect of CuO on self-lubricating properties of ZrO2(Y2O3)–Mo composites at high temperatures

In this paper, ZrO₂ matrix high-temperature self-lubricating composites with addition of CuO as lubricant were prepared using a hot-pressing method by tailoring the content of CuO. The wear and friction behaviour of the composites were investigated from 700 °C to 1000 °C. The composites sliding against an Al₂O₃ ceramic ball exhibited excellent self-lubricating and anti-wear properties at high temperatures. The low friction and wear mechanisms were investigated in detail.     

含二氮杂萘酮联苯结构耐高温聚氨酯胶的合成

采用本体聚合,将自制的含有4—(4’—羟基苯基)—2,3—二氮杂萘—1—酮(DHPZ）^[1—3]作为单体引入双组分聚氨酯的固化剂中,合成了一类新型的含杂萘三联苯结构的聚氨酯胶粘剂。DHPZ的扭曲和非共平面杂环结构使聚合物难以实现长程有序。从而提高了其刚性和耐高温性能。常温拉伸强度不低于20MPa,而且具有较强的耐酸,耐水水解性能。以FT-IR,DSC,TGA等分析手段研究了聚合物的结构和耐热性能。结果表明,新型聚氨酯胶粘剂具有高的玻璃化转变温度（Tg=340～370K）,氮气氛中10%热质量损失温度为570K,在520K的温度下无热质量损失。该胶粘剂可以在高温条件下使用。     

Effect of nickel sulphate and magnesium sulphate on pH of sulphuric acid solutions at elevated temperatures

A flow-through potentiometric technique utilizing an yttria-stabilized zirconia (YSZ) pH sensor has been employed to elucidate the effects of NiSO₄ and MgSO₄ on pH of H₂SO₄ solutions at temperatures of 200 °C and 250 °C. Solution pH was found to increase with increasing NiSO₄ and MgSO₄ concentrations at both temperatures. This trend is attributed to the dissociation of NiSO₄ and MgSO₄ where the SO₄ ^2?(aq) released reacts with H⁺(aq) to form HSO₄ ^?(aq). The conversion of measured potentials into pH values was based on the mixed-solvent electrolyte (MSE) model, which is a speciation model of the new OLI Systems^® software. Both the Henderson equation and exact definition of the diffusion potential were employed in treating the obtained experimental data. Experimental pH values calculated using the diffusion potentials evaluated by either approach are similar, suggesting that the Henderson equation can be effectively used. In addition, LiCl was found to be a suitable alternative to NaCl as the reference electrode solution.