Ni、Cu-Al2O3纳米金属陶瓷粉末的热压

将化学电镀法制备的纳米Ni、Cu包覆Al2O3粉末进行热压。研究了金属Ni、Cu及其含量对Al2O3粉末的烧结致密化、显微组织和性能的影响。在纳米Al2O3粉末表面镀覆适当的金属Ni、Cu可以较有效地提高致密化，降低烧结温度。金属相作为第二相可以大大细化Al2O3晶粒组织。但Ni、Cu的加入伴随着Al2O3硬度和强度下降。硬度变化可以由金属Ni、Cu是软相较好地解释。强度下降则主要归因于包覆粉末中Ni、Cu对Al2O3粉末的润湿性不好所致。     

Mechanical properties of dispersion-strengthened Cu-Al2O3 materials

Conclusions Ductility properties characterized by the relative logarithmic strain-to-rupture or reduction in area are determined by the total volume fraction of Al₂O₃ particles and residual pores. The mean statistical size of ductile rupture pits is independent of the time of milling of the powder mixture. With increasing volume fraction of particles the pit size slightly grows as a result of agglomeration of very fine particles, which nucleate a larger pit in the course of ductile rupture. The effect of Al₂)₃ particles on _0.2 was examined in the light of Orowan's and Ansell-Lenel's relationships. Experimental values of yield stress of the matrix material without disperse particles were found to agree well with Ansell-Lenel's model. It is possible that a more detailed analysis might lead to a more general _0.2 =a+ kl^–m relationship being obtained, where m is close to 1/2.Translated from Poroshkovaya Metallurgiya, No. 4(208), pp. 63–67, April, 1980.     

Effects of Y2O3 on Thermal Shock of Al2O3／TiCN Composites

Advancedstructuralceramics ,suchasoxides ,nitridesandcarbides ,havebecomepreferredrefracto rymaterialsforaviation ,spaceflight ,energyandmet allurgybecauseoftheirchemicalstability ,creepresis tanceandhightemperaturestrength .Buttheyareaf fectedgreatlybyte…     

Nd2O3掺杂对Y2O3-Ta2O5-ZrO2陶瓷相结构及热膨胀性能的影响

采用固相烧结法制备了Nd2O3掺杂Ta2O5-Y2O3-ZrO2体系热障涂层陶瓷材料。分别利用X-射线衍射仪、扫面电子显微镜和热膨胀仪对陶瓷材料的物相组成、显微结构以及热膨胀性进行了分析。结果表明,Nd2O3-Y2O3-Ta2O5-ZrO2陶瓷材料以四方相为主晶相,随着Nd2O3掺入量的增加,出现单斜相和少量其它杂相,且陶瓷材料的体积密度增大,热膨胀系数减小,晶粒也有所减小,表明稀土氧化物Nd2O3具有抑制晶粒长大和抗烧结的作用。     

共沉淀反应条件与分散剂对Cu-Al_2O_3粉末性能的影响

以酸碱含铜刻蚀废液为原料,聚乙烯醇(PVA)为分散剂,并采用添加可溶性铝盐络合共沉淀的方法制备了含铝铜的前驱体粉末,最终采用高温煅烧-氢气还原工艺制备了纳米Al_2O_3弥散强化铜粉末。采用激光粒度仪、SEM-EDS、XRD等研究了络合共沉淀过程中工艺参数对弥散铜粉末及Al_2O_3弥散相粒度的影响。结果表明:通过控制络合共沉淀过程中的反应条件,可制备出粒度小于1.5μm且分布较窄的纳米Al_2O_3弥散强化铜粉末,最佳工艺参数为:母液浓度1.0 mol/L,沉淀氨水浓度20%(体积分数),反应温度70℃,p H值为7;调节分散剂的含量可控制弥散相的粒度及分布,PVA与铜离子的物质的量比为0.4∶1.0时,制备出的纳米Al_2O_3弥散相粒度小于100 nm,粒子间距100~200 nm;粉末经氢气烧结950℃保温60 min,烧结试样的密度为8.45 g/cm~3,硬度为115 HB。     

用球化处理的粉末热压制备Cu-Al2O3复合材料

由机械合金化法(MA)制得纳米Al2O3颗粒弥散镶嵌于较软微米Cu颗粒表面的复合粉,利用球形化工艺改善所制得复合粉的形貌及工艺性能,然后通过热压法制备Cu-Al2O3复合材料.通过电导率测试、抗拉强度测试、密度测试、SEM形貌和断口分析、微区成分分析,研究了Al2O3质量分数分别为0%、0.5%、1.5%、2.5%时Cu-Al2O3复合材料的组织和性能.结果表明,随Al2O3质量分数增加,材料的抗拉强度总体增加,电导率、伸长率总体降低,Al2O3质量分数在1.5%时制得的复合材料具有较高的综合性能,此时σb=298MPa、δ=12.1%、电导率为88%IACS;质量分数继续增加会使纳米Al2O3颗粒发生局部团聚;在拉伸受力时复合材料发生延性断裂.     

Vitrification and Crystallization Behavior of CaO-SiO2-MgO-Al2O3-Fe2O3-Cr2O3 System

Metallurgical and Materials Transactions B - The effect of basicity and Cr2O3 content on vitrification of the CaO-MgO-SiO2-Al2O3-Fe2O3-Cr2O3 system during a melt-quenched process and the...     

氧化钆改性铈酸镧热障涂层材料设计 及涂层抗热震性能研究

La2Ce2O7(LC) 由于具有比 YSZ 更低的热导率、 更高的热膨胀系数和良好的高温相稳定性, 是一种极具前 景的热障涂层陶瓷材料。 但该材料热膨胀系数在 200~400℃温度区间存在异常下降现象, 从而引起涂层过早失效 的问题。 目前, 通过掺杂 Gd2O3 可有效解决 LC 低温段热膨胀系数下降的问题, 但是, Gd2O3 改性 La2Ce2O7 热障 涂层最优掺杂浓度及涂层性能还未见报道。 本文采用化学共沉淀法制备了三种不同浓度 Gd2O3 改性 La2Ce2O7 材 料 ((LaxGd1-x)2Ce2O7(x=0,0.1,0.2,0.3)), 研究了掺杂浓度对其热物理性能及相稳定性的影响, 采用等离子喷涂工艺 制备了(La0.8Gd0.2)2Ce2O7 (LGC)涂层, 研究了涂层的抗热震性能和涂层的失效机理。 研究结果表明： (La0.8Gd0.2)2Ce2O7 (LGC) 材料具有较低的热导率, 室温到 1400℃无相变, 并且经 1400℃长时间热处理无相变; 其制备的双陶瓷结 构 LGC/YSZ 热障涂层 1100℃热震次数可达到 109 次, 较未改性 LC/YSZ 热障涂层提升了大约 60%; 两种涂层的 失效模式相似, 均为陶瓷顶层烧结引起的片状剥落失效。     

二元碱度和Al_2O_3对CaO-SiO_2-FeO-Fe_2O_3-P_2O_5-Al_2O_3-MgO-MnO钢渣中磷酸盐富集的影响

以八元CaO-SiO_2-FeO-Fe_2O_3-P_2O_5-Al_2O_3-MgO-MnO钢渣体系为研究对象,结合热力学计算和实验检测,分析了二元碱度B和Al_2O_3含量对八元钢渣系中磷酸盐富集行为的影响。结果表明:钢渣二元碱度和Al_2O_3含量直接影响钢渣中f-C2S的生成量,进而影响磷酸盐富集相nC_2S-C_3P内P_2O_5的含量。随着二元碱度从1.3提高至2.5,磷酸盐富集率增大,磷酸盐富集相nC2S-C3P中的P_2O_5含量呈现先迅速增大(B从1.3至1.7),然后逐渐减小(B从1.8至2.5)的趋势。当二元碱度和Al_2O_3质量分数分别控制在1.7和12%时,即当满足四元碱度R为1.23时,此八元钢渣体系有较好的磷酸盐富集效果,磷酸盐富集相nC_2S-C_3P内的P_2O_5的质量分数可以达到24.23%。     

Thermal Shock Resistance of Al2 O3/ZrO2 (Y2O3) Composites

ZrO₂ containing 2% (mol fraction) Y₂O₃ and 3% (mol fraction) Y₂O₃ were added into Al₂O₃ matrix, compositing composites with 15% volume fraction of addictives mentioned above. The testing of property and analysis of SEM presented that, after vacuum sintering at 1550 °C, thermal shock resistance of two composites was superior to Al₂O₃ ceramic. The experiment showed that the properties of Al₂O₃ composites was higher than Al₂O₃ ceramic, and Al₂O₃/ZrO₂(3Y) was higher than Al₂O₃/ZrO₂(2Y) in thermal shock resistance. Improvement of thermal shock resistance of composites was attributed to many toughness machanisms of ZrO₂(Y₂O₃). By calculation, the fracture energy of Al₂O₃, Al₂O₃/ZrO₂ (2Y) and Al₂O₃/ZrO₂(3Y) was 38100.8 and 126.2 J·m⁻², respectively. Cracks initiation resistance (R') of Al₂O₃/ZrO₂(3Y) and Al₂O₃/ZrO₂(2Y) was higher than Al₂O₃ ceramic by 1.57 and 1.41 time, respectively, and cracks propagation resistance (R″″) was higher than Al₂O₃ ceramic by 1.46 and 1.38 time, respectively, which was corresponding to the results of residual strength.     

Effects of B2O3 and CaF2 on Melting Temperatures of CaO-SiO2-Fe2O3 System Fluxes

 Fluorite is widely employed as fluxing agent in metallurgy flux, which inevitably leads to serious fluorine pollution. B2O3 is employed as fluxing agent of CaO-SiO2-Fe2O3 steelmaking fluxes to substitute for CaF2. The effects of B2O3 and CaF2 on the melting properties of this system were investigated. The melting temperatures of fluxes including softening temperature (Ts), hemispherical temperature (Th), and flow temperature (Tf) were measured using the hemisphere method. The results indicate that the fluxing effect of B2O3 is more significant than that of CaF2. When the addition amount of B2O3 (mass percent) exceeds 6%, the melting temperatures of fluxes including Ts, Th and Tf are decreased lower than 1300 ℃. The basicity of fluxes has a significant effect on the melting temperature, and the melting temperatures of the fluxes increase with the increase of fluxes basicity. However, when B2O3 is used as fluxing agent, the melting temperature changes little with the basicity increasing from 2. 5 to 5. 0. These characteristics are suitable for steelmaking process. Moreover, Fe2O3 has an important fluxing effect on this CaO-based steelmaking fluxes. This indicates that the fluxes system is suitable for steelmaking process.     

Nb2O5、La2O3掺杂对SrTiO3双功能陶瓷半导化及显微结构的影响

主要研究了Nb2O5和La2O3双施主掺杂对SrTiO3陶瓷半导化及显微结构的影响.采用传统电子陶瓷工艺在1420℃弱还原气氛中(N2+石墨)制备了半导化的SrTiO3陶瓷,讨论了在稀土添加总量为0.9%(摩尔分数)的条件下, Nb2O5La2O3比对SrTiO3陶瓷室温电阻率和显微结构的影响.研究结果表明双施主掺杂不仅可以促进SrTiO3陶瓷半导化而且对显微结构有重要影响.Nb2O5La2O3为21时样品室温电阻率为0.89Ω·cm,显微结构较为理想.在此基础上,获得压敏与介电性能较佳的双功能SrTiO3陶瓷元件.     

Y_2W_3O_(12)和Yb_2W_3O_(12)的制备及其负热膨胀性能

利用液相沉淀法制备了Y2W3O12和Yb2W3O12粉体。经室温XRD测定,Y2W3O12(空间群为Pnca)和Yb2W3O12(空间群为Pbcn)皆为单一的正交相。在50-800℃温度区间对两种粉体进行高温XRD测试,并利用软件TOPAS3.0对其在不同温度下的XRD图谱进行精修,发现Y2W3O12和Yb2W3O12都具有较大的负热膨胀特性,经计算两者的线热膨胀系数(αl)平均值分别为-6.38×10-6℃-1和-4.18×10-6℃-1。与高温固相反应法相比,液相沉淀法大大缩短了粉体的合成周期,降低了合成温度。     

铝镇静钢钙处理后碰撞行为对Al2O3夹杂物变性的作用

 对铝镇静钢LF精炼钙处理后不同时期取钢样,通过SEM-EDS观察钢样中夹杂物,分析钙处理后铝镇静钢中夹杂物变性机制,并提出了一种夹杂物变性的碰撞机制：在钙处理后,由于钙浓度在钙气泡周围较高形成了CaO类夹杂物, 其与钢液中已有的Al2O3类夹杂物相互碰撞结合在一起,然后二者发生化学反应变性为低熔点的液态夹杂物。通过相图分析从理论上指出：Al2O3类夹杂物可与CaO通过碰撞变性,且其变性机制和控速环节与Al2O3类夹杂物通过与钙发生还原反应的变性不同。夹杂物碰撞使变性速率大大加快,几分钟之内即可良好变性。在本次试验中,约有21%的Al2O3类夹杂物通过与CaO碰撞发生变性。实验室试验和其他研究者的工业试验结果均证明：在二次精炼过程中,通过往钢包中喂入CaO类粉末可以使Al2O3夹杂物变性。     

Effects of Support on Catalytic Behavior of Combustion Catalyst La0.8Sr0.2CoO3/γ-Al2O3

Combustion catalyst La0.8Sr0.2CoO3 (LSC) is expected to possess relatively high activity for the oxidation of carbon monoxide and many hydrocarbons. If γ-Al2O3 is used as its support, cobalt ions can easily react with γ-Al2O3 at not very high temperature to form spinel CoAl2O4 or spinel-like, which decreases the activity of the combustion catalyst. In this paper, MgAl2O4 and CaAl2O4 were pre-coated on γ-Al2O3 by impregnation respectively, which formed compound support for LSC. It is shown that, when MgAl2O4 layer is covered on the surface of MgAl2O4 by impregnation, the entering of cobalt ions into γ-Al2O3 lattice is restrained, then LSC formed on the surface of MgAl2O4, which leads to a good catalytic activity of xylene complete oxidation. But the layer of MgAl2O4 should be thick enough to reach 30% (mass fraction) MgO in the support due to large size particle of MgAl2O4 crystalline. If polyvinyl alcohol (PVA) is added into the impregnation solution adequately, MgAl2O4 particles formed on the surface of γ-Al2O3 are getting smaller, and less amount of MgAl2O4 is needed to cover up the surface of γ-Al2O3. If CaAl2O4 layer substituted for MgAl2O4, more closed cover is obtained in virtue of fine particles of CaAl2O4. The activity examination shows that smaller particles of MgAl2O4 or CaAl2O4 can be more effective to hinder cobalt ions entering the lattice of γ-Al2O3, and better activities will be obtained.     

掺杂不同质量分数Y_2O_3、MgO对Al_2O_3陶瓷显微结构及介电性能的影响

利用放电等离子烧结技术制备了不同质量分数Y_2O_3单独掺杂及不同质量分数Y_2O_3、MgO共同掺杂的Al_2O_3陶瓷,研究了烧结助剂掺杂质量分数对Al_2O_3陶瓷显微结构及介电性能的影响。结果表明,孔隙率是影响Al_2O_3陶瓷介电性能的主要因素;单独掺杂质量分数为0.25% Y_2O_3时,Al_2O_3陶瓷得到最优的介电性能,介电常数(ε_r)为9.5±0.2,介质损耗(tanδ)稳定在10~(-3)数量级以内;同时掺杂Y_2O_3和MgO能进一步改善其介电性能,当两者质量分数均为0.25%时,得到最优值,介电常数(ε_r)为10.3±0.2,介质损耗(tanδ)稳定在8×10~(-4)以下。     

Effects of Li2O and Na2O on the Crystallization Behavior of Lime-Alumina-Based Mold Flux for Casting High-Al Steels

With the development of advanced high strength steel (AHSS), a large amount of aluminum was added into steels. The reaction between aluminum in the molten steel and silica based mold flux in the continuous-casting process would tend to cause a series of problems and influence the quality of slabs. To solve the above problems caused by the slag–steel reaction, nonreactive lime-alumina-based mold flux system has been proposed. In this article, the effect of Li₂O and Na₂O on the crystallization behavior of the lime-alumina-silica-based mold flux has been studied by using the single hot thermocouple technology (SHTT) and double hot thermocouple technology (DHTT). The results indicated that Li₂O and Na₂O in the above mold flux system play different roles as they behaved in traditional lime-silica based mold flux, which would tend to inhibit general mold flux crystallization by lowering the initial crystallization temperature and increasing incubation time, especially in the high-temperature region. However, when their content exceeds a critical value, the crystallization process of mold fluxes in low temperature zone would be greatly accelerated by the new phase formation of LiAlO₂ and Na _x Al _y Si _z O₄ crystals, respectively. The crystalline phases precipitated in all samples during the experiments are discussed in the article.