MnO2和Fe2O3对氧化铝质压裂支撑剂微观结构和抗破碎能力的影响

采用无压烧结技术制备了软锰矿掺杂的高强度氧化铝质压裂支撑剂.通过X射线衍射、压汞式孔隙分析、扫描电子显微镜和筒压法分别研究了由软锰矿引入的MnO2和Fe2O3对支撑剂物相组成、孔结构、晶粒尺寸和抗破碎能力的影响.结果表明:当软锰矿掺杂量为0～5%(质量分数,下同)时,烧结样品中包括氧化铝、莫来石和钛酸铝相,软锰矿的掺入未明显改变晶体结构;当软锰矿掺量为5%时,Fe3+取代Al3+与组分中的TiO2反应并形成固溶体,MnO2固溶于Al2O3晶粒中,促进了Al2O3晶粒生长,过剩的Fe2O3和MnO2存在于陶瓷晶界处并在高温煅烧F形成液相促进致密化烧结;未掺杂样品中存在大量连通气孔,显气孔率为14.79%:掺入5%软锰矿后,显气孔率降低至5.29%,样品内部多为均匀分布的近球形闭气孔;在52MPa压力条件下,5%软锰矿掺杂样品的破碎率与未掺杂样品相比减少80.95%,抗破碎能力显著提高.     

信息集锦

添加SiO2 ,CaO和MgO对Al2O3晶粒生长的影响 纯Al2O3在1620℃烧结,其正常晶粒生长形成各自同性的晶粒和曲面的晶界,当同时加入100ppm的SiO2和50ppm的CaO时,形成线性晶界部分,产生拉长的大晶粒,出现异常晶粒生长,研究表明添加SiO2或同时添加SiO2和CaO的Al2O3出现晶粒异常生长与形成多个平面状和线状晶界有关,这些晶界具有单一取向的结构,晶界能低,随后的晶界移动生长即导致晶粒的导常生长。而添加MgO可使晶界变粗糙,促使正常的晶粒生长,纯Al2O3的晶界也是粗糙的,因此,也是正常的晶粒生长。(周耀）洁具釉的硼酸盐助熔…     

掺杂Nb2O5及MgO对细晶BaTiO3系统介电性能影响的研究

研究了Nb2O5和MgO掺杂对细晶BaTiO3陶瓷介电性能的影响.Nb2O5的加入可以有效地抑制BaTiO3陶瓷晶粒的长大,可使陶瓷的平均粒径减少至0.8μm左右,从而改善了陶瓷的介电性能;添加适量的MgO不但展宽了居里峰,而且防止晶粒过渡生长,并拓宽了陶瓷的烧结温度区;有效地控制Nb/Mg的摩尔比可获得良好的材料系统性能参数,使ε≥4600,tgδ≤1.2%,△C/C≤±15%.     

少量掺杂Al2O3、SiO2的Mg-PSZ陶瓷材料的液相烧结

通过在Mg-PSZ陶瓷材料中少量掺杂Al2O3或SiO2,可使材料在较低温度(≤1550℃)下实现液相烧结,使材料的烧结温度大幅度降低.随Al2O3、SiO2掺杂量摩尔分数在1%～4%范围内增加,材料中m-ZrO2相组成增加,相应的烧结密度降低.所形成的镁铝尖晶石相多分布于ZrO2晶粒间,而形成的镁橄榄石相多镶嵌于ZrO2晶粒内.     

偏析对氧化锆晶界电导的影响及提高晶界电导的几种方法

综合评述了稳定剂和杂质SiO2偏析的原理,偏析对晶界电导的影响,分析了偏析与晶粒尺寸大小关系的2种不同观点,介绍了改变烧结条件、掺杂Al2O3、加压、提高降温速度这几种可行的改善晶界电导的方法。     

Sm~(3+)掺杂碱锌硼硅酸盐玻璃的稳定性

为了实现纳米半导体微晶在稀土Sm3+掺杂碱锌硼硅酸盐基础玻璃中的受控成核、生长,系统研究了基础玻璃的SiO2与B2O3摩尔比以及BaO、ZnO、La2O3、Y2O3、Nb2O5等不同的网络中间体对玻璃稳定性的影响。研究表明:控制SiO2与B2O3摩尔比以及BaO、La2O3、Y2O3、Nb2O5在玻璃中的掺入量均能提高玻璃的形成能力,增加玻璃的稳定性;不同的组分对于玻璃稳定性的改善也具有不同的机制,但是并不影响玻璃的析晶产物。     

氧化锡氧化铌共掺杂二氧化钛氧气响应特性的稳定性

研究了氧化锡(SnO2)、氧化铌(Nbb2O3)共掺杂二氧化钛(TiO2)作为厚膜用氧传感器材料的响应特性.X射线衍射分析表明:适量掺杂使厚膜晶粒保持金红石结构,晶胞参数有所增大.扫描电子显微镜显示:厚膜在1 280℃左右长时间(11 h)保温,晶粒仍保持适度尺寸.X射线光电子能谱分析表明;较低的Nb掺杂浓度导致晶粒表面产生高浓度金属缺位(Vm),低温端(300 ℃)的氢气响应时间变短;高温端(600 ℃)的氧气响应时间急剧增大.Nb掺杂浓度较高时,低温端(300 ℃)氢气响应时间变长;高温端(600 ℃)氧气响应时间变短,但仍保持着响应特性的稳定性.结果表明:用摩尔分数x(Sn)=2.31%,x(Nb)=0.48%的组分,既能在同一结构下适度增加晶胞参数,又能相应提高掺杂浓度,可获得工作温度范围(300～600 ℃)内灵敏度和响应速度长期稳定的厚膜材料.     

添加剂对SrTiO3基复合功能陶瓷材料性能的影响

研究了Y2O3、MnCO3、H3BO3和CaCO3添加剂对SrTiO3基复合功能陶瓷材料性能的影响。结果表明,施主Y∧3 的掺杂可促进SrTiO3材料的半导化,通过显微结构观察,当Y含量为1.2%摩尔分数时晶粒最大且较匀致,故Y2O3掺杂量佳为1.2%摩尔分数,受主Mn∧2 倾向于晶界处偏析,有助于形成材料的晶界势垒,提高材料的压敏非线性系数,降低漏电流LL,MnCO3掺杂以0.12%摩尔分数最佳。由于H3BO3具有降低烧结温度,拓宽烧成温度范围,在较低温度时产生液相,使晶粒生长充分、匀致,但产生液相过量又会制约晶粒生长。H3BO3掺杂以1%摩尔分娄为宜。少量的CaCO3有助熔作用,而CaCO3本身又具有晶粒细化作用,过量的CaCO3还使晶粒粗大,通过显微结构观察得到证实,CaCO3掺杂以0.05%摩尔分数为宜。     

掺杂La2O3对刚玉基复相陶瓷的烧结和力学性能的影响

刚玉基复相陶瓷材料具有高硬度、高强度及耐磨性等优异的力学性能,是结构陶瓷领域研究的热点之一,具有广阔的应用前景.以α-Al2O3、SiC和ZrO2为原料,掺杂少量稀土氧化物La2O3,采用无压埋烧工艺,制备了稀土掺杂刚玉基复相陶瓷.通过XRD、SEM等手段研究La2O3添加量对复相陶瓷微观结构和性能的影响.结果表明:掺杂La2O3可将复相陶瓷的烧结温度降低至1540℃,经1540℃烧结的掺杂复相陶瓷强度和硬度分别为183 MPa和18.46 GPa.La2O3位于晶界处抑制晶粒长大,促进晶粒细化,利于样品的致密化,同时其晶界强化作用有利于复相陶瓷强度的提高.     

多种添加物联合作用对Mn-Zn铁氧体性能的影响

采用高温燃烧合成法制备Mn～Zn铁氧体粉体,并对多种添加物,如CaO,Nb2O5,SnO2和Ta2O5对Mn—Zn铁氧体性能的影响进行了深入地研究。结果表明：4种掺杂离子对Mn～Zn铁氧体性能的影响各不相同。掺入的部分Nb^5 和Sn^4 可溶于Mn—Zn铁氧体的晶格内,改变其品格大小,并使初始磁导率μ．与温度θ曲线上第2峰的位置向低温方向移动,但Nb^5 和Sn^4 对晶粒的生长影响较小。由于Ta^5 离子只存在于晶界处,所以对晶格常数和第2峰位置的影响均很小,但Ta^5 的存在有利于晶粒的生长,随Ta^5 的掺入量增加,铁氧体的晶粒尺寸增大,气孔率降低。此外,4种掺杂离子对Mn—Zn铁氧体性能的影响是相互关联的,当添加物的质量分数为CaCO30．05％,Nb2O50．024％,SnO20．15％,Ta2O50．024％时,初始磁导率,μi达到最大,功耗Pv达到最小。     

TiO2-CAS 添加剂对氧化铝陶瓷密度和显微结构的影响

研究了单独引入TiO2、CAS(CaO-Al2O3-SiO2)及协同引入TiO2和CAS时 3 种情形对氧化铝材料显微结构影响.实验表明,单独引入TiO2时,随添加量从0.15%(质量分数,下同)增加到0.60%,Al2O3样品的晶粒形貌由正常生长逐渐向异向生长和异常长大转变;而单独引入CAS,即使添加量达到2.0%,Al2O3晶粒也没有出现异向生长和异常长大;实验还表明,在添加TiO2,同时引入CAS时,可以有效抑制TiO2添加所引起的Al2O3晶粒异常长大和异向生长.对 CAS 添加剂抑制晶粒异常长大和异向生长的原因进行了讨论.     

Effect of niobium doping on the densification and grain growth in alumina

The effect of niobium doping on the densification and grain growth of nano-sized α-Al₂O₃ powders during sintering has been investigated. The dopant concentration added ranged from 0.1 to 0.5 mol%. It was observed that addition of niobium oxide could improve the densification of the pure alumina with a lower sintering temperature, a shorter sintering time. The effect is strengthened by increasing the amount of dopant. It also demonstrated that niobium dopant significantly promotes the grain growth of alumina during sintering and the grain size of alumina increases with increasing the amount of dopant in the added range.     

Anisotropic Grain Growth in α-Al2O3 with SiO2 and TiO2 Additions

Microstructural changes caused by doping α-Al₂O₃ with small amounts of SiO₂ and TiO₂ added singly or together were investigated. When they were sintered at 1450°C for 120 min, singly doped samples developed equiaxed microstructures, but codoped material developed an anisotropic microstructure that contained platelike grains with an average aspect ratio of 3.4. The development of anisotropy thus resulted from a cooperative effect of silicon and titanium. Amorphous material was present at most grain boundaries in the silicon-doped sample. In the codoped sample, only boundaries that exhibited a basal facet were penetrated by amorphous material. Energy dispersive X-ray spectroscopy analysis showed strong titanium enrichment at the edges of platelets. Additional experiments demonstrated that the volume fraction of highly anisotropic platelike grains interspersed with equiaxed grains could be adjusted by using varying amounts of titanium with a constant amount of silicon content. The fracture toughnesses of such materials increased as the structure became more anisotropic.     

Anisotropic kinetic of the kaolinite to mullite reaction sequence in multilayer ceramics

Multilayer ceramics with a composite and organized microstructure were realized from kaolin and alumina fibers to improve strength and fracture toughness. Dilatometry experiments along 3 directions reveal anisotropic shrinkages, which are in correlation with different activation energy for sintering. Mullite growth is strongly anisotropic, inducing the formation of an organized microstructure, where larger mullite crystals are mainly oriented in plane of layer and perpendicular to alumina fibers. Kinetic data from thermal transformations show that the starting reaction mechanism is mullite nucleation, and it is continued by a strongly anisotropic grain growth. It is explained by topotactic transformations at phyllosilicate faces and along alumina arrangements. Mullite growth kinetics is also favored perpendicularly to fiber main dimension by the anisotropy of alumina diffusion coefficient. It shows the limited importance of mullite crystallization in microstructural transformation, but it also shows that controlled mullite growth is central in microstructural arrangement.     

Texture Development by Templated Grain Growth in Liquid-Phase-Sintered α-Alumina

The distribution and orientation of platelet-shaped particles of α-alumina in a fine-grained alumina matrix is shown to template texture development via anisotropic grain growth. The textured microstructure ranges from 4 wt% oriented platelet particles in calcined samples to nearly 100% oriented α-Al₂O₃ grains after sintering at 1400°C. A CaO + SiO₂ liquid phase creates favorable thermodynamic and kinetic conditions for anisotropic grain growth and grain reorientation during sintering. Important criteria for templated grain growth include (1) anisotropic crystal structure and growth, (2) high thermodynamic driving force for template grain growth, and (3) modification of diffusion in the system to continuously provide material to the anisotropically growing template grains.     

Fracture and Fatigue Behavior at Ambient and Elevated Temperatures of Alumina Bonded with Copper/Niobium/Copper Interlayers

Interfacial fracture toughness and cyclic fatigue-crack growth properties of joints made from 99.5% pure alumina partially transient liquid-phase bonded using copper/niobium/copper interlayers have been investigated at both room and elevated temperatures, and assessed in terms of interfacial chemistry and microstructure. The mean interfacial fracture toughness, G _c, was found to decrease from 39 to 21 J/m² as temperature was raised from 25° to 1000°C, with failure primarily at the alumina/niobium interfaces. At room temperature, cyclic fatigue-crack propagation occurred both at the niobium/alumina interface and in the alumina adjacent to the interface, with the fatigue threshold, Δ G _TH, ranging from 20 to 30 J/m²; the higher threshold values in that range resulted from a predominantly near-interfacial (alumina) crack path. During both fracture and fatigue failure, residual copper at the interface deformed and remained adhered to both sides of the fracture surface, acting as a ductile second phase, while separation of the niobium/alumina interface appeared relatively brittle in both cases. The observed fracture and fatigue behavior is considered in terms of the respective roles of the presence of ductile copper regions at the interface which provide toughening, extrinsic toughening due to grain bridging during crack propagation in the alumina, and the relative crack propagation resistance of each crack path, including the effects of segregation at the interfaces found by Auger spectroscopy.     

Sintering of Ultra-High-Purity Alumina Doped Simultaneously with MgO and FeO

The use of ultra-high-purity powder processing and multiple solid-solution additive doping has been evaluated as an effective approach for the fabrication of alumina ceramics. MgO was found to inhibit grain growth more strongly in very pure powders because of its stronger solute drag effect. The degree of inhibition was severe enough to render grain growth insensitive to porosity. By diminishing the dragging influence of pores on grain-boundary motion, MgO guards against abnormal grain growth due to inhomogeneous densification. FeO acted singly in alumina to promote grain growth more than densification. FeO was not, therefore, an effective sintering additive for undoped alumina. FeO did, however, Ceramic benefit the sintering of MgO-doped alumina.     

Determination of Critical Concentrations of Silica and/or Calcia for Abnormal Grain Growth in Alumina

Minimum amounts of SiO₂ and CaO required for inducing abnormal grain growth in alumina were determined using ultrapure alumina (>99.999%) and sintering at 1900°C for 1 h in a contamination-free condition. The critical concentrations of silicon in cationic mole fractions in alumina were 300 ppm without calcium, 200 ppm with 10 ppm calcium, and 150 ppm with 20 ppm calcium. The critical concentration of calcium alone was 30 ppm. These concentrations seemed to match approximately the solubility limits reported in the literature, which suggested that the abnormal grain growth in commercially pure alumina was indeed related with the formation of a small amount of liquid phase during sintering.     

High-Temperature Strength of Sinter-Forged Silicon Nitride with Lutetia Additive

A sinter-forging technique was successfully applied to fabricate a silicon nitride with a lutetia (Lu₂O₃) additive. The sinter-forged specimen had a strongly anisotropic microstructure where rodlike silicon nitride grains preferentially aligned perpendicular to the forging direction. The specimen exhibited superior strength of ∼700 MPa at 1500°C. This strength was highest when compared with previous silicon nitrides at temperatures >1400°C. Such superior high-temperature strength was attributed to grain alignment as well as to the refractory grain-boundary glassy phase and the existence of glass-free grain boundaries.     

Particle/Matrix Interface and Its Role in Creep Inhibition in Alumina/Silicon Carbide Nanocomposites

This study focuses on interfacial bonding between intergranular silicon carbide particles and an alumina matrix, to determine the creep inhibition mechanism of alumina/ silicon carbide nanocomposites. It is revealed that the silicon carbide/alumina interface possesses much stronger bonding than the alumina/alumina interface through three approaches: investigation of fracture toughness and fracture mode and consideration of internal thermal stresses acting at grain boundaries, estimation of equilibrium thickness of intergranular glassy films by force balance, and direct observation of grain boundaries by TEM. The rigid bonding of alumina/silicon carbide interfaces causes inhibition of vacancy nucleation and annihilation at the interfaces, causing remarkably improved creep resistance of the nanocomposite.