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Microwave dielectric properties of (PbCa)(FeNb)O3 ceramics with A site Nd3+ substitution A位Nd3+取代(PbCa)(FeNb)O3陶瓷的微波介电性能
Pub Date : 2004-10-01 DOI: 10.1179/096797804X929
D. Zhou, M. Hu, Shaohu Jiang, J. Huang, H. Gu
Abstract The influence of Nd3+ A site charge unbalanced substitution on the microwave properties and crystal structure of (Pb0.48Ca0.52)(Fe0.5Nb0.5 )O3 ceramics has been investigated. For Nd3+ content x ≤ 2 mol-%, specimens can be produced with a single phase of perovskite structure. Other specimens with Nd3+ content x > 2 mol-% possessed PbO–Nb2O5 pyrochlore phase, with linearly increasing content with increasing x. Permittivity first increased and then gradually decreased as Nd3+ content increased to 20 mol-%. The unloaded quality factor Qf reached a maximum of 5210 GHz when Nd3+ content reached 5 mol-%. At higher Nd3+ content, the relative content of pyrochlore phase began to exceed 14.5%, and Qf degenerated. The temperature coefficient of resonant frequencies could be effectively controlled from 37.8 to 0.9 ppm K-1. A small value of 7.8 ppm K-1 was obtained in the [(Pb0.48Ca0.52)1-x Ndx](Fe0.5Nb0.5)O3 system when x = 0.05 and the permittivity and Qf value were 87.9 and 5210 GHz respectively. The relationship between microwave dielectric properties and crystal structure is also discussed.
摘要研究了Nd3+ A位电荷不平衡取代对(Pb0.48Ca0.52)(Fe0.5Nb0.5)O3陶瓷微波性能和晶体结构的影响。当Nd3+含量x≤2 mol-%时,样品可制成钙钛矿单相结构。其余Nd3+含量为x bbb2o mol-%的试样均为PbO-Nb2O5焦绿石相,随含量增加x呈线性增加,介电常数随Nd3+含量增加到20 mol-%先增大后逐渐减小。当Nd3+含量达到5 mol-%时,空载品质因子Qf达到最大值5210 GHz。当Nd3+含量较高时,焦绿石相的相对含量开始超过14.5%,Qf发生退化。谐振频率温度系数可有效控制在37.8 ~ 0.9 ppm K-1范围内。当x = 0.05时,[(Pb0.48Ca0.52)1-x Ndx](Fe0.5Nb0.5)O3体系的K-1值很小,为7.8 ppm,介电常数和Qf值分别为87.9和5210 GHz。讨论了微波介电性能与晶体结构的关系。
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引用次数: 2
Influence of TiO2, Cr2O3 and ZrO2 on sintering and machinability of fluorophlogopite glass ceramics TiO2、Cr2O3和ZrO2对氟云母玻璃陶瓷烧结和可加工性的影响
Pub Date : 2004-10-01 DOI: 10.1179/096797804X938
B. Eftekhari Yekta, S. Hasheminia, P. Alizadeh
Abstract The influence of Cr2O3, TiO2 and ZrO2 on the sintering, crystallisation and machinability of SiO2–Al2O3–MgO–K2O–B2O3–F glasses was investigated. Optimum fluoromica glass ceramic compositions with desirable sintering behaviour and machinability were obtained by addition of titanium and chromium oxides to the base glass. Texture and relative intensity of mica phase Imica/ISi were determined by XRD analysis and the particle size distribution of chips was studied by drilling. Microhardness and bending strength were also investigated. The relative intensity of mica phase and microhardness were found to be compatible with the experimental results.
摘要:研究了Cr2O3、TiO2和ZrO2对SiO2-Al2O3-MgO-K2O-B2O3-F玻璃烧结、结晶和可加工性的影响。通过在基玻璃中添加钛和铬氧化物,获得了烧结性能和可加工性良好的最佳氟玻璃陶瓷成分。通过XRD分析确定了云母相Imica/ISi的织构和相对强度,通过钻孔研究了晶片的粒度分布。显微硬度和抗弯强度也进行了研究。云母相相对强度和显微硬度与实验结果一致。
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引用次数: 9
Phase interaction and oxygen transport in oxide composite materials 氧化物复合材料中的相相互作用和氧输运
Pub Date : 2004-10-01 DOI: 10.1179/096797804225018633
A. Shaula, V. Kharton, F. Marques, A. Kovalevsky, A. P. Viskup, E. N. Naumovich
Abstract The oxygen permeability of oxide composite membranes containing similar volume fractions of the components, including (La0.9 Sr0.1)0.98 Ga0.8 Mg0.2 O3-δ(LSGM)–La0.8 Sr0.2Fe0.8Co0.2O3-δ (LSFC), LSGM–La2Ni0.8Cu0.2O4+δ (LNC), SrCoO3-δ–Sr2Fe3O6.5 ±δ, Ce0.8Gd0.2O2-δ (CGO)–LSFC and CGO–La0.7Sr0.3MnO3-δ (LSM), was studied at 973–1223 K. In most cases, oxygen transport is substantially affected by component interaction, decreasing ionic conductivity due to cation interdiffusion, and formation of intermediate phases and/or blocking layers at grain boundaries. This interaction is maximised in systems where the phase components have similar structure and thus may form continuous solid solutions, for example LSGM–LSFC, or intermediate compounds such as Roddlesden–Popper phases in LSGM–LNC composites. The results show that, in addition to knowledge of the transport properties and volume fractions of percolating phases, analysis of ionic conduction in oxide composite materials requires assessment of phase interaction and grain boundary processes.
摘要在973 ~ 1223 K温度下,研究了含有相似体积分数组分(La0.9 Sr0.1)0.98 Ga0.8 Mg0.2 O3-δ(LSGM) -La0.8 sr0.2 fe0.8 co0.3 2o3 -δ(LSFC)、LSGM - la2ni0.8 cu0.2 2o4 +δ (LNC)、SrCoO3-δ - sr2fe3o6.5±δ、Ce0.8Gd0.2O2-δ (CGO) -LSFC和CGO - la0.7 sr0.3 mno3 -δ(LSM)的氧化复合膜的氧透性。在大多数情况下,氧的输运受到组分相互作用、阳离子相互扩散导致离子电导率降低以及在晶界处形成中间相和/或阻塞层等因素的影响。在相组分具有相似结构的体系中,这种相互作用最大,因此可能形成连续的固溶体,例如lsgem - lsfc,或中间化合物,如lsgem - lnc复合材料中的rodlesden - popper相。结果表明,除了了解渗透相的输运性质和体积分数外,氧化物复合材料中的离子电导率分析还需要评估相相互作用和晶界过程。
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引用次数: 8
Self-formed mullite containing refractory barium silicate cements and their castable applications 含耐火硅酸钡胶结物的自形成莫来石及其浇注应用
Pub Date : 2004-10-01 DOI: 10.1179/096797804225018705
N. Khalil, M. Zawrah
Abstract Six batches consisting of different percentages of barite, kaolin and calcined alumina were sintered at 1500–1600°C for 3 h to produce self-formed mullite containing barium silicate cements. The compositions of the cement mixes were investigated using X-ray diffraction. Physicomechanical, sintering and refractory properties were tested according to standard specifications. Each of the mixes, composed mainly of varying proportions of mullite and dibarium silicate minerals, showed different behaviour. The best compromise between cementing, sintering and refractory properties was provided by the mix prepared from 60 wt-% barite, 25 wt-% kaolin and 15 wt-% calcined alumina, consisting of about 54 wt-% dibarium silicate and 33 wt-% mullite. Self-formed mullite containing castable prepared from 15 wt-% of a fine powder of the chosen mix as the cement and 85 wt-% of graded aggregate of the same mix showed good volume stability, high mechanical properties, high thermal shock resistance as well as high loadbearing capacity.
摘要以重晶石、高岭土和煅烧氧化铝为原料,在1500 ~ 1600℃下烧结3 h,制备了含硅酸钡的自形成莫来石胶结物。利用x射线衍射对水泥混合料的组成进行了研究。根据标准规范进行了物理力学性能、烧结性能和耐火性能测试。每种混合物主要由不同比例的莫来石和硅酸钡矿物组成,表现出不同的行为。胶结、烧结和耐火性能之间的最佳折衷是由60重量%的重晶石、25重量%的高岭土和15重量%的煅烧氧化铝组成的混合物,由54重量%的硅酸钡和33重量%的莫来石组成。自形成莫来石含浇注料,由所选混合料中15wt -%的细粉作为水泥和85wt -%的级配骨料配制而成,具有良好的体积稳定性、高力学性能、高热震性和高承载能力。
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引用次数: 3
Whiskerisation of polycrystalline SiC fibres during synthesis 合成过程中多晶SiC纤维的晶须化
Pub Date : 2004-10-01 DOI: 10.1179/096797804X4556
K. L. Vyshnyakova, L. Pereselentseva, Z. G. Cambaz, G. Yushin, Y. Gogotsi
Abstract Whiskers of β-SiC have been produced on the surfaces of polycrystalline SiC fibres by carbothermal synthesis. The growth of whiskers occurred simultaneously with siliconisation of the carbon fibres. The chemical composition, structure and morphology of the whiskers were studied using X-ray diffraction (XRD), Raman microspectroscopy, electron energy loss spectroscopy (EELS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the presence of silica on the surface of initially carbonised fibres was essential for whiskerisation. Nucleation and growth of the whiskers followed the vapour–liquid–solid (VLS) mechanism. The diameter of the whiskers produced ranged from 100 to 300 nm and the average aspect ratio was about 300. Owing to the small size of the whiskers, they are expected to provide more efficient reinforcement in composites than conventional whiskers of larger diameter.
摘要采用碳热合成法在多晶SiC纤维表面制备了β-SiC晶须。晶须的生长与碳纤维的硅化同时发生。采用x射线衍射(XRD)、拉曼微光谱(Raman microspectroscopy)、电子能量损失谱(EELS)、扫描电镜(SEM)和透射电镜(TEM)对晶须的化学组成、结构和形貌进行了研究。研究发现,最初碳化纤维表面二氧化硅的存在对晶须形成至关重要。晶须的成核和生长遵循气-液-固(VLS)机制。所制得的晶须直径为100 ~ 300 nm,平均长径比约为300。由于晶须尺寸小,它们有望在复合材料中提供比大直径的传统晶须更有效的增强。
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引用次数: 12
Low cost ceramic moulding composites: impact properties 低成本陶瓷成型复合材料:冲击性能
Pub Date : 2004-08-01 DOI: 10.1179/096797804225018732
G. Ren, P. Hogg, D. Woolstencroft
Abstract Low cost ceramic moulding composites (CMCs) are composed of inorganic metal silicates, fillers and different types of chopped fibre reinforcements such as glass fibres (AR50/1 or AR62/2). The impact properties of CMCs were investigated by instrumented falling weight impact testing. Variations in impact energy absorption were examined as a function of fibre length and volume fraction. Processing and moulding conditions were also studied, revealing differences in interfacial shear strength between matrix and reinforcement when different moulding temperatures were used. This in turn induced differences in energy absorption during impact testing.
低成本陶瓷模压复合材料(cmc)是由无机金属硅酸盐、填料和不同类型的短切纤维增强如玻璃纤维(AR50/1或AR62/2)组成的。采用仪器落重冲击试验研究了复合材料的冲击性能。研究了纤维长度和体积分数对冲击能量吸收的影响。还研究了加工和成型条件,揭示了不同成型温度下基体和钢筋之间界面抗剪强度的差异。这反过来又引起了冲击试验中能量吸收的差异。
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引用次数: 4
Manufacture of refractory insulating bricks using fly ash and clay 用粉煤灰和粘土制造耐火保温砖
Pub Date : 2004-08-01 DOI: 10.1179/096797804225018714
J. Otero, F. Blanco, M. P. García, J. Ayala
Abstract One of the residues or byproducts generated in coal burning power plants that consume pulverised solid fuels is fly ash. Owing to its morphological characteristics, physicochemical properties and pozzolanic activity, this residue has potential for use in the production of refractory insulating bricks in combination with clays, a binder (sodium silicate) and a foaming agent (hydrogen peroxide 50%). The bricks thus obtained present the appropriate characteristics of mechanical resistance, porosity and thermal conductivity.
粉煤灰是燃煤电厂消耗固体燃料后产生的残留物或副产品之一。由于其形态特征、物理化学性质和火山灰活性,这种残留物与粘土、粘结剂(硅酸钠)和发泡剂(过氧化氢50%)结合在一起,有可能用于生产耐火砖。由此获得的砖具有适当的机械阻力、孔隙率和导热性。
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引用次数: 14
Preparation and characterisation of Sb2O3 with or without Cr2O3 and CoO containing ZnO varistors 含或不含Cr2O3和CoO的Sb2O3氧化锌压敏电阻的制备和表征
Pub Date : 2004-08-01 DOI: 10.1179/096797804225018679
H. I. Saleh
Abstract Zinc oxide samples with different contents of Sb2O3 with or without Cr2O3 and CoO have been prepared by conventional ceramic processing for use as varistors. Reaction sintering was performed at 1200 and 1300°C. X-ray studies indicate that the mixtures contained mainly zincite phase together with two different chemical formulas of spinel-like structure, β-Zn7Sb2O12 and Zn2.33Sb0.67O4, at 1200 and 1300°C respectively. ZnCr2O4 and CoCr2O4 were also formed as spinel-like structures besides Zn2.33Sb0.67O4 and zincite phase in the mixtures doped with Cr2O3 and CoO at 1200 and 1300°C. Variation in current–voltage (I–V) characteristics is discussed in terms of microstructural and crystallographic changes in the varistors. The addition of Cr2O3 and CoO to the ZnO varistors containing Sb2O3 has been confirmed to be effective in enhancing non-linear behaviour.
摘要:采用常规陶瓷工艺制备了不同Sb2O3含量的氧化锌样品(含或不含Cr2O3和CoO)用作压敏电阻。反应烧结温度分别为1200℃和1300℃。x射线研究表明,在1200℃和1300℃下,混合物中主要含有锌矿相,并有两种不同的尖晶石状结构化学式β-Zn7Sb2O12和Zn2.33Sb0.67O4。在1200℃和1300℃时,在掺杂Cr2O3和CoO的混合物中,除了Zn2.33Sb0.67O4和锌矿相外,还形成了类似尖晶石的ZnCr2O4和CoCr2O4。从微观结构和晶体学变化的角度讨论了压敏电阻的电流-电压特性变化。在含Sb2O3的ZnO压敏电阻器中添加Cr2O3和CoO可以有效地提高非线性性能。
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引用次数: 1
Structural and optical properties of annealed Ga2O3 films on Si(111) substrates Si(111)衬底退火Ga2O3薄膜的结构和光学性质
Pub Date : 2004-08-01 DOI: 10.1179/096797804225018741
Hyoun-woo Kim, N. Kim, C. Lee
Abstract An investigation has been made into the structural and optical properties of gallium oxide Ga2O3 films grown on Si(111) substrates by the metal organic chemical vapour deposition (MOCVD) technique, and annealed in the temperature range 750–1050°C. Post-deposition annealing of amorphous Ga2O3 was found to generate b phase grains. Photoluminescence spectra indicated that the annealed Ga2O3 films had a blue-green emission at 470 nm and an ultraviolet emission at 365 nm.
采用金属有机化学气相沉积(MOCVD)技术,研究了在Si(111)衬底上生长的氧化镓Ga2O3薄膜的结构和光学性能,并在750 ~ 1050℃范围内进行了退火。非晶Ga2O3沉积后退火生成b相晶粒。光致发光光谱表明,退火后的Ga2O3薄膜在470 nm处有蓝绿色发射,在365 nm处有紫外发射。
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引用次数: 6
Synthesis of mullite aggregates from fly ash: effect on thermomechanical behaviour of low cement castables 粉煤灰合成莫来石骨料:对低水泥浇注料热力学性能的影响
Pub Date : 2004-08-01 DOI: 10.1179/096797804225018651
S. Kumar, S. Das, P. K. Daspoddar
Abstract Refractory aggregates were synthesised from beneficiated fly ash by reaction sintering with calcined alumina at 1600°C, and 83% mullite yield was achieved. The aggregates had low porosity, low thermal expansion and good refractoriness. To study compatibility in castable refractories, the aggregates were used in high alumina cement based low cement castables and their thermomechanical behaviour was studied. Microstructural characterisation revealed that the emergence of new bond phases such as mullite and calcium hexa-aluminate had a beneficial effect on the hot modulus of rupture and creep resistance of castables. An attempt was made to establish a structure–property relationship.
摘要:以粉煤灰为原料,与煅烧氧化铝在1600℃下反应烧结,合成了耐火骨料,莫来石收率达到83%。该集料具有孔隙率低、热膨胀小、耐火度好等特点。为了研究其在浇注耐火材料中的相容性,将骨料应用于高铝水泥基低水泥浇注料中,并对其热力学性能进行了研究。显微组织表征表明,莫来石和六铝酸钙等新结合相的出现对浇注料的断裂热模量和抗蠕变性能有有益的影响。试图建立一种结构-性质关系。
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引用次数: 12
期刊
British Ceramic Transactions
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