Structural stability and electronic properties of Co2N, Rh2N and Ir2N

The structural stability and electronic properties of Co2N, Rh2N and Ir2N were Studied by using the first principles based on the density functional theory. Two Structures were considered for each nitride, orthorhombic Pnnm phase and cubic Pa (3) over bar phase. The results show that they are all mechanically stable. Co2N in both phases are thermodynamically stable due to the negative formation energy, while the remaining two compounds are thermodynamically unstable.

Lanthanum zirconate ceramic toughened by BaTiO3 secondary phase

La2Zr2O7 (LZ) is a promising thermal barrier coating material for the high-temperature applications, which could be significantly toughened by the BaTiO3 piezoelectric phase incorporated into the matrix. The composites of xBaTiO(3)/(l-x)LZ (x=5, 10, 15, 20 vol%, LZ-x-BaTiO3) were densified by means of high-pressure sintering (HPS) under a pressure of 4.5 GPa at 1450 degrees C for 10 min, by which a high relative density above 93% could be obtained.

Synthesis and high-pressure sintering of lanthanum magnesium hexaaluminate

Lanthanum magnesium hexaaluminate is a very important ceramic material for high temperature applications. In this paper lanthanum magnesium hexaaluminate has been synthesized directly by solid-state reaction. The forming mechanism was investigated by XRD. The SEM photographs show that the prepared powders are made of hexagonal plates. These powders can be well sintered at the high temperature (1600 degrees C) under the high pressure (4.5 GPa), and the relative density reaches 94.8%.

Novel Sulfonated Polyimide Ionomers by Incorporating Pyridine Functional Group in the Polymer Backbone

A series of sulfonated polyimides (SPIs) containing pyridine ring in the polymer backbone were synthesized by the polycondensation of 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTDA), 5-(2,6-bis(4-arninophenyl)pyridin-4-yl)-2-methoxy benzene sulfonic acid (SDAM), and 4,4'-diaminodiphenyl ether (ODA). Flexible, transparent, and tough membranes were obtained. Property study revealed that all the membranes displayed high thermal stability with the desulfonation and decomposition temperature higher than 290 and 540 degrees C, respectively, as well as good mechanical property with Young's modulus larger than 1.0 GPa, maximum strength (MS) on a scale of 60-80 MPa, and elongation at break (EB) ranged from 41.79 to 75.17%.

High-pressure sintered yttria stabilized zirconia ceramics

Fast densification of 8YSZ ceramics under a high pressure of 4.5 GPa was carried out at different temperatures (800, 1000, 1450 degrees C), by which a high relative density above 92% could be obtained. FT-Raman spectra indicate that the 8YSZ underwent a phase transition from partially tetragonal to partially cubic phase as temperatures increase from 1000 to 1450 degrees C when sintering under high pressure. The electrical properties of the samples under different high-pressure sintering conditions were measured by complex impedance method. The total conductivity of 0.92 x 10(-2) S cm(-1) at 800 degrees C has been obtained for 8YSZ under high pressure at 1450 degrees C, which is about 200 degrees C lower than that of the samples prepared by conventional pressureless sintering.

Investigation of Chemical Bond Characteristics, Thermal Expansion Coefficients and Bulk Moduli of alpha-R2MoO6 and R2Mo2O7 (R = rare earths) by Using a Dielectric Chemical Bond Method

Theoretical researches are performed on the alpha-R2MoO6 (R = Y, Gd, Tb Dy, Ho, Er, Tm and Yb) and pyrochlore-type R2Mo2O7 (R = Y, Nd, Sm, Gd, Tb and Dy) rare earth molybdates by using chemical bond theory of dielectric description. The chemical bonding characteristics and their relationship with thermal expansion property and compressibility are explored. The calculated values of linear thermal expansion coefficient (LTEC) and bulk modulus agree well with the available experimental values. The calculations reveal that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the lanthanides: the LTEC decreases from 6.80 to 6.62 10(-6)/K and the bulk modulus increases from 141 to 154 GPa when R goes in the order Gd, Tb Dy, Ho, Er, Tm, and Yb in the alpha-R2MoO6 series; while in the R2Mo2O7 series, the LTEC ranges from 6.80 to 6.61 10(-6)/K and the bulk modulus ranges from 147 to 163 GPa when R varies in the order Nd, Sm, Gd, Tb and Dy.

Novel proton exchange membranes based on water resistant sulfonated poly[bis(benzimidazobenzisoquinolinones)]

Novel water resistant sulfonated poly[bis(benzimidazobenzisoquinolinones)] (SPBIBIs) were synthesized from 6,6'-disulfonic-4,4'-binaphthy]-1,1',8,8'-tetracarboxylic dianhydride (SBTDA) and various aromatic ether tetraamines. The resulting polymers with IEC in the range of 2.17-2.87 mequiv g(-1) have a combination of desired properties such as high solubility in common organic solvents, film-forming ability, and excellent thermal and mechanical properties. Flexible and tough membranes, obtained by casting from m-cresol solution, had tensile strength, elongation at break, and tensile modulus values in the range of 87.6-98.4 MPa, 35.8-52.8%, and 0.94-1.07 GPa. SPBIBI membranes with a high degree of sulfonation displayed high proton conductivity and a good resistance to water swelling as well. SPBIBI-b with IEC of 2.80 mequiv g(-1) displayed the conductivity of 1.74 x 10(-1) S cm(-1) at 100 degrees C, which was comparable to that of Nafion (R) 117 (1.78 x 10(-1) S cm(-1), at 100 degrees C).

First Principles Investigation on the Ultra-Incompressible and Hard TaN

The structural, electronic, and mechanical properties of TaN were investigated by use of the density functional theory (DFT). Eight structures were considered, i.e.. hexagonal WC TaN, NiAs, wurtzite, and CoSn structures. cubic NaCl. zinc-blende and CsCl structures. The results indicate that TaN in TaN-type structure is the most stable at ambient conditions among the considered structures. Above 5 GPa, TaN in WC-type structure becomes energetically the most stable phase. They are also stable both thermodynamically and mechanically. TaN in WC-type has the largest shear Modulus 243 GPa and large bulk modulus 337 GPa among the considered structures. The Volume compressibility is slightly larger than diamond, but smaller than c-BN at pressures from 0 to 100 GPa. The compressibility along the c axis is smaller than the linear compressibility of both diamond and c-BN.

Ab initio study on the electronic and mechanical properties of ReB and ReC

The structural, electronic, and mechanical properties of ReB and ReC have been studied by use of the density functional theory. For each compound, six structures are considered, i.e., hexagonal WC, NiAs, wurtzite, cubic NaCl, CsCl, and zinc-blende type structures. The results indicate that for ReB and ReC, WC type structure is energetically the most stable among the considered structures, followed by NiAs type structure. ReB-WC (i.e., ReB in WC type structure) and ReB-NiAs are both thermodynamically and mechanically stable. ReC-WC and ReC-NiAs are mechanically stable and becomes thermodynamically stable above 35 and 55 GPa, respectively. The estimated hardness from shear modulus is 34 GPa for ReB-WC, 28GPa for ReB-NiAs, 35GPa for ReC-WC and 37GPa for ReC-NiAs, indicating that they are potential candidates to be ultra-incompressible and hard materials.

Ferrimagnetic and semiconducting CaCu3Fe2Sb2O12 by first principles

CaCu3Fe2Sb2O12 is mechanically stable, thermodynamically stable at pressures above 18 GPa. Both GGA and GGA + U methods predict that it is a ferrimagnetic semiconductor with Fe3+ in high spin state (S = 5/2). The coupling of Fe-Cu is antiferromagnetic, while that of Cu-Cu is ferromagnetic. The calculated total spin moment is 6.17 mu(B).

First principles investigation on the structural, mechanical and electronic properties of OsC2

The structural, mechanical and electronic properties Of OsC2 were investigated by use of the density functional theory. Seven structures were considered, i.e., orthorhombic Cmca (No. 12, OsSi2), Pmmn (No. 59, 002) and Pnnm (No. 58, OsN2); tetragonal P4(2)/mnm (No. 136, OsO2) and 14/mmm (No. 139, CaC2); cubic Fm-3m (No. 225, CaF2) and Pa-3 (No. 205, PtN2). The results indicate that Cmca in OsSi2 type structure is energetically the most stable phase among the considered structures. It is also stable mechanically. OsC2 in Pmmn phase has the largest bulk modulus 319 GPa and shear modulus 194 GPa. The elastic anisotropy is discussed. (C) 2009 Elsevier B.V. All rights reserved.

高韧性异构聚酰亚胺树脂及其复合材料

采用MPMR合成技术得到了低黏度、高韧性、耐高温异构聚酰亚胺树脂,该树脂预浸液常温储存期大于两个月,亚胺化后纯树脂在320℃熔体黏度<300 Pa.s,树脂浇铸体的弯曲强度>100 MPa,弯曲模量>3.0 GPa,抗拉强度可达80 MPa,断裂伸长率可达6%,固化后T5d>500℃,其中PI-4复合材料在300℃的弯曲强度保持率达到76.5%。

Microstructure, thermal stability and mechanical properties of the novel (W1-xAlx)C-Co (x=0.2, 0.33, 0.4, 0.5) cemented carbide

Bulk novel cemented carbides (W1-xAlx)C-10.1 vol% Co (x = 0.2, 0.33, 0.4, 0.5) are prepared by mechanical alloying and hot-pressing sintering. Hot-pressing (HP) is used to fabricate the bulk bodies of the hard alloys. The novel cemented carbides have good mechanical properties compared with WC-Co. The density and operating cost of the novel material is much lower than a WC-Co system. The material is easy to process and the processing leads to nano-scaled, rounded, particles in the bulk material. The hardness of (W1-xAlx)C-10.1 vol% Co (x = 0.2, 0.33, 0.4, 0.5) hard material is 20.37, 21.16, 21.59 and 22.16 GPa, and the bending strength is 1257, 1238, 1211 and 1293 MPa, with the aluminum content varying from 20% to 50%. The relationship between the microstructure and the mechanical properties of the novel hard alloy is also discussed.

High-pressure sintering the novel light (W0.25Al0.75)C hard material without binder phase

A novel hard material of (W0.25Al75)C has been successfully prepared by the high-pressure sintering process without the addition of any binder phase. The high-pressure is a suitable and powerful technique for sintering the binderless hard material, the relative density of the hard material can reach 99.6% under high-pressure sintering. The density of the novel light hard material is only 6.2371 g cm(-3), which is much lighter than the normal hard material. The hardness of the light hard material can reach 18.89 GPa even the aluminum content get the astonished 75%.

Crystal structures and elastic properties of superhard IrN2 and IrN3 from first principles

First principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3, hexagonal P3(2)21, tetragonal P4(2)/mnm, orthorhombic Pmmn, Pnnm, and Pnn2, and monoclinic P2(1)/c. Our calculation indicates that the P2(1)/c phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of 1.414 A. These characters are consistent with the experimental facts that IrN2 is in lower symmetry and nonmetallic. Our conclusion is also in agreement with the recent theoretical studies that the most stable phase of IrN2 is monoclinic P2(1)/c. The calculated bulk modulus of 373 GPa is also the highest among the considered space groups. It matches the recent theoretical values of 357 GPa within 4.3% and of 402 GPa within 7.8%, but smaller than the experimental value of 428 GPa by 14.7%. Chemical bonding and potential displacive phase transitions are discussed for IrN2. For IrN3, cubic skutterudite structure (Im-3) was assumed.