American Mineralogist
A natural high-pressure phase of titanium oxide with alpha-PbO2-structure has been found in omphacite from coesite-bearing eclogite at Shima in the Dabie Mountains, China. High-resolution transmission electron microscope observations have revealed an orthorhombic lattice, corresponding to alpha-PbO2-type TiO2, with cell parameters a = 0.461 nm, b = 0.540 nm, c = 0.497 nm and space group Pbcn. It occurs as nanometer-thick (< 2 nm) lamellae between multiple twinned rutile crystals, providing additional evidence of very high-pressure, metamorphism at 7 GPa, 900 degrees C. This implies subduction of continental material to a depth of more than 200 kilometers. alpha-PbO-type TiO2 could be an extremely useful index mineral for ultrahigh-pressure.
关键词:
high-pressure phase;ries crater;rutile;polymorph;titanium
材料科学技术（英文）
The wear and friction properties of Ti3SiC2-based materials were studied using the pin-on-disc method. The friction coefficient of Ti3SiC2-based material was not very sensitive to normal load, the steady state value, p, increased from 0.4 to 0.5 when the normal load increased from 7.7 N to 14.7 N. The wear volume for Ti3SiC2 disc increased with increasing normal load or sliding distance in the tests. The average wear rate of Ti3SiC2-based material was 9.9X10(-5) mm(3)/Nm. The debris on the Ti3SiC2 disc was essentially made up of Ti3SiC2 and steel pin materials, while the debris on the steel sliders was generally pip material. The wear mechanism was concluded as the fracture and delamination of Ti3SiC2-based materials followed by adhesive wear of steel sliders.
关键词:
Ti3SiC2;wear and friction;friction coefficient;wear volume;titanium-silicon carbide;friction
Materials Research Innovations
Cu/Ti3SiC2 composite, a new electrofriction material, was prepared, for the first time, by PM method. The microstructure, mechanical and electrical properties of the Cu/Ti3SiC2 composites were investigated and were compared with those of Cu/graphite composites. The results demonstrated that Cu/Ti3SiC2 composites had superior mechanical properties over Cu/graphite composites. At filer content of less than 20 vol%, the electrical conductivity for Cu/Ti3SiC2 composites was higher than that for Cu/graphite composites; at high filer content, the electrical conductivity for Cu/Ti3SiC2 composites was lower than that for Cu/graphite composites because of the presence of residual pores. It was found that like Cu/graphite composite, Cu/Ti3SiC2 was a self-lubricated material. The compressive yield strength, Brinell hardness, relative ratio of compressive for Cu-30 vol% Ti3SiC2 composites are 307 MPa, 140, 15.7% respectively.
关键词:
electronfriction material;copper;Ti3SiC2;graphite;composite;self-lubricating;ti3sic2
SUN Wenqiang
,
CAI Jiuju
,
MAO Hujun
,
GUAN Duojiao
钢铁研究学报(英文版)
As the largest energy consuming manufacturing sector and one of the most important sources of carbon dioxide (CO2) emissions, the China′s iron and steel industry has paid attention to the study of changing trend and influencing factors of CO2 emissions from energy use. The logarithmic mean Divisia index (LMDI) technique is used to decompose total change in CO2 emissions into four factors: emission factor effect, energy structure effect, energy consumption effect, and steel production effect. The results show that the steel production effect is the major factor which is responsible for the rise in CO2 emissions; whereas the energy consumption effect contributes most to the reduction in CO2 emissions. And the emission factor effect makes a weak negative contribution to the increase of CO2 emissions. To find out the detailed relationship between change in energy consumption or steel production and change in CO2 emissions, the correlation equations are also proposed.
关键词:
CO2 emissions
,
energy use
,
LMDI technique
,
steel production
,
energy consumption
Oxidation of Metals
The cyclic-oxidation behavior of Ti3SiC2-base material was studied at 1100degreesC in air. Scale spallation and weight loss were not observed in the present tests and the weight gain would just continue if the experiments were not interrupted. The present results demonstrated that the scale growth on Ti3SiC2-base material obeyed a parabolic rate law up to 20 cycles. It then changed to a linear rate with further increasing cycles. The scales formed on the Ti3SiC2-base material were composed of an inward-growing, fine-grain mixture of TiO2+SiO2 and an outward-growing, coarse-grain TiO2. Theoretical calculations show that the mismatch in thermal expansion coefficients between the inner scale and Ti3SiC2-base matrix is small. The outer TiO2 layer was under very low compressive stress, while the inner TiO2+SiO2 layer was under tensile stress during cooling. Scale spallation is, therefore, not expected and the scale formed on Ti3SiC2-base material is adherent and resistant to cyclic oxidation.
关键词:
cyclic oxidation;Ti(3)Sic(2)-base material;scale spallation;adherence;high-temperature oxidation;titanium-silicon carbide;air
Jingchuan ZHU
,
Zhongda YIN and Zhonghong LAI(Dept. of Metals and Technology
,
Harbin Institute of Technology
,
Harbin
,
150001. China)
材料科学技术（英文）
The fabrication. microstructure and mechanical properties of ZrO2-Ni functionally gradient materials (FGM ) have been studied. FGM as well as non-FG M of ZrO2-Ni system was developed by powder metallurgical process. X-ray diffractometer (XRD ). electron probe microanalyzer (EPMA), scanning electron microscope (SEM ) and optical microscope were employed to investigate the crystalline phases. chemical composition and microstructure Experimental results demonstrate that the composition and microstructure of ZrO2-Ni FGM have the expected gradient distribution. There are no distinct interfaces in the FGM due to the gradient change of components. that is, the constituents are continuous in microstructure everywhere. Moreover, Vickers hardness and flexural strength were measured for the common composites as a function of composition. It is made clear that the mechanical properties of the FGM vary corresponding to the constitutional changes as well
关键词:
Acta Materialia
The oxidation behavior of Ti3SiC2-based material in air has been studied from 900 degreesC to 1200 degreesC. The present work showed that the growth of the oxide scale on Ti3SiC2-based material obeyed a parabolic law from 900 degreesC to 1100 degreesC, while at 1200 degreesC it followed a linear rule. The oxide scale was generally composed of an outer layer of coarse-grained TiO2 (rutile) and an inner layer of fine-grained TiO2 and SiO2 (tridymite) above 1000 degreesC, A discontinuous coarse-grained SiO2 layer was observed within the outer coarse-grained TiO2 layer on the samples oxidized at 1100 degreesC and 1200 degreesC. Marker experiments showed that the oxidation process was controlled by the inward diffusion of oxygen. outward diffusion of titanium and CO or SiO, and that internal oxidation predominated. The TiC content in Ti3SiC2 was deleterious to the oxidation resistance of Ti3SiC2. (C) 2001 Acta Materialia Inc. published by Elsevier Science Ltd. All rights reserved.
关键词:
Ti3SiC2-based material;oxidation;titanium-silicon carbide;alloys
Journal of Physical Chemistry C
Identification of effective catalyst has been a subject of great interest and challenge in developing metal-N-H systems as potential hydrogen storage media. Motivated by the mechanistic understanding of the essential amide/imide conversion, we experimentally examined the possibility of N-H bond activation by using metal catalyst. We prepared the graphite-supported Ru nanoparticles (Ru/C catalyst) and evaluated their effect on the hydrogen storage properties of Mg(NH2)(2) + 2LiH material. Our studies show that the Ru/C catalyst is catalytically active toward both dehydrogenation and rehydrogenation reactions of Mg(NH2)(2) + 2LiH. Moreover, the catalytically enhanced hydrogen sorption kinetics persists well over 10 de/rehydrogenation cycles. Careful examination of the isothermal dehydrogenation behaviors suggests that the enhanced dehydrogenation kinetics may result from the Ru-catalyzed interface reaction between amide and imide solid phases. This is consistent with the Fourier transform infrared results, which show clearly the promoting effect of Ru catalyst on the N-H bond reconstruction. Finally, the catalytic mechanism of Ru catalyst on the reversible dehydrogenation reactions of Mg(NH2)(2) + 2LiH material is discussed.
关键词:
n-h system;self-assembled monolayers;complex hydrides;ammonia;decomposition;surfaces;ru(001);carbon;linh2;nh3
