Reduction in Wear Rate of α-Alumina and Silicon Nitride by Diffusional Surface Modification

1988 ◽  
Vol 140 ◽  
Author(s):  
A.K. Gangopadhyay ◽  
M.E. Fine ◽  
H.S. Cheng
Keyword(s):  
Wear Resistance ◽  
Thermal Expansion ◽  
Surface Modification ◽  
Silicon Nitride ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Surface Region ◽  
Lattice Parameter ◽  
Lower Thermal Expansion ◽  
Wear Modes

AbstractThe surface regions of α-alumina and hot pressed silicon nitride were modified by suitable alloying in order to improve their wear resistance. The surface modification in polycrystalline α-alumina was done by diffusing chromia into the surface region which resulted in the formation of a thin layer of A12O3 - Cr9O3 solid solution which has a lower thermal expansion coefficient than pure α-alumina. Also Cr2O3 has a larger lattice parameter than α-alumina thus during cooling the surface was put into compression. The surface region of hot pressed silicon nitride was modified by diffusing α-alumina into the surface which resulted in the formation of a thin sialon layer. A surface compressive stress was again introduced due to the lower thermal expansion coefficient and larger latticeparameter of sialon compared to silicon nitride.Wear tests were conducted against 52100 steel under both lubricated and unlubricated sliding contact using a block on ring apparatus. The wear resistance of chromia surface alloyed α-alumina was improved considerably over unalloyed α-alumina under both lubricated and unlubricated conditions. The wear resistance of alumina surface alloyed silicon nitride was also improved over unalloyed silicon nitride under both lubricated and unlubricated conditions.Different wear modes were identified by examining the worn surfaces under the scanning electron microscope.

Tem Observations of Interfacial Defects in Mocvd GaAs on Single Crystal Ge Substrates

1998 ◽  
Vol 4 (S2) ◽  
pp. 626-627
Author(s):  
K.M. Jones ◽  
M.M. Al-Jassim ◽  
J.M. Olson
Keyword(s):  
Thermal Expansion ◽  
Solar Cell ◽  
Physical Properties ◽  
Single Crystal ◽  
High Efficiency ◽  
Lattice Parameter ◽  
High Quality ◽  
Stages Of Growth ◽  
Interfacial Defects ◽  
Microstructural Defects

The growth of high quality GaAs layers on single crystal Ge substrates has attracted a great deal of interest in recent years. Currently under development at NREL is the GaAs/GalnP-on-Ge high efficiency multi-junction solar cell. Unlike other heteroepitaxial systems such as GaAs-on-Si, physical properties such as the lattice parameter and thermal expansion coefficient of the Ge and GaAs are much closer. Further, Ge has a bandgap of 0.7 eV that makes it a suitable bottom cell in a multi-junction stack. However, the growth of GaAs on Ge is not a straightforward process, and little is known about the Ge surface and the nucleation of GaAs on Ge in the MOCVD environment. In this study, TEM results show that a number microstructural defects are associated with the Ge/GaAs interface and the initial stages of growth.

Environmentally friendly, scalable exfoliation for few-layered hexagonal boron nitride nanosheets (BNNSs) by multi-time thermal expansion based on released gases

2019 ◽  
Vol 7 (46) ◽  
pp. 14701-14708 ◽  
Author(s):  
Zhi-lin Cheng ◽  
Zhan-sheng Ma ◽  
Hong-liang Ding ◽  
Zan Liu
Keyword(s):  
Thermal Expansion ◽  
Boron Nitride ◽  
Large Scale ◽  
Hexagonal Boron Nitride ◽  
Environmentally Friendly ◽  
Boron Nitride Nanosheets ◽  
Novel Approach

A novel approach to exfoliate BNNSs on a large scale via multi-time thermal expansion is described.

Lattice thermal expansion of Pu1−yAmyO2−xplutonium–americium mixed oxides

2017 ◽  
Vol 50 (6) ◽  
pp. 1782-1790 ◽  
Author(s):  
Romain Vauchy ◽  
Alexis Joly ◽  
Christophe Valot
Keyword(s):  
Thermal Expansion ◽  
Elevated Temperatures ◽  
Mixed Oxides ◽  
Lattice Parameter ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Lattice Thermal Expansion ◽  
Linear Lattice ◽  
The Face

Plutonium–americium mixed oxides, Pu1−yAmyO2−x, with various Am contents (y= 0.018, 0.077, 0.21, 0.49, 0.80 and 1.00) were studiedin situby high-temperature X-ray diffraction. In this study, the lattice thermal expansion of the six compounds subjected to heat treatments up to 1773 K under reconstituted air (N2+ 21% O2+ ∼5 vpm H2O) was investigated. The materials remained monophasic throughout the experiments and, depending upon the americium content, the lattice parameter of the face-centred cubic phase deviated from linear lattice expansion at elevated temperatures as a result of the progressive reduction of Am4+to Am3+.

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