Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Influence of oxygen on thermal stability of nanocrystalline aluminum
  studied by positron annihilation spectroscopy   The thermal stability of nanocrystalline (nc) Al has been studied by means of
positron lifetime spectroscopy and X-ray diffraction (XRD), prepared by
compacting nanoparticles under high pressures. Those nanoparticles were
produced by the flow-levitation (FL) method [1] and the arc-discharge (DC)
method. Effect of oxide at nanoparticle surface on structure stability was
investigated especially in this experiment. The positron lifetime results
reveal that vacancy clusters in grain boundaries are dominant positron traps
according to the high relative intensity of the positron lifetime {\tau}2 in
both samples. The mean grain size of the sample consisting of nanoparticles
with partially oxidized surfaces is almost unchanged after aging at 150 for 84
h, with that of the sample consisting of pure nc Al increasing. The partially
oxidized surfaces of nanoparticles hinder the growth of grain when aging at
150, vacancy clusters related to Al2O3 need longer aging time to decompose,
which implies that the oxide stabilizes the microstructure of the
nanomaterials. The effect is beneficial for nc materials to keep excellent
properties.

30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an