Nanofibers of aluminum oxide Nafen is a new material consisting of aluminum oxide nanofibers with gamma and chi crystal phases. It has fiber diameters of 7-10 nm or 30-40 nm, lengths up to 150 mm, and a specific surface area of 155 m2/g. Nafen is produced via a continuous process that yields over 0.5 kg/hour. TEM images show the fine fiber structure and high length-to-diameter ratio. The fibers are co-aligned in blocks up to 50x50x15 cm with a bulk density of 0.1-0.4 g/cm3. Analysis confirms the gamma and chi phases of polycrystalline

1. Nanofibers of aluminum oxide
physical properties
January 2013

2. Nafen™ is a new material on the market:
alumina nanofibers in gamma / chi phase
Parameter value
Phase gamma / chi
Mean fiber diameter, nm 7-10 / 30-40
Fiber length, mm 1–150
Specific surface area (BET), m2/g 155
Purity, % 99.7
Specific gravity, g/cm3 3.98
Bulk density, g/cm3 0.1 to 0.4
Nafen is unique because of its industrial-scale production technology.
It is synthesized from liquid aluminum melt which ensures continuous
production rate over 0.5 kg/hour even at pilot stage.
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3. GEOMETRY AND MORPHOLOGY

4. TEM micrographs / National University of Science and
Technology MISiS (Moscow, Russia)
TEM images demonstrate fine fiber diameter and length-to-diameter ratio
3

5. Two types of Nafen fibers are currently produced:
with average diameters of 7-10 and 30-40 nm
TEM and fiber diameter distribution for the two types of fibers
8 nm average diameter 35 nm average diameter
4

6. Nafen is produced in blocks of co-aligned fibers
Fibers are co-aligned and arranged in bundles
- distance between fibers in block is 20 to 40 nm
- block size is up to 50x50 cm
- block height is up to 15 cm (along the fibers)
- bulk density is 0.1 to 0.4 g/cm3
- block thermal conductivity is 0.025 W/m•K,
close to that of air
- fibers are easily separated by wetting in water
or alcohols
W-20
SEM
5

7. ELEMENTAL AND PHASE ANALYSIS

8. Elemental analysis (EDX) at various
temperatures and TGA / UCambridge (UK)
Elemental Analysis
Elemental Analysis
37:63
44:5637:63 46:54 46:54 45:55
46:54 46:54 45:55
Saffil
GreyNafen 7 nm
to white
Nafen 12 nm
Grey to white
T, C 20 1000 1270 1400
Al to O weight ratio is close to Al2O3 The material loses up to 10% weight when heated
- Al2O3 corresponds to 48:54 - due to water desorption
- deviation at low temperature is due to - Saffil is shown as a reference alumina material
water adsorption
- small deviation at high temperature is
due to vacant Al bonds on the surface
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9. Phase analysis (XRD) / IC SB RAS (Novosibirsk,
Russia)
Typical diffraction patterns for low-
temperature phases of alumina
- gamma and etha are cubic spinels
- chi is also cubic, but with additional
hexagonal packing (check term)
- chi is identified by the peak at 42.8
Diffraction patterns
of two samples of Nafen
- the phase is identified as mostly chi
for these particular samples, with
some gamma
- different samples have varying
gamma/chi ratio, depending on the
synthesis process parameters
- crystallite size 50-100 nm
Nafen fibers are
polycrystalline alumina in
gamma and chi phases
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10. High-temperature phase transformation (XRD) /
PANanalytical
emperature XRD
At 1200–1400 C, transformation
to alpha phase occurs
Series of XRD spectra during samples heating 10
9

11. SURFACE PROPERTIES

12. нию d=4/ρA. Для значения плотности 3.89
г/см BET specific surface area / БЭТ 155 м2/г, а d=6.6 нм.
3
и удельной поверхности по IC SB RAS
, а d=6.6 нм.
(Novosibirsk, Russia)
Nitrogen adsorption-desorption method (BET)
adsorption
cm3/g
desorption
ции азота образца 29/11 при 77К.
P/P0
7
Specific surface area is measured at 155 cm2/g
- this corresponds to the geometric surface
Рис. 2.2. Изотермы адсорбции-десорбции азота образца
- hence, no micropores or surface defects 29/11 при 77К.
11

13. (Рис.3.4Б), т.е. есть и зубцы, и плоские участки поверхности. Угол 120о характерен для
The surface is ‘saw-shaped’, faceted at various
плоскостей плотнейшей упаковки атомов кислорода (111). Напомним, что для
angles (TEM) / IC SB RAN (Novosibirsk, Russia)
традиционного c-Al O , полученного прокаливанием гиббсита, характерна
2 3
пластинчатая форма кристаллитов с развитой гранью 111.
ционные картины образцов 29/11 и 22.
гласно микроскопии высокого разрешения волокна
убцов равен 120о) (Рис.3.4А), либо перекручены
ие участки поверхности. Угол 120о характерен для
атомов кислорода (111). Напомним, что для
нного прокаливанием гиббсита, характерна
развитой гранью 111. А Б
Рис.3.4А. Волокно, зубчатые края, угол 120о (вид сверху на плоскость (111)).
Рис.3.4Б. Перекрученное волокно. Одна часть с зубчатыми краями (вид сверху на
плоскость (111), вторая с ровными краями (вид сбоку на упаковку полоскостей (111))[111]
11
А Б
ол 120о (вид сверху на плоскость (111)).
дна часть с зубчатыми краями (вид сверху на Рис. 5.8. Ориентация фасеток увеличенного размера (5 нм и более). 12

14. APPENDIX: XRD’s OF DIFFERENT SAMPLES

15. Phase analysis (XRD) / PANanalytical
Sample 1 - Identification
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16. XRD Position 1 s/ Bruker
White fibers - position 1
1700
1600
1500
1400
1300
1200
1100
Lin (Counts)
1000
900
800
700
600
500
400
300
200
100
0
10 20 30 40 50 60 70 80 90
2-Theta - Scale
File: LC-polycap-2mm Coli-sample white-position1.raw
00-050-0741 (I) - Aluminum Oxide - Al2O3 - Cubic - a 7.93900 - c 7.93900 - Face-centered - Fd-3m (227)
00-046-1131 (N) - Aluminum Oxide - Al2O3 - Tetragonal - a 5.59900 - c 23.65700 - Prim itive - P-4m2 (115)
Bruker 21.09.10
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17. XRD Position 2 / Bruker
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18. XRD Position 3 / Bruker
Peaks are sharper and it seems that there is some preferred
orientation (intensity ratio does not fit anymore to the expected one).
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19. APPENDIX: PORE SIZE DISTRIBUTION

20. наблюдаются максимумы /г,при 20 нм (по десорбции) и 40 нм (по адсорбц
и удельной поверхности по БЭТ 155 м а d=6.6 нм.
Pore size distribution / IC SB RAS (Novosibirsk,
видимому, соответствующие порам между волокнами.
Russia)
dV/dD cm3/g nm
adsorption
desorption
Рис. 2.2. Изотермы адсорбции-десорбции азота образца 29/11 при 77К.
Pore diameter D, nm
7
Рис. 2.3. Распределение объѐма пор по размерам.
Maximum pore size (20 nm) corresponds to the inter-fiber distance
- hence, no micropores
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