Question

Write assignments (term paper) about Transparent aluminum

Should you write:

1- introduction:

2-the work

3-saftey requirements

4-advanteges

5-disadvantges

6-concluision

7-refernces

Answer 1

1.Introduction:

transparent aluminum

Transparent aluminum is a form of aluminum that is see-through. Most commonly someone speaking about transparent aluminum is referring to AION (aluminum oxynitride), a ceramic alloy. However, aluminum can exist in an elemental, metallic form made transparent by bombarding with a soft x-ray laser.

Transparent aluminum oxynitride (AlON) has been known as a useful polycrystalline

ceramic material for window, dome, and other optical elements due to its excellent

optical and mechanical properties comparative to sapphire [1-5]. AlON ceramics can

be made by sintering a powder compact to full density with optical transparency [6].

Final properties of ceramic products depend on raw materials, shaping technologies and

optimization of the sintering process.

Many kind of approaches were developed to fabricated the transparent AlON

ceramics, such as reactive sintering[7], pressureless sintering [6], hot pressing and hot

isostatic pressing techniques [5]. Among them, the most common approach is the

reaction sintering using AlN and Al2O3 as raw materials. The advantage of this method

is that it can be used directly to prepare AlON transparent ceramics without the

manufacture of AlON powders which is synthesized over 1650ºC, and it is a cost-

effective method to fabricate dense ceramics. Some researchers have reported the

sintering behavior of AlN–Al2O3 system [7, 8]. Kim et al found that full density was

obtained at 1800 °C and a further increase in temperature led to a decrease in density[9].

Patel et al has also fabricated fully dense and transparent AlON ceramic through

transient liquid phase sintering[10, 11]. Recently, Cheng et al. obtained a fully

transparent AlON ceramic at lower temperature and short time using the microwave

reactive sintering[12, 13].

In order to fabricate high transparency AlON ceramics, any residual pores in the

sintered sample should be eliminated as much as possible. Previous work has

discovered that certain additives can be beneficial to the sintering of AlON. Hartnett,

Gentilemen, and Macquire have reported that additives such as yttrium and lanthanum

improve the sintering and microstructure of AlON, and subsequent researchers have

also reported on the beneficial nature of these additives[14]. Not only must the correct

additive be indentified, but numerous processing variables such as compositions,

maximum temperature, and holding times must be defined if porosity or swelling is to

be avoided.

In this paper, high transparent AlON ceramic (2mm thickness and owns the in-line

transmittance of 80.3% at 2000 nm) was obtained by a solid-state reaction and

pressureless sintering, using 0.16wt% Y2O3 and 0.02wt% MgO as the promoting

additives. The influence of sintering parameters (sintering temperature, holding time)

on the microstructure and the effect of proportion of Al2O3/AlN on the nitridation rate were discussed

2.

Commercial available submicron Al2O3 (AKP3000, 99.99% purity) and AlN (Grade C,

H.C. Stark, Laufenburg, Germany, 99.95% purity) were used as starting materials. The

properties of the starting powders are shown in Table 1. It was found that the addition

of a small amount of MgO and Y2O3 (Aladdin Reagent Co. Ltd., Shanghai, China, 99.99%

purity) increased the densification and improved the transparency of the sintered bodies

during reaction sintering. Therefore the starting mixture contained 65mole percent of

Al2O3, 35mole percent of AlN, to which 0.08-0.16wt% Y2O3 and 0.02-0.04wt% MgO

were added as sintering additives. The powders were ball-milled at 250 rpm for 24h in

absolute alcohol, using a high density alumina bottle and alumina ball media, and dried

at 100°C for 24h in the oven. The mixed powder were sieved through a 200-mesh screen

and uniaxially pressed into 30mm diameter by 4 mm thickness pellets at 10MPa, and

then cold isostatically presses (CIP) at 200 MPa. then calcined at 800℃ in air for 4

hours to remove organic residue. Subsequently the green body was placed in a graphite

crucible, embedded in the mixed power of Al2O3 and AlN powder, sintered in graphite

resistance furnace under a base pressure of 5~15KPa. All the specimens were double

side polished to the thickness of 2.0mm. The polished fragment was chemically etched

in boiling phosphoric acid (H3PO4).

The apparent sintered density was measured by the Archimedes (water immersion)

method. Individual crystalline phases were identified by X-ray diffraction analysis

(XRD, Empyrean, PANalytical). The surface and fracture microstructure of the sintered

specimens were observed using a scanning electron microscope (SEM, Auriga,

Carlzeiss) an optical microscope (OM) (BX-51, OLYPMUS, Japan). The optical

transmittance spectra was measured with a V-570UVIS/NIR spectra photometer Japan.

3.

Applications

Some of the applications of transparent aluminum include the following:

Various defense applications like Recce sensor windows, transparent armor, windows for laser communications and specialty IR domes with different shapes that include hemispherical and hyper-hemispherical domes

Semi-conductor related applications

Refractories

Insulators and heat radiation plates

Optoelectronic devices

Metal matrix composites

Power and multichip modules

Translucent ceramics

High temperature materials and heat sinks

Break rings

Thermally conductive filler

Integrated circuit packages and substrates

4.Adavantages

It has good corrosion resistance and resistance to damage from radiation and oxidation. It is about three times harder than steel of the same thickness. Domes, tubes, transparent windows, rods and plates can be produced from this material using conventional ceramic powder processing methods.

5.Disadavantages

Disadvantages : Aluminum requires special processes to be welded. It is abrasive to tooling, or more accurately, the aluminum oxide coating that forms upon it is. It is more expensive than steel.

6.Result.

Al2O3 particles own spherical morphology with the

average particle size about 700 nm, along with agglomeration because it was normally

difficult to disperse nano-sized particles on a silicon plate after ultrasonic vibration for

SEM imaging. The morphology of AlN particles is irregular and the size ranges from

0.8to 1.8μm. After ball milling, Al2O3 particles and AlN particles mixed together and

uniformly, This indicated that ball milling effectively changed

the particle size and morphology of the mixed powder.

1 SEAl2O3; (b) AlN; (c) Mixture of Al2O3 and

AlN

sample sintered at 1960 ℃for 8h. However, abnormal grain growth prevented

completed sintering of the specimen during densification process. Trapped pores and

second phase worked as scattering center and greatly decrease the optical transmission

of ceramic. Both of these factors had negative effect on the optical quality of AlON

ceramic. The microstructure can well explain the transmittance difference between

fracture surface microstructures of samples sintered

at different temperature for 8h. The sample sintered at 1930 ºC exists a gray color and

the background words can be seen but fuzzy. The reason was that at low sintering

temperature there were defects residing in crystal structure of the prepared samples,

which caused the scattering of light. It can be observed that several pores were trapped

in grains or grain junctions, as shown in Fig. 2(a). When the sintering temperature

increase to 1960℃, the gray color vanished and highly transparent AlON ceramics were

obtained. However, when the temperature reached 1980℃ the transparent AlON

sample turned to be opaque because further increase of temperature usually resulted in

decreased of transmittance caused by excessive liquid phase in grain boundary which

led to low optical quality of AlON ceramic. Fig.2 (c) presents that excessive liquid

phase exists in grain boundary, as shown in the inset picture. Also, it can be see that the

fracture mode of sample was a typical transgranular. The average grain size was

approximately 100μm. No grain boundary phase existed in its microstructure when the

sample sintered at 1960 ℃for 8h. However, abnormal grain growth prevented

completed sintering of the specimen during densification process. Trapped pores and

second phase worked as scattering center and greatly decrease the optical transmission

of ceramic. Both of these factors had negative effect on the optical quality of AlON

ceramic. The microstructure can well explain the transmittance difference between the samples.

7.Conclusion

Highly transparent AlON ceramics have been prepared by reaction sintering methods.

The sintering parameters including temperature (1960℃), holding time (12h), sintering

additives (MgO 0.02wt% and Y2O3 0.16wt% ), have been investigated and optimized.

8.Reference

[1] N. D. Corbin, Aluminum oxynitride spinel: a review. Journal of the European

Ceramic Society, 1989. 5(3): p. 143-154.

[2] D. C. Harris, Durable 3–5 μm transmitting infrared window materials. Infrared

physics & technology, 1998. 39(4): p. 185-201.

[3] T. Hartnett and R. Gentilman. Optical and mechanical properties of highly

transparent spinel and AlON domes. in 28th Annual Technical Symposium.

1984. International Society for Optics and Photonics.

[4] J. W. McCauley and N. D. Corbin, Phase relations and reaction sintering of

transparent cubic aluminum oxynitride spinel (ALON). Journal of the American

Ceramic Society, 1979. 62(9-10): p. 476-479.

[5] J. Wang, F. Zhang, F. Chen, Effect of Y2O3 and La2O3 on the sinterability of γ-

AlON transparent ceramics. Journal of the European Ceramic Society, 2015.

35(1): p. 23-28.

[6] X. Jin, L. Gao, J. Sun, Highly Transparent AlON Pressurelessly Sintered from

Powder Synthesized by a Novel Carbothermal Nitridation Method. Journal of

the American Ceramic Society, 2012. 95(9): p. 2801-2807.

[7] S. Bandyopadhyay, G. Rixecker, F. Aldinger, Effect of Reaction Parameters on

γ-AlON Formation from Al2O3 and AlN. Journal of the American Ceramic

Society, 2002. 85(4): p. 1010-1012.

[8] J. W. McCauley and N. D. Corbin, High temperature reactions and

microstructures in the Al2O3-AlN system, in Progress in nitrogen ceramics.

1983, Springer. p. 111-118.

[9] Y. Kim, H. Park, Y. Lee, Reaction sintering and microstructural development in

the system Al2O3–AlN. Journal of the European Ceramic Society, 2001. 21(13):

p. 2383-2391.

[10] P. Patel, G. Gilde and J. McCauley, Transient liquid phase reactive sintering of

aluminum oxynitride. Patent US-7,045,091 B, 2006. 1: p. 16.05.

[11] P. Patel, Phase equilibrium and kinetics in the multi-component non-oxide Al–

O–N system. 2000, Ph. D., The Johns Hopkins University.

[12] J. Cheng, D. Agrawal and R. Roy, Microwave synthesis of aluminum oxynitride

(ALON). Journal of materials science letters, 1999. 18(24): p. 1989-1990.

[13] J. Cheng, D. Agrawal, Y. Zhang, Microwave reactive sintering to fully

transparent aluminum oxynitride (ALON) ceramics. Journal of materials

science letters, 2001. 20(1): p. 77-79.

[14] M. Bakas and H. Chu. Pressureless Reaction Sintering of AION Using

Aluminum Orthophosphate as a Transient Liquid Phase. in Ceramic

Engineering and Science Proceedings. 2009.

[15] L. Miller and W. D. Kaplan, Solubility limits of La and Y in aluminum

oxynitride at 1870 C. Journal of the American Ceramic Society, 2008. 91(5): p.1693-1696.