Chemical Technology January 2015

Chemical Technology • January 2015

Minerals Processing & Metallurgy

PdIn

Wang

et al

[44] developed a thermally

stable, low-resistance PdIn ohmic contact

-GaAs. A ~5nm layer of In

0,4

0,6

covered the interface between the single

phase intermetallic layer PdIn layer and the

GaAs substrate. Specific contact resistivities

and contact resistances of approximately

1×10

−6

Ωcm

and 0,14 Ωmm respectively,

were obtained.

Catalysis, sensors and

capacitors

Mesoporous, also known as nanoporous,

gold and platinum can be prepared by deal-

loying AuAl

and PtAl

in amanner analogous

to that used in the preparation of Raney

nickel catalysts [40]. The aluminium is then

dissolved from the AuAl

precursor by means

of NaOH to produce a highly porous gold

structure (see Figure 7). Van der Lingen

[41] produced heterogeneous catalysts

by incorporating transition metal oxide(s)

with the porous gold. Furthermore, promoter

elements could also be melted with AuAl

improve catalytic activity. These catalysts

were tested for CO oxidation activity.

Figure 7: HRSEM image of dealloyed AuAl

surface [41].

Pattrick

et al

[22] studied mesoporous

gold catalysts prepared via dealloying of

AuAl

for the selective catalytic reduction

of NO

by propene under lean-burn condi-

tions for potential autocatalyst applications.

It was found that relatively low additions

of platinum group metals (1 at.%) caused

shifts to lower temperature regions of

activity, with the largest shift obtained for

rhodiummost likely due to a strong synergis-

tic interaction between rhodium and gold.

Cortie and Van der Lingen [3] investi-

gated the potential of mesoporous gold

for ultra-capacitors, and preliminary work

revealed a perceived capacitance of about

15 to 28 mF as demonstrated for a sample

containing 2 g of gold when connected as a

cathode. No storage of energy was observed

when the gold was connected as the anode.

A significant number of papers have been

published recently on nanoporous gold, but the

precursor material is 30 wt% gold and 70 wt%

silver. A similar dealloyed structure is obtained

for the gold-silver system as for the AuAl

system.

Potential applications for the nanoporous gold in-

cludes: catalysis for oxygen-assisted coupling re-

actions [36]; CO oxidation [29]; electro-catalysis/

fuel cells [15]; electrochemical immunoassays

and sensors [37, 29, 46, 18].

Conclusions

Precious metal intermetallic compounds are used

in various applications as shown in this article.

Although intermetallic compounds are inherently

brittle, which could restrict their use in applica-

tions, this limitation is overcome by using the

compounds in powder form, coatings and inlays

with bi-metallic castings.

References

References for this article are available from the

editor at

chemtech@crown.co.za

Acknowledgements

1. The Southern African Institute of Mining and

Metallurgy, 2014. Advanced Metals Initiative,

Department of Science and Technology.

2. This paper was originally presented at the Pre-

cious Metals 2013 conference held in Cape

Town, South Africa.

3. The Precious Metals Development Network

(PMDN) is also thanked.

The University of Pretoria wishes to appoint academic staff members in available positions to enhance the current research and teaching capacity in the Department of Chemical Engineering and to position the Department as an international leader. Expertise and experience are sought in the field of Environmental Engineering and in Water Utilisation Engineering. These positions will also be closely associated with multidisciplinary research related to renewable energy systems. The responsibilities will include: • Postgraduate and undergraduate teaching in the programme focus areas of the Department; • Assigned departmental duties (e.g. of an administrative nature); • Continuous research outputs in a productive manner within the research focus areas of the Department; • Expanding existing/initiating new research programmes, raising and managing additional funding from national and international funding agencies and industry to support the activities of the relevant focus group; • Publishing research articles in accredited journals; • Supervising postgraduate Master’s and Doctoral students. UNIVERSITY OF PRETORIA In the pursuit of the ideals of excellence and diversity, the University of Pretoria wishes to invite applications for the following vacancies. FACULTY OF ENGINEERING, BUILT ENVIRONMENT AND INFORMATION TECHNOLOGY DEPARTMENT OF CHEMICAL ENGINEERING 1 x permanent full-time 1 x contract appointment SENIOR LECTURER CLOSING DATE: 13 FEBRUARY 2015 The University of Pretoria is committed to equality, employment equity and diversity. In accordance with the Employment Equity Plan of the University and its Employment Equity goals and targets, preference may be given, but is not limited to candidates from under represented designated groups. The University of Pretoria reserves the right not to make an appointment to the post as advertised. For details regarding the above position and information on how to apply, visit the University’s website at www.up.ac.za and follow the link: Careers@UP. APPLICATION DETAILS

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