Author Archive
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March 1st, 2010
Black gold electroplating
NEW Black gold electroplating on the market!
There is considerable interest in black colour effects on gold jewellery. To date, this has usually been achieved by electroplating black rhodium or black ruthenium layers on carat gold items or by oxidation of special carat gold alloy compositions (see special gold colours on utilisegold.com ) Whilst black rhodium or ruthenium offer satisfactory black coatings, there has been a desire to have a real black gold. At last, Wieland GmbH, Germany, have produced one, called NEOPAL. This is claimed to be “an innovative new decorative surface treatment which deposits a high quality layer of deep black gold plating”. This is a ‘first’ in gold electroplating solutions. I have a ring plated in Neopal; it is a lovely bluish black colour that is very attractive. Neopal is easy to use, with a layer thickness of <10 microns, and has uniform deposition characteristics with a hardness of 60 – 75 HV. For further information, contact Wieland – www.wieland-international.com
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June 4th, 2009
Killing off bugs with gold…….
Silver has received much publicity over its anti-bacterial properties and a myriad of commercial applications are based on these including coatings for catheters and anti-odour socks and clothing. It is well known that gold also has anti-bacterial properties but to date these have not received the same attention. However two items have come to my attention this week that show the future is potentially bright for gold too in this application sector.
Firstly, I note the publication of a new patent, WO 2009/046081 A2, on the 9th April from 3M Inc, titled “Process for limiting the growth of microrgansims”. This is based on their PVD deposition technology used in the manufacture of gold catalysts in applications such as gas masks. In this patent, they deposit fine nanoscale gold of 5nm size or less onto nanoparticulate titanium dioxide by their PVD process to produce a potent antimicrobial material. The resulting material can be effective against a variety of micro-organisms such as bacteria in the presence of other biological material (e.g. protein) and in a variety of different environments and lighting conditions. Photocatalytic activity is also claimed. This process provides a means for disinfecting a surface. Maybe we will learn more of this invention on the 3M stand at GOLD 2009 in Heidelberg next month?
The second item of interest is research carried out at Syracuse University , where Yan-Yeuk Luk, professor of chemistry, and Dacheng Ren, assistant professor of biomedical engineering, have developed a new surface that resists biofilm growth, a development that could lead to improved medical implants and prevention of biofouling. In their research they found that a thin 20nm gold film deposited on a glass slide could be surface treated to produce a surface on which the growth of bacteria could be confined to 2-dimensions. Important differences in the way mammalian cells and bacteria adhere to the surface were discovered too. We shall be following this research up. Watch for more information at a later date.
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April 8th, 2009
Decisions made for GOLD 2009 Programme
At last, the organisers have notified everyone who submitted an abstract for GOLD 2009 on the outcome – and by the scheduled date! With well over 330 abstracts submitted (and still some latecomers arriving), it was a difficult decision on who would give oral presentations and who will display posters on their research. With much hard work by the technical committees, the organisers finally made their decisions at a meeting in mid-February. This was not easy with so many high quality abstracts submitted. Hopefully, we have pleased most people but, inevitably, some will feel disappointed.
We are now busy working on scheduling the oral presentations to produce an interesting, well-balanced programme over the 3 and one-half days of the conference. Again, not an easy task, but we shall succeeed, no doubt. It is clear that the Nanotechnologysector will be much more substantial this time and the bigger number of applications-oriented presentations should give more interest for industrialists looking for exploitation opportunities. We have decided on having a 5th parallel session for some sessions to accommodate the large number of good quality orals that will be presented, rather than shorten the time allowed by each speaker. This need not worry delegates who fear moving back and forth between lecture rooms ( a problem at Gold 2006 in Limerick) as all are close together.
The posters will be divided into 2 sessions this year, again to accommodate the many abstracts submitted. Remember, we are accepting abstracts for posters right up to the start of the conference. So, if you have some interesting research to report, submit an abstract on the conference website (do I need to tell you: it is www.gold2009.org ). I do need to tell you that, if you are attending GOLD 2009, you should register and book your accommodation soon. The hotels are filling up fast, we are told! Otherwise you may need to bring your tent and camp by the river…. Its not long now til we meet in Heidelberg – just before my Birthday, as it happens……..
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March 3rd, 2009
Size Matters for the Strength of Gold
What is the mechanical strength of pure gold?
Well, it appears to depend on size when one reaches the micro-scale, according to Professor William Nix of Stanford University. He gave the Von Hippel Award talk at the MRS Fall Meeting in Boston in November 2007 (transcript in MRS Bulletin, February 2009 vol 34 (2), 82-91) on “Exploiting New Opportunities in Materials Research by Remembering and Applying Old Lessons”. He reports on how the strength of single crystal gold substantially increases at the sub-micron scale. Surprised? I was!
Material Scientists all know that there is a grain size dependency on the strength and ductility of metals and alloys according to the Hall-Petch equation, but this does not apply in the case of single crystal test specimens. Nix reports on the work of Julia Greer and co-workers (J R Greer et al, Acta Mater. 53, 1821, 2005) on simple uniaxial compression testing of small sub-micron pillars, 400nm diameter and 1960 nm high, of single crystal gold, oriented in the <001> direction, which are made by focused-ion beam machining. These tests show very high levels of flow stress – over 500 MPa compared to around 30MPa for bulk gold. Reducing the pillar diameter to 290 nm increases the flow stress to around 750 MPa. Truly amazing values in my opinion.
The reason for the jerky stress-strain curves and high flow stress values seen in these experiments were explained in terms of old literature reports from the 1950s/60s (i.e. ‘learning from old lessons’) on how dislocations multiply, i.e. from other dislocations. Nix comments that if the pillar diameter is smaller than the characteristic dislocation length for multiplication, we can expect moving dislocations to exit the crystal more frequently than they multiply. Nix argues that in such situations, the crystals harden by a ‘dislocation starvation’ mechanism; here, plastic deformation is controlled by dislocation nucleation, which requires very high stresses. He also states that this mechanistic theory is hotly debated and disputed by others. Nonetheless, the high strength values are not in dispute!
It is interesting to speculate how one might make use of this phenomenon in real engineering materials. Anyone got any bright ideas for nano-engineered gold?
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March 2nd, 2009
New patent on Colloidal Gold Production
Colloidal gold is routinely manufactured by many precious metal companies by a process based on the ancient Purple of Cassius route (see L B Hunt, Gold Bull, 9 (4), 24-31, 1976) but with process improvements to give more consistent processes and products. For example, it is used to produce colloidal gold pink enamels for the decoration of pottery and as biomedical diagnostic agents.
The classic Gold Bulletin papers by Turkevich (Gold Bull, 18 (3) 86-91 and 18 (4), 125-131, 1985) describe the process chemistry and properties of the colloids produced. Properties are dependent on colloid particle size but a problem is that it is difficult to produce colloids to a defined particole size in practice at the commercial scale.
Aimed at use as an in-vitro diagnostic agent with improved sensitivity and reliability, a new European patent application from Tanaka KK, Japan, EP2027956 (A1), was published on 25th February 2009. This is aimed at producing gold colloids with a targeted particle size, a sharp size distribution and a uniform, perfectly spherical shape. This process differs from the traditional ones in that it comprises several steps: a nucleation step and one or more subsequent growth steps, each of which involves additions of gold salt solution and reducing agent to the original nucleation solution. In the nucleation stage, a citrate is used as the reducing agent, whereas an ascorbate is used in the growth stages as the reducing agent. The number of growth steps controls the size of colloidal particle attained. The amount of gold salt and ascorbate added in each of the growth stages is defined in terms of a formula related to the number of gold atoms deposited. This method is claimed to produce spherical gold colloids in the size range of about 17 – 220nm plus with a particle size distribution having a standard deviation of 10% or less.
It would be interesting to see how this multi-step approach might be applied to gold catalyst production where nanosized gold particles of tightly controlled size are critical to catalyst performance.
Chris Corti
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