Treating stone to save Maltese Culture

Malta has three UNESCO world heritage sites which need constant conservation. Generally, it is better to preserve the original building material than replace it. The conservation method called consolidation can glue deteriorating stone material to the underlying healthy stone maintaining it, but few consolidants have been tested on local Globigerina limestone. Sophie Briffa (supervised by Daniel Vella) tested a new set of consolidants which are stronger than other compounds but affected the colour of the stone. She applied five different conditions on the stone. The first three were novel treatments. They were based on a hybrid silane (tetraethylorthosilicate (TEOS) and 3-(glycidoxypropyl)trimethoxysilane (GPTMS)) but one had nanoparticles, one had modified nanoparticles, and the other lacked them. The fourth was a simple laboratory-prepared TEOS silane. The fifth was untreated limestone samples for comparison.

The treatments successfully penetrated the stone’s surface. Microscopy coupled with other techniques including mercury intrusion porosimetry carried out in Cadiz, Spain, confirmed this infiltration and the stone’s physical qualities: strength, drilling resistance, and so on. Half of the treated stones underwent accelerated weathering. The consolidants with nanoparticles or modified nanoparticles were stronger than the other treatments. They also maintained the original surface colour and improved the stones’ ability to absorb water. On the other hand, they were less resistant to salt crystallisation that can damage the stone making it brittle.
The best consolidant for Maltese stone has not yet been found. Ideally, it should have a good penetration and good weathering properties that preserve the stone’s appearance. It should allow ‘breathability’ and be reversible. Current stone consolidation techniques are irreversible since they permanently introduce new material into the stone. These are only acceptable since consolidation is a last attempt to save the stone before complete replacement.

French writer Victor Hugo summed up the importance of this research when he said, ‘Whatever may be the future of architecture, in whatever manner our young architects may one day solve the question of their art, let us, while waiting for new monuments, preserve the ancient monuments. Let us… inspire the nation with a love for national architecture’.

This research was performed as part of an M.Sc. in Mechanical Engineering at the Faculty of Engineering. The research was funded by the Strategic Educational Pathways Scholarship (Malta).

Titanium: Smoother and shapelier

Electron Beam Melting (EBM) is a state of the art manufacturing process. Using this process product designers will be limited only by their imagination. This technology uses an additive manufacturing approach where parts are built layer by layer — think of ‘3D printing’. It can use exotic metals like titanium alloys, however it does have limitations such as producing a rough surface finish that hampers its functions.

Christian Spiteri (supervised by Dr Arif Rochman) investigated whether the Electric Discharge Machining process can be used to finish parts produced using EBM to give a smooth surface (difference pictured). He treated titanium products with the Electric Discharge Machining process and microscopy showed that the finished surface consists of a set of micro-craters instead of rough grains. By adding the finishing process, more complex geometries could be created. Overall, adding Electric Discharge Machining to EBM had many benefits.

Dr Arif Rochman (University of Malta) said, ‘EBM parts can be used for a wide range of applications such as implants in the medical sector or complex tool inserts, […] which cannot be manufactured using conventional methods. Understanding the synergy between both processes is a must for product designers and process engineers to be able to manufacture high quality EBM products.’

 This research was performed as part of a M.Sc. (Res) in Mechanical Engineering at the Faculty of Engineering. This research was partially funded by the Strategic Educational Pathways Scholarship (Malta). This Scholarship is part-financed by the European Union – European Social Fund (ESF) under Operational Programme II – Cohesion Policy 2007-2013, ‘Empowering People for More Jobs and a Better Quality Of Life’.