Glass
The advantages of platinum and its alloys
Glass is made by melting minerals such as silicates and soda ash at temperatures up to 1700oC. Platinum and platinum alloys are used in the fabrication of vessels that hold, channel and form the molten glass because platinum's high melting point, strength and resistance to corrosion allow it to withstand the abrasive action of molten glass. Unlike base metal alloys, platinum and platinum alloys do not react to glass, nor do they oxidise or scale at high temperatures. Rhodium is alloyed with platinum in various proportions from 5% rhodium up to 30% rhodium. The addition of rhodium increases the strength of platinum alloy equipment and extends its life. Platinum equipment is used in a large range of glass products, the most important of which are outlined below.
Reinforcement glass fibre
The largest amount of platinum in use in the glass industry is for the production of textile glass fibre, commonly referred to as reinforcement fibre as it is mainly used for strengthening other materials. Its widest application is in glass-reinforced plastics (grp). Glass fibre producers use platinum components to channel the molten glass, but the main use of platinum and rhodium is in the fiberisation process itself. Fiberisation is the drawing of the glass fibres from a platinum alloy container called a "bushing" – a rectangular open topped box, the base of which has many precisely shaped holes, or jets, through which the fibres are drawn.
Liquid crystal displays (LCD)
LCD glass, used in applications such as digital watches and laptop computers, is the most intensive user of platinum and rhodium per unit of glass produced. This is due to the harsh conditions under which the raw materials for the glass are melted (usually at 1650oC) and the quality of glass required, which can be as little as half a millimetre thick and demands zero defects.
Cathode ray tube (CRT) displays
CRT displays refer to the monitors commonly used as TVs and visual display units (VDUs) for computers. There are two parts to the glass needed to make the CRT display - the cone glass panel that forms the back of the monitor, and the screen glass panel at the front. Platinum-rhodium alloys are used mainly in the production of the screen glass.
Optical & ophthalmic glass
In order to produce high quality optical glass, platinum equipment is used in the key areas of melting, conditioning and forming. Pure platinum is the preferred material since the use of alloys containing rhodium and, to a lesser extent, iridium, leads to unwanted colouration of the glass.
Container glass
Container glass refers to non-crystal tableware as well as bottles for drinks, jars for foodstuffs and containers for perfume and other items. The extent to which platinum is used mainly depends on the properties of the glass, which vary considerably according to its composition. Generally, the more corrosive the glass, the more platinum is required.
Ceramic glass
Commonly used in applications such as the flat glass surface of electric cooker hobs, ceramic glass has grown in demand in recent years. Large quantities of pgm equipment are used in the production of this type of glass.
Glass demand for platinum since 1975 is estimated in our market data tables.