Improving the Tribological Properties of Technical Polymers with Metal Sulphide Compounds

Technical thermoplastic materials (e.g., PEEK, PPA and POM) are widely used for tribological applications combined with different filler systems (e.g., glass- or carbon fibres) because of their excellent mechanical properties. The friction and wear behaviour of thermoplastics can be specifically improved by solid lubrication systems such as graphite, PTFE and MoS2. Besides these systems, others such as WoS2 and MnS are becoming scientifically interesting. This work investigates the influence of different solid lubricants—alternative metal sulphides and polymer-based—in combination with different glass fibre contents on the tribological behaviour of unfilled PEEK and glass fibre-filled PPA. For this purpose, compounds were produced and injection-moulded into tribological test specimens that were subsequently tested. It is particularly evident for both matrix materials that the solid lubricant SLS 22 shows a 25% wear rate reduction when compared to MoS2 and, in addition, the proportion of fibre content in PPA shows an additional wear rate reduction by a factor of 10. The friction level could be kept at a similar level compared to the usually utilised solid lubricants. The investigations showed the potential use of metal sulphide filler systems in high-performance thermoplastic with enhanced tribological properties as alternatives to the well-established solid lubricants.

An Overview of Calcite Recovery by Flotation

In general, precipitated calcium carbonate (PCC) is used as a mineral filler in paper industries; while natural calcite (CaCO3) ore is also suitable for industrial use if it is a finely ground high-grade material. Naturally, calcite is found in the form of high- or low-grade ores and it is one of the most widely distributed industrial minerals on the earth’s crust. However, it is rarely found in its pure form and is generally associated with other gangue minerals; the type and percentage of which vary from one deposit to another. These minerals are generally separated by flotation and/or magnetic separation (in the case of iron impurities). Calcite ores typically contain metal sulphide, silicate, or other calcium-containing impurity minerals, which can be removed by flotation. A tremendous amount of research has been performed on refining the flotation process for calcite ores and designing the reagents (specifically, collectors) to increase the efficiency of the process. Metal sulphide/silicate impurity minerals can be removed by the froth-flotation process using amines and xanthate collectors. Alternatively, fatty acids are used as collectors to float calcium-type minerals directly from the ore. This paper reviews the industrial practices and fundamental research related to collectors surrounding calcite ore flotation. This article presents and reviews collectors for the beneficiation of high-grade calcite ores which have been reported in the literature in order to assist judicial choice of collecting agents in flotation.