Ali Osman Kurt

Carbothermal reduction and nitridation of quartz mineral for the production of alpha silicon nitride powders

In this study, α-Si3N4 powder was produced by carbothermal reduction and nitridation (CRN) of quartz from Can-Canakkale. Carbon with a specific surface area of 110 m2g−1 and quartz powders were mixed then the powder mix was placed in an alumina tube furnace and reacted in between 1300-1500°C for 4 hours under nitrogen flow. The quartz powder was carbothermally reduced and nitrided to form silicon nitride powders. XRD results showed that the reaction product was mainly α-Si3N4 and contained some β-Si3N4 and residual quartz. In order to reduce amount of unreacted quartz, the raw materials mixture was grinded either with carbon black or with no carbon. After CRN reactions of separate grinded quartz powders with carbon, residual quartz was disappeared, reaction temperature was decreased and α-Si3N4 rate was increased. Hence, a better mixing of carbon and fine silica enhanced the α phase formation. SEM images and XRD pattern showed that sub micron particles (0.6–0.87m), high α-phase content Si3N4 powders can be produced at 1450°C for 4 h in flowing nitrogen gas during the CRN process.

Sintering and aging behaviours of Al4CuXMg PM alloy

Sintering and aging behaviours of Al–Cu–Mg powder metallurgy (PM) alloy produced from elemental powders were examined. After evaluating results from thermal analysis, tests were carried out on Al–4Cu alloys with magnesium contents of 0.5, 1 and 2 wt-% and it was found that additions of 1 wt-% Mg was most effective for enhancing the transverse rupture strength (TRS) of the Al–Cu PM alloys for both as sintered and after a heat-treatment conditions. Grain size reduction in the range of 14–45% was achieved by adding magnesium into Al–Cu system. Analyses showed that produced alloys were composed of Al, Al2Cu, Al2CuMg and Al7Cu2Fe phases. Differential scanning calorimeter and dilatometer analyses revealed that alloys show swelling behaviour after the eutectic melting reaction at 548°C and swelling rates increasing as a function of magnesium content. Both high hardness value (120 HB) and TRS (650 MPa) were achieved via aging of Al4Cu1Mg alloy for 24 hours.

Production of Sinterable Si3N4 from SiO2-Li2O-Y2O3 Mixture

In this study, fine grained SiO2 was exposed to CRN, and then Si3N4 ceramic powders were produced. Initially, 5 wt% Li2O–5 wt% Y2O3 (based on the final product) and carbon black were added to SiO2, and then powder samples were processed to carbothermal reduction for 3 hours at 1,450°C and 1,475°C under nitrogen gas flow (1 lt/m). In order to burn the access carbon, the powder samples were held at 900°C for 1 hour in furnace atmosphere. Having completed to Li2O and Y2O3 added Si3N4 powders, these were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS) methods. In addition, the values of wt% α-Si3N4 were estimated from XRD peak heights. The optimum temperature and holding time were determined for the best Si3N4 transformation process.

Effects of Sintering Temperature and Time on the Properties of Al-Cu PM Alloy

Abstract Aluminium-based powder metallurgy (PM) alloys have a number of advantages over cast and wrought aluminium alloys. These PM alloys can be produced using either prealloyed or elemental premixes, with the latter offering a longer die life because of their softer nature compared with prealloyed powders. It is found that the use of an Al-Cu premixed PM alloy gives green density values higher than those of Al-Cu prealloyed systems reported in the literature. Most commercial aluminium PM alloys and alloy developments are based on the Al4Cu system. The amount of liquid phase has significant effects on the microstructure and the mechanical properties of sintered products. Lack of a liquid phase results in inadequate mechanical properties, while an excess of liquid phase causes distortion and shape deformation of the compacts formed by sintering. The objective of this study is to determine the properties of an Al4Cu PM alloy produced using an elemental premix. The effects of the amount of liquid phase on microstructural features and mechanical properties are assessed through thermal analyses. It is found that the optimum transverse rupture strength is obtained by sintering at 600 °C for 2 h.

From Earth Minerals to Nitrides

Structural ceramic parts such as those made from Si3N4 or SiAlONs are promising for considering them in replacing metals in the areas where harsh environmental conditions like abrasive corrosion under high stresses along with high temperature effects are dominant. A widespread use of these ceramics depends on the ease of finding them with low cost. This paper highlights some important points on the low cost production technique of Si3N4 or SiAlON ceramics in powdered form via carbothermal synthesis technique using minerals in the light of the current and previous works. The technique gives flexibility of controlling production parameters that affect on the yield and quality of powders produced. A special account is given to the effects of reactants on the production of such ceramic powders. After synthesising ceramics in powdered form, some comparisons were made on the characterisation of the products of homemade ones with that of commercially available ones. After successful experimental works, a raw material of orthoclase clay mineral exhibited a high transformation potential to a mixture of Si3N4 and SiAlON type ceramic powders.

Transformation Potential of Kalemaden Clay – 220 to Technological Ceramics

In this study, the Clay – 220 mineral of Turkish origin from Kalemaden A.S., having a composition of the quarts, kaolinite, feldspar and the others with the weight percent of 36.20, 12.66, 48.03 and 3.11, respectively, was used as a raw material to investigate its transferability potential to a technological ceramic. The mineral was in the form of conglomerate rocks, which were prepared in the consecutive mineral processing procedures before taken it to the stage where carbothermal reduction - nitridation (CRN) was performed in an atmosphere controlled environment. Various process parameters, i.e., temperature, time and N2 – flow rate were tested in order to optimise the CRN process. SiAlON was formed at temperatures as low as 1300oC and its content increased with reaction temperature up to 1475oC. Above 1425oC, SiC becomes more predominant phase in the powdered product after CRN. Fine powders formed at temperature of 1350oC, which is the lowest value reported among the current literature, contain single crystalline phase of β-SiAlON. The results indicated that the best transformations and yield to the SiAlON ceramic were occurred on the previously prepared Clay – 220 samples in powder form that were processed at 1350oC for 6 hours with nitrogen flow rate of 1 lt/min.