Das Zustandsdiagramm Calciumcarbid/Calciumoxyd

Abstract

1. Es wurde ein Verfahren zur Bestimmung des Schmelzpunkts von Calciumcarbidpräparaten ausgearbeitet. 2. Die Herstellung von reinem Calciumcarbid aus Calciummetall und Kohle wird beschrieben. 3. Auf Grund der Schmelzpunktsbestimmungen tritt in dem System CaC2/CaO keine Verbindung auf. Das System ist eutektisch, bei Verwendung von Reincarbid mit der eutektischen Zusammensetzung 51 Gew.‐% CaC2 und der eutektischen Temperatur 1830 ± 10°C. Der Schmelzpunkt des reinen Calciumcarbids ist 2160°C. Löslichkeit im festen Zustand wurde nicht festgestellt. 4. Durch die Verunreinigungen des technischen Carbides wird die eutektische Temperatur erniedrigt (z. B. auf 1760°C), die eutektische Zusammensetzung verschiebt sich etwas nach höheren Carbidgehalten (z. B. 51% CaC2, 41% CaO, 8% Verunreinigungen). 5. Mikroskopische und Röntgen‐Untersuchungen bestätigen das Ergebnis.

Thermodynamic evaluation and optimization of the (Ca+C+O+S) system

“…In both cases the CaC 2 was synthesised directly from metallic calcium and carbon. Their measured melting temperature varied between T = (2403 and 2423) K. By taking into account small amounts of impurities, Juza and Schuster [24] assessed the melting temperature of CaC 2 to be T = 2433 K. In the present study, the melting temperature of pure CaC 2 was set to T = 2433 K. The entropy of fusion was set to 25 J Á mol À1 Á K À1 based on the fact that many ionic compounds with a simple cubic NaCl structure (rock salt structure) have a entropy of fusion close to 25 J Á mol À1 Á K À1 at their melting temperature. According to the NIST-JANAF evaluations [6] of thermodynamic data for pure compounds, the entropy of fusion for compounds exhibiting rock salt structure is as follows: NaCl: 26.22 J Á mol À1 Á K À1 ; KCl: 25.18 J Á mol À1 Á K À1 ; NaBr: 25.60 J Á mol À1 Á K À1 ; KBr: 25.34 J Á mol À1 Á K À1 ; CaO: 24.84 J Á mol À1 Á K À1 ; MgO: 24.84 J Á mol À1 Á K À1 .…”

“…The pseudo-binary (CaC 2 + CaO) system will be treated further in Section 4.1.2. In the present study, the measurements of Juza and Schuster [24] and Juza and Bünzen [23] are considered to be the most reliable for the melting temperature of CaC 2 . In both cases the CaC 2 was synthesised directly from metallic calcium and carbon.…”

“…The level of impurities was rather high, mainly originating from ash-components in the carbon, and the experiments were performed with the sample in contact with graphite material in the experimental setup, which can lead to reaction between the sample and the graphite. Juza and Schuster [24] measured the liquidus temperatures of the (CaC 2 + CaO) system using optical pyrometry. They used CaC 2 synthesised from Ca-metal and carbon in an iron crucible.…”

“…Experiments with technical-grade CaC 2 gave lower melting temperatures due to the higher amounts of impurities in the samples. According to Müller [46], the work of Juza and Schuster [24] should be considered to be the most reliable of the phase diagram studies based on both the experimental setup and the purity of the sample material. In the present study, the (CaC 2 + CaO) interaction parameters were also optimized based on the study of Juza and Schuster [24].…”

Pyrometallurgical Treatment of Apatite Concentrate with the Objective of Rare Earth Element Recovery: Part II

“…From Table 3, it is clear that the combined reduction process is highly endothermic, and it was estimated that 2957 kWh/mt would be required to produce 79.0% CaC 2 at 2050°C, which should be sufficiently fluid for tapping according to Fig. 4 [27]. This energy consumption assumed an off-gas temperature of 727°C [29], and a typical large-scale, e.g., 50 MW, furnace with a thermal efficiency of about 92%.…”