Polythermal methods

C, polythermic method, measured range 20-79.5°C, Udovenko Aleksandrova 1963)... 

Polythermal methods. The temperature of an alloy sample is progressively changed, generally at a well-defined and controlled heating or cooling rate, as some properties of the sample itself are continuously measured. 

The so-called synthesis methods of solubility determination involve the preparation of a solvent-solute mixture of known composition, initially containing excess solute. The complete dissolution of the sohd phase is then observed, either when the mixture is subjected to slow controlled heating (the polythermal methods) or at constant temperature when small quantities of fresh solvent are sequentiahy added over a period of time (the isothermal methods). The disappearance of the sohd phase can be observed visually or monitored by recording some appropriate physical or physicochemical property of the system. 

A standard visual polythermic method and No information is given. ... 

A visual polythermic method (1) was used as well as an isothermal method which involved conductivity measurements. Standard methods of analysis were used but no specific details are given. 

A visual polythermic method (1) was used.. No other details are given. 

A visual polythermic method was used. The isotherms were obtained by interpolation. No details are given. 

For the systems in which the trihydrate or the anhydrous salt was the solid phase, the solubility was determined by evaporating the solution to dryness. Where the hexahydrate was the solid phase, a visual polythermic method was used. Analyses were carried out gravimetrically K O was determined as KCIO P2O5 was determined as Mg2P207l and water was determined by weight loss during calcination. 

Twelve parts of the system were studied by using a visual polythermic method. The cooling agent was solid carbon dioxide, either alone or with acetone. 

A visual polythermic method was used in the temperature range of -20 to +20°C. The disappearance of the last crystal was observed. The mixtures were prepared by weight and heated, while being stirred, at a rate of 0.5 deg/min. The analyses have been described elsewhere (1). 

Polythermal methods have in common that a suspension containing known amounts of solvent and solute in excess is heated and the temperature where last particles dissolve is detected. For detection, visual observation (e.g., under a microscope), turbidity measurements, particle-detecting inline probes (e.g., FBRM probe (Lasentec , Mettler Toledo GmbH)), or calorimetry may be used. Since it is a dynamic method, the results depend on dissolution kinetics of the particular system. In general, polythermal measurements are easier to automate since just a temperature has to be followed and no special analytical technique is required. The above-mentioned Crystall6 multiple reactor system can also be used to perform such kind of measurements. To detect both the dissolution process for derivation of saturation temperatures (clear points) and the formation of particles (cloud points) for determination of the metastable zone width, the... 

Due to equilibrium constraints, polythermal methods typically do not reach the accuracy achievable with isothermal measurements, but provide first information about the general dissolution and recrystallization behavior of a substance. In addition, the identity of the soUd phase for which the solubiUty is measured cannot... 

For the growth of a solid phase with variable composition, or to control macroscopic dopant or impurity distribution, the classical works on crystal growth apply a distribution coefficient term. The difference between a solid solution and a doped crystal is that the term solid solution is restricted to members of an isostractural series whereas dopants may differ a great deal in structure from the host. If polythermal methods are used, the resulting crystals will normally be inhomogeneous, and exceptions to this rule require rather unusual conditions. 

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