Standard melting point

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

This is a Basic (Microsoft Quickbasic 4.5) program for shifting x-axis temperature values, based on melting point standards. 

These derivatives are useful both as starting materials for further reactions (see Section 19-18) and for characterization and identification of the original carbonyl compounds. Oximes, semicarbazones, and phenylhydrazones are often solid compounds with characteristic melting points. Standard tables give the melting points of these derivatives for thousands of different ketones and aldehydes. 

Charsley, E.L. Wame, S.St. Warrington, S.B. Thermo-gravimetric apparatus temperature calibration using melting point standards. Thermochim. Acta 1987, 114, 53-61. 

There are several different types of instrument covered under the term DSC, which have evolved from differential thermal analysis (DTA) and measure the temperature difference between sample and reference pans located in the same furnace. This is then converted to heat flow using a calibration factor. A detailed analysis of DSC requires consideration of the various sources of heat loss, and these are generally captured in the calibration routine for the instrument. Absolute temperature calibration is achieved through the use of pure indium (156.6 °C) and tin (231.9 °C) melting-point standards. A comprehensive analysis of the theory of DSC contrasted with DTA may be found in several reference works (Richardson, 1989, Gallagher, 1997). 

Mangum, B. W. and Thornton, D. D., Ed. (1977), The Gallium Melting-Point Standard, NBS Special Publication 481, Government Printing Office, Washington, D.C. 

Mangum BW (1977) The gallium melting-point standard its role in our temperature measurement system. Clin Chem 23 711-718. 

TMA instmments must be calibrated for both temperature and dimensional motion. The temperature is calibrated using the same type of melting point standards used for DSC. High-purity In, Sn, Zn, and A1 are often used. The LVDT is calibrated by using a standard with a well-known linear coefficient of thermal expansion, such as Al. The initial length of... 

TMA instruments must be calibrated for both temperature and dimensional motion. The temperature is calibrated using the same type of melting point standards used for DSC. High-purity In,... 

Suppose that you had calibrated the thermometer in your melting-point apparatus against a series of melting-point standards. After reading the temperature and converting it using the calibration chart, should you also apply a stem correction Explain. 

The choice of material was restricted to those having first-order solid-state phase changes in the appropriate temperature ranges. Melting points were excluded because several types of specimen holders in common use could not retain liquids. A number of recognized melting point Standards (e.g. Pb, Zn) may contaminate thermocouples and sample holders through alloy formation, and decomposition processes were considered to be unsuitable because the atmosphere could not be controlled in many types of apparatus. 

It is not recommended to use metal powders as melting point standards. The specific surface area of such samples is huge, which can affect the melting point. In addition, a considerable amount of metal oxide can be incorporated into the final metal film for the second heating. 

Water and indium are considered the best melting point standards. The leading edges of the melting curves of Sn and Zn are not always straight. 

Several laboratories use gallium (Ga) as a melting point standard, because it is the only available metal standard at around room temperature (its melting point is 29.76 °C). The use of this standard is not recommended, because Ga is toxic, and, in addition, can easily alloy with the material of the aluminum sample pan. 

Figure 3.7 shows the use of both magnetic and melting point standards in a simultaneous TGA/DTA instrument. The melting points were used initially to establish the magnetic transition temperatures for subsequent independent use to calibrate standalone TGA units. Table 3.3 lists some of the recommended materials used to calibrate the temperature axis of TGA instruments. 

Accurate temperature calibration using NIST-ICTA melting point standards (indium, tin, lead, aluminium, zinc of purity >99.999% accuracy to O.DC or better [59]) is essential. Richardson [60] has critically described standardisation and quality assurance of DSC. Much work has been done to implement peak separation software techniques. 

Finally, since the TGA8S1° detects transitions from their temperature lags, events without associated weight loss, such as melting (seen previously) are also detectable This makes true temperature calibration possible with melting point standards. Classically designed systems with itv temperature measurements that do not detect this lag must use other methods described in the ASTM procedure One such method uses a slight... 

The use of TMA (and DMTA) to measure the properties of thin films and fibers is growing. TMA can be used, for example, to observe the effects of processing on specimen dimensions (e.g. shrinkage and anisotropy) and transition temperatures. As these properties are often measured with long specimens in a tensile arrangement, a new type of temperature calibration may be required. Although no ASTM test method exists for such a purpose, Moscato [3] used indium and lead foils as melting point standards at a... 

Figure 3.23 Temperature calibration by measuring ferromagnetic materials in a magnetic field (above) and using the DTA signal of pure metal melting point standards (below).

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