DE1922262A1 - Apparatus for determining the melting and solidification point - Google Patents

Description

APPARATUS FOR DETERMINING THE MELTING AND SOLIDATION POINT I Status of technology 1. Definition of the melting and solidification point as well as methods and Apparatus for their determination ii Purpose of the invention III The technical problem and its solution 1. Basics of measurement 2. Apparatus IV work process and examples A. Semi-automatic measurements 1. Execution of the provisions 1.1 Determination of the Freezing point (EP) 1.2 Determination of the melting point (Smp) 2. Measurement results and comparisons with other methods 2.1 Determination of the melting point of uniform substances 2.2 Determination of the melting point of technical products 2.3 Determination of the solidification point B. Apparatus for fully automatic measurement V Significant progress (patentability ) V claim 1. main claim 2. subclaims APPARATUS FOR DETERMINING THE MELTING AND SOLIDATION POINT State of the art 1. Definition the melting and solidification point as well as methods and equipment for their determination The melting point (m.p.) is an important and informative criterion for characterization a substance. For a large number of fabrics and technical products he for the specification and for the control or monitoring of the purity as well as the equality -moderation of production processes used.

The same applies to the solidification point (EP), which is at a height of technical products instead of the melting point. this happens usually when a melting point is determined for experimental reasons or due to the substance is badly possible.

How the melting point is characterized by the temperature at the one substance changes from the solid to the liquid state of aggregation, then applies to pure Substances for the solidification point the reverse definition. The smp and EP are more pure Substances have the same temperature value; in the case of inconsistent substances, the definition depends of the EP (as well as partly of the Smp) on the examination method.

(e.g. "temperature breakpoint" of the cooling curve in EP determination according to Din 51 570) and then often does not coincide with the Smp.

For the measurement of the melting point (m.p.) are depending on the nature of the substances and, depending on the requirements for accuracy, the most varied of methods in Use.

Probably the most frequently used method for uniform substances The determination of the melting point is done in melting point tubes closed on one or both sides Determination made in the Thiele apparatus or according to the improved Method - from Bayer.

There are also a number of not so common methods, some of which are: Kofler - heating bench determination of the "softening point" according to Krämer - Sarnow melting point microscope heating table X mentioned methods 1nd apparatuses partly have a materially differentiated area of application for which they deliver useful values.

For example, according to Krämer-Sarnow, no crystalline ones can be found, according to the @@ microscope heating table method do not examine any wax, fat or resinous products. The Kofler heating bank is open for quick series determinations for a series of @@ can be used, but me @ st only delivers rather imprecise values, some of which differ greatly from the external nature of the sample (fine crystalline, coarse crystalline, powdery, etc.) depend.

) he determination of the solidification point (EP) is carried out for paraffins, waxes, Polyesters and similar products in general according to the standardized Din methods 51 556 (EP on the rotating thermometer) and Din 51 570 (breakpoint method).

In the case of kettles, fatty acids and fat-like substances, the titer is usually the same "(- Freezing point of the fatty acids separated from a fat) determined; and according to Dalican, Shukoff, Wolfbauer or Pinkener.

The EP can only be determined on the rotating thermometer for paraffins and wax-like products and often only provides imprecise and scattering Values, since 1.) the simultaneity of the end point determination and temperature reading is insufficient; 2.) for products whose viscosity increases noticeably before the EP, a reasonably accurate measurement is not at all possible.

.) In the case of products that are more coarsely inconsistent, this inconsistency mostly not recognized and (e.g. by specifying a solidification interval) not is taken into account, but an EP is found that largely depends on the mechanical Properties of the partially crystallized components depends.

tit the temperature holding point method according to Din 51 570 are used with suitable Body classes get good scores. The determination is however something lengthy and a sharply defined breakpoint cannot always be determined.

II Purpose of the invention There, as the examples show, many methods the Smp and EP determinations only have a narrow material scope, in addition, often only provide rough values and usually represent very subjective measurements, would be a more generally applicable, more accurate, and more objective method of determination des Smp and EP of importance.

The following describes a method and apparatus with which the determination of the solidification point as well as the melting point of a large one Kiasse of substances is possible within a short time. The process delivers Values which are usually more precise, and which are particularly suitable for the method Substance classes are even considerably more precise than those with the methods described and apparatuses obtained. Furthermore, with the equipment described below an objective, fully automatic Smp and EP measurement and a fully automatic one The -Smp or EP can be monitored during production processes.

III The technical problem and its solution 1. Basics of measurement The basic part of the apparatus by which the following method applies the enamel - and solidification points have been determined is one of the refractometers commonly used in laboratories With prisms that can be heated and cooled, an Abbé refractometer was used.

As is well known, yeast fractometers are used to determine the indices of refraction and the dispersion of liquids as well as of plastic and solid bodies.

The measurement is carried out by setting a limit line (limit angle total reflection) between a light and a dark field on a cross in the upper field of view of the eyepiece and reading the refractive index on a scale. the The borderline required for the measurement is sharply positioned in the case of transparent ones Liquids easily reached with transmitted light. Not for most of them Solid bodies that have been specially pretreated are obtained with falling through or streaking The incident has no border line at all or just a vague interpretation the same.

At temperatures above its melting point (@@@@ gang @n den @@@ an @ gen @@@ t @ nd) b @@ M @@@ ung @ n @m @ efr @ ktometer in transmitted light a sharp boundary line. If you cool down the @@@@ dance, @@ becomes at Kr @@ tn @@@@@@@@@@@ - b @ w. He @ camouflage point.

the borderline between light and dark field suddenly blurred and more or less disappears, and the contrast between light and dark is largely the same the end. (This phenomenon can be explained by the fact that the change in the State of the substance a smaller part of the light @ according to Snellius' Refraction law is broken and more light is reflected or diffusely scattered) When the substance solidified (or crystallized) between the prisms is heated the borderline reappears at the melting point and becomes sharp.

These observations can be used to determine the melting point or to Use determination of the freezing point.

2. Apparatus 2.1: Abbé refractometer (description under III1) 2.2 Thermostat 2.3 Thermocouple with sensitive millèvoltmeter (with the previous Measurements were made using a sisen constantan thermocouple and sin for different measuring ranges switchable light mark millivoltmeter used) As described under III1 1, the temperature of the prisms has to be varied continuously during the measurements. As the temperature reading but not intended for such a mode of operation in the Abbé refractometer the thermometer in the heating or cooling fluid circuit for the relatively fast ones Temperature changes of the Smp and EP measurements indicate values that differ from the true Temperature of the measuring prism because of the poor thermal conductivity of the glass more or less. For precise and quick Smp and EP determinations is therefore a temperature measurement directly on the prisms is necessary. This was done through Use of a thermocouple achieved. With the provisions below the one flat-filed or hammered-out soldering point directly between the Clamped prisms. A disturbance of the optical image by the used 0.3 mm thick wire and the very small soldering point of the thermocouple did not occur to a noticeable extent.

This type of temperature measurement can hit even when quite frozen Cooling and heating speeds determined the temperature of the Smp and EP especially since thermocouples have a very low inertia.

Apparatus directly for the determination of the melting point and EP according to the above are built according to the principle described, it will be advantageous to thin the belden Wires and the small soldering point either in a fine clue of the prism to cement or her. close under the tile l'rlnmen surface area elnzun @ hmelzen or so to let into a fine hole so that the soldering point is level with the prism surface concludes.

IV Procedure - and working examples 1.) Execution of the provisions 1.1 Determination of the solidification point (EP) The thermostat is connected to the yeast fractometer connected and the Kontaktt @ ermometer screwed up. Then you heat up to elnige Just above the expected EP and brings the required tightness (approx. 10 to 50 mg) on the measuring prism. If you have no clue about the P, then the sample is placed on the prism at a low temperature and heated until the sample melts. The lighting prism is now folded down (with not a - cemented or melted-in thermocouple the measuring soldering point between the prisms is clamped) and the border line is set sharp and on the @@ itte of the @reuzes line.

ilit @helfe the Thermo @ tat water cooling is released relatively quickly - cools and the temperature is noted as the freezing point at which the boundary line of one turns sharply to completely unsharp with brightening of the dark field To improve the accuracy of the result, heat up to about 10 over the temperature value obtained according to the above procedure and then cools slowly (approx. # 1 Degree min.). For substances with a sharp melting point and with a sufficient Sensitive millevoltmeter is obtained in this way with an accuracy a speed of approx. + 0.1 ° C s, the practical work often also proceeded as follows: that the solid sample hits the prism, which has already been heated to above its EP or Smp was given. Although the prism manufacturers from applying cold samples advise against the hot measuring prism, (eventue @ l Bruchge @@ hr), are despite a large Number of visits up to now in no single Pall damage to the prisms it will be necessary to use prisms made of glass types that are less @ sensitive gagen @ emper @ door changes are.

1.2 Determination of the melting point (Smp) The substance is in as possible even, thin layer (@@@@@ crystalline lu @ ver are ground up beforehand) on the Méssprism @@ bra @@@, whereby if the prism is not cemented or melted Thermocouple soldering point this is clamped between the prisms.

Then you heat up relatively quickly (about 4 degrees min.) And make a note @ The temperature as the melting point at which the boundary line becomes sharp.

The recuperation of the ness with that melted under the prisms @robe usually delivers more precise values: @an kü @@ t again until the sample solidifies, heats up quickly to a few @rade below the value found and goes the last 1 - 20 lan @ sam, as indicated under @. @, Higher. The point at which the previously blurred or the borderline that is not visible at all appears sharply, gives the melting point of the substance below.

2.) Measurement results and comparisons with other methods 2.1 Melting point determination of uniform substances In order to be able to compare the measurement results obtained by the refractometer method with the literature values, the melting point determinations of completely uniform organic compounds should be mentioned first. With the conditions observed under IV 1.2, the following values were obtained for the substances below: Table: Melting points of pure organic compounds Substance m.p. (° C) m.p. (° C) Refractometer method literature value Refractometer method literature value p- @ chlorobenzene 53 53.0 Diphenylamine 54 53.8 Dibromobenzene 89 88.9 Benzil 95 95.1 Acetanilide 115 115.0 2.2 Melting point - determination of technical products In addition to many crystalline and powdery substances and wax or ffZtt-like products, plastics with a definable melting point (e.g. also in polien form) can be measured.

If the plastic is in the form of a film, cut a piece of it @b and places it together with the thermocouple soldering point (if this is not in the Prism is smocked or cemented) between the two prisms. The Polienstiick should cover the entire frismatic surface. The temperature at which the initially fuzzy linip of the solid polie becomes sharp when heated, indicates the smp.

2.3 Freezing point - determination l) The freezing point was determined for several Para @ fin and wax types and polyesters. ]) The values obtained in this way were compared with the EP values according to Din 51 570 (breakpoint method), and good matches were found. (Table 2) Table 2 Freezing points of waxes and polyesters (measured according to the conditions given under IV1.1) EP (° C) EP (° C) substance according to Din 51 570 refractometer method Paraffin 1 52.7 52.6 Ozokerite 53.7 53.6 Paraffin 2 53.3 5; .3 Paraffin 3 63.2 63.4 Polyester 1 36.7 36.6 Polyester 2 33.4 33.4 Polyester 5 37.2 37.1 Folyester 4 35.4 35.6 Polyester 5 34.5 34.6 H-) Apparatus for fully automatic measurement The image of the substance transmitted in a light-dark field offers a good basis for evaluation by an objective photometer (light-sensitive cell).

Some methods for evaluating the amplified photometer pulses his listed.

1. Direct recording of the photo voltage curve as a function of the temperature measured by the thermocouple.

Because of the change in the brightness ratios specified under III1 the Smp or EP gives itself to itself through a sudden steep jump in the curve recognize.

In the case of highly inconsistent substances, this photo voltage curve depending on the temperature directly as a characteristic for the melting or solidification behavior and draw conclusions about the degree of purity as well allow for the evenness of production processes.

2. Electromagnetic blocking of a pointer instrument (e.g. millivoltmeter) when a certain (adjustable) light value is exceeded by a "light barrier" 3. Use of temperature recorders, which when an adjustable Limit value by a pulse from the light-sensitive cell the smp or EP temperature record.

This is done using a flow cell on the refractometer a fully automatic smp and EP measurement possible.

4. For measurements on substances, Smp or EP are continuously For example, changes in a production run can be done (as already for the measurement of the refractive index often used) Abbé refractometer with flow cuvettes use.

The flow cuvettes can be used for single measurements (as already described) as well as for series measurements and for continuous production monitoring use. In connection with the photometer-controlled Regiestrier described under B) 3 -devices there is the possibility of continuously referring to a production run the @melting point or the solidification point (and next to it with the same device of the refractive index) and to ensure compliance with tolerance limits check.

V We @ en @@@@ ner progress (atentability) are summarized it is followed by @e @points which measure the Smp and EP of a wide range of substances using the method described and with the equipment described is advantageous let be: 1.) with a pparatiir k; inside in their chemical and.

physical properties very different substances both can be examined for the Smp as well as for the EP.

2.) The measurement results are usually more accurate, especially good substance classes suitable for the method are even significantly more precise than those which are achieved with the conventional methods and @pparaturen.

3.) the time required for the Smp or EP determination with the described Apparatus is needed is usually much shorter than most of the others Methods. Especially for series determinations with similar measurement results the time saving is considerable.

4.) By far most of the Smp and EP determinations are open the observation of criteria instructed such as: deliquescence of crystals (microscope hot stage) Determination of a melting zone (Kofler heating bench start of melting ("sagging") the substance end of the melting process (Thiele and Bayer) o the rotation of a solidifying drop (EP determination according to Din 51 556) Here sharply defined It is often difficult to grasp points because of the peculiarity or external nature many substances make this difficult and every observer different subjectively delusions subject.

The "translation" of the subjective image of substance into the Refractometer to be evaluated always the same straight borderline represents an objectification the measurement. This fact has a very positive effect on the measurement accuracy and the reproducibility of the measurement results.

5.) through an appropriate coupling of the photometer with the temperature-indicating one Thermocouple is a fully automatic '@ melting point and freezing point determination possible; if a flow cell is used, there is also an automatic control and monitoring of production @ processes with the help of @@@ scher Smp - or @@@ - @.) the @ cen @ required amount of substances is less than @@ most other methods ( 10-30 mg). Especially when the thermocouple soldering point is completely flush with the Prism upper-fl @@ he closes (which in an experimental device e.g. by inserting of the thermocouple wire would be reached from above through the lighting prism ) the need for jubilation is extremely low.

7.) the apparatus described makes it possible in principle, very generally, the exact temperature point of the transition of a system with homogeneous optical Objectively determine properties in optically h @ terogenic multiphase systems. Therefore with the basic equipment modified accordingly in individual cases have important measurements carried out.

Examples are: n) aniline or aniline mixing point @) Pour point (A suitable variable cooling can be achieved through the Ultra-cryostats can be achieved).) Determination of the. Molecular weight due to the Freezing point depression. (Cryoscopic method) The determination of the depression of the freezing point with such a small amount of liquid (solvent + substance to be examined ! as required for refractometric measurements, would be a molecular weight determination of the smallest amounts of substances using the cryoscopic method.

Furthermore, solvents could be used with a relatively small cryoscopic Constants, but good solubility properties for the substance to be investigated can also be used when the available amount of substance becomes one Determination by the Beckmann method is no longer sufficient.

@because the total volume of the solution is much smaller than for the Beckmann method can be maintained is a more favorable solution ratio (Solvent substance) w @@@ bar, so that still relatively large freezing point depressions occur although the cryoscopic constant of the solvent is small and the absolute amount of the substance to be examined is low.

@@ Very few solvents are known that at the same time have a great cryoscopic constant and a good one L @ severmögen for organic Have had the ability to use the numerous solvents with smaller compounds cryoscope. Constant but good solubility properties for many compounds Can also be used when relatively little test substance is available is certainly of importance in scientific research.

VI claim

Claims (2)

1. Main claim Manufacture of apparatus after the refractometer -Principle characterized in that special devices for temperature measurement, temperature regulation, light measurement and light registration (based on at III2 and IVB), in addition to determining the refractive index of substances, a fast one and precise measurement of the solidification point and melting point according to the instructions under IV1 2 methods described is possible. 2. Subclaims In particular, the production of equipment of the above type claims, characterized by: 1.) the use of thermocouples or resistance thermometers for temperature measurement directly on or melted down or embedded in the measuring or lighting prism when the temperature changes to Purposes of measuring the Smp, EP and refractive index 2.) the use of electrical Heaters for the prisms in combination with flow cooling instead of the Thermostat heating or cooling 3.) the use of photometers for the purpose of automatic assessment of the change in light or Brightness ratios in the beam of the refractometer at the Smp or El 'determination 4.) the control of temperature recorders, Pointer devices and the like for the purpose of automatic Smp or EP measurement according to the Metboden described under IVB 5.) the use of photometers for Light intensity measurement, which work according to the principle of optical zero adjustment 6.) the use of the construction elements or construction principles described under 1 - 5 in connection with flow-through cells or similar devices that allow Carry out continuous, fully automatic Smp and EP measurements, especially for Purposes of the monitoring of production processes and the purity check or Examination of a. -Maintaining tolerance limits in the manufacture of technical products 7.) the use of the construction elements or construction principles described under 1 - 6 for the production of modifiable apparatus, characterized in that in addition to the determination of the refractive index, the dispersion, the Smp and EP determined further criteria can be caused by similar (as described under V 7) optical changes to make noticable