Heating of steels under pressure treatment. Temperature range of brittleness. Metric and SI
Plasticity called the ability of the metal deform without breaking under load .
At tensile test plasticity is determined by two values: relative elongation and relative contraction.
In order to understand how these values are determined, the sample should be compared with the destroyed sample before testing, as is done in Fig. 22 (above). After destruction, the sample turned out to be longer, but it narrowed, especially at the site of neck formation.
Relative extension determines by what amount the sample has elongated after stretching in relation to the original length.
This value is denoted by the letter δ (delta) and is expressed as a percentage:
· l 0- the initial estimated length of the sample in mm;
· l- the final value of the effective length in mm.
The tensile strength is defined as
Relative contraction characterizes the degree of reduction in the cross-sectional area in the neck.
This value is denoted by the letter φ (psi) expressed as a percentage:
· F0- original area mm 2;
· F- area in the neck mm 2 .
Usually mechanical characteristics of metal at high temperatures, reaching the melting point, determined on special installations, including a heating device that simulates the temperature cycle of welding, and a mechanical part and equipped with recording devices.
The specimen to be tested is heated to a temperature at which its properties are to be determined and loaded by recording the curves P = f(T).
On fig. 12.39 shows typical curves characterizing the change in the strength and ductility of alloys at high temperatures. In the region of heating to temperatures close to the equilibrium solidus temperature (Tc), the strength and ductility of the alloys drop sharply.
Plasticity remains at a very low level in a certain temperature range, and then rises again.
Such an ambiguous change in properties can be explained by considering the process of metal crystallization from a liquid state.
After melting, the metal under study is cooled and, starting from the temperature T, solid phase nuclei are formed in it. As long as the amount of the solid phase is small, the metal is in a liquid-solid state, the plasticity of the melt practically does not differ from the plasticity of the liquid, since the crystals of the solid phase move freely in the liquid, without limiting its ability to flow and take any shape (Fig. 12.40 , a). The metal is able to take a new shape under the action of a load without collapsing.
Starting from a certain temperature, called the temperature of the upper limit of the brittleness interval (T VG), the metal passes into the stage of a solid-liquid state, characterized by such an increase in the amount of the solid phase, in which the ability of the liquid to flow between the hardened grains decreases sharply.
During deformation, the grains are wedged, and the further process becomes possible only in the case of plastic deformation of the grains themselves or their displacement relative to each other.
However, the strength of the crystallized solid phase during this period is much greater and, therefore, if destruction occurs, it occurs along the grain boundaries, i.e., it has an intercrystalline character.
The ductility of a metal at this stage of solidification is very small - fractions of a percent. The metal is capable of taking a new shape under the action of a load with destruction along the grain boundaries, including eutectics, the strength of which is lower than the strength of the hardened grains.
With a further decrease in temperature, the strength of the interlayers increases, their volume decreases, and the number of contacts between grains increases. At the same time, the strength of the grain boundaries themselves also increases. At a certain temperature, the boundaries are strengthened so much that the destruction begins to pass not through them, but through the body of the grains themselves (point A).
At the same time, the plastic properties of the material increase, since the deformation is no longer concentrated in small interlayers between the grains, but is perceived by the entire aggregate fairly evenly.
The temperature of a sharp increase in plastic properties is below the equilibrium solidus temperature and is called the lower brittle limit (T NG).
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1 kelvin [K] = 1 degree Celsius [°C]
Initial value
Converted value
Kelvin degree Celsius degree Celsius (centigrade) degree Fahrenheit degree Rankine degree Réaumur
Metric and SI
Learn more about Temperature Difference and Temperature Difference Converter
General information
This temperature difference converter differs from the temperature converter in that here you can compare the temperature interval in different scales. For example, in a temperature converter, 5 °C = 41 °F, and in this temperature difference converter, an interval of 5 °C equals an interval of 9 °F. That is, if, for example, the temperature is increased from 0 °C to 5 °C, then on the Fahrenheit scale it will rise from 32 °F to 32 + 9 = 41 °F. Similarly, a temperature difference of 100°C is equal to a difference of 180°F, so if you raise the temperature from 0°C to 100°C, it will rise from 32°F to 32 + 180 = 212°F in Fahrenheit.
In everyday life, in nature and in science and technology, temperature differences and temperature intervals are of great importance. For example, in climatology, they monitor changes in the difference between average annual temperatures, temperatures at certain times of the year, and other weather features. This helps to identify changes in climate patterns, such as those caused by global warming. In cooking, food undergoes heat treatment and the temperature ranges within which foods are heated affect the taste and whether microorganisms dangerous to humans can be destroyed at such a temperature. In nature, the temperature ranges of a substance affect its state of aggregation. These are not all examples where temperature difference plays an important role, but this article describes the last two examples with cooking and aggregate states of substances.
Change in the state of aggregation of matter
For each substance, there are temperature intervals at which it is in one of three states of aggregation - in a crystalline form, in the form of a liquid, or a gas. The temperature at which solids become liquid is called melting point, and the temperature at which a liquid evaporates and turns into a gas is called boiling point. The temperature range for each state of aggregation, as well as the melting point and boiling point, depend on pressure. We usually talk about the boiling and melting points for normal atmospheric pressure. In this case, the boiling point is called normal boiling point, and the melting point is called normal melting point.
At sufficiently high temperatures, substances acquire special properties - liquids and gases in this case behave in the same way. This state is called critical point.
Usually, substances in the solid, liquid and gaseous state exist at certain temperature ranges and a certain pressure, but sometimes a change in the state of aggregation occurs at other temperatures. For example, liquids often evaporate at temperatures lower than their boiling point. Such evaporation is a slower process compared to evaporation during the boiling process.
pressure and boiling water
Many people know the freezing and boiling point of water at normal atmospheric pressure. Normal melting point of ice (and freezing of water) - 0°C (32°F), and the normal boiling point is 100°C (212°F).
When climbing peaks, climbers are often at low atmospheric pressure. Under these conditions, water boils at lower temperatures. The boiling point drops 1°C every 285 meters (935 feet). For example, at the top of Everest (8,848 meters or 29,029 feet), water boils at 71°C (160°F). At high altitudes, you have to cook food longer or use portable pressure cookers - they reduce the cooking time, as the pressure in them artificially increases, and with it the boiling point rises.
The boiling point of water at a certain pressure is the maximum temperature that water can reach under those conditions. That is why altitude and, accordingly, atmospheric pressure, primarily affect cooking with water, such as boiling. The maximum air temperature is not affected by pressure, so "dry" cooking methods, such as baking, are practically no different from cooking at sea level.
An increase in pressure, on the contrary, raises the boiling point of water, making it higher than 100°C (212°F). This greatly speeds up the cooking process. Pressure cookers work according to this principle - the steam generated during cooking remains inside, thereby increasing the pressure and, accordingly, the temperature.
Temperature difference and temperature intervals in cooking
In cooking, temperature ranges are very important, as the choice of temperature during cooking affects its texture and taste. Temperature has a particularly strong effect on proteins found in foods, as proteins behave differently at different temperatures. At room temperature, the protein molecule is twisted into a ball, and keeps its shape due to chemical bonds within the molecule. As the temperature increases, these bonds weaken and the molecule gradually unwinds and straightens. This affects the taste, consistency and texture of the product. This process is called protein denaturation or coagulation. If the temperature is raised even higher, then the untwisted molecules combine with other molecules and further change the structure of the protein. So the products acquire the “ready” taste familiar to us. This process is affected not only by the temperature, but also by the cooking time. Denaturation can also occur as a result of the contact of proteins with acidic foods.
egg cooking
If you boil or fry eggs at a temperature 63°C to 65°C (145°F to 150°F), then gradually they begin to thicken, as the process of denaturation of the proteins contained in them begins. For some recipes, eggs are cooked at this temperature to produce a semi-liquid yolk and a slightly more liquid white. Soft-boiled eggs, as well as onsen-tamago (from the Japanese “hot spring egg”) of a similar consistency, are prepared in this way. Onsen-tamago was originally cooked in hot springs in Japan, hence the name. They are usually served for breakfast along with rice, miso soup, baked fish and pickled vegetables.
Eggs harden at temperatures between 70°C and 73°C (158°F and 165°F). If you cook them for a long time at a temperature 100°C (212°F) or higher, they lose their softness and become "rubber".
meat cooking
The chemical reactions that occur in meat proteins during heat treatment change its color. The degree of readiness of meat can also be determined by the temperature at which it was cooked. Often, a food thermometer is used to determine the readiness of meat. This is especially useful when cooking thick cuts of meat such as roast beef, roast meat, or poultry. In this case, it is important to measure the temperature inside the meat, and not on the surface, since the inside warms up more slowly than the outside, and its temperature is always lower.
At 50°C (120°F) meat becomes pinkish or white. If you cook it at a lower temperature, from 46°C to 49°C (115°F to 120°F), you get extra-rare, blue or bleu meat fried on the outside and raw on the inside. If the temperature inside the meat has reached 52°C to 55°C (130°F to 140°F), you get meat "with blood", also known as rare or saignant.
As the temperature increases, the meat will brown and brown, especially from the interval between 55°C and 60°C (130°F and 140°F). At this temperature, the meat turns out to be medium raw, that is, medium rare, or à point. The color of the meat darkens as a result of the oxidation of iron, which is contained in the proteins of muscle tissues. At this stage of cooking, the meat releases juice and its structure begins to change.
As the meat heats up 70°C (160°F), it becomes softer as the molecules of collagen, the substance that is responsible for the structural strength of the meat, are gradually destroyed. During this process, collagen is converted into gelatin. Since this is a long process, tough meat, such as meat with muscle tissue that has been heavily used by the animal, or meat from old animals, is best cooked for longer. To make the meat softer, it can also be cut into small pieces. The temperature in the reduced piece rises faster and helps speed up the process of converting collagen to gelatin when exposed to temperature.
If you cook meat at very high temperatures 140°C to 150°C (285°F to 302°F), then a brown crust is also formed, but this is not due to oxidation. In this case, the chemical Maillard reaction occurs - the reaction between amino acids and sugars. It changes the taste of meat and other foods to the familiar "fried" or "baked" taste, and makes the surface of meat and other foods brown. This reaction also occurs in baking bread, making maple syrup, cooking coffee beans, and many other uses.
Meat can turn brown due to another reaction - caramelization. It runs at temperatures between 110°C and 160°C (230°F and 320°F), depending on the sugars contained in the product. During this reaction, the sugars turn brown and take on a caramel flavor. This reaction occurs in any food containing sugar.
food safety
Food is cooked not only to improve its taste, but also to destroy the bacteria in it. If foods are consumed raw (for example, fish in sushi or raw meat), then they are sometimes frozen for the same purpose. Salmonella, which is found in eggs, meat, fish, dairy products, and even some vegetables, can be killed by heating food to between 65°C to 70°C (150°F to 160°F). At 70°C (160°F) these bacteria die instantly, while at lower temperatures the heat treatment must be longer. It used to be thought that you could get rid of salmonella in eggs by simply washing the outside of raw eggs, that is, by making the shell clean. It is now known that salmonella can also infect the inside of the egg, so heat treatment is necessary for safety.
Another microorganism dangerous to health is E. coli. It is found in raw meat, dairy products, vegetables and fruits. Heat treatment at 71°C (160°F) kills this organism.
Salmonella and E. coli can cause an upset stomach, nausea, and diarrhea in a person. These symptoms disappear in many in a week even without treatment, but in some cases the infection is dangerous enough and the patient is admitted to the hospital. In the most severe cases, death is possible. To avoid this infection, you should follow the safety rules and subject food to heat treatment. This is especially important if these products are intended for people at risk: children, pregnant women, the elderly, and those with weakened immune systems. There are so many ways to prepare and process meat, eggs, dairy and other products, so there is always a suitable recipe for even the pickiest person, so it's best not to put your health at risk by eating raw foods.
Pasteurization of foodstuffs can also prevent E. coli and Salmonella infections. During this process, milk, juices and other products are heated to a certain temperature for a set period of time. So, for example, milk can be heated for 30 minutes at 63°C (145°F), 15 seconds at 72°C (161°F) or 2 seconds at 138°C (280°F). During pasteurization, denaturation of enzymes occurs within the microorganisms. In this case, the water in the bacterial cells expands and damages or destroys the walls of these cells. Under the influence of high temperatures during pasteurization, the structure of proteins in bacterial cells changes, as a result, further weakening the walls of these cells. Pasteurization does not kill all bacteria, but reduces their number so much that the likelihood of infection is significantly reduced. Thanks to pasteurization, milk is one of the safest foods when refrigerated and consumed before the expiration date.
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The final structure and mechanical properties of the deformed metal depend on the thermomechanical regime of hot forging, which, along with temperature, is determined by such factors as the degree of deformation, the rate of deformation, and the type of stress state.
The forging temperature range plays the main role here: the maximum heating temperature ensures the highest ductility of the metal being processed, and the minimum forging end temperature prevents undesirable grain growth. The main factors determining the specified allowable stamping temperature range are the chemical composition of the alloy and its physical properties.
The required stamping temperature interval is determined by the time required to perform this operation, and lies within the allowable interval. Sometimes it is advisable to reduce the upper limit of the temperature range due to the need to reduce scale formation or decarburization of the metal.
The hot forging temperature is between the melting and end recrystallization temperatures of the alloy. Near the melting temperature of steel, there is a region of overburning temperatures associated with the melting and oxidation of grain boundaries. Somewhat lower is the overheating temperature zone, which is characterized by significant grain growth. However, the coarse grain structure of most steel grades lends itself well to forging. At the same time, the grain is crushed.
The maximum heating temperature can be in the overheating temperature range, which begins at the critical grain growth temperature.
The establishment of the forging temperature interval is associated with the name of D.K. Chernov (1868), who pointed out that steel should be forged at certain temperatures, which ensure good quality forgings.
For low-carbon steel, the forging temperature region coincides with the single-phase austenitic region and partially extends to the two-phase region, where the free structural component is ferrite.
Hypereutectoid steels are stamped in the austenitic and two-phase regions with structurally free cemetite. Stamping of medium carbon steels should end above the line AC 3 , which provides a stable fine-grained structure.
For mild steel, a lower forging end temperature (between AC 3 and AC 1 ) especially for large forgings.
For hypereutectoid steel, in which the structurally free phase is brittle cementite, the temperature of the end of forging should be as low as possible, and the cooling should be fast to avoid the formation of a cementite network. However, these recommendations are acceptable for steel with a high carbon content, which, due to graphitization, may have a "black fracture".
The maximum forging temperature range for low-carbon steels reaches 600°, for eutectoid steels - 400 ¼ 450°, for hypereutectoid steels - 200 ¼ 300°. For high-alloy and heat-resistant steels, it decreases to 100 ¼ 150°.
The required interval can coincide with the permissible one only in a particular case, if the time spent on stamping is equal to the cooling time of the workpiece in the forging temperature range. Both of these values can vary greatly depending on the complexity of the forging and the pace of work, which depends on the mechanization of the process and the speed of the equipment.
GOST 33454-2015
Group T58
INTERSTATE STANDARD
TEST METHODS FOR ENVIRONMENTALLY HAZARDOUS CHEMICAL PRODUCTS
Melting Point/Melting Range Determination
Testing of chemicals of environmental hazard. Determination of the melting point/melting range
MKS 13.020.01
Introduction date 2016-09-01
Foreword
The goals, basic principles and basic procedure for carrying out work on interstate standardization are established GOST 1.0-92"Interstate standardization system. Basic provisions" and GOST 1.2-2009"Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Rules for the development, adoption, application, updating and cancellation"
About the standard
1 PREPARED by the Interstate Technical Committee for Standardization TC 339 "Safety of Raw Materials, Materials and Substances" based on the official translation into Russian of the English version of the international document specified in paragraph 5
2 INTRODUCED by the Federal Agency for Technical Regulation and Metrology
3 ADOPTED by the Interstate Council for Standardization, Metrology and Certification (Minutes of August 27, 2015 N 79-P)
Voted to accept:
Short country name MK (ISO 3166) 004-97 | Country code by | Abbreviated name of the national standards body |
Ministry of Economy of the Republic of Armenia |
||
Belarus | State Standard of the Republic of Belarus |
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Kazakhstan | State Standard of the Republic of Kazakhstan |
|
Kyrgyzstan | Kyrgyzstandart |
|
Rosstandart |
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Tajikistan | Tajikstandart |
4 Order of the Federal Agency for Technical Regulation and Metrology dated October 21, 2015 N 1611-st the interstate standard GOST 33454-2015 was put into effect as the national standard of the Russian Federation on September 1, 2016.
5 This International Standard is modified from the OECD international document, Test N 102:1995* "Melting point/melting range" (MOD) by changing its structure to conform to the rules established in GOST 1.5(subsection 3.6). A comparison of the structure of this International Standard with that of this international document is given in the supplementary annex DA.
________________
* Access to international and foreign documents mentioned in the text can be obtained by contacting User support. - Database manufacturer's note.
The name of this standard has been changed from the name of the international document to bring it into line with GOST 1.5(subsection 3.6)
6 INTRODUCED FOR THE FIRST TIME
Information about changes to this standard is published in the annual information index "National Standards", and the text of changes and amendments- in monthly information index "National Standards". In case of revision (replacement) or cancellation of this standard, a corresponding notice will be published in the monthly information index "National Standards". Relevant information, notification and texts are also posted in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet
1 area of use
1 area of use
This International Standard specifies methods for determining the melting point/melting range. The methods given in this International Standard can be used for any chemical substance, regardless of its degree of purity.
2 Terms and definitions
In this standard, the term is used with the appropriate definition:
2.1 melting temperature(Melting point): The temperature at which the test substance undergoes a phase transition from a solid state to a liquid state at atmospheric pressure.
3 General
3.1 As a rule, the transition of a substance from a solid state to a liquid occurs in a certain temperature range, therefore, in practice, the temperature of the beginning and end of melting is determined. Ideally, the melting point of a substance is identical to the solidification or freezing point. For some substances (for example, industrial products and mixtures), determining the solidification or freezing point is a simpler procedure. If, due to certain properties of a substance (or industrial product), none of the above parameters can be easily measured, then the pour point (fluidity) is determined.
3.2 The value of the melting point of a substance is significantly affected by the presence of impurities. For this reason, the melting point can also serve as an indicator of the degree of purity of the substance under investigation.
3.3 The choice of a specific test method mainly depends on the state of aggregation of the test substance and the possibility of grinding it.
3.4 A detailed description of the equipment and test methods is given in the standards specified in Annex A. The basic principles of testing are given in and.
3.5 Investigated indicators and units of measurement
The unit of measurement for the melting point in the SI system is kelvin, K. The conversion of temperature values expressed in degrees Celsius to degrees Kelvin is carried out according to the ratio:
T=t+273,15, (1)
where T- thermodynamic temperature, K;
t- temperature, °C.
4 Standard substances
The use of standard substances in all cases when testing a new substance is not required. A list of standard substances used to calibrate equipment is provided in .
5 Method principle
The principle of the method is to determine the temperature or temperature interval of the phase transition of the test substance from a solid state to a liquid state or from a liquid state to a solid state.
6 Comparison of methods
6.1 Characteristics of various methods for determining the melting point (temperature range and accuracy) are presented in Table 1.
Table 1 - Characteristics of various methods for determining the melting point
Temperature range, K | Installed accuracy, K |
|
Capillary/liquid bath | 273 to 573 | |
capillary/metal block | 293 to 573 | |
Kofler heating table | 293 to 573 | |
Determination of melting point under a microscope | 293 to 573 | |
Differential thermal analysis (DTA) Differential Scanning Calorimetry (DSC) | From 173 to 1273 | ±0.5 to 600 K ±2.0 to 1273 K |
Freezing point | 223 to 573 | |
pour point | 223 to 323 |
7 Test procedure
7.1 Capillary tube in liquid bath
7.1.1 Equipment
The test is carried out in the glass apparatus shown in Figure 1. The choice of bath liquid depends on the expected melting point, for example, liquid paraffin can be used for temperatures up to 473 K, silicone oil for temperatures up to 573 K. For temperatures above 523 K, you can use a mixture of three parts sulfuric acid and two parts potassium sulfate (by weight). When using such a mixture, precautions should be taken.
To carry out the test, use thermometers that meet the requirements - or thermometers with characteristics not lower than -. The middle of the mercury bulb of the thermometer should be in contact with the capillary at the location of the test substance sample.
BUT- vessel; AT- cork; With- air valve; D- thermometer; E- auxiliary thermometer; F- liquid carrier; G- a tube with a sample; outer diameter not more than 5 mm; a capillary tube about 100 mm long, about 1 mm inside diameter and about 0.2 to 0.3 mm wall thickness; H- side tube
Figure 1 - Apparatus for determining the melting point
7.1.2 Test procedure
The dry test substance is thoroughly ground and placed in a capillary tube, sealed at one end, so that the filling level is approximately 3 mm after the sample has been compacted. To obtain a uniformly compacted sample, a capillary tube is dropped from a height of approximately 700 mm through a glass tube onto a watch glass. The liquid bath is heated at a rate of about 3 K/min. The contents of the bath must be mixed.
Typically, the capillary tube is placed in the instrument when the temperature of the liquid bath is about 10 K below the expected melting point. From this point on, and throughout the actual melting, the rate of temperature rise should not exceed 1 K/min. At a low rate of temperature rise, finely divided substances usually have the melting stages shown in Figure 2.
Figure 2 - Melting stages of a finely divided substance
Figure 2 shows the following stages of melting a finely divided substance:
- stage A - the beginning of melting, small drops evenly adhere to the wall of the capillary tube;
- stage B - formation of a gap between the sample of the test substance and the wall of the capillary tube due to the compression of the melt;
- stage C - sedimentation and liquefaction of the compressed sample;
- stage D - the final formation of the meniscus of the liquid phase when a part of the sample is in the solid state;
- stage E - the final stage of melting, the absence of solid particles in the melt.
During the determination of the melting temperature, the temperature values at the beginning of the melting (stage A in figure 2) and at the final stage (stage E in figure 2) are recorded.
7.1.3 Melting point calculation
The corrected value of the melting point is calculated from the ratio
T=T+0.00016 (T-T) · n, (2)
where T- corrected value of the melting point;
T- thermometer reading D;
T- thermometer reading E;
n- the number of divisions of the mercury column on the protruding column of the thermometer D(number of divisions on the scale of a standard thermometer between the surface of the heated sample and the level of mercury).
7.2 Capillary tube in a metal block
7.2.1 Equipment
The device for visual observation of the test is shown in Figure 3. The device consists of:
- from a cylindrical metal block, the upper part of which is hollow and forms a chamber;
- a metal plug with two or more holes to allow the installation of capillary tubes in the block;
- electric heating system with adjustable power consumption;
- four windows made of heat-resistant glass on the side walls of the chamber, located diametrically at a right angle;
- an eyepiece for observing the capillary tube opposite one of the windows (the remaining three windows are used to illuminate the inside of the case);
- a thermometer conforming to the standards specified in 7.1.1, or a thermoelectric measuring device with comparable accuracy.
BUT- thermometer; AT- capillary tube; With- eyepiece; D- electrical resistance; E- metal heating block; F- lamp; G- metal stopper
Figure 3 - Apparatus for determining the melting point
7.2.2 Instrument with photodetector
The capillary tube, filled as described in 7.1.2, is placed in a heated metal block. The rate of temperature rise is adjusted to a suitable predetermined linear rate. A beam of light is directed through the sample to a photocell. As the sample melts, the light intensity reaching the photocell increases and the photocell sends a stop signal to a digital indicator that registers the temperature of the heating chamber.
7.3 Kofler heating table
7.3.1 Equipment
The Kofler heating table consists of two plates made of metals with different thermal conductivity. The table is electrically heated and designed so that the temperature gradient is nearly linear along its length. The temperature of the heating table is in the range from room temperature to 573 K. The table is equipped with a graduated temperature scale and a movable pointer.
7.3.2 Test procedure
A thin layer of the test substance is placed on a heating table. Within seconds, a clear dividing line appears between the solid and liquid phases. The temperature on the dividing line is determined by the temperature scale when pointing the movable pointer at the position of the dividing line.
7.4 Microscopic melting point determination
7.4.1 Test procedure
The melting point of the test substance is determined using a microscope, the sample holder of which is a metal plate that is part of the heating chamber. The metal plate has a hole that allows light to enter from the lighting device. The test substance sample is placed on a slide over the opening and covered with another slide to ensure minimal exposure to air. The metal plate is gradually heated until the melting process begins and the temperature is recorded. Measurement accuracy for crystalline substances can be improved by using polarized light.
7.5 Differential thermal analysis (DTA)
Samples of the test substance and the reference substance are simultaneously subjected to an identical controlled temperature program. When the test substance undergoes a phase transition, the corresponding change in enthalpy results in an endothermic (melting) or exothermic (freezing) deviation from the baseline of the recorded thermal curve.
7.6 Differential Scanning Calorimetry (DSC)
Samples of the test substance and the reference substance are simultaneously subjected to an identical controlled temperature program. Record the difference in the energy required to maintain the same temperature of the test substance and the reference substance. When the substance under study undergoes a phase transition, the corresponding change in enthalpy gives a deviation from the baseline of the heat flux curve.
7.7 Freezing point determination
A sample of the test substance is placed in a test tube and continuously mixed. As the sample cools, its temperature is measured at regular intervals. Once the temperature has become constant over several readings (corrected for thermometer error), it is recorded as the freezing temperature. Supercooling should be avoided by maintaining an equilibrium between the solid and liquid phases.
7.8 Determination of the pour point (pour point)
The pour point (pour point) method was developed for petroleum oils and is suitable for the study of oil substances with low melting points. After preheating, the sample of the test substance is gradually cooled and its fluidity is measured for every 3 K decrease in temperature. The lowest temperature at which fluidity of the substance is observed is recorded as the pour point (pour point).
8 Test report
The test report must contain the following information:
- test method;
- chemical identification and impurities (preliminary stage of purification, when carried out);
- the established accuracy of the method;
- melting temperature (average value for at least two measurements that are within the specified accuracy range; if the temperature difference at the beginning and at the final stage of melting is within the accuracy, then the temperature at the final stage of melting is taken as the melting temperature; otherwise, two values \u200b\u200bare recorded temperature; if the substance decomposes or sublimates before melting occurs, then record the temperature at which a similar effect is observed);
- all information and notes relevant to the interpretation of the results, especially with regard to impurities and the physical state of the test substance.
Annex A (informative). List of standards
Annex A
(reference)
ASTM D 97-66 Standard test method for pour point of petroleum oils
ASTM E 324-69 Standard test method for relative initial and final melting points and the melting range of organic chemicals
ASTM E 472-86 Standard practice for reporting thermoanalytical data
ASTM E 473-85 Standard definitions of terms relating to thermal analysis
ASTM E 537-76 Standard method for assessing the thermal stability of chemicals by methods of differential thermal analysis
ANSI/ASTM D 3451-76 Standard recommended practices for testing polymeric powders and powder coatings
BS 4633:1970 Method for the determination of crystallizing point
BS 4634:1970 Method for the determination of melting point and/or melting range
BS 4695:1980 Method for the determination of melting point of petroleum wax (cooling curve)
DIN 51005:2005 Thermal analysis (TA) (Thermische Analyze (TA))
DIN 51421:1972 Determination of the freezing point of aviation fuel, petrol and motor benzenes
DIN 53175:1991 Determination of the solidification point of fatty acids (Bestimmung des Erstarrungspunktes von)
DIN 53181:1991 Binders for paints and similar coating materials, determination of the melting range of resins by capillary method
DIN 53736:1973 Visual determination of the melting point of partially crystalline materials
ISO 3016:1994 Petroleum products. Determination of pour point (Petroleum oils - Determination of pour point)
ISO 1392:1977 Determination of crystallization point. General method (Method for the determination of the crystallizing point)
ISO 2207:1980 Petroleum paraffins. Determination of pour point (Petroleum waxes - Determination of congealing point)
JIS K 00-64 Testing methods for melting point of chemical products
JIS K 00-65 Test methods for freezing point of chemical products
NF T 20-051 Method for determining the crystallization temperature (Methode de determination du point de cristallisation)
NF T 60-114 Paraffin melting point (Point de fusion des paraffines)
NBN 52014 Sampling and analysis of petroleum products: cloud point and pour point limit (Echantillonnage et analyse des produitis de petrole: Point de trouble et point d "ecoulement limite)
Appendix YES (reference). Comparison of the structure of this International Standard with that of an international document
Appendix YES
(reference)
Table YES.1
Structure of this standard | Structure of an international document |
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Subsections | Sections |
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Bibliography | Literature |
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Annex A | List of standards |
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Bibliography
Le Neindre, B. and Vodar B, eds. (1975). IUPAC, Experimental Thermodynamics, Vol. II, Butterworths, London, pp. 803-834. (Experimental thermodynamics) |
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Weissberger, R., ed. (1959). Technique of Organic Chemistry, Vol. I, Part I, Chapter VIII, Physical Methods of Organic Chemistry, 3 ed., Interscience Publ., New York |
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IUPAC (1976). Physicochemical measurements: Catalog of reference materials from national laboratories, Pure and Applied Chemistry, 48, 505-515 |
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ASTM E 1-03 Standard Specification for ASTM Thermometers |
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DIN 12770-1982 Laboratory glassware; liquid-in-glass thermometers; general requirements (Laboratory glass liquid thermometers. General technical requirements) |
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JIS K 8001:2015 General rule for test methods of reagents |
UDC 658.382.3:006.354 | MKS 13.020.01 | ||
Keywords: chemical products, environment, melting point, melting temperature range |
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M.: Standartinform, 2016
