(: September 2002> Quantitative Analysis Technology for Carbon in Refractory Carbonaceous Materials for carbon-containing refractories containing carbon and silicon carbide, such as MgO-C bricks, Al23-MgO-C bricks, and Al23-SiC-C bricks Such as stereotyped refractories and cast iron blast furnace material, shot mud and other monolithic refractories, using gravimetry, gas volumetric method, neutralization titration, condensation gasification method, conductivity method, electricity method, thermal conductivity method, Analytical methods such as the infrared absorption method, the carbon-containing refractories were subjected to quantitative analyses of total carbon, quantitative analysis of free carbon, and quantitative analysis of silicon carbide, and the quality characteristics of the carbon-containing refractories were evaluated.
1 Introduction Carbon-based refractories represented by MgO-C bricks (including SiC-containing refractories) have increased their use in steelmaking production processes. Nowadays, there are a large number of carbon-containing refractories, such as high-quality refractories, which are present in the market. They also include monolithic refractories, such as blast furnace taps and shot screeds, involving a wide range of types. Table 1 shows, as an example, the category classification of mainly carbon-containing refractories (non-fired shaped refractories).
In the case of carbon-containing refractories, how to properly evaluate the quality characteristics is an important issue in management. There have been many reports on the physical properties and microstructure analysis that meet the requirements of the applications. When analyzing the chemical composition of a refractory material, it is usually evaluated by an analysis method classified according to the material. At this time, Si02 is the main body, and whether AI2O3 is the main body, or whether or not Cr203 is contained in silicon carbide (hereinafter referred to as SiC). Chemical decomposition processing steps are also different depending on these compositions. The analytical methods for the main oxide refractory materials were standardized by the IS (Japanese Industrial Standards) very early, but analytical methods for the carbon-containing refractory materials (including SiC) were standardized slowly. Among them, at the Analytical Subcommittee of the Standardization Committee of the Association for Refractory Material Technology, an IS draft was developed in 1995 on the analysis methods for carbon-containing and SiC-containing refractories. In the joint experiment aiming at setting standards at that time, due to many analytical issues, the "Carbon Analysis and Research Association" (hereinafter referred to as the research meeting) was set up in the analysis subcommittee in 1996 and efforts were made to realize the use of refractory materials. Standardization of carbon analysis. Based on the results of these activities, this paper summarizes the quantitative analysis techniques for carbon in carbon-containing refractories.
Table 1 Typical varieties of carbon-containing refractories (non-fired shaped refractories) Refractories Chemical composition/% Alkaline dolomite-carbonaceous 36 Free C secondary refining slag Line magnesium-carbon neutral aluminum-magnesium Carbonaceous secondary refining slag line furnace bottom-Carbon carbide-carbonaceous 5 free C hot metal pretreatment 2 Carbon general analysis principle The analysis method of carbon has long been various. Among them, most of them are gravimetric analysis methods and gas volumetric methods. Table 2 shows a carbon analysis method of a metal material. The general analysis procedure for carbon is to burn the sample in an oxygen gas stream to fully oxidize the evolved gas to become CO 2 gas, which is measured using various detection methods.
However, there are many methods that require skilled operation in terms of analytical methods, and there are also problems such as limiting the range of quantitative concentrations. The current situation is the widespread adoption and application of dedicated analyzers for the combustion industry as carbon analysis instruments for the steel industry.
As an example, a configuration diagram of a carbon analyzer (combustion-infrared absorption method) is shown. The device consists of an oxygen cylinder (A), an oxygen refining section (B, C, D), a combustion tube (E), a combustion gas refining section (F, G), and a carbon dosing section (H).
Problems in Carbon Analysis of Refractory Materials If steel is taken as an example, the carbon content in the steel has a great influence on the quality characteristics of the steel. For this reason, it is generally clear that the analysis is conducted on the basis of precision analysis performed for a micro range that reaches the ppm standard. In the case of steel, since the main component is fixed, the combustion conditions for analysis have been determined.
Table 2 Classification of carbon analysis method Name Analysis method Outline 1 After removing the sulfur oxides and water in the combustion gas by gravimetric method, lime is used to absorb CA, and the mass thereof is weighed.
2 After removing the sulfur oxides in the combustion gas by the gas volumetric method, 0 is collected together with the remaining oxygen gas in a gas measuring tube, and C0 is absorbed by K0H and the like to obtain the volume reduction thereof.
After neutralization titration removes the sulfur oxides from the combustion gases, a certain amount of NaH standard solution is allowed to absorb CCt, and the remaining alkali is titrated with a sulfuric acid standard solution.
(4) After removing sulfur oxides and water in the combustion gas by the condensation and gasification method, CA is condensed and solidified by using a collecting tube cooled with liquid air or the like, and after the remaining oxygen is removed, C2 is vaporized in a certain volume of vacuum. , Measure pressure.
After the sulfur oxides in the combustion gas were removed by the electrical conductivity method, a certain amount of NaOH solution was absorbed into C2, and changes in the electrical conductivity of the alkali solution before and after the absorption were measured.
(6) The coulometric method removes the sulfur oxides in the combustion gas, absorbs a certain amount of weak alkaline solution and absorbs the CQz. The solution is electrolyzed back to the original pH, and the required amount of electricity is obtained.
After the thermal conductivity method removes the sulfur oxides and water from the combustion gas, the synthetic zeolite absorbs C2, heats the trapping tube, desorbs C2, conducts the C2 together with oxygen, and measures the heat caused by CQz. The change in conductivity.
After the infrared absorption method removes the water in the combustion gas, the infrared absorption vessel is guided and the change in the amount of infrared absorption caused by CQz is measured by an integral method or a circulation method.
Schematic diagram of a device for measuring carbon (Resistance Furnace Combustion IR method) In the case of a refractory material, since the main component is not fixed, the combustibility of the material is, of course, inferior to that of the metal. Therefore, for the burning treatment, it is necessary to use a sufficient amount of flux, that is, a flux to reduce the melting point. However, due to the difference in specimens, flammability fluctuations and the like are generated, so that it is disadvantageous in terms of analysis accuracy.
There are other problems with the analysis of carbon-containing refractories. In addition to carbon, there are many materials containing SiC and they need to be quantitatively analyzed.
As an example of an ordinary burning refractories analysis method, stable morphologies are formed due to high-temperature firing. Therefore, in the analysis (chemical analysis) method, even if the finely crushed samples are dried for analysis, no problem. On the other hand, in the analysis of refractories such as carbon and silicon carbide, organic binders and antioxidants may be contained depending on the type. Therefore, crushing and drying processes are also different depending on the material, and care must be taken in handling. .
Statutory (IS) carbon analysis method of ceramic materials As a statutory carbon analysis method for general ceramic materials that are closer to refractory materials, the chemical analysis method for silicon carbide (SiC) materials has been standardized, among which there are silicon carbide powders for precision ceramics. Chemical Analysis (ISR1616), Chemical Analysis of Silicon Carbide Abrasives (ISR 6124).
The chemical analysis method (ISR2011) containing carbon and silicon carbide refractories is based on the carbon analysis method in these standards.
Table 3 summarizes a variety of standard carbon analysis methods such as analysis methods, combustion conditions, and test samples into a comparison table. As an analytical method, the infrared absorption method and the thermal conductivity method are considered to be the main methods in terms of practical use, but in terms of abrasives (R6124), the gas volume method and the electric quantity method are defined.
The R1616 and R6124 standards are all analytical standards for SiC products (raw materials). The R2011 standard is used as an analysis standard for carbon-containing refractories. It is based on materials with a very wide range of composition, and of course, the detailed analysis conditions. It's different.
The analysis of carbon in refractories is based on a general analysis device. The method determined by the use guideline can ensure that the analysis results exceed a certain level. This is based on the premise that the material within the applicable range of the measurement and analysis apparatus is premised, and when the target substance exceeding this range is measured, the use of the apparatus including the material pretreatment operation and the use of a series of users are required. In the end.
Including the seminar's discussion examples, the carbon analysis of carbon-containing refractories was summarized as follows.
Table 3 Comparison of Carbon Analysis Methods (1998) Carbon and (1994) Fine Ceramics Silicon Carbide Fire-resisting Ceramics Silicon Carbide Silica-Grit Abrasives Chemical Analysis Chemical Analysis Chemical Analysis Methodology Carbon for Process Carbon , free carbon, all-carbon, free carbon all-carbon, free analysis project Carbonized carbon, carbonized laurel (1) Combustion (Resistor CD combustion (Resistance (1) Combustion capacity heating) - Infrared method (Burning weight absorption method method) (2 ) Combustion (high-frequency (2) electricity measurement heating) a thermal conductivity method Remarks: Thermal conductivity Remarks: Combustion (high method, infrared suction heating) an infrared absorption method Receiving the whole carbon analysis value Allowed difference Total carbon 0.36 Quantity Method graphite (99.9% with calcium carbonate or known for detection), calcium carbonate or full carbon rate test Samples with known full carbon content of silicon carbide (1) sample simmering, Sn2g mixing 2g mixing Conditions (2) Specimen firing, etc. (1) Combustion capacity method (Combustion weight expulsion combustion-infrared absorption method (or thermal conductivity method) combustion-weight correction method method) Coulometric method Weight correction method Carbon setting allowance Free carbon 0.12 test sample high purity Graphite or known free carbon reference material All-carbon detection line Burning conditions (2) Sample silicon carbide quantitative method Indirect quantitative method (calculation method) Direct quantitative method carbon analysis device of infrared absorption method and thermal conductivity method It has been widely used as a device for analyzing gas components (C, S, 0, etc.) in metals (steels).
In order to accurately analyze the amount of carbon in the carbon-containing refractories having a carbon content of 10% or more by using the analysis equipment having a carbon content of 1% or less (actually, a lower content), it is necessary to use a suitable technique for use. Actually, based on a card survey of the actual state of use of the carbon analyzer performed by each refractory material production company, it has been found that there is a problem of how to maintain the long-term stability of the analyzer in order to perform a high-content carbon analysis.
In terms of specific analysis procedures, it is divided into combustion conditions, selection of measurement samples, free carbon analysis conditions, and the like.
5.1 Combustion conditions The furnace uses resistance heating (tubular furnace type) and high frequency heating.
Since the resistance heating method is easy to control, it can be used for the analysis of total carbon and free carbon. Therefore, the resistance heating method is also used most at the research meeting. The analysis of total carbon generally burns at 1350. As an oxidant, powdered tin (Sn) can be used. Normally, the sample and combustion aid are called a porcelain fire boat, and oxygen is used as a carrier to pass it into a tubular electric furnace to burn it. On the other hand, for the analysis of free carbon, it was 90 (H: it was burned and no combustion aid was used.
In the high-frequency heating system, Cu, Fe, or W (tungsten) can be used as the oxidant, and the sample is weighed into a dedicated high-frequency combustion crucible. This crucible is fixed in the center of the heating coil, oxygen is passed as a carrier, and the sample is burned by a high-frequency current. Photographs of the appearance of the combustion boat and the combustion chamber for carbon analysis are shown.
In any case, when dealing with an actual carbon-containing refractories, the flammability varies depending on the composition range of the target sample. Therefore, it is necessary to confirm the test according to the specified conditions (amount of sample, combustion assisting amount, combustion temperature, etc.) Sample combustion, whether reproducibility of analytical values ​​can be obtained.
Since the carbon analysis using the infrared absorption method and the thermal conductivity method is a relative comparison method for the sample for all-carbon measurement, it is an important problem to determine which sample is to be used for measurement. In the R2011 standard, a test sample for all-carbon analysis is specified, and various samples such as high-purity graphite, calcium carbonate, and a known SiC sample are used. According to the results of the joint analysis, it should be pointed out that since high-purity graphite is weighed in the order of tens of mg, it is easy to produce a weighing error. Determination of the carbon content of the calcium carbonate having a carbon content of at least 10% requires an attention because the volume at the time of weighing is too large. From these points of view, the SiC standard sample having a known content is available as a market product, so it has been an important source of total carbon measurement from an early date.
In the joint experiment when discussing the R2011 standard, many major carbon-containing refractories were quantitatively analyzed for total carbon, but some have not yet been fully analyzed.
At the seminar, conditions including combustion conditions and test specimens were studied, including the use of the device, and efforts were made to improve the analysis accuracy of all-carbon.
In order to verify the accuracy of analysis, SiC raw materials are prepared as more stable standard samples because it is difficult to ensure the homogeneity of the sample due to the presence of pulverized products (brick samples) of actual carbon-containing refractories. In order to achieve this goal, as a standard sample for the measurement of all-carbon analysis for a refractory material, a sample was collectively analyzed at the research meeting and registered.
Free burning temperature for carbon analysis In carbon-containing refractories, there is a problem that should be paid attention in order to analyze the free carbon that coexists with SiC in the material.
As a carbon source, many grades of raw materials such as graphite, SiC, and phenolic resin binder can be used.
To accurately determine the free carbon shared with SiC, hold the combustion temperature.
In the R2011 standard, the combustion temperature condition is defined as 900T, lOmin; the free carbon in the carbon-containing refractories is defined as the carbon insole in which carbon is burned at 900°C.
Regarding the burning temperature of free carbon, there have been various discussions before the seminar. For example, if the free carbon is to be burned more completely, the problem of oxidation of SiC in the combustion process will occur instead. It is also understood what the main material of the refractory material itself is; the effect on the starting temperature of the oxidation reaction due to the particle size of the added SiC material.
In addition, even if the electric furnace is of the same electric resistance heating method, if the temperature measurement position is not correct, there is a possibility that the analysis value of free carbon may be significantly different due to a slight measurement temperature error. Due to the different structure of the resistance furnace, there are subtle differences in the location of the measurement. It is necessary to correctly detect the temperature near the combustion boat. In the joint experiment when R2011 was studied, a combustion temperature of 900 T was set on the basis of the poor combustion of graphite.
If the SiC-based carbon-containing refractories are not included, the effect of the combustion temperature is small. It can be interpreted as a full-carbon analysis value, etc. Using the m-method (900C) for the combustion section 5.4 Free-carbon analysis for the measurement sample Table 4 R11-2 Sample free carbon analysis result / % (mass) * RM-test Materials; ※NIST112b—Test Material (Silicon Carbide); R11 Regarding the combustion temperature of free carbon analysis, it is one of the main topics to determine which sample to use. The combustion cross section of graphite and calcium carbonate at the time of the free carbon analysis by the infrared absorption method is shown. The horizontal axis shows the burning time, and the vertical axis shows the signal intensity of the infrared detector. As can be seen from the figure, there is a large difference in the combustion profile between graphite and calcium carbonate. In a joint experiment in the study of the R2011 standard, a process for measuring free carbon as a refractory material has a process of removing calcium carbonate from the viewpoint of thermal decomposition (combustibility) of calcium carbonate.
At the seminar, in order to verify this problem, it was examined whether or not the calcium carbonate reagent was suitable as a measurement sample for the analysis of free carbon. At the same time, attempts were made to synthesize (adjust) standard samples.
The high-purity graphite, alumina, and silica raw materials were mixed at a certain ratio and mixed with a Heazel mixer to make a synthetic standard sample for a common analysis. Regarding the synthesis of a standard sample, analysis was performed on the premise of changing the combustion temperature. As a sample for measurement, the presence or absence of use was compared. Table 4 shows the results of the joint analysis of the free carbon of the synthetic standard sample R11-2. The total carbon of the R11-2 sample was measured for the first time. Then, the sample for measurement and its combustion conditions were changed and the amount of free carbon was measured. From the results, it was found that the free carbon analysis value of the R11-2 sample showed slightly lower values ​​(tests 1 and 2) under the combustion conditions of 900T and 10 min. For the sake of comparison, when the combustion temperature of the measurement sample and the R11-2 sample were all set at 1×10 and 10 min, the free carbon analysis results were consistent (Tests 3 and 4).
From the results, it is pointed out that the combustibility of the synthetic standard sample under 900 is problematic, or there is a problem with the detection of the combustion gas at 900 T using an infrared absorption device.
With regard to the problem of free carbon measurement samples, no clear conclusions have been drawn at the meeting and it will be a future research topic. 5.5 Analysis of Silicon Carbide Table 5 Carbonaceous Analysis Materials for C, SiC Refractory (RRM1001) Analysis (Assembled)] Approximate Values ​​of Detection Components Carbon Free Carbon After HF Treatment in Analysis of Carbon-Containing Refractories Containing SiC For the SiC content, two methods are specified in the R2011 standard, namely the indirect quantification method and the direct quantification method.
The indirect quantitative method is a method in which the free carbon analysis value is subtracted from the total carbon analysis value when the ratio of free carbon to total carbon is less than 50%, and the amount of SiC is determined by calculation.
Conversely, when the SiC content is small (when the ratio of free carbon to total carbon exceeds 1â„4), a calculation method is used. Due to the large error, direct quantification was used. According to the sample measured by the free carbon, the total carbon was directly analyzed, and the amount of SiC was determined by conversion.
When indirect quantification is used, care must be taken because the analysis error of free carbon directly affects the SiC analysis value.
5.6 Trends in ISO Standards When considering the actual status of future analysis methods, harmonization with ISO standards is an important issue.
Chemical analysis of silicon refractories. The main all-carbon analysis method uses a resistance heating furnace and a high-frequency heating furnace in the combustion method. The detection methods include the Coulomb method (coagulation method), gravimetric method, conductivity method, and infrared absorption method.
The content of SiC is limited to 25% and the analytical method is divided.
The above-mentioned problem of the burning temperature of free carbon is currently under the unified work with the ISO standard, and is likely to be discussed in the future.
One of the main objectives of the preparation of certification standards for carbon analysis at the seminar was to modulate standard samples that can be used in the industry. The selection of a standard sample for measurement is a real headache in the real world. Therefore, a proposal for preparing a standard sample has been proposed from the beginning. Pure substances (high-purity graphite, etc.) that are available on the market are ideal if they can be used directly. However, there are many problems in actual use. In the joint experiment of the seminar, the silicon carbide standard sample (RRM1001) used to verify the accuracy of the analysis was registered as a verification standard sample last year (2001). After the seminar activities were completed (March 2000), the analytical subcommittee continued to reconstruct the analytical values, check the homogeneity of materials in each container, and confirm the particle size and mineral surveys. Refractory Materials Technology Association's price, issued by the Okayama Ceramic Technology Promotion Foundation. Table 5 shows the analysis result table of the certification standard sample R1001.
Concluding remarks The status quo analysis techniques for carbon-containing refractories are summarized. There are many kinds of carbon-containing refractories, and even when evaluating quality characteristics, original evaluation methods cannot be used as they are.
As for the techniques for analysis, it is also necessary to unify how to use a standardized method to evaluate actual and versatile refractory products as a basic technology.
(: August 2002) Improvement of the life of the lining of the rotary kiln The use of periclase-chrome ore mixture and the addition of aluminum and phosphorous iron make chromium magnesia. The filler can increase the service life of the 90m rotary kiln and the 170m rotary kiln masonry by 1.5 times and 0.5 times respectively.
The service life of the lining of a rotary kiln depends not only on the quality of the refractory bricks used in the masonry, but also on the cementitious material (ie the masonry mortar). Masonry clay has many functions.
The clay should have high refractoriness, sufficient strength over a wide temperature range, and high thermal shock resistance. It should not only ensure that each brick is tightly connected together, but also the lining brick and the kiln shell. Form a whole, and easy to use and meet environmental requirements.
Cement is used in the lining masonry of the hot end of the rotary kiln head of magnesia bricks Co.,Ltd.
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