Nitrogen analyses comparison of carbons and graphites.A new study by industry vendors indicates an inconsistency of equipment and the need for greater nitrogen testing accuracy. For years, inconsistent nitrogen analyses of carbons and graphite have puzzled foundrymen. Aware that these variations seemingly arise from incomparable analyses of two basic procedures (the Kjeldahl method The Kjeldahl method in analytical chemistry is a method for the quantitative determination of nitrogen in chemical substances developed by Johan Kjeldahl [1]. The method as described in Julius Cohen's Practical Organic Chemistry and Leco instrumentation), the Carbon Additives Subcommittee of CISA (Certified Information Systems Auditor) The award for successful completion of an examination in information systems audit, control and security from the Information Security Audit and Control Association. See ISACA. set out to determine whether these variations occurred. Funded and authorized by members of CISA's Carbon Additives Subcommittee, the Commercial Testing & Engineering (CT&E) Co. Laboratory, South Holland, Illinois South Holland is a village in Cook County, Illinois, United States. The population was 22,147 at the 2000 census. South Holland also serves as the seat of Thornton Township. South Holland was first settled in 1846 by immigrants from South Holland, the Netherlands. , collected various carbon/ graphite additives, tested them simultaneously and compared the results. Initially, CT&E used its Leco CHN-600 equipment and the Kjeldahl apparatus, ASTM ASTM abbr. American Society for Testing and Materials D3179-89 procedure. The table below lists comparative results in columns 1 and 3. This investigation widened to include another analytical instrument from Antek, Houston, Texas “Houston” redirects here. For other uses, see Houston (disambiguation). Houston (pronounced /'hjuːstən/) is the largest city in the state of Texas and the , for comparison (column 4). Leco Corp., St. Joseph, Michigan St. Joseph is a city in the U.S. state of Michigan. As of the 2000 census, the city population was 8,789. It lies on the shore of Lake Michigan, at the mouth of the St. Joseph River, about 60 miles due east of Chicago. It is the county seat of Berrien County6. St. , cooperated with comparisons from the same batches of candidate materials in two other Leco instruments: CHN-1000 (column 2) and TC436 (column 5).
Comparison of Carbon/Graphite Additives
1 2 3 4 5
Sample LECO LECO KJELDAHL ANTEK LECO
CHN-600 CHN-1000 CT&E ANTEK TC-436
CT&E LECO LECO
A |is less than~1000 700 170 47 121
B |is less than~1000 |is less than~200 380 380 NA
C 12,000 11,800 12,000 8400 10,920
D 10,200 10,400 12,000 15,700 NA
E |is less than~1000 |is less than~200 220 20 117
F |is less than~1000 |is less than~200 210 200 165
G 1600 1650 1610 1100 1587
H 11,600 10,600 12,100 9600 7926
I 4800 4900 4560 930 5493
J 14,200 16,600 13,600 7100 14,535
K 11,400 8400 10,800 10,200 8114
L 13,000 12,400 12,800 9470 11,650
M 2000 1400 600 2100 1362
N |is less than~1000 150 500 200 212
Results in parts per million parts per million mg/kg or ml/l; see ppm. (ppm) are listed below. Included are a range of calcined petroleum cokes, metallurgical cokes, anthracite coal Noun 1. anthracite coal - a hard natural coal that burns slowly and gives intense heat anthracite, hard coal coal - fossil fuel consisting of carbonized vegetable matter deposited in the Carboniferous period , several synthetic types of graphite, a natural graphite and an electrically calcined anthracite anthracite (ăn`thrəsīt'): see coal. anthracite or hard coal Coal containing more fixed carbon than any other form of coal and the lowest amount of volatile (quickly evaporating) material, giving it the . For further insight, details are provided for each process. Leco CHN-600 & CHN-1000 Thermal Conductivity--Carbon, hydrogen and nitrogen are determined by using a weighed quantity of sample in pure oxygen at 1742F (950C). After the products of combustion are accounted for, the carbon as C|O.sub.2~ and hydrogen as |H.sub.2~O are measured by infrared detectors. Nitrogen is measured as |N.sub.2~ in a thermal conductivity cell. CT&E indicates a detection limit of 1000 ppm for its CHN-600 instrument. Any analysis below that number is inconclusive. Leco states a detection limit of 200 ppm for its CHN-1000 instrument. Leco TC-436 Thermal Conductivity--Oxygen and nitrogen determination operates on inert gas inert gas or noble gas, any of the elements in Group 18 of the periodic table. In order of increasing atomic number they are: helium, neon, argon, krypton, xenon, and radon. fusion at temperatures up to 5432F (3000C). Nitrogen is measured as |N.sub.2~ using a thermal conductivity cell. Leco has not stated any detection limits. Kjeldahl (ASTM D-31 79-89)--Nitrogen is converted into ammonium salts by destructive digestion of the sample with a hot, catalyzed mixture of concentrated acid and potassium sulfate potassium sulfate n. A colorless or white crystalline compound, K2SO4, used in glassmaking and fertilizers and as a reagent in analytical chemistry. . These salts are later decomposed de·com·pose v. de·com·posed, de·com·pos·ing, de·com·pos·es v.tr. 1. To separate into components or basic elements. 2. To cause to rot. v.intr. 1. in a hot alkaline solution from which the ammonia is recovered by distillation. The results are determined by titration titration (tītrā`shən), gradual addition of an acidic solution to a basic solution or vice versa (see acids and bases); titrations are used to determine the concentration of acids or bases in solution. . There are no cited limits of data repeatability. Antek Pyro-Chemiluminescence--This procedure is a high-temperature (1832-2012F; 1000-1100C) oxidative pyrolysis py·rol·y·sis n. Decomposition or transformation of a chemical compound caused by heat. pyrolysis (pīrol´isis), n , where nitrogen is converted to nitric oxide nitric oxide or nitrogen monoxide, a colorless gas formed by the combustion of nitrogen and oxygen as given by the reaction: energy + N2 + O2 → 2NO; m.p. −163.6°C;; b.p. −151.8°C;. . The nitric oxide is then mixed with ozone to form metastable met·a·sta·ble adj. Of, relating to, or being an unstable and transient but relatively long-lived state of a chemical or physical system, as of a supersaturated solution or an excited atom. nitrogen dioxide nitrogen dioxide n. A poisonous brown gas, NO2, often found in smog and automobile exhaust fumes and synthesized for use as a nitrating agent, a catalyst, and an oxidizing agent. Noun 1. . As the metastable molecule relaxes to a stable state, light is emitted and sensed by a photo multiplier tube in the 650-900 NM range. Antek states the analytical range is from 0.1-30,000 ppm. Results Through the study, different laboratories reported variations in results with the same sample lot and test instrument. Sample D, for instance, ranged from 10,200-15,700 ppm as reported nitrogen content. All laboratories acknowledged operator experience (or operator error) will enter into nitrogen analyses. Another key finding was that different instruments showed variation. The Kjeldahl results, for example, compared favorably to other instruments provided the carbon or graphite sample was fully dissolved. All candidate materials required five to seven days to solutionize. This lengthy process, along with the fact that it is subject to operator technique, jeopardizes Kjeldahl as a viable nitrogen procedure. "The Kjeldahl method, although chemically feasible for many nitrogen compounds, has some drawbacks," said CT&E officials in their report. "The accuracy is dependent upon apparatus, reagents and technique. Low-level nitrogen analysis is tedious and of questionable value. "Limitations of this method are important as certain nitrogen species are not detectable due to inability of the reagents either to chemically convert bound nitrogen to ammonium sulfate or to physically contact embedded or occluded nitrogen compounds. Time is a critical factor in the accuracy of this analysis as some carbon-based materials require as much as a week to thoroughly digest." CT&E stated its Leco CHN-600 instrument appeared to be high for test materials that are considered to be low nitrogen. CT&E indicated a 1000 ppm detection limit for this instrument, meaning nitrogen is questionable below this point. Therefore, the CHN-600 seems more suited to higher nitrogen levels in excess of 1000 ppm. Leco said its recently developed CHN-1000 has a 200 ppm detection limit. The firm indicated this CHN CHN China CHN Chain CHN Canadian Health Network CHN Coalition on Human Needs CHN California Homeschool Network CHN Cleveland Housing Network CHN Center for Human Nutrition CHN Carbon, Hydrogen, Nitrogen CHN Community Health Nurse series is more attuned at·tune tr.v. at·tuned, at·tun·ing, at·tunes 1. To bring into a harmonious or responsive relationship: an industry that is not attuned to market demands. 2. to higher nitrogen levels (in the 1000-20,000 ppm range). Leco states its TC-436 instrument is attuned to lower nitrogen levels in carbons/graphites, below 1000 ppm. A variation was found in the TC-436 between separate samplings of sample A. The comparative testing indicated nitrogen of 121 ppm, whereas a second, separate test gave 66 ppm. This difference could be attributed to crushing, material homogeneity or exposure of the sample to atmospheric conditions prior to testing. Antek had variations, making its comparison somewhat inconclusive. Antek said its instrument is accurate over a broad range without any detection limits. Sample J, however, was one-half (7100 ppm) the nitrogen content of the other instruments. The cause of these sample testing variations has not been determined, only that the variations exist. The data in Table 1 are results of comparative side-by-side analyses of samples of candidate materials. There are not enough data-points to be considered statistically valid. Future Considerations Variations occur from one laboratory to another, and technique and operator expertise also influence nitrogen analyses. Different instruments also affect the analyses. By reporting these comparisons, it is hoped greater testing accuracy will be forthcoming by narrowing parameters of technique and perhaps round-robin testing that would include individual laboratories, equipment manufacturers and possibly testing societies. Further effort is desirable. Based on the findings of this study, foundrymen must keep in mind: * There are no calibration standards. Different laboratories standardized against different materials. * Sample preparation needs to be standardized. Carbon/graphite samples are usually crushed to pass through a 60 mesh screen (or 250 microns). If crushing creates sample material below 200 mesh (75 microns), this "dust" will create atmospheric adsorption adsorption, adhesion of the molecules of liquids, gases, and dissolved substances to the surfaces of solids, as opposed to absorption, in which the molecules actually enter the absorbing medium (see adhesion and cohesion). on the increased surface area, thus increasing the gas content. This implies a bottom sizing would be necessary to remove a variation. * When citing nitrogen analyses in carbons or graphite, instrument, laboratory, standards and other factors should be identified. |
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