The presence of carbonaceous agg Cretaceous aggregate and reservoir effect in dating of binding materials. Authors;. tions, as well as the chemical pretreatment methods to purify carbonaceous materials for 14C dating. We will discuss criteria to a non-decorated type (II). RADIOCARBON DATING OF GROUND WATER for dead objects or materials removed from the atmosphere either by death of plants or animals or with non-living entities. To examine instrument-based backgrounds in the University of California Keck Carbon Cycle AMS spectrometer, measurements were performed on a set of natural diamonds. Commercially valuable carbon polymers of animal origin include woolcashmere and Russian youg girls. But an important group of meteorites are dark stones with a significant content of carbon. Another important characterization of the meteorites is as differentiated or undifferentiated meteorites. Scrabble Words With Friends. It could Dating of non carbonaceous materials be used to safely store hydrogen for use in a hydrogen based engine in cars.
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This invention relates to shaped articles of carbonaceous material and a process for preparing the same, and more particularly to shaped articles of carbonaceous material impregnated with glass and a process for preparing such articles. Shaped articles of carbonaceous material are made of carbon or graphite. Since such articles are prepared from carbonaceous materials, they have outstanding heat resisting characterisitics, especially great mechanical strength at high temperatures, good lubricity and high abrasion resistance, so that they are widely used as graphite electrodes, crucibles, heat generating members and sliding members and are also useful as machine parts for use in refining or working metals.
However, shaped articles of carbonaceous material have the serious drawback of becoming consumed by being oxidized in the presence of oxidants at high temperatures and further the drawback of being highly permeable to gases and liquids i. Additionally with increases in the speed at which machines are operated, it has been desired in recent years to provide sliding members having higher resistance to abrasion.
Accordingly various proposals have been made to give such shaped carbonaceous articles improved resistance to oxidation and abrasion, high impermeability, etc. As one of the proposals, it is known to impregnate a carbonaceous material with a glass of specific composition, i.
They have somewhat improved but still insufficient resistance to abrasion. Furthermore, the carbonaceous material impregnated with the borate glass has low resistance to chemicals, with the result that the shaped article prepared from the material inevitably deteriorates easily when brought into contact with hot water or an aqueous acid or alkali solution. Thus shaped articles of carbonaceous material still remain to be developed which are satisfactory in any of various properties, such as resistance to oxidation at high temperatures, impermeability, resistance to abrasion, resistance to chemicals, etc.
Another object of the invention is to provide a shaped article of carbonaceous material having greatly improved resistance to abrasion. Another object of the invention is to provide a shaped article of carbonaceous material having high resistance to chemicals. Another object of the invention is to provide a shaped article of carbonaceous material having high impermeability. Still another object of the invention is to provide a shaped article of carbonaceous material which is outstanding in resistance to oxidation and chemicals and in impermeability and which has remarkably improved abrasion resistance.
The shaped article of the carbonaceous material of this invention is characterized in that the carbonaceous material is impregnated with a glass entirely different in composition from the conventional lead glass and borate glass. Because of this feature, the shaped article has the following advantages. The shaped article of the invention has much higher abrasion resistance than the shaped articles of a carbonaceous material impregnated with the conventional lead glass or borate glass.
The article is further outstanding in properties such as impermeability, resistance to chemicals, etc. Accordingly the present article is very useful for a wide variety of applications as a graphite electrode, heat generating member, sliding member or a machine part for use in refining or working metals.
The carbonaceous material to be used in this invention is not particularly limited but can be any of conventional like materials, such as materials consisting predominantly of carbon and graphitic materials. Further the carbonaceous material is not particularly limited in shape but can be of any of various shapes, such as spherical, cylindrical, cubic and rectangular parallelepipidal shapes. The material is not limited by the application for which the resulting article is used but can be any of the carbonaceous materials heretofore used, for example, for graphite electrodes, heat generators, sliding members and machine parts for use in refining or working metals.
Examples of useful third components are glass components which are usually used, such as R 1 2 O wherein R 1 is K, Na, Li or like monovalent metal , R 2 O wherein R 2 is Ca, Ba, Mg or like bivalent metal , R 3 2 O 3 wherein R 3 is Al or like trivalent metal , R 4 O 2 wherein R 4 is Ti, Zr or like tetravalent metal , etc. The borosilicate glass to be used in this invention is prepared easily by a known method, for example, by mixing together the desired components in the specified proportions, fully melting the mixture and slowly or rapidly cooling the melt.
The shaped article of this invention is produced easily by impregnating a carbonaceous material with the glass. The amount of the glass impregnating the material is not definite but is variable, for example, in accordance with the use of the product.
The shaped carbonaceous article of the invention can be produced by any of various known processes provided that the carbonaceous material can be impregnated with the desired amount of glass. It is not always necessary but preferable to remove air from the pores in the carbonaceous material first and thereafter impregnate the material with a melt of borosilicate glass.
The carbonaceous material can be degassed, for example, by subjecting the material to a vacuum. The material may be impregnated with the glass under atmospheric pressure or increased pressure. Described below is a preferable mode of process for preparing a shaped article of carbonaceous material according to the invention. First, a carbonaceous material is held in an upper portion of a pressure container, and borosilicate glass is placed in a low portion of the container.
Subsequently the container is evacuated and then heated to melt the glass. The carbonaceous material is thereafter immersed in the molten glass and thereby impregnated with the glass. The evacuation step degasses the pores of the material, prevents the material from oxidation and further facilitates the following impregnating step. The degree of vacuum to be produced by evacuation is not particularly limited but is widely variable suitably.
Usually it is about 10 -3 to about mm Hg, preferably 10 -2 to mm Hg, more preferably 10 -2 to 50 mm Hg. The period of time during which the carbonaceous material is held immersed in the molten glass is usually about 5 to about minutes, preferably 30 to minutes, more preferably 60 to 90 minutes, although not limited specifically.
The amount of glass impregnating the carbonaceous material can be increased, for example, by injecting an inert gas, such as nitrogen gas, argon gas or a mixture thereof, into the pressure container and performing the impregnating step at an increased internal pressure of about 1 to about atm.
The pressure is variable suitably according to the contemplated use of the resulting product. After the impregnating step, the carbonaceous material is taken out from the container and allowed to cool spontaneously, and the glass deposit around the material is removed therefrom, whereby a shaped article of this invention is produced.
As described above, the amount of glass impregnating the carbonaceous material varies with the pressure applied for the impregnating step. For example when this step is performed at 1 atm. Similarly when the impregnating step is performed at 10, 20, 30, 40 or atm. For a better understanding of the present invention, examples are given below. A carbonaceous material is used which has a bulk density of 1.
A crucible 28 cm in diameter and 58 cm in length of heat resisting alloy is placed into a pressure container 30 cm in diameter and 60 cm in length having a Kanthal heat generating member incorporated therein. The carbonaceous material 15 cm in diameter and 24 cm in length is placed into a cage made of heat resisting alloy and held in an upper portion of the crucible. The glass is placed on the bottom of the crucible.
The cage is then lowered to immerse the carbonaceous material into the glass in a molten state. The vacuum pump is then stopped. The container is thereafter maintained at the same temperature for 40 minutes. Subsequently the cage is raised, the internal pressure of the crucible is returned to 1 atm.
The glass deposit on the surface of the material is removed therefrom, whereby a shaped carbonaceous article of this invention is obtained. Table 1 shows various properties of the shaped articles obtained in Examples 1 to 3 and Comparison Examples 1 and 2. The bulk density listed is calculated from the weight and dimensions, in three directions, of the article concerned.
The electric specific resistivity is measured by the voltage drop method. The modulus of elasticity is measured by the ultrasonic resonance method.
Table 1 reveals that the shaped articles of the invention have considerably improved properties, indicating that the carbonaceous material has been impregnated with the borosilicate glass effectively. Table 2 shows the results. For comparison, the carbonaceous material before impregnation is also similarly checked for oxidation resistance with the results listed in Table 2.
Table 2 shows that the shaped articles of the invention have outstanding resistance to oxidation. The results shown in Table 3 and 5 are according to the following criteria:. The impermeability of each of the article is expressed in terms of viscous permeability coeffecient in Table 3, which for comparison also shows the corresponding value of the carbonaceous material before impregnation. Table 3 shows that the articles of the invention are superior in chemical resistance and impermeability.
The material is treated in the same manner as in Example 1 with use of the same borosilicate glass as used in Example 1 to obtain a shaped article according to the invention. A shaped article of carbonaceous material is prepared according to the invention in the same manner as in Example 4 except that the same borosilicate glass as used in Example 2.
A shaped article of carbonaceous material is prepared according to the invention in the same manner as in Example 4 with the exception of using the same borosilicate glass as used in Example 3. A shaped article of carbonaceous material is prepared in the same manner as in Comparison Example 1 with the exception of using the same carbonaceous material as used in Example 4.
A shaped article of carbonaceous material is prepared in the same manner as in Comparison Example 2 with the exception of using the same carbonaceous material as used in Example 4. Table 4 shows various properties of the shaped articles obtained in Examples 4 to 6 and Comparison Examples 3 and 4. Table 4 shows that the shaped articles of the invention have considerably improved properties, indicating that the carbonaceous material has been impregnated with the borosilicate glass effectively.
The shaped articles prepared above are tested for abrasion resistance by the following method. Each specimen is placed on the surface of a ring rotated by an electric motor and held against the ring under a pressure for 2 hours.
The pressure applied to the specimen is thereafter increased stepwise upon lapse of every two hours. The FIGURE shows the results. Curves A, B, C, D and E are the pressure-abrasion rate curves determined for the shaped articles obtained in Examples 4, 5, 6 and Comparison Examples 3 and 4, respectively. Curve F is the corresponding curve obtained for the carbonaceous material used.
The FIGURE reveals that the shaped articles of the invention have a low abrasion rate and therefore high resistance to abrasion. The shaped articles are further tested for resistance to chemicals and impermeability with the results given in Table 5 below. Table 5 shows that the articles of the invention are superior in chemical resistance and impermeability. A SumoBrain Solutions Company.
Search Expert Search Quick Search. SEARCH RESEARCH MPEP 2. Shaped articles of non-fibrous carbonaceous material. United States Patent A shaped article of a carbonaceous material characterized in that the carbonaceous material is impregnated with a borosilicate glass comprising 25 to 50 wt. Ikeda, Shigeru Kawanishi, JP Hori, Shozi Takatsuki, JP Eguchi, Kiyohisa Kawanishi, JP Matsuo, Kanji Ikeda, JP Zaima, Hidenori Kanazawa, JP Gamada, Yoshifumi Neyagawa, JP Kondo, Teruhisa Toyonaka, JP.
Click for automatic bibliography generation. Tokyo, JP Toyo, Tanso Co. A shaped article of a non-fibrous carbonaceous material wherein the non-fibrous carbonaceous material is impregnated with a borosilicate glass comprising 25 to 50 wt.
A shaped article as defined in claim 1 wherein the borosilicate glass further comprises as a third component at least one compound selected from the group consisting of R 1 2 O wherein R 1 is one of monovalent metals including K, Na and Li, R 2 O wherein R 2 is one of bivalent metals including Ca, Ba and Mg, R 3 2 O 3 wherein R 3 is one of trivalent metals including Al, and R 4 O 2 wherein R 4 is one of tetravalent metals including Ti and Zr. A shaped article as defined in claim 2 wherein the borosilicate glass contains the third component in an amount of 5 to 40 wt.
A shaped article as defined in any one of claims 1 to 3 which is used as a graphite electrode. A shaped article as defined in any one of claims 1 to 3 which is used as a sliding member. A shaped article as defined in any one of claims 1 to 3 which is used as a heat generating member. A shaped article as defined in any one of claims 1 to 3 which is used as a machine part for use in refining or working a metal.
Other features of the present invention will become apparent from the following description. EXAMPLE 1 A carbonaceous material is used which has a bulk density of 1.
Chat or rant, adult content, spam, insulting other members, show more. Harm to minors, violence or threats, harassment or privacy invasion, impersonation or misrepresentation, fraud or phishing, show more. Radiocarbon dating question, help.? When a living organism dies, its carbon decays. The half-life of carbon dating is years. Write an equation M t expressing the amount of carbon left at time t. When did the mastodon die? Are you sure you want to delete this answer? Trending Now Joshua Hupperterz Barack Obama Giancarlo Stanton Gigi Hadid Kirsty Gallacher Retirement Communities Prince George Seizures Treatments Nintendo Switch Toyota Tacoma.
Radiocarbon dating is a radiometric dating method that uses the naturally occurring isotope carbon 14C to determine the age of carbonaceous materials up to about 60, years.
Such raw ages can be calibrated to give calendar dates. The technique of radiocarbon dating was discovered by Willard Libby and his colleagues in  during his tenure as a professor at the University of Chicago. Libby estimated that the steady state radioactivity concentration of exchangeable carbon would be about 14 disintegrations per minute dpm per gram. In , he was awarded the Nobel Prize in chemistry for this work. One of the frequent uses of the technique is to date organic remains from archaeological sites.
Plants fix atmospheric carbon during photosynthesis, so the level of C14 in living plants and animals equals the level of C14 in the atmosphere. Carbon has two stable, nonradioactive isotopes: In addition, there are trace amounts of the unstable isotope carbon 14C on Earth.
Carbon has a half-life of years and would have long ago vanished from Earth were it not for the unremitting cosmic ray impacts on nitrogen in the Earth's atmosphere, which create more of the isotope. The neutrons resulting from the cosmic ray interactions participate in the following nuclear reaction on the atoms of nitrogen molecules N2 in the atmospheric air: Atmospheric 14C, New Zealand and Austria.
The New Zealand curve is representative for the Southern Hemisphere, the Austrian curve is representative for the Northern Hemisphere. Atmospheric nuclear weapon tests almost doubled the concentration of 14C in the Northern Hemisphere . The highest rate of carbon production takes place at altitudes of 9 to 15 km 30, to 50, ft , and at high geomagnetic latitudes, but the carbon spreads evenly throughout the atmosphere and reacts with oxygen to form carbon dioxide.
Carbon dioxide also permeates the oceans, dissolving in the water. For approximate analysis it is assumed that the cosmic ray flux is constant over long periods of time; thus carbon is produced at a constant rate and the proportion of radioactive to non-radioactive carbon is constant: In Hessel de Vries showed that the concentration of carbon in the atmosphere varies with time and locality. For the most accurate work, these variations are compensated by means of calibration curves.
When these curves are used, their accuracy and shape are the factors that determine the accuracy and age obtained for a given sample. Plants take up atmospheric carbon dioxide by photosynthesis, and are ingested by animals, so every living thing is constantly exchanging carbon with its environment as long as it lives. Once it dies, however, this exchange stops, and the amount of carbon gradually decreases through radioactive beta decay.
By emitting an electron and an anti-neutrino, carbon is changed into stable non-radioactive nitrogen This decay can be used to measure how long ago once-living material died. However, aquatic plants obtain some of their carbon from dissolved carbonates which are likely to be very old, and thus deficient in the carbon isotope, so the method is less reliable for such materials as well as for samples derived from animals with such plants in their food chain.
The radioactive decay of carbon follows an exponential decay. A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. The solution to this equation is: Two related times can be defined: From these considerations and the above equation, it results: For a raw radiocarbon date: After replacing values, the raw radiocarbon age becomes any of the following equivalent formulae: Measurements are traditionally made by counting the radioactive decay of individual carbon atoms by gas proportional counting or by liquid scintillation counting, but these are relatively insensitive and subject to relatively large statistical uncertainties for small samples below about 1g carbon.
Sensitivity has since been greatly increased by the use of accelerator-based mass-spectrometric AMS techniques, where all the 14C atoms can be counted directly, rather than only those decaying during the counting interval allotted for each analysis.
The AMS technique allows one to date samples containing only a few milligrams of carbon, although the maximum age reported was, in , around 65, to 80, years.
The anticipation that AMS-based systems might achieve 14C-ages of , years has been unrealized. A variety of sample processing and instrument-based constraints have been postulated. To examine instrument-based backgrounds in the University of California Keck Carbon Cycle AMS spectrometer, measurements were performed on a set of natural diamonds.
Raw radiocarbon ages i. This is the number of radiocarbon years before , based on a nominal and assumed constant - see "calibration" below level of carbon in the atmosphere equal to the level.
They are also based on a slightly-off historic value for the half-life maintained for consistency with older publications see "Radiocarbon half-life" below. See the section on computation for the basis of the calculations. Corrections for isotopic fractionation have not been included. Radiocarbon labs generally report an uncertainty, e.
Traditionally this includes only the statistical counting uncertainty and some labs supply an "error multiplier" that can be multiplied by the uncertainty to account for other sources of error in the measuring process. Additional error is likely to arise from the nature and collection of the sample itself, e.
Such old wood, turned into an artifact some time after the death of the tree, will reflect the date of the carbon in the wood. The current maximum radiocarbon age limit lies in the range between 58, and 62, years approximately 10 half-lives cf refs [1, 3]. This limit is encountered when the radioactivity of the residual 14C in a sample is too low to be distinguished from the radioactivity of the assumed 'dead carbon' blank samples used as background.
Materials for radiocarbon dating are commonly collected from archaeological sites. Common examples of carbonaceous materials include wood used in buildings and charcoal from fires, which incorporate atmospheric carbon dioxide from the time the wood was growing, and more recently, mortar which incorporates atmospheric carbon dioxide from the time that the mortar set. For example, contamination of wood charcoal from a fire by mineral coal which is relatively depleted in 14C would result in a greater age for the sample than that indicated by the pure charcoal; conversely, contamination by recent material would result in a more recent age.
Various pretreatment techniques, including physical identification of specific portions of the sample and chemical separation to insure that only organic parts of the wood are included, have been developed to insure the accuracy of the resulting dates. A raw BP date cannot be used directly as a calendar date, because the level of atmospheric 14C has not been strictly constant during the span of time that can be radiocarbon dated.
The level is affected by variations in the cosmic ray intensity which is affected by variations in the earth's magnetosphere caused by solar storms.
In addition there are substantial reservoirs of carbon in organic matter, the ocean, ocean sediments see methane hydrate , and sedimentary rocks. Changing climate can sometimes disrupt the carbon flow between these reservoirs and the atmosphere. The level has also been affected by human activities—it was almost doubled for a short period due to atomic bomb tests in the s and s and has been lowered by the admixture of large amounts of CO2 from ancient organic sources relatively depleted in 14C —the combustion products of fossil fuels used in industry and transportation, known as the Suess effect.
The atmospheric 14C concentration may differ substantially from the concentration in local water reservoirs. Eroded from CaCO3 or organic deposits, old carbon may be easily assimilated and provide diluted 14C carbon into trophic chains. Standard calibration curves are available, based on comparison of radiocarbon dates of samples that can be independently dated by other methods such as examination of tree growth rings dendrochronology , ice cores, deep ocean sediment cores, lake sediment varves, coral samples, and speleothems cave deposits.
The calibration curves can vary significantly from a straight line, so comparison of uncalibrated radiocarbon dates e. There are also significant plateaus in the curves, such as the one from 11, to 10, radiocarbon years BP, which is believed to be associated with changing ocean circulation during the Younger Dryas period. The accuracy of radiocarbon dating is lower for samples originating from such plateau periods. The version of the calibration curve extends back quite accurately to 26, years BP.
However, since Libby's early work was published to , temporal, latitudinal and continental variations in the carbon exchange reservoir have been observed by Hessel de Vries ; as reviewed by Lerman et al. Subsequently, calibration curves have been developed that allow the correction of raw radiocarbon dates. The reservoir effects that necessitate this correction include: Erosion and immersion of carbonate rocks which are presumed to be older than , years and so should not contain measurable 14C causes an increase in 12C and 13C in the exchange reservoir, which depends on local weather conditions and can vary the ratio of carbon that living organisms incorporate.
This is believed negligible since most erosion will flow into the sea. Volcanic eruptions eject large amount of carbonate into the air, causing an increase in 12C and 13C in the exchange reservoir and can vary the exchange ratio locally. This explains the often irregular dating achieved in volcanic areas. The earth is not affected evenly by cosmic radiation, the magnitude of the radiation depends on land altitude and earth's magnetic field strength at any given location, causing minor variation in the local 14C production.
This is accounted for by having calibration curves for different locations of the globe. However this could not always be performed, as tree rings for calibration were only recoverable from certain locations in .
These effects were first confirmed when samples of wood from around the world, which all had the same age based on tree ring analysis , showed deviations from the dendrochronological age. Calibration techniques based on tree-ring samples have contributed to increase the accuracy since , when they were accurate to years at worst. Relatively recent evidence has allowed scientists to refine the knowledge of one of the underlying assumptions.
A peak in the amount of carbon was discovered by scientists studying speleothems in caves in the Bahamas. Stalagmites are calcium carbonate deposits left behind when seepage water, containing dissolved carbon dioxide, evaporates. Carbon levels were found to be twice as high as modern levels. These discoveries improved the calibration for the radiocarbon technique and extended its usefulness to 45, years into the past.
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