FR2628212A1 - PROCESS FOR PRODUCING A CARBON FURNACE FOR ATOMIC ABSORPTION ANALYSIS - Google Patents

Abstract

A method of producing a carbon furnace for atomic absorption analysis is disclosed. According to the invention, carbon powder is mixed with a thermoset resin monomer or a polymer of an initial condensate as a material of a carbide binder to bind the powder of the mixture and the thermoplastic resin having a functional group for the curing crosslinking in reaction with the thermoset resin component which decomposes on heating, the composition to which a solvent or plasticizer has been added is uniformly kneaded and then the mixture is formed into a tube, treated with water. With dry air to remove the solvent and plasticizer, the curing reaction of the thermoset resin is advanced by decomposing the thermoplastic resin to obtain a fully cured resin which does not exhibit thermal deformation and is carbonized and heat treated at high temperature the mixture cured in an inert atmosphere. The invention applies in particular to analysis by flameless atomic absorption.

Description

QI) FRENCH REPUBLIC Publication No. 2,628,212 (to be used only

  for the NATIONAL INSTITUTES Reproduction Orders) OF INDUSTRIAL PROPERTY National Registration Number: 88 02714 PARIS

  Int CI4: G 01 N 21/74.

  APPLICATION FOR PATENT OF INVENTION A1

  (Filing date: March 3, 1988. Q Applicant (s) Company known as: MITSUBISHI PENCIL Co.,

LTD. -JP.

) Priority

  Inventor (s): Yoshihisa Suda.

  4 Date of the public availability of the

  application: BOPI "Patents" No. 36 of 8 September 1989.

  (References to other national documents

(rt) Holder (s):

Attorney (s): Cabinet Weinstein.

  Process for producing a carbon furnace for atomic absorption analysis

  (The invention relates to a method for producing an oven

  carbon for atomic absorption analysis.

  According to the invention, carbon powder is mixed with a thermoset resin monomer or a polymer of an initial condensate as a material of a carbide binder to bind the powder of the mixture and the thermoplastic resin having a functional group for the Curing crosslinking in reaction with the thermoset resin component which decomposes upon heating, the composition is uniformly kneaded. to which a solvent or a plasticizer is added and then the mixture is shaped into a tube, treated in the dry state to remove the solvent and the plasticizer, the curing reaction of the thermoset resin is advanced N by the decomposition of the thermoplastic resin to obtain

  - a completely hardened resin which does not present any deformation

  Thermal generation and carbonization and heat treatment at high temperature cured mixture in an atmosphere

Co inert.

  The invention applies in particular to absorption analysis

b atomic without flame.

  Nm ___ ... _ ... _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ The present invention relates to a process for producing a carbon furnace for atomic absorption analysis and, more particularly, to a method for producing a carbon furnace for flameless atomic absorption analysis, for measuring a number of seeds of elements with high sensitivity and high precision, with a long life, in comparison with a conventional heating furnace as a heating furnace for analysis by

Atomic absorption without flame.

  As an atomic absorption analysis method makes it possible to measure, as a means of microanalysis of metals, a greater sensitivity and precision than a conventional method of analysis, it has recently developed rapidly. The atomic absorption analysis method primarily employs initially a flame method in which a flame is used in combination with air-hydrogen, oxygen-hydrogen, but recently a method of atomic absorption analysis has frequently been used. Without flame, about 10 to 100 microliters of a sample can be used in an ultrafine amount at a sensitivity of up to 100 to 1000 times in the case of ultramicroanalysis in an environment or in a sample of a living body. In the flameless atomic absorption analysis method, a furnace material is excited to heat it, to heat the measurement atmosphere to a high temperature in order to obtain a measuring element produced at high temperature. The furnace material to be used for measurement can be widely distributed in carbon and metal materials. Conventional carbon material mainly uses natural graphite, artificial graphite and vitreous carbon. The conventional method of producing a carbon furnace comprises

262,821?

  in the case of artificial carbon, the stages of pitch calcination as a carbon material at temperatures close to 1500 C and its graphitization at a temperature of between 2500 and 3000 C. The vitreous carbon is obtained by calcining a polymer organic by molding it at a temperature of about

2000 C as amorphous carbon.

  However, the present carbon-based furnace has drawbacks, such as insufficient sensitivity and precision, and since the production method generally starts with a large block of artificial graphite, it is necessary to cut this large block into small blocks by machine then cut the blocks into a circular column form, perforate them into a cylindrical shape, drill and chamfer, which remarkably increases the number of steps to finally obtain a product and, as a grinding mechanism sprays the block, the chips are remarkably dispersed which not only deteriorates the steps of elaboration but causes disadvantages, such as a decrease in precision, and wear tools. On the other hand, the conventional carbon furnace has drawbacks in that the available number of uses is limited because of the consumption of the furnace material by the oxidation of the graphite on the surface of the furnace by the salt and the acid in the samples and air oxidation of the outer wall, and the service life depends on the seed of the element to be measured to extend between several hundred times at most and several tens of times

at least.

  In order to overcome the disadvantages described above, the carbon material has been improved but the improved carbon material does not satisfy all the problems described above. The modification of the

3 2628212

  Carbon oven surface is attempted for the same purpose. In other words, the carbon furnace is immersed in a solution of 5-6% W or Ta containing% oxalic acid to impregnate the carbon furnace of the solution in the pores of the graphite at reduced pressure, then Dry in the wind by gradually heating the oven up to 2500 C to produce a metal carbide. These steps are repeated two to three times in a metal carbide process or the carbon furnace is introduced into a large furnace, a hydrocarbon gas is introduced at the same time as an inert gas in the large furnace, and heated at high temperatures. temperature to precipitate a pyrocarbon in a pyrolytic graphitization and there is also a combination of pyrolytic graphitization and metal carbide process. However, these methods are all complicated in their uneconomical steps, and have the disadvantages of not only dramatically increasing the cost of the expensive carbon furnace but also reducing the sensitivity to alloying elements with metals such as Co, Pt, Se in metal carbides and pyrolytic products such as Cd, Zn do not always produce an effect on the elements in the

  atomic process at relatively low temperatures.

  Oven metals made of metal include Mo, Ta or W which has a high melting point and high boiling point, and relatively good workability. Mo has a lower melting point than the others, and a high vapor pressure for use in measuring Cd or Pd in a low temperature atomic process. Ta has a high workability but shorter service life than W. W has a high melting point and low vapor pressure for use as furnace material, but it can produce an oxide requiring H2 as a reducing reagent. In the case of metal materials in general, they have a relatively high workability in comparison with the carbon material to be effective for seeds of elements usable in such carbides but have drawbacks such as low sensitivity for the elements that can produce an alloy

with metals like Co, Pt, Se.

  Accordingly, the present invention relates to a method of producing a carbon furnace for atomic absorption analysis, not requiring a large number of machining steps as in a conventional method for the production of a furnace. carbon or a surface treatment of the carbon furnace resulting in a high price due to the complicated processing steps to obtain high sensitivity and high precision measurement results, long life of the carbon furnace, precise dimensions in an easy method of formatting, as well as a great economy. The present invention is the result of studies to achieve the above objective and a thermoplastic resin having a functional group for crosslinking for curing in reaction with a heat decomposed thermoset resin component at the time of heating is mixed with the monomer of the invention. thermoset resin and / or a polymer of an initial condensate as a material of a carbide binder for binding a mixed powder of one or more carbon powders of natural graphite, artificial graphite, furnace graphite, carbon black, coke powder, etc., and has a soluble solvent with the resin component or the composition of the mixture where a plasticizer is added, is mixed with the resulting mixture, the mixture is kneaded, molded into a tube shape, the tube-shaped mixture is treated with heated air to remove the solvent or plasticizer contained, the curing reaction is advanced with the c decomposed components of the thermoplastic resin to form a fully hardened material that does not exhibit thermal deformation, the tube-shaped mixture is chamfers, subjected to secondary processing, such as drilling, is carbonized in an atmosphere of an inert gas and then heated to 20000C or higher for heat treatment to produce a carbon furnace for flameless atomic absorption analysis which has a high sensitivity and high accuracy in measurement for a number of element seeds in comparison with the furnace Conventional carbon has a long life. According to this method, it has been discovered that the. The method of forming was easy and the dimensional accuracy was excellent in comparison with the carbon furnace where only the thermoset resin is used as the carbide binder as in the prior invention disclosed in the disclosure.

Japanese patent.

  No. 239145/1986 in comparison with the method

  Conventional production of a carbon kiln.

  A process for producing a carbon furnace for atomic absorption analysis according to the present invention

  The invention will now be described in detail.

  The method first consists in mixing the powder in a mixture of one or more types of carbon powders with a thermoset resin monomer and / or a polymer of an initial condensate as a material of a carbide binder for binding the mixed powder and the thermoplastic resin having a functional group for crosslinking for curing in reaction with the thermoset resin component decomposed at the time of heating, uniformly knead the composition of the mixture, to which a soluble solvent or lubricating agent with the components of the resin are added to the resulting mixture in a mixer, such as a Henschel mixer, and the kneaded mixture is sufficiently kneaded in a kneader to strongly apply a shearing force to the kneaded mixture, such as a pressure kneader, a co-kneader, mixer, two cylinders or three cylinders. With the steps described above, the resin blend polymer, the simultaneously split carbon powder and the mixed polymerized resin have a high affinity for sufficient dispersion. The kneaded mixture thus obtained is put into

  form into a tube by an extrusion molding machine.

  The kneaded and shaped mixture is then heated in an air oven to volatilize the solvent and plasticizer contained, and is heated near the decomposition temperature of the thermoplastic resin having the functional group. The curing reaction of the thermoset resin is advanced by the functional group produced by the decomposition at this stage for complete cure to produce a calcined and pretreated mixture which is not deformed even by the subsequent heating. The pretreated and calcined mixture which has been completely post-cured is then prepared, for example to chamfer and pierce it to form a carbon oven desired for atomic absorption analysis. Then, the resulting mixture is heated for charring at 800 ° C. or higher and preferably 1000 ° C. or higher in an inert gas atmosphere, such as nitrogen or argon, and is further thermally treated at room temperature. higher temperatures, such as 2000 C or higher and preferably 2500 C or higher in an inert gas or vacuum atmosphere, and more preferably at 2800 C or higher to improve thermal impact resistance and high purity. Most fine dust from

262S212

  metals such as Fe, Si, Ti, Ca, V contained as impurities in the material or to undergo secondary mixing by machining, are subjected to an atomic process at the stage of the high temperature heat treatment for volatilization . Preferably, after the high temperature heat treatment, the mixture is further heated to 700 ° C or higher to remove impurities in a chlorine gas atmosphere. The carbon furnace for atomic absorption analysis thus obtained

  maintains a dimensionally precise shape.

  The materials for the carbide binder to be used in the process of the invention preferably comprise, as thermoset resin, the monomers and / or polymers of an initial condensate of furan resins, phenol resins, xylene resins, toluene resins, resorcinol resins. ; as the thermoset resin for the separation of the functional group from the thermal reaction, such as the halogen, aldehyde, acetyl and methylol groups by thermal decomposition, a resin such as a polyvinyl chloride resin, a chlorinated vinyl, a resin of a polyvinyl chloride / vinyl acetate copolymer, a polyvinyl acetal resin or a vinyl resin as the main chaton and the functional group of the thermal reaction is introduced as a secondary chain. The carbon powders for use in the process of the present invention contain natural graphite, artificial graphite, furnace graphite, carbon black or coke powder. The mixing ratio of the carbon powder with the composition forming the carbon furnace for atomic absorption analysis is adjusted to 10 to 90% by weight. If the mixing ratio of the carbon powder is excessively higher, molding becomes difficult while if the ratio is excessively lower, cracks tend to occur at the time of the high temperature heat treatment. So, we

  a range of 30 to 70% by weight is preferred.

  Examples of the process of this

  invention will now be described in detail.

Example 1

  After having dissolved 25% by weight of an initial furan resin condensate (VF-302 produced by Hitachi Chemical Co., Ltd., Japan) and 25% by weight of a polyvinyl chloride resin (produced by Nippon Zeon Co , Ltd., Japan, average polymerization of 800), in tetrahydrofuran, with a carbide binder, to which 20% by weight of dibutyl phthalate had been added. 50% by weight of natural scaly graphite (having an average grain size of 20) was mixed as a plasticizer, and the carbide binder was regularly dispersed in a kneader. was sufficiently kneaded by two mixing rollers held at 80 ° C surface temperature and the kneaded mixture was molded into a continuous tube of 6.5 mm outer diameter and 4.5 mm internal diameter, in a mold-forming machine. extrusion. The molding was heated at 220 ° C in an air oven to completely remove the plasticizer. On the other hand, the pretreated and calcined fully cured mixture of the furan resin by gaseous HCl produced by the decomposition of the polyvinyl chloride resin was obtained. Then, the calcined pretreated mixture was further elaborated, for example drilled and chamfered and then heated at a rate of increasing the temperature from C / hour to 1000 C in an atmosphere of nitrogen gas, it was left to rest. At 10000C for 5 hours to obtain a carbide at 10000C, the carbide was further heated at a rate of temperature increase from C / nm to 2600C. a state of argon vapor in a high temperature oven and then allowed to stand at 2600 C for 1 hour and cooled to produce a carbon oven for atomic absorption analysis of 6 mm outer diameter, 4 mm of internal diameter and

mm long.

Example 2

  After having dissolved, in a solvent, 20% by weight of an initial furan resin condensate (VF-302 produced by Hitachi Chemical Co. Ltd., Japan) and 30% by weight of a resin of a chloride copolymer of polyvinyl / vinyl acetate (produced by Nippon Zeon Co., Japan, average polymerization of 600), with a carbide binder, where 20% by weight of dibutyl phthalate was added as a plasticizer, and regularly 50% by weight of furnace graphite (produced by Kowa Seiko Co., Ltd having 4 p of average grain size) and mixed with the carbide binder in a kneader, the mixture was then mixed. treated by the same steps as those of Example 1 and was molded into a continuous tube 6.5 mm in outer diameter and 4.5 mm internal diameter. Then, the molding was treated as in example i to obtain a carbon oven for atomic absorption analysis having 6 mm external diameter,

  4 mm internal diameter and 30 mm long.

  The properties of the carbon furnace obtained according to the process of the present invention are compared with the

conventional carbon furnace.

  The AA-1E model produced by Nippon Jourrel Ash, Co., was used as a measuring instrument, the metallic elements of five types, such as Se, Cu, Cd, Pb and Cr were measured, and the absorption ratio carbon oven A for the above instrument is given

to the blackboard.

i TABLE

Weight Absorption Ratio Number

  specificity (1.00 for A) of use

g / cm3 ions \ Se Cu Cd Pb Cr

At 1.70 1.00 1.00 1.00 1.00 1.00 80

  Example 1 1.68 2.00 1.40 1.10 1.15 1.20 580 Example 2 1.69 1.90 1.35 1.00 1.20 1.35 570 As can be understood from the table, the carbon furnace produced according to the process of the present invention has excellent absorption properties and the number of uses as compared to an oven

conventional is important.

Claims (4)

  A process for producing a carbon furnace for atomic absorption analysis, characterized in that it comprises the steps of mixing carbon powder with a thermoset resin monomer and / or a polymer of an initial condensate. As a material of a carbide binder for bonding the mixing powder and a thermoplastic resin having a functional group to crosslink to cure in reaction with the thermoset resin component decomposed at the time of heating, uniformly knead the composition of the mixture where the a solvent or soluble plasticizer is added with the components of the resin to the resulting mixture, then knead sufficiently, put the composition of the mixture into a tube shape and then treat the composition in heated air to remove the solvent and the plasticizer contents, advance the hardening reaction of the thermoset resin by decomposing the thermoplastic resin to produce a completely cured sine which does not exhibit thermal deformation and carbonize and heat treat at high temperature   the mixture cured in an inert atmosphere.   A process according to claim 1, characterized in that the thermally cured resin has the property of being cured by the reactive functional group of the thermoplastic resin selected from the group consisting of monomers and / or a polymer of an initial condensate of furan resins, phenol resins, de-resins   xylene, toluene resins, resorcinol resins.   3. Process according to claim 1, characterized in that the thermoplastic resin comprises a functional group for a thermal reaction, such as halogen, aldehyde, acetyl and methylol groups as a secondary chain for crosslinking for hardening in reaction with the other. thermoplastic resin by the heat of the functional group and a reactive functional group, a vinyl halide resin such as a polyvinyl chloride resin, a chlorinated vinyl chloride resin, a polyvinyl chloride / acetate acetate copolymer resin vinyl and a polyvinyl acetal resin.   4. Method according to claim 1, characterized in that the carbon powders comprise natural graphite, artificial graphite, graphite   furnace, carbon black or coke powder.