Combustion decomposition accelerators

Abstract: The invention relates to non-toxic combustion decomposition accelerators and processes for their production for elemental analysis. The non-toxic accelerators may be either single component or multicomponent. The single component non-toxic accelerators are glass frit, niobium pentoxide, and inorganic phosphate compounds. The multicomponent accelerators are formed from a combination of the foregoing, and most preferably from (a) one or more of niobium pentoxide, tungsten oxide and mixtures thereof, and (b) one or more of glass frit, inorganic phosphate compounds, and mixtures thereof.

Description: This invention relates to combustion accelerators for use in elemental combustion analysis, the compositions thereof and to processes for their production. Elemental combustion analysis is important in many major industries, including food, pharmaceuticals, chemicals, plastics, coal, coke, ceramics, steel, etc. The total quantity of an element or elements in a material is most often used to justify quality of a product. In many cases the element determination must be accurate and performed on a timely basis in order to allow production control to make appropriate adjustments in processing and allow for a timely product delivery. In many combustion analyzers the sample material is combusted in an oxygen environment to release the various forms of elements as oxides. However, different types of elements with different strength of bonding may exist in a material, each of which may dissociate at a varying rate, creating a low analyzed result or a very long analysis time. A typical example is sulfur in various organic and inorganic compounds. To avoid the problems of a low analyzed result or a very long analysis time, vanadium pentoxide (V 2 O 5 ) has traditionally been mixed with the sample to be analyzed, in order to accelerate sulfur release as SO 2 . However, recent concern over the toxicity of vanadium pentoxide has created a need for a new, non-toxic "accelerator" which can be used for elemental composition analysis. In cases where objections to the use of vanadium oxide (V 2 O 5 ) exist, or no vanadium oxide (V 2 O 5 ) is available, high purity tungsten oxide (WO 3 ) has been substituted for vanadium oxide (V 2 O 5 ) as a combustion aid. See LECO Corporation Application Bulletin, Form No. 203-601-229, August, 1992. Like vanadium oxide (V 2 O 5 ), tungsten oxide (WO 3 ) is useful for its ability to assist in elemental oxidation during the combustion analysis process. However, the results obtained by using tungsten oxide (WO 3 ) as the sole accelerator are not as beneficial as those obtained by vanadium oxide (V 2 O 5 ). US-A-5204270 describes the use of fused silica or pure silicon dioxide as a diluent in the characterisation of samples such as coal and polymers. US-A-4537862 discloses a glass frit composition for glazing, enamelling and decorating. These compositions are prepared by melting raw batch glass and then quenching. Patent Abstracts of Japan Vol. 9, no. 24 (p-331), 31 January 1985 and JP59916835A disclose the use of a mixture of glass powder and tungsten oxide in a gas detection material layer of a gas detection element and gas leak warning device. According to the present invention there is provided a method for accelerating the combustion decomposition of a substance to be analyzed, the method comprising heating the substance to at least its decomposition temperature in the presence of a non-toxic accelerator, the non-toxic accelerator comprising a mixture of powdered glass frit and powdered tungsten oxide (WO 3 ). According to the present invention there is further provided a powdered non-toxic combustion decomposition accelerator for elemental analysis comprising a powder mixture of tungsten oxide (WO 3 ) and glass frit. Embodiments of the invention will now be described by way of example. In the preferred embodiment a non-toxic accelerator of the invention is mixed with a substance to be analyzed in a ratio of from about two grams (2.0 gm) to about 0.15 grams accelerator to substance, and placed in a combustion container. This ratio is merely a preferred ratio; the ratio of accelerator to substance can vary within usual ranges used in the art. The container is placed in a combustion analyzer, and the mixture heated from about 450°C to about 1450°C, depending on the substance to be analyzed and the specific test protocol used. The combustion gasses are analyzed for the desired elements. The accelerator may be a multicomponent compound formed by mixing glass frit and tungsten oxide (WO 3 ). In addition to being non-toxic, the accelerators of the preferred embodiment reduce the time required for elemental decomposition in an organic or inorganic compound to at least one half of the analysis time when no accelerator is used. Preferably, the accelerator has a particle size of no more than about 2 mm, with the preferred particle size being from about 0.1 to about 20 µm. The only restriction on the amount of impurities is that the accelerator should not contain as a significant impurity the element being tested for. The glass frit utilized can be a commercially available powder or a special formulated glass frit. Additionally, the glass frit can be either a leaded glass frit or a leadless glass frit. A more preferred glass frit is Ferro 3249, which comprises less than about 5% by weight calcium oxide (CaO), from about 5% to about 15% by weight magnesium oxide (MgO), from about 5% to about 15% by weight aluminum oxide (Al 2 O 3 ), from about 25% to about 50% by weight boron trioxide (B 2 O 3 ), and from about 25% to about 50% by weight silicon dioxide (SiO 2 ). Ferro 3249 glass frit has a frit fusion point of 1024°C; a frit flow point of 1246°C; a specific gravity of 2.40 g/cm 3 ; and a particle size of -325 mesh. There are several different methods of combining the components of the preferred embodiment to form a multicomponent non-toxic accelerator. The components can be processed by any known dry mixing technique, which includes ball milling, jet milling, attrition milling, V-blending, etc. Another method of mixing the components is to process them by using any known wet mixing procedure. Wet mixing in water involves placing the components in water, mixing the solution, drying the mixture, and then grinding the mixture into a fine powder. Alternatively, the components can be processed by wet mixing in a solvent solution. This entails placing the components in a solvent, for example, mixing in isopropyl alcohol as a dispersing medium using a high density polyethylene jar and alumina balls, although there is no particular restriction on the liquid dispersing medium that can be used. The wet slurry produced is then dried and ground into a fine powder. Finally, the components can be dry mixed, wet mixed in a water solution, or wet mixed in a solvent solution, and then heated to a high temperature of between about 300°C to about 1700°C, preferably between about 500°C to about 700°C, thereby melt-mixing the components. The resulting powder melts into a chunk of glass-like material, which is then ground into a fine powder using, for example, a mortar and pestal, of no more than about 2 mm, with the preferred particle size being from about 0.1 to about 20 µm. Tungsten oxide (WO 3 ), can be beneficially mixed with glass frit as opposed to merely using tungsten oxide (WO 3 ) as the sole accelerator. Tungsten oxide (WO 3 ) has been used as a substitute for the traditional accelerator, vanadium oxide (V 2 O 5 ), in cases where objections to the use of vanadium oxide (V 2 O 5 ) powder existed, and/or vanadium oxide (V 2 O 5 ) was unavailable. Substitution of tungsten oxide (WO 3 ) for vanadium oxide (V 2 O 5 ) yielded adequate results, as tungsten oxide (WO 3 ) possesses similar decomposition capabilities. However, tungsten oxide (WO 3 ) performed beneficially only at higher temperatures and for a smaller range of samples. By combining tungsten oxide (WO 3 ) with glass frit, a multicomponent accelerator is produced that is both non-toxic and is useful for application at a broader range of temperatures, thus covering a broader range of samples. The weight ratio of accelerators to each other when a multicomponent non-toxic accelerator is formed is not critical. The multicomponent accelerator can have any ratio in weight among the components. A more preferred range of accelerator components in a multicomponent accelerator comprises, for example, tungsten oxide and glass frit, in a weight ratio from 40:1 to 10:1. In the most preferred embodiment, the ratio by weight of tungsten oxide and glass frit is 20:1. Tungsten oxide can be combined with glass frit components using any of the previously described mixing techniques (dry mixing; wet mixing in water; wet mixing in solvent; mixing followed by heat treatment). Once it is determined which accelerator is to be used for a particular analysis, the accelerator is then mixed with the substance to be analyzed. Any suitable mixing technique can be utilized, such as hand blending the mixture of substance and accelerator using a spatula. The ratio of accelerator to the substance to be analyzed is not critical, and can vary within usual ranges used in the art. Preferably, about 2 grams of accelerator is mixed with approximately 0.15 grams of the substance to be analyzed. The non-toxic accelerators of the preferred embodiment are useful in testing for a broad range of particular elements in the elemental analysis of whatever substance is chosen for examination. The non-toxic accelerators of the preferred embodiment are useful in testing for sulfur, phosphorous, carbon, fluorine, chlorine, bromine, iodine, as well as other elements. The non-toxic accelerators of the preferred embodiment are useful in a wide range of analytical instrumentation applications, such as the SC-444 carbon and sulfur analyzer (made by LECO Corporation), although any suitable instrumentation may be employed. The general testing procedure is as follows. First, an appropriate amount of non-toxic accelerator of the preferred embodiment would be mixed with a desired amount of the substance to be tested. The mixture is then placed in a suitable combustion container. The combustion container with its contents is then placed in the combustion analyzer and heated to a temperature of about 450°C to about 1450°C. Certain photo-organic analyzing equipment exists that employs a combustion temperature of about 750°C. The SC-444 has a combustion range of about 450°C to about 1450°C, with the most preferred combustion temperature being about 1450°C. Once the sample is combusted, the gasses released are then analyzed for their elemental composition.

Claims: A method for accelerating the combustion decomposition of a substance to be analysed, the method comprising heating the substance to at least its decomposition temperature in the presence of a non-toxic combustion decomposition accelerator, the non-toxic combustion decomposition accelerator comprising a mixture of powdered glass frit and powdered tungsten oxide (WO 3 ). A method as claimed in claim 1 wherein the non-toxic combustion decomposition accelerator has a particle size of less than 2 mm. A method as claimed in claim 2 wherein the non-toxic combustion decomposition accelerator has a particle size of from 0.1 to 20 µm. A method as claimed in any preceding claim wherein the substance is heated to a combustion temperature of from 450°C to 1450°C. A method as claimed in claim 4 wherein the substance is heated to a combustion temperature of from 1250°C to 1450°C. A method as claimed in any preceding claim wherein the non-toxic combustion decomposition accelerator has a weight ratio of tungsten oxide (WO 3 ) to glass frit of from 40:1 to 10:1. A method as claimed in claim 6 wherein the non-toxic combustion decomposition accelerator has a weight ratio of tungsten oxide (WO 3 ) to glass frit in the region of 20:1. A method as claimed in any preceding claim wherein all components are combined by dry mixing. A method as claimed in claim 8 wherein the dry mixing is followed by melt mixing at a temperature of from 300°C to 1700°C. A method as claimed in claim 9 wherein the dry mixing is followed by melt -mixing at a temperature of from 500°C to 700°C. A method as claimed in any of claims 1 to 7 wherein all components are combined by wet mixing in a water solution. A method as claimed in claim 11 wherein the wet-mixing in a water solution is followed by heat treating at a temperature of from 300°C to 1700°C. A method as claimed in claim 12 wherein the wet-mixing in a water solution is followed by heat treating at a temperature of from 500°C to 700°C. A method as claimed in any of claims 1 to 7 wherein all components are combined by wet mixing in a solvent solution. A method as claimed in claim 14 wherein the wet mixing in a solvent solution is followed by heat treating at a temperature of from 300°C to 1700°C. A method as claimed in claim 15 wherein the wet mixing in a solvent solution is followed by heat treating at a temperature of from 500°C to 700°C. A powdered non-toxic combustion decomposition accelerator for elemental analysis comprising a powder mixture of tungsten oxide (WO 3 ) and glass frit. A non-toxic combustion decomposition accelerator as claimed in claim 17 wherein the non-toxic combustion decomposition accelerator has a weight ratio of tungsten oxide (WO 3 ) to glass frit of from about 40:1 to about 10:1. A non-toxic combustion decomposition accelerator as claimed in claim 18 wherein the non-toxic combustion decomposition accelerator has a weight ratio of tungsten oxide (WO 3 ) to glass frit of about 20:1. A non-toxic combustion decomposition accelerator as claimed in any of claims 17 to 19 wherein all components are combined by dry mixing, followed by melt-mixing at a temperature of from about 500°C to about 700°C, followed by grinding into a powder. A non-toxic combustion decomposition accelerator as claimed in any of claims 17 to 19 wherein all components are combined by wet mixing in a water solution, followed by heat treating at a temperature of from about 500°C to about 700°C, followed by grinding into a powder. A non-toxic combustion decomposition accelerator as claimed in any of claims 17 to 19 wherein all components are combined by wet mixing in a solvent solution, followed by heat treating at a temperature of from about 500°C to about 700°C, followed by grinding into a powder.

Inventors: CHEN GHING-FONG, GUERRA CARLOS, CHEN, GHING-FONG, GUERRA, CARLOS
Applicants: LECO CORP, LECO CORPORATION
Application year: 1995
Main classification: G01N33
IPC codes: C01B25, B01J27, C03C1, G01N31, B01J23