Silicon dioxide determination method capable of resisting organic silicon matrix interference

Abstract

The invention relates to the field of analytical chemistry and material testing, and mainly relates to a silicon dioxide determination method resistant to organic silicon matrix interference. The invention relates to an organosilicon matrix interference-resistant silicon dioxide determination method, which comprises: introducing an inert atmosphere, and removing oxygen; in the inert atmosphere environment, the temperature of the sample is gradually increased to 500-850 DEG C for treatment; the atmosphere is switched from the inert atmosphere to the oxidizing atmosphere, and treatment continues to be conducted at the temperature of 500-850 DEG C; and cooling and weighing to obtain the final residual mass percentage, namely the percentage of the added silicon dioxide in the sample. According to the application, through an innovative'inert pyrolysis-oxidation sweeping 'procedure, the principle defect that an organic matrix is misjudged as functional silicon dioxide by a traditional muffle furnace ashing method is fundamentally overcome.

Description

Technical Field

[0001] This application relates to the fields of analytical chemistry and materials testing, and mainly to a method for determining silica that is resistant to interference from organosilicon matrix. Background Technology

[0002] Defoamers, as important industrial additives, are widely used in textiles, papermaking, petroleum, food processing, water treatment, and chemical industries to suppress and eliminate harmful foam generated during production. Organosilicon defoamers, especially those based on polydimethylsiloxane (PDMS) with fumed silica (also known as white carbon black) as a key component, have become one of the most widely used and effective types of defoamers due to their low surface tension, good chemical stability, high safety, and high defoaming efficiency.

[0003] Silica (SiO2) plays a crucial role in the preparation of defoamers. It not only helps the organosilicon components to disperse and remain stable in the foaming system by forming a three-dimensional network structure in the base oil, but also acts as a "bubble-breaking point" to adsorb and impact the bubble film. Its low surface tension and unique surface structure significantly enhance the defoaming efficiency and foam-suppressing durability of the defoamer. The content, type (hydrophilic or hydrophobic), particle size, and dispersibility of silica directly affect the final performance of the defoamer. Therefore, accurately identifying and determining the content of added functional silica in defoamers is of vital importance for product quality control, formulation optimization, performance evaluation, and production cost management.

[0004] Ash content testing is a traditional method for determining the content of inorganic substances. Its basic principle is to decompose and volatilize the organic components through high-temperature incineration, leaving the residual inorganic matter as ash. However, defoamers are complex multi-component systems that, in addition to basic silicone oil and silica, often contain surfactants (dispersants, emulsifiers), polyether-modified silicone oils, thickeners, stabilizers, and carrier solvents. These components undergo complex thermal decomposition, oxidation, volatilization, and phase transition behaviors at high temperatures, significantly interfering with the specific determination of silica.

[0005] Currently, the main methods for determining silica content include gravimetric analysis (ash content test), X-ray fluorescence spectrometry (XRF), and titration. Among these, gravimetric analysis is commonly used in industry due to its simplicity and low cost. This method typically involves burning the sample to constant weight in a high-temperature furnace (such as a muffle furnace) and determining the ash content by calculating the mass difference before and after burning.

[0006] However, existing ash content testing methods and related standards have the following significant drawbacks and technical limitations when applied to complex silicone defoamers: First, the pyrolysis of organic components under an oxidizing atmosphere leads to fundamental measurement errors. Existing ash content tests are all conducted in air, under which conditions the organosilicon components in defoamers (such as PDMS and polyether-modified organosilicon) are oxidized to generate a large amount of silica. This study experimentally confirms that the infrared spectra of PDMS and polyether-modified organosilicon of different viscosities after calcination in a muffle furnace at 850℃ are in the range of 1000-1250 cm⁻¹. -1 (Si-O-Si antisymmetric stretching vibration), 750-850cm -1 and 500-600cm -1 All samples showed obvious characteristic absorption peaks of silica. This indicates that traditional ash content testing cannot distinguish between "added functional silica" and "silica generated by the pyrolysis of the organosilicon matrix itself," resulting in severely inflated measurement results that completely fail to reflect the true amount of functional silica added.

[0007] Secondly, high temperatures cause changes in the physicochemical properties of silicon dioxide. High temperatures in complex systems may cause silicon dioxide to sinter, undergo crystal transformation, or react with other metallic impurities to form silicates. These changes will affect the quality and properties of the final ash and introduce measurement errors.

[0008] Meanwhile, there are issues with sample splashing and evaporation loss: low-boiling-point solvents may boil violently during rapid heating; while polymeric components such as silicone oil may form residual carbon that is difficult to burn completely due to cross-linking and solidification. This residual carbon may encapsulate silica particles or explode during subsequent high-temperature burning, leading to sample loss and measurement errors.

[0009] Finally, the lack of specific standard operating procedures and the fact that existing methods do not take into account the complex composition and thermal behavior of defoamers lead to a lack of comparability of results from different laboratories.

[0010] In summary, when existing ash content testing methods are applied to defoamers, due to the fundamental flaws in their operation under an oxidizing atmosphere, they suffer from insurmountable systematic errors. These methods not only fail to address various interference issues but, more importantly, cannot distinguish the source of silica, leading to measurement results that completely deviate from the true content of functional silica.

[0011] Therefore, there is an urgent need to develop a completely new testing principle that can fundamentally avoid the interference caused by the pyrolysis and oxidation of organosilicon components, and achieve a dedicated and accurate determination of the content of added silica. Summary of the Invention

[0012] In view of the shortcomings of the prior art, the purpose of this application is to provide a method for determining silica that is resistant to interference from organosilicon matrix, and to provide a specific and accurate method for determining the content of added silica.

[0013] The technical solution of this application is as follows: A method for determining silica resistant to interference from an organosilicon matrix includes the following steps: Inert atmosphere is introduced to remove oxygen; The samples were treated in the inert atmosphere by gradually increasing the temperature to 500-850℃; The atmosphere was switched from the inert atmosphere to an oxidizing atmosphere, and the treatment continued at 500-850°C. After cooling and weighing, the final residual mass percentage is the percentage of added silica in the sample.

[0014] Furthermore, a method for determining silica resistant to interference from an organosilicon matrix includes the following steps: A high-purity inert atmosphere is introduced at a flow rate of 20-50 mL / min for 5-10 min to remove oxygen; The sample was subjected to a constant temperature treatment at 500-850℃ under an inert atmosphere. Switch the atmosphere from the inert atmosphere to dry air or oxygen atmosphere, and continue to treat at a constant temperature of 500-800℃ for 10-20 minutes to oxidize the trace amount of highly cross-linked pyrolytic carbon produced after inert pyrolysis into carbon dioxide gas for removal. The sample is cooled and weighed in an oxidizing atmosphere (air), and the final residual mass percentage is the percentage of added silica in the sample.

[0015] Furthermore, the inert atmosphere is one or a mixture of nitrogen and argon.

[0016] Nitrogen gas is preferably high-purity N2 (purity > 99.999%).

[0017] Furthermore, the oxidizing atmosphere is either air or O2.

[0018] Furthermore, the sample is subjected to a constant temperature treatment at 600-800℃ under an inert atmosphere. After switching the atmosphere from the inert atmosphere to the oxidizing atmosphere, the mixture is subjected to constant temperature treatment at 600-800℃.

[0019] Furthermore, when introducing the inert atmosphere to completely remove oxygen, the inert atmosphere is introduced at a flow rate of 20-50 mL / min.

[0020] Furthermore, the sample was heated from room temperature to 500-850°C at a rate of 10-20°C / min in the inert atmosphere.

[0021] Furthermore, when switching the atmosphere from the inert atmosphere to the oxidizing atmosphere, the flow rate is 20-50 mL / min.

[0022] Furthermore, an atmosphere-controlled thermogravimetric analyzer was used as the measurement platform.

[0023] Furthermore, after switching the atmosphere from the inert atmosphere to the oxidizing atmosphere, the process is carried out at a constant temperature consistent with the end temperature of the previous stage.

[0024] Furthermore, the inert atmosphere is nitrogen, and the oxidizing atmosphere is air.

[0025] To address the technical problem of existing muffle furnace ashing methods where the organosilicon components (such as PDMS and polyether-modified organosilicon) are oxidized to form silica due to burning in an oxidizing atmosphere, making it impossible to distinguish between added functional silica and organosilicon pyrolysis source silica, resulting in seriously inflated measurement results, this application proposes a novel solution.

[0026] The basic approach of this application is to innovatively employ an atmosphere-controlled thermogravimetric analyzer (TGA) as the measurement platform and design a two-step temperature-atmosphere program of "inert pyrolysis-oxidation cleaning". This method first thoroughly removes organic components (silicone oil, emulsifiers, solvents, etc.) from organosilicon system samples, such as defoamers, through pyrolysis and volatilization under a high-purity nitrogen atmosphere, while ensuring the stability of the added silica filler. Subsequently, the atmosphere is switched to air or oxygen, and trace amounts of residual carbon that may be generated in the inert atmosphere are completely oxidized and removed within an appropriate isothermal time. The final stable residue is the mass of the added silica.

[0027] The overall technical benefits of this application are significant: this method fundamentally avoids the interference of silica generated by the organosilicon components themselves, achieving truly specific and precise quantification of the content of added functional silica in defoamers, with measurement results unaffected by the type, viscosity, or modification method of the base oil. This application provides a reliable and authoritative analytical tool for the formulation analysis, quality control, and performance research of organosilicon systems such as defoamers.

[0028] The method in this application fundamentally solves the fundamental defect of traditional muffle furnace ashing methods that misidentify the organic matrix itself as functional silica through an innovative "inert pyrolysis-oxidation cleaning" procedure.

[0029] Furthermore, no complex blank correction is required during the measurement process, as the interference from organic components has already been eliminated in the first step through physical means (evaporation).

[0030] Compared with the prior art, this application has the following beneficial effects: This application provides, for the first time, a method for the absolute and specific quantitative determination of added silica in defoamers. It completely overturns the underlying logic of traditional ash content testing. Through the core innovation of "atmosphere switching," it precisely targets the "added functional silica" from the highly interfering "total residue," thus solving a long-standing pain point in the industry. The data is accurate, reliable, and authoritative. Detailed Implementation

[0031] This application provides a method for determining silica that resists interference from an organosilicon matrix. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0032] This application provides a method for determining silica that resists interference from organosilicon matrix, comprising the following steps: Step 1: Initial Stability: An atmosphere-controlled thermogravimetric analyzer (TGA) was used as the measurement platform. An inert atmosphere was introduced into the sample chamber at a flow rate of 20-50 mL / min and stabilized for 5-10 min to completely remove oxygen.

[0033] The preferred inert atmosphere is nitrogen (N2) or argon (Ar).

[0034] This application does not simply use TGA, but rather cleverly transforms the neglected thermal behavior of organosilicon into an object to be eliminated by pyrolysis and volatilization under an inert atmosphere rather than oxidation residue.

[0035] This step ensures that the reaction begins in a pure, inert environment, achieving complete pyrolysis of the organic matter rather than oxidation.

[0036] Step 2: Inert pyrolysis: Add 5-8 mg of homogenized sample to the sample chamber and record the sample mass.

[0037] Under a 100% inert atmosphere, the temperature is increased from room temperature to 500-850°C at a rate of 10-20°C / min and held at that temperature for 10-20 minutes.

[0038] Preferably, the temperature is increased from room temperature to 600-800°C.

[0039] More preferably, the temperature is increased from room temperature to 700°C.

[0040] A final pyrolysis temperature of 600-800℃ is a preferred range. For certain organosilicon components that are particularly difficult to pyrolyze, the temperature can be appropriately increased to 850℃; for systems with known low pyrolysis temperatures, the temperature can be appropriately reduced to 550℃, as long as the organic components are completely volatilized. Otherwise, it will interfere with the subsequent oxidation to form silica after the introduction of oxygen.

[0041] The purpose of this step is to allow all organic components to fully pyrolyze and volatilize.

[0042] This stage is crucial for achieving specific quantification. It ensures that over 99.9% of organic components are removed as volatile small molecules, rather than being oxidized into residual SiO2, fundamentally eliminating up to 50% or more of the systematic positive error.

[0043] Step 3: Atmosphere switching and oxidation cleaning: Switch the atmosphere from inert to oxidizing (flow rate 20-50 mL / min), that is, first introduce oxygen atmosphere and then cut off inert atmosphere. It is necessary to maintain atmosphere protection at all times.

[0044] Then hold the temperature at 500-850°C (the same as the final temperature of the previous stage) for 10-20 minutes.

[0045] The oxidizing atmosphere is air and O2.

[0046] The purpose of this step is to oxidize and remove any trace amounts of pyrolytic carbon that may be present.

[0047] This stage ensures that the organic components and trace amounts of carbon produced by pyrolysis in the sample are completely removed, solving the problem of approximately 10% of the interference residue, thereby obtaining a pure and constant quality of added silica.

[0048] Step 4: Cooling and Weighing The program ends, automatically cools to room temperature, and the system automatically records the final residual mass percentage (%).

[0049] Step 5: Result Calculation: Final residual mass percentage (%) = percentage of added silica in the sample (%).

[0050] This method is not only applicable to defoamers, but can also be widely used in any system that requires differentiation between "added inorganic fillers" and "the pyrolysis residue of the organosilicon matrix itself", such as filler analysis of products like silicone rubber, organosilicon sealants, and silicone grease.

[0051] The traditional muffle furnace ashing method involves high-temperature burning in an air atmosphere. Its fatal flaw lies in its inability to distinguish between "added functional silica" and "silica generated by the pyrolysis and oxidation of the organosilicon matrix itself".

[0052] The defoamer samples containing polydimethylsiloxane, allyl polyether-modified silicone, and defoamer samples containing polydimethylsiloxane and allyl polyether-modified silicone but not silica were tested according to GB / T 508-85, the method for determining ash content in petroleum products. The test results showed that: After polydimethylsiloxane (PDMS) is calcined in a muffle furnace at 850°C, its mass residue is as high as about 50%.

[0053] When allyl polyether-modified silicone is burned under the same conditions, approximately 17% of the mass remains.

[0054] Defoamer samples that do not contain silica but contain polydimethylsiloxane and allyl polyether modified silicone can still be tested by the muffle furnace method and still contain about 10% ash. This residue mainly comes from the thermal decomposition products of additives such as PDMS, allyl polyether silicone, and emulsifiers in the formulation.

[0055] The above data shows that the "ash content" measured by the traditional ash content method is a mixed signal composed of residual SiO2 from added SiO2 and SiO2 from the pyrolysis of the organosilicon matrix. The measurement results have no linear relationship with the actual content of "added functional silica" and have been completely distorted and invalid.

[0056] This application first heats the organic components in an inert atmosphere (e.g., N2) to guide them through a "pyrolysis and volatilization" path, thereby physically removing them from the sample. Then, it removes any trace amounts of residual carbon that may be present by using an oxidizing atmosphere (e.g., air), ultimately ensuring that the residue comes from added functional silica.

[0057] The method described in this application solves the two major problems of "interference from the organosilicon matrix" and "interference from additives," which is something that no other scheme that optimizes the traditional muffle furnace process can achieve.

[0058] The present application will be further described below through specific embodiments.

[0059] Example The following method for determining silica to resist interference from organosilicon matrix was used to measure five samples: pure PDMS (high viscosity), pure PDMS (low viscosity), pure allyl polyether modified silica, defoamer known to be free of SiO2, and defoamer known to contain 20% SiO2.

[0060] A method for determining silica resistant to interference from an organosilicon matrix includes the following steps: Step 1: Initial Stability: An atmosphere-controlled thermogravimetric analyzer (TGA) was used as the measurement platform.

[0061] The inert atmosphere is high-purity N2 (purity >99.999%). The sample chamber is circulated with the inert atmosphere at a flow rate of 40 mL / min and stabilized for 10 min to completely remove oxygen.

[0062] Step 2: Inert pyrolysis: Add the sample into the sample chamber and record the sample quality.

[0063] Under a 100% inert atmosphere, the temperature was increased from room temperature to 800°C at a rate of 20°C / min and held at that temperature for 20 minutes.

[0064] Step 3: Atmosphere switching and oxidation cleaning: The oxidizing atmosphere is air. The atmosphere is switched from an inert atmosphere to an oxidizing atmosphere (flow rate 20 mL / min), and the temperature is kept constant at 800℃ for 20 min.

[0065] Step 4: Cooling and Weighing The program ends, automatically cools to room temperature, and the system automatically records the final residual mass percentage (%).

[0066] Step 5: Result Calculation: Final residual mass percentage (%) = percentage of added silica in the sample (%).

[0067] Comparative Example Referring to GB / T 508-1985, five samples were tested using a muffle furnace, including the following steps: Step 1: Pre-treat the crucible at 850℃ until the mass difference between two weighings is no greater than 0.0005g.

[0068] Step 2: Add the sample to the crucible, then place it on a hot plate and gradually heat it to 750℃ for pre-carbonization, and keep it at that temperature for 2 hours.

[0069] Step 3: Transfer the pre-carbonized material from Step 2 to a muffle furnace, gradually heat it to 850℃, and hold it at that temperature for 2 hours.

[0070] Step 4: Turn off the muffle furnace, cool the material in the crucible to room temperature, weigh it, and calculate the ash content.

[0071] The results of the measurements of the five samples in the examples and comparative examples are shown in Table 1.

[0072] Table 1

[0073] The traditional muffle furnace method, due to its inherent flaws, treats both the organic matrix and the additives themselves as analytes, rendering its measurement results for functional silica completely unreliable. The method described in this application, by altering the pyrolysis path, fundamentally avoids this error, and the results closely match the true values.

[0074] Repeatability and precision verification: The sample containing 20% ​​SiO2 was measured 6 times according to the method in the example.

[0075] Average: 20.17% Relative standard deviation (RSD): 0.94% The repeatability and precision verification shows that the method in the embodiments of this application achieves high accuracy while also having excellent reproducibility and precision (RSD<1%).

[0076] Spike recovery verification: The method described in the example was used for determination.

[0077] Recovery rate = 96.0% In the spiked recovery validation, the recovery rate of 96.0% fully demonstrates that the method has strong anti-interference ability and accuracy, and can effectively handle complex matrix samples.

[0078] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of this application.

Claims

1. A method for determining silica resistant to interference from an organosilicon matrix, characterized in that, Includes the following steps: Inert atmosphere is introduced to remove oxygen; The samples were treated in the inert atmosphere by gradually increasing the temperature to 500-850℃; The atmosphere was switched from the inert atmosphere to an oxidizing atmosphere, and the treatment continued at 500-850°C. After cooling and weighing, the final residual mass percentage is the percentage of added silica in the sample.

2. The method for determining silica resistant to interference from organosilicon matrix according to claim 1, characterized in that, The inert atmosphere is one or a mixture of nitrogen and argon.

3. The method for determining silica resistant to interference from organosilicon matrix according to claim 1, characterized in that, The oxidizing atmosphere is either air or O2.

4. The method for determining silica resistant to interference from organosilicon matrix according to claim 1, characterized in that, The sample was treated by gradually heating it to 600-800℃ in the inert atmosphere. After switching the atmosphere from the inert atmosphere to the oxidizing atmosphere, the mixture is subjected to constant temperature treatment at 600-800℃.

5. The method for determining silica resistant to interference from organosilicon matrix according to claim 1, characterized in that, When introducing the inert atmosphere to completely remove oxygen, the inert atmosphere is introduced at a flow rate of 20-50 mL / min.

6. The method for determining silica resistant to interference from organosilicon matrix according to claim 1, characterized in that, The sample was heated from room temperature to 500-850°C at a rate of 10-20°C / min in the inert atmosphere.

7. The method for determining silica resistant to interference from organosilicon matrix according to claim 1, characterized in that, When switching the atmosphere from the inert atmosphere to the oxidizing atmosphere, the flow rate is 20-50 mL / min.

8. The method for determining silica resistant to interference from organosilicon matrix according to claim 1, characterized in that, After switching the atmosphere from the inert atmosphere to the oxidizing atmosphere, the process is kept at a constant temperature consistent with the end temperature of the previous stage.

9. The method for determining silica resistant to interference from organosilicon matrix according to claim 1, characterized in that, The inert atmosphere is nitrogen, and the oxidizing atmosphere is air.

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