High‐temperature calorimetric study of oxide component dissolution in a CaO–MgO–Al2O3–SiO2 slag at 1450°C

Blast‐furnace slags are formed, as iron ore is reduced to metal, as a molten a mixture of refractory and not easily reducible oxides, largely silica, alumina, lime, and magnesia. Their relatively low silica content makes them basic and poor glass formers. Their thermodynamic properties, though important for modeling their formation and reactivity, as well as furnace heat balance, are poorly known. Solution calorimetry of small amounts of solid oxides in a molten oxide solvent at high temperature (up to about 1500°C) permits direct assessment of energetics of dissolution. The enthalpies of solution of slag forming oxides: CaO, SiO₂, Al₂O₃, MgO, and Fe₂O₃ in a simplified model slag of composition: CaO (45.9 mol%), SiO₂ (35.1 mol%), Al₂O₃ (8.3 mol%), MgO (10.7 mol%) were measured by high‐temperature drop solution calorimetry at 1450°C. For this slag composition, enthalpies of solution become more exothermic in the order: Fe₂O₃ (279.3 ± 20.8 kJ/mol), MgO (56.7 ± 9.1 kJ/mol), Al₂O, (41.6 ± 11.3 kJ/mol), CaO (?4.3 ± 2.3 kJ/mol), and SiO₂, (?20.4 ± 4.4 kJ/mol), reflecting the relatively basic character of this low‐silica melt. Within these fairly large experimental errors, characteristic of calorimetry at this high temperature, there is little or no discernible concentration dependence for these heats of solution. The trends seen for these five solutes parallel those seen for heats of solution of the same oxides in other melts at various temperatures, with changes in magnitude reflecting the differences in acid‐base character of the melts. The new data for quartz show systematic behavior which extends the range of basicity studied for the enthalpy of dissolution of silica. The results provide reliable data for future modeling of the thermal balance of steel‐making furnaces and geologic and ceramic systems.     

Stability and calorimetric studies of silico‐ferrites of calcium aluminum and magnesium

In a systematic study on silico‐ferrites of calcium aluminum and magnesium (SFCA phases) this investigation focuses on synthesis of silicon‐free SFCA‐type compounds with low‐MgO contents (~1.00 apfu—atoms per formula unit). Previous studies revealed the existence of iron‐rich SFCA phases similar to the SFCA‐I structure with the chemical composition Ca₃MgAl₆Fe₁₀O₂₈ (Metall Mater Trans B. 2017;48:2207). The experimental results in the quaternary Fe₂O₃‐CaO‐Al₂O₃‐MgO system confirm large stability fields of 2 silicon‐free ferrites FCAM‐I and FCAM‐III, which are members of the homologous series M_14+6nO_20+8n (n = 1, 2). Starting with compositions corresponding to Ca₃MgAl_xFe_16‐xO₂₈ (with increasing aluminum content from x = 0‐12 apfu), it was possible to synthesize these phases with an x‐value ≥2 apfu, which corresponds to Al₂O₃ contents ≥7.14 wt%. Synthesis of pure silicon‐free ferrites with n = 1 (FCAM‐I) and 2 (FCAM‐III) and silicon‐bearing ferrites with n = 0 (SFCA) was possible. Samples were characterized by electron probe microanalysis, powder diffraction, and subsequently studied using relaxation calorimetry measurements in combination with differential scanning calorimetry for determination of the heat capacities and standard entropies S°(298). The corresponding values are S°(298) = 650.3 ± 4.6 J/mol·K for SFCA, S°(298) = 864.5 ± 6.1 J/mol·K for FCAM‐I, and S°(298) = 1206.2 ± 8.4 J/mol·K for FCAM‐III. These thermodynamic data are a step toward a rigorous quantitative thermodynamic modeling of the iron ore sintering process.     

Drop‐and‐catch (DnC) calorimetry using aerodynamic levitation and laser heating

Design, calibration, and operation of a system for drop‐and‐catch (DnC) calorimetry on oxides from temperature above 1500°C are described. This system allows the measurement of heat contents and heats of fusion by drop calorimetry of small (100 mg or less) samples held by containerless levitation at high temperature and dropped in a calorimeter at room temperature. The spheroids, 2‐3 mm in diameter, prepared by laser melting of powders, are aerodynamically levitated in a splittable nozzle levitator and laser heated to the desired temperature monitored by radiation thermometry. The sample is dropped by splitting the nozzle and caught by splittable water‐cooled calorimetric plates at 25°C, which provide complete enclosure of the sample to avoid heat loss by radiation. The drop time is ~0.1 seconds, calorimeter equilibration time after the drop is ~15 minute. DnC experiments are automated with software‐controlled laser power and programmable delay between splitting the nozzle and catching the sample. The fusion enthalpy of Al₂O₃ measured by DnC calorimeter, 120 ± 10 kJ/mol, agrees well with previously reported values. The system can be used for measurements of fusion enthalpies of refractory oxides amenable to laser heating as well as for splat quenching of oxide melts.     

Thermodynamics of copper‐manganese and copper‐iron spinel solid solutions

High‐temperature oxide melt solution calorimetry has been performed to investigate the energetics of spinel solid solutions in the Mn₃O₄‐CuMn₂O₄ and Fe₃O₄‐CuFe₂O₄ systems. The spinel solid solutions were synthesized by a ceramic route and calcined at appropriate temperatures to obtain single phase samples. The drop solution enthalpies of the solid solutions in the Mn₃O₄‐CuMn₂O₄ system are the same within experimental error as the enthalpies of drop solution of mechanical mixtures of the end‐members, indicating a zero heat of mixing, i.e., ideal mixing in terms of enthalpy. In Fe₃O₄‐CuFe₂O₄, the drop solution enthalpy of the solid solutions shows a positive deviation from those of the mechanical mixture of the end‐members, suggesting negative mixing enthalpy. The formation enthalpies of the spinel solid solutions from their constituent oxides plus oxygen and from the elements were also determined.     

A chaos‐based iterated multistep predictor for blast furnace ironmaking process

The prediction and control of the inner thermal state of a blast furnace, represented as silicon content in blast furnace hot metal, pose a great challenge because of complex chemical reactions and transfer phenomena taking place in blast furnace ironmaking process. In this article, a chaos‐based iterated multistep predictor is designed for predicting the silicon content in blast furnace hot metal collected from a pint‐sized blast furnace. The reasonable agreement between the predicted values and the observed values indicates that the established high dimensional chaotic predictor can predict the evolvement of silicon series well, which conversely render the strong indication of existing deterministic mechanism ruling the dynamics of complex blast furnace ironmaking process, i.e., a high‐dimensional chaotic system is suitable for representing the blast furnace system. The results may serve as guidelines for characterizing blast furnace ironmaking process, an extremely complex but fascinating field, with chaos in the future investigation. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

3‐D numerical simulations on flow and mixing behaviors in gas–liquid–solid microchannels

Three‐dimensional (3‐D) gas‐liquid–solid flow and mixing behaviors in microchannels were simulated by coupled volume of fluid and discrete phase method and simulations were validated against observations. The detachment time and length of gas slug are shortened in liquid–solid flow, compared with those in liquid flow due to higher superficial viscosity of liquid–solid mixture, which will move the bubble formation toward the dripping regime. Solid particles mainly distribute in liquid slug and particle flow shows obvious periodicity. With the increase of contact angle of the inner wall, gas slug (0–50°), stratified (77–120°), and liquid drop (160°) flows are observed. The residence time distributions of solid and liquid phases are similar because particles behave as tracers. The backmixing of solid and liquid phases in liquid drop flow is the weakest among the three flow patterns, and the backmixing of gas phase in slug flow is weaker than that in both stratified and liquid drop flows. The results can provide a theoretical basis for the design of microreactors. © 2013 American Institute of Chemical Engineers AIChE J, 59: 1934–1951, 2013     

Flash sintering of a three‐phase alumina,spinel, and yttria‐stabilized zirconia composite

Three‐phase ceramic composites constituted from equal volume fractions of α‐Al₂O₃, MgAl₂O₄ spinel, and cubic 8 mol% Y₂O₃‐stabilized ZrO₂ (8YSZ) were flash‐sintered under the influence of DC electric fields. The temperature for the onset of rapid densification (flash sintering) was measured using a constant heating rate at fields of 50‐500 V/cm. The experiments were carried out by heating the furnace at a constant rate. Flash sintering occurred at a furnace temperature of 1350°C at a field of 100 V/cm, which dropped to 1150°C at a field of 500 V/cm. The sintered densities ranged from 90% to 96%. Higher electric fields inhibited grain growth due to the lowering of the flash temperature and an accelerated sintering rate. During flash sintering, alumina reacted with the spinel phase to form a high‐alumina spinel solid solution, identified by electron dispersive spectroscopy and from a decrease in the spinel lattice parameter as measured by X‐ray diffraction. It is proposed that the solid solution reaction was promoted by a combination of electrical field and Joule heating.     

Early stage dissolution characteristics of aluminosilicate glasses with blast furnace slag‐ and fly‐ash‐like compositions

Supplementary cementitious materials (SCM) have been used by the cement industry for decades to partly replace the portland cement fraction of concrete binders. This is particularly important today in addressing CO₂ emissions from the cement manufacturing process. However, defining the reactivity of these mainly aluminosilicate‐based materials and their influence on portland cement hydration chemistry has challenged the research community and has limited SCM replacement levels in cementitious binders. In this study, aluminosilicate glasses as models for blast furnace slag and fly‐ash systems were synthesized and exposed to different activator solutions in a continuously stirred closed system reactor for a period up to 3 hours. Solution compositions were measured from the very first minutes of dissolution and correlated with results from complementary solid surface analysis. Initial Ca concentration maxima in the first 30 minutes of exposure to the activating solution was a common feature in most dissolution profiles with a subsequent rapid decline attributable to Ca‐reincorporation on the reacting surface. Surface‐specific analysis confirmed Ca and Al enrichment at the surface, suggesting the formation of a Ca‐modified aluminosilicate layer, supporting a dissolution‐reprecipitation mechanism for SCM reactivity. Differing chemistries are thought to be responsible for the Ca and Al reintegration on the reacting surface depending on the pH of the solution; near‐neutral conditions favor Ca‐readsorption and surface condensation reactions, whereas alkaline solutions favor Ca‐reintegration via covalently bound phases.     

Energetics of Substituted Pollucites Along the CsAlSi2O6–CsTiSi2O6.5 Join: A High-Temperature Calorimetric Study

Enthalpies of drop solution for a suite of substituted pollucites with the compositions CsTi _x Al_{1− x} Si₂O_{6+0.5 x} , 0 ≤ x ≤ 1, which are synthesized using the sol–gel method, have been measured in molten lead borate (2PbO·B₂O₃) at 701°C. As Ti⁴⁺ substitutes for Al³⁺, the enthalpies of drop solution become less endothermic and show exothermic heats of mixing within the composition range from x = 0.3 to 1. This nonideal mixing behavior is consistent with the trend seen in variation of lattice parameters, and we interpret it to be a result of the short-range order associated with the framework cations Al³⁺, Si⁴⁺, and Ti⁴⁺ in the structure. Using enthalpies of drop solution of SiO₂, Al₂O₃, TiO₂, and Cs₂O, standard molar enthalpies of formation of these phases from their constituent oxides and from the elements are derived for the first time.     

The effect of storage temperatures below 100°C on the viscosity of a novolak resin propylene glycol solution

The aging of a novolak resin solution used in iron‐making blast furnace taphole clays is reported. The novolak resin propylene glycol solution was aged at temperatures between 2 and 80°C for up to 56 days. The viscosity was measured to evaluate the change in the resin's behavior. A cure reaction was found to occur with the addition of hexamethylenetetramine (HMTA) at temperatures lower than had previously been reported. Methods for handling and storage of taphole clay to avoid excessive increases in viscosity due to aging are discussed. An approach for estimating the long term aging at temperatures of 30 to 50°C was considered using shorter term aging data obtained at 70 and 80°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 267–276, 2004     

Residual compressive strength of fire‐damaged mortar after post‐fire‐air‐curing

The effects of cooling regimes and post‐fire‐air‐curing on compressive strength of mortar were investigated. Mortars were made with CEN reference sand, CEM I 42.5 R cement and natural spring water. The sand–cement and water–cement materials' ratios were chosen as 3.0 and 0.50 for all mixtures, respectively. At 28 days, the specimens were heated to maximum temperatures of 400, 600, 800 and 1000°C. Specimens were then allowed to cool in the air, furnace and water. After cooling, the specimens were air‐recured. Compressive strength test was carried out before air‐recuring and after 7 days of air‐recuring. The highest reduction in compressive strength was observed at 1000°C regardless of cooling regime. Gradual cooling regime in air and furnace without post curing showed almost no difference in terms of compressive strength reduction for four elevated temperatures. Shock cooling in water caused significant reduction in compressive strength compared with both gradual cooling regimes without post curing. After air and furnace cooling regimes, 7 days air‐recured specimens showed further reduction in compressive strength for four elevated temperatures. Specimens cooled in water and subjected to 7 days air‐recuring showed significant strength gain approximately 39, 100 and 130% for 400, 600 and 800°C elevated temperature, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermodynamic Stability of Low‐k Amorphous SiOCH Dielectric Films

Si–O–C‐based amorphous or nanostructured materials are now relatively common and of interest for numerous electronic, optical, thermal, mechanical, nuclear, and biomedical applications. Using plasma‐enhanced chemical vapor deposition (PECVD), hydrogen atoms are incorporated into the system to form SiOCH dielectric films with very low dielectric constants (k). While these low‐k dielectrics exhibit chemical stability as deposited, they tend to lose hydrogen and carbon (as labile organic groups) and convert to SiO₂ during thermal annealing and other fabrication processes. Therefore, knowledge of their thermodynamic properties is essential for understanding the conditions under which they can be stable. High‐temperature oxidative drop solution calorimetry measurement in molten sodium molybdate solvent at 800°C showed that these materials possess negative formation enthalpies from their crystalline constituents (SiC, SiO₂, C, Si) and H₂. The formation enthalpies at room temperature become less exothermic with increasing carbon content and more exothermic with increasing hydrogen content. Fourier transform infrared spectroscopy (FTIR) spectroscopy examined the structure from a microscopic perspective. Different from polymer‐derived ceramics with similar composition, these low‐k dielectrics are mainly comprised of Si–O(C)–Si networks, and the primary configuration of carbon is methyl groups. The thermodynamic data, together with the structural analysis suggest that the conversion of sp² carbon in the matrix to surface organic functional groups by incorporating hydrogen increases thermodynamic stability. However, the energetic stabilization by hydrogen incorporation is not enough to offset the large entropy gain upon hydrogen release, so hydrogen loss during processing at higher temperatures must be managed by kinetic rather than thermodynamic strategies.     

Solution‐Controlled Dissolution of Supplementary Cementitious Material Glasses at pH 13: The Effect of Solution Composition on Glass Dissolution Rates

Supplementary cementitious materials (SCMs) are widely used to partially replace portland clinker in blended cements. Reducing clinker contents further without compromising the development of early strength necessitates a better assessment and enhancement of the reactivity of the available SCMs. To this purpose, the reactivity of synthesized calcium aluminosilicate glasses covering a compositional range from blast‐furnace slags (BFS) over fly ashes to silica fume was analyzed by dissolution experiments. Initial glass dissolution rates were measured at 20°C and pH 13, and with varying initial concentrations of aqueous Al, Ca, and Si. At pH 13, glass dissolution rates were observed to scale linearly with the glass Ca/(Al + Si) molar ratio. Ca‐rich blast‐furnace type glass dissolution was shown to be up to one order of magnitude faster than tectosilicate fly ash and silica fume type glass dissolution, supporting different pathways to dissolution. In solutions that are strongly undersaturated with respect to hydrous glass and hydration products, glass dissolution rates are independent of changes in solution undersaturation and aqueous Si activity. In contrast, dissolution rates decrease with aqueous Ca concentration for all glasses and with aqueous Al concentration for tectosilicate‐type glasses. The insights gained are instrumental in finding ways to enhance SCM reactivity.     

Solubility of N‐Guanylurea Dinitramide in Binary Solvent Mixtures

The solubility of N‐guanylurea dinitramide (GUDN, Fox‐12) in binary solvent mixtures was measured. Binary solvents such as dimethyl sulfoxide (DMSO)/water and N,N‐dimethylacetamide (DMA)/water were investigated. The temperature was in the range of 0 °C to 70 °C for DMA‐water and 20 °C to 70 °C for DMSO‐water. The temperature dependence on the solubility was higher in DMA‐water than in DMSO‐water at the same fraction of water. On the other hand, the modeling data was obtained by using the Apelblat equation. The average relative errors are less than 3 %. Supersaturation for crystallization of GUDN in solution can be easily generated by adding water in DMSO (or DMA).     

Crystallization Behavior of Molecular Compound in Binary Mixture System of 1,3‐Dioleoyl‐2‐Palmitoyl‐sn‐Glycerol and 1,3‐Dipalmitoyl‐2‐Oleoyl‐sn‐Glycerol

Previous studies showed that the stable β‐form of molecular compound (MC) crystals having a double‐chain‐length structure is formed in a binary mixture system of 1,3‐dioleoyl‐2‐palmitoyl‐sn‐glycerol (OPO) and 1,3‐dipalmitoyl‐2‐oleoyl‐sn‐glycerol (POP) with a 1:1 concentration ratio of OPO and POP. The use of MC crystals made of POP and OPO for edible applications, such as margarine, is advantageous due to no‐trans, low‐saturated, and high‐oleic fats. Industrial manufacturing technology involves rapid cooling processes, and the kinetic properties of crystallization of MC of OPO and POP are required. In this study, we clarified the crystallization of MC of OPO and POP under rapid cooling at rates of 1–150 °C min^?1, using synchrotron radiation time‐resolved X‐ray diffraction and differential scanning calorimetry methods. The main results are as follows: (1) POP and OPO crystallized in separate manners without the formation of MC crystals under rapid cooling (>40 °C min^?1), while MC crystals started to form with decreasing rates of cooling in addition to the POP and OPO crystals (<30 °C min^?1); (2) metastable and stable forms sub‐α, α, β′, and β of POP and OPO were formed, whereas the MC crystals of β were formed during the cooling processes; and (3) the heating processes after crystallization by rapid cooling caused separate melting of the metastable and stable forms of POP and OPO crystals and the formation of MC crystals of β made of POP and OPO, as well as melting of the MC crystals alone.     

Formation mechanism and growth of MNbO3, M=K,Na by in situ X‐ray diffraction

Hydrothermal synthesis is a well‐established method to produce complex oxides, and is a potential interesting approach to synthesize stoichiometric lead‐free piezoelectric K_0.5Na_0.5NbO₃. Due to challenges in obtaining the desired stoichiometry of this material, more knowledge is needed on how the end‐members, KNbO₃ and NaNbO₃, are nucleating and growing. Here, we report on the formation mechanisms and growth during hydrothermal synthesis of KNbO₃ and NaNbO₃ by in situ synchrotron powder X‐ray diffraction. We show that tetragonal KNbO₃ crystallites form from dissolved T‐Nb₂O₅ at 250°C‐300°C and 250 bar while orthorhombic NaNbO₃ forms via several crystalline intermediate phases at 225°C‐325°C and 250 bar. The crystallite size of KNbO₃ is decreasing while the crystallite size of NaNbO₃ is increasing with increasing temperature, demonstrating that the presence of intermediate phases is highly important for the nucleation and growth of the final product. The different crystallization schemes explain the challenge in obtaining stoichiometric K_0.5Na_0.5NbO₃ by hydrothermal synthesis.     

Novel Utilization of Fly Ash for High‐Temperature Mortars: Phase Composition,Microstructure and Performances Correlation

In this study, the feasibility of using fly ash to manufacture high‐temperature mortars was investigated. The investigation was set to define preliminary characteristics of new types of mortars based on ordinary and/or refractory cement with fly ash addition, and to establish mutual correlation between thermally induced changes of mineral phases, microstructure, and final performances of the mortars. New mortars, made up of 21% cement (PC‐CEM I 42.5R/HAC‐Secar 70/71), 70% river sand, and 9% fly ash, were chemically, physically, and mechanically characterized to determine possibilities of fly ash re‐utilization for high‐temperature purposes. The fly ash samples, which originated from four different power plants, were mechanically activated. Mortars were heat‐treated up to 1300°C in a laboratory tunnel furnace with retention time 2 h. Thermal stability of crystalline phases were studied by differential thermal analysis (DTA); thermally induced changes in mineral phase composition were analyzed by XRD; and microstructure were investigated by scanning electron microscopy. Correlated results of DTA, XRD, and SEM analyses indicated initiation of sintering processes at approximately 1300°C and formation of thermally stable minerals (rankinite, gehlenite, anorthite, cristobalite). The investigation highlights a sustainable approach of using fly ash in developing ecofriendly mortars for high‐temperature application.     

Fundamental investigations of differences in bonding mechanisms in iron ore sinter formed from magnetite concentrates and hematite ores

Whilst increasing amounts of imported hematite ores are being added with the magnetite concentrates that dominate sinter blends in the People's Republic of China, little is known about the fundamental behaviour of magnetite concentrates during sintering compared to hematite ores. Compacted tablets of fluxed magnetite, magnetite–hematite and hematite concentrates and ores were fired under simulated sintering conditions in the laboratory to establish the fundamental differences in sintering behaviour, mineralogy and bonding mechanisms between magnetite concentrates and hematite ores.

Sinter made from magnetite concentrates (<10% hematite) relies on the formation of a network of fused magnetite–magnetite grains (diffusional bonding) and high temperatures (1350–1370 °C) to obtain satisfactory sinter tumble strength. Magnetite–hematite concentrate mixtures, with <45% hematite, behave during sintering like magnetite concentrates. The large phase field for Magnetite+Liquid under typical sintering compositions and temperatures was found to prevent all but minor formation of Ca-ferrites via hematite from low-basicity (<2.0) sinter blends dominated by magnetite concentrates.

In contrast, hematite ores with high (>2.0) effective basicity are able to form a high tumble strength sinter matrix composed of a network of abundant calcium ferrites (e.g. SFCA, SFCA I) below 1300 °C.     

Thermal and morphological studies of chemically prepared emeraldine‐base‐form polyaniline powder

In this study, emeraldine base (EB)‐form polyaniline (PANI) powder was chemically prepared in 1M HNO₃ aqueous solution. The thermal characteristics and chemical structures of this powder were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and X‐ray diffraction (XRD). A polarizing optical microscope was also used to examine the crystalline morphology of this sample. The results indicated that the EB‐form PANI powder had a discernible moisture content. Moreover, in the first run of DSC thermal analysis, the exothermic peak at 170–340°C was due to the crosslinking reaction occurring among the EB‐form PANI molecular chains. FTIR and XRD examinations further confirmed the chemical crosslinking reaction during thermal treatment. TGA results illustrated that there were two major stages for weight loss of the EB‐form PANI powder sample. The first weight loss, at the lower temperature, resulted from the evaporation of moisture. The second weight loss, at the higher temperature, was due to the chemical structure degradation of the sample. The degradation temperature of the EB‐form PANI powder was around 420–450°C. The degradation temperature of emeraldine salt (ES)‐form PANI powder was lower (around 360–410°C) than that of the EB form (around 420–450°C). From the TGA results, I roughly estimated that 2.74 aniline repeat units, on average, were doped with 1 HNO₃ molecule in the ES‐form PANI. I found a single crystalline morphology of EB‐form PANI, mostly like a conifer leaf. More complex, multilayered dendritic structures were also found. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2142–2148, 2003     

Distribution of monomeric,dimeric and polymeric products of stigmasterol during thermo‐oxidation

When plant sterols are oxidized at moderate temperatures (≤100 °C), products mainly derive from hydroperoxides, but at temperatures close to 200 °C, thermal reactions such as dehydration and condensation become important. Although sterols are often subjected to frying conditions, very little is known of their thermal reactions. In this study, stigmasterol was thermo‐oxidized at 180 °C, and the formation of dimers and polymers and the amounts of monomers were measured by high‐performance size‐exclusion chromatography. The products were further characterized by polarity using solid‐phase extraction fractionation. During heating, the amounts of monomers decreased at a steady rate, and those of dimers and polymers increased. After 3 h of heating, 21% of the material existed in higher‐molecular‐weight products. The amount of polar monomers increased especially during the first hour, demonstrating the formation of oxides and their further reactions, while that of mid‐polar monomers decreased constantly, indicating losses of stigmasterol. Polar dimers contributed to approximately 60% of the dimers, and polar polymers to approximately 78% of the polymers, which suggests that in most higher‐molecular‐weight products at least one of the sterol moieties was oxidized. This study showed that a significant proportion of thermo‐oxidation products are not polar monomeric oxides which are commonly analyzed as oxidation products.