Low-density Graphite Research Articles

Characterization of bipolar plates manufactured with various Pb/C ratios for unitized regenerative fuel cell system.

The weight reduction of the bipolar plate (BP) is essential for commercializing unitized regenerative fuel cells (URFCs). In order to lighten the weight of the bipolar plate, we have used Pb/C composite powder as a cost-effective primary material, which is a mixture of low-density graphite and lead. Further, varied lead-carbon weight ratios (1: 8, 1:4, 1:1, 4:1, and 8:1) were investigated for fabricating the bipolar plate by hot-pressing process adding styrene-butadiene rubber (SBR) as a binder. The specific surface area, porosity, and microstructure characteristics corresponding to the varied lead-graphite ratio of the prepared bipolar plates were studied. The relative difference in conductivity upon the compressibility of the plates is also examined. Finally, the wettability and electrochemical properties of the prepared bipolar plates were evaluated through water contact angle and cyclic voltammetry analysis.

Carbon nanotubes – PEI – Formate dehydrogenase nano-biointerface for the specific bioelectrochemical reduction of CO2 to formate

Reduction of extensive CO2 emissions is one of the key challenges that our society must overcome in order to minimize the effects of global warming and climate change. In this respect, electrochemical reduction of CO2 via redox enzymes is believed to be a promising route to minimize global CO2 concentrations, as they specifically catalyze the selective CO2 reduction in a reversible way at low potentials and mild conditions. In this work, we describe the effective anchoring of the enzyme Desulfovibrio vulgaris Hildenborough FdhAB formate dehydrogenase using electrostatic interactions favoring oriented immobilization, to the surface of MWCNTs-modified low density graphite electrodes with subsequent protection of the enzyme with polyethyleneimine (PEI) polymer. The synergistic effect of MWCNTs and PEI has been studied. High catalytic current densities, up to −230 μA cm−2, as well as a high operational stability of 11 h of continuous long-term measurements, were achieved.

Isotopic ratios for C, N, Si, Al, and Ti in C-rich presolar grains from massive stars

ABSTRACT Certain types of silicon carbide (SiC) grains, e.g. SiC-X grains, and low density (LD) graphites are C-rich presolar grains that are thought to have condensed in the ejecta of core-collapse supernovae (CCSNe). In this work, we compare C, N, Al, Si, and Ti isotopic abundances measured in presolar grains with the predictions of 21 CCSN models. The impact of a range of SN explosion energies is considered, with the high energy models favouring the formation of a C/Si zone enriched in 12C, 28Si, and 44Ti. Eighteen of the 21 models have H ingested into the He-shell and different abundances of H remaining from such H-ingestion. CCSN models with intermediate to low energy (that do not develop a C/Si zone) cannot reproduce the 28Si and 44Ti isotopic abundances in grains without assuming mixing with O-rich CCSN ejecta. The most 28Si-rich grains are reproduced by energetic models when material from the C/Si zone is mixed with surrounding C-rich material, and the observed trends of the 44Ti/48Ti and 49Ti/48Ti ratios are consistent with the C-rich C/Si zone. For the models with H-ingestion, high and intermediate explosion energies allow the production of enough 26Al to reproduce the 26Al/27Al measurements of most SiC-X and LD graphites. In both cases, the highest 26Al/27Al ratio is obtained with H still present at XH ≈ 0.0024 in He-shell material when the SN shock is passing. The existence of H in the former convective He-shell points to late H-ingestion events in the last days before massive stars explode as a supernova.

Charged-particle branching ratios above the neutron threshold in F19 : Constraining N15 production in core-collapse supernovae

Background: Spatially correlated overabundances of N15 and O18 observed in some low-density graphite meteoritic grains have been connected to nucleosynthesis taking place in the helium-burning shell during core-collapse supernovae. Two of the reactions which have been identified as important to the final abundances of N15 and O18 are F18(n,α)N15 and F18(n,p)O18. The relative strengths of the F18(n,α)N15 and F18(n,p)O18 reactions depend sensitively on the relative α0 and p0 decay branches from states above the neutron threshold in F19 in addition to other properties such as the spins, parities, and neutron widths. However, experimental data on the charged-particle decays from these highly excited states are lacking or inconsistent. Purpose: We measure the charged-particle decay branches from states around the neutron threshold in F19. Method: Two experiments were performed using proton inelastic scattering from LiF targets and magnetic spectrographs. The first experiment used the high-resolution Q3D spectrograph at Munich to constrain the properties of levels in F19. A second experiment using the Orsay split-pole spectrograph and an array of silicon detectors was performed in order To measure the charged-particle decay branches from states around the neutron threshold in F19. Results: A number of levels in F19 have been identified along with their corresponding charged-particle decays. The first state above the neutron threshold which has an observed proton-decay branch to the ground state of O18 lies 68 keV (Ex=10.5 MeV) above the neutron threshold. The α-particle decays from the neutron-unbound levels are generally observed to be much stronger than the proton decays. Conclusion:Neutron-unbound levels in F19 are observed to decay predominantly by α-particle emission, supporting the role of F18(n,α)N15 in the production of N15 in the helium-burning shell of supernovae. Improved resonant-scattering reaction data are required in order to be able to determine the reaction rates accurately.1 MoreReceived 10 July 2020Revised 5 October 2020Accepted 16 February 2021DOI:https://doi.org/10.1103/PhysRevC.103.035804©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasEnergy levels & level densitiesExplosive burningH & He induced nuclear reactionsNuclear astrophysicsNucleon induced nuclear reactionsNucleosynthesis in explosive environmentsProperties6 ≤ A ≤ 19Nuclear Physics

Bioelectrocatalytic Activity of W-Formate Dehydrogenase Covalently Immobilized on Functionalized Gold and Graphite Electrodes.

The decrease of greenhouse gases such as CO2 has become a key challenge for the human kind and the study of the electrocatalytic properties of CO2-reducing enzymes such as formate dehydrogenases is of importance for this goal. In this work, we study the covalent bonding of Desulfovibrio vulgaris Hildenborough FdhAB formate dehydrogenase to chemically modified gold and low-density graphite electrodes, using electrostatic interactions for favoring oriented immobilization of the enzyme. Electrochemical measurements show both bioelectrocatalytic oxidation of formate and reduction of CO2 by direct electron transfer (DET). Atomic force microscopy and quartz crystal microbalance characterization, as well as a comparison of direct and mediated electrocatalysis, suggest that a compact layer of formate dehydrogenase was anchored to the electrode surface with some crosslinked aggregates. Furthermore, the operational stability for CO2 electroreduction to formate by DET is shown with approximately 100% Faradaic yield.

Graphite-loaded cotton wool: A green route to highly-porous and solid graphite pellets for thermoelectric devices

The high porosity of thermoelectric materials is a valuable feature to ideally reduce thermal conductivity without degrading electrical conductivity. This paper describes a unique low-temperature and direct method for making highly porous yet solid graphite pellets. Cotton wools were loaded with graphite particles, and pressed to yield low-density graphite pellets. The electrical and thermal properties of the resulting pellets have been studied. A significant reduction in the heat flow through the pellets has been observed as compared to a pure graphite pellet. For the porous pellets, the electrical conductivity was slightly lower than that of pure graphite pellets due to the charge scattering processes of the highly porous network, yet the thermal conductivity was drastically reduced with enhancements in Seebeck coefficients hence, a significant improvement in the thermoelectric property. Overall, the power factor was found to increase from 0.303 μWm−1K−2 for solid graphite pellet to 0.424 μWm−1K−2 for porous graphite pellet, showing a simultaneously improved power factor and reduced thermal conductance. The approach can be extended for other good thermoelectric materials to achieve further enhancements in their properties and useful to reduce material cost.

3D characterization of structure and micro-porosity in two cast irons with spheroidal graphite

Formation of low density graphite phase during solidification increases the volume of semi-solid cast iron with spheroidal graphite (SGI) and resulted pressure could help eliminate shrinkage micro-porosity in casting. Therefore, micro-porosity in casting can be linked to 3D graphite nodule structure. Two experimental SGI's with different levels of shrinkage micro-porosity in castings were intentionally produced by variation in inoculation parameters which influenced graphite nodule structure. 3D-morphological characteristics of graphite nodules and micro-porosity level were determined by μCT scanning. The obtained statistical data was discussed with respect to graphite nodule solidification mode and casting soundness. The capabilities of μCT scanning in predicting micro-shrinkage in SGI casting were compared to the other traditionally used techniques.

Neon isotopes in individual presolar low-density graphite grains from the Orgueil meteorite.

We present He and Ne isotopes of individual presolar graphite grains from a low-density separate from Orgueil. Two grain mounts were analyzed with the same techniques but in a different sequence: The first one was measured with NanoSIMS followed by noble gas mass spectrometry, and the second one in reverse order. No grain contained 4He and only one grain on the second mount contained 3He. On the first mount, the grains had been extensively sputtered with NanoSIMS ion beams prior to noble gas analysis; we found only one grain out of 15 with presolar 22Ne above detection limit. In contrast, we found presolar 22Ne in six out of seven grains on the second mount that was not exposed to an ion beam prior to noble gas analysis. All 22 grains on the two mounts were imaged with scanning electron microscopy (SEM) and/or Auger microscopy. We present evidence that this contrasting observation is most likely due to e-beam-induced heating of the generally smaller grains on the first mount during SEM and Auger imaging, and not primarily due to the NanoSIMS analysis. If thermal contact of the grains to the substrate is absent, such that heat can only be dissipated via radiation, then the smaller, sputter-eroded grains are heated to higher temperatures such that noble gases can diffuse out. We discuss possible gas loss mechanisms and suggest solutions to reduce heating during e-beam analyses by minimizing voltages, beam currents, and dwell times. We also found small amounts of 21Ne in five grains. Using isotope data we determined that the dominant sources of most grains are core-collapse supernovae, congruent with earlier studies of low-density presolar graphite from Murchison. Only two of the grains are most likely from AGB stars, and two others have an ambiguous origin.

Modeling of a Dynamic Thermal Load Generated by a 7TeV Proton Beam Impacting the Beam Dump of the Large Hadron Collider at CERN

The two beam dumps of the Large Hadron Collider (LHC), made up mostly of low-density graphite, are responsible for absorbing the high-energy particle beams when ejected from the accelerator. In the frame-work of the project to improve the luminosity in the LHC, the beam intensity will be increased by a factor of around two in the coming years. The dominant load on the dump assembly is the energy deposited in the material by the 7 TeV proton beam. Thermomechanical simulations have to be performed to ensure the safe operation of the dump through assessing the integrity in the future. To date, the particle beam contains an average energy of 370 MJ, which is sent to the dump in a sweep movement within around 80 µs. Based on the large dimensions of the dump core and considering the highly dynamic nature of this load, an explicit code like LS-Dyna® was deemed to be best suited for these studies. This paper presents the methodology proposed to model the discrete time structure of the load, caused by the interaction between the particle beam and the dump. Results of the application of this technique, to determine the temperature, stresses and wave propagation on the downstream wall of this device, are described here. In addition to the methodology of the load application, the results of standard quasi-static material tests on the low-density graphite material in the beam dump are presented, to assess the general nature of the material behavior. These experiments will be the basis for a dynamic test campaign to construct a comprehensive material model, as the graphite used in this device has never been fully characterized under such loading conditions.

Non-oxidative, controlled exfoliation of graphite in aqueous medium.

We present a simple, non-oxidative and controlled method to synthesize graphene monolayers by exfoliation in water from different solid carbon sources, such as highly ordered pyrolytic graphite and low density graphite. Any water based method is highly desirable due to several attractive features, such as environmental friendliness, low cost and wide compatibility with other water based processes. We show that thin graphene layers can be exfoliated controllably and reproducibly by varying different parameters during exfoliation in aqueous medium. It has been possible to obtain high quality graphene monolayers with a yield of ∼2.45 wt%, which can be increased up to 16.6 wt% by recycling the sediments. Field effect transistors based on exfoliated graphene monolayers have shown n-type doping and a high carrier mobility of 4500 cm(2) V(-1) s(-1) at room temperature and ∼20 000 cm(2) V(-1) s(-1) at low temperature. Density functional calculations corroborate the infrared spectroscopic results and also indicate that the charge transfer preferentially occurs from water molecules to the graphene sheets resulting in n-type doping. We anticipate that exfoliation of high quality graphene layers in aqueous medium would open up a pathway for various graphene based electronic and biological applications.

Laccase-modified gold nanorods for electrocatalytic reduction of oxygen

The multicopper oxidase Trametes hirsuta laccase (ThLc) served as a bioelectrocatalyst on nanostructured cathodes. Nanostructuring was provided by gold nanorods (AuNRs), which were characterized and covalently attached to electrodes made of low-density graphite. The nanostructured electrode was the scaffold for covalent and oriented attachment of ThLc. The bioelectrocatalytic currents measured for oxygen reduction were as high as 0.5mA/cm2 and 0.7mA/cm2, which were recorded under direct and mediated electron transfer regimes, respectively. The experimental data were fitted to mathematical models showing that when the O2 is bioelectroreduced at high rotation speed of the electrode the heterogeneous electron transfer step is the rate-liming stage. The electrochemical measurement hints a wider population of non-optimally wired laccases than previously reported for 5–8nm size Au nanoparticle-modified electrode, which could be due to a larger size of the AuNRs when compared to the laccases as well as their different crystal facets.

CARBON-RICH PRESOLAR GRAINS FROM MASSIVE STARS: SUBSOLAR 12 C/ 13 C AND 14 N/ 15 N RATIOS AND THE MYSTERY OF 15 N

Carbon-rich grains with isotopic anomalies compared to the Sun are found in primitive meteorites. They were made by stars, and carry the original stellar nucleosynthesis signature. Silicon carbide grains of Type X and C, and low-density graphites condensed in the ejecta of core-collapse supernovae. We present a new set of models for the explosive He shell and compare them with the grains showing 12C/13C and 14N/15N ratios lower than solar. In the stellar progenitor H was ingested into the He shell and not fully destroyed before the explosion. Different explosion energies and H concentrations are considered. If the SN shock hits the He-shell region with some H still present, the models can reproduce the C and N isotopic signatures in C-rich grains. Hot-CNO cycle isotopic signatures are obtained, including a large production of 13C and 15N. The short-lived radionuclides 22Na and 26Al are increased by orders of magnitude. The production of radiogenic 22Ne from the decay of 22Na in the He shell might solve the puzzle of the Ne-E(L) component in low-density graphite grains. This scenario is attractive for the SiC grains of type AB with 14N/15N ratios lower than solar, and provides an alternative solution for SiC grains originally classified as nova grains. Finally, this process may contribute to the production of 14N and 15N in the Galaxy, helping to produce the 14N/15N ratio in the solar system.

Third-generation oxygen amperometric biosensor based on Trametes hirsuta laccase covalently bound to graphite electrode

AbstractThe response of low-density graphite electrodes hosting Trametes hirsuta laccase in a direct electron transfer regime is presented for real-time analysis of O

Corrosion behaviour of carbon materials exposed to molten lithium chloride–potassium chloride salt

The corrosion behaviour of four carbon materials namely low density graphite, high density graphite, glassy carbon and pyrolytic graphite were investigated in molten LiCl–KCl electrolyte medium at 600°C for 2000h under high pure argon atmosphere. Structural and microstructural changes in the carbon materials after exposure to molten chloride salt were investigated from the weight change and using scanning electron microscopy, atomic force microscopy, X-ray diffraction and laser Raman spectroscopic techniques. Microstructural analysis of the samples revealed the poor corrosion resistance of high density and low density graphite and severe attack was observed at several places on the surface. On the other hand, glassy carbon and pyrolytic graphite were relatively inert, while pyrolytic graphite showed the best corrosion resistance to molten salt attack. In the order of increasing corrosion resistance to molten salt, the carbon materials were found to follow the sequence: low density graphite<high density graphite<glassy carbon<pyrolytic graphite.

RELICS OF ANCIENT POST-AGB STARS IN A PRIMITIVE METEORITE

Graphite is one of the many presolar circumstellar condensate species found in primitive meteorites. While the isotopic compositions of low-density graphite grains indicate an origin in core-collapse supernovae, some high-density grains have extreme isotopic anomalies in C, Ca and Ti, which cannot be explained by envelope predictions of asymptotic giant branch (AGB) stars or theoretical supernova models. The Ca and Ti isotopic anomalies, however, match the predictions of He-shell abundances in AGB stars. In this study, we show that the C, Ca, and Ti isotopic anomalies are consistent with nucleosynthesis predictions of the H-ingestion phase during a very late thermal pulse (VLTP) event in post-AGB stars. The low $^{12}$C/$^{13}$C isotopic ratios in these grains are a result of abundant $^{12}$C efficiently capturing the protons that are being ingested during the VLTP. Very high neutron densities of $\sim 10^{15}$ cm$^{-3}$, typical of the $i$-process, are achieved during this phase in post-AGB stars. The large $^{42,43,44}$Ca excesses in some graphite grains are indicative of neutron capture nucleosynthesis during VLTP. The comparison of VLTP nucleosynthesis calculations to the graphite data also indicate that apparent anomalies in the Ti isotopic ratios are due to large contributions from $^{46,48}$Ca, which cannot be resolved from the isobars $^{46,48}$Ti during the measurements. We conclude that presolar graphite grains with moderate to extreme Ca and Ti isotopic anomalies originate in post-AGB stars that suffer a very late thermal pulse.

Resonant scattering of22Na + pstudied by the thick-target inverse-kinematic method

Background: In presolar low-density graphite grains, an extraordinarily large ${}^{22}$Ne/${}^{20}$Ne ratio or even nearly pure ${}^{22}$Ne is found, pointing to the condensation of radioactive ${}^{22}$Na in grains. Supernovae and neon-rich novae are the main events that produce ${}^{22}$Na via the explosive hydrogen burning process. The ${}^{22}$Na($p$, $\ensuremath{\gamma}$)${}^{23}$Mg reaction is one of the key reactions that influences the ${}^{22}$Na abundance in ejecta.Purpose:The present work aims to explore the proton resonant states in ${}^{23}$Mg relevant to the astrophysical ${}^{22}$Na($p$, $\ensuremath{\gamma}$)${}^{23}$Mg reaction. The determined ${}^{23}$Mg resonant parameters can be used to evaluate the ${}^{22}$Na($p$, $\ensuremath{\gamma}$)${}^{23}$Mg reaction rate.Method:A low-energy ${}^{22}$Na radioactive ion beam is produced via the ${}^{1}$H(${}^{22}$Ne, ${}^{22}$Na)$n$ reaction, and used to measure the experimental excitation function of the ${}^{22}$Na + $p$ resonant scattering with a conventional thick-target inverse kinematic method. $R$-matrix analysis is applied to deduce the ${}^{23}$Mg resonance parameters from the experimental excitation function.Results: Three proton resonance states in ${}^{23}$Mg are observed. Spins/parities and the proton partial widths are determined. The deduced excitation energies agree with the compiled values.Conclusions: The new spin and parity assignments allow us to perform a shell-model calculation of the $\ensuremath{\gamma}$ widths of the ${}^{23}$Mg resonant states for the evaluation of the ${}^{22}$Na($p$, $\ensuremath{\gamma}$)${}^{23}$Mg astrophysical reaction rate. The two $s$-wave resonant states established in this work at 8.793 and 8.916 MeV in ${}^{23}$Mg, respectively, increase the total reaction rate by about 5% at a temperature greater than 2 GK.

Optimization of a Membraneless Glucose/Oxygen Enzymatic Fuel Cell Based on a Bioanode with High Coulombic Efficiency and Current Density

After initial testing and optimization of anode biocatalysts, a membraneless glucose/oxygen enzymatic biofuel cell possessing high coulombic efficiency and power output was fabricated and characterized. Two sugar oxidizing enzymes, namely, pyranose dehydrogenase from Agaricus meleagris (AmPDH) and flavodehydrogenase domains of various cellobiose dehydrogenases (DH(CDH)) were tested during the pre-screening. The enzymes were mixed, "wired" and entrapped in a low-potential Os-complex-modified redox-polymer hydrogel immobilized on graphite. This anode was used in combination with a cathode based on bilirubin oxidase from Myrothecium verrucaria adsorbed on graphite. Optimization showed that the current density for the mixed enzyme electrode could be further improved by using a genetically engineered variant of the non-glycosylated flavodehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophilus expressed in E. coli (ngDH(CtCDHC310Y)) with a high glucose-turnover rate in combination with an Os-complex-modified redox polymer with a high concentration of Os complexes as well as a low-density graphite electrode. The optimized biofuel cell with the AmPDH/ngDH(CtCDHC310Y) anode showed not only a similar maximum voltage as with the biofuel cell based only on the ngDH(CtCDHC310Y) anode (0.55 V) but also a substantially improved maximum power output (20 μW cm(-2)) at 300 mV cell voltage in air-saturated physiological buffer. Most importantly, the estimated half-life of the mixed biofuel cell can reach up to 12 h, which is apparently longer than that of a biofuel cell in which the bioanode is based on only one single enzyme.

PRODUCTION OF CARBON-RICH PRESOLAR GRAINS FROM MASSIVE STARS

About a year after core collapse supernova, dust starts to condense in the ejecta. In meteorites, a fraction of C-rich presolar grains (e.g., silicon carbide (SiC) grains of Type-X and low density graphites) are identified as relics of these events, according to the anomalous isotopic abundances. Several features of these abundances remain unexplained and challenge the understanding of core-collapse supernovae explosions and nucleosynthesis. We show, for the first time, that most of the measured C-rich grain abundances can be accounted for in the C-rich material from explosive He burning in core-collapse supernovae with high shock velocities and consequent high temperatures. The inefficiency of the $^{12}$C($\alpha$,$\gamma$)$^{16}$O reaction relative to the rest of the $\alpha$-capture chain at $T > 3.5\times10^8 \mathrm{K}$ causes the deepest He-shell material to be carbon rich and silicon rich, and depleted in oxygen. The isotopic ratio predictions in part of this material, defined here as the C/Si zone, are in agreement with the grain data. The high-temperature explosive conditions that our models reach at the bottom of the He shell, can also be representative of the nucleosynthesis in hypernovae or in the high-temperature tail of a distribution of conditions in asymmetric supernovae. Finally, our predictions are consistent with the observation of large $^{44}$Ca/$^{40}$Ca observed in the grains. This is due to the production of $^{44}$Ti together with $^{40}$Ca in the C/Si zone, and/or to the strong depletion of $^{40}$Ca by neutron captures.

Multi-element isotopic analyses of presolar graphite grains from Orgueil

We report C, N, O, Si, Al–Mg, K, Ca, and Ti isotopic analyses of presolar graphite grains from the Orgueil CI chondrite. NanoSIMS isotopic measurements were made on 345 grains from seven density fractions, with grain sizes >1μm: low-density grains from OR1b, OR1c, and OR1d; and high-density grains from OR1f, OR1g, OR1h, and OR1i. In all fractions, except OR1b and OR1h, we found presolar graphite as demonstrated by the large range of 12C/13C ratios (4–2480) measured in individual grains. Some isotopic properties are dependent on density: low-density grains contain 18O, 15N, and 28Si excesses, while the majority of high-density grains contain normal N and O, and are generally enriched in 29Si and 30Si. The 15N, 18O, and 28Si excesses and very high derived isotopic ratios for the extinct radionuclides 26Al, 41Ca, and 44Ti in low-density grains indicate an origin from supernovae. In order to explain the isotopic ratios measured in these grains, we present mixing scenarios between different layers of supernovae and discuss the limitations of various theoretical models. Silicon-30 and 12C excesses in high-density grains and lower values for short-lived radionuclides (26Al and 41Ca) indicate an origin in asymptotic giant branch stars with low metallicities. Some supernova grains, with 44Ca excesses, are also present amongst the high-density grains. Grains with low 12C/13C ratios (without evidence for 44Ti) and large excesses in 42,43Ca and 46,47,49,50Ti probably originate from post-asymptotic giant branch stars, that have suffered a very late thermal pulse, and can achieve low 12C/13C ratios and large neutron capture signatures in Ca and Ti isotopes.We conclude that most low-density graphite grains originate from supernovae while high-density graphite grains have multiple stellar sources: low-metallicity and born-again asymptotic giant branch stars, Type II supernovae, and possibly, J-type stars.

Condensation and mixing in supernova ejecta

Low-density graphite spherules from the Murchison carbonaceous chondrite contain TiC grains and possess excess 28Si and 44Ca (from decay of short-lived 44Ti). These and other isotopic anomalies indicate that such grains formed by condensation from mixtures of ejecta from the interior of a core-collapse supernova with those from the exterior. Using homogenized chemical and isotopic model compositions of the eight main burning zones as end-members, Travaglio et al. (1999) attempted to find mixtures whose isotopic compositions match those observed in the graphite spherules, subject to the condition that the atomic C/O ratio = 1. They were partially successful, but this chemical condition does not guarantee condensation of TiC at a higher temperature than graphite, which is indicated by the spherule textures. In the present work, model compositions of relatively thin layers of ejecta within the main burning zones computed by Rauscher et al. (2002) for Type II supernovae of 15, 21 and 25 M ʘ are used to construct mixtures whose chemical compositions cause equilibrium condensation of TiC at a higher temperature than graphite in an attempt to match the textures and isotopic compositions of the spherules simultaneously. The variation of pressure with temperature and the change in elemental abundances with time due to radioactive decay were taken into account in the condensation calculations. Layers were found within the main Ni, O/Ne, He/C and He/N zones that, when mixed together, simultaneously match the carbon, nitrogen and oxygen isotopic compositions, 44Ti/ 48Ti ratios and inferred initial 26Al/ 27Al ratios of the low-density graphite spherules, even at subsolar 12C/ 13C ratios. Due to the relatively large proportion of material from the Ni zone and the relative amounts of the two layers of the Ni zone required to meet these conditions, predicted 28Si excesses are larger than observed in the low-density graphite spherules, and large negative δ 46Ti/ 48Ti, δ 47Ti/ 48Ti, δ 49Ti/ 48Ti and δ 50Ti/ 48Ti are produced, in contrast to the observed normal δ 46Ti/ 48Ti and δ 47Ti/ 48Ti, large positive δ 49Ti/ 48Ti and smaller positive δ 50Ti/ 48Ti. Although better matches to the observed δ 46Ti/ 48Ti, δ 47Ti/ 48Ti and 28Si excesses can be found using much smaller amounts of Ni zone material and some Si/S zone material, it is very difficult to match simultaneously the Ti and Si isotopic compositions in any mixtures of material from these deep layers with He/C and He/N zone material, regardless of the condensation sequence. The occurrence of Fe-rich, Si-poor metal grains inside the graphite spherules does not have a satisfactory explanation.