Lattice Fringe Spacing Research Articles

Nano-scale 1TaC-3HfC solid solution powder synthesized using a solvothermal method and its densification

A solvothermal approach was used to synthesize single-phase 1TaC-3HfC solid solution powders for the first time. The starting materials were TaCl5 and HfCl4, with carbon introduced by phenolic resin. Powder X-ray diffraction results showed the 1TaC-3HfC solid solution could be prepared with the minimum temperature at 2000 °C for 1 h. Using a combination of characterization techniques, it has been demonstrated that the phase pure powders with crystallite sizes of ~50 nm, the composition of Ta, Hf, and C elements were near stoichiometric and homogeneousely distributed in the particles. The crystal lattice fringe spacing measured in the grain was consistent well with the calculated theoretical value, and the SAED pattern reveals a single-crystalline nature. Ultimately, using the synthesized powder, monolithic 1TaC-3HfC ceramics with high relative density (97%) were obtained after the densification at 2100 °C for 60 min at a pressure of 70 MPa by hot pressing.

Electrochemical investigation of uranyl species reduction in alkaline oxalate electrolyte and microstructural characterization of deposited nanocrystalline UO2 thin films

In this study, electrochemical reduction behaviour of uranyl ions was investigated from an alkaline oxalate complex electrolyte. Detailed results of scan rates, pH and temperature dependent cyclic voltammetry were analysed to extract diffusion coefficients and to elucidate reduction mechanism. A two-step mechanism was established where the first step involving reduction of UO22+ to UO2+ was a slower and reversible in nature and the second step was proton assisted reduction of UO2+ to UO2. Detailed speciation study of the electrolyte confirmed [UO2(C2O4)3]4− as the predominant species in the pH range 5.0 to 8.5. XPS analyses of as-deposited oxide film confirmed about the formation of UO2 with a small percentage of UO3. For annealed films (at 973 K for 1 h), majority of oxide film was present in mixed valence state containing U6+ and U5+ with a small amount of U4+. High resolution transmission electron microscope (HR-TEM) examination of as-deposited film revealed the deposition of an ultra-nanocrystalline UO2 film with average gain size of 3.0 nm. However, annealed sample showed substantial grain growth associated with reduced inter-grain amorphous region. The average grain size obtained was 9.8 nm with lattice fringe spacing was 0.32 nm corresponding to the fcc UO2.

Interfacial reactions at Fe/topological insulator spin contacts.

The authors study the composition and abruptness of the interfacial layers that form during deposition and patterning of a ferromagnet, Fe on a topological insulator (TI), Bi2Se3, Bi2Te3, and SiOx/Bi2Te3. Such structures are potentially useful for spintronics. Cross-sectional transmission electron microscopy, including interfacial elemental mapping, confirms that Fe reacts with Bi2Se3 near room temperature, forming an abrupt 5 nm thick FeSe0.92 single crystalline binary phase, predominantly (001) oriented, with lattice fringe spacing of 0.55 nm. In contrast, Fe/Bi2Te3 forms a polycrystalline Fe/TI interfacial alloy that can be prevented by the addition of an evaporated SiOx separating Fe from the TI.

Crystallization of calcium silicate hydrates on the surface of nanomaterials

AbstractThe poorly crystalline calcium silicate hydrate (C‐S‐H) is the primary binding phase in portland cement concrete. In this paper, the influence of adding anatase phase nano‐TiO2, nano‐SiO2, graphene oxide (GO), and multiwalled carbon nanotubes (CNT) on the crystallization and morphology of C‐S‐H are systematically investigated through tests. C‐S‐H gels were prepared using the double decomposition method, and the nanomaterial additions of nano‐TiO2, nano‐SiO2, GO, and CNT were 2 wt%, 2 wt%, 0.5 wt%, and 0.5 wt%, respectively. X‐ray diffraction (XRD) results show that a more crystalline nanostructure of C‐S‐H is induced by the addition of nano‐TiO2 or GO. This phenomenon is further confirmed by the transmission electron microscopy (TEM) observations. The TEM observations demonstrate that C‐S‐H would grow on the crystal face of TiO2 to form nanocrystalline regions with a lattice fringe spacing of 3.0 Å. When incorporated with GO, it will form a square lattice structure with a lattice constant of 3.1 Å on the surface of GO and later change to the lattice fringe structure with a spacing of 3.1 Å on the region bit away the GO surface. However, when adding nano‐SiO2 or CNT, these nanocrystalline regions are not observed. Further characterization through scanning electron microscopy (SEM) and atomic force microscopy (AFM) has been performed to investigate the effect of nanomaterials on C‐S‐H morphology. Different nanomaterials take a different morphology of C‐S‐H: sheet‐shape structures for pure C‐S‐H, rod‐shape with for C‐S‐H with nano‐TiO2, and granular agglomeration for C‐S‐H with nano‐SiO2. C‐S‐H with GO or CNT forms a structure of C‐S‐H growing on the templates.

Novel synthesis of silicon carbide nanotubes by microwave heating of blended silicon dioxide and multi-walled carbon nanotubes: The effect of the heating temperature

Silicon carbide nanomaterials, especially silicon carbide nanotubes (SiCNTs), are known as excellent materials for high-power and high-temperature harsh environment electronics applications because of the unique properties of SiCNTs, such as a high thermal stability, good chemical inertness and excellent electronic properties. In this article, we presented a novel synthesis of SiCNTs by microwave heating a blend of silicon dioxide (SiO2) and multi-walled carbon nanotubes (MWCNTs) at a ratio of 1:3 at temperatures of 1350°C, 1400°C and 1450°C. The effects of different heating temperatures on the synthesis of SiCNTs were studied. X-ray diffraction revealed the presence of single phase β-SiC for syntheses conducted at 1400°C and 1450°C. Meanwhile, field-emission scanning electron microscopy images showed that no residual silicon dioxide or MWCNTs was observed with syntheses conducted at 1400°C and 1450°C. High-magnification transmission electron microscopy revealed that the tubular structure of the MWCNTs was preserved and that SiCNTs had a lattice fringe spacing of 0.261nm corresponding to the (111) plane of β-SiC. Photoluminescence spectroscopy showed the presence of a β-SiC peak at a wavelength of 465nm, and the band gap energy of SiCNTs was 2.67eV. Fourier transform infrared spectroscopy analysis revealed that the absorption band of the Si–C bond was detected at 803cm−1. The purity of SiCNTs synthesized at 1400°C and 1450°C is high, as indicated by the low weight loss in thermo-gravimetric analysis.

In situ synthesis of SiOC ceramic nanorod-modified carbon/carbon composites with sol–gel impregnation and CVI

SiOC ceramic nanorod-modified C/C composites were successfully synthesized by a three-step technique, involving sol–gel impregnation, isothermal chemical vapor immersion and thermal gradient chemical vapor immersion. The morphology, phase composition, microstructure, element qualitative and quantification of the obtained specimens were investigated by SEM, XRD, TEM and XPS, respectively. The results showed that the tapered SiOC ceramic nanorods were coated by pyrolytic carbon, which have a diameter of hundreds of nanometers and a length of several microns. The interlaminar shear strength test showed that the modified composite possessed excellent mechanical properties. Compared with the unmodified ones, the interlaminar shear strength of SiOC ceramic nanorod-modified C/C composites was enhanced by 45.09 %, which can be ascribed to the change of matrix structure and the improvement in fiber/matrix interface. The low-resolution TEM micrograph shows the general morphology of the SiOC nanorod (a) and SiOC (b) powder dispersed on a holey copper grid. The corresponding high-resolution TEM images (HRTEM) and selected area electron diffraction (SAED) patterns were also exhibited in the insets, respectively. From (a), the nanorod with a length about 10 μm and a tapered shape diameter ranging from 50 to 600 nm was like a single crystalline which may be attributed to the unique formation of the nanorod. Moreover, the nanorods crystal lattice fringe spacing was measured to be 0.25 nm. Moreover, the diffraction rings and the irregular HRTEM image are an inherent characteristic of amorphous SiOC ceramic, as shown in (b).

Tunable Direct Bandgap Optical Transitions in MoS2 Nanocrystals for Photonic Devices

Highly luminescent MoS2 nanocrystals (NCs) with controlled size distribution have been achieved using a simple yet inexpensive and impurity free sono-chemical exfoliation method followed by gradient centrifugation. The size of nanocrystals could be varied within the diameter range of ∼4 to 70 nm. Typical MoS2 nanocrystal has exhibited high crystalline quality with 0.25 nm lattice fringe spacing for (002) planes for 2-H phase of MoS2. Raman spectra has revealed that both out-of-plane and in-plane vibrational modes are stiffen due to the edge effect of MoS2 NCs. The size tunable optical properties of MoS2 NCs have been investigated by optical absorption and photoluminescence spectroscopy. The coexistence of direct band gap emission from 2D MoS2 nanosheets and quantum confined nanocrystals has been achieved. A strong and tunable photoluminescence (560–518 nm) emission due to the quantum size effect of tiny NCs below a critical dimension is reported for the first time. The photocurrent measurement of the Au/M...

Berthierine formation in reservoir rocks from the Siri oilfield (Danish North Sea) as result of fluid–rock interactions: Part I. Characterization

Berthierine as the only authigenic Fe-rich clay mineral occurs in an oil-bearing, glauconite-rich sandstone (Paleocene Heimdal Member of the Lista Formation, Danish North Sea). Based on the results of thin section, transmission and scanning electron microscopy, five different morphological types of berthierine were identified: (1) mainly as grain-coatings partly together with authigenic quartz covering detrital grains, (2) as pore-filling clay in open pores, (3) small crystals in transformed glauconite grains, (4) small crystals associated with siderite in layers of mica/micaceous glauconite, and (5) as elongated crystals in siderite concretions. Although different in occurrence, all berthierine types investigated by microprobe analysis are of similar chemical composition, suggesting similar precipitation conditions. Investigations by transmission electron microscopy reveal that fine berthierine crystals display straight parallel layers with a typical lattice fringe spacing of 0.7 nm, and that their occurrence is intimately connected to oil phases in pore space. Partly, berthierine textures resemble mineralized oil–water emulsions. Berthierine is more abundant in the oil leg than in the water leg, but occurs especially abundant at the oil–water contact. The coexistence of berthierine together with quartz overgrowth, but also its appearance in glauconite indicates that berthierine formed in situ and that it is a product of glauconite dissolution. Berthierine formation is coupled to the reduction of aqueous Fe3+ into Fe2+ derived from glauconite dissolution, and is related to fluid–rock interactions triggered by oil degradation which occurred in the oil-filled zone and at the oil–water contact. The biomarker parameters pristane/n-C17 and phytane/n-C18 indicate an increased extent of oil degradation at the oil–water contact. On the one hand, soluble oil degradation products (methane, carbon dioxide, and hydrogen) changed the hydrogeochemical conditions (such as pH, pe, alkalinity, etc.), and controlled dissolution of glauconite (and feldspar). On the other hand, the changed hydrogeochemical conditions led to berthierine and quartz precipitation in water-wet reservoir intervals.

Reduction of aromatic nitro compounds catalyzed by biogenic CuO nanoparticles

Synthesis of CuO nanoparticles using the peel of Musa balbisiana and its application in reduction of nitro aryl compounds are reported here. CuO nanoparticles were characterized by using XRD, XPS, PL, SEM and TEM techniques. In XRD analysis, significant peaks appeared at 18.3, 24.4, 33.6, 34.6, 35.2, 38.2 and 42.7 respectively. The BET surface area and total pore volume of CuO were found to be 7.479 m2 g−1 and 0.1259 m3 g−1, respectively. The generated CuO nanoparticles exhibited interplanar lattice fringe spacings of 0.16 nm. SEM images indicate the formation of flower-like CuO architecture. The hierarchical CuO architecture is found to be made up of nanosheets which were self assembled to form flower-like nanostructures. The synthesized CuO nanoparticles show efficient catalytic activity in reduction of nitro aryl compounds to corresponding amino compounds with a high yield of conversion (74–96%). The reaction was carried out in a green solvent i.e. water. The catalyst was found to be active for several runs. It was further confirmed by several pieces of experimental evidence.

Occurrence, Structure and Mineral Phases of Nanoparticles in an Anthrosol

Soils contain various kinds of crystalline to amorphous solid particles with at least one dimension in the nanoscale (< 100 nm). These nanoparticles contribute greatly to dynamic soil processes such as soil genesis, trace element cycling, contaminant transport, and chemical reaction. The nano-sized fraction of an Anthrosol was obtained to determine the occurrence, chemical composition, structure, and mineral phases of nanoparticles using high-resolution transmission electron microscopy (HRTEM) equipped with an energy-dispersive X-ray spectroscopy. Selected area electron diffraction or the fast Fourier transform of high-resolution images was used in structural characterization of the nanoparticles with HRTEM. Two nanoscale mineral types, i.e., mineral nanoparticles and nanominerals, were observed in the Anthrosol. Mineral nanoparticles in soil included well crystalline aluminumsilicate nanosheets, nanorods, and nanoparticles. Nanosheets with a length of 120–150 nm and a width of about 10–20 nm were identified as chlorite/vermiculite series. The presence of clear lattice fringe spacing in HRTEM image of nanoparticles indicated that mineral nanoparticles had a relatively good crystallinity. The nanomineral ferrihydrite also existed in the Anthrosol. The HRTEM images and the particle size distribution histogram suggested that these ferrihydrite nanoparticles were quite homogeneous, and had a narrow size distribution range (1–7 nm) with a mean diameter of 3.6 ± 1.6 nm. Our HRTEM observation indicated that mineral nanoparticles and nanominerals were common and widely distributed in Anthrosols. HRTEM and selected area diffraction or lattice fringe spacing characterization provided further proofs to the structure of nanoparticles formed in soil.

Selective hydrogenation of monoterpenes on Rhodium (0) nanoparticles stabilized in Montmorillonite K-10 clay

Rhodium (0) nanoparticles were generated in the nanopores of Montmorillonite K-10 clay by reduction of RhCl3·3H2O impregnated clay with NaBH4. Pore size of the clay and hence the size of Rh nanoparticle was controlled by choosing <2μm fraction of the clay as catalyst support. TEM/HRTEM/SAED images confirmed the growth of well dispersed spherical Rh (0) nanoparticles in 1–3nm diameter range having face centred cubic lattice with inter-planar lattice fringe spacing of 0.23nm corresponding to [111] planes. XPS analysis confirmed the presence of Rh metal in zero oxidation state and absence of other oxidation states of Rh. BET surface area determination through N2 adsorption–desorption isotherm revealed decrease in surface area of the clay support from 298m2/g to 196.4m2/g after incorporation of Rh (0) nanoparticles. The Rh (0) nanoparticles supported clay is proved to be highly active and selective heterogeneous catalyst for hydrogenation of monoterpenes (geraniol, limonene, β-pinene, citronellal and linalool) at ambient temperature and pressure (1–4bar). The number of active sites was calculated using surface statistics and adopting model for full shell clusters. Turnover frequency (TOF) calculations for the catalyst gave encouraging results.

Influence Of ZnO Buffer Layer On Growth Of Sb Doped ZnO Nano Wires Using Nano Particle Assisted Pulsed Laser Deposition (NAPLD) Using Sb As Catalyst

Influence of ZnO buffer layer thickness on the structural and optical properties of the Sb catalyzed/doped ZnO nanowires synthesized using NAPLD has been investigated. Buffer layer with a thickness of 100 nm, 800 nm and 1600 nm coated with Sb are used as a substrate and pure ZnO was used as a target to synthesize Sb doped ZnO nanowires. Introduction of the buffer layer lead to the growth of vertically aligned along with horizontally grown ZnO nano wires. With the increase in buffer layer thickness, the core diameter of the vertically grown ZnO nano wires was subsequently increased. Nano wires synthesized with a buffer layer thickness of 1600 nm showed a significant change in the lattice constants, resulting in measurable lower angle of about 0.06o from XRD, widening of lattice fringe spacing of 0.54 nm from TEM and Suppression of A1T and E1(L0) modes in Raman Spectroscopic. In addition a strong UV emission with absence of visible emission was observed from the room temperature PL. This confirms the generation of Sb doped ZnO nano wire with high crystal quality. Copyright © 2012 VBRI Press.

Structural and optical properties of Sb[sbnd]Al co-doped ZnO nanowires synthesized using Nanoparticle Assisted Pulsed Laser Deposition (NAPLD) with Sb as catalyst

The paper deals with study of SbAl co-doped ZnO nanowires synthesized using Nanoparticle Assisted Pulsed Laser Deposition (NAPLD). The nanowires were synthesized by using ZnO:Al as target and Sb coated Si as substrate. At a growth temperature of 750°C, random oriented high density nanowires with a diameter of about 1μm and a length up to a few tens of micro meters were synthesized. The samples were annealed at 450, 550 and 650°C. The SbAl co-doped ZnO nanowires annealed at 650°C showed a significant change in lattice constant of 0.06° from XRD and widening of lattice fringe spacing of 0.56nm from TEM. From the XPS analysis, a peak at 539.5eV a near binding energy of SbO bond and peak at 76.2eV corresponding to AlO bonds confirms the penetration of oxygen. The suppression of A1T modes and E1(L0) modes from Raman spectroscopy confirms the depletion of oxygen vacancies. Thus resulting in a strong improvement in UV emission and reduction in visible emission as observed from room temperature PL.

Chemoselective reduction of a nitro group through transfer hydrogenation catalysed by Ru0-nanoparticles stabilized on modified Montmorillonite clay

Ru0-nanoparticles of approximately 5 nm size were generated by incipient impregnation of RuCl3 into the nanopores of the acid activated Montmorillonite clay followed by polyol reduction. Acid activation of the clay increases the surface area by generating nanopores (0–10 nm), which act as a host and stabilize nanoparticles in the pores. The generated Ru0-nanoparticles exhibit inter-planar lattice fringe spacing of 0.21 nm of the face centered cubic lattice of Ru0 crystals, and show efficient catalytic activity in the chemoselective transfer hydrogenation reduction of substituted nitrobenzenes to corresponding anilines with high yield of conversion (56–97%) and selectivity (91–100%) depending upon the nature of the substituents. The reactions were carried out in the presence of isopropanol, which served as the solvent as well as the reductant. The catalysts were found to be active for several catalytic runs.

TEM characterization of MBE grown CdTe/ZnTe axial nanowires

CdTe/ZnTe axial nanowires were successfully fabricated by molecular beam epitaxy with the use of Au nano-catalysts and vapour-liquid-solid growth mechanism. Nanowires had zinc-blende structure with numerous stacking faults in the bottom ZnTe part and near perfect crystalline structure in the top CdTe part. Energy dispersive X-ray spectroscopy (EDXS) and lattice fringe spacing analysis revealed nonabrupt nature of hetero-interface, whose width was estimated to be 50-70 nm for the nanowires having a diameter in the range from 40 to 50 nm.

Green synthesis and characterization of superparamagnetic Fe 3O 4 nanoparticles

In this paper, we have first demonstrated a facile and green synthetic approach for preparing superparamagnetic Fe 3O 4 nanoparticles using α- d-glucose as the reducing agent and gluconic acid (the oxidative product of glucose) as stabilizer and dispersant. The X-ray powder diffraction (XRD), X-ray photoelectron spectrometry (XPS), and selected area electron diffraction (SAED) results showed that the inverse spinel structure pure phase polycrystalline Fe 3O 4 was obtained. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results exhibited that Fe 3O 4 nanoparticles were roughly spherical shape and its average size was about 12.5 nm. The high-resolution TEM (HRTEM) result proved that the nanoparticles were structurally uniform with a lattice fringe spacing about 0.25 nm, which corresponded well with the values of 0.253 nm of the (3 1 1) lattice plane of the inverse spinel Fe 3O 4 obtained from the JCPDS database. The superconducting quantum interference device (SQUID) results revealed that the blocking temperature ( T b) was 190 K, and that the magnetic hysteresis loop at 300 K showed a saturation magnetization of 60.5 emu/g, and the absence of coercivity and remanence indicated that the as-synthesized Fe 3O 4 nanoparticles had superparamagnetic properties. Fourier transform infrared spectroscopy (FT-IR) spectrum displayed that the characteristic band of Fe–O at 569 cm −1 was indicative of Fe 3O 4. This method might provide a new, mild, green, and economical concept for the synthesis of other nanomaterials.

Fabrication and characterization of Pd/Ag alloy hollow spheres by the solvothermal method

Pd/Ag alloy hollow spheres have been synthesized in ethylene glycol solution by the solvothermal method and have been characterized extensively. TEM results have revealed the formation of Pd/Ag hollow spheres. Moreover, HRTEM results confirmed the formation of Pd/Ag alloy spheres, where the lattice fringe spacing is 0.229 nm corresponding to the (111) plane of Pd/Ag alloy. SEM, XRD and UV–vis results have further suggested the formation of alloy hollow spheres. The preliminary results showed the reaction time may be an importance factor influencing the formation of Pd/Ag alloy hollow spheres.

Synthesis and structural investigation of Pd/Ag bimetallic nanoparticles prepared by the solvothermal method

Pd/Ag bimetallic nanoparticles have been synthesized successfully by reducing PdCl2 and AgNO3 mixture in ethylene glycol solution using the solvothermal method. The prepared samples have been characterized by UV–vis, XRD, TEM, HRTEM, EDS, and XPS, respectively. Moreover, the bimetallic particles possess alloy and core-shell structure from the HRTEM images. Here, the lattice fringe spacing of Pd/Ag bimetallic nanoparticles corresponds to its (111) plane, which is between that of the Pd and Ag nanoparticles prepared under the same conditions. Furthermore, the possible formation mechanism and factors influencing the formation of Pd/Ag bimetallic nanoparticles, such as reaction temperature and time, have also been investigated.

Analysis of local deformations in heterostructures containing short period superlattices by high-resolution transmission electron microscopy

This work describes the application of the Lattice Fringe Spacing Measurement (LFSM) method to the study of complex multiquantum well heterostructures containing both low-misfit and strain compensated short period superlattices in barriers and wells, respectively. 90°-wedge cross-sectional samples have been used. The adequate choice of both experimental conditions and digitized sampling allows the whole heterostructure to be visualized and studied in a single High Resolution Transmission Electron Microscopy (HRTEM) image. Sample preparation and image processing technique are simple and inexpensive, resulting a fast procedure particularly suited for the analysis of large areas. By this way, in a single HRTEM image we have measured, in the growth direction, the lattice spacings at either side of the multiple grown interfaces as well as the period variations of both types of superlattices; in addition, we have measure on the same image the lattice strain in a direction perpendicular to the growth direction by using the LFSM and the Cumulative Sum methods. We have observed local lateral variations within the wells, with regions tensile or compressively strained, while a vestige of the grown SL remains, indicating the occurrence of a strain induced lateral composition modulation process spontaneously produced during the growth of strain compensated short-period superlattices. This is further confirmed in cross-section prepared by the tripod mechanical polisher method.

Mechanisms of weathering of meteorites recovered from hot and cold deserts and the formation of phyllosilicates

Petrographic, mineralogical and chemical analysis of naturally weathered equilibrated ordinary chondrites collected from ‘ hot’ deserts and Antarctica has revealed striking similarities and also pronounced differences in weathering between the two environments. Terrestrial weathering in all meteorites studied is dominated by oxidation and hydration of Fe,Ni metal, producing Fe-oxides and oxyhydroxides that have partially replaced the metal grains and have also occluded primary intergranular pores to form veins. Troilite weathers readily in ‘ hot’ desert environments but undergoes very little alteration under Antarctic conditions. Most of the primary porosity of ordinary chondrites has been occluded by the time that ∼ 15 to 25% of the initial Fe 0 and Fe 2+ has been oxidised to Fe 3+ in both environments. Results from modelling the volume changes upon alteration of primary minerals to a range of weathering products demonstrates that the primary porosity of most meteorites is sufficient to accommodate weathering products. Dilation of primary pores and brecciation, which has been observed in parts of some meteorites, will only occur if the meteorite is especially metal-rich, or has a low primary porosity. These weathering products are absent from recent falls but have formed in a fall after ∼ 100 yr of museum storage. Cl-bearing akaganéite and hibbingite are common weathering products in Antarctic finds but occur in abundance in only one ‘ hot’ desert meteorite, Daraj 014. The majority of Fe-rich weathering products in meteorites from both environments contain low, but variable concentrations of Si, Mg and Ca. In most meteorites a proportion of these elements are inferred to be present as a very finely crystalline mineral with a ∼ 1.0-nm lattice fringe spacing; where seen within intragranular fractures this mineral has a topotactic relationship with olivine and orthopyroxene. In the heavily-weathered Antarctic finds ALHA 78045 and 77002, Si is concentrated in cronstedtite, a Fe-rich phyllosilicate. An unidentified hydrous Si-Fe-Ni-Mg mineral or gel has also partially replaced taenite in ALHA 78045. In addition to Fe-rich weathering products, ‘ hot’ desert meteorites contain sulphates, Ca-carbonate and silica, whereas such minerals are largely absent from Antarctic finds. The abundance of silicate weathering products in Antarctic meteorites is unexpected and indicates that olivine and pyroxene undergo significant chemical weathering in these environments. As preterrestrial cronstedtite is abundant in CM2 carbonaceous chondrites, the Antarctic environment may be a powerful analog for aqueous alteration in the asteroidal parent bodies of primitive meteorites.