High-pressure Preparation Research Articles

Formation of hierarchically structured martensites in pure iron with ultrahigh strength and stiffness

Strong steels are primarily fabricated by introducing spatial obstacles (e.g., stacking faults and precipitates) that inhibit dislocation slips under stress to achieve high strength. However, for most low-carbon steels, such obstacles are difficult to form mainly because the martensitic transition is kinetically unfavorable by conventional methods, which precludes the attainment of high-strength materials in these steels with low solute contents. Here, we report an innovative high-pressure preparation of martensitic pure Fe with involving nano-effect, which leads to the formation of ultrastrong bulk iron with exceptionally high yield strength, ultimate strength, and hardness of 2.9 GPa, 3.7 GPa, and 9.0 GPa, respectively, exceeding those of high-speed steels. Such extraordinary mechanical properties are closely attributed to its high-density martensites with unique multiscale hierarchical structures formed due to complex phase transitions under pressure.

Microstructure graphitization evolution and multi-scale, multi-mechanism synergistic enhancement of ultra-high strength carbon-graphite materials

Carbon-graphite materials, due to their excellent properties, have become one of the most widely used materials in the world. In order to prepare high-strength, high-density, high-performance carbon-graphite materials quickly and efficiently, we used a high-temperature and high-pressure preparation method to investigate the effect of graphitization transition mechanism and microstructure composition on strength properties under temperature-pressure coupling through physical strength property testing, spectral analysis, microscopic morphology, and nanostructure characterization. The experiment results show that the introduction of high pressure can effectively reduce the graphitization initiation temperature threshold, shorten the preparation time, and substantially improve the strength properties. The flexural strength, compressive strength, and bulk density were measured at 2.8 GPa and 1200 °C, reaching 102.9 MPa, 208.4 MPa, and 2.03 g/cm3, respectively, which were greatly improved compared with the conventional preparation method. The microstructure analysis showed that the high strength resulted from the combined effects of the establishment of the three-dimensional framework structure, the inter-growth connection between the multi-oriented layers, and the strengthening mechanism of the graphene nanoscale defects. This method provides a fast and efficient way to prepare carbon graphite materials for high-temperature resistance, oxidation resistance, high wear resistance, and high strength applications.

High-pressure synthesis, spin-glass behaviour, and magnetocaloric effects in FexTi2S4 heideite sulphides

A rapid high-pressure preparation method (3.5 GPa) yields FexTi2S4 Heideite-type phase. Magnetism offers a complex scenario with AFM to FM-like interactions. The magnetocaloric effect yields significant entropy and relative cooling power.

High-pressure preparation of high-hardness CoCrFeNiMo0.4 high-entropy alloy

The CoCrFeNiMo0.4 high-entropy alloys (HEAs) were synthesized by a high-pressure solid-state reaction at 3–5 GPa and held for 3–10 min at 1200 °C. The microstructure and mechanical properties of the sample were influenced by the pressure and holding time, which was confirmed when the Co, Cr, Fe, Ni, and Mo atoms diffused to form HEAs. The increased pressure hindered the diffusion between atoms and thus inhibited the formation of HEAs. Under the influence of the enthalpy of mixing between elements, Fe had the strongest repulsive force on the system and the weakest diffusion effect, but increasing the holding time promoted the diffusion of Fe atoms. Compared with the microhardness reported in other studies, the maximum hardness in our work was 449.1 HV, which represents a maximum increase of approximately 80%. The synergistic effects of the solid-solution strengthening of the system and the serious lattice distortion effect caused by large Mo atoms and high pressure were the dominant mechanisms responsible for the enhanced microhardness of the sintered HEAs under extreme conditions.

High-pressure preparation and structural analysis of Se-S-As ternary system compounds

Se-S-As ternary polycrystalline compounds were prepared at a synthesis temperature of 900 K under a pressure of 4 GPa. The samples were analyzed by XRD, SEM and EDS. The experimental results showed that the high-pressure conditions promoted the reaction between the ternary compound Se-S-As, and the prepared samples had fairly crystallinity with the sample grain diameter around 50 μm. The results of Se-S-As elemental composition analysis showed that the atomic ratio Se:S: As was close to 8:5:8.

The impact of boron atoms on clathrate-I silicides: composition range of the borosilicide K8-xBySi46-y.

The clathrate-I borosilicide K8-xBySi46-y (0.8 ≤x≤ 1.2 and 6.4 ≤y≤ 7.2; space group Pm3[combining macron]n) was prepared in sealed tantalum ampoules between 900 °C and 1000 °C. By high-pressure preparation at 8 GPa and 1000 °C, a higher boron content is achieved (x = 0.2, y = 7.8). Crystal structure and composition were established from X-ray diffraction data, chemical analysis, WDX spectroscopy, and confirmed by 11B and 29Si NMR, and magnetic susceptibility measurements. The compositions are electron-balanced according to the Zintl rule within one estimated standard deviation. The lattice parameter varies with composition from a = 9.905 Å for K7.85(2)B7.8(1)Si38.2(1) to a = 9.968(1) Å for K6.80(2)B6.4(5)Si39.6(5).

The dielectric signature of glass density

At present, we are witnessing a renewed interest in the properties of densified glasses prepared by isobaric cooling of a liquid at elevated pressure. As high-pressure densification emerges as a promising approach in the development of glasses with customized features, understanding and controlling their unique properties represent a contemporary scientific and technological goal. The results presented herein indicate that the applied high-pressure preparation route leads to a glassy state with higher density (∼1%) and a reduced free volume of about 7%. We show that these subtle structural changes remarkably influence the dielectric response and spectral features of β-relaxation in etoricoxib glass. Our study, combining dynamical and structural techniques, reveal that β-relaxation in etoricoxib is extremely sensitive to the variations in molecular packing and can be used to probe the changes in glass density. Such connection is technologically relevant and may advance further progress in the field.

High-Pressure Preparation of High-Density Cu2ZnSnS4 Materials**Supported by the National Natural Science Foundation of China under Grant Nos 10874178, 11074093, 61205038 and 11274135, the National Found for Fostering Talents of Basic Science under Grant No J1103202, the Ph.D. Programs Foundation of Ministry of Education of China under Grant No 20120061120011, the Open Project of State Key Laboratory of Superhard Materials of

High-density Cu2ZnSnS4 (CZTS) materials are prepared via the mechanical alloying and high pressure sintering method using Cu2S, ZnS and SnS2 as the raw materials. The morphological, structural, compositional and electrical properties of the materials are investigated by using x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy, as well as by the Raman scattering and the Hall Effect measurements. The CZTS synthesized under 5 GPa and 800°C shows a p-type conductivity, with a resistivity of 9.69 × 10−2 Ω·cm and a carrier concentration of 1.45 × 1020 cm−3. It is contributed to by the large grains in the materials reducing the grain boundaries, thus effectively reducing the recombination of the charge carriers.

High-pressure preparation and characterization of (R,R')NiO3 (R,R'= rare earths) perovskites: effect of the variance of the R3+ ionic sizes

In this paper we describe some novel members of the RNiO3 perovskites, containing Ni3+ and presenting metal-insulator transitions coupled to a charge disproportionation effect. This phenomenon is observed in the insulating state as a subtle monoclinic distortion, due to the presence of two unequivalent Ni ions with different coordination environments, corresponding to expanded and contracted octahedra alternating in the three-dimensional network. Here we examine how the introduction of mixed rare-earth cations at the R sublattice affects the metal-insulator transition and the structural features, from high resolution neutron powder diffraction studies.

High-pressure preparation of bulk tungsten material with near-full densification and high fracture toughness

In this work, we present a novel method to sinter tungsten bulk material under high pressure without any additives. The sintering temperatures were greatly reduced in our experiments. The sintered samples can achieve near-full densification (relative density of 99.5%), and have fracture toughness of about 50% higher than that from the traditional methods, without sacrificing hardness. Moreover, the grain sizes of the sintered samples maintained in the initio range. The sintering kinetics, microstructure evolutions, and relationships of mechanical properties versus pressure–temperature conditions were also discussed.

Pinning in $\hbox{MgB}_{2}$- and YBaCuO-Based Superconductors: Effect of Manufacturing Pressure and Temperature

Bulk MgB2- and YBaCuO-based materials are competitive candidates for applications. The properties of both compounds can be significantly improved by high temperature-high pressure preparation methods. The transformation of grain boundary pinning to point pinning in MgB2-based materials with increasing manufacturing temperature from 800 to 1050°C under pressures from 0.1 MPa to 2 GPa correlates well with an increase in critical current density in low and intermediate magnetic fields and with the redistribution of boron and oxygen in the material structure. As the manufacturing temperature increases (to 2 GPa), the discontinuous oxygen-enriched layers transform into distinct Mg-B-O inclusions, and the size and amount of inclusions of higher borides MgBX (X>;2) are reduced. The effect of oxygen and boron redistribution can be enhanced by Ti or SiC addition. The oxygenation of melt-textured YBa2Cu3O7 - δ (MT-YBaCuO) under oxygen pressure (16 MPa) allows one to increase the oxygenation temperature from 440°C to 700-800°C, which leads to an increase of the twin density in the Y123 matrix and to a decrease of dislocations, stacking faults, and the density of microcracks, and as a result, to an increase of the critical current density, Jc, and the trapped magnetic field. In MT-YBaCuO, practically free form dislocations and stacking faults and with a twin density of 22-35 μm-1, Jc of 100 kA/cm2 (at 77 K, 0 T) has been achieved, and the importance of twins in Y123 for pinning was demonstrated experimentally.

High-pressure preparation and characterization of new metastable oxides: the case of NdCu3Mn3MO12 (M = Fe, Cr)

High-pressure synthesis is a powerful technique to stabilize metastable oxides, either containing transition metals in unusual oxidation states, or favouring the formation of dense perovskite-related phases. Happily, many solids synthesized at high pressure-high temperature conditions (where they are fhermodynamically stable) can be "quenched" to ambient conditions, where they are termodynamically metaestable, yet they remain indefinitely kinetically stable. In this paper we illustrate the example of a new family of oxides derived from the CaCu3Mn4O12 perovskite. We have studied the series of nominal composition NdCu3(Mn3M)O12 (M = Fe, Cr) where Mn is replaced by Fe(Cr) cations in the ferrimagnetic perovskite NdCu3Mn4O12. These materials have been synthesized in poly crystalline form under moderate pressure conditions of 2 GPa, in the presence of KClO4 as oxidizing agent. All the samples have been studied by neutron powder diffraction (NPD) below and above the ferromagnetic Curie temperatures. These oxides crystallize in the cubic space group Im3̄ (No. 204). Mn4+/Mn3+ and Fe3+(Cr3+) occupy at random the octahedral B positions of the perovskite structure. The materials have also been characterized by magnetic and magnetotransport measurements. All the samples are ferrimagnetic and show a decrease of TC upon Fe(Cr) introduction since these ions disturb the ferromagnetic interactions within this magnetic sublattice. The introduction of Fe changes the resistivity response from metallic to a semiconductor behavior. However, the magnetoresistance is still considerable at 300 K upon Fe doping, and it is enhanced at 100 K probably due to the decrease in the number of charge carriers from the pure oxide to the Fe-doped compound.

High-pressure preparation and thermoelectric properties of Bi0.85Sb0.15

Nanocrystalline Bi0.85Sb0.15 powders were prepared by a novel mechanical alloying method. The bulk samples were formed by applying a pressure of 6 GPa at different pressing temperatures and times. Electrical conductivity, Seebeck coefficients, and thermal conductivity were measured in the temperature range 80–300 K. The Seebeck coefficient reaches a maximum value of −173 µV/K at 150 K. The largest figure of merit, 3.46 × 10−3 K−1, achieved in this experiment is 50% higher than that of its single-crystal counterpart at 200 K.

High‐Pressure Preparation, Crystal Structure, and Properties of α‐Ln2B4O9 (Ln: Eu, Gd, Tb, Dy): Oxoborates Displaying a New Type of Structure with Edge‐Sharing BO4 Tetrahedra.

AbstractFor Abstract see ChemInform Abstract in Full Text.

High-pressure preparation, crystal structure, and properties of the new rare-earth oxoborate β-Dy 2B 4O 9

In this work we report about a new rare-earth oxoborate β-Dy 2B 4O 9 synthesized under high-pressure/high-temperature conditions from Dy 2O 3 and boron oxide B 2O 3 in a B 2O 3/Na 2O 2 flux with a walker-type multianvil apparatus at 8 GPa and 1000°C. Single crystal X-ray structure determination of β-Dy 2B 4O 9 revealed: P 1 ̄ , a=616.2(1) pm, b=642.8(1) pm, c=748.5(1) pm, α=102.54(1)°, β=97.08(1)°, γ=102.45(1)°, Z=2, R1=0.0151, w R 2=0.0475 (all data). The compound exhibits a new structure type which is built up from bands of linked BO 3- (Δ) and tetrahedral BO 4-groups (□). The Dy 3+-cations are positioned in the voids between the bands. According to the conception of fundamental building blocks β-Dy 2B 4O 9 can be classified with the notation 2Δ6□:Δ〈3□〉=〈4□〉=〈3□〉Δ. Furthermore we report about temperature-resolved in situ powder diffraction measurements and IR-spectroscopic investigations on β-Dy 2B 4O 9.

A system for high pressure preparation and UHV characterization of surface reactions

An apparatus is presented which allows in situ high pressure dosing of gases at surfaces and subsequent characterization of the surface in UHV by established surface sensitive tools. A sample mounting has been constructed that allows dosing of corrosive gases at elevated temperatures and that allows pick-up by a sample transfer rod for transfer to an ion scattering apparatus.

High pressure preparation and neutron-diffraction study of the high T c superconductor YBa 2Cu 4O 8±x

The high-T c superconductor YBa 2Cu 4O 8±x (T c≅80 K) has been synthesized for the first time as a bulk material using high pressure of oxygen and characterized by high accuracy chemical analysis, (±0.001), T c measurements as well as x-ray diffraction. The crystal structure was refined by elastic neutron scattering confirming the model of Marsh et al corresponding to the space group Ammm but with orthorhombic lattice constants a=3.8413(3)Å, b=3.8713(5)Å and c=27.240(2)Å.

High temperature and pressure preparation and properties of iron carbides Fe7C3 and Fe3C

The formation regions of Fe7C3 and Fe3C were determined at high temperature and high pressure in the iron-graphite system. Fe7C3 formed at relatively higher pressures and Fe3C at lower pressures. Both Fe7C3 and Fe3C were isolated from coexisting excess carbon powders by a magnetic method. Fe7C3 had a Curie point of 250° C and a saturation magnetization of 120 emu g−1 at room temperature and Fe3C had those of 210° C and 125 emu g−1. Fe7C3 decomposed to Fe3C and carbon at 600° C, but to α-Fe and carbon at 700° C at atmospheric pressure, and Fe3C to α-Fe and carbon at 700° C. The substitution of other metals (Cr, Mo and W) for iron in these carbides leads to changes in the thermal stabilities and the magnetic properties.

A high pressure preparation lock for surface analysis

AbstractA lock will be described that facilitates the preparation of samples in a small high pressure preparation chamber at pressures up to 30 bar (30 atm) and temperatures up to 800°C and the transport of the treated sample into the analysis chamber, which is under UHV, without reducing the pressure in the preparation chamber.

High-pressure preparation of carbanilide from nitrobenzene, carbonyl sulfide, carbon monoxide, and water

Carbanilide is prepared from nitrobenzene in a procedure which requires only one process step. An aromatic nitro compound is treated with a mixture of carbonyl sulfide, carbon monoxide, and water in an organic base such as pyridine. Yields of 50 mol % of carbanilide from nitrobenzene are obtained. Aniline, a reaction intermediate, is the only other major product. A German patent, 2,317,122, has recently shown that this process can be extended to the preparation of Karyl-N'-alkyl ureas starting with an aryl nitro compound and an alkyl amine.