High Isostatic Pressure Research Articles

Preparation and physical characteristics of graphene ceramics

Graphene, a two-dimensional structure of carbon, due to its structure has unique physico-chemical properties that can be used in numerous research and industry areas. Although this structure is already well known, there are still technological (and cost) barriers which do not allow to produce this material in large quantities and hence prevent its use in various applications. For this reason, many technologies are currently being developed to obtain graphene in forms that would enable its widespread use. The graphene-like ceramics were fabricated by the high isostatic pressure method at different temperatures. This technique allows to obtain dense ceramics with various shapes. The structure and morphology of sintered graphene were investigated by XRD, SEM and the Raman spectroscopy. The hardness, thermal conductivity and electric transport measurements recorded in a wide range of temperatures were used to analyze the physical properties of the obtained ceramics.

Impact of high pressure and thermal processing on probiotic mixed mango and carrot juices

This study aimed to elaborate a mixed mango and carrot juice processed thermally and by high isostatic pressure (HIP) added L. plantarum. L. plantarum caused a decrease in pH and increase in acidity of the juices, but did not change the antioxidant capacity (AC), and α- and β-carotene contents. HIP maintained the microbiological quality, whereas the pasteurized juices showed high psychrotrophic counts after 35 storage days. HIP did not influence the AC, whereas the pasteurized juices showed a decrease in AC and a 30% reduction in carotenoid contents. Pasteurization reduced the polyphenoloxidase and peroxidase activities and HIP promoted a reduction in polyphenoloxidase activity but increased the peroxidase activity (~30%). Mixed juices presented good sensory acceptance (HIP juice showed the highest score). Thus, HIP showed to be more effective than thermal process, the matrix proved to be capable of maintaining the L. plantarum viability, and could be an alternative for dairy products. Practical applications The results showed that the production of the probiotics mixed juices processed by high pressure is industrially interesting, since this process was able to better preserve sensory and nutritional characteristics of the juices compared to the thermal process. In addition, this probiotic product emerges as an alternative for vegetarian’s individuals who have diets with cholesterol restriction or allergy and/or intolerance to dairy products. Furthermore, due the effectiveness of applied conservation processes and biopreservation, these products were safe for consumption during the assessed refrigerated storage period.

Development of a mixed jussara and mango juice with added Lactobacillus rhamnosus GG submitted to sub-lethal acid and baric stresses.

This study evaluated the interference of sub-lethal acid (SLA) stress and high isostatic pressure (HIP) stress on the survival of Lactobacillus rhamnosus GG (LGG) in mixed jussara and mango juice with the pH adjusted to 3.0 and 3.5, during 90days of storage at 6°C. The SLA stress at pH 4.0 previously applied to the LGG cells had no effect on the survival of this bacterium in mixed jussara and mango juices. On the other hand, the application of 200MPa/5min/25°C treatment to LGG cells was shown to be efficient in the cross protection of this bacterium in an acid medium. Pressures above 400MPa/5min/25°C caused a reduction in the viability in an acid medium and lower pressures (< 100MPa) showed similar results compared to control treatment in the LGG survival. No changes in pH, acidity and soluble solids were observed in mixed juices. In addition, these products showed elevated levels of anthocyanins, phenolic compounds and antioxidant capacity. This highlights the capacity of the HIP process to promote the cross protection of LGG in an acid medium.

Flow Cytometry Combined With Single Cell Sorting to Study Heterogeneous Germination of Bacillus Spores Under High Pressure.

Isostatic high pressure (HP) of 150 MPa can trigger the germination of bacterial spores, making them lose their extreme resistance to stress factors, and increasing their susceptibility to milder inactivation strategies. However, germination response of spores within a population is very heterogeneous, and tools are needed to study this heterogeneity. Here, classical methods were combined with more recent and powerful techniques such as flow cytometry (FCM) and fluorescence activated cell sorting (FACS) to investigate spore germination behavior under HP. Bacillus subtilis spores were treated with HP at 150 MPa and 37°C, stained with SYTO16 and PI, and analyzed via FCM. Four sub-populations were detected. These sub-populations were for the first time isolated on single cell level using FACS and characterized in terms of their heat resistance (80°C, 10 min) and cultivability in a nutrient-rich environment. The four isolated sub-populations were found to include (1) heat-resistant and mostly cultivable superdormant spores, i.e., spores that remained dormant after this specific HP treatment, (2) heat-sensitive and cultivable germinated spores, (3) heat-sensitive and partially-cultivable germinated spores, and (4) membrane-compromised cells with barely detectable cultivability. Of particular interest was the physiological state of the third sub-population, which was previously referred to as “unknown”. Moreover, the kinetic transitions between different physiological states were characterized. After less than 10 min of HP treatment, the majority of spores germinated and ended up in a sublethally damaged stage. HP treatment at 150 MPa and 37°C did not cause inactivation of all geminated spores, suggesting that subsequent inactivation strategies such as mild heat inactivation or other inactivation techniques are necessary to control spores in food. This study validated FCM as a powerful technique to investigate the heterogeneous behavior of spores under HP, and provided a pipeline using FACS for isolation of different sub-populations and subsequent characterization to understand their physiological states.

Endospore Inactivation by Emerging Technologies: A Review of Target Structures and Inactivation Mechanisms.

Recent developments in preservation technologies allow for the delivery of food with nutritional value and superior taste. Of special interest are low-acid, shelf-stable foods in which the complete control or inactivation of bacterial endospores is the crucial step to ensure consumer safety. Relevant preservation methods can be classified into physicochemical or physical hurdles, and the latter can be subclassified into thermal and nonthermal processes. The underlying inactivation mechanisms for each of these physicochemical or physical processes impact different morphological or molecular structures essential for spore germination and integrity in the dormant state. This review provides an overview of distinct endospore defense mechanisms that affect emerging physical hurdles as well as which technologies address these mechanisms. The physical spore-inactivation technologies considered include thermal, dynamic, and isostatic high pressure and electromagnetic technologies, such as pulsed electric fields, UV light, cold atmospheric pressure plasma, and high- or low-energy electron beam.

Investigation of the mechanical properties of ODS steels at high temperatures using nanoindentation technique

In this study, mechanical properties of two ODS steels, characterized by the same chemical composition yet manufactured by using two different production methods, namely High Isostatic Pressure (HIP) and Hot Extrusion (HE), have been investigated at high temperature by nanoindentation technique. The hardness of the material was evaluated from room temperature up to 600 °C, while initial creep behavior was estimated at room temperature and at 600 °C. In order to better understand the mechanical response of the materials, especially impact of the surface effects, mechanical maps (hardness and reduced young modulus) have been created.

Comparative impact of thermal and high isostatic pressure inactivation of gram-negative microorganisms on the endotoxic potential of reconstituted powder milk

Foods are a primary source of exogenous microorganisms and chemical motifs thereof that act as endotoxins because they trigger systemic inflammation in the body. One of the main accomplishments of food processing has been to prevent spoilage and protect human health by killing pathogenic microorganisms, but secondary consequences compel us to give more importance to the presence of the toxic chemical motifs that remain behind because they can cause systemic inflammation. To test if the type of inactivation affects the amounts of remnants, the concentrations of such toxic compounds were measured after microbial inactivation by classical thermal treatment and high-pressure processing of cow's milk. Three gram-negative bacteria were individually inoculated in reconstituted powder milk: Escherichia coli ATCC 11229, Pseudomonas fluorescens IB 2312 and Enterobacter aerogenes ATCC 13048, and the endotoxic potential estimated by determining the levels of the toxic chemical motifs known as lipopolysaccharides (LPS). The results indicated that the inactivation of these three microorganisms in cow's milk by classical heat treatment or by high pressure have the general tendency to increase the amounts of LPS, but not to a great extent. Additionally, the increases appeared to be a combination of both the type of microbe and the process.

Influence of the lamella structure and high isostatic pressure on the critical current density in in situ MgB2 wires without a barrier

In this article, the significant impact of a lamellar (layered) structure and a high isostatic pressure on the normal state resistance (Rn), critical temperature (Tc), irreversible magnetic field (Birr), upper magnetic field (Bc2) and critical current densities (Jc) at 4.2 K and 20 K was presented. Our research showed that annealing at temperatures in the range of 630 °C–680 °C (above the melting point of Mg) at atmospheric pressure (0.1 MPa) did not create a lamellar (layered) structure. This led to low Tc, Jc and Birr and high Rn. The analysis, made by using scanning electron microscopy (SEM), showed that the annealing temperature increased up to 700 °C under a pressure of 0.1 MPa, which created a lamellar structure. This led to significant growth of Tc, Jc and Birr and a slight increase of Rn. Moreover, the measurements showed that annealing at temperatures from 630 °C to 700 °C did not change the Bc2 value. In comparison to pressureless heat treatment, annealing under the high isostatic pressure of 1.1 GPa obtained a lamellar structure with layers of lower thickness and higher density. This led to significant increases in Jc and Birr and a visible reduction of Rn. SEM analysis showed that the increase of isostatic pressure up to 0.3 GPa created a lamellar structure with thicker layers and lower density. This microstructure led to lower Jc and Birr and significantly higher Rn. On the other hand, the SEM analysis showed that annealing under 0.8 GPa did not cause the formation of a layered structure, and as a result, it led to significant reductions in Birr and Jc (4.2 K and 20 K) and higher Rn. The increase of the isostatic pressure from 0.1 MPa to 1.1 GPa did not affect Tc (B = 0 T) and Bc2. The results indicated that the layered structure obtained a high density of pinning centers, which were particularly effective at higher magnetic fields. Jc of 100 A/mm2 in 8 T at 4.2 K was obtained in in situ undoped MgB2 wires after annealing at 700 °C for 40 min under an isostatic pressure of 1.1 GPa.

The Influence of High Isostatic Pressure on Critical Current Density in C-Doped MgB2 Wires

This article reports the influence of isostatic pressure (from 0.1 MPa to 1.1 GPa), low annealing temperature of 570 ∘C, and annealing time for the formation of high-field pinning centers in 2% C-doped MgB2 wires. Measurements indicate that 1.1 GPa pressure significantly increases the density of high-field pinning centers below 20 K. However, lower pressure (0.6 GPa) slightly increases the density of high-field pinning centers. Increasing the annealing time from 120 to 210 min leads to a reduction of critical temperature (Tc), irreversibility field (Birr), critical current density (Jc), and upper critical field (Bc2), suggesting that a long annealing time leads to a reduction of high-field pinning center density and the number of connections between superconducting grains. The high pressures and low annealing temperature lead to a high critical current density of 1000 A/mm2 in 7.2 T and 100 A/mm2 in 12.5 T at 4.2 K in MgB2 wires.

The Impact of High Pressure, Doping and the Size of Crystalline Boron Grains on Creation of High-Field Pinning Centers in In Situ MgB2 Wires

In this work, we investigated the influence of isostatic pressure (of 0.1 MPa and 1.1 GPa) during heat treatment, doping, size and shape of crystalline boron grains, and annealing time at low annealing temperature (570 °C) on the formation of high-field pinning centers in MgB2 wires. The results indicate that high isostatic pressure (1.1 GPa) at low annealing temperature (570 ° C) and annealing time of 120 min significantly increases the density of high-field pinning centers in MgB2 wires with small and large boron grains. Transport measurements show that an increase of annealing time from 120 to 210 min at 1.1 GPa slightly decreases the critical current density (Jc) and irreversibility field (Birr) in MgB2 wires with large boron grains, suggesting that longer annealing time weakly affects the density of high-field pinning centers. On the other hand, for MgB2 wires with small boron grains, the annealing time of 210 min significantly reduces J_{mathrm {c}} and B_{text {irr}}. This indicates that the longer annealing time at 1.1 GPa significantly reduces the density of high-field pinning centers. Our studies indicate that dislocations created by the hot isostatic pressure process significantly increase B_{text {irr}} in the temperature range from 5 to 12 K. On the other hand, strains due to the shrinkage of MgB2 material increase B_{text {irr}} in the temperature range from 12 to 34 K. The results show that small grains of crystalline boron and high isostatic pressure lead to a high density of dislocations and strains during transformation to the MgB2 phase.

Production of Ytterbium Ceramic for Medical Radioactive Sources

A method of fabricating ceramic cores from ytterbium-168 enriched ytterbium oxide is presented. This method is based on sintering ytterbium oxide powder under high isostatic pressure of about 8 GPa in order to obtain its B-modification with a monoclinic crystal lattice. The equipment used, sintering regimes, and an analysis of the obtained samples are described. Owing to their high density (to 10.2 g/cm3) the samples hold promise as sources for contact radiation therapy of tumors.

High isostatic pressure and thermal processing of açaí fruit (Euterpe oleracea Martius): Effect on pulp color and inactivation of peroxidase and polyphenol oxidase

The present study evaluated the effect of high isostatic pressure (HIP) on the activity of peroxidase (POD) and polyphenol oxidase (PPO) from açaí. Açaí pulp was submitted to several combinations of pressure (400, 500, 600MPa), temperature (25 and 65°C) for 5 and 15min. The combined effect of HIP technology and high temperatures (690MPa by 2 and 5min at 80°C) was also investigated and compared to the conventional thermal treatment (85°C/1min). POD and PPO enzyme activity and instrumental color were examined after processing and after 24h of refrigerated storage. Results showed stability of POD for all pressures at 25°C, which proved to be heat-resistant and baro-resistant at 65°C. For PPO, the inactivation at 65°C was 71.7% for 600MPa after 15min. In general, the increase in temperature from 25°C to 65°C reduced the PPO relative activity with no changes in color. Although the thermal treatment and the HIP (690MPa) along with high temperature (80°C) reduced the PPO relative activity, and relevant darkening was observed in the processed samples. Thus, it can be concluded that POD is more baro-resistant than PPO in açaí pulp subjected to the same HIP processing conditions and processing at 600MPa/65°C for 5min may be an effective alternative for thermal pasteurization treatments.

Enhancement of pinning centers density and structure by using hot isostatic pressure of 1.2 GPa in Ba(Fe0.92,Co0.08)2As2 superconducting material

We report the influences of the high hot isostatic pressure (HHIP) on Ba(Fe0.92,Co0.08)2As2 superconducting bulks materials. Magnetic measurements showed that this material has a critical temperature (Tc) of 26 K. The HHIP process increases the density of flux pinning centers without altering the dominant flux pinning mechanisms and without decreasing of Tc. Structural studies have shown that the HHIP process increases the density of the material, reduces the size of voids, and thus allows to obtain homogeneous distribution of the components. Additionally, the HHIP process removes cracks in polycrystalline Ba(Fe0.92,Co0.08)2As2, creates more superconducting phase and forms less amount of Ba precipitates.

Effect of high isostatic pressure on the peptidase activity and viability of Pseudomonas fragi isolated from a dairy processing plant

To produce safe and high quality processed milk, high pressure (HP) technology was tested to inactivate undesired microorganisms and their caseinolytic activity. A Pseudomonas fragi strain, isolated from the inner surface of a cheese-making machine from a dairy plant, was shown to harbour the aprX gene and cause casein proteolysis. Single-cycle HP processing of P. fragi-spiked milk at 450 MPa and 25 °C for 20 min decreased bacteria viability to lower levels and reduced peptidase activity by 14%. However when HP processing was performed at 50 °C, a synergistic effect on peptidase was observed, reaching 40% inactivation. Multiple HP treatment cycles at 450 MPa and 25 °C were less effective and reduced peptidase activity by only 23%. HP treatment could aid in the challenge to reduce AprX peptidase activity produced by microbial contaminants, but partial inactivation of peptidase was not effective in preventing UHT milk coagulation during storage at room temperature.

Formation of High-Field Pinning Centers in Superconducting MgB2 Wires by Using High Hot Isostatic Pressure Process

This paper demonstrates the effects of hot isostatic pressure (HIP) on the structure and transport critical parameters of in situ MgB2 wires without a barrier. Our results show that only HIP and nano-boron allow the formation of more high-field pinning centers, which lead to the increase in critical current density (Jc) at high applied magnetic fields. Nano-boron and annealing at a low pressure increase the Jc in the low magnetic field. This indicates that nano-particles create more high-field pinning centers. In addition, the results show that nano-boron improves the connection between the grains. Scanning electron microscope results show that HIP increases the reaction rate between Mg and B, density, and homogeneity of the MgB2 material. Additionally, HIP allows to create a structure with small grains and voids and eliminates the significance of the number of voids. High isostatic pressure allows to obtain high Jc of 10 A/mm2 (at 4.2 K) in 10 T and increases irreversible magnetic field (Birr) and upper critical field (Bc2). Measurements show that these wires have high critical temperature of 37 K.

Comparative study of the effect of high pressure processing on the residual activity of milk coagulants in buffer and in ultrafiltered cheese

This study aimed to evaluated how the high isostatic pressure (HIP) affects the milk coagulation activity (MCA) of different coagulants in Ultrafiltered (UF) cheese and in a sodium phosphate (SP) buffer solution when processed at 25 °C at different pressures (100–450 MPa) and time (2–16 min). Results showed that all the enzymes had greater sensitivity to HIP when processed in UF cheese (inactivation up to 74.4% higher) than in SP buffer solution, being the maximum condition evaluated (450 MPa/16 min) able to reduces the residual activity of all the enzymes up to 94% and 60% in UF cheese and SP buffer, respectively. In terms of activity increase, higher increase in MCA occurred in UF cheese at pressures up to 275 MPa for recombinant chymosin (20%), calf rennet (24%) and R. miehei protease (17%) and at pressure up to 151 MPa for porcine pepsin (6%) and bovine rennet (8%). Therefore, the results highlight the importance of the media in the consequence of the HIP effects on enzyme and that HIP processing could be an interesting alternative to accelerate proteolysis in matured cheeses (using activity increase conditions) or to allows extension of the shelf life in fresh cheeses (using inactivation conditions), reducing undesirable changes caused by residual coagulant activity.

Variation of Tc, lattice parameter and atomic ordering in Nb3Sn platelets irradiated with 12 MeV protons: correlation with the number of induced Frenkel defects

Nb3Sn platelets with thicknesses between 0.12 and 0.20 mm produced by a high isostatic pressure process at 1250 °C were irradiated at 300 K with 12 MeV protons. The effects of irradiation on the lattice parameter a, the atomic order parameter S and the transition temperature Tc were measured as a function of proton fluence. In view of the presence of multiple energy radiation sources in future accelerators, the present proton data are compared with neutron irradiation data from the literature. The fluences for both types of radiation were replaced by the dpa number, the ‘displacements per atom’, calculated using the FLUKA code, which is proportional to the number of radiation induced Frenkel defects. It was found that the variation of both a and S for Nb3Sn after proton and neutron irradiation as a function of dpa fall almost on the same curve, in analogy to the recently reported correlation between Tc and the dpa number. By a simultaneous irradiation of two adjacent thin Nb3Sn platelets, we have shown that this correlation is not only valid for the state of ‘steady energy loss’ (protons traveling through the first platelet) but also for the state of higher damage at the Bragg peak (second platelet). It follows that the number of radiation induced Frenkel defects in the A15 grains, calculated via the dpa number, can be considered as a ‘universal’ parameter, allowing the calculation of the variation of Tc, a and S of Nb3Sn under the effect of multiple high energy radiation sources, as in future superconducting accelerators.

Development of a juçara and Ubá mango juice mixture with added Lactobacillus rhamnosus GG processed by high pressure

This study evaluated the development of a juçara and Ubá mango juice mixture and the influence of pasteurization, high isostatic pressure (HIP) and the addition of a probiotic culture of Lactobacillus rhamnosus GG on the physicochemical, microbiological, functional and sensory characteristics of the products obtained. The pasteurized juices (82 °C/1 min) showed larger amounts of total phenolics, greater antioxidant capacity and lower lipid levels as compared to juice processed using HIP (600 MPa/5 min/25 °C). Juice with added L. rhamnosus GG differed with respect to pH, acidity and proteins as compared to those without, due to the fermentative action of the probiotic bacteria. The addition of L. rhamnosus GG to the juice did not affect its acceptance. The levels of L. rhamnosus above 108 CFU/mL during the 30 days of storage at 4 °C, demonstrate its viability in this product, which is potentially probiotic. In addition, consumers preferred the juice processed by HIP.

Superior transport Jc obtained in in-situ MgB2 wires by tailoring the starting materials and using a combined cold high pressure densification and hot isostatic pressure treatment

The best Jc performance (8×104A·cm−2 at 10T, 4.2K) has been obtained in our work among all the in-situ powder-in-tube (PIT) MgB2 wires reported so far by tailoring their boron and magnesium precursors, as well as employing appropriate high pressure during the manufacturing process. Moreover, the second stage densification using the special HIP has been applied to commercial long-length wire. Our work suggests that the economical starting precursors and the combination of cold and hot densification techniques could represent a promising alternative for industrial and economical production of practical MgB2 wires with excellent Jc.

Experimental research of high field pinning centers in 2% C doped MgB2 wires at 20 K and 25 K

High field pinning centers in MgB2 doped with 2 at. % carbon under a low and a high hot isostatic pressures have been investigated by transport measurements. The field dependence of the transport critical current density was analyzed within the different pinning mechanisms: surface pinning, point pinning, and pinning due to spatial variation in the Ginzburg-Landau parameter (Δκ pinning). Research indicates that a pressure of 1 GPa allows similar pinning centers to Δκ pinning centers to be obtained. This pinning is very important, because it makes it possible to increase the critical current density in high magnetic fields at 20 K and 25 K. Our results indicate that the δTc and δl pinning mechanisms, which are due to a spatial variation in the critical temperature (Tc) and the mean free path, l, respectively, create dislocations. The high density of dislocations with inhomogeneous distribution in the structure of the superconducting material creates the δl pinning mechanism. The low density of dislocations with inhomogeneous distribution creates the δTc pinning mechanism. Research indicates that the hot isostatic pressure process makes it possible to obtain a high dislocation density with a homogeneous distribution. This allows us to obtain the δTc pinning mechanism in MgB2 wires. In addition, a high pressure increases the crossover field from the single vortex to the small vortex bundle regime (Bsb) and improves the δTc pinning mechanism. Our research has proved that a high pressure significantly increases the crossover field from the small bundle to the thermal regime (Bth), with only a modest decrease in Tc of 1.5 K, decreases the thermal fluctuations, increases the irreversibility magnetic field (Birr) and the upper critical field (Bc2) in the temperature range from 4.2 K to 25 K, and reduces Birr and Bc2 above 25 K.