Pressure High Temperature Processing Research Articles

Effect of feedstock diamond powder property on microstructure and mechanical properties of polycrystalline diamond compacts

Polycrystalline diamond compact (PDC) is used widely for machining, petroleum drilling, and mining. Up until now, the effect of feedstock diamond powder property, especially the specific surface area of diamond powder, has rarely been investigated on the mechanical property of PDCs. In this study, diamond powders with different specific surface areas have been employed for the synthesizing of PDCs using high-pressure high-temperature (HPHT) process. The research shows that the microstructure, residual stress, and especially the wear resistance of PDCs were significantly affected by the specific surface area of diamond powders. Compared with the ordinary diamond powders, the diamond powders with higher specific surface area promote the formation of diamond-diamond bonding more significantly during HPHT process and contribute to the noticeably higher wear resistance of PDCs.

Microstructure and thermoelectric properties of chlorine-filled CoSb3 skutterudites synthesized by HPHT process

Filled CoSb3-based skutterudites are promising middle-temperature thermoelectric materials. However, p-type skutterudites containing electropositive fillers require additional charge compensation by doping atoms at the framework, which leads to enhanced carrier scattering. In this work, p-type filled CoSb3 materials with electronegative guest Cl were successfully prepared by high-pressure high-temperature (HPHT) process. A high filling fraction of Cl in void sites reaching ∼23% was obtained without charge compensation. Cl filler exhibited p-type electron acceptor behavior and can increase hole concentration of pristine CoSb3 to a magnitude of 1019 cm−3. As the content of Cl rose, abnormal spinal morphology and fine nano grain were observed in Cl-filled skutterudites. In turn, lattice thermal conductivity of Cl0.6Co4Sb12 sample significantly reduced by 46% when compared to pristine CoSb3 at room temperature due to enhanced scattering of point defect, rattler, and grain boundary. In sum, HPHT process looks promising for using Cl as additional p-type dopant candidate to yield significantly enhanced phonon scattering.

Two-step high-pressure high-temperature synthesis of nanodiamonds from naphthalene**Project supported by the National Key R&D Program of China (Grant No. 2018YFB0406500), the National Natural Science Foundation of China (Grant Nos. U1804155, U1604263, and 11804307), and the China Postdoctoral Science Foundation (Grant Nos. 2018M630830 and 2019T120631).

Nanodiamonds have outstanding mechanical properties, chemical inertness, and biocompatibility, which give them potential in various applications. Current methods for preparing nanodiamonds often lead to products with impurities and uneven morphologies. We report a two-step high-pressure high-temperature (HPHT) method to synthesize nanodiamonds using naphthalene as the precursor without metal catalysts. The grain size of the diamonds decreases with increasing carbonization time (at constant pressure and temperature of 11.5 GPa and 700 °C, respectively). This is discussed in terms of the different crystallinities of the carbon intermediates. The probability of secondary anvil cracking during the HPHT process is also reduced. These results indicate that the two-step method is efficient for synthesizing nanodiamonds, and that it is applicable to other organic precursors.

Influence of pulsed current during high pressure sintering on crystallite size and phase composition of diamond with Ti[sbnd]B bonding phase

Diamond production by sintering and synthesis is known from the mid-fifties of the twentieth century. The sintering technology of PCD materials has not significantly changed even to this day. Nonetheless, there are publications providing a lot of success in the field of synthesis of diamond composite materials sintering using SPS technology, yet these studies are limited to pressures mainly up to 140MPa. In this work HP SPS (High Pressure Spark Plasma Sintering) device, was used to sinter diamond composite with titanium‑boron bonding phase. Thus obtained material was then compared with HP-HT (High Pressure High Temperature) sintered sample, to investigate the influence of the heating by means of direct pulsed current on the crystallite size and phase composition of diamond with 10wt% of Ti+2B bonding phase. Both HP SPS and HP-HT processes were carried out at 8.0±0.2GPa and at the temperature of 1650±50°C during 20s of holding time. The XRD analysis carried out showed that the different type of current used for heating has significant influence on kinetics of the sintering, which is visible in differences in phase composition and level of lattice strain, when comparing standard HP-HT with HP SPS methods.

Boron-doped diamond synthesized at high-pressure and high-temperature with metal catalyst

The boron-doped diamond (BDD) powder consisting of 40–100µm particles was synthesized at 5GPa and 1500–1600°C from a mixture of 50wt% graphite and 50wt% Ni–Mn catalyst with an addition of 1wt% or 5wt% boron powder. The size of crystal domains of doped and non-doped diamond was evaluated as a coherent scattering region by X-ray diffraction (XRD) and using small-angle neutron scattering (SANS), being ≥180nm (XRD) and ~100nm (SANS). Magnetic impurities of NiMnx originating from the catalyst in the synthesis, which prevent superconductivity, were detected by magnetization measurements at 2–300K. X-ray photoelectron spectroscopy, the temperature dependence of the resistivity, XRD, and Raman spectroscopy reveal that the concentration of electrically active boron is as high as (2±1)×1020cm−3 (0.1at%). To the best of our knowledge, this is the highest boron content for BDD synthesized in high-pressure high-temperature process with metal catalysts.

Mechanical alloying as a new synthesis route for metastable silicon clathrates

Stability studies by ab-initio calculations for the best-known binary Ba-Si clathrates reveal that Ba24Si100 is the most stable composition and that the latter can be stabilized in a relatively small energy range, of the order of a few kJ/mol.at. This suggested alternative synthesis routes, easier and cheaper to the commonly used high pressure-high temperature processes. Here, for the first time, we confirmed the theoretical prediction and were successful in the synthesis of the phase Ba24Si100 by mechanical alloying. The influence of the milling parameters is discussed in order to get a crystalline phase with 90% purity.

High-Pressure-High-Temperature Processing Reduces Maillard Reaction and Viscosity in Whey Protein-Sugar Solutions.

The aim of the study was to determine the influence of pressure in high-pressure-high-temperature (HPHT) processing on Maillard reactions and protein aggregation of whey protein-sugar solutions. Solutions of whey protein isolate containing either glucose or trehalose at pH 6, 7, and 9 were treated by HPHT processing or conventional high-temperature (HT) treatments. Browning was reduced, and early and advanced Maillard reactions were retarded under HPHT processing at all pH values compared to HT treatment. HPHT induced a larger pH drop than HT treatments, especially at pH 9, which was not associated with Maillard reactions. After HPHT processing at pH 7, protein aggregation and viscosity of whey protein isolate-glucose/trehalose solutions remained unchanged. It was concluded that HPHT processing can potentially improve the quality of protein-sugar-containing foods, for which browning and high viscosities are undesired, such as high-protein beverages.

Oxidation and reduction of nanodiamond particles in colloidal solutions by laser irradiation or radio-frequency plasma treatment

Functionalized nanodiamond particles (NDs) represent carbon nanomaterial with unique properties for various applications. Here we report on a new approach to surface modification of NDs by their exposure to radio frequency (RF) plasma or laser irradiation (LI) plasma directly in aqueous solution. By using grazing angle reflectance Fourier transform infrared spectroscopy and supporting analysis by X-ray photoelectron spectroscopy, zeta-potential, and Kelvin force microscopy we show that surface chemistry of NDs produced by detonation process (DNDs) or high-pressure high-temperature process (HPHT NDs) works in different way. Moieties on as-received NDs are dominated by COOH and COC groups due to wet chemical cleaning procedures. On DNDs, both RF and LA treatment lead to removal of sp2 shell and additional oxidation of the surface to C OC groups. On HPHT NDs the RF treatment leads to reduction of COC groups that are transformed into COH and CH moieties. Thus at least partial hydrogenation of colloidal HPHT NDs seems feasible.

Furan formation as a function of pressure, temperature and time conditions in spinach purée

In recent studies, innovative high-pressure high-temperature processing (HPHT) has presented itself as an interesting alternative for furan reduction in sterilized, vegetable-based foods. In order to explain the observed furan reduction following HPHT treatment, furan formation was studied under a range of pressure, temperature and time conditions, using spinach purée as a case study. For all the treatments, no furan was detected during the dynamic heating-up phase, followed by a steady increase in furan concentrations at isothermal(-isobaric) conditions. The increase in furan concentrations at isothermal(-isobaric) treatment conditions could be adequately described by an empirical, zero-order model. A pressure level of 600 MPa did not affect the rate of furan formation in spinach purée, as opposed to the processing temperature and time. As a result, the reduced furan concentrations for HPHT processing could be explained by the faster heating and cooling rates, resulting in shorter processing times as compared with conventional retort processing.

Color Enhancement of Natural Sapphires by High Pressure High Temperature Process

We employed the high-pressure high temperature (HPHT) process to enhance the colors of natural sapphires to obtain a vivid blue. First, we analyze the content of the coloring agent Fe₂O₃ using the wavelength dispersive X-ray fluorescence (WD-XRF) method. The HPHT procedure operates under 1 GPa at various temperatures of 1700, 1750, and 1800℃ for 5 minutes using a cubic press. We determine the color changes using the optical microscopic images, UV-VIS near-infrared (NIR) spectra, micro-Raman spectra, and Fourier transform-infrared (FT-IR) spectra for all sapphire samples before and after the treatment. The optical microscopic results indicate that the HPHT process can enhance the sapphire color to a vivid blue at temperatures above 1750℃. The UV-VIS-NIR spectra identify the color changes explicitly and quantitatively through providing the Lab color scales and color differences. Both results demonstrate that the colors of natural sapphires can be enhanced to a vivid blue using the HPHT process above 1750℃ under 1 GPa for 5 minutes.

Evaluating the potential of high pressure high temperature and thermal processing on volatile compounds, nutritional and structural properties of orange and yellow carrots

The present study compares the impact of thermal and high pressure high temperature (HPHT) processing on volatile profile (via a non-targeted headspace fingerprinting) and structural and nutritional quality parameter (via targeted approaches) of orange and yellow carrot purees. The effect of oil enrichment was also considered. Since oil enrichment affects compounds volatility, the effect of oil was not studied when comparing the volatile fraction. For the targeted part, as yellow carrot purees were shown to contain a very low amount of carotenoids, focus was given to orange carrot purees. The results of the non-targeted approach demonstrated HPHT processing exerts a distinct effect on the volatile fractions compared to thermal processing. In addition, different coloured carrot varieties are characterised by distinct headspace fingerprints. From a structural point of view, limited or no difference could be observed between orange carrot purees treated with HPHT or HT processes, both for samples without and with oil. From nutritional point of view, only in samples with oil, significant isomerisation of all-trans-β-carotene occurred due to both processing. Overall, for this type of product and for the selected conditions, HPHT processing seems to have a different impact on the volatile profile but rather similar impact on the structural and nutritional attributes compared to thermal processing.

Infiltration and diffusion of carbon into polycrystalline yttria (Y2O3) under high pressure and high temperature

Interactions between polycrystalline yttria (Y2O3) and graphitic carbon during high-pressure high-temperature processing can take two main forms: (i) major carbon ingress into fractured grain boundaries of Y2O3 by an infiltration mechanism, and (ii) minor carbon ingress into intact grain boundaries of Y2O3 by a diffusion mechanism. In the latter case, when grain coarsening occurs, excess carbon particles form at grain boundaries, since there is little or no solubility of carbon in the Y2O3 grains themselves, irrespective of crystal structure. Segregation of carbon to grain boundaries can reduce grain-boundary strength. For example, high-purity fine-grained Y2O3, which is originally characterized by transgranular fracture, displays intergranular fracture after carbon ingress into it.

The effect of High Pressure and High Temperature processing on carotenoids and chlorophylls content in some vegetables

The effect of High Pressure (HP) and High Pressure High Temperature (HPHT) processing on carotenoid and chlorophyll content of six vegetables was evaluated. In general, carotenoid content was not significantly influenced by HP or HPHT treatments (625 MPa; 5 min; 20, 70 and 117 °C). Regarding chlorophylls, HP treatment caused no degradation or slight increases, while HPHT processes degraded both chlorophylls. Chlorophyll b was more stable than chlorophyll a at 70 °C, but both of them were highly degraded at 117 °C. HPHT treatment at 117 °C provided products with a good retention of carotenoids and colour in the case of red vegetables. Even though the carotenoids also remained in the green vegetables, their chlorophylls and therefore their colour were so affected that milder temperatures need to be applied. As an industrial scale equipment was used, results will be useful for future industrial implementation of this technology.

Reduction of Furan Formation by High-Pressure High-Temperature Treatment of Individual Vegetable Purées

The present study addressed the need for furan mitigation measures at the level of food production, where the effects of extrinsic (process-related) and intrinsic (product-related) properties on furan formation in vegetable-based systems were investigated. For the first time in the literature, the effect of high-pressure high-temperature (HPHT) processing on the formation of furan was demonstrated. HPHT processing was proven to be an interesting alternative for furan reduction in vegetable-based systems, when aiming for sterilization intensities. Following HPHT treatment, the furan concentrations of a wide range of individual vegetable purées dropped to levels close to the analytical limits (1–2 ng/g purée). A higher processing cost might limit the use of HPHT processing to high-value added products, which means that for many other conduction-heated food products, conventional heating would remain the standard technology. As a first step towards control of furan formation in the latter products, a mixed model regression was used to identify the major precursors in vegetable-based systems. Significant correlations were observed for vitamin C and sugars, which were attributed to the efficiency of the conversion and high concentrations, respectively. Next to furan, the HPHT- and thermally treated purées were analyzed for 2- and 3-methylfuran, which are likely to undergo the same metabolic fate as furan. For most of the vegetables tested, the total amount of methylfuran found in the thermally treated purées could not be ignored. Similarly to furan, there was a clear reduction in the concentrations found in the HPHT-treated purées.

초고압을 이용한 나노급 마그네시아 분말의 저온 소결 연구

We performed high pressure high temperature (HPHT) sintering for the 20 nm MgO powders at the temperatures from 600 o C to 1200 o C for only 5 min under 7 GPa pressure condition. To investigate the microstructure evolution and physical property change of the HPHT sintered MgO samples, we employed a scanning electron microscopy (SEM), density and Vickers hardness measurements. The SEM results showed that the grain size of the sintered MgO increased from 200 nm to 1.9 µm as the sintering temperature increased. The density results showed that the sintered MgO achieved a more than 95% of the theoretical density in overall sintering temperature range. Based on Vickers hardness test, we confirmed that hardness increased as temperature increased. Our results implied that we might obtain the dense sintered MgO samples with an extremely short time and low temperature HPHT process compared to conventional electrical furnace sintering process.

Headspace components that discriminate between thermal and high pressure high temperature treated green vegetables: Identification and linkage to possible process-induced chemical changes

For the first time in literature, this study compares the process-induced chemical reactions in three industrially relevant green vegetables: broccoli, green pepper and spinach treated with thermal and high pressure high temperature (HPHT) processing. Aiming for a fair comparison, the processing conditions were selected based on the principle of equivalence. A comprehensive integration of MS-based metabolic fingerprinting techniques, advanced data preprocessing and statistical data analysis has been implemented as untargeted/unbiased multiresponse screening tool to uncover changes in the volatile fraction. For all vegetables, thermal processing, compared to HPHT, seems to enhance Maillard and Strecker degradation reaction, triggering the formation of furanic compounds and Strecker aldehydes. In most cases, high pressure seems to accelerate (an)aerobic thermal degradation of unsaturated fatty acids leading to the formation of aliphatic aldehydes and ketones. In addition, both thermal and HPHT processing accelerated the formation of sulfur-containing compounds. This work demonstrated that the approach is effective in identifying and comparing different process-induced chemical changes, adding depth to our perspective in terms of studying a highly complex chemical changes occurring during food processing.

갈색 Type I 다이아몬드의 고압 열처리에 따른 표면 흑연화 생성 연구

We investigated color and graphite layer formation on the surface of Type I tinted brown diamonds exposed for 5 minutes under a high-pressure high-temperature (HPHT) condition in a stable graphite regime. We executed the HPHT processes of Process I, varying the temperature from 1600℃ to 2300℃ under 5.2 GPa pressure for 5 minutes, and Process II, varying the pressure from 4.2 to 5.7 GPa at 2150℃ for 5 minutes. Optical microscopy and micro-Raman spectroscopy were used to check the microstructure and surface layer phase evolution. For Process I, we observed a color change to vivid yellow and greenish yellow and the growth of a graphite layer as the temperature increased. For Process II, the graphite layer thickness increased as the pressure decreased. We also confirmed by 531 nm micro-Raman spectroscopy that all diamonds showed a 1440 cm ?1 characteristic peak, which remained even after HPHT annealing. The results implied that HPHT-treated colored diamonds can be distinguished from natural stones by checking for the existence of the 1440 cm ?1 peak with 531 nm micro-Raman spectroscopy.

고온고압법에 의한 Type II, Type I aB 갈색 다이아몬드의 색향상

It is possible to enhance the color of the natural diamond with a high pressure high temperature(HPHT) process. We employed a pyrophyllite tube cell and cubic press apparatus for HPHT treatment on the brown colored Type Ⅱ (5.6 ㎬/ 1700℃/ 52 min), and Type Ⅰ aB(5.6 ㎬/ 1650℃/ 30 min) diamond samples. We investigated the microstructure, Types, fluorescence, properties of the diamonds with an optical microscopy, FT-IR, photoluminescence(PL) spectroscopy, Diamond-View, and micro-Raman spectroscopy. Two tinted brown diamonds changed into colorless just after the HPHT process. Optical microscopy showed that no crack and significant inclusion evolution occurred during the HPHT process except the small graphite spot appeared in Type Ⅰ aB sample. FTIR spectrum confirmed that no Type, amber center, and platelet defect change with the HPHT treatment. Diamond-View could not distinguish the HPHT treated diamonds from the naturals. PL spectroscopy showed that N3 and H3 color centers remained even after HPHT process. Consequently, we successfully changed the color of diamonds into colorless by 5.6 ㎬ HPHT process.

Effect of high pressure–high temperature process on meat product quality

High pressure/high temperature (HPHT) processing is an innovative way to sterilize food and has been proposed as an alternative to conventional retorting. By using elevated temperatures and adiabatic compression, it allows the inactivation of vegetative microorganisms and pathogen spores. Even though the microbial inactivation has been widely studied, the effect of such process on sensorial attributes of food products, especially meat products, remains rare. The aim of this study was to investigate the potential of using HPHT process (500 MPa/115 °C) instead of conventional retorting to stabilize Toulouse sausages while retaining high organoleptic quality. The measurements of texture, color, water-holding capacity and microbial stability were investigated. It was possible to manufacture stable products at 500 MPa/115 °C/30 min. However, in these conditions, no improvement of the quality was found compared with conventional retorting.

Xylanase B from the hyperthermophile Thermotoga maritima as an indicator for temperature gradients in high pressure high temperature processing

Abstract Within the scope of high pressure food sterilization, an important issue that should be taken into account in refining process and equipment design is the time- and position-dependent temperature gradient that exists throughout the pressure vessel and the product load. Since enzymes from thermophilic microorganisms show good prospects for the development of indicators to map out the temperature non-uniformity in high pressure high temperature (HPHT) processing, in this work, the potential of xylanase B from Thermotoga maritima (XTMB) was investigated. Its inactivation at isothermal–isobaric conditions was best described by a first-order model. The pressure dependence of the D values was negligible at HPHT, the temperature dependence however was substantial. The Thermal Death Time (TDT) model, and its corresponding parameters, describing this large temperature dependence were successfully validated under dynamic processing conditions, relevant for industrial HPHT applications. Industrial relevance Despite extensive research progress on high pressure high temperature (HPHT) processing as a new food sterilization technique, food industry should be aware of a possible non-uniform temperature distribution, occurring in the pressure vessel and its consequence for the quality and safety of treated products. Since direct measurement of the temperature distribution is not feasible with the measuring devices currently available and constructive computation of the temperature profile by numerical simulation is inadequate, the development of specific temperature-sensitive wireless sensors, or pressure–temperature–time indicators (pTTIs) can be put forward. In this work, xylanase B from Thermotoga maritima (XTMB) was evaluated as a potential enzymatic indicator for mapping the temperature non-uniformity in HPHT processing.