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العلماء يطورون تقنية تحويل النفايات البلاستيكية إلى ألماس

Scientists turn plastic into diamonds using laser.

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العلماء يطورون تقنية تحويل النفايات البلاستيكية إلى ألماس 

وجد العلماء طريقة لصنع الماس من الزجاجات البلاستيكية المستعملة. وهي تقنية يمكن أن تساعد ​​في الحد من النفايات البلاستيكية.

ويمكن لهذا الألماس النانوي المعاد تدويره أن يتضمن مجموعة واسعة من التطبيقات، بما في ذلك أجهزة الاستشعار الطبية وتوصيل الأدوية.


وصمم فريق العلماء من مركز هيلمهولتز درسدن روسندورف (HZDR) وجامعة روستوك والمدرسة متعددة التقانات الفرنسية، تجربة في مركز المعجل الخطي ستانفورد (SLAC) في مختبر المسرع الوطني في كاليفورنيا، هذه التجربة المثيرة لمعرفة المزيد عن ظاهرة “مطر الماس” على الكواكب الجليدية العملاقة مثل نبتون وأورانوس.

وداخل هذه الكواكب الجليدية العملاقة درجات حرارة تصل إلى عدة آلاف من الدرجات المئوية، والضغط أكبر بملايين المرات مما هو عليه في الغلاف الجوي للأرض.


Scientists turn plastic into diamonds using laser.



ويُعتقد أن هذه الظروف قادرة على تفكيك المركبات الهيدروكربونية، ثم ضغط مكون الكربون إلى ماسات تغوص في أعماق نوى الكواكب.

ولتقليد هذه العملية، أطلق العلماء ليزرا عالي الطاقة على بلاستيك البولي إيثيلين تيريفثاليت (PET)، وهي مادة هيدروكربونية شائعة الاستخدام في العبوات أحادية الاستخدام، ووجدوا أن موجة الصدمة الناتجة عن هذه الومضات شهدت نمو هياكل صغيرة شبيهة بالماس.

وقال دومينيك كراوس، الفيزيائي في مركز هيلمهولتز درسدن روسندورف (HZDR) والأستاذ في جامعة روستوك: “يتمتع البولي إيثيلين تيريفثاليت بتوازن جيد بين الكربون والهيدروجين والأكسجين لمحاكاة النشاط في الكواكب الجليدية”.

ومن المعروف أن خليطا من المركبات المكونة من الهيدروجين والكربون توجد على بعد نحو 5 آلاف ميل تحت سطح أورانوس ونبتون.

ويتضمن هذا الميثان، وهو جزيء يحتوي على كربون واحد فقط مرتبط بأربع ذرات هيدروجين، ما يسبب اللون الأزرق المميز لنبتون.

وفي دراسة أجريت عام 2017، نجح فريق مختبر المسرع الوطني في محاكاة عملية المطر الماسي لأول مرة عن طريق إطلاق الليزر البصري على البوليسترين.

واستخدم البوليسترين لتقليد بنية الميثان، حيث أنه يحتوي أيضا على الهيدروجين والكربون فقط.

وأنتجت الأشعة السينية الشديدة موجات صدمة داخل المادة، ولاحظ العلماء دمج ذرات الكربون في هياكل الماس الصغيرة التي يصل عرضها إلى بضعة نانومترات.

وأشار سيغفريد غلينزر، مدير قسم كثافة الطاقة العالية في مركز المعجل الخطي ستانفورد، إلى أن “الأمر أكثر تعقيدا داخل الكواكب. وهناك الكثير من المواد الكيميائية في هذا المزيج. ولذا، ما أردنا اكتشافه هنا هو نوع التأثير الذي تحدثه هذه المواد الكيميائية الإضافية”.

وبالإضافة إلى الكربون والهيدروجين، يُعتقد أن عمالقة الجليد تحتوي على كميات كبيرة من الأكسجين.

وسعى العلماء إلى اكتشاف تأثير الأكسجين على تكوين الماس النانوي داخل نبتون وأورانوس. وللقيام بذلك، كرروا تجربتهم السابقة مع فيلم من بلاستيك البولي إيثيلين تيريفثاليت (PET)- وهو هيدروكربون يحتوي أيضا على الأكسجين – والذي يعيد إنتاج تكوين الكواكب بشكل أكثر دقة.

واستخدموا ليزرا ضوئيا عالي الطاقة في مركز المعجل الخطي ستانفورد لتسخين العينة لفترة وجيزة حتى 6000 درجة مئوية. وأدى ذلك إلى حدوث موجة صدمة ضغطت المادة لبضع نانوثانية إلى مليون ضعف الضغط الجوي.

وباستخدام طريقة تسمى حيود الأشعة السينية، راقب العلماء الذرات وإعادة ترتيبها إلى مناطق ماسية صغيرة، وقاسوا أيضا حجم وسرعة نموها.

ومع وجود الأكسجين في المادة، وجدوا أن الألماس النانوي قادر على النمو عند ضغوط ودرجات حرارة أقل مما لوحظ سابقا.

وقال الدكتور كراوس: “كان تأثير الأكسجين هو تسريع انقسام الكربون والهيدروجين وبالتالي تشجيع تكوين الألماس النانوي. وهذا يعني أن ذرات الكربون يمكن أن تتحد بسهولة أكبر وتشكل الماس”.

ويتوقع العلماء أن الماس داخل نبتون وأورانوس سيصبح في الواقع أكبر بكثير من تلك المنتجة في هذه التجارب، ويحتمل أن يزن ملايين القراريط.

وقد يدعم هذا الافتراض بأنه، على مدى آلاف السنين، داخل عمالقة الجليد “تمطر حرفيا ألماسا”.

وبالإضافة إلى الماس، عثر الفريق على دليل في التجارب على أن “الماء فائق التأين” قد يتشكل داخل الكواكب. ويحدث هذا عندما تتفكك جزيئات الماء نتيجة درجات الحرارة المرتفعة والضغط.

ثم تشكل ذرات الأكسجين هيكلا شبكيا منتظما، حيث يمكن لذرات الهيدروجين المتبقية أن تطفو حولها، وعند شحنها، يمكنها توصيل الكهرباء. ويمكن للتيارات التي تحملها هذه المرحلة الفريدة من الماء أن تفسر الحقول المغناطيسية غير العادية في أورانوس ونبتون.

وقد تؤثر هذه النتائج، التي نُشرت في Science Advances، على فهمنا لعمالقة الجليد خارج نظامنا الشمسي، والتي قد تواجه نفس الظواهر.

ونظرا لأن وجود الأكسجين يجعل تكوين الماس أكثر احتمالا، فمن المحتمل أنه يحدث أيضا على كواكب أخرى في ظل ظروفها الداخلية الفريدة.

ويخطط العلماء لإجراء تجارب مماثلة على عينات تحتوي على الإيثانول والماء والأمونيا، وجميعها موجودة على أورانوس ونبتون، للاقتراب من محاكاة ما يمكن أن يحدث داخل الكواكب الأخرى.

المصدر: ديلي ميل


Making nanodiamonds out of bottle plastic

Research team uses laser flashes to simulate the interior of ice planets – and spurs a new process for producing miniscule diamonds

What goes on inside planets like Neptune and Uranus? To find out, an international team headed by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the University of Rostockand France’s École Polytechnique conducted a novel experiment. They fired a laser at a thin film of simple PET plastic and investigated what happened using intensive laser flashes. One result was that the researchers were able to confirm their earlier thesis that it really does rain diamonds inside the ice giants at the periphery of our solar system. And another was that this method could establish a new way of producing nanodiamonds, which are needed, for example, for highly-sensitive quantum sensors. The group has presented its findings in the journal Science Advances (DOI: 10.1126/sciadv.abo0617).


The conditions in the interior of icy giant planets like Neptune and Uranus are extreme: temperatures reach several thousand degrees Celsius, and the pressure is millions of times greater than in the Earth’s atmosphere. Nonetheless, states like this can be simulated briefly in the lab: powerful laser flashes hit a film-like material sample, heat it up to 6,000 degrees Celsius for the blink of an eye and generate a shock wave that compresses the material for a few nanoseconds to a million times the atmospheric pressure. “Up to now, we used hydrocarbon films for these kinds of experiment,” explains Dominik Kraus, physicist at HZDR and professor at the University of Rostock. “And we discovered that this extreme pressure produced tiny diamonds, known as nanodiamonds.”

Using these films, however, it was only partially possible to simulate the interior of planets – because ice giants not only contain carbon and hydrogen but also vast amounts of oxygen. When searching for suitable film material, the group hit on an everyday substance: PET, the resin out of which ordinary plastic bottles are made. “PET has a good balance between carbon, hydrogen and oxygen to simulate the activity in ice planets,” Kraus explains. The team conducted its experiments at SLAC National Accelerator Laboratory in California, the location of the Linac Coherent Light Source (LCLS), a powerful, accelerator-based X-ray laser. They used it to analyze what happens when intensive laser flashes hit a PET film, employing two measurement methods at the same time: X-ray diffraction to determine whether nanodiamonds were produced and so-called small-angle scattering to see how quickly and how large the diamonds grew.


A big helper: oxygen

“The effect of the oxygen was to accelerate the splitting of the carbon and hydrogen and thus encourage the formation of nanodiamonds,” says Dominik Kraus, reporting on the results. “It meant the carbon atoms could combine more easily and form diamonds.” This further supports the assumption that it literally rains diamonds inside the ice giants. The findings are probably not just relevant to Uranus and Neptune but to innumerable other planets in our galaxy as well. While such ice giants used to be thought of as rarities, it now seems clear that they are probably the most common form of planet outside the solar system.

The team also encountered hints of another kind: In combination with the diamonds, water should be produced – but in an unusual variant. “So-called superionic water may have formed,” Kraus opines. “The oxygen atoms form a crystal lattice in which the hydrogen nuclei move around freely.” Because the nuclei are electrically charged, superionic water can conduct electric current and thus help to create the ice giants’ magnetic field. In their experiments, however, the research group was not yet able to unequivocally prove the existence of superionic water in the mixture with diamonds. This is planned to happen in close collaboration with the University of Rostock at the European XFEL in Hamburg, the world’s most powerful X-ray laser. There, HZDR heads the international user consortium HIBEFwhich offers ideal conditions for experiments of this kind.


Precision plant for nanodiamonds

In addition to this rather fundamental knowledge, the new experiment also opens up perspectives for a technical application: the tailored production of nanometer-sized diamonds, which are already included in abrasives and polishing agents. In the future, they are supposed to be used as highly-sensitive quantum sensors, medical contrast agents and efficient reaction accelerators, for splitting CO2for example. “So far, diamonds of this kind have mainly been produced by detonating explosives,” Kraus explains. “With the help of laser flashes, they could be manufactured much more cleanly in the future.”

The scientists’ vision: A high-performance laser fires ten flashes per second at a PET film which is illuminated by the beam at intervals of a tenth of a second. The nanodiamonds thus created shoot out of the film and land in a collecting tank filled with water. There they are decelerated and can then be filtered and effectively harvested. The essential advantage of this method in contrast to production by explosives is that “the nanodiamonds could be custom cut with regard to size or even doping with other atoms,” Dominik Kraus emphasizes. “The X-ray laser means we have a lab tool that can precisely control the diamonds’ growth.”

Learn more:

https://www.hzdr.de/db/Cms?pOid=67015&pNid=99


Ordinary Plastic Turned into Diamonds Via Laser Beam in the Blink of An Eye

A thin film of plastic was, for the first time ever, turned into tiny diamonds in the blink of an eye after being shot at with a laser beam.

Synthetic diamonds are valuable for their hardness and are used to make high-quality cutting and polishing tools, but equally so for their thermal conductivity, and electrical insulation.

Opening up synthetic diamond production from plastic could lead to more demand for water bottles and other containers which often end up in the sea.

The breakthrough also has implications for planetary science, and the researchers who managed this philosopher’s stone-like transformation said it sheds light on what goes on inside the ice giants Neptune and Uranus.

How exactly was something that costs pennies turned into the hardest and one of the rarest minerals on Earth?

At their fundamental level, diamonds are simply a solid form of carbon, arranged in a particular crystalline structure alongside hydrogen and oxygen.

In tests, a sheet of PET (polyethylene terephthalate) plastic used for packaging food and beverages was heated by a laser beam up to 6,000°C. PET is made of petroleum, which is known in the industry as a “hydrocarbon.”

The test compressed the plastic under a weight equal to millions of times Earth’s atmospheric pressure for a few billionths of a second. This incredible experience reconfigured the molecules of the plastic into a nanodiamond.

“So far, diamonds of this kind have mainly been produced by detonating explosives,” said Professor Dominik Kraus, of the University of Rostock, Germany, and a co-author of the study. “With the help of laser flashes, they could be manufactured much more cleanly in the future.”

The laser fired ten flashes at the plastic film, after which the nanodiamonds formed and dropped in a collecting tank filled with water. There they are decelerated and can then be filtered and gathered

Up to now, we used hydrocarbon films for these kinds of experiments. And we discovered that this extreme pressure produced tiny diamonds,” Krauss explained. “PET has a good balance between carbon, hydrogen and oxygen to simulate the activity in ice planets.”

Proving it can be done with plastic takes the concept to an entirely new level of convenience for production on Earth, as well as reveals how nanodiamonds might form in large quantities on ice giants like Neptune and Uranus.

Ice giants contain carbon, hydrogen and vast amounts of oxygen. The new study published in Science Advances confirmed it really does rain diamonds inside ice giants at the solar system’s edge.

“The effect of the oxygen was to accelerate the splitting of the carbon and hydrogen and thus encourage the formation of nanodiamonds. It meant the carbon atoms could combine more easily and form diamonds.”

Temperatures in the interior of Neptune and Uranus reach several thousand degrees Celsius and the pressure is millions of times greater than Earth’s atmosphere. Above, the outer atmosphere of gasses is one of the coldest places in the solar system.

This creates storms that produce hailstones of diamonds. Scientists believed this was the case for 40 years, and recent studies have further reinforced this hypothesis.

Learn more:

https://www.goodnewsnetwork.org/ordinary-plastic-turned-into-diamonds-via-laser-beam-in-the-blink-of-an-eye/



Diamond formation kinetics in shock-compressed C─H─O samples recorded by small-angle x-ray scattering and x-ray diffraction

Abstract

Extreme conditions inside ice giants such as Uranus and Neptune can result in peculiar chemistry and structural transitions, e.g., the precipitation of diamonds or superionic water, as so far experimentally observed only for pure C─H and H2O systems, respectively. Here, we investigate a stoichiometric mixture of C and H2O by shock-compressing polyethylene terephthalate (PET) plastics and performing in situ x-ray probing. We observe diamond formation at pressures between 72 ± 7 and 125 ± 13 GPa at temperatures ranging from ~3500 to ~6000 K. Combining x-ray diffraction and small-angle x-ray scattering, we access the kinetics of this exotic reaction. The observed demixing of C and H2O suggests that diamond precipitation inside the ice giants is enhanced by oxygen, which can lead to isolated water and thus the formation of superionic structures relevant to the planets’ magnetic fields. Moreover, our measurements indicate a way of producing nanodiamonds by simple laser-driven shock compression of cheap PET plastics.


INTRODUCTION

Ice giant planets such as Neptune and Uranus are highly abundant in our galaxy (1). The interiors of these celestial objects are thought to be mainly composed of a dense fluid mixture of water, methane, and ammonia (2). Because of the high pressures and temperatures deep inside these planets, the material mixture will likely undergo chemical reactions and structural transitions (35). An example of these reactions is the possible dissociation of hydrocarbons (6) and subsequent phase separation, allowing the formation of diamonds (7) and presumably metallic hydrogen or superionic water (38), which may act as a heat source and help to explain the generation of the unique magnetic fields modeled for the ice giants (911).

Recent laser shock experiments on polystyrene [PS; (C8H8)n] in combination with x-ray techniques have provided the first in situ evidence for the formation of diamonds in compressed hydrocarbons at planetary-relevant states in the laboratory (1214). However, the presence of water and therefore large amounts of oxygen needs to be considered for further conclusions on processes inside the ice giants. Thus, investigating C─H─O samples provides a more realistic scenario than studying pure hydrocarbon or water systems (15). A separation of carbon from H2O is likely required for a superionic phase of water to be present inside Neptune and/or Uranus (3). If carbon would form bonds with oxygen, such structures, which could help to explain the peculiar magnetic field observed for both planets, may be inhibited.

Thanks to the advent of x-ray free-electron laser (XFEL) facilities and increasingly mature experimental capabilities, probing the internal structure of materials under dynamic compression to mimic planetary interiors has seen tremendous progress in recent years. While x-ray diffraction (XRD) identifies crystalline and liquid correlations on the angstrom level, small-angle x-ray scattering (SAXS) (16) is sensitive to feature sizes on the order of 1 to 100 nm. Therefore, combining SAXS and XRD in a single experiment has a great potential to enable accurate measurements of the nanodiamond size distribution and nucleation process initiated inside the plastic samples, which provides direct access to the kinetics of the carbon-hydrogen phase separation reaction relevant to the interiors of planets (13).

Here, the size distribution and the growth process of nanodiamonds, created from shock-compressed polyethylene terephthalate [PET; (C10H8O4)n, stoichiometrically a mixture of carbon and H2O], are characterized by in situ XRD and SAXS consistently at two different XFEL facilities, which shows the importance of the pressure P–temperature T state on the diamond formation kinetics. Standard velocity interferometer for any reflector (VISAR) diagnostics and the recently published equation of state data for PET (15) are applied to estimate the PT state of the shocked PET sample, allowing us to compare the XRD data to density functional theory molecular dynamics (DFT-MD) simulations, where they show excellent agreement. Our results provide insights of unprecedented quality into chemistry relevant to planetary interiors and the general capabilities for simultaneously characterizing structural transitions on both angstrom and nanometer scale in dynamic compression experiments. At the same time, as diamond formation is achieved by a single-shock compression in contrast to more elaborate compression histories required in previous experiments (12), our study points toward a new way to efficiently produce nanodiamonds using cheap PET plastics as initial material.


RESULTS

Experimental method

We performed the discussed experiments at two different XFEL facilities: the Matter in Extreme Conditions (MEC) endstation of the Linac Coherent Light Source (LCLS) of SLAC National Accelerator Laboratory (1718) (Fig. 1) and the SPring-8 Angstrom Compact free electron LAser (SACLA) (1920). At LCLS, the structural changes and density variations of compressed PET can be observed by in situ XRD and SAXS with the LCLS pulse of 9.5-keV photon energy and 50-fs duration. The XRD and SAXS detectors were capable of recording single-photon events, and the data were integrated azimuthally after masking the beamstop and the parasitic scattering. More details on the experimental setup and the applied diagnostics can be found in Materials and Methods. A similar setup was used at SACLA and is depicted in fig. S1 of the Supplementary Materials.



Examples of raw data images from XRD and SAXS from PET under ambient conditions and a shocked state are illustrated in Fig. 1. Shocked and ambient data apply the same color scale per diagnostic. The drive laser ablates the aluminum coating that is visible in the XRD lineouts of cold PET samples. Hence, these peaks disappear for driven targets (see Fig. 1). In the shocked state, the symmetric scattering characteristic of ambient PET in the SAXS image vanishes. In turn, the SAXS signal increases strongly in the higher–wave number q range of the detector and results in a bright ring-shaped feature, which corresponds to the pattern consistent with densely packed nanospheres (21). Contemporaneously, strong diamond diffraction is observed by XRD, which demonstrates the formation of nanodiamonds being traceable by two complementary x-ray techniques.


Diamond formation kinetics

Figure 2 depicts the temporal evolution of 100-μm PET samples shock-compressed to ~100 GPa at the LCLS in the form of raw in situ XRD and in situ SAXS data with their corresponding azimuthally integrated lineouts. The individual pressures were determined by measuring the shock velocity and using the known PET Hugoniot curve (15). In each XRD lineout, the diamond (111) peak illustrated by the shaded area was modeled to be approximately Lorentzian, while the signal below is given by the contribution of a liquid C─H─O mixture, which is well represented by a Gaussian in the k range below the diamond peak (14). The Gaussian shape is also in good agreement with DFT-MD simulations of the liquid (see Materials and Methods and Supplementary Materials for more details). Due to the experimental geometry, the signal-to-background ratio of the diamond (220) peak is substantially lower than for the (111) reflection. As the (220) peak also sits on top of a liquid correlation peak, the solid contribution is difficult to distinguish quantitatively from the background. Thus, the analysis of the formation characteristics of the nanodiamonds mainly focuses on the more prominent (111) peak. We use the Lorentzian fit to obtain the center and the width of the diamond (111) peak. The Scherrer formula (22) was then applied to estimate the minimum crystallite size of a few nanometers based on the width of the diamond Bragg peak of around 0.2 Å−1. This value is considerably smaller than the peak width of the liquid mixture peak of 1–2 Å−1 by Lütgert et al.(15) and estimations from DFT-MD simulations. With this clear feature separation, the diamond fraction (the absolute amount of carbon atoms in the shock-compressed PET foil that ended up in diamond lattices) was estimated from the diamond peak integral between the liquid peak and the experimental data (14). The diamond diffraction peak area increases with proceeding time during the compression process before shock breakout at the sample rear side (it refers to the cases when the probing times are at 7, 8, and 9 ns since the breakout time at ~100 GPa is about 9.8 ns). Compressed diamond densities of up to 3.87 g/cm3 were deduced from the position of the diamond Bragg peak at 3.14 ± 0.01 Å−1 compared to the ambient diamond density of 3.51 g/cm3 at 3.05 Å−1. The diamond peak area stops increasing after shock breakout, and the peak position moves back to lower q (~3.06 Å−1) as the crystallites are relaxing to ambient density. In SAXS, a substantial increase in total scattering intensity for the progressing shock wave is observed when diamond formation can be seen in XRD data. The described SAXS ring feature is not visible for drives where no diamond formation has been observed. Therefore, the signal is assumed to be generated by the nanodiamonds where both the relative volume fraction and the size distribution of the crystallites affect the overall shape and intensity of the SAXS signal. SAXS is also sensitive to demixing processes without the formation of crystalline structures, as long as density differences are present between the separated states. Therefore, we can conclude that at pressures below and above the conditions where diamond formation is observed, our sample remains in a mixed state.


The high-quality SAXS signals obtained by the detector allow the nanoparticle size distribution to be deduced. Here, we use two different methods for SAXS data analysis (see Materials and Methods and Supplementary Materials for details on the applied methods). Figure 3 shows the obtained nanoparticle distribution derived from the SAXS lineouts in Fig. 2C. As an analytical model, we assumed a Schulz distribution (2324) with the polydispersity p = σ/R ≈ 0.1, where the effective radius R was obtained by fitting the shape of the SAXS lineouts, and σ was the root mean square deviation from R. Because of the high data quality and a sufficient qrange, the radius distribution of the nanodiamonds can also be obtained by Monte Carlo methods without assuming a specific distribution function. Here, the mean radius of particles increases from 1.6 to 2 nm with increasing delay time between the drive laser and x-ray probe. After the shock breakout, which results in a pressure release of the partially solid and liquid system, the Monte Carlo results indicate that the radius distribution becomes highly dispersed (see Fig. 3). At this stage, the analytical model results in systematically larger effective radii. However, the simple assumption of a Schulz distribution for moderately dispersed systems seems no longer valid at this point. In summary, the growth of the mean particle size with progressing shock propagation has been observed by both methods, indicating that the nanodiamonds increase their size until the shock breakout releases the high-pressure conditions.


Effect of pressure

PET samples were driven to different shock pressures by varying the pulse energy of the drive laser to investigate the effect of pressure and temperature on the diamond formation in shock-compressed C─H─O samples. At pressures below 74 GPa, both XRD and SAXS data did not show diamond formation. For intermediate pressures between 74 and 125 GPa, diamond features are present in the data. However, they disappear above 125 GPa. At this upper bound in pressure, temperatures approach the diamond melting line (25), reaching approximately 6000 K along the PET Hugoniot (15). Results from the different facilities, LCLS and SACLA, provide excellent agreement on this observation, which reduces a potential effect of systematic errors in the individual experimental setups.

Using DFT-MD simulations, we can compare our experimental XRD lineouts with calculated diffraction patterns of the compressed C─H─O mixtures with various carbon-to-water ratios at different pressures along the PET Hugoniot. The simulated patterns are reasonably consistent with the residual liquid structure and inferred temperatures from our experimental data (see Materials and Methods and Supplementary Materials for more details).

It is observed that the SAXS intensity during shock propagation is directly correlated to the diamond content recorded by XRD (see fig. S3 for details). Moreover, data from both SAXS analysis methods consistently showed evidence that the nanodiamond particle sizes grow with increasing pressure (see fig. S4 for details). One reasonable explanation is that high pressure promotes and accelerates the growth of the particle size, resulting in a larger size at higher pressure as probed by x-ray techniques during the propagation of shock waves with various intensities through samples of the same thickness.

DISCUSSION

Using XRD, we were able to confirm the diamond formation from compressed PET in laser-driven shock experiments. In SAXS data, a prominent signal was observed that we identified with nanoparticles with several nanometers in diameter. Since this feature occurred when a strong diamond signal was detected in in situ XRD data, we infer that the nanoparticles observed in SAXS are likely to be diamond crystals. Therefore, SAXS provides a sensitive instrument to study diamond formation in shock-compressed experiments, even when the signal of nanoparticles is weak and XRD is impeded by the liquid background peak. These findings were reproduced over different target materials and different setups at different international laser facilities (LCLS and SACLA).

In Fig. 4, our results for shock-compressed PET are illustrated in a phase diagram together with previous data from PS (12), models for planetary interiors (42628), theoretical predictions for diamond melting (25), and C─H phase separation (29) as well as the assumed hydrogen insulator-metal transition (30). The data points where we observe diamond formation in plastics are marked by diamond symbols in the purple shaded area. This area overlaps with the predicted isentropes of Uranus and Neptune (26) (represented by only one curve because of the small differences), but is a little bit higher in temperature than the more recent models (427), and slightly intersects the recently predicted isentrope for Jupiter (28). In PET, diamond forms under PT conditions where no C─H separation has been observed for PS on the principal Hugoniot. As the temperature on the PET Hugoniot is only marginally smaller, especially at lower pressures, this suggests that the oxygen atoms in PET are key for explaining the difference, in agreement with first-principles studies of mixtures relevant to the interiors of ice giants (3). In the first-principles studies, it was found that the presence of O increases the lifetimes of C─C bonds, resulting in the clustering of C atoms and the demixing of the liquid mixtures in such environments (3).


Research paper:

https://www.science.org/doi/10.1126/sciadv.abo0617

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