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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Sucrose‐Based Dense, Pure, and Highly‐Crystalline Graphitic Materials for Lithium‐Ion Batteries

At present, most synthetic graphite materials commonly used as anode active ingredients in lithium-ion cells are produced by graphitization of petroleum cokes. The carbon footprint associated with synthetic graphite production is significant. Thus, bio-derived and cheap precursors, such as saccharides, would be an attractive alternative for the sustainable production of graphitic carbons. However, they are non-graphitizing at temperatures as high as 3000 °C, preserving the curved, fullerene-like structure of graphene layers and microporosity. Consequently, many lithium ions are consumed during the formation of solid electrolyte interphase films and passivated in the nanovoids. Here, a method for the production of pure, crystalline, graphitic materials based on sucrose disposed of microporosity is presented, which also works with a variety of saccharides and other organic precursors of hard carbons—generally considered incapable of such transformation. This process employs catalytic graphitization by Si particles at high temperatures. Finally, the electrochemical response of such derived sucrose-based graphite in Li-ion half-cells demonstrated its feasibility to serve as an anode active material for rechargeable Li-ion batteries.

Si particles↗
DOE OSTI2014

NanoSIMS, TEM, and XANES studies of a unique presolar supernova graphite grain

We report on isotopic and microstructural investigations of a unique presolar supernova (SN) graphite grain, referred to as G6, isolated from the Orgueil CI chondrite. G6 contains complex heterogeneities in its isotopic composition and in its microstructure. Nano-scale secondary ion mass spectrometer isotope images of ultramicrotome sections reveal heterogeneities in its C, N, and O isotopic compositions, including anomalous shell-like structures. Transmission electron microscope studies reveal a nanocrystalline core surrounded by a turbostratic graphite mantle, the first reported nanocrystalline core from a low-density SN graphite grain. Electron diffraction analysis shows that the nanocrystalline core consists of randomly oriented 2-4 nm graphene particles, similar to those in cores of high-density (HD) presolar graphite grains from asymptotic giant branch stars. G6's core also exhibits evidence for planar stacking of these graphene nano-sheets with a domain size up to 4.5 nm, which was unobserved in the nanocrystalline cores of HD graphite grains. We also report on X-ray absorption near-edge structure measurements of G6. The complex isotopic- and micro-structure of G6 provides evidence for mixing and/or granular transport in SN ejecta.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Non Destructive Thermal Analysis and In Situ Investigation of Creep Mechanism of Graphite and Ceramic Composites using Phase-sensitive THz Imaging & Nonlinear Resonant Ultrasonic Spectroscopy

In this project, we conducted a comprehensive study on nuclear graphite properties with terahertz (THz) imaging. Graphite samples from Idaho National Laboratory were carefully imaged by continuous wave (CW) THz. The CW THz imaging of graphite shows that the samples from different billet with different fabricating conditions have different pore size and structure. Based on this result, we then used a phase sensitive THz system to study the graphite properties. In this exploration, various graphite were studied. By imaging nuclear graphite samples in reflection mode at nine different incident polarization angles using THz time-domain spectroscopy, we find that different domain distributions and levels of porosity will introduce polarization dependence in THz reflectivity. Sample with higher density is less porous and has a smaller average domain distribution. As a consequence, it is less polarization-dependent and the polarization-dependent frequency is higher. The results also show that samples oxidized at higher temperatures tend to be more polarization dependent. The graphite from the external billet is more polarization dependent compared to that from the center billet. In addition, we performed laser-based ultrasonic measurements on these graphite samples. The denser, unoxidized samples allow surface acoustic waves to propagate more rapidly than in the samples that had already undergone oxidation. Therefore, for the oxidized samples, the denser samples show less polarization-dependence, higher polarization-dependent frequency, and allow the surface acoustic waves propagate faster.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

Organic Matter in Itokawa Particles

The first Hayabusa mission returned samples from the near-Earth S-type asteroid 25143 Itokawa to Earth in 2010[1]. Although Itokawa has a lithology related to ordinary chondrites(OCs) that typically have low organic contents, several Itokawa particles were found to contain organic matter (OM)[2-5]. However, there was not an explicit conclusion to the origin of the observed OMin these early studies. We have extended our search for OM into other Itokawa grains. Here, we report extraterrestrial OM (macromolecular carbon and amino acids) observed in six Itokawa particles(including a category1 particle: RA-QD02-0162[#62; also nicknamed “Amazon”],and five category3 carbon-rich particles:RA-QD02-0012[#12], RA-QD02-0078[#78], RB-CV-0029[#29], RB-CV-0080 [#80] and RB-QD04-0052[#52]).All allocated Itokawa samples were initially analysed by spot and point-by-point mapping Raman spectroscopic analysis at the Open University, UK. Amazon was then transferred and mounted into indium on an aluminium stub, which was studied with a NanoSIMS 50L ion microprobe for its H,C,N isotopic compositions. The rest of the samples were mounted in sterile gold foils, and the amino acid contents of their acid hydrolysed hot water extracts were obtained with a liquid chromatography with tandem fluorescence and accurate mass detection at NASA Goddard Space Flight Center, USA. Based on the observation of the Raman parameters(e.g. the peak locations and widths of the defect (D) and graphite (G) bands)[6], a significant variety of carbonaceous materials has been observed in Amazon. The carbonaceous materials include primitive and unaltered OM that shares similarity with the IOM in primitive (CI,CM,CR) carbonaceous chondrites, as well as OM that has been heavily graphitised. The organic structure of the heated material is best represented by nanocrystalline graphite, comparable to that observed for metamorphosed meteorites (e.g., L3–6 Inman, Tieschitz and New Concord,CV3 Allende, and EH4 Indarch),suggesting peak metamorphic temperatures (PMT) of >~600°C. The thermal history recorded in the graphitic OM agrees with PMT estimates for returned Itokawa regolith grains (600–800°C)[7].We have obtained the H,C,N isotopic compositions for the primitive OM in Amazon, which exhibits unambiguously extraterrestrial isotopic signatures (δD = +4868±2288‰; δ13C = −24±5‰; δ15N = +344±20‰), contrasting to the typically negative isotopic values obtained for terrestrial organic matter[8]. The δD and δ13C values of the organic material in Amazon are comparable to OCs, however, the δ15N value is higher than that typically observed for OCs (δ15N = −47 to +36‰), and is similar to that of CRs (δ15N = +153 to +309‰)[9].Our data suggest a genetic link between the primitive organic material observed in Itokawa to CRs and IDPs for they share similar D, 13C and 15N enrichments[10].The high carbon contents of the five category 3 Itokawa particles suggest potentially higher OM abundances, hence we extracted and analysed amino acids in these samples. Although terrestrial contamination was observed primarily as L-protein amino acids, several terrestrially uncommon non-protein amino acids were also observed at low abundances, such as β-aminoisobutyric acid (β-AIB),β-amino-n-butyric acid (β-ABA), and β-alanine. Itokawa amino acid content observed here was dissimilar to thermally altered OCs, but preliminarily analogous to more aqueously altered CR2s.Continued evolution of Itokawa is evident by the in fall of primitive organic material derived from CRs/IDPs, accounting for a complex interplay between the remnant Itokawa silicates with exogenous organics. The results reported here are the first evidence of extraterrestrial OM in asteroid material from a sample-return mission, showcasing a working protocol for analysing samples returned by the Hayabusa2 and OSIRIS-REx missions

Q. H. S. Chan↗
DOE OSTI2016

Graphene Nanocomposites with High Molecular Weight Poly(ε-caprolactone) Grafts: Controlled Synthesis and Accelerated Crystallization

Grafting of high molecular weight polymers to graphitic nanoplatelets is a critical step toward the development of high performance graphene nanocomposites. However, designing such a grafting route has remained a major impediment. Herein, we report a "grafting to" synthetic pathway by which high molecular weight polymer, poly(e-caprolactone) (PCL), is tethered, at high grafting density, to highly anisotropic graphitic nanoplatelets. The efficacy of this tethering route and the resultant structural arrangements within the composite are confirmed by neutron and X-ray scattering measurements in the melt and solution phase. In the semicrystalline state, Xray analysis indicates that chain tethering onto the graphitic nanoplatelets results in conformational changes of the polymer chains, which enhance the nucleation process and aid formation of PCL crystallites. This is corroborated by the superior thermal properties of the composite, manifested in accelerated crystallization kinetics and a significant increase in the thermal degradation temperature. Lastly, in principle, this synthesis route can be extended to a variety of high molecular weight polymers, which can open new avenues to solution-based processing of graphitic nanomaterials and the fabrication of complex 3D patterned graphitic nanocomposites.

36 MATERIALS SCIENCE↗
NASA NTRS1996

An acoustic emission and acousto-ultrasonic analysis of impact damaged composite pressure vessels

The use of acoustic emission to characterize impact damage in composite structures is being performed on composite bottles wrapped with graphite epoxy and kevlar bottles. Further development of the acoustic emission methodology will include neural net analysis and/or other multivariate techniques to enhance the capability of the technique to identify dominant failure mechanisms during fracture. The acousto-ultrasonics technique will also continue to be investigated to determine its ability to predict regions prone to failure prior to the burst tests. Characterization of the stress wave factor before, and after impact damage will be useful for inspection purposes in manufacturing processes. The combination of the two methods will also allow for simple nondestructive tests capable of predicting the performance of a composite structure prior to its being placed in service and during service.

Workman, Gary L.↗
DOE OSTI2019

Magnetic Properties of Fullerene–Thermally Exfoliated Graphite Composites Doped with Sodium

The magnetic properties (field range H = 0–50 kOe, temperature range T = 3–300 K), and structural features of a sodium-doped carbon composite material based on fullerene C{sub 60} and thermally exfoliated graphite (TEG) are studied. The material is obtained with different ratios of the components by sintering at a pressure of 7 GPa and T = 600°C, at which it is found that significant amorphization of the crystal lattice of the initial C{sub 60} occurs. The dia-, para-, and ferromagnetic components (M{sub D}, M{sub PM}, and M{sub FM}) were separated from the total magnetic moment of the samples under study. It is found that a sodium dopant has no effect on the magnetic properties of the composite. Analysis of the M{sub PM}(H) field dependences by using the Brillouin function for the fullerene-containing sample (i.e., without TEG) makes it possible to determine the quantum number of the total angular momentum of paramagnetic (PM) centers. Its value is found to be J = 1, which corresponds to elementary magnetic moment μ{sub PM} = 2μ{sub B} of a PM center. The concentration of PM centers is estimated at the level of N{sub PM} ≈ (2–5) × 10{sup 18} g{sup –1} for most samples, including the material without TEG. The introduction of TEG into the initial composition and an increase in its proportion in the composite leads to a strong increase in the magnetic moment, which is explained by an increase in both the J value and the concentration of PM centers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1978

Large antenna structure technologies required for 1985-2000

Topics discussed include: (1) material degradation as related to graphite composites and thermal control coatings; (2) thermal distortions considering postulated end-of-life conditions for extended lifetime (over 10 years); (3) examination of built-in shape versus actively controlled surfaces; (4) testing philosophy of super large antenna structures; and (5) examination of some possibilities which may require new or different technology.

Wannlund, W. R.↗
DOE OSTI2016

In situ synthesis and characterization of uranium carbide using high temperature neutron diffraction

Advances in neutron flux, neutron instrumentation, and sample environments over the past years allowed the development of unique techniques to characterize material synthesis and processing. The available infrastructure at LANL allows to apply these techniques to radioactive materials or materials containing actinides. Here, we present capabilities and results to characterize materials in situ at temperatures above 2000 Celsius degrees such as in loss-of-coolant accidents. Temperatures in excess of 2000 C. degrees are not readily achieved and neutrons are one of a few probes to characterize materials under these conditions. Research in refractory materials, phase diagram studies or accident scenarios for nuclear materials are research areas where such extreme conditions are required. As an example, we present the formation of UC{sub x} from UO{sub 2+x} and graphite in situ using high temperature neutron diffraction with particular focus on resolving the conflicting reports on the crystal structure of non-quenchable cubic UC{sub 2}. The ability to follow the reaction UO{sub 2}+C → UC{sub x}+CO{sub y} in situ with neutron diffraction allows us to conclude that the reaction occurs within minutes over a temperature range of 60 Celsius degrees. The initiation of the reaction is far below the reaction temperature of 2000 C. degrees reported for this reaction in standard text books on actinide chemistry. This may be due to the unusually small ∼100 nm grain size of our UO{sub 2} initial powder. Furthermore, the holding time of several hours reported in the literature would be unnecessary. The neutron diffraction data collected for the cubic high temperature UC{sub 2} phase unambiguously confirmed the disordered C-C dumbbells and excluded structures previously determined by X-ray diffraction.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2001

Dynamic Finite Element Predictions for Mars Sample Return Cellular Impact Test #4

The nonlinear, transient dynamic finite element code, MSC.Dytran, was used to simulate an impact test of an energy absorbing Earth Entry Vehicle (EEV) that will impact without a parachute. EEVOs are designed to return materials from asteroids, comets, or planets for laboratory analysis on Earth. The EEV concept uses an energy absorbing cellular structure designed to contain and limit the acceleration of space exploration samples during Earth impact. The spherical shaped cellular structure is composed of solid hexagonal and pentagonal foam-filled cells with hybrid graphite-epoxy/Kevlar cell walls. Space samples fit inside a smaller sphere at the center of the EEVOs cellular structure. Pre-test analytical predictions were compared with the test results from a bungee accelerator. The model used to represent the foam and the proper failure criteria for the cell walls were critical in predicting the impact loads of the cellular structure. It was determined that a FOAM1 model for the foam and a 20% failure strain criteria for the cell walls gave an accurate prediction of the acceleration pulse for cellular impact.

Fasanella, Edwin L.↗
NASA NTRS1985

New bismaleimide matrix resins for graphite fiber composites

Two new bismaleimide resins based on the N,N'-m-phenylene-bis(m-amino-benzamide) structure have been synthesized and characterized. The mixtures of the two resins gave better handling, processing, mechanical, and thermal properties in graphite composites than did the individual resins. The mechanical strength of the cured graphite composites prepared from the 1:1 copolymer of the two bismaleimide resins was excellent at both ambient and elevated temperatures. The physical and mechanical properties of the composites from the new bismaleimide matrix resin systems are compared with conventional composites based on epoxy and other bismaleimide systems. The copolymer system provides another method for improving bismaleimide resins.

Hsu, M.-T. S.↗
NASA NTRS1985

New bismaleimide matrix resins for graphite fiber composites

Two new bismaleimide resins based on the N, N'-m-phenylene-bis(m-amino-benzamide) structure have been synthesized and characterized. The mixtures of the two resins gave better handling, processing, mechanical, and thermal properties in graphite composites than did the individual resins. The mechanical strength of the cured graphite composites prepared from the 1:1 copolymer of the two bismaleimide resins was excellent at both ambient and elevated temperatures. The physical and mechanical properties of the composites from the new bismaleimide matrix resin systems are compared with conventional composites based on epoxy and other bismaleimide systems. The copolymer system provides another method for improving bismaleimide resins.

Hsu, M.-T. S.↗
DOE OSTI2012

Lithium-based surfaces controlling fusion plasma behavior at the plasma-material interface

The plasma-material interface and its impact on the performance of magnetically confined thermonuclear fusion plasmas are considered to be one of the key scientific gaps in the realization of nuclear fusion power. At this interface, high particle and heat flux from the fusion plasma can limit the material's lifetime and reliability and therefore hinder operation of the fusion device. Lithium-based surfaces are now being used in major magnetic confinement fusion devices and have observed profound effects on plasma performance including enhanced confinement, suppression and control of edge localized modes (ELM), lower hydrogen recycling and impurity suppression. The critical spatial scale length of deuterium and helium particle interactions in lithium ranges between 5-100 nm depending on the incident particle energies at the edge and magnetic configuration. Lithium-based surfaces also range from liquid state to solid lithium coatings on a variety of substrates (e.g., graphite, stainless steel, refractory metal W/Mo/etc., or porous metal structures). Temperature-dependent effects from lithium-based surfaces as plasma facing components (PFC) include magnetohydrodynamic (MHD) instability issues related to liquid lithium, surface impurity, and deuterium retention issues, and anomalous physical sputtering increase at temperatures above lithium's melting point. The paper discusses the viability of lithium-based surfaces in future burning-plasma environments such as those found in ITER and DEMO-like fusion reactor devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1990

On diamond, graphitic and amorphous carbons in primitive extraterrestrial solar system materials

Carbon is among the most abundant elements in the universe and carbon chemistry in meteorites and comets is an important key to understanding many Solar System and interstellar processes. Yet, the mineralogical properties and interrelations between various structural forms of elemental carbon remain ambiguous. Crystalline elemental carbons include rhombohedral graphite, hexagonal graphite, cubic diamond, hexagonal diamond (i.e., lonsdaleite or carbon-2H) and chaoite. Elemental carbon also occurs as amorphous carbon and poorly graphitized (or turbostratic) carbon but of all the forms of elemental carbon only graphite is stable under physical conditions that prevail in small Solar System bodies and in the interstellar medium. The recent discovery of cubic diamond in carbonaceous chondrites and hexagonal diamond in chondritic interplanetary dust particles (IDPs) have created a renewed interest in the crystalline elemental carbons that were not formed by shock processes on a parent body. Another technique, Raman spectroscopy, confirms a widespread occurrence of disordered graphite in the Allende carbonaceous chondrite and in chondritic IDPs. Elemental carbons have also been identified by their characteristic K-edge features in electron energy loss spectra (EELS). However, the spectroscopic data do not necessarily coincide with those obtained by selected area electron diffraction (SAED). In order to interpret these data in terms of rational crystalline structures, it may be useful to consider the principles underlying electron diffraction and spectroscopic analyses. Electron diffraction depends on electron scattering, on the type of atom and the distance between atoms in a crystal lattice. Spectroscopic data are a function of the type of atom and the energy of bonds between atoms. Also, SAED is a bulk sampling technique when compared to techniques such as Raman spectroscopy or EELS. Thus, it appears that combined analyses provide contradictory results and that amorphous, or short-range ordered, carbon identified by conventional TEM imaging and SAED may show evidence for sp(3) bonds in EELS spectra. It is suggested that complex, nanometer-scale, mineralogical interrelations are common to all elemental carbons irrespective of their origin. The subsequent thermal history, or energy balance, will determine the ultimate microstructure.

Rietmeijer, Frans J. M.↗
DOE OSTI2019

Generation and characterization of carbon fiber microstructure in atomistic simulations

A clear understanding of carbon fiber (CF) microstructure is necessary for the development of high strength CFs. Here, we present an atomistic approach for generating and characterizing realistic mi- crostructures of CFs. Large-scale reactive molecular dynamics simulations are used to generate a set of distinct CF microstructures. Comprehensive characterization of the simulated microstructures is enabled by the development of a suite of computational structural analysis tools capable of evaluation of hy- bridization states of carbon atoms, populations and orientations of individual carbon rings, degree of graphitization, and pore size distribution. The calculation of X-ray diffraction profiles provides a direct link between the structural features of simulated samples and experimental data available for CFs. The CF generation algorithm is shown to produce microstructures with experimental densities and with structural characteristics matching those of PAN-based CFs. The key structural features affecting the properties of CFs, such as the relative fractions of graphitic, turbostratic and amorphous micro- constituents, degree of alignment, pore size distributions, and chemical cross-linking can be effectively controlled in simulations, thus enabling efficient exploration of structureeproperties relationships in CFs. The capabilities of the developed approach are illustrated by performing computational analysis of the mechanical deformation and fracture of CFs under axial tensile loading.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Study of Tritium Transport in Nuclear-Grade Graphite and Molten Fluoride Salt Systems

High-temperature salts are proposed as coolant in recent reactor technologies including Fluoride Salt-Cooled High Temperature Reactor (FHR) with fluoride salt as primary and secondary loop coolant, Molten Salt Reactors (MSRs) with fuel salt, and high-magnetic-field fusion machines with salt coolant blanket. The baseline coolant is {sup 7}Li{sub 2}BeF{sub 4} (flibe) due to its good thermal-hydraulic and neutronic properties. Tritium produced in flibe due to neutron irradiation makes the issue of tritium transport an area of great interest. In the temperature range of 427- 704 deg. C, tritium readily diffuses through metallic reactor structural materials, which makes tritium control and capture a key technical challenge. It is anticipated that tritium can be captured by graphite, as graphite material showed a high affinity for tritium in the Molten Salt Reactor Experiment (MSRE) due to the porous and irregular crystallite microstructure. Two types of nuclear grade graphite which used as core components for FHR: matrix graphite, which encapsulates the TRISO (Tri-structural-isotropic) fuel particles in FHR, and high purity, isotropic nuclear grade graphite IG-110 which can be used as moderator and reflector in reactor core for both fission and fusion reactor. The microstructure of matrix graphite and IG-110 is different from that of matrix graphite, due to the raw material and manufacturing processes. There are three phenomena important for predicting tritium transport in graphite-salt systems: tritium species diffusion in molten flibe; tritium species transport at the salt-graphite interface; and tritium species transport in graphite. In this summary microstructure characterization of IG-110 and matrix graphite, characterization of graphite-salt interface as well as techniques for trace tritium detection in graphite are discussed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2001

Dynamic Finite Element Predictions for Mars Sample Return Cellular Impact Test #4

The nonlinear finite element program MSC.Dytran was used to predict the impact pulse for (he drop test of an energy absorbing cellular structure. This pre-test simulation was performed to aid in the design of an energy absorbing concept for a highly reliable passive Earth Entry Vehicle (EEV) that will directly impact the Earth without a parachute. In addition, a goal of the simulation was to bound the acceleration pulse produced and delivered to the simulated space cargo container. EEV's are designed to return materials from asteroids, comets, or planets for laboratory analysis on Earth. The EEV concept uses an energy absorbing cellular structure designed to contain and limit the acceleration of space exploration samples during Earth impact. The spherical shaped cellular structure is composed of solid hexagonal and pentagonal foam-filled cells with hybrid graphite-epoxy/Kevlar cell walls. Space samples fit inside a smaller sphere at the enter of the EEV's cellular structure. The material models and failure criteria were varied to determine their effect on the resulting acceleration pulse. Pre-test analytical predictions using MSC.Dytran were compared with the test results obtained from impact test #4 using bungee accelerator located at the NASA Langley Research Center Impact Dynamics Research Facility. The material model used to represent the foam and the proper failure criteria for the cell walls were critical in predicting the impact loads of the cellular structure. It was determined that a FOAMI model for the foam and a 20% failure strain criteria for the cell walls gave an accurate prediction of the acceleration pulse for drop test #4.

Fasanella, Edwin L.↗
DOE OSTI2017

Tris(trimethylsilyl) phosphite (TMSPi) and triethyl phosphite (TEPi) as electrolyte additives for lithium ion batteries: Mechanistic insights into differences during LiNi 0.5 Mn 0.3 Co 0.2 O 2 - Graphite full cell cycling

Here, tris(trimethylsilyl) phosphite (TMSPi) has emerged as an useful electrolyte additive for lithium ion cells. This work examines the use of TMSPi and a structurally analogous compound, triethyl phosphite (TEPi), in LiNi 0.5 Mn 0.3 Co 0.2 O 2 -graphite full cells, containing a (baseline) electrolyte with 1.2 M LiPF6 in EC: EMC (3:7 w/w) and operating between 3.0-4.4 V. Galvanostatic cycling data reveal a measurable difference in capacity fade between the TMSPi and TEPi cells. Furthermore, lower impedance rise is observed for the TMSPi cells, because of the formation of a P-and O-rich surface film on the positive electrode that was revealed by X-ray photoelectron spectroscopy data. Elemental analysis on negative electrodes harvested from cycled cells show lower contents of transition metal (TM) elements for the TMSPi cells than for the baseline and TEPi cells. Our findings indicate that removal of TMS groups from the central P-O core of the TMSPi additive enables formation of the oxide surface film. This film is able to block the generation of reactive TM-oxygen radical species, suppress hydrogen abstraction from the electrolyte solvent, and minimize oxidation reactions at the positive electrode-electrolyte interface. In contrast, oxidation of TEPi does not yield a protective positive electrode film, which results in inferior electrochemical performance.

25 ENERGY STORAGE↗