Pressure And Temperature Research Articles

New MgSiO_{4}H_{2} Phases as Potential Primary Water Carriers into the Deep Earth.

Dense hydrous magnesium silicate MgSiO_{4}H_{2} is widely regarded as a primary water carrier into the deep Earth. However, the stability fields of MgSiO_{4}H_{2} based on the prevailing structure model are narrower than experimental results at relevant pressure and temperature (P-T) conditions, casting doubts about this prominent mineral as a water carrier into the great depths of the Earth. Here, we report on an advanced structure search that identifies two new crystal structures, denoted as α- and β-MgSiO_{4}H_{2}, that are stable over unprecedentedly wide P-T conditions of 17-68GPa and up to 1860K, covering the entire experimentally determined range. Moreover, we performed x-ray diffraction measurements with backscattering electron image, combined with abinitio simulations, to demonstrate the formation of MgSiO_{4}H_{2} and AlOOH solid solutions that exhibit further enhanced P-T stability fields, making them robust carriers of water into the deepest lower mantle. These findings establish and elucidate the new MgSiO_{4}H_{2} phases as potential primary water carriers into the vast depths of the lower mantle, creating a distinct paradigm for the deep Earth water cycle.

Property of Quark-Gluon Plasma

During the nascent stages of the universe's evolution, matter existed in the form of quarkgluon plasma (QGP), characterized by its presence under conditions of exceedingly high temperature andpressure. Presently, the ability to replicate the QGP state has been attained through relativistic heavy.ion collision experiments, Key indicators of QGP generation encompass the initial collision configurationwhich exerts a discernible infuence on the subsequent momentum and scattering angles of emitted hadronsThis study endeavors to recapitulate the findings of the CMS XeXe collision experiment by meticulouslyscrutinizing data stemming from PbPb collisions at a center-of-mass energy of s = 5.02 TeV. Specificallyour focus centers on an exhaustive analysis of the transverse momentum (pt), azimuthal angle (), ancpseudorapidity () of scattered particles. 'Through this comprehensive approach, we aim to corroborate theimplications drawn from the ClMS XeXe experiment, thereby contributing to a deeper understanding of themechanisms underlying quark-gluon plasma creation and behavior

NUMERICAL AND EXPERIMENTAL INVESTIGATIONOF STEAM FILM CONDENSATION ON A VERTICAL TUBE

NUMERICAL AND EXPERIMENTAL INVESTIGATIONOF STEAM FILM CONDENSATION ON A VERTICAL TUBE

Influence of water on the thermoelastic properties of Fe bearing ringwoodite: A first-principles study

Using first-principles density functional theory (DFT), we model the thermoelastic properties of hydrated ringwoodite (γ-(Fe, Mg)2SiO4), a potential water reservoir in the Earth's mantle transition zone (MTZ). Our calculations indicate that hydration, in general, leads to a reduction in the sound wave velocity of ringwoodite. However, increased pressure tends to suppress this reduction. For our 1.56 wt% H2O containing ringwoodite model, we find that the suppression is so large that at pressure and temperature (P-T) conditions relevant to the lower part of the MTZ the sound wave velocities for the hydrous (1.56 wt% H2O) ringwoodite become very similar to that of the anhydrous ringwoodite. However, when the water concentration is increased to 3.3 wt%, the pressure-induced suppression of the velocity reduction due to hydration is not so significant. We have given a plausible explanation for the same on the basis of the electronic structure of the hydrous ringwoodite models. We conclude that in the lower part of the MTZ, seismic wave data is sufficiently robust to detect regions of very high-water content (∼3.3 wt%). However, if the water concentration is less than 1.56 wt%, sound wave velocities may not be able to precisely detect the state of hydration of the MTZ.

INTRINSIC STRESS IN CARBON COATINGS DEPOSITED FROM HYDROCARBON ION FLOW

Within the model of the nonlocal thermoelastic peak (NTP) of low-energy ion, the emergence of intrinsic stress in carbon coatings deposited from the flow of ions of hydrocarbon molecules is theoretically studied. The expression is obtained for intrinsic stress depending on species and ion energy. The time dependence of temperature and pressure in the NTP of CH4+, C2H2+ and C6H6+ ions was studied The position of NTP of ions of different species and energies on the P,T phase diagram of carbon was found and their trajectories were constructed. The position of the NTP trajectories of various ions with respect to the regions of structural stability of carbon was analyzed. The conditions for the predominant formation of sp3 bonds in the NTP of ion are discussed.

CO2 absorption using LIs functionalized with amino acids

A comparative study was conducted on the absorption of carbon dioxide (CO2) using ionic liquids (ILs) based on imidazole derivatives as cations and amino acids as anions ([BMI][AA] and [OMI][AA]). The synthesized ILs were characterized using Fourier Transform Infrared Spectroscopy, and absorption studies were conducted using a pressurized batch system under stable pressure and temperature conditions. Amino acids demonstrated an enhancement in the absorption of this acidic gas when compared to monoethanolamine, which is the most commonly used commercial absorbent compound.

A unified presentation of phase stability analysis including all major specifications

The major specifications for phase equilibrium are: pressure and temperature (PT), volume, temperature and moles (VTN), pressure, enthalpy and moles (PHN), pressure, entropy and moles (PSN), internal energy, volume and moles (UVN) and entropy, volume and moles (SVN). For some of these specifications, stability testing is not well documented in the literature. It appears that derivations of stability criteria for PHN, PSN and SVN stability are presented here for the first time, as well as the possibility to solve the stability problem in their hyperspaces. Two general stability criteria are derived, which include all state functions and specifications. The general tangent plane distance (TPD) function degenerates to the TPD function corresponding to any desired specifications. The formalism is not model dependent. It is shown that stability testing for any specifications naturally reduces to either PT stability (when pressure is a specification, as in PHN and PSN stability) or VTN stability (when volume is a specification, as in UVN and SVN stability), by solving the appropriate nonlinear equation in temperature. In other words, there is no need (moreover, it is shown that there it is not even recommended) to minimize a specific TPD function in its hyperspace (defined by natural variables of the state function). This paper presents the first unified treatment of phase stability testing including all major specifications; beyond its theoretical importance, an important practical consequence is a unified calculation framework for phase stability testing, allowing a versatile numerical treatment and using existing highly robust and efficient procedures for PT, volume-based PT or VTN stability, whatever the specifications.

State of the art of hydraulic packer testing in clay rocks in the Swiss national radioactive waste disposal program

Abstract. To provide input for site selection and the safety case for deep geological repositories for radioactive waste, Nagra has drilled a series of deep boreholes in northern Switzerland. As part of the hydrogeological characterization of this exploratory drilling campaign, hydraulic packer tests in the sedimentary rocks were carried out under the supervision of Nagra, in depths from 300 to 1130 m b.g.l. (below ground level). Single or straddle-packer hydraulic tests were conducted in different low-permeability rocks. The hydraulic testing equipment used was specially designed to reduce uncertainty associated with the low-permeability testing conditions and included a downhole hydraulic shut-in valve (DHSIV), a hydraulic piston, a probe carrier, and inflatable packer(s). Pressure and temperature are monitored with sensors connected to the bottom of the borehole, the test interval, the annulus above the upper packer, and the test tubing above the DHSIV. Hydraulic test sequences consisted of multiple withdrawal and shut-in phases. Test phases started with a compliance phase to allow some of the pressure and temperature transients caused by tool installation and packer inflation to dissipate, followed by a pressure static recovery phase to allow the test interval pressure to establish a recovery trend after being isolated. In general, in the low-permeability formations the active test sequence consisted of a pulse withdrawal performed using a hydraulically operated piston displacing a precisely defined volume, a slug withdrawal, and lastly a slug-withdrawal shut-in phase. The pressure data collected during the hydraulic tests were analyzed using the well-test simulator nSIGHTS®. The use of a numerical model is necessary for the analyses of the tests in low-permeability rocks as borehole history and temperature equilibration during the test can have a significant impact on test responses. Analyses started with the definition of a borehole-formation conceptual flow model based on geological information and interpretation of diagnostic plots. Input model parameters composed of non-fitting parameters and fitting parameters are defined. Preliminary automated calibrations are performed to identify the appropriate conceptual model and obtain baseline estimates of the fitting parameters for each tested interval. Perturbation analyses entailing hundreds to thousands of optimizations are performed to obtain the final best-fit parameter values and the corresponding uncertainty ranges. Our presentation will give an overview on methodologies and workflows with emphasis on the numerical design and analysis techniques applied to the hydraulic packer tests performed. The applied methodology provided high-quality results and reliable estimates of the hydraulic conductivities in the low-permeability rocks. The results from the hydraulic packer tests will be presented, and implications for further research by Nagra will be discussed.

Multiphase flow modeling at the component level for the Swiss deep geological repository

Abstract. In a deep geological repository for radioactive waste, anaerobic corrosion of various metals lead to the formation of hydrogen. In Switzerland, the implementor (i.e., Nagra) is commissioned to describe and evaluate safety-relevant processes related to gas that can affect the long-term evolution of low- and intermediate-level waste (L/ILW), high-level waste (HLW), and combined L/ILW and HLW repositories. Key tasks include the evaluation of gas and radionuclide release pathways and the pressure and temperature evolution in the repository using multiphase and multicomponent flow and transport models. The Swiss repository design foresees the installation of multiple seals (engineered barriers) in the repository: (i) the V1 seals next to the waste emplacement caverns and tunnels, (ii) the V2 seals located in the access tunnels toward the emplacement caverns and tunnels, and (iii) the V3 seals positioned in the shafts of the repository. These seals are designed to satisfy a wide range of requirements, including requirements related to the hydraulic evolution of the repository and the associated transport of gas, water, and radionuclides. A modeling workflow is currently being developed that integrates modeling performed both at the repository scale using site-specific models and at the component scale using semi-generic models. The repository-scale models are built to assess the thermo-hydraulic evolution in the entire repository, whereas the component-scale models allow for more detailed evaluations of the gas and water flows in key structures of the repository, such as the V1, V2, and V3 seals as well as the emplacement caverns and tunnels. This conference contribution describes the methodology and workflow developed to integrate these models, with a focus on the development and functionality of the component-scale models.

Investigating the effect of spray system on the containment condition of VVER1000/V446 NPP during LBLOCA and TLOFW accidents

The containment system serves as the last barrier against the release of fission products. However, over pressurization or hydrogen detonation can compromise its effectiveness, as evidenced by the Fukushima nuclear power plant (NPP) disaster. This study describes the efficacy of the spray system in reducingcontainment pressure andtemperature, as well as,itsimpacton hydrogen mitigation during large break loss of coolant accident (LBLOCA) and total loss of feed water (TLOFW) accident in the VVER-1000/V446NPP. The evaluation is conductedusing theMELCOR 1.8.6code.The results of the LBLOCA analysis demonstrate that the spray system significantly reduces the pressure and temperature of the containment. It also enhances hydrogen mitigation by increasing the amount of recombined hydrogen by around 4% and reducing the onset time of hydrogen recombination by 90,000 s. In the TLOFW accident scenario, the spray system is effective in reducing the containment pressure from 0.41 MPa to 0.27 MPa. The investigation of hydrogen behavior in the reactor containment atmosphere reveals that the simultaneous operation of the spray and the hydrogen recombiner systems is the most effective strategy for hydrogen mitigation. However, activating the spray system without the passive autocatalytic recombiners (PARs) function can lead to an increase in the hydrogen mole fraction in all containment compartments, thereby increasing the likelihood of hydrogen combustion.

Petrological study of an eclogite-facies metagranite from the Champtoceaux Complex (La Picherais, Armorican Massif, France)

Abstract. The high-pressure metagranite of La Picherais belongs to the Cellier Unit (part of the lower allochthon of the Champtoceaux Complex; Armorican Massif, western France), where it crops out as an undeformed body embedded within the orthogneisses of the Cellier Unit and is closely associated with numerous mafic eclogite lenses and seldom metahornfels. The petrographic observations of this metagranite reveal the presence of well-developed reaction textures: (1) pseudomorph after plagioclase, (2) garnet and phengite coronae at biotite–plagioclase interfaces, (3) garnet and phengite coronae at biotite–K-feldspar interfaces, and (4) garnet and rutile coronae at ilmenite–plagioclase interfaces, attesting that it underwent high-pressure and low-temperature conditions after the granite intrusion and its cooling. The analysis of the coronae and of a xenolith inclusion found in this granite points to pressure (P) and temperature (T) estimates of P>1.7 GPa and T=600–650 ∘C for the peak of metamorphism. P–T estimates performed on the mafic eclogite collected in the vicinity of the metagranite give values of 2.0–2.2 GPa and 640–680 ∘C, in good agreement with previous estimates made in other places within the Cellier Unit. The La Picherais metagranite is a key example of undeformed high-pressure metagranite allowing the study of the reactivity and degree of transformation of quartzofeldspathic rocks during subduction and constitutes a Variscan equivalent of the Alpine Monte Mucrone or Brossasco–Isasca metagranitoids.

The Effect of Salinity on the Strength Behavior of Hydrate-Bearing Sands

The first prerequisite for the efficient and safe exploitation of gas hydrate resources is to accurately analyze the primary mechanical performance of hydrate-bearing sediments (HBSs). The mechanical performance of HBSs is complex and affected by many factors, including the reservoir environment in situ (temperature, pore pressure, salinity). Several published studies have demonstrated a correlation of the mechanical behavior of hydrates with temperature and pressure (T-PP). However, the research on the effect of salinity on the mechanical properties of hydrates or HBSs is still a relatively blank field. This study found that the strength of HBSs decreased with increasing salinity. This phenomenon can be attributed to the influence of salinity on the phase equilibrium state of hydrates. NaCl changed the relationship between the phase equilibrium curve of the hydrate and the T-PP conditions. The distance between the T-PP conditions and equilibrium curve was reduced with increasing salinity, which in turn led to a decline in sample strength. Moreover, the effect of the phase equilibrium of hydrates on the mechanical performance of HBSs was further explored. NaCl was added to HBSs to regulate the phase equilibrium state of the hydrate. When the T-PP conditions were on the phase equilibrium curve, the strength behaviors of HBSs showed a high degree of consistency.

Towards joint in situ determination of pressure and temperature in the large volume press exclusively from X-ray diffraction.

Since high-pressure devices have been used at synchrotron facilities, accurate determination of pressure and temperature in the sample has been a crucial objective, particularly for experiments that simulate the Earth's interior. However, in some cases using a thermocouple may have a high likelihood of failure or is incompatible with a high-pressure assembly. To address these challenges and similar issues, we aim to expand a previously proposed solution: to jointly estimate pressure and temperature (PT) through in situ X-ray diffraction, to cover a wider range of internal PT calibrants tested over larger PT ranges. A modifiable Python-based software is offered to quickly obtain results. To achieve these aims, in situ large volume press experiments are performed on pellets of intimately mixed powders of a halide (NaCl, KCl, KBr, CsCl) or MgO and a metal (Pt, Re, Mo, W, Ni) in the pressure range 3-11 GPa and temperature range 300-1800 K. Although the pressure range was chosen for practical reasons, it also covers an equally important depth range in the Earth (down to 350 km) for geoscience studies. A thermocouple was used to validate the PT conditions in the cell assemblies. The key results show that choosing the appropriate calibrant materials and using a joint PT estimation can yield surprisingly small uncertainties (i.e. <±0.1 GPa and <±50 K). This development is expected to benefit current and future research at extreme conditions, as other materials with high compressibility or high thermal pressure, stable over large PT ranges, may be discovered and used as PT calibrants.

Effect of faceting on olivine wetting properties

Abstract Grain-scale pore geometry primarily controls the fluid distribution in rocks, affecting material transport and geophysical response. The dihedral angle (θ) in the olivine-fluid system is a key parameter determining pore fluid geometry in mantle wedges. In the system, curved and faceted olivine-fluid interfaces define θ, resulting in faceted-faceted (FF), faceted-curved (FC), and curved-curved (CC) angles. The effect of faceting on θ under various pressure and temperature (P-T) conditions and fluid compositions, however, has not been constrained, and mineralogical understanding remains unresolved. This study evaluated facet-bearing θ and their proportions in olivine-multicomponent aqueous fluid systems. Our results show that 1/3 of olivine-fluid θ are facet-bearing angles, regardless of the P-T conditions and fluid composition. Faceting produces larger dihedral angles than CC angles. The grain boundary plane (GBP) distribution reveals that the GBPs of faceted interfaces at triple junctions have low Miller index faces ({100}, {010}, and {101}). The misorientation angle/axis distributions of adjacent grain pairs are in accord with a theoretical distribution of random olivine aggregate. Moreover, the calculation of the FF angles for adjacent grain pairs with low Miller index GBPs reproduces measured angle values based on the olivine crystal habit. Therefore, our study suggests that the FF angle is strongly affected by olivine crystallography. The presence of faceting increases θ and a critical fluid fraction (φc) for percolation, lowering permeability. In the mantle wedge, where olivine crystallographic preferred orientation (CPO) is expected owing to corner flow, increasing the FF angle proportion with associated changes in fluid pore morphology will lead to permeability anisotropy, and controlling the direction of the fluid flow, and it will result in geophysical anomalies such as seismic wave attenuation and high electrical conductivity.

Hydrothermal sulfate surges promote rare earth element transport and mineralization

Abstract The generation of sulfate-rich hydrothermal fluids is of great significance to investigate because it is closely associated with the formation of many important ore deposits, such as hydrothermal rare earth element (REE) deposits. However, the transport of REEs in sulfate-rich hydrothermal fluids is complicated by the retrograde solubility of common sulfate minerals depicted in current thermodynamic models. We present in situ and ex situ hydrothermal experimental evidence suggesting that the solubility of alkali sulfate changes from retrograde at low pressures to prograde at elevated pressures. Accordingly, we propose a sulfate surge temperature and pressure (T-P) window (250 °C, 90 MPa), above which the solubility of alkali sulfate increases significantly with increasing P and T. Although REE sulfates are weakly soluble in water, sulfate-rich hydrothermal fluids can transport high contents of REEs under the T-P conditions above the sulfate-surge window. Our results indicate that depressurization, cooling, and alkali loss are key factors controlling REE mineralization, which agrees well with geological observations.

Robustness and efficiency of phase stability testing at VTN and UVN conditions

Beyond the well-documented conventional phase equilibrium calculations at pressure and temperature (PT) specifications, other specifications, such as volume, temperature and moles (VTN) and internal energy, volume and moles (UVN) have received an increasingly interest in the last years. Whatever the selected set of independent variables, phase stability at UVN conditions can be asserted by solving simpler VTN or PT stability problems (a non-linear equation is solved only once at UVN specifications for temperature). In VTN stability, modified Newton iterations were previously used to achieve convergence, since successive substitution iterations (SSI) may exhibit problematic convergence. A mathematical analysis of convergence properties of the successive substitution (SSI) method for VTN stability reveals its potential instability, unlike for PT stability, in which SSI is very robust. This problem can be theoretically overcome by using a damping factor, but severe damping may lead to unacceptable slow convergence rates. It is shown that the SSI method should never be used alone, combined undamped SSI-standard Newton method is neither robust nor efficient as claimed previously and must be avoided; moreover, damped SSI can be used with caution only in early iteration stages. The convergence behavior of several methods for VTN stability is analyzed for a variety of mixtures and the numbers of iterations are compared with those reported in the literature. Several domains in the molar density-temperature plane were identified, where SSI is either systematically not detecting a phase split (converging to the trivial solution from all initial guesses) or systematically diverges. Our calculation procedures are highly robust and systematically faster than previous methods (for some test points up to one or even two orders of magnitude) and are able to find the global minimum of the TPD function in all test cases, unlike previously proposed SSI/Newton methods, which either are strongly attracted by local minima or they diverge. This paper gives for the first time a detailed mathematical and numerical analysis of the convergence behavior of SSI and combined SSI-Newton methods in VTN stability testing.

Laminar premixed burning characteristics of methanol/ethanol/air at high temperature and pressure

A numerical study was conducted to evaluate the laminar burning characteristics of methanol/ethanol/air flames under engine operating conditions. Methanol and ethanol are common burning oil of biomass that can replace fossil fuels and have a high laminar combustion rate relative to gasoline. Few scholars have studied the laminar combustion characteristics of methanol/ethanol mixture. This study aims to analyze the similarities and differences of methanol/ethanol/air flames for different methanol percentages and equivalence ratios in a wide range of pres?sure and temperature conditions. Chemkin software with chemical reaction kinetic mechanism of Mittal was used and validated against experimental data from the literature. The results showed that methanol significantly increases the laminar burning velocities and the net heat release rate. The maximum laminar burning ve?locities is obtained at the equivalence ratio of 1.1. Due to the high calorific value of ethanol, the adiabatic flame temperature of ethanol are slightly higher than that of methanol. The hydrodynamic instabilities of methanol/ethanol/air flame increase at first and then decrease with the increase of equivalence ratio. Finally, sensitiv?ity analysis show that H + O2 &lt; = &gt; O + OH (R1) mainly influences the laminar burning velocities.

Seismic signals induced by the Metasomatism of mantle wedge by siliceous melts: Insights from the elasticity of orthopyroxene at high pressure and temperature

Large amounts of silica held by slabs during subduction prefer to concentrate into the eclogite melts and further lead to the metasomatism of the overlying mantle wedge. However, the metasomatism process mediated by siliceous melts in the mantle wedge and the seismic signals associated remain poorly constrained. Peridotite in the mantle wedge is sufficiently silica undersaturated. Therefore, SiO2-rich melts would react with olivine in the peridotite to form orthopyroxene (opx). The local enrichment of opx has also been proposed to account for the observed low VP/VS ratio in the mantle wedges of a few subduction zones, revealing the metasomatism by silica saturated melts there. But the anomalously low VP/VS regions in a few subduction zones are inconsistent with the widespread metasomatism of the mantle wedge. In this study, we determined the elasticity of Fe-bearing opx (Mg0.875Fe0.125)SiO3 at high pressure and temperature (P-T) conditions. The VP/VS ratio of opx has a strong dependence on the pressure and temperature conditions, and only exhibits low VP/VS at low pressure and high temperature. Although the enrichment of opx may be widespread, it can only produce a discernible low VP/VS ratio at subduction zones with proper thermal conditions. Together with the elasticities of other major minerals in the upper mantle, we investigated the effect of opx enrichment on VP/VS ratio at mantle wedge conditions. The VP/VS ratio linearly decreases with the opx volume fraction (Ω), and the relationship can be described as VP/VS = 1.772 − 0.142Ω. Combining our high-quality mineral elasticity data with seismic tomography and thermal structure, we constrained the mineral proportions in the northern wedge of the Alaska subduction zone. The opx enriched area coincides well with the anomalously low VP/VS domain, indicating the strong metasomatism by siliceous melts in this mantle wedge.

A re-evaluation of the peak P-T conditions of eclogite-facies metamorphism of the Paleozoic Acatlán Complex (Mexico) reveals deeper subduction.

Eclogites in the Acatlán Complex, southern Mexico, record the subduction history of the complex. Previous studies indicate that the proto-Acatlán Complex reached < 50km depth during subduction. Yet, a recent study reported higher pressures for a single eclogite, questioning the maximum depth reached by the complex during subduction. In this work, I re-calculate eclogite pressure and temperature (P-T) conditions using thermobarometric methods applicable to eclogite-facies mafic rocks to a set of eclogites cropping out throughout the high-pressure belt of the Acatlán Complex-the Piaxtla Suite. I find that Acatlán eclogites record substantially-and systematically-greater pressures than previously reported. Calculations show that eclogites from the central part of the Piaxtla Suite (in the Piaxtla area) record consistent pressures of ~ 2.0GPa and temperatures ranging between 460 and 675°C. Eclogites from the northern part of the Piaxtla Suite (Mimilulco and Santa Cruz Organal areas) lack phengite, thus pressures were not calculated; temperatures calculated for these rocks at a fixed pressure (2.0GPa) yield contrasting temperatures (511°C and 870°C, respectively). Mimilulco eclogite likely records similar pressures (~ 2.0GPa) to other Piaxtla eclogites, whereas the pressures of Santa Cruz Organal eclogites might have been different, and likely experiencing a different thermal history compared to the rest of the eclogites from the Piaxtla Suite. Overall, these results indicate that the Acatlán Complex subducted to greater depths than previously thought implying a faster burial-exhumation cycle of the proto-Acatlán Complex.

Thermal Conductivity of Hydrous Wadsleyite Determined by Non‐Equilibrium Molecular Dynamics Based on Machine Learning

AbstractThe thermal conductivity of minerals is a fundamental parameter in understanding the evolution and dynamics of the Earth. Wadsleyite, the major mineral in the mantle transition zone (MTZ), can contain abundant water. However, how water affects its thermal conductivity remains unknown. Here, we predicted the thermal conductivity of dry and hydrous wadsleyite at high pressure and temperature (P‐T) by combining non‐equilibrium molecular dynamics and machine learning potential trained with data from first‐principles calculations. We found that the thermal conductivity of wadsleyite is anisotropic and is reduced by ∼10% in the P‐T conditions of the MTZ by the presence of 0.81 wt.% water. The heat flow toward the slab tends to follow the direction with the lowest thermal conductivity due to the lattice‐preferred orientation of wadsleyite and olivine. Both hydration and thermal‐conductivity anisotropy slow down the heating of slabs, allowing hydrous minerals and metastable olivine to survive in the deeper mantle.