Heating-cooling Cycles Research Articles

Anionic Regulation toward Bi3+ Selective Occupation for Full-Spectrum White Light Emission.

An activator's selective occupation of a host is of great significance for designing high-quality white light-emitting diode phosphors, while achieving a full-spectrum single-phase white light emission phosphor is challenging. In this study, a boron phosphate solid-solution Na2Y2(BO3)2-x(PO4)xO:0.005 Bi3+ (NYB2-xPxO:0.005 Bi3+) white phosphor was designed by selectively occupying Bi3+ activators in the mixed anionic groups. The substitutes of the anionic unit (BO3)3- by the (PO4)3- unit are supposed to force part of the Bi3+ ion to enter the Na lattice site, which produces an intense orange-red emission peaked at 590 nm. In parallel, spectral tuning from blue to white light and an internal quantum efficiency of 56.42% was obtained, and the thermal stabile luminescence intensity remains at 94.2% of the initial intensity after four heating-cooling cycles from 30 to 210 °C (luminescent intensity is 83.6% of room temperature (RT) at 150 °C, with excellent thermal stability and recovery performance). Finally, an excellent color rendering index (Ra = 90.8 and R9 = 85) was demonstrated for white light-emitting diode devices using only an NYB1.5P0.5O:0.005 Bi3+ phosphor and a near-ultraviolet (n-UV) 365 nm LED chip. This work delves into the different selective occupancy of Bi3+ ions and explores a new avenue for the design of phosphors for full-spectrum white light emission.

Thermo-mechanical characteristics of laterally loaded energy piles under multiple heating-cooling cycles in mountain area

In this paper, model tests of energy piles used in mountain area under asymmetry filed condition with and without an external lateral load under multiple heating-cooling cycles were conducted. The asymmetry of the soil will produce asymmetric temperature field and stress field in mountain area. The variation of pile top displacement, horizontal soil pressure, and pile bending moment due to cyclic temperature load were measured and analyzed. The results showed that the pile top horizontal displacement with an external lateral load decreased when the energy pile was heated and increased when it was cooled. However, the variation trends of pile top horizontal displacement with and without an external lateral load showed a significant difference. When the pile subjected to an external load was heated, the soil pressure at the upper part behind the pile would increase and that at the lower part would decrease, and the change was opposite during cooling. The bending moment would be changed by the thermal load, and it increased during heating with an external lateral load, while the variation of bending moment was not obvious during cooling.

Study on the Evolution of Physical Parameters and Dynamic Compression Mechanical Properties of Granite after Different Heating and Cooling Cycles

The study of the evolution law of basic physical parameters and dynamic compression performance of deep granite under the environment of the heating-cooling cycle is of great significance for the stability evaluation of deep underground engineering and the development of deep resources. In this study, heating-cooling cycle tests and dynamic compression tests were conducted on a large number of fine-grained granite specimens with heating temperatures from 200 to 600 °C and times from one to twenty times using a box-type high-temperature muffle furnace and Hopkinson pressure bar (SHPB) test system, and the evolution law of basic physical parameters and dynamic compression mechanical properties of fine-grained granite were studied using theoretical and fitting analysis. The test results showed that: the changes of the basic physical parameters of granite have obvious temperature effect; 600 °C is a threshold value for the changes of each physical parameter of granite; the sensitivity of each physical parameter to the number of heating and cooling cycles is small before 600 °C; and the sensitivity of each physical parameter to the number of heating and cooling cycles significantly increases at 600 °C. The dynamic compressive strength and elastic modulus of granite decreased with the increase in heating and cooling cycles, and the maximum decrease rate was 89.1% and 85.9%, respectively, and the strain rate linearly increased with the increase in heating and cooling cycles, and the maximum strain rate was 123 s-1. The temperature, the number of heating and cooling cycles, and the impact air pressure, all had significant effects on the damage mode and crushing degree of granite.

Investigating Fundamental Principles of Nonequilibrium Assembly Using Temperature-Sensitive Copolymers.

Both natural biomaterials and synthetic materials benefit from complex energy landscapes that provide the foundation for structure-function relationships and environmental sensitivity. Understanding these nonequilibrium dynamics is important for the development of design principles to harness this behavior. Using a model system of poly(ethylene glycol) methacrylate-based thermoresponsive lower critical solution temperature (LCST) copolymers, we explored the impact of composition and stimulus path on nonequilibrium thermal hysteretic behavior. Through turbidimetry analysis of nonsuperimposable heat-cool cycles, we observe that LCST copolymers show clear hysteresis that varies as a function of pendent side chain length and hydrophobicity. Hysteresis is further impacted by the temperature ramp rate, as insoluble states can be kinetically trapped under optimized temperature protocols. This systematic study brings to light fundamental principles that can enable the harnessing of out-of-equilibrium effects in synthetic soft materials.

Kombinasi Fermentasi Bakteri Asam Laktat dan Pemanasan Bertekanan-Pendinginan dalam Pembentukan Pati Resisten Tepung Talas Beneng (Xanthosoma undipes K. Koch)

The study aimed to determine the effect of lactic acid bacteria, fermentation time, and pressurized heating-cooling cycle on the formation of resistant starch content of beneng taro (Xanthosoma undipes K. Koch) flour. The materials used were beneng corm, isolates of lactic acid bacteria Lactobacillus casei and Streptococcus thermophilus, and MRSB media. The experimental design was randomized block design factorial with two factors: fermentation time (0, 18, and 24 hours) and pressurized-cooling heating (1, 2, and 3- cycles) in 3 replicates. The data were analyzed using analysis of variance and if necessary continued with Duncan's Multiple Range Test at a level of 95%. The tested parameters were the content of resistant starch, amylose, and amylopectin and the data were treated using variance of analysis. The results showed that the combination of L. casei and S. thermophillus produced the highest resistant starch content of 5.66%. Fermentation time of 18 and 24 hours produced resistant starch content of 4.46% and 4.51%, respectively. Autoclaving-cooling of 1-, 2-, and 3-cycle produced a similar type of resistant starch of 3.81%, 4.26%, and 4.16%, respectively. Therefore, the combination of L. casei and S. thermophillus fermented in 18 hours and 1-cycle of autoclaving-cooling is recommended to produce resistant beneng taro flour starch content.
 
 Keywords: fermentation, autoclaving-cooling, resistant starch, taro beneng, Xanthosoma undipes K. Koch

Study on warpage and filling behavior of glass in non-isothermal hot embossing

Non-isothermal hot embossing has great potential in the mass production of glass micro optical components due to the relatively short heating-cooling cycle time. However, warpage was induced by the temperature gradient inside the glass replica during hot embossing, resulting in a deteriorated optical performance. Therefore, it is non-trivial to investigate the effects of process parameters on warping and filling behaviors of glass in non-isothermal hot embossing. Firstly, a high-quality microhole was fabricated on monocrystalline silicon carbide (SiC) mold by focused ion beam (FIB) lithography. By using a novel home-made gravity-assisted hot embossing machine, the geometric information (i.e., warpage and microstructures) on SiC mold was transferred into the surface of N-BK7 glass replica. The experimental results indicate that high embossing temperature enables not only the minimization of warpage but also the enhancement of microstructure replication accuracy. Furthermore, increasing embossing force enhances filling capacity but increases warpage amplitude. Interestingly, fast heating/cooling rates and short embossing time enable a small warpage as well as a high embossing efficiency. By optimizing the process parameters, especially the embossing temperature, a small warpage amplitude of 3 μm and a high transfer ratio of 99.11% were achieved, which can meet the high requirement of precision optical components.

Effect of molecular chain mobility on the electrothermal stability of polyethylene/multi-walled carbon nanotube electrothermal composites

In this study, we pay close attention to the structure design of high-temperature electrothermal composites. Two kinds of high density polyethylene-based electrothermal composites filled with multi-walled carbon nanotubes (5960G1/MWCNTs and 5000 S/MWCNTs) prepared by melt compounding is employed as examples. The relationship between molecular weight of matrix and electrothermal properties of composites are studied through the investigation of the changes of microstructure and conductive network in the composites during heating-cooling cycles. Benefiting from the increased high-molecular-weight component and decrease of molecular chain mobility, 5960G1/MWCNTs composites shows excellent electrothermal stability with the surface temperature stabilized at about 120 °C within 10 h (applied voltage of 18 V). In addition, owing to the protection of internal conductive network from low molecular chain mobility of the 5960G1, a reduced disruption of conductive network from the thermal expansion of 5960G1/MWCNTs composite can be ensured by the low deformation of matrix with high molecular weight chains, in turn, 5960G1/MWCNTs composite exhibits good electrothermal repeatability at sequent heating-cool cycles. Thus, high molecular weight polyethylene as a matrix favors high temperature use of electrothermal materials and is expected to be applied in the field of commercial high-temperature electrical heating cables.

Probing the improved heat stabilizing capacity of dry heat conjugated whey protein in oil-in-water emulsions: A microrheological study

Dry heat conjugation of whey protein has been shown before to improve its heat stabilizing properties when applied as an emulsifier. However, the range of feasible heating conditions of these conjugates has not yet been evaluated. Microrheology, a non-destructive method, was utilized in this study to determine the acceptable heating range for whey protein stabilized-emulsions. Practically, oil-in-water emulsions stabilized by whey protein-lactose conjugates were subjected to either an in-situ thermal treatment, including a heating-cooling cycle, or to an isothermal period. The observed microstructural rearrangements were also confirmed by examining the bulk emulsion behavior through oscillatory rheology.The obtained results indicated that microrheology could unravel the range of heating temperatures and durations for emulsions stabilized by whey protein concentrate (WPC) that was dry heated for 8 and 48 h as compared to the native WPC. The improved heat stability was a result of the conjugates’ ability to prevent the formation of an oil droplet network. Consequently, the conjugated WPC-stabilized emulsions remained mainly viscous with a low elasticity index (EI) and macroscopic viscosity index (MVI) during heating. Furthermore, the microrheology findings were found to be largely in line with bulk rheological properties: both methods indicated a comparable temperature for the onset of network formation upon applying a temperature sweep. The insights from this study may help to stimulate the industrial application of whey protein-sugar conjugates as heat stable natural emulsifiers.

Unraveling the structural details and thermoelectric transports of 2D-3D hetero-structure composites

With in-depth research on the thermoelectric properties of the single-phase traditional three-dimensional (3D) and emerging two-dimensional (2D) materials, there is a deficit in the study of the 2D-3D hetero-structure phases, whose structural details and transport features still require a clear understanding. In this work, taking 2D-SnSe and 3D-PbSe as research objects, we prepared mixture-phase composites with the coexistence of 2D and 3D phases and studied the relationship between the thermoelectric transports and phase structures. By conducting the powder X-ray diffraction measurements and Rietveld refinements, we obtained the dynamic 2D-3D hetero-structure compositions of weight percentages with heating-cooling cycles. Subsequently, we estimated the lattice thermal conductivity from the experimental measurements and theoretical calculations as functions of 2D-3D compositions. We discovered that the lattice thermal conductivity reduction became more obvious in the samples with small amounts of hetero-structure phases, benefiting from the extra scattering of phonons by the higher density of hetero-structure interfaces. Moreover, we observed the 2D-3D hetero-structures at the microscopic scale by HADDF-STEM, experimentally confirming the presence of low symmetrical-PbSe and high symmetrical-SnSe phases. This study gave a perspective and investigation method to unravel both the structural details and transport properties of 2D-3D hetero-structure composites, which might provide new strategies for optimizing thermoelectric performance by depressing the thermal transports in hetero-structure materials.

Pullulan Films with PCMs: Recyclable Bio-Based Films with Thermal Management Functionality

The use of phase-changing materials (PCMs) is a practical and powerful way of buffering thermal fluctuations and maintaining the isothermal nature of the storage process. In this study, melamine formaldehyde microcapsules with paraffin cores were used as PCMs; pullulan films with PCMs were prepared by the film-casting method; and the composite films prepared were analysed with regard to their chemical structure, thermal properties, thermal stability, and recyclability. Uniform films displaying thermal management functionality were prepared. The amount of 75 wt.% PCM were added to the pullulan film structure which enabled the preparation of a composite film that displayed 104.85 J g−1 of heat storage during heating and 103.58 J g−1 of heat release during cooling. Multiple heating and cooling cycles showed that the composite films maintained their thermal management functionality after multiple heating-cooling cycles. The PCMs could be recovered with a yield of approximately 95% by the application of a simple dissolution and filtration process. The morphology, chemical structure, and thermal properties of the PCMs were maintained after the recovery process. The bio-based composite films with thermal management functionality and recyclability are proposed as an innovative, practical, and effective system for thermoactive storage and packaging applications.

Performance of a Belled Pile Influenced by Pile Head Freedom Response to a Cooling–Heating Cycle

This paper demonstrates the influence of pile head freedom on the thermomechanical performance of a belled pile. Field tests on the belled pile response to a cooling–heating cycle and incremental structural construction are carried out. The temperature changes, axial strain profiles, and pressures at the pile toe are recorded through the buried instruments. The variation in the degrees of freedom, tensile forces, and inferred pile head settlements along the pile depth for different test procedures are analyzed using the measured data. The degree of freedom close to the pile head calculated from strain rates decreases with the structure mass with a gradient of −2.8×10−5/kN. The reducing effect of the incremental superstructure on pile freedom decreases along with the orientation of the pile depth. Compared with the inferred thermal displacement of the pile without an applied structural load, the values decrease by about 10% when the pile was subjected to incremental floors, and an elastic recoverable characteristic response to cooling–heating-recovery phases is observed. Compared with the equal-diameter pile, the belled pile showed a significant constraint close to the toe. Mechanical loads can decrease the cracking risk because of a possible tensile force under cooling conditions.

Investigation of KNO2-KNO3-K2CO3 mixed molten salts with higher working temperature for supercritical CO2 concentrated solar power application

In the present work, the new eutectic composition of KNO2-KNO3-K2CO3 ternary salt for sCO2 solar thermal power generation is predicted by thermodynamic calculation, then the thermophysical properties of the eutectic salt are investigated by experiments combined with theoretical calculation, further studies are focused on its corrosivity. The results show that the predicted ternary molten salt is confirmed as 0.259KNO2–0.687KNO3–0.054K2CO3. Due to mixing a small amount of K2CO3, the upper limit of the operating temperature of the eutectic salt can reach 750.1 °C, and the melting point and the freezing point have a good thermal stability in the heating-cooling cycles. The calculated specific heat is lower than the measured one which can maintain at 1.407 J/(g·K) in the range of 400–450 °C. With the increase of temperature, the density decreases linearly and the thermal diffusivity tends to increase, thus there is a slight growing in thermal conductivity with an average value of 0.3 W/(m·K). The novel eutectic salt has an energy storage density of 865 MJ/m3. Although containing a low concentration of K2CO3, the eutectic salt shows low corrosion to 310S stainless steel. After the corrosion test of 240 h at 600 °C, the mass loss of stainless steel maintains a constant at 0.067 mg/cm2. The above results indicate that 0.259KNO2–0.687KNO3–0.054K2CO3 eutectic salt is a promising high-temperature thermal storage material for solar thermal power generation.

Synthesis of Thermally Stable and Highly Luminescent Cs5 Cu3 Cl6 I2 Nanocrystals with Nonlinear Optical Response.

Low-dimensional Cu(I)-based metal halide materials are gaining attention due to their low toxicity, high stability and unique luminescence mechanism, which is mediated by self-trapped excitons (STEs). Among them, Cs5 Cu3 Cl6 I2 , which emits blue light, is a promising candidate for applications as a next-generation blue-emitting material. In this article, an optimized colloidal process to synthesize uniform Cs5 Cu3 Cl6 I2 nanocrystals (NCs) with a superior quantum yield (QY) is proposed. In addition, precise control of the synthesis parameters, enabling anisotropic growth and emission wavelength shifting is demonstrated. The synthesized Cs5 Cu3 Cl6 I2 NCs have an excellent photoluminescence (PL) retention rate, even at high temperature, and exhibit high stability over multiple heating-cooling cycles under ambient conditions. Moreover, under 850-nm femtosecond laser irradiation, the NCs exhibit three-photon absorption (3PA)-induced PL, highlighting the possibility of utilizing their nonlinear optical properties. Such thermally stable and highly luminescent Cs5 Cu3 Cl6 I2 NCs with nonlinear optical properties overcome the limitations of conventional blue-emitting nanomaterials. These findings provide insights into the mechanism of the colloidal synthesis of Cs5 Cu3 Cl6 I2 NCs and a foundation for further research.

Effect of thermal cycles on the engineering properties and durability of sustainable fibrous high-strength concrete

In this research, the effect of heat–cool cycles (HCCs) on high-strength concrete (HSC) containing steel fibres (SFs), polypropylene fibres (PPFs), and date palm fibres (DPFs), which were named fibrous high-strength concrete (FHSC), was studied. To produce FHSC, three doses of 0.2, 0.6, and 1 percent of each fibre were used. All samples were tested after 28 days of normal water curing and 270 days of exposure to HCCs (continuing the authors’ project and research published at 28 and 180 days). This entails heating for 2 days at 60 C in the oven and cooling for another 2 days at room temperature for 270 days. The experiment’s findings revealed that fibre reinforcement in concrete enhances its strength and durability. By incorporating the three types of fibres into high-strength concrete, with and without HCCs, the modulus of rupture was significantly increased. In both conditions, including with or without the implementation of HCCs, incorporating the three fibre types into the HSC showed a significant increase in toughness. As a result, natural date palm fibres can produce sustainable FHSC that can withstand harsh environmental conditions. Moreover, compared to the previous study conducted by the authors at 180 days, there is a slight severity in both the pattern of decrease and increase of the studied characteristics at 270 days caused by the effect of thermal cycles and fibres.

Water-resistant gum-based phase change composite for thermo-regulating insulation packaging

The world's current energy crisis calls for green energy solutions that can preserve energy while incorporating renewable. As such, we have developed a leakage-proof phase change material (PCM) embedded in a biopolymeric matrix as a lightweight yet strong bio-based phase change composite (PCC) for passive energy storage and insulation purposes in packaging. This bio-based composite consists of gum tragacanth (GT) biopolymer and polyethylene glycol (PEG) PCM. It is further incorporated with biochar (BC) or mineral additive, i.e., Cloisite Na+, to enhance its mechanical strength and thermal stability, which are among the main challenges for insulation materials. A hydrophobic layer of octadecyl isocyanate (ODI) is developed on the surface of the composite to increase its water resistance. The composite provides a hydrophobic surface with a minor water uptake capacity of 3.6 ± 0.3 % after one-week immersion in the water. It shows high latent heat storage up to 160 J g−1 and a stable phase change behavior, as demonstrated by over 100 differential scanning calorimetry heating-cooling cycles. It also possesses notable compressive mechanical properties, which were improved significantly after incorporating BC and Cloisite Na+. The thermal conductivity of the composite is as low as 0.035 W m−1 K−1 manifesting in better thermal regulation compared with commercial polyethylene foams. This energy-positive bio-based solution combines the advantages of excellent insulation as a highly porous, lightweight, and strong composite with the latent heat and thermal inertia of PCM, making it suitable for transportation packaging of temperature-sensitive products.

Improving the detectability and confirmation of hidden surface corrosion on metal sheets using active infrared thermography

This research aims to provide a simple approach to detecting and determining hidden corrosion using active infrared thermography with improved consistency in distinguishing hidden defect areas of metal sheets (galvanized steel and stainless steel) commonly used as part of building envelopes. Early studies on detecting hidden defects focused primarily on defects resulting from material loss. Equally important is the early detection of corroded metal surfaces hidden from the observer's plane of view through non-invasive means. In this study, two heating configurations using portable heaters were explored, along with two analysis approaches to aid in detecting and confirming the presence of hidden corroded surfaces. Metal sheets with or without hidden surface corrosion are detected, distinguished, and confirmed by observing differences in their mean surface temperatures and temperature distribution. The detection and confirmation involve two simple analysis approaches: (1) observing the differences in mean surface temperature and visual thermal contrast of the non-corroded surface available for monitoring during the heating-cooling cycle; and (2) comparing the distribution of temperature probability at a given temperature. The new method is considerably more practical as it would require only heating the region of interest to a temperature of no more than 70 °C using a portable heat source and detailed analysis requiring temperature distribution between 40 and 70 °C. The results from the detection and confirmation approaches also conform with basic principles of heat transfer, making the detection and analysis method not only practical but also scientifically sound. This method may potentially be adopted in building surveys, early detection, and post-monitoring of hidden corroded surfaces that may impact building envelope deterioration and structural integrity.

Mechanical and durability behaviour of fiber reinforced concrete

Fiber Reinforced Concrete (FRC) is broadly used in the construction of large buildings, industrial floors, and pavements due to the presence of exceptional mechanical and durable properties, having modest production cost. The impact of different types of fiber and environmental conditions on the strength and durability of ordinary concrete, such as steel fiber, polypropylene(PP) fiber, and natural palm tree fiber, varies. A variety of conventional material tests were performed to analyze the compressive strength and flexural properties. The experimental results showed that fiber stomping may take place at higher fiber volume fractions, resulting in mixing and casting issues. Based on the mechanical properties and anti-dry-shrinkage cracking resistance of FRC, the suitable fiber length and volume fractions were determined. In 28 days of water curing, adding small amounts of PP fiber can significantly increase compressive strength, flexural strength, and durability. However, in 6 months of wet-dry and heat-cool cycles, steel fiber performed better than PP fiber. The study also found that early shrinking of cracks decreases with an increase in fiber volume fraction, and no cracks are observed when a volume of 0.20% is used. These results can be used as a testimonial for the material proportion design of concrete.

Preparation and formation process of high efficient and stable CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals with mixed phase

CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> dual-phase nanocrystals are prepared by adding the mixture ligand of oleylamine and tetradecyl-phosphonic acid (OLA-TDPA) to CsPbBr<sub>3</sub> perovskite nanocrystals through ligand post-treatment. The structure, the morphology, optical property and the stability of CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> dual-phase nanocrystals are characterized by X-ray diffraction, transmission electron microscopy (high-resolution TEM), UV-vis spectrophotometer, fluorescence spectrophotometer, and transient fluorescence spectrophotometer. The as-obtained nanocrystals have a high photoluminescence quantum yield of 78% and long fluorescence lifetime of 476 ns when prepared at the optimal molar ratio of CsPbBr<sub>3</sub>, TDPA and OLA (1∶1∶15). Moreover, the nanocrystal is quite stable at room temperature for at least 25 days, and has a good thermal stability in five heating-cooling cycles at temperature in a range between 293 K and 328 K. The formation of dual-phase nanocrystals go through two stages of surface passivation/dissolution and recrystallization to generate CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals. In the first stage (<i>t</i> ≤ 1 h), the m OLA-TDPA mixing ligand can form (RNH<sub>3</sub>)<sub>2</sub>PO<sub>3</sub> X type ligand and exchanges with [RNH<sub>3</sub>]<sup>+</sup>-[RCOO]<sup>–</sup> at the surface of CsPbBr<sub>3</sub> nanocrystals, which can effectively passivate surface defects by strong interaction with Pb<sup>2+</sup> and high ligand content at surface, thus improving the quantum yield and fluorescence life of CsPbBr<sub>3</sub> nanocrystals with spherical shape. In the second stage, with the increase of reaction time, PbBr<sub>2</sub> partially dissolves from the surface of CsPbBr<sub>3</sub> nanocrystals, then some CsPbBr<sub>3</sub> nanocrystals transform into lead-depleted Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals with hexagonal phase, thus improving the stability of nanocrystals. This work has a certain reference value for promoting the applications of high efficient and stable perovskite nanocrystals.

Влияние механической деформации на магнитные свойства и магнитокалорический эффект в пленках Gd

In W/Gd/W/MgO heterostructures, the dependence of mechanical stresses in the Gd film on the crystallographic orientation of the MgO substrate was revealed. Variations in the interplanar spacings in MgO in different orientations create tensile elastic stresses up to 0.22 GPa in the Gd film, which are transferred through the damping layer W. It is found that these stresses affect the isothermal magnetization curves, the corresponding change in the magnetic part of the entropy at the Curie point Tc = 293 K, and the relative cooling capacity (RCP). This allows us to consider mechanical stresses as a factor in controlling the magnetocaloric cycle, which increases the efficiency of the refrigeration machine, when mechanical loading is synchronized with the heating-cooling cycles of the ferromagnet.

Temperature-induced densification in compressed basaltic glass revealed by in-situ ultrasonic measurements

Abstract Acoustic velocities of a model basalt glass (64 mol% CaMgSi2O6 + 36 mol% CaAl2Si2O8) were measured along different pressure-temperature (P-T) paths. One set of experiments involved isothermal compression-decompression cycles, performed at temperatures of 300, 641, 823, and 1006 K and pressures up to 12.2 GPa. The other set of experiments involved constant-load heating-cooling cycles at temperatures up to 823 K and pressures up to 7.5 GPa. Both sets of experiments were performed in a multi-anvil apparatus using a synchrotron-based ultrasonic technique. Our results show that the glass compressed isothermally at 300 K (cold-compression) displays anomalously decreasing compressional (VP) and shear (VS) wave velocities with increasing pressure until ~8 GPa. Beyond 8 GPa, both VP and VS start to increase sharply with pressure and irreversible densification of the glass occurred, producing large hysteresis loops of velocities upon decompression. However, for the glass compressed isothermally at increasingly higher temperatures (hot-compression), the velocity minima gradually shift to lower pressures. At temperature close to the glass transition temperature Tg, the velocity minima disappear completely, displaying a monotonic increase of velocities during compression and higher VP and VS during decompression. In addition, constant-load heating-cooling experiments show that velocities generally decrease slightly with increasing temperature, but start to increase once heated above a threshold temperature (~650 K). During cooling the velocities increase almost linearly with decreasing temperature, resulting in higher velocities (~1.5–2.5% higher) when returned to 300 K. This implies that a temperature-induced densification may have occurred in the glass at high pressures. Raman spectra on recovered samples show that the hot-compressed and high-P heated glasses contain distinctly densified and depolymerized structural signatures compared to the initial glass and the cold-compressed glass below the velocity transition pressure PT (~8 GPa). Such densification may be attributed to the breaking of bridging oxygen bonds and compaction in the intermediate-range structure. Our results demonstrate that temperature can facilitate glass densification at high pressures and point out the importance of P-T history in understanding the elastic properties of silicate glasses. Comparison with melt velocity suggests that hot-compressed glasses may better resemble the pressure dependence of velocity of silicate melts than cold-compressed glasses, but still show significantly higher velocities than melts. If the abnormal acoustic behaviors of cold-compressed glasses were used to constrain melt fractions in the mantle low-velocity regions, the melt fractions needed to explain a given velocity reduction would be significantly underestimated at high pressures.