Exothermic Peak Temperature Research Articles

On the Promotion of TKX‐50 Thermal Activity with Aluminum

AbstractIt is significant to investigate the effect of aluminum (Al) on the thermal activity of Dihydroxylammonium 5, 5′‐bistetrazole‐1, 1′‐diolate (TKX‐50) for the application of TKX‐50‐based composite solid propellant. In this work, TKX‐50/Al composites with different particle sizes and contents of Al were blended, and the thermal decomposition and combustion properties were investigated by differential scanning calorimetry (DSC), thermal decomposition kinetic methods, laser ignition experiments, and constant‐volume combustion cell test. The results showed that the exothermic peak temperatures for thermal decomposition of TKX‐50 were gradually advanced with the decrease of Al particle size. With the increase of Al nanoparticles (nAl) content, the peak temperatures of TKX‐50 first decreased and then increased. As the content of nAl was 50 %, the activation energy of TKX‐50 changed from 226.51 kJ ⋅ mol−1 to 215.23 kJ ⋅ mol−1, and the critical temperature of thermal explosion decreased by 13.54 °C after the addition of nAl. In addition, a small amount of nAl could promote the combustion of TKX‐50 that is reflected on the accelerated burning rate, increased maximum combustion pressure and pressurization rate. Overall, nAl with high specific surface area and high reactivity is a great thermal activity enhancement additive for TKX‐50.

A SHORT REVIEW: THE EFFECT OF NANOMATERIALS FOR THERMAL DECOMPOSITION OF SOLID PROPELLANT OXIDIZER AP

This review attempts to discuss data related to the work of kinds of literature on various nanomaterials such as ferrites, oxides, and chromates of transition metals which lead to gain prominent attention in the field of thermal decomposition of solid propellant oxidizer mainly ammonium perchlorate (AP). The effect of catalysts like metal oxides, inorganic and organic compounds, etc., is discussed for the thermal decomposition of ammonium perchlorate (AP). This study underscores the experimental effectiveness of these catalysts in the decomposition process of solid propellants which enhances fast decomposition through decreasing their exothermic peak temperature. Such kind of improvements in propellant oxidizer and binder fuel help to increase the efficiency of rocket missiles.
 GRAPHICAL ABSTRACT
 This short review includes the discussion on thermolysis of propellant oxidizers and their composite solid propellants from the few prime lists of literature. This aims to understand the behavior of nanomaterials as a catalyst for the thermal decomposition of propellant oxidizer ammonium perchlorate. Ammonium perchlorate has a polyhedron-like shape that undergoes decomposition upon heating from room temperature to ~420 ℃ with gaseous by-products. In the presence of catalyst, the decomposition occurred at a lower temperature than the pure ammonium perchlorate. Thus, it can be used in the formulation of propulsion systems that mainly improve their burn rate ultimately helpful in rocketry.

Decomposition and combustion of HTPB-based composite propellants containing intercalated HMX crystals with desired high energy but low burn rate

Two types of qy-HMX (insensitive HMX with improved energy density, numbered 1 and 2) have been used and studied as an ingredient of HTPB-based composite propellants (CPs), and the decomposition and combustion performances have been investigated. It has been shown that the main exothermic peak temperature of blank CPs containing 21 wt% of qy-HMX-1 is 258.9 °C, which is 4.7 °C higher than that of HMX-containing one, indicating improved thermostability. The corresponding heat of explosion for blank qy-HMX-2-based CPs was measured to be 5830 J∙g−1, which is 300 J∙g−1 higher than that of HMX-based one. Interestingly, the qy-HMX-2-based CPs has higher energy density than corresponding CL-20-based ones, but it has much lower burn rate under the same pressure, e.g. 4.38 mm∙s−1 at 3 MPa for the former vs. 9.03 mm∙s−1 for the latter. Under the effect of typical conventional catalysts such as nano-CuO and nano-Fe2O3, the qy-HMX-1-based CPs showed increased heat of explosion and higher burn rate. In addition, the particle sizes of condensed combustion products (CCPs) of CPs containing qy-HMX-2 are much smaller than that of HMX-based one, where the Al4C3 was produced as its unique CCPs ingredient.

Reducing the melting point and curing temperature of aromatic cyano-based resins simultaneously through a Brønsted acid-base synergistic strategy

High melting points (Mp) and high curing temperatures are two key processing problems that limit the application of aromatic cyano-based (AC) resins. A Brønsted acid-base synergistic strategy based on an acid-base eutectic and mechanisms for nucleophilic addition and ionization equilibrium are proposed to reduce the Mp and curing temperature of AC resins. Blends of 4,5-dicyanoimidazole (DCI, Brønsted acid) and amine-containing phthalonitriles (4‐(4 or 2 or 3)‐aminophenoxy) phthalonitrile, APNs, Brønsted bases) were selected as model acid-base systems to study the synergistic behaviors in processing. The results show that the Mp and the peak exothermic temperature (Trp) of APN-DCI blends can be reduced by more than 31 °C and 85 °C compared with their intrinsic components, respectively. DSC and XRD show that the decrease in the Mp of the blends is induced by the formation of eutectics. A positive relationship between △pKa and the curing reactivity is confirmed by theory and experimental methods. The cured products show outstanding thermal and mechanical properties compared with reported AC resins. This research provides a new convenient route for regulating the curing behavior of AC resins and will significantly promote the development of high-performance AC resins.

Zinc oxide nanorods effect in micro structural and mechanical characteristics of aluminium composite material

In the present study, aluminium zinc oxide (Al-ZnO) nanorods composites with 3.5 and 5 wt% ZnO in Al were manufactured using powder metallurgy and microwave hybrid sintering. A fairly uniform reinforcement distribution and clear interface was perceived in the micro structural and energy dispersive spectroscopy analysis of composite material. It was observed from XRD analysis that no secondary (intermetallic) phase of Al and ZnO were present in the composite material. The simultaneous thermal analysis of the composites was done to understand the variation in the exothermic peak temperature and weight change percentage of composite material. The developed composite material with 5 wt% ZnO exhibited promising results in terms of micro-hardness (∼2 times), nano hardness (∼3.5 times) and elastic modulus (∼1.9 times) greater value compared to Al. The increased addition of ZnO nanorods in aluminium shows enrichment in properties rendering the material suitable for different engineering applications.

Effect of Al–Mg–Mn Alloy on the Ignition Performance of RDX, HMX and CL-20

Aluminized explosives are known as non-ideal explosives due to their incomplete energy release. In order to improve its energy release, Al–Mg–Mn was used to replace aluminum. In this article, Thermogravimetric (TG) and Differential scanning calorimetry (DSC) techniques were used to study the ignition performance of three explosives (RDX, HMX and CL-20) with different mass fractions (0%, 10 wt.%, 20 wt.%, 30 wt.%) of Al–Mg–Mn alloy powder. The results were compared with those of the formulations with the addition of aluminum. The results suggested that the effect of the addition of Al–Mg–Mn on the extrapolated ignition temperature and exothermic peak temperature of the ignition reaction of aluminized explosives is basically similar to that of Al. However, the addition of Al–Mg–Mn increased the exothermic enthalpy. Explosives with the addition of Al–Mg–Mn alloy powder could release 1.7–17.4% more energy, depending on the mass fraction. On the other hand, unlike aluminum which reacts only during the ignition of CL-20, Al–Mg–Mn was involved in the exothermic reaction of all three explosives. During the exothermic decomposition of explosives, the more active magnesium in Al–Mg–Mn will be oxidized, and magnesium vapor will overflow along the grooves and crevices on the surface of the particles, thus destroying the surface oxidation shell and prompting the active ingredients inside to participate in the reaction.

REMOVED: Catalysis of reduced tin oxide in various epoxy resins

Epoxy resins are the most widely used thermoset materials for various applications, including electronic devices such as semiconductor packaging. In this study, tin (Sn) catalysis in diverse epoxy binary systems containing amine, acid or anhydride was explored by using various differential scanning calorimetry (DSC) techniques and rheological properties. Catalytic effects of Sn were observed in epoxy–anhydride and epoxy–diacid systems but not in epoxy–amine systems. For instance, the incorporation of 1 vol% Sn into the epoxy–succinic anhydride and epoxy–pimelic acid systems reduced the DSC exothermic peak temperature from 295 °C to 202 °C and 243–196 °C, respectively. By contrast, Sn presented no catalytic effect in epoxy–amine systems. Sn catalysis was investigated using isothermal curing temperatures and time. The onset temperature during viscosity measurements for the epoxy–anhydride and epoxy–diacid systems substantially decreased as a function of Sn concentration. These catalytic effects of Sn metal particles (oxidized in air) in the epoxy–anhydride and epoxy–diacid systems can be utilized to accelerate the reactions of epoxy resins and to anticipate the reaction conditions in various applications such as electronic devices involving Sn and epoxy resins. • Sn catalysis was observed in epoxy-anhydride and epoxy-diacid curing systems. • Epoxy-amine curing system did not show the Sn catalytic effect. • Various DSC and rheometry measurement techniques were used. • Latent catalytic effects were also examined.

Study on tri-imidazole derivatives modified with triazine-trione structure as latent curing agents for epoxy resin

In this paper, four novel kinds of triazine-trione based tri-imidazole derivatives (IM-TT, 2MI-TT, 2EI-TT and EMI-TT) were synthesized through the addition reaction between triglycidyl isocyanurate (TGIC) and imidazole (IM), 2-methylimidazole (2MI), 2-ethylimidazole (2EI) and 2-ethyl-4-methylimidazole (EMI), respectively. The triazine-trione based tri-imidazole derivatives were blended with epoxy resin and the reactivity, thermal latency and thermal property were investigated. The results on curing behaviors indicated that the curing exothermic peaks of the blends with triazine-trione based tri-imidazole derivatives shifted to higher temperatures compared with those with commercial imidazoles. The curing exothermic peak temperatures (Tps) of the synthesized tri-imidazole derivatives were increased by 23–32 ℃ compared with the unmodified imidazoles. In addition, Rheological behavior results indicated that the EP blends with tri-imidazole derivatives also exhibited excellent storage stability which was as long as 38 days under room temperature. Last but not the least, the EP blends with triazine-trione based tri-imidazole derivatives also exhibited high glass transition temperatures due to introducing of triazine-trione structures with high crosslinking density. The glass transition temperatures (Tgs) of the prepared thermosets ranged from 128 to 152 ℃. The triazine-trione based tri-imidazole derivatives provide a way to prepare latency epoxy resin with high high glass transition temperature and long storage stability.Article HighlightsFour novel kinds of triazine-trione based tri-imidazole derivatives were synthesized.The EP cured with the tri-imidazole derivatives displayed great thermostability.The EP cured with the tri-imidazole derivatives exhibited long storage stability.

Preparation of Bio‐Based Polybenzoxazine/Pyrogallol/Polyhedral Oligomeric Silsesquioxane Nanocomposites: Low Dielectric Constant and Low Curing Temperature

AbstractIn this work, a bio‐based benzoxazine monomer (C‐s) is synthesized from cardanol, stearylamine, and paraformaldehyde through solvent‐free method. Pyrogallol is used as a curing catalyst for the ring‐opening polymerization of benzoxazine. Differential scanning calorimeter (DSC) results reveal that doping with pyrogallol reduces the exothermic peak temperature (Tp) of C‐s from 256 to 174 °C. The polybenzoxazine/pyrogallol/polyhedral oligomeric silsesquioxane (PC‐s/py/POSS) nanocomposites are prepared via thermal curing. The doping of aminopropyl isobutyl POSS (POSS‐NH2) can reduce the dielectric constant of polybenzoxazine. The dielectric constant of PC‐s/py/POSS is 2.64 at 1 MHz when the doping amount of POSS‐NH2 is 10 wt%. The results of thermogravimetric analysis (TGA) and water absorption test indicate that the PC‐s/py/POSS nanocomposites possess good thermal stability and water resistance. In summary, the PC‐s/py/POSS nanocomposites with low curing temperature and low dielectric constant are expected to be applied to the low dielectric materials for microelectronic applications.

Unique thermal and combustion behaviors of composite propellants containing a high-energy insensitive nitropyrimidine derivative

Owing to the novel insensitive high-energy-density material 2,4,6-triamino-5-nitropyrimidine-1,3-dioxide (ICM-102) has lower sensitivity and higher energy(see in Table S1, Supporting Information), it has great advantages in the application of low-vulnerability propellants. In this paper, the evaluation of ICM-102-containing composite propellants has been carried out, where the decomposition and combustion performances of these propellants have been comprehensively investigated. It has been shown that the main exothermic decomposition peak temperature can be increased from 235 ºC to 350 ºC, when 6 to 10 wt% of ICM-102 was used to replace RDX, but heat release rate was largely increased. Moreover, the burning rate of ICM-102 containing propellants at 3 MPa is in the range of 6.97–7.75 mm•s − 1, depending on its content. The pressure exponent (0.5–3 MPa) is between 0.34–0.44. Compared with the typical propellants with RDX, the burn rate and the flame temperature of ICM-102- containing propellants are higher. In addition, the particle size distributions of condensed combustion products of ICM-102 propellants are narrower and smaller than that of RDX-based one. It also shows that extra products such as aluminum carbide (Al20C) and aluminum oxide nitride (Al5O6N) were produced once ICM-102 was used.

Enhanced decomposition of laminated ammonium perchlorate composite

In order to improve the thermal decomposition performances of ammonium perchlorate (AP), the laminated AP composite was prepared by ice-template induced self-assembly method. In this study, Iron-Konjac glucomannan (Fe3+-KGM) hydrosol rich in AP was selected as the freezing precursor. Through directional freezing of precursor and recrystallization of AP molecules, the laminated AP composite was obtained. The results showed that the thickness of the lamellar composite structure is about 10 to 30 μm, and the recrystallized AP particles are uniformly dispersed in the gel system. The oxygen bomb test results show that the micro-/nano-layered structure can significantly improve the sample’s combustion heat value. Thermal analyses indicated that with the increasing Fe3+ content, the peak exothermic temperature of lamellar AP composite at different heating rates both showed a decreasing trend. With 10 wt% Fe(NO3)3·9H2O added, the decomposition peak temperature decreased from 433.0 to 336.2 °C at a heating rate of 5 °C/min, and the apparent activation energy (Ea) decreased dramatically from 334.1 kJ/mol to 255.4 kJ/mol. A possible catalytic thermal decomposition mechanism of lamellar AP composite catalyzed by Fe3+ was proposed. This work is beneficial to the structural design of other energetic materials.

Tailor made CuO/ZIF-8 hybrid structure as a potential candidate for thermocatalytic degradation of nitrocellulose

CuO/ZIF-8 hybrid structure was obtained by adding the PVP-modified foliaceous CuO microstructures during the preparation of ZIF-8 polygon particles as a promising candidate for promoting the thermolysis process of NC. Thermoanalysis and pyrolysis kinetics based on the DSC and TG/DTG data revealed that the CuO/ZIF-8-NC decomposition had a weightlessness rate of 77.81%, heat release of 2882.5 J⋅g–1, the exothermic peak temperature of 471.25 K, and activation energy of 172.2 ± 16.0 kJ⋅mol–1, indicating that CuO/ZIF-8 has better catalytic activity than CuO and ZIF-8. The reconstructed nth-order kinetic models for NC/catalysis complexes were obtained using a modified fitting algorithm based on the results of isoconversional kinetic analysis, indicating that CuO/ZIF-8, CuO, and ZIF-8 had different catalytic effects on the thermolysis pathways of NC. This study suggests that CuO/ZIF-8 composite may have prospective application as a high potential and unique catalyst for accelerating NC pyrolysis.

Bio‐inspired Synthesis of Energetic Microcapsules Core‐Shell Structured with Improved Thermal Stability and Reduced Sensitivity via In Situ Polymerization for Application Potential in Propellants

AbstractTo further improve the comprehensive performances of conventional nitramine energetic crystals hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX), 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX), and 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (CL‐20), especially their thermal stability and safety properties, is the main pursue in the field of energetic materials. Enlightened by means of the composition of attachment proteins from mussels, this research demonstrates that polydopamine (PDA) self‐polymerization could be used to prepare core‐shell structure energetic composites by surface coating technology. The results reveal that energetic crystal cores are mostly well‐coated by PDA more than 6 h; the combined characteristics of explosives and PDA indicating the main interface interaction force is hydrogen bonding. Moreover, the optimal polymorph of HMX (β) and CL‐20(ε) are maintained in the preparation process. Besides, another interesting phenomenon can be observed that the polycrystalline phase transition of endothermic and the decomposition temperature of exothermic peak for energetic crystals have been increased evidently, benefitting from the heat resisting of PDA layer. Moreover, thermal decomposition has been studied and calculated under different heating rates. Furthermore, the impact sensitivity of the PDA modified composites obtained is tested as well and decreased by 2–4 times compared with pristine energetic crystals. Therefore, this fabrication strategy in this study would provide a potential application of energetic@PDA in high‐strength and high‐energy propellants.

Laboratory Research and Evaluation on Design and Application Performance of High-Performance Cold-Mix Resin.

To improve the safety of orthotropic steel bridge decks and the construction efficiency of bridge deck pavement by enhancing the performance of pavement materials, a new-generation, high-performance cold-mix resin was prepared by carrying out the combination of micro-characteristic analysis and performance test. Meanwhile, the pavement performance and fatigue performance of high-performance cold-mix resin mixtures and hot-mix epoxy saphalt mixtures as a control group were studied experimentally. The results show that different kinds of epoxy resins show bisphenol structure in essence. The curing exothermic peak temperature of the cold-mix resin increases with the heating rate. Both the specific heat capacity (△CP) of cold-mix resin and cold-mix resin asphalts exhibit a sudden change between −20 °C and 40 °C. In resin asphalt mixtures, cold-mix resin forms the network structure skeleton whereas the asphalt distributed in the form of tiny particles. The dosage of respective component has a significant effect on the tensile strength and elongation at break of cold-mix resin. Compared with hot-mix epoxy asphalt mixtures, cold-mix resin mixtures exhibit comparable water stability and high and low-temperature performance, as well as greater fatigue life.

The thermal catalytic effects of CoFe-Layered double hydroxide derivative on the molecular perovskite energetic material (DAP-4)

The application of nano-catalytic materials in molecular perovskite energetic materials is of great significance to promote the development of molecular perovskite energetic materials in explosive formulations and propellants. In this paper, the thermal catalytic effects of CoFe-layered double hydroxide derivative on the molecular perovskite energetic material (DAP-4) were studied. In this study, we successfully prepared a new type of CoFe-based photothermal agent (CoFe-500) by heating CoFe layered double hydroxide nanosheets in an Ar atmosphere at 500 °C. And the micromorphology, structure composition, thermal decomposition performances of CoFe-500 and DAP-4/CoFe-500 composite were characterized. The experimental results showed that with the addition of CoFe-500, the initial decomposition temperature and peak exothermic temperature of DAP-4 showed a decreasing trend. With 10 wt% CoFe-500 added, the initial decomposition temperature and peak exothermic temperature of DAP-4 decreased from 305.6 °C to 166.3 °C and 379.0 °C–322.5 °C, respectively (10 °C/min heating rate). The apparent activation energy (Ea) of pure DAP-4 is 172.27 kJ/mol and 175.13 kJ/mol calculated by the Kissinger and Ozawa method, respectively. And with 10 wt% CoFe-500 added, the Ea is reduced to 119.11 kJ/mol and 122.84 kJ/mol, respectively. The possible thermal catalytic decomposition mechanism of DAP-4/CoFe-500 composites was proposed from the thermal analysis and mass spectrometry test results. This work is meaningful to further understand the decomposition performances of DAP-4 in the presence of nano-layered double hydroxide.

The kinetics of thermal decomposition and hot-stage microscopy of selected energetic cocrystals

The thermal decomposition of four energetic cocrystals composed of 4-amino-3,5-dinitropyrazole (ADNP)/diaminofurazan (DAF), 2,4,6-trinitrotoluene (TNT)/ 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL20), 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX)/CL20, and 1-methyl-3,5-dinitro-1,2,4-triazole (MDNT)/CL20 were studied using simultaneous differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), and hot-stage microscopy. The kinetic parameters of their thermal decomposition reaction were determined using the Kissinger and Ozawa kinetic analysis methods. Each cocrystal’s peak exothermic temperature (decomposition temperature), activation energy, and pre-exponential constant are reported. Furthermore, these parameters from each cocrystal were compared to the same parameters from the corresponding stoichiometric physical mixture in order to identify changes in behavior attributable to the cocrystallization process. For ADNP/DAF, the cocrystal shows an 8% increase in the peak exotherm temperature and a 11-13% decrease in peak activation energy as compared to its physical mixture. For TNT/CL20, this comparison shows a much smaller change in the peak exotherm temperature (

Mechanical, Curing Parameters and Water Absorption of Hybrid Date Palm Leaf-Orange Peel Fibers Reinforced Unsaturated Polyester Composites

In this study, polymer-hybrid natural fibers composites were prepared using unsaturated polyester resin (UPR) as the matrix and a filler using date palm leaf fiber (DPLF) and orange peel fiber (OPF). The effect of DPLF and OPF on mechanical behavior (tensile strength and elongation at break), moisture absorption, UPR gel time (tgel) and peak exothermic temperature (Tpeak) were determined. The composites of UPR reinforced with DPLF and OPF were processed by hand lay-up technique. The UPR weight fraction was maintained at 90%, and DPLF/OPF proportions varied so that the percentage of natural fiber was 10 wt%. Seven (07) composites were prepared (C1, C2, C3, C4, C5, C6 and C7) with different DPLF:OPF ratios (0:0, 1:0, 0.75:0.25, 0.5:0.5, 0.33:0.67, 0.25:0.75, 0:1) respectively in order to screen the possible interactions. DPLF were surface modified using 6% Alkali treatment, OPF were used without surface modification. Unlike DPLF, OPF showed considerable increase of UPR tgel and Tpeak which act as natural inhibitor. Tensile strength and fracture strength were also impacted negatively and positively depending on the different fiber proportions. Absorption tests showed a decrease in the composites hydrophobicity which increases significantly with higher DPLF proportions.

Synthesis of 3D Porous Network Nanostructure of Nitrated Bacterial Cellulose Gel with Eminent Heat‐Release, Thermal Decomposition Behaviour and Mechanism

AbstractIn this study, a novel three‐dimensional (3D) porous cross‐link network structure of nitrated bacterial cellulose (NBC) nano‐gel, as an energetic gel matrix for fabrication of nanocomposite energetic materials, (nEMs) was synthesized by sol‐gel synthetic and the freeze‐drying technology. The analysis results revealed that the unique network structure with abundant of nano‐porous, which made the thermal behaviour of the NBC gel different from that of raw NBC. The thermal decomposition kinetic and mechanism of the NBC gel indicated that the exothermic peak temperature of the gel matrix decreased at low concentration, and the activation energy (Ea) of the gel0.5 (150000 J ⋅ mol−1) was much lower than that of raw NBC (223510 J ⋅ mol−1). However, the decomposition kinetic parameters of this study were not enough to illustrate the thermal properties, and which needs more effort to study them and complete. Furthermore, the initial reaction of gel decomposition was the splitting of urethane bond, and then the scission of −O−NO2 bonds happened, and the macromolecular chains’ breakage site of gel first occurred at −C−O−C− in the ring. After then, the chains of NBC break at −C−O−C− between the rings; notably, the heat‐release of gel was several times than that of raw NBC, which was liberated during the process of thermal decomposition. This promising research may provide potential application in preparing binder‐based nEMs and the basic theory of thermo‐analysis used in propellants and explosives.

Evolution of polyacrylonitrile precursor fibers and the effect of stretch profile in wet spinning

AbstractWet spinning of polyacrylonitrile‐based polymers is a common technique to manufacture carbon fiber precursors. Understanding the role of stretch profile on structural evolution will support efforts to reduce cost and improve process robustness. Fiber stretch generally occurs in three sequential stages: jet stretch, wet stretch (first draw), and hot draw (second draw). In this study, total fiber stretch was kept constant, but distributed differently across the stretch stages yielding three different fiber variants. Samples were collected and analyzed after each stretch stage in order to correlate process parameters to structural information. For all variants, orientation of the ordered phase increases gradually for each stage of stretch while activation energy for the structural relaxation decreases. Alternatively, crystallite size increases substantially during hot draw, which is shown to have the most pronounced effect on cyclization behavior. Given the process conditions, the variant with the lowest jet stretch and highest hot draw demonstrates the highest tenacity and modulus along with the greatest orientation, crystallite size, and highest peak exotherm temperature.

Effects of Water-to-Cement Ratios on the Properties of Magnesium Potassium Phosphate Cement Prepared with Lithium-Extracted Magnesium Residue

Salt lake magnesium phosphate cement (SLMKPC) was prepared by mixing potassium dihydrogen phosphate (KH2PO4) with lithium-extracted magnesium residue (MR). The hydration-hardening process and the variation in the phase composition and microstructure of hydration products with the change of the water-cement-ratio (W/C) were studied by measuring the setting time, hydration exothermic temperature, and compressive strength of the hardened slurry. It was found that W/C ratios had significant effects on the setting time, hydration exothermal temperature curve, and compressive strength of SLMKPC. With the increase of W/C, the setting time was prolonged significantly. The exothermic hydration peak temperature first increased and then decreased, and the number of exothermic peaks gradually changed from one to two. The optimal compressive strength was obtained when W/C = 0.2–0.3. Hydration products changed significantly with the increase of W/C, the MgKPO4·6H2O (MKP) in the matrix was more stable when W/C = 0.2 and 0.3 than when W/C = 0.25, 0.35, and 0.4. When W/C = 0.3, SLMKPC had a compact structure with a certain operating space and better mechanical properties.