Polyimide Resin Research Articles

Nanoporous and IPN structural composite material of cyanate ester modified by hollow silica and polyimide

Cyanate ester resin (CE), a high-performance and low dielectric materials, was modified with amino hollow silica (HSMs-NH2) and polyimide resin (PI) to form an IPN structure. Reducing the crosslinking density of the composite system and accompanying with its steric hindrance effect, PI increased the free volume of the composite material. The hollow structure introduced by HSMs-NH2 further enhanced a low dielectric property. IPN structure and HSMs-NH2 also significantly improved the impact toughness of HSMs-NH2/PI/CE composites. The bonding between the Si–O–Si and HSMs-NH2 offered an excellent heat resistance and as well surface bonding capability to matrix, which reduced the decomposition and effectively improved their thermal stability. Simultaneously, profited by the hydrophobicity of Si–O–Si, HSMs-NH2/PI/CE composite materials enabled to keep low dielectric properties in humid environments.

Fabrication and electrical properties of flexible polymer-based MIM capacitors of high-k nanolaminate dielectrics of HfO2–SnO2–TiO2 with ultrathin Al2O3 insertion layer by plasma-enhanced atomic layer deposition

Abstract Flexible metal–insulator–metal (MIM) capacitors of high-k nanolaminate HfO2–SnO2–TiO2 thin films were fabricated on several polymer substrates of polyethylene terephthalate, polyimide and epoxy resin at 80 °C by plasma-enhanced atomic layer deposition. The electrical properties were optimized by adjusting the sub-cycle ratio of Hf: Sn: Ti to 6: 5: 4. In order to reduce the leakage current density of flexible capacitors, the ultrathin Al2O3 layer varying from 0.5 to 1.5 nm was inserted to form Al2O3/HfO2–SnO2–TiO2/Al2O3 stacking capacitors. The effect of the Al2O3 insertion layer thickness and the super-cycle number of HfO2–SnO2–TiO2 on the capacitance density, leakage, and quadratic voltage linearity was investigated. Under optimal processing, flexible MIM capacitors could stand 40 000 bending cycles at curvature radius of 8.2 mm, indicative of better electrical stability. Moreover, compared with the polymer-based HfO2–SnO2–TiO2 capacitors, the introduction of 1 nm Al2O3 ultrathin layer greatly decreases the leakage current density by 4 orders of magnitude (10−8 A cm−2) with relative lower voltage linearity (350–540 ppm V−2), but the capacitance density also declines (∼3 fF μm−2) simultaneously. Despite this, the method of inserting Al2O3 ultra-thin layer is still an effective method to improve the electrical performances of polymer-based HfO2–SnO2–TiO2 nanolaminate capacitors for flexible electronics.

Direct Writing of graphene/graphitic foam through picosecond pulsed laser-induced transformation of soluble polyimide suspension

We report the direct writing of graphene/graphitic foam with high electrical conductivity using laser-induced-transformation of polyimide (PI) resin films on glass surfaces. Raman spectroscopy of the treated surfaces indicated that average laser power irradiation between 900 and 1500 kW/cm2 transformed the PI film into a few layered graphene-dominated film, and the increase in irradiation power above 1500 kW/cm2 led to the formation of graphitic (multilayered graphene) material. The electrical conductivity of the transformed film was between 5800±750 S m-1 (lower power irradiation) and 1250±300 S m-1 (higher laser power irradiation). SEM imaging showed that the transformed material has a closed cell foam morphology enclosed between the smooth top and bottom layers. The results indicate that heat treatment of the polyimide suspension films, and subsequent ultra-short, pulsed laser irradiation resulted in a closed-cell graphene/graphitic foam with high electrical conductivity. The pore aspect ratio, density, and film conductivity are used to estimate the conductivity of the solid phases in the laser-treated films at different powers. Laser-induced transformation of the PI suspension into graphene/graphitic foam is conducive to additive manufacturing and may enable the direct printing of graphitic foam-based three-dimensional components.

Ultrahigh absorption dominant EMI shielding polyimide composites with enhanced piezoelectric property

Piezoelectric sensors have been widely used in wearable electronic devices with improved integration, which is prone to cause electromagnetic interference (EMI) pollution and affects its operation stability. How to design the materials with integrated piezoelectric sensing and EMI shielding performance is of great significance. In this paper, the Fe3O4@PPy/PINF (FPN) composite film was prepared by depositing pyrrole (Py) on the surface of Fe3O4 nanoparticles and combining it with polyimide (PI) nanofibrous membrane via vacuum-assisted suction filtration. In addition, after encapsulation with a highly soluble fluorine-containing polyimide (FPI) resin, a structurally stable FPI-Fe3O4@PPy/PINF (PFPN) composite film was obtained. The prepared PFPN composites show excellent EMI shielding effectiveness (44.58 dB) through the secondary reflection and multiple absorption effects. Remarkably, the value of the absorption coefficient A can reach 0.74, showing outstanding absorption characteristics. In addition, PFPN composite film also shows unexpected piezoelectric properties with high sensitivity of S = 0.8, short response (25 ms) and recovery (45 ms) time. Its piezoelectric output can reach 4.2 V with stable cyclic output property (>15000 times). This kind of composite film with ultra-low reflection characteristics and favorable piezoelectricity presents a wide range of potential applications in the self-powered wearable electronic fields.

Thermal protective and hydrophobic coating on polyimide resin matrix composites surface for improved aging resistance

AbstractPolyimide composites are easily degraded in high temperature and high humidity environments for long service, which reduces their reliability and stability in aerospace, electronic components, weapons, and other fields. In this paper, the inorganic and organic multiphase double‐layer coating was prepared. The insulating layer was made of vinyl polysilazane resin as the base material and hollow glass microspheres as the filler. The hydrophobic layer consisted of polydimethylsiloxane as the base material, hollow phenolic microspheres, and nano‐TiO2 as the filler. The heat resistance, hydrophobic properties, and aging resistance of the coated polyimide resin matrix composites were studied. The results showed that the thickness of the double‐layer coating was about 200 μm. Under the 200°C thermal insulation test, the maximum temperature drop can be achieved at 59.7°C. After adding 5 wt% TiO2, the static contact angle of composites was increased from 86.2° to 127.7°. Significantly, the hydrophobic performance was improved by 48.1%, which was due to the construction of micro‐nano structures in the surface layer coating. In the accelerated hydrothermal aging tests, the bending properties of coated composite materials can be improved by 8.5%, 3.2%, and 8.7% in water, alkali, and acid environments, respectively. The moisture absorption of glass fiber and the pyrolysis of polyimide led to the degradation of the mechanical properties. The existence of heat‐resistant and hydrophobic coating could effectively eliminate this adverse effect, which was of great significance for polyimide composites to cope with various service environments.Highlights A novel coating consisting of thermal insulating and hydrophobic layers was developed on glass fiber reinforced polyimide composites (G/PI) composites. The maximum temperature drop of coating can be achieved at 59.7°C. The static contact angle of coated G/PI composites was increased from 86.2° to 127.7°. In the aging tests, the protective effect of the coating resulted in improved mechanical strengths of G/PI composites. The microscopic damage morphology was performed to analyze the anti‐aging properties of the coating.

Design of novel silicon-containing alkynyl diamines and their related thermosetting polyimide resins

In order to improve the PI resin’s processability and thermal properties, a novel diamine monomer bis(p-aminophenylethynyl)dimethylsilane was designed and synthesized by introducing silicon and alkyne groups in this paper. And a new thermosetting polyimide resin SiOPI with silicon and alkynyl structures in the main chain was prepared using 4,4′-oxobis (phthalic anhydride) (ODPA) as the dianhydride monomer with this diamine monomer. The structures of the diamine monomer and the polyimide were characterized by H nuclear magnetic resonance spectroscopy (1H NMR), Fourier transform infrared spectroscopy (FT-IR), mass spectrometry (MS), and X-ray diffraction (XRD), respectively. The incorporation of silyl groups into the PI increases the flexibility of the resin and provides good solubility and processability. The SiOPI is well soluble in DMF, DMSO and THF. The resin has a viscosity of less than 200 Pa·s at 50–88°C and has a wide processability range. By virtue of the introduction of alkyne groups, the cured polyimide forms dense reticulated structures, analogous to the benzene ring, giving the resin excellent heat resistance and mechanical property. The glass transition temperature (Tg) of SiOPI reached 367°C, and the heat loss temperature at 5% (Td5) is 540.9°C, the heat loss temperature at 10% (Td10) is 592.2°C, and the residual carbon rate at 800°C (R800°C) is 65.76% in a nitrogen atmosphere. The tensile strength of c-SiOPI is 257.6 MPa at room temperature and 232.9 MPa with a retention rate of 90.41% at 300°C, respectively.

5‐aminobenzimidazole@graphene oxide nanosheets doped polyimide nanocomposites: Low‐temperature curing and improved mechanical properties

AbstractThe preparation of polyimide matrix composites with low curing temperature and high mechanical properties is of great importance. In this study, a low‐cost and multi‐functional nanofiller, 5‐aminobenzimidazole grafted graphene oxide (5‐ABZ@GO) has been designed. By nucleophilic attack on 5‐aminobenzimidazole basic groups and doping of GO, the above requirements of polyimide composites were skillfully realized. The results show that when the addition of 5‐ABZ@GO is 1%, the 5‐ABZ@GO/PI nanocomposites can achieve complete imidized at 200°C. Moreover, the nanocomposite prepared by imidization at 200°C has good mechanical and thermal properties (tensile strength is 141.64 MPa, modulus is 6.05 GPa, T5% is as high as 543.5°C), which is better than the PI composites prepared at 320°C. This study provides an innovative approach to preparing polyimide composites that meet mechanical performance requirements while utilizing comparatively lower curing temperatures, low curing temperature polyimide resins provide a new path for integrated composites with structure–function integration.

Relationship between Tg of Polyimide Resin and Resist Sensitivity in Three-Component Chemically Amplified Polyimide Resist

Relationship between Tg of Polyimide Resin and Resist Sensitivity in Three-Component Chemically Amplified Polyimide Resist

A Water-Soluble Thermoplastic Polyamide Acid Sizing Agents for Enhancing Interfacial Properties of Carbon Fibre Reinforced Polyimide Composites.

Carbon-fiber-reinforced polyimide (PI) resin composites have gained significant attention in the field of continuous-fiber-reinforced polymers, in which the interfacial bonding between carbon fiber and matrix resin has been an important research direction. This study designed and prepared a water-soluble thermoplastic polyamide acid sizing agent to improve the wettability of carbon fiber, enhance the van der Waals forces between carbon fiber and resin and strengthen the chemical bonding between the sizing agent and the alkyne-capped polyimide resin by introducing alkyne-containing functional groups into the sizing agent. This study found that the addition of a sizing layer effectively bridged the large modulus difference between the fiber and resin regions, resulting in the formation of an interfacial layer approximately 85 nm thick. This layer facilitated the transfer of stress from the matrix to the reinforced carbon fiber, leading to a significant improvement in the interfacial properties of the composites. Adjusting the concentration of the sizing agent showed that composites treated with 3% had the best interfacial properties. The interfacial shear strength increased from 82.08 MPa to 108.62 MPa (32.33%) compared to unsized carbon fiber. This research is significant for developing sizing agents suitable for carbon-fiber-reinforced polyimide composites.

Cure Kinetics and Thermal Decomposition Behavior of Novel Phenylacetylene-Capped Polyimide Resins.

Based on a novel phenylacetylene capped polyimide (PI) with unique high-temperature resistance, its curing kinetics and thermal decomposition behavior were investigated. The curing mechanism and kinetics were studied by differential scanning calorimetry (DSC), and the activation energy (Ea) and pre-exponential factor (A) of the curing reaction were calculated based on the Kissinger equation, Ozawa equation, and Crane equation. According to the curve of conversion rate changing with temperature, the relationship between the dynamic reaction Ea and conversion rate (α) was calculated by the Friedman equation, Starink equation, and Ozawa-Flynn-Wall (O-F-W) equation, and the reaction Ea in different stages was compared with the results of molecular dynamics. Thermogravimetric analysis (TGA) and a scanning electron microscope (SEM) were used to analyze the thermal decomposition behavior of PI resins before and after curing. Temperatures at 5% and 20% mass loss (T5%, T20%), peak decomposition temperature (Tmax), residual carbon rate (RW), and integral process decomposition temperature (IPDT) were used to compare the thermal stability of PI resins and cured PI resins. The results display that the cured PI has excellent thermal stability. The Ea of the thermal decomposition reaction was calculated by the Coats-Redfern method, and the thermal decomposition behavior was analyzed. The thermal decomposition reaction of PI resins at different temperatures was simulated by molecular dynamics, the initial thermal decomposition reaction was studied, and the pyrolysis mechanism was analyzed more comprehensively and intuitively.

Synthesis and properties of thermoplastic polyetherimide resins modified by 1,4-bis(2,3-dicarboxyphenoxy)-2-tert-butylbenzene dianhydride (3,3′-TBHQDA)

In order to prepare thermoplastic polyimide (PI) resins with good comprehensive performances, the modification of thermoplastic polyetherimides (PEIs) by 1,4-bis(2,3-dicarboxyphenoxy)-2-tert-butylbenzene dianhydride (3,3′-TBHQDA) was systematically investigated. The PEI-a-x and PEI-b-x series of polyetherimides were synthesized by chemical imidization of the diamine monomer m-phenylenediamine (m-PDA) with different contents of 1,4-bis(3,4-dicarboxyphenoxy)-2-tert-butylbenzene dianhydride (4,4′-TBHQDA) and 3,3′-TBHQDA or 4,4′-(4,4′-isopropylidenediphenoxy) bis(phthalic anhydride) (4,4′-BPADA) and 3,3′-TBHQDA. These PEIs had glass transition temperatures (Tgs) in the range of 217–264 °C, low melt viscosities of 79–2367 Pa s, good transmittances of 87–88 % at 450 nm, and displayed good mechanical properties with tensile modulus of 2.8–3.2 GPa, tensile strengths of 89.6–118.4 MPa, and elongations at break of 3.9–6.4 %. The introduction of 3,3′-TBHQDA successfully improved thermal properties and melt processability of the PEIs. Among them, PEI-a-50 and PEI-b-50 displayed better comprehensive performances in PEI-a-x and PEI-b-x series, respectively, with moderate Tgs (256 and 249 °C, respectively), extremely low melt viscosities (161 and 297 Pa s at 400 °C, respectively), high transmittances at 450 nm (87 %), and good mechanical properties (tensile modulus of 3.1 and 2.8 GPa, tensile strengths of 105.6 and 106.3 MPa, respectively).

Enhancing the bond strength of magnetron-sputtered copper layers on polyimide and polyether ether ketone surfaces through surface modification

This study explores the fabrication of composites involving polyimide (PI) and polyether ether ketone (PEEK) resins with Cu using chemical treatment and sandblasting, followed by plasma cleaning in a vacuum environment charged with Ar. To enhance the bonding strength of Cu to PI and PEEK, vacuum magnetron sputtering was used to deposit an intermediate transition layer of titanium and a plated seed layer of Cu onto the resin. For PI/copper composites, the copper layer’s highest bonding strength was achieved through sandblasting and plasma cleaning for 150 s at a bias voltage of 100 V. For PEEK/Cu composites, the optimal bonding strength of the copper layer was observed after 80 s of plasma cleaning. Surface roughness is important in the bonding strength of the copper layer. Additionally, the Ti transition layer strengthens bonding forces between Cu and both PI and PEEK. X-ray photoelectron spectroscopy revealed Ti–O bond formation with oxygen in the resins and Ti–C bonds within the carbon, indicating chemical interactions that bolstered Cu adhesion to resins. Adjusting the bias voltage had varying effects on the bonding strength of resin/Cu. For PI/Cu, the bonding force decreased with increasing bias voltage (20–150 V) owing to excessive bias voltage causing surface defects on the plated Cu layer, which reduced the density of the plated Cu layer. Conversely, the PEEK/Cu bonding force initially increased with increasing bias voltage due to enhanced surface bombardment. Beyond an optimal point, the bonding force in PEEK/Cu decreased due to unfavorable effects on layer density.

Enhancing UV Stability of Perovskite Solar Cells with Transparent Fluorinated Polyimide

Ultraviolet (UV)-induced degradation is one of the major problems in the field of perovskite solar cells (PSCs). Therefore, exploring materials and techniques to prevent UV light from penetrating into the device is urgently necessary. Here, we developed a special transparent fluorinated polyimide (FPI) resin, which can be directly spin-coated on the front side of conventional indium-doped tin oxide substrates (glass/ITO). Most aromatic polyimides strongly absorb visible light and are colored. The FPI we designed and synthesized bears electron-acceptor CF 3 - groups, which reduces the intra-/intermolecular charge-transfer (CT) effect, enabling FPI to possess high transmittance in the visible range while completely blocking UV light. As a result, the FPI coating slightly pulls down the initial power conversion efficiency (PCE) (21.02% to 20.19%). Remarkably, the coating significantly improves the PSC UV stability. Upon an 8-h enhanced UV aging test in air, the FPI/glass/ITO-based PSC is able to retain 85.0% of its initial PCE. In contrast, the control device (glass/ITO-based PSC) only keeps 40.9% of its initial PCE. The protective effect of FPI is even more prominent in current popular 3D/2D high-performance PSCs because UV light can seriously damage the 2D layer. The unencapsulated 3D/2D device based on FPI/glass/ITO substrate has a very high PCE retention of up to 80% after 12-h enhanced UV aging test in air, comparing to 36% for the control 3D/2D device without FPI. This work demonstrates that FPI and its possible derivatives could provide a feasible avenue to handle UV-induced degradation for PSCs effectively.

Effect of plasma treatment on high temperature interfacial properties of Chinese-made T800 CFRP

ABSTRACT The surface of Chinese-manufactured T800 carbon fiber (CF) underwent air ICP plasma treatment to enhance its interfacial bonding with polyimide resin at high temperatures. This treatment significantly improved the high-temperature interlaminar shear strength (ILSS) of the CF/PI composite. Optimal treatment, achieved at a power of 200W, resulted in an ILSS retention rate of 67.34% at 300°C and maintained ILSS at 66.46MPa at 350°C. At this power level, the CF surface developed protrusions, increasing its roughness to 155.70 nm and its oxygen content to 18.32%. Additionally, the ratio of polar to nonpolar groups increased to 0.98, and the ID/IG value rose to 2.781. These changes were important reasons for enhancing the high-temperature ILSS of CF/PI composite.

The cooperatively crosslinking between GO-COOH/TiO2 @PAO microcapsules and polyimide to improve the mechanical and tribological properties of PEEK/PI composites

The PEEK fabric-reinforced polyimide resin containing microcapsules with excellent mechanical and lubrication properties is reported. The GO-COOH/TiO2 @PAO double-wall microcapsules (Capsule) were prepared by interfacial condensation polymerization of titanium butoxide (TBT) and self-assembly between GO-COOH and TiO2 shell. A double crosslink of chemical bond (amide or ester) and hydrogen bond were constructed between microcapsules and polyimide (PI) to improve the mechanical properties of PEEK fabric-reinforced polyimide resin (PEEK/PI). It was identified that the addition of Capsules induced a 12.98% decrease in friction coefficient and 56.85% in the wear rate of the composites. This superior frictional behavior was primarily attributed to the combined effect of the boundary lubrication of PAO6, load-bearing effect of TiO2 and PEEK fabric, and friction-reducing of GO-COOH.

Upcycling Waste Thermosetting Polyimide Resins into High-Performance and Sustainable Low-Temperature-Resistance Adhesives.

Thermosetting polyimide (PI) has attracted extensive attention for its excellent properties, but the approaches to its end-of-life management are not sustainable, posing great threat to the ecosystem. Herein, this work proposes a mild, sustainable, and full recovery path for recycling waste carbon fiber reinforced phenylethynyl end-capped PI resin composites. In addition to recycling reaction reagent and woven carbon fiber, degraded products (DPETI) can be fully and directly used as high-performance and sustainable adhesives. DPETI exhibits strong adhesion to various surfaces, with a maximum adhesion strength of 1.84MPa. Due to the strong supramolecular polymerization behavior without solvent dependence, DPETI demonstrates higher adhesive strength of 2.22MPa in the extreme environment (-196 °C), which is maintained even after 10 cycles. This work sparks a new thinking for plastic wastes recycling that is to convert unrecyclable wastes into new and sustainable materials, which has the potential to establish new links within circular economies and influence the development of materials science.

Ultrasonic Attenuation of Carbon-Fiber Reinforced Composites

Ultrasonic attenuation measurements were conducted on cross-ply and quasi-isotropic lay-ups of eight types of carbon-fiber reinforced composites (CFRPs) using through-transmission methods with diffraction correction. Attenuation values were substantially higher than those of unidirectional composites and other structural materials. Wave modes, fiber distributions, matrix resins, and consolidation methods affected total attenuation. Transverse mode, quasi-isotropic lay-up, and polyimide and thermoplastic resins generally produced higher attenuation. No clear trends from the fiber distribution were revealed, indicating that it is not feasible presently to predict the attenuation of various lay-ups from the unidirectional values. That is, direct attenuation tests for different laminate lay-ups are needed. This work expanded the existing attenuation database by properly determining the attenuation coefficients of two additional layup types of CFRP laminates. Results showed the merit of ultrasonic attenuation measurements for quality control and structural health monitoring applications. A crucial benefit of the through-transmission methods is that they enable the prediction of Lamb wave attenuation in combination with software like Disperse (ver. 2.0.20a, Imperial College, London, UK, 2013).

GREEN CHEMISTRY FOR PROTECTION OF HIGH TEMPERATURE (> 250°C) ELECTRONICS

A new modified “green” thermoset resin was developed and evaluated as an alternative encapsulation packaging material in comparison to traditional higher temperature resistant resins such as epoxies, silicones, cyanate esters and polyimide resins. Where epoxies and silicones have shown to provide good reliability for applications up to 150 – 200°C, high temperature applications, often required other chemistries, such as cyanate ester or polyimides. However, cyanate ester and/or polyimide based resins have recently been affected by new European environmental legislation making their usability, and especially environmental and health acceptance, not viable for the medium and long term. In combination to these environmental concerns, the current significant growth of the market for high power and high temperature electronics, also in more “consumer-type” applications, imply the need for “green” chemistry, capable to respond to high temperature (> 250°C) requirements. This paper will describe new materials, based on hybrid chemistry, in line with current European chemical (SVHC-compliant) regulations, responding to the current and future harsh environment requirements. DSC analysis was done to demonstrate the newly developed green chemistry provides Tg values well over 250°C. The combination of a hybrid chemistry with optimized adhesion properties, high Tg and low coefficient of thermal expansion seem to provide mechanical features which can address the problem of mechanical fatigue of traditional epoxy solutions, which did historically not provide the solutions which often, non-environmental friendly solutions, based on poly-imides or cyanate esters could offer.

Nanocone-shaped Ni-electroplated carbon fiber composite films for electromagnetic shielding applications

This study developed a series of lightweight composite films with adjustable reflectivity and superior mechanical properties. Carbon fiber (CF) was electroplated with both conventional and nanocone-shaped Ni coatings to create Ni-plated carbon fiber (CF@Ni), which was then further classified into conventional Ni carbon fiber (CF@CN) and nanocone-shaped Ni carbon fiber (CF@NN). CF@Ni fibers were sheared and filtered to produce Ni-plated carbon fiber fabric (CFF@Ni), which was then encapsulated in polyimide resin (PI) to form the final thin film materials (CF@Ni/PI). The shielding performance and mechanical properties of these CF@Ni/PI thin films have been comprehensively investigated. The study found that the nanocone-shaped Ni-plated samples exhibited superior performance. Absorption loss was dominant when a relatively low amount of Ni-plated carbon fiber was added, while reflection loss dominated when a relatively high amount was added. Adding 0.3 g of nanocone-shaped Ni carbon fiber created a 1.2 mm thin film with a shielding effectiveness of 71 dB and a tensile strength of 22.4 MPa. Additionally, the thin film demonstrated excellent flexibility and durability. Due to its exceptional mechanical properties and flexibility, this composite film holds significant potential in the fields of microelectronics and intelligent electronic devices.

A Study on a New Type of High-Performance Resin-Coated Sand for Petroleum Fracturing Proppants

This study investigates a new type of high-performance coated sand as a petroleum fracturing proppant material. Modified quartz sand was coated with a layer of low-density resin to reduce the overall density of the proppant, thereby improving the suspension of the proppant in the fracturing fluid. Resins play an important role in the preparation of coated sand fracturing proppants. The mechanism of sand formation was studied by examining the phase composition and microstructure of the coated sand proppant. The results demonstrate that when the polyimide resin content is 6% and the curing temperature is 180 °C, the proppant exhibited the best performance with an apparent density of 1.592 g/cm3 and a breakage ratio of only 3.22% under 55.2 MPa. Compared with the widely used epoxy resin-coated support agent and phenolic resin-coated support agent in the early stage, their crushing rate decreased by 5% and their acid solubility decreased by 2%. Hence, this study is worthy of attention.