硅酸盐学报

氢氧化钠对钙矾石的合成及在高温环境下转变的影响

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张响 ¹^,² , 卢晓磊 ¹^,² , 宋建国 ¹^,² , 贾坚 ¹^,² , 杨庆春 ¹^,² , 杜鹏 ¹^,² , 程新 ¹^,²

硅酸盐学报 | 研究论文 2025,53(2): 428-436

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硅酸盐学报 |研究论文 2025 , 53 (2) : 428 -436

氢氧化钠对钙矾石的合成及在高温环境下转变的影响

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张响¹^,², 卢晓磊¹^,², 宋建国¹^,², 贾坚¹^,², 杨庆春¹^,², 杜鹏¹^,², 程新¹^,²

作者信息

^1．山东省建筑材料制备与测试技术重点实验室，济南大学，济南 250022

^2．济南大学材科科学与工程学院，济南 250022

通讯作者:

卢晓磊（1986—），男，博士，副教授。

程新（1963—），男，博士，教授。

作者简介:

张响（2000—），男，硕士研究生。

Effect of NaOH on Synthesis and Transformation of Ettringite Under High Temperature Environment

Xiang ZHANG¹^,², Xiaolei LU¹^,², Jianguo SONG¹^,², Jian JIA¹^,², Qingchun YANG¹^,², Peng DU¹^,², Xin CHENG¹^,²

Affiliations

^1.Shandong Provincial Key Laboratory of Preparation and Measurement of Building Materials, University of Jinan, Jinan 250022, China

^2.School of Material Science and Engineering, University of Jinan, Jinan 250022, China

Corresponding Author:

LU Xiaolei (1986-), male, Ph.D., Associate Professor. E-mail: mse_luxl@ujn.edu.cn;

CHENG Xin (1963-), male, Ph.D., Professor. chengxin@ujn.edu.cn

ZHANG Xiang (2000-), male, Master candidate. E-mail: 1045364170@qq.com

出版时间: 2025-02-20 doi: 10.14062/j.issn.0454-5648.20240015

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摘要

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碱对钙矾石合成及其向单硫型水化硫铝酸钙（AFm）转变具有重要影响。为了探究氢氧化钠（NaOH）对合成钙矾石及其转变的影响规律，通过在溶液法合成钙矾石中添加少量NaOH，详细讨论了高温环境下钙矾石向AFm演变过程。结果表明：添加NaOH的钙矾石样品较纯杂质较少，其形貌由长直粗棒状变为弯曲针棒状，晶胞参数减小，且Na⁺易取代钙矾石中部分Ca²⁺格位。此外高温环境下NaOH显著促进了钙矾石向AFm转变，其转变过程可分为3个阶段。首先大部分钙矾石直接转变为AFm相；随后液相中Na⁺与SO₄^2-同AFm反应生成中间相U-phase，同时液相中的Ca²⁺和SO₄^2-再次与AFm反应形成钙矾石，随后钙矾石又开始转变为中间相U-phase；最终由U-phase全部转变成稳定的AFm。

关键词

氢氧化钠 / 高温 / 钙矾石 / 单硫型水化硫铝酸钙 / 转化

Abstract

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Introduction

Ettringite plays an important role in the early strength and volume stability of cement. In a high-concentration sodium sulfate solution, Na⁺ and SO₄^2- will be embedded between the structural layers of AFm to form a sodium-substituted AFm phase(U-phase). Therefore, the stability of ettringite and AFm under high temperatures and alkaline environments requires attention. Ettringite will not only transform into AFm but also form U-phase in a high-temperature and alkaline environment. However, the specific process of the mutual transformation of ettringite and AFm under the combined action of high temperature and alkalinity is still unclear. The phase transition of hydration products is bound to affect the performance of cement-based materials in high-temperature and high-alkalinity environments. Therefore, it is important and necessary to clarify the transformation process of Ettringite to AFm. Based on this, ettringite was first synthesized by adding a small amount of NaOH to the solution system, and the effect of NaOH on the synthesis and transformation of ettringite was explored, especially the effect on the evolution of the above-mentioned synthesized ettringite to AFm in an environment of 105 ℃. A detailed discussion was conducted, which provided new understanding of the stability of ettringite in high-alkali and high-temperature environments and also provided theoretical support for the performance degradation of cement-based materials under such conditions.

Methods

The raw materials Ca(OH)₂ and Al₂(SO₄)₃·18H₂O were used to synthesize the ettringite sample by solution method, and the alkaline environment was adjusted by NaOH. Samples were taken at high temperature at designed time intervals to explore the transformation process of ettringite and washed with deionized water and anhydrous ethanol in turn, dried in a vacuum drying oven at 40 ℃, and ground into powder. The phase composition of all samples was tested by the D8 ADVANCE X-ray diffractometer, and the structure of the samples was analyzed by TOPAS V6 software. ZEISS Gemini 360 FE-SEMs was used to observe the microscopic morphology of the samples. The thermal stability of the samples was tested by a NETZSCH STA449F3 synchronous thermal analyzer. Based on density functional theory (DFT), the Castep module in Materials Studio was used to optimize the crystal structure and calculate the electronic structure properties.

Results and discussion

The addition of NaOH is beneficial to the formation of ettringite and has an inhibitory effect on the formation of dihydrate gypsum. Under certain alkalinity conditions, the formation of ettringite is favorable. With the increase of NaOH addition, the short rod-shaped ettringite decreases and tends to be fine needle-shaped, with a certain curvature parallel to the c-axis. The increase in OH^- ion concentration causes [Al(OH)₆]³ to form rapidly, resulting in an accelerated nucleation rate of ettringite and a smaller crystal size. In addition, the addition of NaOH reduces the crystal cell parameter c and the crystal cell volume of ettringite. The defect formation energy of Na⁺ replacing Ca1, Ca2, Al1 and Al2 sites in the ettringite crystal structure is Na@Al1>Na@Al2>Na@Ca1>Na@Ca2 from large to small, it can be concluded that Na@Ca2 is the most stable crystal configuration, which indicates that Na⁺ is more inclined to replace the Ca2 site. Compared with the N-0 sample without NaOH added, the decomposition temperature of the small-sized ettringite synthesized in the NaOH environment is lower, and the stability of the sample is relatively weak.

NaOH has a particularly significant effect on the transformation of ettringite to AFm. The intermediate phase U phase exists in the transformation of ettringite to AFm. The rod-shaped ettringite first split to varying degrees at both ends to form a flaky AFm phase. In addition, there are a small number of small needle-shaped rod-shaped ettringite crystals attached to the surface of AFm and transform from AFm into a thicker hexagonal flaky U phase., and finally form a stable AFm phase. Na⁺ and SO₄^2- are co-embedded between the layers of the AFm structure, resulting in a larger interlayer spacing of U-phase compared to AFm.

Conclusions

The ettringite samples synthesized by adding a small amount of NaOH at room temperature have fewer impurities than pure ones, the unit cell parameters are reduced, and Na ions easily replace some Ca2 sites in ettringite. With the increase in NaOH addition, the morphology of the synthesized ettringite changes from thick rods to curved needle rods, and the thermal stability of the ettringite decreases. The ettringite synthesized by adding a small amount of NaOH has an intermediate phase U-phase during the transformation to AFm under a high temperature environment, and all of them are transformed into the AFm phase after being kept at a high temperature of 105 ℃ for 24 h; however, the ettringite samples without NaOH almost do not undergo transformation. The transformation process of ettringite to AFm under NaOH and a high-temperature environment can be divided into three stages. Stage 1 (within 3 h): In this stage, most of the calcium sulfoxide directly transforms into the AFm phase. Stage 2 (4-6 h): Two reactions occur in the system. One is that Na⁺ and SO₄^2- ions react with AFm to form the intermediate phase U-phase with a larger interlayer spacing. At the same time, Ca²⁺ and SO₄^2- ions in the liquid phase react with AFm again to form calcium sulfoxide, which then decomposes into the intermediate phase U-phase; Stage 3 (8-24 h): The U-phase begins to gradually transform into the larger AFm stable phase.

Key words

sodium hydroxide / high temperature / ettringite / monosulfoaluminate / transformation

引用本文

张响, 卢晓磊, 宋建国, 贾坚, 杨庆春, 杜鹏, 程新. 氢氧化钠对钙矾石的合成及在高温环境下转变的影响. 硅酸盐学报, 2025 , 53 (2) : 428 -436 . DOI: 10.14062/j.issn.0454-5648.20240015

Xiang ZHANG, Xiaolei LU, Jianguo SONG, Jian JIA, Qingchun YANG, Peng DU, Xin CHENG. Effect of NaOH on Synthesis and Transformation of Ettringite Under High Temperature Environment[J]. Journal of the Chinese Ceramic Society, 2025 , 53 (2) : 428 -436 . DOI: 10.14062/j.issn.0454-5648.20240015

基金

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国家自然科学基金(52341201; 52102020; U22A20126)
山东省泰山学者攀登计划

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2025年第53卷第2期

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文章信息

doi: 10.14062/j.issn.0454-5648.20240015

接收时间：2024-01-07
首发时间：2026-10-22
出版时间：2025-02-20

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收稿日期：2024-01-07
修回日期：2024-03-14

基金

国家自然科学基金(52341201; 52102020; U22A20126)

山东省泰山学者攀登计划

作者信息

^1．山东省建筑材料制备与测试技术重点实验室，济南大学，济南 250022

^2．济南大学材科科学与工程学院，济南 250022

通讯作者:

卢晓磊（1986—），男，博士，副教授。

程新（1963—），男，博士，教授。

参考文献

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https://castjournals.cast.org.cn/joweb/gsyxb/CN/10.14062/j.issn.0454-5648.20240015

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2种不同金属材料的力学参数

科 Family	属数 Number of genus	种数 Number of species	占总种数比例 Percentage of total species (%)	属 Genus	种数 Number of species	占总种数比例 Percentage of total species (%)
鹅膏菌科Amanitaceae	2	11	5.26	鹅膏菌属 Amanita	10	4.78
小菇科 Mycenaceae	2	12	5.74	丝盖伞属 Inocybe	5	2.39
多孔菌科 Polyporaceae	8	14	6.70	蜡蘑属 Laccaria	5	2.39
红菇科 Russulaceae	3	23	11.00	小皮伞属 Marasmius	6	2.87
				小菇属 Mycena	11	5.26
				光柄菇属 Pluteus	5	2.39
				红菇属 Russula	17	8.13
				栓菌属 Trametes	5	2.39

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