Activation of Anhydrate Phosphogypsum by K_2SO_4 and Hemihydrate Gypsum

Lime pretreated phosphogypsum（PG） was calcined at 500 ℃ to produce anhydrate gypsum cement. Due to the slow hydration of anhydrate gypsum, additives, K2SO4 and hemihydrate gypsum were selected to accelerate the hydration of anhydrate. The hydration characteristics, the resistance to hydrodynamic water, and the mineralogical studies were investigated. The experimental results suggest that activated by K2SO4 and hemihydrate, anhydrate PG hydrates much more rapidly than that in the presence of only K2SO4 or in the absence of additives. The binder has proper setting time, good strength development, and relatively better resistance to water. The hardened binder has hydrated products of rod or stick like shaped dihydrate gypsum crystals.

Authigenic Gypsum in Gas-Hydrate Associated Sediments from the East Coast of India (Bay of Bengal)

Authigenic gypsum crystals, along with pyrite and carbonate mineralization, predominantly calcites were noticed in distinct intervals in a 32 m long piston core, collected in the gas hydratebearing sediments in the northern portion of the Krishna-Godavari basin, eastern continental margin of India at a water depth of 1691 m. X-ray diffraction and energy dispersive spectrum studies confirm presence of pyrite, gypsum, calcite, and other mineral aggregates. The occurrence of gypsum in such deep sea environment is intriguing, because gypsum is a classical evaporite mineral and is under saturated with respect to sea water. Sedimentological, geochemical evidences point to diagenetic formation of the gypsum due to oxidation of sulphide minerals （i.e. pyrite）. Euhedral, transparent gypsum crystals, with pyrite inclusions are cemented with authigenic carbonates, possibly indicating that they were formed authigenically in situ in the gas hydrate-influenced environment due to late burial diagenesis involving sulphate reduction and anaerobic oxidation of methane （AOM）. Therefore, the authigenic gypsums found in sediments of the Krishna-Godavari and Mahanadi offshore regions could be seen as one of the parameters to imply the presence of high methane flux possibly from gas hydrate at depth.

Modification on the Performance of the Hemihydrate Gypsum with the Plant Source Polymer of Dry Matcha Powder

The objective of this study was to assess the feasibility of using the plant-source polymer of the matcha powder as a composite admixture for hemihydrate gypsum. Hemihydrate gypsum was mixed with different contents of matcha powder, and then the water requirement for the normal consistency, setting times, density, strength, hydration and microstructure of the hardened mixture were evaluated. The experimental results showed that it increased the water requirement for the normal consistency, and it regulated the setting times and reduced the density. Hemihydrate gypsum with more matcha powder had the higher water requirement, longer setting times and lower density. Less than 1% matcha powder had slight impact on the strength of hardened paste, but more than 1% matcha powder had a remarkable one. Matcha powder changed the hydration process and prolonged the induction and acceleration period. Small needlelike crystals were transformed into longer, larger and thicker ones as more matcha powder was mixed. This case is closely related to the prolongation of the induction and acceleration period. Besides, more and larger pores were observed in the hardened paste with more matcha powder. It is attributed to the appearances of the tea polyphenol in matcha powder and the larger and longer crystal morphology in hardened paste as well as the high water requirement for the normal consistency. These results are important to the application of matcha powder as a composite admixture for the hemihydrate gypsum as well as the prosperity and development of the tea industry.

Improved length of calcium sulfate crystal seeds and whiskers via ball milling and hydration treatment

Elucidating the effect of growth periods on the quality of calcium sulfate whiskers(CSWs)prepared from calcium sulfate dihydrate(DH)is imperative.Herein,crystal seeds and whiskers were prepared from DH in a water–glycerol system.Longer whiskers were obtained from crystal seeds prepared via hydration of DH for 30 s than via ball milling for 5 min followed by hydration for 20 s.The attachment of cetyltrimethyl ammonium bromide and glycerol additives to the whisker tops promoted whisker growth.The whisker sponges exhibited good thermal barrier properties and compression cycle stability.

Effect of Low pH on Forming Process of Desulfurization Gypsum Composite Boards Strengthened by Melamine-formaldehyde Resin

Through exploring the effects of low pH on the composite system of desulfurization gypsum(DG)enhanced by melamine-formaldehyde resin(MF),it is found that the inducing of sulfate-ion,in contrast to chloride and oxalate ions,favors the longitudinal growth of the crystalline form of the hydration product,which was relatively simple and had the highest length to width(L/D)ratio.At the same time,MF can also improve L/D ratio of gypsum hydration products,which favors the formation of hydrated whiskers.Finally,in a composite system composed of hemihydrate gypsum,MF,and glass fibers,when dilute sulfuric acid was used to regulate pH=3-4,the tight binding formed among the components of the composite system compared to pH=5-6.The hydration product of gypsum adheres tightly to glass fiber surface and produces a good cross-linking and binding effect with MF.The flexural strength,compressive strength,elastic modulus,and water absorption of the desulphurized gypsum composite board is 22.7 MPa,39.8 MPa,5608 MPa,and 1.8%,respectively.

磷建筑石膏矿渣水泥的水化过程与耐水性能

通过凝结时间、流动度、孔溶液pH值、抗折强度、抗压强度、吸水率、软化系数、水化热和水化产物分析测试,探究了磷建筑石膏(CPG)掺量对石膏矿渣水泥水化过程与耐水性能的影响.结果表明:随着CPG掺量的增加,石膏矿渣水泥的凝结时间缩短,流动度减小,吸水率与3 d水化累计放热量均增大;水泥净浆孔溶液的pH值在水化早期快速下降,56 d时保持不变;当CPG掺量从40%增加到70%时,56 d水泥净浆孔溶液的pH值从11.02减小到10.62,水泥胶砂的软化系数从0.98减小到0.91,主要水化产物均为二水石膏和钙矾石,并且钙矾石的含量随着CPG掺量的增加而减少.

过硫钛石膏矿渣水泥的水化特性

这是一篇矿物材料领域的论文。借鉴工业副产石膏与矿渣复合制备胶凝材料的经验,设计了若干组过硫钛石膏矿渣水泥,对该水泥的标准稠度用水量、凝结时间、力学性能和耐水性进行了研究,并对水化产物进行了XRD和SEM分析。结果表明,钛石膏会增大标准稠度用水量,并延长凝结时间,对力学性能和耐水性均有不利影响。通过适当增加熟料掺量可以弥补钛石膏的不利影响,当熟料掺量达到25%时,复合胶凝材料的28 d抗压强度达到30 MPa。在钛石膏和熟料掺量较高的实验组中,水化产物主要以钙矾石和水化硅(铝)酸钙为主,而矿渣掺量较高和熟料掺量较低的实验组中,水化产物主要是无定形水化硅(铝)酸钙。

激发剂种类及掺量对Ⅱ型无水石膏活性的影响

Ⅱ型无水石膏通常结构致密、凝结缓慢、水化率低,需激发其潜在胶凝活性后,方可应用于建筑材料等领域.给出了Ⅱ型无水石膏样品的制备工艺和测试方法,较深入地研究探索了硫酸盐类、非硫酸盐类、复合激发剂及激发剂掺量对Ⅱ型无水石膏胶凝活性的激发效果.结果表明,硫酸盐类激发剂能显著缩短Ⅱ型无水石膏的凝结时间、提高其水化率和力学性能,硫酸钾和硫酸钠的激发效果相对较好、最适掺量为1%;非硫酸盐激发效果总体不如硫酸盐,其中草酸钠效果最好、最适掺量为2%;适配且适量的复合激发剂可高效激发Ⅱ型无水石膏;掺加硫酸钾、硫酸钠、十八水合硫酸铝的Ⅱ型无水石膏,其强度随激发剂掺量增加而提高,掺加草酸钠或硫酸铝钾的,强度无明显变化.

脱硫石膏对碱激发胶凝材料性能及微观结构的影响

将工业副产脱硫石膏引入碱激发胶凝材料,拟解决其高碱含量时凝结硬化过快问题,同时考察力学性能和水化反应特征,研究脱硫石膏对碱激发胶凝材料宏观性能影响规律,采用X射线衍射(XRD)、扫描电子显微镜(SEM)等微观分析手段探索脱硫石膏对碱激发胶凝材料的作用机理。结果表明:脱硫石膏的引入可以有效延缓碱激发胶凝材料的凝结时间,且脱硫石膏掺量与凝结时间呈正相关,与强度、水化速率和累积放热量呈负相关,综合考虑,脱硫石膏掺量不宜超过9%(质量分数);脱硫石膏掺入后,碱激发胶凝材料水化产物中并未生成大量钙矾石晶体,且微观结构疏松,从而导致材料强度降低。

石膏矿渣基多元固废低碳胶凝材料的制备及水化性能

以矿渣为基体,采用石膏和碱性激发剂为主要材料可制备无熟料水泥,由于它减碳效益显著又称为低碳胶凝材料。分别研究了粉煤灰、钢渣、锂渣等工业固废对石膏矿渣基胶凝材料性能的影响,通过XRD、SEM、TG-DTG等表征方法研究掺入固废后的胶凝材料体系的水化硬化性能。结果表明:三种工业固废都会不同程度延缓胶凝材料的凝结时间和降低早期抗压强度,但单掺20%以内的粉煤灰和锂渣对后期抗压强度会有一定提高。在脱硫石膏和碱的激发下各组材料和矿渣相互促进水化,早期水化产物以钙矾石(AFt)和水化硅酸钙(C-S-H)凝胶为主,后期水化产物的数量不断增加,针棒状的AFt晶体穿插在C-S-H凝胶内,使硬化浆体的结构更加致密,强度逐渐增加。

高掺量SBR的粒径对硫铝酸盐水泥-石膏砂浆性能的影响

研究了在高掺量(15%)下不同粒径的丁苯乳液对硫铝酸盐水泥-石膏砂浆的物理性能和水化特性的影响。结果表明:小粒径的丁苯乳液更有利于提升硫铝酸盐水泥-石膏砂浆的流动度、抗折强度、拉伸黏结强度,并且降低了其抗压强度、毛细孔吸水率和孔隙率。除此之外,小粒径的丁苯乳液比大粒径的丁苯乳液加快了CSA水泥-石膏的水化,促进AFt的生长。

柠檬酸对建筑石膏水化的影响及其机理研究

系统研究了柠檬酸对建筑石膏凝结硬化过程及二水石膏晶体形貌的影响,以及不同pH值下的柠檬酸缓凝效果,并结合光电子能谱分析技术对其作用机理进行了分析.结果表明:柠檬酸使建筑石膏的水化放热变缓,液相过饱和度和早期水化率降低;柠檬酸与二水石膏表面的钙离子产生化学结合,其结合层覆盖在二水石膏晶胚表面,降低了晶核的表面活性,增加了成核势垒,使二水石膏晶体成核数目减少,速率减慢,诱导期延长;柠檬酸对二水石膏[111]面钙离子的选择性吸附,抑制了二水石膏在C轴上的生长,改变了二水石膏的晶体形貌,使其由针状转化为短柱状;由于二水石膏晶胚减少,晶体生长时间较充分,导致晶体尺寸明显粗化,且柠檬酸掺量越大,晶体粗化现象越严重.

大分子缓凝剂对建筑石膏水化进程的影响及缓凝机理

研究了大分子缓凝剂(骨胶)对建筑石膏水化进程、液相离子浓度与过饱和度及二水石膏晶体形貌的影响,结合X光电子能谱分析技术对其缓凝机理进行了分析。结果表明:骨胶能抑制建筑石膏早期水化,使其水化放热减缓,早期水化率降低,凝结时间延长;骨胶对二水石膏晶体形貌影响较小,但使二水石膏晶体尺度明显增大;骨胶与二水石膏晶核表面钙元素作用,在其表面形成化学吸附层,降低晶核表面能,抑制二水石膏晶核生长,使建筑石膏水化进程变缓。

脱硫石膏-粉煤灰活性掺合料设计及水化特性

针对电厂两大工业废渣——烟气脱硫石膏及粉煤灰,通过试验研发用于混凝土的活性复合矿物掺合料。以适当比例复合后的脱硫石膏及粉煤灰等量取代水泥掺入到水泥砂浆中,通过活性激发措施,以胶砂流动度、早期强度以及强度发展规律等作为控制指标探索脱硫石膏及粉煤灰的最优配比,同时通过微细观结构的SEM观测评价脱硫石膏-粉煤灰活性矿物掺合料在水泥基材料中的作用效应。结果表明,脱硫石膏及粉煤灰以1:2的比例复合等量取代水泥30%掺入水泥砂浆中,可获得较为优异的胶砂流动度、早期强度,而后期强度能赶上甚至超过基准水泥胶砂;SEM表明由于脱硫石膏及其它外加组分的活性激发效应,粉煤灰的活性得到有效激发,早期有明显的钙矾石生成。脱硫石膏-粉煤灰复合矿物掺合料的研发可大量消纳燃煤电厂的工业废渣,且在水泥基材料体系中具有优异的水化及低成本特性,具有显著的"绿色"效应,符合中国"可持续发展"的战略要求。

FDN减水剂对建筑石膏水化和硬化体结构的影响

采用SEM扫描电镜、氮吸附法和MIP压汞测孔技术,水化温度、水化率和电导率等测试手段,研究了萘系减水剂FDN对建筑石膏水化进程及其硬化体强度、孔结构、晶体形貌的影响.结果表明:FDN可显著提高建筑石膏硬化体强度,当FDN掺量在1.0%(质量分数)以内时,建筑石膏硬化体强度增长较快;FDN对建筑石膏水化进程、水化产物形貌影响甚微,但可明显改善硬化体孔结构,使其孔隙率降低、孔径细化,而这正是减水剂增加建筑石膏硬化体强度的原因所在.

复合助剂改性建筑石膏的性能及其水化研究

从材料复合理论出发,试验研究了聚合物与矿物助剂组成的复合助剂对建筑石膏强度、耐水性、凝结时间等性能的影响,并通过正交试验优化出了综合性能较优的复合助剂改性建筑石膏的配制参数;采用X射线衍射分析(XRD)、扫描电镜图像分析(SEM)研究了复合助剂改性建筑石膏水化产物的形态及其分布状况.结果表明:由聚合物5010粉、白水泥、硅粉组成的复合助剂能有效改善建筑石膏的强度、黏结性和耐水性;复合助剂在石膏水化过程中一方面对结晶二水石膏的生长具有一定抑制作用,使二水石膏晶粒尺寸减小且分布更加均匀,另一方面可增加石膏水化产物中非晶相物质的含量,提高颗粒之间的胶结作用,增大石膏硬化体结构的致密性.

三聚磷酸钠对建筑石膏水化进程的影响及缓凝机理研究

系统研究了三聚磷酸钠对建筑石膏水化进程、液相离子浓度与过饱和度及二水石膏晶体形貌的影响,结合X光电子能谱分析技术对其缓凝机理进行了分析。结果表明:三聚磷酸钠使建筑石膏水化放热变缓,早期水化率降低,诱导期延长;三聚磷酸钠使液相离子浓度和过饱和度降低,二水石膏晶体粗化,晶型由针状转化为短柱状;三聚磷酸钠使二水石膏晶核表面钙元素2p电子结合能发生1.267eV化学位移,它与二水石膏表面的钙元素作用,在其表面形成化学吸附层,阻碍二水石膏晶核生长;三聚磷酸钠形成磷酸钙难溶盐覆盖在建筑石膏表面抑制其溶解和三聚磷酸钠在二水石膏晶核表面形成化学吸附层阻碍其生长是三聚磷酸钠缓凝的内在原因。

含不同石膏种类的超硫酸盐水泥的水化行为

针对不同石膏对超硫酸盐水泥水化行为的影响,测试了分别掺有硬石膏、二水石膏和磷石膏的超硫酸盐水泥的各龄期抗压强度,对比了其早期放热速率及放热曲线的差异,以及水化产物相的变化.结果表明:上述3类超硫酸盐水泥3d抗压强度均为14MPa左右;磷石膏基超硫酸盐水泥28,90d抗压强度分别为41.2,49.1MPa,明显高于其他两种水泥.超硫酸盐水泥早期强度主要受水化速率的影响.后期强度测试结果表明,磷石膏的激发效果优于硬石膏及二水石膏,用其制备的水泥浆体后期形成更多的水化硅酸钙与钙矾石,硬化浆体更加密实.

激发剂作用下的盐石膏废渣的水化过程

运用Kondo模型,研究了在激发剂硫酸钠作用下盐石膏废渣的水化过程.盐石膏废渣的水化过程分为3个阶段,第1、第3阶段受扩散作用控制;第2阶段受相边界反应控制.分别研究了激发剂溶液浓度和温度对相边界反应阶段水化速率的影响,结果表明,在0—0.60 mol.L-1范围内,增大激发剂溶液浓度可使水化速率常数k增大,在12℃≤T≤34℃范围内,升高温度会使水化速率常数k减小.对盐石膏废渣水化产物的X射线衍射分析表明,水化过程中有复盐Na4Ca(SO4)3生成.复盐作为异质颗粒,降低了二水硫酸钙的成核表面能势垒,加速了水化.

缓凝剂对建筑石膏水化过程和硬化体微结构的影响

测定柠檬酸、聚合磷酸钠、骨胶3类缓凝剂对石膏性能的影响,通过不同水化时间的水化率和水化温度测定,研究了缓凝剂对建筑石膏水化过程的影响,采用SEM形貌分析和压汞法孔结构分析研究缓凝剂对石膏硬化体微结构的影响。结果表明,这3种缓凝剂均延缓了石膏的水化进程,使凝结时间延长,强度降低,低掺量时柠檬酸缓凝作用最显著;缓凝剂改变了二水石膏晶体生长习性,使晶体由针状转变为短柱状,晶体尺寸明显增加;缓凝剂使硬化体孔径分布粗化,孔结构劣化。