改性硅酸盐水泥的水化动力学研究

将磷铝酸盐水泥熟料掺入到硅酸盐水泥中制备改性水泥,从水化动力学的角度研究其水化情况,并与硅酸盐水泥的相应行为进行了对比.首先通过测定水化放热速率、新拌水泥浆体中的Ca2+和SiO44-离子浓度、电导率及pH值研究了改性硅酸盐水泥的水化历程,并求得了水化动力学方程.其次,测定了改性硅酸盐水泥的净浆与砂浆的强度,并用XRD等分析方法初步探讨论了改性水泥的水化机理.研究发现,改性硅酸盐水泥的水化历程与硅酸盐水泥相似,也经历初始期、诱导期、加速期、减速期和稳定期,但水化放热速率明显提高;在加速期,两者的水化反应均主要由自动催化反应控制,在减速期,均主要由扩散过程控制,但反应速率常数前者明显高于后者.无论是砂浆强度,还是净浆强度,前者也均高于后者,且凝结时间相对缩短.XRD图谱显示,前者的C3S/C2S衍射峰强度的降低率高于相应龄期的硅酸盐水泥.上述结果均意味着改性硅酸盐水泥的水化速度明显高于硅酸盐水泥;水化加速的机理为磷铝酸盐熟料水化吸收了水化浆体中OH-离子,使水化体系的OH-离子浓度减少,从而加速了C3S、C2S的水化反应.     

QXRD方法定量分析水泥浆体中MgO的水化程度

采用QXRD法(Quantitative X-ray diffraction)对掺两种MgO膨胀剂水泥浆体中主要水化产物进行定量分析,以ZnO为内标物计算水化产物中非晶相的含量,并计算养护不同龄期水泥浆体中MgO的水化程度.结果 表明:40℃水养条件下,60 d时掺高活性MgO水泥浆体中MgO基本水化完全,而掺低活性MgO水泥浆体中MgO还有15％未水化;水泥浆体中MgO在早期具有较快的水化速率,后期水化速率变缓;相同龄期内,高活性MgO具有较快的水化速率,水化程度较高,但产生的膨胀量小于低活性MgO产生的膨胀量.     

粉煤灰对水泥水化与强度的影响

采用测定化学结合水含量的方法反映水泥浆体的水化程度,并通过对水泥硬化浆体强度的分析,评价粉煤灰对水泥水化和力学性能的影响。结果表明,粉煤灰加速了水泥熟料的水化反应,却减缓了水泥-粉煤灰体系的水化进程。掺加粉煤灰虽然降低了水泥浆体的早期强度,但对水泥浆体后期强度的发展有利。     

机械活化煅烧煤矸石水泥的早期水化过程

用差热-热重分析和X射线衍射、等温量热计、扫描电子显微镜研究了机械活化煅烧煤矸石比表面积的变化对其水泥早期水化过程的影响,同时,用甘油-乙醇法测定了整个水化过程中Ca(OH)2含量.结果表明:机械活化煅烧煤矸石的比表面积越大,其水泥水化加速期延续的时间越长,水化放热速率越低;在水化减速期早期阶段的水化放热速率越高,二次水化产物形成的时间越早,在整个水化期间内水化产物中的Ca(OH)2含量越低.煅烧煤矸石水泥开始水化后,共产生4个水化放热峰,依次为初始放热峰、生成水化硅酸钙和Ca(OH)2放热峰、熟料水化生成钙矾石的放热峰及煤矸石被大量激发所形成的放热峰.     

基于化学分析的水泥浆体中游离氧化钙的水化反应

基于化学分析与TG-DSC分析有机结合,面向以CaO为关键组分的水泥浆体中的游离氧化钙,进行了水化反应研究。结果表明,在水泥浆体中,膨胀熟料游离氧化钙的反应速度非常快,处于恒温状态时,水胶比0.4的水泥浆体中添加水进行搅拌,2h之后,游离氧化钙水化反应可达到将近30%,在24h之后,水化反应可直接超出50%,在7d之后,水化反应便可完全完成;葡萄糖酸钠缓凝剂可在一定程度上延迟膨胀熟料游离氧化钙的水化反应,但是效果并不显著。     

Na2SO4对煅烧煤矸石的激发效应

利用TG-DSC、XRD、等温量热计、SEM、Ca(OH)2含量测定等方法,比较研究了掺与不掺Na2SO4时煅烧煤矸石水泥早期水化过程中的Ca(OH)2含量、水化放热速率、水化产物及其形貌、浆体力学强度的差别,分析了Na2SO4对水泥早期水化过程中煅烧煤矸石的激发作用.结果表明,掺入Na2SO4后,水泥试样在水化减速期早期阶段的水化放热速率高,二次水化产物形成的时间早.这反映出Na2SO4对水泥中煅烧煤矸石有明显的激发效应.其外,水泥浆体试样中Ca(OH)2含量明显降低,水泥水化加速期延续的时间短,水化放热速率高;结果还表明,在水化早期,掺Na2SO4的煅烧煤矸石水泥有较多的CSH凝胶和AFt,较少的Ca(OH)2.     

CaO类膨胀剂对碱矿渣水泥砂浆限制膨胀率影响研究

通过XRD、SEM、水化热等方法研究了CaO类膨胀剂对碱矿渣水泥砂浆限制膨胀率的影响。结果表明:在6%~10%范围内,随着膨胀剂掺量的增加,碱矿渣水泥砂浆限制膨胀率增大、3 d抗压强度提高,但7 d以后抗压强度明显降低;内掺膨胀剂后水化放热加速峰提前,但放热速率及总放热量降低;XRD及SEM测试结果表明Ca(OH)_2是CaO类膨胀剂在碱矿渣水泥砂浆中的主要产物。尽管CaO类膨胀剂能够在碱矿渣胶凝体系中产生膨胀,但由于生成Ca(OH)_2速度与碱矿渣水化速度协调性不足,以至其不能发挥有效补偿收缩作用。     

速凝剂与石灰石粉对水泥浆体性能的影响

通过不同掺量的速凝剂和石灰石粉对水泥浆体凝结时间、流动度、粘度、胶砂强度和水化进程的影响研究,探讨速凝剂与石灰石粉共同作用下对水泥浆体性能的影响。结果表明:石灰石粉能够提高水泥净浆的流动度和粘度,并且其流动度和粘度损失随着石灰石粉掺量的增加而增大。速凝剂掺量为5%时,石灰石粉掺量为5%,水泥的凝结时间进一步缩短,水泥胶砂3 d、7 d和28 d的抗压强度略有提高,当石灰石粉超过5%时,水泥的凝结时间随着石灰石粉掺量的增加反而延长,水泥的胶砂抗折、抗压强度随着石灰石粉掺量的增加而降低。水泥水化初始期和加速期的水化放热速率随着速凝剂掺量的增加而增加,掺加速凝剂后,水化加速期提前10 h,同时石灰石粉也能够提高水泥水化初始期和加速期的水化放热速率。掺加速凝剂后,水泥水化放热量反而降低了一半,但是加入石灰石粉后,水泥水化放热量增加。     

基于Krstulovic-Dabic模型的复合胶凝体系水化特性研究

将粉煤灰、矿粉、膨胀剂、纳米硅、粘改剂等掺合料按一定比例加入基准水泥中,采用等温量热仪测试了复合胶凝体系在5℃、20℃和30℃下的水化放热速率曲线.同时基于Krstulovic-Dabic模型,计算了相应的水化动力学参数,讨论了温度和掺合料对水化动力学参数的影响,探讨了复合胶凝体系复杂的水化机理.结果表明,复合胶凝体系的水化放热速率峰值随温度升高呈指数增加,而峰值到达时间则随温度升高呈指数减小,水化动力学参数随温度升高显著增大.掺合料的加入降低了复合胶凝体系的水化动力学参数和水化放热速率峰值,并使放热峰值提前出现,特别是膨胀剂和纳米二氧化硅作用显著.计算得到的反应速率曲线与测试得到的实际速率曲线的拟合精度受到温度和掺合料的影响.     

聚羧酸减水剂对铝酸三钙-石膏体系水化调控机理研究

本文通过测定不同掺量的聚羧酸减水剂(PCE)作用下铝酸三钙(C3A)-石膏体系水化热,并采用XRD、SEM、Raman分析了水化产物微观结构的形成规律,研究了PCE对铝酸三钙-石膏体系水化调控机理.结果表明:水灰比为0.6,摩尔比为1∶1的铝酸三钙-石膏体系,水化24 ～ 48 h时出现水化热温峰,并生成大量的Aft(钙矾石);PCE掺量不同对铝酸三钙-石膏体体系的水化调控存在延缓与加速水化的双重作用,当掺量为0.1％ ～0.3％时,PCE抑制铝酸三钙-石膏体系水化放热及AFt的形成;当掺量为0.5％时,PCE促进铝酸三钙-石膏体系水化放热,加速AFt的形成.     

MgO-Al-C质材料的水化机理及抗水化性能

采用X射线衍射仪、扫描电子显微镜、Fourier变换红外光谱仪等研究了MgO-Al-C质材料水化前后的物相组成、微观结构及O-H键强弱的变化,探讨了MgO-Al-C质材料的水化机理.在此基础上,以板状刚玉取代部分电熔镁砂颗粒,以改善MgO-Al-C质材料的抗水化性能.结果表明:MgO-Al-C质材料除因加热过程中Al粉...     

环氧乙烷非催化水合反应最佳水合比的确定

在选择环氧乙烷非催化水合反应的水合比时,仅从降低乙烯单耗的角度考虑是不完善的。更要从增效的角度,根据乙二醇和二乙二醇的市场价格及装置设计所允许的水合比变化区间,确定最适宜的水合比。利用Aspen Plus软件对一个非催化水合反应分离的流程进行了模拟,给出了确定最佳水合比的方法和示例。     

氯氧镁水泥水化历程的影响因素及水化动力学

为了深入研究氯氧镁水泥的水化机理,进而对其性能进行预测和改进,采用美国TAM Air热导式等温量热仪研究了氯氧镁水泥的水化动力学。测定了不同条件下氯氧镁水泥体系的水化放热过程,根据水化放热曲线,研究了该体系水化各阶段的动力学过程,探讨了实验因素对该体系水化过程的影响,并通过实验数据拟合得到了氯氧镁水泥水化过程的动力学方程。结果表明:氯氧镁水泥水化过程的不同阶段受不同作用机理控制,加速期是受成核控制的自动催化反应时期,衰减期受扩散作用控制,而减速期受自动催化反应和扩散作用双重控制。同时,原料MgO的活性、反应温度及矿物外加剂的种类和数量都不同程度地影响了该体系的水化过程。     

Hydration of Tricalcium Silicate

The kinetics of paste, bottle, and ball-mill hydration of 3CaO SiO₂ and the effects of additions of electrolytes and alcohols were studied. Paste and bottle hydrations proceed through periods of induction, acceleration, and decay. If 3CaO SiO₂ is hydrated in an excess of H₂O, as in bottle hydration, the reaction rate is lower than that for paste hydration. The ball-mill hydration rate is much the highest and is controlled by the removal of the hydrate layer coating the 3CaO SiO₂ particles. Electrolytes always accelerate and alcohols retard the reaction rate. Experimental results are discussed with reference to modern theories of the 3CaO SiO₂ hydration mechanism.     

丙烯醛水合工艺

本文对以丙烯醛为原料,通过水合反应合成3-羟基丙醛的工艺进行了介绍。     

Hydration of tricalcium silicate

Results of following the quantities of free Ca(OH)₂ and of tricalcium silicate (C₃S) during the hydration of C₃S, and also the influence of the presence of free CaO on this reaction are in accordance with the hypothesis of Stein & Stevels with regard to the hydration of C₃S. at the first contact between C₃S and water, a surface hydrate, invisible by electron microscope methods, is considered to be formed and to retard the reaction strongly. This hydrate is thought to change into one which retards the hydration reaction less and changes later into a third hydrate, tobermorite gel.     

Hydration of Germanium Oxide Carnotite

The quaternary invariant point was reached in the CaO–GeO₂–P₂O₅–H₂O system by the hydration of germanium oxide carnotite. Complete reaction was achieved although the kinetics were very slow. Three products were identified by X-ray diffraction: calcium germanate hydrate, hydroxyapatite, and calcium hydroxide. Energy dispersive X-ray analyses established the compositions of the three phases present in the heterogeneous microstructure. Calcium germanate hydrate exhibited a fibrous habit and was present as large individual fibers as well as small thin fibers. The small fibers were intermixed with hydroxyapatite. The latter was observed to form feltlike assemblages. Stacked calcium hydroxide plates were unequivocally observed.     

Hydration products of calcium aluminoferrite

Hydration products of Ca₂AlFeO₅, steam cured at 72 C, have been identified using X-ray diffraction and Mössbauer spectroscopy. Iron-bearing phases are hydrogarnet Ca₃Fe_yAl_2?y(OH)₁₂ with y = 0.22, and non-crystalline ferrihydrite Fe(OH)₃.nH₂O. These two are readily distinguished in Mössbauer spectra at 4.2 K where they give, respectively, a single unsplit absorption line and a magnetically split hyperfine pattern with H_hf = 501 kOe. Addition of 5 wt% lime to the calcium aluminoferrite increases the proportion of iron in the hydrogarnet to y = 0.32 while leaving the ferrihydrite unchanged, whereas 5 wt% gypsum eliminates iron from the hydrogarnet entirely and produces an even more disordered non-crystalline ferric hydrate.     

Hydration of fly ash-portland cements

Hydration products of fly ash-portland cements were studied with x-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) as part of a continuing research effort to understand the pozzolanic activity of fly ashes. It was found that the amount of calcium hydroxide crystals in the cement pastes is diminished due to the addition of fly ash to the cement. Ettringite was produced in the early age, and the consumption of sulfate by the formation of ettringite was accelerated by the addition of fly ash. A partial conversion of ettringite to monosulfate within the first 7 days of hydration in the fly ash-portland cement pastes, but the formation of ettringite continued to form up to at least 28 days of hydration in the pastes without fly ash. Examination of the fly ash bearing pastes showed, in all cases, varying amounts of calcium hydroxide and unreacted portland cement, with minor quartz and gehlenite hydrate. It appears that hydration reactions actually occur in the fly ash cement pastes more or less on a particle-by-particle basis.