自交联醋苯丙防水乳液的制备与性能研究

通过种子乳液聚合法制备了有机硅改性的醋酸乙烯酯-苯乙烯-丙烯酸丁酯(醋苯丙)三元共聚防水乳液.通过对乳液红外光谱和透射电镜的分析,发现有机硅成功引入醋苯丙乳液并起到室温自交联的作用,乳胶粒为核壳结构.着重考察了有机硅用量、醋酸乙烯酯单体用量对乳液防水性能的影响.实验结果表明改性醋苯丙乳液的防水性能优于传统苯丙乳液,且成本更低.     

核-壳苯丙微乳液最低成膜温度的研究

通过核-壳微乳液聚合技术合成了具有较高玻璃化转变温度(Tg)的苯丙微乳液,研究了核-壳单体用量比、壳单体组成、交联剂、聚合物极性对乳液最低成膜温度(MFT)的影响;同时比较了三种成膜助剂对乳液MFT的作用。研究发现,成膜温度随核-壳比的增大而上升;交联剂羟甲基丙烯酰胺(NMA)能有效地降低成膜温度;醇酯—12是一种良好的成膜助剂,同一成膜助剂对极性不同的乳胶粒子MFT的降低效果明显不同。     

核/壳苯丙乳液的单因素优化合成

采用种子乳液聚合技术与预乳化工艺,合成了具有核/壳结构的苯丙乳液。试验了单体配比,乳化体系,温度控制,乳化单体滴加程序等工艺条件对核/壳苯丙乳液性能、质量的影响,得到了聚合工艺稳定,综合性能良好的核/壳苯丙乳液。     

核壳结构苯丙乳液上光油的研制

采用预乳化工艺及半连续种子聚合法,通过St-BA-MMA-AA四元共聚反应,制得了具有核壳结构的苯丙乳液。讨论了乳胶粒子大小及形态对MFT的影响,并研究了乳化剂用量、阴／非离子乳化剂配比、核壳两阶段乳化剂配比及功能性单体的用量及加入方式对乳液性能的影响。     

半连续种子乳液预聚法合成核-壳型苯丙乳液的研究进展

苯丙乳液是由苯乙烯和丙烯酸酯单体经乳液聚合后制得的,通过添加功能单体(交联剂等)可以形成核-壳结构。半连续种子乳液预聚法是合成核-壳型苯丙乳液较先进的方法之一,所得苯丙乳液性能优越,并且在胶粘剂、施胶剂及涂料等领域中得到广泛应用。综述了半连续种子乳液预聚法合成核-壳型苯丙乳液的研究进展,详细介绍了某些物质(如有机硅、含氟化合物和乳化剂等)对苯丙乳液性能的影响。最后对核-壳型苯丙乳液的发展方向进行了展望。     

木器涂料用苯丙乳液最低成膜温度的研究

针对木器涂料用核-壳型苯丙乳液,研究了壳层玻璃化转变温度(T_g)、核壳质量比、交联单体三方面因素对乳液最低成膜温度(MFT)的影响,以及成膜助剂二丙二醇丁醚(DPNB)、二丙二醇甲醚(DPM)的使用效果。研究发现,壳层T_g降低能有效降低MFT,并强化DPNB+DPM的使用效果,核壳质量比能大幅度影响MFT;交联会使乳液MFT大幅上升,但双丙酮丙烯酰胺(DAAM)-己二酰肼(ADH)交联型乳液对DPNB+DPM的响应良好,同等添加量时等于或优于非交联乳液。     

影响苯丙乳液机械稳定性的分析

分析了苯丙乳液配方,考察了单体配比、合成工艺、乳化剂、亲水单体对苯丙乳液机械稳定性的影响,从中可知,乳化剂、亲水单体影响较大。然后根据影响因素从乳液角度出发对其进行了改进,采用核壳工艺、亲水单体的配合使用制备出了机械稳定性好的苯丙乳液。     

有机硅-苯丙乳液最低成膜温度的研究

采用半连续法制备了稳定的有机硅-苯丙乳液，研究了软硬单体配比和有机硅单体含量对共聚物玻璃化转变温度(Tg)和乳液最低成膜温度(MFT)的影响：并选用3种成膜助剂(TXL、DPD和二乙二醇二乙醚)分别考察了成膜助剂的种类和用量对乳液产品MFT的影响。结果表明，共聚物T和乳液的MFT呈较好的线性关系，该乳液体系MFT/Tg约为0．97；乳液产品的MFT随成膜助剂用量的增加而大幅降低，其中二乙二醇二乙醚的效果最好。     

聚合工艺和组成对苯丙乳液最低成膜温度的影响

通过对不同聚合工艺和组成制得的苯丙聚合物乳液 ,测其最低成膜温度 (MFT) ,结果发现 :利用种子乳液聚合 ,核主要组成为聚苯乙烯 ,壳主要组成为聚丙烯酸丁酯 ,所制得的核壳聚合物乳液与同组成无规共聚所得乳液相比 ,MFT能下降 2 5℃左右。其意义有二 :( 1 )该乳液可在较低温度下使用 ,从而拓宽了施工温度范围。 ( 2 )若制得与常规共聚乳液相同MFT时 ,该方法所制得的乳液由于可少用价格高昂的丙烯酸丁酯 ,多用价廉的苯乙烯 ,从而降低乳液成本 ,使该类产品具有较强的市场竞争力。     

丙烯腈改性苯丙乳液的合成与性能分析

对以苯乙烯、丙烯酸丁酯、甲基丙烯酸为反应单体,丙烯腈为功能性单体,采用了核/壳聚合技术的合成苯丙乳液进行了研究。研究了丙烯腈的用量、软硬单体的比例、乳化剂及温度对乳液及其涂膜的性能影响。并对试样进行了红外光谱分析和热重分析。研究结果表明:改性的苯丙乳液比纯苯丙乳液的热性能有所提高,膜的耐溶剂性、耐磨性、耐水性、硬度等均有所提高,并得出丙烯腈用量为8%时效果最佳。     

Polymorphism of LiGa5O8 and of LiGa5O8-MgGa2O4Solid Solutions

High-temperature X-ray diffraction and differential thermal analyses showed that LiGa₅O₈ exists in two polymorphs related by the first-order transition at 1138°±3°C of the low-temperature simple-cubic form, space group (probably) O⁷, to the high-temperature spinel (fcc) form, space group O _h ⁷. The transition is rapid, and the high-temperature form in pure LiGa₅O₈ could not be quenched to room temperature under the conditions used. However, the high-temperature polymorph can be quenched under equilibrium conditions when 40 mol% or more MgGa₂O₄ is present. The subsolidus equilibrium relations in the system MgGa₂O₄-LiGa₅O₈ are discussed.     

Magnetoresistance of CuxCo1-xFe2O4 Ferrites

Magnetoresistance measurements (Δ/R) were carried out on Cu _x Co_{1- x} Fe₂O₄ samples with x =1, 0.75, 0.50, 0.25 and cobalt ferrite in the range of magnetic intensity (H) from 1.0 to 4.5 kG. Linear plots were obtained between log (Δ/R) and log H for all compositions except that of cobalt ferrite. The values of n at x =0.5 do not agree with the results of some authors. The discrepancy may be attributed to the value of magnetic field intensity at which such measurements were carried out. The similarity of features of n and μ_D with composition leads us to believe that the magnetoresistance may arise from the scattering of conduction electrons by localized electrons involving the s-d exchange interaction.     

Sintering of Si3N4-Y2O3-Al2O3

Sintering kinetics of the system Si₃N4-Y2O₃-Al₂O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si₃N₄ were studied with additions of 4 to 17 wt% Y₂O₃ and 4 wt% A1₂O₃. Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si₃N₄ and glass or β '-Si₃N₄, α '-Si₃N₄, and glass. The compositions and amounts of the residual glassy phases are estimated.     

Expansive properties of the mixture C4ASH12 − 2CS III. Effects of temperature and restraint

The effects of temperature and restraint upon the hydration and the expansion of $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}\text{? 2}\text{C}\text{S}$ mixture compacts in different contact solutions have been investigated. Temperatures above 20°C do apparently hinder the formation of an impervious felt-like layer of ettringite around the $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}$ particles, thus greatly reducing the retarding effect of the lime. An uniaxial restraint of 1 Kg/cm² is enough to reduce sensibly the expansions which remain however high (about 100%). The results can be satisfactorily interpreted by the reaction and expansion mechanism hypothesized in our previous papers.     

Raman Study of Glasses of Ba2TiSi2O8 and Ba2TiGe2O8

Raman spectra are reported for fresnoite (Ba₂Ti(Si,Ge)₂O₈ glasses, and comparison is made between the Raman spectra of the corresponding crystalline powders and glasses of Ba₂TiSi₂O₈ and Ba₂TiGe₂O₈. The Ba₂TiGe₂O₈ glass spectra show correspondence with the Ba₂TiGe₂O₈ crystalline Raman spectra; the v _s(Ge–O–Ge) mode occurs at 518 cm⁻¹ in the glass and at 521 cm⁻¹ in the crystalline material. Five-fold coordinated titanium is the majority species present in the Ba₂TiGe₂O₈ glass as revealed by a strong band at 824 cm⁻¹ in the I glass spectrum. The Ba₂TiSi₂O₈ glass spectra are similar to the Ba₂TiSi₂O₈ crystalline spectrum; the strongest band is found at 836 cm⁻¹ in the I glass spectrum. Through comparison with the previous Raman data of other titania silicate glasses, we conclude that the Ba₂TiSi₂O₈ glass has a structure similar to the crystalline phase.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.     

Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

Wet Milling of Fe/Al/Al2O3 and Fe2O3/Al/Al2O3 Powder Mixtures

Wet milling of Al₂O₃-aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al₂O₃ and Fe₂O₃/Al/Al₂O₃ powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe₂O₃/Al/Al₂O₃ powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al₂O₃ powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8.     

In situ laser raman spectroscopy of the sulfiding of Moγ-Al2O3 catalysts

Raman spectra of sulfided $\text{Mo}\text{γ-}\text{Al}{}_2\text{O}{}_3$ catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% $\text{H}{}_2\text{S}\text{H}{}_2$ at 400 °C, MoS₂ structures were observed. A stepwise sulfiding using 10% $\text{H}{}_2\text{S}\text{H}{}_2$, with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface “MoS₂” phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO₃ species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow.