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1.
本文选用不同类型的复合分散剂对纳米TiO2粉体在水体系中的分散效果进行了比较,探讨了分散剂的种类、用量及超声时间对纳米TiO2粉体在水体系中分散稳定性的影响;采用粒径分布图及粒径分布参数和沉淀法对分散体系进行了综合分析,确定了合适的分散剂并优化了分散剂的配比。  相似文献   

2.
制备纳米Al2O3是为进一步制备纳米Al2O3/高分子复合材料提供优质原料.优化了采用NH4Al(SO4)2和NH4HCO3为原料的反向沉淀-NH4AlO(OH)HCO3前驱体热分解的制备工艺,制备出了粒径约在11nm,团聚较少、分布均匀的纳米Al2O3粉体,并用电子透射显微镜(TEM)、X射线衍射(XRD)对其进行了表征分析.实验表明,优化了的工艺可以有效地抑制团聚,控制粒径.  相似文献   

3.
陈磊  景宣 《造纸化学品》2013,25(2):19-22
为了改善纳米γ-Fe2O3粉体的表面活性,通过γ-氨丙基三乙氧基硅烷(KH-550)的水解和缩合反应对纳米γ-Fe2O3粉体进行表面改性。采用正交试验设计,以表面偶联包覆量为指标研究了偶联剂浓度、反应温度和反应时间对KH-550表面改性纳米γ-Fe2O3的影响。采用电子透射电镜(TEM)、红外线光谱分析仪(FTIR)和粒径分析仪表征。研究发现:最佳表面改性工艺条件为偶联剂质量分数为4.5%、反应温度为55℃和反应时间6 h;KH-550能与纳米γ-Fe2O3形成化学结合;表面改性后的纳米γ-Fe2O3能有效地阻止颗粒之间的相互团聚,纳米粉体的平均粒径减小43.9%,粒径分布更加集中,分散性能得到改善。  相似文献   

4.
食品粉粒体混合:混合机理与混合均匀度影响因素探讨   总被引:1,自引:0,他引:1  
将单体营养强化剂或预混的多种营养强化剂按要求加入到某种食物载体中即为食物强化.食物强化是营养干预的主要手段.粉粒体状食物的强化要求营养强化剂在食物载体中应均匀分布.粉粒体状强化食品的生产是一个基于多种不同物性颗粒粉体混合的复杂过程,明晰粉粒体混合的基本原理及易造成粉粒体混合物分级的主要原因,能够为生产合格的粉粒体状强化食品奠定重要技术基础.本文综述了对流混合、扩散混合、剪切混合等粉体混合理论,并分析了三种混合机理在混合过程中的作用,探讨了粉体颗粒个体的粒径、形状、密度及水分含量等因素对粉体混合均匀度的影响,经比较分析后认为粉体颗粒粒径差异造成的影响最为显著,这可能是因为粉体颗粒粒径指标的差异倍数远远大于颗粒个体在形状、密度等其它指标上的差异.  相似文献   

5.
以广佛手为研究对象,用普通粉碎方式以及超微粉碎的方式制备不同粒径的广佛手粉(FC),并探究不同粒径粉体理化性质及其对多糖提取率的影响。实验结果表明,超微粉碎可以显着降低FC的粒径,延长超微粉碎时间,能减小粒径,使颗粒更细、更均匀,且经过超微粉碎的粉体其化学组成并不会发生改变。超微粉碎显著提升了粉体水溶性,降低了粉体持水性,粉碎后粒径大小对上述性质均有显著影响。粒径降低水溶性显著提升,持水性显著下降,粒径D50为20.01 μm的粉体水溶性高达64.49%,持水性仅有8.64%。在色泽方面,随着粒径降低,亮度值逐渐增大、红度值逐渐减小、黄度则先增大后减小。超微粉碎能在一定范围内提高广佛手多糖提取率,其中粒径D50为21.55 μm的广佛手超微粉多糖提取效率最高,达到了7.68%。该研究为广佛手的利用和新产品开发提供了一定的理论依据。  相似文献   

6.
对相同成分、不同粒径的3种远红外粉体悬浮液的分散性能及在皮革上的应用情况进行了研究。用超声波细胞粉碎机来解聚悬浮液中粉体颗粒,并用吸光度来表征其分散效果,结果表明:最大吸收波长与粒径大小无关;同一波长下,粒径越大,其吸光度越大;粒径越大,其最佳分散剂用量越小,而最佳超声解聚条件越强。相同质量浓度的粉体悬浮液处理皮革后,用升温和降温性能表征皮革的保暖性,结果表明:经远红外粉处理的蓝湿革的保暖性能,明显优于未经远红外粉处理的蓝湿革,且粉体越细,处理的蓝湿革的保暖性能越好。  相似文献   

7.
涂政  林家正  褚飞洋  叶阳 《食品科学》2022,43(5):111-117
为探究不同粒径超微红茶粉体冷藏特性及降脂功效,本实验以粒径26.116?μm(约600?目)、9.612?μm(约1?600?目)和4.338?μm(约3?600?目)超微红茶粉体为对象,研究其在4?℃下冷藏180?d后理化特性和体外对胰脂肪酶活性的抑制能力,以及这3?种粒径超微红茶粉体对肥胖大鼠体质量及血脂水平的影响。结果表明,600?目超微红茶粉体冷藏后茶多酚(18.17%)和茶红素(11.82%)质量分数显著高于1?600?目(分别为17.36%和10.76%)和3?600?目(分别为16.93%和10.42%)超微红茶粉体(P<0.05),茶褐素质量分数(3.96%)显著低于1?600?目(4.67%)和3?600?目(4.89%)超微红茶粉体(P<0.05);3?种粒径超微红茶粉体能明显抑制胰脂肪酶活性(半抑制浓度为560.672~591.521?μg/mL),且灌胃35?d后,与肥胖大鼠相比,体质量(392.5~396.3?g)及血清总胆固醇(1.756~2.052?mmol/L)、甘油三酯(3.611~4.308?mmol/L)、低密度脂蛋白胆固醇(3.004~3.097?mmol/L)和高密度脂蛋白胆固醇(1.268~1.456?mmol/L)水平均得到显著改善,但各粒径间差异不显著(P>0.05)。综上所述,600~3?600?目超微红茶粉体粒径越大越有助于冷藏中原始化学成分的保留,且对肥胖大鼠降脂功效差异较小。  相似文献   

8.
以钛酸丁酯为前驱物,采用溶胶-凝胶法制备锐钛矿型纳米TiO2,用XRD、FT-IR、SEM表征产物的结构和形貌,并研究其在模拟自然光下催化降解活性艳红X-3B的性能.结果表明,该光催化剂的制备条件为6mL水,40 mL无水乙醇,3mL冰乙酸,水解温度为27℃,煅烧温度为500℃.该光催化剂降解活性艳红X-3B的降解率可达90.09%.制备的TiO2粉体为锐钛矿结构,含有微量杂质,单晶粒径20nm左右;粉体的分散性较好,一次粒径为200~300nm,虽存在二次团聚,但不严重.  相似文献   

9.
目的 研究流化床气流超微粉碎不同操作参数对玉米淀粉颗粒粒度的影响。方法 以玉米淀粉为原料,通过流化床气流粉碎处理,考察原料不同含水量、不同粉碎气体压力、分级轮转速、持料量等参数条件下气流粉碎处理对淀粉颗粒粒径、粒度分布、比表面积、粉体密度及流动性的影响。结果 结果表明,不同操作参数对淀粉颗粒粒度影响显著,在原料含水量6.18%,气体压力0.8 MPa、持料量1.0 kg、分级转速3600 r/min操作参数条件下获得微细化玉米淀粉粒径最小,D50为5.22 μm,淀粉粒径大小显著降低,微细化玉米淀粉的粒度分布较窄且均匀,颗粒比表面积较原淀粉增大1.8倍,为0.65 m2/g,颗粒球形度较好;粉碎降低了淀粉粉体密度,最佳条件下淀粉松装密度和振实密度分别为0.48 g/cm3和0.70 g/cm3,粉体流动性变差。结论 该研究为玉米淀粉资源的加工与应用提供了理论依据和技术支持。  相似文献   

10.
螺旋藻超高压撞击流破壁实验研究   总被引:2,自引:0,他引:2  
本文将螺旋藻用300MPa对撞式超高压撞击流处理,比较处理前后的显微特征、粒度分布以及粉体表征,考察了撞式超高压撞击流技术对螺旋藻细胞破的壁效果。结果表明对撞式超高压撞击流粉碎后,D98由粉碎前的22.25μm减小到10.772μm;D50由3.706μm减小到1.601μm;体积平均粒径由5.771μm减小到2.65μm;面积平均粒径由1.998μm减小到0.848μm;表面积/体积由3.0032m2/cm3增大到7.0793m2/cm3;粉体显微特征明显减小。对撞式超高压撞击流可以有效粉碎螺旋藻细胞,为螺旋藻破壁加工提供一种方法。  相似文献   

11.
The uranium carbonate andersonite Na2Ca[UO2(CO3)3] x 6H2O was synthesized and identified with classical analytical and spectroscopic methods. The classical methods applied were powder X-ray diffraction (XRD), nitric acid digestion, and scanning electron microcopy combined with energy-dispersive spectroscopy (SEM/EDS). To characterize andersonite spectroscopically, time-resolved laser-induced fluorescence spectroscopy (TRLFS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) were used. Natural and synthetic andersonite samples were characterized with the nondestructive TRLFS by six fluorescence emission bands at 470.6, 486.1, 505.4, 526.7, 549.6, and 573.9 nm. In addition, andersonite was characterized by FT-IR measurements by the appearance of the asymmetric stretching vibration of the uranyl cation [v3(UO2(2+))] at 902 cm(-1) with a shoulder at 913 cm(-1). XPS measurements verified the composition of the synthetic andersonite sample. The measured intensity ratios of the XPS lines agree with the stoichiometry of Na2Ca[UO2(CO3)3] x 6H2O. The XPS features of the inner valence molecular orbitals are characteristic of the [UO2(CO3)3]4- structural moiety. These spectroscopic methods can be used to identify in a fingerprinting procedure secondary U(VI) phases in mixtures with other phases or as thin coatings on mineral and rock surfaces.  相似文献   

12.
The gas-phase kinetic coefficients of OH radicals with two primary fluorinated alcohols, CF(3)CH(2)CH(2)OH (k(1)) and CF(3)(CH(2))(2)CH(2)OH (k(2)), potential replacements of hydrofluorocarbons (HFCs), are reported here as a function of temperature (T = 263-358 K) for the first time. k(1) and k(2) (together referred as k(i)) were measured under pseudo-first-order conditions with respect to the initial OH concentration using the pulsed laser photolysis/laser induced fluorescence technique. The observed temperature dependence of k(i) (in cm(3) molecule(-1) s(-1)) is described by the following Arrhenius expressions: k(1)(T) = (2.82 ± 1.28) × 10(-12) exp{-(302 ± 139)/T} cm(3) molecule(-1) s(-1) and k(2)(T) = (1.20 ± 0.73) × 10(-11) exp{-(425 ± 188)/T} cm(3) molecule(-1) s(-1).The uncertainties in the Arrhenius parameters are at a 95% confidence level (± 2σ). Uncertainties in k(i)(T) include both statistical and systematic errors. Activation energies were (2.5 ± 1.2) kJ/mol and (3.6 ± 1.6) kJ/mol for the OH-reaction with CF(3)CH(2)CH(2)OH and CF(3)(CH(2))(2)CH(2)OH, respectively. The global lifetime (τ) at 275 K for CF(3)CH(2)CH(2)OH and CF(3)(CH(2))(2)CH(2)OH due to the OH-reaction was estimated to be ca. 2 weeks and 5 days, respectively. The reported Arrhenius parameters can be used in 3D models that take into account the geographical region and season of emissions for estimating a matrix of instantaneous lifetimes. As a consequence of the substitution of the -CH(3) group by a -CH(2)OH group in HFCs, such as CF(3)CH(2)CH(3) and CF(3)(CH(2))(2)CH(3), the tropospheric lifetime with respect to the OH reaction is significantly shorter and, since their radiative forcing is similar, global warming potentials of CF(3)CH(2)CH(2)OH and CF(3)(CH(2))(2)CH(2)OH are negligible. Therefore, CF(3)CH(2)CH(2)OH and CF(3)(CH(2))(2)CH(2)OH seem to be suitable alternatives to HFCs.  相似文献   

13.
To solve the disposal problems of residual sludges, wastewater treatment sludge (WWTS) and drinking-water treatment sludge (DWTS) were tested as components for production of ceramsite. SiO2 and Al2O3 were the major acidic oxides in WWTS and DWTS, so their effect on characteristics of ceramsite was also investigated to optimize the process. Results show that WWTS and DWTS can be utilized as resources for producing ceramsite with optimal contents of SiO2 and Al203 ranging 14-26% and 22.5-45%, respectively. Ceramsite within the optimal SiO2 and Al2O3 contents ranges was characterized using thermal analysis, X-ray diffraction (XRD), morphological structures analyses, and compressive strength measurements. Significant weight loss below 600 degrees C is through the release of structural water and gases. Bloating and crystallization in ceramsite above 900 degrees C are caused by the oxidation and volatilization of inorganic substances. Higher strength ceramsite with less Na-Ca feldspars and amorphous silica and more densified surfaces can be obtained at 18% < or = Al203 < or = 26% and 30% < or = SiO2 < or = 45%, while porous ceramsite with complex crystalline phases and lower strength can be obtained at 14% < or = Al2O3 < 18% and 22.5% < or = SiO2 < 30%. This revolutionary technology of utilization of WWTS and DWTS can produce high performance ceramsite, in accordance with the concept of sustainable development.  相似文献   

14.
纳米Al2O3溶胶的稳定性及PVDF/Al2O3杂化膜的性能研究   总被引:1,自引:1,他引:0  
以异丙醇铝(AIP)为原料,采用溶胶-凝胶法,制备了纳米氧化铝(Al2O3)溶胶。研究了酸解剂、酸铝比[n(H+)/n(Al3+)]、陈化时间等因素对溶胶粒径和稳定性的影响,得到了制备稳定、透明纳米Al2O3溶胶的最佳工艺条件,即酸解剂HNO3;n(H+)/n(Al3+)=0.18~0.25;陈化时间20 h。为了改善聚偏氟乙烯(PVDF)膜的性能,通过PVDF与AIP的原位聚合,制备了不同PVDF含量的PVDF/Al2O3杂化膜。采用扫描电镜(SEM)、原子力显微镜(AFM)、红外光谱(FI-IR)、差示扫描量热法(DSC)、热失重分析(TGA)等手段对膜的结构和性能进行了表征。结果表明:杂化膜的纯水通量随着PVDF浓度的增大呈下降趋势,截留率则随着PVDF浓度的增大逐渐升高;AIP的加入使得杂化膜两相之间存在键合,可以增强Al2O3和PVDF之间的化学连接,从而提高杂化膜的亲水性和机械强度;添加AIP后,杂化膜的热分解温度向低温移动,即杂化膜的热稳定性下降;而AIP对PVDF膜的熔点影响不明显。  相似文献   

15.
设p,q是适合3pq的奇素数.根据二次和四次Diophantine方程的结果,运用初等数论方法证明当且仅当(p,q)=(7,13)时方程组x+1=3pqa~2,x~2-x+1=3b~2有正整数解(x,a,b)=(4 367,4,2 521).  相似文献   

16.
A novel sorbent for SO2 removal has been investigated. The sorbent is obtained by conventional incipient wetness impregnation of abandoned biomaterials (straw or dried leaves) with an aqueous solution of Na2CO3. A material with the composition 80 wt % Na2CO3/straw shows a desulfurization activity which is both higher and faster than that of the reference sample Na2CO3/gamma-Al2O3. The breakthrough and stoichiometric SO2 adsorption efficiencies for 80 wt % Na2CO3/straw reach 48.9% and 80.6%, respectively, at a temperature of 80 degrees C. The adsorption efficiencies are almost constant in the temperature range 70 to 300 degrees C. According to IR and XPS analysis the main products observed on the spent sorbent are sulfite below 150 degrees C and sulfate at 300 degrees C. The Na2CO3 in 80 wt % Na2CO3/straw can potentially be recycled by the oxidation of the straw with concomitant reduction of the sulfite species to elemental sulfur, making the proposed process CO2 neutral.  相似文献   

17.
 3-Mercapto-2-methylpropanol, an odorous compound recently identified in red wines, was extracted from a red wine variety, using a low-temperature vacuum distillation coupled with a specific reversible thiol capture. The analysis of the diacetylated wine extract by enantioselective multidimensional gas chromatography with mass spectrometry detection revealed the presence of only one enantiomer, (R)-3-mercapto-2-methylpropanol. Although both of the optical isomers are characterized by the same broth and sweat odour, they have very different odour thresholds. The amounts of (R)-3-mercapto-2-methylpropanol in young Cabernet-Sauvignon and Merlot wines can exceed its perception threshold, thus suggesting its contribution to the aroma of these wines. Received: 8 June 1999  相似文献   

18.
Perfluorinated carboxylic acids are widely distributed in the environment, including remote regions, but their sources are not well understood. Perfluoropropionic acid (PFPrA, CF(3)CF(2)C(O)OH) has been observed in rainwater but the observed amounts can not be explained by currently known degradation pathways. Smog chamber studies were performed to assess the potential of photolysis of perfluoro-2-methyl-3-pentanone (PFMP, CF(3)CF(2)C(O)CF(CF(3))(2)), a commonly used fire-fighting fluid, to contribute to the observed PFPrA loadings. The photolysis of PFMP gives CF(3)CF(2)C·(O) and ·CF(CF(3))(2) radicals. A small (0.6%) but discernible yield of PFPrA was observed in smog chamber experiments by liquid chromatography-mass spectrometry offline chamber samples. The Tropospheric Ultraviolet-Visible (TUV) model was used to estimate an atmospheric lifetime of PFMP with respect to photolysis of 4-14 days depending on latitude and time of year. PFMP can undergo hydrolysis to produce PFPrA and CF(3)CFHCF(3) (HFC-227ea) in a manner analogous to the Haloform reaction. The rate of hydrolysis was measured using (19)F NMR at two different pHs and was too slow to be of importance in the atmosphere. Hydration of PFMP to give a geminal diol was investigated computationally using density functional theory. It was determined that hydration is not an important environmental fate of PFMP. The atmospheric fate of PFMP seems to be direct photolysis which, under low NO(x) conditions, gives PFPrA in a small yield. PFMP degradation contributes to, but does not appear to be the major source of, PFPrA observed in rainwater.  相似文献   

19.
Hexavalent chromium, Cr(VI), can be immobilized under neutral to alkaline conditions by reduction to Cr(III); similarly, the mobility of naturally occurring Cr in soils and sediments can be limited by its occurrence in the +III oxidation state. Conversely, the oxidation of Cr(IIi) to Cr(VI) increases both its toxicity and often its mobility. Dissolution of Cr-(OH)3(s) in 0.01 M NaNO3 suspensions was examined in batch experiments in the presence and absence of the strong oxidant sodium hypochlorite (NaOCI). Dissolution of Cr(OH)3(s) (1.0 g/L) was accelerated in the presence of excess strong oxidant (20 mM) at pH 9 by a factor of ca. 200 and to a lesser extent at pH 2 and 3. Linear kinetics of oxidative dissolution was observed at pH 9 and 3. In contrast, the rate of Cr release at pH 2 decreased rapidly with time, and within 2.5 h, the dissolution reaction was completely inhibited. Under oxidizing conditions, Cr released into solution is expected to be present as Cr(VI), which sorbs strongly to Cr(OH)3(s) at low pH. Cr(VI) sorption followed a Langmuir isotherm and reached maximum sorption densities of 308 +/- 8 and 271 +/- 10 micromol/g at pH 3 and 2, respectively. However, sorption of Cr(VI) (putatively formed during oxidative dissolution) cannot explain the observed inhibition of the reaction because (1) sorption occurs at both pH 2 and 3 but inhibition only at pH 2 and (2) preequilibration of Cr(OH)3(s) with Cr(VI) did not affectthe rate of dissolution observed upon the addition of the oxidant. Thus, we hypothesize that the inhibition of (net) oxidative dissolution at pH 2 may be the result of secondary precipitation of a chromic hydroxy chromate phase.  相似文献   

20.
To compare the β-carotene contents in different Chinese sweet potato (SP) varieties and to choose a variety of SP rich in β-carotene for the study of the effect of processing methods on β-carotene retention, β-carotene in thirteen varieties of sweet potato from China was measured by HPLC. The results showed that β-carotene contents were significantly correlated with SP flesh colours, with the orange-red fleshed SP varieties being higher in β-carotene.β-carotene contents in SP were affected by many factors, and this was demonstrated using the variety of Yanshu No.5, showing that the β-carotene contents in SP grown in different farming sites in the same area ranged from 53.2 to 84.3 mg kg− 1 fresh weight. Moreover, β-carotene distributes unevenly in one SP root, with highest concentrations in the core. The β-carotene content was positively related to the root size.Five processing methods including boiling, steaming, microwave cooking, frying, and post steam-drying were simulated in the study to check their effects on the true retention of β-carotene in SP. Compared to boiling, steaming resulted in much more loss of β-carotene and microwave cooking resulted in the biggest loss of β-carotene among the five processing methods.

Industrial relevance

Orange-fleshed sweet potato can be prepared for sale and consumption, using methods that protect the β-carotene content. This can aid in promoting sweet potato as a staple food as well as a snack food for supplying vitamin A for both rural and urban populations. Prepared orange-fleshed sweet potato can contribute to alleviating vitamin A deficiency in China as well as other low-income countries.  相似文献   

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