利用脱硫石膏水热合成硫酸钙晶须

以脱硫石膏为原料,采用水热法工艺制备硫酸钙晶须.借助电导率、化学电位、XRD和SEM等分析方法,在不同反应条件下研究了硫酸钙晶须生长的变化规律,随着反应温度、反应时间、固液比和初始pH值的增加,硫酸晶须的长径比呈先增加后减小的趋势.在本实验条件下最佳工艺参数为:反应温度140℃,反应时间120min,固液比为1∶10,初始pH值为5,原料粒度1.36μm.此时所制备的硫酸钙晶须长径比可以达到82.57.     

盐泥制备硫酸钙晶须工艺研究

以盐泥和硫酸为原料,采用常压酸化法制备硫酸钙晶须。考察反应温度、反应时间、搅拌速度、原料配比等因素对硫酸钙晶须的影响。通过实验得出优化工艺条件为:反应温度80℃,反应时间30min,搅拌速度150 r/min,原料配比(盐泥、硫酸、水的质量比)1∶1.84∶2。在该条件下,晶须产率为33.28%,晶须平均长径比为85,白度为68.4%,硫酸钙纯度达到92.75%。     

水热法合成超细硫酸钙晶须

以CaSO4.2H2O为原料,采用水热法合成了超细硫酸钙晶须.以扫描电镜作为分析超细硫酸钙晶须直径的手段,得出制备超细硫酸钙晶须的最优工艺条件为反应温度120℃、料浆初始pH值9.8~10.1、料浆质量分数5%、原料粒度18.1μm.在此条件下,制备出了平均直径为0.19μm,长径比为98的超细硫酸钙晶须产品.得出的结论对超细硫酸钙晶须的工业化生产具有重要的指导意义.     

复配型晶体调控剂对硫酸钙晶须生长的影响

以预处理的工业废渣磷石膏为原料,氯化亚铁与十二烷基磺酸钠(FeCl_2·4H_2O+SDS)复配物作晶体调控剂,采用水热法成功制备了硫酸钙晶须,利用SEM和XRD分别对硫酸钙晶须的表面形貌、物相特征进行了表征,研究了复配晶体调控剂掺量对硫酸钙晶须性能的影响,并对复配型晶体调控剂的作用机理进行了分析。研究结果表明,晶体调控剂能够显著增大硫酸钙晶须的长度和长径比,改善晶须的形貌,随着其掺量的增加,晶须长度、长径比均呈现先增加后减小的趋势,其最佳掺量(质量分数)为1.0%,此时晶须的平均长径比为139.50。     

硫酸钙晶须的表面改性研究

采用硼酸酯表面活性剂SBW-181对硫酸钙晶须进行了单因素条件改性试验,分别考察了改性剂用量、改性温度、改性时间和搅拌速率等工艺因素对硫酸钙晶须表面改性的影响.试验结果表明:硼酸酯表面活性剂SBW-181对硫酸钙晶须的改性效果较好,在最佳工艺条件下,改性产品的活化指数为0.996,接触角为103.4°.建立了硼酸酯表面活性剂SBW-181与硫酸钙晶须的作用模型.得出的结论对硫酸钙晶须表面改性的工业化生产具有重要的指导意义,并为硫酸钙晶须的应用研究奠定了理论基础.     

常压盐溶液法从烟气脱硫石膏制备硫酸钙晶须研究

对在常压盐溶液中用钙基湿法烟气脱硫石膏制备硫酸钙晶须的工艺过程进行试验研究,考察了温度、CaCl2浓度、H2SO4浓度和搅拌速率对脱硫石膏转化过程的影响。结果表明,在一定浓度的CaCl2和H2SO4溶液中,脱硫石膏可转化生成α-CaSO4.0.5H2O晶须,最适宜的转化条件为:w(CaCl2)=5.0%、w(H2SO4)=0.8%、结晶温度为102℃,搅拌速率为160r/min。在此条件下转化6h制得的α-CaSO4.0.5H2O晶须平均长度为236μm,长径比为95。     

MgSO_4/MgCl_2对脱硫石膏溶解度及其晶须结晶的影响

以预处理后脱硫石膏为原料,采用水热法制备了硫酸钙晶须。研究了添加剂MgSO_4、MgCl_2对晶须显微结构、长径比和脱硫石膏溶解度的影响,探讨了MgSO_4、MgCl_2在反应溶液体系中的解离特性及作用机理。研究结果表明:MgSO_4、MgCl_2都可以改善硫酸钙晶须的结晶,提高晶须的长径比,且不影响其物相组成。在MgSO_4添加量(质量分数)为2.0%、MgCl_2添加量(质量分数)为1.5%时,制备的晶须长径比分别为80和110。在反应溶液中,MgSO_4的加入降低了脱硫石膏的溶解度,同离子效应起主导作用,而MgCl_2的加入则增加了其溶解度。MgSO_4(0)中性离子对调节反应溶液中各离子浓度的相对稳定起主导作用,MgCl_2改善晶须结晶的作用效果优于MgSO_4。     

半水硫酸钙晶须制备稳定一体化

使用优选稳定剂对半水硫酸钙晶须进行制备稳定一体化处理,研究了稳定剂用量对半水硫酸钙晶须形貌及稳定性的影响.通过SEM和XRD等检测手段对晶须产品进行了表征,结果表明:在制备过程中加入稳定剂油酸钠,当用量为0.025%时,半水硫酸钙晶须可保持形状稳定,但制备后静置72h后,晶型已全部转化为二水硫酸钙;采用分段加药的方式,即制备时加入0.025%硬脂酸钠,制备后加入0.15%油酸钠,半水硫酸钙晶须形貌与晶型可保持不变,实现了半水硫酸钙晶须的制备稳定一体化.     

硫酸钙晶须的制备及其改性聚丙烯性能的研究

在不同反应条件下制备了不同长径比的硫酸钙晶须(CSW),利用硅烷偶联剂KH550(相对于CSW质量的2%)在110℃下对CSW进行干法改性.以硫酸钙晶须作为增强改性剂制备了PP/CSW复合材料.力学性能与差示扫描量热分析(DSC)结果表明:不同长径比的CSW对PP的力学性能和结晶性能均有提高;采用平均长径比为29的CSW添加剂,当添加的质量分数为20%时,复合材料的拉伸强度、弯曲模量分别比纯PP的提高了11%、104%;结晶温度比纯PP的提高了12℃;几种CSW对复合材料的热稳定性和耐热性都有改善,且随着CSW质量分数的增加,材料的热稳定性和耐热性提高越显著.     

水化时间和温度对半水硫酸钙晶须水化过程的影响

对水热法产物半水硫酸钙晶须水化过程进行了研究,重点考察了水化时间和温度对晶须水化过程的影响。结果表明,在水化温度为25~90℃范围内,水化产物中半水硫酸钙晶须含量随着水化时间的增加而减少,最终全部转化为片状、薄板状或者块状二水硫酸钙;随着水化温度的增加,水化诱导期延长,特别是在90℃时,半水硫酸钙晶须可稳定存在60min;根据水化产物观测结果以及物相组成分析发现,水化机理主要分为水化诱导期、半水硫酸钙晶须溶解以及二水硫酸钙重结晶3部分。     

The structural basis of calcium transport by the calcium pump

The sarcoplasmic reticulum Ca2+-ATPase, a P-type ATPase, has a critical role in muscle function and metabolism. Here we present functional studies and three new crystal structures of the rabbit skeletal muscle Ca2+-ATPase, representing the phosphoenzyme intermediates associated with Ca2+ binding, Ca2+ translocation and dephosphorylation, that are based on complexes with a functional ATP analogue, beryllium fluoride and aluminium fluoride, respectively. The structures complete the cycle of nucleotide binding and cation transport of Ca2+-ATPase. Phosphorylation of the enzyme triggers the onset of a conformational change that leads to the opening of a luminal exit pathway defined by the transmembrane segments M1 through M6, which represent the canonical membrane domain of P-type pumps. Ca2+ release is promoted by translocation of the M4 helix, exposing Glu 309, Glu 771 and Asn 796 to the lumen. The mechanism explains how P-type ATPases are able to form the steep electrochemical gradients required for key functions in eukaryotic cells.     

Three types of neuronal calcium channel with different calcium agonist sensitivity

How many types of calcium channels exist in neurones? This question is fundamental to understanding how calcium entry contributes to diverse neuronal functions such as transmitter release, neurite extension, spike initiation and rhythmic firing. There is considerable evidence for the presence of more than one type of Ca conductance in neurones and other cells. However, little is known about single-channel properties of diverse neuronal Ca channels, or their responsiveness to dihydropyridines, compounds widely used as labels in Ca channel purification. Here we report evidence for the coexistence of three types of Ca channel in sensory neurones of the chick dorsal root ganglion. In addition to a large conductance channel that contributes long-lasting current at strong depolarizations (L), and a relatively tiny conductance that underlies a transient current activated at weak depolarizations (T), we find a third type of unitary activity (N) that is neither T nor L. N-type Ca channels require strongly negative potentials for complete removal of inactivation (unlike L) and strong depolarizations for activation (unlike T). The dihydropyridine Ca agonist Bay K 8644 strongly increases the opening probability of L-, but not T- or N-type channels.     

Structural changes in the calcium pump accompanying the dissociation of calcium

In skeletal muscle, calcium ions are transported (pumped) against a concentration gradient from the cytoplasm into the sarcoplasmic reticulum, an intracellular organelle. This causes muscle cells to relax after cytosolic calcium increases during excitation. The Ca(2+) ATPase that carries out this pumping is a representative P-type ion-transporting ATPase. Here we describe the structure of this ion pump at 3.1 A resolution in a Ca(2+)-free (E2) state, and compare it with that determined previously for the Ca(2+)-bound (E1Ca(2+)) state. The structure of the enzyme stabilized by thapsigargin, a potent inhibitor, shows large conformation differences from that in E1Ca(2+). Three cytoplasmic domains gather to form a single headpiece, and six of the ten transmembrane helices exhibit large-scale rearrangements. These rearrangements ensure the release of calcium ions into the lumen of sarcoplasmic reticulum and, on the cytoplasmic side, create a pathway for entry of new calcium ions.     

氢氧化钙和碳酸钙混合物的分析方法

在甲醇存在下,用EDTA四钠盐能准确而精密地络合滴定Ca(OH)2和CaCO3混合物.当甲醇与水的体积比在0.2～0.6之间时,CaCO3 对Ca(OH)2的滴定不干扰,且能准确滴定Ca(OH)2.本法可用来监测石灰乳碳化的全过程.     

天门冬氨酸钙和葡萄糖酸钙兔体内吸收度的研究

用原子吸收分光光度法测定兔血清钙浓度,结果表明,天门冬氨酸钙和葡萄糖酸钙的吸收度无显著性差异。     

Depletion of intracellular calcium stores activates a calcium current in mast cells.

In many cell types, receptor-mediated Ca2+ release from internal stores is followed by Ca2+ influx across the plasma membrane. The sustained entry of Ca2+ is thought to result partly from the depletion of intracellular Ca2+ pools. Most investigations have characterized Ca2+ influx indirectly by measuring Ca(2+)-activated currents or using Fura-2 quenching by Mn2+, which in some cells enters the cells by the same influx pathway. But only a few studies have investigated this Ca2+ entry pathway more directly. We have combined patch-clamp and Fura-2 measurements to monitor membrane currents in mast cells under conditions where intracellular Ca2+ stores were emptied by either inositol 1,4,5-trisphosphate, ionomycin, or excess of the Ca2+ chelator EGTA. The depletion of Ca2+ pools by these independent mechanisms commonly induced activation of a sustained calcium inward current that was highly selective for Ca2+ ions over Ba2+, Sr2+ and Mn2+. This Ca2+ current, which we term ICRAC (calcium release-activated calcium), is not voltage-activated and shows a characteristic inward rectification. It may be the mechanism by which electrically nonexcitable cells maintain raised intracellular Ca2+ concentrations and replenish their empty Ca2+ stores after receptor stimulation.     

过氧化钙合成工艺的研究

研究了在氢氧化钙-氯化铵-双氧水法常温下制备过氧化钙的工艺条件中，反应温度、反应时间、稳定剂用量、氢氧化钙过量数、双氧水的浓度及氯化铵用量对过氧化氢利用率的影响．     

Formation mechanism of calcium hexaluminate

To investigate the formation mechanism of calcium hexaluminate (CaAl₁₂O₁₉, CA₆), the analytically pure alumina and calcia used as raw materials were mixed in CaO/Al₂O₃ ratio of 12.57:137.43 by mass. The raw materials were ball-milled and shaped into green specimens, and fired at 1300–1600°C. Then, the phase composition and microstructure evolution of the fired specimen were studied, and a first principle calculation was performed. The results show that in the reaction system of CaO and Al₂O₃, a small amount of CA₆ forms at 1300°C, and greater amounts are formed at 1400°C and higher temperatures. The reaction is as follows: CaO·2Al₂O₃ (CA₂) + 4Al₂O₃ → CA₆. The diffusions of Ca2+ in CA₂ towards Al₂O₃ and Al3+ in Al₂O₃ towards CA₂ change the structures in different degrees of difficulty. Compared with the difficulty of structural change and the corresponding lattice energy change, it is deduced that the main formation mechanism is the diffusion of Ca2+ in CA₂ towards Al₂O₃.