Fracture strength of copy-milled and conventional In-Ceram crowns

The purpose of this study was to compare the fracture resistance of copy-milled and conventional In-Ceram crowns. Four groups of 10 uniform sized all-ceramic anterior crowns were fabricated for this test: (1) In-Ceram Spinell (2) In-Ceram Alumina (3) Celay In-Ceram Spinell, and (4) Celay In-Ceram Alumina crowns. All specimens were cemented on stainless steel master die with resin cement and stored in 37 degrees C water for one day prior to loading into a universal testing machine. Using a steel ball at a crosshead speed of 0.5 mm min-1, the crowns were loaded at 30 degrees C angle until catastrophic failure occurred. Mean fracture strength was analysed and compared. Under the conditions of this study and the materials used, the following conclusions were drawn: 1. The strength of Celay In-Ceram anterior crowns had a slightly higher fracture strength than conventional In-Ceram crowns. 2. In-Ceram Alumina crowns had a significantly higher fracture strength than In-Ceram Spinell crowns in both conventional and copy milling methods.     

Peculiar Porous Aluminum Oxide Films Produced via Electrochemical Anodizing in Malonic Acid Solution with Arsenazo-I Additive

The influence of arsenazo-I additive on electrochemical anodizing of pure aluminum foil in malonic acid was studied. Aluminum dissolution increased with increasing arsenazo-I concentration. The addition of arsenazo-I also led to an increase in the volume expansion factor up to 2.3 due to the incorporation of organic compounds and an increased number of hydroxyl groups in the porous aluminum oxide film. At a current density of 15 mA·cm⁻² and an arsenazo-I concentration 3.5 g·L⁻¹, the carbon content in the anodic alumina of 49 at. % was achieved. An increase in the current density and concentration of arsenazo-I caused the formation of an arsenic-containing compound with the formula Na_1,5Al₂(OH)_4,5(AsO₄)₃·7H₂O in the porous aluminum oxide film phase. These film modifications cause a higher number of defects and, thus, increase the ionic conductivity, leading to a reduced electric field in galvanostatic anodizing tests. A self-adjusting growth mechanism, which leads to a higher degree of self-ordering in the arsenazo-free electrolyte, is not operative under the same conditions when arsenazo-I is added. Instead, a dielectric breakdown mechanism was observed, which caused the disordered porous aluminum oxide film structure.     

牙科玻璃渗透陶瓷凝胶注模成型的影响因素研究

目的 探索凝胶注模成型技术结合玻璃渗透技术应用于牙科氧化锆增韧氧化铝(ZTA)全瓷材料制作的可行性。方法 ①利用凝胶注模成型技术制备氧化锆增韧氧化铝陶瓷,经过1 150℃、1 200℃、1 250℃半烧结;采用干压成型法制备陶瓷素坯,1 200℃半烧结。测试4组样品的烧结线收缩率、烧结后孔隙率及孔径分布。②将上述4组样品与Tyszblat专利为基础的优化玻璃料在1 150℃条件下进行玻璃渗透20 min;另外将1 200℃凝胶组素坯分别渗透20 min、40 min、60 min。测定各组样本的渗透深度。结果 ①1 250℃凝胶组渗透深度明显小于1 150℃凝胶组和1 200℃凝胶组,而1 150℃凝胶组渗透后形变较大;1 200℃干压组的孔隙率和孔径明显小于3组凝胶注模成型样本。②随着渗透时间的延长,渗透深度逐渐增加,渗透锋面也随时间延长变得不平整,而渗透时间与渗透深度的平方成正比。结论 凝胶注模成型的ZTA陶瓷能够进行较好的玻璃渗透,具有应用于牙科全瓷修复体制作的潜力。     

玻璃渗透氧化铝陶瓷树脂粘接耐久性的研究

目的分析含有不同类型酸性树脂单体的硅烷偶联剂及不同类型树脂粘接剂的相互组合对玻璃渗透氧化铝陶瓷树脂粘接耐久性的影响。方法使用3种硅烷偶联剂处理玻璃渗透氧化铝陶瓷的表面,使用2种双重固化树脂粘接剂与之粘接。测量试件在0和30 000次冷热循环后的粘接强度。结果冷热循环前,粘接剂A与未硅烷化处理陶瓷间的粘接强度显著低于其他硅烷化处理组,粘接剂A、B与偶联剂B处理的陶瓷间的粘接强度显著低于其与偶联剂A和C的粘接强度。冷热循环30 000次后,粘接剂A与未硅烷化处理陶瓷组的试件全部脱落;而其他硅烷化处理陶瓷组中,只有偶联剂A处理的陶瓷表面与粘接剂A和B间的粘接强度达到了5 MPa以上。结论使用10-甲基丙烯酰氧癸基磷酸酯作为硅烷水解剂的硅烷偶联剂处理的玻璃渗透氧化铝陶瓷能够与不同类型的树脂粘接剂获得较好的粘接耐久性。     

A comparison of silica and alumina columns for high-performance liquid chromatographic separations of basic drugs and plasma constituents following on-line solid-phase extraction with column switching

A comparison has been made of a silica and an alumina column with respect to retention behaviour in high-performance liquid chromatography of pure drug solutions and plasma profiles following on-line solid-phase extraction. Using methanol—ammonium nitrate buffer (80:20, v/v) as eluent, it was found that these systems lend themselves well to the column switching technique. Increasing the pH of the mobile phase produced similar shifts in retention for basic drugs on both columns, but fewer plasma interferents are retained on the alumina column as compared to the silica column under the same operating conditions.     

Structural degradation of ceramics

Fabrication procedures for alumina are summarized and the potential for improving the mechanical strength indicated. Engineering performance of alumina is discussed, particularly in relation to femoral heads, giving emphasis to statistical variations in strength and time dependent strength degradation processes.     

Stimulation induced changes in extracellular free calcium in normal cortex and chronic alumina cream foci of cats

Changes in extracellular [Ca²⁺]₀ (δ Ca) were measured with ion selective microelectrodes in the sensorimotor cortex of cats, surrounding alumina cream lesions and in the contralateral homotopic cortex. The lesions were produced by topical application of alumina cream 6 months-6 years prior to experiments. In normal cortex, stimulus induced reductions of [Ca²⁺]₀ were found to be maximal (up to 0.45 mM) in depths of 200–300 μm below the cortical surface. At depths of 600 μm and more below the cortical surface, [Ca²⁺]₀ usually rose by up to 0.2 mM above baseline. In the vicinity of the chronic lesion as well as in contralateral cortex [Ca²⁺]₀ fell initially during stimulation in all depths. close to the lesion δ Ca was as high as 0.8 mM and sites of maximal δ Ca were found to be located deeper in the cortex. About 5 mm from the scar as well as in the contralateral homotopic cortex, maximum δ Ca levels were found in a depth of 200–300 μm. It is suggested that Ca²⁺ dependent mechanisms are involved in epileptogenesis in chronic epileptic foci.     

EXPERIMENT AND RESEARCH ON DEVELOPMENT AND CHARACTERIZATIONS OF ANODIC ALUMINA MEMBRANE FOR USE IN HEMODIALYSIS

Chronic kidney disease is a worldwide publichealth problem. In the United States, there is an in-creasing incidence and prevalence of kidney failure,with high cost and poor outcomes. Till up to Decem-ber 31, 2000, the number of end-stage renal diseases( ESRD) has increased to approximately 378,862, inwhich 65 percent are being treated with hemodialy-sis[1]. In China there are 41,755 ESRD patients un-dergoing dialysis, in which 89. 5 percent are beingtreated with hemodialysis[2]. These fac…     

氧化铝陶瓷膜富集醋香附挥发油的工艺研究

目的 考察100、300、800 nm和1、2μm 5种不同孔径氧化铝陶瓷膜分离醋香附（vinegar-processed Cyperi Rhizoma）挥发油的工艺,探索陶瓷膜用于中药挥发油分离的可行性,为实现油水混合物的规模化分离提供实验依据。方法 采用水蒸气蒸馏法获得醋香附油水混合物,考察醋香附油水混合物粒径分布、平均膜孔径与稳定膜通量之间的相关性,采用化学需氧量定量评价挥发油截留率,并通过油水分离前后陶瓷膜表面宏观和溶液微观性质的变化来定性验证油水分离效果。结果 2种小孔径氧化铝陶瓷膜（平均孔径100、300 nm）在0.10～0.20 MPa压力下挥发油截油率较高,但膜通量低,且易造成膜孔堵塞;2种中等孔径氧化铝陶瓷膜（平均孔径800 nm、1μm）在增加压力后通量显著增加,但挥发油截油率略有降低,分别在0.05 MPa和0.03 MPa时达到最佳分离效果;1种大孔径氧化铝陶瓷膜（平均孔径2μm）在不同压力下通量均较高,但挥发油截油率较低。结论 在0.05 MPa和0.03 MPa 2种压力下,800 nm和1μm孔径氧化铝陶瓷膜可实现醋香附油水混合物中挥发油成分的富集,为深...