Cutaneous cryosurgery in family medicine: dimethyl ether-propane spray versus liquid nitrogen

OBJECTIVE: To compare the efficacy, tolerance and safety of two types of cryotherapy, performed by family physicians, for benign cutaneous lesions: low freezing (-59 degrees C) with dimethyl either-propane cryogenic spray (DMEP) and intense freezing (196 degrees C) with conventional liquid nitrogen (LN). DESIGN: A randomised, multi-centered, controlled clinical trial, with single-blind assessment. SETTING: Three primary care teaching teams in the Community of Madrid. PATIENTS AND OTHER PARTICIPANTS: Ten MIR from family & community medicine intervened. There were 124 patients, who had 174 benign cutaneous lesions, suitable for cryotherapy. There were 3 voluntary withdrawals, none because of an adverse reaction. Interventions, in each case there was local application for a standard time of the randomised agent. Control-group intervention, 81 cases: swab soaked in LN. Study-group intervention, 93 cases: swab saturated with DMEP spray. Maximum of three freezings per case, at weekly intervals. MEASUREMENTS AND MAIN RESULTS: A doctor made a blind assessment of the results (elimination, adverse reaction, aesthetic result) 15 days after treatment. CONCLUSIONS: No clinically relevant differences between the efficacy, tolerance and safety of the two cryogenic agents used in primary care were found. The low freezing of DMEP was sufficient for the cryotherapy of benign lesions.     

Rate of nitrogen desorption from liquid iron-carbon and iron-chromium alloys with argon

The rate of nitrogen desorption from inductively stirred liquid iron, iron-carbon, and iron-chromium alloys with argon carrier gas has been measured by the sampling method for a wide range of nitrogen, carbon, and chromium contents mainly at 1600 °C. The results obtained by the present work and other data of previous investigators are used to clarify the reaction mechanism of nitrogen desorption from liquid iron. The rate of nitrogen desorption from liquid iron and iron alloys is second order with respect to nitrogen content in the metal under the present condition, and mutual relationships among interfacial chemical reaction, liquid-phase mass transfer, and gas-phase mass transfer are elucidated. The effects of oxygen and sulfur on the rate of nitrogen desorption are given byk _' ^{c ’} = 3.15ƒ_N ² [1/(1 + 300a₀ + 130a_s)]. Carbon dissolved in iron increases the rate of nitrogen desorption, and chromium decreases it. The effects of these alloying elements can be explained by the change of the nitrogen activity in the metal. This paper is based on a presentation made at the G. R. Fitterer Symposium on Nitrogen in Metals and Alloys held at the 114th annual AIME meeting in New York, February 24–28, 1985, under the auspices of the ASM-MSD Thermodynamic Activity Committee.     

Rate of nitrogen desorption from liquid iron-carbon and iron-chromium alloys with argon

The rate of nitrogen desorption from inductively stirred liquid iron, iron-carbon, and iron-chromium alloys with argon carrier gas has been measured by the sampling method for a wide range of nitrogen, carbon, and chromium contents mainly at 1600 °C. The results obtained by the present work and other data of previous investigators are used to clarify the reaction mechanism of nitrogen desorption from liquid iron. The rate of nitrogen desorption from liquid iron and iron alloys is second order with respect to nitrogen content in the metal under the present condition, and mutual relationships among interfacial chemical reaction, liquid-phase mass transfer, and gas-phase mass transfer are elucidated. The effects of oxygen and sulfur on the rate of nitrogen desorption are given byk _' ^{c ’} = 3.15?_N ² [1/(1 + 300a₀ + 130a_s)]. Carbon dissolved in iron increases the rate of nitrogen desorption, and chromium decreases it. The effects of these alloying elements can be explained by the change of the nitrogen activity in the metal.     

固定式气体灭火系统的设计问题初探

气体灭火系统是近几年才迅速发展并逐渐普及的一种灭火方式，因此，对于设计人员来说，正确掌握其性能及计算特点就显得十分必要。本文着重就固定式气体灭火系统的设计中应注意的几个问题进行一些探讨。     

转炉底吹氮氩切换对氮质量分数影响

为了研究转炉底吹气体对钢水终点氮质量分数影响,研究了迁钢210 t顶底复吹转炉底吹模式对转炉终点氮质量分数的影响,并基于钢液脱氮和吸氮理论对试验结果进行了分析。应用实践结果表明,随着铁水碳质量分数增加以及终点氧质量分数降低,终点氮质量分数逐渐降低;在铁水条件、副原料、转炉终点、底吹流量以及过程操作一致条件下,随着氮氩切换时间节点延长,钢液增氮量逐渐增加。当切换时间节点为吹氧比56%以内,底吹氮氩切换对终点钢水氮质量分数影响较小,当切换时间节点为吹氧比高于56%时,终点钢水氮质量分数增幅较大。     

Fluid dynamics of vertical submerged gas jets in liquid metal processing systems

High speed cinematography and a pressure trace technique have been used to investigate the fluid dynamics of inert gas jets injected vertically upward into water, molten tin, lead-tin alloy, and iron. Two flow regimes of jet behavior were observed: one in which unstable bubbles were produced at the jet nozzle, and one in which a steady cone of gas emerged from the nozzle and broke up continuously into small bubbles. The transition between bubbling and continuous jet flow was controlled by the mass flow of gas per unit area of the jet and occurred at a flow rate of approximately 40 g/cm² s in all of the systems studied.     

Carbon or nitrogen alloyed quenched and tempered stainless steels - a comparative study

Some conventional stainless quenched and tempered steel grades were modified by substituting nitrogen for carbon and by variing the contents of chromium, molybdenum and nickel. Results of a comparative study of carbon and nitrogen steels are presented in a wide range of tempering temperatures. In nickelmartensitic steels nickel can be partially substituted by nitrogen without harming the properties. Due to their finer microstructure nitrogen steels with 15-17 %Cr, 2 %Ni and 0.2 %N, at the same strength level, offer higher toughness and better corrosion resistance than the respective conventional steel X20 CrNi 17 2.     

A study of the solidification of argon bubbles in aluminium

A study has been carried out of the solidification of argon in a wide range of argon bubble sizes in aluminium. Using a cryogenic stage samples have been cooled to 78K and the freezing range and lattice parameter of solid argon determined. The results indicate that for very small crystal sizes diffraction from argon will be difficult to detect, at intermediate sizes the argon solidifies epitaxially with the host matrix and for large bubble sizes random crystals may form.     

Kinetics of aluminum oxidation during argon injection into liquid steel

Specification of the argon stirring process. Investigations of the aluminum oxidation kinetics in steel melts for deep drawing steel qualities. Experimental results on the influence of iron oxide, P₂O₅ and MnO concentration in the ladle slag. Exposition of a reaction model under the assumption of an instantaneous and irreversible reaction between dissolved oxygen and aluminum. Discussion about the use of the results for an improved process control during rinsing treatment.     

120 t钢包底吹氩气物理模拟

为了优化国内某钢厂钢包的底吹位置和气体流量等工艺参数,更好地提高钢水洁净度,对120 t钢包建立1∶3水模型,模拟研究了底吹位置和气体流量对钢液混匀时间和钢渣覆盖情况的影响.结果表明,底吹位置不同时,混匀时间存在明显差异;随着气体流量增大,钢包混匀时间整体呈下降趋势,但减小幅度越来越小,吹气流量有最佳值;底吹位置为0....     

A new interpretation of mechanisms of nitrogen desorption from liquid iron

Mechanisms of nitrogen desorption from liquid iron were discussed in detail. It is proposed that association of nitrogen atoms at the surface to form a molecule occurs by two separate mechanisms operating in parallel: single site mechanism meaning that an adsorbed atom reacts with an atom coming from the bulk using one adsorption site, and dual site mechanism meaning that two adsorbed atoms diffuse to and react with each other over two adsorption sites, and that association via these two parallel mechanisms is rate controlling for the interfacial reaction of nitrogen desorption. A model for the second order rate constant of nitrogen desorption from liquid iron was theoretically derived, and was found to be in close agreement with the results reported in literature, for both normal pressure and reduced pressures.