Search Documents

By Rob Lederer, Chris Batten

Traditionally coal model digital terrain models (DTM) are created from lithological information obtained from broad scale exploration holes. The grid layout and distance between holes means that models do not commonly display local variations of seam dip, faulting and shearing. Due to this, issues can often arise when designing the loading of blast patterns based on potential variances between model and actual coal seam locations. Many sites will often attempt to create more accurate models through the collection of data from coal edge pickups on highwalls and in blast faces, along with information recorded by drillers (touch coal holes) from both production and presplit holes for both the current and previous blasts.

Jan 1, 2012

By A. Consigny

New "clean technologies" to treat mining and metallurgical effluents containing dissolved metals have been successfully applied at mine sites in North America and Asia, treating water flows up to 24,000 m3/day. These clean technologies offer significant benefits compared to conventional alternatives and provide a sustainable solution that eliminates residual waste sludge, improves water conservation, generates revenues from wastewater, and delivers overall improvements to the environment. This paper will profile these technologies, and provide best practice case study examples of their application at mining operations, including data for water chemistry, flows, water quality, capital and operating costs, and life cycle costs of treatment.

Jan 1, 2011

By A Melloy, D Holt, M Jurak

Oaky North is AustraliaÆs highest producing underground coal mine. In 2011, the mine produced 8.7 Mt of high-quality coking coal. The high quantities are a result of the constant strive for optimising the operating time of major production units, which involves investing numerous resources, including diesel equipment, in supporting and maintaining their operation.In July 2011 it was identified that the diesel particulate matter (DPM) levels in the underground workings were above acceptable levels, due to the high level of diesel activity. Over the next 12 months, several controls were implemented to reduce exposure to personnel: the main ventilation system was upgraded; the production forecast was adjusted to better manage the diesel fleet, removing surges in diesel usage; and an electronic diesel tag board was introduced to centrally manage the distribution of diesel usage around the mine.From the start of the campaign in emission reduction, an intense DPM monitoring regime was established. Within a few months of the introduction of the centralised tag board, there was a major reduction in emission levels. After the installation and commissioning of the new main fans, the emission levels dropped further, such that over-exposures are now a rarity.Oaky North continues to explore new systems to better utilise their diesel fleet while still maintaining control over DPM emissions.CITATION:Melloy, A, Holt, D and Jurak, M, 2013. Reduction in diesel particulate matter at Oaky North, in Proceedings The Australian Mine Ventilation Conference , pp 187-190 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 1, 2013

By Phillip E. Butler

Since early 1973, the Pennsylvania Department of Transportation (PennDOT) has been actively engaged in the utilization of coal mine refuse in the design and construction of highway embankments. The Soils and Geological Engineering Division of the Bureau of Materials, Testing and Research has the task of managing the program which includes field investigations, laboratory testing, engineering evaluation, planning, coordination, implementation, construction control, and review of construction performance. The objectives of the utilization program, in removing colliery refuse banks and utilizing the material in construction, are the environmental and aesthetic rehabilitation of those areas in the Anthracite and Bituminous coal fields which have been plagued for such a long time by air and water pollution, and unsightly landscapes; and the economic rehabilitation of those areas occupied by refuse banks by providing usable land which can now be developed as residential, business, or industrial sites.

Jan 1, 1975

By James P. Kimball

Jan 1, 1885

By Edgar J. Briceño

El presente texto señala el resultado de algunas pruebas realizadas en el período de 1974 y 1979 en la concentradora de Toquepala, a fin de mejorar el proceso de producción en la industria minera. Para ello, se ejecutaron 14 pruebas a nivel de planta, de donde se seleccionaron seis, las cuales se ejecutaron también a nivel de laboratorio para así compararlas con lo standard. Las seis pruebas referidas son: Evaluación de forros de jebe en molienda, evaluación de diferentes tamaños de bolas, evaluación del espumante Celaproht-16, efectos de Asmol Polhalla m- 59 en sedimentación y filtrado de las colas de planta de Molibdenita, evaluación del espumante Ucon R-23 y lonas tampereen en el filtrado,

Oct 14, 1980

By W. E. Rice

THE ceramic industry has to do with forming or molding articles of clay, and imparting to them their characteristic properties of permanence, strength and color by subjecting them to heat treatment in kilns. This heat treatment is commonly known as "firing" or "burning." The art of firing clay ware antedates the industrial use of coal; hence wood was the fuel first used, and the earliest kilns were built to burn wood. The majority of the clay ware produced today is fired in periodic kilns that are essentially enlarged structures similar to the earliest enclosed kilns; a kiln consists of a large chamber 16 to 32 ft. dia. (or rectangular) in which the ware is charged and fired either in direct contact with flame or hot gases from the fuel, or in saggers which shield the ware from direct contact with the gases. The fuel is burned in a number of small furnaces built in the thick .wall that encloses the chamber; these furnaces are from 16 to 36 in. wide and from 3 to 5 ft. long; some of them have horizontal or sloping grates, but many have no, grates; the last are called "dead-bottom" furnaces. The temperature necessary to mature the charge in the kiln varies for different clays; for some it is as low as 1800°, and for others as high as 2700° F. Wood was an ideal fuel for the low temperatures that were used in early kilns; it burns freely and produces along, clean flame, which promotes uniform distribution of the heat in the kiln; it does not coke and so restrict the passage of air through the fuel bed; the ash does not melt in the fuel bed to form clinker; and the ash that is carried into the chamber and deposited on the charge does not contain iron and sulfur to discolor the clay. The extent of the ceramic industry now precludes the general use of wood in kilns, so that today this industry is one of the large users -of bituminous coal, burning more than eight million tons annually in kilns. Manufacturing plants usually are at or near the source of clay, with deposits of coal suitable for kilns occurring near the clay. The cost of coal is the largest single item of expense in the manufacture of clay ware, and, because all coals are not equally suitable for the process, the careful selection of coal is important. In this selection the desidera-

Jan 1, 1932

By Theo Lehner

The Rönnskär smelter has wide experience in the field of recycling of non-ferrous metals. Today, smelting and refining from primary and secondary raw materials are integrated in a complex flow sheet. Boliden operates a lead flash smelter, a lead refinery, a copper smelter and refinery, a sulphuric acid and sulphur dioxide plant, a slag fuming plant and precious metal plant at its Rönnskär smelter in the North of Sweden. The Business Area Smelter Operations also incorporates Boliden Bergsöe, Sweden's lead-acid battery recycler, and Norzink, Norway, where recycled zinc accounts for more than 20% of it's production. Raw materials for the Rönnskär smelter include concentrates, ashes, slags, metallic scrap, electronic scrap and electric arc furnace (EAF) steel-making dust. This paper briefly describes current operations and illustrates current measures to improve productivity. Limits to recycling as experienced by a non-ferrous smelter are, illustrated. The deportment of critical elements contained in raw materials is also discussed.

Jan 1, 1998

By Robert Gilman Brown

The original power-plant of the Standard Company has been described* by Mr. T. H. Leggett, late president and manager of the company; but since the presentation of his paper considerable additions have been made, which will be found interesting because of the engineering features involved and of the attainment of a high degree of flexibility with the inflexible, two-wire, alternating system of electrical transmission. Although these additions have been completed during the last year, they constitute, to a large extent, only the carrying out of plans that belonged to the original conception of the installation. The regular operation of the water-power through the winter proved very difficult; there was a considerable length of ditch to be kept open, and, as the stream is small and any freezing night may stop the whole flow of water, there was the .additional trouble of having no reserve to draw upon. The rule for the winter is, that after a night of hard frost water begins to move in the canon before noon on all but the coldest days. To obviate the nuisance of the anchor-ice, and to make available all of the water, a dam of sufficient height to impound several days' run of water has been built across the canon, 3875 feet above the power-house, and provided with pressurepipe well below the surface. In place of the 1571 feet of pipeline from penstock to power-house, there has been substituted a line 3875 feet long to bring water direct from the dam. The dam is of logs, cribbed up in squares of about 12 feet, ballasted with earth and rock and sheathed on the water-face with 3-inch plank.

Jan 1, 1897

By S. G. Kumar, R. G. Reddy

"Niobium aluminides offer the advantage of higher high temperature capability compared to other intermetallic aluminides due to the refractory nature of niobium. However, the reaction sequence in Nb-Al system is sluggish and currently there is a great interest in the processing aspects of these materials. In the present study, a systematic investigation was undertaken to compare the effect of different powder metallurgy processing routes on the phase relations and microstructure of 66Nb-22AH2Ti (in atom percent) alloy. The three different process routes adopted were: (i) cold pressing followed by reaction sintering; (ii) cold pressing and hot pressing followed by sintering; and (iii) arc melting, hydride-dehydride process to make the alloy powder followed by cold pressing and then sintering. The samples are analyzed by XRD, Optical Microscopy, SEM-EDS and EPMA. The analysis showed that alloy pellets made from pre-alloyed powders i.e., arc melting followed by hydride-dehydride process, gave good densification and more Nb3Al formation.1. IntroductionTo improve the performance standards of turbine engines, materials scientists are challenged to develop materials that have· high thrust-to-weight ratio with high specific strength, high specific modulus and good environmental properties at elevated temperatures. The conventional high temperature materials like nickel based superalloys are high in density and hence many of the high temperature materials scientists have focussed their attention on intermetallic aluminides like Fe-AI, Nb-AI, Ni-AI and Ti-AI in recent years. The phase relations and properties of alloys based on Fe-AI, Ni-AI and Ti-AI are fairly well known whereas little is known about the alloys based on niobium aluminides."

Jan 1, 1996

By F. A. Renninger

Limestone and dolomite are the most common rock types mined and quarried as industrial minerals in the United States. In 1993 over 720 million tons of limestone and dolomite valued at over 3.1 billion dollars were extracted and consumed throughout the nation. While the greatest volume of this vast production is used as aggregate for construction purposes, few people realize how critical limestone and dolomite are to our food chain and our national goals of clean air and water. Limestone, including dolomite, can truly be called nature's gift to the environment. Without a reliable, economical source of limestone the quality of our environment would be severely comprised and the standard of living of our citizens dramatically reduced.

Jan 1, 1995

By H. I. Aaronson, C. Wells

Configurations of ferrite crystals have been found in a plain carbon steel which appear to have resulted from the nucleation of new ferrite crystals at the interphase boundaries of previously formed crystals despite the high carbon concentrations which necessarily develop at these boundaries. This phenomenon has been termed sympathetic nucleation. An attempt has been made to reconcile the occurrence of sympathetic nu-cleation with current nucleation theory. THIS investigation is one of a series on the formation of proeutectoid ferrite from austenite. From the viewpoint of chemical composition, this reaction consists of the nucleation and diffusional growth of crystals of carbon-poor ferrite within a matrix of carbon-rich austenite. The austenite adjacent to the austenite-ferrite boundaries will be greatly enriched in carbon, approximately to the value of the y/(a + y) equilibrium curve or its metastable extrapolation at the temperature of transformation. Those areas of austenite appreciably farther removed from the growing ferrite, on the other hand, will be relatively unaltered in composition, especially at the earlier stages of transformation. Since rates of nucleation are considered to decrease exponentially with decreasing supersaturation,' the frequency with which ferrite nuclei appear at austenite-ferrite boundaries should be negligible in relation to that at which they form in other regions of the austenite. During this investigation, however, many groupings of ferrite crystals have been found which appear to have resulted from the nucleation of ferrite at austenite-ferrite boundaries. This phenomenon has been given the name of sympathetic 71.1tcleation. A number of micrographs of morphological configurations caused by sympathetic nucleation will be presented, after which an explanation for this reaction will be proposed in terms of current nucleation theory. Some of the structures to be considered are composed of bainite, an aggregate of ferrite and carbide, rather than of ferrite. Since ferrite and bainite differ only in that bainite forms under conditions which result in the nucleation of carbides behind the advancing austenite-ferrite boundaries,' it will usually be unnecessary, for the purpose of this paper, to distinguish between the two reaction products. All studies were performed on an electric furnace steel (obtained from the Vanadium Alloy Steel Co.) containing 0.29 pct C, 0.76 pct Mn, 0.25 pct Si, 0.005 pct P, and 0.007 pct S. The alloy was cast as a 150 Ib, 7x7 in. cross section ingot and forged into bars 2x2 in. in cross section. These bars were homogenized for 48 hr at 1250°C in an Endo-Gas atmosphere. The depth to which decarburization penetrated during this heat treatment was determined by chemical and microscopic analyses and the affected metal was removed by machining. Specimens for isothermal transformation studies were cut from the remaining material; most of these specimens were 1/2x1/4X1/16 in., though some with a thickness of 1/32 in. were prepared for use at the shorter reaction times and lower reaction temperatures. Specimens were austenitized for 30 min at 1300°C, isothermally reacted for various times at temperatures ranging from 775" to 475 "C, and then quenched in iced water. The austenite grain sizes within individual specimens ranged from ASTM Nos. 1 through —4. A commercial heat-treating salt which was continuously deoxidized by an immersed graphite crucible served to minimize the loss of carbon during austenitizing; thick covers of powdered graphite and immersed graphite rods effectively prevented decarburization in the lead pots employed for the isothermal reaction treatments. The heat-treated specimens were sectioned and mounted in Bakelite. Following the completion of standard grinding and mechanical polishing procedures, the specimens were electrolytically polished with a Buehler-Waisman apparatus and etched in 2 pct nital. Experimental Results Rules of Evidence for Sympathetic Nucleation—On the basis of observations made on a single plane of polish, one precipitate crystal may be considered to have been sympathetically nucleated at the inter-phase boundary of another precipitate crystal when the following conditions are fulfilled: 1) The sympathetically nucleated crystal is not in contact with a grain boundary or a subboundary in the matrix phase. 2) The shape, size, and location of the crystal at whose boundary sympathetic nucleation occurred (hereafter termed the base crystal) and the crystal formed by sympathetic nucleation substantially pre-clude the possibility that the plane of polish em-ployed may have concealed the fact that both crys-tals actually nucleated at a grain boundary or a sub-boundary in the matrix phase.

Jan 1, 1957

By Margaret Anne Stephenson

While the concepts of Aboriginal title share a similar jurisprudence in both Australia and Canada resource development regimes on Aboriginal title lands differ significantly. In Australia, the process is the right to negotiate with mining proponents. In Canada, the process is the duty to consult with government regarding mining projects. This paper compares and assesses the processes for ?consultation and negotiation? with Indigenous peoples when development actions (particularly in the context of mining resource development) impact Indigenous property rights and how agreement making can be progressed. This paper will question whether the resource development processes afford Indigenous people?s property rights full respect when mining developments on Indigenous lands are proposed.

Aug 1, 2013

By W. L. Staker

The Bureau of Mines investigated the use of shredded automobile scrap for copper cementation. Air agitation was used to improve the cementation rate and prevent excessive buildup of copper on the iron. The pieces of scrap were too large to be properly evaluated in the laboratory; therefore, a pilot scale test unit was constructed and the process tested at field locations. Pregnant solution was obtained from industrial leaching operations, processed in the test unit and the barren solution and cement copper were returned to the plant process stream. The test results showed that the air-agitated launder containing auto-mobile scrap was an effective means for recovering copper from leach solutions. A continuous l4-day test run was made without a noticeable decrease in cementation efficiency. The most suitable scrap product was obtained from incinerated automobile hulks shredded in a hammer type of shredder. However, it was necessary to remove small pieces such as nuts and bolts because they interfered with the discharge of the copper product.

Jan 1, 1976

By R. D. Leitch, J. G. Calverley

"INTRODUCTION Although many investigators have provided information on the strength and other properties of concrete the published literature cites few data on the effect of mixing cement with acid mine waters or on acid resistance of concrete in contact with mine waters. Most of the reported work on the effect of impure waters has dealt with the resistance of cement specimens to ""sulfate waters,"" that is, waters or soils with a relatively high sodium sulfate content. The ""Merriman test"" is used commonly to determine the corrosion resistance of cements for 28 days, but it does not seem certain that a cement having a high sulfate resistance in the Merriman or similar tests necessarily will show correspondingly great resistance to the sulfates of iron and, particularly, to sulfuric acid, which usually are present in acid mine waters. Extensive use of cement mortar for laying up masonry stoppings in coal and other mines and for constructing concrete mine haulageways and shaft linings, coal-storage and other retaining walls, highway bridges, culverts, and many other types of construction where it is difficult to obtain fresh water for mixing or where the structures are later exposed to contact with acid waters makes it important to know the effect of these conditions on cement and whether there is a cement better suited for such work than ordinary portland cement.CONDUCT OF THE INVESTIGATIONFor a short time early in 1935 the opportunity to obtain at least some additional information on the effect of acid mine water on cements was presented by the Relief Works Division, which provided money for irregular and indefinite employment for several months. Purchase of apparatus or material was not permitted under this arrangement, and indefinite duration of the work, intermittent employment, and finally complete cessation of the work prevented planning for extensive investigation of this particular problem."

Jan 1, 1940

By R. Bhaskar

The advantages of recirculation of air in underground mines have been well recognized, and several papers have been written on the subject. Issues of concern to the various segments of the mining industry relate to the health and safety of workers, specifically, methane and respirable dust build-up in the air, high humidity and temperature at the work face. This paper presents a survey of various studies pertaining to recirculation as a prelude to the experimental and quantitative studies performed by the authors. Experiments were performed at a trona mine on the transportation and deposition of dust along the return airways, for three different velocities. Modeling studies were performed using dust deposition models. The model predicted data were compared with experimental data in order to lay the foundation for the development of advanced predictor models for recirculation in trona mines. Two models for dust deposition were analyzed. The model predicted data are in divergence from the experimental data, indicating the need to develop better models.

Jan 1, 1992

By P. Schloth, H. van Swygenhoven, N. Chobaut, J-M. Drezet

"In the current trend toward thicker aluminium plates, a major concern is the stress build-up during quenching which causes distortions during machining. Indeed, cooling rates are not high enough, especially at the core of such thick plates, to prevent any precipitation and quench induced precipitates lower the hardening potential. Multi-scale modelling is required when predicting macro-scale stresses after quenching for thick heat treatable aluminium components. The reason is the instantaneous strong coupling between phase precipitation at the nano-scale and material hardening due to precipitation or softening owing to solute depletion at the microscale. For thick parts, quenching intensities decrease when going from the skin to the core of the component, thus introducing a gradient of nanostructure and consequently a gradient of mechanical properties. In addition, large thermally induced deformations lead to high macroscale residual stresses although part of them is relaxed by plastic deformation. These stresses have been measured in water quenched thick plates of 7040 and 7449 aluminium alloys using neutron diffraction and layer removal techniques and the results when compared with a thermomechanical finite element model of quenching highlight the influence of precipitation.IntroductionIn the processing route of heat-treatable aluminium alloys (AA), a critical step is quenching from the solutionizing temperature. High cooling rates are desired, as they avoid formation of coarse precipitates, which reduce mechanical properties. Fast quenching, however, cannot be achieved in the centre of thick components, where the quenching rate can be more than one order of magnitude lower than at the surface. The existence of a thermal gradient between core and surface leads to a differential thermal deformation which is accommodated by elastic and plastic deformation to comply with the compatibility of deformation. Whenever the material yields, especially at high temperature when the yield strength is low, residual stress remains after quenching due to the irreversibility of plastic deformation. After quenching, the plates are in a state of residual stress that causes unacceptable distortions during machining and may reduce service life drastically. Since stress relaxation is negligible during ageing treatments [1 ], agehardened aluminium parts are usually stress relieved prior to ageing. This is typically achieved by applying plastic deformation: stretching from 1.5 to 3 % in the rolling direction (L) can reduce the internal stresses by a factor of approximately 10 [2, 3]. However, complex geometries or thicker components like thick sheets require other approaches. Reducing the quenching rate by using boiling water for instance leads to lower residual stresses [1, 4]."

Jan 1, 2013

By George A. Komadina

Pima Mining Company has recently completed their expansion tripling the plant capacity to 18,000 tons per day and now is in the process off expanding to 30,000 tons per day with completion scheduled for the summer of 1967. This paper briefly discusses the additions to the mining department and support areas with a more detailed report on the complete new crushing plant and additions to the concentrator. The crushing plant includes a 54-inch gyratory crusher, three 7-foot standard and seven 7-foot short head crushers along with necessary screens, feeders, and conveyor belts to produce a minus 1/2-inch rod mill feed. The concentrator consists of ten milling sections, each containing one 10-foot by 16-foot rod and two 10.5-foot by 13-foot ball mills, classification is done with cyclones. Pulp from each section is floated in 50 cells of 66-inch Fagergren flotation machines to produce a rougher concentrate which is cleaned in six stages of Denver cleaners to produce a final concentrate The various mill products are thickened with disposal made in conventional manner. Plant instrumentation is discussed in the paper.

Jan 1, 1967

By A H. Bagherieh, S Mesroghli, H Jorjani, S Chehreh Chelgani

The rare earth elements (REEs) assay and recovery in leaching processes is being determined using expensive analytical methods, ICP-AES, and ICP-MS. This paper presents a neural network model to predict the effects of operational variables on the lanthanum, cerium, yttrium, neodymium recovery in the leaching of apatite concentrate. The effects of leaching times: ten to 40 min, pulp densities: 30 to 50 per cent, acid concentrations: 20 to 60 per cent and agitation rates: 100 to 200 rpm were investigated and optimised on REEs recovery in laboratory at a leaching temperature of 60¦C. The obtained data, on the laboratory optimisation process were used for training and testing of a neural network. A feed-forward artificial neural network with 4-5-5-1 arrangement, was capable of estimating the REEs leaching recovery. Neural network predicted values were in good agreement with the experimental results. The correlations of R = 1 in training stages, and R =  0.971, 0.952, 0.985 and 0.98 in testing stages were results for Ce, Nd, La and Y recovery predictions respectively and that theses values are considerably acceptable. It was shown that the proposed neural network model accurately reproduces all the effects of operation variables, and can be used in the simulation of a REEs leaching plant.

Jan 1, 2008

By P. T. Bissert, L. Yan, J. R. Srednicki, J. A. Yonkey

"Refuge alternatives (RAs) are required in underground coal mines to support life post-disaster. RAs are mandated by MSHA to maintain an apparent temperature (AT) at or below 95°F (35°C) while providing a safe and livable shelter for a minimum of 96 hours. Because strata composition and mine temperatures will affect the final AT within an occupied RA, NIOSH researchers have collaborated with five underground coal mines across the US to characterize the effects of geographic location and seasonal temperature fluctuations on mine air temperature, relative humidity, and mine strata temperatures. The data collected indicates that some mines will experience greater temperature fluctuations than others, based on geographic location. The mine which demonstrated the greatest temperature differential over the course of the year resulted in a mine air temperature that ranged from 53.4°F (11.9°C) to 84.2°F (29.0°C) and a rib surface temperature that ranged from 55.4°F (13.0°C) to 82.8°F (28.2°C). This data suggests that the location and seasonal peak temperature can significantly affect the mine strata temperature, which could lead to a fully occupied RA exceeding the 95°F (35°C) AT limit over the course of 96 hours. The data reported in this paper could be used to examine the heat buildup inside an RA for actual mine conditions. Thermal simulations could be implemented to evaluate maximum occupancy ratings based on actual mine temperatures and strata compositions. INTRODUCTION In the event of a mine disaster, miners’ primary focus is to escape. Should their attempt be futile, they can enter a refuge alternative (RA) to await rescue. In 2008, the Mine Safety and Health Administration (MSHA) mandated that underground coal mines implement RAs within 1,000 ft (304.8 m) of the working face and spaced within one-hour travel distances in outby areas where persons work such that persons in outby areas are never more than than a 30-minute travel distance from an RA or safe exit. These RAs are required to provide a safe and habitable shelter for a minimum of 96 hours and to prevent the apparent temperature (AT) from exceeding 95°F (35°C) [1]. There is concern throughout the industry that in some cases the internal ambient of occupied RAs may exceed the 95°F (35°C) AT limit due to the potentially hot mine atmosphere as well as the metabolic heat generated by RA occupants and the carbon dioxide scrubbing system. The National Institute for Occupational Safety and Health (NIOSH) has conducted tests in its Safety Research Coal Mine (SRCM) and its Experimental Mine (EM) to investigate heat buildup in RAs. It was found that the number of occupants in an RA may need to be reduced based on the ambient mine temperature, which varies from mine to mine [2]. Further testing and analyses were completed to evaluate the mechanisms (conduction, convection, radiation) by which heat is transferred from an RA to the mine surroundings. Additionally, the effects of varying mine strata compositions on the heat buildup inside an RA were studied [3]. The mine strata temperatures will increase due to heat transfer from within an RA. Depending on the mine strata composition, some mines may be more thermally conductive than others. For example, sandstone is much more conductive than shale or coal (i.e. it disippates heat at a quicker rate). All things being equal, the air temperature inside of an RA after 96 hours will be higher for a mine with strata that has low thermal conductivity compared to a mine with high thermal conductivity."

Jan 1, 2017