Influence of Different Heater Structures on the Temperature Field of AlN Crystal Growth by Resistance Heating

Based on the actual hot zone structure of an AlN crystal growth resistance furnace, the global numerical simulation on the heat transfer process in the AlN crystal growth was performed. The influence of different heater structures on the growth of AlN crystals was investigated. It was found that the top heater can effectively reduce the axial temperature gradient, and the side heater 2 has a similar effect on the axial gradient, but the effect feedback is slightly weaker. The axial temperature gradient tends to increase when the bottom heater is added to the furnace, and the adjustable range of the axial temperature gradient of the side 1 heater + bottom heater mode is the largest. Our work will provide important reference values for AlN crystal growth by the resistance method.

Sodium rare earth metal amides Na3 RE(NH2)6 (RE = La–Nd, Er, Yb) from ammonothermal synthesis

The amides Na3 RE(NH2)6 have been obtained from the metals in supercritical ammonia under ammonobasic conditions at 573 K and 70 MPa for RE = La–Nd, and at 473 K and 40 MPa for RE = Er, Yb. All compounds are formed in the hot zone within a temperature gradient, indicating a retrograde solubility under the applied process conditions. These amides represent soluble intermediates in ammonothermal binary rare earth metal nitride synthesis. All compounds were obtained as microcrystalline powders, while single crystals of those amides containing the heavier rare earth metals could be isolated. The crystal structures were solved and refined from single-crystal and powder X-ray diffraction intensity data. The results of vibrational spectroscopy are reported. Thermal analysis measurements under inert gas atmosphere demonstrated a decomposition to the respective black binary rare earth metal nitrides REN1−δ .

The Neural Correlates of Access Consciousness and Phenomenal Consciousness Seem to Coincide and Would Correspond to a Memory Center, an Activation Center and Eight Parallel Convergence Centers

An increasing number of authors suggest that the neural correlates of consciousness (NCC) have no selective, executive, or metacognitive function. It is believed that attention unconsciously selects the contents that will become conscious. Consciousness would have only the fundamental function of transforming the selected contents into a format easily used by high-level processors, such as working memory, language, or autobiographical memory. According to Dehaene, the neural correlates (NC) of access consciousness (AC; cognitive consciousness) constitute a widespread network in the frontal, parietal, and temporal cortices. While Tononi localized the correlates of phenomenal consciousness (PC; subjective consciousness) to a posterior “hot zone” in the temporo-parietal cortex. A careful examination of the works of these two groups leads to the conclusion that the correlates of access and PC coincide. The two consciousnesses are therefore two faces of the same single consciousness with both its cognitive and subjective contents. A review of the literature of the pathology called “neglect” confirms that the common correlates include 10: a memory center, an activation center, and eight parallel centers. From study of the “imagery” it can be deduced that these eight parallel centers would operate as points of convergence in the third person linking the respective eight sensory-motor-emotional areas activated by external perceptions and the corresponding memories of these perceptions deposited in the memory center. The first four centers of convergence appear in the most evolved fish and gradually reach eight in humans.

How to Put Predictive Maintenance to use on the Internet of Things

In an ever-changing world of increased automation and process efficiencies, and with Industry 4.0 and the Internet of Things at the forefront of these efforts, the most successful heat treaters globally employ a predictive maintenance platform that allows them to anticipate disruption before it occurs. In this presentation, you will:• Understand how costs associated with furnace downtime compare with and without predictive maintenance.• Learn the fundamentals of predictive maintenance and how it’s changing the heat treating industry.• Hear a series of practical, data-driven examples in which the software anticipated hazards—like a broken (open) heating element or diffusion pump heater failure—avoiding potential part quality issues and hot zone damage.• See real-life business cases on aged furnaces, where the risk and frequency of unplanned downtime is significantly higher. We will show all the benefits of monitoring furnace health with real-time diagnoses.

Gas Cooling – Is Pressure or Velocity Most Important?

This paper will debunk the age-old theory that the smaller the vacuum furnace, the faster it will quench supposition. Our study compared the cooling rates of two vacuum high pressure gas quenching furnaces - a large 10-bar vacuum furnace equipped with a 600 HP blower motor to a smaller 10-bar vacuum furnace equipped with a 300 HP motor. In comparing the critical cooling temperatures for H13 in the 1850°F to 1300°F range, the furnace that is almost three times larger in volume (110 cubic feet versus a 40 cubic feet of hot zone) cooled the same workload almost identically to its smaller counterpart. These tests prove a very important fact - that the gas flow or velocity is more meaningful than pressure (bar) when it relates to cooling rates.

Maximum Possible Cooling Rate in Ultrafast Chip Nanocalorimetry: Fundamental Limitations Due to Thermal Resistance at the Membrane/Gas Interface

Ultrafast chip nanocalorimetry opens up remarkable possibilities in materials science by allowing samples to be cooled and heated at extremely high rates. Due to heat transfer limitations, controlled ultrafast cooling and heating can only be achieved for tiny samples in calorimeters with a micron-thick membrane. Even if ultrafast heating can be controlled under quasi-adiabatic conditions, ultrafast controlled cooling can be performed if the calorimetric cell is located in a heat-conducting gas. It was found that the maximum possible cooling rate increases as 1/r0 with decreasing radius r0 of the hot zone of the membrane. The possibility of increasing the maximum cooling rate with decreasing r0 was successfully implemented in many experiments. In this regard, it is interesting to answer the question: what is the maximum possible cooling rate in such experiments if r0 tends to zero? Indeed, on submicron scales, the mean free path of gas molecules lmfp becomes comparable to r0, and the temperature jump that exists at the membrane/gas interface becomes significant. Considering the limitation associated with thermal resistance at the membrane/gas interface and considering the transfer of heat through the membrane, we show that the controlled cooling rate can reach billions of K/s, up to 1010 K/s.

Maximum Possible Colling Rate in Ultrafast Chip Nanocalorimetry: Fundamental Limitations Due to Thermal Resistance at the Membrane/Gas Interface

Ultrafast chip nanocalorimetry opens up remarkable possibilities in materials science by allowing samples to be cooled and heated at extremely high rates. Due to heat transfer limitations, controlled ultrafast cooling and heating can only be achieved for tiny samples in calorimeters with a micron-thick membrane. Even if ultrafast heating can be controlled under quasi-adiabatic conditions, ultrafast controlled cooling can be performed if the calorimetric cell is located in a heat-conducting gas. It was found that the maximum possible cooling rate increases as 1/r0 with decreasing radius r0 of the hot zone of the membrane. The possibility of increasing the maximum cooling rate with decreasing r0 was successfully implemented in many experiments. In this regard, it is interesting to answer the question: what is the maximum possible cooling rate in such experiments if r0 tends to zero? Indeed, on submicron scales, the mean free path of gas molecules lmfp becomes comparable to r0, and the temperature jump that exists at the membrane/gas interface becomes significant. Considering the limitation associated with thermal resistance at the membrane/gas interface and considering the transfer of heat through the membrane, we show that the controlled cooling rate can reach billions of K/s, up to 1010 K/s.

Transcrustal Magmatic Systems: Evidence from Andesites of the Southern Taupo Volcanic Zone

Studies synthesizing field work, numerical simulations, petrology, geochemistry, and geophysical observations indicate that the compositional diversity of arc lavas results from evolution of mantle-derived magmas by mixing, assimilation, and fractional crystallization. This evolution occurs within complexes called transcrustal magmatic systems. The mafic lower parts of such zones, called hot zones, are difficult to probe. However, a satellite vent near the stratovolcano Ruapehu in the southern Taupo Volcanic Zone (New Zealand) comprises materials that may originate from a hot zone. Magnesian andesites (Mg#64-69) from the Ohakune scoria cone contain primitive olivine (Fo85-91), high Mg# clinopyroxene (Mg#81-88), and orthopyroxene (Mg#76-83), but lack plagioclase. Disequilibrium of Ohakune crystals and groundmass suggests that the crystal cargo of Ohakune andesites was scavenged from deeper and more primitive levels of the magmatic system. Mineral constraints on temperature and pressure indicate that the hot zone initially formed at mid- to lower-crustal pressures (3.5-7.0±2.8 kbar). We interpret the mafic mineralogy and presence of disequilibrium features as evidence that these andesites and their crystal cargo are products of a hot zone in the middle to lower crust. Products of the hot zone may appear before products of the systems that form the bases of mature stratovolcanoes such as Ruapehu.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5494984